Experimental evidence of high pressure decoupling between charge transport and structural dynamics in a protic ionic glass-former

In this paper the relaxation dynamics of ionic glass-former acebutolol hydrochloride (ACB-HCl) is studied as a function of temperature and pressure by using dynamic light scattering and broadband dielectric spectroscopy. These unique experimental data provide the first direct evidence that the decoupling between the charge transport and structural relaxation exists in proton conductors over a wide T-P thermodynamic space, with the time scale of structural relaxation being constant at the liquid-glass transition (τ_α = 1000 s). We demonstrate that the enhanced proton transport, being a combination of intermolecular H⁺ hopping between cation and anion as well as tautomerization process within amide moiety of ACB molecule, results in a breakdown of the Stokes-Einstein relation at ambient and elevated pressure with the fractional exponent k being pressure dependent. The dT_g/dP coefficient, stretching exponent β_KWW and dynamic modulus E_a/ΔV^# were found to be the same regardless of the relaxation processes studied. This is in contrast to the apparent activation volume parameter that is different when charge transport and structural dynamics are considered. These experimental results together with theoretical considerations create new ideas to design efficient proton conductors for potential electrochemical applications.

Molecular dynamics of itraconazole at ambient and high pressure

Comprehensive molecular dynamics studies of vitrified and cryogrounded itraconazole (Itr) were performed at ambient and elevated pressure. DSC measurements yielded besides melting and glass transition observed during heating and cooling of both samples two further endothermic events at around T = 363 K and T = 346 K. The nature of these transitions was investigated using X-ray diffraction, broadband dielectric spectroscopy and Density Functional Theory calculations. The X-ray measurements indicated that extra ordering in itraconazole is likely to occur. Based on calculations and theory derived by Letz et al. the transition observed at T = 363 K was discussed in the context of formation of the nematic mesophase. In fact, additional FTIR measurements revealed that order parameter variation in Itr shows a typical sequence of liquid crystal phases with axially symmetric orientational order; i.e. a nematic phase in the temperature range 361.7 K to 346.5 K and a smectic A phase below 346.5. Moreover, dielectric measurements demonstrated that except for the structural relaxation process, there is also slower mode above the glass transition temperature in both vitrified and cryogrounded samples. We considered the origin of this mode taking into account DFT calculations, rod like shape of itraconazole and distribution of its dipole moment vectors. For the dielectric data collected at elevated pressure, evolution of the steepness index versus pressure was determined. Finally, the pressure coefficient of the glass transition temperature was evaluated to be equal to 190 K GPa(-1).

Mutarotation in biologically important pure L-fucose and its enantiomer

The sugar specific mutarotation reaction in biologically important L-fucose and its enantiomer in the pure, anhydrous, supercooled liquid state has been studied. Kinetics measurements in the temperature range 313-328 K at ambient pressure have been performed by means of dielectric spectroscopy, a method widely used for studying the molecular dynamics of glass-forming liquids. The kinetic curves have been obtained by tracking the equilibration process in sugar melted and quenched to the desired temperature. Thereafter, an activation energy equal to Ea = 140 kJ mol(-1) for D-fucose and Ea = 123 kJ mol(-1) for L-fucose has been derived from the Arrhenius fit of temperature dependent rate constants. It was also shown that the kinetics curves at the lowest temperatures studied have sigmoidal shape, which was connected to the high concentration of furanosidic forms.

A new way of stabilization of furosemide upon cryogenic grinding by using acylated saccharides matrices. The role of hydrogen bonds in decomposition mechanism

Recently it was reported that upon mechanical milling of pure furosemide significant chemical degradation occurs (Adrjanowicz et al. Pharm. Res.2011, 28, 3220-3236). In this paper, we present a novel way of chemical stabilization amorphous furosemide against decomposing that occur during mechanical treatment by preparing binary mixtures with acylated saccharides. To get some insight into the mechanism of chemical degradation of furosemide induced by cryomilling, experimental investigations supported by density functional theory (DFT) computations were carried out. This included detailed studies on molecular dynamics and physical properties of cryoground samples. The main thrust of our paper is that we have shown that furosemide cryomilled with acylated saccharides forms chemically and physically stable homogeneous mixtures with only one glass transition temperature, Tg. Finally, solubility measurements have demonstrated that furosemide cryomilled with acylated saccharides (glucose, maltose and sucrose) is much more soluble with respect to the crystalline form of this active pharmaceutical ingredient (API).

Education of Sport University students regarding first-aid procedures after dental trauma

AIM

The aim of this survey was to establish the current state of knowledge with regard to first-aid procedures and to compare the effectiveness of an educational lecture and a subsequent educational session.

METHODS

A questionnaire to assess the attitudes and anticipated behaviours of Sport University students related to first-aid procedures following dental injury was administered to the students 3 times (after 3 and 12 months). A lecture on the subject of dental trauma was given just after the first questionnaire survey. A randomly selected students group received an extra educational task.

RESULTS

The present study revealed a low level of initial knowledge of physical education students concerning first-aid measures in the case of dental trauma. A 30 minute lecture and an extra educational task significantly improved the knowledge evel. Even after one year the knowledge level was still high and sufficient to properly react when faced with dental trauma.

CONCLUSION

Our research proves that the inclusion of dental trauma as a topic in the Sport University students' curricular training and paedagogical education should be introduced in the form of a clear and concise lecture.

Tracking of Proton Transfer Reaction in Supercooled RNA Nucleoside

In this paper we address a longstanding debate concerning the proton transfer reaction of DNA and RNA compounds. The sample tested is β-uridine, one of the four basic components of RNA, which has been suggested to have the capacity to adopt lactam and lactim tautomeric forms. The essential biological importance of this RNA nucleoside has motivated a number of experimental and theoretical investigations in the past. However, the kinetics of the proton transfer reaction of this compound has not been examined. Herein, we employ dielectric spectroscopy and refractive index measurements to experimentally characterize lactam-lactim transformation in the supercooled liquid state. We quantify the kinetics of β-uridine tautomerization and suggest a mechanism for the configurational changes. The obtained data are compared to quantum chemical calculations. Finally the biological importance of our results is discussed.

Role of hydrogen bonds and molecular structure in relaxation dynamics of pentiol isomers

Although the presence of hydrogen bonds determines most properties of associated materials, their role in relaxation dynamics of liquids remains unclear. Very recently Nakanishi and Nozaki [M. Nakanishi and R. Nozaki, Phys. Rev. E 84, 011503 (2011)] proposed a simplified model for the description of the molecular dynamics of H-bonding network and tested its validity for several polyols. The authors concluded that relaxation dynamics is controlled mainly by the number of hydroxyl groups, whereas the role of molecular architecture can be neglected. This conclusion, as demonstrated herein, fails in the case of pentiols. When we take into account the role of molecular architecture for development of H-bonded structures, it is still possible to satisfactorily describe molecular dynamics in polyols with the use of the Nakanishi and Nozaki model.

The importance of the activation volume for the description of the molecular dynamics of glass-forming liquids

High pressure dielectric measurements were carried out on hydrogen bonded d-glucose and two van der Waals peracetyl saccharides, i.e. α pentaacetyl glucose and α octaacetyl maltose. In this study we found that after removing H bonds, the molecular dynamics of both modified saccharides is very sensitive to pressure, as reflected by a large value of the pressure coefficient of the glass transition temperature, equal to 270 K GPa(-1) and 280 K GPa(-1) for α pentaacetyl glucose and α octaacetyl maltose, respectively. On the other hand, dT(g)/dP for d-glucose is much lower, equal to 67 K GPa(-1). Our result confirms the general rule that the hydrogen bonding glass-forming liquids exhibit much lower values of dT(g)/dP compared to the van der Waals systems. Additionally, on the basis of results reported herein and also recent literature data for polyalcohols, we point out that the activation volume correlates fairly well with the molecular volume in the case of hydrogen bonding liquids. On the other hand, much larger values of the activation volumes at T(g) with respect to the molecular volumes were found for both peracetyl saccharides.

Theoretical and experimental studies on the internal mobility of two sulfonylurea agents: glibenclamide and glimepiride

Molecular dynamics of glibenclamide and glimepiride in their glassy state were studied by means of broadband dielectric spectroscopy. In both compounds we found a γ-relaxation process, with nearly the same value of activation energy. Further, we were able to identify the origin of γ relaxation by performing calculations within the framework of density functional theory. It was found that rotation of the chain end included cyclohexyl and neighboring carbonyl group is related to the observed mode in dielectric spectra. The calculated activation energy was only a few kJ per mole lower than the energies obtained from experiment. It is demonstrated that this fast γ process is insensitive to pressure. Finally, another secondary mode in glibenclamide, predicted by computations, was confirmed from dielectric measurements at elevated pressure. Our calculations indicate that this mode should be pressure-sensitive.

Comparative dielectric studies on two hydrogen-bonded and van der Waals liquids

Broadband dielectric measurements were performed in a wide range of temperatures on glucose, maltose, and their acetyl derivatives. We have indicated that molecular dynamics above and below the glass transition temperature differ considerably for the hydrogen-bonded and van der Waals systems. We have shown that structural relaxation dispersions of D-glucose and maltose are broader than those obtained for peracetyl carbohydrates. Moreover, glass transition temperatures of the former systems are much higher than for the latter ones. In the glassy state of both glucose and its acetyl derivatives only one well-separated secondary relaxation process was identified. In the case of maltose and peracetyl maltose a completely different situation was observed. In the former carbohydrate two secondary modes were detected, whereas in the latter one only a faster relaxation process was visible in the glassy state. This finding is discussed in greater detail on the basis of density functional theory calculations.

Nanoscale domains with nematic order in supercooled vitamin-A acetate: molecular dynamics studies

Vitamin-A acetate is one of the most versatile vitamins. It is applied in medicine because of its antioxidative properties, in tumor therapy because of its cytostatic activity, and in cosmetics because of its nutritional additives. Herein, using broadband dielectric spectroscopy, the molecular dynamics of supercooled and glassy vitamin-A acetate was investigated. It was shown that dielectric measurements carried out at ambient and elevated pressures reveal a number of relaxation processes associated with different types of molecular motions: α, δ, and ν processes-observed above the glass transition temperature and the next two modes: β and γ identified in the glassy state. The occurrence of the δ mode in the dielectric spectrum may imply the existence of nanoscale domains with nematic order. This hypothesis is further checked by atomic force microscopy measurements. Finally, we have determined the value of the glass transition temperature (T(g)) as well as the steepness index (m(P)) at various T-P conditions.

Dielectric relaxation study on tramadol monohydrate and its hydrochloride salt

Dielectric relaxation measurements as well as differential scanning calorimetry and X-ray diffraction investigations were performed on tramadol monohydrate and its hydrochloride salt. Examined samples do not crystallize during cooling and in consequence they reach the glassy state. In the case of the hydrochloride tramadol we are able to monitor alpha-relaxation process despite large contribution of dc conductivity to the loss spectra. It is the first such study on the salt of the drug. Up to now the dielectric spectroscopy has been regarded as useless in measuring such kind of API (active pharmaceutical ingredient). In this paper we also made some suggestions about the nature of the secondary relaxations in the amorphous tramadol monohydrate and its salt. The knowledge about the molecular mechanisms, which govern the observed secondary relaxations seems to be the key in predicting the stability of the amorphous form of the examined API. Finally additional dissolving measurements on the amorphous and crystal tramadol hydrochloride were performed. As a result we understood that dissolution properties of the amorphous form of the considered drug are comparable to those of crystalline one. However, we have found out that amorphous tramadol hydrochloride has greater ability to form tablets than its crystalline equivalent. This finding shows that amorphous drugs can be alternative even for the freely solved pharmaceuticals such as tramadol hydrochloride, because the former one has better ability to form tablets. It implies that during tabletting of the amorphous drugs there is no need to use any excipients and chemicals improving compaction properties of the API.

Dynamics of the slow mode in the family of six-carbon monosaccharides monitored by dielectric spectroscopy

Broadband dielectric measurements performed on D-glucose, L-sorbose, D-fructose and D-galactose revealed that, except for the structural relaxation process, one can detect in the liquid phase of these carbohydrates a much slower relaxation mode. Recently we have demonstrated that in D-glucose this relaxation mode might be related to the long range correlation of density fluctuations (LRCDF), also called Fischer clusters (FC). Based on the dielectric data obtained for the four monosaccharides we were able to make a more general conclusion about the characteristic dielectric features of the slow mode in the whole family of carbohydrates. We found out that the timescale separation between structural and considered relaxation reaches up to six decades at the glass transition temperature and the dielectric strength decreases significantly with lowering temperature. Another very interesting feature of the slow process is that it can be described by an almost exponential response function. We have found out that the fragility of the slow process lies within the range m = 44-50. Finally, we have also shown that there is a close link between structural and slow relaxation.

Identifying the origins of two secondary relaxations in polysaccharides

The main goal of this paper is to identify the molecular origins of two secondary relaxations observed in mechanical as well as in dielectric spectra in polysaccharides, including cellulose, and starches, such as pullulan and dextran. This issue has been actively pursued by many research groups, but consensus has not been reached. By comparing experimental data of monosaccharides, disaccharides, and polysaccharides, we are able to make conclusions on the origins of two secondary relaxations in polysaccharides. The faster secondary relaxations of polysaccharides are similar to the faster secondary relaxations of mono-, di-, and oligosaccharides. These include comparable relaxation times and activation energies in the glassy states, and also all the faster secondary relaxations have larger dielectric strengths than the slower secondary relaxation. The similarities indicate that the faster secondary relaxations in the polysaccharides have the same origin as that in mono-, di-, and oligosaccharides. Furthermore, since the relaxation time of the faster secondary relaxation in several mono- and disaccharides was found to be insensitive to applied pressure, the faster secondary relaxations of the polysaccharides are identified as internal motions within their monomeric units. The slower secondary relaxations in polysaccharides also have similar characteristics to those of the slower secondary relaxations of the disaccharides (maltose, cellobiose, sucrose, and trehalose), which indicates the analogous motions govern the slower process in these two groups of carbohydrates. Earlier we have shown in disaccharides that the rotation of the monomeric units around the glycosidic bond is responsible for this process. The same motion can occur in polysaccharides in the form of a local chain rotation. These motions involve the whole molecule in disaccharides and a local segment in polysaccharides. It is intermolecular in nature (with relaxation time pressure dependent, as found before in a disaccharide), and hence, it is the precursor of the structural alpha-relaxation. These results lead us to identify the slower secondary relaxation of the polysaccharides as the Johari-Goldstein beta-relaxation, which is supposedly a universal and fundamental process in all glass-forming substances.

The sheep as a knee osteoarthritis model: early cartilage changes after meniscus injury and repair

The purpose of this study was to analyse cartilage changes after traumatic meniscal lesions and to provide a detailed description of the model used with a view to reducing the number of animals used in future studies. The sheep's knee was chosen, as ovine biomechanics are similar to that of humans. In two groups of 10 animals each, a radial tear in the medial meniscus was either sutured with polydioxanone (PDS) or left untreated (sham-operated). Half of the animals in each group were sacrificed after six months, the other half after one year. The time periods to achieve weight bearing, meniscus healing, joint effusion (magnetic resonance imaging scan) and knee cartilage in the medial, lateral and patellofemoral compartments were evaluated in comparison to the opposite knee (control). Osteoarthritis (OA) was assessed by a modified Outerbridge classification and confirmed by scanning electron microscopy. Only one sutured meniscus remained completely adapted. In all other meniscus lesions, the rupture healed with a scar. In the PDS and sham-operated groups, OA was significantly higher in the medial knee compartment than in the lateral compartment and in controls (P < 0.001). In the operated groups, joint effusion was higher in the right hindlimb knee than in the normal left hindlimb knee (control) after six and 12 months (P < 0.001). Non-treated, displaced and even adapted sutured radial ovine meniscus tears produced intense OA within less than six months. Therefore, this animal model is suitable for assessment of new therapeutic regimens in meniscal surgery.