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At least 541 records · Page 30Linked to original sources
PubMed2004

Liquid-crystal blazed grating with azimuthally distributed liquid-crystal directors.

We propose a novel formation method of arbitrary phase profiles of circular light by controlling azimuthal angles of liquid-crystal directors; its principle is described theoretically. A new liquid-crystal blazed grating is demonstrated by use of the proposed method. It is revealed that the first-order diffraction efficiency reaches the maximum value (theoretically 100%, experimentally approximately 90%) at an optimum applied voltage when the phase difference between the extraordinary and ordinary rays agrees with one-half the wavelength. Furthermore, the polarization states of the diffracted light beams are analyzed by Stokes parameter measurements, and unique polarization-splitting properties are revealed.

Journal Article↗
PubMed2006

Simple optical method for determination of crystal orientation in photorefractive crystals.

A simple optical method for determination of crystallographic orientations +/-x, +/-y, and +/-z in photorefractive crystals based on light amplification via backward two-wave mixing (TWM) is presented. We consider a photorefractive Fe-doped lithium niobate crystal (LiNbO(3):Fe) with a standard x-y-z cut as an example to illustrate the principle, manipulation, and experimental results of this method in detail. Also we see that the direction of the light amplification, namely, the direction of the nonreciprocal steady-state energy transfer, strongly depends on the direction of the grating vector with respect to the corresponding crystallographic axes mainly under the diffusion mechanism. Finally, a way of determining the sign of the charge carriers in photorefractive materials is proposed.

Journal Article↗
PubMed1990

Ultrastructural localization of Charcot-Leyden crystal protein (lysophospholipase) to intracytoplasmic crystals in tumor cells of primary solid and papillary epithelial neoplasm of the pancreas.

Charcot-Leyden crystals (CLC), composed of a single protein with lysophospholipase activity, have been traditionally associated with eosinophil-rich disorders. Atypically shaped and typical CLC were noted by electron microscopy in the surgical sample from a patient with solid and papillary epithelial neoplasm of the pancreas. This rare primary tumor of the pancreas with limited aggressive behavior also contained damaged and partially or completely degranulated eosinophils in the tumor stroma. We localized CLC protein by ultrastructural immunogold staining to the CLC within vacuolar structures and in vesicles of tumor cell cytoplasm as well as to the cytoplasm and nucleus of eosinophils in the tumor stroma. These findings provide evidence that epithelial tumor cells contain Charcot-Leyden crystal protein that most likely originates from tumor stroma eosinophils. Tumor stroma eosinophils have generally been associated with improved prognoses in a wide variety of epithelial neoplasms. The role of tumor CLC protein (lysophospholipase) in these settings deserves further investigation.

Adult↗
PubMed1976

Crystallization and preliminary crystal data of iron-containing superoxide dismutase from Pseudomonas ovalis.

Large single crystals of iron-containing superoxide dismutase from Pseudomonas ovalis were prepared from 50% saturated ammonium sulfate solution, at pH 4.5, on gentle evaporation of the solvent at 4 degrees. The crystals were monoclinic, space group P2, with unit cell dimensions a = 81.9 A, b = 49.0 A, c = 61.0 A, and beta = 106 degrees. Considerations of cell volume and protein molecular weight indicated 1 molecule of superoxide dismutase in the assymmetric unit, the smallest number reported so far for superoxide dismutases.

Binding Sites↗
PubMed2005

Crystal growth and vibrational spectroscopic studies of the semiorganic non-linear optical crystal--bisthiourea zinc chloride.

The semiorganic non-linear optical crystal bisthiourea zinc chloride (BTZC) was grown by mixed solvent slow evaporation technique. The solubilities under various solvents in different proportions have been studied. Vibrational spectra were recorded to determine the symmetries of molecular vibrations. The observed Raman and infrared bands were also assigned and discussed. The optical transmission spectral study was also carried out. The property of second harmonic generation of BTZC was also verified.

Bismuth↗
PubMed2005

Single crystal EPR and optical absorption studies of Cu2+ ion in L-arginine sulphophosphate monohydrate--a nonlinear optical crystal.

The EPR spectra of Cu2+ ion in L-arginine sulphophosphate monohydrate (LASP), a nonlinear optical material (NLO) have been studied at room temperature. Two magnetically inequivalent interstitial Cu2+ sites in the lattice were identified. The principal values of g- and A-tensors indicate that the symmetry of the electrostatic field around the Cu2+ ion is rhombic. Bonding parameters have been evaluated and the ground state wave function of Cu2+ ion is constructed. The ground state is found to be an admixure of x2 - y2 and 3z2 - r2 orbitals. By correlating EPR and optical absorption spectra the crystal field parameters have been evaluated.

Arginine↗
PubMed1982

Trace metal-citric acid complexes as inhibitors of calcification and crystal growth. I. Effects of Fe(III), Cr(III) and Al(III) complexes on calcium phosphate crystal growth.

The crystal growth of calcium phosphate has been shown to be inhibited by a low molecular weight Fe(III)-citric acid complex formed when there are high ratios of citrate:iron at neutral pH in aqueous solution. Synergism with citric acid was also observed in systems containing Al(III) or Cr(III) ion, but different unknown complexes seemed to be involved. These results are in qualitative agreement with a preceding study involving calcification of an organic matrix. Since chelating agents like citric acid can compete with the storage proteins for iron, we suggest that the Fe(III)-citrate complexes studied here may be formed in vivo and participate in regulating biologic calcification.

Aluminum↗
PubMed1982

Trace metal-citric acid complexes as inhibitors of calcification and crystal growth. II. Effects of Fe(III), Cr(III) and Al(III) complexes on calcium oxalate crystal growth.

The high molecular weight Fe(III)-citric acid complex, formed at low ratios of citrate:iron in solution, has been shown to be an effective inhibitor of calcium oxalate crystal growth. This appears to be a specific reaction, since 2 other similar metal ions. Al(III) and Cr(III), exhibit no synergism with citric acid in this system. Because the low molecular weight Fe(III)-citric acid complex, formed at high ratios of citrate:iron, inhibits calcium phosphate precipitation but has no effect on calcium oxalate, the Fe(III)-citric acid system might have a selective biologic role in regulating the growth of calcium-containing urinary calculi in vivo.

Aluminum↗
PubMed2002

Crystal packing and hydrogen bonding in platinum(II) nucleotide complexes: X-ray crystal structure of [Pt(MeSCH(2)CH(2)SMe)(5'-GMP-N7)(2)].6H(2)O.

We have synthesised the complex [Pt(CH(3)SCH(2)CH(2)SCH(3))(5'-GMP-N7)(2)].6H(2)O (1), where 5'-GMP is 5'-guanosine monophosphate, and determined its X-ray crystal structure. Pt(II) adopts a square-planar geometry in which the bases are coordinated head-to-tail (HT) in the Delta configuration. The nucleotide conformation in this complex is almost identical to that in the previously reported complex [Pt(en)(5'-GMP-N7)(2)].9H(2)O (2), in which there is outer sphere macrochelation via intramolecular H-bonding between the monoanionic phosphate groups and the coordinated ethylenediamine (en) NH. It is therefore apparent that intermolecular interactions rather than intramolecular H-bonding determines the orientation of the sugar-phosphate side-chain in these Pt(II) bisnucleotide complexes in the solid state.

Crystallization↗
PubMed2000

Crystallization of retinol dehydratase from Spodoptera frugiperda: improvement of crystal quality by modification by ethylmercurythiosalicylate.

Retinol dehydratase is a sulfotransferase which is presumed to catalyze the dehydration of its substrate via a transient retinyl sulfate intermediate. Crystals (space group P2(1), unit-cell parameters a = 82.05, b = 66.61, c = 84.90 A, beta = 111.29 degrees ) are significantly improved by covalent modification of the protein with ethylmercury.

Animals↗
PubMed2002

An overview on 2-methyl-2,4-pentanediol in crystallization and in crystals of biological macromolecules.

2-Methyl-2,4-pentanediol (MPD) is the most popular chemical additive used for crystallization of biological macromolecules. However, the mechanism of its action on proteins in aqueous solution is not well understood. We have carried out a systematic analysis of the conformation and environment of MPD molecules bound to proteins. We find that the majority of MPD molecules adopt their most stable conformer. They prefer to bind to hydrophobic sites with a distinct preference for leucine side chains. Most MPD binding sites involve amino-acid residues in helical or beta-sheet structures. MPD binding to proteins is penetrative, leading to displacement of water molecules in grooves and cavities (sometimes ligand-binding and active sites) on the protein surface. This results in a large reduction of solvent-accessible area, which can have significant implications for protein stability. The packing of the MPD molecules by the protein is not optimal and usually some other solvent molecules are also bound along with it. Our analysis suggests that MPD is not as strong a denaturant as often suggested. It promotes stabilization of the protein by preferential hydration, which is facilitated by attachment of MPD molecules to the hydrophobic surface.

Binding Sites↗
PubMed2003

Crystallization and initial crystal characterization of the N-terminal DH/PH domain of Trio.

Trio is a multidomain signaling protein that plays an important role in neurite outgrowth, axon guidance and skeletal muscle development. Trio contains two DH/PH tandem domains that respectively activate the small GTPases RhoG/Rac and RhoA. The N-terminal DH/PH domain, TrioN, crystallizes in space group P3(1)21, with one TrioN molecule in the asymmetric unit and diffracts to 1.7 A resolution. The unit-cell parameters are a = b = 99.5, c = 98.3 A, alpha = beta = 90, gamma = 120 degrees. A greater than 90% complete native data set has been collected and structure determination using the multiple isomorphous replacement (MIR) method is ongoing.

Crystallization↗
PubMed2005

Anaerobic purification and crystallization to improve the crystal quality: ferredoxin II from Desulfovibrio gigas.

Sulfate-reducing bacteria (SRB), which are strict anaerobes, contain an electron-transfer chain from pyridine nucleotides to molecular oxygen. This unique enzymatic equipment allows the bacterium to produce ATP when exposed to air from the degradation of internal reserves of polyglucose. Ferredoxin II (Fd II) is a small electron-transfer protein isolated from the strict anaerobic sulfate-reducing bacterium Desulfovibrio gigas. The protein contains 58 amino acids and an iron-sulfur cluster. The cluster [3Fe-4S] spontaneously undergoes conversion to [4Fe-4S] when it is used as an electron mediator in the phosphoroclastic reaction. The iron-sulfur geometries and interconversion mechanism appear to have physiological significance between the oxidized and reduced states. Crystallization of Fd II in an anaerobic environment was achieved at a higher resolution of 1.37 A and the differences between the anaerobic and aerobic structures will reveal the unique iron-storage function and electron-transfer mechanism of ferredoxin II from D. gigas.

Crystallization↗
PubMed2005

Heavy-atom Database System: a tool for the preparation of heavy-atom derivatives of protein crystals based on amino-acid sequence and crystallization conditions.

Heavy-atom Database System (HATODAS) is a WWW-based tool designed to assist the heavy-atom derivatization of proteins. The conventional procedure for the preparation of derivatives is usually a time-consuming 'trial-and-error' process. The present program provides a solution for this problem using a database of known heavy-atom derivatives. A database search suggests potential heavy-atom reagents for any target protein based on its amino-acid sequence and crystallization conditions. A mining of the database identified 93 preferred motifs for heavy-atom binding. The motifs are observed frequently at the actual heavy-atom-binding sites encountered in the process of structure determination.

Amino Acid Motifs↗
PubMed1999

The incorporation of a non-natural amino acid (aza-tryptophan) may help to crystallize a protein and to solve its crystal structure. Application to bacteriophage lambda lysozyme.

Until now, wild-type bacteriophage lambda lysozyme had been impossible to crystallize. This difficulty could be overcome by the replacement of the four tryptophan residues by aza-tryptophans. Analysis of the intermolecular and intramolecular contacts in this modification allows understanding of the differences in behaviour between the native and modified molecules. Furthermore, this mutation was very useful for the creation of new heavy-atom binding sites and for the solution of the non-crystallographic symmetry, which is extremely important for phase improvement. This procedure seems to be generally applicable, at least in the search for new possibilities for heavy-atom binding sites.

Aza Compounds↗