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In this Communication, we present experimental studies that put new insight into the puzzling nature of the Debye relaxation found in the supercooled liquid state of racemic ibuprofen. The appearance of D-relaxation in the loss spectra of non-hydrogen bonding methylated derivate of ibuprofen has proven that Debye relaxation is related solely with conformational changes of the carboxyl group, termed in this paper as synperiplanar-antiperiplanar. Our studies indicate that the presence of hydrogen bonding capabilities is not here the necessary condition to observe Debye process, however, their occurrence might strongly influence α- and D-relaxations dynamics. Interestingly, the activation energy of the D-process in ibuprofen methyl ester on approaching Tg was found to be perfectly consistent with that reported for ibuprofen by Affouard and Correia [J. Phys. Chem. B 114, 11397-11402 (2010)] (∼39 kJ/mol). Finally, IR measurements suggest that the equilibrium between conformers concentration depends on time and temperature, which might explain why the appearance of D-relaxation in supercooled ibuprofen depends on thermal history of the sample. [ABSTRACT FROM AUTHOR]

The organic liquid ROY, i.e., 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile, has been a subject of detailed study in the last few years. One interest in ROY lies in its polymorph-dependent fast crystal growth mode below and above the glass transition temperature. This growth mode is not diffusion controlled, and the possibility that it is enabled by secondary relaxation had been suggested. However, a previous study by dielectric relaxation spectroscopy had not been able to find any resolved secondary relaxation. The present paper reports new dielectric measurements of ROY in the liquid and glassy states at ambient pressure and elevated pressure, which were performed to provide more insight into the molecular dynamics as well as the crystallization tendency of ROY. In the search of secondary relaxation, a special glassy state of ROY was prepared by applying high pressure to the liquid state, from which secondary relaxation was possibly resolved. Thus, the role of secondary relaxation in crystallization of ROY remains to be clarified. Notwithstanding, the secondary relaxation present is not necessarily the sole enabler of crystallization. In an effort to search for possible cause of crystallization other than secondary relaxation, we also performed crystallization kinetics studies of ROY at different T and P combinations while keeping the structural relaxation time constant. The results show that crystallization of ROY speeds up with pressure, opposite to the trend found in the crystallization of ibuprofen studied up to 1 GPa. The dielectric relaxation and thermodynamic properties of ROY with phenolphthalein dimethylether (PDE) are similar in many respects, but PDE does not crystallize. Taking all the above into account, besides the secondary relaxation, the specific chemical structure, molecular interactions and packing of the molecules are additional factors that could affect the kinetics of crystallization found in ROY. [ABSTRACT FROM AUTHOR]

Broadband dielectric measurements on leucrose were performed under ambient and high pressure. We showed that in this disaccharide, there are two secondary relaxation modes, a slower one sensitive to pressure and a faster one that is not. This finding clearly indicates that the faster secondary relaxation originates from the intramolecular motion. This conclusion contradicted previous interpretations of this mode observed for trehalose and maltitol, systems very closely related to leucrose. In addition, pressure sensitivity of the slower relaxation confirms our recent interpretation about the character of this process. Furthermore, we discovered that unlike the faster relaxation, the slower secondary relaxation is sensitive to the thermodynamic history of measurements. Finally, monitoring the changes in maximum loss of the slower secondary relaxation measured at the same pressure and temperature conditions for glasses obtained via different thermodynamic routes enabled us to draw a conclusion about the density of the formed glasses. Our observations may be helpful in establishing a new method of suppressing crystallization of amorphous drugs. [ABSTRACT FROM AUTHOR]

Abstract: Kinetics of mutarotation in supercooled, anhydrous D-fructose was followed by means of dielectric spectroscopy. We have noticed that structural relaxation of sugar is sensitive to the mutarotation process, thus it is possible to construct kinetic curve by plotting relaxation times of α relaxation as well as static permittivity versus time. Kinetics obtained from these two parameters is totally different. Sigmoidal shape of curve plotted from relaxation times at low temperatures is noted. In this article, we present probable explanation of this phenomenon. Moreover we perform tests of 2 kinetics models to properly describe sigmoidal curve. Finally, optical measurements were performed to verify dielectric spectroscopy as a method to monitor mutarotation. [Copyright &y& Elsevier]

Verapamil hydrochloride (VH) is a very popular calcium channel blocker. Solubility of its crystalline form in the blood reaches only 10–20%. Thus, it seems to be very important to improve its bioavailability. In this article, we show that the preparation of the amorphous form of VH enhance its dissolution rate. In addition we performed dielectric measurements to describe molecular dynamics of this active pharmaceutical ingredient (API). Since examined sample is typical ionically conducting material, to gain information about structural relaxation we employed the dielectric modulus formalism. The temperature dependence of the structural relaxation time can be described over the entire measured range by a single Vogel–Fulcher–Tamman (VFT) equation. From the VFT fits the glass transition temperature was estimated as Tg = 320.1 K. Below glass transition temperature one clearly visible secondary relaxation, with activation energy Ea = 37.8 kJ/mol, was reported. Deviations of experimental data from KWW fits on high-frequency flank of α-peak indicate the presence of an excess wing in tested sample. Based on Kia Ngai's coupling model we identified the excess wing as true Johari–Goldstein process. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:828–839, 2010 [ABSTRACT FROM AUTHOR]

Very recently Kwon et al. [H.-J. Kwon, J.-A. Seo, H. K. Kim, and Y. H. Hwang, J. Chem. Phys. 134, 014508 (2011)] published an article on the study of dielectric relaxation in trehalose and maltose glasses. They carried out broadband dielectric measurements at very wide range of temperatures covering supercooled liquid as well as glassy state of both saccharides. It is worth to mention that authors have also applied a new method for obtaining anhydrous glasses of trehalose and maltose that enables avoiding their caramelization. Four relaxation processes were identified in dielectric spectra of both saccharides. The slower one was identified as structural relaxation process the next one, not observed by the others, was assigned as Johari-Goldstein (JG) β-relaxation, while the last two secondary modes were of the same nature as found by Kaminski et al. [K. Kaminski, E. Kaminska, P. Wlodarczyk, S. Pawlus, D. Kimla, A. Kasprzycka, M. Paluch, J. Ziolo, W. Szeja, and K. L. Ngai, J. Phys. Chem. B 112, 12816 (2008)]. In this comment we show that the authors mistakenly assigned the slowest relaxation process as structural mode of disaccharides. We have proven that this relaxation process is an effect of formation of thin layer of air or water between plate of capacitor and sample. The same effect can be observed if plates of capacitor are oxidized. Thus, we concluded that their slowest mode is connected to the dc conduction process while their β JG process is primary relaxation of trehalose and maltose. [ABSTRACT FROM AUTHOR]

Abstract: Some examples of recent advances in experiment and theory that have impact on solution of the glass transition problem are briefly discussed. The fundamental importance of a special class of secondary relaxations called the Johari–Goldstein β-relaxations becomes clear from the recent advances. The main part of the paper addresses a recent research problem, which is the purported anomalous temperature dependence of the relaxation time of another secondary (γ) relaxation found by fitting dielectric relaxation data in several glass-formers. We show the anomalous T-dependence of this faster γ-relaxation is caused by the influence exerted by the slower Johari–Goldstein β-relaxation in the vicinity. [Copyright &y& Elsevier]