High-performance liquid chromatographic assay and preclinical pharmacological studies of pibenzimol (bisbenzimidazole)

A sensitive and selective high-performance liquid chromatographic assay with ultraviolet or fluorescence detection has been developed for the experimental antitumor agent pibenzimol. Drug is isolated from plasma or other aqueous solutions with reversed-phase C18 disposable extraction columns and chromatography afforded with a deactivated reversed-phase C18 column and phosphate buffer--methanol mobile phase. Plasma standard curves are linear for concentrations for pibenzimol from 0.01 to 5.0 micrograms/ml. Pibenzimol is stable in fresh human plasma and whole blood. Pibenzimol appears to bind to plasma proteins; however, drug adsorption to glass, plastic, membranes, and filters precludes accurate determination of pibenzimol plasma protein binding. Plasma concentrations of pibenzimol fall rapidly following rapid intravenous administration to rabbits, but parent drug is detectable in plasma 24 h after drug administration. The 24-h urinary recovery of pibenzimol is 10-20%.     

Number fluctuation analysis of random locomotion. Statistics of a Smoluchowski process

We analyze a scheme, originally suggested by Smoluchowski, by which a diffusion coefficientD can be estimated by measuring the number of particles occupying a fixed region of a surface at various times. An expression is derived relating the variance of the estimated valueD to several experimental parameters. This expression is evaluated numerically to determine how statistical uncertainty depends on adjustable variables. Particular attention is given to experiments involving locomotion of migrating leukocytes.     

Shear wave modes and velocity correlation spectra in liquids

The coupling of the atomic velocity to the transverse current is investigated in a model of liquid rubidium by analyzing the frequency spectra associated with the velocity autocorrelation function in terms of the current correlation functions.     

Nuclear spectral energy functions beyond the shell model

We predictl=0 nucleons in¹²C to have a negative (binding) energy centered around –22 MeV with a full width at half-maximum of 5.3 MeV. Thel=1 (P _3/2 nucleons) are predicted to have a much narrower spectral energy function centered around –10.6 MeV. A strongly correlated translational invariant wave function was used to describe the ground state nucleus. A central two-nucleon potential was utilized in the hyperspherical harmonic method to approximately solve the Schrödinger equation for the ground state wave function. Both confirmation and failings of the independent particle shell model are exposed.     

Anomalous preexponential factor for hydrogen desorption from platinum single crystals?

Abnormally low values found by some authors for the preexponential for hydrogen desorption from platinum surfaces have recently been explained by an adsorbate induced change in the dynamical characteristics of the surface itself. This possibility has been investigated in the present work exploiting the Debye-Waller effect in He beam diffraction from a hydrogen covered Pt(997) surface. Essentially no dependence of adsorbate induced attenuation of the diffracted beam intensities on the primary He-beam energy has been observed. Therefore no indications have been found for changes in the perpendicular component of platinum surface vibrations due to adsorbed hydrogen. Likewise, heats of adsorption, obtained from He diffraction experiments, do not depend on the primary energy of the He beam. This result supports the obtained normal value for the preexponential factor of $\text{ca. 10}{}^{\mathrm{?2}}\text{cm}{}^2\text{atom · s}$ (Poelsema et al., Surface Sci. 111 (1981) 519).     

Hyperfine structure in the EPR spectrum of O−2 on GaAs surfaces

It is shown that a previous interpretation of hyperfine structure in the O^?₂ — GaAs surface EPR spectrum is incorrect. The experimental spectrum is reproduced and re-interpreted in a consistent way. The surface Ga orbital is almost entirely p-like.     

RADIATION ACTIVATION OF CARCINOGENS AND THE ROLE OF OH AND O2-

Abstract— Radiation-induced covalent binding of labelled carcinogens to DNA has been investigated under a variety of conditions using ultrafiltration or millipore filtration of TCA precipitable complexes. High yields of carcinogen binding at high DNA concentrations are also observed for a variety of small molecules and are not carcinogen-specific. At high carcinogen concentrations, radiation-induced unstable electrophilic carcinogenic species are produced, and undergo free-radical reactions which simulate cellular redox reactions involved in metabolic carcinogen activation, leading to the formation of covalently bound carcinogen adducts to DNA as a potential target macromolecule. The yields of carcinogen-DNA adducts increase linearly with dose and depend upon carcinogen concentration. The results of scavenger studies indicate that the oxidising species O₂^- and OH are the principal activating species. Rate constants for the selective radiation-induced oxidation reactions of various chemical carcinogens with superoxide have been measured by a competition kinetic method using pulse radiolysis. The relatively long-lived superoxide radical reacts with carcinogens at a rate which is two orders of magnitude slower than the diffusion-controlled rate for the hydroxyl radical, thus allowing a measure of O₂^- specificity in the presence of competing reactants within the cell.     

Necklaces,symmetries and self-reciprocal polynomials

The connection between a certain class of necklaces and self-reciprocal polynomials over finite fields is shown. For n?2, self-reciprocal polynomials of degree 2n arising from monic irreducible polynomials of degree n are shown to be either irreducible or the product or two irreducible factors which are necessarily reciprocal polynomials. Using DeBruijn's method we count the number of necklaces in this class and hence obtain a formula for the number of irreducible self-reciprocal polynomials showing that they exist for every even degree. Thus every extension of a finite field of even degree can be obtained by adjoining a root of an irreducible self-reciprocal polynomial.     

The noncumulative effect of methyl substituents on the rate of addition of benzeneselenenyl chloride to olefins1

The rates and products of addition of benzeneselenenyl chloride to ethylene and its six Me substituted derivatives have been determined in methylene chloride at 25°. Unlike the addition of 4-chlorobenzenesulfenyl chloride to this same series of compounds, the effect of Me groups on the rates of addition is not cumulative. Also the regiochemistry of the product is different. For arenesulfenyl chloride additions, products of anti-Markownikoff orientation are formed preferentially under conditions of kinetic control. Under similar conditions regiospecific formation of the Markownikoff adduct is observed for the addition of benzeneselenenyl chloride to methylpropene and 2-methyl-2-butene. These data indicate a difference in both rate and product determining transition states between additions of arenesulfenyl and selenenyl chlorides to alkenes.