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51.
R D Green 《Journal of supramolecular structure》1980,13(2):175-182
Previous work in our laboratory led us to postulate that N2a cells release adenosine into growth medium, where it acts at the extracellular adenosine receptors to modulate the sensitivity of the cells to the cyclic AMP-elevating effect of adenosine [Green, RD, J Pharmacol Exp Ther 201:610, 1977]. We have now devised a high-performance liquid chromatographic (HPLC) procedure capable of quantitating the concentrations of adenosine in cells and tissue culture media. Growth media of N2a cells and a variant of N2a cells deficient in hypoxanthine-guanine phosphoribosyltransferase (HGPRT-) contain 10-20 nM adenosine, while that of a variant deficient in adenosine kinase (AK-) is elevated severalfold. It appears that the concentration of adenosine in growth media is determined by both the rate at which it is released by cells into the medium and the rate at which it is metabolized by adenosine deaminase present in the serum in the growth medium. Both N2a and AK- cells release considerable amounts of adenosine into serum-free medium (SFM) over a short period. Adenosine release is greater from AK- cells and is accelerated by erythro-9-(2-hydroxy-3-nonyl)-adenine (EHNA), a potent adenosine deaminase inhibitor. This accelerated release is retarded by dipyridamole and homocysteine. Surprisingly, dipyridamole and 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone (Ro 20 1724), a potent phosphodiesterase inhibitor, stimulate basal adenosine release from N2a but not from AK- cells. It remains to be determined if this is due to an effect of these compounds on adenosine kinase. These results give further support for the hypothesis that adenosine in growth medium modulates the sensitivity of the cells to the cyclic AMP-elevating affect of adenosine, and furthermore they suggest that adenosine in growth media may tonically stimulate adenylate cyclase and affect processes controlled by the cyclic AMP:cyclic AMP-dependent protein kinase system. 相似文献
52.
Photoelectron spectra of several substituted dimethylanilines, nitrobenzenes, acetophenones and nitrosobenzenes have been studied with a view to examine the electronic effects of substituents on the various φ and n levels. The results are discussed in the light of molecular orbital calculations and electronic absorption spectra. Correlation of substituent effects on the IE's with π-electron densities and Hammett substituent constants has enabled rationalization of all available data on mono- and disubstituted benzenes. The IE's generally increase with the electron-withdrawing power of the substituents. 相似文献
53.
YueMingLIU FengMeiZHANG HaiHongWU HaiJiaoZHANG JianGuoYANG XingTianSHU MingYuanHE 《中国化学快报》2004,15(10):1258-1260
A SAPO-11 silicoaluminophosphate molecular sieve with stable crystal structure was synthesized for the first time. After removing template by calcination, its crystal space group still retains Icm2 which the as-synthesized has. The catalyst deriving from the present SAPO-I 1 materials shows higher isomerization selectivity and higher paraffin hydroisomerization yield than those reported elsewhere. 相似文献
54.
Thomas P.E.Auf Der Heyde Craig S. Green Derek E. Needham David A. Thornton Gareth M. Watkins 《Journal of Molecular Structure》1981
The infrared spectra of the complexes [M(pyO)(H2O)Cl2] (M = Mn, Fe, Co, Ni, Cu; pyO = pyridine N-oxide) have been determined. Assignments of ν M-Opy, νM-OH2 and ν M-Cl are made by observing the effects of deuterating the coordinated pyO and H2O and replacing chloride by bromide in the Mn(II) complex. Assignments of metal—ligand modes in the mixed ligand complexes [M(pyO)(dmso)X2] (dmso = dimethylsulphoxide) are made by comparison with the spectra of (ML2X2] (L = pyO, dmso) and by observing the effects of deuteration of pyO and dmso. Structural aspects of the spectra are discussed. 相似文献
55.
The theory is presented for rotational excitation of 1Π molecules by collisions with rare gas atoms. It is shown that collision dynamics are described by the two electronic potential energy surfaces which correlate with the electronically degenerate Λ components (doublets) in the diatomic molecule. Because the ±Λ degeneracy can alternatively be described as being in the rotational rather than in the electronic degree of freedom, one can reformulate the collision dynamics in terms of a single effective electronic potential which then depends on Φ, the angle of rotation about the diatomic axis. The form of this Φ dependence is found to be identical to that postulated to explain experimental data for collisional transfer of laser-induced fluorescence. 相似文献
56.
Storr T Obata M Fisher CL Bayly SR Green DE Brudziñska I Mikata Y Patrick BO Adam MJ Yano S Orvig C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,11(1):195-203
Seven discrete sugar-pendant diamines were complexed to the {M(CO)(3)}(+) ((99m)Tc/Re) core: 1,3-diamino-2-propyl beta-D-glucopyranoside (L(1)), 1,3-diamino-2-propyl beta-D-xylopyranoside (L(2)), 1,3-diamino-2-propyl alpha-D-mannopyranoside (L(3)), 1,3-diamino-2-propyl alpha-D-galactopyranoside (L(4)), 1,3-diamino-2-propyl beta-D-galactopyranoside (L(5)), 1,3-diamino-2-propyl beta-(alpha-D-glucopyranosyl-(1,4)-D-glucopyranoside) (L(6)), and bis(aminomethyl)bis[(beta-D-glucopyranosyloxy)methyl]methane (L(7)). The Re complexes [Re(L(1)-L(7))(Br)(CO)(3)] were characterized by (1)H and (13)C 1D/2D NMR spectroscopy which confirmed the pendant nature of the carbohydrate moieties in solution. Additional characterization was provided by IR spectroscopy, elemental analysis, and mass spectrometry. Two analogues, [Re(L(2))(CO)(3)Br] and [Re(L(3))(CO)(3)Br], were characterized in the solid state by X-ray crystallography and represent the first reported structures of Re organometallic carbohydrate compounds. Conductivity measurements in H(2)O established that the complexes exist as [Re(L(1)-L(7))(H(2)O)(CO)(3)]Br in aqueous conditions. Radiolabelling of L(1)-L(7) with [(99m)Tc(H(2)O)(3)(CO)(3)](+) afforded in high yield compounds of identical character to the Re analogues. The radiolabelled compounds were determined to exhibit high in vitro stability towards ligand exchange in the presence of an excess of either cysteine or histidine over a 24 h period. 相似文献
57.
Karl S. Coleman Simon Turberville Malcolm L.H. Green 《Journal of organometallic chemistry》2005,690(3):653-658
A new ferrocenyl-N-heterocyclic carbene ligand precursor 1,1′-bis[(1-tert-butylimidazolium)-3-methyl]ferrocene dichloride has been synthesised and structurally characterised. The imidazolium salt was readily deprotonated in situ with KN(SiMe3)2 and reacted with [PdCl2 (cod)] to afford the structurally characterised palladium (II) complex trans-[PdCl2(C∧fc∧C)], where (cod) = 1,5-cyclooctadiene and (C∧fc∧C) = 1,1′-di-tert-butyl-3,3′-(1,1′-dimethyleneferrocenyl)-diimidazol-2-ylidene. 相似文献
58.
Simple binary solids can be found to adopt unprecedented structures when confined into nanometre-sized cavities, such as the inner cylindrical bore of single-walled carbon nanotubes (SWNT). In the case of the discussed Lal(x)@SWNT encapsulation composite, the Lal2 "crystal" fragment adopts the structure of bulk Lal3, with one third of the iodine positions unoccupied. A complete characterisation of the encapsulation composite was achieved using an enhanced digital restoration approach of high-resolution transmission electron microscopy (HRTEM) images. The resulting complex exit surface wave provides information about the precise structural data of both filling material and host SWNT, establishing the SWNT's chirality and thus enabling a prediction of the composite's overall electron-transport properties. 相似文献
59.
Evolutionary approaches are regularly used to isolate single molecules with desired activities from large populations of nucleic acids (approximately 10(15)). Several methods have also been developed to generate libraries of mRNA-encoded peptides and proteins for the in vitro selection of functional polypeptides. In principal, such mRNA encoding systems could be used with libraries of nonbiological polymers if the ribosome can be directed to polymerize tRNAs carrying unnatural amino acids. The fundamental problem is that current chemical aminoacylation systems cannot easily produce sufficient amounts of the numerous misacylated tRNAs required to synthesize a complex library of encoded polymers. Here, we show that bulk-aminoacylated tRNA can be transformed into N-monomethylated aminoacyl tRNA and translated. Because poly-N-methyl peptide backbones are refractory to proteases and are membrane permeable, our method provides an uncomplicated means of evolving novel drug candidates. 相似文献
60.
Minimizing molecular mobility for desiccation preservation of biologics close to ambient temperature using trehalose glasses require quantitative characterization of their enthalpic relaxation at various end water contents. Differential scanning calorimetry (DSC) was used to characterize three different water contents: 0%, 1.5% and 10% over a wide range of aging temperatures. Results showed the characteristic time (τ) varies both with the water content and the aging temperature. τ increased with lowered aging temperature but showed a non-monotonous relationship as a function of water content. Fragility of trehalose glasses was analyzed using thermophysical parameters obtained from relaxation studies. The study showed trehalose to be a fragile glass former at all water contents, with 0% water samples showing a relatively stronger glass. A compromise between molecular mobility and glass fragility led to an optimal water content close to 1.5% and an aging temperature close to room temperature. This would ensure a τ value of 9000 h, which corresponds to a storage period of a year. 相似文献