The influence of second-nearest neighbor interactions on the thermodynamic properties of B2 phases with substitutional defects

In order to explain some discrepancies between the theoretical predictions and the experimental data for the thermodynamic properties of substitutional B 2 phases,Chang's theoretical model is extended by including the influence of second-nearest neighbor interactions. For this purpose a new parameter is introduced which is defined as the ratio of the interchange energies between second-nearest and first-nearest neighbors. Theoretical equations are derived for the compositional dependence of the activity and the partial molar enthalpy. Using literature data, the following phases are re-evaluated in terms of the disorder parameter and the newly introduced parameter : -AuZn, -AuCd, -AgMg, and -NiZn. Very good agreement is found between the theoretical curves and the experimental data for the four systems. The values of obtained range from 0.0 for -NiZn to 0.5 for -AuZn. The inclusion of second-nearest neighbor interactions has little influence on the values of . It is shown that the behavior of the activity curve in -AuZn can be explained in a physically more meaningful way by including interactions between all second-nearest neighbors rather than interactions between gold substitutional defects only, as was done byLibowitz.With 5 Figures     

Radiation-induced reactions of cholesterol in an aqueous medium

⁶⁰Co -ray radiolysis of cholesterol /3-hydroxy-5-cholestene/ /I/ in the two-phase system /water-ethyl acetate/ and in the presence of air has been studied using TLC and GC methods. The following products were observed in the irradiated mixture: 3, 7-dihydroxy-5-cholestene /II/, G O. 36, 3-hydroxy-7-keto-5-cholestene /III/, G 1.48, 3-hydroxy-7-keto-5-cholestane /IV/, G 0.22, 3,5,6-trihydroxy-5-cholestane /V/, G 0.83, 5,6-epoxy-3-hydroxy-5-cholestane /VIa/, G 0.26, 5,6-epoxy-3-hydroxy-5-cholestane /VIb/, G 0.24, and 2, 3-dihydroxy-5-cholestene /VII/, G 0.22. The dose dependence of the formation of these products shows that the cholesterol derivatives substituted in the position 7 /II–IV/ are formed from a common precursor — the radical Ia. On the other hand, the products of the 5–C=C double bond reactions /V and VI/ are formed independently. Also the product VII is formed independently. A reaction scheme that is in agreement with these results is proposed.     

Sedimentation equilibrium of suspensions of colloidal particles at finite concentrations

Equilibrium concentration profiles of non-dilute colloidal suspensions are calculated by means of the Carnahan-Starling expression for the osmotic compressibility of hard sphere liquids. The profiles depend on the average volume fraction of the suspension, , and on the field interaction parameter, ₀ (reciprocal of the Péclet number at infinite dilution). Profiles are computed for values of and ₀ typical of those encountered in sedimentation field-flow fractionation experiments. It is found that, in most cases, the volume fraction at the depletion wall is negligibly small and that the volume fraction at the accumulation wall ₀, depends on the ratio <>₀/₀ only. An inflexion point is found in the concentration profile if ₀ is larger than 0.13 whatever the value of ₀.     

An Alternative Method of Introducing Fugacity

In current textbooks fugacity is introduced according to its differential or integral mathematical formulation. In this article an alternative method of explanation is offered. It is suggested that the real state of a pure gas can be described by comparing it to a hypothetical idealized state. The differences between these two states can then be expressed in terms of a function, , defined as (T,P) = _real(T,P) - _ideal(T,P) where _real and _ideal are the chemical potentials of the gas in its real and ideal states, respectively. The function is a molar excess quantity and is expressed as (T,P) = RT1n where is the fugacity coefficient. This approach introduces fugacity deductively through the function, which leads to , the fugacity coefficient. This method is also appropriate for introducing the activity of solution components and the fugacity of a real gas in gaseous mixtures.     

Quantum-chemical study of allylic compounds with two bonded heavy atoms

It has been shown by the CNDO method that the bathochromic shift of the long-wave absorption band in the transition from allylstannane to compounds of the type C=C-C-Sn-X and C=C-Sn-X (where X is a heavy atom) is connected with the formation of a low-energy vacant *_S-X orbital, localized mainly in the region of the Sn-X chemical bond, and of an occupied _Sn-X orbital, the energy of which is somewhat higher than of the _C-Sn orbital. The dependence of the position of the long-wave absorbance region on conformation is related to the fact that, in planar and nonplanar conformers, the long-wave transitions are of a different type ( * and *, respectively); the bathochromic shift is determined to a large degree by the difference in the energies of the highest occupied MO ( - ) in the s-trans form. In the nonplanar conformers the heavy atom orbitals interact with the -orbital of the ethylene moiety through the bridge group; this leads to a significant delocalization of the HOMO and to a considerable change in its energy. On the other hand, their interaction with the *-orbital in compounds of the C=C-C-Sn-X type is very low and does not favor the delocalization of lower vacant MO. In vinyldistannane the *-orbital is noticeably delocalized, due to the interaction with the *_Sn-Sn orbital in planar and with the *_Sn-Sn orbital in nonplanar conformers.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 636–641, March, 1992.     

Evaluation of the electronic density at critical points of hydrogen bonds: PM7 a good alternative to ab-initio methods

Hydrogen bonds are of vital importance in the formation and functioning of organic molecules; their characterization with theoretical tools is a task of interest to the scientific community. Commonly, the electron density at the bond critical point is used to characterize bonds. Generally this task is carried out with ab-initio methods. In this study, the PM7 semi-empirical approach is used to evaluate the quality of the electron density at the hydrogen bond critical points (HBCPs). The research takes into account dimers, nucleobases and alpha-helices bonded by hydrogen bonds: $$, $$, $$, $$, $$, and $$. The results are compared with second-order Møller–Plesset and density functional theory. The findings demonstrate that PM7 is a reliable alternative for explaining the electron density trends at the HBCPs.     

Dynamic shear modulus in the splitting region of poly(alkyl methacrylates)

A systematic study of the dynamic shear modulusG ^*=G+G in three poly(alkyl methacrylates) (PEMA, PnPMA, PnBMA) at frequencies between 0.001 and 500 rad/s is presented. As the splitting frequencies _s are low, aging effects can be observed in the splitting region. There is a systematic shift of the splitting frequency _s to lower values with increasing length of the alkyl side group. In PnBMA a separate shear appearance is observed about two frequency decades below the local mode . This is discussed in terms of the concept of minimal cooperativity. Aging effects are: Shift of the maximum loss frequency to lower values, peak sharpening of the relaxation, and intensity changes of and . These effects are discussed in terms of the sequential aging concept. Aging leads to a pronounced bending of the traces upwards from the equilibrium line in the Arrhenius diagram. These non-equilibrium phenomena are promoted by the small slope m=d(log )/dT of the trace in the splitting region.Dedicated to Prof. E. W. Fischer at the occasion of his 65th Birthday Lieber Herr Fischer, die Hallenser Polymerphysiker danken Ihnen aufrichtig für die warmherzige und effektive Förderung der Polymerwissenschaften im Raum Halle-Merseburg.     

Adsorption isotherm for a solid electrode: The link between the differential surface tension and capacitance curves

Investigation of thermodynamically equilibrium single-component adsorption from a liquid solution on a solid electrode with allowance made for elastic deformation of its surface is continued. A full electrocapillarity equation is derived from thermodynamics equations for an interphase layer in the absence of irreversible processes. Thermodynamic aspects of the Shuttleworth equation are discussed and the equation is compared with two-dimensional Murnaghan formulas for elastic isotropic media. An adsorption isotherm equation and compatibility equations that had been derived previously are examined in a special case where the derivative of a surface concentration with respect to depends solely on (=()) and a rigorous solution of these is obtained for a deformed electrode ( 0). The effect of and dimensionless electrode potential on the extreme (at an infinitely high adsorbate concentration) value of is studied. The model of two parallel capacitors is considered in detail for a general case. Owing to the use of capacitance curves for an elastically stretched electrode, a formula that expresses the differential surface tension of a nondeformed electrode through such curves is derived for the first time ever.To the memory of my motherTranslated from Elektrokhimiya, Vol. 41, No. 1, 2005, pp. 20–34.Original Russian Text Copyright © 2005 by Podgaetskii.     

Determination of Attogram Quantities of Silver via Quenching of the Solid Substrate Room-Temperature Phosphorescence of Rhodamine B Based on the Catalysis of its Oxidation by Potassium Persulfate

A new method of SS-RTP for the determination of trace silver has been established. This method is based on the fact that Ag⁺, when activated by ,-bipyridyl (bipy) in a media of HAc–NaAc (pH=4.9), can catalyze the reaction of Rhodamine B (RhoB) oxidized by K₂S₂O₈, thus causing the Solid Substrate Room-Temperature Phosphorescence (SS-RTP) of RhoB to be quenched. The activating efficiency of bipy is 6.7 times higher than that of o-phenanthroline (phen). The reduction of the phosphorescence intensity (I_p) of RhoB is directly proportional to the concentration of Ag⁺ ions in the range of 1.6016.0agspot^–1 (0.40µLspot^–1). The regression equation of the working curve can be expressed as I_p=18.78+5.100m_Ag+ (agspot^–1) (r=0.9994, n=6), the detection limit is 0.28agspot^–1. This rapid, accurate and sensitive method has been successfully applied to the determination of trace silver in tea and human hair samples, and the results agree well with the Atomic Absorption Spectroscopy (AAS) method. The mechanism of the catalyzing reaction is also discussed.     

Similarity and dissimilarity in posets

The relevance of partially ordered sets (or posets) in a wide diversity of contexts in chemistry is emphasized, and the utility of distance functions (or metrics) on such posets is noted. First a notion of scale similarity is introduced to make comparisons within certain so-called scaled posets, for which there is formulated natural comparators, which in turn lead to associated distance functions. Beyond taking note of several chemically relevant examples of these scaled posets and their consequent associated similarity measures, a second chemically relevant class of so-called shifted posets is similarly developed, with examples. Even further extension of some aspects of the current approach is indicated, and finally the multi-posetic character of chemical periodic law is suggested.     

Steroid glycosides ofNicotiana tabacum seeds I. The structures of nicotianosides A, B, and E

Two steroid glycosides of the spirostan series — nicotianosides A and B — and one glycoside of the furostan series — nicotianoside E — have been isolated from the seeds ofNicotiana tabacum L. Nicotianoside A is (25S)-5-spirostan-3-ol 3-O--D-glucopyranoside, nicotianoside B is (25S)-5-spirostan-3-ol 3-O-[O--L-rhamnopyranosyl-(12)-gb-D-glucopyranoside], and nicotianoside E is (25S)-5-furostan-3,22,26-triol 26-O--glucopyranoside 3-O-[O--L-rhamnopyranosyl-(12)--D-glucopyranoside].Institute of Genetics, Academy of Sciences of the Republic of Moldava, Kishinev, ul. Lesnaya, 20. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 737–742, November–December, 1994.     

Triterpene glycosides ofLeontice eversmannii

Conclusions The structure of leontoside D-a hederagenin pentaoside-has been established. The O-glycosidic moiety of leontoside D is O--D-glucopyranosido-(1 4)-O--L-arabopyranose, and the O-acyl moiety is O--L-rhamnopyranosido-(1 4)-O--D-glucopyranosido-(1 6)-O--D-glucopyranose.Khimiya Prirodnykh Soedinenii, Vol. 4, No. 3, pp. 153–158, 1968     

Nonadiabatic transitions at the limit of almost-adiabatic perturbations with random motion along the terms

Conclusions The investigation carried out has shown that in the diffusion approximation, which is valid when the effective length of the free path =v_ov is much smaller than the dimension of the nonadiabatic region, an adiabatic limit is achieved only under the condition v_v 1. This case cannot be described when (4) is assumed to be valid for , since this equation is fulfilled only when v_v 1. It is perfectly natural that the use of Eq. (4) produces a strong interaction between the terms of the quantum subsystem, i.e., we do not attain an adiabatic limit. In the work it was shown that at the adiabatic limit the rate of transitions between the terms decreases rapidly with increasing v_v.The condition v_v 1 strongly restricts the region for the applicability of (4) and, therefore, of (12). In this sense, expression (21) is a significant generalization of (14), since it was obtained only under the. assumption and V_D 1. However, the range of parameters which satisfy these inequalities corresponds to a fairly narrow group of processes; therefore, it would be of interest to also investigate the region of a. This question will be the subject of the next report.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 17, No. 1, pp.3–9, January–February, 1981.In conclusion, we express our sincerest thanks to I. V. Aleksandrov, S. Ya. Umanskii, and M. Ya. Ovchinnikova for numerous and useful discussions.     

Multivariate Statistical Assessment of Air Quality: A Case Study

The present paper deals with the application of several chemometrical methods (cluster and principal components analysis, source apportioning on absolute principal components scores) to an aerosol data collection from Unterloibach, Austria. It is shown that seven latent factors explaining almost 80% of the total variance are responsible for the data structure and are conditionally identified as secondary aerosol, mineral dust, oil burning, lead smelter, coal burning, salt and fertilizer emission sources. Furthermore, the contribution of each identified source to the formation of the particle total mass and chemical compounds total concentration is calculated. Thus, a reliable assessment of the air quality in the region is performed. The requirements of the sustainability concept for ecological indicators in this case is easily transformed into a multivariate statistical problem taking into account not separate indicators but the specific multivariate nature of aerosol pollution.     

Cardiac glycosides of Cheiranthus allioni. V

Conclusions Two additional cardiac glycosides, glucoerysimoside and glucoerysimosol, have been isolated from the seeds ofCheiranthus allioni Hort. Glucoerysimoside is strophanthidin 3-[O--D-digitoxopyranosyl-(4 1)-O--D-glucopyranosyl-(4 1)--D-glucopyranoside]. Glucoerysimosol is a new cardenolide having the same carbohydrate component, but its aglycone is strophanthidol. From these glycosides a new trisaccharide has been obtained which has been characterized as 4-O--cellobiosyl-D-digitoxose.Khar'kov Scientific-Research Institute of Pharmaceutical Chemistry. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 566–571, September–October, 1970.     

Detection and determination of benzophenone present in diphenylhydantoin sodium formulations and drug substance

Summary The detection of benzophenone in sodium diphenylhydantoin formulations and drug substance is carried out by thin-layer chromatography on silica gel 60 F using toluene/methanol/ethyl acetate/acetic acid/chloroform (802015105) or ethyl acetate/methanol/ammonium hydroxide (85105) as solvent and UV-light for visualizing. The determination is performed by measuring the absorption at 248 nm. The method is recommended for production monitoring.

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Nachweis und Bestimmung von Benzophenon in Natriumdiphenylhydantoin-Formulierungen und -Reinsubstanz

Zusammenfassung Der Nachweis erfolgt dünnschicht-chromatographisch auf Silicagel 60 F mit Toluol/Methanol/Äthylacetat/Essigsäure/Chloroform (802015105) oder Äthylacetat/Methanol/Ammoniak (85105) als Lösungsmittel und durch Sichtbarmachung mit UV-Licht. Die Bestimmung wird durch Absorptionsmessung bei 248 nm vorgenommen. Das Verfahren wird zur Produktionskontrolle empfohlen.

     

Order and disorder in mixed metal linear chains: The homo and heterobimetallic EDTA (M(H2O)4OIOII)[M′(EDTA)] · 6H2O complexes (M = Mg,Mn, Co,Zn and Ni; M′ = Co,Ni, Cu and Zn)

Summary Polymetallic solid solutions of the ethylenediaminetetracetic acid (EDTA) and six divalent metal ions exist in the range: MgMnCoZnNiCu(EDTA) · 6H₂O where + + + + + =2, 01, 0,,2, 0, 1.This type of structure is characterized by the presence of two different octahedral carboxylate-bridged coordination sites forming infinite zig-zag chains. Visible and i.r. spectra and t.g.a. analysis show that there is occupational preference for the two coordination sites in the crystalline structure.Due to this preference, and also to the structural features, the heterobimetallic MM(EDTA) · 6H₂O compounds constitute a structurally new class of materials which can be described as ordered alternating-heterobimetallic polymeric coordination complexes.     

Oxidatively induced reactions of a diimine platinum(IV) tetramethyl complex

The oxidation of the Pt(IV) tetramethyl complex [ArNCHCHNAr]PtMe₄ (Ar = 2,6-Me₂C₆H₃) has been investigated in acetonitrile and dichloromethane. Cyclic voltammetry demonstrates that the irreversible oxidation of [ArNCHCHNAr]PtMe₄ occurs at a slightly less positive oxidation potential than the irreversible oxidation of the analogous Pt(II) species [ArNCHCHNAr]PtMe₂. The product distribution arising from the oxidation depends strongly on the reaction conditions and includes cationic Pt(IV) species (acetonitrile, dichloromethane solvents) and Pt(II) species (dichloromethane only). Evidence is presented that suggests that homolytic cleavage of a weakened PtC bond in is involved in the oxidatively induced reactions.