PubMed · 12409191
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Philip L Yeagle, Dr A G Lee. 2002-10-11. Membrane protein structure.. https://doi.org/10.1016/s0005-2736(02)00603-x
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The physical stability and solid-state recrystallization of spray-dried 'amorphous' lactose particles were visualized using environmentally controlled atomic force microscopy (EC-AFM) and conventional optical microscopy. The morphology and crystalline state were investigated as a function of relative humidity (RH) and were correlated with bulk gravimetric vapor sorption measurements that were run in parallel. The metastable nature of amorphous spray-dried lactose particles was apparent at low RHs (<30% RH). Visualization of the recrystallization transformation of amorphous lactose during moisture uptake at 58 and 75% RH suggested only a proportion of the collapsed particles undergoes nucleation and crystal growth. The irregular surface morphology of the recrystallized particles suggested a secondary nucleation and growth process. Primary nucleation of alpha-lactose monohydrate within the non-recrystallized particles required exposure to elevated RH (94% RH). In relation to bulk measurements of moisture-induced amorphous recrystallization of spray-dried lactose, the results suggest that recrystallization of amorphous lactose, above a critical RH, may be induced by the presence of very low levels of a seed material, which may dramatically reduce the activation energy barrier for nucleation and crystal growth.
Vibrational spectra of M4LiH3(XO4)4 family, where M=K, Rb, X=S, Se together with Na5H3(SeO4)4.2H2O and Na2SeO4.H2SeO3.H2O crystals were compared. Similarities and differences are described. The spectroscopic manifestation of the presence of hydrogen bonds is discussed. Position of the bands corresponding to bending type of vibrations (in-plane and out-of plane) of hydrogen bonds is analyzed in the function of temperature. Small dynamic splitting of the bands due to weak interactions between ions is noticed.
The FTIR spectra of both the pure NH and isotopically substituted ND (<10% and >90% D) polycrystalline cytosine were recorded in the range 400-4000 cm(-1) as a function of temperature (10-300 K). For the first time, uncoupled NH(D) stretching mode bands of amine and imine groups were observed in the spectra of isotopically diluted cytosine at low temperatures. These bands correspond to the three distinct H-bonds that are present in the crystal, in agreement with the available data obtained by structural methods. At least nine bands were observed below 1000 cm(-1) and, in consonance with their temperature and isotopic exchange behavior, were assigned to the NH proton out-of-the-plane bending modes. Six of these bands were found to correspond to additional "disordered" H-bonds, which could not be observed by structural methods. Empirical correlations of spectral and thermodynamic parameters enabled to estimate the contribution of the H-bonds to the sublimation enthalpy of the crystal, in agreement with independent experimental data.