Sodium Chlorate Crystals Research Articles

Experimental evidence of chiral symmetry breaking in crystallization from primary nucleation

Chiral symmetry breaking in stirred crystallization of sodium chlorate (NaClO 3) is believed to occur via nucleation of a single chiral “mother crystal” that produces a new generation of crystals which inherit its chirality. We here report results of stirred crystallizations resulting in massive “instantaneous” primary nucleation and total symmetry breaking. The results of these experiments suggest that the current explanation for chiral symmetry breaking via nucleation of a single “mother crystal” is not adequate and that the mechanism to explain the chiral symmetry breaking in crystallization remains as an open question.

Two-photon excitation in nuclear quadrupole resonance

We introduce a novel magnetic resonance experiment in which nuclear quadrupole resonance (NQR) is observed following excitation at 1/2 the resonant frequency. Such two-photon excitation has recently been demonstrated in nuclear magnetic resonance, and may also have practical application to NQR. We show analytically that for axially symmetric quadrupole interactions ( η=0), two-photon NQR in zero magnetic field produces observable magnetization only perpendicular to the rf excitation coil, necessitating a second coil for detection. If η≠0 or an external magnetic field is applied, magnetization observable in the excitation coil is produced. We demonstrate the phenomenon experimentally by exciting the 35Cl resonance in a single crystal of sodium chlorate in the presence of a weak magnetic field.

Effect of beta radiation on the crystallization of sodium chlorate from water: a new type of asymmetric synthesis.

Sodium chlorate is an achiral molecule that crystallizes from water in the chiral space group P2(1)3. In the absence of chiral perturbations, a random distribution of (+) and (-) crystals is obtained. Kondepudi(2) has shown that constantly stirring an evaporating NaClO(3) solution gives mostly either (+) or (-) crystals. Repeating this experiment many times gives equal numbers of (+) and (-) sets of crystals. Herein we report that when evaporating aqueous NaClO(3) is subjected to beta particles from an Sr-90 source, an asymmetric distribution of (+) and (-) crystals favoring the (+) crystals is obtained. The beta particles are energetic polarized electrons that are approximately 80% of left-handed helicity. By a poorly understood mechanism, the spin polarized electrons produce chiral nucleating sites that favor formation of the (+)-NaClO(3) crystals. Exposure of the evaporating solution instead to energetic positrons from an Na-22 source yields mainly (-)-NaClO(3) crystals. Polarized positrons are of predominantly right-handed helicity. One may conclude that the chirality of the radiation is correlated with the chirality of the crystals being generated.

Increase in dissolution rate of sodium chlorate induced by elastic strain

Recent experimental studies carried out on the kinetics of crystal growth in solution have revealed that mechanically induced elastic strain can have a strong influence on the crystal growth rate. We present experimental evidence to show that it can also strongly affect the dissolution rate. Sodium chlorate crystals held in an undersaturated sodium chlorate solution and uniaxially stressed in compression to values up to 15 MPa dissolved up to about 1.3 times faster than crystals free of stress. The increase in dissolution rate varies linearly with the stress.

Chiral symmetry breaking in crystallization: the role of convection

Chiral symmetry breaking in stirred crystallization of sodium chlorate ( NaClO3) occurs via the production of secondary crystals from a single "mother crystal." Martin, Tharrington, and Wu [Phys. Rev. Lett. 77, 2826 (1996)] investigated this phenomenon and concluded that it was mechanical crushing of a crystal by the stir bar, not convection, that produces secondary crystals from a single crystal. Here we report the generation of secondary crystals of sodium chlorate when a saturated solution of sodium chlorate is simply made to flow over a sodium bromate ( NaBrO3) crystal. This clearly shows that fluid flows alone can generate and disperse secondary nuclei.

Asymmetric Synthesis of an Organic Compound with High Enantiomeric Excess Induced by Inorganic Ionic Sodium Chlorate This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports, and Culture. We thank Mr. Koji Ohtake for experimental work in the early stage, Prof. Naoyuki Koide and Dr. Takashi Mihara from the Department of Chemistry of

Morphologically chiral crystals of sodium chlorate induce highly enantioselective synthesis. Thus the addition of diisopropylzinc to 2-(tert-butylethynyl)pyrimidine-5-carbaldehyde in the presence of d- and l-NaClO3 gives the (S)- and (R)-alkanol, respectively, in high yields and with high ee values (see scheme).

Growth Rates Of Sodium Chlorate Crystals Grown From Aqueous Solution In Relation To Internal Strain

Observations of growth kinetics of crystals of sodium chlorate with cubic {100} macromorphology in relation to growth conditions and dislocation structure of the newly grown parts of the crystals with supersaturation applied during the process of regeneration of the seed are reported. It was found that at lower initial supersaturations applied during regeneration of the seed the density of dislocation propagating into the growing crystal and then growth rate of (100) face, at supersaturation constant for all experiments, are lower. Thus, the supersaturation applied during regeneration of the seed is a critical factor in determining the dislocation structure at the seed-crystal interface.

Secondary nucleation of sodium chlorate studied with the aid of asymmetric crystallization

AbstractThe size‐dependent breeding of sodium chlorate crystals can be determined by carrying out experiments with seed crystals of optical antipodes of different sizes that undergo absolutely identical experimental conditions. Small portions of right‐ and left‐handed seed crystals of different sizes were used. The number density distributions of the two opposite forms led to the total numbers of D‐ and L‐crystals. The nucleation from different seed sizes under identical experimental conditions was found to be proportional to L4 in agreement with Clontz et al. [1] and Bennett et al. [2]. A computer program for the modelling of batch crystallization was used to calculate the development of the nucleation process. The data for the supersaturation course and for the development of the population of the right‐ and left‐handed crystals are in good agreement with the experimental results. Only few generations (one or two) of secondary nucleation are being built during the process because of the strong influence of the size of crystals on the nucleation rate. The formation of two generations of secondary nuclei could be observed during three‐hour batch crystallization runs.

Three-dimensional model of the disappearance of triangular faces in the crystal habit

The disappearance of triangular faces of any shape is a particular case of disappearance of faces of any shape which requires a separate description. Therefore, the previously derived formulae to evaluate the length of any edge of a face of any shape and to evaluate the critical growth velocity, above which the edge disappears, have been applied to a face of a shape of any triangle. It has been mathematically proved that the triangular face, contrary to the faces of any other shape, may disappear only by transformation to a corner and the transformation to one of the edges is not possible. All theoretical predictions have been verified by computer modeling performed for sodium chlorate crystals.

Chiral Etch Pits on Sodium Chlorate Crystals

AbstractMicrotopography of {100}, {110}, {111}, and {210} surfaces of sodium chlorate crystals etched in various solvents has been studied by optical microscopy. It has been established that etch pits formed on left‐ and right‐handed crystals are chiral, and directions of dissolution steps reveal bond chains of the structure.

Growth of the tetrahedral faces of sodium chlorate crystals in the presence of dithionate impurity

It has been established that trace amounts of S 2O 2- 6 anions initiate the appearance of new faces, { 111 }, on sodium chlorate crystals grown from aqueous solution. The present study compares the growth mechanisms of the {111} habit faces and { 111 } type faces using laser interferometry techniques. The {111} faces show dislocation layer growth in which the impurity influences the growth by causing the gradual deceleration of step movement. In contrast, the { 111 } faces incorporate crystal units into an atomically rough surface. Under these circumstances the impurity on the surface creates a barrier to continuous growth. The strong impurity interaction with the { 111 } faces can be explained by the close structural similarity of the -SO 3 portion of the S 2O 2- 6 ions to the ClO - 3 ions situated on these faces. This allows the dithionate ion to substitute for ClO - 3, disturbing the structure and energy of the interface and inhibiting growth.

On the nature of growth hillocks on sodium chlorate crystals

AbstractOptical examination of as‐grown {100} surfaces of sodium chlorate crystals grown from aqueous solution revealed the presence of elliptical growth hillocks. The hillocks were present on both enantiomorphous forms and originated from dislocations, inclusions, and microcrystals attached to the growing surface. The value of the surface entropy factor equal to 4.55 at 313 K suggests that crystals grow via/or with the participation of dislocation mechanism, and the hillocks are dislocation growth centers. Compound mechanism controlled growth of some crystals because edge nucleation and dislocation centers operated simultaneously on the same surfaces.

Morphology and growth kinetics of large sodium chlorate crystals grown in the presence and absence of sodium dithionate impurity

A study has been made of the influence of variations in cooling rate (supersaturation) and impurity content of the changes in morphology (habit and surface features) of sodium chlorate crystals grown from aqueous solution. The habit was found to vary from pure cubic at high cooling rates to cuboid with relatively small {110} and (111), (111), (111), and (111) faces at low cooling rates. Optical examination of the as grown surfaces of the resulting crystals revealed the presence of growth hillocks and surface features characteristic of dislocation-associated growth mechanisms. This speculation was supported by the distribution of dislocations in the various growth sectors, identified by Lang topography

Growth and habit modification of sodium chlorate crystals

Single crystals of sodium chlorate were grown in the presence of selective impurities. The morphology of these crystals changed completely from cubic to tetrahedral form. Experiments were performed in the presence of different concentrations of impurities to ascertain their role in modifying the habit of these crystals. The presence of impurity in the solution was found to affect the habit of the crystals, although it does not appear to enter into the lattice.

Application of real time phase shift interferometer to the measurement of concentration field

A real time phase shift interferometer developed by Nakadate is applied to the measurement of the concentration distribution around a growing or dissolving crystal. Use of the polarized light interferometer allowed either a grey level picture depending on a two-dimensional phase distribution or a three-dimensional perspective profile of the concentration field to be displayed on a TV monitor in real time. The sensitivity of the interferometer is increased at least by a factor of 20 to 30 compared with the conventional two-beam interferometer. The time resolution was also improved so that succesive phase distribution could be obtained at the time resolution of 1/60 s. Using the Abel transformation method, a quasi-three-dimensional concentration profile of a sodium chlorate crystal was calculated, which made it possible to measure the actual surface concentration.

Microstructural and optical changes induced by X-ray irradiation of single crystals of sodium chlorate

Crystals of sodium chlorate, exposed to various levels of X-ray irradiation from a synchrotron source, have been examined using X-ray topography, optical microscopy and UV–VIS spectroscopy. Two principal effects were observed during irradiation. First, a yellow coloration due to increased optical absorption with peaks at 290 and 420 nm was detected after an X-ray dose of 0.5 MRad. This has been attributed to the formation of radiation-induced colour centres. Secondly, after an accumulated dose of 3.1 MRad, significant changes in X-ray topographic images were observed. These comprised of an increase in integrated intensity and a vertical compression of the images. Both effects are due to sample curvature (convex towards the X-ray source) resulting from depth-dependant generation of point defects during irradiation. Throughout the investigation no development of new dislocations was observed and no changes were detected in the configurations of existing dislocations. Over a period of 2 to 3 weeks after irradiation, substantial (but incomplete) relaxation of the sample curvature was observed, together with partial bleaching of the optical absorption. In addition, numerous cavities formed within the crystals, particularly in the vicinity of solvent inclusions. All of these changes occurred at room temperature (25°C) and again no variation in the density or configuration of dislocations was observed. The defect-related processes potentially responsible for the observed behaviour are discussed. While some interdependence between optical bleaching and either curvature relaxation or cavity growth cannot be ruled out, it is apparent that two completely different defect types are associated with the latter two effects.

Growth rate dispersion in small crystals and its relation to mosaic spread

High mosaic spread is a common feature of a number of complex materials (such as certain zeolites and protiens) for which the preparation of large single crystals is prohibited. In one previous systematic study, a direct correlation between growth rate and mosaic spread was found for very small crystals of sodium chlorate. This work has attempted to explore the generality of the effect by extending measurements to a wider range of simple materials. Small crystals (5–200 μm) of ammonium dihydrogen phosphate (ADP), sodium chlorate and sucrose, generated by secondary nucleation in aqueous solution, have been grown under constant conditions of supersaturation. A wide dispersion of growth rates was observed for each material using optical microscopy. A number of individual crystals of known growth rate were successfully retrieved from solution and an assessment of the mosaic spread of each crystal was made using synchroton radiation Laue diffraction at Daresbury Laboratory. All of the crystals produced diffraction patterns comprising small, sharp spots, indicative of low mosaic spread ( <0.5°). No correlation was found between growth rate and mosaic spread for these relatively simple structures. In addition, individual crystals of sucrose have also been examined immediately after creation in solution and subsequently grown-on at constant supersaturation. The Laue patterns obtained for each crystal, both before and after growth, exhibited low mosaic spread, yet each crystal grew at different rate. It is suggested that radiation damage can account for the previously published discrepancies, and acceptable radiation doses are calculated for the determination of mosaic spread in these materials.

Polarization measurements in near‐infrared—fourier transform spectroscopy

AbstractIn principle, Raman measurements provide information about vibrational frequencies and intensities. Working with polarized light provides additional information about the Raman scattering tensor components. The special conditions relating to the near‐infrared‐Fourier transform (NIR‐FT) Raman technique may preclude adaptation of some of the techniques employed for measurements with linear polarized light in ‘classical’ Raman spectroscopy in the visible range. The experimental conditions for measurements of depolarization ratios of liquids (benzene, mesitylene, p‐xylene and carbon tetrachloride) using different experimental geometries with an NIR‐FT‐Raman spectrometer were elucidated. The FT technique allows the rapid and simple determination of depolarization ratios with a quality sufficient to assign the bands to totally or non‐totally symmetric species. The possibility of determining the orientation of molecules in non‐crystalline solids is also demonstrated. Finally, the feasibility of measuring the different components of the Raman scattering tensor of a single crystal of sodium chlorate is considered.

Uniaxial stress dependence of the nuclear quadrupole resonance frequency of 35Cl in NaClO3

Measurements of the NQR frequency of the 35Cl nucleus in single crystals of sodium chlorate were made as a function of isothermal uniaxial stress along the (100), (110) and (111) crystalline directions, in the pressure range 0-4 MPa, at several temperatures around room temperature. A linear and directional behaviour is observed. A model is developed in order to obtain the linear terms of the static and dynamic contributions to the total variation in the electric field gradient (EFG) at the nucleus site. Also an averaged Gruneisen parameter of the rotational modes of ClO3- was estimated; this was found to have a negative value at room temperature. From the results it is inferred that the static and dynamic contributions have the same order of magnitude. The self-energy term due to anharmonicity of the rotational modes was obtained at room temperature. The result is a positive value of the same order of magnitude as the thermal strain contribution.

Measurements of concentration profile by diffraction techniques

A phase measurement device by diffraction (PMDD) is described that is suitable to study concentration gradients (or temperature gradients) in aqueous solutions. It measures phase variations by measuring slight displacements of the diffraction pattern. Use of the instrument is illustrated by measurement of the concentration gradient beneath a growing sodium chlorate crystal. Its simplicity and the low electrical power required make it suitable for use either on earth or in space.