A thermochemical analysis of inhalational anesthetics

The mechanism of the anesthetic process is of interest both to the clinician and to the pharmacologist. However, this is still an unsettled issue and a multitude of models have been proposed for the process. Noticing that most models propose either a molecular perturbation by the agents or an effect on some colligative property, we explore in this article the thermodynamical consequences of these postulations. Comparison of these with experimental findings is then made. The comparison shows the inconsistency of many of the models with the facts: (i) it refutes the long accepted conviction, culminated in the unitary hypothesis, that general anesthetics act not at a particular receptor site but invariably on all. Some consequences of this finding are demonstrated. (ii) it implies that a simple phospholipid medium is not feasible as an anesthetic site. (iii) it infers that proteins do have the properties required from anesthetic sites.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday     

Nitrosation of Phenolic Compounds: Effects of Alkyl Substituents and Solvent

Summary.  Nitrosation reactions of phenol, o-cresol, 2,6-dimethylphenol, o-tert-butylphenol, 2-hydroxyacetophenone, and 2-allylphenol in water and water/acetonitrile were studied. Kinetic monitoring of the reactions was accomplished by spectrophotometric analysis of the nitrosated products at 345 nm. The dominant reaction was C-nitrosation via a mechanism consisting of an attack on the nitrosatable substrate by NO⁺/NO₂H₂ ⁺ followed by a slow proton transfer. The values of the rate constants of phenolic C-nitrosation were increased by electron donating substituents, and a good Hammett correlation was observed with ρ = −6.1. The results also revealed the strong effect of pH and the permitivity of the reaction medium on the rate constant, whose maximum values were observed for pH ≈ 3, decreasing strongly for higher pH values. The study in water/acetonitrile with up to 25% acetonitrile showed that it is possible to inhibit the reaction strongly by increasing the percentage of the organic component. The conclusions drawn show that (i) it is possible to predict the rate of nitrosation of phenolics as a function of the meta-substituents on the phenol ring and (ii) the nitrosation of phenolics can be strongly inhibited by increasing the pH of the reaction medium as well as by lowering its dielectric constant. Received July 13, 2001. Accepted (revised) September 18, 2001     

Compatibility mechanisms between EVA and complex impact heterophasic PP-EPx copolymers as a function of EP content

Compatibility mechanisms between EVA and complex heterophasic iPP-EPx copolymers have been studied as a function of EP content. Systematic studies were made in order to characterize the thermal, morphological and mechanical behavior, before and after blending a series of PP-EPx/EVA concentrations. Multiple melting, proportional to the EP content, was observed for the neat copolymers and an explanation was given for its evolution in terms of rejection-like secondary crystallization. After blending with EVA, the generation of a single T_g was taken as an indication of compatibility between both polymers. A morphological transition toward compatibility was first determined at 20 wt.% EVA which was in correlation with a morphological change from isolated spherical domains to interconnected voids. A second morphological transition from interconnected voids to fibrous crystals was observed above 40 wt.% EVA. This last transition marked the beginning of compatibility. Overall, the evolution of blends was explained in terms of the nature of the complex heterophasic copolymers. Tensile mechanical studies were also consistent with morphological changes. Increases in the x content in EPx and in EVA concentration worked in favor of impact resistance.     

Depolymerization of poly(2,6-dimethyl-1,4-phenylene oxide) under oxidative conditions

Depolymerization of an engineering plastic, poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), was accomplished by using 2,6-dimethylphenol (DMP) under oxidative conditions. The addition of an excess amount of DMP to a solution of PPO in the presence of a CuCl/pyridine catalyst yielded oligomeric products. When PPO (M(n)=1.0x10(4), M(w)/M(n)=1.2) was allowed to react with a sufficient amount of DMP, the molecular weight of the product decreased to M(n)=4.9x10(2) (M(w)/M(n)=1.5). By a prolonged reaction with the oxidant, the oligomeric product was repolymerized to produce PPO essentially identical to the starting material, making the oligomer useful as a reusable resource. During the depolymerization reaction, an intermediate phenoxyl radical was observed by ESR spectroscopy. Kinetic analysis showed that the rate of the oxidation of PPO was about 10 times higher than that of DMP. These results show that a monomeric phenoxyl radical attacks the polymeric phenoxyl to induce the redistribution via a quinone ketal intermediate, leading to the substantial decrease in the molecular weight of PPO, which is much faster than the chain growth.     

Analysis of sorption and bioavailability of different species of mercury on model soil components using XAS techniques and sensor bacteria

The present work studies the adsorption behaviour of mercury species on different soil components (montmorillonite, kaolinite and humic acid) spiked with CH₃HgCl and CH₃HgOH at different pH values, by using XAS techniques and bacterial mercury sensors in order to evaluate the availability of methyl mercury on soil components. The study details and discusses different aspects of the adsorption process, including sample preparation (with analysis of adsorbed methyl mercury by ICP-OES), the various adsorption conditions, and the characterization of spiked samples by XAS techniques performed at two synchrotron facilities (ESRF in Grenoble, France and HASYLAB in Hamburg, Germany), as well as bioavailability studies using mercury-specific sensor bacteria. Results show that XAS is a valuable qualitative technique that can be used to identify the bonding character of the Hg in mercury environment. The amount of methyl in mercury adsorbed to montmorillonite was pH-dependent while for all soil components studied, the bond character was not affected by pH. On the other hand, clays exhibited more ionic bonding character than humic acids did with methyl mercury. This interaction has a higher covalent character and so it is more stable for CH₃HgOH than for CH₃HgCl, due to the higher reactivity of the hydroxyl group arising from the possible formation of hydrogen bonds.The bioavailability of methyl mercury adsorbed to montmorillonite, kaolinite and humic acids was measured using recombinant luminescent sensor bacterium Escherichia coli MC1061 (pmerBR_BSluc). In case of contact exposure (suspension assays), the results showed that the bioavailability was higher than it was for exposure to particle-free extracts prepared from these suspensions. The highest bioavailability of methyl mercury was found in suspensions of montmorillonite (about 50% of the total amount), while the bioavailabilities of kaolinite and humic acids were five times lower (about 10%). The behaviour of methyl mercury in the presence of montmorillonite could be explained by the more ionic bonding character of this system, in contrast to the more covalent bonding character observed for humic acids. Thus, XAS techniques seem to provide promising tools for investigating the mechanisms behind the observed bioavailabilities of metals in various environmental matrices, an important topic in environmental toxicology.     

Reactions of Sulphate Radicals with Substituted Pyridines: A Structure–Reactivity Correlation Analysis

The kinetics of the oxidation of pyridine, 3‐chloropyridine, 3‐cyanopyridine, 3‐methoxypyridine and 3‐methylpyridine mediated by SO₄ ^{< M ‐>} radicals are studied by flash photolysis of peroxodisulphate, S₂O₈^2?, at pH 2.5 and 9. The absolute rate constants for the reactions of both, the basic and acid forms of the pyridines, are determined and discussed in terms of the Hammett correlation. The monosubstituted pyridines react about 10 times faster with sulphate radicals than their protonated forms, the pyridine ions. The organic intermediates are identified as the corresponding hydroxypyridine radical adducts and their absorption spectra compared with those estimated employing the time‐dependent density functional theory with explicit account for bulk solvent effects. A reaction mechanism which accounts for the observed intermediates and the pyridinols formed as products is proposed.     

基于芳香四羧酸构筑的两种配位聚合物的荧光及磁性质（英文）

在溶剂热条件下,基于芳香四羧酸合成了2种新颖的配位聚合物:{[Zn2(tptc)(1,4-bimb)2]·H2O}n(1)和{[Ni(tptc)0.5(1,2-bimb)(H2O)]·H2O}n(2),其中,tptc为对-三联苯-3,3″,5,5″-四羧酸,1,4-bimb为1,4-二(咪唑-1-亚甲基)苯,1,2-bimb为1,2-二(咪唑-1-亚甲基)苯。结构分析表明,1为三维结构,拓扑符号为(86);2为二维层状网络,通过氢键相互作用进一步扩展为三维超分子结构。此外,我们还研究了1对阳离子、阴离子的荧光感应以及2的磁性质。     

A theoretical investigation of the gas-phase oxidation reaction of the saturated tert-butyl radical.

The radical-radical reaction mechanisms and dynamics of ground-state atomic oxygen [O(3P)] with the saturated tert-butyl radical (t-C4H9) are investigated using the density functional method and the complete basis set model. Two distinctive reaction pathways are predicted to be in competition: addition and abstraction. The barrierless addition of O(3P) to t-C4H9 leads to the formation of an energy-rich intermediate (OC4H9) on the lowest doublet potential energy surface, which undergoes subsequent direct elimination or isomerization-elimination leading to various products: C3H6O + CH3, iso-C4H8O + H, C3H7O + CH2, and iso-C4H8 + OH. The respective microscopic reaction processes examined with the aid of statistical calculations, predict that the major addition pathway is the formation of acetone (C3H6O) + CH3 through a low-barrier, single-step cleavage. For the direct, barrierless H-atom abstraction mechanism producing iso-C4H8 (isobutene) + OH, which was recently reported in gas-phase crossed-beam investigations, the reaction is described in terms of both an abstraction process (major) and a short-lived addition dynamic complex (minor).     

Electron Transfer and Charge Transfer: Twin Themes in Unifying the Mechanisms of Organic and Organometallic Reactions

The broad varieties of organic and organometallic reactions merge into a common unifying mechanism by considering all nucleophiles and electrophiles as electron donors (D) and electron acceptors (A), respectively. Comparison of outer-sphere and inner-sphere electron transfers with the aid of Marcus theory provides the thermochemical basis for the generalized free energy relationship for electron transfer (FERET) in Equation (37) and its corollaries in Equations (43) and (44) that have wide predictive applicability to electrophilic aromatic substitutions, olefin additions, organometallic cleavages, etc. The FERET is based on the conversion of the weak nucleophile–electrophile interactions extant in the ubiquitous electron donor—acceptor (EDA) precursor complex [D, A] to the radical ion pair [D^⊕, A^?], for which the free energy change can be evaluated from the charge-transfer absorption spectra according to Mulliken theory. FERET analysis thus indicates that the charge-transfer ion pairs [D^⊕, A^?] are energetically equivalent to the transition states for nucleophile/electrophile transformations. The behavior of such ion pairs can be directly observed immediately following the irradiation of the charge-transfer bands of various EDA complexes with a 25-ps laser pulse. Such studies confirm the radical ion pair [Arene^⊕, NO₂] as a viable intermediate in electrophilic aromatic nitration, as presented in the electron-transfer mechanism between arenes and the nitryl cation (NO) electrophile.