Nascent Crystals Research Articles

Physical Basis of Functioning of Antifreeze Protein

Antifreeze proteins, expressed in cold-blooded organisms, prevent ice formation in their bodies, and thus help them to survive in extremely cold winter temperatures. However, the mechanism of action of these proteins is still not clear. In any case, it is not simply a decrease in the temperature of normal ice formation. In this work, investigating the ice-binding protein (a mutant form of the antifreeze protein cfAFP from the spruce budworm Choristoneura fumiferana, which overwinters in needles), we showed that this antifreeze protein does not at all lower the freezing point of water and, paradoxically, increases the melting point of ice. On the other hand, calculations based on the theory of crystallization show that at temperatures of 0 ° to –30°C ice can only appear on surfaces that contact water, but not in the body of water. These facts suggest a new perspective on the role of antifreeze proteins: their task is not (as it is commonly believed) to bind with nascent ice crystals already formed in the organism and stop their growth, but to bind to those surfaces, on which ice nuclei can appear, and thus completely inhibit the ice formation in supercooled water or biological fluid.

The Calcium Looping process for energy storage: Insights from in situ XRD analysis

This work reports a novel in situ XRD analysis on the multicycle calcination/carbonation of natural limestone and dolomite at relevant conditions for thermochemical energy storage (TCES) in concentrated solar power (CSP) plants. The experiments allow analysing noninvasively the time evolution of the different phases involved in the Calcium Looping (CaL) process. Our work has revealed new key features to understand the progressive loss of multicyclic carbonation reactivity of the CaO derived from calcination. The CaCO3 structure formed in the first step of dolomite decomposition has smaller unit cell volume than the CaCO3 naturally present in limestone. The CaO that stems from decomposition of the CaCO3 derived from dolomite first decomposition shows a greater carbonation reactivity compared to the CaO derived from limestone. The smaller size of the CaO nascent crystals and their relatively higher reactivity for dolomite compared to limestone is related to the presence of inert MgO crystals, which prevent CaO sintering and crystallite growth. However, the size of the MgO crystals derived from dolomite decomposition increases monotonically with time, which progressively hampers their hindrance effect. Our work also shows a positive correlation between the growth of the CaO crystallite size and the decline of preferred orientation in the CaO (100) plane as the number of cycles is increased and CaO loses reactivity. The observed evolution with the cycles of CaO crystallite size and reactivity can be attributed to the incompletion of carbonation. The unreacted CaO that remains in the calcination step suffers severe sintering which hinders its reactivity. Thus, the fraction of fresh, reactive CaO derived from CaCO3 decomposition that nucleates on the old and less reactive CaO declines progressively with the cycles.

P1237TISSUE-NONSPECIFIC ALKALINE PHOSPHATASE, A CULPRIT DURING ARTERIAL MEDIA CALCIFICATION BUT INDISPENSABLE DURING PHYSIOLOGICAL BONE FORMATION/-MINERALIZATION IN RATS

Abstract Background and Aims Vascular media calcification is frequently seen in elderly and patients with chronic kidney disease (CKD), diabetes and osteoporosis. Pyrophosphate is a well-known calcification inhibitor that binds to nascent hydroxyapatite crystals and prevents further incorporation of inorganic phosphate into these crystals. However, the enzyme tissue-nonspecific alkaline phosphatase (TNAP), which is highly expressed in calcified arteries, degrades extracellular pyrophosphate into phosphate ions, by which pyrophosphate loses its ability to block vascular calcification. Here, we aimed to evaluate whether a TNAP inhibitor is able to prevent the development of arterial calcification in a rat model of warfarin-induced vascular calcification. Method To induce vascular calcification, rats received a diet containing 0.30% warfarin and 0.15% vitamin K1 throughout the entire study and were subjected to the following daily treatments: (i) vehicle (n=10) or (ii) 10 mg/kg/day TNAP-inhibitor (n=10) administered via an intraperitoneal catheter from start of the study until sacrifice at week 7. Calcium, phosphorus and parathyroid hormone (PTH) levels were determined in serum samples as these are important determinants of vascular calcification. As TNAP is also expressed in the liver, serum alanine aminotransferase (ALT) and aspartate (AST) levels were analyzed. At sacrifice, vascular calcification was evaluated by measurement of the total calcium content in the arteries and quantification of the area % calcification on Von Kossa stained sections of the aorta. The mRNA expression of osteo/chondrogenic marker genes (runx2, TNAP, SOX9, collagen 1 and collagen 2) was analyzed in the aorta by qPCR to verify whether vascular smooth muscle cells underwent reprogramming towards bone-like cells. Bone histomorphometry was performed on the left tibia to measure static and dynamic bone parameters as TNAP also regulates physiological bone mineralization. Results No differences in serum calcium, phosphorus and PTH levels was observed between both study groups. Warfarin exposure resulted in distinct calcification in the aorta and peripheral arteries. Daily dosing with the TNAP inhibitor (10 mg/kg/day) for 7 weeks significantly reduced vascular calcification as indicated by a significant decrease in calcium content in the aorta (vehicle 3.84±0.64 mg calcium/g wet tissue vs TNAP inhibitor 0.70±0.23 mg calcium/g wet tissue) and peripheral arteries and a distinct reduction in area % calcification on Von Kossa stained aortic sections as compared to vehicle condition. The inhibitory effects of SBI-425 on vascular calcification were without altering serum liver markers ALT and AST levels. Furthermore, TNAP-inhibitor SBI-425 did not modulate the mRNA expression of osteo/chondrogenic marker genes runx2, TNAP, SOX9, collagen 1 and 2. Dosing with SBI-425 resulted in decreased bone formation rate and mineral apposition rate, and increased osteoid maturation time and this without significant changes in osteoclast- and eroded perimeter. Conclusion Dosing with TNAP inhibitor SBI-425 significantly reduced the calcification in the aorta and peripheral arteries of a rat model of warfarin-induced vascular calcification and this without affecting liver function. However, suppression of TNAP activity should be limited in order to maintain adequate physiological bone mineralization.

Flash DSC study on the annealing behaviors of poly(l-lactide acid) crystallized in the low temperature region

We employed commercialized fast-scan chip-calorimeter (Flash DSC1) in assistant with Fourier Transform Infrared Spectroscopy (FTIR) and Atomic Force Microscope (AFM) to investigate the annealing behaviors of poly (l-lactic acid) with dominant alfa’-crystals crystallized in the low temperature region. The results put together various annealing behaviors observed previously in different temperature regions, and suggested that continuous crystal perfection and discontinuous melting-recrystallization are competing with each other on the transition from alfa’-crystals to the more stable alfa-crystals. Both two processes fit well into the unified scenario of the conventional annealing behaviors of polymer crystals; therefore, our observations confirm that alfa’-crystals contain no intrinsic crystalline lattice difference from alfa-crystals, except for their different extents of crystal perfection resulting in the shifting of melting points. In addition, we found that fast recrystallization right after melting yields less stable crystals than those nascent crystals grown from the initial melt, confirming again the consequence of instant crystallization without enough time of crystal perfection as the extreme example in alfa’-crystals.

Theoretical Investigation of Phase Transitions of Graphite and Cubic 3C Diamond Into Hexagonal 2H Diamond Under High Pressures

Possible techniques for experimentally obtaining hexagonal diamond are studied in the scope of the density functional theory method. It has been found that hexagonal diamond may be created as a result of structural transition at 61–68 GPa uniaxial compression from orthorhombic AB graphite and at 57–66 GPa from hexagonal AA graphite. Also the formation of hexagonal diamond is shown to take place in case of very strong (300–380 GPa) compression of cubic diamond. X‐ray and electron‐microscopic data on nanodiamonds from meteorite craters are analyzed for the presence of hexagonal diamond. The analysis shows that impact‐origin carbon materials do not contain pure cubic and hexagonal diamonds, and the layers of nascent crystals of diamond polytypes are randomly packed.

Correlation between Thermal and Mechanical Response of Nascent Semicrystalline UHMWPEs

In spite of the abstract nature, entanglements are the folklore of polymer science, and their presence is realized in the semicrystalline and amorphous solid state as well as in the molten state (melt) of polymers. For example, the entangled state in the noncrystalline region is known to be the determining factor in melting kinetics and also in uniaxial as well as biaxial deformation of linear ultrahigh molecular weight polyethylenes (UHMWPEs). In this paper we aim to investigate a possible correlation between the melting of crystals and the ease of deformation of the semicrystalline polymer. Considering that the entanglement density, and the associated topological constraints residing in the noncrystalline region, can be influenced by the polymerization conditions, a series of UHMWPEs have been synthesized. For a set of polymers synthesized at fixed pressure, the characteristic melting time of the as-synthesized nascent crystals (τ1) measured by temperature-modulated DSC (TM-DSC) is found to decrease wit...

Protein-crystal Interactions in Calcium Oxalate Kidney Stone Formation

We have studied the ability of urinary molecules in altering the precipitation of kidney stone-related calcium oxalate monohydrate (COM) crystals and correlated the resulting morphologies with those of idiopathic COM kidney stones. We found that weakly acidic but highly glycosylated polyelectrolytes (Tamm Horsfall protein (THP), fetuinA, hyaluronic acid) do not significantly affect crystallization, and that THP and fetuinA show the tendency to aggregate in the presence of nascent crystals. It is proposed that highly glycosylated polyelectrolytes encapsulate nascent urinary crystals, prevent their aggregation, and thus act supportive in crystal excretion. Strong effects on crystallization were observed in the presence of the highly acidic molecules osteopontin (OPN), citrate, and the non-urinary glycosaminoglycans heparin and dextran sulfate. OPN formed non-structured concretions comparable with those found in the core of stones, while citrate formed platelets closely resembling crystal shapes found in the mantle region. However, it is unclear how the columnar growth in the mantle takes place. It is assumed that changing polyelectrolyte compilations/concentrations affect stone forming processes (e.g. equilibria, enhanced self-assembly), perhaps resulting in these structures. We have indeed shown that peptides can induce the formation of such structures. Moreover, heparin and dextran sulfate inhibited COM formation; implicating that these molecules could assist OPN, citrate but also THP in preventing stone formation.

Symmetry breaking and silver in gold nanorod growth.

Formation of anisotropic nanocrystals from isotropic single-crystal precursors requires an essential symmetry breaking event. Single-crystal gold nanorods have become the model system for investigating the synthesis of anisotropic nanoparticles, and their growth mechanism continues to be the subject of intense investigation. Despite this, very little is known about the symmetry breaking event that precedes shape anisotropy. In particular, there remains limited understanding of how an isotropic seed particle becomes asymmetric and of the growth parameters that trigger and drive this process. Here, we present direct atomic-scale observations of the nanocrystal structure at the embryonic stages of gold nanorod growth. The onset of asymmetry of the nascent crystals is observed to occur only for single-crystal particles that have reached diameters of 4-6 nm and only in the presence of silver ions. In this size range, small, asymmetric truncating surfaces with an open atomic structure become apparent. Furthermore, {111} twin planes are observed in some immature nanorods within 1-3 monolayers of the surface. These results provide direct observation of the structural changes that break the symmetry of isotropic nascent nanocrystals and ultimately enable the growth of asymmetric nanocrystals.

Direct Route to Colloidal UHMWPE by Including LLDPE in Solution during Homogeneous Polymerization of Ethylene.

The usual aggregation and precipitation driven by crystallization of nascent PE during homogeneous polymerization of ultra-high molecular weight polyethylene (UHMWPE) is inhibited by including linear low-density polyethylene (LLDPE) in the catalyst solution prior to addition of ethylene monomer. Co-crystallization of newly formed PE and dissolved LLDPE creates a polymer brush on the fold surfaces of the nascent crystallites. Consequently, aggregation is inhibited by steric stabilization. Scanning electron microscopy (SEM) images show that individual lamellae (approximately 10-20 nm thick) typically have lateral dimensions of 0.5 μm × 3.5 μm and form "bowtie" shaped stacks that are approximately 200-500 nm thick. This simple method for stabilizing nascent crystals against precipitation is enabling fundamental studies of their metastable "disentangled" state and may open scalable routes to compounding UHMWPE.

Membrane Protein Structure Determination Using Crystallography and Lipidic Mesophases: Recent Advances and Successes

The crystal structure of the β(2)-adrenergic receptor in complex with an agonist and its cognate G protein has just recently been determined. It is now possible to explore in molecular detail the means by which this paradigmatic transmembrane receptor binds agonist, communicates the impulse or signaling event across the membrane, and sets in motion a series of G protein-directed intracellular responses. The structure was determined using crystals of the ternary complex grown in a rationally designed lipidic mesophase by the so-called in meso method. The method is proving to be particularly useful in the G protein-coupled receptor field where the structures of 13 distinct receptor types have been determined in the past 5 years. In addition to receptors, the method has proven to be useful with a wide variety of integral membrane protein classes that include bacterial and eukaryotic rhodopsins, light-harvesting complex II (LHII), photosynthetic reaction centers, cytochrome oxidases, β-barrels, an exchanger, and an integral membrane peptide. This attests to the versatility and range of the method and supports the view that the in meso method should be included in the arsenal of the serious membrane structural biologist. For this to happen, however, the reluctance to adopt it attributable, in part, to the anticipated difficulties associated with handling the sticky, viscous cubic mesophase in which crystals grow must be overcome. Harvesting and collecting diffraction data with the mesophase-grown crystals are also viewed with some trepidation. It is acknowledged that there are challenges associated with the method. Over the years, we have endeavored to establish how the method works at a molecular level and to make it user-friendly. To these ends, tools for handling the mesophase in the pico- to nanoliter volume range have been developed for highly efficient crystallization screening in manual and robotic modes. Methods have been implemented for evaluating the functional activity of membrane proteins reconstituted into the bilayer of the cubic phase as a prelude to crystallogenesis. Glass crystallization plates that provide unparalleled optical quality and sensitivity to nascent crystals have been built. Lipid and precipitant screens have been designed for a more rational approach to crystallogenesis such that the method can now be applied to an even wider variety of membrane protein types. In this work, these assorted advances are outlined along with a summary of the membrane proteins that have yielded to the method. The prospects for and the challenges that must be overcome to further develop the method are described.

Performance of a non-phosphorus antiscalant on inhibition of calcium-sulfate precipitation

The aim of this study is to report on the performance of a novel non-phosphorus antiscalant, acrylic acid (AA)-allylpolyethoxy carboxylate (APEC), being developed for calcium-sulfate scale inhibition in industrial water systems. The performance of AA-APEC on calcium-sulfate scale inhibition was compared with that of the two commercial inhibitors, polyamino polyether methylene phosphonates (PAPEMP) and polyacrylic acid (PAA), containing the same polyethylene glycol segments or carboxyl functional groups as AA-APEC. The study indicated that AA-APEC could act as a highly effective calcium sulfate inhibitor, having strong ability to inhibit the precipitation of calcium sulfate at a dosage of 2 mg L(-1), showing approximately 83.6% inhibition. The results also showed that AA-APEC dosage, the solution pH, inhibiting temperature, concentration of Ca(2+), and SO(4)(2-) all play important roles in inhibiting calcium-sulfate precipitation. The precipitation thermodynamics and kinetics at different temperatures were also discussed. X-ray diffractometer (XRD) and scanning electron microscope (SEM) analysis showed that AA-APEC strongly affected the texture and the morphology of the deposited calcium sulfate. Calcium sulfate has been inhibited through stabilization by adsorption onto crystal growth sites of nascent crystals altering their morphology.

Crystallizing membrane proteins for structure–function studies using lipidic mesophases

The lipidic cubic phase method for crystallizing membrane proteins has posted some high-profile successes recently. This is especially true in the area of G-protein-coupled receptors, with six new crystallographic structures emerging in the last 3½ years. Slowly, it is becoming an accepted method with a proven record and convincing generality. However, it is not a method that is used in every membrane structural biology laboratory and that is unfortunate. The reluctance in adopting it is attributable, in part, to the anticipated difficulties associated with handling the sticky viscous cubic mesophase in which crystals grow. Harvesting and collecting diffraction data with the mesophase-grown crystals is also viewed with some trepidation. It is acknowledged that there are challenges associated with the method. However, over the years, we have worked to make the method user-friendly. To this end, tools for handling the mesophase in the pico- to nano-litre volume range have been developed for efficient crystallization screening in manual and robotic modes. Glass crystallization plates have been built that provide unparalleled optical quality and sensitivity to nascent crystals. Lipid and precipitant screens have been implemented for a more rational approach to crystallogenesis, such that the method can now be applied to a wide variety of membrane protein types and sizes. In the present article, these assorted advances are outlined, along with a summary of the membrane proteins that have yielded to the method. The challenges that must be overcome to develop the method further are described.

Thermodynamic Origin of the Vitreous Transition.

The vitreous transition is characterized by a freezing of atomic degrees of freedom at a temperature Tg depending on the heating and cooling rates. A kinetic origin is generally attributed to this phenomenon instead of a thermodynamic one which we develop here. Completed homogeneous nucleation laws reflecting the energy saving due to Fermi energy equalization of nascent crystals and their melt are used. They are applied to bulk metallic glasses and extended to inorganic glasses and polymers. A transition T*g among various Tg corresponds to a crystal homogeneous nucleation temperature, leading to a preliminary formation of a cluster distribution during the relaxation time preceding the long steady-state nucleation time of crystals in small samples. The thermally-activated energy barrier ΔG*2ls/kBT at T*g for homogeneous nucleation is nearly the same in all glass-forming melts and determined by similar values of viscosity and a thermally-activated diffusion barrier from melt to cluster. The glass transition T*g is a material constant and a linear function of the energy saving associated with charge transfers from nascent clusters to the melt. The vitreous transition and the melting temperatures alone are used to predict the free-volume disappearance temperature equal to the Vogel-Fulcher-Tammann temperature of fragile glass-forming melts, in agreement with many viscosity measurements. The reversible thermodynamic vitreous transition is determined by the disappearance temperature T*g of the fully-relaxed enthalpy Hr that is not time dependent; the observed specific heat jump at T*g is equal to the proportionality coefficient of Hr with (T*g − Ta) for T ≤ T*g as expected from the enthalpy excess stored by a quenched undercooled melt at the annealing temperature Ta and relaxed towards an equilibrium vitreous state. However, the heat flux measurements found in literature over the last 50 years only gave an out-of-equilibrium Tg since the enthalpy is continuous at T*g without visible heat jump.

Structure of the HIV-1 Full-Length Capsid Protein in a Conformationally Trapped Unassembled State Induced by Small-Molecule Binding

The capsid (CA) protein plays crucial roles in HIV infection and replication, essential to viral maturation. The absence of high-resolution structural data on unassembled CA hinders the development of antivirals effective in inhibiting assembly. Unlike enzymes that have targetable, functional substrate-binding sites, the CA does not have a known site that affects catalytic or other innate activity, which can be more readily targeted in drug development efforts. We report the crystal structure of the HIV-1 CA, revealing the domain organization in the context of the wild-type full-length (FL) unassembled CA. The FL CA adopts an antiparallel dimer configuration, exhibiting a domain organization sterically incompatible with capsid assembly. A small compound, generated in situ during crystallization, is bound tightly at a hinge site (“H site”), indicating that binding at this interdomain region stabilizes the ADP conformation. Electron microscopy studies on nascent crystals reveal both dimeric and hexameric lattices coexisting within a single condition, in agreement with the interconvertibility of oligomeric forms and supporting the feasibility of promoting assembly-incompetent dimeric states. Solution characterization in the presence of the H-site ligand shows predominantly unassembled dimeric CA, even under conditions that promote assembly. Our structure elucidation of the HIV-1 FL CA and characterization of a potential allosteric binding site provides three-dimensional views of an assembly-defective conformation, a state targeted in, and thus directly relevant to, inhibitor development. Based on our findings, we propose an unprecedented means of preventing CA assembly, by “conformationally trapping” CA in assembly-incompetent conformational states induced by H-site binding.

Circular patterns of calcium oxalate crystals induced by defective Langmuir-Blodgett film

The injury of the renal epithelial cell membrane can promote the nucleation of nascent crystals, as well as adhesion of crystals on it. It thus accelerates the formation of renal calculi. In this paper, the defective Langmuir-Blodgett (LB) films were used as a model system to simulate the injured renal epithelial cell membrane. The microcosmic structure of the defective LB film and the molecular mechanism of the effect of this film on nucleation, growth, deposited patterns and adhesion of calcium oxalate monohydrate (COM) were investigated. The circular defective domains were formed in dipalmitoylphosphatidylcholine (DPPC) LB film after the film was treated by potassium oxalate. These domains could induce ring-shaped patterns of COM crystals. In comparison, the LB film without pretreatment by potassium oxalate only induced random growth of hexagonal COM crystals. As the crystallization time increased, the size of COM crystals in the patterns increased, the crystal patterns changed from empty circles to solid circles, and the number of the circular patterns with small size (5–20 μm) increased. The results would shed light on the molecular mechanism of urolithiasis induced by injury of the renal epithelial membrane at the molecular and supramolecular level.

Classical Molecular Dynamics of Clathrate−Methane−Water−Kinetic Inhibitor Composite Systems

Classical molecular dynamics simulations of clathrate-methane-water and an inhibitor of clathrate formation are performed using different inhibitor/water ratios and a hydrate system modeled as a 5 12 6 2 cavity. Vinylpyrrolidone, vinylvalerolactam, L-proline, 1-formylpyrrolidine, and dimethylaminoethyl methacrylate are used as models of clathrate formation kinetic inhibitors. The goal is to get new insights into the behavior of these composite systems in the early stages of clathrate formation, where the inhibitor is thought to perform its main inhibition effect. Before performing the simulations for the clathrate systems, evidence was searched to find if the chosen combination of force fields reproduced the cage effect for an infinitely diluted methane-water system, and the distribution of water and methane surrounding clathrate-like structures. The systems are analyzed via visualization of the trajectories and examination of the radial distribution functions and the mean-square displacements. The inhibitors can be grouped into hydrophilic and hydrophobic types, and their behavior toward water is analyzed on the basis of their structure and intermolecular interactions. It is found that at the initial stages of clathrate formation the hydrophobic inhibitors may act by blocking the surface of the nascent crystals, whereas the hydrophilic ones act mainly by disruption of the water structure.

A Study of the Use of Novel Self-ordering Functionalized Polymers to Control Crystal Growth

ABSTRACTIn this research, the ability of a series of novel oligomeric organic species to control crystal nucleation and growth of inorganic crystals was investigated. The issues under consideration were (i) the relative balance of hydrophobicity and hydrophilicity which might be programmed into a polymer; (ii) the impact metal binding, or bridging on its activity in a crystallization reaction; (iii) the mode of self organisation. An homologous series of alkyl substituted sulphonated calixarenes were used to probe these issues.The ability of a metal cation to either bridge adjacent calix[4]arenes or to adsorb into the molecular cavity had an impact upon the interaction of these molecules with the nascent crystals; selective and specific adsorption behaviours were revealed by the expression of smooth well defined new faces in the equilibrium morphology of the crystals. When the hydrophobicity index was high (increased molecular weight of alkyl substituent) these compounds segregated at the gas/liquid interface and, as a consequence of cation-induced ordering, were able to induce the oriented nucleation of crystals. When the metal ion was preferentially adsorbed into the molecular cavity the complex induced twinning in the crystal form. These studies have revealed that, in contrast to earlier studies which argued for the only for an epitaxial relationship between the polymer and crystal, a tunable range of several chemical characteristics can be programmed into a polymeric substrates if they are to be used to control nucleation and growth.

Crystallization-Induced Microdomain Coalescence in Lamellar Diblock Copolymers Studied by Dynamic Monte Carlo Simulations

A numerical study of microdomain coalescence induced by the soft-confined crystallization of lamellar diblock copolymers has been reported. It was found that under high temperatures those crystallites showing their orientational preferences perpendicular to the lamellar microdomains are responsible for the occurrence of coalescence, whereas the segregation strength just plays a subsidiary role. In addition, the lamellar microdomains are well preserved with undulations at the stage of primary crystallization but be broken out by the crystal thickening at the subsequent stage of isothermal annealing. Down with the temperature, there exists an abrupt transition from perpendicular to random in the preference of crystallite orientations. Annealing the nascent crystals of variable orientational preferences demonstrates that at low temperatures a randomization in the crystallite orientations may prevent microdomains from coalescing. The mechanisms of undulation and coalescence were thus discussed on the basis of the microphase-interface tension enhanced by the crystal thickening.

Low-temperature synthesis and microstructural control of titania nano-particles

Nanocrystalline titania powders were synthesized at low temperature (⩽100°C) by a sol–gel method that achieved fine control of particle size and polymorph fraction. X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–Vis spectroscopy were used to characterize the phase assemblages, crystal size and band gap of the powders. It was demonstrated that larger, well-ordered titania crystals can be obtained by increasing aging temperature and time. These processing parameters can be adjusted to select specific polymorphs from the gel precursors with particular size and shape. The quantum size effect was observed in the size-controlled nanocrystalline titania particles, leading to a blue shift in UV absorption with decreasing in particle size. The anatase to rutile transformation, which may proceed with brookite as a transition phase, is dependent on both particle size and surface structure of the nascent crystals.

Bio-inspired Crystal Growth Induced by Novel Organic Compounds

AbstractThe growth of biogenic inorganic crystals demands much attention given the exceptional control of nucleation and growth that is evidenced in biological systems. In many cases the biological mineralization products are crystals engineered to express unique forms and habits; this being linked to the bio-function of minerals. It is acknowledged that the formation of these biogenic minerals is controlled by a complex directory of organic macromolecules which are chemically tailored to mediate the crystallization sequelae. In this study, an homologous series of sulphonated calix[4]arenes (further modified by the addition of an alkyl substituent (R = (CH2)nCH3; n = 0-7)) were selected as chemical and structural mimics for some of the active components in the acidic macromolecules known to be associated with many biogenic mineral phases. Here, these calix[4]arenes were assayed for their ability to control the growth of barium sulphate. Their presence in the crystallization liquor induced the twinning of the barium sulphate crystals; two forms of twinning were observed. Interpenetrant (2-31) twins were noted for substituted calix[4]arenes when R = (CH2)2CH3; and interpenetrant {610} twins when R = (CH2)nCH3; n = 0-7. When R = (CH2)nCH3; n = 0 or 1, the crystals also evidenced a novel acicular growth form. These effects were linked to the chemical properties of the calixarenes and structural recognition motifs created at the calix[4]arene/barium sulphate interface following the adsorption of these sulphonated moieties onto the nascent crystals. The results offer an insight into the mechanisms which may mediate such effects in vivo.