2H NMR studies of supercooled and glassy aspirin

Nath, R.; Nowaczyk, A.; Geil, Burkhard; Böhmer, Roland

doi:10.1016/j.jnoncrysol.2007.05.180

Cited by 20 publications

(20 citation statements)

References 34 publications

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“…From the Arrhenius relation, s c = s 0 exp(E a /kT max ), and a preexponential factor [9] of s 0 = 10 À12 s, the energy of activation can be estimated as E a /k % 600 K. This result is in the range of the energy barrier characterizing the motion of the methyl group for T > 40 K reported in Ref. [10]. The results for temperatures below 40 K, shown in this study, indicate slowing molecular dynamics and a quasi linear decrease of 1/T m upon cooling the sample, in accord with published theoretical predictions [11].…”

Section: Discussionmentioning

confidence: 65%

EPR study of crystalline and glassy ethanol

Kveder¹,

Merunka²,

Jokić³

et al. 2008

Journal of Non-Crystalline Solids

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Section: Discussionmentioning

confidence: 65%

EPR study of crystalline and glassy ethanol

Kveder¹,

Merunka²,

Jokić³

et al. 2008

Journal of Non-Crystalline Solids

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“…The non-Arrhenius temperature dependence coupled with non-exponential relaxation appears to be typical for systems undergoing glassy dynamics. 59,63,71 …”

Section: Resultsmentioning

confidence: 99%

Glassy Dynamics of Protein Methyl Groups Revealed by Deuteron NMR

et al. 2013

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We investigated site-specific dynamics of key methyl groups in the hydrophobic core of chicken villin headpiece subdomain (HP36) over the temperature range between 298 and 140K using deuteron solid-state NMR longitudinal relaxation measurements. The relaxation of the longitudinal magnetization is weakly non-exponential (glassy) at high temperatures and exhibits a stronger degree of non-exponentiality below about 175K. In addition, the characteristic relaxation times deviate from the simple Arrhenius law. We interpret this behavior via the existence of distribution of activation energy barriers for the three-site methyl jumps, which originates from somewhat different methyl environments within the local energy landscape. The width of the distribution of the activation barriers for methyl jumps is rather significant, about 1.4 kJ/mol. Our experimental results and modeling allow for the description of the apparent change at about 175K without invoking a specific transition temperature. For most residues in the core, the relaxation behavior at high temperatures points to the existence of conformational exchange between the sub-states of the landscape, and our model takes into account the kinetics of this process. The observed dynamics are the same for dry and hydrated protein. We also looked at the effect of F58L mutation inside the hydrophobic core on the dynamics of one of the residues and observed a significant increase in its conformational exchange rate constant at high temperatures.

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“…For this reason, there has been a great deal of interest for the pharmaceutical industry in making amorphous pharmaceuticals and others to study their physical properties. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Often the pharmaceuticals have chemical bonds and structures that are not common to the glass-formers studied in the physics or chemistry laboratories. Thus, extraordinary molecular dynamics and physical properties may be expected from the study of the glass-forming pharmaceuticals.…”

Section: Introductionmentioning

confidence: 99%

Fundamentals of ionic conductivity relaxation gained from study of procaine hydrochloride and procainamide hydrochloride at ambient and elevated pressure

Wojnarowska¹,

Swiety-Pospiech²,

Grzybowska³

et al. 2012

The Journal of Chemical Physics

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The pharmaceuticals, procaine hydrochloride and procainamide hydrochloride, are glass-forming as well as ionically conducting materials. We have made dielectric measurements at ambient and elevated pressures to characterize the dynamics of the ion conductivity relaxation in these pharmaceuticals, and calorimetric measurements for the structural relaxation. Perhaps due to their special chemical and physical structures, novel features are found in the ionic conductivity relaxation of these pharmaceuticals. Data of conductivity relaxation in most ionic conductors when represented by the electric loss modulus usually show a single resolved peak in the electric modulus loss M(")(f) spectra. However, in procaine hydrochloride and procainamide hydrochloride we find in addition another resolved loss peak at higher frequencies over a temperature range spanning across T(g). The situation is analogous to many non-ionic glass-formers showing the presence of the structural α-relaxation together with the Johari-Goldstein (JG) β-relaxation. Naturally the analogy leads us to name the slower and faster processes resolved in procaine hydrochloride and procainamide hydrochloride as the primary α-conductivity relaxation and the secondary β-conductivity relaxation, respectively. The analogy of the β-conductivity relaxation in procaine HCl and procainamide HCl with JG β-relaxation in non-ionic glass-formers goes further by the finding that the β-conductivity is strongly related to the α-conductivity relaxation at temperatures above and below T(g). At elevated pressure but compensated by raising temperature to maintain α-conductivity relaxation time constant, the data show invariance of the ratio between the β- and the α-conductivity relaxation times to changes of thermodynamic condition. This property indicates that the β-conductivity relaxation has fundamental importance and is indispensable as the precursor of the α-conductivity relaxation, analogous to the relation found between the Johari-Goldstein β-relaxation and the structural α-relaxation in non-ionic glass-forming systems. The novel features of the ionic conductivity relaxation are brought out by presenting the measurements in terms of the electric modulus or permittivity. If presented in terms of conductivity, the novel features are lost. This warns against insisting that a log-log plot of conductivity vs. frequency is optimal to reveal and interpret the dynamics of ionic conductors.

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2H NMR studies of supercooled and glassy aspirin

Cited by 20 publications

References 34 publications

EPR study of crystalline and glassy ethanol

EPR study of crystalline and glassy ethanol

Glassy Dynamics of Protein Methyl Groups Revealed by Deuteron NMR

Fundamentals of ionic conductivity relaxation gained from study of procaine hydrochloride and procainamide hydrochloride at ambient and elevated pressure

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