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611.
Kitchin SJ Tutoveanu G Steele MR Porter EL Harris KD 《The journal of physical chemistry. B》2005,109(48):22808-22813
Solid state dynamic properties have been investigated for the racemic (DL) and enantiomerically pure (L) crystalline forms of the amino acid serine [HO x CH2 x CH(NH3(+)) x CO2(-)] using 2H NMR line shape analysis and 2H NMR spin-lattice relaxation time measurements for samples of DL-serine and L-serine deuterated in the NH3(+) and OH groups. 2H NMR line shape analysis indicates that, for both L-serine and DL-serine, the ND3(+) group undergoes a 3-site 120 degrees jump motion, with jump frequencies in the intermediate motion regime (10(3) s(-1) to 10(8) s(-1)) in the temperature range 153-313 K. However, at a given temperature, the jump frequency is substantially higher for L-serine (e.g., at 233 K, the jump frequency is 5.0 x 10(6) s(-1) for L-serine and 6.0 x 10(4) s(-1) for DL-serine). The OD group is not dynamic on the 2H NMR time scale within the temperature range studied. The results from both 2H NMR line shape analysis (LA) and 2H NMR spin-lattice relaxation time measurements (SLR) indicate that the activation energy for the 3-site 120 degree jump motion of the ND3(+) group is significantly higher for DL-serine [38.0 +/- 1.0 kJ mol(-1) (LA); 39.7 +/- 0.8 kJ mol(-1) (SLR)] than for L-serine [23.4 +/- 0.8 kJ mol(-1) (LA); 23.8 +/- 0.3 kJ mol(-1) (SLR)]. The difference in activation energies between DL-serine and L-serine is substantially greater than any reported previously for an amino acid in different crystal forms. 相似文献
612.
C. J. Porter C. J. Proctor E. A. Larka J. H. Beynon 《Journal of mass spectrometry : JMS》1982,17(7):331-334
Translational energy release measurments on metastable ions are used in the comparison of the structures of isomeric ions. Metastable ions, m2+, formed from m1+ ions as the result of a high energy process in the ion source are compared with isomeric metastable ions formed as daughters from fragmentation of metastable m1+ ions in a field. In the case of o-, m- and p-nitrophenol the structure of the [C5H5O]+ ions formed from [C6H5O]+ ions by these two independent methods is different as verified by comparison of the behaviour of [C5H5O]+ ions formed from several other compounds. 相似文献
613.
Biochemical characteristics, metabolism, and antitumor activity of several acetylated hexosamines 总被引:1,自引:0,他引:1
R J Bernacki M Sharma N K Porter Y Rustum B Paul W Korythyk 《Journal of supramolecular structure》1977,7(2):235-250
We have synthesized several potential inhibitors and/or modifiers of the carbohydrate portion of plasma membrane glycoconjugates. These include fluorinated and actylated analogs of D-glucosamine, D-galactosamine, and D-mannosamine. These compounds have been tested to determine their effects on both[14C] glucosamine and [3H] leucine incorporation into glycoconjugate and on cell growth and viability using P-288 murine lymphoma cells maintained in tissue culture. The most cytotoxic agent tested was 2-acetamido-2-deoxy-1,3,4,6-tetra-O-acetyl-beta-D-glucopyranose or simply beta-pentaacetylglucosamine which prevented cell growth at 10(-4)-10(-3) M. beta-Pentaacetylglucosamine cytotoxicity was correlated with its high lipid solubility, having an octanol/water partition coefficient of 0.424 as compared with 0.278 for the alpha-anomer and 0.017 for N-acetylglucosamine. In vitro metabolism studies with [4C]- and/or [3H]-labeled pentaacetylglucosamine have indicated intracellular de-O-acetylation leading to the biosynthesis of UDP-N-acetylglucosamine, followed by the incorporation of this sugar into cellular glycoprotein. Concomitant with the formation of increased amounts of this nucleotide sugar, intracellular UTP and CTP pools fell to one third normal within 3 h after the administration of 1 mM pentaacetylglucosamine. At present it is unclear whether the cytotoxicity of beta-pentaacetylglucosamine or other similar agents is due to alterations in nucleotide and nucleotide-sugar pools causing a decrease in energy charge and polynucleotide biosynthesis or is due to a direct effect on membrane glycoconjugate biosynthesis. 相似文献
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618.
T. D. Porter 《Combinatorica》1992,12(3):317-321
For a graphG, let (U,V)=max{e(U), e(V)} for a bipartition (U, V) ofV(G) withUV=V(G),UV=Ø. Define (G)=min(U,V
){(U,V)}. Paul Erds conjectures
. This paper verifies the conjecture and shows
.This work was part of the author's Ph. D. thesis at the University of New Mexico. Research Partially supported by NSA Grant MDA904-92-H-3050. 相似文献
619.
620.
Hikasa K Hagiwara K Kawabata S Barnett RM Groom DE Trippe TG Wohl CG Yost GP Armstrong B Wagman GS Stone J Porter FC Morrison RJ Cutkosky RE Montanet L Gieselmann K Aguilar-Benitez M Caso C Crawford RL Roos M Törnqvist NA Hayes KG Höhler G Manley DM Olive KA Shrock RE Eidelman S Schindler RH Hernández JJ Conforto G Eichler RA 《Physical review D: Particles and fields》1992,46(11):5210