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Sample records for acid racemization dating

  1. Amino acid racemization dating of fossil bones, I. inter-laboratory comparison of racemization measurements

    USGS Publications Warehouse

    Bada, J.L.; Hoopes, E.; Darling, D.; Dungworth, G.; Kessels, H.J.; Kvenvolden, K.A.; Blunt, D.J.

    1979-01-01

    Enantiomeric measurements for aspartic acid, glutamic acid, and alanine in twenty-one different fossil bone samples have been carried out by three different laboratories using different analytical methods. These inter-laboratory comparisons demonstrate that D/L aspartic acid measurements are highly reproducible, whereas the enantiomeric measurements for the other amino acids show a wide variation between the three laboratories. At present, aspartic acid measurements are the most suitable for racemization dating of bone because of their superior analytical precision. ?? 1979.

  2. Paleoanthropological applications of amino acid racemization dating of fossil bones and teeth.

    PubMed

    Bada, J L

    1987-03-01

    The general principals of the amino acid racemization based dating technique are discussed. The results obtained at Olduvai Gorge (Tanzania) and Zhoukoudian (China) are presented as an illustration of the paleoanthropological application of racemization dating. Tooth enamel provides the best material for the racemization dating of Middle to Lower Pleistocene deposits, although in some cases bones also yield reliable ages. The racemization method provides a means of dating teeth and bones which are too old for radiocarbon dating. Only small samples are required and processing procedures are straightforward. The technique is particularly useful in paleoanthropological studies since hominid fossils can be directly dated.

  3. Racemization reaction of aspartic Acid and its use in dating fossil bones.

    PubMed

    Bada, J L; Protsch, R

    1973-05-01

    In the time interval datable by radiocarbon, and at the temperatures of most archeological sites, a substantial amount of racemization of aspartic acid takes place. By determination of the amount of racemization of aspartic acid in bones from a particular location which have been dated by the radiocarbon technique, it is possible to calculate the in situ first-order rate constant for interconversion of the L- and D enantiomers of aspartic acid. Once this "calibration" has been calculated, the reaction can be used to date other bones from the deposit that are either too old to be dated by radiocarbon or that are too small for radiocarbon dating. The only assumption required with this approach is that the average temperature experienced by the "calibration" sample is representative of the average temperature experienced by older samples. This "calibration" technique is used herein to date bones from the Olduvai Gorge area in Tanzania, Africa.

  4. Racemization Reaction of Aspartic Acid and Its Use in Dating Fossil Bones

    PubMed Central

    Bada, Jeffrey L.; Protsch, Reiner

    1973-01-01

    In the time interval datable by radiocarbon, and at the temperatures of most archeological sites, a substantial amount of racemization of aspartic acid takes place. By determination of the amount of racemization of aspartic acid in bones from a particular location which have been dated by the radiocarbon technique, it is possible to calculate the in situ first-order rate constant for interconversion of the L- and D enantiomers of aspartic acid. Once this “calibration” has been calculated, the reaction can be used to date other bones from the deposit that are either too old to be dated by radiocarbon or that are too small for radiocarbon dating. The only assumption required with this approach is that the average temperature experienced by the “calibration” sample is representative of the average temperature experienced by older samples. This “calibration” technique is used herein to date bones from the Olduvai Gorge area in Tanzania, Africa. PMID:16592082

  5. Aspartic acid racemization dating of Holocene brachiopods and bivalves from the southern Brazilian shelf, South Atlantic

    NASA Astrophysics Data System (ADS)

    Barbour Wood, Susan L.; Krause, Richard A.; Kowalewski, Michał; Wehmiller, John; Simões, Marcello G.

    2006-09-01

    The extent of racemization of aspartic acid (Asp) has been used to estimate the ages of 9 shells of the epifaunal calcitic brachiopod Bouchardia rosea and 9 shells of the infaunal aragonitic bivalve Semele casali. Both taxa were collected concurrently from the same sites at depths of 10 m and 30 m off the coast of Brazil. Asp D/L values show an excellent correlation with radiocarbon age at both sites and for both taxa ( r2Site 9 B. rosea = 0.97, r2Site 1 B. rosea = 0.997, r2Site 9 S. casali = 0.9998, r2Site 1 S. casali = 0.93). The Asp ratios plotted against reservoir-corrected AMS radiocarbon ages over the time span of multiple millennia can thus be used to develop reliable and precise geochronologies not only for aragonitic mollusks (widely used for dating previously), but also for calcitic brachiopods. At each collection site, Bouchardia specimens display consistently higher D/L values than specimens of Semele. Thermal differences between sites are also notable and in agreement with theoretical expectations, as extents of racemization for both taxa are greater at the warmer, shallower site than at the cooler, deeper one. In late Holocene marine settings, concurrent time series of aragonitic and calcitic shells can be assembled using Asp racemization dating, and parallel multi-centennial to multi-millennial records can be developed simultaneously for multiple biomineral systems.

  6. Amino acid racemization dating of Upper Pleistocene - Holocene terrestrial gastropods from a Mediterranean region (Murcia, SE Spain)

    NASA Astrophysics Data System (ADS)

    Garcia-Mayordomo, Julian; Ortiz, Jose E.; Torres, Trinidad; Insua-Arevalo, Juan M.; Martinez-Diaz, Jose J.; Altolaguirre, Yul; Canales-Fernandez, Maria L.; Martin-Banda, Raquel

    2014-05-01

    The amino acid racemization method has become a widely used geochronological tool for dating Quaternary deposits. The method is based on the fact that living organisms contain only L-amino acids which gradually racemize into D-amino acids after death. Thus, the D/L ratio increases with time after death until it is equal to 1, that is, when equilibrium is reached. Gastropod shells are particularly useful for amino acid racemization dating. Because the amino acid racemization method is not a numerical dating method in isolation, it needs to be calibrated, mainly with radiometric dating methods. The racemization process is genus- and temperature-dependent. In this work we present a preliminary analysis that compares the radiometric age estimated from different dating methods of a number of gastropods recovered in localities from Murcia (Southeastern Spain), with the age obtained through the amino acid racemization method. Taking advantage of recent paleoseismological research in the Murcia region (SE Spain), 28 gastropods specimens were collected from different trenches dug in young Quaternary alluvial deposits. The specimens were subsequently classified and then analyzed according to the standards protocols of the Biomolecular Stratigraphy Laboratory (UPM, Madrid School of Mines). The species found were Otala lactea, Iberus gualterianus, Sphincterochila candidissima and Theba pisana. The D/L ratios of aspartic acid, leucine, phenylalanine and glutamic acid were determined, and the corresponding average age of each specimen was calculated introducing the D/L values in the age calculation algorithm of Torres et al. (1997) for gastropods of central and southern Spain. The racemization age for each locality was then compared to the radiometric age of the deposit where the specimens were collected. To this respect, the samples were classified in different groups considering the reliability on the age control method. The most reliable sample consists only on dates obtained

  7. Amino acid racemization dating of marine shells: A mound of possibilities

    PubMed Central

    Demarchi, Beatrice; Williams, Matt G.; Milner, Nicky; Russell, Nicola; Bailey, Geoff; Penkman, Kirsty

    2011-01-01

    Shell middens are one of the most important and widespread indicators for human exploitation of marine resources and occupation of coastal environments. Establishing an accurate and reliable chronology for these deposits has fundamental implications for understanding the patterns of human evolution and dispersal. This paper explores the potential application of a new methodology of amino acid racemization (AAR) dating of shell middens and describes a simple protocol to test the suitability of different molluscan species. This protocol provides a preliminary test for the presence of an intracrystalline fraction of proteins (by bleaching experiments and subsequent heating at high temperature), checking the closed system behaviour of this fraction during diagenesis. Only species which pass both tests can be considered suitable for further studies to obtain reliable age information. This amino acid geochronological technique is also applied to midden deposits at two latitudinal extremes: Northern Scotland and the Southern Red Sea. Results obtained in this study indicate that the application of this new method of AAR dating of shells has the potential to aid the geochronological investigation of shell mounds in different areas of the world. PMID:21776187

  8. Dating human bone: is racemization dating species-specific?

    PubMed

    Moini, Mehdi; Rollman, Christopher M; France, Christine A M

    2013-12-01

    Our recently developed dating technique based on the racemization rate of aspartic acid was applied to dating human bone, as well as that of other mammals, utilizing capillary electrophoresis mass spectrometry. First, several well-dated (mostly (14)C-dated and with strong archeological evidence) human bones ranging in age from 150 to ~10,000 years were used to develop a calibration curve for human bone. The D/L ratio of aspartic acid for these specimens ranged from 2.4% to ~10%, with a correlation coefficient of better than 0.99, indicating a strong linear relationship between the d/l ratio of aspartic acid and the age of the specimens. This calibration curve can now be used to date human archeological specimens of unknown age, up to ~10,000 years. However, when the technique was applied to well-dated mixed species of larger mammal bones such as bison, whale, llama, etc., the calibration curve showed a slower rate of racemization with a lower correlation (0.88). As additional large mammal bones with less certain age (i.e., using archeological evidence alone with no (14)C-dating) were dated the correlation coefficient decreased to 0.70. The correlation coefficient decreased further to 0.58 when the racemization data from all mammals (including human) were added to the calibration curve, indicating the importance of using well-dated, species-specific specimens for forming a calibration curve. This conclusion is consistent with our previously published calibration curve for a single species of silk (Bombyx mori), which followed the expected reversible first-order kinetics. These results support species specificity of amino acid racemization dating.

  9. Wide range of racemization of amino acids in peptides from human fossil bone and its implications for amino acid racemization dating

    SciTech Connect

    Kimber, R.W.L.; Hare, P.E. )

    1992-02-01

    Aspartic acid from an HCl hydrolyzed portion of 20-25th Dynasty Egyptian bone gave a D/L value of 0.28. Various peptide and molecular weight fractions separated before hydrolysis from another aliquot of the same bone portion yielded D/L aspartic acid values ranging from 0.09 to 0.68. Higher molecular weight and higher content of hydrophobic amino acids are factors leading to lower D/L aspartic acid values. Insoluble, high molecular weight polypeptide residues showed very low D/L aspartic acid values of 0.09. The authors propose that particularly stable peptides be isolated and characterized and then used for comparison with similarly isolated peptides from other fossil bone samples for purposes of age estimation.

  10. Comparison of amino acid racemization geochronometry with lithostratigraphy, biostratigraphy, uranium-series coral dating, and magnetostratigraphy in the Atlantic Coastal Plain of the southeastern United States

    USGS Publications Warehouse

    McCartan, L.; Owens, J.P.; Blackwelder, B. W.; Szabo, B. J.; Belknap, D.F.; Kriausakul, N.; Mitterer, R.M.; Wehmiller, J. F.

    1982-01-01

    The results of an integrated study comprising litho- and biostratigraphic investigations, uranium-series coral dating, amino acid racemization in molluscs, and paleomagnetic measurements are compared to ascertain relative and absolute ages of Pleistocene deposits of the Atlantic Coastal Plain in North and South Carolina. Four depositional events are inferred for South Carolina and two for North Carolina by all methods. The data suggest that there are four Pleistocene units containing corals that have been dated at about 100,000 yr, 200,000 yr, 450,000 yr, and over 1,000,000 yr. Some conflicts exist between the different methods regarding the correlation of the younger of these depositional events between Charleston and Myrtle Beach. Lack of good uranium-series dates for the younger material at Myrtle Beach makes the correlation with the deposits at Charleston more difficult. ?? 1982.

  11. Comparison of amino acid racemization geochronometry with lithostratigraphy, biostratigraphy, uranium-series coral dating, and magnetostratigraphy in the Atlantic Coastal Plain of the southeastern United States

    NASA Astrophysics Data System (ADS)

    McCartan, L.; Owens, J. P.; Blackwelder, B. W.; Szabo, B. J.; Belknap, D. F.; Kriausakul, N.; Mitterer, R. M.; Wehmiller, J. F.

    1982-11-01

    The results of an integrated study comprising litho- and biostratigraphic investigations, uranium-series coral dating, amino acid racemization in molluscs, and paleomagnetic measurements are compared to ascertain relative and absolute ages of Pleistocene deposits of the Atlantic Coastal Plain in North and South Carolina. Four depositional events are inferred for South Carolina and two for North Carolina by all methods. The data suggest that there are four Pleistocene units containing corals that have been dated at about 100,000 yr, 200,000 yr, 450,000 yr, and over 1,000,000 yr. Some conflicts exist between the different methods regarding the correlation of the younger of these depositional events between Charleston and Myrtle Beach. Lack of good uranium-series dates for the younger material at Myrtle Beach makes the correlation with the deposits at Charleston more difficult.

  12. Prompt transgression and gradual salinisation of the Black Sea during the early Holocene constrained by amino acid racemization and radiocarbon dating

    NASA Astrophysics Data System (ADS)

    Nicholas, William Anthony; Chivas, Allan R.; Murray-Wallace, Colin V.; Fink, David

    2011-12-01

    The restricted environment of the Black Sea is particularly sensitive to climatic and oceanographic fluctuations, owing to its connection with the Mediterranean Sea via the narrow Bosphorus Strait. The exact mechanism and timing of the most recent connection between these water bodies is controversial with debate on the post-glacial history of the Black Sea being dependent on radiocarbon dating for numerical ages. Here we present new 23 accelerator mass spectrometer (AMS) radiocarbon ages on peat and bivalve molluscs, supported by the first amino acid racemization (AAR) dating of bivalve molluscs ( n = 66) in the Black Sea. These data indicate infilling of the Black Sea during the early Holocene from an initial depth 107 m below sea-level, and 72 m below that of the Bosphorus Sill. These data combined with a review of previous radiocarbon ages has enabled a unique perspective on the post-glacial Black Sea. A sea-level curve based on conventional and AMS radiocarbon ages on peat and AMS-based ages on Dreissena sp. shells indicate the water-level in the earlier lake phase continued, until the early Holocene, to be lower than the Bosphorus Sill after the Younger Dryas ended. However, the absence of AMS-dated mollusc ages from the shelves of this basin older than the Younger Dryas is suggestive of sub-aerial exposure of the shelves, and comparatively lower water-levels when the Younger Dryas began. Thus post-glacial outflow from the Black Sea occurred through a lowered or open Bosphorus seaway. Basin-wide radiocarbon ages on peat indicate a prompt increase in water-level from that of the pre-existing and unconnected palaeo-lake during the earliest Holocene (9600-9200 cal a BP). Mass colonisation of the Black Sea by Mediterranean taxa did not occur until salinity had risen sufficiently, a process which took 1000 a or more from the initial transgressive event. This gradual change in salinity contrasts with the prompt transgression which would have taken ˜400 a to occur.

  13. Concordance of collagen-based radiocarbon and aspartic-acid racemization ages.

    PubMed

    Bada, J L; Schroeder, R A; Protsch, R; Berger, R

    1974-03-01

    By determining the extent of racemization of aspartic acid in a well-dated bone, it is possible to calculate the in situ first-order rate constant for the interconversion of the L and D enantiomers of aspartic acid. Collagen-based radiocarbon-dated bones are shown to be suitable samples for use in "calibrating" the racemization reaction. Once the aspartic-acid racemization reaction has been "calibrated" for a site, the reaction can be used to date other bones from the deposit. Ages deduced by this method are in good agreement with radiocarbon ages. These results provide evidence that the aspartic-acid racemization reaction is an important chronological tool for dating bones either too old or too small for radiocarbon dating. As an example of the potential application of the technique for dating fossil man, a piece of Rhodesian Man from Broken Hill, Zambia, was analyzed and tentatively assigned an age of about 110,000 years.

  14. Amino Acid Racemization and the Preservation of Ancient DNA

    NASA Technical Reports Server (NTRS)

    Poinar, Hendrik N.; Hoss, Matthias

    1996-01-01

    The extent of racemization of aspartic acid, alanine, and leucine provides criteria for assessing whether ancient tissue samples contain endogenous DNA. In samples in which the D/L ratio of aspartic acid exceeds 0.08, ancient DNA sequences could not be retrieved. Paleontological finds from which DNA sequences purportedly millions of years old have been reported show extensive racemization, and the amino acids present are mainly contaminates. An exception is the amino acids in some insects preserved in amber.

  15. Abiotic racemization kinetics of amino acids in marine sediments.

    PubMed

    Steen, Andrew D; Jørgensen, Bo Barker; Lomstein, Bente Aa

    2013-01-01

    The ratios of d- versus l-amino acids can be used to infer the sources and composition of sedimentary organic matter. Such inferences, however, rely on knowing the rates at which amino acids in sedimentary organic matter racemize abiotically between the d- and the l-forms. Based on a heating experiment, we report kinetic parameters for racemization of aspartic acid, glutamic acid, serine, and alanine in bulk sediment from Aarhus Bay, Denmark, taken from the surface, 30 cm, and 340 cm depth below seafloor. Extrapolation to a typical cold deep sea sediment temperature of 3°C suggests racemization rate constants of 0.50×10(-5)-11×10(-5) yr(-1). These results can be used in conjunction with measurements of sediment age to predict the ratio of d:l amino acids due solely to abiotic racemization of the source material, deviations from which can indicate the abundance and turnover of active microbial populations.

  16. Aspartic acid racemization in tooth enamel from living humans.

    PubMed Central

    Helfman, P M; Bada, J L

    1975-01-01

    The aspartic acid in human tooth enamel shows increasing racemization with age. This increase is not seen in the metabolically active protein hemoglobin. The rate constant for the racemization reaction of aspartic acid in human tooth enamel was found to be 8.29 X 10(-4) yr-1. This rate constant suggests that in any protein with a long in vivo lifetime, D-aspartic acid will accumulate with age (about 8% of total aspartic acid in enamel will be the D-enantiomer after 60 years). Thus, racemization may play some role in the aging process affecting metabolically stable tissues in long-lived homeotherms. Aspartic acid racemization in toogh enamel also provides a biochronological tool for assessing the age of living mammals. PMID:1059082

  17. Predicting protein decomposition: the case of aspartic-acid racemization kinetics.

    PubMed Central

    Collins, M J; Waite, E R; van Duin, A C

    1999-01-01

    The increase in proportion of the non-biological (D-) isomer of aspartic acid (Asp) relative to the L-isomer has been widely used in archaeology and geochemistry as a tool for dating. the method has proved controversial, particularly when used for bones. The non-linear kinetics of Asp racemization have prompted a number of suggestions as to the underlying mechanism(s) and have led to the use of mathematical transformations which linearize the increase in D-Asp with respect to time. Using one example, a suggestion that the initial rapid phase of Asp racemization is due to a contribution from asparagine (Asn), we demonstrate how a simple model of the degradation and racemization of Asn can be used to predict the observed kinetics. A more complex model of peptide bound Asx (Asn + Asp) racemization, which occurs via the formation of a cyclic succinimide (Asu), can be used to correctly predict Asx racemization kinetics in proteins at high temperatures (95-140 degrees C). The model fails to predict racemization kinetics in dentine collagen at 37 degrees C. The reason for this is that Asu formation is highly conformation dependent and is predicted to occur extremely slowly in triple helical collagen. As conformation strongly influences the rate of Asu formation and hence Asx racemization, the use of extrapolation from high temperatures to estimate racemization kinetics of Asx in proteins below their denaturation temperature is called into question. In the case of archaeological bone, we argue that the D:L ratio of Asx reflects the proportion of non-helical to helical collagen, overlain by the effects of leaching of more soluble (and conformationally unconstrained) peptides. Thus, racemization kinetics in bone are potentially unpredictable, and the proposed use of Asx racemization to estimate the extent of DNA depurination in archaeological bones is challenged. PMID:10091247

  18. A critical evaluation of the application of amino acid racemization to geochronology and geothermometry

    NASA Technical Reports Server (NTRS)

    Williams, K. M.; Smith, G. G.

    1977-01-01

    Attempts have been made to determine the age of biological samples by measuring the racemization of amino acids in protein samples. The pitfalls and inherent complications in diagenetic racemization studies are reviewed, and recent advances in improving techniques are outlined. Methodological topics include isolation of amino acids from geological samples, resolution of amino acid enantiomers, and the effects of acid hydrolysis. The theory and kinetics of amino acid racemization are discussed with attention to the derivation of the rate expression for amino acid racemization, isoleucine and the equilibrium constant, the mechanism of amino acid racemization, the racemization of 'bound' versus 'free' amino acids, and factors affecting the racemization rates of free amino acids in aqueous solution. Applications of amino acid racemization kinetics to geochronology is considered with reference to shells, marine sediments, and bones. Potential complications include heating and diagenesis, diagenetic formation of amino acids, the effect of clays, species effect, and contamination.

  19. Age estimation in forensic sciences: Application of combined aspartic acid racemization and radiocarbon analysis

    SciTech Connect

    Alkass, K; Buchholz, B A; Ohtani, S; Yamamoto, T; Druid, H; Spalding, S L

    2009-11-02

    Age determination of unknown human bodies is important in the setting of a crime investigation or a mass disaster, since the age at death, birth date and year of death, as well as gender, can guide investigators to the correct identity among a large number of possible matches. Traditional morphological methods used by anthropologists to determine age are often imprecise, whereas chemical analysis of tooth dentin, such as aspartic acid racemization has shown reproducible and more precise results. In this paper we analyze teeth from Swedish individuals using both aspartic acid racemization and radiocarbon methodologies. The rationale behind using radiocarbon analysis is that above-ground testing of nuclear weapons during the cold war (1955-1963) caused an extreme increase in global levels of carbon-14 ({sup 14}C) which have been carefully recorded over time. Forty-four teeth from 41 individuals were analyzed using aspartic acid racemization analysis of tooth crown dentin or radiocarbon analysis of enamel and ten of these were split and subjected to both radiocarbon and racemization analysis. Combined analysis showed that the two methods correlated well (R2=0.66, p < 0.05). Radiocarbon analysis showed an excellent precision with an overall absolute error of 0.6 {+-} 04 years. Aspartic acid racemization also showed a good precision with an overall absolute error of 5.4 {+-} 4.2 years. Whereas radiocarbon analysis gives an estimated year of birth, racemization analysis indicates the chronological age of the individual at the time of death. We show how these methods in combination can also assist in the estimation of date of death of an unidentified victim. This strategy can be of significant assistance in forensic casework involving dead victim identification.

  20. Age estimation in forensic sciences: application of combined aspartic acid racemization and radiocarbon analysis.

    PubMed

    Alkass, Kanar; Buchholz, Bruce A; Ohtani, Susumu; Yamamoto, Toshiharu; Druid, Henrik; Spalding, Kirsty L

    2010-05-01

    Age determination of unknown human bodies is important in the setting of a crime investigation or a mass disaster because the age at death, birth date, and year of death as well as gender can guide investigators to the correct identity among a large number of possible matches. Traditional morphological methods used by anthropologists to determine age are often imprecise, whereas chemical analysis of tooth dentin, such as aspartic acid racemization, has shown reproducible and more precise results. In this study, we analyzed teeth from Swedish individuals using both aspartic acid racemization and radiocarbon methodologies. The rationale behind using radiocarbon analysis is that aboveground testing of nuclear weapons during the cold war (1955-1963) caused an extreme increase in global levels of carbon-14 ((14)C), which has been carefully recorded over time. Forty-four teeth from 41 individuals were analyzed using aspartic acid racemization analysis of tooth crown dentin or radiocarbon analysis of enamel, and 10 of these were split and subjected to both radiocarbon and racemization analysis. Combined analysis showed that the two methods correlated well (R(2) = 0.66, p < 0.05). Radiocarbon analysis showed an excellent precision with an overall absolute error of 1.0 +/- 0.6 years. Aspartic acid racemization also showed a good precision with an overall absolute error of 5.4 +/- 4.2 years. Whereas radiocarbon analysis gives an estimated year of birth, racemization analysis indicates the chronological age of the individual at the time of death. We show how these methods in combination can also assist in the estimation of date of death of an unidentified victim. This strategy can be of significant assistance in forensic casework involving dead victim identification.

  1. Age estimation in forensic sciences: application of combined aspartic acid racemization and radiocarbon analysis.

    PubMed

    Alkass, Kanar; Buchholz, Bruce A; Ohtani, Susumu; Yamamoto, Toshiharu; Druid, Henrik; Spalding, Kirsty L

    2010-05-01

    Age determination of unknown human bodies is important in the setting of a crime investigation or a mass disaster because the age at death, birth date, and year of death as well as gender can guide investigators to the correct identity among a large number of possible matches. Traditional morphological methods used by anthropologists to determine age are often imprecise, whereas chemical analysis of tooth dentin, such as aspartic acid racemization, has shown reproducible and more precise results. In this study, we analyzed teeth from Swedish individuals using both aspartic acid racemization and radiocarbon methodologies. The rationale behind using radiocarbon analysis is that aboveground testing of nuclear weapons during the cold war (1955-1963) caused an extreme increase in global levels of carbon-14 ((14)C), which has been carefully recorded over time. Forty-four teeth from 41 individuals were analyzed using aspartic acid racemization analysis of tooth crown dentin or radiocarbon analysis of enamel, and 10 of these were split and subjected to both radiocarbon and racemization analysis. Combined analysis showed that the two methods correlated well (R(2) = 0.66, p < 0.05). Radiocarbon analysis showed an excellent precision with an overall absolute error of 1.0 +/- 0.6 years. Aspartic acid racemization also showed a good precision with an overall absolute error of 5.4 +/- 4.2 years. Whereas radiocarbon analysis gives an estimated year of birth, racemization analysis indicates the chronological age of the individual at the time of death. We show how these methods in combination can also assist in the estimation of date of death of an unidentified victim. This strategy can be of significant assistance in forensic casework involving dead victim identification. PMID:19965905

  2. Patterns of racemization and epimerization of amino acids in land snail shells over the course of the Holocene

    SciTech Connect

    Goodfriend, G.A. )

    1991-01-01

    The patterns of racemization of six amino acids and of epimerization of isoleucine over the course of the Holocene were studied in a series of 38 radiocarbon-dated samples of the land snail Trochoidea seetzeni from the Negev Desert in southern Israel. The D/L ratios of each of the amino acids show a strong correlation with age (r = 0.84-0.94) and thus good age predictive ability. The patterns in faster-racemizing amino acids do not conform to first-order kinetics. Transformation to parabolic kinetics linearizes these faster-racemizing amino acids, except for aspartic acid (which shows a very high initial rate of racemization). After transformation, each amino acid shows an equally good correlation with age (r = 0.91-0.93). The D/L ratios of the various amino acids covary very strongly, even after the covariation due to sample age is removed from the data set. Thus, analysis of more than one amino acid provides largely redundant information on sample age. Nevertheless, because of differences in racemization rates, some amino acids provide better time resolution in different time ranges - aspartic acid is especially useful for very young samples, and glutamic acid and isoleucine for older samples. Neither the depth of burial of the samples nor the burial mode appears to affect the rate of racemization or epimerization.

  3. Concentration variations of amino acids in mammalian fossils: effects of diagenesis and the implications for amino acid racemization analysis

    SciTech Connect

    Blackwell, B.; Rutter, N.W.

    1985-01-01

    Detailed amino acid analysis of bones, teeth, and antler from several mammal species have shown that concentrations of several amino acids can be related to three factors: type of material analyzed, diagenetic alteration of the material, and relative age of the fossil. Concentrations of several amino acids are significantly different in enamel compared to those of dentine or cement. This can be used to check that no contamination of one material by another has occurred, which is critical for using the data for amino acid dating, since all three materials have different racemization rates for some acids. With increased in growth of secondary minerals, generally reduced amino acid concentrations are observed. Interacid ratios and concentrations vary significantly the norms expected for the type of material with increasing degrees of alteration. These effects can be linked to abnormal racemization ratios observed in the same samples. Therefore, abnormal concentrations and/or interacid ratios can be used to detect samples in which the D/L amino acid ratios otherwise appear normal, thereby insuring better accuracy of amino acid racemization analysis. For unaltered fossils, with increasing sample age regardless the type of material, some amino acids steadily degrade, while others actually increase in concentration initially due to their generation as by-products of decay. Preliminary studies indicate that this progressive alteration can used to complement racemization data for determining relative stratigraphic sequences.

  4. Excellent amino acid racemization results from Holocene sand dollars

    NASA Astrophysics Data System (ADS)

    Kosnik, M.; Kaufman, D. S.; Kowalewski, M.; Whitacre, K.

    2015-12-01

    Amino acid racemization (AAR) is widely used as a cost-effective method to date molluscs in time-averaging and taphonomic studies, but it has not been attempted for echinoderms despite their paleobiological importance. Here we demonstrate the feasibility of AAR geochronology in Holocene aged Peronella peronii (Echinodermata: Echinoidea) collected from Sydney Harbour (Australia). Using standard HPLC methods we determined the extent of AAR in 74 Peronella tests and performed replicate analyses on 18 tests. We sampled multiple areas of two individuals and identified the outer edge as a good sampling location. Multiple replicate analyses from the outer edge of 18 tests spanning the observed range of D/Ls yielded median coefficients of variation < 4% for Asp, Phe, Ala, and Glu D/L values, which overlaps with the analytical precision. Correlations between D/L values across 155 HPLC injections sampled from 74 individuals are also very high (pearson r2 > 0.95) for these four amino acids. The ages of 11 individuals spanning the observed range of D/L values were determined using 14C analyses, and Bayesian model averaging was used to determine the best AAR age model. The averaged age model was mainly composed of time-dependent reaction kinetics models (TDK, 71%) based on phenylalanine (Phe, 94%). Modelled ages ranged from 14 to 5539 yrs, and the median 95% confidence interval for the 74 analysed individuals is ±28% of the modelled age. In comparison, the median 95% confidence interval for the 11 calibrated 14C ages was ±9% of the median age estimate. Overall Peronella yields exceptionally high-quality AAR D/L values and appears to be an excellent substrate for AAR geochronology. This work opens the way for time-averaging and taphonomic studies of echinoderms similar to those in molluscs.

  5. Amino acid racemization on Mars: implications for the preservation of biomolecules from an extinct martian biota

    NASA Technical Reports Server (NTRS)

    Bada, J. L.; McDonald, G. D.; Miller, S. L. (Principal Investigator)

    1995-01-01

    Using kinetic data, we have estimated the racemization half-lives and times for total racemization of amino acids under conditions relevant to the surface of Mars. Amino acids from an extinct martian biota maintained in a dry, cold (<250 K) environment would not have racemized significantly over the lifetime of the planet. Racemization would have taken place in environments where liquid water was present even for time periods of only a few million years following biotic extinction. The best preservation of both amino acid homochirality and nucleic acid genetic information associated with extinct martian life would be in the polar regions.

  6. Ontogenetic trends in aspartic acid racemization and amino acid composition within modern and fossil shells of the bivalve Arctica

    NASA Astrophysics Data System (ADS)

    Goodfriend, Glenn A.; Weidman, Christopher R.

    2001-06-01

    Ontogenetic trends (umbo to growth edge of shell) in aspartic acid (Asp) racemization and amino acid composition and their evolution over time are examined in serial samples of annual growth bands from a time-series of three live-collected and two fossil (ca. 500 and 1000 y BP) shells of the long-lived bivalve Arctica islandica. The rate of Asp racemization is shown to be higher in the umbonal portion of the shells (laid down when the clams are young) but constant from a biological age of 10 to 20 y to more than 100 y. Corresponding changes are also seen in amino acid composition and concentration: with increasing biological age of the clam: total amino acid concentration increases substantially, the acidic amino acids Asp, glutamic acid, and alanine decrease in relative concentration (mole-percent) and more basic amino acids including tyrosine, phenylalanine, and lysine increase in relative concentration. These ontogenetic trends are generally retained in the fossil shells. These trends may reflect changing protein composition related to changes in growth rate. Clams grow considerably faster in their youth than when they are older, as indicated by changes in the annual growth increments. Production of more acidic proteins, which play a role in crystal growth, may be favored during the phase of faster growth, whereas more structural proteins, perhaps enhancing structural strength of the shell, may be favored during later growth. These ontogenetic differences in protein composition affect the observed rates of racemization of the protein pool. Some weak diagenetic trends in amino acid composition and abundance may be represented in the time series of shells. These results emphasize the importance of standardization of the location from which samples are taken from shells for dating by amino acid racemization analysis.

  7. Amino Acid Racemization in Pseudomonas putida KT2440

    PubMed Central

    Radkov, Atanas D.

    2013-01-01

    d-Amino acids have been shown to play an increasingly diverse role in bacterial physiology, yet much remains to be learned about their synthesis and catabolism. Here we used the model soil- and rhizosphere-dwelling organism Pseudomonas putida KT2440 to elaborate on the genomics and enzymology of d-amino acid metabolism. P. putida KT2440 catabolized the d-stereoisomers of lysine, phenylalanine, arginine, alanine, and hydroxyproline as the sole carbon and nitrogen sources. With the exception of phenylalanine, each of these amino acids was racemized by P. putida KT2440 enzymes. Three amino acid racemases were identified from a genomic screen, and the enzymes were further characterized in vitro. The putative biosynthetic alanine racemase Alr showed broad substrate specificity, exhibiting measurable racemase activity with 9 of the 19 chiral amino acids. Among these amino acids, activity was the highest with lysine, and the kcat/Km values with l- and d-lysine were 3 orders of magnitude greater than the kcat/Km values with l- and d-alanine. Conversely, the putative catabolic alanine racemase DadX showed narrow substrate specificity, clearly preferring only the alanine stereoisomers as the substrates. However, DadX did show 6- and 9-fold higher kcat/Km values than Alr with l- and d-alanine, respectively. The annotated proline racemase ProR of P. putida KT2440 showed negligible activity with either stereoisomer of the 19 chiral amino acids but exhibited strong epimerization activity with hydroxyproline as the substrate. Comparative genomic analysis revealed differences among pseudomonads with respect to alanine racemase genes that may point to different roles for these genes among closely related species. PMID:23995642

  8. Effect of molecular chirality on racemate stability: alpha-amino acids with nonpolar R groups.

    PubMed

    Huang, Jun; Yu, Lian

    2006-02-15

    A racemate of two opposite and resolvable enantiomers is generally assumed to be more stable than the corresponding conglomerate. Demonstrating this structure-stability relation, however, has proved difficult owing to a sampling bias (data available only for systems whose racemates are stable enough to exist) and a possible kinetic bias (racemates may be easier to crystallize than conglomerates from racemic media). As a new approach to studying the relation, we determined how the relative stability of the conglomerate and the racemate changes with the molecule's degree of chirality in a series of alpha-amino acids with nonpolar R groups. We found that the excess energy of the conglomerate over the racemate, (E(C) - E(R)), increases with the size of the R group, a measure of the molecule's chirality. If valid in general, this relation demonstrates a tendency for chiral molecules to form racemates rather than conglomerates. Because of the entropy effect on crystal stability, however, the excess free energy of the conglomerate over the racemate, (G(C) - G(R)), shows no simple relation with the degree of chirality at the temperatures of study (-3 to 180 degrees C).

  9. Are the Crystal Structures of Enantiopure and Racemic Mandelic Acids Determined by Kinetics or Thermodynamics?

    PubMed

    Hylton, Rebecca K; Tizzard, Graham J; Threlfall, Terence L; Ellis, Amy L; Coles, Simon J; Seaton, Colin C; Schulze, Eric; Lorenz, Heike; Seidel-Morgenstern, Andreas; Stein, Matthias; Price, Sarah L

    2015-09-01

    Mandelic acids are prototypic chiral molecules where the sensitivity of crystallized forms (enantiopure/racemic compound/polymorphs) to both conditions and substituents provides a new insight into the factors that may allow chiral separation by crystallization. The determination of a significant number of single crystal structures allows the analysis of 13 enantiopure and 30 racemic crystal structures of 21 (F/Cl/Br/CH3/CH3O) substituted mandelic acid derivatives. There are some common phenyl packing motifs between some groups of racemic and enantiopure structures, although they show very different hydrogen-bonding motifs. The computed crystal energy landscape of 3-chloromandelic acid, which has at least two enantiopure and three racemic crystal polymorphs, reveals that there are many more possible structures, some of which are predicted to be thermodynamically more favorable as well as slightly denser than the known forms. Simulations of mandelic acid dimers in isolation, water, and toluene do not differentiate between racemic and enantiopure dimers and also suggest that the phenyl ring interactions play a major role in the crystallization mechanism. The observed crystallization behavior of mandelic acids does not correspond to any simple "crystal engineering rules" as there is a range of thermodynamically feasible structures with no distinction between the enantiopure and racemic forms. Nucleation and crystallization appear to be determined by the kinetics of crystal growth with a statistical bias, but the diversity of the mandelic acid crystallization behavior demonstrates that the factors that influence the kinetics of crystal nucleation and growth are not yet adequately understood.

  10. Numerical dating of a Late Quaternary spit-shoreline complex at the northern end of Silver Lake playa, Mojave Desert, California: A comparison of the applicability of radiocarbon, luminescence, terrestrial cosmogenic nuclide, electron spin resonance, U-series and amino acid racemization methods

    USGS Publications Warehouse

    Owen, L.A.; Bright, Jordon; Finkel, R.C.; Jaiswal, M.K.; Kaufman, D.S.; Mahan, S.; Radtke, U.; Schneider, J.S.; Sharp, W.; Singhvi, A.K.; Warren, C.N.

    2007-01-01

    A Late Quaternary spit-shoreline complex on the northern shore of Pleistocene Lake Mojave of southeastern California, USA was studied with the goal of comparing accelerator mass spectrometry (AMS) radiocarbon, luminescence, electron spin resonance (ESR), terrestrial cosmogenic radionuclide (TCN) surface exposure, amino acid racemization (AAR) and U-series dating methods. The pattern of ages obtained by the different methods illustrates the complexity of processes acting in the lakeshore environment and highlights the utility of a multi-method approach. TCN surface exposure ages (mostly ???20-30 ka) record the initial erosion of shoreline benches, whereas radiocarbon ages on shells (determined in this and previous studies) within the spit, supported by AAR data, record its construction at fluctuating lake levels from ???16 to 10 ka. Luminescence ages on spit sediment (???6-7 ka) and ESR ages on spit shells (???4 ka) are anomalously young relative to radiocarbon ages of shells within the same deposits. The significance of the surprisingly young luminescence ages is not clear. The younger ESR ages could be a consequence of post-mortem enrichment of U in the shells. High concentrations of detrital thorium in tufa coating spit gravels inhibited the use of single-sample U-series dating. Detailed comparisons such as this provide one of the few means of assessing the accuracy of Quaternary dating techniques. More such comparisons are needed. ?? 2007 Elsevier Ltd and INQUA.

  11. A comparative study of the kinetics of amino acid racemization/epimerization in fossil and modern mollusk shells

    SciTech Connect

    Goodfriend, G.A. Carnegie Inst. of Washington, Washington DC ); Meyer, V.R. )

    1991-11-01

    The present study examines the question of whether heating experiments on modern shell material accurately model the pattern of kinetics of racemization/epimerization in fossils. Using one modern sample and four fossil samples (dating to 9700-1700 yr B.P.) of a species of land snail from the Negev Desert, the kinetic behavior of the samples in laboratory heating experiments are compared. Results are then compared to the Holocene trend in kinetic patterns observed in a large series of radio-carbon-dated shells. For most amino acids (alanine, alloisoleucine/isoleucine, phenylalanine, and glutamic acid), the fossil material displays the same pattern of kinetics in relation to time as the modern shells; deviant patterns are observed for aspartic acid, proline, and methionine. Adherence to a first order kinetic pattern in heated shells occurs only in alloisoleucine/isoleucine (within the range of D/L ratios studied). Differences in the temperature dependence of racemization/epimerization rates are found between modern and fossil samples. In most cases this relationship when extrapolated to natural temperatures, does not agree well with observed rates of racemization/epimerization in the fossil series. However the pattern of change in rate of racemization/epimerization with time in heating experiments generally follows the trend observed in the fossil series rather well. The experiments indicate that heating experiment results for certain amino acids, such as the widely used alloisoleucine/isoleucine, do give good predictions of kinetic patterns in relation to time in fossils but that predictions of the temperature dependence of rates are less accurate.

  12. The Formation of Racemic Amino Acids by UV Photolysis of Interstellar Ice Analogs

    NASA Technical Reports Server (NTRS)

    Bernstein, Max P.; Dworkin, Jason P.; Sandford, Scott A.; Cooper, George; Allamandola, Louis J.; DeVincenzi, Donald (Technical Monitor)

    2001-01-01

    Small biologically relevant organic molecules including the amino acids glycine, alanine, and marine were formed in the laboratory by the UV (Ultraviolet) photolysis of realistic interstellar ice analogs, composed primarily of H2O, and including CH3OH, NH3, and HCN, under interstellar conditions. N-formyl glycine, cycloserine (4-amino-3-isoxazolidinone), and glycerol were detected before hydrolysis, and glycine, racemic alanine, racemic marine, glycerol, ethanolamine, and glyceric acid were found after hydrolysis. This suggests that some meteoritic amino acids (and other molecules) may be the direct result of interstellar ice photochemistry, expanding the current paradigm that they formed by reactions in liquid water on meteorite parent bodies.

  13. Are the Crystal Structures of Enantiopure and Racemic Mandelic Acids Determined by Kinetics or Thermodynamics?

    PubMed

    Hylton, Rebecca K; Tizzard, Graham J; Threlfall, Terence L; Ellis, Amy L; Coles, Simon J; Seaton, Colin C; Schulze, Eric; Lorenz, Heike; Seidel-Morgenstern, Andreas; Stein, Matthias; Price, Sarah L

    2015-09-01

    Mandelic acids are prototypic chiral molecules where the sensitivity of crystallized forms (enantiopure/racemic compound/polymorphs) to both conditions and substituents provides a new insight into the factors that may allow chiral separation by crystallization. The determination of a significant number of single crystal structures allows the analysis of 13 enantiopure and 30 racemic crystal structures of 21 (F/Cl/Br/CH3/CH3O) substituted mandelic acid derivatives. There are some common phenyl packing motifs between some groups of racemic and enantiopure structures, although they show very different hydrogen-bonding motifs. The computed crystal energy landscape of 3-chloromandelic acid, which has at least two enantiopure and three racemic crystal polymorphs, reveals that there are many more possible structures, some of which are predicted to be thermodynamically more favorable as well as slightly denser than the known forms. Simulations of mandelic acid dimers in isolation, water, and toluene do not differentiate between racemic and enantiopure dimers and also suggest that the phenyl ring interactions play a major role in the crystallization mechanism. The observed crystallization behavior of mandelic acids does not correspond to any simple "crystal engineering rules" as there is a range of thermodynamically feasible structures with no distinction between the enantiopure and racemic forms. Nucleation and crystallization appear to be determined by the kinetics of crystal growth with a statistical bias, but the diversity of the mandelic acid crystallization behavior demonstrates that the factors that influence the kinetics of crystal nucleation and growth are not yet adequately understood. PMID:26244445

  14. Racemization of aspartic acid and phenylalanine in the sweetener aspartame at 100 degrees C.

    PubMed Central

    Boehm, M F; Bada, J L

    1984-01-01

    The racemization half-lives (i.e., the time required to reach a D/L = 0.33) at pH 6.8 for aspartic acid and phenylalanine in the sweetener aspartame (L-aspartyl-L-phenylalanine methyl ester) were determined to be 13 and 23 hours, respectively, at 100 degrees C. Racemization at this pH does not occur in aspartame but rather in its diketopiperazine decomposition product. Our results indicate that the use of aspartame to sweeten neutral pH foods and beverages that are then heated at elevated temperature could generate D-aspartic acid and D-phenylalanine. The nutritive consequences of these D-amino acids in the human diet are not well established, and thus aspartame should probably not be used as a sweetener when the exposure of neutral pH foods and beverages to elevated temperatures is required. At pH 4, a typical pH of most foods and beverages that might be sweetened with aspartame, the half-lives are 47 hours for aspartic acid and 1200 hours for phenylalanine at 100 degrees C. Racemization at pH 4 takes place in aspartame itself. Although the racemization rates at pH 4 are slow and no appreciable racemization of aspartic acid and phenylalanine should occur during the normal use of aspartame, some food and beverage components could conceivably act as catalysts. Additional studies are required to evaluate whether the use of aspartame as a sugar substitute might not in turn result in an increased human consumption of D-aspartic acid and D-phenylalanine. PMID:6591191

  15. Racemization of aspartic acid and phenylalanine in the sweetener aspartame at 100 degrees C.

    PubMed

    Boehm, M F; Bada, J L

    1984-08-01

    The racemization half-lives (i.e., the time required to reach a D/L = 0.33) at pH 6.8 for aspartic acid and phenylalanine in the sweetener aspartame (L-aspartyl-L-phenylalanine methyl ester) were determined to be 13 and 23 hours, respectively, at 100 degrees C. Racemization at this pH does not occur in aspartame but rather in its diketopiperazine decomposition product. Our results indicate that the use of aspartame to sweeten neutral pH foods and beverages that are then heated at elevated temperature could generate D-aspartic acid and D-phenylalanine. The nutritive consequences of these D-amino acids in the human diet are not well established, and thus aspartame should probably not be used as a sweetener when the exposure of neutral pH foods and beverages to elevated temperatures is required. At pH 4, a typical pH of most foods and beverages that might be sweetened with aspartame, the half-lives are 47 hours for aspartic acid and 1200 hours for phenylalanine at 100 degrees C. Racemization at pH 4 takes place in aspartame itself. Although the racemization rates at pH 4 are slow and no appreciable racemization of aspartic acid and phenylalanine should occur during the normal use of aspartame, some food and beverage components could conceivably act as catalysts. Additional studies are required to evaluate whether the use of aspartame as a sugar substitute might not in turn result in an increased human consumption of D-aspartic acid and D-phenylalanine.

  16. Racemization in reverse: evidence that D-amino acid toxicity on Earth is controlled by bacteria with racemases.

    PubMed

    Zhang, Gaosen; Sun, Henry J

    2014-01-01

    D-amino acids are toxic for life on Earth. Yet, they form constantly due to geochemical racemization and bacterial growth (the cell walls of which contain D-amino acids), raising the fundamental question of how they ultimately are recycled. This study provides evidence that bacteria use D-amino acids as a source of nitrogen by running enzymatic racemization in reverse. Consequently, when soils are inundated with racemic amino acids, resident bacteria consume D- as well as L-enantiomers, either simultaneously or sequentially depending on the level of their racemase activity. Bacteria thus protect life on Earth by keeping environments D-amino acid free.

  17. Amino acid racemization in amber-entombed insects: implications for DNA preservation

    NASA Technical Reports Server (NTRS)

    Bada, J. L.; Wang, X. S.; Poinar, H. N.; Paabo, S.; Poinar, G. O.

    1994-01-01

    DNA depurination and amino acid racemization take place at similar rates in aqueous solution at neutral pH. This relationship suggests that amino acid racemization may be useful in accessing the extent of DNA chain breakage in ancient biological remains. To test this suggestion, we have investigated the amino acids in insects entombed in fossilized tree resins ranging in age from <100 years to 130 million years. The amino acids present in 40 to 130 million year old amber-entombed insects resemble those in a modern fly and are probably the most ancient, unaltered amino acids found so far on Earth. In comparison to other geochemical environments on the surface of the Earth, the amino acid racemization rate in amber insect inclusions is retarded by a factor of >10(4). These results suggest that in amber insect inclusions DNA depurination rates would also likely be retarded in comparison to aqueous solution measurements, and thus DNA fragments containing many hundreds of base pairs should be preserved. This conclusion is consistent with the reported successful retrieval of DNA sequences from amber-entombed organisms.

  18. Comparison of acid anhydrides with carboxylic acids in enantioselective enzymatic esterification of racemic menthol.

    PubMed

    Xu, J; Zhu, J; Kawamoto, T; Atsuo, T; Hu, Y

    1997-01-01

    Optical resolution of racemic menthol has been efficiently achieved by lipase-catalyzed enantioselective esterification in an organic solvent. The performance of the reaction using an acid anhydride as an acyl donor was compared with that using its corresponding free acid. The reactivities of acid anhydrides were found to be higher than their corresponding free acids, but acid anhydrides were also found to be easily hydrolyzed into free acids under the catalysis of the same enzyme. The existence of a too-high concentration of an acid anhydride in a micro-aqueous reaction system will cause dehydration and thus deactivation of the enzyme, and will enhance non-selective esterification of a chiral alcohol, which will reduce the optical purity of the product. All these drawbacks, however, could be effectively overcome in a semi-batch reaction system into which propionic anhydride was continuously fed. This system showed some advantages over a batch reaction system using free propionic acid: the reaction time of dl-menthol was shortened by half, the stability of the enzyme was much enhanced, and the optical purity of the product (l-menthyl ester) was kept at a similarly high level (> 98% ee). PMID:9631262

  19. Assessing amino acid racemization variability in coral intra-crystalline protein for geochronological applications

    NASA Astrophysics Data System (ADS)

    Hendy, Erica J.; Tomiak, Peter J.; Collins, Matthew J.; Hellstrom, John; Tudhope, Alexander W.; Lough, Janice M.; Penkman, Kirsty E. H.

    2012-06-01

    Over 500 Free Amino Acid (FAA) and corresponding Total Hydrolysed Amino Acid (THAA) analyses were completed from eight independently-dated, multi-century coral cores of massive Porites sp. colonies. This dataset allows us to re-evaluate the application of amino acid racemization (AAR) for dating late Holocene coral material, 20 years after Goodfriend et al. (GCA56 (1992), 3847) first showed AAR had promise for developing chronologies in coral cores. This re-assessment incorporates recent method improvements, including measurement by RP-HPLC, new quality control approaches (e.g. sampling and sub-sampling protocols, statistically-based data screening criteria), and cleaning steps to isolate the intra-crystalline skeletal protein. We show that the removal of the extra-crystalline contaminants and matrix protein is the most critical step for reproducible results and recommend a protocol of bleaching samples in NaOCl for 48 h to maximise removal of open system proteins while minimising the induced racemization. We demonstrate that AAR follows closed system behaviour in the intra-crystalline fraction of the coral skeletal proteins. Our study is the first to assess the natural variability in intra-crystalline AAR between colonies, and we use coral cores taken from the Great Barrier Reef, Australia, and Jarvis Island in the equatorial Pacific to explore variability associated with different environmental conditions and thermal histories. Chronologies were developed from THAA Asx D/L, Ala D/L, Glx D/L and FAA Asx D/L for each core and least squares Monte Carlo modelling applied in order to quantify uncertainty of AAR age determinations and assess the level of dating resolution possible over the last 5 centuries. AAR within colonies follow consistent stratigraphic aging. However, there are systematic differences in rates between the colonies, which would preclude direct comparison from one colony to another for accurate age estimation. When AAR age models are developed from

  20. Assessing amino acid racemization variability in coral intra-crystalline protein for geochronological applications.

    PubMed

    Hendy, Erica J; Tomiak, Peter J; Collins, Matthew J; Hellstrom, John; Tudhope, Alexander W; Lough, Janice M; Penkman, Kirsty E H

    2012-06-01

    Over 500 Free Amino Acid (FAA) and corresponding Total Hydrolysed Amino Acid (THAA) analyses were completed from eight independently-dated, multi-century coral cores of massive Porites sp. colonies. This dataset allows us to re-evaluate the application of amino acid racemization (AAR) for dating late Holocene coral material, 20 years after Goodfriend et al. (GCA56 (1992), 3847) first showed AAR had promise for developing chronologies in coral cores. This re-assessment incorporates recent method improvements, including measurement by RP-HPLC, new quality control approaches (e.g. sampling and sub-sampling protocols, statistically-based data screening criteria), and cleaning steps to isolate the intra-crystalline skeletal protein. We show that the removal of the extra-crystalline contaminants and matrix protein is the most critical step for reproducible results and recommend a protocol of bleaching samples in NaOCl for 48 h to maximise removal of open system proteins while minimising the induced racemization. We demonstrate that AAR follows closed system behaviour in the intra-crystalline fraction of the coral skeletal proteins. Our study is the first to assess the natural variability in intra-crystalline AAR between colonies, and we use coral cores taken from the Great Barrier Reef, Australia, and Jarvis Island in the equatorial Pacific to explore variability associated with different environmental conditions and thermal histories. Chronologies were developed from THAA Asx D/L, Ala D/L, Glx D/L and FAA Asx D/L for each core and least squares Monte Carlo modelling applied in order to quantify uncertainty of AAR age determinations and assess the level of dating resolution possible over the last 5 centuries. AAR within colonies follow consistent stratigraphic aging. However, there are systematic differences in rates between the colonies, which would preclude direct comparison from one colony to another for accurate age estimation. When AAR age models are developed

  1. Crystallization and sublimation of non-racemic mixtures of natural amino acids: a path towards homochirality

    NASA Astrophysics Data System (ADS)

    Tarasevych, Arkadii V.; Guillemin, Jean-Claude

    2012-07-01

    Homochirality of biologically important molecules such as amino acids and sugars is a prerequisite for the origin of life. There are different forces or mechanisms in the Universe to trigger off the primary imbalance in the enantiomeric ratio. Very likely the initial bias of one type of enantiomers over the other on Earth was arisen from the inflow of extraterrestrial matter (carbonaceous meteorites). The phase transitions (crystallization, sublimation) of non-racemic mixtures of enantiomers are ones of the most probable mechanisms for the homochirogenesis[1]. The sublimation, almost uninvestigated subject and forgotten for 30 years, revealed recently a pathway to the enantioenrichment of natural amino acids[2]. Starting from a mixture with a low content of an enantiopure amino acid a partial sublimation gives a considerable enrichment. In our further experiments we combined two first-order phase transitions of amino acid(s) mixtures: crystallization and sublimation. The results show the possibility of the transfer of enantiopurity between different amino acids[3]. Subliming a crystallized mixture of racemic amino acids with an enantiopure one we found that the sublimate is a non-racemic mixture of the same handedness for all components. The significance of the studies can be realized taking into account that just 5 of 22 proteinogenic amino acids are able to homochiral self-organization. The relevance of these studies to the Prebiotic Earth and to the evolution of the single handedness of biological molecules will be discussed. [1] Blackmond, Phil. Trans. R. Soc. B 2011, 366, 2878. [2] Guillemin et al., Chem. Commun. 2010 , 46, 1482. [3] Tarasevych, Guillemin et al., submitted.

  2. Is amino acid racemization a useful tool for screening for ancient DNA in bone?

    PubMed Central

    Collins, Matthew J.; Penkman, Kirsty E. H.; Rohland, Nadin; Shapiro, Beth; Dobberstein, Reimer C.; Ritz-Timme, Stefanie; Hofreiter, Michael

    2009-01-01

    Many rare and valuable ancient specimens now carry the scars of ancient DNA research, as questions of population genetics and phylogeography require larger sample sets. This fuels the demand for reliable techniques to screen for DNA preservation prior to destructive sampling. Only one such technique has been widely adopted: the extent of aspartic acid racemization (AAR). The kinetics of AAR are believed to be similar to the rate of DNA depurination and therefore a good measure of the likelihood of DNA survival. Moreover, AAR analysis is only minimally destructive. We report the first comprehensive test of AAR using 91 bone and teeth samples from temperate and high-latitude sites that were analysed for DNA. While the AAR range of all specimens was low (0.02–0.17), no correlation was found between the extent of AAR and DNA amplification success. Additional heating experiments and surveys of the literature indicated that d/l Asx is low in bones until almost all the collagen is lost. This is because aspartic acid is retained in the bone within the constrained environment of the collagen triple helix, where it cannot racemize for steric reasons. Only if the helix denatures to soluble gelatin can Asx racemize readily, but this soluble gelatine is readily lost in most burial environments. We conclude that Asx d/l is not a useful screening technique for ancient DNA from bone. PMID:19493899

  3. Does aspartic acid racemization constrain the depth limit of the subsurface biosphere?

    SciTech Connect

    Onstott, T. C.; Aubrey, A.D.; Kieft, T L; Silver, B J; Phelps, Tommy Joe; Van Heerden, E.; Opperman, D. J.; Bada, J L.

    2014-01-01

    Previous studies of the subsurface biosphere have deduced average cellular doubling times of hundreds to thousands of years based upon geochemical models. We have directly constrained the in situ average cellular protein turnover or doubling times for metabolically active micro-organisms based on cellular amino acid abundances, D/L values of cellular aspartic acid, and the in vivo aspartic acid racemization rate. Application of this method to planktonic microbial communities collected from deep fractures in South Africa yielded maximum cellular amino acid turnover times of ~89 years for 1 km depth and 27 C and 1 2 years for 3 km depth and 54 C. The latter turnover times are much shorter than previously estimated cellular turnover times based upon geochemical arguments. The aspartic acid racemization rate at higher temperatures yields cellular protein doubling times that are consistent with the survival times of hyperthermophilic strains and predicts that at temperatures of 85 C, cells must replace proteins every couple of days to maintain enzymatic activity. Such a high maintenance requirement may be the principal limit on the abundance of living micro-organisms in the deep, hot subsurface biosphere, as well as a potential limit on their activity. The measurement of the D/L of aspartic acid in biological samples is a potentially powerful tool for deep, fractured continental and oceanic crustal settings where geochemical models of carbon turnover times are poorly constrained. Experimental observations on the racemization rates of aspartic acid in living thermophiles and hyperthermophiles could test this hypothesis. The development of corrections for cell wall peptides and spores will be required, however, to improve the accuracy of these estimates for environmental samples.

  4. Does aspartic acid racemization constrain the depth limit of the subsurface biosphere?

    PubMed

    Onstott, T C; Magnabosco, C; Aubrey, A D; Burton, A S; Dworkin, J P; Elsila, J E; Grunsfeld, S; Cao, B H; Hein, J E; Glavin, D P; Kieft, T L; Silver, B J; Phelps, T J; van Heerden, E; Opperman, D J; Bada, J L

    2014-01-01

    Previous studies of the subsurface biosphere have deduced average cellular doubling times of hundreds to thousands of years based upon geochemical models. We have directly constrained the in situ average cellular protein turnover or doubling times for metabolically active micro-organisms based on cellular amino acid abundances, D/L values of cellular aspartic acid, and the in vivo aspartic acid racemization rate. Application of this method to planktonic microbial communities collected from deep fractures in South Africa yielded maximum cellular amino acid turnover times of ~89 years for 1 km depth and 27 °C and 1-2 years for 3 km depth and 54 °C. The latter turnover times are much shorter than previously estimated cellular turnover times based upon geochemical arguments. The aspartic acid racemization rate at higher temperatures yields cellular protein doubling times that are consistent with the survival times of hyperthermophilic strains and predicts that at temperatures of 85 °C, cells must replace proteins every couple of days to maintain enzymatic activity. Such a high maintenance requirement may be the principal limit on the abundance of living micro-organisms in the deep, hot subsurface biosphere, as well as a potential limit on their activity. The measurement of the D/L of aspartic acid in biological samples is a potentially powerful tool for deep, fractured continental and oceanic crustal settings where geochemical models of carbon turnover times are poorly constrained. Experimental observations on the racemization rates of aspartic acid in living thermophiles and hyperthermophiles could test this hypothesis. The development of corrections for cell wall peptides and spores will be required, however, to improve the accuracy of these estimates for environmental samples.

  5. Does Aspartic Acid Racemization Constrain the Depth Limit of the Subsurface Biosphere?

    NASA Technical Reports Server (NTRS)

    Onstott, T C.; Magnabosco, C.; Aubrey, A. D.; Burton, A. S.; Dworkin, J. P.; Elsila, J. E.; Grunsfeld, S.; Cao, B. H.; Hein, J. E.; Glavin, D. P.; Kieft, T. L.; Silver, B. J.; Phelps, T. J.; Heerden, E. Van; Opperman, D. J.; Bada, J. L.

    2013-01-01

    Previous studies of the subsurface biosphere have deduced average cellular doubling times of hundreds to thousands of years based upon geochemical models. We have directly constrained the in situ average cellular protein turnover or doubling times for metabolically active micro-organisms based on cellular amino acid abundances, D/L values of cellular aspartic acid, and the in vivo aspartic acid racemization rate. Application of this method to planktonic microbial communities collected from deep fractures in South Africa yielded maximum cellular amino acid turnover times of approximately 89 years for 1 km depth and 27 C and 1-2 years for 3 km depth and 54 C. The latter turnover times are much shorter than previously estimated cellular turnover times based upon geochemical arguments. The aspartic acid racemization rate at higher temperatures yields cellular protein doubling times that are consistent with the survival times of hyperthermophilic strains and predicts that at temperatures of 85 C, cells must replace proteins every couple of days to maintain enzymatic activity. Such a high maintenance requirement may be the principal limit on the abundance of living micro-organisms in the deep, hot subsurface biosphere, as well as a potential limit on their activity. The measurement of the D/L of aspartic acid in biological samples is a potentially powerful tool for deep, fractured continental and oceanic crustal settings where geochemical models of carbon turnover times are poorly constrained. Experimental observations on the racemization rates of aspartic acid in living thermophiles and hyperthermophiles could test this hypothesis. The development of corrections for cell wall peptides and spores will be required, however, to improve the accuracy of these estimates for environmental samples.

  6. Enantioconvergent Nucleophilic Substitution Reaction of Racemic Alkyne-Dicobalt Complex (Nicholas Reaction) Catalyzed by Chiral Brønsted Acid.

    PubMed

    Terada, Masahiro; Ota, Yusuke; Li, Feng; Toda, Yasunori; Kondoh, Azusa

    2016-08-31

    Catalytic enantioselective syntheses enable a practical approach to enantioenriched molecules. While most of these syntheses have been accomplished by reaction at the prochiral sp(2)-hybridized carbon atom, little attention has been paid to enantioselective nucleophilic substitution at the sp(3)-hybridized carbon atom. In particular, substitution at the chiral sp(3)-hybridized carbon atom of racemic electrophiles has been rarely exploited. To establish an unprecedented enantioselective substitution reaction of racemic electrophiles, enantioconvergent Nicholas reaction of an alkyne-dicobalt complex derived from racemic propargylic alcohol was developed using a chiral phosphoric acid catalyst. In the present enantioconvergent process, both enantiomers of the racemic alcohol were transformed efficiently to a variety of thioethers with high enantioselectivity. The key to achieving success is dynamic kinetic asymmetric transformation (DYKAT) of enantiomeric cationic intermediates generated via dehydroxylation of the starting racemic alcohol under the influence of the chiral phosphoric acid catalyst. The present fascinating DYKAT involves the efficient racemization of these enantiomeric intermediates and effective resolution of these enantiomers through utilization of the chiral conjugate base of the phosphoric acid. PMID:27490239

  7. Enantioconvergent Nucleophilic Substitution Reaction of Racemic Alkyne-Dicobalt Complex (Nicholas Reaction) Catalyzed by Chiral Brønsted Acid.

    PubMed

    Terada, Masahiro; Ota, Yusuke; Li, Feng; Toda, Yasunori; Kondoh, Azusa

    2016-08-31

    Catalytic enantioselective syntheses enable a practical approach to enantioenriched molecules. While most of these syntheses have been accomplished by reaction at the prochiral sp(2)-hybridized carbon atom, little attention has been paid to enantioselective nucleophilic substitution at the sp(3)-hybridized carbon atom. In particular, substitution at the chiral sp(3)-hybridized carbon atom of racemic electrophiles has been rarely exploited. To establish an unprecedented enantioselective substitution reaction of racemic electrophiles, enantioconvergent Nicholas reaction of an alkyne-dicobalt complex derived from racemic propargylic alcohol was developed using a chiral phosphoric acid catalyst. In the present enantioconvergent process, both enantiomers of the racemic alcohol were transformed efficiently to a variety of thioethers with high enantioselectivity. The key to achieving success is dynamic kinetic asymmetric transformation (DYKAT) of enantiomeric cationic intermediates generated via dehydroxylation of the starting racemic alcohol under the influence of the chiral phosphoric acid catalyst. The present fascinating DYKAT involves the efficient racemization of these enantiomeric intermediates and effective resolution of these enantiomers through utilization of the chiral conjugate base of the phosphoric acid.

  8. Enigmatic Isovaline: Investigating the Stability, Racemization, and Formation of a Non-biological Meteoritic Amino Acid

    NASA Technical Reports Server (NTRS)

    Hudson, Reggie; Moore, Marla; Lewis, Ariel; Dworkin, Jason

    2008-01-01

    Among the Murchison meteoritic amino acids, isovaline stands out as being both nonbiological (non-protein) and having a relatively high abundance. While approximately equal amounts of D- and L-isovaline have been reported in Murchison and other CM meteorites, the molecule's structure appears to prohibit its racemization in aqueous solutions. We recently have investigated the low-temperature solid-phase chemistry of both isovaline and valine with an eye toward each molecule's formation, stability, and possible interconversions of D and L enantiomers. Ion-irradiated isovaline- and valinecontaining ices were examined by IR spectroscopy and highly-sensitive liquid chromatography/time-of-flight mass spectral methods to assess both amino acid destruction and racemization. Samples were studied in the presence and in the absence of water-ice, and the destruction of both isovaline and valine was measured as a function of radiation dose. In addition, we have undertaken experiments to synthesize isovaline, valine, and their amino acid isomers by solid-phase radiation-chemical pathways other than the oft-invoked Strecker process. This presentation will review and summarize some of our recent findings. -- Our work has been supported by a grant to the Goddard Center for Astrobiology through the NASA Astrobiology Institute. Experiments were performed in the Cosmic Ice Laboratory (RLH, MHM, AL) and the Astrobiology Analytical Laboratory (JPD, DPG) at the NASA Goddard Space Flight Center.

  9. Rhodium-catalysed asymmetric allylic arylation of racemic halides with arylboronic acids

    NASA Astrophysics Data System (ADS)

    Sidera, Mireia; Fletcher, Stephen P.

    2015-11-01

    Csp2-Csp2 cross-coupling reactions between arylboronic acid and aryl halides are widely used in both academia and industry and are strategically important in the development of new agrochemicals and pharmaceuticals. Csp2-Csp3 cross-coupling reactions have been developed, but enantioselective variations are rare and simply retaining the stereochemistry is a problem. Here we report a highly enantioselective Csp2-Csp3 bond-forming method that couples arylboronic acids to racemic allyl chlorides. Both enantiomers of a cyclic chloride are converted into a single enantiomer of product via a dynamic kinetic asymmetric transformation. This Rh-catalysed method uses readily available and inexpensive building blocks and is mild and broadly applicable. For electron-deficient, electron-rich or ortho-substituted boronic acids better results are obtained with racemic allyl bromides. Oxygen substitution in the allyl halide is tolerated and the products can be functionalized to provide diverse building blocks. The approach fills a significant gap in the methods for catalytic asymmetric synthesis.

  10. Use Of Amino Acid Racemization To Investigate The Metabolic Activity Of ?Dormant? Microorganisms In Siberian Permafrost

    NASA Astrophysics Data System (ADS)

    Tsapin, A.; McDonald, G.

    2002-12-01

    search for extraterrestrial life or its remnants is based on studying the most probable environments in which life (extant or extinct) may be found, and determining the maximum period of time over which such life could be preserved. The terrestrial permafrost, inhabited by cold adapted microbes, can be considered as an extraterrestrial analog environment. The cells and their metabolic end-products in Earth's permafrost can be used in the search for possible ecosystems and potential inhabitants on extraterrestrial cryogenic bodies. The study of microorganisms (or their remnants) that were buried for a few million years in permafrost provides us with a unique opportunity to determine the long-term viability of (micro)organisms. We have analyzed the degree of racemization of aspartic acid in permafrost samples from Northern Siberia (Brinton et al. 2002, Astrobiology 2, 77), an area from which microorganisms of apparent ages up to a few million years have previously been isolated and cultured. We find that the extent of aspartic acid racemization in permafrost cores increases very slowly up to an age of approximately 25,000 years (around 5 m depth). The apparent temperature of racemization over the age range 0-25,000 years, determined using measured aspartic acid racemization rate constants, is ?19 C. This apparent racemization temperature is significantly lower than the measured environmental temperature (?11 to ?13 C), and suggests active recycling of D-aspartic acid in Siberian permafrost up to an age of around 25,000 years. This indicates that permafrost organisms are capable of repairing some molecular damage incurred while they are in a ?dormant? state over geologic time.

  11. Growth kinetics of racemic heptahelicene-2-carboxylic acid nanowires on calcite (104)

    NASA Astrophysics Data System (ADS)

    Einax, Mario; Richter, Tobias; Nimmrich, Markus; Rahe, Philipp; Stará, Irena G.; Starý, Ivo; Kühnle, Angelika; Maass, Philipp

    2016-10-01

    Molecular self-assembly of racemic heptahelicene-2-carboxylic acid on a dielectric substrate at room temperature can be used to generate wire-like organic nanostructures consisting of single and double molecular rows. By means of non-contact atomic force microscopy, we investigate the growth of the wire-like pattern after deposition by experimental and theoretical means. From analyzing the time dependence of the mean row length, two distinct regimes were found. At the early post-deposition stage, the mean length grows in time. Subsequently, a crossover to a second regime is observed, where the mean row length remains nearly constant. We explain these findings by a mean-field rate equation approach providing a comprehensive picture of the growth kinetics. As a result, we demonstrate that the crossover between the two distinct regimes is accomplished by vanishing of the homochiral single rows. At later stages only heterochiral double row structures remain.

  12. Aspartic acid racemization in dentin of the third molar for age estimation of the Chaoshan population in South China.

    PubMed

    Chen, Shisheng; Lv, Yanyi; Wang, Dian; Yu, Xiaojun

    2016-09-01

    Aspartic acid racemization in teeth has been increasingly used to estimate chronological age with a considerably high accuracy in forensic practice. The Chaoshan population in South China is relatively isolated in geography, and has specific lifestyle and dietary inhibits. It is still unknown whether this method is suitable for this population. The aim of this study was to analyze the relationship between chronological age and the d/l aspartic acid ratio in dentin in the third molar tooth of the Chaoshan population. Fifty-eight non-carious third molar teeth (31 mandibles and 27 maxillae), from 58 living individuals of known age (24 males and 34 females), were retrieved. Dentin was extracted from these teeth. The d- and l-aspartic acids in dentins were separated and detected by high performance liquid chromatography (HPLC). Linear regression was performed between the d/l aspartic acid ratio of dentins and chronological age. Results showed that the correlation coefficient (r) was 0.969, and the mean absolute error (MAE) was 2.19 years, its standard deviation (SD) was ±1.53 years, indicating excellent correlation. There was no significant difference in racemization rates of dentin between sexes (P=0.113, F=2.6), or between mandibles and maxillae (P=0.964, F=0.000). Results indicate that the ratio of the d and l forms of aspartic acid of dentins, in the third molar, is closely correlated with chronological age, special lifestyle do no obviously affect the accuracy of the age estimations by aspartic acid racemization of the dentin in the third molar and that aspartic acid racemization in the third molar dentin can be used as an accurate method to estimate chronological age in the Chaoshan population in South China.

  13. Enantioselective Crystallization of Sodium Chlorate in the Presence of Racemic Hydrophobic Amino Acids and Static Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Zorzano, María-Paz; Osuna-Esteban, Susana; Ruiz-Bermejo, Marta; Menor-Salván, Cesar; Veintemillas-Verdaguer, Sabino

    2014-06-01

    We study the bias induced by a weak (200 mT) external magnetic field on the preferred handedness of sodium chlorate crystals obtained by slow evaporation at ambient conditions of its saturated saline solution with 20 ppm of added racemic (dl) hydrophobic amino acids. By applying the Fisher test to pairs of experiments with opposing magnetic field orientation we conclude, with a confidence level of 99.7%, that at the water-air interface of this saline solution there is an enantioselective magnetic interaction that acts upon racemic mixtures of hydrophobic chiral amino acids. This interaction has been observed with the three tested racemic hydrophobic amino acids: dl-Phe, dl-Try and dl-Trp, at ambient conditions and in spite of the ubiquitous chiral organic contamination. This enantioselective magnetic dependence is not observed when there is only one handedness of added chiral amino-acid, if the added amino acid is not chiral or if there is no additive. This effect has been confirmed with a double blind test. This novel experimental observation may have implications for our view of plausible initial prebiotic scenarios and of the roles of the geomagnetic field in homochirality in the biosphere.

  14. Chemical Principles Revisited: Archaeological Dating.

    ERIC Educational Resources Information Center

    Rowe, M. W.

    1986-01-01

    Discusses methods used to date archaeological artifacts and other remains. They include: (1) nuclear dating techniques (radiocarbon dating, accelerator radiocarbon dating, thermoluminescence, and others); (2) chemical dating techniques (amino acid racemization, obsidian hydration dating, elemental content changes, and thermal analysis dating); and…

  15. Kinetic resolution of racemic mandelic acid esters by N,N'-dioxide-scandium-complex-catalyzed enantiomer-selective acylation.

    PubMed

    Zhang, Yuheng; Liu, Xiaohua; Zhou, Lin; Wu, Wangbin; Huang, Tianyu; Liao, Yuting; Lin, Lili; Feng, Xiaoming

    2014-11-24

    A simple and efficient acylative kinetic resolution of racemic mandelic acid esters was accomplished with a chiral N,N'-dioxide-scandium(III) complex under mild and base-free reaction conditions. A variety of mandelic acid esters performed well in the reaction, obtaining both acylated products (up to 49% yield, 97% ee) and recovered substrates (up to 49% yield, 95% ee) in high enantioselectivities with perfect selectivity factors (up to 247). The enantioselective recognition and catalytic models were also proposed for the catalytic KR reaction.

  16. Evaluation of acid-labile S-protecting groups to prevent Cys racemization in Fmoc solid-phase peptide synthesis

    PubMed Central

    Hibino, Hajime; Miki, Yasuyoshi; Nishiuchi, Yuji

    2014-01-01

    Phosphonium and uronium salt-based reagents enable efficient and effective coupling reactions and are indispensable in peptide chemistry, especially in machine-assisted SPPS. However, after the activating and coupling steps with these reagents in the presence of tertiary amines, Fmoc derivatives of Cys are known to be considerably racemized during their incorporation. To avoid this side reaction, a coupling method mediated by phosphonium/uronium reagents with a weaker base, such as 2,4,6-trimethylpyridine, than the ordinarily used DIEA or that by carbodiimide has been recommended. However, these methods are appreciably inferior to the standard protocol applied for SPPS, that is, a 1 min preactivation procedure of coupling with phosphonium or uronium reagents/DIEA in DMF, in terms of coupling efficiency, and also the former method cannot reduce racemization of Cys(Trt) to an acceptable level (<1.0%) even when the preactivation procedure is omitted. Here, the 4,4′-dimethoxydiphenylmethyl and 4-methoxybenzyloxymethyl groups were demonstrated to be acid-labile S-protecting groups that can suppress racemization of Cys to an acceptable level (<1.0%) when the respective Fmoc derivatives are incorporated via the standard SPPS protocol of phosphonium or uronium reagents with the aid of DIEA in DMF. Furthermore, these protecting groups significantly reduced the rate of racemization compared to the Trt group even in the case of microwave-assisted SPPS performed at a high temperature. © 2013 The Authors. European Peptide Society published by John Wiley & Sons, Ltd. PMID:24357151

  17. Temperature calibration of amino acid racemization: age implications for the Yuha skeleton

    USGS Publications Warehouse

    Bischoff, J.L.; Childers, W.M.

    1979-01-01

    D/L of aspartic acid ranged from 0.52 to 0.56 for femur samples of the Yuha skeleton. Subsurface temperature measurements made at the burial site indicate average annual temperature is 18??C and diagenetic temperature is 21.6??C. These data and a relation derived for the dependence of the aspartic acid rate constant on diagenetic temperature indicate an age of 23,600. The result is consistent with 14C and 230Th dating of calcrete found coating the bones. ?? 1979.

  18. Fabrication of chiral amino acid ionic liquid modified magnetic multifunctional nanospheres for centrifugal chiral chromatography separation of racemates.

    PubMed

    Liu, Yating; Tian, Ailin; Wang, Xiong; Qi, Jing; Wang, Fengkang; Ma, Ying; Ito, Yoichiro; Wei, Yun

    2015-06-26

    As the rapid development of nanotechnology, the magnetic nanospheres modified with special chiral selective ligands show a great potentiality in enantiomeric separation. In this study, magnetic nanospheres modified with task-specific chiral ionic liquid were designed for the separation of chiral amino acids. These modified magnetic nanospheres were effective in a direct chiral separation of five racemic amino acids (D- and L-cysteine, D- and L-arginine, D- and L-leucine, D- and L-glutamine and D- and L-tryptophan). Furthermore, a new online method for complete separation of the enantiomers via the magnetic nanospheres was established with centrifugal chiral chromatography using a spiral tube assembly mounted on a type-J coil planet centrifuge. One kind of chiral compounds, D- and L-tryptophan was resolved well using this method. These results demonstrated that the modified nanospheres display a good chiral recognition ability, and can be used as a potential material for chiral separation of various racemates.

  19. Immobilized chiral tropine ionic liquid on silica gel as adsorbent for separation of metal ions and racemic amino acids.

    PubMed

    Qian, Guofei; Song, Hang; Yao, Shun

    2016-01-15

    Tropine-type chiral ionic liquid with proline anion was immobilized on silica gel by chemical modification method for the first time, which was proved by elemental, infrared spectrum and thermogravimetric analysis. Secondly, the performance of this kind of ionic liquid-modified silica gel was investigated in the adsorption of some metal ions, which included Cu(2+), Fe(3+), Mn(2+) and Ni(2+). Then the effects of time, initial concentration and temperature on adsorption for Cu(2+) ions were studied in detail, which was followed by the further research of adsorption kinetics and thermodynamics. The adsorption could be better described by pseudo-second-order kinetics model and that the process was spontaneous, exothermic and entropy decreasing. In the mode of 'reuse after adsorption', the ionic liquid-modified silica gel with saturated adsorption of Cu(2+) was finally used in resolution of racemic amino acids for the first time. The static experiment showed that adsorption rate of two enantiomers was obviously different. Inspired by this, the complex was packed in chromatographic column for the separation of racemic amino acids and d-enantiomers were firstly eluted by water or ethanol. Steric hindrance was found as one of key influencing factors for its effect on the stability of the complex.

  20. Immobilized chiral tropine ionic liquid on silica gel as adsorbent for separation of metal ions and racemic amino acids.

    PubMed

    Qian, Guofei; Song, Hang; Yao, Shun

    2016-01-15

    Tropine-type chiral ionic liquid with proline anion was immobilized on silica gel by chemical modification method for the first time, which was proved by elemental, infrared spectrum and thermogravimetric analysis. Secondly, the performance of this kind of ionic liquid-modified silica gel was investigated in the adsorption of some metal ions, which included Cu(2+), Fe(3+), Mn(2+) and Ni(2+). Then the effects of time, initial concentration and temperature on adsorption for Cu(2+) ions were studied in detail, which was followed by the further research of adsorption kinetics and thermodynamics. The adsorption could be better described by pseudo-second-order kinetics model and that the process was spontaneous, exothermic and entropy decreasing. In the mode of 'reuse after adsorption', the ionic liquid-modified silica gel with saturated adsorption of Cu(2+) was finally used in resolution of racemic amino acids for the first time. The static experiment showed that adsorption rate of two enantiomers was obviously different. Inspired by this, the complex was packed in chromatographic column for the separation of racemic amino acids and d-enantiomers were firstly eluted by water or ethanol. Steric hindrance was found as one of key influencing factors for its effect on the stability of the complex. PMID:26711153

  1. Chemo-enzymatic Baeyer-Villiger oxidation of 4-methylcyclohexanone via kinetic resolution of racemic carboxylic acids: direct access to enantioenriched lactone.

    PubMed

    Drożdż, Agnieszka; Chrobok, Anna

    2016-01-21

    A new method for the asymmetric chemo-enzymatic Baeyer-Villiger oxidation of prochiral 4-methylcyclohexanone to (R)-4-methylcaprolactone in the presence of (±)-4-methyloctanoic acid, Candida Antarctica lipase B and 30% aq. H2O2 has been developed. A mechanism for the asymmetric induction based on kinetic resolution of racemic carboxylic acids is proposed.

  2. Racemic DNA crystallography.

    PubMed

    Mandal, Pradeep K; Collie, Gavin W; Kauffmann, Brice; Huc, Ivan

    2014-12-22

    Racemates increase the chances of crystallization by allowing molecular contacts to be formed in a greater number of ways. With the advent of protein synthesis, the production of protein racemates and racemic-protein crystallography are now possible. Curiously, racemic DNA crystallography had not been investigated despite the commercial availability of L- and D-deoxyribo-oligonucleotides. Here, we report a study into racemic DNA crystallography showing the strong propensity of racemic DNA mixtures to form racemic crystals. We describe racemic crystal structures of various DNA sequences and folded conformations, including duplexes, quadruplexes, and a four-way junction, showing that the advantages of racemic crystallography should extend to DNA.

  3. Racemic amino acids from the ultraviolet photolysis of interstellar ice analogues

    NASA Technical Reports Server (NTRS)

    Bernstein, Max P.; Dworkin, Jason P.; Sandford, Scott A.; Cooper, George W.; Allamandola, Louis J.

    2002-01-01

    The delivery of extraterrestrial organic molecules to Earth by meteorites may have been important for the origin and early evolution of life. Indigenous amino acids have been found in meteorites-over 70 in the Murchison meteorite alone. Although it has been generally accepted that the meteoritic amino acids formed in liquid water on a parent body, the water in the Murchison meteorite is depleted in deuterium relative to the indigenous organic acids. Moreover, the meteoritical evidence for an excess of laevo-rotatory amino acids is hard to understand in the context of liquid-water reactions on meteorite parent bodies. Here we report a laboratory demonstration that glycine, alanine and serine naturally form from ultraviolet photolysis of the analogues of icy interstellar grains. Such amino acids would naturally have a deuterium excess similar to that seen in interstellar molecular clouds, and the formation process could also result in enantiomeric excesses if the incident radiation is circularly polarized. These results suggest that at least some meteoritic amino acids are the result of interstellar photochemistry, rather than formation in liquid water on an early Solar System body.

  4. Racemic amino acids from the ultraviolet photolysis of interstellar ice analogues.

    PubMed

    Bernstein, Max P; Dworkin, Jason P; Sandford, Scott A; Cooper, George W; Allamandola, Louis J

    2002-03-28

    The delivery of extraterrestrial organic molecules to Earth by meteorites may have been important for the origin and early evolution of life. Indigenous amino acids have been found in meteorites-over 70 in the Murchison meteorite alone. Although it has been generally accepted that the meteoritic amino acids formed in liquid water on a parent body, the water in the Murchison meteorite is depleted in deuterium relative to the indigenous organic acids. Moreover, the meteoritical evidence for an excess of laevo-rotatory amino acids is hard to understand in the context of liquid-water reactions on meteorite parent bodies. Here we report a laboratory demonstration that glycine, alanine and serine naturally form from ultraviolet photolysis of the analogues of icy interstellar grains. Such amino acids would naturally have a deuterium excess similar to that seen in interstellar molecular clouds, and the formation process could also result in enantiomeric excesses if the incident radiation is circularly polarized. These results suggest that at least some meteoritic amino acids are the result of interstellar photochemistry, rather than formation in liquid water on an early Solar System body.

  5. Racemic synthesis and solid phase peptide synthesis application of the chimeric valine/leucine derivative 2-amino-3,3,4-trimethyl-pentanoic acid.

    PubMed

    Pelà, M; Del Zoppo, L; Allegri, L; Marzola, E; Ruzza, C; Calo, G; Perissutti, E; Frecentese, F; Salvadori, S; Guerrini, R

    2014-07-01

    The synthesis of non natural amino acid 2-amino-3,3,4-trimethyl-pentanoic acid (Ipv) ready for solid phase peptide synthesis has been developed. Copper (I) chloride Michael addition, followed by a Curtius rearrangement are the key steps for the lpv synthesis. The racemic valine/leucine chimeric amino acid was then successfully inserted in position 5 of neuropeptide S (NPS) and the diastereomeric mixture separated by reverse phase HPLC. The two diastereomeric NPS derivatives were tested for intracellular calcium mobilization using HEK293 cells stably expressing the mouse NPS receptor where they behaved as partial agonist and pure antagonist.

  6. NON-RACEMIC AMINO ACID PRODUCTION BY ULTRAVIOLET IRRADIATION OF ACHIRAL INTERSTELLAR ICE ANALOGS WITH CIRCULARLY POLARIZED LIGHT

    SciTech Connect

    De Marcellus, Pierre; Nuevo, Michel; Danger, Gregoire; Deboffle, Dominique; Le Sergeant d'Hendecourt, Louis; Meinert, Cornelia; Filippi, Jean-Jacques; Meierhenrich, Uwe J.; Nahon, Laurent E-mail: ldh@ias.u-psud.fr

    2011-02-01

    The delivery of organic matter to the primitive Earth via comets and meteorites has long been hypothesized to be an important source for prebiotic compounds such as amino acids or their chemical precursors that contributed to the development of prebiotic chemistry leading, on Earth, to the emergence of life. Photochemistry of inter/circumstellar ices around protostellar objects is a potential process leading to complex organic species, although difficult to establish from limited infrared observations only. Here we report the first abiotic cosmic ice simulation experiments that produce species with enantiomeric excesses (e.e.'s). Circularly polarized ultraviolet light (UV-CPL) from a synchrotron source induces asymmetric photochemistry on initially achiral inter/circumstellar ice analogs. Enantioselective multidimensional gas chromatography measurements show significant e.e.'s of up to 1.34% for ({sup 13}C)-alanine, for which the signs and absolute values are related to the helicity and number of CPL photons per deposited molecule. This result, directly comparable with some L excesses measured in meteorites, supports a scenario in which exogenous delivery of organics displaying a slight L excess, produced in an extraterrestrial environment by an asymmetric astrophysical process, is at the origin of biomolecular asymmetry on Earth. As a consequence, a fraction of the meteoritic organic material consisting of non-racemic compounds may well have been formed outside the solar system. Finally, following this hypothesis, we support the idea that the protosolar nebula has indeed been formed in a region of massive star formation, regions where UV-CPL of the same helicity is actually observed over large spatial areas.

  7. Enzymatic dynamic kinetic resolution of racemic N-formyl- and N-carbamoyl-amino acids using immobilized L-N-carbamoylase and N-succinyl-amino acid racemase.

    PubMed

    Soriano-Maldonado, Pablo; Las Heras-Vazquez, Francisco Javier; Clemente-Jimenez, Josefa María; Rodriguez-Vico, Felipe; Martínez-Rodríguez, Sergio

    2015-01-01

    Taking advantage of the catalytic promiscuity of L-carbamoylase from Geobacillus stearothermophilus CECT43 (BsLcar) and N-succinyl-amino acid racemase from Geobacillus kaustophilus CECT4264 (GkNSAAR), we have evaluated the production of different optically pure L-α-amino acids starting from different racemic N-formyl- and N-carbamoyl-amino acids using a dynamic kinetic resolution approach. The enzymes were immobilized on two different solid supports, resulting in improved stability of the enzymes in terms of thermostability and storage when compared to the enzymes in solution. The bienzymatic system retained up to 80% conversion efficiency after 20 weeks at 4 °C and up to 90% after 1 week at 45 °C. The immobilization process also resulted in a great enhancement of the activity of BsLcar toward N-formyl-tryptophan, showing for the first time that substrate specificity of L-carbamoylases can be influenced by this approach. The system was effective for the biosynthesis of natural and unnatural L-amino acids (enantiomeric excess (e.e.) >99.5%), such as L-methionine, L-alanine, L-tryptophan, L-homophenylalanine, L-aminobutyric acid, and L-norleucine, with a higher performance toward N-formyl-α-amino acid substrates. Biocatalyst reuse was studied, and after 10 reaction cycles, over 75% activity remained. PMID:24993356

  8. Hypocholesterolemic activity of racemic dichlorophenoxypropionic acid or its enantiomers in rats

    SciTech Connect

    Ohta, F.; Gaudemer, F.; Lutton, C.

    1987-12-01

    Abundant circumstantial evidence has shown that chronic hyperlipidemia is one of the major clinical manifestations of ischemic heart disease (IHD) and many drugs have been developed which reduce serum lipids. Clofibrate has been one of the most effective drugs used for lowering serum cholesterol and reducing the morbidity of patients suffering from IHD. However, prolonged treatment with clofibrate has been reported to cause higher incidences of gastrointestinal disorders and to induce cholesterol oversaturation of bile. These deleterious side effects have resulted in a restriction of the use of clofibrate and new drugs exerting selective and non toxic hypolipidemic actions have been intensively researched. (Dichloro-2,4 phenoxy)-2 propionic acid, structurally-related to fibrates with an asymmetric carbon is well know for its herbicide effectiveness. However, nobody has investigated its possible effect on cholesterol /sup 14/C-acetate metabolism. The purpose of this study is to explore the effects of this compound on cholesterol metabolism in the rat and to compare them with those of clofibrate. It is the first time that a low concentration (0.04 mmole) of this well-known pesticide has been shown to lower plasma cholesterol when added to the diet.

  9. Kinetic resolution of racemic 2-hydroxy-γ-butyrolactones by asymmetric esterification using diphenylacetic acid with pivalic anhydride and a chiral acyl-transfer catalyst.

    PubMed

    Nakata, Kenya; Gotoh, Kouya; Ono, Keisuke; Futami, Kengo; Shiina, Isamu

    2013-03-15

    Various optically active 2-hydroxy-γ-butyrolactone derivatives are produced via the kinetic resolution of racemic 2-hydroxy-γ-butyrolactones with diphenylacetic acid using pivalic anhydride and (R)-benzotetramisole ((R)-BTM), a chiral acyl-transfer catalyst. Importantly, the substrate scope of this novel protocol is fairly broad (12 examples, s-value; up to over 1000). In addition, we succeeded in disclosing the reaction mechanism to afford high enantioselectivity using theoretical calculations and expounded on the substituent effects at the C-3 positions in 2-hydroxylactones.

  10. Polymorphic Crystallization and Crystalline Reorganization of Poly(l-lactic acid)/Poly(d-lactic acid) Racemic Mixture Influenced by Blending with Poly(vinylidene fluoride).

    PubMed

    Yu, Chengtao; Han, Lili; Bao, Jianna; Shan, Guorong; Bao, Yongzhong; Pan, Pengju

    2016-08-18

    The effects of poly(vinylidene fluoride) (PVDF) on the crystallization kinetics, competing formations of homocrystallites (HCs) and stereocomplexes (SCs), polymorphic crystalline structure, and HC-to-SC crystalline reorganization of the poly(l-lactic acid)/poly(d-lactic acid) (PLLA/PDLA) racemic mixture were investigated. Even though the PLLA/PDLA/PVDF blends are immiscible, blending with PVDF enhances the crystallization rate and SC formation of PLLA/PDLA components at different temperatures that are higher or lower than the melting temperature of the PVDF component; it also facilitates the HC-to-SC melt reorganization upon heating. The crystallization rate and degree of SC crystallinity (Xc,SC) of PLLA/PDLA components in nonisothermal crystallization increase after immiscible blending with PVDF. At different isothermal crystallization temperatures, the crystallization half-time of PLLA/PDLA components decreases; its spherulitic growth rate and Xc,SC increase as the mass fraction of PVDF increases from 0 to 0.5 in the presence of either a solidified or a molten PVDF phase. The HCs formed in primary crystallization of PLLA/PDLA components melt and recrystallize into SCs upon heating; the HC-to-SC melt reorganization is promoted after blending with PVDF. We proposed that the PVDF-promoted crystallization, SC formation, and HC-to-SC melt reorganization of PLLA/PDLA components in PLLA/PDLA/PVDF blends stem from the enhanced diffusion ability of PLLA and PDLA chains. PMID:27414064

  11. [The neuroprotective action of enantiomers and racemate of 2-(3,7-dioxo-2,4,6,8-tetraazabicyclo[3.3.0]oct-2-yl)-4-methylthiobutanoic acid].

    PubMed

    Kravchenko, A N; Baranov, V V; Anikina, L V; Vikharev, Iu B; Bushmarinov, I S; Neliubina, Iu V

    2012-01-01

    Neurotropic, neuroprotective and antioxidant actions of the enantiomers and the racemate of 2-(3,7-dioxo-2,4,6,8-tetraazabicyclo[3.3.0]oct-2-yl)-4-methylthiobutanoic acid were investigated. Only (+)-(S)-2-(3,7-dioxo-2,4,6,8-tetraazabicyclo[3.3.0]oct-2-yl)-4-methylthiobutanoic acid was found to have neuroprotective properties. A distereoselective synthesis of enantiomers and racemate was performed by condensations of (S), (R) and (R,S)-N-carbamoylmethionines with 4,5-dihydroxyimidazolidin-2-one (DHI), respectively. By the X-ray method, the major racemate was proved to crystallize from water as a conglomerate. No antioxidant activity was revealed.

  12. Racemic protein crystallography.

    PubMed

    Yeates, Todd O; Kent, Stephen B H

    2012-01-01

    Although natural proteins are chiral and are all of one "handedness," their mirror image forms can be prepared by chemical synthesis. This opens up new opportunities for protein crystallography. A racemic mixture of the enantiomeric forms of a protein molecule can crystallize in ways that natural proteins cannot. Recent experimental data support a theoretical prediction that this should make racemic protein mixtures highly amenable to crystallization. Crystals obtained from racemic mixtures also offer advantages in structure determination strategies. The relevance of these potential advantages is heightened by advances in synthetic methods, which are extending the size limit for proteins that can be prepared by chemical synthesis. Recent ideas and results in the area of racemic protein crystallography are reviewed.

  13. Cytotoxic activity of new racemic and optically active N-phosphonoalkyl bicyclic β-amino acids against human malignant cell lines.

    PubMed

    Todorov, Petar T; Wesselinova, Diana W; Pavlov, Nikola D; Martinez, Jean; Calmes, Monique; Naydenova, Emilia D

    2012-10-01

    The cytotoxic effects of novel racemic and optically active constrained N-phosphonoalkyl bicyclic β-amino acids were tested against a panel of human tumor cell lines. All of the compounds investigated exhibited different concentration-dependent antiproliferative effects against the HT-29, MDA-MB-231, HepG2 and HeLa cell lines after 24 h treatment. The most sensitive cells were the HeLa cells at various concentrations of the four compounds tested. The aminophosphonate 3 exerted the most pronounced antiproliferative effect against the HeLa cells (inhibition of the cell vitality up to 70% at 0.5 mg/ml) and was not toxic to the normal Lep3 cells at lower concentration. Furthermore, the N-phosphonophenyl derivatives 1 and 2 displayed antiproliferative effect against mainly the MDA-MB-231 tumour cells at higher concentration.

  14. Sediment accumulation, stratigraphic order, and the extent of time-averaging in lagoonal sediments: a comparison of 210Pb and 14C/amino acid racemization chronologies

    NASA Astrophysics Data System (ADS)

    Kosnik, Matthew A.; Hua, Quan; Kaufman, Darrell S.; Zawadzki, Atun

    2015-03-01

    Carbon-14 calibrated amino acid racemization (14C/AAR) data and lead-210 (210Pb) data are used to examine sediment accumulation rates, stratigraphic order, and the extent of time-averaging in sediments collected from the One Tree Reef lagoon (southern Great Barrier Reef, Australia). The top meter of lagoonal sediment preserves a stratigraphically ordered deposit spanning the last 600 yrs. Despite different assumptions, the 210Pb and 14C/AAR chronologies are remarkably similar indicating consistency in sedimentary processes across sediment grain sizes spanning more than three orders of magnitude (0.1-10 mm). Estimates of long-term sediment accumulation rates range from 2.2 to 1.2 mm yr-1. Molluscan time-averaging in the taphonomically active zone is 19 yrs, whereas below the depth of final burial (~15 cm), it is ~110 yrs/5 cm layer. While not a high-resolution paleontological record, this reef lagoon sediment is suitable for paleoecological studies spanning the period of Western colonization and development. This sedimentary deposit, and others like it, should be useful, albeit not ideal, for quantifying anthropogenic impacts on coral reef systems.

  15. Court date for EPA acid rain rule

    SciTech Connect

    Lobsenz, G.

    1994-03-04

    In an acid rain rulemaking that appears headed straight for the courtroom, the Environmental Protection Agency this week announced new limits on emissions of nitrogen oxides from coal-fired power plants. The regulations, announced March 1, are expected to achieve a 1.8 million ton per year reduction in power plant NOx emissions, which are considered a major contributor to acid rain. The agency issued companion regulations last year to cut power plant discharges of sulfur dioxide, the other major acid rain pollutant. The NOx rulemaking elicited contradictory responses from utility industry officials. One point of contention involves the agency's definition of low-NOx burner technology, a key regulatory determination. If a utility installs EPA-defined low-NOx burner technology and still cannot meet the new NOx limits, it can apply for a less stringent [open quotes]alternative emission limit.[close quotes] The other issue likely to be raised by industry officials involves the January 1995 compliance deadline for utilities included in Phase I of the NOx program. While EPA will allow individual utilities to seek a deadline extension until April 1996 in the event of operational difficulties, the agency rejected the industry's request for an across-the-board extension.

  16. Post-translational amino acid racemization in the frog skin peptide deltorphin I in the secretion granules of cutaneous serous glands.

    PubMed

    Auvynet, Constance; Seddiki, Nabila; Dunia, Irene; Nicolas, Pierre; Amiche, Mohamed; Lacombe, Claire

    2006-01-01

    The dermal glands of the South American hylid frog Phyllomedusa bicolor synthesize and expel huge amounts of cationic, alpha-helical, 24- to 33-residue antimicrobial peptides, the dermaseptins B. These glands also produce a wide array of peptides that are similar to mammalian hormones and neuropeptides, including a heptapeptide opioid containing a D-amino acid, deltorphin I (Tyr-DAla-Phe-Asp-Val-Val-Gly NH2). Its biological activity is due to the racemization of L-Ala2 to D-Ala. The dermaseptins B and deltorphins are all derived from a single family of precursor polypeptides that have an N-terminal preprosequence that is remarkably well conserved, although the progenitor sequences giving rise to mature opioid or antimicrobial peptides are markedly different. Monoclonal and polyclonal antibodies were used to examine the cellular and ultrastructural distributions of deltorphin I and dermaseptin B in the serous glands by immunofluoresence confocal microscopy and immunogold-electron microscopy. Preprodeltorphin I and preprodermaseptins B are sorted into the regulated pathway of secretion, where they are processed to give the mature products. Deltorphin I, [l-Ala2]-deltorphin I and dermaseptin B are all stored together in secretion granules which accumulate in the cytoplasm of all serous glands. We conclude that the L- to D-amino acid isomerization of the deltorphin I occurs in the secretory granules as a post-translational event. Thus the specificity of isomerization depends on the presence of structural and/or conformational determinants in the peptide N-terminus surrounding the isomerization site.

  17. Partial resolution of racemic trans-4-[5-(4-alkoxyphenyl)-2,5-dimethylpyrrolidine-1-oxyl-2-yl]benzoic acids by the diastereomer method with (R)- or (S)-1-phenylethylamine.

    PubMed

    Uchida, Yoshiaki; Uematsu, Toshifumi; Nakayama, Yoichi; Takahashi, Hiroki; Tsue, Hirohito; Tanaka, Koichi; Tamura, Rui

    2008-03-01

    The partial resolution is described of a series of racemic trans-4-[5-(4-alkoxyphenyl)-2,5-dimethylpyrrolidine-1-oxyl-2-yl]benzoic acids (1), which are the key intermediates for the synthesis of chiral organic radical liquid crystalline compounds and are crystallized to give racemic compounds. Racemic acid 1 [(+/-)-1] with a long alkyl chain (C7 to C13) could be resolved by the conventional diastereomeric salt formation using (R)- or (S)-1-phenylethylamine (2) as the resolving agent, whereas resolution of (+/-)-1 with a short alkyl chain (C4 to C6) was unsuccessful. Use of six equiv of (R)- or (S)-2 for the initial diastereomeric salt formation of (+/-)-1 with a C7-C13 alkyl chain, followed by recrystallization of the resulting salts once or twice, gave 2S,5S- or 2R,5R-enriched 1, respectively, in an ee range of 75-92% and with an overall recovery of 11-27%, based on the original quantity of (+/-)-1. PMID:17597116

  18. Liquid chromatographic resolution of amino acid esters of acyclovir including racemic valacyclovir on crown ether-based chiral stationary phases.

    PubMed

    Ahn, Seong Ae; Hyun, Myung Ho

    2015-03-01

    Valacyclovir, a potential prodrug for the treatment of patients with herpes simplex and herpes zoster, and its analogs were resolved on two chiral stationary phases (CSPs) based on (3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6 covalently bonded to silica gel. In order to find out an appropriate mobile phase condition, various mobile phases consisting of various organic modifiers in water containing various acidic modifiers were applied to the resolution of valacyclovir and its analogs. When 30% acetonitrile in water containing any of 0.05 M, 0.10 M, or 0.15 M perchloric acid was used as a mobile phase, valacyclovir and its analogs were resolved quite well on the two CSPs with the separation factors (α) in the range of 2.49 ~ 6.35 and resolutions (RS ) in the range of 2.95 ~ 12.21. Between the two CSPs, the CSP containing residual silanol protecting n-octyl groups on the silica surface was found to be better than the CSP containing residual silanol groups.

  19. Liquid chromatographic resolution of amino acid esters of acyclovir including racemic valacyclovir on crown ether-based chiral stationary phases.

    PubMed

    Ahn, Seong Ae; Hyun, Myung Ho

    2015-03-01

    Valacyclovir, a potential prodrug for the treatment of patients with herpes simplex and herpes zoster, and its analogs were resolved on two chiral stationary phases (CSPs) based on (3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6 covalently bonded to silica gel. In order to find out an appropriate mobile phase condition, various mobile phases consisting of various organic modifiers in water containing various acidic modifiers were applied to the resolution of valacyclovir and its analogs. When 30% acetonitrile in water containing any of 0.05 M, 0.10 M, or 0.15 M perchloric acid was used as a mobile phase, valacyclovir and its analogs were resolved quite well on the two CSPs with the separation factors (α) in the range of 2.49 ~ 6.35 and resolutions (RS ) in the range of 2.95 ~ 12.21. Between the two CSPs, the CSP containing residual silanol protecting n-octyl groups on the silica surface was found to be better than the CSP containing residual silanol groups. PMID:25626672

  20. Calibration of amino acid racemization (AAR) kinetics in United States mid-Atlantic Coastal Plain Quaternary mollusks using 87Sr/ 86Sr analyses: Evaluation of kinetic models and estimation of regional Late Pleistocene temperature history

    USGS Publications Warehouse

    Wehmiller, J. F.; Harris, W.B.; Boutin, B.S.; Farrell, K.M.

    2012-01-01

    The use of amino acid racemization (AAR) for estimating ages of Quaternary fossils usually requires a combination of kinetic and effective temperature modeling or independent age calibration of analyzed samples. Because of limited availability of calibration samples, age estimates are often based on model extrapolations from single calibration points over wide ranges of D/L values. Here we present paired AAR and 87Sr/ 86Sr results for Pleistocene mollusks from the North Carolina Coastal Plain, USA. 87Sr/ 86Sr age estimates, derived from the lookup table of McArthur et al. [McArthur, J.M., Howarth, R.J., Bailey, T.R., 2001. Strontium isotopic stratigraphy: LOWESS version 3: best fit to the marine Sr-isotopic curve for 0-509 Ma and accompanying Look-up table for deriving numerical age. Journal of Geology 109, 155-169], provide independent age calibration over the full range of amino acid D/L values, thereby allowing comparisons of alternative kinetic models for seven amino acids. The often-used parabolic kinetic model is found to be insufficient to explain the pattern of racemization, although the kinetic pathways for valine racemization and isoleucine epimerization can be closely approximated with this function. Logarithmic and power law regressions more accurately represent the racemization pathways for all amino acids. The reliability of a non-linear model for leucine racemization, developed and refined over the past 20 years, is confirmed by the 87Sr/ 86Sr age results. This age model indicates that the subsurface record (up to 80m thick) of the North Carolina Coastal Plain spans the entire Quaternary, back to ???2.5Ma. The calibrated kinetics derived from this age model yield an estimate of the effective temperature for the study region of 11??2??C., from which we estimate full glacial (Last Glacial Maximum - LGM) temperatures for the region on the order of 7-10??C cooler than present. These temperatures compare favorably with independent paleoclimate information

  1. Enhanced catalysis and enantioselective resolution of racemic naproxen methyl ester by lipase encapsulated within iron oxide nanoparticles coated with calix[8]arene valeric acid complexes.

    PubMed

    Sayin, Serkan; Akoz, Enise; Yilmaz, Mustafa

    2014-09-14

    In this study, two types of nanoparticles have been used as additives for the encapsulation of Candida rugosa lipase via the sol-gel method. In one case, the nanoparticles were covalently linked with a new synthesized calix[8]arene octa valeric acid derivative (C[8]-C4-COOH) to produce new calix[8]arene-adorned magnetite nanoparticles (NP-C[8]-C4-COOH), and then NP-C[8]-C4-COOH was used as an additive in the sol-gel encapsulation process. In the other case, iron oxide nanoparticles were directly added into the sol-gel encapsulation process in order to interact electrostatically with both C[8]-C4-COOH and Candida rugosa lipase. The catalytic activities and enantioselectivities of two novel encapsulated lipases (Enc-NP-C[8]-C4-COOH and Enc-C[8]-C4-COOH@Fe3O4) in the hydrolysis reaction of racemic naproxen methyl ester were evaluated. The results showed that the activity and enantioselectivity of the lipase were improved when the lipase was encapsulated in the presence of calixarene-based additives. Indeed, the encapsulated lipases have an excellent rate of enantioselectivity, with E = 371 and 265, respectively, as compared to the free enzyme (E = 137). The lipases encapsulated with C[8]-C4-COOH and iron oxide nanoparticles (Enc-C[8]-C4-COOH@Fe3O4) retained more than 86% of their initial activities after 5 repeated uses and 92% with NP-C[8]-C4-COOH.

  2. Deuteration protects asparagine residues against racemization.

    PubMed

    Lowenson, Jonathan D; Shmanai, Vadim V; Shklyaruck, Denis; Clarke, Steven G; Shchepinov, Mikhail S

    2016-09-01

    Racemization in proteins and peptides at sites of L-asparaginyl and L-aspartyl residues contributes to their spontaneous degradation, especially in the biological aging process. Amino acid racemization involves deprotonation of the alpha carbon and replacement of the proton in the opposite stereoconfiguration; this reaction is much faster for aspartate/asparagine than for other amino acids because these residues form a succinimide ring in which resonance stabilizes the carbanion resulting from proton loss. To determine if the replacement of the hydrogen atom on the alpha carbon with a deuterium atom might decrease the rate of racemization and thus stabilize polypeptides, we synthesized a hexapeptide, VYPNGA, in which the three carbon-bound protons in the asparaginyl residue were replaced with deuterium atoms. Upon incubation of this peptide in pH 7.4 buffer at 37 °C, we found that the rate of deamidation via the succinimide intermediate was unchanged by the presence of the deuterium atoms. However, the accumulation of the D-aspartyl and D-isoaspartyl-forms resulting from racemization and hydrolysis of the succinimide was decreased more than five-fold in the deuterated peptide over a 20 day incubation at physiological temperature and pH. Additionally, we found that the succinimide intermediate arising from the degradation of the deuterated asparaginyl peptide was slightly less likely to open to the isoaspartyl configuration than was the protonated succinimide. These findings suggest that the kinetic isotope effect resulting from the presence of deuteriums in asparagine residues can limit the accumulation of at least some of the degradation products that arise as peptides and proteins age. PMID:27169868

  3. Synthesis of nano-sized stereoselective imprinted polymer by copolymerization of (S)-2-(acrylamido) propanoic acid and ethylene glycol dimethacrylate in the presence of racemic propranolol and copper ion.

    PubMed

    Alizadeh, Taher; Bagherzadeh, Azam; Shamkhali, Amir Nasser

    2016-06-01

    A new chiral functional monomer of (S)-2-(acrylamido) propanoic acid was obtained by reaction of (l)-alanine with acryloyl chloride. The resulting monomer was characterized by FT-IR and HNMR and then utilized for the preparation of chiral imprinted polymer (CIP). This was carried out by copolymerization of (l)-alanine-derived chiral monomer and ethylene glycol dimethacrylate, in the presence of racemic propranolol and copper nitrate, via precipitation polymerization technique, resulting in nano-sized networked polymer particles. The polymer obtained was characterized by scanning electron microscopy and FT-IR. The non-imprinted polymer was also synthesized and used as blank polymer. Density functional theory (DFT) was also employed to optimize the structures of two diasterometric ternary complexes, suspected to be created in the pre-polymerization step, by reaction of optically active isomers of propranolol, copper ion and (S)-2-(acrylamido) propanoic acid. Relative energies and other characteristics of the described complexes, calculated by the DFT, predicted the higher stability of (S)-propranolol involved complex, compared to (R)-propranolol participated complex. Practical batch extraction test which employed CIP as solid phase adsorbent, indicated that the CIP recognized selectively (S)-propranolol in the racemic mixture of propranolol; whereas, the non-imprinted polymer (NIP) showed no differentiation capability between two optically active isomers of propranolol. PMID:27040217

  4. Dual Role of Hydrophobic Racemic Thioesters of α-Amino Acids in the Generation of Isotactic Peptides and Co-peptides in Water; Implications for the Origin of Homochirality

    NASA Astrophysics Data System (ADS)

    Illos, Roni A.; Clodic, Gilles; Bolbach, Gerard; Weissbuch, Isabelle; Lahav, Meir

    2010-02-01

    Thioesters of α-amino acids are considered as plausible monomers for the generation of the primeval peptides. DL-Leucine-thioethyl esters (LeuSEt), where the L-enantiomer was tagged with deuterium atoms, undergo polycondensation in water or in bicarbonate or imidazole buffer solutions to yield mainly heterochiral (atactic) peptides and diketopiperazine, as analyzed by MALDI-TOF and ESI mass-spectrometry. In variance, when polymerization of DL(d10) -Leu, first activated with N,N'-carbonyldiimidazole, then initiated with ethanethiol or with DL(d3) -LeuSEt yielded a library of peptides up to 30 detectable residues where those of homochiral sequence (isotactic) are the dominant diastereoisomers. At these conditions, racemic β-sheets are formed and operate as stereoselective templates in the process of chain-elongation. Isotopic L: L(d10)-Leu co-peptides were obtained in the polymerization of L(d10)-Leu with L-LeuSEt. By contrast, mixtures of oligo- D-Leu and oligo- L(d10)-Leu were obtained in the polymerization of mixtures of D-LeuSEt with activated L(d10)-Leu. Isotactic co-peptides containing Leu and Val residues were formed in the polymerization of mixtures of activated DL(d8)-Val with DL(d3) -LeuSEt in water, implying that the racemic β-sheets exert regio-enantio-selection but not chemo-selection. A reaction pathway is suggested, where LeuSEt operates both as initiator of the reaction as well as a multimer.

  5. Single amino acid radiocarbon dating of Upper Paleolithic modern humans.

    PubMed

    Marom, Anat; McCullagh, James S O; Higham, Thomas F G; Sinitsyn, Andrey A; Hedges, Robert E M

    2012-05-01

    Archaeological bones are usually dated by radiocarbon measurement of extracted collagen. However, low collagen content, contamination from the burial environment, or museum conservation work, such as addition of glues, preservatives, and fumigants to "protect" archaeological materials, have previously led to inaccurate dates. These inaccuracies in turn frustrate the development of archaeological chronologies and, in the Paleolithic, blur the dating of such key events as the dispersal of anatomically modern humans. Here we describe a method to date hydroxyproline found in collagen (~10% of collagen carbon) as a bone-specific biomarker that removes impurities, thereby improving dating accuracy and confidence. This method is applied to two important sites in Russia and allows us to report the earliest direct ages for the presence of anatomically modern humans on the Russian Plain. These dates contribute considerably to our understanding of the emergence of the Mid-Upper Paleolithic and the complex suite of burial behaviors that begin to appear during this period.

  6. Amino acids in modern and fossil woods

    NASA Technical Reports Server (NTRS)

    Lee, C.; Bada, J. L.; Peterson, E.

    1976-01-01

    The amino acid composition and the extent of racemization in several modern and fossil woods are reported. The method of analysis is described, and data are presented on the total amino acid concentration, the amino acid ratios, and the enantiomeric ratios in each sample. It is found that the amino acid concentration per gram of dry wood decreases with age of the sample, that the extent of racemization increases with increasing age, and that the amounts of aspartic acid, threonine, and serine decrease relative to valine with increasing age. The relative racemization rates of amino acids in wood, bone, and aqueous solution are compared, and it is shown that racemization in wood is much slower than in bone or aqueous solution. Racemization results for woods from the Kalambo Falls area of Zambia are used to calculate a minimum age of 110,000 years for the transition between the Sangoan and Acheulian industries at that site. This result is shown to be consistent with numerous radiometric dates for older Acheulian sites in Africa and to compare well with geologically inferred dates for the beginning of the Eemian and the end of the Acheulian industry in southern Africa.

  7. Rationally re-designed mutation of NAD-independent l-lactate dehydrogenase: high optical resolution of racemic mandelic acid by the engineered Escherichia coli

    PubMed Central

    2012-01-01

    Background NAD-independent l-lactate dehydrogenase (l-iLDH) from Pseudomonas stutzeri SDM can potentially be used for the kinetic resolution of small aliphatic 2-hydroxycarboxylic acids. However, this enzyme showed rather low activity towards aromatic 2-hydroxycarboxylic acids. Results Val-108 of l-iLDH was changed to Ala by rationally site-directed mutagenesis. The l-iLDH mutant exhibited much higher activity than wide-type l-iLDH towards l-mandelate, an aromatic 2-hydroxycarboxylic acid. Using the engineered Escherichia coli expressing the mutant l-iLDH as a biocatalyst, 40 g·L-1 of dl-mandelic acid was converted to 20.1 g·L-1 of d-mandelic acid (enantiomeric purity higher than 99.5%) and 19.3 g·L-1 of benzoylformic acid. Conclusions A new biocatalyst with high catalytic efficiency toward an unnatural substrate was constructed by rationally re-design mutagenesis. Two building block intermediates (optically pure d-mandelic acid and benzoylformic acid) were efficiently produced by the one-pot biotransformation system. PMID:23176608

  8. Single amino acid radiocarbon dating of Upper Paleolithic modern humans

    PubMed Central

    Marom, Anat; McCullagh, James S. O.; Higham, Thomas F. G.; Sinitsyn, Andrey A.; Hedges, Robert E. M.

    2012-01-01

    Archaeological bones are usually dated by radiocarbon measurement of extracted collagen. However, low collagen content, contamination from the burial environment, or museum conservation work, such as addition of glues, preservatives, and fumigants to “protect” archaeological materials, have previously led to inaccurate dates. These inaccuracies in turn frustrate the development of archaeological chronologies and, in the Paleolithic, blur the dating of such key events as the dispersal of anatomically modern humans. Here we describe a method to date hydroxyproline found in collagen (∼10% of collagen carbon) as a bone-specific biomarker that removes impurities, thereby improving dating accuracy and confidence. This method is applied to two important sites in Russia and allows us to report the earliest direct ages for the presence of anatomically modern humans on the Russian Plain. These dates contribute considerably to our understanding of the emergence of the Mid-Upper Paleolithic and the complex suite of burial behaviors that begin to appear during this period. PMID:22517758

  9. 40 CFR 72.69 - Issuance and effective date of acid rain permits.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ...) AIR PROGRAMS (CONTINUED) PERMITS REGULATION Federal Acid Rain Permit Issuance Procedures § 72.69 Issuance and effective date of acid rain permits. (a) After the close of the public comment period, the Administrator will issue or deny an Acid Rain permit. The Administrator will serve a copy of any Acid...

  10. 40 CFR 72.69 - Issuance and effective date of acid rain permits.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ...) AIR PROGRAMS (CONTINUED) PERMITS REGULATION Federal Acid Rain Permit Issuance Procedures § 72.69 Issuance and effective date of acid rain permits. (a) After the close of the public comment period, the Administrator will issue or deny an Acid Rain permit. The Administrator will serve a copy of any Acid...

  11. 40 CFR 72.69 - Issuance and effective date of acid rain permits.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ...) AIR PROGRAMS (CONTINUED) PERMITS REGULATION Federal Acid Rain Permit Issuance Procedures § 72.69 Issuance and effective date of acid rain permits. (a) After the close of the public comment period, the Administrator will issue or deny an Acid Rain permit. The Administrator will serve a copy of any Acid...

  12. 40 CFR 72.69 - Issuance and effective date of acid rain permits.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...) AIR PROGRAMS (CONTINUED) PERMITS REGULATION Federal Acid Rain Permit Issuance Procedures § 72.69 Issuance and effective date of acid rain permits. (a) After the close of the public comment period, the Administrator will issue or deny an Acid Rain permit. The Administrator will serve a copy of any Acid...

  13. 40 CFR 72.69 - Issuance and effective date of acid rain permits.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...) AIR PROGRAMS (CONTINUED) PERMITS REGULATION Federal Acid Rain Permit Issuance Procedures § 72.69 Issuance and effective date of acid rain permits. (a) After the close of the public comment period, the Administrator will issue or deny an Acid Rain permit. The Administrator will serve a copy of any Acid...

  14. Pd(II)-catalyzed regio-, enantio-, and diastereoselective 1,4-addition of azlactones formed in situ from racemic unprotected amino acids and acetic anhydride.

    PubMed

    Weber, Manuel; Peters, René

    2012-12-01

    A multicomponent reaction is reported generating highly enantioenriched and diastereomerically pure quaternary amino acid derivatives via 1,4-addition of azlactones to enones. The azlactone intermediates are generated in situ from unprotected α-amino acids and acetic anhydride. Previous attempts using bis-palladacycle catalysts required the use of a large excess of benzoic anhydride (which is very difficult to remove from the products), since acetic anhydride provided regioisomeric product mixtures. Key for the high regioselectivity is a pentaphenylferrocene monopalladacycle catalyst. PMID:23193999

  15. Kinetic resolution of racemic α-hydroxyphosphonates by asymmetric esterification using achiral carboxylic acids with pivalic anhydride and a chiral acyl-transfer catalyst.

    PubMed

    Shiina, Isamu; Ono, Keisuke; Nakahara, Takayoshi

    2013-11-25

    A practical protocol is developed to directly provide chiral α-acyloxyphosphonates and α-hydroxyphosphonates from (±)-α-hydroxyphosphonates utilizing the transacylation process to generate the mixed anhydrides from acid components and pivalic anhydride in the presence of organocatalysts (s-value = 33-518).

  16. A computer simulation study of racemic mixtures

    NASA Astrophysics Data System (ADS)

    Largo, J.; Vega, C.; MacDowell, L. G.; Solana, J. R.

    A simple model for a chiral molecule is proposed. The model consists of a central atom bonded to four different atoms in tetrahedral coordination. Two different potentials were used to describe the pair potentials between atoms: the hard sphere potential and the Lennard-Jones potential. For both the hard sphere and the Lennard-Jones chiral models, computer simulations have been performed for the pure enantiomers and also for the racemic mixture. The racemic mixture consisted of an equimolar mixture of the two optically active enantiomers. It is found that the equations of state are the same, within statistical uncertainty, for the pure enantiomer fluid and for the racemic mixture. Only at high pressures does the racemic mixture seem to have a higher density, for a given pressure, than the pure enantiomer. Concering the structure, no difference is found in the site-site correlation functions between like and unlike molecules in the racemic mixture either at low or at high densities. However, small differences are found for the site-site correlations of the pure enantiomer and those of the racemic mixtures. In the Lennard-Jones model, similar conclusions are drawn. The extension of Wertheim's first-order perturbation theory, denoted bonded hard sphere theory (ARCHER, A. L., and JACKSON, G., 1991, Molec. Phys. , 73 , 881; AMOS, M. D., and JACKSON, G., 1992, J. chem. Phys. , 96 , 4604), successfully reproduces the simulation results for the hard chiral model. Virial coefficients of the hard chiral model up to the fourth have also been evaluated. Again, no differences are found between virial coefficients of the pure fluid and of the racemic mixture. All the results of this work illustrate the quasi-ideal behaviour of racemic mixtures in the fluid phase.

  17. Enantiomeric resolution of multiple chiral centres racemates by capillary electrophoresis.

    PubMed

    Ali, Imran; Suhail, Mohd; Al-Othman, Zeid A; Alwarthan, Abdulrahman; Aboul-Enein, Hassan Y

    2016-05-01

    Enantiomeric resolution of multichiral centre racemates is an important area as some multichiral centre racemates are of great medicinal importance. However, enantioseparation of such types of racemates is a challenging task. Amongst many analytical techniques, capillary electrophoresis is a powerful technique and may be used to resolve such racemates. Only few papers are available describing enantiomeric resolution of such racemates. Therefore, efforts have been made to describe the enantiomeric resolution of multichiral centre racemates by capillary electrophoresis. This article discusses the importance of multichiral racemates, the need for capillary electrophoresis in enantiomeric resolution and chiral resolution of multichiral centre racemates using various chiral selectors. Further, attempts have been made to discuss the future challenges and prospects of enantiomeric resolution of multichiral racemates. The various chiral selectors used for the purpose are chiral crown ether, cyclodextrins, polysaccharides, macrocyclic glycopeptide antibiotics and ligand exchange.

  18. Dating silk by capillary electrophoresis mass spectrometry.

    PubMed

    Moini, Mehdi; Klauenberg, Kathryn; Ballard, Mary

    2011-10-01

    A new capillary electrophoresis mass spectrometry (CE-MS) technique is introduced for age estimation of silk textiles based on amino acid racemization rates. With an L to D conversion half-life of ~2500 years for silk (B. mori) aspartic acid, the technique is capable of dating silk textiles ranging in age from several decades to a few-thousand-years-old. Analysis required only ~100 μg or less of silk fiber. Except for a 2 h acid hydrolysis at 110 °C, no other sample preparation is required. The CE-MS analysis takes ~20 min, consumes only nanoliters of the amino acid mixture, and provides both amino acid composition profiles and D/L ratios for ~11 amino acids.

  19. Characterization and quantification of racemic and meso-ethylenediamine-N,N'-bis(2-hydroxy-5-sulfophenylacetic) acid/iron (III) by ion-pair ultra-high performance liquid chromatography coupled with diode array detector and electrospray tandem mass spectrometry.

    PubMed

    Biasone, Alessandro; Cianci, Giusto; Di Tommaso, Donata; Piaggesi, Alberto; Tagliavini, Emilio; Galletti, Paola; Moretti, Fabio

    2013-03-22

    EDDHSA/Fe is a promising substitute of EDDHA/Fe to fight iron chlorosis. o,o-EDDHSA structure contains two chiral carbons giving the racemic and meso couples of stereoisomers. Ion-pair HPLC and UHPLC-UV/Vis-ESI-MS/MS methods were developed for the determination of racemic and meso-o,o-EDDHSA/Fe in commercial samples of chelates. The lack of a commercial EDDHSA standard was overcome by sulfonation of a commercial available o,o-EDDHA standard and subsequent quantification by (1)H-NMR. Assignment of configurations was carried out starting from racemic and meso-o,o-EDDHA/Fe by direct sulfonation to give the corresponding o,o-EDDHSA/Fe isomers. The performances of these methods were assessed in terms of intra and inter-day precision, linearity and selectivity. The high selectivity and lower detection limit (nanomolar) of the UHPLC-ESI-MS/MS method could allow to deepen the knowledge relative to meso and rac-o,o-EDDHSA/Fe interactions with plants, its fate in different soil conditions, its mobility and other environmental aspects. PMID:23411145

  20. Determination and stereochemistry of proteinogenic and non-proteinogenic amino acids in Saudi Arabian date fruits.

    PubMed

    Ali, Hatem Salama Mohamed; Alhaj, Omar Amin; Al-Khalifa, Abdulrahman Saleh; Brückner, Hans

    2014-09-01

    Whereas an abundance of literature is available on the occurrence of common proteinogenic amino acids (AAs) in edible fruits of the date palm (Phoenix dactylifera L.), recent reports on non-proteinogenic (non-coded) AAs and amino components are scarce. With emphasis on these components we have analyzed total hydrolysates of twelve cultivars of date fruits using automated ion-exchange chromatography, HPLC employing a fluorescent aminoquinolyl label, and GC-MS of total hydrolysates using the chiral stationary phases Chirasil(®)-L-Val and Lipodex(®) E. Besides common proteinogenic AAs, relatively large amounts of the following non-proteinogenic amino acids were detected: (2S,5R)-5-hydroxypipecolic acid (1.4-4.0 g/kg dry matter, DM), 1-aminocyclopropane-1-carboxylic acid (1.3-2.6 g/kg DM), γ-amino-n-butyric acid (0.5-1.2 g/kg DM), (2S,4R)-4-hydroxyproline (130-230 mg/kg DM), L-pipecolic acid (40-140 mg/kg DM), and 2-aminoethanol (40-160 mg/kg DM) as well as low or trace amounts (<70 mg/kg DM) of L-ornithine, 5-hydroxylysine, β-alanine, and in some samples (<20 mg/kg DM) of (S)-β-aminoisobutyric acid and (<10 mg/kg DM) L-allo-isoleucine. In one date fruit, traces of α-aminoadipic acid could be determined. Enantiomeric analysis of 6 M DCl/D2O hydrolysates of AAs using chiral capillary gas chromatography-mass spectrometry revealed the presence of very low amounts of D-Ala, D-Asp, D-Glu, D-Ser and D-Phe (1.2-0.4%, relative to the corresponding L-enantiomers), besides traces (0.2-1%) of other D-AAs. The possible relevance of non-proteinogenic amino acids in date fruits is briefly addressed.

  1. Geochemical evolution of amino acids in dentine of Pleistocene bears.

    PubMed

    De Torres, T; Ortiz, J E; García, M J; Llamas, J F; Canoira, L; De La Morena, M A; Juliá, R

    2001-08-01

    A linear correlation was established between aspartic acid racemization ratio from cave bear dentine collagen and absolute dating. The high correlation coefficient obtained allowed age calculation through amino acid racemization. Aspartic acid and glutamic acid racemization kinetics have also been explored in dentine from a North American black bear (Ursus americanus Pallas). Three sample sets were prepared for kinetic heating experiments in nitrogen atmosphere: one water soaked, one with a water-saturated nitrogen atmosphere, and one without any moisture. It was possible to show that the presence of water is a factor controlling amino acid racemization rate. The aspartic acid in a heating experiment at 105 degrees C shows an "apparent kinetics reversal" which can be explained by a progressive hydrolysis of amino acid chains (proteins and polypeptides). Because of the low potential of collagen preservation over long periods of time, the apparent kinetics reversal phenomenon will not affect the dating of old material where no traces of collagen remain. An apparent kinetics reversal was not observed in glutamic acid, which racemizates more slowly. PMID:11466777

  2. Direct dating of human fossils.

    PubMed

    Grün, Rainer

    2006-01-01

    The methods that can be used for the direct dating of human remains comprise of radiocarbon, U-series, electron spin resonance (ESR), and amino acid racemization (AAR). This review gives an introduction to these methods in the context of dating human bones and teeth. Recent advances in ultrafiltration techniques have expanded the dating range of radiocarbon. It now seems feasible to reliably date bones up to 55,000 years. New developments in laser ablation mass spectrometry permit the in situ analysis of U-series isotopes, thus providing a rapid and virtually non-destructive dating method back to about 300,000 years. This is of particular importance when used in conjunction with non-destructive ESR analysis. New approaches in AAR analysis may lead to a renaissance of this method. The potential and present limitations of these direct dating techniques are discussed for sites relevant to the reconstruction of modern human evolution, including Florisbad, Border Cave, Tabun, Skhul, Qafzeh, Vindija, Banyoles, and Lake Mungo.

  3. Enantioseparation of racemic mixtures based on solvent sublation.

    PubMed

    Jiao, Feipeng; Yang, Weijie; Wang, Fen; Tian, Lingxing; Li, Lin; Chen, Xiaoqing; Mu, Kelang

    2012-08-01

    A method of solvent sublation was developed for the enantioseparation of racemic ofloxacin (rac Oflx) and racemic tryptophan (rac Trp). In this method, dibenzoyl-L-tartaric acid (L-DBTA) and di-(2-ethylhexyl) phosphoric acid (D2EHPA) and sodium lauryl sulfate (SDS) were used as chiral coextractants and foamer, respectively. Several important parameters influencing the separation performances, such as pH in aqueous phase, concentrations of rac mixtures, L-DBTA, D2EHPA, and SDS, were investigated. Under the optimal operation conditions, the enantiomeric excess and enantioselectivity were 60.08% and 5.58 for Oflx and 65.09% and 6.31 for Trp, respectively. The yields of D-enantiomer and L-enantiomer were 34.23% and 8.54% for Oflx and 18.59% and 3.93% for Trp, respectively. The results suggest that the enantioselectivities have been enhanced compared with the traditional chiral extraction. This technique is an efficient chiral separation method, with many advantages such as low expenditures of organic solvent, low consumption of chiral extractant, and easy realization of multistage operation.

  4. Racemization of Isobornyl Chloride via Carbocations: A Nonclassical Look at a Classic Mechanism

    ERIC Educational Resources Information Center

    Rzepa, Henry S.; Allan, Charlotte S. M.

    2010-01-01

    Our understanding of carbonium ions as intermediates in chemical reaction mechanisms derives from the early work of Julius Stieglitz and the more famous Hans Meerwein, the latter studying the racemization of isobornyl chloride when treated with Lewis acids. This review analyzes how key mechanistic concepts for this reaction evolved and gives the…

  5. Novel routes to either racemic or enantiopure α-amino-(4-hydroxy-pyrrolidin-3-yl)acetic acid derivatives and biological evaluation of a new promising pharmacological scaffold.

    PubMed

    Cecioni, Samy; Aouadi, Kaïss; Guiard, Julie; Parrot, Sandrine; Strazielle, Nathalie; Blondel, Sandrine; Ghersi-Egea, Jean-François; Chapelle, Christian; Denoroy, Luc; Praly, Jean-Pierre

    2015-06-15

    Cycloaddition between (+) or (-)-menthone-derived nitrones and N-benzyl-3-pyrroline afforded enantiopure spiro-fused heterocycles. The reaction occurred enantio- and diastereo-selectively on the less hindered side of the nitrone, the 3-pyrroline N-benzyl group being oriented outwards, thus controlling the configurations of three simultaneously created chiral centers. From either (+) or (-)-menthone, both enantiomeric cycloadducts were synthesized in excellent yield. Removing the chiral auxiliary and the N-benzyl group delivered a series of enantiopure 4-hydroxy-3-glycinyl-pyrrolidine derivatives in 3-5 steps and 36 to 81 overall yields. Using two other achiral nitrones, shorter routes to racemic analogues were developed. Two of the synthesized compounds markedly lowered extracellular glutamate level and modestly interacted with cannabinoid type-1 receptors. As these two neuroactive compounds were devoid of in vitro toxicity and did not cross the blood brain interface, they might represent potential pharmacological agents to target peripheral organs.

  6. Enzymatic saccharification and fermentation of cellulosic date palm wastes to glucose and lactic acid

    PubMed Central

    Alrumman, Sulaiman A.

    2016-01-01

    The bioconversion of cellulosic wastes into high-value bio-products by saccharification and fermentation processes is an important step that can reduce the environmental pollution caused by agricultural wastes. In this study, enzymatic saccharification of treated and untreated date palm cellulosic wastes by the cellulases from Geobacillus stearothermophilus was optimized. The alkaline pre-treatment of the date palm wastes was found to be effective in increasing the saccharification percentage. The maximum rate of saccharification was found at a substrate concentration of 4% and enzyme concentration of 30 FPU/g of substrate. The optimum pH and temperature for the bioconversions were 5.0 and 50 °C, respectively, after 24 h of incubation, with a yield of 31.56 mg/mL of glucose at a saccharification degree of 71.03%. The saccharification was increased to 94.88% by removal of the hydrolysate after 24 h by using a two-step hydrolysis. Significant lactic acid production (27.8 mg/mL) was obtained by separate saccharification and fermentation after 72 h of incubation. The results indicate that production of fermentable sugar and lactic acid is feasible and may reduce environmental pollution by using date palm wastes as a cheap substrate. PMID:26887233

  7. Dating and context of three middle stone age sites with bone points in the Upper Semliki Valley, Zaire.

    PubMed

    Brooks, A S; Helgren, D M; Cramer, J S; Franklin, A; Hornyak, W; Keating, J M; Klein, R G; Rink, W J; Schwarcz, H; Smith, J N

    1995-04-28

    The extent to which the earliest anatomically modern humans in Africa exhibited behavioral and cognitive traits typical of Homo sapiens sapiens is controversial. In eastern Zaire, archaeological sites with bone points have yielded dates older than 89(-15)+22 thousand years ago by several techniques. These include electron spin resonance, thermoluminescence, optically stimulated luminescence, uranium series, and amino acid racemization. Faunal and stratigraphic data are consistent with this age. PMID:7725099

  8. Spin crossover properties of enantiomers, co-enantiomers, racemates, and co-racemates.

    PubMed

    Qin, Long-Fang; Pang, Chun-Yan; Han, Wang-Kang; Zhang, Feng-Li; Tian, Lei; Gu, Zhi-Guo; Ren, Xuehong; Li, Zaijun

    2016-04-25

    Through multi-component self-assembly of chiral phenylethylamine, 1-alkyl-2-imidazolecarboxaldehyde and iron(ii) ions, two couples of enantiomeric iron(ii) complexes , , and with the formula of fac-Λ or Δ-[Fe(L)3](2+)(L = R or S-1-phenyl-N-(1-alkyl-1H-imidazol-2-ylmethylene)ethanamine) have been designed and synthesized as building blocks. Further binary cocrystallization of the prefabricated enantiomers enabled us to construct spin crossover co-enantiomers and , racemates and , and co-racemate . Compared with in a high spin state and with spin crossover at 291 K, the co-enantiomers exhibited gradual spin crossover at a higher temperature of 301 K, and the racemic alloys showed hysteresis loops induced by desolvation above room temperature. It was demonstrated that molecular chirality could be used effectively for stereochemical engineering of spin crossover materials. In addition, crystal packing, intramolecular π-π stacking, intermolecular C-Hπ interactions and solvent effects were elucidated to be responsible for the distinct spin crossover properties. This collective structural and magnetic study not only enriched the spin crossover library, but also provided a full comparison of optically pure, homochiral, and racemic materials with similar molecular structures. PMID:27021212

  9. Racemization of undesired enantiomers: Immobilization of mandelate racemase and application in a fixed bed reactor.

    PubMed

    Wrzosek, Katarzyna; Rivera, Mariel A García; Bettenbrock, Katja; Seidel-Morgenstern, Andreas

    2016-03-01

    Production of optically pure products can be based on simple unselective synthesis of racemic mixtures combined with a subsequent separation of the enantiomers; however, this approach suffers from a 50% yield limitation which can be overcome by racemization of the undesired enantiomer and recycling. Application of biocatalyst for the racemization steps offers an attractive option for high-yield manufacturing of commercially valuable compounds. Our work focuses on exploiting the potential of racemization with immobilized mandelate racemase. Immobilization of crude mandelate racemase via covalent attachment was optimized for two supports: Eupergit(®) CM and CNBr-activated Sepharose 4 Fast Flow. To allow coupling of enzymatic reaction with enantioselective chromatography, a mobile phase composition compatible with both processes was used in enzymatic reactor. Kinetic parameters obtained analyzing experiments carried out in a batch reactor could be successfully used to predict fixed-bed reactor performance. The applicability of the immobilized enzyme and the determined kinetic parameters were validated in transient experiments recording responses to pulse injections of R-mandelic acid. The approach investigated can be used for futher design and optimization of high yield combined resolution processes. The characterized fixed-bed enzymatic reactor can be integrated e.g. with chromatographic single- or multicolumn steps in various configurations.

  10. Nephroprotective effect of date fruit extract against dichloroacetic acid exposure in adult rats.

    PubMed

    El Arem, Amira; Thouri, Amira; Zekri, Mouna; Saafi, Emna Behija; Ghrairi, Fatma; Zakhama, Abdelfattah; Achour, Lotfi

    2014-03-01

    The aim of this study was to investigate the protective effects of aqueous date extract (ADE) on dichloroacetic acid (DCA)-induced nephrotoxicity. In vitro, total phenolic content estimated in the ADE were 417.71mg gallic acid equivalents/100g fresh weights (FW), while total flavonoid and tannins contents were 285.23 and 73.65mg catechin equivalents/100g FW, respectively. The ADE has strong scavenging activity. Ferulic, caffeic and p-coumaric acids are the major's compounds. Nephrotoxicity was induced in male Wistar rats by the administration of 0.5 and 2g/L DCA as drinking water. Some of these rats received also by gavage ADE (4mL/kg) before the administration of DCA. After two months of experiment, DCA administration caused elevated levels of renal MDA, significant depletion of GSH levels, altered the antioxidant enzyme activities and deteriorated the renal functions as assessed by the increased plasma urea, uric acid and creatinine levels compared to control rats. The treatment with the ADE significantly normalized the increased plasma levels of creatinine, urea and uric acid, reduced the elevated MDA levels, significantly normalized the antioxidant enzyme activities and GSH level and restored the altered kidney histology in rats treated with DCA. Therefore, it was speculated that ADE protects rats from kidney damage through its antioxidant capacity.

  11. Racemization kinetics of meluadrine tartrate in aqueous solution.

    PubMed

    Matsuo, K; Yamamoto, Y; Kado, N; Yamazaki, M; Nagata, O; Kato, H; Tsuji, A

    2001-01-01

    The kinetics of racemization of meluadrine tartrate in aqueous solution was investigated by HPLC, over the pH range of 1.2 to 12 at 40, 60 and 80 degrees C. The racemization was followed by measuring both the residual (R)-enantiomer and formed (S)-enantiomer of meluadrine. The pH-racemization rate profile of meluadrine showed a minimum racemization rate constant between pH 4 and 6, and the rate constant increased rapidly with decreasing pH below pH 3. In the basic region, the racemization rate constant showed a maximum at around pH 9. Four pathways of racemization of meluadrine are proposed, depending on the dissociation state of the phenolic and amino groups. The calculated racemization rate-pH profile agreed well with the observations. The values of activation energy (95-115 kJ/mol) suggest that a similar quinoid intermediate is involved throughout the pH range examined. The objective of this study is to clarify the racemization mechanism of benzylalcohol derivative with phenoric group. This study offers fundamental knowledge for the other benzylalcohol derivatives, which have similar moiety structure.

  12. Racemization and the origin of optically active organic compounds in living organisms

    NASA Technical Reports Server (NTRS)

    Bada, J. L.; Miller, S. L.

    1987-01-01

    The organic compounds synthesized in prebiotic experiments are racemic mixtures. A number of proposals have been offered to explain how asymmetric organic compounds formed on the Earth before life arose, with the influence of chiral weak nuclear interactions being the most frequent proposal. This and other proposed asymmetric syntheses give only sight enantiomeric excess and any slight excess will be degraded by racemization. This applies particularly to amino acids where half-lives of 10(5)-10(6) years are to be expected at temperatures characteristic of the Earth's surface. Since the generation of chiral molecules could not have been a significant process under geological conditions, the origins of this asymmetry must have occurred at the time of the origin of life or shortly thereafter. It is possible that the compounds in the first living organisms were prochiral rather than chiral; this is unlikely for amino acids, but it is possible for the monomers of RNA-like molecules.

  13. Utilization of date stones for production of activated carbon using phosphoric acid

    SciTech Connect

    Haimour, N.M. . E-mail: nomanhaimour@hotmail.com; Emeish, S. . E-mail: s_emiesh@yahoo.com

    2006-07-01

    Date stone wastes have been utilized for production of activated carbon by chemical activation with phosphoric acid using a fluidized-bed reactor. The effects of the activation time, activation temperature, impregnation ratio, and particle size on the yield and the adsorptive capacity towards iodine were studied. The yield and the quality of the activated carbon prepared by using H{sub 3}PO{sub 4} were compared with that prepared from date stones using the same equipment, and under similar conditions by using ZnCl{sub 2} as an oxidizing agent. The maximum value of the iodine number of the activated carbon produced using H{sub 3}PO{sub 4} in this work was about 495 under the following conditions: impregnation ratio 0.4, activation time 60 min, activation temperature 800 deg. C, particle size 0.60 mm. The iodine number for the produced activated carbon was higher when phosphoric acid was used, compared to that when zinc chloride was used as impregnation reagent; however, the yield obtained when H{sub 3}PO{sub 4} was used was lower than the yield when ZnCl{sub 2} was used. The iodine number increases significantly with increasing the activation temperature. By increasing the impregnation ratio at the same temperature, the iodine number decreased sharply and an oscillation is noticed for all the cases but it was clearer at 800 deg. C. The average variation of the iodine number for the whole range of particle size used in this work is {+-}10%.

  14. Synthesis and Antifeedant Activity of Racemic and Optically Active Hydroxy Lactones with the p-Menthane System.

    PubMed

    Grudniewska, Aleksandra; Kłobucki, Marek; Dancewicz, Katarzyna; Szczepanik, Maryla; Gabryś, Beata; Wawrzeńczyk, Czesław

    2015-01-01

    Two racemic and two enantiomeric pairs of new δ-hydroxy-γ-lactones based on the p-menthane system were prepared from racemic and optically active cis- and trans-piperitols. The Johnson-Claisen rearrangement of the piperitols, epoxidation of the γδ-unsaturated esters, and acidic lactonization of the epoxy esters were described. The structures of the compounds were confirmed spectroscopically. The antifeedant activities of the hydroxy lactones and racemic piperitone were evaluated against three insect pests: lesser mealworm, Alphitobius diaperinus (Panzer); Colorado potato beetle, Leptinotarsa decemlineata (Say); and peach-potato aphid, Myzus persicae (Sulz.). The chemical transformation of piperitone by the introduction of a lactone moiety and a hydroxy group changed its antifeedant properties. Behavioral bioassays showed that the feeding deterrent activity depended on the insect species and the structure of the compounds. All hydroxy lactones deterred the settling of M. persicae. Among chewing insects, the highest sensitivity showed A. diaperinus adults. PMID:26132506

  15. Synthesis and Antifeedant Activity of Racemic and Optically Active Hydroxy Lactones with the p-Menthane System

    PubMed Central

    Grudniewska, Aleksandra; Kłobucki, Marek; Dancewicz, Katarzyna; Szczepanik, Maryla; Gabryś, Beata; Wawrzeńczyk, Czesław

    2015-01-01

    Two racemic and two enantiomeric pairs of new δ-hydroxy-γ-lactones based on the p-menthane system were prepared from racemic and optically active cis- and trans-piperitols. The Johnson-Claisen rearrangement of the piperitols, epoxidation of the γδ-unsaturated esters, and acidic lactonization of the epoxy esters were described. The structures of the compounds were confirmed spectroscopically. The antifeedant activities of the hydroxy lactones and racemic piperitone were evaluated against three insect pests: lesser mealworm, Alphitobius diaperinus (Panzer); Colorado potato beetle, Leptinotarsa decemlineata (Say); and peach-potato aphid, Myzus persicae (Sulz.). The chemical transformation of piperitone by the introduction of a lactone moiety and a hydroxy group changed its antifeedant properties. Behavioral bioassays showed that the feeding deterrent activity depended on the insect species and the structure of the compounds. All hydroxy lactones deterred the settling of M. persicae. Among chewing insects, the highest sensitivity showed A. diaperinus adults. PMID:26132506

  16. Optimization of date syrup for enhancement of the production of citric acid using immobilized cells of Aspergillus niger

    PubMed Central

    Mostafa, Yasser S.; Alamri, Saad A.

    2012-01-01

    Date syrup as an economical source of carbohydrates and immobilized Aspergillus niger J4, which was entrapped in calcium alginate pellets, were employed for enhancing the production of citric acid. Maximum production was achieved by pre-treating date syrup with 1.5% tricalcium phosphate to remove heavy metals. The production of citric acid using a pretreated medium was 38.87% higher than an untreated one that consumed sugar. The appropriate presence of nitrogen, phosphate and magnesium appeared to be important in order for citric acid to accumulate. The production of citric acid and the consumed sugar was higher when using 0.1% ammonium nitrate as the best source of nitrogen. The production of citric acid increased significantly when 0.1 g/l of KH2PO4 was added to the medium of date syrup. The addition of magnesium sulfate at the rate of 0.20 g/l had a stimulating effect on the production of citric acid. Maximum production of citric acid was obtained when calcium chloride was absent. One of the most important benefits of immobilized cells is their ability and stability to produce citric acid under a repeated batch culture. Over four repeated batches, the production of citric acid production was maintained for 24 days when each cycle continued for 144 h. The results obtained in the repeated batch cultivation using date syrup confirmed that date syrup could be used as a medium for the industrial production of citric acid. PMID:23961184

  17. Optimization of date syrup for enhancement of the production of citric acid using immobilized cells of Aspergillus niger.

    PubMed

    Mostafa, Yasser S; Alamri, Saad A

    2012-04-01

    Date syrup as an economical source of carbohydrates and immobilized Aspergillus niger J4, which was entrapped in calcium alginate pellets, were employed for enhancing the production of citric acid. Maximum production was achieved by pre-treating date syrup with 1.5% tricalcium phosphate to remove heavy metals. The production of citric acid using a pretreated medium was 38.87% higher than an untreated one that consumed sugar. The appropriate presence of nitrogen, phosphate and magnesium appeared to be important in order for citric acid to accumulate. The production of citric acid and the consumed sugar was higher when using 0.1% ammonium nitrate as the best source of nitrogen. The production of citric acid increased significantly when 0.1 g/l of KH2PO4 was added to the medium of date syrup. The addition of magnesium sulfate at the rate of 0.20 g/l had a stimulating effect on the production of citric acid. Maximum production of citric acid was obtained when calcium chloride was absent. One of the most important benefits of immobilized cells is their ability and stability to produce citric acid under a repeated batch culture. Over four repeated batches, the production of citric acid production was maintained for 24 days when each cycle continued for 144 h. The results obtained in the repeated batch cultivation using date syrup confirmed that date syrup could be used as a medium for the industrial production of citric acid.

  18. Asymmetric Suzuki Cross-Couplings of Activated Secondary Alkyl Electrophiles: Arylations of Racemic α-Chloroamides

    PubMed Central

    Lundin, Pamela M.; Fu, Gregory C.

    2010-01-01

    A nickel-catalyzed stereoconvergent method for the enantioselective Suzuki arylation of racemic α-chloroamides has been developed. This process represents the first example of an asymmetric arylation of an α-haloamide, of an enantioselective arylation of an α-chlorocarbonyl compound, and of an asymmetric Suzuki reaction with an activated alkyl electrophile or an arylboron reagent. The method is also applicable to the corresponding enantioselective cross-coupling of α-bromoamides. The coupling products can be transformed without racemization into useful enantioenriched α-arylcarboxylic acids and primary alcohols. An unprecedented (and modest) kinetic resolution of the α-chloroamide has been observed; a mechanistic study indicates that the selectivity likely reflects the discrimination by the chiral catalyst of the two enantiomeric α-chloroamides in an irreversible oxidative-addition process. PMID:20698665

  19. The use of date waste for lactic acid production by a fed-batch culture using Lactobacillus casei subsp. rhamnosus.

    PubMed

    Nancib, Aicha; Nancib, Nabil; Boubendir, Abdelhafid; Boudrant, Joseph

    2015-01-01

    The production of lactic acid from date juice by Lactobacillus caseisubsp. rhamnosus in batch and fed-batch cultures has been investigated. The fed-batch culture system gave better results for lactic acid production and volumetric productivity. The aim of this work is to determine the effects of the feeding rate and the concentration of the feeding medium containing date juice glucose on the cell growth, the consumption of glucose and the lactic acid production by Lactobacillus casei subsp. rhamnosus in fed-batch cultures. For this study, two concentrations of the feeding medium (62 and 100 g/L of date juice glucose) were tested at different feeding rates (18, 22, 33, 75 and 150 mL/h). The highest volumetric productivity (1.3 g/L.h) and lactic acid yield (1.7 g/g) were obtained at a feeding rate of 33 mL/h and a date juice glucose concentration of 62 g/L in the feeding medium. As a result, most of the date juice glucose was completely utilised (residual glucose 1 g/L), and a maximum lactic acid production level (89.2 g/L) was obtained.

  20. Characterization of racemic species of chiral drugs using thermal analysis, thermodynamic calculation, and structural studies.

    PubMed

    Li, Z J; Zell, M T; Munson, E J; Grant, D J

    1999-03-01

    The identification of the racemic species, as a racemic compound, a racemic conglomerate, or a racemic solid solution (pseudoracemate), is crucial for rationalizing the potential for resolution of racemates by crystallization. The melting points and enthalpies of fusion of a number of chiral drugs and their salts were measured by differential scanning calorimetry. Based on a thermodynamic cycle involving the solid and liquid phases of the enantiomers and racemic species, the enthalpy, entropy and Gibbs free energy of the racemic species were derived from the thermal data. The Gibbs free energy of formation, is always negative for a racemic compound, if it can exist, and the contribution from the entropy of mixing in the liquid state to the free energy of formation is the driving force for the process. For a racemic conglomerate, the entropy of mixing in the liquid state is close to the ideal value of R ln 2 (1.38 cal.mol-1. K-1). Pseudoracemates behave differently from the other two types of racemic species. When the melting points of the racemic species is about 30 K below that of the homochiral species, is approximately zero, indicating that the racemic compound and racemic conglomerate possess similar relative stabilities. The powder X-ray diffraction patterns and 13C solid-state nuclear magnetic resonance spectra are valuable for revealing structural differences between a racemic compound and a racemic conglomerate. Thermodynamic prediction, thermal analysis, and structural study are in excellent agreement for identifying the nature of the racemic species.

  1. Solubility properties of racemic praziquantel and its enantiomers.

    PubMed

    el-Arini, S K; Giron, D; Leuenberger, H

    1998-11-01

    The purpose of this study was to characterize the solubility and thermodynamic properties of the optical isomers of the anti-schistosomal drug, praziquantel (PZQ) and to compare these properties to those of the racemic product used in commercial preparations (Biltricide, generic drugs). The crystalline enantiomers of PZQ exhibited different thermal properties than the racemic drug. The melting points and the enthalpies of fusion obtained from the differential scanning calorimetry (DSC) scans were nearly identical between the isomers and were substantially lower than those of racemic PZQ [(+/-)-PZQ]. The DSC results indicate that (+/-)-PZQ is a racemic compound and not a racemic mixture. This was confirmed by powder x-ray diffraction analysis and the IR spectra. The 30 degrees decrease in the melting point was reflected in increased solubility of the enantiomers, which amounted to twice that of the racemic PZQ. The behavior of the isomers in the presence of beta-cyclodextrin (beta-CD) was studied in water at 37 degrees C. The solubility data (phase solubility diagrams) were linear for up to the highest concentration of added beta-CD investigated. The apparent stability constants determined from the phase solubility diagrams showed that both the (+) and (-) enantiomers as well as (+/-)-PZQ exhibited moderate affinity to form a 1:1 complex in solution with beta-CD. The findings of this study may be of importance when efforts are considered to improve pharmaceutical formulation of this anti-schistosomal drug. PMID:9834959

  2. Formation of solid solutions between racemic and enantiomeric citalopram oxalate.

    PubMed

    de Diego, Heidi Lopez; Bond, Andrew D; Dancer, Robert James

    2011-05-01

    The X-ray powder diffractograms of racemic citalopram oxalate and (S)-citalopram oxalate are very similar, but the melting point of the racemate is higher than that of the pure enantiomer. The higher melting point indicates that the racemate is a racemic compound, rather than a conglomerate. The crystal structure of the enantiomer contains two molecules of (S)-citalopram in the asymmetric unit. The conformation of the two molecules is different but they approximate mirror images of each other if the aromatic groups are interchanged. The crystal structure of the racemate is essentially isostructural with that of the enantiomer, having almost the same cell parameters but containing a crystallographic inversion centre that is not retained in the enantiomer structure. The closely-comparable crystal structures permit solid solutions to be formed between racemic and enantiomeric citalopram oxalate. Phase diagrams of the (R)-citalopram and (S)-citalopram oxalate system are constructed, and they show that solid solutions are formed at all ratios of the two enantiomers.

  3. Antinociceptive activity of NK1 receptor antagonists: non-specific effects of racemic RP67580.

    PubMed Central

    Rupniak, N. M.; Boyce, S.; Williams, A. R.; Cook, G.; Longmore, J.; Seabrook, G. R.; Caeser, M.; Iversen, S. D.; Hill, R. G.

    1993-01-01

    1. Release of substance P in the dorsal horn is considered a primary event in the perception of pain. The profile of racemic RP67580, a non-peptide antagonist at the NK1 (substance P) receptor, was examined in a range of antinociception tests on rodents. 2. At doses up to 30 mg kg-1, s.c. racemic RP67580 exhibited antinociceptive activity in writhing and formalin paw tests in mice and gerbils. Acetic acid induced writhing and the licking response to formalin were reduced to 40-50% of the level observed in vehicle-treated animals (P < 0.05). However, this agent was not active in mouse tail flick, rat paw pressure or rat and guinea-pig formalin paw tests. 3. Like racemic RP67580, the calcium channel blockers nifedipine (30 mg kg-1, i.p.) and verapamil (10 or 20 mg kg-1, s.c.) inhibited the response to formalin by approximately 60% in gerbils (P < 0.05 compared with vehicle-treated animals). 4. Evidence for calcium channel antagonist activity of RP67580 was obtained in vitro. Racemic RP67580 inhibited calcium entry into depolarized strips of guinea-pig ileum longitudinal muscle myenteric plexus (apparent KB = 587 +/- 115 nM), inhibited [3H]-diltiazem binding to rabbit skeletal membranes (IC50 = 298 nM) and depressed high threshold calcium currents in neurones cultured from rat cortex (10% inhibition at 10 microM). 5. These findings indicate that the acute antinociceptive effects of RP67580 may not be attributable to a specific interaction with NK1 receptors and may be mediated via calcium channel blockade. PMID:8306108

  4. Glutamate racemization and catabolism in Fusobacterium varium.

    PubMed

    Ramezani, Mohammad; Resmer, Kelly L; White, Robert L

    2011-07-01

    The pathways of glutamate catabolism in the anaerobic bacterium Fusobacterium varium, grown on complex, undefined medium and chemically defined, minimal medium, were investigated using specifically labelled (13)C-glutamate. The metabolic end-products acetate and butyrate were isolated from culture fluids and derivatized for analysis by nuclear magnetic resonance and mass spectrometry. On complex medium, labels from L-[1-(13)C]glutamate and L-[4-(13)C]glutamate were incorporated into C1 of acetate and equally into C1/C3 of butyrate, while label derived from L-[5-(13)C]glutamate was not incorporated. The isotopic incorporation results and the detection of glutamate mutase and 3-methylaspartate ammonia lyase in cell extracts are most consistent with the methylaspartate pathway, the best known route of glutamate catabolism in Clostridium species. When F. varium was grown on defined medium, label from L-[4-(13)C]glutamate was incorporated mainly into C4 of butyrate, demonstrating a major role for the hydroxyglutarate pathway. Upon addition of coenzyme B(12) or cobalt ion to the defined medium in replicate experiments, isotope was located equally at C1/C3 of butyrate in accord with the methylaspartate pathway. Racemization of D-glutamate and subsequent degradation of L-glutamate via the methylaspartate pathway are supported by incorporation of label into C2 of acetate and equally into C2/C4 of butyrate from D-[3-(13)C]glutamate and the detection of a cofactor-independent glutamate racemase in cell extracts. Together the results demonstrate a major role for the methylaspartate pathway of glutamate catabolism in F. varium and substantial participation of the hydroxyglutarate pathway when coenzyme B(12) is not available.

  5. Uranium series dating of human skeletal remains from the del mar and sunnyvale sites, california.

    PubMed

    Bischoff, J L; Rosenbauer, R J

    1981-08-28

    Uranium series analyses of human bone samples from the Del Mar and Sunnyvale sites indicate ages of 11,000 and 8,300 years, respectively. The dates are supported by internal concordancy between thorium-230 and protactinium-231 decay systems. These ages are significantly younger than the estimates of 48,000 and 70,000 years based on amino acid racemization, and indicate that the individuals could derive from the population waves that came across the Bering Strait during the last sea-level low.

  6. Uranium series dating of human skeletal remains from the del mar and sunnyvale sites, california.

    PubMed

    Bischoff, J L; Rosenbauer, R J

    1981-08-28

    Uranium series analyses of human bone samples from the Del Mar and Sunnyvale sites indicate ages of 11,000 and 8,300 years, respectively. The dates are supported by internal concordancy between thorium-230 and protactinium-231 decay systems. These ages are significantly younger than the estimates of 48,000 and 70,000 years based on amino acid racemization, and indicate that the individuals could derive from the population waves that came across the Bering Strait during the last sea-level low. PMID:17789030

  7. Uranium series dating of human skeletal remains from the Del Mar and Sunnyvale sites, California

    SciTech Connect

    Bischoff, J.L.; Rosenbauer, R.J.

    1981-08-28

    Uranium series analyses of human bone samples from the Del Mar and Sunnyvale sites indicate ages of 11,000 and 8300 years, respectively. The dates are supported by internal concordancy between thorium-230 and protactinium-231 decay systems. These ages are significantly younger than the estimates of 48,000 and 70,000 years based on amino acid racemization, and indicate that the individuals could derive from the population waves that came across the Bering Strait during the last sea-level low.

  8. Uranium series dating of human skeletal remains from the Del Mar and Sunnyvale sites, California

    USGS Publications Warehouse

    Bischoff, J.L.; Rosenbauer, R.J.

    1981-01-01

    Uranium series analyses of human bone samples from the Del Mar and Sunnyvale sites indicate ages of 11,000 and 8,300 years, respectively. The dates are supported by internal concordancy between thorium-230 and protactinium-231 decay systems. These ages are significantly younger than the estimates of 48,000 and 70,000 years based on amino acid racemization, and indicate that the individuals could derive from the population waves that came across the Bering Strait during the last sea-level low. Copyright ?? 1981 AAAS.

  9. Preparative separation of underivatized amino acids for compound-specific stable isotope analysis and radiocarbon dating of hydrolyzed bone collagen.

    PubMed

    Tripp, Jennifer A; McCullagh, James S O; Hedges, Robert E M

    2006-01-01

    Analysis of stable and radioactive isotopes from bone collagen provides useful information to archaeologists about the origin and age of bone artifacts. Isolation and analysis of single amino acids from the proteins can provide additional and more accurate information by removing contamination and separating a bulk isotope signal into its constituent parts. In this paper, we report a new method for the separation and isolation of underivatized amino acids from bone collagen, and their analysis by isotope ratio MS and accelerator MS. RP chromatography is used to separate the amino acids with nonpolar side chains, followed by an ion pair separation to isolate the remaining amino acids. The method produces single amino acids with little or no contamination from the separation process and allows for the measurement of accurate stable isotope ratios and pure samples for radiocarbon dating.

  10. Stereoselective sulphate conjugation of racemic terbutaline by human liver cytosol.

    PubMed

    Walle, T; Walle, U K

    1990-07-01

    1. The enantioselectivity of the sulphation of racemic terbutaline by phenolsulphotransferases was examined in vitro using cytosol from human livers (n = 3) and [35S]-3'-phosphoadenosine-5'-phosphosulphate (PAP35S) as the sulphate donor. 2. The radioactive sulphate conjugate formed was isolated by h.p.l.c. and its enantiomers were separated intact by h.p.l.c. after chiral derivatization. 3. Sulphation of racemic terbutaline occurred with the same apparent Km value for both enantiomers (270 microM). The extent of sulphation of the (+)-enantiomer was double that of the (-)-enantiomer, solely due to a difference in their apparent Vmax values. 4. Sulphation of racemic prenalterol, a structural analogue of terbutaline, also showed a two-fold preference for the (+)-enantiomer. 5. These findings suggest that enantioselective sulphate conjugation of chiral phenolic sympathomimetic amine drugs may lead to enantioselective pharmacokinetics that should be considered in the clinical use of these drugs. PMID:2390423

  11. Induced circularly polarized luminescence arising from anion or protein binding to racemic emissive lanthanide complexes

    NASA Astrophysics Data System (ADS)

    Carr, Rachel; Puckrin, Robert; McMahon, Brian K.; Pal, Robert; Parker, David; Pålsson, Lars-Olof

    2014-06-01

    A circularly polarized luminescence (CPL) spectrometer has been built and used to study the binding interaction of lactate and four different proteins with racemic EuIII and TbIII complexes in aqueous solution. Lactate binding gives rise to strong induced CPL spectra, and the observed emission dissymmetry factors vary linearly with enantiomeric composition. Particularly strong induced TbIII CPL also characterizes the binding interaction of alpha-1-acid glycoprotein with a dissociation constant, Kd, of 2.5 μM.

  12. Racemic cobalt phosphonates incorporating flexible bis(imidazole) co-ligands.

    PubMed

    Feng, Jian-Shen; Cai, Zhong-Sheng; Ren, Min; Bao, Song-Song; Zheng, Li-Min

    2015-11-01

    By incorporating flexible bis(imidazol-1-ylmethyl)benzene (bix) co-ligands, four new racemic cobalt phosphonates with formulae Co3(3-ppap)2(1,4-bix)2(H2O)4·4H2O (1), Co3(3-ppap)2(1,3-bix)2(H2O)4·5H2O (2), Co3(3-ppap)2(1,2-bix)2(H2O)4·4H2O (3) and Co3(ppa)2(1,2-bix)2·4H2O (4) are isolated, where 3-ppapH3 represents 3-phenyl-3-((phosphonomethyl)amino)propanoic acid and ppaH3 is 2-phenyl-2-(phosphonomethylamino)acetic acid. Compounds 1-3 crystallize in the monoclinic space group P21/c and show two-dimensional structures in which the Co3(3-ppap)2 chains are bridged by 1,4-bix, 1,3-bix and 1,2-bix ligands in trans-modes, respectively. Within the chain, a racemic dimer of Co2(3-ppap)2(2-) is found, where the Co atoms are doubly bridged by O-P-O units from the (S)- and (R)-3-ppap(3-) ligands. The dimers are connected by another crystallographically independent Co atom through O-P-O linkages to form an infinite racemic chain. The packing modes of the layers in 1-3 are quite different, however, which are ABAB in the cases of 1 and 3 while ABCDABCD in the case of 2, attributed to the positional isomerism of the bix co-ligands. Compound 4 displays a chain structure in which the 1,2-bix bridges the Co atoms in cis-mode within the chain. Magnetic properties are investigated for all compounds.

  13. Determining D/L Ratios of Amino Acids Found in Ice Above Lake Vostok Using ESI/CIT Mass Spectroscopy

    NASA Technical Reports Server (NTRS)

    Tsapin, A.; Kanik, I.; Beegle, L. W.; Wu, L.; Cooks, R. G.

    2003-01-01

    Astrobiology is an area where longevity of (micro) organisms is of great interest. Cryospheres are common phenomena in the solar system, particularly on satellites, comets and asteroids, as well as at least some of the planets. Recent data from the Mars Global Surveyor mission suggest the possibility of permafrost or perhaps even liquid water under the Martian surface [2]. These environments may be the areas in which the probability of finding life is the highest. This issue is of concern due to the probable evolution of planetary environments such as that of Mars from more hospitable to less hospitable conditions over the history of the solar system. In addition, evaluation of the possible transfer of living organisms between planets via impact ejecta [3] is dependent on knowledge of the maximum time periods over which microorganisms can remain dormant and subsequently revive and reproduce.Amino acid racemization dating, or aminostratigraphy, has been used for many years to date biological systems, and has been examined as a possible biosignature detection technique for Mars. We have suggested using amino acid racemization as one of the most indicative biosignatures [4]. Only life systems produce preferential synthesis of L-amino acids versus D-amino acids. Almost all amino acids in terrestrial organisms can be found only in the L-enantiomeric form.We studied the level of amino acid racemization, specifically of aspartic acid, in permafrost samples from eastern Siberia. Also we analyzed samples of ice from borehole drilled to lake Vostok, Antarctica.

  14. Application of direct crystallization for racemic compound propranolol hydrochloride.

    PubMed

    Wang, Xiujuan; Lu, Jie; Ching, Chi Bun

    2007-10-01

    The application of direct crystallization integrating with chromatography to the resolution of a racemic compound propranolol hydrochloride was studied and the crystallization progression was clearly illustrated in terms of the diagram of solubility and metastable zone widths with different enantiomeric compositions. The solubility and metastable zone widths of propranolol hydrochloride in the mixture of methanol and isopropanol were determined using an in situ Lasentec Focused Beam Reflectance Measurement (FBRM) probe. The direct crystallizations were carried out in an automatic lab reactor (Mettler Toledo LabMax) system. The optical purity of final product crystals was examined using differential scanning calorimetry (DSC), HPLC and PXRD. The crystal size distribution and morphology were analyzed using Malvern Mastersizer and Jeol SEM. It was found that optically pure crystal product could be obtained within certain safe supersaturation limit and there was no evidence of polymorph or solvate/hydrate transformation during the crystallization process. There was no selectivity of crystal growth or nucleation between the pure enantiomer and its racemate when the solution reaches the temperature lower than saturation temperature of the racemate. Hence, the critical supersaturation control of a solution was essential to obtain pure enantiomers from a partially resolved racemate. PMID:17549769

  15. Cysteine Racemization on IgG Heavy and Light Chains

    PubMed Central

    Zhang, Qingchun; Flynn, Gregory C.

    2013-01-01

    Under basic pH conditions, the heavy chain 220-light chain 214 (H220-L214) disulfide bond, found in the flexible hinge region of an IgG1, can convert to a thioether. Similar conditions also result in racemization of the H220 cysteine. Here, we report that racemization occurs on both H220 and L214 on an IgG1 with a λ light chain (IgG1λ) but almost entirely on H220 of an IgGl with a κ light chain (IgG1κ) under similar conditions. Likewise, racemization was detected at significant levels on H220 and L214 on endogenous human IgG1λ but only at the H220 position on IgG1κ. Low but measurable levels of d-cysteines were found on IgG2 cysteines in the hinge region, both with monoclonal antibodies incubated under basic pH conditions and on antibodies isolated from human serum. A simplified reaction mechanism involving reversible β-elimination on the cysteine is presented that accounts for both base-catalyzed racemization and thioether formation at the hinge disulfide. PMID:24142697

  16. Chiral separation of metolachlor ethane sulfonic acid as a groundwater dating tool

    Technology Transfer Automated Retrieval System (TEKTRAN)

    We have studied the hydrologic fate of metolachlor and its two predominant metabolites, metolachlor ethane sulfonic acid (MESA) and metolachlor oxanilic acid, in groundwater and base flows of streams for several years. These two metabolites are excellent markers for groundwater processes related to...

  17. Using chiral identification of metolachlor ethane sulfonic acid as a groundwater dating tool

    Technology Transfer Automated Retrieval System (TEKTRAN)

    We have studied the hydrologic fate of metolachlor and its two predominant metabolites, metolachlor ethane sulfonic acid (MESA) and metolachlor oxanilic acid, in groundwater and base flows of streams for several years. These two metabolites are excellent markers for groundwater processes related to...

  18. Influence of racemic higenamine on the sinus node.

    PubMed

    Yu, Fengxia; Kong, Lingting; Wang, Shujuan

    2013-02-01

    The aim of this study was to explore the mechanism of racemic higenamine in the treatment of sick sinus syndrome (SSS). A total of 40 New Zealand rabbits were randomly divided into normal sinus node and damaged sinus node (SND) groups, and each group was randomly divided into treatment and control groups (n=10). The SND model was established by formaldehyde wet dressing of the sinus node area. The treatment groups were administered an intravenous infusion of 0.04 mg/kg racemic higenamine via the marginal ear vein within 5 min. The electrophysiological indicators of sinoatrial function, including the sinus node recovery time (SNRT), corrected sinus node recovery time (CSNRT), total sinoatrial conduction time (TSACT) and sinus cycle length (SCL), were determined before and 20 min after medication and the changes in these indicators were evaluated. The two control groups were administered 10 ml physiological saline. Following the administration of racemic higenamine, the SNRT, CSNRT, TSACT and SCL in the normal sinus node and SND groups were significantly shortened compared with those in the control groups (P<0.01). The electrophysiological influence of racemic higenamine on sinoatrial function in the SND group was significantly greater than that in the normal sinus node group (P<0.01), and its effect in the treatment of arrhythmia caused by a damaged sinus node was statistically significant (P<0.05). The main electrophysiological mechanism of racemic higenamine in the treatment of SSS was the enhancement of sinus node self-discipline and improvement of sinoatrial and atrioventricular conduction function.

  19. Oxyma-based phosphates for racemization-free peptide segment couplings

    PubMed Central

    Mitachi, Katsuhiko; Kurosu, Yuki E.; Hazlett, Brandon T.; Kurosu, Michio

    2016-01-01

    Glyceroacetonide-Oxyma [(2,2-dimethyl-1,3-dioxolan-4-yl)methyl 2-cyano-2-(hydroxyimino)acetate (1)] displayed remarkable physico-chemical properties as an additive for peptide-forming reactions. Although racemization-free amide-forming reactions have been established for N-urethane-protected α-amino acids with EDCI, 1, and NaHCO3 in water or DMF-water media, amide-forming reactions of N-acyl-protected α-amino acids and segment couplings of oligopeptides still require further development. Diethylphosphoryl-Glyceroacetonide-Oxyma (DPGOx, 3) exhibits relative stability in aprotic solvents and is an effective coupling reagent for N-acyl-protected α-amino acids and oligo peptide segments. The conditions reported here is also effective in lactam-forming reactions. Unlike most of the reported coupling reagents, simple aqueous work-up procedures can remove the reagent and by-products generated in the reactions. PMID:26856693

  20. 14C dating of bone using (gamma) Carboxyglutamic Acid and Carboxyglycine (Aminomalonate)

    SciTech Connect

    Southon, J R; Burky, R T; Kirner, D L; Taylor, R E; Hare, P E

    1999-04-27

    Radiocarbon determinations have been obtained on {gamma}-carboxyglutamic acid [Gla] and {alpha}-carboxyglycine (aminomalonate) [Am] as well as acid- and base-hydrolyzed total amino acids isolated from a series of fossil bones. As far as they are aware, Am has not been reported previously in fossil bone and neither Gla nor Am {sup 14}C values have been measured previously. Interest in Gla, an amino acid found in the non-collagen proteins osteocalcin and matrix Gla-protein (MGP), proceeds from the suggestion that it may be preferentially retained and more resistant to diagenetic contamination affecting {sup 14}C values in bones exhibiting low and trace amounts of collagen. The data do not support these suggestions. The suite of bones examined showed a general tendency for total amino acid and Gla concentrations to decrease in concert. Even for bones retaining significant amounts of collagen, Gla (and Am extracts) can yield {sup 14}C values discordant with their expected age and with {sup 14}C values obtained on total amino-acid fractions isolated from the same bone sample.

  1. Copper-catalyzed divergent kinetic resolution of racemic allylic substrates.

    PubMed

    Pineschi, Mauro; Di Bussolo, Valeria; Crotti, Paolo

    2011-10-01

    When a racemic mixture is fully consumed the products may still be enantiomerically enriched. In particular, the regiodivergent kinetic resolution is a process in which a single chiral catalyst or reagent reacts with a racemic substrate to form regioisomers possessing an opposite configuration on the newly-formed stereogenic centers. This review reports the major advances in the field of the copper-catalyzed regiodivergent and stereodivergent kinetic resolution of allylic substrates with organometallic reagents. The chiral recognition matching phenomena found with particular allylic substrates with the absolute configuration of the chiral catalyst allows in some cases an excellent control of the regio- and stereoselectivity, sheding some light on the so-called "black-box" mechanism of a copper-catalyzed asymmetric allylic alkylation. PMID:21837639

  2. Geochemistry of amino acids in shells of the clam Saxidomus

    USGS Publications Warehouse

    Kvenvolden, K.A.; Blunt, D.J.; McMenamin, M.A.; Straham, S.E.

    1980-01-01

    Concentrations of amino acids and their corresponding d l enantiomeric ratios have been measured in shells of the bivalve mollusk Saxidomus from eleven localities, ranging in age from modern to probably more than 500,000 yr, along the Pacific coast of North America. Natural logarithms of amino acid concentrations correlate well with d l ratios, and the relationship provides a possible guide to the selection of fossils for use in amino acid dating. The relative order of the extents of racemization of amino acids at any given time appears to change with increasing sample age. Application of the amino acid dating method to shells from Whidbey Island, Washington, yields an age of about 80,000 yr, in contrast to the previously determined radiocarbon age of 36,000 yr which was measured on some shell carbonate and considered a minimum age. The amino acid age is compatible with the geologic record in the area. ?? 1980.

  3. [Gamma-hydroxybutyric acid (GHB): more than a date rape drug, a potentially addictive drug].

    PubMed

    Karila, Laurent; Novarin, Johanne; Megarbane, Bruno; Cottencin, Olivier; Dally, Sylvain; Lowenstein, William; Reynaud, Michel

    2009-10-01

    According to available information, GHB and its precursors--gamma-butyrolactone (GBL) and 1,4-butanediol (1,4BD)--are used especially in a nightlife scene characterized by the search for amplified sensations through the combination of electronic music, marathon dancing, and substance abuse. Evidence indicates that GHB/GHL is used particularly in some subpopulations and in places, such as in gay nightclubs. Commonly known as Gorliquid ecstasy, it was misused in the 1980s for its bodybuilding effects and in the 1990s as a recreational drug at music venues. In the same period, media coverage of the use of GHB in sexual assault (often referred to as date rape) brought the drug into the spotlight. GHB/GHL addiction is a recognized clinical entity evidenced by severe withdrawal symptoms when the drug is abruptly discontinued after regular or chronic use. There is evidence that negative health and social consequences may occur in recreational and chronic users. Nonfatal overdoses and deaths related to GHB have been reported. These undesirable effects and especially the deaths appear to have prompted campaigns to limit the use of GHB. Clinicians must also be aware of GBL, which is being sold and used as a substitute for GHB.

  4. [Gamma-hydroxybutyric acid (GHB): more than a date rape drug, a potentially addictive drug].

    PubMed

    Karila, Laurent; Novarin, Johanne; Megarbane, Bruno; Cottencin, Olivier; Dally, Sylvain; Lowenstein, William; Reynaud, Michel

    2009-10-01

    According to available information, GHB and its precursors--gamma-butyrolactone (GBL) and 1,4-butanediol (1,4BD)--are used especially in a nightlife scene characterized by the search for amplified sensations through the combination of electronic music, marathon dancing, and substance abuse. Evidence indicates that GHB/GHL is used particularly in some subpopulations and in places, such as in gay nightclubs. Commonly known as Gorliquid ecstasy, it was misused in the 1980s for its bodybuilding effects and in the 1990s as a recreational drug at music venues. In the same period, media coverage of the use of GHB in sexual assault (often referred to as date rape) brought the drug into the spotlight. GHB/GHL addiction is a recognized clinical entity evidenced by severe withdrawal symptoms when the drug is abruptly discontinued after regular or chronic use. There is evidence that negative health and social consequences may occur in recreational and chronic users. Nonfatal overdoses and deaths related to GHB have been reported. These undesirable effects and especially the deaths appear to have prompted campaigns to limit the use of GHB. Clinicians must also be aware of GBL, which is being sold and used as a substitute for GHB. PMID:19762202

  5. Enantioselective separation of racemic secondary amines on a chiral crown ether-based liquid chromatography stationary phase.

    PubMed

    Steffeck, Robert J; Zelechonok, Yury; Gahm, Kyung H

    2002-02-22

    The first general enantioselective separation of racemic secondary amines on a crown ether-based liquid chromatography chiral stationary phase (CSP) is presented. The CSP is based on (+)- or (-)-(18-crown-6)-2,3,11,12-tetracarboxylic acid covalently bonded to silica gel. A mobile phase containing methanol, acetonitrile, triethylamine and acetic acid was employed in these separations of secondary amines with crown ether CSPs. The separation mechanism is believed to be the secondary amine forming a complex which includes crown ether coordination and electrostatic interaction of the positively charged amine with a carboxylate anion of the immobilized crown ether.

  6. A resolution approach of racemic phenylalanine with aqueous two-phase systems of chiral tropine ionic liquids.

    PubMed

    Wu, Haoran; Yao, Shun; Qian, Guofei; Yao, Tian; Song, Hang

    2015-10-30

    Aqueous two-phase systems (ATPS) based on tropine type chiral ionic liquids and inorganic salt solution were designed and prepared for the enantiomeric separation of racemic phenylalanine. The phase behavior of IL-based ATPS was comprehensive investigated, and phase equilibrium data were correlated by Merchuk equation. Various factors were also systematically investigated for their influence on separation efficiency. Under the appropriate conditions (0.13g/g [C8Tropine]pro, 35mg/g Cu(Ac)2, 20mg/g d,l-phenylalanine, 0.51g/g H2O and 0.30g/g K2HPO4), the enantiomeric excess value of phenylalanine in solid phase (mainly containing l-enantiomer) was 65%. Finally, the interaction mechanism was studied via 1D and 2D NMR. The results indicate that d-enantiomer of phenylalanine interacts more strongly with chiral ILs and Cu(2+) based on the chiral ion-pairs space coordination mechanism, which makes it tend to remain in the top IL-rich phase. By contrast, l-enantiomer is transferred into the solid phase. Above chiral ionic liquids aqueous two-phase systems have demonstrated obvious resolution to racemic phenylalanine and could be promising alterative resolution approach for racemic amino acids in aqueous circumstance.

  7. Racemization of the Succinimide Intermediate Formed in Proteins and Peptides: A Computational Study of the Mechanism Catalyzed by Dihydrogen Phosphate Ion

    PubMed Central

    Takahashi, Ohgi; Kirikoshi, Ryota; Manabe, Noriyoshi

    2016-01-01

    In proteins and peptides, d-aspartic acid (d-Asp) and d-β-Asp residues can be spontaneously formed via racemization of the succinimide intermediate formed from l-Asp and l-asparagine (l-Asn) residues. These biologically uncommon amino acid residues are known to have relevance to aging and pathologies. Although nonenzymatic, the succinimide racemization will not occur without a catalyst at room or biological temperature. In the present study, we computationally investigated the mechanism of succinimide racemization catalyzed by dihydrogen phosphate ion, H2PO4−, by B3LYP/6-31+G(d,p) density functional theory calculations, using a model compound in which an aminosuccinyl (Asu) residue is capped with acetyl (Ace) and NCH3 (Nme) groups on the N- and C-termini, respectively (Ace–Asu–Nme). It was shown that an H2PO4− ion can catalyze the enolization of the Hα–Cα–C=O portion of the Asu residue by acting as a proton-transfer mediator. The resulting complex between the enol form and H2PO4− corresponds to a very flat intermediate region on the potential energy surface lying between the initial reactant complex and its mirror-image geometry. The calculated activation barrier (18.8 kcal·mol−1 after corrections for the zero-point energy and the Gibbs energy of hydration) for the enolization was consistent with the experimental activation energies of Asp racemization. PMID:27735868

  8. Groundwater dating using radiocarbon in fulvic acid in groundwater containing fluorescein

    NASA Astrophysics Data System (ADS)

    Nakata, Kotaro; Kodama, Hiroki; Hasegawa, Takuma; Hama, Katsuhiro; Iwatsuki, Teruki; Miyajima, Tohru

    2013-05-01

    Natural DO14C is recognized as one of the most useful tracers in the estimation of groundwater age. Fluorescent dye is commonly used as an indicator of drilling fluid contamination during borehole investigation. Fluorescein (FS) is one of the most frequently used fluorescent dyes, yet as it contains little radiocarbon it may affect DO14C age when it is mixed with natural DOC. In this study, fulvic acid (FA) was isolated from groundwater containing FS and DO14C value of isolated FA was measured. Separation methods were proposed by using the difference between sorption and desorption behavior of FA and FS onto synthetic adsorbent resin. DO14C measurement on FA from a mixture of FA and FS is estimated by removing FS from the mixture and correcting for the amount of C derived from FS. Furthermore, DO14C age is compared with the groundwater age estimated by He. The results show that the values of DO14C age for separated FA estimated by the two methods had good agreement with those that corresponded to groundwater age estimated by He. This result indicates that DO14C is a useful indicator of groundwater age even for groundwater contaminated with FS.

  9. Amino acid epimerization dating of Quaternary coastal deformation in SE Iberian Peninsula: The region between Aguas and Antas Rivers' mouths

    NASA Astrophysics Data System (ADS)

    Torres, Trinidad; Ortiz, José E.; Sánchez-Palencia, Yolanda

    2016-05-01

    The coastal area between the mouths of the Aguas and Antas Rivers presents a deformed system of raised marine deposits, some of which have been strongly affected by active tectonics. The use of amino acid epimerization dating of Glycymeris shells from raised coastal deposits allowed determining the age of these marine deposits, all of them linked to highstand sea levels in the Mediterranean realm, with ages between MIS 11 and MIS 1. These results allowed corroborating the age of some previously studied sites, and using new sampling sites, the general aminostratigraphy for the Quaternary raised marine deposits on the Mediterranean coast was confirmed. The main deformation event took place after MIS 11 and continued until MIS 5, and was linked to the activity of the Palomares Fault.

  10. Spontaneous Resolution of Racemic Camphorates in the Formation of Three-Dimensional Metal-Organic Frameworks

    PubMed Central

    Chen, Shumei; Zhang, Jian; Bu, Xianhui

    2009-01-01

    Reported here is a rare example of enantioselective processes between organic racemic ligands (DL-camphorates) with in situ formed chiral metal complexes. Such enantioselectivity leads to a double spontaneous resolution of two pairs of distinctly different racemates (the ΛΔ-Zn(Htea) units and the DL-camphorate ligands) into two chiral 3-D frameworks containing only one enantiommeric form from each racemate. This work demonstrates unique enantioselectivity in the self-assembly of MOFs containing multiple chiral features, which points to a new avenue for the preparation of chiral framework materials and for the resolution of racemates. PMID:19537824

  11. Spontaneous resolution of racemic camphorates in the formation of three-dimensional metal-organic frameworks.

    PubMed

    Chen, Shumei; Zhang, Jian; Bu, Xianhui

    2009-07-20

    Reported here is a rare example of enantioselective processes between organic racemic ligands (DL-camphorates) with in situ formed chiral metal complexes. Such enantioselectivity leads to a double spontaneous resolution of two pairs of distinctly different racemates [the LambdaDelta-Zn(Htea) units and the DL-camphorate ligands] into two chiral three-dimensional frameworks containing only one enantiommeric form from each racemate. This work demonstrates unique enantioselectivity in the self-assembly of metal-organic frameworks containing multiple chiral features, which points to a new avenue for the preparation of chiral framework materials and for the resolution of racemates. PMID:19537824

  12. Discovery of a solid solution of enantiomers in a racemate-forming system by seeding.

    PubMed

    Huang, Jun; Chen, Shuang; Guzei, Ilia A; Yu, Lian

    2006-09-13

    A racemic liquid of opposite enantiomers usually crystallizes as a racemic compound (racemate), rarely as a conglomerate, and even more rarely as a solid solution. We discovered a Type II solid solution (mixed crystal) of the enantiomers of the chiral drug tazofelone (TZF) by seeding its racemic liquid with enantiomerically pure crystals (enantiomorphs). Without seeding, the racemic liquid crystallized as a racemic compound. The crystal structure of this solid solution resembles that of the enantiomorph but has static disorder arising from the random substitution of enantiomers. This solid solution is a kinetic product of crystallization made possible by its faster growth rate compared to that of the competing racemate (by 4- to 40-fold between 80 and 146 degrees C). The free energy of the solid solution continuously varies with the enantiomeric composition between those of the conglomerate and the racemates. The existence of the TZF solid solution explains the absence of eutectic melting between crystals of different enantiomeric compositions. The ability of TZF to simultaneously form racemate and solid solution originates from its conformational flexibility. Similar solid solutions of enantiomers may exist in other systems and may be discovered in similar ways. The study demonstrates the use of cross-nucleation for discovering and engineering crystalline materials to optimize physical properties.

  13. Sobrerol enantiomers and racemates: solid-state spectroscopy, thermal behavior, and phase diagrams.

    PubMed

    Bettinetti, G; Giordano, F; Fronza, G; Italia, A; Pellegata, R; Villa, M; Ventura, P

    1990-06-01

    The characterization of the solid state of sobrerol enantiomers and racemates has been accomplished by a number of techniques on solid phase such as thermal analysis (DSC) and spectroscopy (IR, 13C NMR, and X-ray diffraction both on powders and on single crystal). Experimental and theoretical binary phase diagrams of cis- and trans-sobrerol enantiomers and their mixtures have been drawn and are discussed. Thermal analysis allowed, moreover, the detection of cis racemate polymorphism. Finally, the quantitative analysis of the cis racemate as an impurity of the trans racemate by means of microcalorimetric determinations is reported.

  14. A ferroelectric liquid crystal conglomerate composed of racemic molecules

    PubMed

    Walba; Korblova; Shao; Maclennan; Link; Glaser; Clark

    2000-06-23

    We describe the design and synthesis of a ferroelectric liquid crystal composed of racemic molecules. The ferroelectric polarization results from spontaneous polar symmetry breaking in a fluid smectic. The ferroelectric phase is also chiral, resulting in the formation of a mixture of macroscopic domains of either handedness at the isotropic-to-liquid crystal phase transition. This smectic liquid crystal is thus a fluid conglomerate. Detailed investigation of the electrooptic and polarization current behavior within individual domains in liquid crystal cells shows the thermodynamically stable structure to be a uniformly tilted smectic bow-phase (banana phase), with all layer pairs homochiral and ferroelectric (SmC(S)P(F)).

  15. The pyrolysis of (-)-(S)-nicotine: racemization and decomposition.

    PubMed

    Clayton, Peter; Lu, Annhelen; Bishop, Louise

    2010-05-01

    The pyrolytic behaviour of (-)-(S)-nicotine in methanol was investigated using on-line pyrolysis GC/MS to establish whether racemization to the R(+) antipode occurs and to identify other products of pyrolysis. The conditions used included pyrolysing the sample for 15 seconds in an atmosphere of 9% oxygen in nitrogen (275 ml/min total flow) across the temperature range of 200 degrees C-1000 degrees C. A chiral Cyclodex-B analytical column (30 m x 0.25 mm i.d. x 0.25 microm film thickness) was used to separate the enantiomers of nicotine, although the two enantiomer peaks were not baseline resolved. The results of the experiment shows that there is no increase in (+)-(R)-nicotine levels across a wide temperature range. This suggests that the elevated levels of (+)-R-nicotine observed in tobacco smoke (compared to tobacco leaf material) are not due to the pyrolytic auto-racemization of (-)-(S)-nicotine but are a result of more complex interactions between (-)-(S)-nicotine and other smoke components. The pyrolysis of isotopically labelled nicotine established that nicotine undergoes thermal decomposition to beta-nicotyrine which in turn may decompose to other products.

  16. Separation and enrichment of enantiopure from racemic compounds using magnetic levitation.

    PubMed

    Yang, Xiaochuan; Wong, Shin Yee; Bwambok, David K; Atkinson, Manza B J; Zhang, Xi; Whitesides, George M; Myerson, Allan S

    2014-07-18

    Crystallization of a solution with high enantiomeric excess can generate a mixture of crystals of the desired enantiomer and the racemic compound. Using a mixture of S-/RS-ibuprofen crystals as a model, we demonstrated that magnetic levitation (MagLev) is a useful technique for analysis, separation and enantioenrichment of chiral/racemic products. PMID:24875274

  17. Intermolecular and low-frequency intramolecular Raman scattering study of racemic ibuprofen

    NASA Astrophysics Data System (ADS)

    Lazarević, J. J.; Uskoković-Marković, S.; Jelikić-Stankov, M.; Radonjić, M.; Tanasković, D.; Lazarević, N.; Popović, Z. V.

    We report the low-temperature Raman scattering study of racemic ibuprofen. Detailed analysis of the racemic ibuprofen crystal symmetry, related to the vibrational properties of the system, has been presented. The first principle calculations of a single ibuprofen molecule dynamical properties are compered with experimental data. Nineteen, out of 26 modes expected for the spectral region below 200 cm-1, have been observed.

  18. [Effects of sowing date and planting density on the seed yield and oil content of winter oilseed rape].

    PubMed

    Zhang, Shu-Jie; Li, Ling; Zhang, Chun-Lei

    2012-05-01

    A field experiment was conducted to investigate the effects of different sowing date and planting density on the seed yield and seed oil content of winter oilseed rape (Brassica napus). Sowing date mainly affected the seed yield of branch raceme, while planting density affected the seed yields of both branch raceme and main raceme. The seed oil content was less affected by sowing date. The proportion of the seed yield of main raceme to the seed yield per plant increased with increasing planting density, and the seed oil content of main raceme was about 1% higher than that of branch raceme. Consequently, the seed oil production per plot increased significantly with increasing planting density. In the experimental region, the sowing date of winter oilseed rape should be earlier than mid-October. When sowing in late October, the seed yield would be decreased significantly. A planting density of 36-48 plants x m(-2) could improve the seed yield and oil content of winter oilseed rape.

  19. Site-directed mutagenesis provides insight into racemization and transamination of alanine catalyzed by Treponema denticola cystalysin.

    PubMed

    Cellini, Barbara; Bertoldi, Mariarita; Paiardini, Alessandro; D'Aguanno, Simona; Voltattorni, Carla Borri

    2004-08-27

    In addition to alpha, beta-elimination of L-cysteine, Treponema denticola cystalysin catalyzes the racemization of both enantiomers of alanine accompanied by an overall transamination. Lys-238 and Tyr-123 or a water molecule located on the si and re face of the cofactor, respectively, have been proposed to act as the acid/base catalysts in the proton abstraction/donation at Calpha/C4' of the external aldimine. In this investigation, two site-directed mutants, K238A and Y123F, have been characterized. The Lys --> Ala mutation results in the complete loss of either lyase activity or racemase activity in both directions or transaminase activity toward L-alanine. However, the K238A mutant is able to catalyze the overall transamination of D-alanine, and only D-alanine is the product of the reverse transamination. For Y123F the k(cat)/K(m) is reduced 3.5-fold for alpha, beta-elimination, whereas it is reduced 300-400-fold for racemization. Y123F has approximately 18% of wild type transaminase activity with L-alanine and an extremely low transaminase activity with D-alanine. Moreover, the catalytic properties of the Y124F and Y123F/Y124F mutants rule out the possibility that the residual racemase and transaminase activities displayed by Y123F are due to Tyr-124. All these data, together with computational results, indicate a two-base racemization mechanism for cystalysin in which Lys-238 has been unequivocally identified as the catalyst acting on the si face of the cofactor. Moreover, this study highlights the importance of the interaction of Tyr-123 with water molecules for efficient proton abstraction/donation function on the re face. PMID:15210695

  20. From Homochiral Clusters to Racemate Crystals: Viable Nuclei in 2D Chiral Crystallization.

    PubMed

    Seibel, Johannes; Parschau, Manfred; Ernst, Karl-Heinz

    2015-07-01

    The quest for enantiopure compounds raises the question of which factors favor conglomerate crystallization over racemate crystallization. Studying nucleation and crystal growth at surfaces with submolecular-resolution scanning tunneling microscopy is a suitable approach to better understand intermolecular chiral recognition. Racemic heptahelicene on the Ag(100) surface shows a transition from homochiral nuclei to larger racemic motifs, although the extended homochiral phase exhibits higher density. The homochiral-heterochiral transition is explained by the higher stability of growing nuclei due to a better match of the molecular lattice to the substrate surface. Our observations are direct visual proof of viable nuclei.

  1. Fe uptake from meso and D,L-racemic Fe(o,o-EDDHA) isomers by strategy I and II plants.

    PubMed

    Cerdán, Mar; Alcañiz, Sara; Juárez, Margarita; Jordá, Juana D; Bermúdez, Dolores

    2006-02-22

    One of the most efficient fertilizers to correct Fe deficiency in calcareous soils and waters with high bicarbonate content is based on ferric ethylenediamine-N,N'-bis(o-hydroxyphenylacetic) acid [Fe(o,o-EDDHA)]. Fe(o,o-EDDHA) forms two groups of geometric isomers known as meso and D,L-racemic. To determine the Fe uptake from meso and D,L-racemic Fe(o,o-EDDHA), four iron-efficient plants, two plants representative of strategy I (tomato and pepper) and two plants representative of strategy II (wheat and oats), were grown in hydroponic culture. Results indicated that strategy II plants took up iron from both Fe(o,o-EDDHA) isomers equally. However, strategy I plants took mainly the iron associated with the meso form (the lowest stability isomer). PMID:16478264

  2. Stereocomplex Formation in Incompatible Racemic Chiral Polylactide Block Copolymers

    NASA Astrophysics Data System (ADS)

    Sun, Lu; Zhu, Lei

    2006-03-01

    Stereocomplexes in incompatible racemic chiral polylactide (PLA) block copolymers have not been widely studied. In this work, we synthesized PLLA and PDLA containing block copolymers by ring opening polymerization of L- and D-lactides from hydroxyl-terminated hydrophilic [poly(ethylene oxide) (PEO)] and hydrophobic [poly(ethylene-co-1,2-butylene) (PEB)] oligomers, respectively. Two samples PEO-b-PLLA (2,000-5,400) and PEB-b-PDLA (4,200-5,400) were chosen. The stereocomplexes were cast from equal molar blends of above two block copolymers in chloroform solution, followed by two different thermal treatments before stereocomplex formation; The blend was either heated to 250 C and quickly quench to 160 C or heated to 250 C for 15 min and quench to 160 C for stereocomplex crystal growth. Before the formation of stereocomplexes, lamellar and cylindrical morphologies were observed in blends for the first and second thermal treatments, respectively, as evidenced by small-angle X-ray scattering (SAXS). After complete crystal growth, the 100% stereocomplexes was confirmed by differential scanning calorimetry and wide-angle X-ray diffraction (WAXD). The morphologies of stereocomplexes grown from these two pre-existing microphases (lamellar vs. cylindrical) were studied by time-resolved SAXS and transmission electron microscopy (TEM).

  3. Comparison of the biophysical properties of racemic and d-erythro-N-acyl sphingomyelins.

    PubMed Central

    Ramstedt, B; Slotte, J P

    1999-01-01

    In this study stereochemically pure d-erythro-sphingomyelins (SMs) with either 16:0 or 18:1(cisDelta9) as the N-linked acyl-chain were synthesized. Our purpose was to examine the properties of these sphingomyelins and acyl-chain matched racemic (d-erythro/l-threo) sphingomyelins in model membranes. Liquid-expanded d-erythro-N-16:0-SM in monolayers was observed to pack more densely than the corresponding racemic sphingomyelin. Cholesterol desorption to beta-cyclodextrin was significantly slower from d-erythro-N-16:0-SM monolayers than from racemic N-16:0-SM monolayers. Significantly more condensed domains were seen in cholesterol/d-erythro-N-16:0-SM monolayers than in the corresponding racemic mixed monolayers, when [7-nitrobenz-2-oxa-1, 3-diazol-4-yl]phosphatidylcholine was used as a probe in monolayer fluorescence microscopy. With monolayers of N-18:1-SMs, both the lateral packing densities (sphingomyelin monolayers) and the rates of cholesterol desorption (mixed cholesterol/sphingomyelin monolayers) was found to be similar for d-erythro and racemic sphingomyelins. The phase transition temperature and enthalpy of d-erythro-N-16:0-SM in bilayer membranes were slightly higher compared with the corresponding racemic sphingomyelin (41.1 degrees C and 8.4 +/- 0.4 kJ/mol, and 39.9 degrees C and 7.2 +/- 0.2 kJ/mol, respectively). Finally, d-erythro-sphingomyelins in monolayers (both N-16:0 and N-18:1 species) were not as easily degraded at 37 degrees C by sphingomyelinase (Staphylococcus aureus) as the corresponding racemic sphingomyelins. We conclude that racemic sphingomyelins differ significantly in their biophysical properties from the physiologically relevant d-erythro sphingomyelins. PMID:10465760

  4. Antioxidant and antiatherogenic properties of phenolic acid and flavonol fractions of fruits of 'Amari' and 'Hallawi' date (Phoenix dactylifera L.) varieties.

    PubMed

    Borochov-Neori, Hamutal; Judeinstein, Sylvie; Greenberg, Amnon; Volkova, Nina; Rosenblat, Mira; Aviram, Michael

    2015-04-01

    Date (Phoenix dactylifera L.) fruit phenolic-acid or flavonol fractions were examined in vitro for antioxidant and antiatherogenic properties. Two fractions of each subgroup were prepared from two date varieties, 'Amari' and 'Hallawi', by solid phase extraction on C18. The fractions were analyzed for phenolics composition by RP-HPLC and tested for ferric-reducing antioxidant power, free radical scavenging capacity, inhibition of Cu(2+)-induced LDL oxidation, and enhancement of HDL-mediated cholesterol efflux from macrophages. All four fractions exhibited variable capacities to reduce ferric ions, scavenge radicals, and inhibit LDL oxidation. Flavonol fractions were considerably better inhibitors of LDL oxidation compared to phenolic acid fractions, with IC50's of 9-31 nmol GAE mL(-1) compared to 85-116 nmol GAE mL(-1), respectively. Only the flavonol fractions stimulated cholesterol removal from macrophages. Within each subgroup, the levels of all the activities varied with fraction composition. The results demonstrated strong structure-activity relationships for date phenolics and identified date flavonols as potential antiatherogenic bioactives. PMID:25765921

  5. A Study on Amino Acids: Synthesis of Alpha-Aminophenylacetic Acid (Phenylglycine) and Determination of its Isoelectric Point.

    ERIC Educational Resources Information Center

    Barrelle, M.; And Others

    1983-01-01

    Background information and procedures are provided for an experimental study on aminophenylacetic acid (phenylglycine). These include physical chemistry (determination of isoelectric point by pH measurement) and organic chemistry (synthesis of an amino acid in racemic form) experiments. (JN)

  6. Experimental and theoretical study of racemization, stability and tautomerism of vitamin C stereoisomers.

    PubMed

    Dabbagh, Hossein A; Azami, Fatemeh

    2014-12-01

    Experimental degradation of vitamin C (VC) in water was monitored using specific rotation, FT-IR and (1)H NMR at room temperature and at 80-90°C. The optical activity was reduced (100%) to zero after 6 and 63 days at 80-90°C (≅25% in less than 24h) and room temperature, respectively. (1)H NMR and FT-IR was performed after these periods which indicated the formation of a complex mixture at higher stirring time and elevated temperature. These observations indicated that vitamin C is unstable in solution at room temperature or at elevated temperature. The solid VC did not lose optical activity after several mounts at room temperature. The instability of VC was related to isomerization (loss of optical activity) of the l-enantiomer either to d-enantiomer (racemization), degradation to undesired products or tautomerization to other isomers. Theoretical investigation (at B3LYP/6-311++G(d,p) and MP2/6-311++G(d,p) levels of theory in vacuo and aqueous phases) formulated tautomerization for RS-stereoisomers of ascorbic acids (AA). The mechanism for deactivation of VC was examined.

  7. Locally designed pulse shaping for selective preparation of enantiomers from their racemate

    NASA Astrophysics Data System (ADS)

    Hoki, K.; Ohtsuki, Y.; Fujimura, Y.

    2001-01-01

    We present a method for the design of laser fields to control a selective preparation of enantiomers from their racemate. An expression for two components of the laser pulses [EX(t) and EY(t)] propagating along the Z axis is derived using a locally optimized control theory in the density operator formalism. This expression was applied to a selective preparation of (R-, L-) enantiomers from preoriented phosphinotioic acid (H2POSH) at low temperatures. The target operator was set for the populations to be localized in one side of the double-well potential. First, a simple one-dimensional model was treated. Then, a two-dimensional model in which a free rotation around the preoriented torsional axis is included was briefly considered. In the one-dimensional model, almost complete preparation of the enantiomers was obtained. The optimal electric field consists of a sequence of two linearly polarized pulses with the same phases but with different magnitudes. This means that the resultant electric field is linearly polarized with the polarization for obtaining the R-form nearly parallel to its S-H bond. The optimal electric field transfers the L-form into the R-form while suppressing the reverse process. In the two-dimensional model, the enantiomer selective preparation is controlled by a sequence of circularly polarized pulses.

  8. Characterization of a meso-chiral isomer of a hexanuclear Cu(II) cage from racemization of the L-alanine Schiff base.

    PubMed

    Rajesh, Chinnaiyan Mahalingam; Ray, Manabendra

    2014-09-14

    We are reporting structural characterization of two new hexanuclear cages (H3O)2[Cu3(μ3-OH)(μ3-NH3)(0.5)(L)3]2·8H2O (1) and (H3O)2[Cu3(μ3-OH)(μ3-H2O)(0.5)(L)3]2·8H2O (1a) where L(2-) is the dianionic form of the Schiff base of L-alanine and salicylaldehyde. The complex 1 has two C3 symmetric hydroxo bridged trinuclear halves joined by an ammonia or water molecule at the center through H-bonding. Each of the trinuclear halves is enantiopure but of opposite chirality to the other half, making the hexanuclear unit a meso isomer. Temperature dependent magnetic measurements showed the presence of ferromagnetic interactions among trinuclear Cu(II) units, a rare occurrence among trinuclear Cu(II) complexes. Characterization of the LiHL showed it to be enantiopure. Addition of a base, monitored using optical rotation, showed that racemization occurs as a result of base addition. The racemization depends on the base as well as the temperature. Base or Cu(II) induced racemization of amino acid derivatives has been indicated in a number of cases in the past but structural characterization of the products or formation of this type of chiral hexanuclear architecture was never reported. Structures of the complex and the ligand have a number of interesting H-bonding situations.

  9. Dating Violence

    MedlinePlus

    ... Parents of Teens Crime, Teens, and Trauma Assault Bullying and Harassment Child Sexual Abuse Dating Violence Sexual ... Parents of Teens Crime, Teens, and Trauma Assault Bullying and Harassment Child Sexual Abuse Dating Violence Sexual ...

  10. Radiocarbon Dating

    SciTech Connect

    Buchholz, B A

    2007-12-20

    Radiocarbon dating can be used to determine the age of objects that contain components that were once alive. In the case of human remains, a radiocarbon date can distinguish between a crime scene and an archeological site. Documents, museum artifacts and art objects can be dated to determine if their age is correct for the historical context. A radiocarbon date does not confirm authenticity, but it can help identify a forgery.

  11. Dating Violence

    ERIC Educational Resources Information Center

    Stader, David L.

    2011-01-01

    Dating violence is a form of student-on-student victimization and is a serious school safety issue. Research indicates that at a minimum, 10 percent of high school students are victims of dating violence in one form or another. Among female high school students that date, some data indicate that as many as 30 percent may be victims of dating…

  12. Kinetic model-based feed-forward controlled fed-batch fermentation of Lactobacillus rhamnosus for the production of lactic acid from Arabic date juice.

    PubMed

    Choi, Minsung; Al-Zahrani, Saeed M; Lee, Sang Yup

    2014-06-01

    Arabic date is overproduced in Arabic countries such as Saudi Arabia and Iraq and is mostly composed of sugars (70-80 wt%). Here we developed a fed-batch fermentation process by using a kinetic model for the efficient production of lactic acid to a high concentration from Arabic date juice. First, a kinetic model of Lactobacillus rhamnosus grown on date juice in batch fermentation was constructed in EXCEL so that the estimation of parameters and simulation of the model can be easily performed. Then, several fed-batch fermentations were conducted by employing different feeding strategies including pulsed feeding, exponential feeding, and modified exponential feeding. Based on the results of fed-batch fermentations, the kinetic model for fed-batch fermentation was also developed. This new model was used to perform feed-forward controlled fed-batch fermentation, which resulted in the production of 171.79 g l(-1) of lactic acid with the productivity and yield of 1.58 and 0.87 g l(-1) h(-1), respectively.

  13. Quasi-Racemic X-ray Structures of K27-Linked Ubiquitin Chains Prepared by Total Chemical Synthesis.

    PubMed

    Pan, Man; Gao, Shuai; Zheng, Yong; Tan, Xiaodan; Lan, Huan; Tan, Xianglong; Sun, Demeng; Lu, Lining; Wang, Tian; Zheng, Qingyun; Huang, Yichao; Wang, Jiawei; Liu, Lei

    2016-06-15

    Quasi-racemic crystallography has been used to determine the X-ray structures of K27-linked ubiquitin (Ub) chains prepared through total chemical synthesis. Crystal structures of K27-linked di- and tri-ubiquitins reveal that the isopeptide linkages are confined in a unique buried conformation, which provides the molecular basis for the distinctive function of K27 linkage compared to the other seven Ub chains. K27-linked di- and triUb were found to adopt different structural conformations in the crystals, one being symmetric whereas the other triangular. Furthermore, bioactivity experiments showed that the ovarian tumor family de-ubiquitinase 2 significantly favors K27-linked triUb than K27-linked diUb. K27-linked triUb represents the so-far largest chemically synthesized protein (228 amino acids) that has been crystallized to afford a high-resolution X-ray structure. PMID:27268299

  14. Evaluation of Fe and Ru Pincer-Type Complexes as Catalysts for the Racemization of Secondary Benzylic Alcohols.

    PubMed

    Bornschein, Christoph; Gustafson, Karl P J; Verho, Oscar; Beller, Matthias; Bäckvall, Jan-E

    2016-08-01

    Fe and Ru pincer-type catalysts are used for the racemization of benzylic alcohols. Racemization with the Fe catalyst was achieved within 30 minutes under mild reaction conditions, with a catalyst loading as low as 2 mol %. This reaction constitutes the first example of an iron-catalyzed racemization of an alcohol. The efficiency for racemization of the Fe catalyst and its Ru analogue was evaluated for a wide range of sec-benzylic alcohols. The commercially available Ru complex proved to be highly robust and even tolerated the presence of water in the reaction mixture. PMID:27311070

  15. Enantiomeric Excesses of Acid Labile Amino Acid Precursors of the Murchison Meteorite

    NASA Technical Reports Server (NTRS)

    Pizzarello, Sandra

    1998-01-01

    Amino acids present in carbonaceous chondrite are extracted in water in part as free compounds and in approximately equal part as acid labile precursors. On the assumption that they would be free of contamination, the precursors of two Murchison amino acids that have terrestrial occurrence, alanine and glutamic acid, have been targeted for analysis of their enantiomeric ratios. Pyroglutamic acid, the precursor of glutamic acid, was found with an L-enantiomeric excess comparable to that of the free acid, while alanine's precursor, N-acetyl alanine, appears approximately racemic. Also alpha-imino propioacetic acid, a proposed end product of alanine synthesis in the meteorite, was analyzed and found racemic.

  16. The effects of acid leaching on 40Ar/39Ar age dating results using samples from the Walvis Ridge hotspot trail

    NASA Astrophysics Data System (ADS)

    Klath, J. F.; Koppers, A. A.; Heaton, D. E.; Schnur, S.

    2013-12-01

    In this study we systematically explore how acid leaching can be used to reduce the negative effects of seawater alteration on the 40Ar/39Ar age dating of submarine basalts. Koppers et al (2000) showed that acid leaching of groundmass samples generated more consistent ages as well as ages more concordant with phenocrystic mineral phases, compared to samples that were left untreated. By studying the effects of progressively increasing the strength and length of acid treatment, we will show how acid leaching of groundmass separates reduces alteration while leaving the initial eruption signature intact. Samples were chosen from the Walvis ridge hotspot trail in the southeast Atlantic. Three samples were selected based on degree and style of alteration. Two samples (basalt and basaltic andesite) appear highly altered in thin section. The basalt contains diffuse iddingsite alteration that is pervasive throughout the groundmass. The basaltic andesite displays focused secondary mineral phases within and around abundant vesicles. The third sample, a trachyte, shows relatively minor degrees of alteration in thin section. These groundmass separates were divided into four splits and treated with a progressively stronger acid and for longer duration. One split from each rock was left untreated to act as a baseline. Of the other three splits from each sample, one was treated with a mild leach (1N HCl and 1N HNO3), one a strong leach (1N HCl, 1N HNO3, 6N HCl, and 3N HNO3), and lastly the strong leach performed twice. The samples were then handpicked to remove any remaining visible alteration. The untreated samples were picked as well, removing the most distinctly altered grains. All splits were analyzed by electron microprobe, x-ray fluorescence (XRF) and the incremental heating 40Ar/39Ar dating method. We will report on the results of an image analysis of microprobe backscatter images and elemental maps taken of individual groundmass grains. This analysis will show the location

  17. Analysis of metolachlor ethane sulfonic acid chirality in groundwater: A tool for dating groundwater movement in agricultural settings

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Chemical chirality of pesticides can be a useful tool for studying environmental processes. The chiral forms of metolachlor ethane sulfonic acid (MESA), an abundant metabolite of metolachlor, and metolachlor were examined over a 6 year period in groundwater and a groundwater-fed stream in a riparia...

  18. Radiocarbon Dating.

    PubMed

    Van Strydonck, Mark

    2016-04-01

    Although most historians and art historians consider the radiocarbon dating technique not to be very precise by their criteria, the method has gained much importance over the last decades. Radiocarbon dating is increasingly used in the field of textile research and old polychrome statues, but also objects made of ivory, stucco, paper, and parchment are dated with the technique. Especially after the introduction of the AMS technique, a boom of this type of research has been noticed.

  19. Radiocarbon Dating.

    PubMed

    Van Strydonck, Mark

    2016-04-01

    Although most historians and art historians consider the radiocarbon dating technique not to be very precise by their criteria, the method has gained much importance over the last decades. Radiocarbon dating is increasingly used in the field of textile research and old polychrome statues, but also objects made of ivory, stucco, paper, and parchment are dated with the technique. Especially after the introduction of the AMS technique, a boom of this type of research has been noticed. PMID:27573138

  20. A nanoscale view of supramolecular stereochemistry in self-assembled monolayers of enantiomers and racemates.

    PubMed

    Mamdouh, Wael; Uji-I, Hiroshi; Gesquière, André; De Feyter, Steven; Amabilino, David B; Abdel-Mottaleb, Mohamed M S; Veciana, Jaume; De Schryver, Frans C

    2004-10-26

    The effect that molecular chirality has on the formation of monolayer structures by pure enantiomers and their racemates at the liquid/solid interface has been investigated for two chiral compounds (1 and 2) which differ from each other by the presence or absence of an ester function in their respective molecular structures. 1 shows pseudoracemate formation when the achiral graphite support is exposed to a solution containing a racemate while 2 shows racemic conglomerate formation. This difference is rationalized in terms of the orientation of the pure enantiomers with respect to the graphite substrate and highlights the importance of molecular structure and its influence on balancing the interplay between molecular conformation and molecular packing on the surface. For 1, nonstoichiometric mixtures of both enantiomers have been investigated, and the results are discussed in the framework of the sergeant and soldiers principle. These results are important for the understanding and prediction of spontaneous resolution in monolayer systems.

  1. An evaluation of Mesodon and other larger terrestrial gastropod shells for dating late Holocene and historic alluvium in the Midwestern USA

    USGS Publications Warehouse

    Rakovan, Monica T.; Rech, Jason A.; Pigati, Jeffery S.; Nekola, Jeffery C.; Wiles, Gregory C.

    2013-01-01

    Understanding the history of stream erosion and changes in channel morphology is important for managing and restoring unstable streams. One of the significant challenges in this type of research is establishing accurate dating of late Holocene and historic alluvium. Here we evaluate the potential of using 14C dating and amino acid racemization (AAR) to date large terrestrial gastropod shells that are often preserved within alluvial sediments. Many terrestrial gastropods incorporate old carbon from limestone or other carbonate rocks into their shells and therefore are unsuitable for radiocarbon dating. Recent studies, however, have shown that some taxa avoid this ‘limestone problem’ and can yield reliable 14C ages. In this study, we measured the 14C activity of specimens for the genera Mesodon, Ventridens, and Allogona collected live and from alluvial sequences dated independently by dendrochronology, 14C dating of wood, and/or 137Cs analyses. Mesodon zaletus contained old carbon in similar concentrations (up to ~ 30%) found in previous studies of other large taxa and should be avoided for 14C dating when possible. In contrast, shells of Ventridens ligera and Allogona profunda showed minimal limestone effects and therefore may be suitable for dating late Holocene alluvium. These results highlight the importance of taxonomic identification of gastropod taxa prior to their use for 14C dating and demonstrate that shell fragments that are not identifiable should be avoided. We also measured d/l ratios (n = 17) of aspartic and glutamic acid from eight different taxa of terrestrial gastropods recovered from four late Holocene and historic stratigraphic sequences. Average d/l ratios of aspartic and glutamic acid from historic sediments < 300 years old are lower in shells from younger stratigraphic units, indicating that AAR can be used to differentiate between multiple historic stratigraphic units.

  2. Early human occupation of Western Europe: Paleomagnetic dates for two paleolithic sites in Spain

    PubMed Central

    Oms, O.; Parés, J. M.; Martínez-Navarro, B.; Agustí, J.; Toro, I.; Martínez-Fernández, G.; Turq, A.

    2000-01-01

    The lacustrine deposits infilling the intramontane Guadix-Baza Basin, in the Betic Range of Southern Spain, have yielded abundant well-preserved lithic artifacts. In addition, the lake beds contain a wide range of micromammals including Mimomys savini and Allophaiomys burgondiae and large mammals such as Mammuthus and Hippopotamus together with the African saber-toothed felid Megantereon. The association of the lithic artifacts along with the fossil assemblages, themselves of prime significance in the Eurasian mammal biochronology, is providing new insight into the controversy of the human settlement in Southern Europe. Despite the importance of the artifacts and fossil assemblage, estimates of the geological age of the site are still in conflict. Some attempts at dating the sediments have included biochronology, uranium series, amino acid racemization, and stratigraphic correlation with other well-dated sections in the basin, but so far have failed to yield unambiguous ages. Here we present paleomagnetic age dating at the relevant localities and thus provide useful age constraints for this critical paleoanthropological and mammal site. Our data provide firm evidence for human occupation in Southern Europe in the Lower Pleistocene, around 1 mega-annum ago. The current view of when and how hominids first dispersed into Europe needs to be reevaluated. PMID:10973485

  3. Characteristics of chiral and racemic ketoprofen drugs using terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Du, Yong; Liu, Jianjun; Hong, Zhi

    2013-08-01

    Absorption spectra of chiral S-(+)- and racemic RS-ketoprofen pharmaceutical molecules in crystalline form were recorded in the terahertz region between 6 and 66 cm-1 (0.2 ~ 2.0 THz) by using time-domain terahertz spectroscopic (THz-TDS) measurement. Different distinctive absorption features were observed which are strikingly sensitive to the change of subtle conformational structures within such isostructural crystal molecules. The results suggest that the THz-TDS technique can be definitely used for distinguishing between chiral and racemic compounds in pharmaceutical and biological fields.

  4. Racemic R,S-venlafaxine hydrochloride-DNA interaction: Experimental and computational evidence

    NASA Astrophysics Data System (ADS)

    Shahabadi, Nahid; Hadidi, Saba; Ghasemian, Zeinab; Taherpour, Avat(Arman)

    2015-06-01

    The interaction of racemic R,S-venlafaxine hydrochloride (rac-VEN) drug with calf thymus deoxyribonucleic acid (ct-DNA) was studied using various physico-chemical techniques and molecular docking at simulated physiological conditions (pH = 7.4). The fluorescence study shows that ct-DNA interacted with rac-VEN and quenched its intrinsic fluorescence in a static quenching process. These results are further supported by UV-Vis spectra. The binding constant of rac-VEN with ct-DNA (0.57 × 104) obtained from the spectroscopic techniques, which is more in keeping with the groove binding with DNA. Furthermore, the competition experiment using Hoechst33258 indicated that rac-VEN may bind to ct-DNA by a minor groove binding mode. In addition, iodide quenching effect on the fluorescence of rac-VEN before and after the interaction with ct-DNA is another evidence to groove binding. The thermodynamic parameters are calculated by van't Hoff equation, which demonstrated that hydrogen bonds and van der Waals interactions played major roles in the binding reaction. Molecular simulation studies carried out by using the AutoDock4 and Spartan10 programs. From the best docking map, we found that R and S-isomers fit in the A6T7T8/T19A18A17 region in minor groove of B-DNA. Finally, these results indicated that the docking of S-VEN-B-DNA is more stable than R-VEN-B-DNA.

  5. The "racemic approach" in the evaluation of the enantiomeric NorA efflux pump inhibition activity of 2-phenylquinoline derivatives.

    PubMed

    Carotti, Andrea; Ianni, Federica; Sabatini, Stefano; Di Michele, Alessandro; Sardella, Roccaldo; Kaatz, Glenn W; Lindner, Wolfgang; Cecchetti, Violetta; Natalini, Benedetto

    2016-09-10

    Among the mechanisms adopted by bacteria, efflux pumps (EPs) have been recognized as being significantly involved in contributing to resistance to commonly used antibacterial agents. However, little is known about their three-dimensional structures or the steric requirements for their inhibition. Lack of such knowledge includes NorA, one of the most studied Staphylococcus aureus EPs. In the present study, the use of two commercialized Cinchona alkaloid-based zwitterionic chiral stationary phases allowed the enantioseparation of four 2-((2-(4-propoxyphenyl)quinolin-4-yl)oxy)alkylamines 1-4 previously found to be potent S. aureus NorA efflux pump inhibitors when tested as racemates. In the identified optimal polar-ionic conditions (MeOH/THF/H2O-49/49/2 (v/v/v)+25mM formic acid, 12.5mM diethylamine), repeated consecutive injections of 1 allowed the isolation of sufficient amount of its enantiomers (2.6mg and 2.8mg, for (R)-1 and (S)-1, respectively) and then to evaluate their ability to inhibit the S. aureus NorA efflux pump. The biological evaluation highlighted the main contribution of the (R)-1 enantiomer to both the EtBr efflux inhibition and synergistic effect with against SA-1199B (norA+/A116E GrlA) respect to the racemate activity. The comparison between the experimental electronic circular dichroism and the time-dependent density functional theory calculations spectra of the two isolated enantiomeric fractions allowed for all compounds a clear and easy assignment of the enantiomeric elution order. PMID:27429367

  6. X-ray Structure of Native Scorpion Toxin BmBKTx1 by Racemic Protein Crystallography Using Direct Methods

    SciTech Connect

    Mandal, Kalyaneswar; Pentelute, Brad L.; Tereshko, Valentina; Kossiakoff, Anthony A.; Kent, Stephen B.H.

    2009-04-08

    Racemic protein crystallography, enabled by total chemical synthesis, has allowed us to determine the X-ray structure of native scorpion toxin BmBKTx1; direct methods were used for phase determination. This is the first example of a protein racemate that crystallized in space group I41/a.

  7. Highly heteroselective ring-opening polymerization of racemic lactide initiated by divalent ytterbium complexes bearing amino bis(phenolate) ligands.

    PubMed

    Yang, Sheng; Du, Zhu; Zhang, Yong; Shen, Qi

    2012-10-01

    Polymerization of racemic lactide initiated by divalent ytterbium complexes supported by either dimethylamino-amino bis(phenolate) or methoxy-amino bis(phenolate) ligands proceeds rapidly at room temperature in a living fashion to give heterotactic polylactide with the racemic enchainment of monomer units P(r) ranging from 0.97-0.99.

  8. Structure elucidation of the Pribnow box consensus promoter sequence by racemic DNA crystallography

    PubMed Central

    Mandal, Pradeep K.; Collie, Gavin W.; Srivastava, Suresh C.; Kauffmann, Brice; Huc, Ivan

    2016-01-01

    It has previously been shown that the use of racemic mixtures of naturally chiral macromolecules such as protein and DNA can significantly aid the crystallogenesis process, thereby addressing one of the major bottlenecks to structure determination by X-ray crystallographic methods—that of crystal growth. Although previous studies have provided convincing evidence of the applicability of the racemic crystallization technique to DNA through the study of well-characterized DNA structures, we sought to apply this method to a historically challenging DNA sequence. For this purpose we chose a non-self-complementary DNA duplex containing the biologically-relevant Pribnow box consensus sequence ‘TATAAT’. Four racemic crystal structures of this previously un-crystallizable DNA target are reported (with resolutions in the range of 1.65–2.3 Å), with further crystallographic studies and structural analysis providing insight into the racemic crystallization process as well as structural details of this highly pertinent DNA sequence. PMID:27137886

  9. Total chemical synthesis and X-ray structure of kaliotoxin by racemic protein crystallography

    SciTech Connect

    Pentelute, Brad L.; Mandal, Kalyaneswar; Gates, Zachary P.; Sawaya, Michael R.; Yeates, Todd O.; Kent, Stephen B.H.

    2010-11-05

    Here we report the total synthesis of kaliotoxin by 'one pot' native chemical ligation of three synthetic peptides. A racemic mixture of D- and L-kaliotoxin synthetic protein molecules gave crystals in the centrosymmetric space groupP that diffracted to atomic-resolution (0.95 {angstrom}), enabling the X-ray structure of kaliotoxin to be determined by direct methods.

  10. Enantioselective Regulation of Lactate Racemization by LarR in Lactobacillus plantarum

    PubMed Central

    Desguin, Benoît; Goffin, Philippe; Bakouche, Nordine; Diman, Aurélie; Viaene, Eric; Dandoy, Damien; Fontaine, Laetitia; Hallet, Bernard

    2014-01-01

    Lactobacillus plantarum is a lactic acid bacterium that produces a racemic mixture of l- and d-lactate from sugar fermentation. The interconversion of lactate isomers is performed by a lactate racemase (Lar) that is transcriptionally controlled by the l-/d-lactate ratio and maximally induced in the presence of l-lactate. We previously reported that the Lar activity depends on the expression of two divergently oriented operons: (i) the larABCDE operon encodes the nickel-dependent lactate racemase (LarA), its maturases (LarBCE), and a lactic acid channel (LarD), and (ii) the larR(MN)QO operon encodes a transcriptional regulator (LarR) and a four-component ABC-type nickel transporter [Lar(MN), in which the M and N components are fused, LarQ, and LarO]. LarR is a novel regulator of the Crp-Fnr family (PrfA group). Here, the role of LarR was further characterized in vivo and in vitro. We show that LarR is a positive regulator that is absolutely required for the expression of Lar activity. Using gel retardation experiments, we demonstrate that LarR binds to a 16-bp palindromic sequence (Lar box motif) that is present in the larR-larA intergenic region. Mutations in the Lar box strongly affect LarR binding and completely abolish transcription from the larA promoter (PlarA). Two half-Lar boxes located between the Lar box and the −35 box of PlarA promote LarR multimerization on DNA, and point mutations within one or both half-Lar boxes inhibit PlarA induction by l-lactate. Gel retardation and footprinting experiments indicate that l-lactate has a positive effect on the binding and multimerization of LarR, while d-lactate antagonizes the positive effect of l-lactate. A possible mechanism of LarR regulation by lactate enantiomers is proposed. PMID:25349156

  11. Dating lacustrine episodes in the eastern Sahara by the epimerization of isoleucine in ostrich eggshells

    USGS Publications Warehouse

    Miller, G.H.; Wendorf, F.; Ernst, R.; Schild, R.; Close, A.E.; Friedman, I.; Schwarcz, H.P.

    1991-01-01

    The eggshell of the African ostrich, Struthio camelus, closely approximates a closed system for the retention of indigenous proteinaceous residues. Epimerization of the protein amino acid isoleucine follows linear first-order kinetics in laboratory simulations nearly to racemic equilibrium, and the variation in D/L ratio within a single fragment, or between fragments of the same age, is significantly less than in other carbonate systems. These observations suggest that the extent of isoleucine epimerization (aIle/Ile ratio) in ostrich eggshell offers the potential for high-resolution geochronology of Quaternary deposits. From the simulation experiments, and dated early Holocene samples for which we have in situ mean annual sediment temperature measurements, Arrhenius parameters have been calculated; the activation energy is 30.33 kcal mol-1, similar to that of other carbonate systems. We have measured the aIle/Ile ratio in ostrich eggshell associated with lacustrine episodes at Bir Tarfawi and Bir Sahara East, two depressions in what is currently the hyperarid eastern Sahara. The ratios can be used directly to indicate qualitatively the time represented by each series of lake sediment, and to correlate disjunct lacustrine deposits within and between the basins. Uranium-series disequilibrium dating of algal mats contained within some of the lake beds indicate that a major wet interval occurred about 130 ka ago. Using the U-series date for calibration, the amino acid ratios are used to date the most recent lacustrine interval to about 100 ka B.P., and two older intervals, one about 200 ?? 25 ka B.P., and an older interval that occurred prior to 250 ka ago. ?? 1991.

  12. 40 CFR 75.4 - Compliance dates.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... designated under the Acid Rain permit which governs that unit and contains the approved substitution or... become applicable upon the issuance date of the Acid Rain permit. For combustion sources seeking to enter... following dates: (i) January 1, 1995; or (ii) 90 days after the issuance date of the Acid Rain permit...

  13. Date Rape

    MedlinePlus

    ... erasers GHB (gamma hydroxybutyric acid), called cherry meth, energy drink, gook ketamine , called bump, special K, and super acid These drugs can be mixed in to drinks and are almost impossible to detect, especially in dark-colored drinks such as cola or dark beer, ...

  14. Enantioselective Synthesis of (2R, 3S)- and (2S, 3R)-4,4,4-trifluoro-N-Fmoc-O-tert-butyl-threonine and their Racemization-free Incorporation into Oligopeptides via Solid-phase Synthesis

    PubMed Central

    Xiao, Nu; Jiang, Zhong-Xing; Yu, Y. Bruce

    2010-01-01

    An efficient method for the enantioselective synthesis of (2R, 3S)- and (2S, 3R)-4,4,4-trifluoro-N-Fmoc-O-tert-butyl-threonine (tfT) on multi-gram scales was developed. Absolute configurations of the two stereoisomers were ascertained by X-ray crystallography. Racemization-free coupling conditions for the incorporation of tfT into oligopeptides were then explored. For solution-phase synthesis, tfT racemization was not an issue under conventional coupling conditions. For solid-phase synthesis, the following conditions were identified to achieve racemization-free synthesis: if tfT (3.0 eq.) was not the first amino acid to be linked to the resin (1.0 eq.), the condition is: 2.7 eq. DIC/3.0 eq. HOBt as the coupling reagent at 0 °C for 20 h; if tfT (3.0 eq.) was the first amino acid to be linked to the resin (1.0 eq.), then 1.0 eq. of CuCl2 needs to be added to the coupling reagent. PMID:17702025

  15. A functional role of Rv1738 in Mycobacterium tuberculosis persistence suggested by racemic protein crystallography

    DOE PAGES

    Bunker, Richard D.; Mandal, Kalyaneswar; Bashiri, Ghader; Chaston, Jessica J.; Pentelute, Bradley L.; Lott, J. Shaun; Kent, Stephen B. H.; Baker, Edward N.

    2015-04-07

    Racemic protein crystallography was used to determine the X-ray structure of the predicted Mycobacterium tuberculosis protein Rv1738, which had been completely recalcitrant to crystallization in its natural L-form. Native chemical ligation was used to synthesize both L-protein and D-protein enantiomers of Rv1738. Crystallization of the racemic {D-protein + L-protein} mixture was immediately successful. The resulting crystals diffracted to high resolution and also enabled facile structure determination because of the quantized phases of the data from centrosymmetric crystals. The X-ray structure of Rv1738 revealed striking similarity with bacterial hibernation factors, despite minimal sequence similarity. As a result, we predict that Rv1738,more » which is highly up-regulated in conditions that mimic the onset of persistence, helps trigger dormancy by association with the bacterial ribosome.« less

  16. Enantioselective esterification of (R,S)-2-methylalkanoic acid with Carica papaya lipase in organic solvents.

    PubMed

    Chang, Chun-Sheng; Ho, Ssu-Ching

    2011-11-01

    Isooctane was the best reaction medium for the enantioselective esterification of (R,S)-2-methylalkanoic acid with n-butanol using Carica papaya lipase as catalyst. Increasing linear alkyl-chain length of racemic 2-methylalkanoic acids from ethyl to hexyl increased the enantioselectivity (E) from 2.1 to 98.2 for the esterification of racemic 2-methylalkanoic acids with n-butanol at 35°C. Decreasing reaction temperature from 40 to 20°C increased the enantioselectivity (E) from 14 to 33 for the esterification of racemic 2-methylhexanoic acids with n-butanol. We obtained a maximum enantioselectivity, of E = 24.3, for the enantioselective esterification of racemic 2-methylhexanoic acids with n-butanol in isooctane at water activity 0.33, and at 35°C.

  17. Stereoselective oxidation of racemic 1-arylethanols by basil cultured cells of Ocimum basilicum cv. Purpurascens.

    PubMed

    Itoh, Ken-ichi; Nakamura, Kaoru; Utsukihara, Takamitsu; Sakamaki, Hiroshi; Horiuchi, C Akira

    2008-05-01

    The biotransformation of racemic 1-phenylethanol (30 mg) with plant cultured cells of basil (Ocimum basilicum cv. Purpurascens, 5 g wet wt) by shaking 120 rpm at 25 degrees C for 7 days in the dark gave (R)-(+)-1-phenylethanol and acetophenone in 34 and 24% yields, respectively. The biotransformation can be applied to other 1-arylethanols and basil cells oxidized the (S)-alcohols to the corresponding ketones remaining the (R)-alcohols in excellent ee.

  18. Organocatalytic kinetic resolution of racemic secondary nitroallylic alcohols combined with simultaneous desymmetrization of prochiral cyclic anhydrides.

    PubMed

    Roy, Suparna; Chen, Kan-Fu; Gurubrahamam, Ramani; Chen, Kwunmin

    2014-10-01

    This study describes an organocatalytic kinetic resolution of racemic secondary nitroallylic alcohols (2) combined with simultaneous desymmetrization of prochiral cyclic anhydrides (1). The experimental results revealed that enantioselective alcoholysis of 3-substituted glutaric anhydrides afforded hemiesters (3) with high levels of enantioselectivities (up to 99% ee) in the presence of cinchonidine-derived thiourea catalyst (IV). The highly optical enrichment (up to 95% ee) of (S)-nitroallylic alcohols (2) was recovered.

  19. From Racemic Alcohols to Enantiopure Amines: Ru-Catalyzed Diastereoselective Amination

    PubMed Central

    2015-01-01

    A commercially available ruthenium(II) PNP-type pincer catalyst (Ru-Macho) promotes the formation of α-chiral tert-butanesulfinylamines from racemic secondary alcohols and Ellman’s chiral tert-butanesulfinamide via a hydrogen borrowing strategy. The formation of α-chiral tert-butanesulfinylamines occurs in yields ranging from 31% to 89% with most examples giving >95:5 dr. PMID:25170560

  20. From racemic alcohols to enantiopure amines: Ru-catalyzed diastereoselective amination.

    PubMed

    Oldenhuis, Nathan J; Dong, Vy M; Guan, Zhibin

    2014-09-10

    A commercially available ruthenium(II) PNP-type pincer catalyst (Ru-Macho) promotes the formation of α-chiral tert-butanesulfinylamines from racemic secondary alcohols and Ellman's chiral tert-butanesulfinamide via a hydrogen borrowing strategy. The formation of α-chiral tert-butanesulfinylamines occurs in yields ranging from 31% to 89% with most examples giving >95:5 dr. PMID:25170560

  1. Rhodium-catalyzed dynamic kinetic asymmetric transformations of racemic allenes by the [3+2] annulation of aryl ketimines.

    PubMed

    Tran, Duc N; Cramer, Nicolai

    2013-09-27

    Racemization required: Rhodium(I)-catalyzed C-H activation directed by unprotected ketimines initiates selective [3+2] cycloaddition with allenes, providing access to highly substituted indenylamines. The reaction proceeds through the dynamic kinetic asymmetric transformation of racemic allenes. The catalyst controls the enantio- and diastereoselectivity, the regioselectivities of the C-H activation and allene incorporation, as well as the E/Z ratio.

  2. Racemization as a stereochemical measure of dynamics and robustness in shape-shifting organic molecules

    PubMed Central

    He, Maggie; Bode, Jeffrey W.

    2011-01-01

    Bullvalene is a structurally unique dynamic molecule thought to interconvert among 1.2 million degenerate isomers. The incorporation of different chemical substituents onto the bullvalene core should lead to a “shape-shifting” molecule that can interconvert among thousands of discrete structural isomers. Previous NMR spectroscopy and HPLC studies on substituted bullvalenes ascertained the fact that these compounds are dynamic, but they could not attest to whether the molecules are only interconverting among only a few isomers or if a multitude of structures are being accessed. Here we confirm the remarkable shape-shifting property of a tetrasubstituted bullvalene by means of a racemization experiment. We show that a single, though fleeting, chiral, enantioenriched tetrasubstituted bullvalene isomer can spontaneously equilibrate to a racemic population of dynamic compounds. Despite the fact that conversion from one enantiomer of a bullvalene isomer to the other may require dozens or even hundreds of rearrangements and involve many potential pathways, CD spectroscopy and HPLC analysis of different bullvalene populations showed that multiple pathways exist and result in the complete racemization of an initial enantioenriched chiral bullvalene. These oligosubstituted bullvalenes represent a very rare example of an entity that can spontaneously transform itself into different discrete structures using ambient thermal energy. The confirmation that these shape-shifting organic molecules are chemically robust yet structurally dynamic is an important step toward their further use as materials, sensors, and biologically active compounds. PMID:21873220

  3. An Integrated Experimental and Computational Approach for Characterizing the Kinetics and Mechanism of Triadimefon Racemization.

    PubMed

    Cheng, Qianyi; Teng, Quincy; Marchitti, Satori A; Dillingham, Caleb M; Kenneke, John F

    2016-09-01

    Enantiomers of chiral molecules commonly exhibit differing pharmacokinetics and toxicities, which can introduce significant uncertainty when evaluating biological and environmental fates and potential risks to humans and the environment. However, racemization (the irreversible transformation of one enantiomer into the racemic mixture) and enantiomerization (the reversible conversion of one enantiomer into the other) are poorly understood. To better understand these processes, we investigated the chiral fungicide, triadimefon, which undergoes racemization in soils, water, and organic solvents. Nuclear magnetic resonance (NMR) and gas chromatography / mass spectrometry (GC/MS) techniques were used to measure the rates of enantiomerization and racemization, deuterium isotope effects, and activation energies for triadimefon in H2 O and D2 O. From these results we were able to determine that: 1) the alpha-carbonyl carbon of triadimefon is the reaction site; 2) cleavage of the C-H (C-D) bond is the rate-determining step; 3) the reaction is base-catalyzed; and 4) the reaction likely involves a symmetrical intermediate. The B3LYP/6-311 + G** level of theory was used to compute optimized geometries, harmonic vibrational frequencies, nature population analysis, and intrinsic reaction coordinates for triadimefon in water and three racemization pathways were hypothesized. This work provides an initial step in developing predictive, structure-based models that are needed to identify compounds of concern that may undergo racemization. Chirality 28:633-641, 2016. © 2016 Wiley Periodicals, Inc. PMID:27479933

  4. Structural characterization and Hirshfeld surface analysis of racemic baclofen

    NASA Astrophysics Data System (ADS)

    Maniukiewicz, Waldemar; Oracz, Monika; Sieroń, Lesław

    2016-11-01

    The crystal structure of baclofen, (R,S) [4-amino-3-(4-chlorophenyl)butanoic acid], (C10H12ClNO2, Mr = 213.66) has been determined by single crystal X-ray diffraction analysis. The title compound crystallizes in the orthorhombic space group Pbca (No. 61) with a = 9.2704(5), b = 7.0397(4), c = 30.4015(15) Å, V = 1984.0(2) Å3 and Z = 8. The molecules exist as zwitterions, adopting a gauche conformation with respect to the Cαsbnd Cβ bond, and held in a cross-linked chain arrangement by strong Nsbnd H⋯O hydrogen bonds and Csbnd Cl⋯π interactions. The electrostatic molecular potential as well as the intermolecular interactions of the title compound were analyzed by the Hirshfeld surfaces. The FT-IR spectrum is also reported. The DTA, TG and DTG results indicate that baclofen is stable up to 205 °C.

  5. Meteoritic Amino Acids: Diversity in Compositions Reflects Parent Body Histories

    PubMed Central

    2016-01-01

    The analysis of amino acids in meteorites dates back over 50 years; however, it is only in recent years that research has expanded beyond investigations of a narrow set of meteorite groups (exemplified by the Murchison meteorite) into meteorites of other types and classes. These new studies have shown a wide diversity in the abundance and distribution of amino acids across carbonaceous chondrite groups, highlighting the role of parent body processes and composition in the creation, preservation, or alteration of amino acids. Although most chiral amino acids are racemic in meteorites, the enantiomeric distribution of some amino acids, particularly of the nonprotein amino acid isovaline, has also been shown to vary both within certain meteorites and across carbonaceous meteorite groups. Large l-enantiomeric excesses of some extraterrestrial protein amino acids (up to ∼60%) have also been observed in rare cases and point to nonbiological enantiomeric enrichment processes prior to the emergence of life. In this Outlook, we review these recent meteoritic analyses, focusing on variations in abundance, structural distributions, and enantiomeric distributions of amino acids and discussing possible explanations for these observations and the potential for future work. PMID:27413780

  6. Meteoritic Amino Acids: Diversity in Compositions Reflects Parent Body Histories.

    PubMed

    Elsila, Jamie E; Aponte, José C; Blackmond, Donna G; Burton, Aaron S; Dworkin, Jason P; Glavin, Daniel P

    2016-06-22

    The analysis of amino acids in meteorites dates back over 50 years; however, it is only in recent years that research has expanded beyond investigations of a narrow set of meteorite groups (exemplified by the Murchison meteorite) into meteorites of other types and classes. These new studies have shown a wide diversity in the abundance and distribution of amino acids across carbonaceous chondrite groups, highlighting the role of parent body processes and composition in the creation, preservation, or alteration of amino acids. Although most chiral amino acids are racemic in meteorites, the enantiomeric distribution of some amino acids, particularly of the nonprotein amino acid isovaline, has also been shown to vary both within certain meteorites and across carbonaceous meteorite groups. Large l-enantiomeric excesses of some extraterrestrial protein amino acids (up to ∼60%) have also been observed in rare cases and point to nonbiological enantiomeric enrichment processes prior to the emergence of life. In this Outlook, we review these recent meteoritic analyses, focusing on variations in abundance, structural distributions, and enantiomeric distributions of amino acids and discussing possible explanations for these observations and the potential for future work. PMID:27413780

  7. Meteoritic Amino Acids: Diversity in Compositions Reflects Parent Body Histories.

    PubMed

    Elsila, Jamie E; Aponte, José C; Blackmond, Donna G; Burton, Aaron S; Dworkin, Jason P; Glavin, Daniel P

    2016-06-22

    The analysis of amino acids in meteorites dates back over 50 years; however, it is only in recent years that research has expanded beyond investigations of a narrow set of meteorite groups (exemplified by the Murchison meteorite) into meteorites of other types and classes. These new studies have shown a wide diversity in the abundance and distribution of amino acids across carbonaceous chondrite groups, highlighting the role of parent body processes and composition in the creation, preservation, or alteration of amino acids. Although most chiral amino acids are racemic in meteorites, the enantiomeric distribution of some amino acids, particularly of the nonprotein amino acid isovaline, has also been shown to vary both within certain meteorites and across carbonaceous meteorite groups. Large l-enantiomeric excesses of some extraterrestrial protein amino acids (up to ∼60%) have also been observed in rare cases and point to nonbiological enantiomeric enrichment processes prior to the emergence of life. In this Outlook, we review these recent meteoritic analyses, focusing on variations in abundance, structural distributions, and enantiomeric distributions of amino acids and discussing possible explanations for these observations and the potential for future work.

  8. Efficient preparation of (R)-2-chloromandelic acid via a recycle process of resolution.

    PubMed

    Hu, Yu; Wu, Chang; Wu, Xue-Ying; Li, Shao-Lei; Sun, Xiao-Xia; Tang, Ze-Biao

    2015-03-01

    Efficient preparation of (R)-2-chloromandelic acid based on a recycle process of resolution is described. In the process, the desired was obtained by coordination-mediated resolution with D-O,O'-di-(p-toluoyl)-tartaric acid in the presence of Ca(2+) . Meanwhile, the undesired could be racemized in the presence of sodium hydroxide and the product was suitable for further resolution. A carbanion mechanism for the racemization of is proposed.

  9. Diversity of lactic acid bacteria from modified atmosphere packaged sliced cooked meat products at sell-by date assessed by PCR-denaturing gradient gel electrophoresis.

    PubMed

    Audenaert, Kris; D'Haene, Klaas; Messens, Kathy; Ruyssen, Tony; Vandamme, Peter; Huys, Geert

    2010-02-01

    The predominant lactic acid bacteria (LAB) microbiota associated with three types of modified atmosphere packaged (MAP) sliced cooked meat products (i.e. ham, turkey and chicken) was analyzed at sell-by date using a combination of culturing and molecular population fingerprinting. Likewise routine analyses during industrial MAP production, meat samples were plated on the general heterotrophic Plate Count Agar (PCA) and on the LAB-specific de Man, Rogosa, Sharpe (MRS) agar under different temperature and atmosphere conditions. Subsequently, community DNA extracts were prepared from culturable bacterial fractions harvested from both media and used for PCR targeting the V3 hyper-variable region of the 16S rRNA gene followed by denaturing gradient gel electrophoresis (DGGE) of PCR amplicons (PCR-DGGE). Irrespective of aerobic or anaerobic incubation conditions, V3-16S rDNA DGGE fingerprints of culturable fractions from PCA and MRS medium displayed a high level of similarity indicating that LAB constituted the most dominant group in the culturable bacterial community. Comparison of DGGE profiles of fractions grown at 20, 28 or 37 degrees C indicated that part of the culturable community consisted of psychrotrophs. Four DGGE bands were common among cooked ham, turkey and chicken products, suggesting that these represent the microbiota circulating in the plant where all three MAP product types were sliced and packaged. Based on band sequencing and band position analysis using LAB reference strains, these four bands could be assigned to Lactobacillus sakei and/or the closely related Lactobacillus fuchuensis, Lactobacillus curvatus, Carnobacterium divergens and Leuconostoc carnosum. In conclusion, the PCR-DGGE approach described in this study allows to discriminate, identify and monitor core and occasional LAB microbiota of MAP sliced cooked meat products and provides valuable complementary information to the current plating procedures routinely used in industrial plants.

  10. Acoustic and thermal anomalies in a liquid-glass transition of racemic S(+)-R(-) ketoprofen

    NASA Astrophysics Data System (ADS)

    Shibata, Tomohiko; Takayama, Haruki; Kim, Tae Hyun; Kojima, Seiji

    2014-01-01

    Acoustic and thermal properties of pharmaceutical racemic S(+)-R(-) ketoprofen were investigated in wide temperature range including glassy, supercooled liquid and liquid states by Brillouin scattering and temperature modulated DSC. Sound velocity and acoustic attenuation exhibited clear changes at 265 K indicating a liquid-glass transition and showed the typical structural relaxation above Tg. The high value of the fragility index m = 71 was determined by the dispersion of the complex heat capacity. New relaxation map was suggested in combination with previous study of dielectric measurement.

  11. [Racemation of the benzodiazepines camazepam and ketazolam and receptor binding of enantiomers].

    PubMed

    Blaschke, G; Kley, H; Müller, W E

    1986-06-01

    The chiral benzodiazepines camazepam (1) and ketazolam (2) were resolved into the enantiomers by chromatography on the optically active adsorbent poly[(S)-N-(1-cyclohexylethyl)-methacrylamide] and fractional crystallisation or repeated chromatography, respectively. The IC50 values of the isomers and of the racemates of both compounds were determined by displacement of radioactively labelled 3H-flunitrazepam and 3H-propyl-beta-carboline-carboxylate from their specific binding sites. (+)-Camazepam exhibits 14fold higher affinity compared to the (-)-enantiomer. In contrast only slight differences in the receptor affinity are observed with the ketazolam enantiomers.

  12. Estimation of past intermittent methane seep activity using radiocarbon dating of Calyptogena shells in the eastern Nankai subduction zone

    NASA Astrophysics Data System (ADS)

    Yagasaki, K.; Ashi, J.; Yokoyama, Y.; Miyairi, Y.; Kuramoto, S.

    2013-12-01

    Radioisotope carbon dating samples from the deep ocean has always been a difficult phenomenon due to the carbon offset present. This research presents a way of utilizing such method to date shell samples in order to study past fault activities. The research presented will be based on the preliminary data collected thus far. The Nankai and the Tokai regions are common areas for cold seeps, where seepage of hydrogen sulfide and methane rich fluid occurs. These various substances encourage the growth of Calyptogena colonies to flourish at these sites. Cold seeps generally occur at tectonically active continental margins and are mostly ephemeral. This suggests that the cold seep events are possibly influenced by the tectonic activity during the plate divergence. In 1997, a submersible dive by Shinkai 2000 discovered an unusually large Calyptogena colony ranging over 200 m2 off Daini Tenryu Knoll. Majority of the shells were fossilized with few live shells remaining. It is assumed that past tectonic events in the region may have caused a high flux of methane fluid or gas to be released, making it possible to support such a vast scale colony to survive until their eventual death. Previous attempt to reconstruct the cold seep activity history through amino acid racemisation dating revealed two different age grouped shells. Further data using a different method is required to prove its reliability, as acid racemization dating technique can easily be affected by seawater temperature changes and microbial activity. This consequently alters the protein structure of the sample and its overall age. As 14C radioisotope dating is not affected by temperature change, it will provide additional information to the accuracy of the acid racemisation dating of the shell. However, the possibility of contamination is likely due to the shells incorporating older carbon from the sediments during their early stages of growth. The old carbon value can be calculated by subtracting the formerly

  13. Origin, Microbiology, Nutrition, and Pharmacology of D-Amino Acids

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Exposure of food proteins to certain processing conditions induces two major chemical changes: racemization of all L-amino acids (LAA) to D-amino acids (DAA) and concurrent formation of crosslinked amino acids such as lysinoalanine (LAL). The diet contains both processing-induced and naturally-form...

  14. Thermodynamics of sublimation, crystal lattice energies, and crystal structures of racemates and enantiomers: (+)- and (+/-)-ibuprofen.

    PubMed

    Perlovich, German L; Kurkov, Sergey V; Hansen, Lars Kr; Bauer-Brandl, Annette

    2004-03-01

    Thermodynamic differences between ibuprofen (IBP) racemate and the (+)-enantiomer were studied by X-ray diffraction, thermoanalysis, and crystal energy calculations. The thermodynamic functions of sublimation (as a measure of crystal lattice energy) were obtained by the transpiration method. The sublimation enthalpies (DeltaH(sub)) of (+/-)-IBP and (+)-IBP are 115.8 +/- 0.6 and 107.4 +/- 0.5 kJ. mol(-1), respectively. Using the temperature dependency of the saturated vapor pressure, the relative fractions of enthalpy and entropy of the sublimation process were calculated, and the sublimation process for both the racemate and the enantiomer was found to be enthalpy driven (62%). Two different force fields, Mayo et al. (M) and Gavezzotti (G), were used for comparative analysis of crystal lattice energies. Both force fields revealed that the van der Waals term contributes more to the packing energy in (+)-IBP than in (+/-)-IBP. The hydrogen bonding energy, however, contributes at 29.7 and 32.3% to the total crystal lattice energy in (+)-IBP and (+/-)-IBP (M), respectively. Furthermore, different structure fragments of the IBP molecule were analyzed with respect to their contribution to nonbonded van der Waals interactions. The effect of the C-H distance on the van der Waals term of the crystal lattice energy was also studied.

  15. Enzymatic Hydrolytic Resolution of Racemic Ibuprofen Ethyl Ester Using an Ionic Liquid as Cosolvent.

    PubMed

    Wei, Tao; Yang, Kunpeng; Bai, Bing; Zang, Jie; Yu, Xuan; Mao, Duobin

    2016-01-01

    The aim of this study was to develop an ionic liquid (IL) system for the enzymatic resolution of racemic ibuprofen ethyl ester to produce (S)-ibuprofen. Nineteen ILs were selected for use in buffer systems to investigate the effects of ILs as cosolvents for the production of (S)-ibuprofen using thermostable esterase (EST10) from Thermotoga maritima. Analysis of the catalytic efficiency and conformation of EST10 showed that [OmPy][BF₄] was the best medium for the EST10-catalyzed production of (S)-ibuprofen. The maximum degree of conversion degree (47.4%), enantiomeric excess of (S)-ibuprofen (96.6%) and enantiomeric ratio of EST10 (177.0) were achieved with an EST10 concentration of 15 mg/mL, racemic ibuprofen ethyl ester concentration of 150 mM, at 75 °C , with a reaction time of 10 h. The reaction time needed to achieve the highest yield of (S)-ibuprofen was decreased from 24 h to 10 h. These results are relevant to the proposed application of ILs as solvents for the EST10-catalyzed production of (S)-ibuprofen. PMID:27420042

  16. Chiral bis(amino alcohol)oxalamide gelators-gelation properties and supramolecular organization: racemate versus pure enantiomer gelation.

    PubMed

    Makarević, Janja; Jokić, Milan; Raza, Zlata; Stefanić, Zoran; Kojić-Prodić, Biserka; Zinić, Mladen

    2003-11-21

    Four new chiral bis(amino alcohol)oxalamides (1-4: amino alcohol=leucinol, valinol, phenylglycinol, and phenylalaninol, respectively) have been prepared as low-molecular-weight organic gelators. Their gelation properties towards various organic solvents and mixtures were determined and these were then compared to related bis(amino acid) oxalamide gelators. Spectroscopic (FTIR, (1)H NMR) and X-ray diffraction studies revealed that the primary organization motif of (S,S)-1 and racemate 1 (rac-1) in lipophilic solvents involved the formation of inverse bilayers. The X-ray crystal structure of (S,S)-1 also shows this type of bilayer organization. The crystal structure of rac-2 reveals meso bilayers of hydrogen-bonded aggregates. Within the bilayers formed, the gelator molecules are connected by cooperative hydrogen bonding between oxalamide units and OH groups, while the interbilayer interactions are realized through lipophilic interactions between the iBu groups of leucinol. Oxalamide meso-1 lacks any gelation ability and crystallizes in monolayers. In dichloromethane rac-1 forms an unstable gel; this is prone to crystallization as a result of the formation of symmetrical meso bilayers. In contrast, in aromatic solvents rac-1 forms stable gels; this indicates that enantiomeric bilayers are formed. Oxalamide rac-1 is capable of gelling a volume of toluene three times larger than (S,S)-1. A tranmission electron microscopy investigation of rac-1 and (S,S)-1 toluene gels reveals the presence of thinner fibers in the former gel, and, hence, a more compact network that is capable of immobilizing a larger volume of the solvent. The self-assembly of these types of gelator molecules into bilayers and subsequent formation of fibrous aggregates can be explained by considering the strength and direction of aggregate forces (supramolecular vectors) in three-dimensional space. PMID:14639640

  17. Organic geochemistry of amino acids: Precambrian to recent

    SciTech Connect

    Engel, M.H.; Macko, S.A.

    1985-01-01

    Since the discovery of amino acids in fossils (Abelson, 1954), considerable effort has been made to elucidate the origin and distribution of amino acids in geologic materials. Racemization and decomposition reactions of amino acids and peptides derived via the natural hydrolysis of protein constituents of organisms have been extensively studied. While the ubiquity of amino acids presents a challenge for discerning their indigeneity in geologic samples, careful analyses have resulted in successful applications of amino acid racemization and decomposition reactions for investigations of geochronologic, paleoclimatic, stratigraphic, diagenetic and chemotaxonomic problems for Quaternary age samples. An investigation of amino acids in sediments from Baffin Island fjords indicates that their distribution may also provide data with respect to the relative contributions of marine and terrigenous organic matter to recent sediments. While the absence of unstable amino acids and the presence of racemic amino acids in a sample may preclude very recent contamination, the possibility of retardation of amino acid racemization rates subsequent to geopolymer formation must also be considered. Studies of amino acids in Paleozoic, Mesozoic and early Cenozoic age samples are limited. Precambrian samples, however, have received much attention, given the potential (however slight) for isolating compounds representative of the earliest living systems. A future approach for elucidating the origin(s) of amino acids in ancient samples may be analyses of their individual stable isotopic compositions.

  18. Unconventional preparation of racemic crystals of isopropyl 3,3,3-trifluoro-2-hydroxypropanoate and their unusual crystallographic structure: the ultimate preference for homochiral intermolecular interactions.

    PubMed

    Aceña, José Luis; Sorochinsky, Alexander E; Katagiri, Toshimasa; Soloshonok, Vadim A

    2013-01-14

    This work reports the first example of the transformation of conglomerate (R)- and (S)-crystals into racemic crystals via sublimation. Crystallographic analysis of racemic isopropyl 3,3,3-trifluoro-2-hydroxypropanoate did not reveal the highly expected heterochiral dimer indicating that this compound is capable of forming exclusively homochiral oligomers via infinite multi-centred H-bonding networks.

  19. Complete transfer of chirality in an intramolecular, thermal [2 + 2] cycloaddition of allene-ynes to form non-racemic spirooxindoles.

    PubMed

    Brummond, Kay M; Osbourn, Joshua M

    2011-01-01

    A thermal [2 + 2] cycloaddition reaction of allene-ynes has been used to transform chiral non-racemic allenyl oxindoles into chiral non-racemic spirooxindoles containing an alkylidene cyclobutene moiety. The enantiomeric excesses were determined by chiral lanthanide shift NMR analysis and the transfer of chiral information from the allene to the spirooxindole was found to be greater than 95%.

  20. Synthesis of α-aminoboronic acids.

    PubMed

    Andrés, Patricia; Ballano, Gema; Calaza, M Isabel; Cativiela, Carlos

    2016-04-21

    This review describes available methods for the preparation of α-aminoboronic acids in their racemic or in their enantiopure form. Both, highly stereoselective syntheses and asymmetric procedures leading to the stereocontrolled generation of α-aminoboronic acid derivatives are included. The preparation of acyclic, carbocyclic and azacyclic α-aminoboronic acid derivatives is covered. Within each section, the different synthetic approaches have been classified according to the key bond which is formed to complete the α-aminoboronic acid skeleton.

  1. Enantioselective sorption of the chiral fungicide metalaxyl on soil from non-racemic aqueous solutions: Environmental implications.

    PubMed

    Celis, Rafael; Gámiz, Beatriz; Facenda, Gracia; Hermosín, María C

    2015-12-30

    Mechanisms governing the enantioselectivity of the processes that determine the behavior of chiral pollutants in the environment need to be better understood. Understanding these mechanisms should help improve predictions of the hazards and risks chiral compounds can pose to people and the environment. We report the results of batch sorption experiments indicating that the sorption of the chiral fungicide metalaxyl on soil from non-racemic initial solutions was enantioselective. While from a racemic initial solution the two enantiomers of metalaxyl were sorbed on the soil to the same extent, increasing the fraction of R-enantiomer in the initial solution led to enhanced sorption of this enantiomer and to reduced sorption of the S-enantiomer. Considering the shape of the sorption isotherms (S-type) and the sorption behavior of model sorbents, we attributed this effect to molecular interactions between metalaxyl enantiomer species at the sorbed state, where R-R metalaxyl interactions appeared to be more favorable than R-S metalaxyl interactions. We discuss important environmental implications of the proposed mechanism, such as those related to the fact that the biological degradation of metalaxyl is known to be an enantioselective process that can yield non-racemic residues in soils shortly after application of the fungicide as a racemic mixture.

  2. Quantum control of molecular handedness in a randomly oriented racemic mixture using three polarization components of electric fields

    NASA Astrophysics Data System (ADS)

    Hoki, Kunihito; González, Leticia; Fujimura, Yuichi

    2002-05-01

    A new laser control scenario is presented for obtaining substantial amounts of enantiomeric enrichment from a randomly oriented racemic mixture. This is carried out by using three polarization components of electric fields; one is used for orientation, the other two for controlling the chirality. The effectiveness is demonstrated by numerical simulations on the enantiomeric enrichment of the axial chiral H2POSH molecule.

  3. Determination of the D and L isomers of some protein amino acids present in soils

    NASA Technical Reports Server (NTRS)

    Pollock, G. E.; Cheng, C.-N.; Cronin, S. E.

    1977-01-01

    The D and L isomers of some protein amino acids present in soils were measured by using a gas chromatographic technique. The results of two processing procedures were compared to determine the better method. Results of the comparison indicated that the determination of D and L percentages requires amino acid purification if one is to obtain accurate data. It was found that very significant amounts of D-alanine, D-aspartic acid, and D-glutamic acid were present in the contemporary soils studied. Valine, isoleucine, leucine, proline, and phenylalanine generally contained only a trace to very small amounts of the D isomer. It is probable that the D-amino acids from the alanine, aspartic, and glutamic acids are contributed to the soil primarily via microorganisms. The finding of very significant quantities of some D-amino acids (about 5-16%) in present-day soils may alert some investigators of geological sediments to a possible problem in using amino acid racemization as an age-dating technique.

  4. Infrared discrimination of enantiomerically enriched and racemic samples of methamphetamine salts.

    PubMed

    Chappell, J S

    1997-08-01

    A relatively rapid and simple means of enantiomer determination is described for the determination of methamphetamine, a common drug of abuse. The method employs the well known technique of infrared transmission spectrometry on solid samples dispersed within an alkali metal halide matrix. This approach exploits the solid-state, ion-exchange reaction between methamphetamine hydrochloride and a potassium iodide matrix and the subsequent formation of the hydriodide salt in situ. The infrared properties of the hydriodide salt are distinct for enantiomerically enriched and racemic samples, and therefore are readily distinguished by infrared transmission spectrometry. This technique uses materials and instrumentation that are generally available to most crime laboratories. The applicability of this method to some other amine drugs is discussed.

  5. A functional role of Rv1738 in Mycobacterium tuberculosis persistence suggested by racemic protein crystallography

    PubMed Central

    Bunker, Richard D.; Mandal, Kalyaneswar; Bashiri, Ghader; Chaston, Jessica J.; Pentelute, Bradley L.; Lott, J. Shaun; Kent, Stephen B. H.; Baker, Edward N.

    2015-01-01

    Protein 3D structure can be a powerful predictor of function, but it often faces a critical roadblock at the crystallization step. Rv1738, a protein from Mycobacterium tuberculosis that is strongly implicated in the onset of nonreplicating persistence, and thereby latent tuberculosis, resisted extensive attempts at crystallization. Chemical synthesis of the l- and d-enantiomeric forms of Rv1738 enabled facile crystallization of the d/l-racemic mixture. The structure was solved by an ab initio approach that took advantage of the quantized phases characteristic of diffraction by centrosymmetric crystals. The structure, containing l- and d-dimers in a centrosymmetric space group, revealed unexpected homology with bacterial hibernation-promoting factors that bind to ribosomes and suppress translation. This suggests that the functional role of Rv1738 is to contribute to the shutdown of ribosomal protein synthesis during the onset of nonreplicating persistence of M. tuberculosis. PMID:25831534

  6. A functional role of Rv1738 in Mycobacterium tuberculosis persistence suggested by racemic protein crystallography.

    PubMed

    Bunker, Richard D; Mandal, Kalyaneswar; Bashiri, Ghader; Chaston, Jessica J; Pentelute, Bradley L; Lott, J Shaun; Kent, Stephen B H; Baker, Edward N

    2015-04-01

    Protein 3D structure can be a powerful predictor of function, but it often faces a critical roadblock at the crystallization step. Rv1738, a protein from Mycobacterium tuberculosis that is strongly implicated in the onset of nonreplicating persistence, and thereby latent tuberculosis, resisted extensive attempts at crystallization. Chemical synthesis of the L- and D-enantiomeric forms of Rv1738 enabled facile crystallization of the D/L-racemic mixture. The structure was solved by an ab initio approach that took advantage of the quantized phases characteristic of diffraction by centrosymmetric crystals. The structure, containing L- and D-dimers in a centrosymmetric space group, revealed unexpected homology with bacterial hibernation-promoting factors that bind to ribosomes and suppress translation. This suggests that the functional role of Rv1738 is to contribute to the shutdown of ribosomal protein synthesis during the onset of nonreplicating persistence of M. tuberculosis. PMID:25831534

  7. Affinity and efficacy of racemic, (+)-, and (-)-methacholine in muscarinic inhibition of [3H]-noradrenaline release.

    PubMed

    Fuder, H; Jung, B

    1985-02-01

    The right postganglionic sympathetic nerves of rat isolated perfused hearts (previously loaded with [3H]-noradrenaline) were stimulated electrically with 10 trains of 10 pulses at 10 Hz. The inhibition by methacholine of stimulation-evoked [3H]-noradrenaline overflow into the perfusate (determined in the presence of corticosterone, desipramine, phentolamine, and propranolol) was taken as a measure for activation of presynaptic muscarinic receptors. The evoked [3H]-noradrenaline overflow was inhibited by (+)-, racemic, and (-)-methacholine in a reversible and concentration-dependent manner. The concentration causing 50% inhibition (IC50) was 0.1, 0.26, and 65 microM, respectively, resulting in an isomeric potency ratio IC50 (+)/IC50(-) of 650. The dissociation constant KA of the (+/-)- or (+)-methacholine-presynaptic receptor complex was determined after fractional receptor inactivation according to Furchgott & Bursztyn (1967) with phenoxybenzamine or propylbenzilylcholine mustard as irreversible antagonists of muscarinic receptors. KA for (-)-methacholine was estimated according to Mackay (1966). KA of (+)-, (+/-)-, and (-)-methacholine were 2.5, 4 and 440 microM, resulting in an isomeric affinity ratio KA (+)/KA(-) of 180. The discrepancy between the isomeric IC50 ratio and the isomeric KA ratio is explained by a higher intrinsic efficacy of the (+)-enantiomer compared to the (-)-enantiomer. Thus, (+)-methacholine has to occupy fewer receptors to induce a given inhibition of release than its antipode as revealed by a plot of fractional receptor occupancy vs response. The results show that, in the effector system of presynaptic muscarinic inhibition, methacholine enantiomers differ greatly not only in affinity for the receptor, but also to some extent in the efficiency of signal transmission, and both parameters contribute to the high isomeric potency ratio. The activity of the racemate is fully accounted for by the activity of the (+)-enantiomer.

  8. Non-racemic Antifolates Stereo-selectively Recruit Alternate Cofactors and Overcome Resistance in S. aureus

    PubMed Central

    Keshipeddy, Santosh; Reeve, Stephanie M.; Anderson, Amy C.; Wright, Dennis L.

    2016-01-01

    While antifolates such as Bactrim (trimethoprim-sulfamethoxazole; TMP-SMX) continue to play an important role in treating community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA), resistance-conferring mutations, specifically F98Y of dihydrofolate reductase (DHFR), have arisen and compromise continued use. In an attempt to extend the lifetime of this important class, we have developed a class of propargyl-linked antifolates (PLAs) that exhibit potent inhibition of the enzyme and bacterial strains. Probing the role of the configuration at the single propargylic stereocenter in these inhibitors required us to develop a new approach to non-racemic 3-aryl-1-butyne building blocks by the pairwise use of asymmetric conjugate addition and aldehyde dehydration protocols. Using this new route, a series of non-racemic PLA inhibitors was prepared and shown to possess potent enzyme inhibition (IC50 values < 50 nM), antibacterial effects (several with MIC values < 1 µg/mL) and to form stable ternary complexes with both wild-type and resistant mutants. Unexpectedly, crystal structures of a pair of individual enantiomers in the wild-type DHFR revealed that the single change in configuration of the stereocenter drove the selection of an alternative NADPH cofactor, with the minor α-anomer appearing with R-27. Remarkably, this cofactor switching becomes much more prevalent when the F98Y mutation is present. The observation of cofactor site plasticity leads to a postulate for the structural basis of TMP resistance in DHFR and also suggests design strategies that can be used to target these resistant enzymes. PMID:26098608

  9. Is RK-682 a promiscuous enzyme inhibitor? Synthesis and in vitro evaluation of protein tyrosine phosphatase inhibition of racemic RK-682 and analogues.

    PubMed

    Carneiro, Vânia M T; Trivella, Daniela B B; Scorsato, Valéria; Beraldo, Viviane L; Dias, Mariana P; Sobreira, Tiago J P; Aparicio, Ricardo; Pilli, Ronaldo A

    2015-06-01

    RK-682 (1) is a natural product known to selectively inhibit protein tyrosine phosphatases (PTPases) and is used commercially as a positive control for phosphatase inhibition in in vitro assays. Protein phosphatases are involved in several human diseases including diabetes, cancer and inflammation, and are considered important targets for pharmaceutical development. Here we report the synthesis of racemic RK-682 (rac-1) and a focused set of compounds, including racemic analogues of 1, dihydropyranones and C-acylated Meldrum's acid derivatives, the later obtained in one synthetic step from commercially available starting material. We further characterized the behavior of some representative compounds in aqueous solution and evaluated their in vitro PTPase binding and inhibition. Our data reveal that rac-1 and some derivatives are able to form large aggregates in solution, in which the aggregation capacity is dependent on the acyl side chain size. However, compound aggregation per se is not able to promote PTPase inhibition. Our data disclose a novel family of PTPase inhibitors (C-acylated Meldrum's acid derivatives) and that rac-1 and derivatives with an exposed latent negatively charged substructure (e.g.: the tetronic acid core of 1) can bind to the PTPase binding site, as well promiscuously to protein surfaces. The combined capacity of compounds to bind to proteins together with their intrinsic capacity to aggregate in solution seems essential to promote enzyme aggregation and thus, its inhibition. We also observed that divalent cations, such as magnesium frequently used in enzyme buffer solutions, can deplete the inhibitory activity of rac-1, thus influencing the enzyme inhibition experiment. Overall, these data help to characterize the mechanism of PTPase inhibition by rac-1 and derivatives, revealing that enzyme inhibition is not solely dependent on compound binding to the PTPase catalytic site as generally accepted in the literature. In addition, our

  10. S,S-1,2-Dicyclohexylethane-1,2-diol and its racemic compound: a striking exception to Wallach's rule.

    PubMed

    Patrick, Brian O; Brock, Carolyn Pratt

    2006-06-01

    The structures of enantiopure S,S-1,2-dicyclohexylethane-1,2-diol and its racemic compound (rac-S,S-1,2-dicyclohexylethane-1,2-diol) have been determined at 295 and 173 K. The crystals of the enantiopure material are more than 4% denser than the crystals of the racemic compound, but the melting points indicate that the crystals of the less dense racemic compound are considerably more stable than those of the racemic conglomerate. This apparent exception to the correlation of crystal density and melting point is explained. The enantiopure crystals have four molecules in the asymmetric unit (Z' = 4). Two of the molecules have the conformation observed for the one independent molecule of the racemic compound and two have a higher energy conformation; the overall P2(1) structure is a perturbed version of a P2(1)2(1)2(1) structure with Z' = 2. The enantiopure and racemic crystals have the same hydrogen-bonding motif, but the motif in the former appears to be significantly strained. A reason why crystals of enantiopure material might be systematically less dense than crystals of its racemic compound and to be more likely to have Z' > 1 is suggested.

  11. The optical nature of methylsuccinic acid in human urine

    NASA Technical Reports Server (NTRS)

    Zeitman, B.; Lawless, J. G.

    1975-01-01

    Methylsuccinic acid was isolated from human urine, derivatized as the di-S-(+)-2-butyl ester, and analyzed using a gas chromatographic system capable of separating the enantiomers of the derivative. The R-(+)-isomer was found to be present. Methylsuccinic acid is potentially important as a criterion for abiogenicity, having been obtained as a racemic mixture from sources known to be abiotic.

  12. Teen Dating Violence

    MedlinePlus

    ... dating violence prevention initiative seeks to reduce dating violence and increase healthy relationships in high-risk urban communities through comprehensive, multisector prevention. Division of Adolescent ...

  13. A Multi-Enzymatic Cascade Reaction for the Stereoselective Production of γ-Oxyfunctionalyzed Amino Acids

    PubMed Central

    Enoki, Junichi; Meisborn, Jaqueline; Müller, Ann-Christin; Kourist, Robert

    2016-01-01

    A stereoselective three-enzyme cascade for synthesis of diasteromerically pure γ-oxyfunctionalized α-amino acids was developed. By coupling a dynamic kinetic resolution (DKR) using an N-acylamino acid racemase (NAAAR) and an L-selective aminoacylase from Geobacillus thermoglucosidasius with a stereoselective isoleucine dioxygenase from Bacillus thuringiensis, diastereomerically pure oxidized amino acids were produced from racemic N-acetylamino acids. The three enzymes differed in their optimal temperature and pH-spectra. Their different metal cofactor dependencies led to inhibitory effects. Under optimized conditions, racemic N-acetylmethionine was quantitatively converted into L-methionine-(S)-sulfoxide with 97% yield and 95% de. The combination of these three different biocatalysts allowed the direct synthesis of diastereopure oxyfunctionalized amino acids from inexpensive racemic starting material. PMID:27092111

  14. [From the racemate to the eutomer: (S)-ketamine. Renaissance of a substance?].

    PubMed

    Adams, H A; Werner, C

    1997-12-01

    The pharmacological profile of ketamine: Until recently, clinically available ketamine was a racemic mixture containing equal amounts of two enantiomers, (S)- and (R)-ketamine. The pharmacological profile of racemic ketamine is characterized by the so called dissociative anesthetic state and profound sympathomimetic properties. Among the different sites of action, N-methyl-D-aspartate (NMDA)-receptor antagonism is considered to be the most important neuropharmacological mechanism of ketamine. Effects on opiate receptors, monoaminergic and cholinergic transmitters, and local anesthetic effects are obvious as well. Following intravenous administration, a rapid onset of action is seen within 1 min, lasting for about 10 min. The anaesthetic state is terminated due to redistribution, followed by hepatic and renal elimination with a half-life period of 2-3 h. For alternative administration, the intramuscular and oral route is also appropriate. The most important adverse effects are hallucinations and excessive increases in blood pressure and heart rate. These reactions can be attenuated or avoided by combining of ketamine with sedative or hypnotic drugs like midazolam and/or propofol. During controlled ventilation, increases in intracranial pressure are unlikely to occur. The special pharmacological profile of (S)-ketamine: In general, the pharmacological properties of (S)-ketamine are comparable to the racemic compound. On the different sites of action, qualitatively comparable effects were found, but significant quantitative differences also became obvious. When compared with (R)-ketamine and the racmic mixture, the analgesic and anesthetic potency of (S)-ketamine is threefold or twofold higher. Thus, a 50% reduction of dosage is possible to achieve comparable clinical results. Because of the faster elimination of (S)-ketamine, better control of anesthesia will be provided. In summary, the pharmacokinetic improvements of (S)-ketamine are characterized by a reduced drug

  15. Non-cyclooxygenase prostaglandin synthesis in the sea whip coral, Plexaura homomalla: an 8(R)-lipoxygenase pathway leads to formation of an alpha-ketol and a Racemic prostanoid

    SciTech Connect

    Brash, A.R.; Baertschi, S.W.; Ingram, C.D.; Harris, T.M.

    1987-11-25

    Plexaura homomalla is a rich natural source of prostaglandins and recent evidence suggest the prostaglandin biosynthesis could occur through a lipoxygenase pathway. We have investigated the metabolism of arachidonic acid in homogenates and acetone powders of the fresh frozen coral. The biosynthesis of natural prostaglandins was not detected. However, we find a prominent 8(R)-lipoxygenase pathway leading to an alpha-ketol, characterized by high pressure liquid chromatography, gas chromatography-mass spectrometry, and NMR as 8-hydroxy, 9-keto-eicosa-5Z, 11Z, 14Z-trienoic acid, and a prostaglandin A-like cyclopentenone identified as 9-oxo-(8, 12-cis)-prosta-5Z, 10, 14Z-trienoic acid. These reactions appear analogous to the transformation of linolenic acid hydroperoxide by isomerase and cyclase of corn and flaxseed. From analysis of the absolute configurations of the coral products, and from additional stable isotope labeling experiments in H/sub 2//sup 18/O and D/sub 2/O, we deduce that both compounds arise via conversion of 8(R)-HPETE to an 8(R), 9-allene oxide, 8R,9-oxido-eicosa-5Z, 9, 11Z, 14Z-tetraenoic acid. This unstable intermediate undergoes hydrolysis to form the alpha-ketol or cyclization to give the cyclopentenone. Significantly, we find that the prostaglandin-like product is a racemic mixture of cis side chain enantiomers, pointing to its nonenzymatic origin from the allene oxide. The alpha-ketol is formed with partial racemization and inversion of configuration, also compatible with formation in a nonenzymatic reaction. We conclude that the isomerase and cyclase reactions may merely reflect nonenzymatic breakdown of the enzymatically formed allene oxide.

  16. Influences of harvest date and location on the levels of beta-carotene, ascorbic acid, total phenols, the in vitro antioxidant capacity, and phenolic profiles of five commercial varieties of mango (Mangifera indica L.).

    PubMed

    Manthey, John A; Perkins-Veazie, Penelope

    2009-11-25

    Mango (Mangifera indica L.) is a tropical fruit grown worldwide with excellent nutritional value and widely attributed health-promoting properties. Extensive studies have been made of the high concentrations of phenolic antioxidants in mango peels, seeds, and leaves, yet less is known about the phenolic antioxidants of mango fruit pulp. Five varieties of mangoes from four countries were evaluated with multiple harvests over 1 year to compare the beta-carotene, ascorbic acid, and total phenolic contents and antioxidant capacities of the fruit pulp and to compare the phenolic profiles of the individual varieties. To minimize ripeness variability, only soft fruit (0.5-1 N compression) with a minimum of 10% soluble solids were used for these measurements. Ascorbic acid ranged from 11 to 134 mg/100 g of pulp puree, and beta-carotene varied from 5 to 30 mg/kg among the five varieties. Total phenolic content ranged from 19.5 to 166.7 mg of gallic acid equivalents (GAE)/100 g of puree. The varieties Tommy Atkins, Kent, Keitt, and Haden had similar total phenolic contents, averaging 31.2+/-7.8 mg GAE/100 g of puree, whereas the variety Ataulfo contained substantially higher values. Similar trends were observed in the DPPH radical scavenging activities among the five varieties. In contrast, the country of origin and harvest dates had far less influence on these parameters. Ataulfo mangoes contained significantly higher amounts of mangiferin and ellagic acid than the other four varieties. Large fruit-to-fruit variations in the concentrations of these compounds occurred within sets of mangoes of the same cultivar with the same harvest location and date.

  17. 40 CFR 63.609 - Compliance dates.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... Emission Standards for Hazardous Air Pollutants From Phosphoric Acid Manufacturing Plants § 63.609 Compliance dates. (a) Each owner or operator of an existing affected source at a phosphoric acid... existing phosphoric acid manufacturing plant shall fulfill the applicable requirements of § 63.606 no...

  18. 40 CFR 63.609 - Compliance dates.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... Emission Standards for Hazardous Air Pollutants From Phosphoric Acid Manufacturing Plants § 63.609 Compliance dates. (a) Each owner or operator of an existing affected source at a phosphoric acid... existing phosphoric acid manufacturing plant shall fulfill the applicable requirements of § 63.606 no...

  19. 40 CFR 63.609 - Compliance dates.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... Emission Standards for Hazardous Air Pollutants From Phosphoric Acid Manufacturing Plants § 63.609 Compliance dates. (a) Each owner or operator of an existing affected source at a phosphoric acid... existing phosphoric acid manufacturing plant shall fulfill the applicable requirements of § 63.606 no...

  20. 40 CFR 63.609 - Compliance dates.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... Emission Standards for Hazardous Air Pollutants From Phosphoric Acid Manufacturing Plants § 63.609 Compliance dates. (a) Each owner or operator of an existing affected source at a phosphoric acid... existing phosphoric acid manufacturing plant shall fulfill the applicable requirements of § 63.606 no...

  1. 40 CFR 63.609 - Compliance dates.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... Emission Standards for Hazardous Air Pollutants From Phosphoric Acid Manufacturing Plants § 63.609 Compliance dates. (a) Each owner or operator of an existing affected source at a phosphoric acid... existing phosphoric acid manufacturing plant shall fulfill the applicable requirements of § 63.606 no...

  2. Dating and Marriage

    MedlinePlus

    ... Family : Dating & Marriage Subscribe Translate Text Size Print Dating and Marriage Dating and Marriage If you are living with HIV, ... Living! Having HIV does not prevent you from dating or marrying—it just may require a little ...

  3. A functional role of Rv1738 in Mycobacterium tuberculosis persistence suggested by racemic protein crystallography

    SciTech Connect

    Bunker, Richard D.; Mandal, Kalyaneswar; Bashiri, Ghader; Chaston, Jessica J.; Pentelute, Bradley L.; Lott, J. Shaun; Kent, Stephen B. H.; Baker, Edward N.

    2015-04-07

    Racemic protein crystallography was used to determine the X-ray structure of the predicted Mycobacterium tuberculosis protein Rv1738, which had been completely recalcitrant to crystallization in its natural L-form. Native chemical ligation was used to synthesize both L-protein and D-protein enantiomers of Rv1738. Crystallization of the racemic {D-protein + L-protein} mixture was immediately successful. The resulting crystals diffracted to high resolution and also enabled facile structure determination because of the quantized phases of the data from centrosymmetric crystals. The X-ray structure of Rv1738 revealed striking similarity with bacterial hibernation factors, despite minimal sequence similarity. As a result, we predict that Rv1738, which is highly up-regulated in conditions that mimic the onset of persistence, helps trigger dormancy by association with the bacterial ribosome.

  4. Chiral-phase high-performance liquid chromatography of rotenoid racemates

    USGS Publications Warehouse

    Abidi, S.L.

    1987-01-01

    The high-performance liquid chromatograhic (HPLC) behavior of parent rotenoids (type I) and the hydroxyl-analogues (type II) on three different chiral stationary phases (CSPs) was studied. Separations of optical isomers were achieved in various degrees depending largely upon the rotenoidal structures and the CSP types employed. Enantiomers of all but elliptone compounds were separable on β-cyclodextrin-bonded silica (CDS). Without exception, the 12a-hydroxyrotenoid antipodes were resolved on Pirkle's phenylglycine-bonded silica (PGS) despite unsuccessful attenmpts to resolve the type I rotenoidal racemates. Conversely, optical resolution of the latter rotenoids was accomplished by using a helical polytriphenylmethylacrylate-coated silica (TPS) column and the observed separation factors (α values) ranged from 1.14 to 1.90. The results from HPLC of type II rotenoids on TPS (α = 1.00–1.63) suggested that variations in E-ring structures had profound influence on the resolution outcome. Conjugated double bonds on the E-ring and the desisopropylation of the five-membered E-ring ot type II rotenoids appeared to be important structural features for chiral recognition involving the TPS substrate. In both reversed-phase (CDS) and normal-pahse (PGS and TPS) HPLC modes, the less polar enantiomers were the 6aβ,12aβ-rotenoids as observed in most cases, though this relationship was reversed in the cases of deguelin and hydroxyelliptone probably due to conformational effects of rotenoidal ring systems.

  5. Enantioselective pharmacokinetics of ketoprofen in calves after intramuscular administration of a racemic mixture.

    PubMed

    Plessers, E; Watteyn, A; Wyns, H; Pardon, B; De Baere, S; De Backer, P; Croubels, S

    2015-08-01

    The pharmacokinetic properties of ketoprofen were determined in 4-week-old calves after intramuscular (i.m.) injection of a racemic mixture at a dose of 3 mg/kg body weight. Due to possible enantioselective disposition kinetics and chiral inversion, the plasma concentrations of the R(-) and S(+) enantiomer were quantified separately, using a stereospecific HPLC-UV assay. A distinct predominance of the S(+) enantiomer was observed, as well as significantly different pharmacokinetic parameters between R(-) and S(+) ketoprofen. More in specific, a greater value for the mean area under the plasma concentration-time curve (AUC(0→∞)) (46.92 ± 7.75 and 11.13 ± 2.18 μg·h/mL for the S(+) and R(-) enantiomer, respectively), a lower apparent clearance (Cl/F) (32.8 ± 5.7 and 139.0 ± 25.1 mL/h·kg for the S(+) and R(-) enantiomer, respectively) and a lower apparent volume of distribution (V(d)/F) (139 ± 14.7 and 496 ± 139.4 mL/kg for the S(+) and R(-) enantiomer, respectively) were calculated for the S(+) enantiomer, indicating enantioselective pharmacokinetics for ketoprofen in calves following i.m. administration.

  6. Unexpected differences between D- and L- tyrosine lead to chiral enhancement in racemic mixtures.

    PubMed

    Shinitzky, Meir; Nudelman, Fabio; Barda, Yaniv; Haimovitz, Rachel; Chen, Effie; Deamer, David W

    2002-08-01

    We report here an unexpected difference in the solubilities of D- and L-tyrosine in water, which could be discerned by their rate of crystallization and the resulting concentrations of their saturated solutions. A supersaturated solution of 10 mM L-tyrosine at 20 degrees C crystallized much more slowly than that of D-tyrosine under the same conditions, and the saturated solution of L-tyrosine was more concentrated than that of D-tyrosine. Supersaturated solutions of 10 mM DL-tyrosine in water formed precipitates of predominantly D-tyrosine and DL-tyrosine, resulting in an excess of L-tyrosine in the saturated solution. The experimental setups were monitored independently by UV-absorption, radioactivity tracing, optical rotation and X-ray diffraction. The process of nucleation and crystallization of D- and L-tyrosine is characterized by an exceptionally high cooperativity. It is possible that minute energy differences between D- and L-tyrosine, originating from parity violation or other non-conservative chiral discriminatory rules, could account for the observations. The physical process that initiated chiral selection in biological systems remains a challenging problem in understanding the origin of life, and it is possible that chiral compounds were concentrated from supersaturated racemic mixtures by preferential crystallization.

  7. Racemic salbutamol and levosalbutamol in mild persistent asthma: A comparative study of efficacy and safety

    PubMed Central

    Maiti, Rituparna; Prasad, Chenimilla Nagender; Jaida, Jyothirmai; Mukkisa, Sruthi; Koyagura, Narendar; Palani, Anuradha

    2011-01-01

    Aim: The effect of monotherapy with racemic salbutamol and levosalbutamol on symptoms, quality of life, and pulmonary function has been assessed and compared in mild persistent asthma. Materials and Methods: A randomized, open, parallel clinical study was conducted on 60 patients of mild persistent asthma. After baseline assessments, salbutamol was prescribed to 30 patients and levosalbutamol to another 30 for 4 weeks. The efficacy variables were change in asthma symptom scoring, pulmonary function test, and Mini Asthma Quality of Life Questionnaire (MiniAQLQ) scoring. At follow-up, the patients were re-evaluated and analyzed by statistical tools. Results: Shortness of breath (P<0.001), chest tightness (P=0.033), wheeze (P=0.01), cough (P=0.024), and overall asthma symptom score (P<0.001) were significantly decreased in the levosalbutamol group in comparison to the salbutamol group. Results of MiniAQLQ revealed that improvement in symptoms (P=0.018), activity limitations (P=0.03), environmental stimuli (P=0.013)-related scoring and overall MiniAQLQ scoring (P<0.001) was statistically significant in the levosalbutamol group. Percentage reversibility of forced expiratory volume at one second (P=0.034), forced vital capacity (P=0.029), peak expiratory flow rate (P=0.0003) was found to be superior in the levosalbutamol group. Conclusion: Levosalbutamol was found to be superior compared to recemic salbutamol in mild persistent asthma. PMID:22144765

  8. A colorimetric sensor array for the detection of the date-rape drug γ-hydroxybutyric acid (GHB): a supramolecular approach.

    PubMed

    Baumes, Laurent A; Buaki Sogo, Mireia; Montes-Navajas, Pedro; Corma, Avelino; Garcia, Hermenegildo

    2010-04-19

    γ-Hydroxybutyric acid (GHB), a colourless, odourless and tasteless chemical, has become one of the most dangerous illicit drugs of abuse today. At low doses, this drug is a central nervous system depressant that reduces anxiety and produces euphoria and relaxation, sedating the recipient. There is an urgent need for simple, easy-to-use sensors for GHB in solution. Here, we present a colorimetric sensor array based on supramolecular host-guest complexes of fluorescent dyes with organic capsules (cucurbiturils) for the detection of GHB. PMID:20309968

  9. Difference in the dynamic properties of chiral and racemic crystals of serine studied by Raman spectroscopy at 3-295 K.

    PubMed

    Kolesov, B A; Boldyreva, E V

    2007-12-27

    Single-crystal polarized Raman spectra (60-4000 cm(-1) at 3 < or = T < or = 295 K) were measured for chiral L- and racemic DL-serine, alpha-amino-beta-hydroxypropionic acid, (NH3)+CH(CH2OH)(COO)-. The Raman spectra of dl-serine do not show any striking changes with temperature or on storage. In contrast to that, the dynamical properties of L-serine change at about 140 K. These changes can be interpreted as the reorientation of the side chain -CH2OH fragments of the zwitterions with respect to the backbone C-C bonds, resulting in the positional disorder of the O-H...O intermolecular H-bonds. The redistribution in the intensities of the Raman spectra of the crystals of L-serine stored for a long time (about a year) indicates the changes in the orientation of the molecular fragments in the direction normal to the axes of the head-to-tail chains. The difference in the thermodynamic functions of L- and DL-serine reported previously [Drebushchak, V. A.; Kovalevskaya, Yu. A.; Paukov, I. E.; Boldyreva, E. V. J. Therm. Anal. Calorim. 2007, 89 (2), 649-654] is explained by the difference in the spectra of external vibrations of the crystals. PMID:18052147

  10. 40 CFR 62.3652 - Effective date.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Indiana Metals, Acid Gases, Organic Compounds and Nitrogen Oxide Emissions from Existing Municipal Waste Combustors with the Capacity to Combust Greater Than 250 Tons Per Day of Municipal Solid Waste § 62.3652 Effective date. The effective date...

  11. 40 CFR 62.3652 - Effective date.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Indiana Metals, Acid Gases, Organic Compounds and Nitrogen Oxide Emissions from Existing Municipal Waste Combustors with the Capacity to Combust Greater Than 250 Tons Per Day of Municipal Solid Waste § 62.3652 Effective date. The effective date...

  12. 40 CFR 62.3652 - Effective date.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Indiana Metals, Acid Gases, Organic Compounds and Nitrogen Oxide Emissions from Existing Municipal Waste Combustors with the Capacity to Combust Greater Than 250 Tons Per Day of Municipal Solid Waste § 62.3652 Effective date. The effective date...

  13. 40 CFR 62.3652 - Effective date.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Indiana Metals, Acid Gases, Organic Compounds and Nitrogen Oxide Emissions from Existing Municipal Waste Combustors with the Capacity to Combust Greater Than 250 Tons Per Day of Municipal Solid Waste § 62.3652 Effective date. The effective date...

  14. 40 CFR 62.3652 - Effective date.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Indiana Metals, Acid Gases, Organic Compounds and Nitrogen Oxide Emissions from Existing Municipal Waste Combustors with the Capacity to Combust Greater Than 250 Tons Per Day of Municipal Solid Waste § 62.3652 Effective date. The effective date...

  15. 40 CFR 62.3632 - Effective date.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Indiana Landfill Gas Emissions from Existing Municipal Solid Waste Landfills § 62.3632 Effective date. The effective date of the plan for municipal solid waste landfills is May 30, 2000. Metals, Acid Gases, Organic Compounds and Nitrogen...

  16. 40 CFR 62.3632 - Effective date.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Indiana Landfill Gas Emissions from Existing Municipal Solid Waste Landfills § 62.3632 Effective date. The effective date of the plan for municipal solid waste landfills is May 30, 2000. Metals, Acid Gases, Organic Compounds and Nitrogen...

  17. 40 CFR 62.9637 - Effective date.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Pennsylvania Landfill Gas Emissions from Existing Municipal Solid Waste Landfills (section 111(d) Plan) § 62.9637 Effective date. The effective date of the plan for municipal solid waste landfills is January 28, 2004. Metals, Acid Gases,...

  18. 40 CFR 62.9637 - Effective date.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Pennsylvania Landfill Gas Emissions from Existing Municipal Solid Waste Landfills (section 111(d) Plan) § 62.9637 Effective date. The effective date of the plan for municipal solid waste landfills is January 28, 2004. Metals, Acid Gases,...

  19. 40 CFR 62.3632 - Effective date.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Indiana Landfill Gas Emissions from Existing Municipal Solid Waste Landfills § 62.3632 Effective date. The effective date of the plan for municipal solid waste landfills is May 30, 2000. Metals, Acid Gases, Organic Compounds and Nitrogen...

  20. 40 CFR 62.3632 - Effective date.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Indiana Landfill Gas Emissions from Existing Municipal Solid Waste Landfills § 62.3632 Effective date. The effective date of the plan for municipal solid waste landfills is May 30, 2000. Metals, Acid Gases, Organic Compounds and Nitrogen...

  1. 40 CFR 62.3632 - Effective date.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Indiana Landfill Gas Emissions from Existing Municipal Solid Waste Landfills § 62.3632 Effective date. The effective date of the plan for municipal solid waste landfills is May 30, 2000. Metals, Acid Gases, Organic Compounds and Nitrogen...

  2. Pharmacokinetics and extrapulmonary beta 2 adrenoceptor activity of nebulised racemic salbutamol and its R and S isomers in healthy volunteers

    PubMed Central

    Lipworth, B. J.; Clark, D. J.; Koch, P.; Arbeeny, C.

    1997-01-01

    BACKGROUND: Racemic salbutamol remains one of the most commonly used bronchodilators in the treatment of reversible airways obstruction. Data from animal and human studies suggest that the S-isomer, whilst contributing no bronchodilator activity, may induce increased bronchial hyperreactivity and may explain the adverse effects of regular racemic salbutamol on asthmatic disease control. The purpose of this study was to evaluate the dose-response effects of racemic (+/-) salbutamol and its R(-) and S(+) isomers in terms of pharmacokinetics and pharmacodynamics at extrapulmonary beta 2 adrenoceptors when given by the inhaled route to healthy volunteers. METHODS: Twelve healthy volunteers of mean age 20.6 years were studied in a double blind, placebo controlled, crossover design comparing cumulative doubling doses of nebulised R-salbutamol (R) and S-salbutamol (S) isomers (200 micrograms/400 micrograms/800 micrograms/1600 micrograms/3200 micrograms) and racemic salbutamol (RS) (400 micrograms/800 micrograms/1600 micrograms/3200 micrograms/6400 micrograms). Doses were administered at 20 minute intervals (t0/t20/t40/t60/t80) and measurements were made of extrapulmonary beta 2 responses as an increase in finger tremor and heart rate and fall in plasma potassium at baseline and each dose level (t0/t20/t40/t60/t80/t100). Plasma levels of salbutamol were measured at 15 minutes after each dose with a further sample at 30 minutes after the last dose (t110). RESULTS: Pharmacodynamics showed dose related beta 2 responses for R-salbutamol and RS-salbutamol but not for the S isomer, and a plateau in response was not reached within the administered dose range. No differences in responses were found between R-salbutamol and RS-salbutamol when compared on a 1:2 microgram basis. The effects of the S isomer were indistinguishable from those of placebo. For all beta 2 responses there were differences between R-salbutamol and S-salbutamol (for t100 response as change from placebo

  3. [Preparation of L-phenylalanine chiral ligand-exchange chromatographic stationary phase by atom transfer radical polymerization and resolution of racemates].

    PubMed

    Sun, Yang; Xu, Fei; Gong, Bolin

    2011-09-01

    A novel stationary phase was synthesized for chiral ligand-exchange chromatography via atom transfer radical polymerization (ATRP). Glycidyl methacrylate (GMA) was grafted onto the surface of the silica by ATRP using bromoisobutyryl bromide as an initiator, and the organic metal compound formed in the CuCl/2,2'-bipyridine(Bpy) system as a catalyst at room temperature. The chiral stationary phase was then synthesized by grafting L-phenylalanine on the surface of the silica. The stationary phase was characterized by means of elementary analysis and evaluated in detail to determine its separability. The amount of L-phenylalanine on the surface of silica was calculated to be 4.32 mg/m2. The results showed that the good enantioseparations of some DL-amino acids were obtained using ligand-exchange chromatography on the synthesized chiral stationary phase (50 degrees C) with 0.05 mol/L KH2PO4 and 0.1 mmol/L Cu(Ac)2 solution (pH 4.5) as the mobile phase at a flow rate of 1.0 mL/min and a wavelength of 223 nm. The influences of the mobile phase pH, concentration of Cu (II), and temperature of column on the resolution of DL-amino acids by ligand-exchange chromatography were investigated. The results showed that these conditions could affect the resolution of racemates. Compared with the column prepared by radical method using L-phenylalanine directly bonded onto the surface of the silica, the synthesized stationary phase showed a better separation ability, and the DL-aspartic acids and DL-asparagines could be separated at baseline.

  4. Food Product Dating

    MedlinePlus

    ... Formula What do can codes mean? Dates on Egg Cartons UPC or Bar Codes Storage Times Refrigerator ... primarily on perishable foods such as meat, poultry, eggs and dairy products. "Closed" or "coded" dating might ...

  5. Highly enantioselective esterification of racemic ibuprofen in a packed bed reactor using immobilised Rhizomucor miehei lipase.

    PubMed

    Sánchez; Valero; Lafuente; Solà

    2000-07-01

    A systematic study of the enantioselective resolution of ibuprofen by commercial Rhizomucor miehei lipase (Lipozyme(R) IM20) has been carried out using isooctane as solvent and butanol as esterificating agent. The main variables controlling the process (temperature, ibuprofen concentration, ratio butanol:ibuprofen) have been studied using an orthogonal full factorial experimental design, in which the selected objective function was enantioselectivity. This strategy has resulted in a polynomial function that describes the process. By optimizing this function, optimal conditions for carrying out the esterification of racemic ibuprofen have been determined. Under these conditions, enantiomeric excess and total conversion values were 93.8% and 49.9%, respectively, and the enantioselectivity was 113 after 112 h of reaction. These conditions have been considered in the design of a continuous reactor to scale up the process. The esterification of ibuprofen was properly described by pseudo first-order kinetics. Thus, a packed bed reactor operating as a plug-flow reactor (PFR) is the most appropriate in terms of minimizing the residence time compared with a continuous stirred tank reactor (CSTR) to achieve the same final conversion. This reactor shows a similar behavior in terms of enantioselectivity, enantiomeric excess, and conversion when compared with batch reactors. A residence-time distribution (RTD) shows that the flow model is essentially a plug flow with a slight nonsymmetrical axial dispersion (Peclet number = 43), which was also corroborated by the model of CSTR in series. The stability of the system (up to 100 h) and the possibility of reutilization of the enzyme (up to four times) lead to consider this reactor as a suitable configuration for scale up of the process.

  6. Radiometric Dating Does Work!

    ERIC Educational Resources Information Center

    Dalrymple, G. Brent

    2000-01-01

    Discusses the accuracy of dating methods and creationist arguments that radiometric dating does not work. Explains the Manson meteorite impact and the Pierre shale, the ages of meteorites, the K-T tektites, and dating the Mount Vesuvius eruption. (Author/YDS)

  7. Chiral fluorinated α-sulfonyl carbanions: enantioselective synthesis and electrophilic capture, racemization dynamics, and structure.

    PubMed

    Hellmann, Gunther; Hack, Achim; Thiemermann, Eric; Luche, Olaf; Raabe, Gerhard; Gais, Hans-Joachim

    2013-03-18

    Enantiomerically pure triflones R(1) CH(R(2) )SO2 CF3 have been synthesized starting from the corresponding chiral alcohols via thiols and trifluoromethylsulfanes. Key steps of the syntheses of the sulfanes are the photochemical trifluoromethylation of the thiols with CF3 Hal (Hal=halide) or substitution of alkoxyphosphinediamines with CF3 SSCF3 . The deprotonation of RCH(Me)SO2 CF3 (R=CH2 Ph, iHex) with nBuLi with the formation of salts [RC(Me)SO2 CF3 ]Li and their electrophilic capture both occurred with high enantioselectivities. Displacement of the SO2 CF3 group of (S)-MeOCH2 C(Me)(CH2 Ph)SO2 CF3 (95 % ee) by an ethyl group through the reaction with AlEt3 gave alkane MeOCH2 C(Me)(CH2 Ph)Et of 96 % ee. Racemization of salts [R(1) C(R(2) )SO2 CF3 ]Li follows first-order kinetics and is mainly an enthalpic process with small negative activation entropy as revealed by polarimetry and dynamic NMR (DNMR) spectroscopy. This is in accordance with a Cα S bond rotation as the rate-determining step. Lithium α-(S)-trifluoromethyl- and α-(S)-nonafluorobutylsulfonyl carbanion salts have a much higher racemization barrier than the corresponding α-(S)-tert-butylsulfonyl carbanion salts. Whereas [PhCH2 C(Me)SO2 tBu]Li/DMPU (DMPU = dimethylpropylurea) has a half-life of racemization at -105 °C of 2.4 h, that of [PhCH2 C(Me)SO2 CF3 ]Li at -78 °C is 30 d. DNMR spectroscopy of amides (PhCH2 )2 NSO2 CF3 and (PhCH2 )N(Ph)SO2 CF3 gave NS rotational barriers that seem to be distinctly higher than those of nonfluorinated sulfonamides. NMR spectroscopy of [PhCH2 C(Ph)SO2 R]M (M=Li, K, NBu4 ; R=CF3 , tBu) shows for both salts a confinement of the negative charge mainly to the Cα atom and a significant benzylic stabilization that is weaker in the trifluoromethylsulfonyl carbanion. According to crystal structure analyses, the carbanions of salts {[PhCH2 C(Ph)SO2 CF3 ]Li⋅L}2 (L=2 THF, tetramethylethylenediamine (TMEDA)) and [PhCH2 C(Ph)SO2 CF3 ]NBu4 have

  8. Mass spectrometric detection and formation of D-amino acids in processed plant saps, syrups, and fruit juice concentrates.

    PubMed

    Pätzold, Ralf; Brückner, Hans

    2005-12-14

    Liquid and syrupy dietary saps and juices of plant origin, characterized by the presence of large quantities of saccharides (glucose, fructose, or sucrose) and containing amino acids, were analyzed for the presence of D-amino acids using enantioselective gas chromatography-mass spectrometry. D-amino acids were detected in processed saps and juices of trees (maple, palm, birch), fruits (grape, apple, pear, pomegranate, date), and various other plants (agave, beetroot, sugar cane, carob). D-Ala was detected in all plant products and amounted to approximately 34% D-Ala (relative to L-Ala + D-Ala) in Canadian maple syrups, to approximately 13% in palm saps, and to 48 and 13% D-Ala, respectively, in concentrated grape juices (Spanish Arrope and Turkish Pekmez). Varying amounts and kinds of other D-amino acids were also detected. To test the hypothesis that racemization, that is, partial conversion of L-amino acids into their corresponding D-enantiomers, occurs at reversible stages of the Maillard reaction, the Amadori compound fructose-L-phenylalanine was synthesized. On heating at 200 degrees C for 5 (20) min, release of 10.8% (24.2%) D-Phe was detected. From the data it is concluded that the Amadori compounds formed in the course of the Maillard reaction are pecursors of D-amino acids in foodstuffs.

  9. Total syntheses of cis-cyclopropane fatty acids: dihydromalvalic acid, dihydrosterculic acid, lactobacillic acid, and 9,10-methylenehexadecanoic acid.

    PubMed

    Shah, Sayali; White, Jonathan M; Williams, Spencer J

    2014-12-14

    cis-Cyclopropane fatty acids (cis-CFAs) are widespread constituents of the seed oils of subtropical plants, membrane components of bacteria and protozoa, and the fats and phospholipids of animals. We describe a systematic approach to the synthesis of enantiomeric pairs of four cis-CFAs: cis-9,10-methylenehexadecanoic acid, lactobacillic acid, dihydromalvalic acid, and dihydrosterculic acid. The approach commences with Rh2(OAc)4-catalyzed cyclopropenation of 1-octyne and 1-decyne, and hinges on the preparative scale chromatographic resolution of racemic 2-alkylcycloprop-2-ene-1-carboxylic acids using a homochiral Evan's auxiliary. Saturation of the individual diastereomeric N-cycloprop-2-ene-1-carbonylacyloxazolidines, followed by elaboration to alkylcyclopropylmethylsulfones, allowed Julia-Kocienski olefination with various ω-aldehyde-esters. Finally, saponification and diimide reduction afforded the individual cis-CFA enantiomers. PMID:25321346

  10. Experiments on the origins of optical activity. [in amino acids

    NASA Technical Reports Server (NTRS)

    Bonner, W. A.; Flores, J. J.

    1975-01-01

    An investigation was conducted concerning the asymmetric adsorption of phenylalanine enantiomers by kaolin. No preferential adsorption of either phenylalanine enantiomer could be detected and there was no resolution of the racemic phenylalanine by kaolin. The attempted asymmetric polymerization of aspartic acid by kaolin is also discussed along with a strontium-90 bremsstrahlung radiolysis of leucine.

  11. Synthesis and evaluation of the racemate and individual enantiomers of C-11 labeled methylphenidate as radioligands for the presynaptic dopaminergic neuron

    SciTech Connect

    Ding, Y.S.; Fowler, J.S.; Volkow, N.D.

    1994-05-01

    Methylphenidate (MP, ritalin) is a psychostimulant drug widely used to treat attention deficit hyperactivity disorder and narcolepsy. Its therapeutic properties are attributed to inhibition of the dopamine (DA) transporter enhancing synaptic DA. MP has two chiral centers and is marketed as the dl-threo racemic form. However, its pharmacological activity is believed due solely to the d-enantiomer. We have synthesized [{sup 11}C]d,l-threo-methylphenidate ([{sup 11}C]MP) in order to examine its pharmacokinetics in vivo and to examine its suitability as a radioligand for PET studies of the presynaptic DA neuron. [{sup 11}C]MP was prepared by O-{sup 11}C-alkylation of a protected derivative of ritalinic acid with labeled methyl iodide. Serial studies at baseline and after treatment with methylphenidate (0.5 mg/kg, 20 min prior); GBR 12909 (1.5 mg/kg; 30 min prior); tomoxetine (1.5 mg/kg, 20 min prior) and citalopram (2.0 mg/kg, 30 min prior) were performed to assess non-specific binding and binding to the DA, norepinephrine and serotonin transporters respectively. Only MP and GBR 12909 changed the SR/CB distribution volume ratio (decrease of 38 and 37% respectively) demonstrating selectivity for DA transporters over other monoamine transporters. We then pursued the synthesis of enantiomerically pure C-{sup 11} labeled d- and l-MP by using enantiomerically pure protected d- and l-ritalinic acids as precursors. A striking difference in SR/CB ratio (3.3 and 1.1 for d- and l-respectively at 1 hr. after i.v. injections) strongly suggests that the pharmacological specificity of MP resides entirely in the d-isomer and the binding of l-isomer was mostly non-specific. Further evaluations are underway. Radioligand reversibility, selectivity and the fact that MP is an approved drug are advantages of using [{sup 11}C]MP.

  12. Distribution and enantiomeric composition of amino acids in the Murchison meteorite

    NASA Technical Reports Server (NTRS)

    Engel, M. H.; Nagy, B.

    1982-01-01

    Studies of the amino acid contents and enantiomeric compositions of a single stone from the Murchison meteorite are reported. Water-extracted and 6M HCl-extracted samples from the meteorite interior of meteorite fragments were analyzed by gas chromatography and combined gas chromatography-chemical ionization mass spectrometry. Examination of the D/L ratios of glutamic acid, aspartic acid, proline, leucine and alanine reveals those amino acids extractable by water to be partially racemized, whereas the acid-extracted amino acids were less racemized. The amino acid composition of the stone is similar to those previously reported, including the absence of serine, threonine, tyrosine phenylalanine and methionine and the presence of unusual amino acids including such as isovaline, alpha-aminoisobutyric acid and pseudoleucine. It is concluded that the most likely mechanism accounting for the occurrence of nonracemic amino acid mixtures in the Murchison meteorite is by extraterrestrial stereoselective synthesis or decomposition reactions.

  13. Enantioselective esterification of racemic ibuprofen in isooctane by immobilized lipase on cellulose acetate-titanium iso-propoxide gel fiber.

    PubMed

    Ikeda, Yuko; Kurokawa, Youichi

    2002-01-01

    Lipase (Candida rugosa) was entrap-immobilized on cellulose acetate-titanium iso-propoxide gel fiber by the sol-gel method. The immobilized lipase was used for the direct synthesis of (S)-ibuprofen ester from racemic ibuprofen using propyl alcohol as an acyl acceptor in isooctane. The activity of the immobilized lipase was decreased to about 10-20% that of native lipase. However, the reaction was more enantioselective compared to that with native lipase. The stability for repeated use was improved by immobilization.

  14. Copper-catalysed asymmetric allylic alkylation of alkylzirconocenes to racemic 3,6-dihydro-2H-pyrans

    PubMed Central

    Rideau, Emeline

    2015-01-01

    Summary Asymmetric allylic alkylation is a powerful reaction that allows the enantioselective formation of C–C bonds. Here we describe the asymmetric alkylation of alkylzirconium species to racemic 3,6-dihydro-2H-pyrans. Two systems were examined: 3-chloro-3,6-dihydro-2H-pyran using linear optimization (45–93% ee, up to 33% yield, 5 examples) and 3,6-dihydro-2H-pyran-3-yl diethyl phosphate with the assistance of a design of experiments statistical approach (83% ee, 12% yield). 1H NMR spectroscopy was used to gain insight into the reaction mechanisms. PMID:26734091

  15. Tuning of the electronic properties of a cyclopentadienylruthenium catalyst to match racemization of electron-rich and electron-deficient alcohols.

    PubMed

    Verho, Oscar; Johnston, Eric V; Karlsson, Erik; Bäckvall, Jan-E

    2011-09-26

    The synthesis of a new series of cyclopentadienylruthenium catalysts with varying electronic properties and their application in racemization of secondary alcohols are described. These racemizations involve two key steps: 1) β-hydride elimination (dehydrogenation) and 2) re-addition of the hydride to the intermediate ketone. The results obtained confirm our previous theory that the electronic properties of the substrate determine which of these two steps is rate determining. For an electron-deficient alcohol the rate-determining step is the β-hydride elimination (dehydrogenation), whereas for an electron-rich alcohol the re-addition of the hydride becomes the rate-determining step. By matching the electronic properties of the catalyst with the electronic properties of the alcohol, we have now shown that a dramatic increase in racemization rate can be obtained. For example, electron-deficient alcohol 15 racemized 30 times faster with electron-deficient catalyst 6 than with the unmodified standard catalyst 4. The application of these protocols will extend the scope of cyclopentadienylruthenium catalysts in racemization and dynamic kinetic resolution. PMID:21882268

  16. Differential Influences of Ethanol on Early Exposure to Racemic Methylphenidate Compared with Dexmethylphenidate in Humans

    PubMed Central

    Straughn, Arthur B.; Reeves, Owen T.; Bernstein, Hilary; Bell, Guinevere H.; Anderson, Erica R.; Malcolm, Robert J.

    2013-01-01

    Enantioselective hydrolysis of oral racemic methylphenidate (dl-MPH) by carboxylesterase 1 (CES1) limits the absolute bioavailability of the pharmacologically active d-MPH isomer to approximately 30% and that of the inactive l-MPH to only 1–2%. Coadministration of dl-MPH with ethanol results in elevated d-MPH plasma concentrations accompanied by CES1-mediated enantioselective transesterification of l-MPH to l-ethylphenidate (EPH). The present study tested the hypothesis that administration of the pure isomer dexmethylphenidate (d-MPH) will overcome the influence of ethanol on d-MPH absorption by eliminating competitive CES1-mediated presystemic metabolism of l-MPH to l-EPH. Twenty-four healthy volunteers received dl-MPH (0.3 mg/kg) or d-MPH (0.15 mg/kg), with or without ethanol (0.6 g/kg). During the absorption phase of dl-MPH, concomitant ethanol significantly elevated d-MPH plasma concentrations (44–99%; P < 0.005). Furthermore, immediately following the ethanol drink the subjective effects of “high,” “good,” “like,” “stimulated,” and overall “effect” were significantly potentiated (P ≤ 0.01). Plasma l-EPH concentrations exceeded those of l-MPH. Ethanol combined with pure d-MPH did not elevate plasma d-MPH concentrations during the absorption phase, and the ethanol-induced potentiation of subjective effects was delayed relative to dl-MPH-ethanol. These findings are consistent with l-MPH competitively inhibiting presystemic CES1 metabolism of d-MPH. Ethanol increased the d-MPH area under the curve (AUC)0-inf by 21% following dl-MPH (P < 0.001) and 14% for d-MPH (P = 0.001). In men receiving d-MPH-ethanol, the d-MPH absorption partial AUC0.5–2 hours was 2.1 times greater and the time to maximum concentration (Tmax) occurred 1.1 hours earlier than in women, consistent with an increased rate of d-MPH absorption reducing hepatic extraction. More rapid absorption of d-MPH carries implications for increased abuse liability. PMID:23104969

  17. Racemic ketamine in adult head injury patients: use in endotracheal suctioning

    PubMed Central

    2013-01-01

    Introduction Endotracheal suctioning (ETS) is essential for patient care in an ICU but may represent a cause of cerebral secondary injury. Ketamine has been historically contraindicated for its use in head injury patients, since an increase of intracranial pressure (ICP) was reported; nevertheless, its use was recently suggested in neurosurgical patients. In this prospective observational study we investigated the effect of ETS on ICP, cerebral perfusion pressure (CPP), jugular oxygen saturation (SjO2) and cerebral blood flow velocity (mVMCA) before and after the administration of ketamine. Methods In the control phase, ETS was performed on patients sedated with propofol and remifentanil in continuous infusion. If a cough was present, patients were assigned to the intervention phase, and 100 γ/kg/min of racemic ketamine for 10 minutes was added before ETS. Results In the control group ETS stimulated the cough reflex, with a median cough score of 2 (interquartile range (IQR) 1 to 2). Furthermore, it caused an increase in mean arterial pressure (MAP) (from 89.0 ± 11.6 to 96.4 ± 13.1 mmHg; P <0.001), ICP (from 11.0 ± 6.7 to 18.5 ± 8.9 mmHg; P <0.001), SjO2 (from 82.3 ± 7.5 to 89.1 ± 5.4; P = 0.01) and mVMCA (from 76.8 ± 20.4 to 90.2 ± 30.2 cm/sec; P = 0.04). CPP did not vary with ETS. In the intervention group, no significant variation of MAP, CPP, mVMCA, and SjO2 were observed in any step; after ETS, ICP increased if compared with baseline (15.1 ± 9.4 vs. 11.0 ± 6.4 mmHg; P <0.05). Cough score was significantly reduced in comparison with controls (P <0.0001). Conclusions Ketamine did not induce any significant variation in cerebral and systemic parameters. After ETS, it maintained cerebral hemodynamics without changes in CPP, mVMCA and SjO2, and prevented cough reflex. Nevertheless, ketamine was not completely effective when used to control ICP increase after administration of 100 γ/kg/min for 10

  18. Dating the Crucifixion

    NASA Astrophysics Data System (ADS)

    Humphreys, Colin J.; Waddington, W. G.

    1983-12-01

    The date of the Crucifixion has been debated for many years, but there has been no agreement on the year nor the day. Astronomical calculations have now been used to reconstruct the Jewish calendar in the first century AD and to date a lunar eclipse that biblical and other references suggest followed the Crucifixion. The evidence points to Friday 3 April AD 33 as the date when Jesus Christ died.

  19. Enantioselective Pharmacokinetics of α-Lipoic Acid in Rats.

    PubMed

    Uchida, Ryota; Okamoto, Hinako; Ikuta, Naoko; Terao, Keiji; Hirota, Takashi

    2015-09-21

    α-Lipoic acid (LA) is widely used for nutritional supplements as a racemic mixture, even though the R enantiomer is biologically active. After oral administration of the racemic mixture (R-α-lipoic acid (RLA) and S-α-lipoic acid (SLA) mixed at the ratio of 50:50) to rats, RLA showed higher plasma concentration than SLA, and its area under the plasma concentration-time curve from time zero to the last (AUC) was significantly about 1.26 times higher than that of SLA. However, after intravenous administration of the racemic mixture, the pharmacokinetic profiles, initial concentration (C₀), AUC, and half-life (T1/2) of the enantiomers were not significantly different. After oral and intraduodenal administration of the racemic mixture to pyrolus-ligated rats, the AUCs of RLA were significantly about 1.24 and 1.32 times higher than that of SLA, respectively. In addition, after intraportal administration the AUC of RLA was significantly 1.16 times higher than that of SLA. In conclusion, the enantioselective pharmacokinetics of LA in rats arose from the fraction absorbed multiplied by gastrointestinal availability (FaFg) and hepatic availability (Fh), and not from the total clearance.

  20. Enantioselective Pharmacokinetics of α-Lipoic Acid in Rats

    PubMed Central

    Uchida, Ryota; Okamoto, Hinako; Ikuta, Naoko; Terao, Keiji; Hirota, Takashi

    2015-01-01

    α-Lipoic acid (LA) is widely used for nutritional supplements as a racemic mixture, even though the R enantiomer is biologically active. After oral administration of the racemic mixture (R-α-lipoic acid (RLA) and S-α-lipoic acid (SLA) mixed at the ratio of 50:50) to rats, RLA showed higher plasma concentration than SLA, and its area under the plasma concentration-time curve from time zero to the last (AUC) was significantly about 1.26 times higher than that of SLA. However, after intravenous administration of the racemic mixture, the pharmacokinetic profiles, initial concentration (C0), AUC, and half-life (T1/2) of the enantiomers were not significantly different. After oral and intraduodenal administration of the racemic mixture to pyrolus-ligated rats, the AUCs of RLA were significantly about 1.24 and 1.32 times higher than that of SLA, respectively. In addition, after intraportal administration the AUC of RLA was significantly 1.16 times higher than that of SLA. In conclusion, the enantioselective pharmacokinetics of LA in rats arose from the fraction absorbed multiplied by gastrointestinal availability (FaFg) and hepatic availability (Fh), and not from the total clearance. PMID:26402669

  1. Choosing a Calving Date

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Calving date affects cost and timing of production events. Due to the polyestrous nature of beef females, producers can choose a calving date that fits their production system and geographic region. Any time an entire production system is considered, decision making becomes complex. Any calving syst...

  2. Pests of stored dates

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Dates are a major food crop across a large band of Africa and Eurasia, and to a lesser extent elsewhere. In most of its growing range, dates are threatened with infestation in the field by a complex of pests including nitidulid beetles and pyralid moths of the Subfamily Phycitinae. They are further ...

  3. Radiometric Dating in Geology.

    ERIC Educational Resources Information Center

    Pankhurst, R. J.

    1980-01-01

    Described are several aspects and methods of quantitatively measuring geologic time using a constant-rate natural process of radioactive decay. Topics include half lives and decay constants, radiogenic growth, potassium-argon dating, rubidium-strontium dating, and the role of geochronology in support of geological exploration. (DS)

  4. Date Palm Germplasm

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This book chapter reviews date palm genetic resources and their conservation. Date palm (Phoenix dactylifera) is an important food crop in the Middle East and North Africa. Its center of origin and diversity most probably is the area near Iraq/Iran. From there, it spread throughout its present range...

  5. Racemic ketamine in comparison to S-ketamine in combination with azaperone and butorphanol for castration of pigs.

    PubMed

    Bettschart-Wolfensberger, R; Stauffer, S; Hässig, M; Flaherty, D; Ringer, S K

    2013-12-01

    In this prospective blinded randomised study, 28 male 9 week old pigs of bodyweight 25 kg, were anaesthetised for castration using 5 mg/kg azaperone, 0.2 mg/kg butorphanol and 0.4 mg/kg meloxicam, in conjunction with either 15 mg/kg racemic ketamine (Keta-Race) or 9 mg/kg S-ketamine (S-Keta), all drugs being injected intramuscularly. Anaesthesia induction, maintenance and recovery were timed and scored. Insufficient anaesthesia was supplemented with ¼ the initial dose of ketamine or S-ketamine, respectively, administered intravenously. A t-test was utilised for analysis of timings, and, for repeated recovery time data, ANOVA was used. In relation to quantification and timing of supplemental drug doses, a chi square test was used and the scoring was analysed by two sample Wilcoxon rank-sum test. Ketamine re-dosing was required in 23 animals on a total of 46 occasions distributed evenly throughout both groups. The only group differences occurred during recovery, with the S-Keta group showing earlier movements, sternal recumbency and ability to stand. Three pigs in each group showed muscle fasciculations during the recovery period, while an additional two animals of the Keta-Race group exhibited marked and unacceptable paddling in recovery. In conclusion, S-ketamine at a dose rate of 60 % of that of racemic ketamine induced comparable anaesthesia for castration in pigs, but with superior recovery characteristics.

  6. D:L-AMINO Acids and the Turnover of Microbial Biomass

    NASA Astrophysics Data System (ADS)

    Lomstein, B. A.; Braun, S.; Mhatre, S. S.; Jørgensen, B. B.

    2015-12-01

    Decades of ocean drilling have demonstrated wide spread microbial life in deep sub-seafloor sediment, and surprisingly high microbial cell numbers. Despite the ubiquity of life in the deep biosphere, the large community sizes and the low energy fluxes in the vast buried ecosystem are still poorly understood. It is not know whether organisms of the deep biosphere are specifically adapted to extremely low energy fluxes or whether most of the observed cells are in a maintenance state. Recently we developed and applied a new culture independent approach - the D:L-amino acid model - to quantify the turnover times of living microbial biomass, microbial necromass and mean metabolic rates. This approach is based on the built-in molecular clock in amino acids that very slowly undergo chemical racemization until they reach an even mixture of L- and D- forms, unless microorganisms spend energy to keep them in the L-form that dominates in living organisms. The approach combines sensitive analyses of amino acids, the unique bacterial endospore marker (dipicolinic acid) with racemization dynamics of stereo-isomeric amino acids. Based on a heating experiment, we recently reported kinetic parameters for racemization of aspartic acid, glutamic acid, serine and alanine in bulk sediment from Aarhus Bay, Denmark. The obtained racemization rate constants were faster than the racemization rate constants of free amino acids, which we have previously applied in Holocene sediment from Aarhus Bay and in up to 10 mio yr old sediment from ODP Leg 201. Another important input parameter for the D:L-amino acid model is the cellular carbon content. It has recently been suggested that the cellular carbon content most likely is lower than previously thought. In recognition of these new findings, previously published data based on the D:L-amino acid model were recalculated and will be presented together with new data from an Arctic Holocene setting with constant sub-zero temperatures.

  7. Date fruit: chemical composition, nutritional and medicinal values, products.

    PubMed

    Tang, Zhen-Xing; Shi, Lu-E; Aleid, Salah M

    2013-08-15

    Date fruit has served as a staple food in the Arab world for centuries. Worldwide production of date fruit has increased almost threefold over the last 40 years, reaching 7.68 million tons in 2010. Date fruit can provide many essential nutrients and potential health benefits to the consumer. Date fruit goes through four ripening stages named kimri, khalal, rutab and tamer. The main chemical components of date fruit include carbohydrates, dietary fibre, enzymes, protein, fat, minerals, vitamins, phenolic acids and carotenoids. The chemical composition of date fruit varies according to ripening stage, cultivar, growing environment, postharvest conditions, etc. The nutritional and medicinal activities of date fruit are related to its chemical composition. Many studies have shown that date fruit has antioxidant, antimutagenic, anti-inflammatory, gastroprotective, hepatoprotective, nephroprotective, anticancer and immunostimulant activities. Various date fruit-based products such as date syrup, date paste, date juice and their derived products are available. Date by-products can be used as raw materials for the production of value-added products such as organic acids, exopolysaccharides, antibiotics, date-flavoured probiotic-fermented dairy produce, bakery yeasts, etc. In this paper the chemical composition and nutritional and medicinal values of date fruit as well as date fruit-based products are reviewed.

  8. Comparison of chiral separations of aminophosphonic acids and their aminocarboxylic acid analogs using a crown ether column.

    PubMed

    Barnhart, Wesley W; Xia, Xiaoyang; Jensen, Randy; Gahm, Kyung H

    2013-07-01

    Crown ethers are capable of complexing with primary amines and have been utilized in chromatography to separate amino acid racemates. This application has been extended to resolve (1-amino-1-phenylmethyl)phosphonic acid and (1-aminoethyl)phosphonic acid racemates, along with their aminocarboxylic acid analogs (2-phenylglycine and alanine, respectively), via a ChiroSil RCA crown ether based chiral stationary phase. Effects of the organic modifier, temperature, and acid type and concentration on retention and selectivity were also investigated. Trends in retention and selectivity varied between aminophosponic acids and their aminocarboxylic analogs. Computer modeling and (1)H NMR analyses were performed to potentially gain a better understanding of interactions of the aforementioned molecules with the ChiroSil RCA chiral stationary phase. Theoretical predictions of the most stable conformations for (R)- and (S)-enantiomers were compared to elution order; it was found that the elution order agreed with molecular modeling such that the longest retention correlated with the predicted most stable complex between the enantiomer and crown ether. (1)H NMR demonstrated interactions of aminophosphonic and aminocarboxylic racemates with (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid in solution and was utilized to determine enantiomeric excess of (1-amino-1-phenylmethyl)phosphonic acid after its enantioenrichment via crystallization through diastereomeric salt formation with the crown ether followed by filtration. PMID:23703726

  9. Comparison of chiral separations of aminophosphonic acids and their aminocarboxylic acid analogs using a crown ether column.

    PubMed

    Barnhart, Wesley W; Xia, Xiaoyang; Jensen, Randy; Gahm, Kyung H

    2013-07-01

    Crown ethers are capable of complexing with primary amines and have been utilized in chromatography to separate amino acid racemates. This application has been extended to resolve (1-amino-1-phenylmethyl)phosphonic acid and (1-aminoethyl)phosphonic acid racemates, along with their aminocarboxylic acid analogs (2-phenylglycine and alanine, respectively), via a ChiroSil RCA crown ether based chiral stationary phase. Effects of the organic modifier, temperature, and acid type and concentration on retention and selectivity were also investigated. Trends in retention and selectivity varied between aminophosponic acids and their aminocarboxylic analogs. Computer modeling and (1)H NMR analyses were performed to potentially gain a better understanding of interactions of the aforementioned molecules with the ChiroSil RCA chiral stationary phase. Theoretical predictions of the most stable conformations for (R)- and (S)-enantiomers were compared to elution order; it was found that the elution order agreed with molecular modeling such that the longest retention correlated with the predicted most stable complex between the enantiomer and crown ether. (1)H NMR demonstrated interactions of aminophosphonic and aminocarboxylic racemates with (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid in solution and was utilized to determine enantiomeric excess of (1-amino-1-phenylmethyl)phosphonic acid after its enantioenrichment via crystallization through diastereomeric salt formation with the crown ether followed by filtration.

  10. Dating the Vinland Map

    ScienceCinema

    None

    2016-07-12

    Scientists from Brookhaven National Laboratory, the University of Arizona, and the Smithsonian Institution used carbon-dating technology to determine the age of a controversial parchment that might be the first-ever map of North America.

  11. Syntheses, structures and photocatalytic properties of five new praseodymium-antimony oxochlorides: from discrete clusters to 3D inorganic-organic hybrid racemic compounds.

    PubMed

    Zou, Guo-Dong; Wang, Ze-Ping; Song, Ying; Hu, Bing; Huang, Xiao-Ying

    2014-07-14

    Five novel praseodymium-antimony oxochloride (Pr-Sb-O-Cl) cluster-based compounds, namely (2-MepyH)2[Fe(1,10-phen)3]2[Pr4Sb12O18Cl14.6(OH)2.4(Hsal)]·H2O (1), (2-MepyH)2[Fe(1,10-phen)3]4{[Pr4Sb12O18Cl13.5(OH)0.5](bcpb)2[Pr4Sb12O18Cl13.5(OH)0.5]}·42H2O (2), (3-MepyH)2[Fe(1,10-phen)3]{[Pr4Sb12O18Cl13(H2O)2](bcpb)}·2(3-Mepy)·3H2O (3), [Fe(1,10-phen)3]2{[Pr4Sb12O18Cl10(H2O)2](bcpb)2}·3(3-Mepy)·13H2O (4), and (2-MepyH)6[Fe(1,10-phen)3]10{[Pr4Sb12O18Cl13(OH)2]2[Pr4Sb12O18Cl9][Pr4Sb12O18Cl9(OH)2]2(Hpdc)10(pdc)2}·110H2O (5) (2-Mepy = 2-methylpyridine, 3-Mepy = 3-methylpyridine, 1,10-phen = 1,10-phenanthroline, H2sal = salicylic acid, H3bcpb = 3,5-bis(4-carboxyphenoxy)benzoic acid, H3pdc = 3,5-pyrazoledicarboxylic acid) have been solvothermally synthesized and structurally characterized. Compound 1 is the first zero-dimensional (0D) Pr-Sb-O-Cl cluster decorated by an organic ligand. Compounds 2-4 are constructed from the same H3bcpb ligands but adopt different structures: 2 represents a rare example of a one-dimensional (1D) nanotubular structure based on high-nuclearity clusters; 3 exhibits a two-dimensional (2D) mono-layered structure, in which left-handed and right-handed helical chains are alternately arranged, while 4 features a double-layered structure with an unprecedented (3,3,6)-connected 3-nodal topological net. Compound 5 is a unique three-dimensional (3D) 2-fold interpenetrating racemic compound, simultaneously containing three kinds of Pr-Sb-O-Cl-pdc clusters. UV-light photocatalytic H2 evolution activity was observed for compound 3 with Pt as a co-catalyst and MeOH as a sacrificial electron donor. In addition, the magnetic properties of compounds 1 and 5 are also studied.

  12. Syntheses, structures and photocatalytic properties of five new praseodymium-antimony oxochlorides: from discrete clusters to 3D inorganic-organic hybrid racemic compounds.

    PubMed

    Zou, Guo-Dong; Wang, Ze-Ping; Song, Ying; Hu, Bing; Huang, Xiao-Ying

    2014-07-14

    Five novel praseodymium-antimony oxochloride (Pr-Sb-O-Cl) cluster-based compounds, namely (2-MepyH)2[Fe(1,10-phen)3]2[Pr4Sb12O18Cl14.6(OH)2.4(Hsal)]·H2O (1), (2-MepyH)2[Fe(1,10-phen)3]4{[Pr4Sb12O18Cl13.5(OH)0.5](bcpb)2[Pr4Sb12O18Cl13.5(OH)0.5]}·42H2O (2), (3-MepyH)2[Fe(1,10-phen)3]{[Pr4Sb12O18Cl13(H2O)2](bcpb)}·2(3-Mepy)·3H2O (3), [Fe(1,10-phen)3]2{[Pr4Sb12O18Cl10(H2O)2](bcpb)2}·3(3-Mepy)·13H2O (4), and (2-MepyH)6[Fe(1,10-phen)3]10{[Pr4Sb12O18Cl13(OH)2]2[Pr4Sb12O18Cl9][Pr4Sb12O18Cl9(OH)2]2(Hpdc)10(pdc)2}·110H2O (5) (2-Mepy = 2-methylpyridine, 3-Mepy = 3-methylpyridine, 1,10-phen = 1,10-phenanthroline, H2sal = salicylic acid, H3bcpb = 3,5-bis(4-carboxyphenoxy)benzoic acid, H3pdc = 3,5-pyrazoledicarboxylic acid) have been solvothermally synthesized and structurally characterized. Compound 1 is the first zero-dimensional (0D) Pr-Sb-O-Cl cluster decorated by an organic ligand. Compounds 2-4 are constructed from the same H3bcpb ligands but adopt different structures: 2 represents a rare example of a one-dimensional (1D) nanotubular structure based on high-nuclearity clusters; 3 exhibits a two-dimensional (2D) mono-layered structure, in which left-handed and right-handed helical chains are alternately arranged, while 4 features a double-layered structure with an unprecedented (3,3,6)-connected 3-nodal topological net. Compound 5 is a unique three-dimensional (3D) 2-fold interpenetrating racemic compound, simultaneously containing three kinds of Pr-Sb-O-Cl-pdc clusters. UV-light photocatalytic H2 evolution activity was observed for compound 3 with Pt as a co-catalyst and MeOH as a sacrificial electron donor. In addition, the magnetic properties of compounds 1 and 5 are also studied. PMID:24869770

  13. Comparison of uranium-series, radiocarbon, and amino acid data from marine molluscs, Baffin Island, Arctic Canada

    SciTech Connect

    Szabo, B.J.; Miller, G.H.; Andrews, J.T.; Stuiver, M.

    1981-10-01

    Uranium-series and /sup 14/C dates and the extent of amino acid racemization are reported for 24 marine shell samples from three areas of Baffin Island, Arctic Canada. When the radiometric dates are plotted against the ratio of D-alloisoleucene:L-isoleucene in the shells, five broad age groups are recognized. The uranium-series data indicate that /sup 231/Pa is incompletely retained in most fossil shells and that /sup 230/Th is lost from some of the samples. Therefore, their apparent ages are minimum. However, a few dated samples in each group have yielded useful age results, and the minimum ages of the five groups of samples are estimated as 7,000 to 11,000, greater than or equal to70,000, greater than or equal to136,000, greater than or equal to190,000 and >300,000 yr. Calculated integrated thermal histories based on the epimerization reaction in the mollusc Hiatella arctica Linne give paleotemperature estimates of around -5/sup o/C, compared to the present mean annual air temperature of about -11/sup o/C.

  14. Saponification of esters of chiral alpha-amino acids anchored through their amine function on solid support.

    PubMed

    Cantel, Sonia; Desgranges, Stéphane; Martinez, Jean; Fehrentz, Jean-Alain

    2004-06-01

    Anchoring an alpha-amino acid residue by its amine function onto a solid support is an alternative to develop chemistry on its carboxylic function. This strategy can involve the use of amino-acid esters as precursors of the carboxylic function. A complete study on the Wang-resin was performed to determine the non racemizing saponification conditions of anchored alpha-amino esters. The use of LiOH, NaOH, NaOSi(Me)3, various solvents and temperatures were tested for this reaction. After saponification and cleavage from the support, samples were examined through their Marfey's derivatives by reversed phase HPLC to evaluate the percentage of racemization.

  15. The Importance of the 5-Alkyl Substituent for the Violet Smell of Ionones: Synthesis of Racemic 5-Demethyl-α-ionone.

    PubMed

    Chierici, Serena; Bugoni, Serena; Porta, Alessio; Zanoni, Giuseppe; Vidari, Giovanni

    2015-06-01

    The synthesis and the odor tonalities of racemic 5-demethyl-α-ionone are described. This synthetic ionone derivative did not show the typical floral-woody violet smell of α-ionone, definitely proving the importance of a suitably sized and spatially oriented alkyl substituent at C(5) for stimulating olfactory receptors of ionones.

  16. Intermixed adatom and surface-bound adsorbates in regular self-assembled monolayers of racemic 2-butanethiol on Au(111).

    PubMed

    Ouyang, Runhai; Yan, Jiawei; Jensen, Palle S; Ascic, Erhad; Gan, Shiyu; Tanner, David; Mao, Bingwei; Niu, Li; Zhang, Jingdong; Tang, Chunguang; Hush, Noel S; Reimers, Jeffrey R; Ulstrup, Jens

    2015-04-01

    In situ scanning tunneling microscopy combined with density functional theory molecular dynamics simulations reveal a complex structure for the self-assembled monolayer (SAM) of racemic 2-butanethiol on Au(111) in aqueous solution. Six adsorbate molecules occupy a (10×√3)R30° cell organized as two RSAuSR adatom-bound motifs plus two RS species bound directly to face-centered-cubic and hexagonally close-packed sites. This is the first time that these competing head-group arrangements have been observed in the same ordered SAM. Such unusual packing is favored as it facilitates SAMs with anomalously high coverage (30%), much larger than that for enantiomerically resolved 2-butanethiol or secondary-branched butanethiol (25%) and near that for linear-chain 1-butanethiol (33%).

  17. Catalytic Kinetic Resolution of a Dynamic Racemate: Highly Stereoselective β-Lactone Formation by N-Heterocyclic Carbene Catalysis

    PubMed Central

    Johnston, Ryne C.; Cohen, Daniel T.; Eichman, Chad C.

    2014-01-01

    This study describes the combined experimental and computational elucidation of the mechanism and origins of stereoselectivities in the NHC-catalyzed dynamic kinetic resolution (DKR) of α-substituted-β-ketoesters. Density functional theory computations reveal that the NHC-catalyzed DKR proceeds by two mechanisms, depending on the stereochemistry around the forming bond: 1) a concerted, asynchronous formal (2+2) aldol-lactonization process, or 2) a stepwise spiro-lactonization mechanism where the alkoxide is trapped by the NHC-catalyst. These mechanisms contrast significantly from mechanisms found and postulated in other related transformations. Conjugative stabilization of the electrophile and non-classical hydrogen bonds are key in controlling the stereoselectivity. This reaction constitutes an interesting class of DKRs in which the catalyst is responsible for the kinetic resolution to selectively and irreversibly capture an enantiomer of a substrate undergoing rapid racemization with the help of an exogenous base. PMID:25045464

  18. Improved catalytic activity of homochiral dimeric cobalt-salen complex in hydrolytic kinetic resolution of terminal racemic epoxides.

    PubMed

    Kureshy, Rukhsana I; Singh, Surendra; Khan, Noor-Ul H; Abdi, Sayed H R; Ahmad, Irshad; Bhatt, Achyut; Jasra, Raksh V

    2005-11-01

    Enantiomerically pure epoxides (99%, ee) and diols (98%, ee) from racemic epichlorohydrin, 1,2-epoxypropane, 1,2-epoxyhexane, 1,2-epoxyoctane, and 1,2-epoxydodecane were obtained in 2-12 h by hydrolytic kinetic resolution (HKR) using the recyclable dimeric homochiral Co(III)-salen complex 1' (0.2 mol %) derived from 5,5-(2',2'-dimethylpropane)-di-[(R,R)-{N-(3-tert-butylsalicylidine)-N'-(3',5'-di-tert-butylsalicylidine)}-1,2-cyclohexanediamine] with cobalt(II) acetate. Unlike its monomeric version, the catalyst could be recycled several times without loss in performance. The use of BF(4) as counter ion in HKR reactions was also investigated.

  19. Synthesis of racemic and chiral BEDT-TTF derivatives possessing hydroxy groups and their achiral and chiral charge transfer complexes

    PubMed Central

    Krivickas, Sara Jane; Hashimoto, Chiho; Yoshida, Junya; Ueda, Akira; Takahashi, Kazuyuki; Wallis, John D

    2015-01-01

    Summary Chiral molecular crystals built up by chiral molecules without inversion centers have attracted much interest owing to their versatile functionalities related to optical, magnetic, and electrical properties. However, there is a difficulty in chiral crystal growth due to the lack of symmetry. Therefore, we made the molecular design to introduce intermolecular hydrogen bonds in chiral crystals. Racemic and enantiopure bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) derivatives possessing hydroxymethyl groups as the source of hydrogen bonds were designed. The novel racemic trans-vic-(hydroxymethyl)(methyl)-BEDT-TTF 1, and racemic and enantiopure trans-vic-bis(hydroxymethyl)-BEDT-TTF 2 were synthesized. Moreover, the preparations, crystal structure analyses, and electrical resistivity measurements of the novel achiral charge transfer salt θ21-[(S,S)-2]3[(R,R)-2]3(ClO4)2 and the chiral salt α’-[(R,R)-2]ClO4(H2O) were carried out. In the former θ21-[(S,S)-2]3[(R,R)-2]3(ClO4)2, there are two sets of three crystallographically independent donor molecules [(S,S)-2]2[(R,R)-2] in a unit cell, where the two sets are related by an inversion center. The latter α’-[(R,R)-2]ClO4(H2O) is the chiral salt with included solvent H2O, which is not isostructural with the reported chiral salt α’-[(S,S)-2]ClO4 without H2O, but has a similar donor arrangement. According to the molecular design by introduction of hydroxy groups and a ClO4 − anion, many intermediate-strength intermolecular hydrogen bonds (2.6–3.0 Å) were observed in these crystals between electron donor molecules, anions, and included H2O solvent, which improve the crystallinity and facilitate the extraction of physical properties. Both salts are semiconductors with relatively low resistivities at room temperature and activation energies of 1.2 ohm cm with E a = 86 meV for θ21-[(S,S)-2]3[(R,R)-2]3(ClO4)2 and 0.6 ohm cm with E a = 140 meV for α'-[(R,R)-2]2ClO4(H2O), respectively. The variety of donor

  20. (±)-Pestalachloride D, an Antibacterial Racemate of Chlorinated Benzophenone Derivative from a Soft Coral-Derived Fungus Pestalotiopsis sp

    PubMed Central

    Wei, Mei-Yan; Li, Dan; Shao, Chang-Lun; Deng, Dong-Sheng; Wang, Chang-Yun

    2013-01-01

    A new antibacterial chlorinated benzophenone derivative, (±)-pestalachloride D (1), along with a related analog, (±)-pestalachloride C (2), was recently isolated from the marine-derived fungus Pestalotiopsis sp. isolated from a soft coral Sarcophyton sp. collected from Yongxing Island in the South China Sea. Both chiral HPLC analysis and single-crystal X-ray data indicated that 1 is a racemic mixture. Interestingly, 1 did not exhibit any effect in the zebrafish embryo teratogenicity assay, while 2 led to abnormal growth. The potential impact on zebrafish embryo growth is discussed based on their crystal structures. The main difference of crystal structures between 1 and 2 is that the six-member non-aromatic ring (O4, C10, C9, C8, C2′, and C3′) in 1 exhibits a distorted chair conformation, while 2 shows a distorted boat conformation. Moreover, compounds 1 and 2 both exhibited moderate antibacterial activity. PMID:23538869

  1. Selective preparation of enantiomers from a racemate by laser pulses: model simulation for oriented atropisomers with coupled rotations and torsions

    NASA Astrophysics Data System (ADS)

    Hoki, K.; Kröner, D.; Manz, J.

    2001-06-01

    We design a laser pulse which drives a racemate of oriented atropisomers at low temperature to a preferential target enantiomer. The overall laser pulse consists of a series of individual circularly polarized laser pulses which induce corresponding selective transitions between coupled rotational and torsional states. The underlying theory is derived in detail for a model system. It consists of two fragments which may carry out torsional and rotational motions around a molecular bond which is oriented along the direction of the laser pulses. Exemplarily, results are demonstrated for the model system H 2POSH in the electronic ground state, based on a quantum chemical ab initio potential and on the components of the dipole functions describing the laser-dipole interaction. The series of laser pulses for the preparation of the pure enantiomers for this demanding system is based on analogous results for simpler scenarios, originally starting from local control.

  2. (±)-Pestalachloride D, an antibacterial racemate of chlorinated benzophenone derivative from a soft coral-derived fungus Pestalotiopsis sp.

    PubMed

    Wei, Mei-Yan; Li, Dan; Shao, Chang-Lun; Deng, Dong-Sheng; Wang, Chang-Yun

    2013-04-01

    A new antibacterial chlorinated benzophenone derivative, (±)-pestalachloride D (1), along with a related analog, (±)-pestalachloride C (2), was recently isolated from the marine-derived fungus Pestalotiopsis sp. isolated from a soft coral Sarcophyton sp. collected from Yongxing Island in the South China Sea. Both chiral HPLC analysis and single-crystal X-ray data indicated that 1 is a racemic mixture. Interestingly, 1 did not exhibit any effect in the zebrafish embryo teratogenicity assay, while 2 led to abnormal growth. The potential impact on zebrafish embryo growth is discussed based on their crystal structures. The main difference of crystal structures between 1 and 2 is that the six-member non-aromatic ring (O4, C10, C9, C8, C2', and C3') in 1 exhibits a distorted chair conformation, while 2 shows a distorted boat conformation. Moreover, compounds 1 and 2 both exhibited moderate antibacterial activity.

  3. Biocatalytic resolution of enantiomeric mixtures of 1-aminoethanephosphonic acid.

    PubMed

    Brzezińska-Rodak, Małgorzata; Klimek-Ochab, Magdalena; Zymańczyk-Duda, Ewa; Kafarski, Paweł

    2011-07-14

    Several fungal strains, namely Bauveria bassiana, Cuninghamella echinulata, Aspergillus fumigatus, Penicillium crustosum and Cladosporium herbarum, were used as biocatalysts to resolve racemic mixtures of 1-aminoethanephosphonic acid using L/D amino acid oxidase activity. The course of reaction was analyzed by 31P-NMR in the presence of cyclodextrin used as chiral discriminating agent. The best result (42% e.e of R-isomer) was obtained with a strain of Cuninghamella echinulata.

  4. Fully Convergent Chemical Synthesis of Ester Insulin: Determination of the High Resolution X-ray Structure by Racemic Protein Crystallography

    PubMed Central

    Avital-Shmilovici, Michal; Mandal, Kalyaneswar; Gates, Zachary P.; Phillips, Nelson B.; Weiss, Michael A.; Kent, Stephen B.H.

    2013-01-01

    Efficient total synthesis of insulin is important to enable the application of medicinal chemistry to the optimization of the properties of this important protein molecule. Recently we described ‘ester insulin’ – a novel form of insulin in which the function of the 35 residue C-peptide of proinsulin is replaced by a single covalent bond – as a key intermediate for the efficient total synthesis of insulin. Here we describe a fully convergent synthetic route to the ester insulin molecule from three unprotected peptide segments of approximately equal size. The synthetic ester insulin polypeptide chain folded much more rapidly than proinsulin, and at physiological pH. Both the D-protein and L-protein enantiomers of monomeric DKP ester insulin (i.e. [AspB10, LysB28, ProB29]ester insulin) were prepared by total chemical synthesis. The atomic structure of the synthetic ester insulin molecule was determined by racemic protein X-ray crystallography to a resolution of 1.6 Å. Diffraction quality crystals were readily obtained from the racemic mixture of {D-DKP ester insulin + L-DKP ester insulin}, whereas crystals were not obtained from the L-ester insulin alone even after extensive trials. Both the D-protein and L-protein enantiomers of monomeric DKP ester insulin were assayed for receptor binding and in diabetic rats, before and after conversion by saponification to the corresponding DKP insulin enantiomers. L-DKP ester insulin bound weakly to the insulin receptor, while synthetic L-DKP insulin derived from the L-DKP ester insulin intermediate was fully active in binding to the insulin receptor. The D- and L-DKP ester insulins and D-DKP insulin were inactive in lowering blood glucose in diabetic rats, while synthetic L-DKP insulin was fully active in this biological assay. The structural basis of the lack of biological activity of ester insulin is discussed. PMID:23343390

  5. Chromatographic separation of fructose from date syrup.

    PubMed

    Al Eid, Salah M

    2006-01-01

    The objective of this study is to provide a process for separating fructose from a mixture of sugars containing essentially fructose and glucose, obtained from date palm fruits. The extraction procedure of date syrup from fresh dates gave a yield of 86.5% solids after vacuum drying. A process for separating fructose from an aqueous solution of date syrup involved adding the date syrup solutions (20, 30 and 40% by weight) to a chromatographic column filled with Dowex polystyrene strong cation exchange gel matrix resin Ca2 + and divinylbenzene, a functional group, sulfonic acid, particle size 320 microm, with a flow rate of 0.025 and 0.05 bed volume/min, under 30 and 70 degrees C column temperature. After the date sugar solution batch, a calculated quantity of water was added to the column. Glucose was retained by the resin more weakly than fructose and proceeded faster into the water batch flowing ahead. Three fractions were collected: a glucose-rich fraction, a return fraction, and a fructose-rich fraction. The return fraction is based on when the peaks of fructose and glucose were reached, which could be determined by means of an analyzer (polarimeter) based on the property of glucose and fructose solutions to turn the polarization level of polarized light. A high yield of fructose is obtained at 70 degrees C column temperature with a flow rate of 0.025 bed volume/min and date syrup solution containing 40% sugar concentration. The low recovery by weight obtained using date syrup solutions having a sugar concentration of 20 and 30%, encourages the use of a concentration of 40%. However, with the 40% date syrup supply the average concentrations of glucose and fructose in the return fractions were more than 40%, which can be used for diluting the thick date syrup solution extracted from dates.

  6. Chromatographic separation of fructose from date syrup.

    PubMed

    Al Eid, Salah M

    2006-01-01

    The objective of this study is to provide a process for separating fructose from a mixture of sugars containing essentially fructose and glucose, obtained from date palm fruits. The extraction procedure of date syrup from fresh dates gave a yield of 86.5% solids after vacuum drying. A process for separating fructose from an aqueous solution of date syrup involved adding the date syrup solutions (20, 30 and 40% by weight) to a chromatographic column filled with Dowex polystyrene strong cation exchange gel matrix resin Ca2 + and divinylbenzene, a functional group, sulfonic acid, particle size 320 microm, with a flow rate of 0.025 and 0.05 bed volume/min, under 30 and 70 degrees C column temperature. After the date sugar solution batch, a calculated quantity of water was added to the column. Glucose was retained by the resin more weakly than fructose and proceeded faster into the water batch flowing ahead. Three fractions were collected: a glucose-rich fraction, a return fraction, and a fructose-rich fraction. The return fraction is based on when the peaks of fructose and glucose were reached, which could be determined by means of an analyzer (polarimeter) based on the property of glucose and fructose solutions to turn the polarization level of polarized light. A high yield of fructose is obtained at 70 degrees C column temperature with a flow rate of 0.025 bed volume/min and date syrup solution containing 40% sugar concentration. The low recovery by weight obtained using date syrup solutions having a sugar concentration of 20 and 30%, encourages the use of a concentration of 40%. However, with the 40% date syrup supply the average concentrations of glucose and fructose in the return fractions were more than 40%, which can be used for diluting the thick date syrup solution extracted from dates. PMID:16849117

  7. Radiocarbon Dating the Anthropocene

    NASA Astrophysics Data System (ADS)

    Chaput, M. A.; Gajewski, K. J.

    2015-12-01

    The Anthropocene has no agreed start date since current suggestions for its beginning range from Pre-Industrial times to the Industrial Revolution, and from the mid-twentieth century to the future. To set the boundary of the Anthropocene in geological time, we must first understand when, how and to what extent humans began altering the Earth system. One aspect of this involves reconstructing the effects of prehistoric human activity on the physical landscape. However, for global reconstructions of land use and land cover change to be more accurately interpreted in the context of human interaction with the landscape, large-scale spatio-temporal demographic changes in prehistoric populations must be known. Estimates of the relative number of prehistoric humans in different regions of the world and at different moments in time are needed. To this end, we analyze a dataset of radiocarbon dates from the Canadian Archaeological Radiocarbon Database (CARD), the Palaeolithic Database of Europe and the AustArch Database of Australia, as well as published dates from South America. This is the first time such a large quantity of dates (approximately 60,000) has been mapped and studied at a global scale. Initial results from the analysis of temporal frequency distributions of calibrated radiocarbon dates, assumed to be proportional to population density, will be discussed. The utility of radiocarbon dates in studies of the Anthropocene will be evaluated and potential links between population density and changes in atmospheric greenhouse gas concentrations, climate, migration patterning and fire frequency coincidence will be considered.

  8. The Realities of Date Rape.

    ERIC Educational Resources Information Center

    Presley, Cara; Watson, Jennifer; Williams, Audrey R.

    This poster presentation addresses the issue of date rape, specifically in the college environment. Highlighted are date rape statistics, demographics, and date rape drugs. Also discussed are date rape warnings and prevention strategies. It is concluded that college and university administrators must place the issue of date rape and acquaintance…

  9. The Dating Game.

    ERIC Educational Resources Information Center

    Zerger, Monte J.

    1998-01-01

    Presents activities to cultivate the tendency to see special qualities in numbers that can be played on certain calendar days. Includes games on the constant of the day, Fibonacci and golden ratio dates, primes, powers, December 25, and the day of the year. (ASK)

  10. 40 CFR 62.3351 - Effective date.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Illinois Metals, Acid Gases, Organic Compounds and Nitrogen Oxide Emissions from Existing Municipal Waste Combustors with the Capacity to Combust Greater Than 250 Tons Per Day of Municipal Solid Waste § 62.3351 Effective date. The Federal...

  11. 40 CFR 62.3351 - Effective date.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Illinois Metals, Acid Gases, Organic Compounds and Nitrogen Oxide Emissions from Existing Municipal Waste Combustors with the Capacity to Combust Greater Than 250 Tons Per Day of Municipal Solid Waste § 62.3351 Effective date. The Federal...

  12. 40 CFR 62.3351 - Effective date.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Illinois Metals, Acid Gases, Organic Compounds and Nitrogen Oxide Emissions from Existing Municipal Waste Combustors with the Capacity to Combust Greater Than 250 Tons Per Day of Municipal Solid Waste § 62.3351 Effective date. The Federal...

  13. Synthesis and optical resolution of an allenoic acid by diastereomeric salt formation induced by chiral alkaloids.

    PubMed

    Nyhlén, Jonas; Eriksson, Lars; Bäckvall, Jan-E

    2008-01-01

    A synthetic procedure for the preparation of 4-cyclohexyl-2-methyl-buta-2,3-dienoic acid in the two optically active forms has been developed. Synthesis of the racemic allenoic acid was made by an efficient route with good overall yield. Resolution of the enantiomers was achieved by forming the cinchonidine and cinchonine diastereomeric salt, respectively, and the enantiomers were isolated in up to 95% enantiomeric excess. The absolute configuration of the allenoic acid was determined by X-ray crystallography.

  14. 76 FR 77831 - 2012 Presidential Candidate Matching Fund Submission Dates and Post Date of Ineligibility Dates...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-12-14

    ... Submit Statements of Net Outstanding Campaign Obligations AGENCY: Federal Election Commission. ACTION: Notice of matching fund submission dates and submission dates for statements of net outstanding campaign... statements of net outstanding campaign obligations (``NOCO statement'') after their dates of...

  15. 40 CFR 63.1160 - Compliance dates and maintenance requirements.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... Facilities and Hydrochloric Acid Regeneration Plants § 63.1160 Compliance dates and maintenance requirements.../or hydrochloric acid regeneration plant subject to this subpart shall achieve initial compliance with... reconstructed steel pickling facility and/or hydrochloric acid regeneration plant subject to this subpart...

  16. 40 CFR 63.1160 - Compliance dates and maintenance requirements.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... Facilities and Hydrochloric Acid Regeneration Plants § 63.1160 Compliance dates and maintenance requirements.../or hydrochloric acid regeneration plant subject to this subpart shall achieve initial compliance with... reconstructed steel pickling facility and/or hydrochloric acid regeneration plant subject to this subpart...

  17. 40 CFR 63.1160 - Compliance dates and maintenance requirements.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... Facilities and Hydrochloric Acid Regeneration Plants § 63.1160 Compliance dates and maintenance requirements.../or hydrochloric acid regeneration plant subject to this subpart shall achieve initial compliance with... reconstructed steel pickling facility and/or hydrochloric acid regeneration plant subject to this subpart...

  18. 40 CFR 63.1160 - Compliance dates and maintenance requirements.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... Facilities and Hydrochloric Acid Regeneration Plants § 63.1160 Compliance dates and maintenance requirements.../or hydrochloric acid regeneration plant subject to this subpart shall achieve initial compliance with... reconstructed steel pickling facility and/or hydrochloric acid regeneration plant subject to this subpart...

  19. 40 CFR 63.1160 - Compliance dates and maintenance requirements.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... Facilities and Hydrochloric Acid Regeneration Plants § 63.1160 Compliance dates and maintenance requirements.../or hydrochloric acid regeneration plant subject to this subpart shall achieve initial compliance with... reconstructed steel pickling facility and/or hydrochloric acid regeneration plant subject to this subpart...

  20. Helical sense selective domains and enantiomeric superhelices generated by Langmuir-Schaefer deposition of an axially racemic chiral helical polymer

    NASA Astrophysics Data System (ADS)

    Rodríguez, R.; Ignés-Mullol, J.; Sagués, F.; Quiñoá, E.; Riguera, R.; Freire, F.

    2016-02-01

    The chiral polymer poly-(R)-1 behaves in solution, despite its chiral pendants, as a dynamic axially racemic (i.e., 1 : 1) mixture of left- and right-handed helices, but its deposition on graphite by a Langmuir-Schaefer (LS) technique leads to a helical sense-selective packing that forms separate enantiomeric domains of left- and right-handed helical chains observed by high resolution atomic force microscopy (AFM). The polymer structure within these domains is very uniform, seldom altered by the presence of reversals, grouped always in contiguous pairs maintaining a single helical sense along the polymer chain. The LS deposition technique has been shown to be crucial to obtain good quality monolayers from poly-(R)-1 and other poly(phenylacetylene)s (PPAs: poly-2, poly-3 and poly-4) with short pendants, where spin coating, drop casting and Langmuir-Blodgett (LB) failed, and suggests that this technique could be the method of choice for the preparation of 2D monolayers for high resolution AFM studies of PPAs with short pendants. Key helical parameters (i.e., sense, pitch, packing angle) are easily measured in this way.The chiral polymer poly-(R)-1 behaves in solution, despite its chiral pendants, as a dynamic axially racemic (i.e., 1 : 1) mixture of left- and right-handed helices, but its deposition on graphite by a Langmuir-Schaefer (LS) technique leads to a helical sense-selective packing that forms separate enantiomeric domains of left- and right-handed helical chains observed by high resolution atomic force microscopy (AFM). The polymer structure within these domains is very uniform, seldom altered by the presence of reversals, grouped always in contiguous pairs maintaining a single helical sense along the polymer chain. The LS deposition technique has been shown to be crucial to obtain good quality monolayers from poly-(R)-1 and other poly(phenylacetylene)s (PPAs: poly-2, poly-3 and poly-4) with short pendants, where spin coating, drop casting and Langmuir

  1. Synthesis, controlled release properties, and increased antifungal activities of novel cis- and trans-racemate complexes of propiconazole.

    PubMed

    Chen, Xi; Yang, Chunlong

    2009-03-25

    Twenty novel metal complexes M(1)(cis-L)(2)Y(2), M(1)(trans-L)(2)Y(2,) M(2)(cis-L)(4)Y(2), and M(2)(trans-L)(4)Y(2) (M(1) = Zn(II), Co(II), Cu(II); M(2) = Mn(II), Ni(II); Y = OAc, Cl, ClO(4), and NO(3)) were synthesized by reacting bivalent transitional metal salt MY(2).nH(2)O (n = 0-6) with ligands cis-racemate of propiconazole (cis-L) and trans-racemate of propiconazole (trans-L), respectively. All of these synthesized complexes were identified by atomic absorption spectrometry, elemental analysis, and IR and UV spectra. The cumulative release studies of some selected complexes in static water were performed; all determined complexes were found to exhibit attractive controlled release properties, yet the ligand release rates of cis-L complexes were slower than those of trans-L complexes. Meanwhile, it was found that the release rate of ligand cis-L from representative complex Zn(cis-L)(2)Cl(2) was affected obviously by different conditions, such as temperature, pH, and PVA film coating. The antifungal activities of the ligands and their complexes against five selected plant pathogenic fungi were evaluated; the results demonstrated that the toxicity of cis-L was 3.39-5.95 times greater than that of trans-L, and all of the synthesized complexes showed superior activities of 1.19-6.36 times to those of their ligands, especially Zn complexes having toxicities 2.62-6.36 times greater than those of their ligands. Moreover, the cis-L complexes had more sensitive activities than their relevant trans-L complexes; for example, Zn(cis-L)(2)Cl(2) appeared to be 5.00-8.67 times stronger than Zn(trans-L)(2)Cl(2) complex. In addition, the mechanism of increased antifungal activities of the title complexes in comparison with their ligands was discussed preliminarily.

  2. On the reported optical activity of amino acids in the Murchison meteorite

    USGS Publications Warehouse

    Bada, J.L.; Cronin, J.R.; Ho, M.-S.; Kvenvolden, K.A.; Lawless, J.G.; Miller, S.L.; Oro, J.; Steinberg, S.

    1983-01-01

    In analyses of extracts from the Murchison meteorite (a carbonaceous chondrite), Engel and Nagy1 reported an excess of L-enantiomers for several protein amino acids but found that the non-protein amino acids were racemic. They suggested that the excess of L-isomers might have resulted from an asymmetric synthesis or decomposition. Their results disagree with those obtained previously2-4 and they claim this is due to improved methodology. In fact, their extraction method and analytical procedure (gas chromatography-mass spectrometry, GC-MS) was similar to those used in the original report2 of amino acids in the Murchison meteorite except that they used specific ion monitoring in the GC-MS measurements. We found the results of Engel and Nagy odd in that likely contaminants (the protein amino acids ala, leu, glu, asp and pro) were nonracemic while unlikely contaminants (isovaline and ??-amino-n-butyric acid) were racemic. For example, Engel and Nagy report that the leucine is ???90% L-enantiomer in the water-extracted sample whereas isovaline (??-methyl-??-aminobutyric acid) is racemic. It would be most unusual for an abiotic stereoselective decomposition or synthesis of amino acids to occur with protein amino acids but not with non-protein amino acids. We now show here that the explanation of terrestrial contamination is consistent with their results and is much more probable. ?? 1983 Nature Publishing Group.

  3. Dating Violence among College Students

    ERIC Educational Resources Information Center

    Iconis, Rosemary

    2013-01-01

    Dating violence is a significant problem on college campuses. More than one-fifth of the undergraduate dating population are physically abused by their dating partners and an even greater percentage are psychologically abused. Researchers have identified risk factors for college student dating violence. Preventive interventions are strongly…

  4. 210Pb dating

    USGS Publications Warehouse

    Swarzenski, Peter W.

    2014-01-01

    Roughly fifty years ago, a small group of scientists from Belgium and the United States, trying to better constrain ice sheet accumulation rates, attempted to apply what was then know about environmental lead as a potential geochronometer. Thus Goldberg (1963) developed the first principles of the 210Pb dating method, which was soon followed by a paper by Crozaz et al. (1964), who examined accumulation history of Antarctic snow using 210Pb. Shortly thereafter, Koide et al. (1972, 1973) adapted this technique to unravel sediment deposition and accumulation records in deep-sea environments. Serendipitously, they chose to work in a deep basin off California, where an independent and robust age model had already been developed. Krishanswami et al. (1971) extended the use of this technique to lacustrine deposits to reconstruct depositional histories of lake sediment, and maybe more importantly, contaminant inputs and burial. Thus, the powerful tool for dating recent (up to about one century old) sediment deposits was established and soon widely adopted. Today almost all oceanographic or limnologic studies that address recent depositional reconstructions employ 210Pb as one of several possible geochronometers (Andrews et al., 2009; Gale, 2009; Baskaran, 2011; Persson and Helms, 2011). This paper presents a short overview of the principles of 210Pb dating and provides a few examples that illustrate the utility of this tracer in contrasting depositional systems. Potential caveats and uncertainties (Appleby et al., 1986; Binford, 1990; Binford et al., 1993; Smith, 2001; Hancock et al., 2002) inherent to the use and interpretation of 210Pb-derived age-models are also introduced. Recommendations as to best practices for most reliable uses and reporting are presented in the summary.

  5. Laboratory for Radiokrypton Dating

    NASA Astrophysics Data System (ADS)

    Zappala, J. C.; Jiang, W.; Bailey, K. G.; Lu, Z. T.; Mueller, P.; O'Connor, T. P.

    2015-12-01

    Due to its simple production and transport in the terrestrial environment, 81Kr (half-life = 230,000 yr) is the ideal tracer for old water and ice with mean residence times in the range of 105-106 years, a range beyond the reach of 14C. 81Kr-dating is now available to the earth science community at large thanks to the development of an efficient and selective atom counter based on the Atom Trap Trace Analysis (ATTA) method. ATTA is a laser-based atom counting method where individual neutral atoms of the desired isotope are selectively captured by laser beams, and their fluorescence detected via a CCD camera. ATTA is unique among trace analysis techniques in that it is free of interferences from any other isotopes, isobars, atomic or molecular species. The ATTA instrument at Argonne's Laboratory for Radiokrypton Dating is capable of measuring both 81Kr/Kr and 85Kr/Kr ratios of environmental samples in the range of 10-14-10-10. For 81Kr-dating in the age range of 150 kyr - 1500 kyr, the required sample size is 5 micro-L STP of krypton gas, which can be extracted from approximately 100 kg of water or 40 kg of ice. For 85Kr/Kr analysis, the sample size can be smaller by an order of magnitude. We are continually developing the method towards higher counting efficiency, smaller sample sizes requirements, and higher sample throughput rates. In the past four years, we have performed radiokrypton analysis of over 150 groundwater and ice samples extracted by collaborators from all seven continents. Sample collection and purification was performed by groups including the University of Chicago, the University of Illinois at Chicago, the University of Bern, and the International Atomic Energy Agency. This work is supported by the U.S. DOE, Office of Nuclear Physics, under contract DE-AC02-06CH11357.

  6. Vulcanism and Radiocarbon Dates

    DOE R&D Accomplishments Database

    Libby, L. M.; Libby, W. F.

    1972-10-01

    We consider whether the long term perturbation of radiocarbon dates, which is known to be approximately a sin function of period about 8000 years and amplitude of about 8% peak-to-peak, could have been caused in any major part by vulcanism. We conclude that this is not the case. On the contrary, present day volcanoes are a far less important source of inert CO{sub 2} (about 100 fold less) than is man's burning of fossil fuels which has caused the Suess dilution of about 2%. (auth)

  7. Amino acids in the Yamato carbonaceous chrondrite from Antarctica

    NASA Technical Reports Server (NTRS)

    Shimoyama, A.; Ponnamperuma, C.; Yanai, K.

    1979-01-01

    Evidence for the presence of amino acids of extraterrestrial origin in the Antarctic Yamato carbonaceous chrondrite is presented. Hydrolyzed and nonhydrolyzed water-extracted amino acid samples from exterior, middle and interior portions of the meteorite were analyzed by an amino acid analyzer and by gas chromatography of N-TFA-isopropyl amino acid derivatives. Nine protein and six nonprotein amino acids were detected in the meteorite at abundances between 34 and less than one nmole/g, with equal amounts in interior and exterior portions. Nearly equal abundances of the D and L enantiomers of alanine, aspartic acid and glutamic acid were found, indicating the abiotic, therefore extraterrestrial, origin of the amino acids. The Antarctic environment and the uniformity of protein amino acid abundances are discussed as evidence against the racemization of terrestrially acquired amino acids, and similarities between Yamato amino acid compositions and the amino acid compositions of the Murchison and Murray type II carbonaceous chrondrites are indicated.

  8. (+)-Gibberellin C: hydrogen-bonding pattern of the monohydrate of a non-racemic pentacyclic diterpenoid.

    PubMed

    Thompson, H W; Brunskill, A P; Lalancette, R A

    2000-12-01

    In the monohydrate of the title compound, (+)-2beta, 4aalpha-dihydroxy-1,7-dimethyl-8-oxo-4bbeta,7alpha- gibbane-1alpha, 10beta-dicarboxylic acid-1,4a-lactone, C(19)H(24)O(6).H(2)O, intermolecular hydrogen bonding progresses helically along b from carboxyl to ketone [O...O = 2.694 (5) A]. The carboxyl and lactone carbonyl groups in translationally related molecules within a helix both accept hydrogen bonds from the same water of hydration. The oxygen of this water in turn accepts a hydrogen bond from the hydroxyl group of a third screw-related molecule in an adjacent counterdirectionally oriented helix, yielding a complex three-dimensional hydrogen-bonding array. Intermolecular O...H-C close contacts were found to the carboxyl and lactone carbonyls, the hydroxyl, and the water. PMID:11119009

  9. Identification of isomerization and racemization of aspartate in the Asp-Asp motifs of a therapeutic protein.

    PubMed

    Zhang, Jennifer; Yip, Holly; Katta, Viswanatham

    2011-03-15

    A thermally stressed Fab molecule showed a significant increase of basic variants in imaged capillary isoelectric focusing (iCIEF) analysis. Mass analyses of the reduced protein found an increase in -18Da species from both light chain and heavy chain. A tryptic peptide map identified two isoAsp-containing peptides, both containing Asp-Asp motifs and located in complementarity-determining regions (CDRs) of light chains and heavy chains, respectively. The approaches of hydrolyzing succinimide in H(2)(18)O followed by tryptic digestion were used to label and identify the sites of isomerization. This method enabled identification of the isomerization site by comparing the MS/MS spectra of isomerized peptides with and without (18)O incorporation. The light chain peptide L2 VTITCITSTDID(12)DDMNWYQQKPGK underwent simultaneous isomerization and recemization at residue Asp-12 after thermal stress as evidenced by the coinjection of synthetic peptide L2 with l-Asp-12, l-isoAsp-12, d-Asp-12, and d-isoAsp-12, respectively. A thermal stress study of the synthetic peptide (l-)L2 showed that the isomerization and racemization did not occur, indicating that the Asp degradation in this Asp-Asp motif is more related to the protein conformation than the primary sequence. Another isomerization site was identified as Asp-24 in the heavy chain peptide H5 QAPGQGLEWMGWINTYTGETTYAD(24)DFK. No other isomerizations were detected in CDR peptides containing either Asp-Ser or Asp-Thr motifs.

  10. A comparative Analysis of In Vitro and In Vivo Efficacies of the Enantiomers of Thioridazine and Its Racemate

    PubMed Central

    Christensen, Jørn B.; Hendricks, Oliver; Chaki, Shaswati; Mukherjee, Sayanti; Das, Ayan; Pal, Tapan K.; Dastidar, Sujata G.; Kristiansen, Jette E.

    2013-01-01

    A long list of chemotherapeutical drugs used in the treatment of the peripheral and the central nervous systems possess anti-microbial activity. Some of these neurotropic compounds are chiral, with the one stereo isomeric form exaggerating reduced neurotropism. This is the case for the levorotatory form of thioridazine. The phenothiazine thioridazine is an interesting compound, characterized by exhibiting a significant growth inhibiting activity on a wide array of micro-organisms. Thioridazine is characterized by another challenging feature, because the compound is concentrated in certain human tissue cells. The present study describes a comparative study of the two enantiomers as well as the racemic form of thioridazine. The study exploits the stereochemical aspect and the in vitro and in vivo potential of these compounds, with a focus on the effects on Gram negative organism Salmonella enterica serover Typhimurium. In summary, the results of this study yielded a significant antibacterial activity of all forms of thioridazine, indicating the levorotatory (–)- form to be superior in terms of both its in vitro and in vivo efficacies. PMID:23505431

  11. Helical sense selective domains and enantiomeric superhelices generated by Langmuir-Schaefer deposition of an axially racemic chiral helical polymer.

    PubMed

    Rodríguez, R; Ignés-Mullol, J; Sagués, F; Quiñoá, E; Riguera, R; Freire, F

    2016-02-14

    The chiral polymer poly-(R)-1 behaves in solution, despite its chiral pendants, as a dynamic axially racemic (i.e., 1 : 1) mixture of left- and right-handed helices, but its deposition on graphite by a Langmuir-Schaefer (LS) technique leads to a helical sense-selective packing that forms separate enantiomeric domains of left- and right-handed helical chains observed by high resolution atomic force microscopy (AFM). The polymer structure within these domains is very uniform, seldom altered by the presence of reversals, grouped always in contiguous pairs maintaining a single helical sense along the polymer chain. The LS deposition technique has been shown to be crucial to obtain good quality monolayers from poly-(R)-1 and other poly(phenylacetylene)s (PPAs: poly-2, poly-3 and poly-4) with short pendants, where spin coating, drop casting and Langmuir-Blodgett (LB) failed, and suggests that this technique could be the method of choice for the preparation of 2D monolayers for high resolution AFM studies of PPAs with short pendants. Key helical parameters (i.e., sense, pitch, packing angle) are easily measured in this way. PMID:26791332

  12. Single-walled carbon nanotube-based polymer monoliths for the enantioselective nano-liquid chromatographic separation of racemic pharmaceuticals.

    PubMed

    Ahmed, Marwa; Yajadda, Mir Massoud Aghili; Han, Zhao Jun; Su, Dawei; Wang, Guoxiu; Ostrikov, Kostya Ken; Ghanem, Ashraf

    2014-09-19

    Single-walled carbon nanotubes were encapsulated into different polymer-based monolithic backbones. The polymer monoliths were prepared via the copolymerization of 20% monomers, glycidyl methacrylate, 20% ethylene glycol dimethacrylate and 60% porogens (36% 1-propanol, 18% 1,4-butanediol) or 16.4% monomers (16% butyl methacrylate, 0.4% sulfopropyl methacrylate), 23.6% ethylene glycol dimethacrylate and 60% porogens (36% 1-propanol, 18% 1,4-butanediol) along with 6% single-walled carbon nanotubes aqueous suspension. The effect of single-walled carbon nanotubes on the chiral separation of twelve classes of pharmaceutical racemates namely; α- and β-blockers, antiinflammatory drugs, antifungal drugs, dopamine antagonists, norepinephrine-dopamine reuptake inhibitors, catecholamines, sedative hypnotics, diuretics, antihistaminics, anticancer drugs and antiarrhythmic drugs was investigated. The enantioselective separation was carried out under multimodal elution to explore the chiral recognition capabilities of single-walled carbon nanotubes using reversed phase, polar organic and normal phase chromatographic conditions using nano-liquid chromatography. Baseline separation was achieved for celiprolol, chlorpheniramine, etozoline, nomifensine and sulconazole under multimodal elution conditions. Satisfactory repeatability was achieved through run-to-run, column-to-column and batch-to-batch investigations. Our findings demonstrate that single-walled carbon nanotubes represent a promising stationary phase for the chiral separation and may open the field for a new class of chiral selectors.

  13. Helical sense selective domains and enantiomeric superhelices generated by Langmuir-Schaefer deposition of an axially racemic chiral helical polymer.

    PubMed

    Rodríguez, R; Ignés-Mullol, J; Sagués, F; Quiñoá, E; Riguera, R; Freire, F

    2016-02-14

    The chiral polymer poly-(R)-1 behaves in solution, despite its chiral pendants, as a dynamic axially racemic (i.e., 1 : 1) mixture of left- and right-handed helices, but its deposition on graphite by a Langmuir-Schaefer (LS) technique leads to a helical sense-selective packing that forms separate enantiomeric domains of left- and right-handed helical chains observed by high resolution atomic force microscopy (AFM). The polymer structure within these domains is very uniform, seldom altered by the presence of reversals, grouped always in contiguous pairs maintaining a single helical sense along the polymer chain. The LS deposition technique has been shown to be crucial to obtain good quality monolayers from poly-(R)-1 and other poly(phenylacetylene)s (PPAs: poly-2, poly-3 and poly-4) with short pendants, where spin coating, drop casting and Langmuir-Blodgett (LB) failed, and suggests that this technique could be the method of choice for the preparation of 2D monolayers for high resolution AFM studies of PPAs with short pendants. Key helical parameters (i.e., sense, pitch, packing angle) are easily measured in this way.

  14. The Origin of Amino Acids in Lunar Regolith Samples

    NASA Technical Reports Server (NTRS)

    Cook, Jamie E.; Callahan, Michael P.; Dworkin, Jason P.; Glavin, Daniel P.; McLain, Hannah L.; Noble, Sarah K.; Gibson, Everett K., Jr.

    2016-01-01

    We analyzed the amino acid content of seven lunar regolith samples returned by the Apollo 16 and Apollo 17 missions and stored under NASA curation since collection using ultrahigh-performance liquid chromatography with fluorescence detection and time-of-flight mass spectrometry. Consistent with results from initial analyses shortly after collection in the 1970s, we observed amino acids at low concentrations in all of the curated samples, ranging from 0.2 parts-per-billion (ppb) to 42.7 ppb in hot-water extracts and 14.5 ppb to 651.1 ppb in 6M HCl acid-vapor-hydrolyzed, hot-water extracts. Amino acids identified in the Apollo soil extracts include glycine, D- and L-alanine, D- and L-aspartic acid, D- and L-glutamic acid, D- and L-serine, L-threonine, and L-valine, all of which had previously been detected in lunar samples, as well as several compounds not previously identified in lunar regoliths: -aminoisobutyric acid (AIB), D-and L-amino-n-butyric acid (-ABA), DL-amino-n-butyric acid, -amino-n-butyric acid, -alanine, and -amino-n-caproic acid. We observed an excess of the L enantiomer in most of the detected proteinogenic amino acids, but racemic alanine and racemic -ABA were present in some samples.

  15. Engineering Porous Organic Cage Crystals with Increased Acid Gas Resistance.

    PubMed

    Zhu, Guanghui; Hoffman, Christopher D; Liu, Yang; Bhattacharyya, Souryadeep; Tumuluri, Uma; Jue, Melinda L; Wu, Zili; Sholl, David S; Nair, Sankar; Jones, Christopher W; Lively, Ryan P

    2016-07-25

    Both known and new CC3-based porous organic cages are prepared and exposed to acidic SO2 in vapor and liquid conditions. Distinct differences in the stability of the CC3 cages exist depending on the chirality of the diamine linkers used. The acid catalyzed CC3 degradation mechanism is probed via in situ IR and a degradation pathway is proposed and supported with computational results. CC3 crystals synthesized with racemic mixtures of diaminocyclohexane exhibited enhanced stability compared to CC3-R and CC3-S. Confocal fluorescent microscope images reveal that the stability difference in CC3 species originates from an abundance of mesoporous grain boundaries in CC3-R and CC3-S, allowing facile access of aqueous SO2 throughout the crystal, promoting decomposition. These grain boundaries are absent from CC3 crystals made with racemic linkers. PMID:27253350

  16. Enantioselective Iodolactonization of Disubstituted Olefinic Acids Using a Bifunctional Catalyst

    PubMed Central

    Fang, Chao; Paull, Daniel H.; Hethcox, J. Caleb; Shugrue, Christopher R.; Martin, Stephen F.

    2012-01-01

    The enantioselective iodolactonizations of a series of diversely-substituted olefinic carboxylic acids are promoted by a BINOL-derived, bifunctional catalyst. Reactions involving 5-alkyl- and 5-aryl-4(Z)-pentenoic acids and 6-alkyl- and 6-aryl-5(Z)-hexenoic acids provide the corresponding γ- and δ-lactones having stereogenic C–I bonds in excellent yields and >97:3 er. Significantly, this represents the first organocatalyst that promotes both bromo- and iodolactonization with high enantioselectivities. The potential of this catalyst to induce kinetic resolutions of racemic unsaturated acids is also demonstrated. PMID:23199100

  17. Laboratory for Radiokrypton Dating

    NASA Astrophysics Data System (ADS)

    Lu, Z.; Bailey, K.; Jiang, W.; Müller, P.; O'Connor, T. P.; Zappala, J. C.

    2013-12-01

    Due to its simple production and transport processes in the terrestrial environment, the long-lived noble-gas isotope 81Kr (half-life = 230 kyr) is the ideal tracer for studying old water and ice in the age range of 10^5-10^6 years, a range beyond the reach of 14C. 81Kr dating, a concept pursued in the past four decades by numerous laboratories employing a variety of techniques, is now available for the first time to the earth science community at large. This is made possible by the development of ATTA-3 (Jiang et al., GCA 91, 1-6; 2012), an efficient and selective atom counter based on the Atom Trap Trace Analysis method (Chen et al., Science 286, 1139-1141; 1999). The instrument is capable of measuring both 81Kr/Kr and 85Kr/Kr ratios of environmental samples in the range of 10^-14-10^-10. For 81Kr-dating in the age range of 150 - 1,500 kyr, the required sample size is 5 - 10 micro-L STP of krypton gas, which can be extracted from approximately 100 - 200 kg of water or 40 - 80 kg of ice. For 85Kr/Kr analysis, the required sample size is generally smaller by an order of magnitude because of the isotope's higher initial abundance in the atmosphere. The Laboratory for Radiokrypton Dating is currently equipped to analyze up to 120 samples per year. With future equipment upgrades, this limit can be increased as demand grows. In the period since November 2011, the Laboratory has measured both 81Kr/Kr and 85Kr/Kr ratios in over 50 samples that had been extracted by collaborators from six different continents. The samples were from groundwater wells in the Great Artesian Basin (Australia), Guarani Aquifer (Brazil), and Locust Grove (Maryland); from brine wells of the Waste Isolation Pilot Plant (New Mexico); from geothermal steam vents in Yellowstone National Park; from near-surface ice at Taylor Glacier, Antarctica; and from deep mines in South Africa. Sample collection and purification was performed by groups including the University of Illinois at Chicago, University

  18. Spontaneous resolution of a racemic nickel(II) complex and helicity induction via hydrogen bonding: the effect of chiral building blocks on the helicity of one-dimensional chains.

    PubMed

    Ou, Guang-Chuan; Jiang, Long; Feng, Xiao-Long; Lu, Tong-Bu

    2008-04-01

    The reactions of a racemic four-coordinated nickel(II) complex [Ni(alpha-rac-L)](ClO4)2 (containing equal amount of SS and RR enantiomers) with l- and d-phenylalanine in acetonitrile/water gave two less-soluble six-coordinated enantiomers of {[Ni( f-SS-L)(l-Phe)](ClO4)}n (Delta-1) and {[Ni(f- RR-L)(d-Phe)](ClO4)}n (Lambda-1), respectively. Evaporation the remaining solutions gave two six-coordinated diastereomers of {[Ni 3(f- RR-L)3(l-Phe)2(H 2O)](ClO4)4}n (a-2) and {[Ni3(f- SS-L)3(d-Phe)2(H2O)](ClO4)4}n (b-2), respectively (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, Phe(-) = phenylalanine anion). The reaction of [Ni(alpha-rac-L)](ClO4)2 with dl-Phe(-) gave a conglomerate of c-1; in which, the SS and RR enantiomers preferentially coordinate to l- and d-Phe(-) respectively to give a racemic mixture of Delta-1 and Lambda-1, and the spontaneous resolution occurs during the reaction, in which each crystal crystallizes to become enantiopure. Removing Phe(-) from Delta-1 and Lambda-1 using perchloric acid gave two enantiomers of [Ni(alpha-SS-L)](ClO4)2 (S-3) and [Ni(alpha-RR-L)](ClO4)2 (R-3). Dissolving S-3 and R-3 in acetonitrile gave two six-coordinated enantiomers of [Ni( f-SS-L)(CH3CN)2](ClO4)2 (S-4) and [Ni( f- RR-L)(CH3CN)2](ClO4)2 (R-4), while dissolving [Ni(alpha-rac-L)](ClO4)2 in acetonitrile gave a racemic twining complex [Ni(f-rac-L)(CH3CN)2](ClO4)2 (rac-4). Delta-1 and Lambda-1 belong to supramolecular stereoisomers, which are constructed via hydrogen bond linking of [Ni( f-SS-L)(l-Phe)](+) and [Ni(f-RR-L)(d-Phe)](+) monomers to form 1D homochiral right-handed and left-handed helical chains, respectively. The reaction of S-3 with d-Phe(-) gave {[Ni(f-SS-L)(d-Phe)](ClO4)}n (5), which shows a motif of a 1D hydrogen bonded zigzag chain instead of a 1D helical chain. Compound a-2/ b-2 contains dimers of [{Ni(f-RR-L)}2(l-Phe)(H2O)](3+)/[{Ni( f- SS-L)}2(d-Phe)(H2O)](3+) and 1D zigzag chains of {[Ni(f-RR-L)(l-Phe)](+)}n /{[Ni

  19. Development of a Method for the N-Arylation of Amino Acid Esters with Aryl Triflates.

    PubMed

    King, Sandra M; Buchwald, Stephen L

    2016-08-19

    A general method for the N-arylation of amino acid esters with aryl triflates is described. Both α- and β-amino acid esters, including methyl, tert-butyl, and benzyl esters, are viable substrates. Reaction optimization was carried out by design of experiment (DOE) analysis using JMP software. The mild reaction conditions, which use t-BuBrettPhos Pd G3 or G4 precatalyst, result in minimal racemization of the amino acid ester. This method is the first synthetic application of the t-BuBrettPhos Pd G4 precatalyst. Mechanistic studies show that the observed erosion in enantiomeric excess is due to racemization of the amino acid ester starting material and not of the product. PMID:27498618

  20. Enzymes involved in the glycidaldehyde (2,3-epoxy-propanal) oxidation step in the kinetic resolution of racemic glycidol (2,3-epoxy-1-propanol) by Acetobacter pasteurianus.

    PubMed

    Wandel, U; Machado, S S.; Jongejan, J A.; Duine, J A.

    2001-02-01

    It is already known that kinetic resolution of racemic glycidol (2,3-epoxy-1-propanol) takes place when Acetobacter pasteurianus oxidizes the compound to glycidic acid (2,3-epoxy-propionic acid) with glycidaldehyde (2,3-epoxy-propanal) proposed to be the transient seen in this conversion. Since inhibition affects the feasibility of a process based on this conversion in a negative sense, and the chemical reactivity of glycidaldehyde predicts that it could be the cause for the phenomena observed, it is important to know which enzyme(s) oxidise(s) this compound. To study this, rac.- as well as (R)-glycidaldehyde were prepared by chemical synthesis and analytical methods developed for their determination. It appears that purified quinohemoprotein alcohol dehydrogenase (QH-ADH type II), the enzyme responsible for the kinetic resolution of rac.-glycidol, also catalyses the oxidation of glycidaldehyde. In addition, a preparation exhibiting dye-linked aldehyde dehydrogenase activity for acetaldehyde, most probably originating from molybdohemoprotein aldehyde dehydrogenase (ALDH), which has been described for other Acetic acid bacteria, oxidised glycidaldehyde as well with a preference for the (R)-enantiomer, the selectivity quantified by an enantiomeric ratio (E) value of 7. From a comparison of the apparent kinetic parameter values of QH-ADH and ALDH, it is concluded that ALDH is mainly responsible for the removal of glycidaldehyde in conversions of glycidol catalysed by A. pasteurianus cells. It is shown that the transient observed in rac.-glycidol conversion by whole cells, is indeed (R)-glycidaldehyde. Since both QH-ADH and ALDH are responsible for vinegar production from ethanol by Acetobacters, growth and induction conditions optimal for this process seem also suited to yield cells with high catalytic performance with respect to kinetic resolution of glycidol and prevention of formation of inhibitory concentrations glycidaldehyde.

  1. Violence in Adolescent Dating Relationships

    ERIC Educational Resources Information Center

    Jouriles, Ernest N.; Platt, Cora; McDonald, Renee

    2009-01-01

    Beginning with a definition of dating and dating violence among adolescents, this article explores the factors which impact such violence. It concludes with a review of two school-based prevention/intervention programs (Safe Dates and The Youth Relationships Project). (Contains 1 table.)

  2. Antinociceptive Effect of Racemic Flurbiprofen and Caffeine Co-Administration in an Arthritic Gout-Type Pain in Rats.

    PubMed

    Liévano-Reyes, Ricardo; Pérez-Méndez, Hermínia Ines; Solís-Oba, Aida; Jaramillo-Morales, Osmar Antonio; Espinosa-Juárez, Josué Vidal; López-Muñoz, Francisco Javier

    2016-06-01

    Preclinical Research Drug combinations are routinely used in the treatment of pain. In drug associations, adjuvants such as caffeine, are employed with different non-steroidal anti-inflammatories drugs (NSAIDs), however, at present does not exist studies showing the effect of the combination of racemic flurbiprofen (rac-Flur) in association with caffeine. The objective of this work was to evaluate the combination of rac-Flur + caffeine oral in arthritic gout-type pain in rats. The antinociceptive effects of the rac-Flur alone and in combination with caffeine were analyzed on a pain-induced functional impairment model in rat. rac-Flur induced a dose-dependent antinociceptive effect and caffeine did not present any effect. The combination of rac-Flur and caffeine achieve a higher percentage of antinociceptive effect compared with the individual administration of rac-Flur. The dose-response curve (DRCs) shows that the combination of rac-Flur (31.6 mg/kg) + caffeine (17.8 mg/kg) exhibited the maximal antinociceptive efficacy (294.0 ± 21.2 area units), while rac-Flur alone (31.6 mg/kg) showed 207.2 ± 35.2 au, thus indicating an increase in efficacy (potentiation). Furthermore, the DRCs of the combinations presented a displacement to the left, indicating a change in the potency. Caffeine is able to increase the effect of rac-Flur in the arthritic gout-type pain in rats. Drug Dev Res 77 : 192-198, 2016.   © 2016 Wiley Periodicals, Inc. PMID:27241234

  3. Antinociceptive Effect of Racemic Flurbiprofen and Caffeine Co-Administration in an Arthritic Gout-Type Pain in Rats.

    PubMed

    Liévano-Reyes, Ricardo; Pérez-Méndez, Hermínia Ines; Solís-Oba, Aida; Jaramillo-Morales, Osmar Antonio; Espinosa-Juárez, Josué Vidal; López-Muñoz, Francisco Javier

    2016-06-01

    Preclinical Research Drug combinations are routinely used in the treatment of pain. In drug associations, adjuvants such as caffeine, are employed with different non-steroidal anti-inflammatories drugs (NSAIDs), however, at present does not exist studies showing the effect of the combination of racemic flurbiprofen (rac-Flur) in association with caffeine. The objective of this work was to evaluate the combination of rac-Flur + caffeine oral in arthritic gout-type pain in rats. The antinociceptive effects of the rac-Flur alone and in combination with caffeine were analyzed on a pain-induced functional impairment model in rat. rac-Flur induced a dose-dependent antinociceptive effect and caffeine did not present any effect. The combination of rac-Flur and caffeine achieve a higher percentage of antinociceptive effect compared with the individual administration of rac-Flur. The dose-response curve (DRCs) shows that the combination of rac-Flur (31.6 mg/kg) + caffeine (17.8 mg/kg) exhibited the maximal antinociceptive efficacy (294.0 ± 21.2 area units), while rac-Flur alone (31.6 mg/kg) showed 207.2 ± 35.2 au, thus indicating an increase in efficacy (potentiation). Furthermore, the DRCs of the combinations presented a displacement to the left, indicating a change in the potency. Caffeine is able to increase the effect of rac-Flur in the arthritic gout-type pain in rats. Drug Dev Res 77 : 192-198, 2016.   © 2016 Wiley Periodicals, Inc.

  4. Enantiomeric excesses in meteoritic amino acids

    NASA Technical Reports Server (NTRS)

    Cronin, J. R.; Pizzarello, S.

    1997-01-01

    Gas chromatographic-mass spectral analyses of the four stereoisomers of 2-amino-2,3-dimethylpentanoic acid (dl-alpha-methylisoleucine and dl-alpha-methylalloisoleucine) obtained from the Murchison meteorite show that the L enantiomer occurs in excess (7.0 and 9.1%, respectively) in both of the enantiomeric pairs. Similar results were obtained for two other alpha-methyl amino acids, isovaline and alpha-methylnorvaline, although the alpha hydrogen analogs of these amino acids, alpha-amino-n-butyric acid and norvaline, were found to be racemates. With the exception of alpha-amino-n-butyric acid, these amino acids are either unknown or of limited occurrence in the biosphere. Because carbonaceous chondrites formed 4.5 billion years ago, the results are indicative of an asymmetric influence on organic chemical evolution before the origin of life.

  5. Enantiomer resolution by pressure increase: inferences from experimental and topological results for the binary enantiomer system (R)- and (S)-mandelic acid.

    PubMed

    Rietveld, Ivo B; Barrio, Maria; Tamarit, Josep-Lluis; Do, Bernard; Céolin, René

    2011-12-15

    In pharmacy, racemic compounds are often problematic, because generally only one of the enantiomers possesses therapeutic activity and it is often difficult to separate them. Even though this problem is likely as old as the pharmaceutical industry, one thermodynamically obvious way of separating racemic crystals has never been studied experimentally, which is by using pressure. Data have been obtained on the equilibria of the (R)- and (S)-mandelic acid system as a function of pressure and temperature. With the use of thermodynamic arguments including the Clapeyron, Schröder, and Prigogine-Defay equations, it has been demonstrated that the conglomerate (crystals of separated enantiomers) becomes more stable than the racemic compound at approximately 0.64 GPa and 460 K. Even though this pressure is still higher than at the bottom of the Mariana Trench, there are no technical obstacles to produce such conditions, making pressure a viable option for separating enantiomers.

  6. Controlled synthesis of racemic indenyl rare-earth metal complexes via the cooperation between the intramolecular coordination of donor atoms and a bridge.

    PubMed

    Zhou, Shuangliu; Wu, Zhangshuan; Zhou, Lingmin; Wang, Shaowu; Zhang, Lijun; Zhu, Xiancui; Wei, Yun; Zhai, Jinhua; Wu, Jie

    2013-06-01

    The reactions of Me2Si(C9H6CH2CH2-DG)2 (DG = NMe2 (1), CH2NMe2 (2), OMe (3), and N(CH2CH2)2O (4)) with [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 in toluene afforded a series of racemic divalent rare-earth metal complexes: {η(5):η(1):η(5):η(1)-Me2Si(C9H5CH2CH2-DG)2}RE (DG = NMe2, RE = Yb (6) and Eu (7); DG = CH2NMe2, RE = Yb (8), Eu (9), and Sm (10); DG = OMe, RE = Yb (11) and Eu (12); DG = N(CH2CH2)2O, RE = Yb (13) and Eu (14)). Similarly, the racemic divalent rare-earth metal complexes {η(5):η(1):η(5):η(1)-Me2Si(C9H5CH2CH2CH2NMe2)(C9H5CH2CH2OMe)}RE (RE = Yb (15) and Eu (16)) were also obtained. The reaction of Me2Si(C9H5CH2CH2OMe)2Li2 with NdCl3 gave a racemic dimeric neodymium chloride {η(5):η(1):η(5)-Me2Si(C9H5CH2CH2OMe)2NdCl}2 (17), whereas the reaction of Me2Si(C9H5CH2CH2NMe2)2Li2 with SmCl3 afforded a racemic dinuclear samarium chloride bridged by lithium chloride {η(5):η(1):η(5):η(1)-Me2Si(C9H5CH2CH2NMe2)2SmCl}2(μ-LiCl) (18). Further reaction of complex 18 with LiCH2SiMe3 provided an unexpected rare-earth metal alkyl complex {η(5):η(1):η(5):η(1):σ-Me2Si(C9H5CH2CH2NMe2)[(C9H5CH2CH2N(CH2)Me]}Sm (19) through the activation of an sp(3) C-H bond α-adjacent to the nitrogen atom. Complexes 19 and {η(5):η(1):η(5):η(1):σ-Me2Si(C9H5CH2CH2NMe2)[(C9H5CH2CH2N(CH2)Me]}Y (20) were also obtained by one-pot reactions of Me2Si(C9H5CH2CH2NMe2)2Li2 with RECl3 followed by treatment with LiCH2SiMe3. All compounds were fully characterized by spectroscopic methods and elemental analysis. Complexes 6-10 and 14-20 were further characterized by single-crystal X-ray diffraction analysis. All of the prepared rare-earth metal complexes were racemic, suggesting that racemic organo rare-earth metal complexes could be controllably synthesized by the cooperation between a bridge and the intramolecular coordination of donor atoms.

  7. Amino acid preservation in saline halite core samples: Analogs for Martian dry evaporitic regions

    NASA Astrophysics Data System (ADS)

    Bada, J.; Aubrey, A.; Lowenstein, T.; Timofeeff, M.

    2008-12-01

    Recent data returned from several Mars spacecraft show substantial evidence for mineral precipitation from bodies of liquid water. Evaporitic minerals such as gypsum, kieserite and poly-hydrated magnesium sulfates have been detected remotely by orbiting spacecraft [1], jarosite has been detected in situ by the MER Opportunity [2], and chlorides are highly abundant upon the surface of Mars [3], often in correlation with siliclastic deposits [4]. Terrestrial environments can provide analogs for these systems identified on the Martian surface, and in-depth characterization of the terrestrial systems can provide valuable insights into processes that may have occurred on Mars during the late Noachian/early Hesperian. This is especially true in ancient playa or evaporative basin environments where deep core sampling offers a method of observing the geochemical diagenetic changes with time within a constrained environment. Deep coring can provide samples upwards of 200 ka within hundreds of meters of core [5]. The analysis of these sections can allow for the determination of preservation of various biosignatures from extinct microbial communities as well as their in situ diagenetic rates. Amino acids are powerful biomarkers that can be used to estimate biomass [6] and determine ages of extinct microbial communities [7]. Preliminary data for a core sample collected from Saline Valley, CA, shows the effect of time on amino acid biosignatures. The core has been dated by U-series: 35 feet, 20.9 ± 1.1 ka; 127 feet, 61.1 ±2.8 ka; 204 feet, 73.9 ±4.8 ka; and 310 feet, 150.3 ± 7.8 ka. The abundance of amino acids is observed to decrease drastically over the first 20 ka and then stabilize, although the overall composition changes. Acidic amino acids along with alanine and valine are the dominant amino acids. The enantiomeric (D/L) ratios generally increase with age because of in situ racemization, although the enantiomeric ratios for alanine and glutamic acid show a decrease

  8. Chemical synthesis and X-ray structure of a heterochiral {D-protein antagonist plus vascular endothelial growth factor} protein complex by racemic crystallography

    SciTech Connect

    Mandal, Kalyaneswar; Uppalapati, Maruti; Ault-Riché, Dana; Kenney, John; Lowitz, Joshua; Sidhu, Sachdev S.; Kent, Stephen B.H.

    2012-10-23

    Total chemical synthesis was used to prepare the mirror image (D-protein) form of the angiogenic protein vascular endothelial growth factor (VEGF-A). Phage display against D-VEGF-A was used to screen designed libraries based on a unique small protein scaffold in order to identify a high affinity ligand. Chemically synthesized D- and L- forms of the protein ligand showed reciprocal chiral specificity in surface plasmon resonance binding experiments: The L-protein ligand bound only to D-VEGF-A, whereas the D-protein ligand bound only to L-VEGF-A. The D-protein ligand, but not the L-protein ligand, inhibited the binding of natural VEGF{sub 165} to the VEGFR1 receptor. Racemic protein crystallography was used to determine the high resolution X-ray structure of the heterochiral complex consisting of {l_brace}D-protein antagonist + L-protein form of VEGF-A{r_brace}. Crystallization of a racemic mixture of these synthetic proteins in appropriate stoichiometry gave a racemic protein complex of more than 73 kDa containing six synthetic protein molecules. The structure of the complex was determined to a resolution of 1.6 {angstrom}. Detailed analysis of the interaction between the D-protein antagonist and the VEGF-A protein molecule showed that the binding interface comprised a contact surface area of approximately 800 {angstrom}{sup 2} in accord with our design objectives, and that the D-protein antagonist binds to the same region of VEGF-A that interacts with VEGFR1-domain 2.

  9. Radiocarbon Dating, Memories, and Hopes

    DOE R&D Accomplishments Database

    Libby, W. F.

    1972-10-01

    The history of radiocarbon dating from 1939 to the present is reviewed. The basic principles of radiocarbon dating are that cosmic rays make living things radioactive with {sup 14}C to a certain level fixed by the environment and that at death the intake of food stops so no replenishment of the {sup 14}C steadily lost by the immutable decay occurs. Therefore measurement of the degree of decay gives the time lapse since death, i.e., the radiocarbon age. The equipment developed and experiments performed to measure the specific activity of specimens to be dated are described. The results obtained by world-wide experimenters are discussed. These showed that on simultaneity radiocarbon dating is apparently reliable but that absolute dates may be incorrect by as much as 600 to 700 y. The value of radiocarbon dating to archaeologists, geologists, climatologists, and historians is stressed. (LCL)

  10. Enantioselective excited-state quenching of racemic Tb (III) and Eu (III) Tris (pyridine-2,6-dicarboxylate) by vitamin B 12 derivatives

    NASA Astrophysics Data System (ADS)

    Meskers, Stefan C. J.; Dekkers, Harry P. J. M.

    1999-08-01

    Enantioselectivity in the dynamic quenching of the luminescence of the Δ and Λ enantiomers of racemic Tb(III)(pyridine-2,6-dicarboxylate=DPA) 33- and Eu(DPA) 33- by a series of corrinoids is demonstrated by time resolved luminescence and circular-polarization-of-luminescence (CPL) spectroscopy. Studied are cyanocobalamin (vitamin B 12), aquacobalamin (B 12a) and its conjugated base hydroxocobalamin (HOCbl), dicyanocobinamide ((CN) 2Cbi) and the heptamethyl ester of dicyanocobyrinic acid ((CN) 2Cby(OMe) 7). For this set of quenchers (Q), the diastereomeric quenching rate constants ( kqΔ and kqΛ) are reported together with the degree of enantioselectivity Eq=( kqΔ- kqΛ)/( kqΔ+ kqΛ). In the systems with Tb, values of the average rate constant kqavg(=( kqΔ+ kqΛ)/2) are 1.0, 2.9 and 0.53 10 8 M -1 s -1 for CNCbl, (CN) 2Cbi, (CN) 2Cby(OMe) 7 with Eq=-0.24, -0.20, +0.01 (standard error of Eq is 0.01). The quenching by B 12a is strongly dependent on pH and ionic strength ( I); when I=12 mM we find kqavg=5.3, Eq=-0.23 at pH 6.7 and kqavg=1.3, Eq=-0.27 at pH 8.9. Corresponding rates for Eu are 0.41, 27, 3.4 10 7 M -1 s -1 and for B 12a, 7.3 and 1.2 10 7 M -1 s -1, corresponding values for Eq -0.27, -0.29, +0.02, -0.21 and -0.29. The quenching reaction is modeled as a pre-equilibrium involving the formation of an encounter complex (association constant K) followed by the actual electronic energy transfer step (rate ket). By relating the quenching data with molecular structure it is argued that the binding in the encounter complex involves two hydrogen bonds between the uncoordinated carboxylate oxygen atom of two DPA ligands of Ln(DPA) 33- and two amide groups of the corrinoid, presumably involving the a and g, the a and b, or the b and g side chains. For some corrinoid/Ln(DPA) 33- complexes the association constants and enantioselectivities in the ground state are known (Spectrochimica Acta 55A (1999) 1837-1855), which allows for an estimate of the average rate of

  11. Increased renal net acid excretion in prematures below 1,600 g body weight compared with prematures and small-for-date newborns above 2,100 g on alimentation with a commercial preterm formula.

    PubMed

    Kalhoff, H; Wiese, B; Kunz, C; Diekmann, L; Stock, G J; Manz, F

    1994-01-01

    In 76 low birth weight infants with an actual body weight ranging from 1,210 to 2,540 g and fed a commercial preterm formula, urine samples were collected and blood acid base status was measured on day 38 (+/- 17, mean +/- SD) of life. Infants with an actual body weight below 1,600 g demonstrated a higher daily weight gain (22 +/- 3 vs. 14 +/- 5 g/kg/day), lower blood pCO2 (35.4 +/- 5.0 vs. 38.9 +/- 3.8 mm Hg), lower urine pH (5.8 +/- 0.5 vs. 6.5 +/- 0.3), higher renal net acid (1.86 +/- 0.38 vs. 1.28 +/- 0.55 mmol/kg/day) and higher phosphorus excretion (0.67 vs. 0.52 mmol/kg/day) than infants with an actual body weight above 2,100 g. Urinary ionogram data of these 2 groups of infants show that the increased renal net acid excretion of the smaller prematures is the result of a lower urinary excretion of sodium, potassium and chloride, due to a higher daily weight gain, probably a higher retention of these minerals, and a higher urinary phosphorus excretion probably due to an age-specific lower intestinal calcium absorption, and therefore a lower rate of calcium and phosphorus retention. Considering the low renal capacity for hydrogen ion excretion, very low birth weight infants still run a considerable risk for disturbances of acid base metabolism due to the high mean level of net acid excretion in nutrition with preterm formulas and an additional age-specific augmentation of renal acid load.

  12. Stereochemistry for engineering spin crossover: structures and magnetic properties of a homochiral vs. racemic [Fe(N3O2)(CN)2] complex.

    PubMed

    Wang, Qiang; Venneri, Shari; Zarrabi, Niloofar; Wang, Hongfeng; Desplanches, Cédric; Létard, Jean-François; Seda, Takele; Pilkington, Melanie

    2015-04-21

    The Schiff-base condensation of the R,R-(+)-diamine () with 2,6-diacetyl pyridine in the presence of Fe(II) affords the macrocyclic complex [Fe(dpN3O2)(CN)2] () (dp = diphenyl) with ligand centred chirality comprising of a 1 : 1 mixture of LS 6- and HS 7-coordinate Fe(II) centres. Variable temperature magnetic susceptibility and Mössbauer studies reveal that () undergoes an incomplete thermal SCO transition with a T1/2 = 250 K as well as a LIESST effect. In contrast its racemic counterpart () comprises of mostly LS Fe(II) and exhibits no LIESST properties.

  13. VIEW OF DATE DRIVE, SHOWING DATE PALMS. NOTE TRELLIS ON ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    VIEW OF DATE DRIVE, SHOWING DATE PALMS. NOTE TRELLIS ON TYPE 11 FACILITY, FACILITY 808. VIEW FACING NORTHWEST - Camp H.M. Smith and Navy Public Works Center Manana Title VII (Capehart) Housing, Intersection of Acacia Road and Brich Circle, Pearl City, Honolulu County, HI

  14. Hydration rind dates rhyolite flows.

    PubMed

    Friedman, I

    1968-02-23

    Hydration of obsidian has been used to date rhyolite flows, containing obsidian or porphyritic glass, at Glass Mountain (Medicine Lake Highlands) and Mono Lake, California. The method is simple and rapid and can be used to date flows that erupted between 200 and approximately 200,000 years ago. PMID:17768978

  15. Radiocarbon Dating: An Annotated Bibliography.

    ERIC Educational Resources Information Center

    Fortine, Suellen

    This selective annotated bibliography covers various sources of information on the radiocarbon dating method, including journal articles, conference proceedings, and reports, reflecting the most important and useful sources of the last 25 years. The bibliography is divided into five parts--general background on radiocarbon, radiocarbon dating,…

  16. Ionium dating of igneous rocks.

    PubMed

    Kigoshi, K

    1967-05-19

    Local fractionation of uranium and thorium, between minerals within a sample of igneous rock at the time of crystallization, makes it possible to date its solidification by use of ionium and uranium. Results on samples of granite, pumice, and lava suggest that this method of dating is reliable.

  17. Hydration rind dates rhyolite flows.

    PubMed

    Friedman, I

    1968-02-23

    Hydration of obsidian has been used to date rhyolite flows, containing obsidian or porphyritic glass, at Glass Mountain (Medicine Lake Highlands) and Mono Lake, California. The method is simple and rapid and can be used to date flows that erupted between 200 and approximately 200,000 years ago.

  18. Hydration rind dates rhyolite flows

    USGS Publications Warehouse

    Friedman, I.

    1968-01-01

    Hydration of obsidian has been used to date rhyolite flows, containing obsidian or porphyritic glass, at Glass Mountain (Medicine Lake Highlands) and Mono Lake, California. The method is simple and rapid and can be used to date flows that erupted between 200 and approximately 200,000 years ago.

  19. Childhood Maltreatment and Date Rape.

    ERIC Educational Resources Information Center

    Sanders, Barbara; Moore, Dina L.

    1999-01-01

    Study compares women college students who reported unwanted sexual experiences judged to constitute date rape with controls who reported no rape. Findings suggest that compared to controls, date-rape group had significantly higher scores on measures of overall childhood stress. Concludes that early forms of maltreatment (not specifically sexual)…

  20. Optical resolution by preferential crystallization of (RS)-2-benzoylamino-2-benzyl-3-hydroxypropanoic acid and its use in synthesizing optically active 2-amino-2-methyl-3-phenylpropanoic acid.

    PubMed

    Shiraiwa, Tadashi; Suzuki, Masahiro; Sakai, Yoshio; Nagasawa, Hisashi; Takatani, Kazuhiro; Noshi, Daisuke; Yamanashi, Kenji

    2002-10-01

    To synthesize optically active 2-amino-2-methyl-3-phenylpropanoic acid (1), (RS)-2-benzoylamino-2-benzyl-3-hydroxypropanoic acid [(RS)-2] was first optically resolved using cinchonidine as a resolving agent to yield optically pure (S)- and (R)-2 in yields of about 70%, based on half of the starting amount of (RS)-2. Next, the racemic structure of (RS)-2 was examined based on melting point, solubility, IR spectrum, and binary and ternary phase diagrams, with the aim of optical resolution by preferential crystallization of (RS)-2. Results indicated that the (RS)-2 exists as a conglomerate at room temperature, although it forms a racemic compound at the melting point. The optical resolution by preferential crystallization yielded (S)- and (R)-2 with optical purities of about 90%, which were fully purified by recrystallization. After O-tosylation of (S)- and (R)-2, reduction by zinc powder and sodium iodide gave (R)- and (S)-1, respectively.

  1. Cocrystallizing natural RNA with its unnatural mirror image: biochemical and preliminary X-ray diffraction analysis of a 5S rRNA A-helix racemate

    SciTech Connect

    Förster, Charlotte; Brauer, Arnd B. E.; Lehmann, Daniel; Borowski, Tordis; Brode, Svenja; Fürste, Jens P.; Perbandt, Markus; Betzel, Christian

    2007-10-01

    A 5S rRNA A-helix 7-mer oligonucleotide was chemically synthesized both as d-RNA and as l-RNA, biochemically investigated, crystallized as a stochiometric racemate and examined by X-ray diffraction. Chemically synthesized RNAs with the unnatural l-configuration possess enhanced in vivo stability and nuclease resistance, which is a highly desirable property for pharmacological applications. For a structural comparison, both l- and d-RNA oligonucleotides of a shortened Thermus flavus 5S rRNA A-helix were chemically synthesized. The enantiomeric RNA duplexes were stochiometrically cocrystallized as a racemate, which enabled analysis of the d- and l-RNA enantiomers in the same crystals. In addition to a biochemical investigation, diffraction data were collected to 3.0 Å resolution using synchrotron radiation. The crystals belonged to space group P3{sub 1}21, with unit-cell parameters a = b = 35.59, c = 135.30 Å, γ = 120° and two molecules per asymmetric unit.

  2. Organocatalytic aza-Michael/retro-aza-Michael reaction: pronounced chirality amplification in aza-Michael reaction and racemization via retro-aza-Michael reaction.

    PubMed

    Cai, Yong-Feng; Li, Li; Luo, Meng-Xian; Yang, Ke-Fang; Lai, Guo-Qiao; Jiang, Jian-Xiong; Xu, Li-Wen

    2011-05-01

    A detailed experimental investigation of an aza-Michael reaction of aniline and chalcone is presented. A series of Cinchona alkaloid-derived organocatalysts with different functional groups were prepared and used in the aza-Michael and retro-aza-Michael reaction. There was an interesting finding that a complete reversal of stereoselectivity when a benzoyl group was introduced to the cinchonine and cinchonidine. The chirality amplification vs. time proceeds in the quinine-derived organocatalyst containing silicon-based bulky group, QN-TBS, -catalyzed aza-Michael reaction under solvent-free conditions. In addition, we have demonstrated for the first time that racemization was occurred in suitable solvents under mild conditions due to retro-aza-Michael reaction of the Michael adduct of aniline with chalcone. These indicate the equilibrium of retro-aza-Michael reaction and aza-Michael reaction produce the happening of chirality amplification in aza-Michael reaction and racemization via retro-aza-Michael reaction under different conditions, which would be beneficial to the development of novel chiral catalysts for the aza-Michael reactions.

  3. SERF-filtered experiments: new enantio-selective tools for deciphering complex spectra of racemic mixtures dissolved in chiral oriented media.

    PubMed

    Farjon, Jonathan; Merlet, Denis

    2011-05-01

    The use of chiral liquid crystals as NMR solvent is a powerful tool to visualize and quantify enantiomers. This technique is much more robust than traditional liquid state techniques. Recent developments have been performed to simplify proton spectra obtained in these solvents which are usually complex to analyze. In the different published sequences the enantiomeric differentiation can be visualized but none of them rely the different (1)H-(1)H couplings to have a coherent set for each enantiomer especially in cases of racemic mixtures. In this work to overcome such limitations, we present a new NMR pulse sequence using semi-selective pulses to assign for each enantiomer the different (1)H-(1)H couplings. The aim is to obtain the signal of only one enantiomer, through a first Selective ReFocussing (SERF) filtering block implemented for the enantio-selection followed by a second SERF block for measuring a chosen coupling. The whole sequence is called (1)H SERF-filtered-SERF. These techniques permit for the first time to assign all dipolar couplings to each enantiomer of racemic mixtures dissolved in chiral oriented media. We demonstrate that using this experiment it is possible to visualize enantio-differentiation even in the case where the multiplets are not resolved in the SERF experiments, pushing back the limits of the enantiomeric visualization.

  4. Radiocarbon dating with electrostatic accelerators: dating of milligram samples.

    PubMed

    Bennett, C L; Beukens, R P; Clover, M R; Elmore, D; Gove, H E; Kilius, L; Litherland, A E; Purser, K H

    1978-07-28

    The recently developed direct counting technique for radiocarbon atoms has been used to measure the relative numbers of such atoms in various geological samples which had earlier been dated by the beta-ray counting method. Sample weights ranged from 3.5 to 15 milligrams. The dates determined by the two methods are consistent with each other. Further experience with the new method is also reported.

  5. Effect of HF leaching on 14C dates of pottery

    NASA Astrophysics Data System (ADS)

    Goslar, Tomasz; Kozłowski, Janusz; Szmyt, Marzena; Czernik, Justyna

    2013-01-01

    This paper presents the experiments with 14C dating of two potsherds, which contained carbon dispersed rather homogeneously in their clay fabric. After AAA treatment, the potsherds still appeared to be contaminated with young carbon, presumably connected with humic acids. To make removal of humic acids more effective, we treated the sherds with HF acid of different concentration. The 14C results obtained demonstrate that HF treatment indeed helps to remove humic contaminants, but it also mobilizes carbon bound to raw clay, which may make 14C dates too old. We conclude therefore, that using a simple combination of HF and AAA treatment seems insufficient in reliable 14C dating of carbon homogeneously dispersed in the volume of potsherds.

  6. Dating sediments using luminescence signals

    SciTech Connect

    Wintle, A. )

    1993-05-01

    Before siting a nuclear power station or a nuclear waste repository, it is necessary to establish that the area has been free of earthquake activity for a sufficient period of time. Evidence of past earthquake activity is often provided by faults in surface sediments. Age limits for fault formation can be set by obtaining the depositional ages of the sediment unit in which the fault was formed and the overlying sediment. A useful technique would be one that dating could be applied to the mineral grains that make up the sediments and that would give the time that has passed since the grains were blown or washed into position. Luminescence dating techniques, of which the most well known is thermo-luminescence (TL), provide such information. This approach has been successful in dating movement on the Wasatch Fault in Utah. A combination of TL and radiocarbon dates indicated that three faulting events had occurred within the past 5000 years. 2 refs., 1 fig.

  7. Radiocarbon dating of terrestrial carbonates

    USGS Publications Warehouse

    Pigati, Jeffrey S.; Rink, W. Jack; Thompson, Jeroen

    2014-01-01

    Terrestrial carbonates encompass a wide range of materials that potentially could be used for radiocarbon (14C) dating. Biogenic carbonates, including shells and tests of terrestrial and aquatic gastropods, bivalves, ostracodes, and foraminifera, are preserved in a variety of late Quaternary deposits and may be suitable for 14C dating. Primary calcareous deposits (marls, tufa, speleothems) and secondary carbonates (rhizoliths, fracture fill, soil carbonate) may also be targeted for dating when conditions are favorable. This chapter discusses issues that are commonly encountered in 14C dating of terrestrial carbonates, including isotopic disequilibrium and open-system behavior, as well as methods used to determine the reliability of ages derived from these materials. Recent methodological advancements that may improve the accuracy and precision of 14C ages of terrestrial carbonates are also highlighted.

  8. Microscale radiocarbon dating of paintings

    NASA Astrophysics Data System (ADS)

    Hendriks, Laura; Hajdas, Irka; McIntyre, Cameron; Küffner, Markus; Scherrer, Nadim C.; Ferreira, Ester S. B.

    2016-03-01

    In this paper, radiocarbon dating of paintings using minimal sample sizes has been investigated, in an effort to address the problem of limited access to sample material in paintings. 14C analyses were conducted on signed and dated paintings from two Swiss artists of the twentieth century. The selected paintings dated from the 1930s and 1960s, provided the opportunity to evaluate the dating accuracy on paintings realized before and after 1950 AD when the 14C bomb peak was created, as a result of the nuclear tests conducted in the 1950/1960s. The work focused on the one hand on minimizing the size of the canvas sample required for accelerator mass spectrometer radiocarbon measurement on the gas ion source of the MICADAS and, on the other hand, on testing the possibility of dating the organic binder of the paint. Following careful characterization of the paint composition by X-ray fluorescence spectroscopy, Fourier transformed infrared spectroscopy, and Raman spectroscopy, paints containing no other carbon source than the natural organic binder were identified and dated.

  9. Thermal synthesis and hydrolysis of polyglyceric acid. [in orgin of life studying

    NASA Technical Reports Server (NTRS)

    Weber, Arthur L.

    1989-01-01

    Polyglyceric acid was synthesized by thermal condensation of glyceric acid at 80 C in the presence and absence of two mole percent of sulfuric acid catalyst. The acid catalyst accelerated the polymerization over 100-fold and made possible the synthesis of insoluble polymers of both L- and DL-glyceric acid by heating for less than 1 day. Racemization of L-glyceric acid yielded less than 1 percent D-glyceric acid in condensations carried out at 80 C with catalyst for 1 day and without catalyst for 12 days. The condensation of L-glyceric acid yielded an insoluble polymer much more readily than condensation of DL-glyceric acid. Studies of the hydrolysis of poly-DL-glyceric acid revealed that it was considerably more stable under mild acidic conditions compared to neutral pH. The relationship of this study to the origin of life is discussed.

  10. Dating of Modern Human Evolution

    NASA Astrophysics Data System (ADS)

    Grun, R.

    Dating studies on palaoeanthropological sites is usually carried out on material associ- ated with the human remains, such as the sediment, charcoal or other fauna rather than the human specimen itself. The reason lies in the fact that most dating techniques are destructive and because the hominid remains are too rare to be sacrificed for dating. This indirect dating approach is in many cases not satisfactory, because: (i) the human remains are often buried into the sediments and the association with other materials is uncertain (e.g. Skhul, Qafzeh, etc.); (ii) faunal remains or minerals from the sediment are re-worked from older deposits (see e.g. present discussion of the age of the Homo erectus remains in Indonesia; (iii) the hominid fossils were discovered at a time when no careful excavations were carried out and it is impossible to correlate the specimen with other datable material (which applies tonearly 90% of all palaeoanthropological specimens). For example, the hominid burial site of Qafzeh in Israel has been dated by several independent dating laboratories with a multitude of methods. However, the data are still not accepted by some because the dating has not been carried out on the hominid specimen. Until recently, hominid fossils could only be dated by radiocarbon. This method reaches back to about 40,000 years. As a consequence, all the older fossils could not be analysed and many important questions in our understanding of human evolution could not be addressed. Human remains are scarce and extremely valuable, therefore any sort of destruction has to be kept to an absolute minimum. This is of particular importance in Australia where any human fossils are sacred. Thus, for the analysis of hominid material it was necessary to develop a more or less non-destructive techniques. This has been ac- complished in recent years by the application of ESR dating of tooth enamel and a combination of gamma spectrometric and TIMS U-series dating of bones. The exam

  11. The fruit of the date palm: its possible use as the best food for the future?

    PubMed

    Al-Shahib, Walid; Marshall, Richard J

    2003-07-01

    The fruits (dates) of the date palm (Phoenix dactylifera L.) contain a high percentage of carbohydrate (total sugars, 44-88%), fat (0.2-0.5%), 15 salts and minerals, protein (2.3-5.6%), vitamins and a high percentage of dietary fibre (6.4-11.5%). The flesh of dates contains 0.2-0.5% oil, whereas the seed contains 7.7-9.7% oil. The weight of the seed is 5.6-14.2% of the date. The fatty acids occur in both flesh and seed as a range of saturated and unsaturated acids, the seeds containing 14 types of fatty acids, but only eight of these fatty acids occur in very low concentration in the flesh. Unsaturated fatty acids include palmitoleic, oleic, linoleic and linolenic acids. The oleic acid content of the seeds varies from 41.1 to 58.8%, which suggests that the seeds of date could be used as a source of oleic acid. There are at least 15 minerals in dates. The percentage of each mineral in dried dates varies from 0.1 to 916 mg/100 g date depending on the type of mineral. In many varieties, potassium can be found at a concentration as high as 0.9% in the flesh while it is as high as 0.5% in some seeds. Other minerals and salts that are found in various proportions include boron, calcium, cobalt, copper, fluorine, iron, magnesium, manganese, potassium, phosphorous, sodium and zinc. Additionally, the seeds contain aluminum, cadmium, chloride, lead and sulphur in various proportions. Dates contain elemental fluorine that is useful in protecting teeth against decay. Selenium, another element believed to help prevent cancer and important in immune function, is also found in dates. The protein in dates contains 23 types of amino acids, some of which are not present in the most popular fruits such as oranges, apples and bananas. Dates contain at least six vitamins including a small amount of vitamin C, and vitamins B(1) thiamine, B(2) riboflavin, nicotinic acid (niacin) and vitamin A. The dietary fibre of 14 varieties of dates has been shown to be as high as 6.4-11.5% depending

  12. Highly diastereoselective 1,3-dipolar cycloadditions of chiral non-racemic nitrones to 1,2-diaza-1,3-dienes: an experimental and computational investigation.

    PubMed

    Majer, Roberta; Konechnaya, Olga; Delso, Ignacio; Tejero, Tomas; Attanasi, Orazio A; Santeusanio, Stefania; Merino, Pedro

    2014-11-28

    Asymmetric 1,3-dipolar cycloadditions between 1,2-diaza-1,3-dienes and chiral non-racemic nitrones to give 3-substituted-5-diazenyl isoxazolidines were studied both experimentally and theoretically. Whereas cyclic nitrones provide complete selectivity for the cycloaddition reaction (only one isomer is obtained), acyclic nitrones derived from D-glyceraldehyde and D-galactose lead to 1 : 1 mixtures of two isomers. A DFT analysis based on reactivity indices correctly predicts the regiochemistry of the reaction in agreement with the high electron-withdrawing character of the diazenyl group. The same theoretical studies considering solvent effects (PCM model) based on transition state theory are in qualitative agreement with the observed experimental results.

  13. Crystallization of Enantiomerically Pure Proteins from Quasi-Racemic Mixtures: Structure Determination by X-Ray Diffraction of Isotope-Labeled Ester Insulin and Human Insulin.

    PubMed

    Mandal, Kalyaneswar; Dhayalan, Balamurugan; Avital-Shmilovici, Michal; Tokmakoff, Andrei; Kent, Stephen B H

    2016-03-01

    As a part of a program aimed towards the study of the dynamics of human insulin-protein dimer formation using two-dimensional infrared spectroscopy, we used total chemical synthesis to prepare stable isotope labeled [(1-(13) C=(18) O)Phe(B24) )] human insulin, via [(1-(13) C=(18) O)Phe(B24) )] ester insulin as a key intermediate product that facilitates folding of the synthetic protein molecule (see preceding article). Here, we describe the crystal structure of the synthetic isotope-labeled ester insulin intermediate and the product synthetic human insulin. Additionally, we present our observations on hexamer formation with these two proteins in the absence of phenol derivatives and/or Zn metal ions. We also describe and discuss the fractional crystallization of quasi-racemic protein mixtures containing each of these two synthetic proteins.

  14. Bacterial defluorination of 4-fluoroglutamic acid.

    PubMed

    Donnelly, Clár; Murphy, Cormac D

    2007-12-01

    Fluorinated amino acids are used as enzyme inhibitors, mechanistic probes and in the production of pharmacologically active peptides. Because enantiomerically pure 4-fluoroglutamate is difficult to prepare, the selective degradation of the L-isomer is a potentially convenient method of obtaining D-4-fluoroglutamate from the racemate. In this paper, we describe our investigations on the degradation of 4-fluoroglutamate by bacteria. Fluoride ion was detected in resting-cell cultures of a number of bacteria that were incubated with racemic 4-fluoroglutamate. Analysis of the culture supernatants by chiral gas chromatography-mass spectrometry revealed that only the L-isomer was degraded. The degradation of 4-fluoroglutamate was also examined in cell-free extracts of Streptomyces cattleya and Proteus mirabilis, and it was observed that equimolar concentrations of fluoride ion and ammonia were generated. The activity was located in the soluble fraction of cell extracts, thus is not related to the L-2-amino-4-chloro-4-pentenoic acid dehydrochlorinase previously identified in membrane fractions of P. mirabilis.

  15. Scandium versus yttrium{amino-alkoxy-bis(phenolate)} complexes for the stereoselective ring-opening polymerization of racemic lactide and β-butyrolactone.

    PubMed

    Chapurina, Yulia; Klitzke, Joice; Casagrande, Osvaldo de L; Awada, Mouhamad; Dorcet, Vincent; Kirillov, Evgueni; Carpentier, Jean-François

    2014-10-14

    Scandium and yttrium amide complexes Ln{ONXO(R1,R2)}(N(SiHMe2)2)(THF)n (Ln = Sc, n = 0 or Y, n = 1; X = NMe2 or OMe; R(1) = Cumyl or p-Cl-Cumyl; R(2) = Me or Cumyl) were prepared by aminolysis of Ln[N(SiHMe2)2]3(THF) with the corresponding tetradentate diamino- or alkoxy-amino-bis(phenol) pro-ligands {ONXO(R1,R2)}H2. In the solid state and in toluene solution, the scandium complexes are monomeric and 5-coordinated, while the analogous yttrium complexes all bear an extra THF-coordinated molecule and are 6-coordinated. Sc{ONXO(R1,R2)}(N(SiHMe2)2) complexes are single-site initiators for the ring-opening polymerization (ROP) of racemic lactide but are less active than their yttrium analogues Y{ONXO(R1,R2)}(N(SiHMe2)2)(THF); also, in contrast to the latter ones, they are inactive in the ROP of the more demanding racemic β-butyrolactone. On the other hand, the scandium amide complexes feature a significantly improved control over the ROP of lactide, yielding PLAs with much narrower molecular weight distributions (Đ(M) < 1.1 for Sc vs. 1.5-2.0 for Y). The yttrium complex with the very bulky o,p-dicumyl-substituted ligand is more heteroselective than its scandium analogue (P(r) = 0.88 vs. 0.83), while the opposite is observed with complexes based on p-methyl-substituted ligands (P(r) = 0.50 in toluene or 0.72-0.75 in THF for Y vs. P(r) = 0.75-0.83 for Sc in toluene). These reactivity and selectivity trends are rationalized by a much more sterically crowded coordination sphere in scandium than in yttrium complexes.

  16. The truth about the lower plasma concentration of the (-)-isomer after racemic doxazosin administration in rats: Stereoselective inhibition of the (-)-isomer by the (+)-isomer at CYP3A.

    PubMed

    Kong, Dezhi; Li, Qing; Zhang, Panpan; Zhang, Wei; Zhen, Yaqin; Ren, Leiming

    2015-09-18

    Doxazosin (DOX), a long-lasting α1-adrenoceptor antagonist, is used clinically as a racemate that consists of two optical isomers. In humans and rats, following oral administration of racemic DOX [(±)-DOX], the plasma concentration of the (-)-isomer is lower than that of the (+)-isomer, but the mechanism for this interaction is not known. In this study, a chiral HPLC with fluorescence detection was used to measure the drug concentrations for analysis of the stereoselective metabolism of DOX in in vivo and in vitro experiments. We found that the plasma levels of the (-)-isomer were significantly lower than those of the (+)-enantiomer following i.v. administration of (±)-DOX to the rats and that the depletion rate constant (kdep) of (-)-DOX (0.0107±0.0007L/min) was significantly larger than that of (+)-DOX (kdep 0.0088±0.0005L/min) (p<0.05) when (±)-DOX was incubated with rat liver microsomes (RLMs). However, (-)-DOX was not depleted faster than (+)-DOX following their separate incubation with RLMs. The metabolism of (-)- or (+)-isomer in RLMs was catalysed by CYP3A because the depletion of the compounds was inhibited by ketoconazole (a potent CYP3A-selective inhibitor) similarly. More importantly, the kdep of (+)-DOX in the 1.0/2.0 and 0.5/2.5 (+)-DOX/(-)-DOX mixtures was significantly lower than that of (-)-DOX in the 1.0/2.0 and 0.5/2.5 (-)-DOX/(+)-DOX mixtures (p<0.05). In conclusion, although (-)-DOX is not depleted faster than (+)-DOX when only a single isomer of DOX is incubated with rat liver microsomes, it is depleted much faster than (+)-DOX when a mixture of the two isomers was used, suggesting a prominent and stereoselective inhibition of the (-)-isomer over the (+)-isomer at the CYP3A enzyme.

  17. 21 CFR 1312.25 - Expiration date.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 9 2010-04-01 2010-04-01 false Expiration date. 1312.25 Section 1312.25 Food and... SUBSTANCES Exportation of Controlled Substances § 1312.25 Expiration date. An export permit shall not be valid after the date specified therein, which date shall conform to the expiration date specified in...

  18. 21 CFR 1312.25 - Expiration date.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 9 2013-04-01 2013-04-01 false Expiration date. 1312.25 Section 1312.25 Food and... SUBSTANCES Exportation of Controlled Substances § 1312.25 Expiration date. An export permit shall not be valid after the date specified therein, which date shall conform to the expiration date specified in...

  19. 21 CFR 1312.25 - Expiration date.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 9 2012-04-01 2012-04-01 false Expiration date. 1312.25 Section 1312.25 Food and... SUBSTANCES Exportation of Controlled Substances § 1312.25 Expiration date. An export permit shall not be valid after the date specified therein, which date shall conform to the expiration date specified in...

  20. 21 CFR 1312.25 - Expiration date.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 9 2011-04-01 2011-04-01 false Expiration date. 1312.25 Section 1312.25 Food and... SUBSTANCES Exportation of Controlled Substances § 1312.25 Expiration date. An export permit shall not be valid after the date specified therein, which date shall conform to the expiration date specified in...

  1. 21 CFR 1312.25 - Expiration date.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 9 2014-04-01 2014-04-01 false Expiration date. 1312.25 Section 1312.25 Food and... SUBSTANCES Exportation of Controlled Substances § 1312.25 Expiration date. An export permit shall not be valid after the date specified therein, which date shall conform to the expiration date specified in...

  2. Online Dating and Conjugal Bereavement

    ERIC Educational Resources Information Center

    Young, Dannagal Goldthwaite; Caplan, Scott E.

    2010-01-01

    This study examined self-presentation in the online dating profiles of 241 widowed and 280 divorced individuals between 18 and 40 years old. A content analysis of open-ended user-generated profiles assessed the presence or absence of various themes, including the user's marital status, the backstory of their lost relationship, and whether they…

  3. Dating techniques in archaeology and paleoanthropology

    SciTech Connect

    Taylor, R.E.

    1987-02-15

    Archaeologists have an increasing array of physical dating methods at their disposal. R.E. Taylor of the University of California discusses available techniques, recent advances in radiocarbon dating, and current developments in radiocalcium dating.

  4. Dating Techniques in Archaeology and Paleoanthropology.

    ERIC Educational Resources Information Center

    Taylor, R. E.

    1987-01-01

    Discusses some of the new physical dating methods being used by archaeologists and paleoanthropologists to study the material remains of ancient primates. Describes the quaternary physical dating techniques, advances in radiocarbon dating, and the radiocalcium data method. (TW)

  5. Asymmetric Reduction of Lactam-Based β-Aminoacrylates. Synthesis of Heterocyclic β(2)-Amino Acids.

    PubMed

    Campello, Hugo Rego; Parker, Jeremy; Perry, Matthew; Ryberg, Per; Gallagher, Timothy

    2016-08-19

    The ability to affect asymmetric reduction of heterocyclic β-aminoacrylates 1 (n = 1-3) has been assessed with pyrrolidine and piperidone variants generating the corresponding N-heterocyclic β(2)-amino acids 3b and 5b with high enantioselectivity (≥97% ee) using a Rh/WALPHOS catalyst combination. The use of the carboxylic acid substrate was essential; the corresponding esters do undergo reduction but led to racemic products. The seven-ring azepanone variant (as the carboxylic acid 9b) underwent reduction, but only a minimal level of asymmetric induction was observed. PMID:27508307

  6. Kinetic resolution of acids in acylation reactions in the presence of chiral tertiary amines

    SciTech Connect

    Potapov, V.M.; Dem'yanovich, V.M.; Khlebnikov, V.A.

    1988-07-10

    Asymmetric synthesis has now become an important method for the production of optically active compounds, and its most attractive form is asymmetric catalysis. This work was devoted to an investigation into asymmetric catalysis with chiral tertiary amines in acylation reactions. During the acylation of alcohols and amines by the action of racemic 2-phenylpropionic and 2-methyl-3-phenylpropionic acids in the presence of S-nicotine the initial acids are resolved kinetically. The (R)-2-phenylpropionic acid obtained in this way had an optical purity of 0.5-1.5%.

  7. 31 CFR 536.302 - Effective date.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... FOREIGN ASSETS CONTROL, DEPARTMENT OF THE TREASURY NARCOTICS TRAFFICKING SANCTIONS REGULATIONS General... of specially designated narcotics traffickers designated after that date, the earlier of the date...

  8. 31 CFR 536.302 - Effective date.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... FOREIGN ASSETS CONTROL, DEPARTMENT OF THE TREASURY NARCOTICS TRAFFICKING SANCTIONS REGULATIONS General... of specially designated narcotics traffickers designated after that date, the earlier of the date...

  9. 31 CFR 536.302 - Effective date.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... FOREIGN ASSETS CONTROL, DEPARTMENT OF THE TREASURY NARCOTICS TRAFFICKING SANCTIONS REGULATIONS General... of specially designated narcotics traffickers designated after that date, the earlier of the date...

  10. 31 CFR 536.302 - Effective date.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... FOREIGN ASSETS CONTROL, DEPARTMENT OF THE TREASURY NARCOTICS TRAFFICKING SANCTIONS REGULATIONS General... of specially designated narcotics traffickers designated after that date, the earlier of the date...

  11. 31 CFR 536.302 - Effective date.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... FOREIGN ASSETS CONTROL, DEPARTMENT OF THE TREASURY NARCOTICS TRAFFICKING SANCTIONS REGULATIONS General... of specially designated narcotics traffickers designated after that date, the earlier of the date...

  12. Separation of phenylsuccinic acid enantiomers using biphasic chiral recognition high-speed countercurrent chromatography.

    PubMed

    Sun, Genlin; Tang, Kewen; Zhang, Panliang; Yang, Weijun; Sui, Guoqing

    2014-07-01

    High-speed countercurrent chromatography (HSCCC) combined with biphasic chiral recognition was successfully applied to the resolution of phenylsuccinic acid enantiomers. D-Isobutyl tartrate and hydroxypropyl-β-cyclodextrin were employed as lipophilic and hydrophilic selectors dissolved in the organic stationary phase and aqueous mobile phase, respectively. The two-phase solvent system was made up of n-hexane/methyl tert-butyl ether/water (0.5:1.5:2, v/v/v). Impacts of the type and concentration of chiral selectors, the pH value of the aqueous phase solution as well as the temperature on the separation efficiency were investigated. By means of preparative HSCCC, pure enantiomer was obtained by separating 810 mg of racemate with a purity >99.5% and a recovery rate between 82 and 85%. The experimental results indicate that biphasic recognition HSCCC provide a promising means for efficient separation of racemates.

  13. Radiocarbon dating of biogenetic opal.

    PubMed

    Wilding, L P

    1967-04-01

    Approximately 75 grams of biogenetic opal were isolated from 45 kilograms of soil by employing gross particle-size and sink-float specific gravity fractionation procedures. After pretreatment of the sample to remove extraneous organic and inorganic carbon contaminants, the carbon occluded within opal phytoliths was dated at 13,300 +/- 450 years before the present. Therefore, biogenetic opal is stable for relatively long periods.

  14. Privacy: after the compliance date.

    PubMed

    Mikels, Debbie

    2004-01-01

    This article reviews successful strategies in preparing for HIPAA Privacy compliance. There are ongoing challenges organizations will face after the compliance date, such as managing research issues, identifying all business associates and managing the accounting of disclosures process. Finally, health information professionals must play an active role in ensuring that patient information is protected, while providing appropriate access as new uses for information are developed.

  15. Gender differences in D-aspartic acid content in skull bone.

    PubMed

    Torikoshi-Hatano, Aiko; Namera, Akira; Shiraishi, Hiroaki; Arima, Yousuke; Toubou, Hirokazu; Ezaki, Jiro; Morikawa, Masami; Nagao, Masataka

    2012-12-01

    In forensic medicine, the personal identification of cadavers is one of the most important tasks. One method of estimating age at death relies on the high correlation between racemization rates in teeth and actual age, and this method has been applied successfully in forensic odontology for several years. In this study, we attempt to facilitate the analysis of racemized amino acids and examine the determination of age at death on the basis of the extent of aspartic acid (Asp) racemization in skull bones. The specimens were obtained from 61 human skull bones (19 females and 42 males) that underwent judicial autopsy from October 2010 to May 2012. The amount of D-Asp and L-Asp, total protein, osteocalcin, and collagen I in the skull bones was measured. Logistic regression analysis was performed for age, sex, and each measured protein. The amount of D-Asp in the female skull bones was significantly different from that in the male skull bones (p = 0.021), whereas the amount of L-Asp was similar. Thus, our study indicates that the amount of D-Asp in skull bones is different between the sexes.

  16. Resolution of 1- and 2-naphthylmethoxyacetic acids, NMR reagents for absolute configuration determination, by use of L-phenylalaninol.

    PubMed

    Arita, Shoko; Yabuuchi, Tetsuya; Kusumi, Takenori

    2003-08-01

    Racemic 1- and 2-naphthylmethoxyacetic acids (1NMA and 2NMA), the chiral anisotropic reagents used for absolute configuration determination of chiral secondary alcohols and primary amines, were conveniently resolved to enantiomers (>99% ee) by condensation with L-phenylalaninol (2-amino-3-phenylpropanol), chromatographic separation of the diastereomers, and hydrolysis. This method enables large-scale preparation of enantiomeric 1NMA and 2NMA. PMID:12840826

  17. Polymerization of amino acids containing nucleotide bases

    NASA Technical Reports Server (NTRS)

    Ben Cheikh, Azzouz; Orgel, Leslie E.

    1990-01-01

    The nucleoamino acids 1-(3'-amino,3'-carboxypropyl)uracil (3) and 9-(3'-amino,3'-carboxypropyl)adenine (4) have been prepared as (L)-en-antiomers and as racemic mixtures. When 3 or 4 is suspended in water and treated with N,N'-carbon-yldiimidazole, peptides are formed in good yield. The products formed from the (L)-enantiomers are hydrolyzed to the monomeric amino acids by pronase. Attempts to improve the efficiency of these oligomerizations by including a polyuridylate template in the reaction mixture were not successful. Similarly, oligomers derived from the (L)-enantiomer of 3 did not act as templates to facilitate the oligomerization of 4.

  18. 24 CFR 1710.21 - Effective dates.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... developer in writing prior to such 30th day that: (1) The effective date has been suspended in accordance... date by developer. (1) A developer, or owner, may request that the effective date of its Statement of... shall be suspended as of the date the request was executed by the developer or owner. (3) The...

  19. 12 CFR 1010.21 - Effective dates.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... notifies the developer in writing prior to such 30th day that: (1) The effective date has been suspended in... effective date by developer. (1) A developer, or owner, may request that the effective date of its Statement... shall be suspended as of the date the request was executed by the developer or owner. (3) The...

  20. 24 CFR 1710.21 - Effective dates.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... developer in writing prior to such 30th day that: (1) The effective date has been suspended in accordance... date by developer. (1) A developer, or owner, may request that the effective date of its Statement of... shall be suspended as of the date the request was executed by the developer or owner. (3) The...

  1. 12 CFR 1010.21 - Effective dates.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... notifies the developer in writing prior to such 30th day that: (1) The effective date has been suspended in... effective date by developer. (1) A developer, or owner, may request that the effective date of its Statement... shall be suspended as of the date the request was executed by the developer or owner. (3) The...

  2. 24 CFR 1710.21 - Effective dates.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... developer in writing prior to such 30th day that: (1) The effective date has been suspended in accordance... date by developer. (1) A developer, or owner, may request that the effective date of its Statement of... shall be suspended as of the date the request was executed by the developer or owner. (3) The...

  3. 12 CFR 1010.21 - Effective dates.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... notifies the developer in writing prior to such 30th day that: (1) The effective date has been suspended in... effective date by developer. (1) A developer, or owner, may request that the effective date of its Statement... shall be suspended as of the date the request was executed by the developer or owner. (3) The...

  4. School Counselors' Role in Dating Violence Intervention

    ERIC Educational Resources Information Center

    Craigen, Laurie M.; Sikes, April; Healey, Amanda; Hays, Danica

    2009-01-01

    Dating violence among adolescents is a major public health concern. The purpose of this paper is to examine five factors of which school counselors must be aware in order to recognize, intervene, and report incidence of dating violence. These factors are (a) understanding the diverse definitions of dating violence, (b) recognizing dating violence…

  5. 31 CFR 546.303 - Effective date.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 31 Money and Finance: Treasury 3 2010-07-01 2010-07-01 false Effective date. 546.303 Section 546....303 Effective date. The term effective date refers to the effective date of the applicable prohibitions and directives contained in this part as follows: (a) With respect to a person whose property...

  6. 31 CFR 541.302 - Effective date.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 31 Money and Finance: Treasury 3 2010-07-01 2010-07-01 false Effective date. 541.302 Section 541... § 541.302 Effective date. The term effective date refers to the effective date of the applicable prohibitions and directives contained in this part as follows: (a) With respect to a person whose property...

  7. 31 CFR 542.302 - Effective date.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ....302 Effective date. With respect to a person whose property or interests in property are blocked pursuant to a designation under § 542.201(a), the effective date is the earlier of the date on which either... 31 Money and Finance: Treasury 3 2010-07-01 2010-07-01 false Effective date. 542.302 Section...

  8. 31 CFR 594.302 - Effective date.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 31 Money and Finance: Treasury 3 2010-07-01 2010-07-01 false Effective date. 594.302 Section 594... Definitions § 594.302 Effective date. The term effective date refers to the effective date of the applicable prohibitions and directives contained in this part as follows: (a) With respect to a person whose property...

  9. 31 CFR 547.303 - Effective date.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 31 Money and Finance: Treasury 3 2010-07-01 2010-07-01 false Effective date. 547.303 Section 547... General Definitions § 547.303 Effective date. The term effective date refers to the effective date of the... property and interests in property are blocked pursuant to § 547.201(a)(1), 12:01 a.m. eastern...

  10. 31 CFR 543.303 - Effective date.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 31 Money and Finance: Treasury 3 2010-07-01 2010-07-01 false Effective date. 543.303 Section 543... Definitions § 543.303 Effective date. The term effective date refers to the effective date of the applicable prohibitions and directives contained in this part as follows: (a) With respect to a person whose property...

  11. 38 CFR 21.7135 - Discontinuance dates.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...) Eligibility expires. If the veteran is pursuing a course on the date of expiration of eligibility as... Bill-Active Duty) Payments-Educational Assistance § 21.7135 Discontinuance dates. The effective date of... dependent. If more than one type of reduction or discontinuance is involved, the earliest date will...

  12. 38 CFR 21.3332 - Discontinuance dates.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... expiration of the eligible person's entitlement. (e) Date of interruption of course as determined by the... special training allowance as provided in this section on the earliest date of the following: (a) The ending date of the course. (b) The ending date of the period of enrollment as certified by the...

  13. 38 CFR 21.3332 - Discontinuance dates.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... expiration of the eligible person's entitlement. (e) Date of interruption of course as determined by the... special training allowance as provided in this section on the earliest date of the following: (a) The ending date of the course. (b) The ending date of the period of enrollment as certified by the...

  14. 38 CFR 21.3332 - Discontinuance dates.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... expiration of the eligible person's entitlement. (e) Date of interruption of course as determined by the... special training allowance as provided in this section on the earliest date of the following: (a) The ending date of the course. (b) The ending date of the period of enrollment as certified by the...

  15. 38 CFR 21.7135 - Discontinuance dates.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ...) Eligibility expires. If the veteran is pursuing a course on the date of expiration of eligibility as... Bill-Active Duty) Payments-Educational Assistance § 21.7135 Discontinuance dates. The effective date of... dependent. If more than one type of reduction or discontinuance is involved, the earliest date will...

  16. 38 CFR 21.3332 - Discontinuance dates.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... expiration of the eligible person's entitlement. (e) Date of interruption of course as determined by the... special training allowance as provided in this section on the earliest date of the following: (a) The ending date of the course. (b) The ending date of the period of enrollment as certified by the...

  17. Radioactive dating of the elements

    NASA Technical Reports Server (NTRS)

    Cowan, John J.; Thielemann, Friedrich-Karl; Truran, James W.

    1991-01-01

    The extent to which an accurate determination of the age of the Galaxy, and thus a lower bound on the age of the universe, can be obtained from radioactive dating is discussed. Emphasis is given to the use of the long-lived radioactive nuclei Re-187, Th-232, U-238, and U-235. The nature of the production sites of these and other potential Galactic chronometers is examined along with their production ratios. Age determinations from models of nucleocosmochronology are reviewed and compared with age determination from stellar sources and age constraints form cosmological considerations.

  18. KetoABNO/NOx Cocatalytic Aerobic Oxidation of Aldehydes to Carboxylic Acids and Access to α-Chiral Carboxylic Acids via Sequential Asymmetric Hydroformylation/Oxidation.

    PubMed

    Miles, Kelsey C; Abrams, M Leigh; Landis, Clark R; Stahl, Shannon S

    2016-08-01

    A method for aerobic oxidation of aldehydes to carboxylic acids has been developed using organic nitroxyl and NOx cocatalysts. KetoABNO (9-azabicyclo[3.3.1]nonan-3-one N-oxyl) and NaNO2 were identified as the optimal nitroxyl and NOx sources, respectively. The mildness of the reaction conditions enables sequential asymmetric hydroformylation of alkenes/aerobic aldehyde oxidation to access α-chiral carboxylic acids without racemization. The scope, utility, and limitations of the oxidation method are further evaluated with a series of achiral aldehydes bearing diverse functional groups.

  19. The Next Generation MOD: A Microchip Amino Acid Analyzer for Detecting Extraterrestrial Life

    NASA Technical Reports Server (NTRS)

    Mathies, R. A.; Hutt, L. D.; Bada, J. L.; Glavin, D.; Grunthaner, F. J.; Grunthaner, P. J.

    2000-01-01

    The MOD (Mars Organic Detector) instrument which has selected for the definition phase of the BEDS package on the 2005 Mars Explorer Program spacecraft is designed to simply detect the presence of amino acids in Martian surface samples at a sensitivity of a few parts per billion (ppb). An additional important aspect of amino acid analyses of Martian samples is identifying and quantifying which compounds are present, and also distinguishing those produced abiotically from those synthesized by either extinct or extant life. Amino acid homochirality provides an unambiguous way of distinguishing between abiotic vs. biotic origins. Proteins made up of mixed D- and L-amino acids would not likely have been efficient catalysts in early organisms because they could not fold into bioactive configurations such as the a-helix. However, enzymes made up of all D-amino acids function just as well as those made up of only L-amino acids, but the two enzymes use the opposite stereoisomeric substrates. There are no biochemical reasons why L-amino acids would be favored over Damino acids. On Earth, the use of only L-amino acids in proteins by life is probably simply a matter of chance. We assume that if proteins and enzymes were a component of extinct or extant life on Mars, then amino acid homochirality would have been a requirement. However, the possibility that Martian life was (or is) based on D-amino acids would be equal to that based on L-amino acids. The detection of a nonracemic mixture of amino acids in a Martian sample would be strong evidence for the presence of an extinct or extant biota on Mars. The finding of an excess of D-amino acids would provide irrefutable evidence of unique Martian life that could not have been derived from seeding the planet with terrestrial life (or the seeding of the Earth with Martian life). In contrast, the presence of racemic amino acids, along with non-protein amino acids such as alpha-aminoisobutyric acid and isovaline, would be indicative

  20. Online dating and conjugal bereavement.

    PubMed

    Young, Goldthwaite Dannagal; Caplan, Scott E

    2010-08-01

    This study examined self-presentation in the online dating profiles of 241 widowed and 280 divorced individuals between 18 and 40 years old. A content analysis of open-ended user-generated profiles assessed the presence or absence of various themes, including the user's marital status, the backstory of their lost relationship, and whether they engaged in sense-making regarding that lost relationship. Results indicated that about one-third of widowed individuals discussed their loss in their profiles. In addition, about one-third of the widowed profiles included explicit reference to a philosophy of life, and about 16% mentioned sense-making or cognitive reappraisals of their bereavement. Many profiles included some articulation of a vision of a future partnership. Results also revealed a significant correlation between widowed individuals including a backstory and their likelihood of exhibiting sense-making in their profiles. Finally, unlike the widowed users, divorcees provided much briefer mentions of their lost relationships, used less sense-making language, and were less likely to articulate an explicit vision of future partnerships. Overall, the results suggest that for widowed individuals, online dating sites may function as venues to explore their past experiences and engage in the construction of a post-loss identity or a post-loss "ideal self".

  1. Peripheral and/or central effects of racemic-, S(+)- and R(−)-flurbiprofen on inflammatory nociceptive processes: a c-Fos protein study in the rat spinal cord

    PubMed Central

    Buritova, Jaroslava; Besson, Jean-Marie

    1998-01-01

    We have evaluated the effects of intravenous or intraplantar racemic-, S(+)- and R(−)-flurbiprofen on both the carrageenan-evoked peripheral oedema and spinal c-Fos immunoreactivity, an indirect index of neurons involved in spinal nociceptive processes. Three hours after intraplantar injection of carrageenan (6 mg in 150 μl of saline) in awake rats, a peripheral oedema and numerous c-Fos protein-like immunoreactive (c-Fos-LI) neurons in L4–L5 segments were observed. c-Fos-LI neurons were essentially located in the superficial (I–II) and deep (V–VI) laminae of the dorsal horn. Intravenous racemic-flurbiprofen (0.3, 3 and 9  mg kg−1) dose-relatedly reduced the carrageenan-evoked oedema and spinal c-Fos expression (r=0.64, r=0.88 and r=0.84 for paw diameter, ankle diameter and number of c-Fos-LI neurons; P<0.05, P<0.001 and P<0.001 respectively). Similar effects to those of intravenous racemic-flurbiprofen were obtained with intravenous S(+)-flurbiprofen (0.3, 3 and 9 mg kg−1) which dose-relatedly reduced the number of c-Fos-LI neurons (r=0.69, P<0.01) and diameters of paw and ankle (r=0.56 and r=0.52 respectively, P<0.05 for both). For the dose of 0.3 mg kg−1 i.v., R(−)-flurbiprofen did not modify the number of c-Fos-LI neurons and produced a weak reduction of oedema at only the ankle level (23±12% reduction, P<0.05). However, a ten times higher dose of R(−)-flurbiprofen (3 mg kg−1 i.v.) was necessary to obtain effects comparable to those of S(+)- or racemic-flurbiprofen (0.3 mg kg−1 i.v.). Intraplantar racemic-flurbiprofen (1, 10 and 30 μg) dose-relatedly reduced the carrageenan-enhanced ankle diameter (r=0.81, P<0.001) and the number of c-Fos-LI neurons in L4–L5 segments (r=0.83, P<0.001), with a 60±3% reduction of the number of c-Fos-LI neurons (P<0.001), and 30±3 and 67±7% reduction of paw and ankle diameter respectively (P<0.001 for both) for the dose of 30 μg. For intraplantar S(+)-flurbiprofen (1, 10

  2. [The knowledge about "date rape drugs" among Polish students].

    PubMed

    Dziuban', Agata; Ratecka, Anna; Brzyski, Piotr; Foryś, Zofia; Gomółka, Ewa; Ogonowska, Dorota

    2009-01-01

    The Main Department of Police in Poland notes about 2000 rapes a year. Some of the crimes are performed with "Date Rape Drugs". The term means substances helping comitting a rape such as GHB (gamma hydroxybutyric acid), ketamine, flunitrazepam and other benzodiazepines derivatives, MDMA ("ecstasy"), marihuana, amphetamine. The substances are often joined with alcohol. The victims are usually young women, and not all the cases are recorded by the police or physicians, because the victims often do not remember details of the event. The toxicological analysis of blood or urine would be helpful to explain the circumstances of the case and to prove using "Date Rape Drug". The samples for toxicological determinations should be collected as soon as possible (24 to 72 hours after admission). Preventing violence with "Date Rape Drugs" include wide education by media, police, teachers and parents. The purpose of the research was to check the level of knowledge about "Date Rape Drugs". The consciousness of risk behavior when the kind of substances is used and the ways of preventing the risk of being a sexual victim were checked. Material for the research were the results of questionnaire prepared by The Department of Medicine Sociology Collegium Medicum Jagiellonian University in Krakow, carried out on 740 students. Most of respondents (77%) were women. The age of respondents was between 19-36 years (mean 21.41; SD - 1.29). The results of the research showed, that respondents didn't have completed knowledge about "Date Rape Drugs". They did not know the ways of recognizing and preventing the risk of being given this kind of substances. The main source of information about "Date Rape Drugs" were internet and colleagues. There is a need to start education about "Date Rape Drugs" by serious institutions such as the police and schools in Poland. This is the best way to prevent young people against a risk of being given "Date Rape Drugs" and being a victim of sexual crimes. PMID

  3. A revised dated phylogeny of the arachnid order Opiliones.

    PubMed

    Sharma, Prashant P; Giribet, Gonzalo

    2014-01-01

    Dating the Opiliones tree of life has become an important enterprise for this group of arthropods, due to their ancient origins and important biogeographic implications. To incorporate both methodological innovations in molecular dating as well as new systematic discoveries of harvestman diversity, we conducted total evidence dating on a data set uniting morphological and/or molecular sequence data for 47 Opiliones species, including all four well-known Palaeozoic fossils, to test the placement of both fossils and newly discovered lineages in a single analysis. Furthermore, we investigated node dating with a phylogenomic data set of 24,202 amino acid sites for 14 species of Opiliones, sampling all extant suborders. In this way, we approached molecular dating of basal harvestman phylogeny using different data sets and approaches to assess congruence of divergence time estimates. In spite of the markedly different composition of data sets, our results show congruence across all analyses for age estimates of basal nodes that are well constrained with respect to fossil calibrations (e.g., Opiliones, Palpatores). By contrast, derived nodes that lack fossil calibrations (e.g., the suborders Cyphophthalmi, and Laniatores) have large uncertainty intervals in diversification times, particularly in the total evidence dating analysis, reflecting the dearth of calibration points and undersampling of derived lineages. Total evidence dating consistently produced older median ages than node dating for ingroup nodes, due to the nested placement of multiple Palaeozoic fossils. Our analyses support basal diversification of Opiliones in the Ordovician-Devonian period, corroborating the inferred ancient origins of this arthropod order, and underscore the importance of diversity discovery-both paleontological and neontological-in evolutionary inference. PMID:25120562

  4. A revised dated phylogeny of the arachnid order Opiliones

    PubMed Central

    Sharma, Prashant P.; Giribet, Gonzalo

    2014-01-01

    Dating the Opiliones tree of life has become an important enterprise for this group of arthropods, due to their ancient origins and important biogeographic implications. To incorporate both methodological innovations in molecular dating as well as new systematic discoveries of harvestman diversity, we conducted total evidence dating on a data set uniting morphological and/or molecular sequence data for 47 Opiliones species, including all four well-known Palaeozoic fossils, to test the placement of both fossils and newly discovered lineages in a single analysis. Furthermore, we investigated node dating with a phylogenomic data set of 24,202 amino acid sites for 14 species of Opiliones, sampling all extant suborders. In this way, we approached molecular dating of basal harvestman phylogeny using different data sets and approaches to assess congruence of divergence time estimates. In spite of the markedly different composition of data sets, our results show congruence across all analyses for age estimates of basal nodes that are well constrained with respect to fossil calibrations (e.g., Opiliones, Palpatores). By contrast, derived nodes that lack fossil calibrations (e.g., the suborders Cyphophthalmi, and Laniatores) have large uncertainty intervals in diversification times, particularly in the total evidence dating analysis, reflecting the dearth of calibration points and undersampling of derived lineages. Total evidence dating consistently produced older median ages than node dating for ingroup nodes, due to the nested placement of multiple Palaeozoic fossils. Our analyses support basal diversification of Opiliones in the Ordovician-Devonian period, corroborating the inferred ancient origins of this arthropod order, and underscore the importance of diversity discovery—both paleontological and neontological—in evolutionary inference. PMID:25120562

  5. A revised dated phylogeny of the arachnid order Opiliones.

    PubMed

    Sharma, Prashant P; Giribet, Gonzalo

    2014-01-01

    Dating the Opiliones tree of life has become an important enterprise for this group of arthropods, due to their ancient origins and important biogeographic implications. To incorporate both methodological innovations in molecular dating as well as new systematic discoveries of harvestman diversity, we conducted total evidence dating on a data set uniting morphological and/or molecular sequence data for 47 Opiliones species, including all four well-known Palaeozoic fossils, to test the placement of both fossils and newly discovered lineages in a single analysis. Furthermore, we investigated node dating with a phylogenomic data set of 24,202 amino acid sites for 14 species of Opiliones, sampling all extant suborders. In this way, we approached molecular dating of basal harvestman phylogeny using different data sets and approaches to assess congruence of divergence time estimates. In spite of the markedly different composition of data sets, our results show congruence across all analyses for age estimates of basal nodes that are well constrained with respect to fossil calibrations (e.g., Opiliones, Palpatores). By contrast, derived nodes that lack fossil calibrations (e.g., the suborders Cyphophthalmi, and Laniatores) have large uncertainty intervals in diversification times, particularly in the total evidence dating analysis, reflecting the dearth of calibration points and undersampling of derived lineages. Total evidence dating consistently produced older median ages than node dating for ingroup nodes, due to the nested placement of multiple Palaeozoic fossils. Our analyses support basal diversification of Opiliones in the Ordovician-Devonian period, corroborating the inferred ancient origins of this arthropod order, and underscore the importance of diversity discovery-both paleontological and neontological-in evolutionary inference.

  6. [Molecular dating in the genomic era].

    PubMed

    Douzery, Emmanuel J P; Delsuc, Frédéric; Philippe, Hervé

    2006-04-01

    The comparison of DNA and protein sequences of extant species might be informative for reconstructing the chronology of evolutionary events on Earth. A phylogenetic tree inferred from molecular data directly depicts the evolutionary affinities of species and indirectly allows estimating the age of their origin and diversification. Molecular dating is achieved by assuming the molecular clock hypothesis, i.e., that the rate of change of nucleotide and amino acid sequences is on average constant over geological time. If paleontological calibrations are available, then absolute divergence times of species can be estimated. However, three major difficulties potentially hamper molecular dating : (1) a limited sample of genes and organisms, (2) a limited number of fossil references, and (3) pervasive variations of molecular evolutionary rates among genomes and species. To circumvent these problems, different solutions have been recently proposed. Larger data sets are built with more genes and more species sampled through the mining of an increasing number of genomes. Moreover, independent key fossils are identified to calibrate molecular clocks, and the uncertainty on their age is integrated in subsequent analyses. Finally, models of molecular rate variations are constructed, and incorporated in the so-called relaxed molecular clock approaches. As an illustration of these improvements, we mention that the debated age of the animal (bilaterian metazoans) diversification may have occurred between 642-761 million years ago (Mya), roughly 100 Ma before the Cambrian explosion. Among mammals, the initial diversification of major placental groups may have taken place around 100 Mya, well before the Cretaceous/Tertiary boundary marking the extinction of dinosaurs.

  7. [Molecular dating in the genomic era].

    PubMed

    Douzery, Emmanuel J P; Delsuc, Frédéric; Philippe, Hervé

    2006-04-01

    The comparison of DNA and protein sequences of extant species might be informative for reconstructing the chronology of evolutionary events on Earth. A phylogenetic tree inferred from molecular data directly depicts the evolutionary affinities of species and indirectly allows estimating the age of their origin and diversification. Molecular dating is achieved by assuming the molecular clock hypothesis, i.e., that the rate of change of nucleotide and amino acid sequences is on average constant over geological time. If paleontological calibrations are available, then absolute divergence times of species can be estimated. However, three major difficulties potentially hamper molecular dating : (1) a limited sample of genes and organisms, (2) a limited number of fossil references, and (3) pervasive variations of molecular evolutionary rates among genomes and species. To circumvent these problems, different solutions have been recently proposed. Larger data sets are built with more genes and more species sampled through the mining of an increasing number of genomes. Moreover, independent key fossils are identified to calibrate molecular clocks, and the uncertainty on their age is integrated in subsequent analyses. Finally, models of molecular rate variations are constructed, and incorporated in the so-called relaxed molecular clock approaches. As an illustration of these improvements, we mention that the debated age of the animal (bilaterian metazoans) diversification may have occurred between 642-761 million years ago (Mya), roughly 100 Ma before the Cambrian explosion. Among mammals, the initial diversification of major placental groups may have taken place around 100 Mya, well before the Cretaceous/Tertiary boundary marking the extinction of dinosaurs. PMID:16597406

  8. Preferential Stereocomplex Crystallization in Enantiomeric Blends of Cellulose Acetate-g-Poly(lactic acid)s with Comblike Topology.

    PubMed

    Bao, Jianna; Han, Lili; Shan, Guorong; Bao, Yongzhong; Pan, Pengju

    2015-10-01

    Although stereocomplex (sc) crystallization is highly effective for improving the thermal resistance of poly(lactic acid) (PLA), it is much less predominant than homocrystallization in high-molecular-weight (HMW) poly(l-lactic acid)/ poly(d-lactic acid) (PLLA/PDLA) racemic blends. In this contribution, the sc crystallization of HMW PLLA/PDLA racemic blends was facilitated by using comblike PLAs with cellulose acetate as the backbone. Competing crystallization kinetics, polymorphic crystalline structure, and structural transition of comblike PLLA/PDLA blends with a wide range of MWs were investigated and compared with the corresponding linear/comblike and linear blends. The HMW comblike blend is preferentially crystallized in sc polymorphs and exhibits a faster crystallization rate than does the corresponding linear blend. The sc crystallites are predominantly formed in nonisothermal cold crystallization and isothermal crystallization at temperatures above 120 °C for the comblike blends. Except for the facilitated sc formation in primary crystallization, synchrotron radiation WAXD analysis indicates that the presence of a comblike component also facilitates the transition or recrystallization from homocrystallite (hc) to sc crystallite upon heating. Preferential sc formation of comblike blends is probably attributable to the favorable interdigitation between enantiomeric branches and the increased mobility of polymer segments. After crystallization under the same temperature, the comblike blends, which mainly contain sc crystallites, show smaller long periods and thinner crystalline lamellae than do the corresponding PLLA with homocrystalline structures.

  9. Retrospective Birth Dating of Cells

    SciTech Connect

    L.Spalding, K; Bhardwaj, R D; Buchholz, B A; Druid, H; Frisen, J

    2005-04-19

    The generation of cells in the human body has been difficult to study and our understanding of cell turnover is limited. Extensive testing of nuclear weapons resulted in a dramatic global increase in the levels of the isotope {sup 14}C in the atmosphere, followed by an exponential decrease after the test ban treaty in 1963. We show that the level of {sup 14}C in genomic DNA closely parallels atmospheric levels, and can be used to establish the time point when the DNA was synthesized and cells were born. We use this strategy to determine the age of cells in the cortex of the adult human brain, and show that whereas non-neuronal cells are exchanged, occipital neurons are as old as the individual, supporting the view that postnatal neurogenesis does not take place in this region. Retrospective birth dating is a generally applicable strategy that can be used to measure cell turnover in man under physiological and pathological conditions.

  10. Sexual assault in dating relationships.

    PubMed

    Rhynard, J; Krebs, M; Glover, J

    1997-03-01

    This article focuses on acquaintance rape, which under Canadian law constitutes a form of sexual assault. Frequency of acquaintance rape often is underestimated due to under-reporting, resulting in a local perception that acquaintance rape rarely occurs in a small Canadian community. A survey was conducted to determine whether acquaintance rape does occur in this community. One hundred sixty-four male and female students from grades 8-12 completed a questionnaire. Twenty-six percent of respondents reported being forced into some type of sexual activity. Based on the survey, this article explores the type of force used, the relationship between acquaintance rape and use of alcohol and drugs, and the relationship between acquaintance rape and the ability to indicate to a partner to stop a behavior. Results confirmed a need to develop programs to prevent rather than merely respond to issues of sexual assault on a date. PMID:9071669

  11. Thermoluminescence dating of Hawaiian basalt

    USGS Publications Warehouse

    May, Rodd James

    1979-01-01

    The thermoluminescence (TL) properties of plagioclase separates from 11 independently dated alkalic basalts 4,500 years to 3.3 million years old and 17 tholeiitic basalts 16 years to 450,000 years old from the Hawaiian Islands were investigated for the purpose of developing a TL dating method for young volcanic rocks. Ratios of natural to artificial TL intensity, when normalized for natural radiation dose rates, were used to quantify the thermoluminescence response of individual samples for age-determination purposes. The TL ratios for the alkalic basalt plagioclase were found to increase with age at a predictable exponential rate that permits the use of the equation for the best-fit line through a plot of the TL ratios relative to known age as a TL age equation. The equation is applicable to rocks ranging in composition from basaltic andesite to trachyte over the age range from about 2,000 to at least 250,000 years before present (B.P.). The TL ages for samples older than 50,000 years have a calculated precision of less than :t 10 percent and a potential estimated accuracy relative to potassium-argon ages of approximately :t 10 percent. An attempt to develop a similar dating curve for the tholeiitic basalts was not as successful, primarily because the dose rates are on the average lower than those for the alkalic basalts by a factor of 6, resulting in lower TL intensities in the tholeiitic basalts for samples of equivalent age, and also because the age distribution of dated material is inadequate. The basic TL properties of the plagioclase from the two rock types are similar, however, and TL dating of tholeiitic basalts should eventually be feasible over the age range 10,000 to at least 200,000 years B.P. The average composition of the plagioclase separates from the alkalic basalts ranges from oligoclase to andesine; compositional variations within this range have no apparent effect on the TL ratios. The average composition of the plagioclase from the tholeiitic

  12. Biotransformations of 2-hydroxy-2-(ethoxyphenylphosphinyl)acetic acid and the determination of the absolute configuration of all isomers.

    PubMed

    Majewska, Paulina

    2015-08-01

    2-Hydroxy-2-(ethoxyphenylphosphinyl)acetic acid, a new type of organophosphorus compound possessing two stereogenic centers, was investigated. Racemic 2-butyryloxy-2-(ethoxyphenylphosphinyl)acetic acid was synthesized and hydrolyzed using four bacterial species as biocatalysts. In all cases the reaction was more or less stereoselective and isomers bearing a phosphorus atom with an (SP)-configuration were hydrolyzed preferentially. The observed (1)H and (31)P NMR chemical shifts of Mosher esters of 2-hydroxy-2-(ethoxyphenylphosphinyl)acetic acid were correlated with the configurations of both stereogenic centers of all four stereoisomers.

  13. Identification of diamino acids in the Murchison meteorite

    NASA Astrophysics Data System (ADS)

    Meierhenrich, Uwe J.; Muñoz Caro, Guillermo M.; Hendrik Bredehöft, Jan; Jessberger, Elmar K.; Thiemann, Wolfram H.-P.

    Amino acids identified in the Murchison chondritic meteorite by molecular and isotopic analysis are thought to have been delivered to the early Earth by asteroids, comets, and interplanetary dust particles where they may have triggered the appearance of life by assisting in the synthesis of proteins via prebiotic polycondensation reactions [Oró, J. (1961) Nature 190, 389-390; Chyba, C. F. & Sagan, C. (1992) Nature 355, 125-132]. We report the identification of diamino acids in the Murchison meteorite by new enantioselective GC-MS analyses. DL-2,3-diaminopropanoic acid, DL-2,4-diaminobutanoic acid, 4,4'-diaminoisopentanoic acid, 3,3'-diaminoisobutanoic acid, and 2,3-diaminobutanoic acid were detected in the parts per billion range after chemical transformation into N,N-diethoxycarbonyl ethyl ester derivatives. The chiral diamino acids show a racemic ratio. Laboratory data indicate that diamino acids support the formation of polypeptide structures under primitive Earth conditions [Brack, A. & Orgel, L. E. (1975) Nature 256, 383-387] and suggest polycondensation reactions of diamino acids into early peptide nucleic acid material as one feasible pathway for the prebiotic evolution of DNA and RNA genomes [Joyce, G. F. (2002) Nature 418, 214-221]. The results obtained in this study favor the assumption that not only amino acids (as the required monomers of proteins) form in interstellar/circumstellar environments, but also the family of diamino monocarboxylic acids, which might have been relevant in prebiotic chemistry.

  14. Amino Acids from Icy Amines: A Radiation-Chemical Approach to Extraterrestrial Synthesis

    NASA Technical Reports Server (NTRS)

    Dworkin, J. P.; Moore, M. H.

    2010-01-01

    Detections of amino acids in meteorites go back several decades, with at least 100 such compounds being reported for the Murchison meteorite alone. The presence of these extraterrestrial molecules raises questions as to their formation, abundance, thermal stability, racemization, and possible subsequent reactions. Although all of these topics have been studied in laboratories, such work often involves many variables and unknowns. This has led us to seek out model systems with which to uncover reaction products, test chemical predictions, and sited light on underlying reaction mechanisms. This presentation will describe one such study, focusing on amino-acid formation in ices.

  15. Extraterrestrial Amino Acids in Orgueil and Ivuna: Tracing the Parent Body of CI Type Carbonaceous Chondrites

    NASA Technical Reports Server (NTRS)

    Meyer, Michael (Technical Monitor); Ehrenfreund, Pascale; Glavin, Daniel P.; Bota, Oliver; Cooper, George; Bada, Jeffrey

    2001-01-01

    Amino acid analyses using HPLC of pristine interior pieces of the CI carbonaceous chondrites Orgueil and Ivuna have found that beta-alanine, glycine, and gamma-amino-n-butyric acid (ABA) are the most abundant amino acids in these two meteorites, with concentrations ranging from approx. 600 to 2,000 parts per billion (ppb). Other alpha-amino acids such as alanine, alpha-ABA, alpha-aminoisobutyric acid (AIB), and isovaline are present only in trace amounts (less than 200 ppb). Carbon isotopic measurements of beta-alanine and glycine and the presence of racemic (D/L 1) alanine and beta-ABA in Orgueil suggest that these amino acids are extraterrestrial in origin. In comparison to the CM carbonaceous chondrites Murchison and Murray, the amino acid composition of the CIs is strikingly distinct, suggesting that these meteorites came from a different type of parent body, possibly an extinct comet, than did the CM carbonaceous chondrites.

  16. Extraterrestrial amino acids in Orgueil and Ivuna: Tracing the parent body of CI type carbonaceous chondrites

    PubMed Central

    Ehrenfreund, Pascale; Glavin, Daniel P.; Botta, Oliver; Cooper, George; Bada, Jeffrey L.

    2001-01-01

    Amino acid analyses using HPLC of pristine interior pieces of the CI carbonaceous chondrites Orgueil and Ivuna have found that β-alanine, glycine, and γ-amino-n-butyric acid (ABA) are the most abundant amino acids in these two meteorites, with concentrations ranging from ≈600 to 2,000 parts per billion (ppb). Other α-amino acids such as alanine, α-ABA, α-aminoisobutyric acid (AIB), and isovaline are present only in trace amounts (<200 ppb). Carbon isotopic measurements of β-alanine and glycine and the presence of racemic (D/L ≈ 1) alanine and β-ABA in Orgueil suggest that these amino acids are extraterrestrial in origin. In comparison to the CM carbonaceous chondrites Murchison and Murray, the amino acid composition of the CIs is strikingly distinct, suggesting that these meteorites came from a different type of parent body, possibly an extinct comet, than did the CM carbonaceous chondrites. PMID:11226205

  17. Racemization at C-2 of naringin in sour oranges with increasing maturity determined by chiral high-performance liquid chromatography.

    PubMed

    Caccamese, Salvatore; Bianca, Salvatore; Santo, Davide

    2007-05-16

    Naringin is the major flavanone-7-O-glycoside of sour orange, and it is mainly responsible for the bitter taste of the fruit. The relative content of (2S)- and (2R)-naringin in the albedo of sour oranges during maturation in the entire season was determined by normal phase HPLC using Chiralcel OD-H as chiral stationary phase and n-hexane/ethanol doped with 0.5% of TFA as mobile phase. HPLC traces were complicated by the presence of (2S)-neohesperidin, and a software-guided analysis was developed to assess the relative amount of the C-2 diastereomers of naringin. A sigmoid curve was obtained showing variation from 94% of (2S)-naringin in very immature fruits to 69.7% in mature fruit samples. Spontaneous epimerization of (2S)-naringin in the ethanolic solutions of the albedo was noted after prolonged keeping for less acid samples. The separation of the C-2 diastereomers of other flavanoid-7-O-glycosides present in Citrus (neoeriocitrin, neohesperidin, and eriocitrin) was also obtained by chiral HPLC and afforded the identification, including stereochemistry, of the eluting peaks in the HPLC traces of the albedo extracts. PMID:17417869

  18. New Radiocarbon Dates on Upper Mid-West Proboscideans: Determining Date Robustness

    NASA Astrophysics Data System (ADS)

    Hodgins, G.; Widga, C.; Lengyel, S. N.; Saunders, J.; Walker, J. D.

    2013-12-01

    With the objective of refining the picture of Megafaunal extinction patterns in the upper Midwest in the terminal Pleistocene, we have assembled for radiocarbon dating specimens from more than 80 distinct Mammut and Mammuthus remains from potentially late sites. So far, we have measurements for 65 bones, tusks and teeth, nearly double the extant number of published dates . These new specimens were all from museums rather than excavation sites, and 60% were known to be coated with a consolidant. The predominant consolidant was Butvar B-76, however shellac, Elmer's Glue, Glyptol were also noted in the conservation records, or deduced from knowledge of a particular museum's practices. Given the objective of the project is to identify extinction patterns, coupled with the wide prevalence of consolidants amongst the specimen set, it was imperative that testing be carried out to confirm that radiocarbon laboratory protocols removed the consolidants, so that ultimately the dates can be considered robust. To this end, key specimens were dated three times using different sample preparation protocols. These were 1) a solvent extraction followed by a modified Longin-plus -Base continuous flow collagen extraction method used in the NSF-Arizona AMS facility, 2) the solvent/modified Longin method plus ultrafiltration, and 3) solvent/modified Longin method plus hydroxyproline single amino acid dating. Among the specimens subjected to triplicate testing were some of the youngest late Wisconsin proboscidean specimens from the Upper Midwest Region. The data reveal general agreement between the different protocols, and suggested either limited penetration of consolidants into the specimens, or that the standard laboratory cleaning protocols were sufficient to remove traces from deep within bone, tooth or tusk tissue. The preservation of each specimen, recorded in terms of collagen content, C/N ratio and stable isotope values, indicated that most were actually well preserved, implying

  19. Preparation of water samples for carbon-14 dating

    USGS Publications Warehouse

    Feltz, H.R.; Hanshaw, Bruce B.

    1963-01-01

    For most natural water, a large sample is required to provide the 3 grams of carbon needed for a carbon-14 determination. A field procedure for isolating total dissolved-carbonate species is described. Carbon dioxide gas is evolved by adding sulfuric acid to the water sample; the gas is then collected in a sodium hydroxide trap by recycling in a closed system. The trap is then transported to the dating laboratory where the carbon-14 is counted.

  20. 16 CFR 1207.2 - Effective date.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... STANDARD FOR SWIMMING POOL SLIDES § 1207.2 Effective date. This part 1207 shall become effective July 17, 1976. All swimming pool slides manufactured after that date must meet the requirements of this...

  1. 16 CFR 1207.2 - Effective date.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... STANDARD FOR SWIMMING POOL SLIDES § 1207.2 Effective date. This part 1207 shall become effective July 17, 1976. All swimming pool slides manufactured after that date must meet the requirements of this...

  2. 16 CFR 1207.2 - Effective date.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... STANDARD FOR SWIMMING POOL SLIDES § 1207.2 Effective date. This part 1207 shall become effective July 17, 1976. All swimming pool slides manufactured after that date must meet the requirements of this...

  3. 7 CFR 987.13 - Free dates.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... RIVERSIDE COUNTY, CALIFORNIA Order Regulating Handling Definitions § 987.13 Free dates. Free dates means... to acquire them at prices reasonably comparable with prices received domestically) and which are...

  4. What Is Rape and Date Rape?

    MedlinePlus

    ... What is rape and date rape? What is rape and date rape? Get help National Sexual Assault Hotline 800-656- ... drinking, it is NOT your fault. What is sexual assault? Sexual assault and abuse is any kind of ...

  5. 40 CFR 62.4671 - Effective date.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... Industrial Solid Waste Incineration Units § 62.4671 Effective date. The effective date of this portion of the State's plan applicable to existing commercial and industrial solid waste incineration units is May...

  6. 40 CFR 62.4671 - Effective date.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... Industrial Solid Waste Incineration Units § 62.4671 Effective date. The effective date of this portion of the State's plan applicable to existing commercial and industrial solid waste incineration units is May...

  7. 40 CFR 62.9191 - Effective date.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... Industrial Solid Waste Incineration Units § 62.9191 Effective date. The effective date of this portion of the State's plan applicable to existing commercial and industrial solid waste incineration units is...

  8. 40 CFR 62.9191 - Effective date.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... Industrial Solid Waste Incineration Units § 62.9191 Effective date. The effective date of this portion of the State's plan applicable to existing commercial and industrial solid waste incineration units is...

  9. 40 CFR 62.4671 - Effective date.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... Industrial Solid Waste Incineration Units § 62.4671 Effective date. The effective date of this portion of the State's plan applicable to existing commercial and industrial solid waste incineration units is May...

  10. 40 CFR 62.4671 - Effective date.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... Industrial Solid Waste Incineration Units § 62.4671 Effective date. The effective date of this portion of the State's plan applicable to existing commercial and industrial solid waste incineration units is May...

  11. 40 CFR 62.9191 - Effective date.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... Industrial Solid Waste Incineration Units § 62.9191 Effective date. The effective date of this portion of the State's plan applicable to existing commercial and industrial solid waste incineration units is...

  12. 40 CFR 62.9191 - Effective date.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... Industrial Solid Waste Incineration Units § 62.9191 Effective date. The effective date of this portion of the State's plan applicable to existing commercial and industrial solid waste incineration units is...

  13. Teaching the Mathematics of Radioactive Dating.

    ERIC Educational Resources Information Center

    Shea, James H.

    2001-01-01

    Describes a method used to teach the concept of radiometric dating using mathematical equations. Explores the lack of information in textbooks on how to solve radiometric dating problems using mathematical concepts. (SAH)

  14. 40 CFR 62.4626 - Effective date.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... Phosphate Fertilizer Plants § 62.4626 Effective date. (a) The effective date of the portion of the plan applicable to phosphate fertilizer plants is July 12, 1982. Fluoride Emissions From Existing Primary...

  15. 40 CFR 62.602 - Effective date.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Arizona Landfill Gas Emissions from Existing Municipal Solid Waste Landfills § 62.602 Effective date. The effective date of EPA approval of...

  16. 40 CFR 62.7102 - Effective date.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Nevada Landfill Gas Emissions from Existing Municipal Solid Waste Landfills § 62.7102 Effective date. The effective date of EPA approval...

  17. 40 CFR 62.7102 - Effective date.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Nevada Landfill Gas Emissions from Existing Municipal Solid Waste Landfills § 62.7102 Effective date. The effective date of EPA approval...

  18. 40 CFR 62.602 - Effective date.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Arizona Landfill Gas Emissions from Existing Municipal Solid Waste Landfills § 62.602 Effective date. The effective date of EPA approval of...

  19. 40 CFR 62.602 - Effective date.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Arizona Landfill Gas Emissions from Existing Municipal Solid Waste Landfills § 62.602 Effective date. The effective date of EPA approval of...

  20. 40 CFR 62.602 - Effective date.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Arizona Landfill Gas Emissions from Existing Municipal Solid Waste Landfills § 62.602 Effective date. The effective date of EPA approval of...

  1. 40 CFR 62.7102 - Effective date.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Nevada Landfill Gas Emissions from Existing Municipal Solid Waste Landfills § 62.7102 Effective date. The effective date of EPA approval...

  2. 40 CFR 62.7102 - Effective date.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Nevada Landfill Gas Emissions from Existing Municipal Solid Waste Landfills § 62.7102 Effective date. The effective date of EPA approval...

  3. 40 CFR 62.7102 - Effective date.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Nevada Landfill Gas Emissions from Existing Municipal Solid Waste Landfills § 62.7102 Effective date. The effective date of EPA approval...

  4. 40 CFR 62.602 - Effective date.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... PROMULGATION OF STATE PLANS FOR DESIGNATED FACILITIES AND POLLUTANTS Arizona Landfill Gas Emissions from Existing Municipal Solid Waste Landfills § 62.602 Effective date. The effective date of EPA approval of...

  5. 40 CFR 62.4626 - Effective date.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... Phosphate Fertilizer Plants § 62.4626 Effective date. (a) The effective date of the portion of the plan applicable to phosphate fertilizer plants is July 12, 1982. Fluoride Emissions From Existing Primary...

  6. 40 CFR 62.4626 - Effective date.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... Phosphate Fertilizer Plants § 62.4626 Effective date. (a) The effective date of the portion of the plan applicable to phosphate fertilizer plants is July 12, 1982. Fluoride Emissions From Existing Primary...

  7. 16 CFR 1207.2 - Effective date.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... STANDARD FOR SWIMMING POOL SLIDES § 1207.2 Effective date. This part 1207 shall become effective July 17, 1976. All swimming pool slides manufactured after that date must meet the requirements of this...

  8. 16 CFR 1207.2 - Effective date.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... STANDARD FOR SWIMMING POOL SLIDES § 1207.2 Effective date. This part 1207 shall become effective July 17, 1976. All swimming pool slides manufactured after that date must meet the requirements of this...

  9. 40 CFR 62.1362 - Effective date.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    .../medical/infectious Waste Incinerators § 62.1362 Effective date. The effective date for the portion of the plan applicable to existing hospital/medical/infectious waste incinerators is August 21,...

  10. Efficient optical resolution of amino acid by alanine racemaze chiral analogue supported on mesoporous carbon

    NASA Astrophysics Data System (ADS)

    Jang, D.; Kim, K.; Park, D.; Kim, G.

    2012-09-01

    Optically pure D-amino acids are industrially important chiral building blocks for the synthesis of pharmaceuticals, food ingredients, and drug intermediates. Chemoenzymatic dynamic kinetic-resolution processes have recently been developed for deracemization of amino acids. S-ARCA would be a good candidate for the selective adsorption of D amino acid through the imine formation reaction. The organic phase containing S-ARCA adsorbent, TPPC or Ionic Liquid (as a phase transfer catalyst) in MC were coated on the surfaces of mesoporous carbon C-SBA-15(CMK). The aqueous solution of racemic D/L-amino acid and NaOH were added to the carbon support coated with ARCA. The D/L ratios on ARCA and in solution were determined with increasing reaction time. S-ARCA has a unique property for the selective adsorption of D- amino acid (up to 90% selcetivity) in the racemic mixture. The fixed bed reactor containing ARCA/carbon support was also adopted successfully for the selective separation of amino acid.

  11. 38 CFR 21.7131 - Commencing dates.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... be effective on the latest of the following dates: (i) Date of the veteran's marriage, or birth of... servicemember is paid a reduced rate of educational assistance under § 21.7139 (c) and (d) of this part, the rate will be increased or assistance will commence effective the earlier of the following dates:...

  12. 40 CFR 63.863 - Compliance dates.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 10 2010-07-01 2010-07-01 false Compliance dates. 63.863 Section 63..., Sulfite, and Stand-Alone Semichemical Pulp Mills § 63.863 Compliance dates. (a) The owner or operator of... startup date after March 13, 2001 must comply with the requirements in this subpart immediately...

  13. 40 CFR 63.826 - Compliance dates.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 10 2010-07-01 2010-07-01 false Compliance dates. 63.826 Section 63... Emission Standards for the Printing and Publishing Industry § 63.826 Compliance dates. (a) The compliance date for an owner or operator of an existing affected source subject to the provisions of this...

  14. 7 CFR 987.12 - Marketable dates.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... size requirements in effect pursuant to § 987.39, and any additional applicable requirements in effect... established by the Committee, with the approval of the Secretary, for any specific variety. (c) Export dates. Export dates are marketable whole or pitted dates that are inspected and certified as meeting the...

  15. 19 CFR 351.701 - Applicability dates.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 19 Customs Duties 3 2011-04-01 2011-04-01 false Applicability dates. 351.701 Section 351.701 Customs Duties INTERNATIONAL TRADE ADMINISTRATION, DEPARTMENT OF COMMERCE ANTIDUMPING AND COUNTERVAILING DUTIES Applicability Dates § 351.701 Applicability dates. The regulations contained in this part...

  16. 19 CFR 351.701 - Applicability dates.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 19 Customs Duties 3 2010-04-01 2010-04-01 false Applicability dates. 351.701 Section 351.701 Customs Duties INTERNATIONAL TRADE ADMINISTRATION, DEPARTMENT OF COMMERCE ANTIDUMPING AND COUNTERVAILING DUTIES Applicability Dates § 351.701 Applicability dates. The regulations contained in this part...

  17. 16 CFR 1301.8 - Effective date.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 16 Commercial Practices 2 2010-01-01 2010-01-01 false Effective date. 1301.8 Section 1301.8 Commercial Practices CONSUMER PRODUCT SAFETY COMMISSION CONSUMER PRODUCT SAFETY ACT REGULATIONS BAN OF UNSTABLE REFUSE BINS § 1301.8 Effective date. The effective date of this ban shall be June 13, 1978....

  18. 7 CFR 953.120 - Nomination date.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... STATES Rules and Regulations Change in Date for Completing Nominations, Term of Office, and Fiscal Period § 953.120 Nomination date. The names of committee nominees shall be supplied to the Secretary in such... 7 Agriculture 8 2010-01-01 2010-01-01 false Nomination date. 953.120 Section 953.120...

  19. 7 CFR 987.13 - Free dates.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 7 Agriculture 8 2013-01-01 2013-01-01 false Free dates. 987.13 Section 987.13 Agriculture... RIVERSIDE COUNTY, CALIFORNIA Order Regulating Handling Definitions § 987.13 Free dates. Free dates means... to acquire them at prices reasonably comparable with prices received domestically) and which are...

  20. 7 CFR 987.13 - Free dates.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 7 Agriculture 8 2012-01-01 2012-01-01 false Free dates. 987.13 Section 987.13 Agriculture... RIVERSIDE COUNTY, CALIFORNIA Order Regulating Handling Definitions § 987.13 Free dates. Free dates means... to acquire them at prices reasonably comparable with prices received domestically) and which are...

  1. 7 CFR 987.13 - Free dates.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 7 Agriculture 8 2011-01-01 2011-01-01 false Free dates. 987.13 Section 987.13 Agriculture... RIVERSIDE COUNTY, CALIFORNIA Order Regulating Handling Definitions § 987.13 Free dates. Free dates means... to acquire them at prices reasonably comparable with prices received domestically) and which are...

  2. 7 CFR 987.13 - Free dates.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 7 Agriculture 8 2014-01-01 2014-01-01 false Free dates. 987.13 Section 987.13 Agriculture... RIVERSIDE COUNTY, CALIFORNIA Order Regulating Handling Definitions § 987.13 Free dates. Free dates means... to acquire them at prices reasonably comparable with prices received domestically) and which are...

  3. 40 CFR 51.1004 - Attainment dates.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 2 2014-07-01 2014-07-01 false Attainment dates. 51.1004 Section 51....5 National Ambient Air Quality Standards § 51.1004 Attainment dates. (a) Consistent with section 172(a)(2)(A) of the Act, the attainment date for an area designated nonattainment for the PM2.5...

  4. 29 CFR 4007.11 - Due dates.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... Due dates. (a) In general. For flat-rate and variable-rate premiums, the premium filing due date for... variable-rate premium payment must be made by the last day of the sixteenth full calendar month following... payment year. (ii) The due date for the variable-rate premium required by § 4006.3(b) of this chapter...

  5. 29 CFR 4007.11 - Due dates.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... Due dates. (a) In general. In general: (1) The flat-rate and variable-rate premium filing due date is... payment year. (2) If the variable-rate premium paid by the premium filing due date is estimated as described in § 4007.8(g)(1)(ii), a reconciliation filing and any required variable-rate premium payment...

  6. 29 CFR 4007.11 - Due dates.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... Due dates. (a) In general. For flat-rate and variable-rate premiums, the premium filing due date for... variable-rate premium payment must be made by the last day of the sixteenth full calendar month following... payment year. (ii) The due date for the variable-rate premium required by § 4006.3(b) of this chapter...

  7. 29 CFR 4007.11 - Due dates.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... Due dates. (a) In general. For flat-rate and variable-rate premiums, the premium filing due date for... variable-rate premium payment must be made by the last day of the sixteenth full calendar month following... payment year. (ii) The due date for the variable-rate premium required by § 4006.3(b) of this chapter...

  8. 40 CFR 51.1004 - Attainment dates.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 2 2012-07-01 2012-07-01 false Attainment dates. 51.1004 Section 51....5 National Ambient Air Quality Standards § 51.1004 Attainment dates. (a) Consistent with section 172(a)(2)(A) of the Act, the attainment date for an area designated nonattainment for the PM2.5...

  9. 40 CFR 57.106 - Expiration date.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 6 2014-07-01 2014-07-01 false Expiration date. 57.106 Section 57.106 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) PRIMARY NONFERROUS SMELTER ORDERS General § 57.106 Expiration date. Each NSO shall state its expiration date. No...

  10. 37 CFR 42.206 - Filing date.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 37 Patents, Trademarks, and Copyrights 1 2013-07-01 2013-07-01 false Filing date. 42.206 Section... date. (a) Complete petition. A petition to institute a post-grant review will not be accorded a filing date until the petition satisfies all of the following requirements: (1) Complies with § 42.204 or §...

  11. 40 CFR 57.106 - Expiration date.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 5 2011-07-01 2011-07-01 false Expiration date. 57.106 Section 57.106 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) PRIMARY NONFERROUS SMELTER ORDERS General § 57.106 Expiration date. Each NSO shall state its expiration date. No...

  12. 40 CFR 57.106 - Expiration date.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 6 2013-07-01 2013-07-01 false Expiration date. 57.106 Section 57.106 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) PRIMARY NONFERROUS SMELTER ORDERS General § 57.106 Expiration date. Each NSO shall state its expiration date. No...

  13. 40 CFR 57.106 - Expiration date.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 5 2010-07-01 2010-07-01 false Expiration date. 57.106 Section 57.106 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) PRIMARY NONFERROUS SMELTER ORDERS General § 57.106 Expiration date. Each NSO shall state its expiration date. No NSO issued under this regulation...

  14. 40 CFR 57.106 - Expiration date.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 6 2012-07-01 2012-07-01 false Expiration date. 57.106 Section 57.106 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) PRIMARY NONFERROUS SMELTER ORDERS General § 57.106 Expiration date. Each NSO shall state its expiration date. No...

  15. 37 CFR 42.206 - Filing date.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 37 Patents, Trademarks, and Copyrights 1 2014-07-01 2014-07-01 false Filing date. 42.206 Section... date. (a) Complete petition. A petition to institute a post-grant review will not be accorded a filing date until the petition satisfies all of the following requirements: (1) Complies with § 42.204 or §...

  16. Paleomagnetic dating of liesegang bands

    SciTech Connect

    Cochran, K.A.; Elmore, R.

    1985-01-01

    Paleomagnetic analysis, in conjunction with petrographic studies, was used to date the formation of hematite liesegang bands in the Ordovician Upper Arbuckle Group in southern Oklahoma. The hematite bands form symmetrical patterns on both sides of calcite-filled fractures in dolomite beds. The bands decrease in abundance and become more diffuse away from the fractures. Dedolomite is common near the fractures. Samples from distinctly banded dolomite near the fractures contain a relatively strong chemical remanent magnetization (CRM) with a southeasterly declination and shallow inclination. Samples farther from the fractures that are less distinctly banded or have no bands contain a weaker and less table CRM. Petrographic evidence and stable demagnetization to 600/sup 0/C indicate that the CRM resides in hematite. Samples were collected from both flanks of the Arbuckle Anticline (late Pennsylvanian folding), and a fold test demonstrates that the CRM is post-folding. The pole position for the CRM corresponds to the Early Permian (approx. 280 Ma) part of the Apparent Polar Wander Path for stable North America. These results suggest that the liesegang bands formed in the Early Permian, probably by rhythmic precipitation of hematite from fluids that moved out from the fractures. The fluids also apparently caused dedolomitization and precipitation of calcite in intercrystalline pore spaces. These fluids were probably the source of iron for the bands, although iron released from dedolimitization of ferroan dolomite may have been a local source.

  17. Two 1999 Dates Worth Noting

    NASA Technical Reports Server (NTRS)

    Stern, David P.

    1999-01-01

    Two dates in 1999 can serve as pivots for space-related educational outreach. On August 11 a total solar eclipse will sweep across Europe and also across the Near East, where it will come remarkably close to matching the ancient eclipse (probably in 129 BC) used by Hipparchus to estimate the distance of the Moon. Using published eclipse data, students may conduct a similar calculation for 1999 and in the process obtain insights about astronomy, history and the way scientists work. October 19, 1999 will be the 100th anniversary of the day when a teen-age Robert Goddard climbed a cherry tree near the Worcester home where his family was staying, intending to prune it. Sitting in that tree, Goddard began daydreaming about space flight, and by the time he came down he had resolved to dedicate his life to implementing that dream. He later marked that day as "Anniversary day," a personal holiday. Material on both subjects can be reached from http://www-spof.gsfc.nasa.gov/stargaze/Sintro.htm, sections 8a and 26. The section on Goddard includes his experiments with a ballistic pendulum and the DeLaval nozzle, which laid the essential scientific foundation of spaceflight and which is also suitable for classroom presentation.

  18. Three 2D Ag(I)-framework isomers with helical structures controlled by the chirality of camphor-10-sulfonic acid.

    PubMed

    Guo, Peng

    2011-02-28

    Three 2D Ag(I)-framework isomers were constructed from enantiopure camphor-10-sulfonic acids or racemic camphor-10-sulfonic acids, together with achiral 4-aminobenzoic acids. In complex 1, (+)-camphor-10-sulfonic acids bridge the single left-handed helices that are made up of Ag ions and 4-aminobenzoic acids, generating a homochiral 2D layer. In such a structure, the interweaving of triple left-handed homohelices was also found. It is worth noting that the helicity of complex 2 could be controlled by the handedness of the camphor-10-sulfonic acid. In complex 2, there are right-handed helical structures, including single right-handed and triple right-handed helical structures connected by (-)-camphor-10-sulfonic acids. For a comparative study, (±)-camphor-10-sulfonic acids were utilized to synthesize complex 3, in which equal numbers of right-handed or left-handed double-helical chains are created. All the complexes were characterized by single-crystal X-ray structure determination, powder X-ray diffraction, IR, TGA and element analysis. Circular dichroism spectra of complexes 1 and 2 were been studied to confirm the fact that enantiopure bridging ligands do not racemize. PMID:21264423

  19. Three 2D Ag(I)-framework isomers with helical structures controlled by the chirality of camphor-10-sulfonic acid.

    PubMed

    Guo, Peng

    2011-02-28

    Three 2D Ag(I)-framework isomers were constructed from enantiopure camphor-10-sulfonic acids or racemic camphor-10-sulfonic acids, together with achiral 4-aminobenzoic acids. In complex 1, (+)-camphor-10-sulfonic acids bridge the single left-handed helices that are made up of Ag ions and 4-aminobenzoic acids, generating a homochiral 2D layer. In such a structure, the interweaving of triple left-handed homohelices was also found. It is worth noting that the helicity of complex 2 could be controlled by the handedness of the camphor-10-sulfonic acid. In complex 2, there are right-handed helical structures, including single right-handed and triple right-handed helical structures connected by (-)-camphor-10-sulfonic acids. For a comparative study, (±)-camphor-10-sulfonic acids were utilized to synthesize complex 3, in which equal numbers of right-handed or left-handed double-helical chains are created. All the complexes were characterized by single-crystal X-ray structure determination, powder X-ray diffraction, IR, TGA and element analysis. Circular dichroism spectra of complexes 1 and 2 were been studied to confirm the fact that enantiopure bridging ligands do not racemize.

  20. Enrichment of Non-Terrestrial L-Proteinogenic Amino Acids by Aqueous Alteration on the Tagish Lake Meteorite Parent Body

    NASA Technical Reports Server (NTRS)

    Glavin, Daniel P.; Elsila, Jamie E.; Burton, Aaron S.; Callahan, Michael P.; Dworkin, Jason P.; Herd, Christopher D. K.

    2012-01-01

    The distribution and isotopic and enantiomeric compositions of amino acids found in three distinct fragments of the Tagish Lake C2-type carbonaceous chondrite were investigated via liquid chromatography fluorescence detection time-of-flight mass spectrometry and gas chromatography isotope ratio mass spectrometry. Large L-enantiomeric excesses (L(sub ee) approx. 43 to 59%) of the a-hydrogen aspartic and glutamic amino acids were measured in Tagish Lake, whereas alanine, another alpha-hydrogen protein amino acid, was found to be nearly racemic (D approx. L) using both techniques. Carbon isotope measurements of D- and L-aspartic acid and D- and L-alanine in Tagish Lake fall well outside of the terrestrial range and indicate that the measured aspartic acid enantioenrichment is indigenous to the meteorite. Alternate explanations for the Lexcesses of aspartic acid such as interference from other compounds present in the sample, analytical biases, or terrestrial amino acid contamination were investigated and rejected. These results can be explained by differences in the solid-solution phase behavior of aspartic acid, which can form conglomerate enantiopure solids during crystallization, and alanine, which can only form racemic crystals.