On the homogeneity range of the κ phases in the Hf-Mo-{Si,P, S,Ge, As,Se} systems

A survey of the various two- and three-phase equilibria involving the κ phases in the subsolidus regions of the ternary Hf-Mo-{Si, P, S, Ge, As, Se} systems has been made. The κ phases have homogeneity ranges, accompanied by variations in the unit-cell volumes. The hexagonal κ-phase structure is composed of a transition metal sublattice with triangular prismatic and octahedral interstices. The nonmetal atoms may occupy one or both types of interstices. Phase-analytical and crystallographic results suggest a variable degree of hafnium substitution on the molybdenum sites in the metal sublattice as the major cause of the variations in composition observed. The κ phase in the Hf-Mo-S system exhibits a particularly large extension of the homogeneity range. This fact might be interpreted in terms of an enhanced thermodynamic stability of this phase, connected with the filling of both octahedral and triangular prismatic sites by sulfur in the structure, in contrast to the empty octahedral sites in the remaining κ phases.     

A Unified Strategy Targeting the Thiodiketopiperazine Mycotoxins Exserohilone,Gliotoxin, the Epicoccins,the Epicorazines,Rostratin A and Aranotin

A unified synthetic strategy directed towards mycotoxins belonging to the thiodiketopiperazine family is reported. The building blocks for a number of natural products—including exserohilone, gliotoxin, the epicoccins, the epicorazines, rostratin A and aranotin—have been synthesised stereoselectively from a common precursor. This key intermediate was constructed through an efficient and highly diastereoselective [2+2] cycloaddition between a ketene and an enecarbamate derived from L ‐pyroglutamic acid. The annelation of the second ring was accomplished through ring‐closing metathesis and enol ether–olefin ring‐closing metathesis to provide both cis‐ and trans‐annelated azabicyclic cyclohexenones, as well as an annelated seven‐membered cyclic enol ether. A Pd‐catalysed elimination of allyl acetate gave rise to the cyclohexadienol structure of gliotoxin. Dimerisation of one building block to afford the diketopiperazine core was demonstrated.     

Information Theory, the Shape Function, and the Hirshfeld Atom

Following the work of Nalewajski and Parr, there has been a surge of interest in the use of information theory to describe chemical bonding and chemical reactions. However, the measure of “information” used by Nalewajski and Parr is not any of the usual conventional entropies, chiefly because the electron density is not normalized to one. The consequences of this are discussed, and a solution is constructed using the shape function and an “entropy of mixing” term. The same revision, however, cannot be made when if the Tsallis entropy, instead of the Shannon form, is used. This serves to emphasize that the Hirshfeld atom is a very specific result, associated only with logarithmic measures of information. A less specific derivation due to Nalewajski provides one resolution to this quandary; this derivation is analyzed in detail.     

Biogeochemical migration of heavy metals, Ti, V, Mo, Ta, W, and U, in the profile of a low-laid peatbog in the country between the Ob and Tom rivers

Biogeochemical migration of heavy metals in the course of marsh formation is mainly determined by physical-chemical processes, such as the oxidation-reduction zonality of the peatbog thickness and the state of humous substances (the quality of humus adsorptive barriers). In the process of peatbog formation V, U, Ta are the weakly captured elements while Mo is captured to a relatively higher extent. Elements as Ti and W are found in separate layers. No technogenic degradation of the marsh ecosystem in the Ob and Tom has been observed.     

血清铁、锌、钙、镁、磷与妊娠的关系探讨

为探讨血清铁、锌、钙、镁、磷在孕妇体内的水平，做好围产期孕妇的保健工作，提高孕产妇的健康水平和新生儿健康素质，抽取125例孕中期妇女空腹静脉血，采用透射比浊法测定了其血清铁、锌、钙、镁、磷的含量。结果表明，铁、锌、钙、镁、磷的异常在孕妇中有一定的发生率，其中尤以钙与锌的缺乏最为多见。提示应定期检测孕妇血清铁、锌、钙、镁、磷水平，并采取相府的防治措施．以提高孕产妇及新生儿的健康水平。     

Amedeo Avogadro The Man, the Hypothesis, and the Number

Amedeo Avogadro was a multifaceted and prolific scientist active in many areas of physics and chemistry, but most of his results did not make a scientific impact. His hypothesis, equal volumes = equal number of molecules remained in obscurity until Cannizaro rekindled it by making it a stepping-stone in the development of the atomic theory.     

An investigation of the efficacy of organotin compounds for the control of the cotton stainer,Dysdercus cingulatus,the mosquito,Anophelese stephensi,and the common house fly,Musca domestica

A series of commercial organotin compounds was screened for efficacy against the three insect species Dysdercus cingulatus (cotton stainer), Anophelese stephensi (mosquito) and Musca domestica (house fly). Tributyltin species in the general order Bu₃SnCl>(Bu₃Sn)₂O>Bu₃Sn(linoleate) were more effective than two triphenyltin compounds. Tricyclohexyltin hydroxide, dimethyltin chloride, phenyltin trichloride and a diethyltin dichloridephenanthroline adduct were less effective.     

Scholarship, Education, and the Internet

A lecture demonstration of primary kinetic isotope effect using the bromination of acetone and acetone-d₆ is described.     

Structural Chemistry,the journal,the discipline,bridge building,and our personal and professional practice

Structural Chemistry - This paper was written on the occasion of the 30th special Jubilee volume of Structural Chemistry journal in 2019. It offered us a unique opportunity to look at our common...     

Isolation,analysis, biosynthesis,and modification of the alkaloid cytisine

Information on methods of isolation and analysis of the alkaloid cytisine and its derivatives and questions of structure and modification over the last 25 years are generalized.Institute of Organic Synthesis and Coal Chemistry, Khazakhstan Academy of Sciences, Karaganda. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 301–313, May–June, 1991.     

Radiochemistry at the Koninklijke/Shell-Laboratorium,Amsterdam, the Netherlands

Conclusion As this brief survey has indicated, the Radiochemistry group at KSLA is deeply involved in many areas of process development. Sometimes directly, as in source or tracer application, at other times indirectly such as through activation analysis. The activities reflect the strong emphasis on process development in KSLA as a whole.     

SiOM(M=Li,Be,B,Na,Mg,Al)分子结构的DFT研究

利用Gaussian-94计算程序,B3LYP方法,6-311+G(2d)6d基组,对SiOM(M=Li,Be,B,Na,Mg,Al)诸体系的几何结构进行优化.结果表明,M既可与SiO中的Si键合,也可与O键合.第一和第二主族的SiOM体系以折线形构型为最稳定构型,而第三主族则以近直线形或直线形构型为最稳定构型.从Si-O间键长R_SiO、力常数f_SiO及自然键轨道分析可知,第一主族的SiOLi和SiONa的最稳定构型中SiO-M间的离子键成分较大,可近似看作离子键;而对SiOLi,SiOBe,SiOB和SiOMg体系的以Si为中心的构型,M-SiO间的离子键成分很小,不能看作离子键,可认为M与SiO之间存在着弱相互作用     

Catalysis in the Synthesis of S,N-Heterocycles and O,N-, S,N-, and O,S,N-Macroheterocycles

The review systemizes and generalizes published data on the catalytic syntheses of six-, seven-, and eight-membered S,N-heterocycles and O,N-, S,N-, and O,S,N-macroheterocycles.     

Ab initio investigation of the hydration of the tetrahedral perchlorate, perbromate, selenate, arsenate, and vanadate anions

The geometries, energies, and vibrational frequencies of various isomers of XO(4)(m-)(H2O)n, x = Cl, Br, Se, As, V; n = 0-6, m = 1-3 are calculated at various levels up to MP2/6-31+G*. These properties are studied as a function of increasing cluster size. The experimental and theoretical vibrational spectra are compared where available.     

An ab initio study of the structures and the harmonic and anharmonic stretching force constants of the cyanides HCN,LiCN, FCN,ClCN and isocyanides HNC,LiNC, FNC,ClNC

Equilibrium structures and both harmonic and anharmonic stretching force constants have been calculated ab initio for the four cyanides HCN, LiCN, FCN, and C1CN, and the four isocyanides HNC, LiNC, FNC, and ClNC, using several basis sets of about triple-zeta quality. The CN and NC bond lengths, as well as diagonal stretching force constants, are nearly the same throughout both series. Trends in the off-diagonal stretching force constants are discussed, and dipole moment values are correlated with the structural type, XCN and XNC, and the electronegativity of the ligand X.     

A theoretical (DFT, GIAO-NMR, NICS) study of the carbocations and oxidation dications from azulenes, homoazulene, benzazulenes, benzohomoazulenes, and the isomeric azulenoazulenes

Protonation of parent azulene (1), homoazulene (8), representative isomeric benzazulenes (9, 9A, and 9B), and benzohomoazulenes (10, 10A, and 10B) as well as the mono- and diprotonation of isomeric azulenoazulenes (11-16) were studied by DFT at the B3LYP/6-31G(d) level. The most likely carbocations were identified based on relative protonation energies. For comparison, complete experimental 13C NMR data were obtained for parent azulenium ion 1H+ and guaiazulenium ion 2H+ in TFA. The oxidation dications derived from benzazulenes (9, 9A, and 9B), benzohomoazulenes (10, 10A, and 10B) and azulenoazulenes (11, 16) were also investigated. For azulenoazulene dications the singlet and triplet states are both minima, but except for 11(2+) and 13(2+), the triplet states are higher in energy. Structural/geometrical changes in the carbocations were examined. GIAO-NMR, NPA charges (and changes in charges), and NICS (and delta NICS) were employed to compute the NMR chemical shifts (delta delta 13C values) in order to derive charge delocalization maps and to gauge relative aromaticitylantiaromaticity in the energetically most favored carbocations and oxidation dications. The emerging trends are discussed and compared. Creation of tropylium or homotropylium entities in the carbocations (monoprotonated) and carbodications (diprotonated) is identified as an important driving force governing the protonation outcomes. Consideration of the AM1-derived delta delta Hf values (and the DFT-derived delta delta G values) suggests that the two-electron oxidation of azulenoazulenes should be experimentally feasible. Given their antiaromatic (paratropic) character, azulenoazulene dications represent interesting targets for NMR study. GIAO-derived charge delocalization mapping allows the most likely sites for nucleophilic attack on the dications to be identified.     

Annual General meeting of the Department of the Biochemistry,Biophysics, and Chemistry of Physiologically active compounds of the Academy of Sciences of the USSR,March 16, 1976, Moscow

Chronicles

Annual General meeting of the Department of the Biochemistry, Biophysics, and Chemistry of Physiologically active compounds of the Academy of Sciences of the USSR, March 16, 1976, Moscow     

Theoretical study on the factors controlling the stability of the borate complexes of ribose, arabinose, lyxose, and xylose

Recent experimental studies suggest that complexation with borate minerals stabilizes ribose, and that the borate complex of ribose is more stable than those of related aldopentoses, that is, arabinose, lyxose, and xylose. These findings have revived the debate on the plausibility of the RNA-world theory, because they provide an explanation for the stabilization and selection of ribose in prebiotic conditions. In this paper we unravel the factors that make the ribose-borate complex the most stable one. For this purpose, we have investigated the structure and stability of the ribose-, arabinose-, lyxose-, and xylose-borate complexes using density functional theory and a continuum solvent approach. The computed results reveal that in the aldopentose-borate complexes, the electrostatic field of the borate is strong enough to change the orientation of the nearby hydroxyl groups compared to noncomplexed aldopentoses. In addition, we show that the distinct stability of the ribose-borate 2:1 complex can be attributed to 1) a strong hydrogen bond between the ribose 3-OH and one of the negatively charged borate oxygen atoms, and 2) a favorable contact between the aqueous medium and the 5-CH(2)OH group due to the space separation between the 5-CH(2)OH group and the borate anion.     

Calculated electron impact cross sections for the K-shell ionization of Fe,Co, Mn,Ti, Zn,Nb, and Mo atoms using the DM formalism

We used the Deutsch-Märk (DM) formalism to calculate atomic K-shell electron impact ionization cross sections for the elements Fe, Co, Mn, Ti, Zn, Nb, and Mo. The calculated K-shell ionization cross sections are compared with recently measured K-shell ionization cross sections. Good to satisfactory agreement was found for all atoms with the exception of Ti. Moreover, when compared to other available K-shell ionization cross sections for these atoms, calculated using other theoretical methods and semiempirical formulae, the predictions of the DM formalism achieve a level of agreement with experimental data that is as good or better than the predictions from the other methods.