PICOSECOND FLUORESCENCE STUDY OF PHOTOSYNTHETIC MUTANTS OF Chlamydomonas reinhardii: ORIGIN OF THE FLUORESCENCE DECAY KINETICS OF CHLOROPLASTS

Abstract— The fluorescence decay kinetics of photosynthetic mutants of Chlamydomonas reinhardii which lack photosystem II (PS II), photosystem I (PS I), and both PS II and PS I have been measured. The PS II mutant strain8–36C exhibits fluorescence decay lifetime components of 53, 424 and 2197 ps. The fluorescence decay of a PS I mutant strain12–7 contains two major fluorescence decay components with lifetimes of 152 and 424 ps. The fluorescence decay of mutant strain C2, which lacks both PS II and PS I, is nearly single exponential with a lifetime of 2561 ± 222 ps. In simulations in which it is assumed that wild-type decays are a simple sum of the major decay components of the isolated parts of the photosynthetic unit as measured in the mutants, curves are obtained that fit the wild-type C. reinhardii fluorescence decay data when the absorption cross-sections of PS II and PS I are weighted approximately equally. The 89 ps lifetime component in the wild-type is an average of 53 and 152 ps components arising from excitation transfer to and trapping in PS I and PS II. The single step transfer time in PS I is estimated to be between 100 and 700 fs depending on assumptions about array size. We find that between two and four visits to the PS I reaction center are required before final trapping.     

The foam analogy: from phases to elasticity

By mapping the interactions of colloidal particles onto the problem of minimizing areas, the physics of foams can be used to understand the phase diagrams of both charged and fuzzy colloids. We extend this analogy to study the elastic properties of such colloidal crystals and consider the face-centered cubic, body-centered cubic and A15 lattices. We discuss two types of soft interparticle potentials corresponding to charged and fuzzy colloids, respectively, and we analyze the dependence of the elastic constants on density as well as on the parameters of the potential. We show that the bulk moduli of the three lattices are generally quite similar, and that the shear moduli of the two non-close-packed lattices are considerably smaller than in the face-centered cubic lattice. We find that in charged colloids, the elastic constants are the largest at a finite screening length, and we discuss a shear instability of the A15 lattice.     

Anomalous grazing incidence small-angle x-ray scattering studies of platinum nanoparticles formed by cluster deposition

The size evolution of platinum nanoparticles formed on a SiO2/Si(111) substrate as a function of the level of surface coverage with deposited clusters has been investigated. The anisotropic shapes of sub-nanometer-size nanoparticles are changed to isotropic on the amorphous substrate as their sizes increased. Using anomalous grazing incidence small-angle x-ray scattering (AGISAXS), the scattering from nanoparticles on the surface of a substrate is well separated from that of surface roughness and fluorescence. We show that AGISAXS is a very effective method to subtract the background and can provide unbiased information about particle sizes of less than 1 nm.     

Gas chromatographic optimization studies on the side chain and ring regioisomers of methylenedioxymethamphetamine

Gas chromatographic (GC) optimization studies are conducted for the 10 methylenedioxyphenethylamine regioisomeric substances related to the drug of abuse 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy). These 10 compounds, having the same molecular weight and equivalent major mass spectral fragments, are not completely resolved using typical GC-mass spectrometry screening methods for illicit drugs. MDMA coelutes with at least one nondrug regioisomer under standard drug screening conditions. Separation of the 10 regioisomers is studied using stationary phases of varying polarities. Resolution optimization shows that very slow program rates give the best separation for the nonpolar stationary phases, requiring analysis times of as much as 85 min. Narrow-bore columns containing the same nonpolar stationary phases improve the analysis time to approximately 29 min. The polar stationary phase DB-35MS allows high-temperature programming rates, yielding complete resolution of all 10 compounds in less than 7 min. Temperature program optimization studies on the DB-35MS phase allow the separation time to be reduced to approximately 4.5 min.     

Exotic differentiable structures and general relativity

We review recent developments in differential topology with special concern for their possible significance to physical theories, especially general relativity. In particular we are concerned here with the discovery of the existence of non-standard (fake or exotic) differentiable structures on topologically simple manifolds such asS ⁷, ⁴ andS ³ X ¹. Because of the technical difficulties involved in the smooth case, we begin with an easily understood toy example looking at the role which the choice of complex structures plays in the formulation of two-dimensional vacuum electrostatics. We then briefly review the mathematical formalisms involved with differentiable structures on topological manifolds, diffeomorphisms and their significance for physics. We summarize the important work of Milnor, Freedman, Donaldson, and others in developing exotic differentiable structures on well known topological manifolds. Finally, we discuss some of the geometric implications of these results and propose some conjectures on possible physical implications of these new manifolds which have never before been considered as physical models.     

Epicardial development in the rat: a new perspective.

Development of the epicardium is critical to proper heart formation. It provides all of the precursor cells that form the coronary system and supplies signals that stimulate cardiac myocyte proliferation. The epicardium forms from mesothelial cells associated with the septum transversum and is referred to as the proepicardium (PE). Two different methods by which these PE cells colonize the developing heart have been described. In avians, PE cells form a bridge to the heart over which PE cells migrate onto the heart. In fish and mammals, PE cells form vesicles of cells that detach from the mesothelium, float through the pericardial cavity, and attach to the heart. A previous study of rat PE development investigated this process at the histological level. Protein markers have been developed since this study. Thus, we investigated this important developmental process coupled with these new markers using other visualization techniques such as scanning electron microscopy (SEM) and confocal microscopy. Finally, a novel, three-dimensional (3-D) culture system was used to confirm the identity of the PE cells. In this study, we found convincing evidence that the rat PE cells directly attach to the heart in a manner similar to that observed in avians.     

A COMPARISON OF MAMMALIAN CELL SENSITIVITY TO EITHER 254 nm OR ARTIFICIAL "SOLAR" SIMULATED RADIATION

The sensitivity of six mammalian cell strains to either germicidal (254 nm) or artificial "solar" simulated radiation was tested. The solar simulator used had an output similar, in some respects, to natural sunlight. Cellular capacity for Herpes simplex virus production was used as the assay procedure. The tested cells were a strain of African green monkey kidney cells and five human skin fibroblast cell strains. The latter included a "normal" cell strain, and four photosensitive cell strains; three of which were strains of xeroderma pigmentosum cells, and one strain of Bloom's syndrome cells. When comparing the D¹⁰ values, the different cell strains varied by a factor of six in response to germicidal radiation, but only by a factor of two to artificial "solar" simulated radiation. The relative sensitivity of the cells to either type of radiation also varied from 1.7 to 10.9. Large variations in response occurred even among the xeroderma pigmentosum cell strains. These responses suggest that mammalian cell sensitivity to 254 nm radiation may not be a true indicator of a cell's responses to natural sunlight.     

Separation of C27, C28 and C29 sterols by reversed-phase high-performance liquid chromatography on small particles.

The application of reversed-phase high-performance liquid chromatography to the analytical- and preparative-scale separation of sterols has been evaluated. The capacity factors, k', for a number of compounds chromatographed on a muBondapak C18 (LESS THAN 10 MUM) COLUMN ARE PRESENTED. C27, C28 and C29 sterols and also sterols differing in degree of unsaturation could be readily separated as their acetates in this system. The present reversed-phase chromatographic method is apparently not as selective as silver nitrate-silica gel thin-layer chromatography for the position of unsaturation in the sterol molecule.     

Muonium formation and the “missing fraction” in vapors

The vapor phase fractional polarizations of positive muons thermalizing as the muonium atom (P _M) and in diamagnetic environments (P _D) has been measured in H₂O, CH₃OH, C₆H₁₄, C₆H₁₂, CCl₄, CHCl₃, CH₂Cl₂ and TMS, in order to compare with the corresponding fractions measured in the condensed phases. There is a marked contrast in every case, with the vapor phase results being largely understandable in terms of a charge exchange/hot atom model. Unlike the situation in the corresponding liquids, there is no permanent lost fraction in the vapor phase in the limit of even moderately high pressures (1 atm); at lower pressures, depolarization is due to hyperfine mixing and is believed to be well understood. For vapor phase CH₃OH, C₆H₁₄, C₆H₁₂, and TMS therelative fractions are found to be pressure dependent, suggesting the importance of termolecular hot atom (or ion) reactions in the slowing down process. For vapor phase H₂O and the chloromethanes, the relative fractions are pressure independent. For CCl₄,P _M=P _D0.5 in the vapor phase vs.P _D=1.0 in the liquid phase; fast thermal reactions of Mu likely contribute significantly to this difference in the liquid phase. For H₂O,P _M 0.9 andP _D0.1 in the vapor phase vs.P _D 0.6 andP _M0.2 in the liquid phase. Water appears to be the one unequivocal case where the basic charge exchange/hot atom model is inappropriate in the condensed phase, suggesting, therefore, that radiation induced spur effects play a major role.