The single crystals of α and γ polymorphs of glycine were grown from aqueous solutions at ambient conditions. The metastable α-form was crystallized from pure aqueous solution and the stable γ-form from aqueous solution in the presence of a critical concentration of a selective additive sodium chloride. Attempt to grow sizable β-form single crystals were not successful because of their high instability. In stability terms at ambient conditions these three glycine polymorphs are like this: β<α<γ. The form of crystallization was confirmed by X-ray powder diffraction (XRD). The α- and β-forms crystallize in the monoclinic system with centrosymmetric space groups P2 1/n and P2 1, respectively, and the γ-form crystallizes in trigonal-hexagonal system with non-centrosymmetric space group P3 2. At high-humidity conditions, the room temperature polymorphic phase transformations from α to γ and solution-mediated phase transformation from β to α were confirmed by XRD. The transformation from γ to α while heating well above the room temperature observed at around 179 °C was recorded by thermogravimetry (TG) and differential thermal analysis (DTA) and confirmed by differential scanning calorimetry (DSC). The morphology of the grown polymorphs were analysed by goniometry. CHN analysis shows the non-existance of sodium chloride species in the grown γ-glycine single crystals. The optical transparancy of the γ-form was recorded by UV-vis-Near IR spectroscopy.
"It is stable, but at high humidity it gradually transforms into the g-glycine.   g-glycine crystallises in the polar non-centrosymmetric space group P3 1 .[2,9À11] This form can be obtained from acidic (pH < 2.5) or basic (pH > 10) solution  or by addition of different compounds containing alkaline monovalent ions "
[Show abstract][Hide abstract] ABSTRACT: In glycine crystal the transformation from γ to α modification has been investigated using differential scanning calorimetry (DSC) and low-frequency dielectric spectroscopy methods on powder and monocrystalline samples. In monocrystalline samples the transition begins at 457.5 K. The first step is connected with cracking of the sample and growing of the ac conductivity which reaches maximum at 458.5 K. Next, ac conductivity achieves a huge maximum at the transition point 462.8 K. Additional small anomaly in the complex dielectric constant was revealed at 335 K. In powder samples this transformation measured by the DSC method goes uniformly. For these samples the ac conductivity begins to grow rapidly from 455 K and grows 2.5 times in the range of 383–387 K. In powder samples the ac conductivity at the transition point is seven times greater than in the monocrystalline samples. Conductivity anomalies are accompanied by changes in the real part of the dielectric constant.
"Therefore, we consider that the crystallization takes place not through photochemical process  , but through various femtosecond laser-induced phenomena such as cavitation bubble and shock wave. The femtosecond laser can excite not only water but also glycine via multiphoton absorption  "
[Show abstract][Hide abstract] ABSTRACT: We demonstrate femtosecond laser-induced crystallization of glycine from its supersaturated solution depending on laser tunable parameters (pulse energy and repetition rate) and focal position, and examine the crystallization probability, crystal morphology, and crystal polymorph. The generation of cavitation bubble through multiphoton absorption of water depends on input laser pulse energy and repetition rate, which strongly determine morphology and number of the obtained crystals. Significant increase in the crystallization probability is observed by irradiating the femtosecond laser pulses to the air/solution interface, and single pulse-induced single crystal formation is successfully achieved. The crystallization mechanism is discussed in view of inhomogeneous mechanical stress induced by cavitation bubble generation and molecular assembly characteristics of the surface.
[Show abstract][Hide abstract] ABSTRACT: Pure and urea-doped gamma-glycine (γ-glycine) single crystals were grown by solution method with slow evaporation technique. When urea was added as dopant, morphological alterations were noticed in γ-glycine crystals. Structural characterization of the grown crystals was carried out by single and powder X-ray diffraction (XRD) methods and it is observed that the samples crystallize in non-centrosymmetric space groups. UV–visible transmittance studies were performed to analyse optical transparency of pure and urea-doped γ-glycine crystals and found that the crystals were transparent in the entire visible–NIR region. Density and melting point of the grown crystals were measured. Second harmonic generation (SHG) for the grown crystals of this work was confirmed using Nd:YAG laser. Thermogravimetric and differential thermal analyses (TG/DTA) thermograms reveal that the materials have good thermal stability. From Microhardness studies, it is observed that urea-doped γ-glycine crystal is harder than pure (undoped) sample.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.