bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Duck Hepatitis B Virus Reverse Transcription Indicates a Common Mechanism for the Two Template Switches during Plus-Strand DNA Synthesis
Authors: Havert Michael B. , Ji Lin , Loeb Daniel D.
Published: July 2002

The synthesis of the hepadnavirus relaxed circular DNA genome requires two template switches, primer translocation and circularization, during plus-strand DNA synthesis. Repeated sequences serve as donor and acceptor templates for these template switches, with direct repeat 1 (DR1) and DR2 for primer translocation and 5′r and 3′r for circularization. These donor and acceptor sequences are at, or near, the ends of the minus-strand DNA. Analysis of plus-strand DNA synthesis of duck hepatitis B virus (DHBV) has indicated that there are at least three other
cis
-acting sequences that make contributions during the synthesis of relaxed circular DNA. These sequences, 5E, M, and 3E, are located near the 5′ end, the middle, and the 3′ end of minus-strand DNA, respectively. The mechanism by which these sequences contribute to the synthesis of plus-strand DNA was unclear. Our aim was to better understand the mechanism by which 5E and M act. We localized the DHBV 5E element to a short sequence of approximately 30 nucleotides that is 100 nucleotides 3′ of DR2 on minus-strand DNA. We found that the new 5E mutants were partially defective for primer translocation/utilization at DR2. They were also invariably defective for circularization. In addition, examination of several new DHBV M variants indicated that they too were defective for primer translocation/utilization and circularization. Thus, this analysis indicated that 5E and M play roles in both primer translocation/utilization and circularization. In conjunction with earlier findings that 3E functions in both template switches, our findings indicate that the processes of primer translocation and circularization share a common underlying mechanism.
Nine- and Eight-Vertex Polyhedral Dicarbaborane Chemistry: New arachno and hypho Dicarbaboranes from arachno-4,5-C2B7H13: Isolation and Characterization of the [arachno-4,5-C2B7H12]- and [hypho-7,8-C2B6H13]- Anions, and of the Neutral Ligand Derivatives exo-6-(MeNC)-arachno-4,5-C2B7H11 and exo-5-L-hypho-4,9-C2B7H13 (L = NMe3 and NEt3)
Authors: Jelínek Tomáš , Holub Josef , Štíbr Bohumil , Fontaine Xavier L. R. , Kennedy John D.
Published: July 2002

Deprotonation of neutral arachno-4,5-C2B7H13 (1) either with 1, 8-(NMe2)2C10H6 (proton sponge, PS) or with a mixture of aqueous K2CO3 and [NMe4]Cl leads to the isolation in high yield of the [arachno-4,5-C2B7H12]- anion (2). Isostructural with this anion is the ligand derivative exo-6-(MeNC)-arachno-4,5-C2B7H11 (3), which is prepared in 20% yield from the reaction between arachno-4,5-C2B7H13 and MeNC in dichloromethane. Under comparable conditions compound 1 with tertiary amines gives the first representatives of the nine-vertex hypho family of dicarbaboranes, the ligand derivatives exo-5-(NR3)-hypho-4,9-C2B7H13 (4a and 4b, where R = Me and Et, respectively) in moderate yields (20 - 55%), whereas the reaction between 1 and aqueous NaCN results in the selective removal of one boron vertex to yield the eight-vertex [hypho-7,8-C2B6H13]- anion (5) in 61% yield. All compounds isolated were characterized by 11B and 1H NMR spectroscopy, with two-dimensional and selective decoupling techniques giving unambiguous assignments.
Preparation and Evaluation of Skeletal Cobalt-Molybdenum Hydrodesulfurization Catalysts
Authors: Sporka Karel , Hanika Jiří , Jůn Vladimír
Published: July 2002

Preparation of skeletal Co-Mo catalysts by controlled impregnation of aluminosilicate skeletons containing deposited gamma-alumina with aqueous solutions of active component precursors has been investigated. The activity of the laboratory catalysts in gas oil hydrodesulfurization has been determined. Kinetics of impregnation of skeletal supports, the effect of their type, and the dependence of catalyst activity on the content of cobalt and molybdenum sulfides are reported. HDS skeletal catalysts prepared were compared with the extruded types. It was found that skeletal HDS catalysts show the higher activity (related to the content of alumina and Co-Mo sulfides) than the extruded ones due to the less significant effect of internal diffusion. However, if the activity is related to the same volume of catalyst bed, the activity of skeletal catalysts is only one fourth of that of the extruded types.
Chemometric Analysis of Substituent Effects. VI. A Study of ortho Effect in Dissociation of 2,6-Disubstituted Benzoic Acids
Authors: Kulhánek Jiří , Pytela Oldřich
Published: July 2002

Ten 2,6-disubstituted benzoic acids have been synthesized containing all possible combinations of the following substituents: CH3, OCH3, Cl, and NO2. The dissociation constants of these acids have been measured by potentiometric titration in methanol, acetone, dimethyl sulfoxide, dimethylformamide, acetonitrile, pyridine, and 1,2-dichloroethane. The experimental data obtained together with the pK values of 2-substituted benzoic acids in the same solvents have been analyzed from the point of view of ortho effect and additivity of disubstitution. The mutual interaction between substituents was found to represent only 0.12% of the variability due to substitution and to contribute to the overall variability of data less than the interaction between the substituent and solvent by a factor of about 13. The analysis of data by the method of multiple linear regression revealed a contribution of steric effects beside the effects transmitted through the aromatic skeleton. The 2- and 6-substituents effects are additive within the validity of the Hammett equation, and an addition of a multiplicative term describing interactions between the substituents is statistically insignificant. Nonlinear regression has been adopted in the additive model with multiplicative term to find the inner substituent constants including all the effects of substituents from ortho position: the term describing the interaction between 2- and 6-substituents is statistically insignificant in this model. An application of the method of conjugated deviations revealed two statistically significant latent variables. The first one explains 91.5% of the variability of data and is connected with the substituent effects transmitted through the aromatic skeleton. The second one explains 7.5% of variability of data and predominantly reflects the steric effects of substituents.
Synthesis of Alkyl 1,2-Dicyanopyrrolidino[1,2-f]phenanthridine-3-carboxylates
Authors: Potáček Milan , Topinka Tomáš , Dostál Jiří , Humpa Otakar
Published: July 2002

Alkyl 1,2-dicyanopyrrolidino[1,2-f]phenanthridine-3-carboxyla tes II were prepared from 5-(alkoxycarbonylmethyl)phenanthridinium bromides I and fumaronitrile in the presence of triethylamine. The products II underwent spontaneous dehydrogenation to give pyrrolino[1,2-f]phenanthridines III. The structures of the products were determined by spectral methods (IR, NMR, MS).
N-(2-Methyl-2-nitropropyl) and N-Nitroso Derivatives of Some Diamines
Authors: Kafka Stanislav , Klásek Antonín , Sedmera Petr
Published: July 2002

Preparation of ten new derivatives of 1,6-hexanediamine and 1,4-bis(4-aminophenoxy)butane with different combination of N-nitroso and/or N-(2-methyl-2-nitropropyl) groups is presented. The title compounds are potential improvers of vulcanized rubber dynamic properties.
Photocolouration of 2,4,4,6-Tetraaryl-4H-pyrans and Their Heteroanalogues: Importance of Hypervalent Photoisomers
Authors: Böhm Stanislav , Adamec Mojmír , Nešpůrek Stanislav , Kuthan Josef
Published: July 2002

Molecular geometries of 2,4,4,6-tetraphenyl-4H-pyran (Ia), 4,4-(biphenyl-2,2e-diyl)-2,6-diphenyl-4H-pyran (Ib) and their heterocyclic isomers II-V were optimized by the PM3 method and used for the calculation of electronic absorption spectra by the CNDO/S-CI procedure. Comparison of the theoretical data with experimental UV-VIS absorption spectra made possible to select hypervalent molecules IIIa, IIIb, IVa and IVb being responsible for the photocolouration of 4H-pyrans Ia, Ib, while compounds Va, Vb, VI and VII come into account as possible photodegradation products. The bleaching process of the UV illuminated compound Ia is analyzed in terms of dispersive first-order reaction kinetics.
The Model of Linear Aggregate of Ag Colloidal Particles with Variable Inter-Particle Distances
Authors: Šesták Ondřej , Matějka Pavel , Vlčková Blanka
Published: July 2002

A simplified method of calculation of the surface plasmon energy states of the Ag colloidal aggregates characterized by varying inter-particle (inter-sphere) distance has been developed. Ag colloidal aggregate is approximated by a linear (one-dimensional) assembly of N silver spheres (of identical radii r and identical inter-sphere distances D) mutually interacting by a dipole-dipole interaction. The calculations use the following parameters: N from 1 to 25, r = 2, 5 and 10 nm, D = 0, 0.5, 1 and 2 nm, water and/or vacuum embedding media. The perturbation energies Vmin (stabilization energy) and Vmax (destabilization energy) of the excited plasmon state of a linear aggregate of N spheres interacting by the dipole-dipole interaction were calculated as the eigenvalues of perturbation matrix using the above-mentioned parameters. The stabilization energy Vmin increases with increasing number of spheres in the aggregate and with increasing sphere radius, while it decreases with increasing inter-particle (inter-sphere) distance. Calculations of the square values of the eigenvector coefficients show that the contribution of a particular single sphere to the total energy of the aggregate is the highest for the central sphere in the odd-N aggregates and for the two central spheres in the even-N aggregates. The results of the model calculations support the hypothesis that the differences between the surface plasmon absorption curves of the Ag colloid/monomeric adsorbate and of the Ag colloid/polymeric (oligomeric) adsorbate systems have their origin in the difference in the inter-particle distance distributions.
Fischer Indole Synthesis with Selected 2,3-Dideoxy-D-glycero-aldopentose Derivatives. Conversion of D-Xylose to (2S)-3-(Indol-3-yl)propane-1,2-diol
Authors: Lajšic Stevan , Cetkovic Gordana , Popsavin Mirjana , Popsavin Velimir , Miljković Dušan
Published: July 2002

Two independent routes towards (2S)-3-(indol-3-yl)propane-1,2-diol (11) were achieved starting from 3,5-di-O-acetyl-1,2-O-cyclohexylidene-α-D-xylofuranose (1). Ethanethiolysis of 1 afforded acyclic diethyl dithioacetal 2 which was further O-deacetylated to give 3. Selective benzoylation of 3 gave 5-O-benzoyl derivative 4. Treatment of 4 with N-bromosuccinimide in methanol gave methyl furanoside 5 which was further desulfurized over Raney nickel to afford 6. An acid hydrolysis of 6 gave hemiacetal 7 which upon treatment with phenylhydrazine, according to standard Fischer indolization procedure, yielded a mixture of chiral indoles 10. O-Debenzoylation of 10 gave the crystalline diol 11. A more efficient route towards the chiral indole 11 included the initial dethioacetalation of 2 into dimethyl acetal 8 which was further desulfurized over Raney nickel to give the corresponding 2,3-dideoxy derivative 9. Direct Fischer indolization of 9 with phenylhydrazine, followed by O-deacetylation of intermediate 12, afforded the expected indole 11 in good yield.
Carbocyclic Phosphonate-Based Nucleotide Analogs Related to PMEA II. Racemic cis-Configured Derivatives
Authors: Liboska Radek , Masojídková Milena , Rosenberg Ivan
Published: July 2002

Racemic N-(cis-2-phosphonomethoxycycloalkyl) derivatives of heterocyclic bases, a novel type of nucleotide analogs related to 9-(2-phosphonomethoxyethyl)adenine (PMEA), are reported. The synthesis of adenine- (6a, 6b), uracil- (6c) and cytosine- (6d) containing carbocyclic phosphonates is based on the reaction of cis-2-hydroxycycloalkyl derivatives of protected nucleobases with diisopropyl tosyloxymethanephosphonate. The starting purine-containing nucleoside analogs 5a-5f were prepared by the Mitsunobu reaction of protected nucleobases with trans-2-benzyloxycycloalkanols, whereas pyrimidine-containing nucleoside analogs 5g-5k were obtained by configurational inversion at C-2' of the corresponding 1-(trans-2-hydroxycycloalkyl)pyrimidines via ring opening of their 2,2'-anhydro derivatives.
Effect of Solvent Composition on Solubility and Activity of Bovine Leukemia Virus Proteinase
Authors: Hrušková-Heidingsfeldová Olga , Piskáček Martin , Cubínková Romana , Zábranský Aleš , Pichová Iva
Published: July 2002

The solubility and activity of bovine leukemia virus proteinase (BLV PR) has been examined as a function of solvent composition in order to find a buffer system which would enable to prepare samples concentrated sufficiently for crystallization attempts and other studies. Low solubility and frequent precipitation was one of the major difficulties in the course of experiments carried out with BLV PR in several laboratories. We found that buffers composed of polyvalent ions, and containing glycerol, ethylene glycol or dimethyl sulfoxide, enabled to concentrate the enzyme up to 2 mg/ml. Presence of 4-20% of DMSO, isopropyl alcohol or ethylene glycol results in activation of BLV PR, while glycerol does not significantly affect the BLV PR activity. Zinc or magnesium ions substituting for sodium ions in commonly used buffers caused decrease both in solubility and activity of BLV PR.
Combination of the Topliss Approach with the Free-Wilson Analysis in the Study of Antimycobacterial Activityof 4-Alkylthiobenzanilides
Authors: Kuneš Jiří , Jáchym Jiří , Jirásko Petr , Odlerová Želmíra , Waisser Karel
Published: July 2002

On the basis of a preliminary study of the antimycobacterial activity of thiobenzanilides, a group of 4'-isopropyl- and 4'-butylthiobenzanilides have been synthesized and tested against Mycobacterium tuberculosis, Mycobacterium kansasii, Mycobacterium avium and Mycobacterium fortuitum. The effect of the substituents on minimum inhibitory concentrations was calculated by the Free-Wilson method. The separated values were analyzed by the Topliss approach. The substitution of the thiobenzanilide in position 4' by the isopropyl group or butyl group increased the antimycobacterial activity less than the cyclohexyl group. The substitution in position 4 decreased the activity by the steric effect.
Substituent Effect on Acidity of Substituted 2-(4-Nitrobenzoylamino)alkanamides in Methanol-Dimethyl Sulfoxide Mixtures
Authors: Mitaš Petr , Sedlák Miloš , Kaválek Jaromír
Published: July 2002

The dissociation constants of substituted 2-(4-nitrobenzoylamino)alkanamides, N-[2-(4-nitrobenzoylamino)alkanoyl]pyrrolidines, and N-alkyl-4-nitrobenzamides have been measured spectrophotometrically in 60 and 80% v/v DMSO. The pKA values of these N-acids are discussed from the point of view of substituents at the acetamide α-carbon atom.
Synthesis and Antifungal Activity of New Indolylthiazinone Derivatives
Authors: Dzurilla Milan , Kutschy Peter , Tewari Jalpa P. , Ružinský Martin , Šenvický Stanislav , Kováčik Vladimír
Published: July 2002

New 6-(indol-3-yl)-5,6-dihydro-4H-1,3-thiazin-4-one derivatives were prepared by boron trifluoride catalyzed intramolecular cyclization of N'-substituted N-[3-(indol-3-yl)propenoyl]thioureas and by the reaction of 3-(indol-3-yl)propenoyl isothiocyanate with sodium hydrogensulfide. Antifungal activity of the prepared compounds was studied using the fungi Alternaria brassicae and Alternaria brassicicola.
Dependence of in vitro Enzymic Hydrolysis of Alkyl(2-benzoyloxyethyl)dimethylammonium Bromides on the Alkyl Length
Authors: Olaszová Eva , Paulíková Ingrid , Helia Otto , Švajdlenka Emil , Devínský Ferdinand , Lacko Ivan
Published: July 2002

Microsomal esterases were used in the study of the in vitro enzymic hydrolysis of the ester bond in alkyl(2-benzoyloxyethyl)dimethylammonium bromides. These compounds are potential "soft" disinfectants, easily biodegradable to nontoxic biologically inactive hydrolytic products, namely substituted choline and benzoic acid. Formation of the latter product was used to monitor the kinetics of the reaction. It has been found that the rate of enzymic hydrolysis is substantially influenced by different length of the alkyl chain on the ammonium nitrogen. At the same time, interspecies (rat-mouse) and interorgan (liver-kidney) variability has been observed.
Michael Additions of Benzotriazole-Stabilized Carbanions. A Review
Authors: Katritzky Alan R. , Qi Ming
Published: July 2002

The 1,4-addition of benzotriazole-stabilized carbanions to Michael acceptors is reviewed. The selectivity between 1,4- and 1,2-addition depends significantly on the electronic effect of the carbanion (usually lithium is the counterion), the type of the Michael acceptor, and steric effects. Steric hindrance of the benzotriazolyl group probably enhances the regioselectivity. Normally, 1,4-additions to α,β-unsaturated ketone or ester are observed for carbanions stabilized by a benzotriazolyl group and an electron-withdrawing group (e.g. aryl, vinyl, carbonyl). For α,β-unsaturated aldehydes as Michael acceptors, 1,2-addition is more likely, except where electronic effects are very strong. A review with 39 references.
17a-Oxa-17a-homobrassinosteroid Analogues
Authors: Kohout Ladislav , Slavíková Barbora , Strnad Miroslav
Published: July 2002

Synthesis of a 17a-oxa-17a-homobrassinosteroids, i.e. brassinosteroids having two lactone rings, is described. In the bean second internode bioassay, dilactone 16 was the most effective of the compounds synthesized. In the same test, the castasterone analogue 12 exhibited a growth-retarding effect.
Synthesis of Some New Functionalized 2,4,4,6-Tetraphenyl-4H-thiopyrans and Study on Their Photocolouration
Authors: Kroulík Jiří , Chadim Martin , Polášek Miroslav , Nešpůrek Stanislav , Kuthan Josef
Published: July 2002

A series of nineteen new 2,4,4,6-tetraphenyl-4H-thiopyrans both symmetrically and asymmetrically functionalized in the 3- and 5-positions of the 4H-thiopyran ring (-Br, -NO2, -CN) and/or in the 4-positions of the 2- and 6-phenyl groups (-Br, -CN, -OMe, -CO-Ph, -COCF3, -CO2H) was prepared and the influence of the substituents on their photocolouration was followed. The title compounds were prepared by substitution reactions of the parent thiopyrans or by cyclization of suitably substituted 1,3,3,5-tetraarylpentane-1,5-diones. The substances lacking the 3,5-substituents exhibited blue or green UV-photocolouration while the 3- and/or 5-substituted species did not. Typical bleaching process for a selected compound is analyzed in terms of dispersive first-order kinetics.
Synthesis of Ring-Substituted Phenyl Hydrazinecarboxylates and Study of Their Protonation in Dimethyl Sulfoxide Solutions
Authors: Vlasák Petr , Pařík Patrik , Klicnar Jiří , Mindl Jaromír
Published: July 2002

The pKa values of nineteen phenyl hydrazinecarboxylate hydrochlorides R-C6H4OCONHNH2·HCl (R = H, 3- and 4-Cl, 3- and 4-O2N, 4-Me) and their 1-methyl or 2-methyl derivatives were determined by potentiometric titration with tetrabutylammonium hydroxide in DMSO. IR spectra of the hydrazinecarboxylates and their hydrochlorides revealed that the hydrazinecarboxylate protonation occurs at N2. The methods of synthesis of phenyl hydrazinecarboxylate and their N-methyl derivatives were optimized.
Particle Migration in a Helle-Shaw Cell with Non-Parallel Walls
Authors: Wichterlová Jana , Wein Ondřej , Kaštánek František
Published: July 2002

Motion of a single macroscopic particle in a liquid flowing through a narrow channel with slightly non-parallel walls is studied by a visualization method. The experiment is limited to the region of slight inertia effects, Ar < 500. Three kinematic characteristics of the particle motion in the channel, viz. settling velocity in a still liquid, as well as longitudinal and lateral migration velocities under non-zero flow, are determined and correlated in dependence on the operation parameters. Both the longitudinal characteristics strongly depend on the particle-to-channel size ratio and are only slightly affected by inertia effects. On the other hand, the inertia effects play an essential role in the mechanism of lateral migration.
Binding Energies of Organic Charge-Transfer Complexes Calculated by First-Principles Methods
Authors: Rauwolf Cordula , Mehlhorn Achim , Fabian Jürgen
Published: July 2002

Weak interactions between organic donor and acceptor molecules resulting in cofacially-stacked aggregates ("CT complexes") were studied by second-order many-body perturbation theory (MP2) and by gradient-corrected hybrid Hartree-Fock/density functional theory (B3LYP exchange-correlation functional). The complexes consist of tetrathiafulvalene (TTF) and related compounds and tetracyanoethylene (TCNE). Density functional theory (DFT) and MP2 molecular equilibrium geometries of the component structures are calculated by means of 6-31G*, 6-31G*(0.25), 6-31++G**, 6-31++G(3df,2p) and 6-311G** basis sets. Reliable molecular geometries are obtained for the donor and acceptor compounds considered. The geometries of the compounds were kept frozen in optimizing aggregate structures with respect to the intermolecular distance. The basis set superposition error (BSSE) was considered (counterpoise correction). According to the DFT and MP2 calculations laterally-displaced stacks are more stable than vertical stacks. The charge transfer from the donor to the acceptor is small in the ground state of the isolated complexes. The cp-corrected binding energies of TTF/TCNE amount to -1.7 and -6.3 kcal/mol at the DFT(B3LYP) and MP2(frozen) level of theory, respectively (6-31G* basis set). Larger binding energies were obtained by Hobza's 6-31G*(0.25) basis set. The larger MP2 binding energies suggest that the dispersion energy is underestimated or not considered by the B3LYP functional. The energy increases when S in TTF/TCNE is replaced by O or NH but decreases with substitution by Se. The charge-transferred complexes in the triplet state are favored in the vertical arrangement. Self-consistent-reaction-field (SCRF) calculations predicted a gain in binding energy with solvation for the ground-state complex. The ground-state charge transfer between the components is increased up to 0.8 e in polar solvents.
Dynamic Gas Transport in Porous Bidispersed Alumina
Authors: Hejtmánek Vladimír , Čapek Pavel , Šolcová Olga , Schneider Petr
Published: July 2002

A spontaneous temporary rise in the pressure gradient through countercurrent binary transport of inert gases in porous bidispersed alumina was observed in diffusion cell of the Wicke-Kallenbach type. Experimental pressure responses to gas step changes were detected and fitted to a set of partial differential equations. These were based on the transport models Mean Transport Pore Model (MTPM) and Dusty Gas Model (DGM). The dynamic set transport parameters 〈r〉, 〈r2〉 and ψ for both models were obtained using an optimization algorithm and discussed. It was found that the values of the transport radius 〈r〉 are in a good agreement with the mean radius obtained from the measurement of alumina texture.
Simple and Condensed β-Lactams. Part 32. Base- and Acid-Catalyzed Ring Expansions of 3-Substituted 4-Acetylazetidin-2-ones and Related Compounds
Authors: Sápi Attila , Fetter József , Lempert Károly , Kajtár-Peredy Mária , Czira Gábor
Published: July 2002

On treatment with bases, the C3-C4 bonds of the 3-substituted 4-(1-iminoethyl)- or 4-acetylazetidin-2-ones 8f, 8g and 8i are cleaved heterolytically to afford, depending on the nature of the 3-substituent, ring expansion or other products (14, 19 and 27, respectively). Related compound 8h undergoes a base-induced ring transformation to afford compound 23 only after oxidation to the stereoisomeric disulfanes 20. Compound 8d, when treated with HCl, undergoes a ring transformation to pyrrolidin-2-one 32.
Molecular Modification of Anpirtoline, a Non-Opioid Centrally Acting Analgesic
Authors: Rádl Stanislav , Hafner Wieland , Hezký Petr , Krejčí Ivan , Proška Jan , Taimr Jan
Published: July 2002

Molecular modification of anpirtoline (2a) is described. Several methods of preparation of 4-[(3-chlorophenyl)sulfanyl]-1-methylpiperidine (3a) and its demethylation led to the deazaanpirtoline (3c). Nucleophilic substitution of piperidine-4-thiole with 2-chloro-4-nitropyridine, 2,4-dichloro-6-methylpyridine, and 3,6-dichloropyridazine led to 2-chloro-4-(piperidin-4-ylsulfanyl)pyridine (6), 4-chloro-6-methyl-2-(piperidin-4-ylsulfanyl)pyridine (7), and 3-chloro-6-(piperidin-4-ylsulfanyl)pyridazine (8), respectively. 2-Chloro-6-(pyridin-4-ylsulfanyl)pyridine (10) and 4-[(2-chloropyridin-6-yl)sulfanyl]quinoline (11) were obtained from sodium 2-chloropyridine-6-thiolate. Homoanpirtoline analogs with methylene group inserted between the pyridine moiety and the sulfur atom (compound 12b) as well as between the sulfur atom and the piperidine ring (compound 13b) were also prepared.
Non-Traditional Characterization of Petroleum Mixtures in Terms of Selected Components
Authors: Eckert Egon
Published: July 2002

A non-traditional method of characterization of petroleum mixtures in terms of selected real components is described which stems from the results of the mixture analysis and from some of distillation curves - best of all, EFV curve. On the basis of mathematical modelling of the process of obtaining the EFV curve, it is possible to find the composition of a substitute mixture consisting of a lower number of real components of the original mixture. This substitute mixture exhibits very similar vapour-liquid equilibrium behaviour as the original multicomponent mixture, which makes it possible to simplify the calculation of, e.g., a rectification column. At the same time, the need disappears of estimating the thermodynamic data of single mixture components on the basis of empirical relations subject usually to considerable errors so as it is with the commonly employed method of pseudocomponents.
Coupling Reactions of ortho-Substituted Halobenzenes with Alkynes. The Synthesis of Phenylacetylenes and Symmetrical or Unsymmetrical 1,2-Diphenylacetylenes
Authors: Stará Irena G. , Starý Ivo , Kollárovič Adrian , Teplý Filip , Šaman David , Fiedler Pavel
Published: July 2002

The Pd- or Pd/Cu-catalyzed coupling reactions of halobenzenes bearing the methyl, hydroxymethyl, acetoxymethyl, methoxycarbonyl, or both methoxy and 4,4-dimethyl-4,5-dihydro-1,3-oxazol-2-yl groups in the ortho-position with gaseous or metallated acetylene, (trialkylsilyl)acetylenes, and arylacetylenes have been systematically studied. Various functionalized aryl- or diarylacetylenes have been synthesized in good to excellent yields. Whereas additional fluoro, nitro, or methoxy group attached to the benzene ring does not interfere in the coupling reactions, the presence of a methoxycarbonyl requires a careful optimization of reaction conditions to achieve moderate yields.
Reactivity of Sodium Hexaethyl-2,4-dicarba-nido-hexaborate(1-)
Authors: Wrackmeyer Bernd , Schanz Hans-Jörg , Milius Wolfgang , McCammon Catherine
Published: July 2002

Sodium hexaethyl-2,4-dicarba-nido-hexaborate(1-) (6), available from hexaethyl-2,4-dicarba- nido-hexaborane(8) (4) by deprotonation, reacts with deuterated methanol, CD3OD, to give back 4 without H/D exchange of the B-H-B hydrogen atom. The reaction of 6 with diethylboron chloride, Et2BCl, affords hexaethyl-2,4-dicarba-closo-hexaborane(6) (7), the first example of a peralkylated carborane of this type. In contrast, the reaction of 6 with boron tribromide, BBr3, leads mainly to 2,3,4,5,6,7-hexaethyl-2,4-dicarba-closo-heptaborane(7) (8), together with the corresponding 1-bromo derivative (9) and the closo-carborane 7 as side products. The reaction of two equivalents of 6 with FeCl2 gives the air-stable sandwich complex bis[hexaethyl-2,4-dicarba-nido-hexaborate(1-)]iron 10 which was characterised by X-ray structural analysis. All products were characterised by 1H, 11B and 13C NMR spectroscopy, and 57Fe Mössbauer spectroscopy was used to study 10.
Synthesis of 2,2'-Bipyridines with Axially Chiral 1,1'-Binaphthalene Units
Authors: Hodačová Jana , Stibor Ivan
Published: July 2002

Synthesis of a series of novel 2,2'-bipyridine-based ligands bearing the axially chiral 2,2'-dialkoxy-1,1'-binaphthalene units is presented. The oxydimethylene, amidomethylene and amido spacers have been utilised to link the 3 or 3,3' positions of the binaphthalene skeleton with the 6 or 6,6' positions of the 2,2'-bipyridine moieties. The ligands have been synthesised in both racemic and enantiomerically pureRforms.
New Selective Inhibitors of Cytochrome P450 2B4 and an Activator of Cytochrome P450 3A6 in Rabbit Liver Microsomes
Authors: Bořek-Dohalská Lucie , Hodek Petr , Stiborová Marie
Published: July 2002

We investigated interactions of adamantane, diamantane and their two substituted derivatives, 2-isopropenyl-2-methyladamantane (2-PMADA,1) and 3-isopropenyl-3-methyldiamantane (3-PMDIA,2), with various isoforms of rabbit cytochrome P450 (CYP). The data of spectroscopic experiments showed that all the substances are bound to the substrate binding site of rabbit CYP2B4 and CYP3A6.1and2are compounds having higher affinities to these CYP isoforms than adamantane and diamantane. All compounds inhibit CYP2B4 specific enzyme activity (the 7-pentoxyresorufinO-depentylase activity). The 50% inhibition of CYP2B4 was due to 3.82, 0.61, 0.66 and 0.37 μM adamantane, diamantane,1and2, respectively. The products formed during the CYP2B4-mediated metabolism of studied substances are less effective inhibitors than parent compounds. An opposite effect of1on CYP3A6 was determined. The specific enzyme activity of CYP3A6 increased to 138% of control when1was used in the presence of 40 μM erythromycin as a substrate. Here, we report the finding of a new activator of CYP3A6 having the structure quite different from that of CYP3A6 activators known to date.
Synthesis of Aromatic Triynes as Precursors to Helicene Derivatives
Authors: Stará Irena G. , Kollárovič Adrian , Teplý Filip , Starý Ivo , Šaman David , Fiedler Pavel
Published: July 2002

A general and versatile synthetic approach to a broad series of aromatic triynes as precursors to helicene derivatives has been developed. Employing a set of simple tools, triynes comprising the (phenylethynyl)benzene, 1-(phenylethynyl)naphthalene, and 1-(1-naphthylethynyl)- naphthalene moiety have been prepared in good to excellent yields throughout the whole reaction sequence. The methodology allows constructing various types of a junction between the central diarylacetylene moiety and the attached acetylene units to get the target triynes of general formula R-C≡C-CH2-X-CH2-Ar-C≡C-Ar'-CH2-X-CH2-C≡C-R or R-C≡C-CH2CH2-Ar-C≡C-Ar'-CH2CH2-C≡C-R (R = H, CH3, TMS, or TIPS; X = O, NTs, or C(CO2CH3)2; Ar/Ar' = 2-phenylene or 2-naphthylene).
A Stereoselective Peptide-Based Artificial Receptor for Sugar Derivatives
Authors: Eblinger Frank , Schneider Hans-Jörg
Published: July 2002

A lipophilic sugar receptor containing two phenylalanine moieties shows in chloroform complexation free energies of ∆G = 13 kJ/mol for an alkyl glucoside, discriminating the corresponding galactoside by at least 8 kJ/mol. The observed 1H NMR signal shifts at OH groups suggest the hydrogen bonds as the major driving force, in line with preliminary molecular mechanics simulations.
N1-Substituted Hypoxanthine Derivatives from the Reaction of 6-Halopurines with Michael Acceptors Under the Conditions of Heck Reaction
Authors: Havelková Martina , Studenovský Martin , Dvořák Dalimil
Published: July 2002

The reaction of 6-iodo-, 9-benzyl-6-chloropurine and 7-benzyl-6-chloropurine with butyl acrylate, acrylonitrile, methyl vinyl ketone or methyl methacrylate under conditions of the Heck reaction in the presence of TlOAc or AgOAc afforded N1-alkylhypoxanthine derivatives. Formation of these unexpected products can be rationalised as a Tl+- or Ag+-assisted substitution of halogen with acetate anion. The 6-acetoxypurine derivative thus formed then eliminates ketene and gives 7-benzyl- or 9-benzylhypoxanthine. Conjugate addition of these compounds onto Michael acceptors furnishes the N1-substituted hypoxanthine derivatives.
Preparation of New Binaphthol-Based Tridentate Ligands for Enantioselective Synthesis
Authors: Holakovský Roman , Hovorka Martin , Stibor Ivan
Published: July 2002

A versatile method for resolution of 2,2'-dihydroxy-[1,1'-binaphthalene]-3-carboxylic acid has been developed. Four enantiomerically pure tridentate ligands, namely 3-(hydroxy- methyl)[1,1'-binaphthalene]-2,2'-diol (3), 3-[(2-hydroxyethoxy)[1,1'-binaphthalene]-2,2'-diol (4), 3-(2-hydroxy-5-methylbenzyl)[1,1'-binaphthalene]-2,2'-diol (5), and 3-(2-hydroxy-4,6-di-tert-butyl-benzyl)[1,1'-binaphthalene]-2,2'-diol (6), were synthesised in excellent yields and used as chiral modifiers of LiAlH4. A modest enantioselectivity was found for the reduction of acetophenone with LiAlH4 modified with ligand 4.
Unusual cis/trans Isomerism in Octahedral Nickel(II) Complexes with 1,4,8,11-Tetraazacyclotetradecane-1,8-bis(methylphosphonic Acid) as a Ligand
Authors: Kotek Jan , Vojtíšek Pavel , Císařová Ivana , Hermann Petr , Lukeš Ivan
Published: July 2002

Nickel(II) ion reacts with 1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid) (H4L1) at room temperature with formation of cis-[Ni(L1)]2- complex. The complex was crystallised in several forms in dependence on conditions of isolation (temperature, pH, solvent mixture). Crystal structures of cis-O,O-[Ni(H2L1)] (1), cis-O,O-[Ni(H2L1)]·2H2O (2), cis-O,O-[Ni(H3L1)]Cl·H2O (3) and cis-O,O-[Ni(H4L1)]Cl2·2H2O (4) were determined by X-ray diffraction. In all the compounds, Ni2+ is in octahedral cis-O1,O2-trans-N1,N8-cis-O1,N4-[Ni(L1)]2- (hereafter abbreviated as cis-O,O-[Ni(L1)]2-) arrangement with V conformation of the cyclam ring. Complexes 3 and 4 exhibit very unusual coordination through the phosphoryl group of double-protonated phosphonate moiety. Tetraethylester of H4L1 having only poorly coordinating phosphoryl oxygen atoms also forms nickel(II) complex 5 with cis arrangement. Corresponding trans-O,O-[Ni(L1)]2- complex is formed only in strongly acidic medium through conversion of the cis complex; it was characterised by X-ray diffraction as dihydrochloride dihydrate, trans-O,O-[Ni(H4L1)]Cl2·2H2O (6). The analogous compound (NH4)2(trans-O,O-[Ni(L2)])·H2O (7) is obtained quantitatively by reaction of Ni2+ with 4,11-dibenzyl-1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid) (H4L2). Formation of this complex 7 in the III cyclam ring conformation is preferred to the cis complex due to steric hindrance of bulky benzyl groups in cis-[Ni(L2)]2- complex with the V cyclam ring conformation.
P-Chiral Oligonucleotides. Effect of Configuration at Phosphorus on Transport of Tetra(thymidine Methylphosphonate)s Across Organic Liquid Membrane
Authors: Lesnikowski Zbigniew J. , Przepiórkiewicz Marzena , Tamura Yutaka , Kaji Hideko , Wickstrom Eric
Published: July 2002

The stereodependent transport of a P-stereoregular oligonucleotide through a model organic liquid membrane is described. The electroneutral tetra(thymidine methylphosphonate) was used as oligonucleotide. The transportability increased in the order: all-RP> random distribution of P-diastereomers > all-SP. These findings extend our knowledge of the physicochemical properties of single-stranded methylphosphonate oligonucleotides in solution, and might facilitate cellular uptake of future antisense oligonucleotide drugs.
Thermodynamics of Mixtures of Aromatic Hydrocarbons with Alkanols Studied by Light Scattering
Authors: Munk Petr , Cheng Weizhuang , Qin Anwei , Pouchlý Julius
Published: July 2002

Measurement of light scattering of mixtures of aromatic hydrocarbons (benzene, toluene, ethylbenzene) and alkanols (methanol, ethanol, propan-1-ol, butan-1-ol, pentan-1-ol) having sufficiently different refractive indices, produced rather reliable thermodynamic data. From these data it was possible to deduce the composition dependence of the change in Gibbs energy of mixing ∆Gmix. These dependences were measured for eleven binary mixtures. A model of alcohol molecules forming linear aggregates which are in equilibrium was developed and used for interpretation of the data. All ∆Gmix data for the eleven mixtures as well as the ∆Hmix data obtained for these mixtures from literature could be interpreted using just two values that characterized the Gibbs energy and enthalpy of the formation of hydrogen bonds. The analysis also yielded plausible results concerning the contact interactions.
Rapid Immunoassay for Pregnenolone Sulfate and Its Applications in Endocrinology
Authors: Hill Martin , Havlíková Helena , Klak Jan , Bičíková Marie , Pouzar Vladimír , Hampl Richard , Stárka Luboslav
Published: July 2002

The importance of pregnenolone sulfate (PregS) in human physiology has increased in the last decade in connection with its neuroactivating effectviapositive modification ofN-methyl-D-aspartate receptors and negative modulation of GABA receptors. Therefore, a novel rapid radioimmunoassay was developed and evaluated for measurement of PregS in body fluids. Given the differences in concentrations of cross-reacting substances in various biological materials, several modifications of the method were elaborated and used. Circulating levels of PregS were measured in serum of normal subjects. In both sexes, the age dependences exhibited maximum values before 30th year of age. For the first time, circulating levels of the hormone were measured in patients with a mixed anxio-depressive disorder, where they significantly exceeded those in controls. Further, the levels of PregS were evaluated in time profiles of women around parturition and compared with those in umbilical blood at delivery. A significantly decreasing time profile of PregS was found in maternal blood. No correlation between maternal and umbilical blood was found indicating its autonomous production in mother and in fetus. In addition, concentrations of PregS were measured in breast cystic fluid where they exceeded those in circulation more than by two orders of magnitude.
Separation and Preconcentration of Platinum Group Metals and Gold on Modified Silica and XAD Sorbents in the Presence of Cationic Surfactants for Their Determination by ICP-AES
Authors: Komendová-Vlašánková Renata , Sommer Lumír
Published: July 2002

Various modified silica sorbents and unmodified silica were tested for the separation and preconcentration of 10-200 ng cm-3from 50-1 000 cm3sample volume of platinum group metals (PGMs), Pt(IV, II), Pd(II), Ir(IV), Rh(III), Os(VI), Ru(IV) and Au(III) in the form of ion associates of their chloro and bromo complexes with cationic surfactants. [1-(Ethoxycarbonyl)pentadecyl]trimethylammonium bromide (Septonex®), benzyl(dodecyl)dimethylammonium bromide (Sterinol®), trimethyl(tetradecyl)ammonium bromide or hexadecyl(trimethyl)ammonium chloride and 0.1 M HCl or 0.1 M HBr are suitable for the purpose. 100% recovery for Pd(II), Pt(IV) and Au(III) was obtained with octadecyl silicas Separon™ SGX C18, Separon™ SGX RPS and Phenyl™ silica in the presence of 0.006 M Septonex® or 0.003 M Sterinol®. The retained PGMs and Au(III) were eluted with acetonitrile and determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) after evaporation of organic solvent in the presence of 0.1 M HCl. The enrichment factor on Separon™ SGX RPS reaches 100. A 1 000 : 1 excess of Cl-, NO3-, SO42-, Na+, K+, Ca2+, Mg2+, Fe3+or Al3+does not interfere with the preconcentration of PGMs and Au(III) on this sorbent. With the silica-based anion exchanger Separon™ SGX AX, the 100% recovery is observed for Ir(IV), Pd(II), Pt(IV) when the elution is performed with 5 M HCl or 5 M HNO3. Macroporous sorbents Amberlite™ XAD2 and Amberlite™ XAD4 are suitable for the retention of Au(III), Pd(II) and Pt(IV) from 0.1 M HCl and 0.006 M Septonex®. 100% recovery is achieved using acetonitrile as eluent but there is no preference of these sorbents to modified silica. In this way, the recovery of 0.1-0.2 μg cm-3Au(III), Pd(II), Pt(IV) was also successfully tested with spiked matrices of soil extracts, power station dust samples and natural waters.
Determinants of bone and blood lead concentrations in the early postpartum period
Authors: Brown Mary Jean , Hu Howard , Gonzales-Cossio Teresa , Peterson Karen E , Sanin Luz-Helena , Kageyama Maria de Luz , Palazuelos Eduardo , Aro Antonio , Schnaas Lourdes , Hernandez-Avila Mauricio
Published: July 2002

OBJECTIVE

This study investigated determinants of bone and blood lead concentrations in 430 lactating Mexican women during the early postpartum period and the contribution of bone lead to blood lead.

METHODS

Maternal venous lead was measured at delivery and postpartum, and bone lead concentrations, measured with in vivo K-xray fluorescence, were measured post partum. Data on environmental exposure, demographic characteristics, and maternal factors related to exposure to lead were collected by questionnaire. Linear regression was used to examine the relations between bone and blood lead, demographics, and environmental exposure variables.

RESULTS

Mean (SD) blood, tibial, and patellar lead concentrations were 9.5 (4.5) μg/dl, 10.2 (10.1) μg Pb/g bone mineral, and 15.2 (15.1) μg Pb/g bone mineral respectively. These values are considerably higher than values for women in the United States. Older age, the cumulative use of lead glazed pottery, and higher proportion of life spent in Mexico City were powerful predictors of higher bone lead concentrations. Use of lead glazed ceramics to cook food in the past week and increased patellar lead concentrations were significant predictors of increased blood lead. Patellar lead concentrations explained one third of the variance accounted for by the final blood lead model. Women in the 90th percentile for patella lead had an untransformed predicted mean blood lead concentration 3.6 μg/dl higher than those in the 10th percentile.

CONCLUSIONS

This study identified the use of lead glazed ceramics as a major source of cumulative exposure to lead, as reflected by bone lead concentrations, as well as current exposure, reflected by blood lead, in Mexico. A higher proportion of life spent in Mexico City, a proxy for exposure to leaded gasoline emissions, was identified as the other major source of cumulative lead exposure. The influence of bone lead on blood lead coupled with the long half life of lead in bone has implications for other populations and suggests that bone stores may pose a threat to women of reproductive age long after exposure has declined.
Estimation of cumulative exposure to organophosphate sheep dips in a study of chronic neurological health effects among United Kingdom sheep dippers
Authors: Buchanan D , Pilkington A , Sewell C , Tannahill S N , Kidd M W , Cherrie B , Hurley J F
Published: July 2002

OBJECTIVES

To derive a method for retrospectively estimating cumulative exposure to organophosphate (OP) pesticides among a cross section of United Kingdom sheep dippers, as part of a wider epidemiological study of neurological abnormality within this group of workers.

METHODS

A hygiene study of dipping sessions at 20 farms using diazinon based dips was carried out by two experienced occupational hygienists. Observations on the exposure of people to concentrate and dilute dip were recorded throughout each dipping session, together with the other relevant factors including the use and condition of protective clothing. Concentrations of urinary metabolites of diazinon were used to measure actual exposure to OPs. To estimate exposure in the subsequent epidemiological study, an occupational exposure history questionnaire was developed using results from the hygiene study and an empirical exposure model.

RESULTS

In the hygiene study, increased urinary metabolites were associated with the handling of concentrate dip and exposure to dilute dip wash through splashing. Very few dippers wore the recommended protective clothing. The handling of concentrate dip was the principal source of exposure to OPs. Dipping task was used as a surrogate for splashing of dilute dip in retrospective exposure estimation. In the epidemiological study, cumulative exposure to OP sheep dips was highly correlated with the total number of dipping days, but not with age.

CONCLUSIONS

Sheep dip concentrate is the most important source of OP exposure among sheep dippers and estimates of exposure to OPs during routine dipping should take due account of exposure to concentrate dip as well as to the dilute dip wash. The observed use of recommended protective clothing by most subjects was insufficient to allow a proper empirical assessment of its effectiveness.
Evaluation of patients admitted with hypoglycaemia to a teaching hospital in Central Anatolia
Authors: Güven M , Bayram F , Güven K , Kelestimur F
Published: July 2002

Hypoglycaemia is one of the most common endocrine emergencies in practice. We analysed retrospectively the incidence and causes of hypoglycaemia in patients admitted to Erciyes University Medical School in Turkey between January 1991 and June 1998 because of hypoglycaemia. Charts were reviewed according to multiple variables including age, sex, blood glucose levels, renal and liver functions, diagnoses, symptoms, drugs, complications, sequelae, and survival status. During this period, 13 500 patients were hospitalised and hypoglycaemia was reported in 126 (0.9%) patients. The most common causes were diabetic treatments in 54 cases (42%), endocrine deficiencies in 25 cases (20%), and malignancy in 15 cases (12%), respectively. The leading endocrine deficiency was panhypopituitarism. Sheehan's syndrome was the most common cause of panhypopituitarism (44%). No underlying cause was diagnosed in seven cases. Nine patients died (7%) and neurological sequelae were observed in one patient with diabetes mellitus. We conclude that hypoglycaemia accounts for about 1% of hospital admissions. Although the hypoglycaemia could be attributed to hypoglycaemic agents in the treatment of diabetes mellitus in the majority of cases, Sheehan's syndrome was also found to be an important cause of hypoglycaemia in our hospital.
Can myasthenia gravis be diagnosed with the ‘ice pack test’? A cautionary note
Authors: Larner Andrew J , Thomas Dafydd J
Published: July 2002

The ice pack test may be helpful in establishing that ptosis is due to ocular myasthenia gravis, since cold improves neuromuscular transmission. However, the role of the test in determining whether diplopia is of myasthenic origin has yet to be established.