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PubMed1999

Crystallization, characterization and measurement of MAD data on crystals of dengue virus NS3 serine protease complexed with mung-bean Bowman-Birk inhibitor.

Crystallization and preliminary characterization of the essential dengue virus NS3 serine protease complexed with a Bowman-Birk-type inhibitor from mung beans are reported. As the structure proved resistant to solution by molecular replacement and multiple isomorphous replacement methods, multi-wavelength anomalous diffraction data at the LIII edge of a holmium derivative have been measured. Promising Bijvoet and dispersive signals which are largely consistent with expected values have been extracted from the data. The structure, when determined, will provide a structural basis for the design, synthesis and evaluation of inhibitors of the protease for chemotherapy of dengue infections.

Crystallization↗
PubMed1992

Crystal structure of valinomycin-monohydrate cage complexes crystallized from dioxane.

Valinomycin, cyclo-[(L-Val-D-Hyv-D-Val-L-Lac)3-], was crystallized from aqueous dioxane solvent as a monohydrate complex in which water molecules were found within the ion-binding cavity of the ionophore: monoclinic P2(1), a = 14.377 (3), b = 41.554 (14), c = 14.080 (3) A, beta = 118.27 (2) degrees, Z = 4. There are two non-equivalent valinomycin-water complexes and three dioxane molecules in the asymmetric unit. The ionophore molecules adopt two similar but non-identical, octahedral, bracelet, cage conformations that are a consequence of two distinct ways in which the complexed water molecules can deform the normal octahedral coordinate geometry of the metal binding site. In the first complex the water molecule forms hydrogen donor bonds to the carbonyl oxygens of two L-valine residues on one facial side of the cavity, while in the second complex the water molecule is trigonal-planar coordinate and binds to two L-valine residues on one entrant face of the cavity plus a third D-valine residue from the opposite side of the cavity.

Binding Sites↗
PubMed1977

[Effect of tetracycline base crystallization on the conditions properties of the powders and drug forms obtained. The development of directed crystallization procedures for tetracycline base].

The study of the process of tetracycline base crystallization showed that with an increase in the rate of pH, temperature and mixed rotation changes, the specific surface of the crystalline precipitate increased with a simultaneous decrease in the bulk weight, looseness and volume density of the powder. The residual content of tetracycline in the mother solution decreased. The level of the effect of various parameters on the final results was different.

Chemistry, Pharmaceutical↗
PubMedDate not supplied

[Liquid crystals and liquid crystal dispersions of DNA-daunomycin complexes].

The X-ray and optical properties as well as the textures of liquid crystals formed of DNA molecules bound in complex with an anthracycline antibiotic daunomycin were investigated. It was shown that DNA.daunomycin complexes, depending on the extent of alteration of the DNA secondary structure by daunomycin, could yield two types of cholesterics differing in the direction of their spatial twisting as well as nematics. Liquid-crystalline dispersions of DNA.daunomycin complexes have CD spectra with "mirror" bands depending on daunomycin concentration. "Testing" of the orientation of daunomycin molecules on the DNA in liquid-crystalline particles suggested two types of binding.

Animals↗
PubMed2001

Non-destructive NIR-FT-raman analyses in practice. Part II. Analyses of 'jumping' crystals, photosensitive crystals and gems.

Using an improved sampling arrangement we observed the FT Raman spectra of the different phases of a 'jumping crystal', an inositol derivative. The phase transition produced--as consequences of large changes of the unit cell constants--changes in frequency and intensity mainly of CH deformation vibrations. Photochemical reactions, usually produced with light quanta in the visible range, are not activated with the quanta from the Nd:YAG laser at 1064 nm. The Raman spectra of the 'dark' form of a dinitrobenzyl pyridine and afterwards the 'light' form, the product of its illumination in the visible range, were recorded. We could not observe changes of most bands, especially not of the NO2-vibrations; however, a new strong band appeared at 1253 cm(-1), which may be due to the expected NH-photo-isomer. Genuine gemstones and fakes can be unambiguously identified by FT Raman spectroscopy. This is especially useful for the stones whose physical properties are quite similar to those of diamonds--moissanite and zirconia. The quality of diamonds can be estimated from relative band intensities; however, this is not in complete agreement with the internationally accepted visual qualification. Synthetic diamonds produced by CVD (chemical vapor deposition) show remarkable differences from natural ones in their FT-Raman spectra.

Journal Article↗
PubMed1975

Thermodynamic study of a liquid crystal as a liquid phase in gas-liquid chromatography. II. A cholesteric liquid crystal.

Gas-liquid chromatography is utilized for the determination of thermodynamic solution parameters for various organic solutes at infinite dilution in the meso- and isotropic phases of cholesteryl palmitate. The thermodynamic data and trends in values of the activity coefficients for the solutes are discussed in relation to their structure and to the orientations of the liquid crystal.

Cholesterol↗
PubMed2002

Criteria for liquid crystal formation in 5-alkoxy-, 5-alkylamino-, and 5-alkanoyl-tropolone complexes of transition metals (Cu(II), Zn(II), Ni(II), Co(II), UO(2)(VI), VO(IV)). The first uranium metallomesogen. Crystal structure of bis(5-hexadecyloxytropolonato)copper(II).

The mesophase properties of bis(5-alkoxytropolonato)copper(II) complexes are reported and interpreted in terms of d-layer spacings, which indicate considerable intertwining of the alkyl chains. The mesogenic properties depend on the nature of the 5-substituent: to be mesogenic, it must be alkoxy with n > 8, and may not be 5-alkanoyl or 5-alkylamino. The nature of the metal is also important: to be mesogenic, it may be Cu(II) or UO(2)(VI) but not Ni(II), Zn(II), Co(II), or VO(IV). The crystal structure of bis(5-hexadecyloxytropolonato)copper(II) shows how, even in the crystalline state, molecular packing is dominated by the interactions between alkyl chains, together with copper-oxygen interactions. In the Cu(II) complexes, strong interactions occur between Cu atoms and O atoms of neighboring molecules. These are stronger than alkyl-alkyl interactions and therefore dominate alkyl-alkyl interactions between neighbors which otherwise govern the possibility and nature of mesogenic properties. The Cu.O interactions disrupt alkyl-alkyl chain interactions enough to produce a mesophase; such interactions do not obtain in the T(d)() Zn(II) and Co(II) complexes, and indeed, these complexes are not mesogenic. Likewise, alkyl chain interactions by the oxygens of the UO(2)(VI) lead to a mesophase, and U constitutes the heaviest metal ever placed into a mesogenic molecule. In the case of VO(IV), analogous synthetic steps from VOSO(4) led to a new series of binuclear complexes [(VO)(2)(SO(4))(5-alkoxytropoloato)(2)].

Journal Article↗
PubMed2006

Crystal engineering in ionic liquids. The crystal structures of [Mppyr]3[NdI6] and [Bmpyr]4[NdI6][Tf2N].

Single crystals of [mppyr][NdI6] and [bmpyr][NdI6][Tf2N] are the first surprising examples of how the cation of an ionic liquid determines the compound formation from an ionic liquid. Depending upon the variation of the length of the alkyl chain of the quaternary pyrrolidinium cation (C3 and C4, respectively), incorporation of the anion of the ionic liquid, [Tf2N]-, can either be evoked or suppressed.

Journal Article↗
PubMed2006

Comparison of the crystal structures and magnetic properties of the low- and high-temperature forms of AgCuPO4: crystal structure determination, magnetic susceptibility measurements, and spin dimer analysis.

The crystal structure of the low-temperature form of AgCuPO4 (i.e., alpha-AgCuPO4) was determined by powder X-ray diffraction and was compared with that of the high-temperature form of AgCuPO4 (i.e., beta-AgCuPO4). The magnetic properties of the two forms were examined by measuring their magnetic susceptibilities and evaluating the relative strengths of their spin-exchange interactions on the basis of spin-dimer analysis. Both forms of AgCuPO4 have layers of Cu2P2O8 alternating with silver-atom double layers; beta-AgCuPO4 has two Cu2P2O8 layers per unit cell, while alpha-AgCuPO4 has one. The coordinate environment of each Cu2+ ion is close to being a distorted square pyramid in alpha-AgCuPO4, but it is close to being a distorted trigonal bipyramid in beta-AgCuPO4. The magnetic susceptibilities of alpha- and beta-AgCuPO4 are well simulated by an antiferromagnetic alternating-chain model, which leads to J/k(B) = -146.1 K and alphaJ/k(B) = -75.8 K for alpha-AgCuPO4, and J/k(B) = -82.6 K and alphaJ/k(B) = -31.7 K for beta-AgCuPO4 (with the convention in which the spin-exchange parameter between two adjacent spin sites is written as 2J). The spin gaps, delta/k(B), obtained from these parameters are 93.7 K for alpha-AgCuPO4 and 62.3 K for beta-AgCuPO4. The strongest spin exchange in both forms of AgCuPO4 comes from a super-superexchange path, and this interaction is stronger for alpha-AgCuPO4 than for beta-AgCuPO4 by a factor of approximately 2, in good agreement with the experiment. Our analysis supports the use of this model for beta-AgCuPO4 and indicates that the spin lattice of alpha-AgCuPO4 would be better described by a two-dimensional net made up of weakly interacting alternating chains.

Journal Article↗
PubMed1998

Synthesis and Crystal Structure of a New Type of Ionic Technetium(V) Dioxo Phosphine Complexes, [Tc(O)(2)(PR(3))(3)](+). Reactions with Pyridine and Crystal Structures of trans,cis,cis-[Tc(O)(2)(PR(3))(2)(py)(2)](+) Compounds.

New ionic technetium complexes of the type [TcO(2)(PR(3))(3)](+) have been synthesized from the reaction of [TcO(4)](-) with the phosphine in methanol. The crystal structures of two crystallographic forms of [TcO(2)(PEt(3))(3)](BPh(4)) were determined. The first form is monoclinic, space group P2(1)/n with a = 14.353(3) Å, b = 11.731(2) Å, c = 26.478(6) Å, beta = 101.22(1) degrees, and Z = 4. The second form is also monoclinic, space group P2(1)/c with a = 10.043(3) Å, b = 21.122(4), c = 20.994(5) Å, beta = 97.43(2) degrees, and Z = 4. [TcO(2)(PPr(3))(3)](BPh(4)) belongs to the monoclinic C2/c space group with a = 34.097(7) Å, b = 16.944(4) Å, c = 19.033(4) Å, beta = 102.99(1) degrees, and Z = 8. The geometry around the Tc atom is a trigonal bipyramid with the two oxo ligands in the trigonal plane. The Tc-O bond distances are between 1.707(4) and 1.726(3) Å, while the Tc-P bonds vary from 2.507(2) to 2.528(2) Å for the axial ligands and between 2.395(1) and 2.403(1) Å for the equatorial bond. The O-Tc-O angles are in the range 141.5(2)-143.4(2) degrees. The reaction of these complexes with pyridine produced trans,cis, cis-[Tc(O)(2)(PR(3))(2)(py)(2)](+) (py = pyridine). [Tc(O)(2)(PMe(3))(2)(py)(2)](BPh(4)) is monoclinic, space group P2(1)/c with a = 30.346(8) Å, b = 12.865(4) Å, c = 21.464(9) Å, beta = 110.35(2) degrees, and Z = 8, while [Tc(O)(2)(PEt(3))(2)(py)(2)](BPh(4)) is monoclinic, space group P2(1)/c with a = 10.594(6) Å, b = 19.921(7) Å, c = 21.306(10) Å, beta = 95.31(5) degrees, and Z = 4. The geometry around the Tc atom is a distorted octahedron with the oxo ligands located in trans positions to each other, while the phosphine and the pyridine ligands are cis to each other.

Journal Article↗
PubMed2002

67Zn solid-state and single-crystal NMR spectroscopy and X-ray crystal structure of zinc formate dihydrate.

The crystal structure, quadrupole coupling parameters, and the orientation of the electric field gradient tensors for each site of zinc formate dihydrate have been determined. There are two distinct sites in the asymmetric unit: one containing four in-plane waters with two bridging formats, the other containing six bridging formates. The solid-state NMR lineshapes have been assigned to their respective sites by using isotopic labeling and cross-polarization methods. The hydrated site corresponds to the lineshape having a quadrupole coupling constant (Cq) of 9.6 MHz and the anhydrous site has a Cq of 6.2 MHz. The absence of chemical shielding contributions to the observed lineshapes has been verified with a high-field solid-state NMR experiment performed at 18.8 T.

Crystallography, X-Ray↗
PubMed2006

Crystal structures of thermoelectric n- and p-type Ba8Ga16Ge30 studied by single crystal, multitemperature, neutron diffraction, conventional X-ray diffraction and resonant synchrotron X-ray diffraction.

Comprehensive single-crystal structural investigations of n- and p-type Ba8Ga16Ge30 have been carried out using multitemperature neutron and conventional X-ray diffraction as well as resonant synchrotron X-ray diffraction. The data show that the guest atom positions and dynamics are very similar in the two structures, although the barium atoms are slightly more displaced from the cage centers in the p-type structure than in the n-type structure (Deltad = 0.025 A). For both structures Fourier difference maps calculated from very high-resolution neutron diffraction data (sin theta/lambda > 2 A-1) show that the Ba nuclear density at lowest temperatures (15 K) is distributed in a torus around the crystallographic 6d site with maxima in the 24j positions. At room temperature the maxima have shifted to the 24k position. Analysis of atomic displacement parameters give Einstein temperatures of approximately 60(1) K for both structures. Thus, the fundamental difference in the low temperature thermal conductivity observed for p- and n-type Ba8Ga16Ge30 appear not to be directly related to the guest atom behavior as is commonly assumed in thermoelectric research. The neutron data and the resonant synchrotron X-ray data facilitate refinement of Ga/Ge framework occupancies. The Ga atoms have a clear preference for the 6c site with the preference being somewhat stronger for the n-type structure.

Journal Article↗
PubMed2006

Crystal-face dependence and photoetching-induced increases of dye-sensitized photocurrents at single-crystal rutile TiO2 surfaces.

Dye-sensitized photocurrents at (100)-, (001)-, and (110)-cut TiO(2) rutile surfaces were increased by photoetching of TiO(2), but the increasing ratio strongly depended on the cut crystal faces and the illumination intensity for the photoetching. For the (110)-cut surface, the photocurrent increase was moderately large and in proportion to the increase in the surface area of TiO(2) induced by the photoetching, irrespective of the illumination intensity for the photoetching. On the other hand, the photocurrent increases for the (001)- and (100)-cut surfaces, especially that for the (001)-cut surface, were prominent and largely exceeded the increases in the surface area. The results were explained by taking into account the following factors: (1) The (001)- and (100)-cut surfaces were thermodynamically unstable in contrast to the (110)-cut surface and had thicker inactive surface layers (or higher densities of surface defects), produced by surface reconstruction during heat treatment of TiO(2) at 550 degrees C in a hydrogen atmosphere for getting n-type semiconductivity. (2) Photoetching not only increased the surface area through formation of nanoholes and grooves at the surface but also effectively removed the thin inactive surface layers (or surface defects).

Journal Article↗
PubMed2002

Stacking of conical molecules with a fullerene apex into polar columns in crystals and liquid crystals.

Polar liquid crystalline materials can be used in optical and electronic applications, and recent interest has turned to formation strategies that exploit the shape of polar molecules and their interactions to direct molecular alignment. For example, banana-shaped molecules align their molecular bent within smectic layers, whereas conical molecules should form polar columnar assemblies. However, the flatness of the conical molecules used until now and their ability to flip have limited the success of this approach to making polar liquid crystalline materials. Here we show that the attachment of five aromatic groups to one pentagon of a C(60) fullerene molecule yields deeply conical molecules that stack into polar columnar assemblies. The stacking is driven by attractive interactions between the spherical fullerene moiety and the hollow cone formed by the five aromatic side groups of a neighbouring molecule in the same column. This packing pattern is maintained when we extend the aromatic groups by attaching flexible aliphatic chains, which yields compounds with thermotropic and lyotropic liquid crystalline properties. In contrast, the previously reported fullerene-containing liquid crystals all exhibit thermotropic properties only, and none of them contains the fullerene moiety as a functional part of its mesogen units. Our design strategy should be applicable to other molecules and yield a range of new polar liquid crystalline materials.

Journal Article↗
PubMed1988

Additional evidence from x-ray powder diffraction patterns that icosahedral quasi-crystals of intermetallic compounds are twinned cubic crystals.

Analysis of the measured values of Q for the weak peaks (small maxima, usually considered to be background fluctuations, "noise") on the x-ray powder diffraction curves for 17 rapidly quenched alloys leads directly to the conclusion that they are formed by an 820-atom or 1012-atom primitive cubic structure that by icosahedral twinning produces the so-called icosahedral quasi-crystals.

Journal Article↗
PubMed1999

On the prediction of crystal morphology. III. Equilibrium and growth behaviour of crystal faces containing multiple connected nets.

In this paper, the equilibrium and growth behaviour of faces (hkl) with more than one connected net is studied. It is shown that for these types of orientation different surface phases exist under equilibrium conditions as a function of temperature. Depending on the exact bonding topology at the surface, flat, rough or disordered flat phases are found. Moreover, the growth rate R(hkl) of such faces can differ significantly from the usually calculated relative growth rates based on the attachment energy. Monte Carlo simulations confirm the results from the Hartman-Perdok analyses and offer a tool for the prediction of the crystal habit as a function of supersaturation.

Journal Article↗
PubMed2006

SPINE high-throughput crystallization, crystal imaging and recognition techniques: current state, performance analysis, new technologies and future aspects.

This paper reviews the developments in high-throughput and nanolitre-scale protein crystallography technologies within the remit of workpackage 4 of the Structural Proteomics In Europe (SPINE) project since the project's inception in October 2002. By surveying the uptake, use and experience of new technologies by SPINE partners across Europe, a picture emerges of highly successful adoption of novel working methods revolutionizing this area of structural biology. Finally, a forward view is taken of how crystallization methodologies may develop in the future.

Crystallography↗