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In this paper, the molecular dynamics of a series of ester derivatives of ibuprofen (IBU), in which the hydrogen atom from the hydroxyl group was substituted by the methyl, isopropyl, hexyl, and benzyl moieties, has been investigated using Broadband dielectric (BD), Nuclear magnetic resonance (NMR), and Raman spectroscopies. We found that except for benzyl IBU (Ben-IBU), an additional process (slow mode, SM) appears in dielectric spectra in all examined compounds. It is worth noting that this relaxation process was observed for the first time in non-modified IBU (a Debye relaxation). According to suggestions by Affouard and Correia [J. Phys. Chem. B. 114, 11397 (2010)] as well as further studies by Adrjanowicz et al. [J. Chem. Phys. 139, 111103 (2013)] on Met-IBU, it was attributed to synperiplanar–antiperiplanar conformational changes within the molecule. Herein, we have shown that with an increasing molecular weight of the substituent, the relaxation times of the SM become longer and its activation energy significantly increases. Moreover, this new relaxation mode was found to be broader than a simple Debye relaxation in Iso-IBU and Hex-IBU. Additional complementary NMR studies indicated that either there is a significant slowdown of the rotation around the O=C—O—R moiety or this kind of movement is completely suppressed in the case of Ben-IBU. Therefore, the SM is not observed in the dielectric loss spectra of this compound. Finally, we carried out isothermal experiments on the samples which have a different thermal history. Interestingly, it turned out that the relaxation times of the structural processes are slightly shorter with respect to those obtained from temperature dependent measurements. This effect was the most prominent in the case of Hex-IBU, while for Ben-IBU, it was not observed at all. Additional time-dependent measurements revealed the ongoing equilibration manifested by the continuous shift of the structural process, until it finally reached its equilibrium position. Further Raman investigations showed that this effect may be related to the rotational/conformational equilibration of the long hexyl chains. Our results are the first ones demonstrating that the structural process is sensitive to the conformational equilibration occurring in the specific highly viscous systems. [ABSTRACT FROM AUTHOR]

Techniques including dielectric relaxation and enthalpy relaxation are used to investigate the molecular relaxation dynamics of glucose and, fructose in their liquids and glassy states. The results indicate that the slower secondary relaxation bears relations to the [alpha]-relaxation, and hence, it is the true Johari-Goldstein secondary relaxation of the monosaccharides.

High pressure dielectric studies on the H-bonded liquid D-glucose and Orientationally Disordered Crystal (ODIC) 1,6-anhydro-D-glucose (levoglucosan) were carried out. It was shown that in both compounds, the structural relaxation is weakly sensitive to compression. It is well reflected in the low pressure coefficient of the glass transition and orientational glass transition temperatures which is equal to 60 K/GPa for both D-glucose and 1,6-anhydro-D-glucose. Although it should be noted that T0 g /p evaluated for the latter compound seems to be enormously high with respect to other systems forming ODIC phase. We also found that the shape of the a-loss peak stays constant for the given relaxation time independently on the thermodynamic condition. Consequently, the Time Temperature Pressure (TTP) rule is satisfied. This experimental finding seems to be quite intriguing since the TTP rule was shown to work well in the van der Waals liquids, while in the strongly associating compounds, it is very often violated. We have also demonstrated that the sensitivity of the structural relaxation process to the temperature change measured by the steepness index (mp) drops with pressure. Interestingly, this change is much more significant in the case of D-glucose with respect to levoglucosan, where the fragility changes only slightly with compression. Finally, kinetics of ODIC-crystal phase transition was studied at high compression. It is worth mentioning that in the recent paper, Tombari and Johari [J. Chem. Phys. 142, 104501 (2015)] have shown that ODIC phase in 1,6-anhydro-D-glucose is stable in the wide range of temperatures and there is no tendency to form more ordered phase at ambient pressure. On the other hand, our isochronal measurements performed at varying thermodynamic conditions indicated unquestionably that the application of pressure favors solid (ODIC)-solid (crystal) transition in 1,6-anhydro-D-glucose. This result mimics the impact of pressure on the crystallization of fully disordered supercooled van der Waals liquids. [ABSTRACT FROM AUTHOR]

The observation of gravitational waves is hindered by the presence of transient noise (glitches). We study data from the third observing run of the Advanced LIGO detectors, and identify new glitch classes: fast scattering/crown and low-frequency blips. Using training sets assembled by monitoring of the state of the detector, and by citizen-science volunteers, we update the Gravity Spy machine-learning algorithm for glitch classification. We find that fast scattering/crown, linked to ground motion at the detector sites, is especially prevalent, and identify two subclasses linked to different types of ground motion. Reclassification of data based on the updated model finds that ∼27% of all transient noise at LIGO Livingston belongs to the fast scattering class, while ∼8% belongs to the low-frequency blip class, making them the most frequent and fourth most frequent sources of transient noise at that site. Our results demonstrate both how glitch classification can reveal potential improvements to gravitational-wave detectors, and how, given an appropriate framework, citizen-science volunteers may make discoveries in large data sets. [ABSTRACT FROM AUTHOR]

In this paper, we present results of dielectric and shear-mechanical studies for amine (2-ethyl-1-hexylamine) and thiol (2-ethyl-1-hexanethiol) derivatives of the monohydroxy alcohol, 2-ethyl-1-hexanol. The amine and thiol can form hydrogen bonds weaker in strength than those of the alcohol. The combination of dielectric and shear-mechanical data enables us to reveal the presence of a relaxation mode slower than the a-relaxation. This mode is analogous to the Debye mode seen in monohydroxy alcohols and demonstrates that supramolecular structures are present for systems with lower hydrogen bonding strength. We report some key features accompanying the decrease in the strength of the hydrogen bonding interactions on the relaxation dynamics close to the glass-transition. This includes changes (i) in the amplitude of the Debye and a-relaxations and (ii) the separation between primary and secondary modes. [ABSTRACT FROM AUTHOR]

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]

We have studied mutarotation in anhydrous supercooled L-sorbose by means of dielectric spectroscopy. The phenomenon observed in L-sorbose is much faster than in the structurally similar D-fructose. The kinetics of this process has been determined by applying 1st order kinetics model. Activation energy equal to 68 kJ/mol was obtained from temperature dependence of rate constants. To understand differences in mutarotation rate between D-fructose and L-sorbose, quantum mechanical calculations were performed to study mechanism of this phenomenon. The possible impact of water absorbed from air on the mutarotation in supercooled liquid state has been checked. It turned out that the process is probably intermolecular and the water molecules or other carbohydrate molecules assist in the proton transfer process. Finally we have shown that the rate constant can be alternatively determined from frequency of the maximum of peak, obtained by performing Fourier transform of kinetic curve. [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]

Recently, we have studied the mutarotation kinetics in D-fructose by means of dielectric spectroscopy. In the present work we investigate density behavior of D-fructose during mutarotation process. By performing volume measurements at temperature T = 303 K and pressure p = 10 MPa we are able to monitor kinetics of this process. As a result we found nearly the same value of the rate constant as previously determined from dielectric measurements. However, these two experimental methods monitor different molecular aspects of mutarotation phenomenon in D-fructose. Dielectric spectroscopy is sensitive to the decay of former ring as well as to the forming of another, while specific volume measurements are sensitive to the forming of new tautomers only. Calculations of activation energy of mutarotation in D-fructose led us to the conclusion, that mechanism of this reaction in amorphous phase could be based on internal proton transfer. Moreover it was found that the main mutarotation path in quenched D-fructose melt is transformation of α,β-furanose to β-pyranose. [ABSTRACT FROM AUTHOR]

There are a number of chemical compounds that readily convert to other isomers when their crystalline structure is lost (e.g., during melting or dissolution). This phenomenon, commonly known as tautomerism, is a subject of intense research. It is an important problem especially in pharmaceutical industry because various isomers of a drug may have different pharmacological activity. Therefore, it is important to find appropriate experimental technique which enables the determination of the isomerization ability of compounds. In this communication, we demonstrate that broadband dielectric spectroscopy (BDS) method has the potential of detection and monitoring of tautomerism of drugs. To investigate the tautomerism phenomenon we have chosen one of the hypoglycemic agents that belong to the class II of sulfonylurea drugs. Based on density functional theory (DFT) calculations we have analyzed two possible tautomerization pathways of glibenclamide. By using BDS as a tool, we show it can detect the conversion between the isomeric forms through time dependence in the dielectric properties. The activation energy (Ea) of this process is in good agreement with that obtained from DFT analysis. Finally, we discuss the possible effects of tautomerism on basic pharmaceutical parameters such as biological activity or bioavailability in the case of the glibenclamide drug. [ABSTRACT FROM AUTHOR]

Dielectric spectroscopy has been recently used to monitor mutarotation in undercooled D-fructose. This method can be viewed as a universal method to study mutarotation phenomenon in the whole family of monosaccharides. In this paper, we studied kinetics of mutaration of anhydrous D-ribose at ambient pressure as well as pressure effect on the rate constant of this process. Ribose mutarotation behavior is compared to the one obtained for D-fructose. In addition, we attempted to determine the “direction” of mutarotation in undercooled monosaccharides after quenching the melted sample. To this end, analysis of dipole moments of different tautomers of D-fructose and D-ribose have been performed. Conformational analysis of studied carbohydrates was done with use of density functional theory. Geometry optimizations as well as calculations of dipole moments were done on the 6-311++G(d,p)/B3LYP level. Finally, it turned out that data obtained from the mutarotation experiment might be helpful in understanding the origin of γ-process occurring in the whole family of carbohydrates. [ABSTRACT FROM AUTHOR]

In this work we analyzed the structural relaxation times as a function of both temperature and pressure in terms of the entropic models by using dielectric and PVT measurements data presented in our previous research on the ionic liquid verapamil hydrochloride [Z. Wojnarowska, M. Paluch, A. Grzybowski, et al., J. Chem. Phys. 131, 104505 (2009)]. Two different approaches were used to analyze the τα(T,P) dependence: the modified Avramov model as well as the pressure extended Adam–Gibbs model in the forms proposed by Casalini (AGC) and Schwartz (AGS). In every case a satisfactory description of the structural relaxation times was achieved. Additionally, using both mentioned models the pressure dependence of the fragility mP and the glass transition temperature Tg were determined. We also compared the value of dTg/dP|P=0 calculated on the basis of the considered entropic models with the experimental value evaluated in our recent work. Consequently, we were able to estimate which of the examined models in the best way relates the dynamic to the thermodynamic parameters. [ABSTRACT FROM AUTHOR]

Dielectric relaxation measurements on maltose were performed at ambient and increasing pressure. The loss spectra collected below glass transition of this disaccharide revealed presence of two well separated secondary relaxations. Activation energies determined for both modes are Ea=73 kJ/mol and 47 kJ/mol for the slower (β) and faster (γ) relaxation, respectively. From high pressure measurements activation volume ΔV=15.6 ml/mol for the slower secondary relaxation was estimated. Both quantities: activation energy and activation volume for α-process derived from dielectric data, were compared to those obtained from the conformational calculations with use of density functional theory (DFT). We found out satisfactory agreement between both quantities for the molecular motion related to the rotation of the two monosaccharide units around glycosidic linkage in this disaccharide. [ABSTRACT FROM AUTHOR]

Relaxation dynamics of verapamil hydrochloride (VH), which is a representative of ionic liquids, was studied under isobaric and isothermal conditions by using dielectric spectroscopy. In addition we also carried out pressure-temperature-volume (PVT) measurements. The obtained data enable us to examine the structural α-relaxation time τα as a function of temperature, pressure, and volume. Since the examined sample is a typical ionically conducting material, we employed the dielectric modulus formalism to gain information about α-relaxation process. It was found that application of pressure changes the shape of the modulus spectrum. The α-peak becomes narrower with compression. Consequently, it was also shown that the stretching parameter βKWW increases with pressure. Based on experimental data both the isobaric fragility (mp) at various pressures and isothermal fragility (mT) at various temperatures were calculated. Analyzing the effect of pressure on the dependences τα(T) as well as on the shape parameter of the α-peak it was found that a phenomenological correlation between mp and βKWW established for glass forming liquids is also valid for VH under condition of high compression. The pressure dependences of glass-transition temperature determined from dielectric and volumetric measurements have been compared. Moreover, PVT data allow us to assess the relative contribution of thermal energy and free volume fluctuation to the dramatic slowing down of the molecular dynamics in the vicinity of Tg. It is established from the ratio of the isochronic and isobaric expansivities that the thermal energy has a stronger effect on the relaxation times than the free volume, although the latter contribution is significant. Finally, we also discuss the validity of thermodynamic scaling in the case of VH and examine the scaling exponent γ at various thermodynamic conditions. [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]

Dielectric loss spectra of two glass-forming isomers, eugenol and isoeugenol, measured at ambient and elevated pressures in the normal liquid, supercooled, and glassy states are presented. The isomeric chemical compounds studied differ only by the location of the double bond in the alkyl chain. Above the glass transition temperature Tg, the dielectric loss spectra of both isomers exhibit an excess wing on the high frequency flank of the loss peak of the α relaxation and an additional faster γ process at the megahertz frequency range. By decreasing temperature below Tg at ambient pressure or by elevating pressure above Pg, the glass transition pressure, at constant temperature, the excess wing of isoeugenol shifts to lower frequencies and is transformed into a secondary β-loss peak, while in eugenol it becomes a shoulder. These spectral features enable the β-relaxation time τβ to be determined in the glassy state. These changes indicate that the excess wings in isoeugenol and eugenol are similar and both are secondary β relaxations that are not resolved in the liquid state. While in both isoeugenol and eugenol the loss peak of the β relaxation in the glassy state and the corresponding excess wing in the liquid state shifts to lower frequencies on elevating pressure, the locations of their γ relaxation show little change with increasing pressure. The different pressure sensitivities of the excess wing and γ relaxation are further demonstrated by the nearly perfect superposition of the α-loss peak together with excess wing from the data taken at ambient pressure and at elevated pressure (and higher temperature so as to have the same α-peak frequency), but not the γ-loss peak in both isoeugenol and eugenol. On physical aging isoeugenol, the β-loss peak shifts to lower frequencies, but not the γ relaxation. Basing on these experimental facts, the faster γ relaxation is a local intramolecular process involving a side group and the slower β relaxation mimics the structural α relaxation in behavior, involves the entire molecule and satisfies the criteria for being the Johari-Goldstein β relaxation. Analysis and interpretation of the spectra utilizing the coupling model further demonstrate that the excess wings seen in the equilibrium liquid states of these two isomers are their genuine Johari-Goldstein β relaxation. [ABSTRACT FROM AUTHOR]

Several studies are conducted to explain the different molecular motions that are found to be responsible for the slower secondary ([beta]) relaxation in sucrose. The [beta]-relaxation is shown to lead to the translation motion of the entire molecule of the sugar.

The conductivity relaxation measurements in wide range of temperature and pressures were used to study the ion dynamics under pressure in the ionic liquid 1-butyl-1-methylpyrrolidinium bis[oxalate]-borate (BMP-BOB). The results showed that the dynamic response under pressure in the ionic liquid is identical to that found in nonionic glass formers.