Single-step separation of major and rare ribonucleosides and deoxyribonucleosides by high-performance liquid cation-exchange chromatography for the determination of the purity of nucleic acid preparations

A method is described for the separation of 13 major and minor ribo- and deoxyribonucleosides in a single chromatographic run using high-performance liquid chromatography on strongly acidic cation-exchange columns. The method proved useful for the routine determination of small amounts of ribonucleic acid impurities in deoxyribonucleic acid preparations and vice versa. About 3% or even less of nucleic acid contamination in a given sample can be easily detected and quantitatively determined under the conditions used.     

Polarographic determination of cyanide as nickelcyano complex in blood plasma after selective extraction in a methylene blue impregnated polyethylene column

A method for the determination of cyanide in blood plasma by differential pulse polarography (DPP) is described without a drastic acidification of the sample. Cyanide was determined as tetracyanonickelate(II)-anion complex after a microwave-acid assisted cleanup and a selective complex extraction in a polyethylene methylene blue (PE-MB) impregnated column. The cyano complex was eluted from the column with water/acetonitrile and determined by pulse-polarography at –380 mV (Ag/AgCl). The linear range of calibration was obtained from 1.2 to 9.6 μg of cyanide with r = 0.99 and RSD = 9% of 1.2 μg of cyanide. A detection limit of 40 μg L^–1 was calculated and the recoveries of cyanide from spiked samples were about 80%. This method was compared with the classical pyridine-pyrazolone method.     

Langmuir-Blodgett and X-ray Diffraction Studies of Isolated Photosystem II Reaction Centers in Monolayers and Multilayers: Physical Dimensions of the Complex*

Abstract— The photosystem II (PSII) reaction center (RC) is a hydrophobic intrinsic protein complex that drives the water-oxidation process of photosynthesis. Unlike the bacterial RC complex, an X-ray crystal structure of the PSII RC is not available. In order to determine the physical dimensions of the isolated PSII RC complex, we applied Langmuir techniques to determine the cross-sectional area of an isolated RC in a condensed monolayer film. Low-angle X-ray diffraction results obtained by examining Langmuir-Blodgett multilayer films of alternating PSII RC/Cd stearate monolayers were used to determine the length (or height; z-direction, perpendicular to the plane of the original membrane) of the complex. The values obtained for a PSII RC monomer were 26 nm²and 4.8 nm, respectively, and the structural integrity of the RC in the multilayer film was confirmed by several approaches. Assuming a cylindrical-type RC structure, the above dimensions lead to a predicted volume of about 125 nm³. This value is very close to the expected volume of 118 nm³, calculated from the known molecular weight and partial specific volume of the PSII RC proteins. This same type of comparison was also made with the Rhodobacter sphaeroides RC based on published data, and we conclude that the PSII RC is much shorter in length and has a more regular solid geometric structure than the bacterial RC. Furthermore, the above dimensions of the PSII RC and those of PSII core (RC plus proximal antenna) proteins protruding outside the plane of the PSII membrane into the lumenal space as imaged by scanning tunneling microscopy (Seibert, Aust. J. PL Physiol. 22,161–166, 1995) fit easily into the known dimensions of the PSII core complex visualized by others as electron-density projection maps. From this we conclude that the in situ PSII core complex is a dimeric structure containing two copies of the PSII RC.     

Low-energy chlorophyll states in the CP43 antenna protein complex: simulation of various optical spectra. II

The CP43 protein complex of the core antenna of higher plant photosystem II (PSII) has two quasidegenerate "red" absorption states. It has been shown in the accompanying paper I (Dang, N. C., et al. J. Phys. Chem. B 2008, 112, 9921.) that the site distribution functions (SDFs) of red-states A and B are uncorrelated and the narrow holes are burned in subpopulations of chlorophylls (Chls) from states A and B that are the lowest-energy pigments in their particular CP43 complexes and cannot further transfer energy downhill. In this work, we present the results of a series of Monte Carlo simulations using the 3.0-A structure of the PSII core complex from cyanobacteria (Loll, B., et al. Nature 2005, 303, 1040.) to model absorption, emission, persistent, and transient hole burned (HB) spectra. At the current structural resolution, we found calculated site energies (obtained from INDO/S calculations) to be only suggestive because their values are different for the two monomers of CP43 in the PS II dimer. As a result, to probe the excitonic structure, a simple fitting procedure was employed to optimize Chl site energies from various starting values corresponding to different A/B pigment combinations to provide simultaneously good fits to several types of optical spectra. It is demonstrated that the shape of the calculated absorption, emission, and transient/persistent hole-burned spectra is consistent with experimental data and our model for excitation energy transfer between two quasi-degenerate lowest-E states (A and B) with uncorrelated SDFs discussed in paper I. Calculations revealed that absorption changes observed near 670 nm in the non-line-narrowed persistent HB spectra (assigned to photoconversion involving Chl-protein hydrogen-bonding by Hughes (Biochemistry 2006, 45, 12345.) are most likely the result of nonphotochemical hole-burning (NPHB) accompanied by the redistribution of oscillator strength due to modified excitonic interactions. We argue that a unique redistribution of oscillator strength during the NPHB process helps to assign Chls contributing to the low-energy states. It is demonstrated that the 4.2 K asymmetric triplet-bottleneck (transient) hole is mostly contributed to by both A and B states, with the hole profile described by a subensemble of pigments, which are the lowest-energy pigments (B s- and A s-type) in their complexes. The same lowest-energy Chls contribute to the observed fluorescence spectra. On the basis of our excitonic calculations, the best Chl candidates that contribute to the low-energy A and B states are Chl 44 and Chl 37, respectively.     

Operation of a high power,broadly tunable infrared dye laser

We discuss the operation and performance of a ruby pumped infrared dye laser with a wide tuning range and a high out-put power. The longitudinally pumped infrared laser was operated in the Littrow configuration without an intracavity beam expander. The dye, IR 125, exhibited a tunability range that extended from 8325 Å to 9375 Å. The dye laser had a pulse duration of 20 ns and an output power of 12.5 MW with a 2.3 joule ruby pump. The maximum output power of the infrared laser was limited by the damage threshold of the tuning element.     

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