Adsorption of cinnamic and caffeic acids on the surface of highly dispersed silica from different solvents

The adsorption of cinnamic and caffeic acids on initial and partially silylated highly dispersed silica A-300 from polar (water-ethanol solution), low polar (chloroform and dichloroethane), and apolar (hexane and carbon tetrachloride) solvents is investigated. The dependence of adsorption on solvent polarity is established. It is disclosed that the dependences of the adsorption of cinnamic and caffeic acids on the degree of surface hydrophobization have different characters.     

Curing reaction of o-cresol novolac epoxy resin according to hardener change

The investigations of cure kinetics and glass transition temperature (T_g) versus reaction conversion (α) of o-cresol novolac epoxy resin with the change of hardener were performed. All kinetic parameters of the curing reaction such as the reaction rate order, activation energy, and frequency factor were calculated. The curing mechanisms were classified into two types. One was an autocatalytic mechanism and the other was a nth order kinetic mechanism. The constants related to the chain mobility of polymer segments were obtained by using the DiBenedetto equation. We have tried to correlate the relationships between curing mechanism and molecular structures of hardeners from these results. © 1993 John Wiley & Sons, Inc.     

Odd-even behavior of ferroelectricity and antiferroelectricity in two homologous series of bent-core mesogens

Two chiral bent-core mesogens Pn-O-PIMB(n - 2)* (n = 9 and 10) and their oxygen analogues Pn-O-PIMB(n - 2)*-(n - 4)O (n = 8, 9, and 10) with omega-[(S)-amyloxy]alkoxy terminal groups were prepared, and their phase structures were investigated by means of electro-optic, polarization reversal current and second harmonic generation measurements in order to clarify the effect of the interlayer steric interaction on the emergence of polar orderings. The odd-even behavior for the alternative appearance of ferroelectricity and antiferroelectricity was observed in two homologous series; the bent-core mesogens P10-O-PIMB8*, P8-O-PIMB6*-4O, and P10-O-PIMB8*-6O in addition to the previously reported P6-O-PIMB4* and P8-O-PIMB6*, where the length of chains n is even, exhibited ferroelectric phases. On the contrary, the mesogens P7-O-PIMB5*, P9-O-PIMB7*, and P9-O-PIMB7*-5O, where n is odd, showed antiferroelectric phases. It is obvious that the interlayer steric interaction plays a major role for the emergence of a variety of phase structures.     

Complex polarizability as used to analyze dielectric relaxation measurements

The effect of representing dielectric properties in terms of the complex polarizability ^c = – i is examined. Loss curves ( and tan ) are shifted towards higher frequencies, revealing the existence of new relaxations and allowing the clarifications of ones already known. We have calculated the shift ratios (at maximum or tan )/ (at maximum or tan ) from the more conventional empirical equations representing the dielectric behavior. Some examples are given.     

Aggregation of fullerence C60 in o-dichlorobenzene

Aggregation of C₆₀ fullerene in o-phenyl dichloride was studies by the spectrophotometry method.     

Colloidal dispersion of fullerene C60 free of organic solvents

A new procedure for preparing aqueous colloidal dispersion of C₆₀ in water was developed.     

Appearance of long-range magnetic order in a system of small ferromagnetic particles

Using x-ray and magnetic methods as well as small-angle neutron scattering, it is shown for the example of the decomposing alloy Cu₆₄Mn₉Al₂₇ that the appearance of long-range ferromagnetic order in a system of small superparamagnetic particles dissolved in a nonmagnetic matrix is due to cooperative ordering of their magnetic moments. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 12, 959–962 (25 June 1996)     

Remarks on some zero-sum theorems

In the present paper, we give a new proof of a weighted generalization of a result of Gao in a particular case. We also give new methods for determining the weighted Davenport constant and another similar constant for some particular weights.     

Phosphorus‐based Schiff bases and their complexes as nontoxic antioxidants: Structure–activity relationship and mechanism of action

Phosphorus‐based Schiff base were synthesized by treating bis{3‐[2‐(4‐amino‐1.5‐dimethyl‐2‐phenyl‐pyrazol‐3‐ylideneamino)ethyl]‐indol‐1‐ylmethyl}‐phosphinic acid with paraformaldehyde and characterized as a novel antioxidant. Its corresponding complexes [(VO)₂L(SO₄)₂], [Ni₂LCl₄], [Co₂LCl₄], [Cu₂LCl₄], [Zn₂LCl₄], [Cd₂LCl₄], [Hg₂LCl₄], [Pd₂LCl₄], and [PtLCl]Cl₂ were analyzed by Fourier transform‐infrared, (¹H and ¹³C) nuclear magnetic resonance, and mass and UV–Vis spectroscopy. Experimental data showed that the ligand coordinated with the metal ions via donor atoms such as nitrogen to form an octahedral arrangement of the Schiff base around the central transition‐metal atom. The nature of these complexes was identified using the molar ratio and Job's methods, with the results agreeing with a metal‐to‐ligand (M:L) molar ratio of 2:1, expect for Pt, whose M:L was 1:1. Thermodynamic activation parameters such as ?E*, ?H*, ?S*, ?G*, and K were determined from the thermogravimetric analysis curve using the Coats–Redfern method. The antioxidant activities of the prepared compounds were assessed by using 1.1‐diphenyl‐2‐picrylhydrazyl as the free radical, and the results show that the complex Schiff bases were found to possess potent antioxidant activity. The structure–activity relationship of the ligand and its complexes indicates that the presence of electron‐donating moieties, such as Co(II) and Ni(II), in the chemical structure increases the antioxidant activity, whereas the Pt(IV) and Pd(II) complexes diminished the antioxidant activity, indicating the superior activity of the hydroxyl radical (OH^·) over the superoxide radical.