Urinary macromolecules are promoters of calcium oxalate nucleation in human urine: Turbidimetric studies

Calcium oxalate crystallization was induced in the filtered, ultrafiltered (10 kDa) and retentate fractions of 24-h urine specimens obtained from 15 male controls and 10 male stone formers, by administration of an aqueous sodium oxalate challenge to each test solution. Crystallization rates were followed by monitoring of the increase in turbidity in these fractions as a function of time. A laboratory nephelometer, previously calibrated against a Coulter counter, was used for this purpose. In addition, to facilitate interpretation of turbidity data, a Malvern particle size analyzer was used to determine crystal sizes and numbers in control urines. Crystallization rates, crystal numbers and crystal sizes were generally lower in ultrafiltered fractions than in filtered or retentate fractions, indicating that urinary macromolecules are promoters of calcium oxalate nucleation. Data for stone formers suggest that the urinary macromolecules in this group may be more potent nucleation promoters than those in controls.     

Self-catalyzed growth of S layers via an amorphous-to-crystalline transition limited by folding kinetics

The importance of nonclassical, multistage crystallization pathways is increasingly evident from theoretical studies on colloidal systems and experimental investigations of proteins and biomineral phases. Although theoretical predictions suggest that proteins follow these pathways as a result of fluctuations that create unstable dense-liquid states, microscopic studies indicate these states are long-lived. Using in situ atomic force microscopy to follow 2D assembly of S-layer proteins on supported lipid bilayers, we have obtained a molecular-scale picture of multistage protein crystallization that reveals the importance of conformational transformations in directing the pathway of assembly. We find that monomers with an extended conformation first form a mobile adsorbed phase, from which they condense into amorphous clusters. These clusters undergo a phase transition through S-layer folding into crystalline clusters composed of compact tetramers. Growth then proceeds by formation of new tetramers exclusively at cluster edges, implying tetramer formation is autocatalytic. Analysis of the growth kinetics leads to a quantitative model in which tetramer creation is rate limiting. However, the estimated barrier is much smaller than expected for folding of isolated S-layer proteins, suggesting an energetic rationale for this multistage pathway.     

Does Tamm-Horsfall mucoprotein inhibit or promote calcium oxalate crystallization in human urine?

Using two different experimental techniques, Tamm-Horsfall mucoprotein (THM) has been reported both to inhibit and to promote calcium oxalate (CaOx) crystallization in ultrafiltered human urine. In this study, these two techniques were used to compare the effects of THM on CaOx crystallization in the same ultrafiltered urine samples.

Urine was collected from 10 healthy men and ultrafiltered (10000 Da). Each sample was divided and to one half was added sufficient human THM to give a final concentration of 35 mg/L. CaOx crystallization was induced in the samples by addition of an oxalate load and by evaporation.

Using the evaporation technique THM significantly increased the deposition of CaOx determined as ¹⁴C-oxalate, from 9772 cpm to 43652 cpm (P < 0.01). Using the oxalate load method THM had no effect on the metastable limits of the urine with respect to CaOx, and significantly increased the volume of particulate material deposited from 26000 to 39995 μm³/μl - an increase of 54%. This increase was reduced to 21% when values were corrected for the volume of THM particles recorded in control samples to which no oxalate load was added. Using ¹⁴C-oxalate, it was shown that this increase in volume could not be attributed to an enhanced deposition of crystalline CaOx, but was probably the result of an increased polymerization of THM in the presence of CaOx crystals. Despite this, the average size of the particles precipitated in the presence of THM (6.5 μm) was significantly (P < 0.01) less than that observed in the absence of THM (12.1 μm).

It was concluded that the effect of THM on CaOx crystallization in urine depends upon the methodology used to assess it and that promotion would only be expected in vivo in cases of extreme dehydration. Under usual physiological conditions THM would be expected to inhibit CaOx crystal aggregation and to have little effect, if any, on the amount of crystalline material deposited.     

吲哚美辛微观结晶机制及纳米包衣的影响

药物的无定形状态比晶态具有更大的溶解度,可以促进吸收,提高口服生物利用度,但是稳定性差,易转变为晶体状态。本文采用偏光显微镜、扫描电子显微镜、差示扫描量热法、X-射线衍射法和拉曼光谱法等研究无定形吲哚美辛的微观结晶机制,并对药物表面进行喷金包衣,厚度为10 nm,研究结晶行为变化。结果发现,无定形吲哚美辛自由表面的结晶速率远大于其内部,金包衣可显著抑制自由表面的结晶。这提示,自由表面的结晶是影响无定形药物稳定性的关键因素,纳米包衣可用于增强无定形药物的稳定性。     

Water-enhanced crystallization of leucite in dental porcelain

OBJECTIVE: The purpose of this study was to determine whether long-term exposure of dental porcelain to saliva during temporary cementation of a porcelain-fused-to-metal (PFM) restoration could enhance leucite crystallization if the restoration is refired. Such water-enhanced leucite crystallization in dental porcelains could lead to porcelain-metal thermal incompatibility problems. METHODS: Six commercial dental body porcelains and the Component No. 1 (leucite-containing) frit of the Weinstein et al. [13] patent were studied. For each porcelain, 30 coupon specimens were randomly assigned to a treatment group. Ten specimens were placed in artificial saliva, 10 in distilled water, and 10 in a desiccator and were stored for six months. At the end of the six months, an additional 10 coupons of each porcelain were prepared to serve as a control. All 40 specimens of each porcelain were randomized and subjected to one additional firing. Leucite weight fraction was determined by quantitative X-ray powder diffraction analysis via an internal standard technique. RESULTS: Comparisons among the treatments via the least-squares-means test-adjusting for porcelain showed that the saliva group mean leucite weight fraction was significantly higher than that of the other groups. The change in porcelain thermal expansion that would be associated with a leucite change in this range would be between 0.2 x 10(-6) K-1 and 0.3 x 10(-6) K-1. SIGNIFICANCE: The results of this work constitute the first demonstration that moisture absorbed by a porcelain can act as a glass modifier and enhance the crystallization of the glass during subsequent firing. The effect was sufficiently large to generate thermal expansion changes that would exceed the maximum safe mismatch between porcelain and metal.     

Non-Isothermal Kinetic Analysis of the Crystallization of Metallic Glasses Using the Master Curve Method

The non-isothermal transformation rate curves of metallic glasses are analyzed with the Master Curve method grounded in the Kolmogorov-Johnson-Mehl-Avrami theory. The method is applied to the study of two different metallic glasses determining the activation energy of the transformation and the experimental kinetic function that is analyzed using Avrami kinetics. The analysis of the crystallization of Cu₄₇Ti₃₃Zr₁₁Ni₈Si₁ metallic glassy powders gives E_a = 3.8 eV, in good agreement with the calculation by other methods, and a transformation initiated by an accelerating nucleation and diffusion-controlled growth. The other studied alloy is a Nanoperm-type Fe₇₇Nb₇B₁₅Cu₁ metallic glass with a primary crystallization of bcc-Fe. An activation energy of E_a = 5.7 eV is obtained from the Master Curve analysis. It is shown that the use of Avrami kinetics is not able to explain the crystallization mechanisms in this alloy giving an Avrami exponent of n = 1.     

Atomic structure of a nanobody-trapped domain-swapped dimer of an amyloidogenic beta2-microglobulin variant

Atomic-level structural investigation of the key conformational intermediates of amyloidogenesis remains a challenge. Here we demonstrate the utility of nanobodies to trap and characterize intermediates of β2-microglobulin (β2m) amyloidogenesis by X-ray crystallography. For this purpose, we selected five single domain antibodies that block the fibrillogenesis of a proteolytic amyloidogenic fragment of β2m (ΔN6β2m). The crystal structure of ΔN6β2m in complex with one of these nanobodies (Nb24) identifies domain swapping as a plausible mechanism of self-association of this amyloidogenic protein. In the swapped dimer, two extended hinge loops--corresponding to the heptapetide NHVTLSQ that forms amyloid in isolation--are unmasked and fold into a new two-stranded antiparallel β-sheet. The β-strands of this sheet are prone to self-associate and stack perpendicular to the direction of the strands to build large intermolecular β-sheets that run parallel to the axis of growing oligomers, providing an elongation mechanism by self-templated growth.     

Crystallization Behavior and Mechanical Properties of Poly(ε-caprolactone) Reinforced with Barium Sulfate Submicron Particles

Poly(ε-caprolactone) (PCL) was mixed with submicron particles of barium sulfate to obtain biodegradable radiopaque composites. X-ray images comparing with aluminum samples show that 15 wt.% barium sulfate (BaSO₄) is sufficient to present radiopacity. Thermal studies by differential scanning calorimetry (DSC) show a statistically significant increase in PCL degree of crystallinity from 46% to 52% for 25 wt.% BaSO₄. Non-isothermal crystallization tests were performed at different cooling rates to evaluate crystallization kinetics. The nucleation effect of BaSO₄ was found to change the morphology and quantity of the primary crystals of PCL, which was also corroborated by the use of a polarized light optical microscope (PLOM). These results fit well with Avrami–Ozawa–Jeziorny model and show a secondary crystallization that contributes to an increase in crystal fraction with internal structure reorganization. The addition of barium sulfate particles in composite formulations with PCL improves stiffness but not strength for all compositions due to possible cavitation effects induced by debonding of reinforcement interphase.     

Single Femtosecond Laser-Pulse-Induced Superficial Amorphization and Re-Crystallization of Silicon

Superficial amorphization and re-crystallization of silicon in <111> and <100> orientation after irradiation by femtosecond laser pulses (790 nm, 30 fs) are studied using optical imaging and transmission electron microscopy. Spectroscopic imaging ellipsometry (SIE) allows fast data acquisition at multiple wavelengths and provides experimental data for calculating nanometric amorphous layer thickness profiles with micrometric lateral resolution based on a thin-film layer model. For a radially Gaussian laser beam and at moderate peak fluences above the melting and below the ablation thresholds, laterally parabolic amorphous layer profiles with maximum thicknesses of several tens of nanometers were quantitatively attained. The accuracy of the calculations is verified experimentally by high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (STEM-EDX). Along with topographic information obtained by atomic force microscopy (AFM), a comprehensive picture of the superficial re-solidification of silicon after local melting by femtosecond laser pulses is drawn.     

Computational design of a protein crystal

Protein crystals have catalytic and materials applications and are central to efforts in structural biology and therapeutic development. Designing predetermined crystal structures can be subtle given the complexity of proteins and the noncovalent interactions that govern crystallization. De novo protein design provides an approach to engineer highly complex nanoscale molecular structures, and often the positions of atoms can be programmed with sub-Å precision. Herein, a computational approach is presented for the design of proteins that self-assemble in three dimensions to yield macroscopic crystals. A three-helix coiled-coil protein is designed de novo to form a polar, layered, three-dimensional crystal having the P6 space group, which has a “honeycomb-like” structure and hexameric channels that span the crystal. The approach involves: (i) creating an ensemble of crystalline structures consistent with the targeted symmetry; (ii) characterizing this ensemble to identify “designable” structures from minima in the sequence-structure energy landscape and designing sequences for these structures; (iii) experimentally characterizing candidate proteins. A 2.1 Å resolution X-ray crystal structure of one such designed protein exhibits sub-Å agreement [backbone root mean square deviation (rmsd)] with the computational model of the crystal. This approach to crystal design has potential applications to the de novo design of nanostructured materials and to the modification of natural proteins to facilitate X-ray crystallographic analysis.