bluuebunny/crossref_metadata_2025 huggingface dataset:
Photochemistry of α-halocycloalkanones and α,α-dihalocycloalkanones. Ionic and radical photochemical carbon-halogen bond cleavage
Authors: Šket Boris , Zupan Marko
Published: June 2010

The nature of the photochemical carbon-halogen bond cleavage in α-halo cycloalkanones depends on the halogen atom bonded and on the ring size of the cycloalkanone. In the 2-halo-1-indanone series the amount of radical products increased from iodine to chlorine, while in the case of 2-halo-3,4-dihydro-1(2H)-naphthalenone 43% for iodo, 32% for bromo, and 53% for the chloro derivative were found. On the other hand, photochemical carbon-chlorine bond cleavage in 2,2-dichloro-1-indanone led to only radical products, while the formation of both radical and ionic products in the ratio 1 : 1 was observed in the case of 2,2-dibromo-1-indanone. In the 2,2-dihalo-3,4-dihydro-1(2H)-naphthalenone series, the ratio of the radical to ionic products formed strongly depended on the halogen atom bonded: preferential formation of the radical product in the case of the chloro derivative (92%), in contrast to 94% of the ionic products in the case of the bromo derivative, was observed.
6-Amino-6-deoxyhexonolactams
Authors: Kefurt Karel , Kefurtová Zdeňka , Jarý Jiří
Published: June 2010

6-Azido-6-deoxy-D-mannose (III), prepared from methyl 4,6-O-benzylidene-α-D-mannopyranoside, 6-azido-6-deoxy-D-talose (XI), prepared from methyl 6-azido-2,3-O-isopropylidene-α-D-mannopyranoside (VII) via 4-keto derivative VIII, and 6-azido-6-deoxy-L-idose (XVIII), obtained from 5,6-anhydro-1,2-O-isopropylidene-β-L-idofuranose, on oxidation with bromine and subsequent reduction of the azido group afforded the corresponding 6-amino-6-deoxyhexonolactams V, XV, and XXI. 6-Amino-6-deoxyhexonic acids IV and XIV were also prepared.
Experimental antiulcer agents: N-substituted 2-(4-methyl-1-piperazinyl)acetamides as pirenzepine models and some related compounds
Authors: Hulinská Hana , Polívka Zdeněk , Jílek Jiří , Šindelář Karel , Holubek Jiří , Svátek Emil , Matoušová Oluše , Buděšínský Miloš , Frycová Hana , Protiva Miroslav
Published: June 2010

Reactions of N-cyclohexyl-2-chloroacetamide, N-phenyl-2-chloroacetamide, N-(4-dimethylaminophenyl)-2-chloroacetamide, N-(2-nitrophenyl)-N-phenyl-2-chloroacetamide, its 3-nitrophenyl and 4-nitrophenyl analogues, N-(2-benzylphenyl)-2-chloroacetamide, 5-(chloroacetyl)-dibenz[b,f]azepine, and its 10,11-dihydro derivative with piperazine, 1-methylpiperazine, 2-(1-piperazinyl)ethanol, and 3-(1-piperazinyl)propanol resulted in compounds II, III, V-XV, XVIII, XXI, and XXIII, simple analogues of the antiulcer agent pirenzepine (I). Contributions to the syntheses and characterization of mianserin (XIX), bisnor analogue of imipramine (XXV), and pirenzepine (I) are presented. Two 2-aryl-2-(2-pyridyl)thioacetamides XXXVIII and XL were synthesized via nitriles XXXIX and XLI. Compounds XI (VÚFB-17 104) and XXI (VÚFB-17 113) were found to be rather effective as antiulcer agents and anticholinergics.
Bloch and Wannier functions in momentum space
Authors: Calais Jean-Louis
Published: June 2010

Direct calculations of wave functions in momentum space require a study of the formal properties of such functions. Here we discuss the momentum space counterparts of Bloch and Wannier functions, both in general and for two extreme kinds of basis set expansions: plane waves and atomic orbitals.
Rearrangement reactions in the barbaralyl cation
Authors: Jørgensen Karl Anker , Linderberg Jan , Swanstrøm Peter
Published: June 2010

Hyperspherical coordinates are used to define reaction paths for rearrangements of the C9H9+ barbaralyl cation and energy profiles are obtained from Gaussian 82 calculations using an STO-3G basis. A formula for the reaction rate is derived from the current autocorrelation function in the WKB approximation.
Quantum chemical topological study of interaction of carbon monoxide on the Pd (112) surface
Authors: Pancíř Jiří , Haslingerová Ivana , Nachtigall Petr
Published: June 2010

Interaction of carbon monoxide with a stepped (112) Pd surface has been studied by a quantum chemical topological method. The adsorption of CO takes place preferentially in 5-fold hollow bound configurations i.e. on sites associated with steps. In all cases studied the bonding of CO molecule by carbon is energetically more favorable than that by oxygen. The dissociation of CO between neighbor 5-fold hollow positions can take place but is energetically less favorable than the nondissociative chemisorption on the same positions.
Sulfenic acids in the gas phase. Preparation, ionization energies and heats of formation of methane-, ethene-, and benzenesulfenic acid
Authors: Tureček František , Brabec Libor , Vondrák Tomáš , Hanuš Vladimír , Hájíček Josef , Havlas Zdeněk
Published: June 2010

Methane-, ethene-, and ethynesulfenic acids were generated in the gas phase by flash-vacuum pyrolysis of the corresponding tert-butyl sulfoxides at 400 °C and 10-4 Pa. Benzenesulfenic acid was prepared from phenyl 3-buten-1-yl sulfoxide at 350 °C and 10-4 Pa. The sulfenic acids were characterized by mass spectrometry Threshold ionization energies (IE) were measured as IE(CH3SOH) = 9·07 ± 0·03 eV, IE(CH2=CHSOH) = 8·70 ± 0·03 eV, IE(HCCSOH) = 8·86 ± 0·04 eV, and IE(C6H5SOH) = 8·45 + 0·03 eV. Radical cations [CH3SOH].+, [CH2=CHSOH].+, and [HCCSOH].+ were generated by electron-impact-induced loss of propene from the corresponding propyl sulfoxides and their heats of formation were assessed by appearance energy measurements as 685, 824, and 927 kJ mol-1, respectively. Heats of formation of the neutral sulfenic acids and the S-(O) (C), S-(O) (Cd), S-(O) (Ct) and S-(O) (CB) group equivalents were determined. The experimental data, supported by MNDO calculations, point to sulfenate-like structures (R-S-OH) for the sulfenic acids under study.
Effect of electron correlation on SN2 activation barriers. Fourth-order MBPT calculations
Authors: Černušák Ivan , Urban Miroslav
Published: June 2010

The activation barriers for a series of model gas-phase nucleophilic displacement reactions have been calculated at the MBPT(4)/DZ + P + D level. Electron correlation significantly reduces the barrier height, in most cases by about 50%. The role of individual contributions up to the fourth order MBPT is analyzed in detail showing the vital importance of single and triple excitations.
Composite natural orbitals for configuration interaction method
Authors: Yamamoto Yuichi , Noro Takeshi , Ohno Kimio
Published: June 2010

A new method of constructing approximate natural orbitals (NO's) is proposed. A system can usually be regarded as consisting of fragments. The approximate NO's of the entire system are constructed from the NO's of fragments in their ground states. These orbitals are expected to be useful in configuration interaction (CI) calculations of a large system where orbital truncation is necessary. The usefulness of these approximate NO's, which are called composite NO's (CNO's), is demonstrated on C4H6. This molecule may be regarded as a combination of two fragments i.e., C2H4's. Excitation energies calculated by single and double excitation CI with the truncated CNO's (14σ, 7π correlating orbitals) agree reasonably well with those calculated with a full orbital set (37σ, 12π correlating orbitals), while the truncated SCFMO's of the same size give disastrous excitation energies.
The origin of Rydberg orbitals
Authors: Janoschek Rudolf
Published: June 2010

The concept of hybridization and the principle of maximum overlap are invoked to explain the origin of the Rydberg character of the lowest excited MO of LiH. It is found that the nodal surface of this antibonding MO is not bisecting the bond. The origin of the Rydberg character of the lowest singlet and triplet MO's of the H2 molecule is studied by means of an energy partitioning. The repulsion of electrons is found to be responsible for the diffuse character of the excited so-called antibonding MO's. The singlet-triplet separation is controlled to a large extent by one-electron contributions.
Intrinsic energy of partial structure
Authors: Sakurai Katsunori , Nishimoto Kichisuke
Published: June 2010

A modified model Hamiltonian has been proposed for the analysis of a given partial structure in the molecule. With this Hamiltonian, some interesting mirror image relationships have been derived. The calculated results for the intrinsic energies of hexagons (Benzene Character) in hydrocarbons showed that the stability of hexagon is well correlated with the number of Kekule structures.
Assessment of atoms-in-molecules approaches to the diatomic input data generation for the diatomics-in-molecules method
Authors: Polák Rudolf , Vojtík Jan
Published: June 2010

Various versions of the atoms-in-molecules method as a source for diatomic input data, and various approaches of the diatomics-in-molecules method are applied to calculate three lowest valence states of the NH radical. By comparing the results among themselves and with other presently available accurate data, conclusions are drawn concerning the reliability of individual solutions. Also, possible causes for inadequacy of diatomics-in-molecules models are discussed.
Conformational analysis by infrared linear dichroism of solutes in stretched polyethylene: The twist angle in biphenyl and 4,4'-dibromobiphenyl
Authors: Murthy Parvathi S. , Michl Josef
Published: June 2010

A method is proposed for using the IR linear dichroism of molecules embedded in stretched polyethylene and containing two weakly coupled symmetry-related subunits for the determination of the spatial relationship of the subunits. The procedure requires an IR LD measurement on the parent and on an isotopomer in which the equivalence of the subunits has been removed by isotopic substitution, without affecting the molecular shape or the orientation factors. The method has been tested on biphenyl, found to be planar, and 4,4'-dibromobiphenyl, found to be nearly orthogonally twisted in stretched polyethylene. Possible implications for the orientation mechanism are discussed briefly.
Model study of supported bimetallic catalysts
Authors: Knor Zlatko , Šotola Jan
Published: June 2010

Oxidized surface of a tungsten sample has been used as a carrier for palladium and/or molybdenum clusters, prepared by vacuum deposition. Field electron emission microscopy has been applied to study these sandwich systems (Pd, Mo/WOx/W). In this work, nitrogen spill-over between neighbouring molybdenum and palladium clusters (islands) was demonstrated. The crystallographic orientation of these clusters has been studied by field ion microscopy.
Alternating reactivity of free radicals coordinated to chelated transition metals and to hemoproteins
Authors: Tkáč Alexander
Published: June 2010

The mean lifetime of free radicals increases by coordination to transition metals of chelates including hemoproteins (hemoglobin, cytochrome c, catalase), when the radical generation proceeds in non-polar media in temperature range of physiological ones (290-310 K). In polar media (water, methyl- or ethylalcohol, pyridine), or in the presence of effective ligating agents (e.g. bases of nucleic acids), or at slightly elevated temperatures the intermediately stabilized oxygen centred radicals are liberated from the complex and the original high reactivity of the free radical is renewed. It is assumed that in this way sterically unhindered free radicals derived from chemical carcinogens with alternating reactivity could be transported through the microheterogeneous cell matrix.
An alternative route to Nα-methylamino acid derivatives: Synthesis and conformation of some Nα-acetyl-Nα-methylamino acid methylamides
Authors: Hlaváček Jan , Frič Ivo , Buděšínský Miloš , Bláha Karel
Published: June 2010

The methylation of tert-butyl- or isopropyl- esters of Nα-4-toluenesulfonyl-amino acids by dimethylsulfate in aqueous alkaline solution in the presence of a detergent gives the corresponding Nα-methylderivatives. Using this synthetic route the Nα-acetylderivatives of MeAla, MeLeu, MeOrn and MePhe methylamides have been prepared and the solution conformation of these dipeptide units has been investigated. 1H and 13C NMR spectra show that, while in dimethylsulfoxide the tertiary amide group is mostly in cis-conformation, in protic solvents the equilibrium is shifted towards trans-conformation. Circular dichroism spectra reveal some specific features (e.g. high band intensities in protic solvents) which cannot be explained solely on the basis of the increased rigidity caused by the Nα-methyl group. We tried to explain these effects supposing that the tertiary amide group is deviated from the planar arrangement (due to the interaction between the methyl groups, a substituent on Cα and a solvent molecule attached to the oxygen atom) and contributes to the observed circular dichroism as the inherently chiral chromophore.
Conformational analysis of the pyrrolidine ring of the N-methylthiohydantoin of 2-methylproline
Authors: Sleeckx Jef J. M. , Anteunis Marc J. O. , Borremans Frans A. M.
Published: June 2010

The conformational analysis of the pyrrolidine ring in 2-methylproline-N-methylthiohydantoin was achieved from the vicinal proton spin-spin coupling constants obtained from the 360 MHz 1H NMR spectrum in hexadeuterobenzene solution. Two descriptions are consistent with the experimental data. One is a large amplitude torsional oscillation centered between a β-endo envelope (C8) and a β-endo-α-exo twist (C2). The other is a 3 : 1 dynamic equilibrium between two fixed states: a (major) β-exo envelope and a minor N-endo envelope with N-endo-δ-exo twist character. The effect of the 2-methyl group on the pyrrolidine ring conformation is evaluated and discussed.
Partially modified retro-inverso enkephalin analogues containing Gly3Ψ(NH-CO)Phe4 modification, Configurational lability
Authors: Chorev Michael , Gilon Noemy , Roubini Eli , Ackerman Elizabeth , Levian-Teitelbaum Dina , Rosin Marta
Published: June 2010

Two partially modified retro-inverso analogues of Leu-enkephalin in which the peptide bond between Gly3-Phe4 was reversed resulted from the incorporation of the Gly3ψ(NH-CO)Phe4 unit. The presence of racemic 2-benzylmalonyl residue led to diastereomeric mixtures of analogues; H-Tyr-D-Ala-gGly-(RS)-mPhe-Leu-NH2 (I) and H-Tyr-Gly-gGly-(RS)-mPhe-Leu-NH2 (II). Analogue I was more potent than analogue II in the binding assay, induced guinea pig ileum assay as well as in antinociceptive tests. Both activities were naloxone reversible. No analgesia was observed after subcutaneous (SC) administration of 100 mg/kg of either I or II. The problems related to configurational lability of the 2-alkylmalonyl residues in partially modified retro-inverso analogues is addressed.
Simultaneous synthesis of sequence-unrelated peptides derived from proteins of human papillomaviruses
Authors: Krchňák Viktor , Vágner Josef , Hirsch Ivan
Published: June 2010

Amino acid sequences derived from the early (E) and late (L) coding regions of human papillomaviruses (HPV) type 6, 11, and 16 were analysed by means of a computer program for prediction of B-cell determinants. Eight peptides ranging from 9 to 17 amino acids and containing potential B-cell determinants were selected for synthesis. The peptides were synthesized by using a configuration for solid-phase synthesis that enables the simultaneous synthesis of several peptides in flow reactors at low pressure on standard poly(styrene-1% divinylbenzene)resin. Crude peptides were obtained in good yield and purity. They were then further purified by high-performance liquid chromatography for use as solid antigens in site-directed serology.
Cooperative effect of NH bond orientation and triamine six-membered chelate ring rigidity in stereospecific formation of exo-((1,6-diamine-3-azahexane)-(S)-aspartato)cobalt(III) isomers
Authors: Jursík František , Ondráčková Jana
Published: June 2010

Of the six isomers possible, only exo-sym-fac(S), exo-unsym1-fac(S) and exo-Δ-unsym2-fac(R)-[Co(1,6-dah)(S)-Asp]+ (1,6-dah = 1,6-diamine-3-azahexane) isomers were prepared and characterized by electronic absorption and circular dichroism spectra. Isomers formation is stereospecific due to the linear triamine NH bond orientation which causes that of the three sites in mer(R or S)-[Co(1,6-dah)(H2O)3]3+ intermediates, only two are available for initial coordination of aspartic acid as bidentate ligand. In addition to this, 1,6-dah six-membered chelate ring precludes the necessary movement of the five-membered chelate ring backbone so that the linear triamine isomerization is stereospecific. Any mer→ fac intramolecular rearrangement involves the six-membered chelate ring part of 1,6-dah. Stereospecificity is also controlled by the aspartic acid chirality.
Transition-metal catalysis in Michael addition of β-dicarbonyls: Tuning of the reaction conditions
Authors: Kočovský Pavel , Dvořák Dalimil
Published: June 2010

(2,4-Pentanedionato)copper(I), bis(2,4-pentanedionato)copper(II), and tris(2,4-pentadionato)iron(III) together with boron trifluoride etherate catalyze Michael addition of β-dicarbonyls V and VI to 2-cyclohexen-1-one (IV), 2-cyclopenten-1-one (IX), 2-methyl-2-cyclopenten-1-one (X), and 3-thienylidenemalonaldehyde (XIX).
Synthesis of stereoisomeric vincamines
Authors: Koblicová Zdena , Holubek Jiří , Trojánek Jan
Published: June 2010

The synthesis of (±)-vincamine (I), (±)-16-epi-vincamine (XVIII) and (±)-16-epi-21-epi-vincamine (XVII) from 1-ethyl-2,3,4,6,7,12-hexahydroindolo[2,3-a]quinolizine (IV) and 2-chloroacrylonitrile is described. It is characterized by a novel method of oxidation of the key intermediates, (±)-deoxyvincamine (II) and (±)-16-epi-21-epi-deoxyvincamine (XIII) with oxodiperoxymolybdenum (pyridine) (hexamethylphosphoric triamide). The deoxy derivatives II and XIII were prepared by direct or stepwise acid or alkaline hydrolysis of stereoisomeric (±)-eburnane-16-carbonitriles IX-XII, obtained by reduction of the primary imonium salt V, and subsequent esterification. In some cases, the hydrolysis is accompanied by epimerization at C(16).
Phosphonylmethoxyalkyl and phosphonylalkyl derivatives of adenine
Authors: Rosenberg Ivan , Holý Antonín , Masojídková Milena
Published: June 2010

Analogues of the antivirals (2S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine (Ia) and 9-(2-phosphonylmethoxyethyl)adenine (Ib), modified in the alkyl chain, are described. The phosphonylmethoxyalkyl derivatives were prepared by condensation of sodium alkoxides of hydroxyalkyladenines (or their N-protected derivatives) with dimethyl p-toluenesulfonyloxymethanephosphonate (II) followed by alkaline hydrolysis and reactions with halotrimethylsilane, or by reaction of vicinal dihydroxyalkyl derivatives with chloromethanephosphonyl dichloride (XIV) and subsequent cyclization of the intermediates XV in aqueous alkali. In the second case the pure regioisomers were also obtained from substituted dihydroxy derivatives with one free hydroxyl group. The following compounds were prepared in this way: 3-O-methyl ether IIIc and 3-O-octyl ether IVc, 9-(3-phosphonylmethoxypropyl)- (Vc), 9-(4-phosphonylmethoxybutyl)- (Vf), 9-(5-phosphonylmethoxypentyl)- (Vi), 9-(2-phosphonylmethoxypropyl)- (VIc), 9-(1-phosphonylmethoxy-3-hydroxy-2-propyl)- (XIIc), 9-(2-methoxy-3-phosphonylmethoxypropyl)- (XIIIc), erythro-9-(2-phosphonylmethoxy-3,4-dihydroxybutyl)- (VIIc) and threo-9-(4-phosphonylmethoxy-2,3-dihydroxybutyl)adenine (IXc) and its enantiomer (Xc). 9-(2-Phosphonylmethoxy-3,3-dihydroxypropyl)adenine (VIII) was obtained by oxidation of VIIc with sodium periodate, 9-(2-phosphonylmethoxyethoxymethyl)adenine (XIc) by reaction of II with sodium salt of 9-(2-hydroxyethoxymethyl)adenine (XIa). 9-(1,2-Dihydroxy-2-methyl-3-propyl)adenine 1- and 2-phosphonylmethyl ether (XVIb), 9-(3,4-dihydroxybutyl)adenine 3- and 4-phosphonylmethyl ether (XVIIb) and 9-(2,3-dihydroxybutyl)adenine 2- and 3-phosphonylmethyl ether (XVIIIb) were prepared by reaction with chloromethanephosphonyl dichloride (XIV) followed by alkaline treatment. Analogous reaction was also employed in the preparation of regioisomerically pure 1-phosphonylmethyl ethers of 9-(1,2-dihydroxy-3-butyl)adenine (XXIV), 9-(1,2-dihydroxy-2-methyl-3-propyl)adenine (XVIb) and 9-(1,2-dihydroxy-3-nonyl)adenine (XXV). Alkylation of adenine with diethyl chloromethoxymethanephosphonate (XXVII) followed by hydrolysis afforded 9-(phosphonylmethoxymethyl)adenine (XXVIIIb). 9-(Phosphonylmethyl)adenine (XLI) was obtained by condensation of adenine with compound II. Conversion of 9-(ω-hydroxyalkyl)adenines into the ω-halogenoalkyl derivatives followed by reaction with trialkyl phosphite and cleavage was used in the preparation of 9-(2-phosphonylethyl)adenine (XXXIVa), 9-(4-phosphonylbutyl)adenine (XXXIVb) and 9-(2-phosphonylethoxymethyl)adenine (XXXIX). 9-(2-Phosphonyl-2-hydroxyethyl)adenine (Lc) and 9-(3-phosphonyl-3-hydroxypropyl)adenine (Lb) were synthesized by treatment of ω-(adenin-9-yl)alkanals with dialkyl phosphite and subsequent cleavage with halogenotrimethylsilane; the same procedure converted 9-(2-oxopropyl)adenine (XLVIIIa) into 9-(2-phosphonyl-2-hydroxypropyl)adenine (La).
Synthesis and use of benzyl tert-butyl iminodicarbonate, a versatile reagent for the preparation of amines
Authors: Grehn Leif , Ragnarsson Ulf
Published: June 2010

An efficient synthesis of benzyl tert-butyl iminodicarbonate (IV), starting from benzoyl isocyanate, is reported. Reaction of the isocyanate with benzyl alcohol gave benzyl N-benzoylcarbamate (II) which on exhaustive tert-butoxycarbonylation via the non-isolated triacyl amine III, after aminolysis, provided the title compound. The sodium salt V was alkylated with various halides under Gabriel conditions to give in high yields the corresponding benzyloxycarbonyl tert-butoxycarbonyl diprotected amines. Similarly, compound IV was alkylated with alcohols under Mitsunobu conditions to give some additional amines of this type, from which the protecting groups can be removed selectively under mild conditions.
Salt bridges in model peptides
Authors: Sekacis Ilmars , Shenderovich Mark , Nikiforovich Gregory , Liepinš Edvards , Polevaya Ludmila , Chipens Gunars
Published: June 2010

A group of synthetic peptides including Boc-Lys-Phe-X-Y, X = Ala (I, III) or Thr (II), Y = Pro (I, II) or Ala (III) was studied by means of 1H NMR spectroscopy and theoretical conformational analysis. Compound I in DMSO shows two conformers with the trans- and cis-configuration of the peptide bond Ala-Pro. The salt bridge between the Lys ε-amino group and the C-terminal carboxyl is featured by magnetic nonequivalence of the Lys CεH2 protons. The space structure of I and II was found to possess a salt bridge fixed by an unusual turn in the chain formed by the Lys side chain and the C-terminal dipeptide with the trans-peptide bond X-Pro. Since a stable ionic bond in III and in the cis-conformer of I has not been observed, its contribution to stabilization of the space structure of the peptides in DMSO appears rather small.
Complexation of poly(Lys-Ala) and poly(Lys-Ala-Ala-Ala) with pectins and potassium oligogalacturonates
Authors: Bystrický Slavomír , Malovíková Anna , Sticzay Tibor , Bláha Karel
Published: June 2010

The selected model polypeptides poly(Lys-Ala) and poly(Lys-Ala-Ala-Ala) underwent a helix-forming interaction with potassium pectates and pectinates of various esterification degree (E) and with some potassium oligogalacturonates (n = 2-5, 9, 13). Formation of the complex quantitatively monitored by a circular dichroic measurement showed that the specific band distribution of charged side chains of lysine units at the surface of helical structure does not constitute grounds for the local mode of interaction. Potassium pectinate of esterification degree E 57%, corresponding to polypeptides by charge density, does not reveal enhanced complexation values. The complex-forming efficacy continuously decreases with the increase of the esterification degree of pectin. Saturation of charges of the polypeptide was achieved predominantly by the spatial action of the superhelical structure of D-galacturonate chains.
An efficient synthesis of δ-(L-α-aminoadipyl)-L-seryl-D-valine (LLD ASV), a naturally occuring tripeptide from the fermentation of Penicillium chrysogenum
Authors: Liberek Bogdan , Kasprzykowska Regina
Published: June 2010

The synthesis of δ-(L-α-aminoadipyl)-L-seryl-D-valine (LLD ASV), a naturally occuring congener of the well known tripeptide δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine (LLD ACV) which is the linear precursor of isopenicillin N, penicillin N, cephalosporin C is described. An efficient method for producing the requisite α-monobenzyl ester of N-benzyloxycarbonyl-L-homoglutamic acid for subsequent condesation at the side chain δ-carboxy group is presented.
New adsorbents for thymidylate synthase affinity chromatography
Authors: Pawełczak Krzysztof , Krzyżanowski Leszek , Rzeszotarska Barbara , Kempny Michał , Wieczorek Piotr , Ciesla Joanna , Rode Wojciech
Published: June 2010

New affinity adsorbents, intended for chromatography of thymidylate synthase (EC 2.1.1.45) from different sources, consisting of p-[N-[(2-amino-4-hydroxy-6-quinazolinyl)-methyl]-N-2-propynylamino]benzoyl-γ-[α-(3-carboxypropylamino)]glutamyl-glutamyl immobilized either on macroporous copolymer of acrylonitrile and n-butyl acrylate or on macroporous polymer of acrylonitrile itself, both crosslinked with divinylbenzene and having aminoethyl groups, were obtained. Both adsorbents were found to be effective in dUMP-dependent binding of thymidylate synthase from regenerating rat liver.
Muramyl-dipeptide analogues: Synthesis and biological activities
Authors: Ježek Jan , Zaoral Milan , Buděšínský Miloš , Günther Jiří , Rotta Jiří
Published: June 2010

In the search for immunoadjuvant active compounds without pyrogenic activity we prepared N-Ac-norMur-L-Abu-D-Gln-O-Bu (V), N-Ac-Mur-L-Abu-D-Gln-O-Bu (VII) and their respective α-benzylglycosides VI and VIII. All the prepared compounds are nonpyrogenic. In the delayed hypersensitivity test, compound V is inactive, VI is comparable to MDP, VII is more and VIII is less active than MDP.
Synthesis, biological activity and receptor binding affinity of two [8-arginine]vasopressin analogues with inhibitory properties
Authors: Kasprzykowski Franciszek , Grzonka Zbigniew , Slaninová Jiřina , Barth Tomislav , Crause Peter , Fahrenholz Falk
Published: June 2010

Two analogues of arginine-vasopressin: [1-(β-mercapto-β,β-cyclopentamethylenepropionic acid), 2-D-phenylalanine, 7-sarcosine, 8-arginine]vasopressin and [1-(β-mercapto-β,β-cyclopentamethylenepropionic acid), 2-D-phenylalanine, 7-N-methylalanine, 8-arginine]vasopressin were synthesized by solid-phase peptide synthesis method. Both peptides exhibit antioxytocic, antivasopressor and antiglycogenolytic activities, and on the other hand they are weak antidiuretic agonists. The binding affinities of both analogues to oxytocic receptor (guinea pig myometrium membranes) and to hepatic V1 receptor (rat liver membranes) are practically the same as for the parent hormones, whereas the binding affinities to renal V2 receptor (bovine kidney membranes) are 60-90 times lower than for vasopressin.
Synthesis of [3H-TyrB26]-human insulin by enzymic semisynthesis
Authors: Hänsicke André , Beyermann Michael , Oehlke Johannes , Mittag Erhard , Kertscher Uwe , Bespalova Zhanna D. , Titov Mikhail I. , Bienert Michael , Kaufmann Klaus-Dieter , Niedrich Hartmut
Published: June 2010

A procedure is described for tritium labeling of human insulin in position TyrB26 by means of trypsin catalyzed condensation of DiBoc-DOI with [Nε-Boc, 3H-TyrB26]-IOP, subsequent deprotection and purification by HPLC. The tritium labeling of the octapeptide was accomplished by dehalotritiation of the corresponding DitB26-octapeptide which was obtained both by iodination of Nε-Boc-IOP and by total synthesis.
Synthesis of hepatitis B surface antigen pre-S2 region fragments and studies on their immunogenicity
Authors: Lammek Bernard , Maćkiewicz Zbigniew , Derdowska Izabela , Świderska Hanna , Nowosławski Adam , Kupryszewski Gotfryd
Published: June 2010

Two peptide fragments of hepatitis B surface antigen pre-S2 region were synthesized by the solid phase method. The peptides were purified by gel filtration or ion-exchange chromatography on Sephadex SP-C-25. Both peptides induced a cellular and humoral immune response in rabbits. The results showed that fragment 14-22 of pre-S2 region contains one of the antigenic determinants.
MNDO study of the E-Z isomerization mechanism of H2C=NR molecules (R = H, CH3, NH2, OH, F)
Authors: Ertl Peter
Published: June 2010

The geometry and E-Z isomerization mechanism were studied by the MNDO method for H2C=NR molecules with R = H, CH3, NH2, OH and F. All the molecules save H2C=NNH2 possess a plane of symmetry and isomerize by the inversion mechanism, whereas H2C=NNH2 has a nonsymmetrical geometry and the inversion-rotation mechanism is more favourable for its isomerization. Dependent considerably on the substituent at the nitrogen atom, the isomerization barrier height increases in order R = CH3, H, NH2, OH, F.
Extraction-photometric determination of indium with 8-quinolinol in layered crystals of the type A2VB3VI
Authors: Šrámková Jitka , Kotrlý Stanislav , Kalischová Yvona
Published: June 2010

A method for determining indium in milligram samples of indium-doped crystals of bismuth telluride is described. The pH effect of the aqueous phase (Vaq = 40 ml) on the extraction yield is examined, also by considering the results computed with the data so far published. In a single extraction at pH 3·6-4·2 (acetate buffer) the tris(8-quinolinolato)indium(III) chelate is quantitatively transferred to the chloroform phase (Vorg = 10 ml). Bismuth present in excess is masked with thiosulfate. The absorbance of the chloroform extract is measured at 400 nm in a glass cell of 10-mm path-length (or in a 50-mm cell when m(In) < 20 μg). A blank extraction is carried out simultaneously with the use of a solution of pure Bi2Te3 and taken as reference. The calibration within the range of 10 - 130 μg of In(III) is performed by adding a standard indium(III) solution to the matrix solution obtained by dissolving pure Bi2Te3. The accuracy of the method has been checked by analysis of polycrystalline reference materials of known composition. The method is applicable for the analysis of milligram samples containing 0·6 - 5% of indium, with a relative standard deviation of 1 - 4%.
The simultaneous determination of Fe(III) and Cu(II) in the presence of Zn(II) using 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol
Authors: Buršík Vladimír , Kubáň Vlastimil , Sommer Lumír
Published: June 2010

Spectrophotometric methods were employed to study the chelate formation between Fe(III) ions and 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol (BrPADAP) in dimethylformamide (φ = 20%) and Triton X-100 (φ = 0·1%). The ML2 chelate with absorption maxima at 535 and 590 nm and molar absorption coefficients of 6·5 and 8·2 m2 mmol-1 is formed quantitatively in the pH interval 3·5 - 4·0 for at least a seven-fold concentration excess of BrPADAP. Concentrations of c(Fe) = 1·6 - 8·1 μmol l-1 can be determined independently in 0·1M acetate buffer with pH 3·6. Iron and copper ions can be determined simultaneously in the presence of zinc ions in binary or ternary mixtures in the concentration ranges c(Fe) = 2 - 8 μmol l-1 and c(Cu) = c(Zn) = 3 - 16 μmol l-1. The relative deviations in the calculated concentrations, Δcr, are 1 - 4% for Fe and up to 5% for Cu in binary and ternary mixtures with equivalent concentrations up to a concentration excess of one component of five-fold in binary mixtures or of one or two components of up to three-fold in ternary mixtures. The simultaneous determination of Zn(II) is accompanied by a Δcr value of up to 30 - 50% and cannot be recommended under the given experimental conditions.
Heat capacities and enthalpies of fusion and transformation for solvates of some salts with dimethyl sulfoxide and dimethylformamide
Authors: Skokánek Mojmír , Sláma Ivo
Published: June 2010

Molar heat capacities and molar enthalpies of fusion of the solvates Zn(NO3)2 . 2·24 DMSO, Zn(NO3)2 . 8·11 DMSO, Zn(NO3)2 . 6 DMSO, NaNO3 . 2·85 DMSO, and AgNO3 . DMF, where DMSO is dimethyl sulfoxide and DMF is dimethylformamide, have been determined over the temperature range 240 to 400 K. Endothermic peaks found for the zinc nitrate solvates below the liquidus temperature have been ascribed to solid phase transformations. The molar enthalpies of the solid phase transformations are close to 5 kJ mol-1 for all zinc nitrate solvates investigated. The dependence of the molar heat capacity on the temperature outside the phase transformation region can be described by a linear equation for both the solid and liquid phases.
Conformational structure of poly[2-(dimethylamino)ethyl methacrylate], 2-(dimethylamino)ethyl pivalate and of their quaternary iodides. Vibrational and NMR spectra
Authors: Schneider Bohdan , Štokr Jan , Straka Jaroslav , Přádný Martin , Ševčík Stanislav
Published: June 2010

Raman, infrared, and 1H and 13C NMR spectra of 2-(dimethylamino)ethyl pivalate, 2-(pivaloyloxy)ethyltrimethylammonium iodide, poly[2-(dimethylamino)ethyl methacrylate] and of its quaternary iodide were measured. Spectral analysis revealed that in crystalline 2-(dimethylamino)ethyl pivalate and in its quaternary salt, the 2-(dimethylamino)ethyl group exists in the g conformational state. In the liquid state, these compounds also contain a smaller amount of the t conformational structure of the 2-(dimethylamino)ethyl group. In poly[2-(dimethylamino)ethyl methacrylate] and in its quaternary iodide in solution, the population of the g and t conformational structures are similar to those found in 2-(dimethylamino)ethyl pivalate and in its quaternary iodide.
A graph model of the synthon
Authors: Koča Jaroslav
Published: June 2010

A graph model of the synthon (SR-graph) is devised and a procedure for the construction of the minimal graphs of reactions of synthons (SR-graphs) is suggested. Chemical examples illustrating the application of this model are given.
Use of Nafion membranes in laboratory organic electrosynthesis
Authors: Hlavatý Jaromír , Volke Jiří
Published: June 2010

Electrolysis of quaternary ammonium bromides and iodides in a divided cell with a Nafion membrane yields quaternary polyhalogenides at a carbon anode in water-ethanolic anolytes. The electrodialysis of tetrabutylammonium iodide in a cell with a Nafion membrane enables generation of tetrabutylammonium hydroxide. In electrolytic reduction of nitrobenzene in presence of 1,3-dibromopropane, N-phenylisooxazolidine results in an approx. 60% yield. This electrosynthesis takes place in dimethylformamide with tetrabutylammonium bromide at a glassy-carbon cathode in a divided cell. In the electroreduction of lobelanine hydrogensulfate in a divided cell in acid water-ethanolic media at a lead cathode prevalently lobelanidine has been obtained.
An unusually selective photo-induced rearrangement of 4-alkoxycarbonyl-5-formyl-2,3-dihydro-6H-1,3-oxazines. A new route to preparation of condensed lactones
Authors: Oremus Vladimír , Fišera Lubor , Timpe Hans-Joachim , Lammel Ute
Published: June 2010

3-R-Alkoxycarbonyl-5-formyl-2,3-dihydro-6H-1,3-oxazines IIa-IIc (R = methyl, ethyl, isopropyl) as primary photoproducts formed by a rearrangement of 3-R-alkoxycarbonyl-3a,4,6,6a-tetrahydrofuro[3,4-d]isoxazoles Ia-Ic undergo cyclization to bicyclic lactones IIIa-IIIc due to further irradiation. The photochemical transformation of compounds II into III constitutes a new kind of photo-induced rearrangement. The quantum yields are very little dependent on the presence of oxygen and polarity of the solvent. The proposed concerted mechanism of the photorearrangement is discussed.
Synthesis of fagaronine
Authors: Šmidrkal Jan
Published: June 2010

Alkaloids fagaronine (I), dihydrofagaronine (XXV) and oxyfagaronine (XXVI) were synthesized from 2,3-dihydroxynaphthalene (II) and 2-bromo-4,5-dimethoxybenzaldehyde (XI), the key synthetic steps being the preparation of 2-hydroxy-3-methoxy-5-nitronaphthalene (VI) by partial methylation of 2,3-dihydroxy-5-nitronaphthalene (V) and formation of benzo[c]phenanthridone XXI by photocyclization of amide XVI.
Special kinetic models of selection processes in biomacromolecular systems
Authors: Kvasnička Vladimír
Published: June 2010

Physico-chemical models of selection processes on biomacromolecules - replicators are investigated. Three special cases are considered: 1) Replicators are selfreproduced with mutations, 2) selection process involving two or more substrates, and 3) selection process is controlled by external positive inflows of replicators. Simple tools of qualitative theory of differential equations are used, in particular the so-called linearization method based on the eigenvalues of Jacobi matrix evaluated at the given stationary state.
Abnormal liver function tests in the parenteral nutrition fed patient
Authors: Gabe S M , Culkin A
Published: June 2010

Liver dysfunction is common in individuals receiving parenteral nutrition (PN) and particularly in neonates and infants. Abnormalities of liver function tests in patients receiving short term PN are usually transient but in individuals receiving long term PN, substantial liver damage and ultimately end stage liver disease may occur. The aetiology is complex, involving a large number of patient related and nutrition related factors. The terminology intestinal failure associated liver disease (IFALD) is therefore more appropriate than PN associated liver disease. Effort should be made to prevent liver dysfunction by managing sepsis, avoiding parenteral overfeeding, employing cyclical parenteral feeding and encouraging enteral nutrition where possible. Intake of soybean based parenteral lipid emulsions should be reduced in individuals with established IFALD, possibly to be replaced by lipid emulsions containing medium chain triacylglycerol, monounsaturated fatty acids or fish oil although larger clinical studies are needed. Similarly, evidence supporting the widespread use of parenteral choline and taurine supplementation in the prevention or treatment of IFALD remains limited. There are more data to support the use of oral antibiotics to treat bacterial overgrowth and oral ursodeoxycholic acid in neonates. Ultimately, severe IFALD may necessitate referral for small intestine and/or liver transplantation.
Effective management of acute faecal incontinence in hospital: review of continence management systems
Authors: Ousey Karen , Gillibrand Warren , Lui Steve
Published: June 2010

This paper reviews the scientific literature regarding current systems available for the management of acute faecal incontinence (FI) in hospital patients. The review searched Medline from 1950 to October 2009 using the adapted search strategy, as devised by the Cochrane Incontinence Group, in order to identify studies relevant to this review, yielding 197 records. Ten studies fitted the inclusion criteria with none of the studies being randomised control trials. Characteristics identified from the studies included: duration of the management devices, cost implications, length of patient stay, contraindications and patient assessment. The management of acute FI in acute settings is a relatively ignored problem, with little available evidence to support a standardised approach to its management. The review highlights the need for early identification of contraindications when FI management systems are being used, particularly in patients administered antithrombotic drugs such as aspirin.
An energy management framework for energy harvesting embedded systems
Authors: Moser Clemens , Chen Jian-Jia , Thiele Lothar
Published: June 2010

Energy harvesting (also known as energy scavenging) is the process of generating electrical energy from environmental energy sources. There exists a variety of different energy sources such as solar energy, kinetic energy, or thermal energy. In recent years, this term has been frequently applied in the context of small autonomous devices such as wireless sensor nodes. In this article, a framework for energy management in energy harvesting embedded systems is presented. As a possible scenario, we focus on wireless sensor nodes that are powered by solar cells. We demonstrate that classical power management solutions have to be reconceived and/or new problems arise if perpetual operation of the system is required. In particular, we provide a set of algorithms and methods for various application scenarios, including real-time scheduling, application rate control, as well as reward maximization. The goal is to optimize the performance of the application subject to given energy constraints. Our methods optimize the system performance which, for example, allows the usage of smaller solar cells and smaller batteries. Furthermore, we show how to dimension important system parameters like the minimum battery capacity or a sufficient prediction horizon. Our theoretical results are supported by simulations using long-term measurements of solar energy in an outdoor environment. In contrast to previous works, we present a formal framework which is able to capture the performance, the parameters, and the energy model of various energy harvesting systems. We combine different viewpoints, include corresponding simulation results, and provide a thorough discussion of implementation aspects.
Optimality, fairness, and robustness in speed scaling designs
Authors: Andrew Lachlan L.H. , Lin Minghong , Wierman Adam
Published: June 2010

This work examines fundamental tradeoffs incurred by a speed scaler seeking to minimize the sum of expected response time and energy use per job. We prove that a popular speed scaler is 2-competitive for this objective and no "natural" speed scaler can do better. Additionally, we prove that energy-proportional speed scaling works well for both Shortest Remaining Processing Time (SRPT) and Processor Sharing (PS) and we show that under both SRPT and PS, gated-static speed scaling is nearly optimal when the mean workload is known, but that dynamic speed scaling provides robustness against uncertain workloads. Finally, we prove that speed scaling magnifies unfairness under SRPT but that PS remains fair under speed scaling. These results show that these speed scalers can achieve any two, but only two, of optimality, fairness, and robustness.
Small subset queries and bloom filters using ternary associative memories, with applications
Authors: Goel Ashish , Gupta Pankaj
Published: June 2010

Associative memories offer high levels of parallelism in matching a query against stored entries. We design and analyze an architecture which uses
single
lookup into a Ternary Content Addressable Memory (TCAM) to solve the subset query problem for small sets, i.e., to check whether a given set (the query) contains (or alternately, is contained in) any one of a large collection of sets in a database. We use each TCAM entry as a small Ternary Bloom Filter (each 'bit' of which is one of {0,1,wildcard}) to store one of the sets in the collection. Like Bloom filters, our architecture is susceptible to false positives. Since each TCAM entry is quite small, asymptotic analyses of Bloom filters do not directly apply. Surprisingly, we are able to show that the asymptotic false positive probability formula can be safely used if we penalize the small Bloom filter by taking away just one bit of storage and adding just half an extra set element before applying the formula. We believe that this analysis is independently interesting. The subset query problem has applications in databases, network intrusion detection, packet classification in Internet routers, and Information Retrieval. We demonstrate our architecture on one illustrative streaming application -- intrusion detection in network traffic. Be shingling (i.e., taking consecutive bytes of) the strings in the database, we can perform a single subset query and hence a single TCAM search, to skip many bytes in the stream. We evaluate our scheme on the open source CLAM anti-virus database, for
worst-case
as well as random streams. Our architecture appears to be at least one order of magnitude faster than previous approaches. Since the individual Bloom filters must fit in a single TCAM entry (currently 72 to 576 bits), our solution applies only when each set is of a small cardinality. However, this is sufficient for many typical applications. Also, recent algorithms for the subset-query problem use a small-set version as a subroutine
Detecting sources of computer viruses in networks
Authors: Shah Devavrat , Zaman Tauhid
Published: June 2010

We provide a systematic study of the problem of finding the source of a computer virus in a network. We model virus spreading in a network with a variant of the popular SIR model and then construct an estimator for the virus source. This estimator is based upon a novel combinatorial quantity which we term rumor centrality. We establish that this is an ML estimator for a class of graphs. We find the following surprising threshold phenomenon: on trees which grow faster than a line, the estimator always has non-trivial detection probability, whereas on trees that grow like a line, the detection probability will go to 0 as the network grows. Simulations performed on synthetic networks such as the popular small-world and scale-free networks, and on real networks such as an internet AS network and the U.S. electric power grid network, show that the estimator either finds the source exactly or within a few hops in different network topologies. We compare rumor centrality to another common network centrality notion known as distance centrality. We prove that on trees, the rumor center and distance center are equivalent, but on general networks, they may differ. Indeed, simulations show that rumor centrality outperforms distance centrality in finding virus sources in networks which are not tree-like.
Inferring applications at the network layer using collective traffic statistics
Authors: Jin Yu , Duffield Nick , Haffner Patrick , Sen Subhabrata , Zhang Zhi-Li
Published: June 2010

In this paper, we propose a novel technique for inferring the distribution of application classes present in the aggregated traffic flows between endpoints, which exploits both the statistics of the traffic flows, and the spatial distribution of those flows across the network. Our method employs a two-step supervised model, where the bootstrapping step provides initial (inaccurate) inference on the traffic application classes, and the graph-based calibration step adjusts the initial inference through the collective spatial traffic distribution. In evaluations using real traffic flow measurements from a large ISP, we show how our method can accurately classify application types within aggregate traffic between endpoints, even without the knowledge of ports and other traffic features. While the bootstrap estimate classifies the aggregates with 80% accuracy, incorporating spatial distributions through calibration increases the accuracy to 92%, i.e., roughly halving the number of errors.