PHOTOEXCITATION OF RHODOPSIN: CONFORMATION CHANGES IN THE CHROMOPHORE, PROTEIN AND ASSOCIATED LIPIDS AS DETERMINED BY FTIR DIFFERENCE SPECTROSCOPY

Abstract— The visual pigment rhodopsin is the major membrane protein in the rod photoreceptor membrane. Rhodopsin's function is to transduce the light induced isomerization (ll-cis to all-trans) of its internally located retinylidene chromophore into transient expression of signal sites at the surface of the protein. Fourier transform infrared (FTIR) difference spectroscopy has been used to study all of the steps in the photobleaching sequence of rhodopsin. Early protein alterations involving the peptide backbone and aspartic and/or glutamic carboxyl groups were detected which increase upon lumirhodopsin formation and spread to water exposed carboxyl groups by metarhodopsin II. The intensified and frequency shifted hydrogen-out-of-plane vibrations of the chromophore that are present in bathorhodopsin are absent in lumirhodopsin. This indicates that by lumirhodopsin, the chromophore has relaxed relative to its more strained all-frans form in bathorhodopsin. Finally, the transition to metarhodopsin II is found to involve perturbation of the acyl tail region of unsaturated phospholipid molecules possibly in response to small changes in the shape of the rhodopsin.     

A selection of open problems

This is a collection of open problems which touch on Neil Hindman's mathematics and were collected in conjunction with the Conference on Ramsey Theory and Topological Algebra in his honor.     

Zur Bestimmung des Wassers in organischen Substanzen

Ohne Zusammenfassung     

Revisit of rotational motion of axial poly-atomics by molecular dynamics simulation and group theory: liquid benzene at 298, 365, 432, 498, 562 K

The paper reports quantitative physical aspects of the overall rotational motion of axially symmetric poly-atomics on the example of liquid benzene at five temperatures between 298 and 562?K on the basis of the group-theoretical approach proposed by B. Keller and F. Kneub?hl in Helv. Phys. Acta 45,1127 (1972), with a database generated by molecular dynamics simulation of ensemble-averaged orientational fluctuations. It is shown that (i) benzene rotates by a Markov process around an average, in-frame moving rotation axis and (ii) that numerous reported orientational correlation results that claim to display the rotational motion of the molecule, are nevertheless now to be considered irrelevant to their promulgated aim because their analyses omitted to account for the simultaneous inclination motion, as well as its particular time scale, of the average direction of the singular average molecular rotation axis of a benzene molecule.     

193 nm resists and lithography

A review of recent efforts to develop photoresist materials and processes for 193 nm (ArF excimer laser) photolithography is reported. Three categories of resist processes are discussed: (1) conventional single layer, (2) bilayer and (3) surface-imaged resist processes. To date, materials have been developed for each process which exhibit resolution to less than 0.25 μm with sensitivities of less than 50 mJ/cm².     

Imaging of 1-nm-thick films with 193-nm microscopy

We have implemented a reflected-light microscope operating in the deep ultraviolet at 193 nm. Many materials absorb strongly at this wavelength, providing greatly enhanced contrast compared with visible and near-ultraviolet microscopes. Polymer films as thin as 1 nm and SiO(2) films as thin as 3 nm have been imaged with this nonoptimized instrument. We have also calculated image contrast for several thin-film materials that are important in semiconductor processing, and we show that 193-nm light provides 60-485x better contrast than visible light (500 nm) and 4-95x better contrast than near-ultraviolet light (315 nm) for these materials.