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41.
Davydov R Perera R Jin S Yang TC Bryson TA Sono M Dawson JH Hoffman BM 《Journal of the American Chemical Society》2005,127(5):1403-1413
EPR/ENDOR studies have been carried out on oxyferrous cytochrome P450cam one-electron cryoreduced by gamma-irradiation at 77 K in the absence of substrate and in the presence of a variety of substrates including its native hydroxylation substrate, camphor (a), and the alternate substrates, 5-methylenyl-camphor (b), 5,5-difluorocamphor (c), norcamphor (d), and adamantanone (e); the equivalent experiments have been performed on the T252A mutant complexed with a and b. The present study shows that the properties and reactivity of the oxyheme and of both the primary and the annealed intermediates are modulated by a bound substrate. This includes alterations in the properties of the heme center itself (g tensor; (14)N, (1)H, hyperfine couplings). It also includes dramatic changes in reactivity: the presence of any substrate increases the lifetime of hydroperoxoferri-P450cam (2) no less than ca. 20-fold. Among the substrates, b stands out as having an exceptionally strong influence on the properties and reactivity of the P450cam intermediates, especially in the T252A mutant. The intermediate, 2(T252A)-b, does not lose H(2)O(2), as occurs with 2(T252A)-a, but decays with formation of the epoxide of b. Thus, these observations show that substrate can modulate the properties of both the monoxygenase active-oxygen intermediates and the proton-delivery network that encompasses them. 相似文献
42.
Mastropasqua M Braga L Kanematsu M Vaidean G Shrestha R Leonardou P Firat Z Woosley JT Semelka RC 《Magnetic resonance imaging》2005,23(4):557-562
OBJECTIVE: To assess by MR imaging the frequency of hepatic nodules in patients waiting on the liver transplant list and to determine whether certain underlying hepatic diseases were more often associated with the development of such hepatic nodules. MATERIAL AND METHODS: We reviewed the MR and clinical records in all patients seen by the liver transplant service at our center since its inception in January 1998 until September 2002. A total of 371 patients (207 men and 164 women, age range 18-68 years, mean 45 years) were included in the study. The presence of hepatic nodules, size, number and underlying hepatic diseases were determined in all patients. Magnetic resonance imaging was performed on a 1.5-T MR imager using T1-weighted, T2-weighted and multi-phase gadolinium-enhanced sequences. Odds ratio (OR) and 95% confidence intervals (CIs) were computed to evaluate the association between the underlying hepatic disease and the development of hepatic nodule. RESULTS: Among 371 liver transplantation candidates, the most common underlying hepatic disease was hepatitis C virus (HCV) infection, either alone (n=93; 25%) or associated with other hepatic diseases (n=40; 10.8%). Of all patients, 33 (8.9%) had regenerative nodules (RNs), 40 (10.7%) dysplastic nodules (DNs) and 57 (15.3%) hepatocellular carcinomas (HCCs). Hepatocellular carcinoma was observed in 35.3% of patients with HCV infection and alcohol abuse combined, 24.5% with cryptogenic cirrhosis, 25% with hemochromatosis and 19% with alcohol abuse. Patients who had either DNs or HCC were 2.5 times more likely to have either alcohol abuse or HCV, alone or combined, as the substrate of their liver disease (OR 2.54, 95% CI 1.56-4.13). Our data suggest a supra-additive interaction between HCV infection and ethanol in their association with MR imaging detected lesions. CONCLUSION: Patients with cryptogenic cirrhosis, alcohol abuse, HCV infection (alone or combined) and hemochromatosis had the greatest likelihood of having HCC, with the combination of HCV infection and alcohol abuse having the highest of all. 相似文献
43.
A. P. Mishchenko M. E. Sarylova V. M. Gryaznov V. S. Smirnov N. R. Roshan V. P. Polyakova E. M. Savitskii 《Russian Chemical Bulletin》1977,26(7):1490-1492
Conclusions Palladium-copper alloys, which contain from 37 to 42% Cu, have both a high hydrogen permeability and a substantial catalytic activity in the de hydrogenation of 1,2-cyclohexanediol, which makes it possible to use them as membrane catalysts for this reaction.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1620–1622, July, 1977. 相似文献
44.
Summary 7-Amino-1-naphthol-3,6-disulphonic acid forms a stable red coloured complex with trivalent iron. Studies on the composition and stability of this complex are described.
Zusammenfassung 7-Amino-1-naphthol-3,6-disulfonsäure bildet mit Eisen(III) einen beständigen, rotgefärbten Komplex. Über die Untersuchungen zur Zusammensetzung und Stabilität dieses Komplexes wird berichtet.相似文献
45.
G. Roshan Deen Vivien Chua Usman Ilyas 《Journal of polymer science. Part A, Polymer chemistry》2012,50(16):3363-3372
Poly(N‐acryloyl‐N′‐ethyl piperazine‐co‐N‐isopropylacrylamide) hydrogels were prepared by thermal free‐radical copolymerization of N‐acryloyl‐N′‐ethyl piperazine (AcrNEP) and N‐isopropylacrylamide (NIPAM) in solution using N, N′‐methylene bisacrylamide as the crosslinking agent. The gels were responsive to changes in external stimuli such as pH and temperature. The pH and temperature responsive character of the gels was greatly dependent on the monomer content, namely AcrNEP and NIPAM, respectively. The gels swelled in acidic (pH 2) and de‐swelled in basic (pH 10) solutions with a response time of 60 min. With increase in temperature from 23 to 80 °C the swelling of the gels decreased continuously and this effect was different in acidic and basic solutions. The temperature dependence of equilibrium water content of the gels was evaluated by the Gibbs–Helmholtz equation. Detailed analysis of the swelling properties of these new gels in relation to molecular heterogeneity in acidic (pH 2) and basic (pH 10) solutions were performed. Water transport property of the gels was studied gravimetrically. In acidic solution, the diffusion process was non‐Fickian (anomalous) while in basic solution, the diffusion was quasi‐Fickian. The effect was more evident in solution of pH 2 than in pH 10. Various structural parameters of the gels such as number‐average molar mass between crosslink (Mc), the crosslink density (ρc), and the mesh size (ξ) were evaluated. The mesh sizes of the hydrogels were between 64 and 783 Å in the swollen state in acidic solution and 20 and 195 Å in the collapsed state in basic solution. The mesh size increased between three to four times during the pH‐dependent swelling process. The amount of unbound water (free water) and bound water of the gels was also evaluated using differential scanning calorimetry. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
46.
47.
In this paper, we theoretically study the propagation of electromagnetic waves in one-dimensional double-period quasi-regular structures consisting of negative-permittivity and negative-permeability metamaterials. A Drude-type dispersive response for both permittivity and permeability of single-negative metamaterials is considered. From the numerical results performed by transfer matrix method and effective medium theory, it is found that double-period photonic crystals can exhibit an omnidirectional gap at given microwave frequency. Such an omnidirectional gap is insensitive to incident angle and polarization, and is invariant upon the change of scale length. It is also found that this gap exists in all double-period sequences, and it is independent of structure sequence. Moreover, electromagnetic field distributions in this structures show that the fields are localized at each interface of two media. These results can lead to further applications of quasi-regular structures. 相似文献
48.
The effect of substituents in the para position of anilide ion (An) on the N?···H–F → N–H···F? switching in X–An–HF (X = H, Me, CHO, CN, NO, F, NO2, OH and OMe) complexes was investigated by means of B3LYP and MP2 quantum chemical methods. To delve into the mechanistic details of the proton transfer process, potential energy curve and further geometrical parameters involved in H-bonding during the course of the proton transfer process were evaluated at the MP2/6-311++G(2d,2p) level of theory. The changes in H-bond strength because of variation of substituents were well accompanied by changes in formation energy of complexes, structural parameter, electron density, natural charge and charge transfer between subunits. For X = H, Me, CHO, CN, NO, F and NO2 substituents, our results at MP2/6-311++G(2d,2p) level showed that the minimum energy structures correspond to the N···HF H-bonded complexes without proton transfer occurring. On the other hand, for electron-donating substituents OH and OMe, proton is transferred from HF to anilide ion and the minimum energy structures are HNH···F? H-bonded complexes. The nature of HN?···HF and HN–H···F? interactions in complexes was characterized by means of atoms in molecules and natural bond orbital analyses. 相似文献
49.
Roshan James Rajaram K. Nagarale Vinay K. Sachan Christopher Badalucco Prashant K. Bhattacharya Sangamesh G. Kumbar 《先进技术聚合物》2014,25(12):1439-1445
Conductive polymers have found extensive application in fuel cells, sensors and more recently as scaffolds for tissue and organ regeneration. Scaffolds that can transmit electrical impulses have been shown to be beneficial in regeneration of tissues like muscle and nerve that are electroactive in nature. Most cellular events and cell functions are regulated by ion movement, and their imbalance is the cause of several diseases. We report synthesis and characterization of sulfonated polymers of poly(methyl vinyl ether‐alt‐maleic anhydride) (PMVEMA), poly(ether ether ketone) (PEEK), poly(ether sulfone) (PES) and poly(phenylene oxide) (PPO) and evaluate their potential for tissue regeneration. The ionic conductive property stems from the presence of sulfonic groups on the polymer backbone. The structure of the polymer was confirmed using Fourier Transform Infrared Spectroscopy and membrane hydrophicity was determined by water contact angle measurement. The electrical conductivity of these sulfonated membranes was found to be 53.55, 35.39 and 29.51 mS/cm for SPPO, SPEEK and SPMVEMA, respectively. The conductivity was directly proportional to the sulfonic acid content on the polymer backbone. The ionic membranes namely SPPO, SPEEK and SPMVEMA demonstrated superior cell adhesion properties (~7–10 fold higher) than cells seeded onto tissue culture polystyrene. The sulfonated membranes exhibited static water contact angle in the range of 70–76°. The membranes supported the proliferation of human skin fibroblasts over 14 days in culture as evidenced by confocal and electron microscopy imaging. The ionic materials reported in this study may serve as scaffolds for a variety of tissue healing and drug delivery applications. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
50.
Ezio Rizzardo John Chiefari Roshan Mayadunne Graeme Moad San Thang 《Macromolecular Symposia》2001,174(1):209-212
Living radical polymerization methods that allow the preparation of polymers with predetermined molecular weight, narrow molecular weight distribution and tailored architecture (e.g. block, graft, stars) are offering a vast range of new and advanced materials. With applications ranging from surfactants, dispersants, coatings and adhesives, to microelectronics, membranes, drug delivery, and biomaterials they have the potential of revolutionizing a large part of the polymer industry. 相似文献