FREE RADICALS FROM PHOTOREDUCTION OF HEMATOPORPHYRIN IN AQUEOUS SOLUTION

—The anaerobic photoreduction of hematoporphyrin by organic reducing agents in fluid aqueous solutions has been studied by electron spin resonance spectroscopy. Efficient photoreduction occurs with many hydrogen-atom or electron donors, including catechols, pyrogallol. hydroquinone. ascorbate, p -phenylenediamine, cysteine and glutathione. A combination of direct and spin-trapping measurements (using 2-methyl-2-nitrosopropane) has been used to confirm production of radicals from both the porphyrin and the reducing agent in each system.     

A microwave-switched time integration (MISTI) method in the study of spin-polarized radicals

An experiment is described in which polarized free radicals are created in a laser pulse in the absence of a microwave field which is applied at a later time in a continuous wave fashion. In this way the periods of evolution and observation of the magnetization are separated in a two-dimensional experiment. Analysis shows that the variation in the observed time-integrated signal with the evolution period gives the electron spin-lattice time directly. A simple corollary yields the polarization ratio. Comparison is made with more conventional methods for determining these quantities. A further new method is described for determining the polarization ratios of all hyperfine components in a spectrum simultaneously using time-integration spectroscopy(TIS).     

Correlation between structural and electrical profiles in ion-implanted GaAs

Abstract

Damaging effect of diatomic phosphorus ions implanted into silicon was compared with that of atomic ions in the range between 25 and 300 keV/atom. Dose was around 10¹⁴ ions/cm². Target temperature varied between 77 and 533 K. Below and at 300 K the “damage enhancement factor” defined as ratio of damage produced by equivalnet molecular and atomic ion implantation varied from 1 to 1.6 depending on incident energy. At elevated implantation temperature this factor increased by almost an order of magnitude. In interpretation of experimental results, fluctuations in damage structure inside the volume of collision cascades was proposed. Conclusions are believed to be relevant for other molecular implantation, e.g. for the BF₂ ⁺.     

Chemically induced dynamic electron polarization (CIDEP) in nitrogen heterocyclic radicals: a stringent test of polarization theory

Transient ESR spectra are presented of polarized radicals formed following photolysis of quinoxaline, quinoline and pyrazine in solution. Triplet and geminate radical-pair mechanism polarizations are reported and discussed. The phase of the triplet polarization varies with the radical concerned in a manner which confirms the central assumption of the triplet theory.     

PHOTOINDUCED OXYGEN CONSUMPTION IN MELANIN SYSTEMS–II. ACTION SPECTRA and QUANTUM YIELDS FOR PHEOMELANINS

Abstract— Photoinduced oxygen consumption in systems containing synthetic and natural pheomelanins has been studied by ESR spectroscopy using a nitroxide spin probe to monitor oxygen concentration. Action spectra and quantum yields have been determined for melanin from 5-S-cysteinyldopa and for pheomelanins extracted from red human hair and red chicken feathers. For comparison, data also were obtained for eumelanins from black hair and black feathers. The action spectrum for oxygen consumption by cysteinyldopa melanin is closely related to that previously obtained for eumelanins except that it shows slightly less efficiency at intermediate wavelengths (ca. 300–400 nm). Action spectra for the natural pheomelanins resemble either that for cysteinyldopa melanin or that for eumelanin. In general pheomelanins are no more effective than eumelanins in promoting oxygen consumption, i.e. they are no more susceptible to net photooxidation.