Parity violation and parity conservation in unstirred crystallization: Effect of first crystals

Statistics of nucleation of chiral forms was studied to establish the effect of the number of first crystals and their handedness on distributions of enantiomers. Various bimodal, trimodal and unimodal distributions are obtained in unstirred crystallization, depending on the number of initial crystals and growth conditions. The binomial distribution satisfactorily describes experimental distributions of enantiomeric excess and may be used to predict distributions and probabilities of nucleation of enantiomers. The first nucleated crystals determine the handedness of secondary crystals, and number of initial crystals governs statistics of chiral nucleation. According to the binomial distribution if single crystals nucleate as the first, the bimodal distributions result with D and L peaks. If LD, LL, and DD pairs are nucleated as first, trimodal distributions with D, R, and L peaks are created, and if groups of crystals of various handedness nucleate as the first the unimodal distributions of enantiomeric excess with racemate R peaks are formed. Chiral nucleation experiments on sodium bromate were the basis for the theoretical considerations and verifications of predictions resulting from binomial distributions on probabilities of the creation of L and D crystals, and racemates, and the presence of D, L, and R peaks in the distributions. Growth conditions affect the number of the first crystals and effectiveness of cloning, and as a result, the distributions of enantiomers. Formation of pure enantiomers and/or racemates proves that the conservation of chiral symmetry, and the breakage of chiral symmetry can occur in unstirred crystallization. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Chiral symmetry breaking in unstirred crystallization

Statistics of nucleation of chiral forms of sodium bromate from unstirred aqueous solutions was studied. It was established that bimodal, trimodal and unimodal distributions of enantiomers are obtained in unstirred crystallization. It was also found out that probabilities of the creation of L or D crystals and racemates R, as well as the presence of D, L, and R peaks in distributions depend on crystallizer size, supersaturation and temperature. Nucleation at low supersaturations in small, closed crystallizers leads to the formation of pure enantiomers, and to bimodal distributions with D and L peaks at any temperature. At high supersaturations in large, open crystallizers the formation of racemates and unimodal distributions with racemate R peaks results. In open crystallizers at the lowest temperatures and at the highest temperatures used in crystallization from aqueous solution racemates of sodium bromate are preferentially formed, but in a wide range of intermediate‐temperatures apart from racemates, pure enantiomers are efficiently formed which leads to trimodal distributions. The spontaneous formation of pure enantiomers in crystallization from unstirred, unseeded solutions is caused by the chiral symmetry breaking phenomenon, the same as that discovered in stirred crystallization. The conservation of chiral symmetry is, in unstirred crystallization, one of the two possibilities, and the other one is the breakage of symmetry. Both of them occur in nature. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Polymorphism of Compound Existing as Both Racemic Compound Crystals and Mixed Crystals of Enantiomers

Abstract

By recrystallization of certain racemic compound (ST), racemic compound crystals, mixed crystals of two enantiomers, or a mixture of these two types of crystals were obtained, depending on the recrystallization conditions employed. Their crystal forms were determined by X-ray diffraction of the single crystals and powdered materials. The space group and lattice parameters of the mixed crystals were identical with those of the enantiomeric crystals. This polymorphism of ST crystals would be ascribed to the small difference in the thermodynamic stability between the enantiomeric and racemic crystals. The physicochemical properties of ST are described, too.     

Enantiomorphism in sodium chlorate crystals

Creation of enantiomorphous forms in sodium chlorate and enantiomorphous nature of surface micromorphology were studied by optical microscopy. It was shown that when the small number of crystals nucleates spontaneously in unstirred, unseeded solutions then exclusively left- (L) or right-handed (D) crystals can be formed. At the large number of nucleated crystals the probability of the creation of L and D form is nearly the same. L and D crystals can be distinguished by the shape of growth or dissolution centers.     

Optimization of the local crystallization processes of preparing chiral drugs in periodic crystallizers

The regularities of periodic processes of local crystallization of enantiomers and the kinetics of nucleation and growth of crystals are considered. The criteria for optimization of technological processes of preparing chiral drugs with the aim of attaining the maximum yield of final products with a required optical purity are formulated on the basis of experimental data.     

Crystal Structure Analysis of Betti Base 1-((2-hydroxynaphthalen-1-yl)(2-hydroxyphenyl)methyl)urea•2DMF Solvate

A novel Betti base compound, 1-((2-hydroxynaphthalen-1-yl)(2-hydroxyphenyl)methyl)urea, UBB, was synthesized and characterized by spectral, structural and thermal studies. Single crystal X-ray diffraction studies reveal that the racemic mixture of the compound, when crystallized from DMF, yields R-isomer preferentially (prismatic crystals), whereas, when crystallized from 5:1 (v/v) mixture of DMF-THF, it yields S-isomer (rectangular shaped crystals) with two molecules of DMF, included in both the cases. The crystal structure is discussed in terms of supramolecular interactions and molecular modeling. Both R and S enantiomeric DMF solvate crystals are in their chiral triclinic P1 space group.     

Chromatographic,spectroscopic, topographic,and X-ray crystallographic studies of the solid solution formed by racemic 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (3-carboxy-proxyl)

The solid solution formed by the title compound, C₉H₁₆NO₃, has been examined by a variety of techniques and shown to be an equi-molecular mixture of the two enantiomers. Refinement of the disordered structure was based on the orthorhombic space groupPnma witha=8.023(2),b=10.030(3), andc=12.352(2)Å, finalR=0.055. The oxygens of the carboxyl group are disordered and both enantiomers can occupy the same, rather than alternate, crystallographic sites. Results from studies involving IR, GC-MS, and chiral chromatography are also presented. In addition we report on the use of synchrotron X-ray topography to investigate strain in crystals of the solid solution.     

Monte Carlo simulation of a cluster model for the chirality conversion of crystals with grinding

By means of Monte Carlo simulation of a cluster model, we study statistical aspect of the chirality conversion of crystals. The chirality conversion is known to occur in a saturated solution by grinding crystals, and the enantiomeric excess increases exponentially. In the simulation, with crystallization and dissolution of monomers alone, the behavior of the enantiomeric excess observed in experiment cannot be reproduced although the homochirality is realized as a result of statistical fluctuation. By allowing crystallization and dissolution of dimers, the exponential amplification of enantiomeric excess can be realized.     

On the influence on tracht and habit of urea crystals (II)

It is shown that during crystallization urea forms mixed crystals, adsorption mixed crystals, and epitaxial growth from aqueous solutions with inorganic salts, the lattice parameters of which are lying within the tolerance of efficiency parameters of urea. The extent of the formation of mixed crystals is determined by the composition of the solution. The slats added to the solution affect changes of tracht and habit of urea and thus are important for improving storage and transport properties. Similar results can be found for modified melts of urea.     

Zur Beeinflussung von Tracht und Habitus von Harnstoffkristallen (I)

It is shown that during crystallization urea forms mixed crystals, adsorption mixed crystals and epitaxial growth from aqueous solutions with NH₄Cl. The extent of the formation of mixed crystals is fixed by the composition of the solution. The urea NH₄Cl mixed crystals have the effect of morphological transformers on tracht and habit of the crystallized urea, so that advantages in technical application result concerning properties of transport and storage.     

VIIIth International Topical Meeting on Optics of Liquid Crystals (OLC'99)

Abstract

Over the past fifteen years the International Topical Conference on Optics of Liquid Crystals (OLC) has provided a stimulating and interdisciplinary forum for the presentation of the best new work in the field of liquid crystals and related materials. The VIIIth International Topical Meeting on Optics of Liquid Crystals was held at the hotel Wyndham Palmas del Mar Resort and Villas in Humacao, Puerto Rico 27 September–1 October 1999. Eighty-five scientists from 17 different countries around the globe (Asia, Europe, North and South America) came to Puerto Rico to present their scientific work and to discuss all the modern aspects of Optics of Liquid Crystals. As a result 21 invited talks, 32 contributed oral presentations and 51 posters were presented. New results at the forefront of research in the optics of liquid crystals were presnted by leading experts in the field. Invited talks given by N. Clark (USA), F. Derrien (France), B. Jerome (Netherlands), R. Kamien (USA), I.-C. Khoo (USA), L. Komitov, (Sweden), T. Lubensky (USA), S. Marino (Japan), I. Musevich (Slovenia), Y. Shen (USA), K. Singer (USA), G. Sinha (USA), H. Skupin (Germany), R. Stannarius (Germany), R. L. Sutherland (USA), B. Taheri (USA), Y. Tabe (Japan), C. Umeton (Italy), D. Weitz (USA), S. Zilker (Germany), and S. Zumer (Slovenia) covered different important topics such as chiral interactions, surface vibrational spectroscopy, time resolved FTIR, holograms in PDLS, lasing in liquid crystals, quadrupolar molecular nonlinear optics, organic photorefractive systems, optical solitons, different aspects of behaviour, properties and applications of chiral smectic liquid crystals, photo-initiated reorientational dynamics, electro-optic effects in LC films, wave generation in two-dimensional LCs and others.     

Resolution of optical isomers of 4-amino-p-chlorobutyric acid lactam by co-crystallization

4-Amino-p-chlorobutyric acid lactam crystallizes as racemic crystals in the monoclinic space groupP2₁/n, witha=5.006(2),b=6.783(2),c=27.652(2) Å, =92.25(1)°,Z=4,R=0.035 for 1618 unique reflections. As both enantiomers are present in a single crystal it is not possible to effect enantiomeric separation by crystal growth inhibition. This lactam may, however, be co-crystallized with (2R,3R)-(+)-tartaric acid forming a 2:1 complex in which only the (R) enantiomer is present. The complex crystallizes in the monoclinic space groupP2₁ witha=10.074(2),b=10.132(6),c=12.238(6) Å, =99.13(2)°,Z=2,R=0.036 for 2291 unique reflections. Complex formation is effected by hydrogen bonding but enantioselectivity does not involve the chiral center of the title compound directly.     

Study of the crystal shape and its influence on the anti‐tumor activity of tumor necrosis factor‐related apoptosis‐inducing ligand (Apo2L/TRAIL)

This paper describes a method about the crystal shape control improving the anti‐tumor activity of tumor necrosis factor‐related apoptosis‐inducing ligand (Apo2L/TRAIL) in a batch cooling suspension crystallization by selecting pH values as a controllable variable. Three shaped TRAIL crystals could be obtained under different pH conditions, among which the hexagonal plate crystals had the highest specific activities against tumor cell line. The relationship among pH values, trimer contents and the specific activities of crystals and the purified TRAIL solutions were investigated. The results showed that different trimer contents resulted from pH altering in crystals and protein solutions is a main reason for their different specific activities. The studies may supply a new method to improve the bioactivity of TRAIL agent during its production and storage. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoswitching of Helical Twisting Power by Chiral Diarylethene Dopants

Abstract

Photochromic chiral compounds having two diarylethene units were synthesized in an attempt to use them as dopants for photoresponsive liquid crystals. Stable photoswitching of the photochromic dopants induced large pitch changes of chiral nematic liquid crystals composed of K-15 and a small amount of the chiral dopants.     

基于ISIGHT的二维手性声子晶体带隙最优设计

本文首先利用有限元仿真软件COMSOL计算了二维手性声子晶体的带隙,分析了散射体参数与韧带涂层参数变化对带隙的影响规律。在此基础上,确定手性声子晶体带隙最优设计的有效参数设计空间;然后基于ISIGHT优化设计平台嵌入遗传算法,开展二维手性声子晶体带隙的最优设计。在带隙的最优设计过程中,先以二维手性声子晶体的有效构型参数为设计变量,相对带隙宽度最大为目标,设计手性声子晶体单胞构型。再以此优化单胞构型为初始构型,以手性声子晶体的有效材料参数为设计变量,相对带隙宽度最大为目标,进一步实现二维手性声子晶体带隙的最优设计。本工作极大限度地挖掘了二维手性声子晶体带隙最优设计潜能,为充分发挥手性声子晶体在减振降噪中的作用提供了可靠有效的分析设计方法。     

Physical Properties of Ferroelectric Liquid Crystals Incorporating a Boron Atom

Physical properties of a new type of ferroelectric liquid crystal incorporating a boron atom have been studied. Spontaneous polarization, tilt angle and chiral pitch of the new ferroelectric liquid crystals are compared with those of other types of ferroelectric liquid crystals. The alternation of the Ps direction and the twist sense is observed as the chiral center is moved further away from the core.     

Natural crystallization

Natural mineral crystals grow under a broad spectrum of conditions; from vapors, from hydrothermal solutions, from magmas (high temperature solutions), or through metasomatic or metamorphic reactions. In understanding kinetic problems involved in natural crystallization, there are two ways of approach; (1) experimentally stimulating textures of rocks, and (2) decoding the paragenetic information contained in natural crystals. The latter approach is especially important, since in situ observation is impossible. Key Key features which aid in deciphering natural growth processes and conditions include external forms, surface microtopographs of crystal faces, internal inhomogeneity (growth bands, growth sectors, inclusions, twin or exsolution textures), lattice defects (plane defects, dislocations) and impurities (precipitations). Mainly based on the observations of surface microtopographs of natural crystals, characteristics of crystallization in magma, in hydrothermal solution, in vapor phase, in hydrothermal metasomatism and in regional metamorphism are analysed and reviewed in this paper. The difference and similarity between natural and synthetic crystals are also discussed.     

氯酸钠晶体生长的手性对称破损研究

我们使用非搅拌的氯酸钠晶体水溶液,研究了晶体的手性对称破损问题.氯酸钠晶体溶液是通过溶解分析纯 NaClO3 粉末于去离子水中配制而成.采用 Mach-Zehnder 干涉方法和称重法测定晶体的溶解度.使用偏光显微镜鉴定了11545颗晶体的手性.这些晶体是从不同pH条件下的90个自发成核和生长实验中获得.实验结果表明:溶液的pH值可影响到氯酸钠晶体的手性分布.晶体手性分布的pH效应,可用随机动力学理论和胚晶凝聚二次成核理论来定性解释.     

Growth,spectral and thermal properties of KAP single crystals in the presence of DL‐Alanine and L‐Methionine amino acid dopants

Single crystals of potassium acid phthalate (KAP) and amino acid (DL‐Alanine, L‐Methionine) doped KAP were grown from aqueous solutions by slow cooling method. The grown crystals were characterized using powder X Ray diffraction (XRD) and Fourier Transform Infrared (FTIR) analysis. The thermal stability of KAP in the presence of dopants was analysed using Thermogravimetric and Differential Scanning caloriemetric (TGA/ DSC) studies and the maximum temperature for non linear optical application of this compound in the presence of dopants was found out. The transmittance of KAP was found to increase in the presence of dopants. Etch pits were observed for all the crystals using different etchants. Vickers microhardness tests were performed to study the mechanical stability of the crystals. The hardness of DL‐alanine doped KAP is more than that of L‐alanine doped KAP crystal. The dielectric constant and loss were determined as a function of temperature. Frequency response of the dielectric constant and dielectric loss factor have been studied over the frequency range of 50Hz – 5MHz. Second harmonic generation (SHG) was confirmed in all the crystals using the Kurtz and Perry powder technique. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)