bluuebunny/crossref_metadata_2025 huggingface dataset:
A contribution to gas phase ionization of para-hydroxybenzoic acid: An LCAO-MO-SCF treatment
Authors: Böhm Stanislav , Kuthan Josef
Published: June 2010

By means of the ab initio MO calculations using the STO-3G basis set augmented with diffuse p functions accompanied by semi-empirical MNDO calculations, it is demonstrated that the carboxylic group ionization in the isodesmy (A), X = p-OH, is energetically preferred to the phenolic group ionization in the process (B). The reasons of the earlier incorrect interpretations regarding the gas phase acidity of p-hydroxybenzoic acid (a,s-II) are discussed.
Interpretation of properties of aqueous electrolyte solutions in terms of hydration and incomplete dissociation
Authors: Heyrovská Rajalakshmi
Published: June 2010

The existing data on the vapour pressures, densities and e.m.f.s of concentration cells of dilute and concentrated aqueous solutions of strong electrolytes have been interpreted in terms of hydration and incomplete dissociation. Hydration numbers and degrees of dissociation have been presented for several 1 : 1 strong electrolytes at 25 °C. Thus the actual ionic concentrations of strong acids, bases and salts, hitherto inaccessible, have now been made available.
Description of segregation in a horizontal drum mixer by use of the diffusion equation
Authors: Kudrna Vladimír , Rochowiecki Andrzej
Published: June 2010

An attempt has been made to describe the axial segregation of solid particles of two dimensions in a horizontal drum mixer. For this purpose the Kolmogorov's forward diffusion equation with variable diffusion coefficient and zero drift velocity was used. For the case of "pure" segregation this approach has given good results.
Reaction of 4-substituted benzaldehydes and acetophenones with chloroacetonitrile
Authors: Svoboda Jiří , Kocfeldová Zuzana , Paleček Jaroslav
Published: June 2010

Under conditions of phase-transfer catalysis or in homogeneous solution of potassium tert-butoxide the title compounds give stereoisomeric mixtures of substituted 2,3-epoxy nitriles III and IV. Alkaline hydrolysis of epoxy nitriles IV afforded the corresponding 2-arylpropanals in low yields. On treatment with methanol and potassium carbonate, epoxy nitriles III and IV were converted into epoxy esters in good yields.
Addition of secondary amino group to double bond of acrylates
Authors: Horálek Jiří , Krejcar Emil , Churáček Jaroslav
Published: June 2010

The near IR region spectroscopy has been used to follow the addition reactions of the secondary amino groups of the tert-butyl 3-butylaminopropanoate, N,N'-dibutyl-3-aminopropanamide, and dibutylamine to tert-butyl acrylate. The additions are bimolecular reactions of the second order. The respective rate constants found for the above-mentioned compounds are 3·54 . 10-6, 2·34 . 10-5, and 3·18 . 10-6 l mol-1 s-1. The secondary amidic groups increase the nucleophilicity of secondary amino group and hence also the rate of the addition reaction.
Preparation and alkylation reactions of 4-nitrobenzyl and 5-nitrofurfuryl sulfones
Authors: Prousek Josef
Published: June 2010

Substitution reaction of 5-nitrofurfuryl bromide (I) with sodium thiophenoxide and 4-chlorothiophenoxide in dimethyl sulfoxide at 20 °C and oxidation with dimethyl sulfoxide in the reaction medium afforded 5-nitrofurfuryl phenyl sulfone (IVa) and 5-nitrofurfuryl 4-chlorophenyl sulfone (IVb), respectively. Similarly, 4-nitrobenzyl bromide reacted with sodium 4-chlorothiophenoxide to give 4-nitrobenzyl 4-chlorophenyl sulfone (VII) and with sodium phenylsulfinate to afford 4-nitrobenzyl phenyl sulfone (IX). The sulfide intermediates were not isolated. The sulfone IX was used as substrate in alkylation reactions, catalysed by polyethylene glycols. Derivatives IVb and VII were identified by IR and mass spectroscopy, alkylation products by 1H NMR spectroscopy.
N-substituted derivatives of 6,11-dihydrodibenzo[b,e]thiepin-11-amine and related compounds; Synthesis and pharmacological screening
Authors: Valenta Vladimír , Hulinská Hana , Holubek Jiří , Dlabač Antonín , Metyš Jan , Frycová Hana , Protiva Miroslav
Published: June 2010

Reactions of N-(6,11-dihydrodibenzo[b,e]thiepin-11-yl)chloroacetamide (II) with dimethylamine, morpholine, and 2-(1-piperazinyl)ethanol afforded the amino amides III-V. Substitution reactions of 11-chloro-6,11-dihydrodibenzo[b,e]thiepin with ethylenediamine and N,N-dimethylethylenediamine gave the diamines VI and VII. 6,11-Dihydrodibenzo[b,e]thiepin-11-amine (I) was treated with ethyl chloroacetate and ethyl 2-bromopropionate to give the amino esters X and XI which were transformed on the one hand to the acids VIII and IX, and to the amides XII and XIII on the other. (6,11-Dihydrodibenzo[b,e]thiepin -11-yl)methylamine (XVIa) and (10,11-dihydro-5H-dibenzo[a,d]cycloheptene-5-yl)methylamine (XVIb) were transformed via the chloroacetamides XVIIa and XVIIb to the (4-methyl-1-piperazinyl)acetamides XVa and XVb. Compound V showed local anaesthetic and antiarrhythmic activity, the diamine VII had antihistamine and antireserpine effects, the amide XII was found to be an anticonvulsant, and the piperazines XVa and XVb inhibited effectively the formation of the indomethacin-induced gastric ulcers in rats.
Potential antidepressants: N-phenacyl derivatives of (E)-N-methyl-3-(6,11-dihydrodibenzo[b,e]thiepin-11-ylidene)propylamine
Authors: Polívka Zdeněk , Metyšová Jiřina , Valchář Martin , Protiva Miroslav
Published: June 2010

Reactions of (E)-N-methyl-3-(6,11-dihydrodibenzo[b,e]thiepin-11-ylidene)propylamine (V) with phenacyl chloride and 4-chlorophenacyl bromide in chloroform in the presence of sodium or potassium carbonate afforded the title compounds VI and VII. Their hydrochlorides showed very low acute toxicity in mice but in comparison with prothiadene (IV), they were less effective in the common animal tests used for assessing the thymoleptic activity (inhibition of reserpine-induced hypothermia and ptosis in mice, potentiation of yohimbine toxicity in mice, anticataleptic action in rats). These activity relations are in disagreement with those published for the analogous pair of 10,11-dihydrodibenz[b,f]azepine derivatives imipramine (I) and lofepramine (III).
The model rotator phase
Authors: Šebek Josef
Published: June 2010

It is shown that the formation of the so-called rotator phase of alkanes (one of the high temperature crystalline phases) might be connected with a partial increase of the conformational flexibility of chains. The conformations with higher number of kinks per chain, which have been neglected till now, are shown to contribute effectively to the conformational partition function. Small probability of these states given by the Boltzmann exponent is compensated by a large number of ways in which they can be distributed along the chain. The deduced features of the rotator phase seem to be in agreement with the experimentally observed properties.
A study of the inhibited reaction of aluminium single crystal in aqueous solution of sodium hydroxide
Authors: Halaša Ivan , Miadoková Milica
Published: June 2010

The effect of sodium tartarate and calcium ions on the kinetic behaviour of the {110} plane of an aluminium single crystal in aqueous solution of NaOH was investigated in dependence on the concentrations of the substances added, and optimum concentrations for attaining the highest inhibiting effect were established. The effect of temperature and concentration of NaOH on the inhibiting efficiency was also examined. The mechanism of the inhibiting effect is discussed.
Conjugation within the oximino group: A semiquantitative estimation
Authors: Exner Otto , Jehlička Václav
Published: June 2010

The n-π conjugation within the oximino group was estimated on the basis of dipole moments and of bond lengths. The dipole moments were measured on oximes I and O-methyloximes II in benzene solution, the C=N and N-O bond lengths were retrieved from the Cambridge Structural Database for all available derivatives. The results differ somewhat in the quantitative sense but can be always interpreted in terms of the classical mesomeric formulae IV ↔ V. This formalism postulates – in agreement with experiments – a lowered C=N bond order, some double bond character of the N-O bond, planarity of the C=NOR group, and an excess dipole moment (μm) oriented in the sense of a charge transfer from O toward C. Quite different results were obtained for O-acetyloximes III. While their bond lengths could agree with a weakened conjugation, the excess dipole moment is oriented from C towards O and cannot be expressed by any simple formula. Hence the mesomeric formulae may represent an acceptable description of the actual charge distribution in many cases but not in all.
A simple method for the optimization of the decay time in pulse polarography
Authors: Bolzan Jorge A.
Published: June 2010

A simple method for optimization of the minimum decay time, previous to the sampling time of the polarographic current, is described. The former should make compatible two requisites: it should be short enough for obtaining the maximum value of the faradaic current and long enough for the minimum or null value of the double layer decay current. The method is performed with the pulse polarograph only, without ancillary instruments, is fast and its accuracy is fairly comparable with earlier methods, which were more accurate but by far more involved to perform.
Electrochemical oscillations on polarographic I-t curves in bromate solutions
Authors: Olexová Anna , Treindl Ľudovít
Published: June 2010

Polarographic I-t curves obtained with a dropping mercury electrode in solutions of sulphuric acid and bromate ions show oscillations in the region of positive potentials. These are related with the formation of Hg(II) bromate as anodic oxidation product, which is in turn reduced to Hg(I) bromate forming a passivating layer on the Hg electrode. The layer is mechanically disrupted during growth of the drop, whereby the electrode is reactivated and the process goes on giving rise to current oscillations.
Systematic errors in equilibrium composition of ternary liquid-liquid systems and their effect on the calculated number of theoretical stages of countercurrent extraction
Authors: Dojčanský Ján , Bafrncová Soňa , Surový Július
Published: June 2010

The influence of magnitude of systematic errors in the determination of ternary liquid-liquid equilibrium concentrations on the accuracy of the calculated number of theoretical stages of countercurrent extraction is evaluated on using five hypothetical systems differing in the extent of mutual solubility of components, tie-line slope, and type of binodal curve.
Potential antidepressants: 4-(Aminoalkoxy)thioxanthones
Authors: Červená Irena , Holubek Jiří , Svátek Emil , Protiva Miroslav
Published: June 2010

Four different approaches were used for preparing a series of the title compounds. Reactions of the sodium salt of 4-hydroxythioxanthone (V) with dimethylaminoalkyl chlorides gave the ethers VI and VII. Partial demethylation of VII via the carbamate IX afforded the secondary amine VIII. Reactions of the 4-bromobutoxy compound XI with amines resulted in II, XII, and XIII. Reaction of V with 1-chloro-2,3-epoxypropane and the following treatment of the resulting XIV with 2-propanamine gave the amino alcohol XV. The xanthone III was obtained via XVIII similarly like II. The products, especially II and III are cyclic analogues of the antidepressant and cerebral activator "bifemelane" (I) but they do not exhibit the pharmacological profile of antidepressants.
Simultaneous determination of iron and copper in waters by multiligand flow injection analysis
Authors: Kubáň Vlastimil , Gladilovich Dimitrii Borisovich
Published: June 2010

Optical characteristics were measured and optimum conditions established for the simultaneous spectrophotometric determination of iron and copper with reagent mixtures of disodium bathocuproinedisulfonate (I) with disodium bathofenanthrolinedisulfonate (II) or ferrospectral (III) in static or dynamic (FIA) conditions. In the FIA method suggested, 30μl water samples containing Fe and Cu in concentration ratios 1 : 10 to 10 : 1 are injected into a stream of I-II mixed reagent at c(I) = 0·6 mmol l-1 and c(II) = 0·2 mmol l-1 in a medium of 0·1M formate buffer pH 3·5 and 0·01M ascorbic acid; for the two metals, present in concentrations of 4 to 40 μmol l-1, the relative standard deviations of determination do not exceed 2 and 5%, respectively. Alternatively, in the reverse FIA method using a multichannel diode array detector, 25 μl of the mixed reagent under the above conditions is injected into the acid sample stream; for samples containing Fe and Cu in concentrations of 1-43 μmol l-1 in ratios of 10 : 1 to 1 : 15, the relative standard deviation of determination is about 2%. The use of mixed reagents makes for a broader variability of the optical characteristics and conditional equilibrium constants of the reaction products as compared to methods employing a single nonselective reagent; owing to this, improved selectivity, accuracy and precision of determination are achieved with multicomponent flow injection analysis (MC-FIA).
XPS determination of dimensions of metal clusters on supports
Authors: Juška Tomáš
Published: June 2010

The applicability of the XPS technique to the indirect determination of the size of metal clusters on supports was tested on two types of the Ag/Al2O3 system. For clusters formed from vapour deposited layers, relations were derived enabling the size to be determined from photoemission line intensities of the metal measured after deposition at liquid nitrogen temperature and after heating to 25 °C or 400 °C. For metal clusters on supported Ag/α-Al2O3 catalysts, their size was estimated by using two models, viz. the Kerkhof-Moulijn model and the Kuipers-van Leuven-Visser model. Spherical and hemispherical shapes of the clusters were assumed for the two Ag/Al2O3 systems, and the results were confronted with electron microscopy photographs. The Kuipers-van Leuven-Visser model applied to the supported catalyst was found to fit the reality better than the Kerkhof-Moulijn model.
Hydrogen peroxide decomposition on a two-component CuO-Cr2O3 catalyst
Authors: Múčka Viliam , Lang Kamil
Published: June 2010

Some physical and catalytic properties of the two-component copper(II)oxide-chromium(III)oxide catalyst with different content of both components were studied using the decomposition of the aqueous solution of hydrogen peroxide as a testing reaction. It has been found that along to both basic components, the system under study contains also the spinel structure CuCr2O4, chromate washable by water and hexavalent ions of chromium unwashable by water. The soluble chromate is catalytically active. During the first period of the reaction the equilibrium is being established in both homogeneous and heterogeneous catalytic systems. The catalytic activity as well as the specific surface area of the washed solid is a non-monotonous function of its composition. It seems highly probable that the extreme values of both these quantities are not connected with the detected admixtures in the catalytic system. The system under study is very insensitive with regard to the applied doses of gamma radiation. Its catalytic properties are changed rather significantly after the thermal treatment and particularly after the partial reduction to low degree by hydrogen. The observed changes of the catalytic activity of the system under study are very probably in connection with the changes of the valence state of the catalytically active components of the catalyst.
Determination of rare earth elements by ion pair HPLC with post-column derivatization using Arsenazo III
Authors: Kubáň Vlastimil , Gladilovich Dimitrii Borisovich
Published: June 2010

Rare earth elements can be determined on a CGC column 3 x 150 mm packed with Separon SGX C 18 modified with sorbed ammonium dodecyl sulfate (from solutions with c = 5 mmol l-1) by isocratic or stepwise gradient elution with ammonium DL-α-hydroxyisobutyrate solution (20-160 mmol l-1) at pH 4·5. The method of post-column derivatization with a solution of Arsenazo III (5 μmol l-1) in 0·1M formate buffer at pH 2·9-3·0 for photometric detection enables 10-150 or 6-155 ng of rare earth ions in sample (n = 5-7). By preconcentration on the analytical column from 0·1-2·5 ml sample volumes followed by stepwise gradient elution, 30-80 μg of rare earth ions in 1 ml sample can be determined with a reproducibility of 4% or better, the recovery being 90-106%. The procedures were applied to the determination of rare earth elements in samples of apatite, oxide concentrates and a luminophor, and a very good agreement with the results obtained by optical methods was achieved.
Kinetics of the reaction between magnesium oxide and ammonium chloride solution
Authors: Glaser Vladimír , Vídenský Jan , Kužela Miroslav
Published: June 2010

The kinetics of the reaction between magnesium oxide and ammonium chloride solution in a well-stirred batch reactor have been investigated. The results have shown that the rate-controlling step is the dissolution of the solid phase. A kinetic equation has been derived for this variant of reaction mechanism.
Reaction of tetrahydrofuroisoxazoles with molybdenum hexacarbonyl. A new route to preparation of 3-substituted tetrahydro- and dihydrofuran derivatives
Authors: Fišera Lubor , Goljer Igor , Jarošková Libuše
Published: June 2010

3-(4-X-Phenyl)-3a,4,6,6a-tetrahydrofuro[3,4-d]isoxazoles Ia-If (X = H, CH3, CH3O, Cl, F, C6H5) react with molybdenum hexacarbonyl to give not only the expected cis-3-aroyl-4-hydroxytetrahydrofuran III, but also its trans isomer IV and 3-aroyl-2,5-dihydrofuran II. This paper concerns a new preparation of 3-aroyl-2,5-dihydrofuran derivatives starting from 2,5-dihydrofuran via 1,3-dipolar cycloaddition of nitrile oxides, cleavage with molybdenum hexacarbonyl and dehydratation with p-toluenesulfonic acid. The structure of cis-(III) and trans-(IV) derivatives was deduced from both the γ-effect in the 13C NMR and the DQ COSY experiment in the 1H NMR spectra.
3-pyridiniumindolyl-2-thiolates - New type of functionalized indoles
Authors: Gonda Jozef , Kristian Pavol
Published: June 2010

2-Bromomethylphenyl isothiocyanate (I) reacts with pyridines to give 2-isothiocyanatobenzylpyridinium bromides II. Deprotonation of these compounds with sodium ethoxide in ethanol of sodium hydride in dimethyl sulfoxide afforded novel type of functionalized indoles, 3-pyridiniumindolyl-2-thiolates. Reaction of II with KOH or KCN gave products of addition to the NCS group VII and VIII, respectively. Structure of the obtained compounds was proven by IR, 1H NMR, 13C NMR, and mass spectra and was confirmed by X-ray diffraction analysis of 3-pyridiniumindolyl-2-thiolate.
Addition and cycloaddition reactions of furo[3,2-b]pyrroles and their benzo[b] analogues: An NMR study of structure of products
Authors: Krutošíková Alžbeta , Dandárová Miloslava , Alföldi Juraj , Kováč Jaroslav
Published: June 2010

Reaction of furo[3,2-b]pyrroles and their benzo[b] analogues with dimethyl butynedioate and ethyl propyonate were investigated. The reaction course is influenced by substituents on the system. Products of [4 + 2] cycloaddition to the furan or pyrrole nucleus as well as products of Michael addition to the benzo[b]furo[3,2-b]pyrrole system have been found. The structure of the products has been proven by 1H NMR and 13C NMR spectroscopy.
Fluorescent analogues of acyclic inhibitors of S-adenosyl-L-homocysteine hydrolase
Authors: Dvořáková Hana , Holý Antonín , Masojídková Milena
Published: June 2010

Condensation of sodium salt of 2-aminopurine (I) with 4-chloromethyl-2,2-dimethyl-1,3-dioxolane (II) followed by acid hydrolysis afforded 9-(RS)-(2,3-dihydroxypropyl)-2-aminopurine (V). Similarly, sodium salt of lin-benzoadenine (IX) reacted with compound II to give 3-(RS)-(2,3-dihydroxypropyl)-lin-benzoadenine (Xb). Analogues of eritadenine (XVIb) derived from 2-aminopurine (VII) and lin-benzoadenine (XIV) were obtained by reaction of sodium salt of the corresponding base (I or IX) with 2,3-O-cyclohexylidene-D-erythronolactone (VI) and subsequent acid hydrolysis. By action of chloroacetaldehyde on 9-substituted acyclic analogues of adenosine or AMP (XVI) were prepared 9-(2,3-dihydroxypropyl)-1,N6-ethenoadenine (XVIIa), 1,N6-etheno derivative of eritadenine (XVIIb), 3-(1,N6-ethenoadenin-9-yl)-2-hydroxypropanoic acid (XVIIc) and its 2-methylpropyl ester (XVIId), as well as 9-(S)-(3-hydroxy-2-phosphonylmethoxypropyl)-1,N6-ethenoadenine (XVIIe) and 9-(2-phosphonylmethoxyethyl)-1,N6-ethenoadenine (XVIIf). Fluorescence spectra of all the mentioned compounds exhibit parameters corresponding to the substituted fluorophore; however, no pronounced inhibitory effect on SAH-hydrolase from L-1210 mice leukemia cells has been found for any of them.
6,11-Dihydrodibenzo[b,e]thiepin-11-yl 3-quinuclidinyl ethers: New potential intidepressants and antihistamine agents
Authors: Polívka Zdeněk , Metyš Jan , Protiva Miroslav
Published: June 2010

Reactions of 11-chloro-6,11-dihydrodibenzo[b,e]thiepin and its 2-methyl derivative, and further of the methanesulfonates of 2-chloro- and 2-bromo-6,11-dihydrodibenzo[b,e]thiepin-11-ol with 3-quinuclidinol afforded the title ethers I-IV. The 2-methyl compound II (VÚFB-17 088) showed significant antihistamine activity and the 2-chloro compound III (VÚFB-17 089), having antireserpine and anticataleptic activity, proved a potential antidepressant agent.
Enzyme-catalysed partial deacylation of 1,6-anhydro-2,3,4-tri-O-butyryl-β-D-glucopyranose in the presence of methanol
Authors: Zemek Jiří , Kučár Štefan , Anderle Dušan
Published: June 2010

Lipase ex pancreas (EC 3.1.1.3), lipase ex wheat-germ (EC 3.1.1.3), and chymotrypsin (EC 3.4.4.5) are compared in their power to catalyse deacylation of 1,6-anhydro-2,3,4-tri-O-butyryl-β-D-glucopyranose. The action of the three enzymes has been found locoselective. In the use of a hydrolase the selectivity of the reaction was affected by composition of the reaction mixture. Lipase ex porcine pancreas in a solution containing 20% of methanol (v/v) catalysed deacylation preferentially from C-2, but on raising the methanol concentration to 50% (v/v) deacylation from C-4 prevailed over that from C-2. Analogously, at the lower methanol concentration deacylation effected by wheat-germ lipase occurred to a greater extent on C-2, whereas at the higher concentration on C-3. With chymotrypsin ex hog pancreas at the lower concentration of methanol the prevailing deacylation was on C-4, at the higher on C-3. Compared to a chemically catalysed hydrolysis, whether by methanolic hydrogen chloride or hydrazine hydrate, the locoselectivity of an enzyme-catalysed deacylation of 1,6-anhydro-2,3,4-tri-O-butyryl-β-D-glucopyranose is substantially higher.
Interaction of lactate dehydrogenase isoenzymes with ligands
Authors: Barthová Jana , Kučerová Jana , Leblová Sylva
Published: June 2010

Isoenzymes of bovine lactate dehydrogenase (H4, H3M, and H2M2) were prepared by affinity chromatography on a 5'-AMP-Sepharose 4B column. The interaction of isoenzymes with two ligands, coenzyme NADH and the competitive inhibitor Cibacron Blue F3GA was followed by means of kinetic measurements and by affinity electrophoresis. The Michaelis constants of NADH were compared with the inhibition constants of Cibacron Blue and dissociation constants of enzyme-inhibitor complexes. It was found that the M subunit of lactate dehydrogenase exhibits always higher affinity both to NADH and Cibacron Blue in comparison to the H subunit. This finding corresponds to the physiological role of lactate dehydrogenase isoenzymes.
Quantitative relations between structure and antiinflammatory activity of aryloxoalkanoic acids
Authors: Kuchař Miroslav , Maturová Eva , Brunová Bohumila , Grimová Jaroslava , Tomková Hana , Holubek Jiří
Published: June 2010

The antiinflammatory effect of a series of aryloxoalkanoic acids II and of their biphenyl derivatives III was examined by measuring the inhibition of the development of carageenan- and adjuvant-induced edemas. The quantitative relations between the antiinflammatory effect and physicochemical and structural parameters of the compounds tested were evaluated. The equations obtained by the method of regression analysis showed a significant linear dependence of both inhibitory activities on the lipophilicity of the compounds and a considerable effect of some structural changes as expressed by indicator variables. The antiinflammatory effect is especially enhanced in both tests by the presence of a cyclic substituent at the aromatic ring. The high antiinflammatory effect of biphenylyl derivatives III is paralleled by their prolonged action. The prolongation of the effect is most likely a result of a suitable biotransformation of acid III to an efficient metabolite. The structural requirements which resulted from both the regression analysis and from the hypothesis of biotransformation of acids III were utilized in the synthesis of suitably substituted biphenylyloxoalkanoic acids. By this approach derivatives IIIe-i were obtained some of which showed a high antiinflammatory and also protracted effect. 4-(2',4'-Difluorbiphenylyl)-4-oxo-2-methylbutanoic acid (VÚFB-16 066, Flobufen) was chosen for further preclinical development.
On the change of the order od stability of DNA base pairs as a result of the methylation of guanine
Authors: Hobza Pavel , Sandorfy Camille
Published: June 2010

The interaction of the 6-O methylguanine cation with cytosine and thymine was studied using the ab initio SCF method in combination with a London type expression for dispersion energy. The structure of the complex formed with cytosine differs from that found previously with guanine itself.
The sulfur dioxide-hydrogen fluoride complex. Additional information to the experiment from ab initiocalculations
Authors: Gerber Stefan , Huber Hanspeter
Published: June 2010

The structure and D-nuclear quadrupole coupling constant of the title complex are calculated by ab initio SCF methods. The results are compared with recently published experimental data. The calculations yield additional information not amenable to the experiment.
Medium-size polarized basis sets for high-level correlated calculations of molecular electric properties
Authors: Sadlej Andrzej J.
Published: June 2010

The basis set polarization approach is applied to the generation of medium-size polarized GTO/CGTO basis sets for accurate calculations of molecular dipole moments and polarizabilities. The polarized basis sets determined in this paper for H and C through F are employed in SCF HF and MBPT calculations of dipole moments and polarizabilities of FH, H2O, NH3, and CH4. The excellent results obtained at both the SCF HF and MBPT(4) levels of approximation indicate that the present basis sets can be employed for the accurate high-level correlated studies of relatively large molecules The use of those basis sets in calculations of intermolecular interactions is also discussed.
Aromaticity in heterocyclic molecules containing divalent sulfur
Authors: Randić Milan , Nikolić Sonja , Trinajstić Nenad
Published: June 2010

The conjugated circuits model is applied to heterocycles containing divalent sulfur. A novel parametrization is introduced for 4n + 2 and 4n conjugated circuits containing a single sulfur atom. The relative aromatic stabilities of a number of heterocyclic systems containing divalent sulfur are studied. Comparison is made whenever possible with earlier reported resonance energies of these compounds, obtained by using Huckel MO and SCF π-MO models, and appropriate reference structures. Special attention is given to positional isomers. An explanation of the differences amongst such isomers is given.
MM2- und MNDO-rechnungen zur 1,5-laticyclischen dreiring-azo-wechselwirkung und ihr vergleich mit kristallstrukturdaten
Authors: Hünig Siegfried , Peters Karl , Schmitt Michael , von Schnering Hans G.
Published: June 2010

Die passende Geometrie zur Ausbildung einer laticyclischen 1,5-π,σ-Konjugation in starren Systemen benachbarter Azo- und Dreiringeinheiten des Typs B ist die Voraussetzung für die erstmals an V-VII verwirklichte [σ2s + π2s]-Photocycloaddition unter Beteiligung von Azogruppen. Anhand der Röntgenstruktur des Azo/Aziridins XX sowie von MM2-Kraftfeld- und semiempirischer MNDO-Rechnungen für die Verbindungen V-VII werden die geometrischen Erfordernisse einer transannularen Wechselwirkung diskutiert. Diese erfolgt in den Systemen V-VII über einen mittleren Transannularabstand von 280 pm; die Geometrie von Azogruppe und Dreiringeinheit erlaubt eine nahezu lineare Annäherung der wechselwirkenden Orbitale. Unterschiede in der [2 + 2]-Reaktivität verschiedener Dreiringkomponenten (X = CH2, N-R, O)sind nicht in geänderten geometrischen Verhältnissen begründet.
Theoretical investigation of a possible new class of stable aminyl radicals
Authors: Leroy Georges , Sana Michel , Wilante Claude
Published: June 2010

We show in this paper that nitrogen-centred radicals carrying two electron-donor substituents constitute a possible new class of stable aminyl radicals. An interpretation of this original result is given by using a general definition of the thermodynamic stabilization energy.
Multiplicity of many-body wavefunctions using unrestricted Hartree-Fock reference functions
Authors: Purvis George D. , Sekino Hideo , Bartlett Rodney J.
Published: June 2010

Spin multiplicity formulae for the correlated Many Body Perturbation Theory (MBPT) and Coupled Cluster (CC) methods based upon an unrestricted Hartree Fock (UHF) reference function are presented and applied to evaluate the multiplicity in calculations of first row atoms. Spin projection in CC theory is discussed.
Accurate evaluation of SCF and MP2 components of interaction energies. Complexes of HF, OH2, and NH3 with Li+
Authors: Szczęśniak Małgorzata M. , Scheiner Steve
Published: June 2010

High-quality Gaussian basis sets of the well-tempered type, containing three sets of polarization functions on all atoms, are used to investigate the interaction of Li+ with HF, OH2, and NH3. These sets reproduce the SCF and MP2 energies of the various monomers very well and, moreover, accurately treat the multipole moments and polarizabilities of the monomers. When applied to the complexes, the sets are essentially free of primary and secondary basis set superposition error at the SCF level; MP2 extension effects are also completely negligible while basis set superposition effects are small but non-negligible. Analysis of the correlation corrections to the molecular properties, coupled with comparison of the interaction of the bases with a point charge, provides a straightforward explanation of correlation contributions to the interaction energy. Recommendations are provided to guide selection of basis sets for molecular interactions so as to avoid distortion of the various components.
Calculation of electrostatic potentials and fields inside zeolite cavities
Authors: Ángyán János G. , Ferenczy György , Nagy Péter , Náray-Szabó Gábor
Published: June 2010

We present a modification of our bond increment method for the calculation of molecular electrostatic potentials and fields inside zeolite cavities. Introducing a variant of the Mulliken approximation for the off-diagonal matrix elements of the potential and optimizing the parameters of the modified formula, we achieved much better agreement with ab initio STO-3G minimal basis set results than with the original version. For a representative set of 10 small molecules the standard mean deviation between potentials calculated on the van der Waals surface with the ab initio and approximate methods is 9·1 kJ/mol. The relative error decreases from 21 to 9 per cent for the lone-pair regions of molecules modelling zeolite cavities. Applying the modified bond increment method for a realistic faujausite model we have found that the potential and field are almost exclusively of long-range origin. This means that, if using appropriate atomic charges, the monopole approximation gives correct results for electrostatic potentials and fields inside zeolite cavities.
Complex formation and kinematic coupling: C2H4.PtCl3
Authors: Řeřicha Roman , Cyvin Björg N. , Brunvoll Jon , Cyvin Sven J.
Published: June 2010

Normal coordinate analyses including calculations of PED's were performed for C2H4.PtCl3 system modelling Zeise's anion, [(C2H4)PtCl3]-. The wedgewise distorsion of the C2H4 ligand known from the crystallographic data for Zeise's salt, was taken into account. Under these circumstances it was found that the kinematic couplings between the internal ligand and complex framework vibrational modes are rather small. The reliability of some existing assignments of the fundamental frequencies of Zeise's anion is discussed.
Pentamethylcyclopentadienyl rhodium complexes of dihydro-s-indacenophanes: Transannular interactions
Authors: Bickert Peter , Hafner Klaus
Published: June 2010

Transannular interactions in pentamethylcyclopentadienyl rhodium complexes (Me5C5Rh) of 18,22(18,20)-dihydro[2](4,4')biphenylo[2](2,6)-s-indacenophane (IV) and 12,16(12,18)-dihydro[2]pacacyclo[2](4,8)-s-indacenophane (IX) were investigated. The capability of a Me5C5Rh group to reduce electron density in both decks of these phanes was established. The deprotonation product VII of 18a,19,19a,22a,23,23a-η6-(18,22(18,20)-dihydro[2](4,4')biphenylo[2](2,6)-s-indacenophane-η5-(pentamethylcyclopentadienyl)rhodium(III) bis(hexafluoroantimonate) (V) was isolated as the first representative of a class of compounds whose existence had been previously postulated. Evidence for conformational flexibility of the biphenyl deck of IV and its derivatives was obtained. Comparative 1H NMR studies led to a separation of transannular electronic interactions from magnetic anisotropy effects in 15a,16,17,18,18a-η5-(12-monohydro[2]paracyclo[2](4,8)-s-indacenophane)-η5-(pentamethylcyclopentadienyl)rhodium(III) hexafluoroantimonate (X).
A theoretical study on acetylene dimer, acetylene-s-tetrazine and acetylene-benzene associates
Authors: Petrusová Helena , Havlas Zdeněk , Hobza Pavel , Zahradník Rudolf
Published: June 2010

Stabilization energies for the title van der Waals molecules were calculated for various mutual orientations of the subsystems. The interaction energy was expressed as a sum of three contributions: the Hartree-Fock interaction energy, the basis set superposition error and the dispersion energy. The potential energy minima represent reasonably good estimates of the structures of the van der Waals molecules.
Proton magnetic resonance study of the conformation of the pyrrolidine ring in some proline-thiohydantoins
Authors: Sleeckx Jef J. M. , Anteunis Marc J. O. , Borremans Frans A. M.
Published: June 2010

The conformational behaviour of a series of N-substituted thiohydantoins of proline was studied by proton NMR. The pseudorotational parameters of the proline moiety were calculated from the ten vicinal proton-proton coupling constants assuming a two state equilibrium (N ⇋ S). The effect of the different substituents (methyl, phenyl, para-nitrophenyl) at the thiohydantoin nitrogen on the conformation of the pyrrolidine rings is discussed. The spectra of proline-N-methylthiohydantoin were recorded at different temperatures in octadeuterotoluene solution. The conformational analysis of these spectra showed that the ratio of the populations of the N and S forms changes considerably with temperature, while the conformational identity of both the N and S forms remains strictly preserved. These facts provide an additional experimental justification of the two-state assumption, at least so for the present model compounds.
Formation of open-chain asymmetrical cystine peptides on a solid support. Synthesis of pGlu-Asn-Cyt-Pro-Arg-Gly-OH
Authors: Ten Kortenaar Paul B. W. , Van Nispen Jan W.
Published: June 2010

The feasibility of the synthesis of assymetric disulfide-containing peptides on solid phase resins was investigated. Using a fragment of [8-arginine]vasopressin as a model, the conversion of the S-acetamidomethylcysteine-containing peptide-resin into the corresponding S-carboxymethylsulfenyl derivative followed by reaction with free cysteine was studied. Both reactions proceeded smoothly under mild conditions. After cleavage from the resin the peptide was shown to have the correct composition.
Conformational and biological analysis of α-MSH fragment analogues with sterically constrained amino acid residues
Authors: Hruby Victor J. , Cody Wayne L. , Castrucci Ana Maria de Lauro , Hadley Mac E.
Published: June 2010

Conformational and biological analysis of the linear 4-11 fragment analogues, Ac-[Nle4]-α-MSH4-11-NH2 (II) and Ac-[Nle4, D-Phe7]-α-MSH4-11-NH2 (III) and related analogues have been undertaken. In solution, the peptide backbone is flexible, but in the case of D-Phe7 analogues an interaction of the His6, D-Phe7 and Arg8 amino acid side chain groups may be present based on the shielding patterns observed in the proton NMR and on comparison of NT1 values. The importance of the position 7 to the biological and conformational properties was further examined by substitution of either L- or D-phenylglycine (Pgl) or L- and D-1,2,3,4-tetrahydroisoquinoline carboxylic acid (Tic) for phenylalanine-7. Ac-[Nle4, Pgl7]-α-MSH4-11-NH2 (IV), Ac-[Nle4, D-Pgl7]-α-MSH4-11-NH2 (V), Ac-[Nle4, Tic7]-α-MSH4-11-NH2 (VI), and Ac-[Nle4, D-Tic7]-α-MSH4-11-NH2 (VII) were prepared. These substituted analogues were examined for their biological activities and conformational properties with emphasis on the three-dimensional orientation of the aromatic ring in the position 7, and the effects of the aromatic ring on adjacent amino acids, and on biological activities. The relative potencies of the analogues in the frog skin assay system were: II (1·00); III (118); IV (82·4); V (0·18); VI (0·18); and VII (0·14); and in the lizard skin bioassay they were: II (1·00); III (10·0); IV (0·14); V (0·005); VI (0·00025); and VII (0·01). On the basis of the NMR studies the L-phenylglycine substitution results in an enhanced ring stacking interaction between the phenyl ring of Pgl7 and the indole ring of Trp9. The 1,2,3,4-tetrahydroisoquinoline carboxylic acid (Tic) substitution leads to significant backbone restriction and an interaction of the alpha proton of His6 with the carbonyl of Glu5. The possible relationships of these effects to biological activity are discussed.
The melanocyte stimulating activity of N-nitroso-2-chloroethyl-carbamoyl derivatives of α-melanotropin fragments
Authors: Medzihradszky-Schweiger Hedvig , Süli-Vargha Helga , Bódi József , Medzihradszky Kálmán
Published: June 2010

A number of N-nitroso-2-chloroethyl-carbamoyl (Q(NO)) derivatives of α-melanotropin fragments have been synthesized and their effect on the frog skin melanocytes studied. Peptides substituted in this way possess the biological activity of the parent compounds, indicating that they preserved their receptor recognizing ability. These compounds can therefore serve as affinity labels. Some of these derivatives, related to the C-terminal sequence of α-melanotropin show prolonged darkening reaction, which does not influence the subsequent reaction of melanocytes with α-melanotropin. The Q(NO)-derivative of a fragment derived from the classical active site of the hormone shows, however, inhibition of the effect of α-melanotropin. It can be concluded that the latter peptide acts through the melanotropin receptor, while others, related to the C-terminal sequence of the hormone through another mechanism.
Peptide inhibitors of the angiotensin converting enzyme with nonproteinogenic amino acids
Authors: Reissmann Siegmund , Schwuchow Carola , Filatova Margarita P. , Krit Natalya A. , Siems Wolf-Eberhard , Heder Gottfried , Schrader Uwe , Schubert Harald , Müller Bettina , Bardl Bettina , Paegelow Inge
Published: June 2010

To study the structural requirements of the angiotensin converting enzyme we have synthesized and tested two series of acylated tripeptides with the common structure Acyl-AA1-AA2-Pro and Acyl-AA1-Arg-Pro. The structure-activity relationship indicates that the inhibitory activities result from the structure and conformation of the whole molecule. The use of nonproteinogenic amino acids in the positions AA1 and AA2 stabilizes to some degree the peptides against enzymatic degradation. Some of the acylated tripeptides are able to reduce the angiotensin I-induced blood pressure enhancement of normotensive rats. The peptides are applied orally. No good correlation exist between the inhibitory activity of the isolated enzyme and the in vivo activity. The structural requirements for the inhibition of the isolated ACE and the potentiation of the bradykinin action on the guinea pig ileum are different.
2-O-methyl and 2-O-ethyl-tyrosine derivatives of [8-arginine]vasopressin analogs: Highly specific antidiuretic agonists
Authors: Bankowski Krzysztof , Lammek Bernard , Kruszynski Marian , Manning Maurice , Seto Janny , Sawyer Wilbur H.
Published: June 2010

The solid phase synthesis of seven 2-O-methyl- and 2-O-ethyl-tyrosine substituted analogs of [8-arginine]vasopressin (AVP) with enhanced antidiuretic agonistic specificity is reported. These peptides are: [2-O-ethyltyrosine, 8-arginine]vasopressin (I), [2-O-methyltyrosine, 8-D-arginine]vasopressin (II), [2-O-ethyltyrosine, 8-D-arginine]vasopressin (III), [2-O-methyltyrosine, 4-valine, 8-arginine]vasopressin (IV), [2-O-ethyltyrosine, 4-valine, 8-arginine]vasopressin (V), [2-O-methyltyrosine, 4-valine, 8-D-arginine]vasopressin (VI), [2-O-ethyltyrosine, 4-valine, 8-D-arginine]vasopressin (VII). All analogs were tested for antidiuretic, antivasopressor and antioxytocic activities. Although all these new analogs are antidiuretic agonists they are antagonists of vasopressor responses to AVP, and of responses by the rat uterus to oxytocin. Thus, all seven new Tyr(Me) and Tyr(Et) containing analogs exhibit high antidiuretic specificity and have infinite antidiuretic/pressor (A/P) and antidiuretic/oxytocic (A/O) activity ratios. Some of these analogs e.g. Tyr(Me)DAVP, Tyr(Me)VAVP and Tyr(Me)VDAVP, which possess high antidiuretic activity with no pressor or oxytocic agonism, could be useful new pharmacological tools for characterizing receptors mediating specific responses to the neurohypophyseal hormones. They could also be potentially useful in the treatment of diabetes insipidus.
A modified benzhydrylamine - A useful handle reagent for Fmoc based solid phase synthesis of peptide amides
Authors: Funakoshi Susumu , Murayama Eigoro , Guo Lili , Fujii Nobutaka , Yajima Haruaki
Published: June 2010

Usefulness of a dimethoxybenzhydrylamine derivative, 3-(3-(Fmoc-amino-4-methoxyphenylmethyl)-4-methoxyphenyl)propionic acid, for Fmoc-based solid phase synthesis of peptide amides was demonstrated by preparation of three biologically active peptide amides, i.e. tetragastrin, neuromedin B and [8-arginine]vasopressin. 1M trimethylsilyl bromide-thioanisole (molar ratio 1 : 1) in trifluoroacetic acid was recommended as a deprotecting reagent for releasing the peptide amides from the resin.
Di- and tripeptide N-alkyl- and N-aralkyl amides as chymotrypsin inhibitors
Authors: Kasafírek Evžen , Šutiaková Irena , Bartík Michal , Šturc Antonín
Published: June 2010

Two competitive inhibitors of chymotrypsin, Glt-Ala-Ala-Leu-EtPh and Glt-Ala-Ala-Pro-NH-EtPh, were synthesized and their inhibition constants Ki were determined. The Ki-determination was carried also with a set of peptides of type X-(Ala)nNH-Y, where X is 3-carboxypropionyl- or 4-carboxybutyryl-, n is 2 or 3 and Y is methyl, ethyl, diethyl, isopropyl, propyl, butyl, isobutyl and 2-phenylethyl. Chymotrypsin inhibition was observed only with peptides containing an aralkyl residue whereas peptides with an alkyl are without any effect. Glt-Ala-Ala-Leu-NH-EtPh shows the highest Ki-value (80 μmol l-1).
Specific water-soluble substrates for chymotrypsin: Attempts for compensating diminished P1-S1 interactions
Authors: Schellenberger Volker , Schellenberger Ute , Jakubke Hans-Dieter
Published: June 2010

N-Maleyl-L-amino acid and peptide esters were synthesized and employed as substrates for α-chymotrypsin. From the kcat/KM values can be suggested that benzyl esters are significantly better substrates than the appropriate methyl esters. Further improvement in the substrate properties results from the introduction of the p-nitrobenzyl ester moiety. The choline ester of benzyloxycarbonyl-L-phenylalanine with the highest kcat/KM value confirmed the P1' leaving group specificity for positively charged residues. From the kinetic data can be concluded that acyl donors with high kcat/KM values, which are useful in kinetically controlled enzymatic peptide synthesis, need not contain aromatic amino acid residues in the P1 position.
Quantitative relations between chemical structure and hepatotoxicity of thiobenzamides
Authors: Waisser Karel , Macháček Miloš , Lebvoua Jean , Hrbata Jiří , Dršata Jaroslav
Published: June 2010

1H NMR chemical shifts of thioamide protons have been determined for a group of thiobenzamides, and the values obtained have been correlated with the Hammett constants. From the relations found the σm and σp values of thioamide group and some other σ constants describing the total effect of two substituents in the phenyl group have been calculated. The relation between the hepatotoxicity for rats (expressed as log ALT) and the Hammett constants is described by equation of parabola.
Enzymes in preparative organic synthesis: The problem of increasing the yield of product
Authors: Semenov Anatolii N. , Čeřovský Václav , Titov Mikhail I. , Martinek Karel
Published: June 2010

Approaches and methods increasing yield of the desired products in enzymatically catalyzed thermodynamically unfavourable syntheses are reviewed. Attention is paid especially to reactions in biphasic systems (water-water-immiscible organic solvent) and their modifications (micellar systems, pseudo-biphasic systems, aqueous biphasic systems, etc.). The dependence of chemical equilibrium and conversion of enzymatically catalyzed processes on the volume ratio of organic and aqueous phases and on the partition coefficients is described. Enzymatically catalyzed syntheses of peptides, amides, esters, NAD-dependent oxidations of hydroxy groups, etc. are given as examples. Various approaches to enzymatically catalyzed processes and their prospects are discussed.
The reaction distance
Authors: Koča Jaroslav
Published: June 2010

An algorithm is suggested for the calculation of the reaction distance as the minimal number of elementary steps of reorganization of valence electrons during a reaction. The basis for the formulation of this algorithm is the synthon isomerization graph (SR-graph). Chemical examples of application of the algorithm are given.
Homogeneous catalysis of manganese(II) in acid bromate oxidation of olefinic acids
Authors: Sanjeeva Reddy Ch.
Published: June 2010

Manganese(II)-catalysed acid bromate oxidation of acrylic trans-crotonic and trans-cinnamic acids, in the presence of mercury(II), a bromide ion scavenger, exhibits first order in concentration of bromate, and reaches an upper limit with increase in substrate as well as catalyst concentration. Oxidation rate increases with acidity and is not altered when deuterium replaces either α or β proton of the olefinic acid. The catalytic effect of Mn(II) is displayed by its complex forming ability and the proposed mechanism assumes the oxidation of the formed Mn(II)-substrate π complex to Mn(III)-substrate π complex by acid bromate which further converts to products. The formation of a π complex between Mn(II) and the olefinic bond of the substrate is assumed for the first time.