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Neither the macromolecular mass fractions of urine from stone-formers nor those from the matrix of calcium-containing urinary calculi contain factors which promote the crystal growth rate of calcium oxalate crystals in vitro.
The catalytic subunit of cAMP-dependent protein kinase from porcine heart has been crystallized in several different crystal forms. One of these forms diffracts to 3.5 A resolution. It is in monoclinic space group P2(1) with a = 64.24 A, b = 143.58 A, c = 48.40 A, alpha = gamma = 90 degrees and beta = 106.9 degrees.
Two-dimensional crystals of p68, a Ca2+ -binding protein that has homology with members of the lipocortin/calpactin family, were obtained by interaction with a phospholipid monolayer. By measuring surface pressure at constant surface area, p68 was found to interact in a Ca2+ -dependent manner specifically with phosphatidylethanolamine, less so with phosphatidylserine and not at all with phosphatidylcholine. With dimyristoyl-phosphatidylethanolamine, two-dimensional crystalline arrays were formed. Image analysis of electron micrographs of these crystals, which diffracted to about 50 A, revealed p3 symmetry with a unit cell of about 178 A by 178 A; the protein densities showed a two-domain structure giving a cylindrical molecule of about 100 A by 35 A diameter packed as trimers. Three-dimensional microcrystals obtained without lipid or Ca2+ were suitable for electron microscopy and gave a tetragonal unit cell of about 256 A by 68 A. The implications of these observations on the structure and lipid specificity of p68 binding are discussed.
Membrane protein reconstitution into two-dimensional (2-D) ordered arrays is described. The assembly of 2-D crystals may be modeled as a two-step process: the membrane protein is first integrated in the lipid bilayer and then crystallized by removal of excess detergent or lipid and/or by precipitating agents. Lipid-detergent, protein-detergent, and lipid-protein interactions are critical during the first step, while lipid-protein and protein-protein interactions dominate events in the second step. The evidence supporting this model results from quasielastic light scattering analyses and electron microscopy of different lipid-detergent systems and reconstitution experiments with Escherichia coli porin OmpF, Phormidium laminosum photosystem I reaction centers, and integral membrane proteins of mammalian lens fiber cells.
Benzocaine (BZC), butambene (BTN) and isobutambene (BTI) are basic local anaesthetic agents of the ester type, preferentially used for surgery and dental procedures. The compounds, official in the USP (BZC and BTN) and Ph. Eur. (BZC), were each found to exist in two polymorphic crystal forms and their solid state characteristics have been determined by thermomicroscopy, differential scanning calorimetry (DSC), FTIR-, FT-Raman-spectroscopy as well as X-ray powder diffractometry. This work further emphasizes the comparison of solid state characteristics of three compounds with closely related structural features on molecular level, leading to opportunities for the investigation of structure-property relationships. Mod. I0 is the particular thermodynamically stable form at room temperature in all of the three systems. This form is present in commercial products and can be crystallized from solvents at room conditions. Mod. II can be obtained by annealing the supercooled melt or fast cooling of a saturated solution, respectively. The endothermic transformation of mod. II to mod. I0 upon heating confirms that mod. I0 is thermodynamically stable at ambient conditions (heat of transition rule) whereas mod. II is enantiotropically related to mod. I0, i.e. is metastable at temperatures above the transition temperature. The metastable forms show different kinetic stabilities at room temperature.
Dielectric anizotropy and relaxation properties of 2,3-dicyano-1,4-di[3,4,5-tri(dodecyloxy)phenylcarbonyloxy] benzene (DCDPB)-doped E7 and E7 liquid crystal have been investigated by the dielectric spectroscopy method. Dielectric anisotropy property of the LCs changes from the positive type to negative type. Dielectric relaxation properties suggest that LCs exhibit a monodispersive dielectric property. The relaxation frequency of E7 and E7/DCDPB liquid crystals was calculated by means of Cole-Cole plots. Consequently, DCDPB dopant changes the dielectric anizotropy and relaxation parameters of E7 LC.
Two crystal forms of bovine heart creatine kinase, which are suitable for X-ray diffraction studies, have been grown at room temperature using 2-methyl-2,4-pentanediol as the precipitant at pH 7.2. The space group of the orthorhombic form is P2(1)2(1)2, with unit cell dimensions a = 133 A, b = 128 A and c = 65 A, and there is one dimeric molecule in the asymmetric unit. The space group of the tetragonal form is P4(2)2(1)2, with unit cell dimensions a = b = 132 A and c = 75 A, with one subunit in the asymmetric unit. The tetragonal crystals diffract to at least 2.0 A resolution.
Membrane crystals of mitochondrial ubiquinol: cytochrome c reductase of improved size and long-range order and of the cytochrome bc1 subcomplex have been obtained by a dialysis method. The enzyme--Triton X-100 complex was mixed with Triton phospholipid micelles and the Triton slowly removed by dialysis for 48 hours at pH 5.5 at room temperature or above. The effect of varying the pH and temperature on the shape, size and order of the crystals is described.
Raman spectra of randomly-oriented kaolinite, dickite and nacrite show, for coarsely crystalline material, an extra band in the OH stretching region which is absent from the IR spectra of clay-size samples. Oriented single-crystal Raman spectra of these minerals provide confirmation for the assignment of the extra bands to transverse optical modes involving in-phase coupled vibrations of the layer-surface hydroxyl groups. The corresponding IR bands have transition moments nearly perpendicular to the layer surface, and appear at the higher frequencies of the longitudinal optical modes of macroscopic crystals.
Aside from a temperature-induced structural transformation, a new nanoporous coordination polymer [Ag6Cl(atz)4].OH.6H2O (Hatz = 3-amino-1,2,4,-triazole) comprised of interpenetrated Ag3(atz)2 coordination nets exhibits a single-crystal-to-single-crystal transformation of a 5-fold to 6-fold net interpenetration change triggered by guest desorption/absorption.
Many solid-state reactions and phase transformations performed under isothermal conditions give rise to asymmetric, sigmoidally shaped conversion-time (x-t) profiles. The mathematical treatment of such curves, as well as their physical interpretation, is often challenging. In this work, the functional form of a Maxwell-Boltzmann (M-B) distribution is used to describe the distribution of activation energies for the reagent solids, which, when coupled with an integrated first-order rate expression, yields a novel semiempirical equation that may offer better success in the modeling of solid-state kinetics. In this approach, the Arrhenius equation is used to relate the distribution of activation energies to a corresponding distribution of rate constants for the individual molecules in the reagent solids. This distribution of molecular rate constants is then correlated to the (observable) reaction time in the derivation of the model equation. In addition to providing a versatile treatment for asymmetric, sigmoidal reaction curves, another key advantage of our equation over other models is that the start time of conversion is uniquely defined at t = 0. We demonstrate the ability of our simple, two-parameter equation to successfully model the experimental x-t data for the polymorphic transformation of a pharmaceutical compound under crystallization slurry (i.e., heterogeneous) conditions. Additionally, we use a modification of this equation to model the kinetics of a historically significant, homogeneous solid-state reaction: the thermal decomposition of AgMnO4 crystals. The potential broad applicability of our statistical (i.e., dispersive) kinetic approach makes it a potentially attractive alternative to existing models/approaches.
Photonic-bandgap materials, with periodicity in one, two or three dimensions, offer control of spontaneous emission and photon localization. Low-threshold lasing has been demonstrated in two-dimensional photonic-bandgap materials, both with distributed feedback and defect modes. Liquid crystals with chiral constituents exhibit mesophases with modulated ground states. Helical cholesterics are one-dimensional, whereas blue phases are three-dimensional self-assembled photonic-bandgap structures. Although mirrorless lasing was predicted and observed in one-dimensional helical cholesteric materials and chiral ferroelectric smectic materials, it is of great interest to probe light confinement in three dimensions. Here, we report the first observations of lasing in three-dimensional photonic crystals, in the cholesteric blue phase II. Our results show that distributed feedback is realized in three dimensions, resulting in almost diffraction-limited lasing with significantly lower thresholds than in one dimension. In addition to mirrorless lasing, these self-assembled soft photonic-bandgap materials may also be useful for waveguiding, switching and sensing applications.
A linear template in the form of a bipyridine has been developed and is shown to direct a single-crystal-to-single-crystal [2 + 2] photodimerisation of a dicarboxylic acid.
Retroviral entry into cells depends on envelope glycoproteins, whereby receptor binding to the surface-exposed subunit triggers membrane fusion by the transmembrane protein (TM) subunit. We determined the crystal structure at 2.5-A resolution of the ectodomain of gp21, the TM from human T cell leukemia virus type 1. The gp21 fragment was crystallized as a maltose-binding protein chimera, and the maltose-binding protein domain was used to solve the initial phases by the method of molecular replacement. The structure of gp21 comprises an N-terminal trimeric coiled coil, an adjacent disulfide-bonded loop that stabilizes a chain reversal, and a C-terminal sequence structurally distinct from HIV type 1/simian immunodeficiency virus gp41 that packs against the coil in an extended antiparallel fashion. Comparison of the gp21 structure with the structures of other retroviral TMs contrasts the conserved nature of the coiled coil-forming region and adjacent disulfide-bonded loop with the variable nature of the C-terminal ectodomain segment. The structure points to these features having evolved to enable the dual roles of retroviral TMs: conserved fusion function and an ability to anchor diverse surface-exposed subunit structures to the virion envelope and infected cell surface. The structure of gp21 implies that the N-terminal fusion peptide is in close proximity to the C-terminal transmembrane domain and likely represents a postfusion conformation.
Human synovial type IIA phospholipase A(2) (sPLA(2)-IIA) has been implicated in the pathogenesis of a number of inflammatory diseases and is a target for the development of therapeutically useful inhibitors. Biochemical evidence suggests a novel mechanism of inhibition for a series of peptide inhibitors originally derived from the primary sequence of the protein. On co-incubation with one of these inhibitors, single crystals of a hitherto unreported crystallographic form of sPLA2-IIA suitable for diffraction analysis were obtained. The crystals belong to the monoclinic space group C2, with unit-cell parameters a = 140.8, b = 38.9, c = 109.1 A, beta = 125.1 degrees, and diffraction at 2.4 A resolution has been observed.
The crystal structure of pig heart citrate synthase was analyzed at 0.35-nm resolution. Chain tracing was possible and an initial molecular model constructed. The dimensions of the dimer molecule (located on a crystallographic diad) are 7.5 x 6.0 x 9.0 nm. The chain folding is characterized by the predominance of helices and the absence of sheet structure. The electron density accounts for 355 residues per monomer, so that about 80 residues must be disordered in the crystal. The disordered segment in probably N-terminal. The ordered part consists of two closely associated domains, a large domain with 300 residues and a C-terminal domain of 55 residues consisting of 3(anti)parallel helices. The large domain is built from 12 helical segments, some of which are buried in the interior of the molecule. Inhibitor binding studies with citrate and CoA revealed citrate binding sites but showed no electron density for CoA. It is suggested that CoA binds to the disordered, flexible N-terminal domain. Experiments of limited proteolysis with trypsin showed that under conditions a segment of Mr 9000 is cleaved off selectively. The remaining 35 000-Mr part is dimeric.
Characteristics of the powder dispersity of tetracycline base samples prepared by directed crystallization with variation of the process conditions were determined by the sedimentation method. It was found that the speed of the solution agitation had the maximum effect on the level and nature of the dispersity. The rate of the solution temperature and pH changing during the crystallization process had also a significant effect at low agitation speed.
The clinical and pathological features of 12 Reinke crystal-positive and nine probable (crystal-negative) hilus cell tumors of the ovary were reviewed. The patients' ages ranged from 32 to 82 years. The initial manifestation was androgenic in 62% of the cases. The levels of testosterone were high (200-2,400 ng/dl) even though the tumors had a mean diameter of only 2.1 cm. All the tumors were centered in the hilus of the ovary, extending for varying distances into the ovarian stroma. They were composed of polyhedral to rounded cells with generally abundant eosinophilic cytoplasm and often showed a perivascular aggregation of nuclei with avascular pooling of cytoplasm or hyalinization of stroma. Fibrinoid changes in the vessels of the tumors were frequently noted. None of the 10 patients for whom follow-up data of 1-17 years were available died of tumor; virilizing symptoms regressed but did not completely disappear in five of the 10 patients after the removal of the tumor.