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At least 1,711 records · Page 95Linked to original sources
PubMed2003

Antibody recognition of chiral surfaces. Enantiomorphous crystals of leucine-leucine-tyrosine.

Monoclonal antibodies were selected after immunization with crystals of the tripeptide l-leucine-l-leucine-l-tyrosine. They interact with the tripeptide crystals, but do not interact with the tripeptide molecule, with other crystalline surfaces, or with adsorbed protein. The interactions of two antibodies with crystals of l-Leu-l-Leu-l-Tyr and of its enantiomer d-Leu-d-Leu-d-Tyr were characterized in depth. Antibody 48E is stereoselective and enantioselective: it recognizes only the [011] faces of the l-Leu-l-Leu-l-Tyr crystals, and not the enantiomorphous [011] faces of d-Leu-d-Leu-d-Tyr crystals, or any other faces of either crystal. In contrast, antibody 602E is poorly stereoselective and is not enantioselective: it recognizes the crystals of both enantiomers, interacting with a number of different faces of each. The different recognition patterns are explained on the basis of the nature of the interactions and the structure of the interacting surfaces. Understanding this antibody specificity advances our general understanding of surface recognition and transfer of chiral information across biological interfaces.

Adjuvants, Immunologic↗
PubMed2005

Control of localized nanorod formation and patterns of semiconducting CuTCNQ phase I crystals by scanning electrochemical microscopy.

Use of the technique of scanning electrochemical microscopy (SECM) enables the surface of single crystals of 7,7',8,8'-tetracyanoquinodimethane (TCNQ) to be modified in a controlled manner to produce highly dense and micrometer sized regions of semiconducting phase I CuTCNQ nanorod crystals by a nucleation and growth mechanism. This method involves the localized reduction of solid TCNQ to TCNQ- by aqueous phase V(aq)2+ reductant generated at a SECM ultramicroelectrode tip by reduction of V(aq)3+, coupled with the incorporation and reduction of Cu(aq)2+ ions also present in the aqueous electrolyte. SECM parameters can be systematically varied to control the extent of surface modification and the packing density of the CuTCNQ crystals. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images provide evidence that the TCNQ to CuTCNQ solid-solid transformation is accompanied by a drastic localized crystal volume and morphology change achieved by fragmentation of the TCNQ crystal surface. Patterns of semiconducting CuTCNQ (phase I) nanorod shaped crystals have been characterized by SEM, AFM, and infrared (IR) techniques. A reaction scheme has been proposed for the interaction between the electrogenerated mediator V(aq)2+, Cu(aq)2+, and the TCNQ crystal in the nucleation and growth stages of phase I CuTCNQ formation.

Copper↗
PubMed2005

Crystallization pathways of sulfate-nitrate-ammonium aerosol particles.

Crystallization experiments are conducted for aerosol particles composed of aqueous mixtures of (NH(4))(2)SO(4)(aq) and NH(4)NO(3)(aq), (NH(4))(2)SO(4)(aq) and NH(4)HSO(4)(aq), and NH(4)NO(3)(aq) and NH(4)HSO(4)(aq). Depending on the aqueous composition, crystals of (NH(4))(2)SO(4)(s), (NH(4))(3)H(SO(4))(2)(s), NH(4)HSO(4)(s), NH(4)NO(3)(s), 2NH(4)NO(3) x (NH(4))(2)SO(4)(s), and 3NH(4)NO(3) x (NH(4))(2)SO(4)(s) are formed. Although particles of NH(4)NO(3)(aq) and NH(4)HSO(4)(aq) do not crystallize even at 1% relative humidity, additions of 0.05 mol fraction SO(4)(2-)(aq) or NO(3)(-)(aq) ions promote crystallization, respectively. 2NH(4)NO(3) x (NH(4))(2)SO(4)(s) and (NH(4))(3)H(SO(4))(2)(s) appear to serve as good heterogeneous nuclei for NH(4)NO(3)(s) and NH(4)HSO(4)(s), respectively. 2NH(4)NO(3) x (NH(4))(2)SO(4)(s) crystallizes over a greater range of aqueous compositions than 3NH(4)NO(3) x (NH(4))(2)SO(4)(s). An infrared aerosol spectrum is provided for each solid based upon a linear decomposition analysis of the recorded spectra. Small nonzero residuals occur in the analysis because aerosol spectra depend on particle morphology, which changes slightly across the range of compositions studied. In addition, several of the mixed compositions crystallize with residual aqueous water of up to 5% particle mass. We attribute this water content to enclosed water pockets. The results provide further insights into the nonlinear crystallization pathways of sulfate-nitrate-ammonium aerosol particles.

Aerosols↗
PubMed1999

Nucleation and crystallization kinetics of hydrated amorphous lactose above the glass transition temperature.

The crystallization kinetics of amorphous lactose in the presence and absence of seed crystals were investigated at 57.5% relative humidity. Isothermal crystallization studies were conducted gravimetrically in an automated vacuum moisture balance at several temperatures between 18 and 32 degrees C. The crystallization rate constants were then determined from Johnson-Mehl-Avrami (JMA) treatment and isothermal activation energies were obtained from Arrhenius plots. Based on microscopic observations, a reaction order of 3 was used for JMA analysis. The nonisothermal activation energies were determined by differential scanning calorimetry using Kissinger's analysis. Isothermal activation energies for amorphous lactose with and without seed crystals were 89.5 (+/-5.6) kJ/mol and 186.5 (+/-17.6) kJ/mol, respectively. Nonisothermal activation energies with and without seed crystals were 71 (+/-7.5) kJ/mol and 80.9 (+/-8.9) kJ/mol, respectively. The similarity of the isothermal and nonisothermal activation energies for the sample with seeds suggested that crystallization was occurring by growth from a fixed number of preexisting nuclei. Markedly different isothermal and nonisothermal activation energies in the absence of seeds suggested a site-saturated nucleation mechanism, and therefore allowed calculation of an activation energy for nucleation of 317 kJ/mol.

Calorimetry, Differential Scanning↗
PubMed2004

Neutron reflectivity and external reflection FTIR studies of DL-aspartic acid crystallization beneath nylon 6 spread films.

The crystallization of DL-aspartic acid beneath nylon 6 spread films has been studied for 150% supersaturated systems using neutron reflectivity and external reflection FTIR. The neutron reflectivity data showed the gradual incorporation of DL-aspartic acid within a nylon 6 spread film layer over a period of 6-8 h, culminating in over 50 vol % of the "film" layer comprising DL-aspartic acid. Accumulation of further DL-aspartic acid material to produce microscopic/macroscopic surface crystals occurred, but on a more limited scale, resulting in approximately 1-5% surface coverage of crystals over the same period. External reflection FTIR studies revealed very weak bands attributable to DL-aspartic acid in surface regions devoid of visible crystals, in agreement with the neutron reflectivity studies. In regions with visible crystals, much larger and sharper DL-aspartic acid bands were seen. Changes in the intensity of the nylon 6 NH stretch band were often observed during the visible crystallization and dissolution of DL-aspartic acid and were consistent with the reversible accumulation of nylon 6 around the growing crystals.

Aspartic Acid↗
PubMed2006

Anchoring of nematic liquid crystals on viruses with different envelope structures.

The ordering of synthetic liquid crystals near surfaces is known to be dependent on the nanoscopic structure and chemical functionality of surfaces. In this letter, we report that the orientational ordering of synthetic liquid crystals on surfaces decorated with viruses is also dependent on the structures of the viruses. Each of the four virions investigated had diameters of approximately 100 nm, but three of the viruses (influenza virus, La Crosse virus, and vesicular stomatitis virus) were enveloped in a lipid bilayer, whereas one virus (adenovirus) was not. We observed that lipid bilayer-enveloped viruses induce homeotropic (perpendicular) ordering of a nematic liquid crystal upon contact with the liquid crystal. In contrast, nonenveloped virus (adenovirus)-treated surfaces caused a near-planar orientation of the liquid crystal. We conclude that the homeotropic ordering of liquid crystals is a signature of the presence of enveloped viruses present on surfaces. These results suggest new approaches to the design of nanostructured materials that incorporate viruses as well as suggest methods that can be used to amplify the presence of nanoscopic virions into micrometer-sized domains of liquid crystal that can be optically probed.

Adenoviridae↗
PubMed2002

Plasticity and slip system of plate-shaped crystals of L-lysine monohydrochloride dihydrate.

PURPOSE: To identify the slip system of L-lysine monohydrochloride dihydrate (LH) and to relate it to the deformation behavior under uniaxial compression. METHODS: The indentation hardness of the [100] face and the indentation moduli of the [100] and [011] faces of plate-shaped single crystals of LH (LHP) were determined using Knoop and Berkovich indenters, respectively. The deformation behavior during uniaxial compression was studied by the punch-stress vs. punch-displacement profile and by electron microscopy of the deformed crystals within cracked compacts. RESULTS: The different indentation (elastic) moduli of the [100] and [011] faces of the crystals are consistent with the molecular packing density along these planes and suggest anisotropy. The existence of the [001] <100> slip system is proposed based on the pattern of changing indentation hardness with varying orientation of the Knoop indenter. A jagged uniaxial compression profile suggests deformation by mechanical twinning and not simple slip. The hypothesis of deformation by mechanical twinning is supported by the appearance of twin bands along the crystal faces as observed by electron microscopy of the cracked compacts. CONCLUSIONS: During compression, most LHP crystals have their [100] faces oriented normal to, or inclined to, the compression axis, thereby facilitating plastic deformation along the [001] <100> slip system by mechanical twinning. Due to the low attachment energy between them, the [001] planes can also act as cleavage planes. This study demonstrates that knowledge of the crystal structure and slip systems can be used to model the tableting and compaction behavior of molecular crystals, such as LH.

Crystallization↗
PubMed2002

Crystallization behavior of mannitol in frozen aqueous solutions.

PURPOSE: To study the effect of cooling rate, the influence of phosphate buffers and polyvinylpyrrolidone (PVP) on the crystallization behavior of mannitol in frozen aqueous solutions. METHODS: Low-temperature differential scanning calorimetry and powder X-ray diffractometry were used to characterize the frozen solutions. RESULTS: Rapid cooling (20 degrees C/min) inhibited mannitol crystallization, whereas at slower cooling rates (10 degrees C and 5 degrees C/min) partial crystallization was observed. The amorphous freeze-concentrate was characterized by two glass transitions at -32 degrees C and -25 degrees C. When the frozen solutions were heated past the two glass transition temperatures, the solute crystallized as mannitol hydrate. An increase in the concentration of PVP increased the induction time for the crystallization of mannitol hydrate. At concentrations of > or =100 mM, the buffer salts significantly inhibited mannitol crystallization. CONCLUSIONS: The crystallization behavior of mannitol in frozen solutions was influenced by the cooling rate and the presence of phosphate buffers and PVP.

Crystallization↗
PubMed1994

Non-isothermal and isothermal crystallization of sucrose from the amorphous state.

The crystallization of a model compound, sucrose, from the amorphous solid state has been studied non-isothermally using differential scanning calorimetry to determine crystallization temperature, Tc, and isothermally at 30 degrees C by subjecting samples to 32.4% relative humidity and gravimetrically monitoring water vapor uptake and subsequent loss with time due to crystallization. From the measurement of glass transition temperature, Tg, and melting temperature, Tm, for sucrose alone and in the presence of absorbed water it was possible to predict Tc and thus to directly relate the plasticizing effects of water to its tendency to promote crystallization. Colyophilization of sucrose with lactose, trehalose, and raffinose, all having Tg values greater than that of sucrose, increased Tc significantly, even at levels as low as 1-10% w/w. In the isothermal studies the time required for crystallization to commence, due to the plasticizing effects of water, i.e., the induction time, assumed to be mostly affected by rates of nucleation, was greatly increased by the presence of the additives at these low levels, with raffinose producing a greater effect than lactose and trehalose. Similarly, these additives reduced the rate of water loss, i.e., the rate of crystal growth, but now no significant differences were noted between the three additives. The possible relationships of nucleation and crystal growth and the effects of additives on molecular mobility are discussed.

Absorption↗
PubMed1985

Bladder secretion of inhibitors of calcium oxalate crystal growth.

Differences in calcium oxalate crystal growth inhibition were studied in normally voided urine (bladder urine) and in urine collected directly from the kidney (kidney urine) in nine dogs. Urine samples were collected before and 10 days after bilateral ureterostomies. Calcium oxalate crystal growth inhibition was measured in a standard seeded crystal growth system. The alcian blue-precipitable material of the urine samples was determined. Significantly lower values were observed in kidney urine than in bladder urine for calcium oxalate crystal inhibition (mean difference, 0.07 +/- 0.02 inhibitor units/mg creatinine; P less than 0.01) and for the alcian blue-precipitable material (mean difference, 0.07 +/- 0.02 mg/mg creatinine; P less than 0.01). We conclude that the bladder adds calcium oxalate crystal growth inhibition to urine. Glycosaminoglycans from the bladder mucosa may be responsible; however, other acidic polymers such as RNA fragments or glycopeptides have been shown to be a constituent of the alcian blue-precipitable material. These are potent inhibitors of calcium oxalate crystal growth, and their participation in the increase of inhibition observed in bladder urine cannot be excluded. Total calcium oxalate crystal growth inhibition present in normally voided urine may be an overestimation of the actual inhibition present at the level of the kidney, where calculi usually form.

Alcian Blue↗
PubMed2003

Microassembly of semiconductor three-dimensional photonic crystals.

Electronic devices and their highly integrated components formed from semiconductor crystals contain complex three-dimensional (3D) arrangements of elements and wiring. Photonic crystals, being analogous to semiconductor crystals, are expected to require a 3D structure to form successful optoelectronic devices. Here, we report a novel fabrication technology for a semiconductor 3D photonic crystal by uniting integrated circuit processing technology with micromanipulation. Four- to twenty-layered (five periods) crystals, including one with a controlled defect, for infrared wavelengths of 3-4.5 microm, were integrated at predetermined positions on a chip (structural error <50 nm). Numerical calculations revealed that a transmission peak observed at the upper frequency edge of the bandgap originated from the excitation of a resonant guided mode in the defective layers. Despite their importance, detailed discussions on the defective modes of 3D photonic crystals for such short wavelengths have not been reported before. This technology offers great potential for the production of optical wavelength photonic crystal devices.

Crystallization↗
PubMed1980

Crystal-forming proteins of Bacillus thuringiensis. The limited hydrolysis by endogeneous proteinases as a cause of their apparent multiplicity.

The crystals of the entomocidal protein of Bacillus thuringiensis are admixed with proteinases that in the course of their dissolution cause gradual degradation of the "genuine" crystal-forming protein components (i.e. the primary biosynthetic products) to products of lower molecular weight. This phenomenon might explain at least partially the contradictory data on the molecular parameters of the crystal-forming proteins. Preliminary inactivation of the proteinases adsorbed on the crystals allowed us to eliminate this source of the artefacts and to gain more reliable data on the protein composition of the crystals formed by various strains of B. thuringiensis. It has been shown that the crystals formed by all serotypes of B. thuringiensis, with the exception of the serotype V, contain only one protein with a mol. wt. of 145000, 135000 or 130000, depending on the strain. The majority of the strains that belong to the serotype V form crystals consisting of two proteins with mol. wts. of 135000 and 130000, but some of them also have a third component with a mol. wt. of 65000.

Bacillus thuringiensis↗
PubMed2007

The role of neutral lipid nanospheres in Plasmodium falciparum haem crystallization.

The intraerythrocytic malaria parasite constructs an intracellular haem crystal, called haemozoin, within an acidic digestive vacuole where haemoglobin is degraded. Haem crystallization is the target of the widely used antimalarial quinoline drugs. The intracellular mechanism of molecular initiation of haem crystallization, whether by proteins, polar membrane lipids or by neutral lipids, has not been fully substantiated. In the present study, we show neutral lipid predominant nanospheres, which envelop haemozoin inside Plasmodium falciparum digestive vacuoles. Subcellular fractionation of parasite-derived haemozoin through a dense 1.7 M sucrose cushion identifies monoacylglycerol and diacylglycerol neutral lipids as well as some polar lipids in close association with the purified haemozoin. Global MS lipidomics detects monopalmitic glycerol and monostearic glycerol, but not mono-oleic glycerol, closely associated with haemozoin. The complex neutral lipid mixture rapidly initiates haem crystallization, with reversible pH-dependent quinoline inhibition associated with quinoline entry into the neutral lipid microenvironment. Neutral lipid nanospheres both enable haem crystallization in the presence of high globin concentrations and protect haem from H2O2 degradation. Conceptually, the present study shifts the intracellular microenvironment of haem crystallization and quinoline inhibition from a polar aqueous location to a non-polar neutral lipid nanosphere able to exclude water for efficient haem crystallization.

Animals↗
PubMed1990

Comparative analysis of the individual protoxin components in P1 crystals of Bacillus thuringiensis subsp. kurstaki isolates NRD-12 and HD-1.

Two commercially important strains (NRD-12 and HD-1) of the entomopathogenic bacterium Bacillus thuringiensis subsp. kurstaki each contain three genes of partially identical sequence coding for three classes of 130-135 kDa protoxins (termed the 4.5, 5.3 and 6.6 protoxins) that display toxicity towards various lepidopteran larvae. These gene products combine to form the intracellular bipyramidal P1 crystal. Each of the genes from both strains was cloned and expressed in Escherichia coli. Analysis of the cloned genes at the restriction-endonuclease level revealed no detectable differences among genes within a particular gene class. The composition of the P1 crystal from both strains was quantitatively analysed by CNBr cleavage of the purified P1 crystal, with the purified recombinant gene products as reference proteins. Independent verification of the presence of high 6.6-protoxin gene product in the P1 crystal was provided by a rapid in vitro lawn cell toxicity assay directed against a Choristoneura fumiferana (CF-1) insect cell line. The results indicate that, although all three gene products are represented within the P1 crystal of either NRD-12 or HD-1, only the contents of the 4.5 and 5.3 protoxins vary between the two crystals, whereas the 6.6 protoxin contents are similar and represent approximately one-third of the P1 crystal in either strain.

Animals↗
PubMed1998

Activation of S6 kinase in human neutrophils by calcium pyrophosphate dihydrate crystals: protein kinase C-dependent and phosphatidylinositol-3-kinase-independent pathways.

Phosphatidylinositol 3-kinase (PI 3-kinase) has been shown previously to be a central enzyme in crystal-induced neutrophil activation. Since activation of the 70 kDa S6 kinase (p70S6K) has been shown to be dependent on PI 3-kinase activation in mammalian cells, and since the former is a key enzyme in the transmission of signals to the cell nucleus, activation of p70(S6K) was investigated in crystal-stimulated neutrophils. Cytosolic fractions from calcium pyrophosphate dihydrate (CPPD)-crystal-activated neutrophils were separated by Mono Q chromatography and analysed for phosphotransferase activity using a range of substrates and probed by Western analysis using antibodies to p70(S6K) and mitogen-activated protein kinase (MAP kinase). CPPD crystals induced a robust, transient activation (peak activity at 2 min) of p70(S6K) that was fully inhibited by pretreatment with rapamycin. This is the first report of the activation of p70(S6K) in neutrophil signal transduction pathways induced by an agonist. This crystal-induced activation of p70(S6K) could also be inhibited by a protein kinase C (PKC) inhibitor (Compound 3), but not by the PI 3-kinase inhibitor wortmannin. CPPD crystals also activated the ERK1 and ERK2 forms of MAP kinase (wortmannin insensitive), PKC (Compound 3 sensitive) and protein kinase B (wortmannin sensitive) in neutrophils. These data suggest that activation of p70(S6K) may proceed through a PI 3-kinase- and protein kinase B-independent but PKC-dependent pathway in crystal-activated neutrophils.

Androstadienes↗
PubMed1995

The urinary F1 activation peptide of human prothrombin is a potent inhibitor of calcium oxalate crystallization in undiluted human urine in vitro.

1. The urinary F1 activation peptide of prothrombin is the predominant protein incorporated into calcium oxalate crystals precipitated from human urine. The aim of this study was to examine the effect of pure urinary prothrombin F1 on calcium oxalate crystallization in human urine. 2. Urinary prothrombin F1 was purified from demineralized calcium oxalate crystals precipitated from human urine, and its effects on calcium oxalate crystallization induced by addition of an oxalate load were tested in undiluted, ultrafiltered urine from healthy men, at final concentrations of 0 to 10 mg/l. 3. Urinary prothrombin F1 did not affect the amount of oxalate required to induce crystallization, but the volume of material deposited increased in proportion to increasing concentrations of urinary prothrombin F1. However, the mean particle size decreased in reverse order: this was confirmed by scanning electron microscopy, which showed it to be the result of a reduction in crystal aggregation rather than in the size of individual crystals. Analysis of 14C-oxalate data revealed a dose-dependent decrease in calcium oxalate deposition with an increase in urinary prothrombin F1 concentration, indicating that the increase in particle volume recorded by the Coulter Counter resulted from inclusion of urinary prothrombin F1 into the crystalline architecture, rather than increased deposition of calcium oxalate. 4. It was concluded that urinary prothrombin F1 may be an important macromolecular determinant of stone formation.

Calcium Oxalate↗
PubMed1998

Cholesterol crystals as an etiological factor in non-resolving chronic inflammation: an experimental study in guinea pigs.

The presence of cholesterol crystals has been suggested to be a factor interfering with periapical healing after conventional endodontic treatment. This investigation addresses the role of cholesterol crystals in impairing healing by studying the tissue response to the crystals, which were implanted in animals. Pure cholesterol crystals, prepared to a mushy form, were placed in Teflon cages that were implanted subcutaneously in guinea pigs. The cage-contents were retrieved after 2, 4 and 32 wk of implantation and processed for light and electron microscopy. The cages revealed delicate connective tissue that grew in through perforations on the cage-wall. The crystals were densely surrounded by numerous macrophages and multinucleated giant cells, forming a well-circumscribed area of tissue reaction. The cells, however, were unable to eliminate the crystals during an observation period of 8 months. The congregation of macrophages and giant cells, known to be major sources of apical inflammatory and bone resorptive mediators, suggest that accumulation of cholesterol crystals can be a factor in the failure of certain apical periodontitis lesions to resolve after conventional root-filling therapy.

Animals↗
PubMed2000

Effects of phospholipase A2, free fatty acids and 2-lysolecithin on the crystallization of cholesterol in gallbladder bile.

BACKGROUND: Phospholipase A2 (PLA2) and its enzymatic products free fatty acids (FFAs) and 2-lysolecithin are physiological constituents of bile. Their role in the crystallization of cholesterol in gallbladder bile of patients with cholesterol gallstones is still controversial. DESIGN: To clarify this issue we evaluated the activity of PLA2 and the concentration and pattern of FFAs in the gallbladder bile of cholesterol stone patients. We furthermore added PLA2, FFAs and 2-lysolecithin to isotropic gallbladder bile, determined the crystal observation time (COT) and counted the cholesterol crystals in a crystal growth assay for up to 21 days. RESULTS: A PLA2 activity of 1.8 +/- 1.2 U L(-1) and total FFA concentrations of 1.32 +/- 0.71 mmol L(-1) were determined. After incubation of bile for 24 h at 37 degrees C total FFAs increased to 2.72 +/- 1.29 mmol L(-1) (P<0.005). Biliary saturated and unsaturated FFAs were found in equal proportions before and after incubation, pointing to an additional presence of lipases other than PLA2. A COTof 1 day was observed in all gallbladder biles and increased to 1.7 +/- 0.5 days after addition of 5 U L(-1) of PLA2 (P<0.01). An even higher COT of 2.5 +/- 0.8 days was seen after addition of 5 mmol L(-1) of a 'biliary' mixture of FFAs (P<0.005) but the COT remained unchanged after addition of 5 mmol L(-1) of 2-lysolecithin. However, in the crystal growth assay in gallbladder bile addition of 5 U L(-1) of PLA2, of 5 mmol L(-1) of 'biliary' FFAs and of 5 mmol L(-1) of 2-lysolecithin decreased significantly the number of cholesterol crystals formed during follow-up. CONCLUSION: An elevated activity of PLA2 in gallbladder bile may counteract the formation of cholesterol crystals through increased formation of FFAs and 2-lysolecithin. However, regarding the comparatively low activity of PLA2 in gallbladder bile PLA2 seems to be of only minor pathophysiological importance in the formation of cholesterol gallstones.

Adult↗