L-threonine Crystals Research Articles

Deuteration effects on structural, thermal, linear and nonlinear properties of l-threonine single crystals

Deuterated crystals of l-threonine have been grown by slow cooling technique. The grown crystals were subjected to XRD, FTIR, UV–vis–NIR and thermal analyses. Isotopic exchange of protons of in NH and OH sites of l-threonine has been confirmed from the Fourier transform infrared spectroscopy (FTIR). Transmission range of the crystal was determined by UV–vis–NIR spectra. The thermal stability of the crystal was determined by differential scanning calorimetry (DSC). Dielectric measurements were carried out on deuterated l-threonine single crystals at room temperature. The dielectric constant of deuterated crystal remains constant for the entire frequency range studied. The powder SHG efficiency of the deuterated salt was found to be 0.91 times that of KDP. The results have been discussed in detail.

Swift ion irradiation effects on L-threonine amino acid single crystals

Single crystals of L-threonine were subjected to 50 MeVLi3+ ion irradiation at various ion fluences. Radiation induced changes in the structural,electrical, thermal and optical properties of the crystals have been studied in detail. Theion fluence dependence on these properties has also been discussed. Surface modifications inthe crystals have been explored through atomic force microscopy. It has also been observedthat the powder second-harmonic generation efficiency of irradiated L-threonine varies withthe ion fluence studied.

Influence of Isoelectric pH on the Growth Linear and Nonlinear Optical and Dielectric Properties of l-Threonine Single Crystals

Single crystals of l-threonine have been grown from aqueous solutions of different pH values. The crystal grown from the solution of isoelectric pH (PI) was found to have the best linear and nonlinear optical properties. The optical quality of l-threonine was improved greatly in the case of the crystal grown at PI. The morphology of the title crystal has been discussed in detail. The crystalline powder SHG efficiency of l-threonine crystals grown at PI was found to be 1.2 times that of KDP. Capacitance and dielectric loss measurements were also carried out, and the dielectric constant was calculated at room temperature in the frequency range 100 Hz−5 MHz. The dielectric constant of the crystalline sample remains constant for the entire frequency range studied.

Calibration for measured crystal size distribution

The crystal size distribution (CSD) measured by laser diffraction technique is obtained by assuming spherical crystals. If crystals are non-spheres, calibration is responsible for the true crystal size, particle number concentration and population density. In this paper, CSD calibration equations have been deduced. It was shown that when shape factors are size-independent, the weight percent of particles is not affected by crystal shape and calibration is just a horizontal shift of measured CSD. Calibration was taken for plate-like crystals of cefazolin sodium and rod-like crystals of l-threonine. The effect of CSD calibration on crystal growth kinetics has been investigated in l-threonine–water evaporation crystallization system.

Determination of growth and breakage kinetics of l-threonine crystals

The crystal growth and breakage kinetics of l-threonine by evaporation crystallization were studied at the laboratory scale using a 1200 ml crystallizer with draft tube. Evaporation experiments were carried out at three different temperatures and three different stirrer speeds. Crystal breakage phenomena were demonstrated by image analysis and evolution of crystal size distribution. Breakage of binary uniform distribution and volume-independent growth kinetics were extracted by moment method. Moreover, the breakage and growth kinetics were proved to be appropriate for l-threonine/water evaporation process using numeric simulation. The growth kinetic parameters indicated that diffusion should be the rate-controlling step of crystal growth, and higher temperature higher growth rate. The higher exponent of agitation speed for breakage kinetics indicated that the removal of fragments stimulated by stirring should be the main breakage mechanism.

Structural characteristics and second harmonic generation in l-threonine crystals

l-threonine, an organic material with interesting non-linear optical properties, has been grown in solution and characterized by X-ray diffraction, FT infrared spectral, Raman spectral, UV VIS spectral and thermal techniques. The structural and spectral characteristics show that strong hydrogen bonds appearing in l-threonine have an influence on the stabilization of the crystal structure. The main contributions to the second harmonic generation in threonine results from the hydrogen bond and also from the vibrational part due to very intense IR bands of the hydrogen bond vibrations. The OH and NH involved in strong hydrogen bonds are responsible for the higher thermal stability of l-threonine compared to other organic non-linear optical materials. l-threonine is thermally stable up to 270 °C.

Growth, structural and spectral analyses of nonlinear optical l-threonine single crystals

Single crystals of l-threonine, a nonlinear optical material, have been grown from solution by the temperature lowering technique. l-threonine was found to have extremely high solubility in water. Hence it was feasible to grow bulk crystals of l-threonine in aqueous solution. The cell parameters were estimated by powder X-ray diffraction analysis. The vibrational structure of the molecule is elucidated from FT-IR and FT-Raman spectra. Thermal analysis was performed to study the thermal stability of the grown crystals. The transmission spectra of l-threonine show that the lower UV cutoff wavelength lies at 220 nm. Kurtz powder SHG measurements confirm the NLO property of the grown crystal. Microhardness studies have also been carried out on l-threonine crystals.

The effect of agitated drying on the morphology of l-threonine (needle-like) crystals

Experiments have been carried out to study the behavior of l-threonine (needle-like) crystals during agitated drying. For an l-threonine/water system the morphology of the crystals was monitored using light microscopy and image analysis. Analysis of the transient behavior of the crystal size and shape distribution showed that attrition and agglomeration took place simultaneously during the process. The variation of the operating conditions (temperature, agitation and vacuum) revealed that attrition dominated the drying process when the drying rate was low and/or the shear rate was high. For high drying rates and low shear rates, agglomeration became dominant. This study suggests that crystal redissolution had no significant impact on crystal morphology. It was also found that due to their needle-like shape, large l-threonine crystals were very sensitive to attrition. When attrition controlled the drying process, most of the particle size reduction took place below a critical moisture content of 4%. When agglomeration controlled the drying process, most of the crystal size enlargement occurred below a moisture content of 6%.

High-pressure Raman spectra ofL-threonine crystal

Raman spectra of an L-threonine crystal were investigated as a function of pressure in a diamond anvil cell up to 43 kbar at room temperature. It was observed that the crystal undergoes a phase transition between 20.3 and 22.4 kbar. This transition is accompanied by changes in the external mode region of the spectra, by discontinuities of the curves of wavenumber vs pressure and by abrupt changes in the relative intensity of bands, especially those associated with hydrogen bonds. Pressure coefficients for the most intense bands are also given. Copyright © 2000 John Wiley & Sons, Ltd.

Polarized Raman Spectra and Infrared Analysis of Vibrational Modes in L-Threonine Crystals

Polarized Raman and infrared espectra of l-threonine crystals have been obtained at room temperature and an assignment of normal modes is proposed based on group theory analysis. The usefulness of these assignments comes from the fact that some modes are related to important vibrations that can show changes under different pressure and temperature conditions.

Electron Spin Resonance of X-Irradiated Single Crystals of L-Threonine at 77°K

Electron spin resonance spectroscopy was used to study radiation damage at 77°K in single crystals of L-threonine. The cation radical and two other free radicals are trapped at 77°K. The g tensor for the cation radical, is reported. The hyperfine tensors and g tensor are given for the free radical produced by deamination. Possible reaction mechanisms are suggested for the production of these free radicals.