Copolymerization and interaction of acrylonitrile and indene

The donor–acceptor interaction of acrylonitrile (AN) with indene (In) has been investigated by means of ultraviolet spectroscopy and dielectric polarization measurements. The latter method yielded a value of 0.5 for the association constant of the charge-transfer-complex (CTC) and a 4.02 D for its dipole moment. The copolymerization of the two monomers was characterized by a tendency towards alternation when conducted in the bulk. This might be due to the participation of a weak CTC in the process of copolymerization. However, this tendency disappeared in polar solvents such as DMF.     

Facile N-arylation of amines and sulfonamides and o-arylation of phenols and arenecarboxylic acids

An efficient, transition-metal-free procedure for the N-arylation of amines, sulfonamides, and carbamates and O-arylation of phenols and carboxylic acids has been achieved by allowing these substrates to react with a variety of o-silylaryl triflates in the presence of CsF. Good to excellent yields of arylated products are obtained under very mild reaction conditions. This chemistry readily tolerates a variety of functional groups.     

Synthesis of sulfur analogues of methyl and allyl kojibiosides and methyl isomaltoside and conformational analysis of the kojibiosides

The synthesis of methyl and allyl 5′-thio--D-kojibiosides and methyl 5′-thio--D-isomaltoside is described. The phenylselenoglycoside and trichloroacetimidate of 2,3,4,6-tetra-O-acetyl-5-thioglucose have been employed as glycosyl donors to glycosylate glucopyranosyl acceptors with 2-OH and 6-OH positions free. The disaccharides thus obtained are potential glucosidase inhibitors. The conformational preferences of allyl 5′-thiokojibioside (34) were studied by comparison of experimental NOE curves with the theoretical counterparts for the corresponding methyl glycoside 25, derived from a Boltzmann-averaged grid search using the program PIMM91. Very good agreement of experimental NOE curves derived from selective NOE measurments with the theoretical curves is found. The data are consistent with the population of a global minimum structure (Φ=−43, Ψ=−39 degrees) to the extent of 90%, and a second local minimum (Φ=−36, Ψ=−173 degrees) to the extent of 6%. An X-ray crystal structure of 34 at 190 K (R=4.2%) indicates a conformation (Φ=−46, Ψ=−23 degrees) that is similar to that of the global minimum.     

Preparation and characterization of conjugates of silk fibroin and chitooligosaccharides

With the aim of the functionalization of silk fibroin (SF), conjugates of SF and polycationic chitooligosaccharides (COS) were prepared by the chemical modification of SF with cyanuric chloride (CY)-activated COS (COS-CY). The ¹H NMR spectrum of the reaction product between a model compound D-glucosamine and CY suggested that the COS-CY modifier was synthesized by the reaction of the amino group and the terminal anomeric hydroxyl group in COS, with the chlorine atom of CY. The ¹H NMR spectrum and amino acid analysis of the conjugates (COS-CY-SF) clarified that the tyrosine and lysine residues of SF reacted with a second chlorine atom of the triazine ring of the modifier. On the basis of the results of the hexosamine determination and the amino acid analysis of COS-CY-SF, it is estimated that COS-CY-SF consists of 38 wt% COS, 8 wt% CY, and 54 wt% SF. The absorbance at 600 nm as a function of pH for COS-CY-SF and SF indicated that the introduction of a large amount of hexosamine made SF amphiphilic and more water-soluble at lower pH values. The COS-CY-SF conjugates retarded the growth of Escherichia coli after incubation for 24 h at a conjugate concentration of 0.6% (w/v), while SF did not retard the growth at a SF concentration of 0.7% (w/v).     

Synthesis and flocculation performance of graft and random copolymer microgels of acrylamide and diallyldimethylammonium chloride

Graft (from linear homopolymers) and random (from a linear random copolymer) copolymer microgels of diallyldimethylammonium chloride (DADMAC) and acrylamide were synthesized via a free-radical mechanism using a γ-radiation technique. These copolymer microgels were evaluated as flocculants on a model dilute TiO₂ colloid suspension using a turbidimeter and a disc centrifuge photosedimentometer, and their performances were compared with the linear homopolymers and their blends. It was found that microgels produced after an appropriate irradiation time showed improved flocculation behavior over their nonirradiated linear counterparts. The graft microgels performed better than the corresponding random microgels. For a γ-radiation dosage of 100 krad/h, the graft microgels obtained by irradiating a 30% DADMAC (by weight) homopolymer blend for 3 h showed the maximum reduction in the relative turbidity of the TiO₂ suspension as well as the largest fraction of larger particles flocculated. Received: 18 May 1999 Accepted in revised form: 1 June 1999     

Sizes of atoms and ions and covalency of bonding in molecules and crystals

A new system of atomic radii for the elements up to barium inclusive is constructed. Values of the radii are chosen so as the dependence between the dissociation energy of diatomic homonuclear molecules and a depth of atom overlapping is monotonous, and the scatter of data is minimal. The depth of overlapping is calculated as a difference between the sum of atomic radii and an experimental interatomic distance. Conclusions are made that: the radii of free atoms and ions are determined by the value of the electron density equal to 0.01 au; they considerably change in molecules and crystals only as a result of the charge transfer from cation to anion; covalent bonding is well described by the overlapping of free atoms (ions), confined by the surface of the given radius, and its energy depends upon the depth of overlapping of valence electron densities of atoms. A method of overlapping atoms is proposed for the approximate estimation of ionic sizes and charges in bound systems.     

Beauty and fascination of morphologies of the micro- and macrocosmos

Summary Twenty years of experience of the authors with scanning electron microscopy (SEM) led to the idea to present a collection of striking examples of micrographs of intrinsic structural beauty as a birthday present to Professor Fresenius. Harmonic structures, marvellous or scurrilous SEM micrographs of inorganic materials are followed by some examples from the living microcosmos. Sometimes, striking parallelisms to our macroscopic world can be detected, which ultimately lead to some outstanding macroscopic morphologies of the Tyrolean Alps. This is an experiment which tries to encompass fascinating morphologies of the microcosmos and morphologies of the environment of the authors, the Tyrolean Alps. It should empasize the totalitarian aspect of our existence as scientists in a specific environment although one of the authors has recently moved to a less dramatic landscape.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Synthesis and properties of benzophenone-spiropyran and naphthalene-spiropyran conjugates

We have designed and synthesized four compounds integrating luminescent and photochromic components in their molecular skeletons. Two of them combine a nitrospiropyran photochrome with either one or two naphthalene fluorophores and can be prepared in three synthetic steps. The other two consist of a nitrospiropyran photochrome and a benzophenone phosphore connected by either ether or ester linkages and can be prepared in six or five, respectively, synthetic steps. The luminescent components of these assemblies are expected to transfer energy intramolecularly to the photochromic species upon excitation and encourage their photoisomerization. Consistently, the phosphorescence of the benzophenone units and the fluorescence of the naphthalene components are effectively quenched when these species are connected covalently to a nitrospiropyran. Nonetheless, the photoisomerization of the photochrome becomes significantly less efficient after the covalent attachment to the luminescent partner. The fraction of incident radiations absorbed by either the benzophenone or the naphthalene fragment does not promote the isomerization of the photochromic appendage. Instead, irreversible transformations occur upon irradiation of the luminophore-photochrome assemblies. Thus, the covalent attachment of a benzophenone or a naphthalene to a nitrospiropyran is not a viable strategy to improve the photocoloration efficiency of the photochromic component. Even although the very same luminophores are known to sensitize intermolecularly the isomerization of nitrospiropyrans, the transition to covalent luminophore-photochrome assemblies tends to promote degradation, rather than sensitization, upon irradiation.     

Kinetics and mechanisms of hydrolysis and aminolysis of thioxocephalosporins

The effect of replacing the beta-lactam carbonyl oxygen in cephalosporins by sulfur on their reactivity has been investigated. The second-order rate constant for alkaline hydrolysis of the sulfur analogue is 2-fold less than that for the natural cephalosporin. The thioxo derivative of cephalexin, with an amino group in the C7 side chain, undergoes beta-lactam ring opening with intramolecular aminolysis by a reaction similar to that for cephalexin itself. However, the rate of intramolecular aminolysis for the S-analogue is 3 orders of magnitude greater than that for cephalexin. Furthermore, unlike cephalexin, intramolecular aminolysis in the S-analogue occurs up to pH 14 with no competitive hydrolysis. The rate of intermolecular aminolysis of natural cephalosporins is dominated by a second-order dependence on amine concentration, whereas that for thioxocephalosporins shows only a first-order term in amine. The Bronsted beta(nuc) for the aminolysis of thioxo-cephalosporin is +0.39, indicative of rate-limiting formation of the tetrahedral intermediate with an early transition state with relatively little C-N bond formation.     

Design and Synthesis of Cyclodextrin-Based Rotaxanes and Polyrotaxanes

Rotaxanes are compounds in which a ring is threaded by a chain having bulky terminal cap groups. In this article, we review the design, synthesis and characterization of rotaxanes and polyrotaxanes of cyclodextrins threaded by an alkyl chain or a poly(ethylene glycol) as well as the synthesis of a light-driven molecular shuttle based on a cyclodextrin-rotaxane.     

固相法合成苯胺与邻甲氧基苯胺共聚物及其性能

以苯胺和邻甲氧基苯胺为单体,甲磺酸为掺杂酸,用固相法合成了甲磺酸掺杂苯胺与邻甲氧基苯胺共聚物。 通过红外光谱、紫外可见吸收光谱、X射线衍射、透射电子显微镜、循环伏安和电导率等对共聚物进行了结构表征和性能测试。 结果表明,不同摩尔比的苯胺与邻甲氧基苯胺共聚物处于中间氧化态,随邻甲氧基苯胺含量的增大,共聚物的掺杂率降低。 共聚物具有较高的结晶性和纤维状形貌,当苯胺与邻甲氧基苯胺摩尔比为1∶1时,具有较高的电化学活性,其导电率为1.65 S/cm。     

Preparation and properties of lanthanum tungstate and studies of its ion-exchange and electrochemical behaviour

A new inorganic ion-exchanger lanthanum tungstate has been prepared by mixing lanthanum nitrate and sodium tungstate. The refluxed product has been found to be most suitable; therefore, most of the electrochemical and ion-exchange studies were performed on this product. The material is a weak cation exchanger with a capacity of 0.80 mmol per gram. Electrochemical studies are performed by preparing a pellet of this exchanger in polystyrene; charge density and membrane potential have been calculated. The results are discussed.     

Preparation and evaluation of bipyridyl-tagged reagents and scavengers

The synthesis of three bipyridyl-tagged reagents and one scavenger is described. Of the three reagents, the carbodiimide derivative proved to be effective as a coupling reagent for amide formation and the removal of the coupling side product from the reaction mixture by complexation onto a Cu-derivatised resin has been successfully demonstrated. This purification process was thoroughly optimised using a DOE approach and the procedure subsequently applied to the use of a bipyridyl-tagged amine as an isocyanate scavenger. Preliminary results clearly demonstrate the potential of using chelation tags such as bipyridine units as a means for removing solution phase reagents and scavengers from reaction mixtures providing an attractive alternative to their resin-bound and fluorous-tagged counter-parts.     

Kinetics and mechanisms of chlorine dioxide and chlorite oxidations of cysteine and glutathione

Chlorine dioxide oxidation of cysteine (CSH) is investigated under pseudo-first-order conditions (with excess CSH) in buffered aqueous solutions, p[H+] 2.7-9.5 at 25.0 degrees C. The rates of chlorine dioxide decay are first order in both ClO2 and CSH concentrations and increase rapidly as the pH increases. The proposed mechanism is an electron transfer from CS- to ClO2 (1.03 x 10(8) M(-1) s(-1)) with a subsequent rapid reaction of the CS* radical and a second ClO2 to form a cysteinyl-ClO2 adduct (CSOClO). This highly reactive adduct decays via two pathways. In acidic solutions, it hydrolyzes to give CSO(2)H (sulfinic acid) and HOCl, which in turn rapidly react to form CSO3H (cysteic acid) and Cl-. As the pH increases, the (CSOClO) adduct reacts with CS- by a second pathway to form cystine (CSSC) and chlorite ion (ClO2-). The reaction stoichiometry changes from 6 ClO2:5 CSH at low pH to 2 ClO2:10 CSH at high pH. The ClO2 oxidation of glutathione anion (GS-) is also rapid with a second-order rate constant of 1.40 x 10(8) M(-1) s(-1). The reaction of ClO2 with CSSC is 7 orders of magnitude slower than the corresponding reaction with cysteinyl anion (CS-) at pH 6.7. Chlorite ion reacts with CSH; however, at p[H+] 6.7, the observed rate of this reaction is slower than the ClO2/CSH reaction by 6 orders of magnitude. Chlorite ion oxidizes CSH while being reduced to HOCl, which in turn reacts rapidly with CSH to form Cl-. The reaction products are CSSC and CSO3H with a pH-dependent distribution similar to the ClO2/CSH system.     

Oligomers and Polymers of Polyethers and Polyformals

Linear high molecular weight aromatic polyformals are readily obtained from biphenols and excess methylene chloride with solid sodium hydroxide or potassium hydroxide in the presence of a phase transfer catalyst or an aprotic dipolar solvent. By control of the stoichiometry bifunctional oligomers can be obtained which can subsequently be incorporated into a variety of block copolymers.     

Synthesis and structure of hydroxyisoxazolidines and derivatives of hydroxylamine and alkenals

The reactions of N-substituted hydroxylamines with alkenals serve as a method for the synthesis of the corresponding 2-substituted 3(5)-hydroxyisoxazolidines. The reaction pathway is determined by the nature of the substituent attached to the nitrogen atom. Ring-chain isomerism has been detected in these newly obtained compoundsTranslated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1270–1276, September, 1987.     

Gas-phase basicities of serine and dipeptides of serine and glycine

The gas-phase basicities of serine and dipeptides containing amino acid residues of serine and glycine were determined by proton transfer reactions in a Fourier transform ion cyclotron resonance mass spectrometer. The gas-phase basicity (GB) of L-serine was found to be 205.9 kcal/mol, with addition of a hydroxymethyl group (?CH₂OH) increasing the basicity by 4.5 kcal/mol relative to the simplest amino acid glycine (GB = 201.4 kcal/mol). This is attributed to a combination of intramolecular hydrogen bonding, induction, and symmetry effects. For the dipeptides, addition of a hydroxymethyl group does not result in a large increase in basicity relative to the basicity of glycylglycine (GB = 208.0 kcal/mol). The gas-phase basicities determined for glycyl-l-serine, l-serylglycine, and l-sery-l-serine are 209.3,210.6, and 210.9 kcal/mol, respectively. In comparison to glycylglycine, addition of the hydroxymethyl group at the N terminus has a greater impact on basicity than its placement at the C terminus. These data suggest that the protonation site for these dipeptides is the N-terminal amino nitrogen.     

Total synthesis and biological evaluation of halipeptins A and D and analogues

The marine-derived halipeptins A (1a) and D (1d) and their analogues 3a, 3d and 4a, 4d were synthesized starting from building blocks 10, 13, 14a or 14d, 15, and 16. The first strategy for assembling the building blocks, involving a macrolactamization reaction to form the 16-membered ring hydroxy thioamide 52d as a precursor, furnished the epi-isoleucine analogue (4d) of halipeptin D, whereas a second approach involving thiazoline formation prior to macrolactamization led to a mixture of halipeptins A (1a) and D (1d) and their analogues 3a, 3d (epimers at the indicated site) and 4a, 4d (epimers at the indicated site). The same route starting with D-Ala resulted in the exclusive formation of the epimeric halipeptin D analogue 3d. The synthesized halipeptins, together with the previously constructed oxazoline analogues 5d and 6d, were subjected to biological evaluation revealing anti-inflammatory properties for 1a, 1d, and 6d while being noncytotoxic against human colon cancer cells (HCT-116).     

Electronic structures and reactivities of methyl-substituted thienothiazoles and thieno- and furopyridines

The electronic structures of a number of methyl-substituted heterocyclces containing a thiophene or furan ring condensed with a thiazole or pyridine ring and of their quaternary salts and methylene bases were calculated by the Pariser-Parr-Pople method. The features of the electronic structures of the investigated molecules were ascertained. It is shown that methyl-substituted thienothiazoles and thieno- and furopyridines and their quaternary salts are appreciably inferior to the corresponding benzothiazoles and quinoline derivatives used for the synthesis of polymethine dyes with respect to the reactivity of the methyl group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1202–1206, September, 1976.