Kinetics of Light-Induced Intramolecular Charge Transfer and Proton Release in Bacteriorhodopsin

Recent advances in understanding the intramolecular charge transfer and proton release by the light-driven proton pump bacteriorhodopsin (bR) are critically reviewed. The focus is on the time-resolved electrical methods, i.e., photocurrent and photovoltage measurements, and on transient absorption experiments with pH-sensitive dyes. Particular attention is paid to the following topics: charge translocation in the low-pH forms of bR (acid-blue and acid-purple); electrogenicity of the 13-cis cycle; results with bR mutants; surface-bound dyes to detect the proton release at specific sites on either side of the protein; the question of kinetic coupling between the deprotonation of the Schiff base and proton release; and rapid long-range migration of protons along the surface of the purple membrane.     

Acid-Base Equilibria in the System PbO–SiO2

The acid-base equilibria in the liquid silicates in the system PbO–SiO₂ are discussed, Data reported by Richardson and Webb, wherein the PbO activity is determined over a composition range of 0 to 60 mole % SiO₂, are used for comparison with activities computed from structural models with consideration of the acid-base equilibria. The results suggest that the liquid silicates in the system PbO–SiO₂, for the composition and temperature ranges studied, are constituted of a relatively low number of anionic species and that these anions are of a relatively small size (i.e., O_2–, SiO_4–, (SiO₃)₃⁶⁻. and (SiO_2.5)₆⁶⁻).     

The Effect of Different Metal Cation Binding on the Proton Pumping in Bacteriorhodopsin

The first section of this paper is a detailed summary of studies made by us and others on metal cations binding to deionized bacteriorhodopsin (dIbR) and its variants. Our studies include the luminescence experiments of Eu³⁺ binding to dIbR and potentiometric studies of Ca²⁺ binding to dIbR, to deionized bR mutants, to bacterioopsin, and to dIbR with its C-terminus removed. The results suggest the presence of two classes of binding sites, one class has two high-affinity constants, and one has one low-affinity constant. For Ca²⁺ binding, there is one metal cation in each of the two high-affinity sites which are coupled to the charged aspartates 85 and 212 (known to be in the retinal cavity) but not coupled to each other. The low-affinity class can accommodate 0–6 Ca²⁺ ions and most of them are bound to the surface. Mg²⁺ has a slightly smaller value for its binding constant to the highest-affinity site. Thus, one expects more Ca²⁺ than Mg²⁺ bound to the two high-affinity sites. In the second section, we summarize our recent study on the effect of metal cation charge density (Ca²⁺, Mg²⁺, Eu³⁺, Tb³⁺, Ho³⁺, Dy³⁺) on the kinetics of both Schiff base deprotonation and proton transport to the extracellular surface. For all metal cations, the apparent rate constant of the slow components of the deprotonation process is the same as that for the transport process at 22 °C. The temperature studies, however, show this apparent equality to be fortuitous and to result from cancellation of the contribution of the energy and entropy of activation. Thus, while the entropy of activation is positive for the deprotonation process, it is negative for the proton transport process. These kinetic parameters depend weakly on the charge density, but in an opposite sense for the two processes. These results suggest that the deprotonation is not the rate-limiting step for the proton transport process. A possible mechanism is proposed in which a hydrated metal cation is used to induce the deprotonation of the protonated Schiff base and to dissociate one of its H₂O molecules to donate the proton in the L → M process.     

质子泵抑制剂兰索拉唑的合成

以2,3-二甲基-4-硝基吡啶-N-氧化物为原料,通过2个“一锅法”,经4步反应合成兰索拉唑.改进的合成路线缩短了合成工艺流程提高了产品收率,反应条件相对温和.总收率达到39.2％,高于文献报道的18.8％,适合工业化生产.     

质子泵抑制剂研究进展

消化系统是人体的重要器官,也是最容易发病的器官之一。消化系统疾病是常见的多发病之一,直接或间接地影响着人类的健康。据SCRIPONLINE最新的信息,世界上40亿人患有消化系统疾病,其中以溃疡最为常见,其发病率约占人口的10%～12%。美国共有3800万人患胃肠道疾病,其中2000万     

质子泵抑制剂雷贝拉唑钠的合成

以2,3 -二甲基-4-氯吡啶-N-氧化物为起始原料,经取代、酰化、水解、氯代、缩合、氧化、成盐等反应制得雷贝拉唑钠.所得产物经氢谱、质谱确证结构.此工艺路线方法简便,原料易得,便于工业化生产.     

苯并咪唑类质子泵抑制剂的合成研究进展

消化性溃疡病是临床上的多发病,胃酸是引起溃疡的重要因素之一,迅速有效地抑制胃酸分泌是目前治疗消化性溃疡的重要手段.质子泵抑制剂(proton pump inhibitors,PPI)是已发现的作用最强的一类胃酸抑制剂,主要用于治疗胃溃疡、十二指肠溃疡、反流性食管炎和卓-艾综合症等与胃酸分泌失调有关的疾病.这类药物较其他抑制胃酸分泌的药物具有明显的优越性,如抑酸作用强、选择性高、疗效好、治愈率高、与抗生素配伍的复方制剂可消除幽门螺杆菌等[1-4].已成为治疗胃酸有关疾病的首选药物和研究的热点.     

Photoreactions of the Photointermediates of Bacteriorhodopsin

The photochemical reactions of the intermediates of the photochemical cycle of bacteriorhodopsin (bR) are reviewed. These reactions constitute photochemical control of the cycle and provide an independent approach for the investigation of the mechanism of light energy transduction in the purple membrane. The absorption of a light quantum by the K, L, or M intermediates converts them back to bR. These transformations interrupt the photocycle so that no proton transfer occurs after absorption of the second quantum. The action of blue light on the M intermediate causes structural changes of the chromophore, as a result of which the Schiff base is reprotonated from Asp-85, not from Asp-96 as in the usual thermal transition of M. The photoreactions of the L, M, N, and O intermediates lead to the formation of new photoproducts. Studies of the photoconversion of the intermediates can serve as an additional source of information on the nature of photoprocesses in bR: they reveal several conformers of K and bR at 90 K, different M states, two N intermediates, and provide direct evidence for the existence of a thermal back reaction from N to M. The study of the photoreactions of the J, K, L, M, N, and O intermediates is a promising method for elucidating the structures and roles of these states. Reversible photoconversions of bR and its photointermediates provide a basis for potential applications of bR in optical registration of information.     

Acid-Base Interactions and Interphase Formation in Particulate-Filled Polymers

Particulate-filled composites were prepared from CaCO 3 and polymer matrices of various acid-base characters. Interfacial interaction of the components was characterized by the reversible work of adhesion, which was calculated either from dipole-dipole or acid-base interactions. The thickness of the spontaneously formed interlayer was derived from the tensile strength of the composites. The results proved that acid-base interactions play an important role in interphase formation. The strength of interfacial adhesion is determined by the joint effect of dispersion forces and acid-base interactions. Stronger interaction leads to a thicker interphase with decreased mobility. Treatment of CaCO 3 with an aliphatic fatty acid leads to a decrease in the strength of interaction, and to changes both in the thickness and properties of the interphase. In composites containing coated fillers, acid-base interactions influence composite properties less due to the neutral character of the surface.     

Acid-Base Interactions and Interphase Formation in Particulate-Filled Polymers

Particulate-filled composites were prepared from CaCO 3 and polymer matrices of various acid-base characters. Interfacial interaction of the components was characterized by the reversible work of adhesion, which was calculated either from dipole-dipole or acid-base interactions. The thickness of the spontaneously formed interlayer was derived from the tensile strength of the composites. The results proved that acid-base interactions play an important role in interphase formation. The strength of interfacial adhesion is determined by the joint effect of dispersion forces and acid-base interactions. Stronger interaction leads to a thicker interphase with decreased mobility. Treatment of CaCO 3 with an aliphatic fatty acid leads to a decrease in the strength of interaction, and to changes both in the thickness and properties of the interphase. In composites containing coated fillers, acid-base interactions influence composite properties less due to the neutral character of the surface.     

Phase Equilibria and Ordering in the System Zirconia-Hafnia-Yttria

The phase equilibria in the system zirconia-hafnia-yttria were investigated at 1300° and 1600°C by precise lattice parameter measurements and the direct phase-inspection method. Large fluorite solid solution regions were dominant at both investigated temperatures. The extent of ordering within the ternary system was studied in the samples containing 40 mol% yttria at 1300°C. The δ-phase (Zr,Hf)³Y₄O₁₂ formation was established only in those samples with less than 15 mol% hafnia.     

Acid-Base Reactions Between Components in Sodium-Aluminoborosilicate Glasses

The effect of coordination groups of boron, aluminum, and silicon on acid-base properties and specifics of the variation in the redox state of copper in boron-containing melts are investigated. An approximate evaluation of acid-base properties of industrial glasses synthesized in an alkaline-aluminoborosilicate system is implemented.     

Crystal Chemistry and Phase Equilibria in the System CdO-PbO-O

The subsolidus portion of the system CdO-PbO-O was investigated at high temperatures and oxygen pressures in cold-seal pressure vessels. Specially prepared cadmium hydroxide precipitate was used to achieve reaction equilibria. Two ternary oxide phases exist in the system: Cd₂PbO₄ is stable under all conditions investigated; CdPb₂O₅ dissociates (2CdPb₂O₅⇋ Cd₂PbO4+Pb₃O₄+O₂). The P-T univariant curve was mapped. Compatibility triangles illustrate the phase equilibria of the system. Cell constants for Cd₂PbO₄ are: a ₀=5.671, b ₀=9.902, C ₀= 3.139, all ±0.001 Å. The space group was determined as Pbam ( Pba2 ); Cd₂PbO₄ is isostructural with the Sr₂PbO₄ structure type. Derived average metal-oxygen distances are: Cd–O 2.35 and Pb–O 2.08 Å. The structure of CdPb₂O₅ is not known.     

Experimental Phase Equilibria in the PbOx-CaO System

Phase equilibria in the PbO _x -CaO system at oxygen partial pressures of 1.01 10⁵ and 1.01 10³ Pa were experimentally investigated. The temperatures of the eutectic reaction between PbO and PbCa₂O₄ and of the peritectic melting of PbCa₂O₄ were measured via differential thermal analysis at five oxygen partial pressures. The phase transition in air between PbO and Pb₃O₄ was not affected by the coexistence of PbCa₂O₄.     

Low-Temperature Phase Equilibria in the Y-Ba-Cu-O System

Ultrasonically prepared freeze-dried nitrate precursors and high-precision solution calorimetry were used to investigate the low-temperature thermodynamic stabilities of compounds in the Y-Cu-O, Ba-Cu-O, Y-Ba-O, and Y-Ba-Cu-O pseudobinary and pseudoternary systems at 1 atm of oxygen. Y₂Cu₂O₅, Y₂BaCuO_s, and BaCuO₂ were found to be metastable below 682°, 728°, and 710°± 5°C, respectively. The only stable phases in the Y-Ba-Cu-O system at 298 K and 1 atm of oxygen are Ba₂Cu₃O₆, CuO, BaO₂, and Y₂O₃. By compiling the calorimetric and phase equilibria data, a series of Y-Ba-Cu-O isothermal phase diagrams were constructed between 25° and 900°C at 1 atm of oxygen.     

Ternary Phase Equilibria in the Zr-Si-C System

Phase equilibria in the ternary Zr-Si-C system at 1200°C are investigated in this work. A specific effort was made tofabricate a stable or metastable Zr₃SiC₂ phase, analogous to Ti₃SiC₂, but no evidence of such a compound was observed.The existence of the Zr₅Si₄ and Zr₃Si phases, which were previously described in analyses of the Zr-Si binary, isconfirmed in this study and their phase relationships withinthe ternary Zr-Si-C system are established by electronmicroprobe analysis and transmission electron microscopy.     

Phase Equilibria in the Quaternary System Ti-Al-C-N

The quaternary system Ti-Al-C-N and its binary and ternary boundary systems are investigated using powder methods and XRD analysis. Phase equilibria at 1375°C are presented in an isothermal network for alloys up to 50 at.% Ti. In the vertical section Ti₂AIC_1-x-Ti₂AlN_1-x a complete series of solid solutions exists at 1495°C, but a wide miscibility gap occurs at 1375°C. The vertical section Ti₃AlC_1-x-Ti₃AlN_1-x is more complex because of the occurrence of the quaternary, tetragonally distorted phase Ti₃Al(C,N)_1-x ( a = 0.41135(4) nm, c = 0.41366(5) nm) and the transformation of perovskite-type Ti₃AlN_1-x into filled Re₃B-type Ti₃AlN_1-x below 1200°C.     

Equilibria and non-equilibria in the formation of xonotlite and truscottite

The conclusions of Roy and Harker (1960) regarding phase equilibria in the silica-rich part of the CaO-SiO₂-H₂O system are substantially confirmed; in particular, truscottite (C₇S₁₂H_≈3) coexists stably with silica and aqueous solution from below 200°C to approximately 350°C at saturated steam pressures. However, non-equilibrium situations readily occur in which xonotlite (C₆S₆H) is formed when truscottite would be expected. These situations are attributed to incongruent solubility of truscottite, coupled with extreme reluctancr or inability of xonotlite to react with silica and aqueous solution to give truscottite. As a result, if xonotlite forms before truscottite it persists, and any process in which silica is effectively removed from the system, however temporarily, can cause a conversion of truscottite into xonotlite that is for practical purposes irreversible and potentially complete. Such loss of silica could occur through liquid or vapor transport, and may be brought about by temperature gradients.