Nadine Gabas

Mechanism of calcite crystal growth inhibition by the N-terminal undecapeptide of lithostathine.

Pancreatic juice is supersaturated with calcium carbonate. Calcite crystals therefore may occur, obstruct pancreatic ducts, and finally cause a lithiasis. Human lithostathine, a protein synthesized by the pancreas, inhibits the growth of calcite crystals by inducing a habit modification: the rhombohedral {10 1̄4} usual habit is transformed into a needle-like habit through the {112̄0} crystal form. A similar observation was made with the N-terminal undecapeptide (pE1R11) of lithostathine. We therefore aimed at discovering how peptides inhibit calcium salt crystal growth. We solved the complete x-ray structure of lithostathine, including the flexible N-terminal domain, at 1.3 Å. Docking studies of pE1R11 with the (101̄4) and (11 2̄0) faces through molecular dynamics simulation resulted in three successive steps. First, the undecapeptide progressively unfolded as it approached the calcite surface. Second, mobile lateral chains of amino acids made hydrogen bonds with the calcite surface. Last, electrostatic bonds between calcium ions and peptide bonds stabilized and anchored pE1R11 on the crystal surface. pE1R11-calcite interaction was stronger with the (11 2̄0) face than with the (10 1̄4) face, confirming earlier experimental observations. Energy contributions showed that the peptide backbone governed the binding more than did the lateral chains. The ability of peptides to inhibit crystal growth is therefore essentially based on backbone flexibility.

The structure of the agrochemical fungicidal 4-chloro-3-(3,5-dichlorophenyl)-1H-pyrazole (RPA 406194) and related compounds

Abstract The difficulties to obtain convenient monocrystals of the important fungicide RPA 406194 have been overcome by a combination of solid state 13C NMR, X-ray powder diffraction and molecular modeling. The compound, a 3-aryl tautomer, crystallizes forming infinite chains of molecules bonded by N–H⋯N hydrogen bonds, leading to needle-shaped crystals. The tautomerism (equilibrium constant and energy barrier) of this compound in solution has been studied.

Nucleation studies of potassium hydrogen tartrate in model solutions and wines

Abstract The nucleation of potassium hydrogen tartrate (KHT) in water-ethanol model solutions and in wines is investigated by the induction time technique. The results suggest that KHT nucleation in wine is inhibited by natural compounds. The value of the specific surface energy is found to be around 4 mJ m −2 , when derived from a mononuclear mechanism and 6.4, 6.7 and 7.5 mJ m −2 when the polynuclear mechanism is used with volume diffusion-controlled, normal and spiral growth, respectively. Complementary experiments made with a potassium ion selective electrode show that potassium ions are partly associated in solution with organic acids, like tartaric acid. Calculation of KHT supersaturation should therefore take into account the fraction of associated potassium. Further experiments are needed to identify all the associated species and to obtain the dissociation constants of their equilibria.

Influence of additives on the growth morphology of γ-aminobutyric acid

Abstract Specific growth rates of the two main faces (120) and (001) of single γ-aminobutyric (GABA) crystals are measured in a cell under a laminar flow of supersaturated solution within a narrow temperature interval. In the non-diffusion-controlled region with respect to fluid velocity, the effect of supersaturation (σ) on face growth rates, V hkl , fits the BCF model; furthermore, the crossing of the two curves V 120 ( σ ) and V 001 ( σ ) gives rise to morphological changes. Crystal growth studies in the presence of various types of additives show the pronounced influence of positively charged species, such as Cr 3+ and dodecyltrimethylammonium ions, on the relative growth rate V 120 V 001 . This phenomenon is well explained by strong cation adsorption on the (001) face exposing the carboxylic groups of GABA zwitterions.

Dispersion of growth rates of d-xylose crystals in aqueous solutions—influence of the presence of ethanol as a co-solvent and of d-mannose as a co-solute

Abstract New data on the growth rates of d -xylose crystals in aqueous solutions either devoid of d -mannose or containing this sugar as a co-solute and in hydroalcoholic solutions, obtained in a batch isothermal laboratory-scale seeded crystallizer, are reported. Growth kinetics have been evaluated from successive crystal size distributions (CSDs) recorded by means of a laser light scattering size analyser. The experiments have emphasized a broadening of CSD during growth in any type of solution and a decrease of the overall d -xylose growth rate due to the presence of ethanol or d -mannose. Growth kinetic models have been identified from direct analysis of oversize cumulative number CSDs and from the population balance equation. Solutions to population balance equations have proved that growth rate dispersion rather than an intrinsic dependence of the crystal growth rates on crystal size is responsible for the variability of growth. A time-averaged growth rate equation as well as a growth rate diffusivity parameter have been identified in each type of solution.

Using Dynamic Simulation for Risk Assessment: Application to an Exothermic Reaction

In this paper, a solution strategy based on an optimization formulation is proposed for the design of Water Allocation and Heat Exchange Networks (WAHEN) in the process industries. Such typical large problems involve many processes, regeneration units and multi-contaminants. For this purpose, a two-stage methodology is proposed. The first step is the Water Allocation Network (WAN) design by multi-objective optimization, based on the minimization of the number of network connections and of the global equivalent cost (which includes three criteria, i.e., freshwater, regenerated water and wastewater). The ɛ-constraint method is used to deal with the multi-criteria problem. In a second step, the Heat Exchange Network (HEN) is solved by two approaches, Pinch analysis and mathematical programming (MP). In both cases the HEN structure is found when the minimal energy requirement and the total annual cost are minimized for Pinch and MP, respectively. These results are compared and the best HEN network is then coupled to the WAN to verify the feasibility of the network. A case study including a change of phase among the streams is solved. The results show that this two-step methodology can be useful for the treatment of large problems.

Investigations of the effects of some additives on the crystallization of tetrahydrate sodium perborate

The presence of impurities in a system can drastically affect the growth rates of crystals grown from solutions. In this study, growth experiments with tetrahydrate sodium perborate (SPB) crystals in the presence of additives have been performed in a batch fluidized bed crystallizer. First, it has been shown that sodium metaborate (SMB) affects the solubility of SPB, reducing it at low concentration and increasing it at high concentration. Related to this, it also modifies the growth rate of SPB crystals. The effect of various kinds of mineral additives, surfactants and a polymer on growth rate has also been investigated. The retarding action observed in the presence of some of these additives has been interpreted in terms of a Langmuir-type adsorption isotherm. The apparent accelerating effect on growth rate obtained with aluminium sulfate and cetyltrimethyl ammonium bromide, a cationic surfactant, was supposed to be related to an enhancement of nucleation and agglomeration processes.

Growth rate dispersion in seeded batch D-xylose crystallization

Laboratoire de Genie Chimique (URA CNRS 192), ENSIGC, Chemin de la Loge, F-31078 Toulouse Cedex, France Batch crystallization runs of D-xylose from aqueous solutions have been performed. Growth rate kinetics of xylose crystals have been evaluated from successive crystal size distribution records by means of a laser light scattering size analyser. The experiments have emphasized a broadening of the crystal size distribution during growth. Solutions to population balance equations have provided evidence for growth rate dispersion. A time-averaged growth rate equation as well as a growth rate diffusivity parameter have been identified.

Crystal and molecular structure of calcium L(–)-malate trihydrate

The new crystal and molecular structures of a less common hydrated calcium L(−)-malate (calcium (2S) 2-hydroxybutanedioate trihydrate) Ca(C4H4O5)⋅3H2O, are reported. X-ray crystallographic data are as follows: a = 6.6460(3) Å, b = 8.3795(3) Å, c = 8.2707(4) Å, β = 112.640(2)°, V = 425.1(4) Å3, space group P21 (No. 4), Z = 2, Dcalc = 1.767 g cm−3. The calcium ion coordination number is seven. One of the three water molecules present in the unit cell is less strongly bound, only interacting with a calcium ion. In aqueous or hydroalcoholic solution, both di- and trihydrated species crystallize simultaneously.

Effect of an electric field on the heterogeneous nucleation and crystal growth of potassium hydrogen tartrate in wines

Potassium hydrogen tartrate (KHT) is a naturally occurring salt in wines. To avoid the formation of KHT crystals in bottles, it is necessary to stabilize wines before bottling. However, none of the current techniques is fully satisfactory. A new process, called the ‘trap process’, has been developed that consists of cold-crystallizing KHT on a stainless steel packing. To accelerate the heterogeneous nucleation and/or crystal growth rate of the salt, the influence of an external electric field on these phenomena was studied. A potentiostatic circuit maintained a constant potential against a saturated calomel electrode. A preliminary cyclic voltammetry study led to the determination of the most suitable potential values (i.e., inducing no electrochemical reaction). A set of wine stabilization experiments was then performed using the ‘trap process’ with and without potential. The results demonstrated that a potential of +200 mV vs SCE generates an increase in process efficiency, even in the case of wines containing a lot of inhibitors. It also significantly reduces the induction time of nucleation.