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PubMed1988

DSC, X-ray and NMR properties of cholesterol-cholestanol-dihydrate crystals.

The melting point, X-ray diffraction and longitudinal relaxation time (T1) of cholesterol-cholestanol-dihydrate crystals (CC2W) were studied in an effort to produce new experimental data related to atherosclerotic plaques. The crystals were precipitated from ethanolic solutions at several cholesterol: cholestanol (CS:CN) ratios. The melting point of CC2W crystals obtained at the CS:CN ratio 75:25, 50:50, 25:75 was 122-124 degrees C. The X-ray patterns recorded from these crystals of the same CN:CS ratios showed two additional diffraction peaks, as compared to those of CN and CS patterns. On the other hand, the values of T1 relaxation time measured by proton magnetic resonance were different for every CS:CN ratio for the various solution compositions. This latter method seems to be more precise for the detection of the presence of coprecipitated components in the CC2W mixed crystals than X-ray or thermal analysis. The results suggest that CN and CS do not have to be present in equimolar quantities in order for CC2W crystals to be formed. The presence of CC2W in the blood may have significance in the nucleation of cholesterol crystals in atherosclerotic plaques.

Arteriosclerosis↗
PubMed1986

Comparison with the theory of the kinetics and extent of ice crystallization and of the glass-forming tendency in aqueous cryoprotective solutions.

The glass-forming tendency and stability of the wholly amorphous state of various cryoprotective solutions has been studied in recent years (5-10, 20). A lot of experimental data including heats of ice crystallization at various cooling rates and devitrification temperatures have been given. In this article these data have been compared with analytical expressions using a semiempirical model. The theoretical variation of the total quantity of ice crystallized with the cooling rate fits very well with the experimental data, adjusting only one parameter. Using the same model, theoretical differential scanning calorimeter (DSC) crystallization peaks have been obtained for cooling or rewarming. The general shape, height, and width of the theoretical peaks are very similar to those of the experimental peaks. The differences are comparable to the random variations of the experimental peaks from one experiment to another. The analytical expressions obtained here could be used to study the relationship between the kinetics of ice crystallization and cell damage when ice crystallizes incompletely inside or outside the cells. These expressions have been applied to ice crystallization for applications in cryobiology. But they could also probably be used in other fields of research such as crystallization from silicates or other mineral or organic glasses.

Cryoprotective Agents↗
PubMed1989

Ice crystal patterns in artificial gels of extracellular matrix macromolecules after quick-freezing and freeze-substitution.

Artificial gels, composed of collagen with or without hyaluronate (HA), a glycosaminoglycan (GAG), and chondroitin sulfate (CS), were prepared and quick-frozen for the purpose of studying the influence of composition and concentration on ice patterns. Dilute gels were spread on coverslips, plunged into a slush of 30% isopentane/70% propane (-185 degrees C), freeze-substituted, and examined by phase-contrast microscopy. Ice patterns were revealed as "ice cavities" in the gel after freeze-substitution. Ice morphology in the gels was gel-type-specific, suggesting that composition in dilute gels can influence ice pattern formation. Crystallization patterns reflecting high, intermediate, and low rates of freezing were observed in all gel types. Intermediate freezing in differentiating gel-type-specific ice patterns. Gels which included hyaluronate (HA) and chondroitin sulfate (CS) altered the ice crystal pattern commonly observed in collagen gels. Ice structure in collagen gels consisted predominantly of long, parallel crystals in the herringbone pattern. Ice crystals separated gel into thin, unbranched fibers with a primary spacing of approximately 2 microns. Ice morphology in HA gels formed a mosaic consisting of packets of ice crystals. Contiguous packets were often oriented at right angles to each other. Periodic crossbridges interconnect primary gel fibers of HA gels and interrupt the lengthwise growth of ice crystals. Smooth beads were visible on primary strands in HA gels frozen at intermediate velocities. The addition of CS to collagen gels resulted in formation of randomly oriented ice crystals in gels frozen at intermediate rates. CS has little influence on ice morphology at low freezing velocities. Primary strands in CS gels were decorated with rough-surfaced, osmiophilic aggregates.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Two-dimensional crystallization of reaction centers from Chloroflexus aurantiacus.

Two-dimensional crystals of photosynthetic reaction centers from Chloroflexus aurantiacus were obtained from protein-lipid-detergent micelles by detergent dialysis. The size of crystals was up to 2 microns. Some of them were multilayered crystals. However, other crystal forms were also observed. Preliminary image processing analysis showed that crystals of one crystal form referred to two-sided plane group p2 and had the following unit cell parameters: a = 17.6 nm, b = 18.0 nm, gamma = 84 degrees. The contour map of the crystal stain-excluding region was calculated by the Fourier-filtering procedure at about 2 nm resolution.

Bacterial Proteins↗
PubMed1991

Crystallization and preliminary X-ray analysis of methylamine-treated alpha 2-macroglobulin and 3 alpha 2-macroglobulin-proteinase complexes.

Crystals of methylamine-treated alpha 2-macroglobulin (alpha 2M-MA), alpha 2-macroglobulin in complex with two molecules of trypsin, alpha 2M-T2, one molecule of plasmin, alpha 2M-PL, and one molecule of plasmin followed by methylamine-treatment, alpha 2M-PL(MA), have reproducibly been obtained using ammonium sulfate or magnesium sulfate as precipitants. The crystals are fragile tetragonal bipyramids of up to 1.5 mm in length. Crystals of alpha 2M-MA diffracted to at least 9 A resolution, crystals of alpha 2M-T2 diffracted to 10 A resolution and crystals of alpha 2M-PL and alpha 2M-PL(MA) diffracted to 11 A resolution. For alpha 2M-MA the cell parameters were determined as: a=b=257 A, c=555 A; and for alpha 2M-T2 as: a=b=247 A, c=559 A. For both preparations the space group was I4(1)22. As estimated from density measurements, the crystals of alpha 2M-MA and alpha 2M-T2 contain one 360 kDa alpha 2M dimer per asymmetric unit. The volume of the asymmetric unit/molecular weight, Vm, was estimated at 5.6 A3/Da. The crystal parameters of alpha 2M-PL and alpha 2M-PL(MA) were not determined.

Crystallization↗
PubMed1993

Crystallization and preliminary X-ray investigation of the Escherichia coli molecular chaperone cpn60 (GroEL).

The Escherichia coli molecular chaperone, cpn60 (GroEL), has been purified from an overproducing E. coli strain and crystallized. Of the two crystal forms that were obtained, one was found to be suitable for crystallographic and structural studies at low resolution. Preliminary X-ray investigation of the crystals show unit cell dimensions: a = 143.3, b = 154.6 and c = 265 A, with alpha = 82 degrees, beta = 95 degrees and gamma = 107 degrees. The space group is P1 and the crystals diffract to a maximum of 7 A when using CuK alpha X-rays from a rotating anode. Both electron microscopy and non-denaturing electrophoretic analysis of redissolved cpn60 crystals show that cpn60 crystallizes in the native oligomeric form. Comparison between the dimensions of oligomeric cpn60 and the crystallographic unit cell volume suggests that the unit cell contains two oligomeric cpn60 molecules. The VM value for two cpn60 molecules per unit cell is 3.5 A3/Da, corresponding to a water content of 65%. Electrophoretic analysis under denaturing conditions shows that the cpn60 in crystals is heterogeneous, and this probably explains the limited resolution of the diffraction data.

Bacterial Proteins↗
PubMed1984

Crystallization and preliminary x-ray diffraction study of the 3-Fe ferredoxin II from the bacterium Desulfovibrio gigas.

The 3-Fe ferredoxin (FdII) from the bacterium Desulfovibrio gigas has been crystallized at pH 5.0 and 23 degrees C in two different crystal forms. One form is monoclinic, space group C2, with unit cell parameters a = 40.78 A, b = 44.98 A, c = 26.47 A, beta = 104.6 degrees, and one monomer of the FdII tetramer per asymmetric unit. The molecule can be either the monomer of molecular weight 6400 or a dimer of twice this molecular weight with 2-fold symmetry coincident with the 2-fold axis of the crystal. The other crystal form is orthorhombic, space group P2(1)2(1)2 and unit cell parameters a = 109.5 A, b = 37.0 A, c = 30.5 A. The asymmetric unit of this crystal contains two monomers of FdII. The orthorhombic crystal has not been reproduced since the initial crystallization.

Crystallization↗
PubMed1991

Use of chemical modification in the crystallization of isocitrate lyase from Escherichia coli.

Two different crystal forms of isocitrate lyase (ICL) from Escherichia coli have been grown following the chemical modification of the enzyme by either 3-bromopyruvate or ethyl mercuri thiosalicylate (EMTS), contrasting strongly with difficulties in obtaining ordered crystals of the native enzyme. Both crystal forms are obtained using the hanging drop method of vapour diffusion with ammonium sulphate as the precipitant. The crystals diffract well and X-ray photographs of the crystals have established that they are in space groups C222(1) and P3(1) (or its enantiomorph P3(2), respectively. Considerations of the values of Vm and measurements on the crystal density indicate that the asymmetric unit of both crystals contains four subunits.

Crystallization↗
PubMed1992

Pre-nucleation crystallization studies on aminoacyl-tRNA synthetases by dynamic light-scattering.

Dynamic light-scattering (DLS) studies on solutions of proteins approaching their precipitation point were made with asparaginyl- (NRSEC), leucyl- (LRSEC) and valyl- (VRSEC) tRNA synthetases from Escherichia coli. The three aminoacyl-tRNA synthetases have not been crystallized previously. As a control system, we used E. coli polypeptide elongation factor Tu (EF-Tu). Apart from the different proteins used here, the methods we employed differed from previous studies in that (1) instead of making a series of measurements on individual samples at various concentrations, the protein solutions were titrated with the precipitants, and (2) the results of the light-scattering measurements were analysed by a new maximum entropy procedure that calculates a particle size distribution in a highly reproducible way. The particle size distributions of protein solutions titrated with precipitants showed two major peaks in most cases. For both peaks, relative areas and mean diffusion coefficients were determined. The diffusion constants were corrected for the viscosity of the solutions. From comparing the results on the proteins known to crystallize (EF-Tu) with the amorphously precipitating systems (LRSEC, NRSEC) we find two necessary, but not sufficient, conditions for the formation of crystals: the diffusion coefficient of the monomer peak stays constant until very close to the precipitation point; the percentage of large aggregates stays small (less than 10% of the scattered light intensity) during the titration. For VRSEC, both ammonium sulphate and sodium citrate showed a low percentage of large aggregates and a constant diffusion coefficient of the main (protein monomer) peak below the precipitation point. This indicates that both would be possible precipitants for the crystallization of this enzyme. Crystallization trials using both these salts were carried out, and although no condition could as yet be found for obtaining crystals with ammonium sulphate solutions, crystals of the enzyme have been obtained with sodium citrate.

Amino Acyl-tRNA Synthetases↗
PubMed1980

Sporeless mutants of Bacillus thuringiensis. III. The process of crystal formation.

In order to investigate the formation of the parasporal crystal of B. thuringiensis with special reference to the spore, sequential ultrastructural analysis of sporulation was performed using a sporeless mutant strain (sp-) as well as its parent wild strain (sp+). From the logarithmic growth to the end of forespore formation, the same sequential process of sporulation proceeded in both strains and a forespore with double membranes appeared. Thereafter, subsequent sporulation in the sp- strain was either partly or completely arrested and finally spore (mainly the forespore) became deformed. On the other hand, crystal formation took place throughout by the same processes both in sp+ and sp- strains. During the forespore formation, a primordial crystal and an ovoid inclusion appeared and after this stage, the crystal displayed a characteristic diamond-shaped body with lattice fringes increasing its size. No regularity was found in the position of the crystal with respect to the spore. As far as the present ultrastructural observations were concerned, the crystal developed without any special association with the membranes of the spore. However, without the formation of the forespore (including the incipient forespore), no crystal formtion was observed.

Bacillus thuringiensis↗
PubMed1991

Single crystals of V amylose.

Single crystals of V amylose were prepared from dilute solution in water/ethanol over a range of temperatures. The effects of crystallization temperature on crystal morphology and thickness were investigated using transmission electron microscopy. Annealing of these crystals gave rise to large increases in crystal thickness. It is concluded that V amylose crystals behave in a similar way to crystals of linear synthetic polymers.

Amylose↗
PubMed1993

Two-dimensional crystallization of catalase on a monolayer film of poly(1-benzyl-L-histidine) spread at the air/water interface.

Two-dimensional (2D) crystals of beef liver catalase were prepared by adsorption to a film of synthetic polypeptide, poly(1-benzyl-L-histidine) (PBLH), spread at the air/water interface. The crystallization experiments were carried out in the pH range of 4.8-6.4 for catalase solutions at low concentration (10 micrograms/ml). The pH-dependence suggested an electrostatic interaction in the binding of catalase to the PBLH film. At lower pH, small crystals were formed at a low binding rate, and at higher pH the binding was rapid and densely-packed 2D arrays with poor crystallinity were formed. To stimulate crystal growth, a thermal treatment was applied. One-shot heating of the interfacial catalase-PBLH film to 35-40 degrees C was remarkably effective to form larger 2D crystals. The structure of catalase 2D crystals has been analyzed by Fourier filtering of the transmission electron micrographs. The crystal form is a new one, containing four catalase molecules in the unit cell with lattice parameters of alpha = 187 A, b = 225 A and gamma = 92.8 degrees.

Animals↗
PubMed1996

Ionic conductivity, transference numbers, composition and mobility of ions in cross-linked lysozyme crystals.

Micromethods for measurements of electric conductivity, transference numbers and concentrations of inorganic ions within immobilized protein crystals have been developed and applied to study tetragonal lysozyme crystals cross-linked with glutaraldehyde. Donnan equilibria and mobilities of ions in this crystal were calculated using the data of these methods and the data of crystal pH titration. Taken together these results characterize the lysozyme crystal as an ion exchanger whose electrical properties and ion composition differ greatly from those of the external solution. Although anions transfer most of the current in the crystals, anion mobility is considerably lower than that of cations. Mobility of all ions in the crystal is considerably lower than in solution (3.5-50 times for cations and 120-330 times for anions) and depends on steric restrictions and charges of both ions and lysozyme molecules. Similar features in behavior of crystalline and biological channels are discussed.

Chemical Phenomena↗
PubMed2006

Chemical composition, crystal size and lattice structural changes after incorporation of strontium into biomimetic apatite.

Recently, strontium (Sr) as ranelate compound has become increasingly popular in the treatment of osteoporosis. However, the lattice structure of bone crystal after Sr incorporation is yet to be extensively reported. In this study, we synthesized strontium-substituted hydroxyapatite (Sr-HA) with different Sr content (0.3%, 1.5% and 15% Sr-HA in mole ratio) to simulate bone crystals incorporated with Sr. The changes in chemical composition and lattice structure of apetite after synthetic incorporation of Sr were evaluated to gain insight into bone crystal changes after incorporation of Sr. X-ray diffraction (XRD) patterns revealed that 0.3% and 1.5% Sr-HA exhibited single phase spectrum, which was similar to that of HA. However, 15% Sr-HA induced the incorporation of HPO4(2-) and more CO3(2-), the crystallinity reduced dramatically. Transmission electron microscopy (TEM) images showed that the crystal length and width of 0.3% and 1.5% Sr-HA increased slightly. Meanwhile, the length and width distribution were broadened and the aspect ratio decreased from 10.68+/-4.00 to 7.28+/-2.80. The crystal size and crystallinity of 15% Sr-HA dropped rapidly, which may suggest that the fundamental crystal structure is changed. The findings from this work indicate that current clinical dosage which usually results in Sr incorporation of below 1.5% may not change chemical composition and lattice structure of bone, while it will broaden the bone crystal size distribution and strengthen the bone.

Biocompatible Materials↗
PubMed2005

Effects of amino acids on crystal growth of CaC2O4 in reverse microemulsion.

Crystal growth of calcium oxalate (CaC2O4) in bulk aqueous solution, reverse microemulsion of p-octyl polyethylene glycol phenylether (OP)/iso-octyl alcohol (IOA)/cydohexane/water and above microemulsions containing different kinds of amino acids, such as aspartic acid (Asp), tyrosine (Tyr) and tryptophan (Trp) were studied. The results indicated that different crystallization types of the crystals, which were calcium oxalate monohydrate (COM), calcium oxalate dihydrate (COD) and calcium oxalate trihydrate (COT), existed in bulk aqueous solution. But CaC2O4 growth mainly paralleled with (1 01) plane of COM in reverse microemulsion because of the induction of surfactant at water/oil interface. After adding amino acids into microemulsions, the growth of CaC2O4 crystals mainly influenced by the varieties of amino acids and the pH values of the amino acid aqueous solution. When pH values of the solutions was higher than isoelectric points of amino acids, CaC2O4 crystal paralleled with (1 01) plane of COM more easily with the addition of Trp, Tyr, Asp in turn; however, when pH of the solutions was lower than isoelectric points of Trp, CaC2O4 crystal growth paralleled with (020) face of COM. It is obviously that amino acids, pH values of the solutions and surfactant played important roles in the process of crystal growth of CaC2O4 in the microemulsions. The formation mechanism of CaC2O4 was also discussed in different microemulsions at last.

Amino Acids↗
PubMed2004

Direct cell injury associated with eutectic crystallization during freezing.

Freezing induced direct cell injury has been explained by a two-factor hypothesis-intracellular ice formation (IIF) at rapid cooling rates, and solution effects at slow cooling rates. Even though IIF is generally believed to be a major injury mechanism at rapid cooling rates, injury by solution effects is not fully understood and several injury mechanisms have been suggested. Solution effects have generally been considered the result of the elevated electrolyte concentration within the intracellular and extracellular space during freezing. In addition to the injury by this elevated electrolyte concentration, freezing injury associated with eutectic crystallization was investigated. To examine the injury associated with eutectic crystallization, two different experiments were designed and performed. In the first experiment, two groups of AT-1 rat prostate tumor cell suspensions were frozen and thawed on a cryomicroscope in the same way except that eutectic crystallization was initiated in only one group. During the second experiment, AT-1 cells were suspended in several different media, which have different eutectic crystallization temperatures, and exposed to a single cooling-warming cycle with varying end temperature of the protocol on a directional solidification stage. After both experiments, post-thaw viability was evaluated and compared. The post-thaw viability drops significantly upon the occurrence of the eutectic crystallization regardless of suspending media, which suggests direct cell injury associated with eutectic crystallization. Based on these observations, two possible injury mechanisms are anticipated: (i) mechanical damage to the cell membrane due to eutectic crystallization, and (ii) intracellular eutectic formation (IEF). The proposed mechanisms provide a more comprehensive physical explanation of freezing induced cell injury and extend the understanding on solution effects.

Animals↗
PubMed2005

The nucleation and crystallization of fine grained leucite glass-ceramics for dental applications.

OBJECTIVES: The aims of the study were to control the nucleation and crystal growth of selected aluminosilicate glass powders, to produce uniform leucite glass-ceramic microstructures consisting of fine (<1000 nm) grained leucite crystals. METHODS: A starting glass composition of wt%; 64.2% SiO(2), 16.1% Al(2)O(3), 10.9% K(2)O, 4.3% Na(2)O, 1.7% CaO, 0.5% LiO(2) and 0.4% TiO(2) was heated in an electric furnace and later quenched to produce glasses. The glass powders were ball milled to two different particle sizes and heat-treated using one and two-step crystallization heat treatments. Dta, Xrd, and Sem analyses was used to characterise and explore the crystallization kinetics of the glasses. RESULTS: Selected heat treatments of the glass powders produced a uniform distribution of fine tetragonal leucite crystals (mean+/-S.D.) 0.1+/-0.2 microm(2) in the glassy matrix, with minimal matrix microcraking in the glass-ceramics produced. The addition of a two-step heat treatment increased the leucite volume fraction in all instances. SIGNIFICANCE: Selected crystallization heat treatments and powder particle sizes were used to control the leucite crystal size, distribution and volume fraction, in order to produce uniformly distributed ultra fine grained tetragonal leucite glass-ceramics for dental applications.

Aluminum Silicates↗
PubMed2006

Assessing the re-crystallization behaviour of amorphous lactose using the RH-perfusion cell.

Many different reports have studied the crystallization behaviour of lactose, e.g., by exposing samples of amorphous lactose to different relative humidity at constant temperatures. However, only few reports are available investigating the formation of alpha-lactose monohydrate and beta-lactose during re-crystallization. Applying the static ampoule method in the microcalorimeter, the enthalpies of amorphous lactose were reported to be constantly 32 and 48 J/g, respectively, considering the mutarotation of lactose at 25 degrees C and 58% RH, 75% RH and 100% RH. In this study, an alternative microcalorimetric technique, the relative humidity-perfusion cell (RH-perfusion cell) was chosen. The RH-perfusion cell is able to deliver a constant and controlled flow of humidified air to the sample. Investigated compounds were purely amorphous lactose and different powder mixtures of lactose. They consisted of alpha-lactose monohydrate (Pharmatose 325M), beta-lactose (Pharmatose DCL21) or a combination (1:1) thereof as carriers, and different concentrations of amorphous lactose. The determination of the enthalpy of desorption of the just re-crystallization lactose by the RH-perfusion cell was used to discriminate whether the monohydrate or the anhydrous form of lactose was produced. Differences in the re-crystallization behaviour of lactose at 25 degrees C and 58-100% RH were found. At 60-80% RH purely amorphous lactose showed a high heat of desorption which can be attributed to a very high content of formed beta-lactose. Powder mixtures containing high contents of amorphous lactose (8% and 15%, respectively) blended with alpha-lactose monohydrate as a carrier resulted in similar results at the same RH ranges. The high amount of beta-lactose can be due to the equilibrium anomeric composition. Whereas powder mixtures containing beta-lactose as a carrier and amorphous lactose in a concentration of 1%, 8% and 15%, respectively, formed less beta-lactose than the mixtures containing alpha-lactose monohydrate as a carrier. At a relative humidity of 90% none of the powder mixtures showed desorption as to the fact that in all cases only alpha-lactose monohydrate was formed at the surface of the re-crystallized lactose. Furthermore, mixtures of alpha-lactose monohydrate and beta-lactose (1:1) and 8% amorphous lactose were investigated. An increase in formed alpha-lactose monohydrate by increasing RH was found. To consolidate the results, the same mixtures were re-crystallized at different RH in desiccators and subsequently investigated in the solution calorimeter. The results of the pre-mix were confirmed by the solution calorimeter. In summary, purely amorphous lactose and mixtures containing alpha-lactose monohydrate as a carrier show different re-crystallization behaviour compared to mixtures containing beta-lactose as a carrier.

Adsorption↗