The influence of cations on the dissociation behaviour of copolymers of propene and maleic acid and their modified products with taurine in salt-free solution

Potentiometric and conductometric titrations were used to study the dissociation behaviour of poly(propene-co-maleic acid) and poly(propene-co-maleic acid) modified with various contents of taurine (2-aminoethanesulfonic acid) in salt-free solution. Copolymers of propene and maleic acid with different molecular weights were titrated with LiOH, NaOH, and KOH. The influence of molecular weight on pK_a is ascertainable in both the first and second dissociation step. Of the various alkali metal cations studied, lithium had the most significant effect on the dissociation behaviour. The acidic strength decreased in the order lithium > sodium ≥ potassium. After insertion of sulfonic acid groups into poly(propene-co-maleic acid), the influence of strong acidic groups on the dissociation behaviour of carboxylic groups was studied. The contents of taurine were 10, 25, and 50 mol%. The second dissociation step was analyzed in this case. The pK_a values increased with increasing content of taurine for titrations with LiOH and KOH, but not NaOH. When NaOH was used, the pK_a decreases if the polymer was modified with 10% taurine. Higher taurine contents had no influence on the magnitude of pK_a. The results demonstrate the strong influence of short-range electrostatic interactions on the dissociation behaviour of weak polyacids. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1949–1955, 1999     

新型含噻二唑环的二茂铁衍生物的合成与电化学性质研究

Three novel thiadiazolo-ferrocence derivatives containing long chain alkyl group were synthesized and characterized. The voltammetric behaviour of these thiadaizolo-ferrocene derivatives was studied on gold electrode (diameter 1 mm) in CH2Cl2/0.2 mol/L tetra-n-butylammonium hexafluorophosphate. The influence of β-cyclodextrinon the voltammetric behaviour of the compounds was also studied.     

High speed parallel synthesis of banana-shaped molecules and phase transition behaviour of 4-bromo-substituted derivatives

Novel derivative series of the well known bent-shaped P-n-O-PIMB liquid crystal mesogens, referred to as ‘4Br-P-n-O-PIMB’, ‘4Cl-P-n-O-PIMB’ and ‘5Cl-P-n-O-PIMB’, having halogen atoms substituted on the phenyl ring in the central core, were synthesized by solution phase parallel synthesis based on a combinatorial approach. The mesomorphic behaviour and physical properties of all the new compounds were studied by means of optical microscopy, differential scanning calorimetry, X-ray and circular dichroism spectroscopy. We found interesting transitional behaviour for the 4Br-P-n-O-PIMB homologous series. The homologues with alkyl tails having carbon numbers of n=3–10, 12, 14 exhibit rather complicated mesomorphic behaviour, which is strongly sensitive to n. The chiral fluid smectic B2 phase with SmC_AP_A structure and unidentified smectic Bx phase were observed in the homologues with n=9, 10, 12, 14 and n=3–5, respectively. Interestingly, every member exhibits frustrated and/or helical ordered phases at low temperatures, designated as X1, X2, and X3 phases, which result from a spontaneous escape from a macroscopic polarization. The mesomorphic behaviour and mesophase structures differ remarkably from those of the parent P-n-O-PIMB homologues, suggesting that substitution of the halogen atoms at the central core essentially creates a particular interaction between molecules.     

Voltammetry at a de Levie brush electrode as a model for electrochemical supercapacitor behaviour

Electrochemical supercapacitors provide electrical energy storage systems complementary to batteries. Based on the double layer capacitance of high area porous electrode materials, e.g. carbon powders, felts, foams, aerogels or on the redox pseudocapacitance of oxide or polymer films, specific capacitances of the order of 50100 F g⁻¹ are realizable. However, the porous nature of the electrode structures introduces a distribution of resistive and capacitative elements giving rise to electrical behaviour like that of a transmission line, as treated by de Levie, with a resulting complex power spectrum depending on charging or discharging rates. The present paper examines the cyclic voltammetry behaviour of de Levie type wire brush electrodes as models for porous electrodes, in comparison with that of single wire electrodes of the same metal. Comparisons are also made with constant current charging behaviour and with the electrochemical behaviour of specially made, 3 V, non aqueous solution, double layer capacitor modules, examined under similar conditions in relation to the current response profiles of a 5 RC element hardware model circuit. These approaches enable the effects of the distribution of R and C elements on charge acceptance and delivery at various rates to be quantitatively evaluated for various resistivities of the conducting electrolyte in pores.     

From comb polymers to polysoaps: a Monte Carlo attempt

The pivot algorithm is used on a cubic lattice to study comb polymers large enough to have side-chains obeying scaling behaviour. The connectivity of the chain induces the formation of side-chain clusters whose size distribution is investigated as a function of side-chain length n and spacer length m. When an attractive interaction is set between the side-chains, the comb polymer displays the behaviour of an associating polymer below the critical aggregation concentration, as observed experimentally.     

Influence of the Phase Morphology on the Viscoelastic Behaviour of Polymer Blends (PP-EPR)

Summary. Melts of polyethylene-propylene-rubber (EPR, blends of linear polyethylene, linear polypropylene, and PE-PP copolymer) show phase separation. The influence of the phase morphology on the viscoelastic behaviour is studied with the aid of the dynamical moduli. The measured moduli of the fraction of the linear homopolymer of an EPR agree with the moduli calculated from the molar mass distribution of this fraction. In contrast, the copolymer fraction shows a strong rubber-like behaviour (represented by a characteristic relaxation time spectrum). Mixtures of 80 wt% linear PP and of EPRs with low copolymer content are not rubber-like liquids. In addition, the moduli from them can be calculated from the moduli of the components with the aid of Palierne’s emulsion model. This clearly reveals that the linear PP forms the matrix in this case. Mixtures of 80 wt% linear PP and of EPRs with high copolymer content show rubber-like behaviour and Palierne’s emulsion model is not applicable on them. Obviously, the copolymer fraction forms a physical network.     

Ionic impurities in nematic liquid crystal displays

This paper shows that the dielectric anisotropy of conductivity in cells composed of nematic liquid crystal E7 (NLC-E7) is related to the fact that the diffusion constant (D) is greater in a cell with homeotropic alignment than in one with homogeneous alignment (D _∥ > D _⊥). This behaviour can be understood by the study of the dielectric properties of the NLC based on the ionic hopping behaviour and on the analysis of the electrical conductivity in relation to the voltage applied.     

Capillary electrophoresis in mixed aqueous-organic media: Effect of tetrahydrofuran on mobilities, dissociation constants and separation of a series of quinolones

Summary The influence of the composition of aqueous-tetrahydrofuran mixtures on the electrophoretic behaviour of nine quinolones was studied in order to predict the optimum conditions for their separation. The effect of pH, pK _a and activity coefficients on electrophoretic behaviour was established. Standard pH values for buffer solutions of the NIST scale as previously determined in THF-water were used in accordance with IUPAC rules. pH was therefore measured for these media as for water. The pK _a values of quinolones were determined from the electrophoretic mobilities-pH data pairs in different THF-water mixtures. The electrophoretic resolution between pairs of substances was then predicted in order to obtain the optimal experimental conditions for separation methodologies.     

Lipophilicity measurements of protonated basic compounds by reversed-phase high-performance liquid chromatography : II. Procedure for the determination of a lipophilic index measured by reversed-phase high-performance liquid chromatography

The retention behaviour of protonated basic compounds in reversed-phase high-performance liquid chromatography, using methanol-water mixtures as the eluent, is reported. A minimum is found in the relationship between the logarithm of the capacity factor (log k) and the percentage of methanol (x) in the eluent. The deviation from linearity is postulated to be caused by a dual retention mechanism, namely polar interactions between the solute and eluent molecules in water-poor eluents, and hydrophobic expulsion in water-rich ones. The influence of the pH, pK_a and lipophilicity on retention behaviour is also investigated.     

Molecular size scaling in families of protein native folds

The mean size of the most compact native states of globular proteins, independent of folding type, follows the scaling law of collapsed polymers R _g ~ n ^1/3, relating the radius of gyration R _g to the number of protein residues, n. Until now, this behaviour has only been observed within a small subset of unrelated single-domain proteins with n < 300. Here, we employ the SCOP database of protein folds to study systematically the scaling behaviour of well-defined families of domains that share structural and functional characteristics. In the particular case of helical proteins, we identify the folding types that can be associated with scaling laws corresponding to compact behaviour (e.g., the cytochrome-C monodomains) and noncompact behaviour (e.g., the immunoglobulin/albumin-binding and spectrin-repeat domains). Our results quantify the size variations within some folding families, as well as reveal that some distinct folds represent structures with equivalent compactness.     

Using Lateral Substitution to Control Conformational Preference and Phase Behaviour of Benzanilide-based Liquid Crystal Dimers

The inclusion of secondary and tertiary benzanilide-based mesogenic groups into liquid crystal dimers is reported as a means to develop new materials. Furthermore, substitution at the nitrogen atom is shown to introduce an additional synthetic ‘handle’ to modify the molecular structure of the tertiary materials. The design of these materials has proved challenging due to the strong preferences of 3° benzanilides for the E amide conformation. In this work, lateral substitution is used to modify the conformational preferences of the amide linkage and promote liquid crystallinity for a series of N-methyl benzanilide dimers. As the proportion of the E conformer decreases, the nematic-isotropic transition temperatures increase, and enantiotropic nematic behaviour is observed. We also report the synthesis and characterisation of the analogous 2° benzanilide-based materials, which show nematic and twist-bend nematic behaviour. This approach highlights the effects that seemingly small structural modifications, such as the inclusion and position of a methyl group, can have on molecular shape and hence, liquid crystalline behaviour.     

Synthesis,characterization and thermal behaviour of solid 2-methoxybenzoates of trivalent metals

Solid-state Ln(L)₃ compounds, where Ln stands for trivalent Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y and L is 2-methoxybenzoate have been synthesized. Simultaneous thermogravimetry and differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), X-ray powder diffractometry, infrared spectroscopy and complexometry were used to characterize and to study the thermal behaviour of these compounds. The results provided information on the composition, dehydration, coordination mode, structure, thermal behaviour and thermal decomposition.     

Simple Electrochemical Characterization of ortho‐Carborane and some of its exo‐Skeletal Derivatives

Electrochemical behaviour of 12 icosahedral carboranes – ortho‐, meta‐ and para‐carborane with different exo‐skeletal substituents was investigated. The study was done using phosphate buffers, in some cases with 20 % and 30 % dimethyl sulfoxide (DMSO) addition to increase the solubility of studied compounds. Commercial glassy carbon electrode or home‐made screen printed electrodes were used. Distinct electrochemical responses were observed only for the ortho‐carborane and its exo‐skeletal derivatives. The study of different exo‐skeletal substituents on the electrochemical behaviour of the carboranes is crucial for the intended use of these compounds as electrochemical labels of biomolecules.     

Protonierungs- und Deprotonierungskinetik des Systems Azulen-Azuleniumkation,ein Beitrag zur Kenntnis der Hammett'schen Ho-Aciditätsfunktion

Using a flashphotolysis-method to evaluate the rates of the protonation of azulene and the deprotonation of azuleniumcation as a function of H₀ the validity of the Hammett H₀-function was examined. Using this technique it was possible to obtain information on the behaviour of the activity coefficients and to show that the H_c-acidityfunction of Reagan [1] is a better measure of the hydrogen activity than the H₀-function. The dependence of the deprotonation rate on H₀ is explained as a consequence of the different behaviour of the activity coefficients of Hammett-indicators and azulene/azuleniumcation, respectively.     

Gas chromatography of homologous esters : XXVIII. Retention increments of aliphatic C1---C18n-alkyl esters of butanoic acid and its monochloro derivatives on SE-30 and OV-351 capillary columns

The retention behaviour of C₁---C₁₈n-alkyl esters of butanoic 2-, 3- and 4-chlorobutanoic acids was examined isothermally at several temperatures on SE-30 and OV-351 capillary columns. Retention increments showing the effects of each position of chlorine substitution are presented. The considerable enhancement of terminal chlorine substitution is discussed together with the corresponding behaviour of the monochloropropanoate esters.     

Conformational behaviour of non-fused biheterocycles. Part XV. Isomeric phenylisoxazoles

The conformational behaviour of isomeric phenylisoxazoles has been investigated at the STO-3G level optimizing the most significant geometrical parameters. The energy minima of the two isomers having an heteroatom in an ortho position correspond to planar structures, whereas the 4-isomer has a twisted equilibrium conformation. This confirms that H? H non-bonded repulsions are stronger than (lone-pair)-H ones. The similar conformational behaviour of corresponding phenylfurans and phenylisoxazoles shows that the second heteroatom has a negligible effect and that the conformational behaviour of non-fused biheterocycles is dictated by the nature of the ortho substituents.     

Conformation and dynamics of polymer chains in condensed systems

A Stockmayer's type-A chain such as cis-polyisoprene (PI) having dipole components parallel to the chain contour exhibits slow dielectric response, reflecting fluctuation of its end-to-end vector ( dielectric normal modes ). This article reviews our own work on dielectric spectroscopy for studying dynamics and conformational properties of probe PI chains in binary blends with PI or polybutadiene (PB) that does not exhibit normal modes. Through such studies we were able to see the crossover of the probe-chain dynamics from Rouse behaviour in low-molecular-weight (lmw) matrices to pure reptation behaviour in high-molecular-weight (hmw) matrices. We were also able to confirm experimentally Flory's earlier prediction on excluded volumes in dilute blends of hmw probe chains in lmw matrices, for which a proof has never been given before.     

Supramolecular non-symmetric dimers derived from cholesterol: synthesis and phase transitional properties

Three series of novel dimeric supramolecules, possessing both inter- as well as intramolecular H-bonding, have been prepared and investigated for their thermal properties. They were obtained in excellent yields by condensing cholesteryl ω-(3-hydroxy-4-formylphen-oxy)alkanoates with 4-(n-alkoxy)benzohydrazides, 3,4-bis(n-decyl-oxy)benzohydrazide and 3,4,5-tris(n-decyloxy)benzohydrazide. The influence of increase in the number of terminal n-alkoxy tails from one to three and the length and parity of the flexible spacer on phase transitional behaviour have been thoroughly investigated with the aid of microscopic, calorimetric and X-ray diffraction (XRD) techniques. The results of these complementary studies clearly illustrate the dependence of thermal behaviour of the dimers on these structural factors. The rigid intermolecular association via H-bonds through complementary benzohydrazide component enforce their self-assembly into frustrated and polar smectic phases; H-bond force coupled with the bulkiness of steroid moiety affects the electrical switching property of this fluid polar structure.     

Preferential protonation and methylation at the nitrogen atoms of N,N-dimethylamino derivatives of pyridine

The relative reactivity toward protonation and methylation of the two nitrogen atoms in N,N-dimethylaminopyridines has been examined by ¹H NMR. The ring position of the dimethylamino group has no influence on protonation, which occurs in all the derivatives at the heterocyclic nitrogen. The N-methylation reaction does not follow a homogeneous behaviour, occurring at the exocyclic nitrogen in the 2-substituted dimethylamino derivative. The electronic characteristics of the molecules, determined by MO calculations at a semi-empirical level, indicate that both protonation and methylation should occur at the heterocyclic nitrogen; the calculated relative stabilites, however, of the N-protonated and N-methylated forms are in full agreement with the experimental results, and it appears that the anomalous behaviour of 2-dimethylaminopyridine in the N-methylation reaction is caused by steric factors.     

Modelling Growth and Bacteriocin Production by <Emphasis Type="Italic">Pediococcus acidilactici</Emphasis> PA003 as a Function of Temperature and pH Value

To investigate the effect of pH and temperature on the cell growth and bacteriocin production of Pediococcus acidilactici PA003, a lactic acid bacterium isolated from traditionally fermented cabbage, the kinetic behaviour of P. acidilactici PA003 was simulated in vitro during laboratory fermentations by making use of MRS broth. Firstly, primary models were developed for cell growth, glucose consumption, lactic acid and bacteriocin production for a given set of environmental conditions. Based on primary models, further study was undertaken to fit secondary models to describe the influence of temperature and pH on microbial behaviour. The models were validated successfully for all components. The results from the cell yield coefficient for lactic acid production reflected the homofermentative nature of P. acidilactici PA003. Both cell growth and bacteriocin production were very much influenced by changes in temperature and pH. The optimal condition for specific growth rate and biomass concentration was almost the same at pH 6.5 and 35 °C. At 35 °C and pH 6.1, the maximal bacteriocin activity was also achieved. The kinetic models provide useful tools for elucidating the mechanisms of temperature and pH on the kinetic behaviour of P. acidilactici PA003. The information obtained in this paper may be very useful for the selection of suitable starter cultures for a particular fermentation process and is a first step in the optimization of food fermentation processes and technology as well.