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221.
Timberlake GT Yousef AL Chiles SR Moses RA Givens RS 《Photochemistry and photobiology》2005,81(5):1180-1185
Photoactivated bis-diazopyruvamide-N,N'-bis(3-diazopyruvoyl)-2,2'-(ethylenedioxy)bis-(ethylamine), (DPD)-was previously shown to bond materials containing type I collagen. However, tensile strength of bonded collagenous tissue ( approximately 78% water) was low compared with that of dehydrated collagenous gelatin ( approximately 14% water). Here we investigated the role of water in corneal tissue bond strength and in bonding corneal tissue to glass. Bonding corneal tissue to glass may be of value in surgically anchoring keratoprostheses to corneas to alleviate problems with extrusion. Bovine corneal samples were lyophilized for various times resulting in tissue hydrations of zero (no water content) to approximately 3.7 (normal water content). The lyophilized corneal tissue was bonded to solid gelatin sheets, to other corneal samples and to glass using 0.3M DPD in chloroform. Control runs used chloroform only. Samples were irradiated with 100 or 200 J of 320-500 nm light. Strong bonds formed with all three materials when corneal tissue hydration was =1. No bonds or extremely weak bonds formed when tissue hydration levels were >1. No bonding occurred with chloroform alone. Formation of strong bonds only occurs with hydration levels =1 because corneal collagen fibrils are tightly packed and close enough to cross-link with the 1.78 nm long DPD. 相似文献
222.
A model based on classical concepts is derived to describe the effect of the nitro group on proton chemical shifts. The calculated chemical shifts are then compared to ab initio (GIAO) calculated chemical shifts. The accuracy of the two models is assessed using proton chemical shifts of a set of rigid organic nitro compounds that are fully assigned in CDCl3 at 700 MHz. The two methods are then used to evaluate the accuracy of different popular post-SCF methods (B3LYP and MP2) and molecular mechanics methods (MMX and MMFF94) in calculating the molecular structure of a set of sterically crowded nitro aromatic compounds. Both models perform well on the rigid molecules used as a test set, although when using the GIAO method a general overestimation of the deshielding of protons near the nitro group is observed. The analysis of the sterically crowded molecules shows that the very popular B3LYP/6-31G(d,p) method produces very poor twist angles for these, and that using a larger basis set [6-311++G(2d,p)] gives much more reasonable results. The MP2 calculations, on the other hand, overestimate the twist angles, which for these compounds compensates for the deshielding effect generally observed for protons near electronegative atoms when using the GIAO method at the B3LYP/6-311++G(2d,p) level. The most accurate results are found when the structures are calculated using B3LYP/6-311++G(2d,p) level of theory, and the chemical shifts are calculated using the CHARGE program based on classical models. 相似文献
223.
Ferrioxamine B analogues: targeting the FoxA uptake system in the pathogenic Yersinia enterocolitica
Kornreich-Leshem H Ziv C Gumienna-Kontecka E Arad-Yellin R Chen Y Elhabiri M Albrecht-Gary AM Hadar Y Shanzer A 《Journal of the American Chemical Society》2005,127(4):1137-1145
A series of ferrioxamine B analogues that target the bacterium Yersinia enterocolitica were prepared. These iron carriers are composed of three hydroxamate-containing monomeric units. Two identical monomers consist of N-hydroxy-3-aminopropionic acid coupled with beta-alanine, and a third unit at the amino terminal is composed of N-hydroxy-3-aminopropionic acid and one of the following amino acids: beta-alanine (1a), phenylalanine (1b), cyclohexylalanine (1c), or glycine (1d). Thermodynamic results for representatives of the analogues have shown a strong destabilization (3-4 orders of magnitude) of the ferric complexes with respect to ferrioxamine B, probably due to shorter spacers and a more strained structure around the metal center. No significant effect of the variations at the N-terminal has been observed on the stability of the ferric complexes. By contrast, using in vivo radioactive uptake experiments, we have found that these modifications have a substantial effect on the mechanism of iron(III) uptake in the pathogenic bacteria Yersinia enterocolitica. Analogues 1a and 1d were utilized by the ferrioxamine B uptake system (FoxA), while 1b and 1c either used different uptake systems or were transported to the microbial cell nonspecifically by diffusion via the cell membrane. Transport via the FoxA system was also confirmed by uptake experiments with the FoxA deficient strain of Yersinia enterocolitica. A fluorescent marker, attached to 1a in a way that did not interfere with its biological activity, provided additional means to monitor the uptake mechanism by fluorescence techniques. Of particular interest is the observation that 1a was utilized by the uptake system of ferrioxamine B in Yersinia enterocolitica (FoxA) but failed to use the ferrioxamine uptake route in Pseudomonas putida. Here, we present a case in which biomimetic siderophore analogues deliberately designed for a particular bacterium can distinguish between related uptake systems of different microorganisms. 相似文献
224.
Shpeizer BG Clearfield A Heising JM 《Chemical communications (Cambridge, England)》2005,(18):2396-2398
Sol-gel hydrolysis reactions in propanol of two or more metal acetates or alkoxides in n-alkylamines have been found to yield porous mixed oxides with the presence of pores largely in the 10-20 A region. 相似文献
225.
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227.
Abraham Robinson 《Mathematische Annalen》1955,130(4):257-271
228.
229.
Raymond J. Abraham Geoffrey R. Bedford Brian Wright 《Magnetic resonance in chemistry : MRC》1983,21(10):637-642
Some applications illustrating the use of zinc (II) meso-tetraphenylporphyrin (ZnTPP) as a diamagnetic shift reagent are described. The complexation shifts (ΔP) in a series of substituted pyridines are shown to be determined by both the basicity of the coordinating nitrogen atom and steric effects of ortho-substituents. The selectivity of ZnTPP (N»O) in the simplification of the spectra of multifunctional ligands is demonstrated. Addition of the reagent neither affects the rotamer populations of the Inderal side-chain nor produces any distortion of the 2-benzylmorpholine ring. In addition, the substrate-reagent solution may be shaken with D2O to identify exchangeable protons. The application of ZnTPP in structural problems involving substituted imidazo[2,1-b]thiazoles and 2-benzyl-1,3-dioxopyrrolo[3,4-c]pyridines allows unambiguous identification of the possible structural isomers. To overcome the solvent limitations of ZnTPP, the more soluble Co(III)TPPBr can be used successfully as a shift reagent in DMSO-d6, CD3OD and acetone-d6 solutions. 相似文献
230.