Kinetics and mechanisms of chlorine dioxide and chlorite oxidations of cysteine and glutathione

Chlorine dioxide oxidation of cysteine (CSH) is investigated under pseudo-first-order conditions (with excess CSH) in buffered aqueous solutions, p[H+] 2.7-9.5 at 25.0 degrees C. The rates of chlorine dioxide decay are first order in both ClO2 and CSH concentrations and increase rapidly as the pH increases. The proposed mechanism is an electron transfer from CS- to ClO2 (1.03 x 10(8) M(-1) s(-1)) with a subsequent rapid reaction of the CS* radical and a second ClO2 to form a cysteinyl-ClO2 adduct (CSOClO). This highly reactive adduct decays via two pathways. In acidic solutions, it hydrolyzes to give CSO(2)H (sulfinic acid) and HOCl, which in turn rapidly react to form CSO3H (cysteic acid) and Cl-. As the pH increases, the (CSOClO) adduct reacts with CS- by a second pathway to form cystine (CSSC) and chlorite ion (ClO2-). The reaction stoichiometry changes from 6 ClO2:5 CSH at low pH to 2 ClO2:10 CSH at high pH. The ClO2 oxidation of glutathione anion (GS-) is also rapid with a second-order rate constant of 1.40 x 10(8) M(-1) s(-1). The reaction of ClO2 with CSSC is 7 orders of magnitude slower than the corresponding reaction with cysteinyl anion (CS-) at pH 6.7. Chlorite ion reacts with CSH; however, at p[H+] 6.7, the observed rate of this reaction is slower than the ClO2/CSH reaction by 6 orders of magnitude. Chlorite ion oxidizes CSH while being reduced to HOCl, which in turn reacts rapidly with CSH to form Cl-. The reaction products are CSSC and CSO3H with a pH-dependent distribution similar to the ClO2/CSH system.     

Beauty and fascination of morphologies of the micro- and macrocosmos

Summary Twenty years of experience of the authors with scanning electron microscopy (SEM) led to the idea to present a collection of striking examples of micrographs of intrinsic structural beauty as a birthday present to Professor Fresenius. Harmonic structures, marvellous or scurrilous SEM micrographs of inorganic materials are followed by some examples from the living microcosmos. Sometimes, striking parallelisms to our macroscopic world can be detected, which ultimately lead to some outstanding macroscopic morphologies of the Tyrolean Alps. This is an experiment which tries to encompass fascinating morphologies of the microcosmos and morphologies of the environment of the authors, the Tyrolean Alps. It should empasize the totalitarian aspect of our existence as scientists in a specific environment although one of the authors has recently moved to a less dramatic landscape.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Ti-V基储氢合金及其氢化物的物相结构与组分优化设计

Ti-V基储氢合金在室温、常压下即可表现出良好的储氢特性,且质量储氢容量明显高于传统AB₅型储氢合金,从而在氢气的精制和回收、运输和储存及热泵等方面有较早的应用。 此外,在混合气体分离、核反应堆中处理氢的同位素、镍氢电池及燃料电池负极材料等方面也得到了广泛的研究与关注。 基于目前Ti-V基储氢合金的研究现状,概述了该类合金的优势、限制性因素(包括成因)及改性手段。 此外,为了进一步理解Ti-V基合金储氢机理、构建合金组分与储氢特性之间的对应关系,本工作重点围绕Ti-V基储氢合金及其氢化物的结构、组分优化设计展开综述,并对其未来研究方向做出展望。     

Experimental and theoretical investigation of the Raman and hyper-Raman spectra of acetonitrile and its derivatives

The Raman and hyper-Raman spectra of acetonitrile and its deuterated analog have been investigated by combining experimental analysis and theoretical interpretation. It has been observed that the Raman spectra can easily be reproduced at both the Hartree-Fock and Moller-Plesset second-order levels of approximation and that for these fundamental transitions, inclusion of anharmonicity effects is not essential. On the other hand, the hyper-Raman spectra are more difficult to simulate and interpret. In particular, electron correlation has to be included in order to describe properly the intensity of the CN stretching mode. Then, a pseudo-C(infinity v) symmetry was assumed to better fit the experimental observations. This accounts for the fact that the a1- and e-symmetry modes correspond to time-decoupled vibrations. The e-symmetry modes, associated with nuclear motions perpendicular to the molecular axis are indeed subject to relaxation processes and, except the CCN bending mode, not visible in the hyper-Raman spectra of acetonitrile or of its deuterated analog. This assumption is supported by the gradual decrease of the phenomenon when going from acetonitrile to trichloroacetonitrile, where the presence of the heavier chlorine atoms in the latter reduces the relaxation processes.     

Facile N-arylation of amines and sulfonamides and o-arylation of phenols and arenecarboxylic acids

An efficient, transition-metal-free procedure for the N-arylation of amines, sulfonamides, and carbamates and O-arylation of phenols and carboxylic acids has been achieved by allowing these substrates to react with a variety of o-silylaryl triflates in the presence of CsF. Good to excellent yields of arylated products are obtained under very mild reaction conditions. This chemistry readily tolerates a variety of functional groups.     

Application of micro- and nano-HPLC to the determination and characterization of bioactive and biomarker peptides

This article reviews the works published since 2001 (included) on the micro/nano-HPLC analysis of bioactive and biomarker peptides. The main achievements related to the improvement of the detection sensitivity, quantitation repeatability and reproducibility, and separation selectivity are highlighted. A wide attention is paid to the application of micro/nano-HPLC to the analysis of bioactive peptides in biological matrices. The uses of micro/nano-HPLC in peptidomics to discover new endogenous bioactive peptides and to develop quantitation procedures to compare the levels of peptides of interest in two different biological samples are also considered. Finally, the application of micro/nano-HPLC to the analysis of biomarker peptides for various diseases is also included in this review.     

Direct and sensitized photoprocesses of bis-benzimidazole dyes and the effects of surfactants and DNA

The photoprocesses of two bis-benzimidazole dyes, Hoechst 33258 (1) and an analog, where the phenolic group in p-position is replaced by an ethoxy group, Hoechst 33342 (2), were studied. For 1 and 2 in aqueous solution the quantum yield of fluorescence is strongly pH dependent; it decreases from a maximum value of phi f = 0.4 at pH 5 to phi f = 0.02 at pH 8. The effects of absorption and fluorescence, induced by sodium dodecyl sulfate surfactants below and above the critical micelle concentration and by double-stranded DNA, are interpreted by assuming that in bulk aqueous solution the dyes are essentially present as monomers. The strong enhancement of phi f, when the dye is bound to double-stranded DNA or solubilized in micelles, is suggested to be due to different environments at the benzimidazole rings. A quinoid intermediate with absorption maximum at 380 nm is formed for 1 at neutral pH using lambda exc = 248 or 308 nm. N-centered radicals of 1 or 2 in aqueous solution were observed by laser flash photolysis after electron ejection using wavelengths of 193 or 248 nm (mono and biphotonic, respectively). The precursor radical cation escaped observation but is transformed into the above radicals by deprotonation. Electron transfer from 1 in aqueous solution to triplet acetone takes place, and subsequent deprotonation is proposed to yield N-centered radicals. In addition, energy transfer from acetone to 1 is suggested, leading to T-T absorption with the maximum at 700 nm. The photoprocesses are discussed and the results compared with those known from pulse radiolysis.     

Resurrection and Reactivation of Acetylcholinesterase and Butyrylcholinesterase

Organophosphorus (OP) nerve agents and pesticides present significant threats to civilian and military populations. OP compounds include the nefarious G and V chemical nerve agents, but more commonly, civilians are exposed to less toxic OP pesticides, resulting in the same negative toxicological effects and thousands of deaths on an annual basis. After decades of research, no new therapeutics have been realized since the mid-1900s. Upon phosphylation of the catalytic serine residue, a process known as inhibition, there is an accumulation of acetylcholine (ACh) in the brain synapses and neuromuscular junctions, leading to a cholinergic crisis and eventually death. Oxime nucleophiles can reactivate select OP-inhibited acetylcholinesterase (AChE). Yet, the fields of reactivation of AChE and butyrylcholinesterase encounter additional challenges as broad-spectrum reactivation of either enzyme is difficult. Additional problems include the ability to cross the blood brain barrier (BBB) and to provide therapy in the central nervous system. Yet another complication arises in a competitive reaction, known as aging, whereby OP-inhibited AChE is converted to an inactive form, which until very recently, had been impossible to reverse to an active, functional form. Evaluations of uncharged oximes and other neutral nucleophiles have been made. Non-oxime reactivators, such as aromatic general bases and Mannich bases, have been developed. The issue of aging, which generates an anionic phosphylated serine residue, has been historically recalcitrant to recovery by any therapeutic approach—that is, until earlier this year. Mannich bases not only serve as reactivators of OP-inhibited AChE, but this class of compounds can also recover activity from the aged form of AChE, a process referred to as resurrection. This review covers the modern efforts to address all of these issues and notes the complexities of therapeutic development along these different lines of research.     

Synthesis and structure of hydroxyisoxazolidines and derivatives of hydroxylamine and alkenals

The reactions of N-substituted hydroxylamines with alkenals serve as a method for the synthesis of the corresponding 2-substituted 3(5)-hydroxyisoxazolidines. The reaction pathway is determined by the nature of the substituent attached to the nitrogen atom. Ring-chain isomerism has been detected in these newly obtained compoundsTranslated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1270–1276, September, 1987.     

Synthesis and characterization of norverapamil and quantification of verapamil and nor-verapamil in plasma

Verapamil is a calcium channel blocking agent which has found widespread use in the management of supraventricular tachyarrhythmias, angina pectoris, hypertrophic cardiomyopathy and hypertension. It is converted to its biologically active metabolite nor-verapamil in liver by cytochrome P450. In present communication, synthesis and characterization of nor-verapamil and development of reverse phase high performance liquid chromatographic method for the quantification of nor-verapamil along with verapamil in plasma has been carried out. The characterization of nor-verapamil was carried out using GC-MS, FT-IR and NMR spectroscopy. The separation was carried out with an isocratic JASCO RP-HPLC system using 5 μm KYA TECH HiQ Sil C₁₈ HS column (250 mm × 4.6 mm internal diameter) as a stationary phase and methanol: water: 0.01 M orthophosphoric acid: triethylamine [70: 30: 2: 0.5, v/v/v/v] as mobile phase. The flow rate was maintained at 1.0 mL/min and UV detection at 222 nm. The calibration for verapamil and nor-verapamil were found to be linear over concentration range of 50–300 ng/mL with correlation coefficient (n = 6) of 0.9995 and 0.9997, respectively. This method was validated according to USFDA guidelines. The method was found to be simple, accuare, precise sensitive and selective for the determination of verapamil and nor-verapamil in plasma and thus useful in bioequivalence studies of verapamil.     

离子的极化和形变

离子的极化和形变是无机化学教学中的一对重要概念,这对概念可以用于解释化合物的结构及许多物理和化学性质.然而一些教科书在介绍这对概念时,大都把极化作用限于阳离子,把形变作用限于阴离子,而忽略了阴离子的极化作用和阳离子的形变作用.同时,在应用这对概念解释化合物结构和性质时,条理上也不十分清晰,甚至还出现自相矛盾的情况,使得...     

Preparation and properties of metallacyclobutanes of nickel and palladium

Bis(phosphine)-3,3-dimethylnickela- and palladacyclobutanes have been prepared by intramolecular C-H insertion reaction of the corresponding dineopentyl metal complexes. Nickelacyclobutane complexes decompose when heated thereby undergoing competitive carbon-carbon bond cleavage to give isobutene and ethylene, with reductive elimination affording 1,1-dimethylcyclopropane and skeletal isomeri-zation of the metallacyclic ring yielding 3-methyl-1-butene, whereas the palladium analog gave no significant amounts of CC bond cleavage products.Added phos-phine was seen to have an effect on CC bond scission of nickelacyclobutane complexes. Nickelacyclobutane complexes in solution are thought to be in equilibrium with olefin-coordinated nickel-carbene complex on the basis of available experimental evidence from hydrogenolysis, carbene-trap reactions with olefins and reaction with carbon monoxide     

Determination of Mo,W and Zr in molybdates and tungstates of zirconium and titanium

Molybdate and tungstate of zirconium and titanium gels, used as matrices of ⁹⁹Mo/^99mTc and ¹⁸⁸W/¹⁸⁸Re generators, were synthesized under different conditions, in order to establish their performance and to choose the most appropriate gel to produce commercially. This type of generators demands a high content of Mo or W (>25%) in the matrices, since they use ⁹⁹Mo and ¹⁸⁸W of low specific activities. Therefore, it is of vital importance, to know the concentration of W and Mo in these gels, to determine their viability as matrices of the ⁹⁹Mo/^99mTc and ¹⁸⁸W/¹⁸⁸Re generators. There are different analytical methods to determine Mo and W, however, the presence of Zr and Ti in these gels, in many occasions, interfere in the analysis, imposing the previous separation of both metals before their determination. Therefore, the preparation time of the sample, the cost and the generation of chemical waste of these analyses are increasing. In order to eliminate these difficulties, the concentration of Mo, W and Zr of approximately 43 gels of molybdate and tungstate of zirconium and titanium, were evaluated by NAA without preparation of the samples. The results of this study reveal that the conditions of preparation of the gels influence directly their Mo and W content. In general, the titanium molybdate gels possess, on the average, a larger content of Mo (37%) than the zirconium molybdate gels (30%), while the titanium tungstenate gels contain only 8.5%.     

Crystal and molecular structure of aroyl- and acetylhydrazones of acet- and benzaldehydes

Aroyl- and acetylhydrazones of acet- (I) and benzaldehydes (IV) and benzoylhydrazones of acet- (II) and benzaldehydes (III) were studied by x-ray structural and quantum-chemical methods in order to establish their structures. Compund (I) was the EEZ structure in the crystal. Calculations and spectral data showed that the EEE form occurs in nonpolar solvents and in the gas phase. According to crystallographic data molecules (I)–(IV) are the E-isomers (relative to the N-N bond) and the hydrazone fragments are planar. Intermolecular N-H...O H-bonds from in the crystals. The data obtained suggest that the majority of acylhydrazones are conformationally rigid on dissolution although exceptions do occur. Apparently the reasons for the difference of acetyl- and benzoylhydrazones in electrocarboxylation reactions are electronic and not steric factors.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 75–81, January, 1991.     

Tutorial and comprehensive computational study of acceptance and transmission of sinusoidal and digital ion guides

A quadrupoles acceptance is a measure of its ability to catch ions with certain trajectories. One way to calculate acceptance is the method of ellipses. The method arose partly from a simplification that trajectories could be calculated for an electrode axis independently of others. It has been used to calculate the acceptance and transmission of sine‐driven quadrupole mass filters for over 50 years. Although the method is straightforward, it is generally described with little detail or presented as a confusing string of equations. As such, it may not be decipherable by all practitioners. For this reason, the first half of this paper presents a practical explanation of the method of ellipses and the concepts that make it work. Only equations necessary to describe the method are introduced. The tutorial also prepares the reader for the second half, which presents an alternative approach for calculating acceptance based on an array of initial trajectories. The alternative approach is used to compare the acceptance of simplified sinusoidal and digital ion guides. The method of ellipses was applied to validate results of the new approach for calculation of acceptance.     

Synthesis and characterization of triazenide and triazene complexes of ruthenium and osmium

Triazenide [M(eta2-1,3-ArNNNAr)P4]BPh4 [M = Ru, Os; Ar = Ph, p-tolyl; P = P(OMe)3, P(OEt)3, PPh(OEt)2] complexes were prepared by allowing triflate [M(kappa2-OTf)P4]OTf species to react first with 1,3-ArN=NN(H)Ar triazene and then with an excess of triethylamine. Alternatively, ruthenium triazenide [Ru(eta2-1,3-ArNNNAr)P4]BPh4 derivatives were obtained by reacting hydride [RuH(eta2-H2)P4]+ and RuH(kappa1-OTf)P4 compounds with 1,3-diaryltriazene. The complexes were characterized by spectroscopy and X-ray crystallography of the [Ru(eta2-1,3-PhNNNPh){P(OEt)3}4]BPh4 derivative. Hydride triazene [OsH(eta1-1,3-ArN=NN(H)Ar)P4]BPh4 [P = P(OEt)3, PPh(OEt)2; Ar = Ph, p-tolyl] and [RuH{eta1-1,3-p-tolyl-N=NN(H)-p-tolyl}{PPh(OEt)2}4]BPh4 derivatives were prepared by allowing kappa1-triflate MH(kappa1-OTf)P4 to react with 1,3-diaryltriazene. The [Os(kappa1-OTf){eta1-1,3-PhN=NN(H)Ph}{P(OEt)3}4]BPh4 intermediate was also obtained. Variable-temperature NMR studies were carried out using 15N-labeled triazene complexes prepared from the 1,3-Ph15N=N15N(H)Ph ligand. Osmium dihydrogen [OsH(eta2-H2)P4]BPh4 complexes [P = P(OEt)3, PPh(OEt)2] react with 1,3-ArN=NN(H)Ar triazene to give the hydride-diazene [OsH(ArN=NH)P4]BPh4 derivatives. The X-ray crystal structure determination of the [OsH(PhN=NH){PPh(OEt)2}4]BPh4 complex is reported. A reaction path to explain the formation of the diazene complexes is also reported.     

Sulfur-containing aminoacid derivatives of cholchicine and cholchamine and derivatives of isothiouronium and mercaptoethylamine

New sulfur-containing derivatives of cholchicine and cholchamine with reduced toxicity and preserved pharmacological properties (cytostatic activity for human cancer cells) are prepared. The ability of the new compounds to affect radiation treatment is studied, enabling cholchicine derivatives with more significant radio-sensitizing properties to be found. Institute of Oncology and Radiology, Academy of Sciences of the Republic of Uzbekistan, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 640–650, September–October, 1999.     

Mass and NMR spectra of haplophyllidine and perforine and of their derivatives

Conclusions The mass and NMR spectra of haplophyllidine, perforine, and their derivatives have been studied. The influence of the open and cyclic forms of the molecular ion on the nature of the fragmentation has been discussed. The main routes of fragmentation of the compounds considered are due to the presence of substituents at C₈ and C₄.Khimiya Prirodnykh Soedinenii, Vol. 5, No. 4, pp. 273–279, 1969     

Graphical analysis and visualization of three-dimensional properties of molecules and solids

A simple approach is presented for visualizing three-dimensional properties of molecular and crystalline systems by using PC-based molecular drawing software. This allows a scientist with lower-cost PC-graphics capability to carry out analysis of data, such as wave functions and electron density, which would otherwise require a dedicated graphics workstation and expensive specialized software. In this approach, a data set [x,y,z,f1(x,y,z)] is transformed to a new set of data [x,y,z] for values of f1 meeting specified requirements. The function f1, which varies throughout a chemical system is difficult to visualize. However, a more manageable data set is obtained if the set of Cartesian coordinates corresponding to locations in the system where f1 has a specified value are used. This set of points can then be visualized and plotted with standard graphics software or PC-based molecular modeling programs. In addition, the use of PC-based molecular graphics permits one to superimpose the data describing molecular properties on drawings of the molecular geometry. The entire object can then be rotated to facilitate a clear analysis of the property of the molecule.