The nucleation of C-S-H via prenucleation clusters.

The nucleation and growth of calcium-silicate-hydrate (C-S-H) is of fundamental importance for the strength development and durability of the concrete. However, the nucleation process of C-S-H is still not fully understood. The present work investigates how C-S-H nucleates by analyzing the aqueous phase of hydrating tricalcium silicate (C3S) by applying inductively coupled plasma-optical emission spectroscopy as well as analytical ultracentrifugation. The results show that the C-S-H formation follows non-classical nucleation pathways associated with the formation of prenucleation clusters (PNCs) of two types. Those PNCs are detected with high accuracy and reproducibility and are two species of the 10 in total, from which the ions (with associated water molecules) are the majority of the species. The evaluation of the density and molar mass of the species shows that the PNCs are much larger than ions, but the nucleation of C-S-H starts with the formation of liquid precursor C-S-H (droplets) with low density and high water content. The growth of these C-S-H droplets is associated with a release of water molecules and a reduction in size. The study gives experimental data on the size, density, molecular mass, and shape and outlines possible aggregation processes of the detected species.

Binary Colloidal Nanoparticle Concentration Gradients in a Centrifugal Field at High Concentration.

Binary colloidal nanoparticles have been found to form different types of crystalline phases at varied radial positions in a centrifugal field by Chen et al. ( ACS Nano 2015, 9, 6944-50). The variety of binary phase behaviors resulted from the two different nanoparticle concentration gradients, but to date, the gradients can only be empirically controlled. For the first time, we are able to measure, fit, and simulate binary hard-sphere colloidal nanoparticle concentration gradients at high particle concentrations up to 30 vol %, which enables tailor-made gradients in a centrifugal field. By this means, a continuous range of binary particle concentration ratios can be accessed in one single experiment to obtain an extended phase diagram. By dispersing two differently sized silica nanoparticles labeled with two different fluorescence dyes in a refractive index matching solvent, we can use a multi-wavelength analytical ultracentrifuge (MWL-AUC) to measure the individual concentration gradient for each particle size in sedimentation-diffusion equilibrium. The influence of the remaining slight turbidity at high concentration can be corrected using the MWL spectra from the AUC data. We also show that the experimental concentration gradients can be fitted using a noninteracting nonideal sedimentation model. By using these fitted parameters, we are able to simulate nanoparticle concentration gradients, which agreed with the subsequent experiments at a high concentration of 10 vol % and thus allowed for the simulation of binary concentration gradients of hard-sphere nanoparticles in preparative ultracentrifuges (PUCs). Finally we demonstrated that by simulating the concentration gradients in PUCs, a continuous and extended binary nanoparticle phase diagram can be obtained by simply studying the structure evolution along the centrifugal field for one single sample instead of a large number of experiments with discrete compositions as in conventional studies.

Optical glucose sensing using ethanolamine-polyborate complexes.

Wound monitoring is essential to tackle chronic complications at their infancy and thus objectively scrutinize any delay in the epithelization process. Since glucose in wound exudates is recognized as key bio-marker in wound monitoring, the development of a cost-efficient detection method for glucose would aid at tackling early-stage infections in wounds. For the first time, we present a novel platform for one-step synthesis of non-enzymatic, cost-efficient optical glucose sensors. These are based on complexes formed by the interactions between polyborates and ethanolamines. The complexes, synthesized by just heating a solution of boric acid and ethanolamines at 150 °C, were characterized using 13C-NMR, 1H-NMR, 11B-NMR, analytical ultracentrifugation and DFT. The results show that the complexes in solution are extremely small (hydrodynamic diameter of around 0.5 nm) and that the polyborates species interact with the ethanolamines via both moderate and weak hydrogen bondings. These complexes were then tested on glucose concentrations ranging from 0 to 10 mM, showing significant changes in the fluorescent emission between the glucose level expressed in an healable wound (5.0-7.6 mM) and a chronic one (0.3-1.0 mM).

Infiltration of biomineral templates for nanostructured polypyrrole.

Biomineral templates like sea urchin spine, nacre or eggshell were applied in the polymerisation of pyrrole. The insufficient infiltration of pyrrole into the CaCO3 structure of the biomineral templates was improved using three different and universally applicable approaches and the electrochemical properties of the received polypyrrole were examined.

Functionalisation of silica-carbonate biomorphs.

Biomorphs are a unique class of self-organised silica-carbonate mineral structures with elaborate shapes. Here we report first approaches to modify these complex inorganic architectures through silane chemistry, binding of nanoparticles, and organic polymerisation. This leads to functional nanostructures in which the complexity of the originally inorganic template is preserved, and offers new diagnostic tools to study the mechanisms underlying their formation.

Effects of carboxymethyl cellulose-based saliva substitutes with varying degrees of saturation with respect to calcium phosphates on artificial enamel lesions.

The aim of the present study was to evaluate the effects of experimental saliva substitutes based on carboxymethyl cellulose (CMC) differing in degrees of saturation with respect to calcium phosphates on the mineral loss of enamel in vitro. Demineralized bovine specimens (subsurface lesions) were exposed to one of six experimental CMC-based solutions with theoretical degrees of saturation with respect to octacalcium phosphate (S(OCP)) of S0, S0.5, S1, S2, S4, and S8 for 10 weeks. A previously studied saliva substitute (Glandosane) and two aqueous solutions (C0 and C1) served as controls. Mineral losses and lesion depths before and after storage were evaluated from microradiographs. Free and bound calcium as well as phosphate and fluoride concentrations were determined. According to these measurements, S(OCP) of S2, S4, and S8 was 0.3, 1.1, and 3.4, respectively. Storage in Glandosane and both negative controls resulted in significant demineralization (p < 0.05). Only S2 significantly remineralized the specimens (p < 0.05). All other solutions showed neutral effects. No significant differences in mineralization between S0 and C0 as well as between S1 and C1 could be observed (p > 0.05). It can be concluded that a CMC-based solution actually unsaturated with respect to octacalcium phosphate (S2) shows most pronounced remineralization capability under the conditions chosen. This might be explained by a more favorable balance between calcium bound to CMC in an adsorbed layer at the enamel-liquid interface and heterogeneous nucleation of calcium phosphates within a solution compared to solutions either supersaturated or having lower levels of saturation.

Time-resolved SAXS study of the effect of a double hydrophilic block-copolymer on the formation of CaCO3 from a supersaturated salt solution.

The effect of a double hydrophilic block-copolymer additive (made of polyaspartic acid and polyethyleneglycol, pAsp(10)-b-PEG(110)) on the initial formation of calcium carbonate from a supersaturated salt solution has been studied in situ by means of time-resolved synchrotron small-angle X-ray scattering (SAXS). A stopped-flow cell was used for rapidly mixing the 20 mM aqueous reactant solutions of calcium chloride and sodium carbonate. In reference measurements without polymer additive the very rapid formation of primary, overall spherical CaCO(3) particles with a radius of ca. 19 nm and a size polydispersity of ca. 26% was observed within the first 10 ms after mixing. A subsequent, very rapid aggregation of these primary particles was evidenced by a distinct upturn of the SAXS intensity at smallest angles. During the aggregation process the size of the primary particles remained unchanged. From an analysis of the absolute scattering intensity the mass density of these particles was determined to 1.9 g/cm(3). From this rather low density it is concluded that those precursor particles are amorphous, which has been confirmed by simultaneous wide-angle X-ray diffraction measurements. Upon adding 200 pm of the block-copolymer no influence on the size, the size polydispersity and morphology of the primary particles, nor on the kinetics of their formation and growth, was found. On the other hand, the subsequent aggregation and precipitation process is considerably slowed down by the additive and smaller aggregates result. The crystalline morphology of the sediment was studied in situ by WAXS ca. 50 min after mixing the reactants. Several diffraction rings could be detected, which indicate that a transformation of the metastable, amorphous precursor particles to randomly oriented vaterite nanocrystallites has taken place. In addition, a few isolated Bragg spots of high intensity were detected, which are attributed to individual, oriented calcite microcrystals that nucleated at the wall of the capillary.

Formation of BaSO4 fibres with morphological complexity in aqueous polymer solutions.

BaSO4 fibres with morphological complexity were formed in aqueous solution with polyacrylate and partially monophosphonated poly(ethyleneoxide)-block-poly(methacrylic acid) additives by a simple precipitation reaction. For polyacrylate, formation of the fibrous deposits was strongly dependent on the level of supersaturation (S) and Ba2+:polymer molar ratio (R). At S = 60 to 80, and R = 3 to 14, highly anisotropic crystalline fibres consisting of bundles of BaSO4 nanofilaments were formed after several weeks, although the yield was low. The nanofilaments were also organized into cone-shaped aggregates at S = 80, and at lower R values these formed higher-order structures that consisted of multiple cone-on-cone assemblies with remarkable self-similarity. Increasing the supersaturation produced ovoid or cross-shaped dendritic particles for the range of molar ratios studied. In contrast, BaSO4 crystallisation in the presence of a partially phosphonated block copolymer gave a high yield of BaSO4 fibres up to 100 microm in length, and consisting of co-aligned bundles of 30 nm-diameter defect-free single-crystal nanofilaments with a uniform growth tip. A model for the defect-free growth of BaSO4 nanofilaments in aqueous polymer solutions based on amorphous precursor particles, vectorially directing forces and van der Waals attraction is proposed.

A systematic examination of the morphogenesis of calcium carbonate in the presence of a double-hydrophilic block copolymer.

In this paper, a systematic study of the influence of various experimental parameters on the morphology and size of CaCO3 crystals after room-temperature crystallization from water in the presence of poly(ethylene glycol)-block-poly(methacrylic acid) (PEG-b-PMAA) is presented. The pH of the solution, the block copolymer concentration, and the ratio [polymer]/[CaCO3] turned out to be important parameters for the morphogenesis of CaCO3, whereas a moderate increase of the ionic strength (0.016 M) had no influence. Depending on the experimental conditions, the crystal morphologies can be tuned from calcite rhombohedra via rods, ellipsoids or dumbbells to spheres. A morphology map is presented which allows the prediction of the crystal morphology from a combination of pH, and CaCO3 and polymer concentration. Morphologies reported in literature for the same system but under different crystallization conditions agree well with the predictions from the morphology map. A closer examination of the growth of polycrystalline macroscopic CaCO3 spheres by TEM and time-resolved dynamic light scattering showed that CaCO3 macrocrystals are formed from strings of aggregated amorphous nanoparticles and then recrystallize as dumbbell-shaped or spherical calcite macrocrystal.

Crystal Design of Barium Sulfate using Double-Hydrophilic Block Copolymers.

Peach, peanut, fiber, and flower (see picture) crystal morphologies are achieved from the precipitation of simple minerals in the presence of specifically adsorbing polymers. These crystal design effects are illustrated using BaSO(4) and double-hydrophilic block copolymers, the latter featuring carboxylate, sulfonate, phosphonate, and aspartic acid groups.

Surfactant-encapsulated clusters (SECs): (DODA)20(NH4)[H3Mo57V6(NO)6O183(H2O)18], a case study.

We present a comprehensive study of the partially reduced polyoxomolybdate [H3-Mo57V6(NO)6O183(H2O)18]21-encapsulated in a shell of dimethyldioctadecylammonium (DODA) surfacmolecules. Treatment of an aqueous solution of (NH4)21[H3Mo57V6-(NO)6O183(H2O)18] . 65H2O (1a) with a trichloromethane solution of the surfactant leads to instant transfer of the encapsulated complex anion into the organic phase. Results from vibrational spectroscopy. analytical ultracentrifugation, small-angle X-ray scattering, transmission electron microscopy, elemental analysis, and Langmuir compression isotherms are consistent with a single polyoxometalate core encapsulated within a shell of 20 DODA molecules. The molar mass of the supramolecular assembly is 20249 gmol(-1) and the diameter is 3.5 nm. A material with the empirical formula (DODA)20(NH4)[H3-Mo57V6NO)6O183(H2O)18] (2) was isolated as a dark violet solid, which readily dissolves in organic solvents. Slow evaporation of solutions of 2 on solid substrates forces the hydrophobic particles to aggregate into a cubic lattice. Annealing these so-formed films at elevated temperature causes de-wetting with terrace formation similar to liquid crystals and block copolymers. Compound 2 forms a stable Langmuir monolayer at the air-water interface; Langmuir-Blodgett multilayers are readily prepared by repeated transfer of monolayers on solid substrates. The films were characterized by optical ellipsometry, Brewster angle microscopy, transmission electron microscopy, and X-ray reflectance.

Interaction of kappa-carrageenan with nickel, cobalt, and iron hydroxides.

In a previous paper, it was shown that the functional polysaccharide kappa-carrageenan acts as an efficient stabilizer to prevent the precipitation of iron oxides and hydroxides up to very high pH values (Jones, et al. Colloid Polym. Sci. 2000, 278, 491-501). Here, this process was investigated for its application to synthesize stable cobalt and nickel oxide particles. Nickel hydroxide nanoparticles were well stabilized for long periods, while the hydroxide of cobalt(II), although initially stable at pH 13, progressively showed some complex structure rearrangement, invoked by alkaline oxidation of the primary particles. The final product of this oxidation/self-assembly process are spherical, fluffy superstructures of cobalt(III) oxide platelets with an overall diameter of 12 microns, in coexistence with 65-75% of free kappa-carrageenan.

Synthesis and characterization of hydrophobic ferritin proteins

Alkylated derivatives of the iron storage protein, ferritin, have been prepared by carbodiimide-activated coupling of long chain (C9, C12, C14) primary amines to surface carboxylic acid residues. In the case of a nonyl-derivatized protein, alkylation results in covalent modification of approximately 400 of the 520 amino acid carboxyl groups in the protein molecule. The hydrophobic proteins have a net positive charge in water and can be transferred from THF/water mixtures into dichloromethane, ethyl acetate and toluene by addition of small amounts of NaCl. Transmission electron microscopy, analytical ultracentrifugation, and polyacrylamide gel electrophoresis indicate that the hydrophobic proteins dissolve in the organic solvents as structurally intact, non-aggregated macromolecules which can be subsequently back-extracted into water.

Hydrodynamic properties of human erythrocyte band 3 solubilized in reduced Triton X-100.

The oligomeric state and function of band 3, purified by sulfhydryl affinity chromatography in reduced Triton X-100, was investigated. Size exclusion high-performance liquid chromatography showed that a homogeneous population of band 3 dimers could be purified from whole erythrocyte membranes. The elution profile of band 3 purified from membranes that had been stripped of its cytoskeleton before solubilization was a broad single peak describing a heterogeneous population of oligomers with a mean Stokes radius of 100 A. Sedimentation velocity ultracentrifugation analysis confirmed particle heterogeneity and further showed monomer/dimer/tetramer equilibrium self-association. Whether the conversion of dimer to the form described by a Stokes radius of 100 A was initiated by removal of cytoskeletal components, alkali-induced changes in band 3 conformation, or alkali-induced loss of copurifying ligands remains unclear. After incubation at 20 degrees C for 24 h, both preparations of band 3 converted to a common form characterized by a mean Stokes radius of 114 A. This form of the protein, examined by equilibrium sedimentation ultracentrifugation, is able to self-associate reversibly, and the self-association can be described by a dimer/tetramer/hexamer model, although the presence of higher oligomers cannot be discounted. The ability of the different forms of the protein to bind stilbene disulfonates revealed that the dimer had the highest inhibitor binding affinity, and the form characterized by a mean Stokes radius of 114 A to have the lowest.

Stabilization of Metal Nanoparticles in Aqueous Medium by Polyethyleneoxide-Polyethyleneimine Block Copolymers.

The branched polyethyleneoxide-polyethyleneimine (PEO)n-b-PEI block copolymers are synthesized and fractionated. The (PEO)n-b-PEI block copolymers are found to be able to form micelles in aqueous solution after addition of certain metal compounds (H2PtCl6, Na2PtCl4, RhCl3). The degree of copolymer polydispersity seems to play an important role in metal nanoparticle stabilization. Comparison of diblock and branched copolymers shows that as a rule branched block copolymers are the better stabilizing systems for metal nanoparticles. In the case of micelle formation due to interaction with metal compounds, fine control on colloid morphology can be provided, which leads to very uniform particles. Variation of different parameters (such as concentration, pH, type of reducing agent) affects the nanoparticle morphology as well. Copyright 1999 Academic Press.

Morphological Characterization of the Molecular Superstructure of Polyphenylene Ethynylene Derivatives.

Two different polyphenylene ethynylene derivatives, one partly hydrophobic and one hydrophilic, were investigated with a combination of X-ray and light scattering techniques and hydrodynamic techniques, as well as scanning force microscopy and transmission electron microscopy to elucidate their molecular structure and aggregation behavior in tetrahydrofuran and water, respectively. It turns out that both polymers possess a rod-like molecular architecture which, however, is the basis of a cascade of aggregation steps. Both, electron microscopy and X-ray analysis support the concept of a primary back-to-back aggregation of polymer chains into cylindrically shaped aggregates with high anisometry. The thickness of these aggregates was between 4.0 and 4.5 nm. The aggregates of the hydrophobic polymer further associate into fibrils and these fibrils form clusters of globular shape, though with high internal anisometry. Copyright 1999 Academic Press.

Ultracentrifugation studies on the transmembrane domain of the human erythrocyte anion transporter band 3 in the detergent C12E8.

The dilute solution behaviour of the transmembrane domain (TMD) of the human erythrocyte anion exchanger Band 3 was studied by analytical ultracentrifugation. Sedimentation velocity and equilibrium studies of the TMD solubilized with the detergent C12E8 demonstrate that the protein is a stable dimer in the concentration range 0.1 to 1 mg/ml. There is no evidence of a dissociation at low concentrations or of an association at higher concentrations. Hydrodynamic calculations applying a prolate ellipsoid of revolution and assuming a hydration of w = 0.35 result in an asymmetrical particle with an axial ratio (a/b) of approximately 3.5.

An ultracentrifugal approach to quantitative characterization of the molecular assembly of a physiological electron-transfer complex: the interaction of electron-transferring flavoprotein with trimethylamine dehydrogenase.

The interaction between two physiological redox partners, trimethylamine dehydrogenase and electron-transferring flavoprotein, has been characterized quantitatively by analytical ultracentrifugation at 4 degrees C. Analysis of sedimentation-equilibrium distributions obtained at 15 000 rpm for mixtures in 10 mM potassium phosphate, pH 7.5, by means of the psi function [Wills, P. R., Jacobsen, M. P. & Winzor, D. J. (1996) Biopolymers 38, 119-130] has yielded an intrinsic dissociation constant of 3-7 microM for the interaction of electron-transferring flavoprotein with two equivalent and independent sites on the homodimeric enzyme. This investigation indicates the potential of sedimentation equilibrium for the quantitative characterization of interactions between dissimilar macromolecules.

The ELLIPS suite of macromolecular conformation algorithms.

This paper describes a series of four programmes for the PC based on ellipsoidal representations of macromolecular shape in solution using Universal shape functions, ELLIPS1 is based on simple ellipsoid of revolution models (where two of the three axes of the ellipsoid are fixed equal to each other). If the user types in a value for a shape function from sedimentation or other types of hydrodynamic measurement, it will return a value for the axial ratio of the ellipsoid. ELLIPS2 is based on the more general triaxial ellipsoid with the removal of the restriction of two equal axes. The user enters the three semi-axial dimensions of the molecule or the equivalent two axial ratios and ELLIPS2 returns the value of all the hydrodynamic shape functions. It also works of course for ellipsoids of revolution. ELLIPS3 and ELLIPS4 do the reverse of ELLIPS2, that is they both provide a method for the unique evaluation of the triaxial dimensions or axial ratios of a macromolecule (and without having to guess a value for the so-called "hydration") after entering at least three pieces of hydrodynamic information: ELLIPS3 requires EITHER the intrinsic viscosity with the second virial coefficient (from sedimentation equilibrium, light scattering of osmometry) and the radius of gyration (from light or x-ray scattering) OR the intrinsic viscosity with the concentration dependence term for the sedimentation coefficient and the (harmonic mean) rotational relaxation time from fluorescence depolarisation measurements. ELLIPS4 evaluates the tri-axial shape of a macromolecule from electro-optic decay based Universal shape functions using another Universal shape function as a constraint in the extraction of the decay constants.

Alteration of the quaternary structure of glutamate dehydrogenase from Clostridium symbiosum by a single mutation distant from the subunit interfaces.

X-ray crystallographic studies have previously shown that glutamate dehydrogenase from Clostridium symbiosum is a homohexamer. Mutation of the active-site aspartate-165 to histidine causes an alteration in the structural properties of the enzyme. The mutant enzyme, D165H exists predominantly as a single species of lower molecular mass than the wild-type enzyme as indicated by gel filtration and sedimentation velocity analysis. The latter technique gives an S20,w value for D165H of (6.07 +/- 0.01)S which compares with (11.08 +/- 0.01)S for the wild-type, indicative of alteration of the homohexameric quaternary structure of the native enzyme to a dimeric form, a result confirmed by sedimentation equilibrium experiments. Further support for this is provided by chemical modification by Ellman's reagent of cysteine-144 in the mutant, a residue which is buried at the dimer-dimer interface in the wild-type enzyme and is normally inaccessible to modification. The results suggest a possible structural route for communication between the active sites and subunit interfaces which may be important for relaying signals between subunits in allosteric regulation of the enzyme.