KINETIC BEHAVIOR OF EPR SIGNAL I: INDUCTION EFFECTS IN INTACT ALGAE

Abstract— There is considerable evidence that the light-induced narrow EPR signal I at g = 2·0025 in green algae is a reflection of the turnover of the photosynthetic reaction center, P700. A lag period or induction effect of the formation of this signal, subsequent to a dark period in whole fresh cells, is similar to induction effects for the bleaching of P700. The rate of formation of the signal is slower the longer the preceding dark period. DCMU does not much affect the induction phenomenon, but heating the cells to 60° abolishes it. Some substance or process which exists in the intact cell is altered by light and is detectable by its effect on signal I and on the rate of light-induced oxidation of P700 and cytochrome.     

Superfluidity and dimerization in a multilayered system of fermionic polar molecules

We consider a layered system of fermionic molecules with permanent dipole moments aligned perpendicular to the layers by an external field. The dipole interactions between fermions in adjacent layers are attractive and induce interlayer pairing. Because of the competition for pairing among adjacent layers, the mean-field ground state of the layered system is a dimerized superfluid, with pairing only between every other layer. We construct an effective Ising-XY lattice model that describes the interplay between dimerization and superfluid phase fluctuations. In addition to the dimerized superfluid ground state, and high-temperature normal state, at intermediate temperature, we find an unusual dimerized "pseudogap" state with only short-range phase coherence. We propose light-scattering experiments to detect dimerization.     

Estimation of mean and median pO2 values for a composite EPR spectrum

Electron paramagnetic resonance (EPR)-based oximetry is capable of quantifying oxygen content in samples. However, for a heterogeneous environment with multiple pO2 values, peak-to-peak linewidth of the composite EPR lineshape does not provide a reliable estimate of the overall pO2 in the sample. The estimate, depending on the heterogeneity, can be severely biased towards narrow components. To address this issue, we suggest a postprocessing method to recover the linewidth histogram which can be used in estimating meaningful parameters, such as the mean and median pO2 values. This information, although not as comprehensive as obtained by EPR spectral-spatial imaging, goes beyond what can be generally achieved with conventional EPR spectroscopy. Substantially shorter acquisition times, in comparison to EPR imaging, may prompt its use in clinically relevant models. For validation, simulation and EPR experiment data are presented.     

TEM study of the origin of the surface microroughness in DSL photoetched Si-implanted GaAs wafers

TEM has been used to study the origin of the surface microroughness that formed in both ²⁹Si as-implanted and rapid thermal annealed LEC undoped GaAs wafers after DSL photoetching. The degree of microroughness increased as the implant dose increased from 3 × 10¹² to 3 × 10¹⁴ atoms/cm². It has been found that such a microroughness is due to the fine-scale damage induced by the implantation in the as-implanted wafers and to interstitial dislocation loops in the implanted and then annealed wafers. Microroughness appears during DSL etching because such defects are effective recombination centres for the holes involved in the dissolution of the GaAs surface so that the wafers etch slower at the point-defect clusters and dislocation loops.     

Surface crystallization of amorphous solid water

We demonstrate that the crystallization of thin, supported amorphous solid water layers is initiated at the water surface. This is concluded from the observation of sequential crystallization of amorphous water at the surface, in the bulk, and at the water-support interface. A surface nucleation model quantitatively reproduces the observed transformation kinetics at the three sites.     

Spectral properties and ring conformation of some novel 2,3-dihydro-1H-1,4-diazepinium cations

A series of 2,3-dihydro-1H-1,4-diazepinium salts, which includes fused ring systems of known ring-junction configuration, has been prepared. A study of the spectral properties indicates that this ring system is largely planar and is sufficiently flexible to permit cis and trans fusion at the 2,3-bond to 5- or 6-membered rings without significant distortion.     

A synthetic entry into the 2- and 3-substituted-methyl 2,3-dihydro-1,4-benzoxazine series

Nmr spectroscopy has been used to demonstrate that the reported preparation of supposed 3-bromomethyl-2,3-dihydro-1,4-benzoxazine ( 3 ) is in error, the product of the reaction being in reality a monocyclic compound, 4 . An alternative entry to the 3-substituted series is described in the synthesis of the 3-hydroxymethyl derivative, 10 , the structure of which was established by nmr and mass spectroscopy. The previous assignment of structure to 2-carbethoxy-2,3-dihydro-1,4-benzoxazine, prepared by an ambiguous route, and to compounds derived from this ester, is shown to be correct.     

Quantum chemical calculations on thioridazine

Quantum chemical CNDO /2 calculations for the conformational preference of the side chain of thioridazine as a function of angle indicated the crystallographically determined structure gave the lowest energy. There is also a small region of conformational flexibility within the first 90° of rotation of the side chain. This is commensurate with the results which we had obtained previously for our similar calculations for promazine and its Cl and CF₃ derivatives, perazine and its Cl and CF₃ derivatives, and for the hypothetical hitherto unknown N-piperidinopromazine and its Cl and CF₃ derivatives. The conformational profile of thioridazine resembles that of the perazines. The calculated gross atomic populations on the alkyl nitrogen in thioridazine was within the range we had previously found necessary for neuroleptic activity.     

Trends in Radiation Polymerization

Previously it was generally assumed that high energy radiation could only initiate radical polymerization in solutions of monomers. However, examples of radiation-induced polymerization have recently become known that proceed via an ionic mechanism. Thus, solutions of a monomer can be polymerized ionically, preferably in the presence of a solid, at low temperatures. Suprisingly, this may also be accomplished with ultra-pure, mainly anhydrous systems, even at room temperature. The nature of the ions has not yet been fully elucidated.