Aromaticity effect on supramolecular aggregation. Aromatic vs. cyclic monohydroxy alcohols.

In this paper, the steric hindrance effect related to the presence of either a cyclic or aromatic ring on the self-association process in the series of monohydroxy alcohols (MAs), from cyclohexanemethanol to 4-cyclohexyl-1-butanol and from benzyl alcohol to 4-phenyl-1-butanol, was studied using X-Ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FTIR) spectroscopy, Broadband Dielectric Spectroscopy (BDS) and the Pendant Drop (PD) methods. Based on FTIR results, it was shown that phenyl alcohol (PhA) and cyclohexyl alcohol (CA) derivatives reveal substantial differences in the association degree, the activation energy of dissociation, and the homogeneity of supramolecular nanoassociates suggesting that the phenyl ring exerts a stronger steric impact on the self-assembling of molecules than cyclohexyl one. Additionally, XRD data revealed that phenyl moiety introduces more heterogeneity in the organization of molecules compared to the cyclic one. The changes in the self-association process of alcohols were also reflected in differences in the molecular dynamics of the H-bonded aggregates, as well as in the Kirkwood factor, defining the long-range correlation between dipoles, which were slightly higher for CAs with respect to those determined for PhAs. Unexpectedly it was also found that the surface layers of PhAs were more organized than those formed by CAs. Thus, these findings provided insight into the impact of aromaticity on the self-assembly process, H-bonding pattern, supramolecular structure, and intermolecular dynamics of the studied alcohols.

The impact of the length of alkyl chain on the behavior of benzyl alcohol homologues - the interplay between dispersive and hydrogen bond interactions.

In this work, we examined the effect of the length of alkyl chain attached to the benzene ring on the self-assembling phenomena for a series of phenyl alcohol (PhA) derivatives, from phenylmethanol (benzyl alcohol) to 7-phenyl-1-heptanol, by means of X-Ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FTIR) spectroscopy, and Broadband Dielectric Spectroscopy (BDS) methods. XRD data in the reciprocal and real spaces showed a gradual increase in the local order with the elongation of the alkyl chain. However, the position and full width at half maximum of the main diffraction peak exhibited a non-systematic behavior. To better understand this fact, PhAs were subjected to FTIR spectroscopic studies. These investigations revealed that the association degree and the activation energy of dissociation increase as the alkyl chain length grows. On the other hand, BDS data showed a non-monotonic variation in the Kirkwood correlation factor with increasing length of the alkyl chain, indicating a competition between interactions of the non-polar and polar parts of the molecules in the studied PhAs. Finally, it was also found that the molar surface entropy for PhAs increases with the number of methylene groups, approaching values reported for alkanes, which indicates suppression of the surface order for PhAs with a long alkyl chain. This variability of the various parameters as a function of the length of the side chain shows that the interplay between soft interactions has a strong impact on the local structure and intra and intermolecular dynamics of the studied PhAs.

Dramatic slowing down of the conformational equilibrium in the silyl derivative of glucose in the vicinity of the glass transition temperature.

The vitrification process is usually preceded by a significant change (around 6-8 decades) in the viscosity, structural relaxation times, or diffusion that occurs in a relatively small range of temperatures in fragile liquids. Along with this phenomenon, conformations of the molecules vary as well. In fact, this process is studied in bulk polymers and high molecular weight materials deposited in the form of thin films. On the other hand, spatial rearrangement of small glass formers in the supercooled liquid state has not been intensively investigated, so far. Herein, data obtained from measurements carried out using various experimental techniques on supercooled 1,2,3,4,6-penta-O-(trimethylsilyl)-d-glucopyranose (S-GLU) have revealed that rotations of silyl moieties along with the deformation in the saccharide ring are significantly slowed down in the vicinity of the glass transition temperature (Tg). These intramolecular reorganizations affect the structural relaxation time, atomic pair distribution function, integrated intensity, as well as a number of bands and signals observed, respectively, in the Raman and NMR spectra. Data reported herein offer a better understanding of the conformational variation and time scale of this process in the complex and flexible molecules around the Tg.

Studying tautomerism in an important pharmaceutical glibenclamide confined in the thin nanometric layers.

The uniform thin films with variable thicknesses (d = 49, 120, 220 nm) of active pharmaceutical ingredient (API) glibenclamide (GCM) was spin-coated and investigated using broadband dielectric, grazing incident FTIR spectroscopies, atomic force microscopy, and ellipsometry. Data analysis revealed that nanoconfined systems consist of a mixture of amide and imidic acid forms of this pharmaceutical, wherein the ratios of both tautomeric forms in the thin films were different with respect to the molten supercooled bulk system. Moreover, changes in the populations of glibenclamide tautomers, i.e. higher amide to imides ratio in the spatially restricted API with respect to the bulk sample, had a strong impact on the character of the proton transfer reaction. In this context, the kinetic curves constructed on the base of infrared data for the bulk system follow the sigmoidal shape, characteristic for the autocatalytic reaction, while results obtained for the confined samples provide exponential character and indicate first-order transformation. This allows hypothesizing that the autocatalytic nature of the tautomerism in the bulk sample is most likely related to the formation of the amide tautomers which further catalyze the progress of imide-amide transformation. Our results are the first studies showing that the change in the thickness of the film may affect the properties and isomerization kinetics in a pharmaceutical systems. Finally, our data open a new perspective for developing new drug delivery systems.

Studying molecular dynamics of the slow, structural, and secondary relaxation processes in series of substituted ibuprofens.

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.

Unexpected Crossover in the kinetics of mutarotation in the supercooled region: the role of H-bonds.

Intra- and intermolecular studies on the molten L-sorbose have been carried out at variable temperature conditions to determine the crosover temperature (T c ). In addition, isothermal time-dependent FTIR and Raman measurements were performed to probe the pace of mutarotation and activation energy of this reaction in the studied saccharide, which varied from 53-62 kJ/mol up to 177-192 kJ/mol below and above T c , respectively. To explain the change in activation barrier for the mutarotation a complementary analysis using difference FTIR spectra collected around T c = 365 K in the hydroxyl region has been done. It was found that the alteration of kinetic parameters and molecular dynamics around T c are strictly related to the variation in the strength of H-bonds which above T c are significantly weaken, increasing the freedom of rotation of functional groups and movement of individual molecules. That phenomenon most likely affects the proton transfer, underlying molecular mechanism of mutarotation, which may lead to the significant increase in activation barrier. The new insight into a molecular aspect of the mutarotation around T c has created an opportunity to better understanding the relationship between physics of condensed matter and the potential role of H-bonds dynamics on the progress of the chemical reaction in highly viscous systems.

A study on the progress of mutarotation above and below the Tg and the relationship between constant rates and structural relaxation times.

Comprehensive FTIR studies on the progress of mutarotation in d-fructose mixed with maltitol have been carried out over a wide range of temperatures, both above and below the glass transition temperature Tg. In addition to the analysis of single bands, we have developed a completely new approach considering the full spectral range to follow the overall progress of the reaction. We have found that at the calorimetric Tg, there is a clear change in the temperature dependence of constant rates. The activation barrier for mutarotation changes from around 59 kJ mol-1 (the supercooled state) to around 249 kJ mol-1 (the glassy state). This dramatic variation in the activation barrier is consistent with the change in the mechanism of this specific chemical conversion, as theoretically considered by Wlodarczyk et al. [Phys. Chem. Chem. Phys., 2014, 16, 4694-4698]. Alternatively, it can also be connected to the change in the viscosity of the sample. Additionally, we investigated the relationship between constant rates (k) of mutarotation, structural relaxation times (τα), and dc conductivity (σdc) above and below the glass transition temperature. It was found that there was a linear correlation between all these quantities; they scale with various exponents changing at Tg. Our results also indicate that a single activation barrier might not be sufficient to describe the mutarotation process.

Ultrasonic processing of SbSI nanowires for their application to gas sensors.

Ultrasonic processing has been applied to create durable electrical contacts between antimony sulfoiodide (SbSI) nanowires and Au microelectrodes on glass substrate. After DC electric field alignment of SbSI nanowires between the microelectrodes, the sample was irradiated with ultrasound using chromium copper alloy sonotrode ended with silicon carbide (SiC) single crystal. The SEM and AFM investigations have showed that the ends of SbSI nanowires have been well compacted and bonded with microelectrodes. Ultrasonic processing has caused 420% increase of DC electric conductance of the junctions between Au microelectrodes and SbSI nanowires. The fabricated structures of SbSI nanowires bonded to Au microelectrodes are useful e.g. as nitrous oxide (N2O) gas sensors. These low power devices can operate at room temperature and do not require heating system for recovery.

Molecular dynamics, physical stability and solubility advantage from amorphous indapamide drug.

This study for the first time investigates physicochemical properties of amorphous indapamide drug (IND), which is a known diuretic agent commonly used in the treatment of hypertension. The solid-state properties of the vitrified, cryomilled and ball-milled IND samples were analyzed using X-ray powder diffraction (XRD), mass spectrometry, nuclear magnetic resonance (NMR), infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS). These analytical techniques enabled us (i) to confirm the purity of obtained amorphous samples, (ii) to describe the molecular mobility of IND in the liquid and glassy state, (iii) to determine the parameters describing the liquid-glass transition i.e. Tg and dynamic fragility, (iv) to test the chemical stability of amorphous IND in various temperature conditions and finally (v) to confirm the long-term physical stability of the amorphous samples. These studies were supplemented by density functional theory (DFT) calculations and apparent solubility studies of the amorphous IND in 0.1 M HCl, phosphate buffer (pH=6.8), and water (25 and 37 °C).

Structural characterization of rondorfite, calcium silica chlorine mineral containing magnesium in tetrahedral position [MgO4]6-, with the aid of the vibrational spectroscopies and fluorescence.

Raman and infrared spectra of rondorfite Ca8Mg(SiO4)4Cl2, a calcium chlorosilica mineral containing magnesium in tetrahedral position, has been studied in terms of spectra-structure relations. Raman spectra have been measured at different excited laser lines: 780 nm, 532 nm, 488 nm and 457 nm. This mineral is characterized by a single sharp intense Raman band at 863 cm(-1) assigned to the ν1 [SiO4]4- (Ag) symmetric stretching mode in the magnesiosilicate pentamer. Due to symmetry restriction the other Raman bands have a small intensity. Two Raman bands observed at 564 cm(-1) and 526 cm(-1) are associated simultaneously with ν4 [MgO4]6- and ν4 [SiO4]4- symmetric and antisymmetric modes where magnesium occurs in the tetrahedral configuration. The weak bands at 422 cm(-1) and 386 cm(-1) are associated with the ν2 bending mode of CaO6 in octahedral configuration, respectively. Moreover the infrared spectrum shows very weak bands associated with the hydroxyl group and/or water molecule. Additionally, the strong fluorescence phenomenon was observed and related to the presence of chlorine atoms, magnesium Mg2+ ions in atypical configuration or point defects.

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 ß-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 ß-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.

Do intermolecular interactions control crystallization abilities of glass-forming liquids?

Broadband dielectric spectroscopy was used to investigate molecular dynamics of three very similar systems: D-glucose, α-pentaacetylglucose, and ß-pentaacetylglucose in a wide range of temperatures. We found out that two latter systems (differing only in location of the acetyl group attached to the first carbon in the sugar ring) reveal completely opposite tendencies to crystallization. Therefore, the aim of this Article was to investigate in detail molecular dynamics of both pentaacetylglucoses to assess what are the underlying of different crystallization abilities of so closely related carbohydrates. To analyze the kinetics of crystallization, we used Avrami and Avramov approaches. Interestingly, we found out that both α-and ß-pentaacetylglucose exhibit completely different crystallization mechanisms. In the first case, the value of Avrami exponent was estimated to be n = 2, whereas for the second carbohydrate this exponent was equaled to n = 5.5. Additionally, we have carried out isothermal time-dependent dielectric measurements on D-glucose to demonstrate that this saccharide is more stable than its acetyl derivatives. Results presented in this Article indicate that besides molecular mobility, the character of the intermolecular interactions might also be another important factor governing crystallization process. Surprisingly, this issue is not often addressed during studies on crystallization abilities of different glass-formers. Finally, additional optical measurements were carried out to get more detailed information about nucleation density, activation barrier for a crystal growth, and morphology of crystallization structures.

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: ß 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.

Study of the amorphous glibenclamide drug: analysis of the molecular dynamics of quenched and cryomilled material.

Glibenclamide (GCM) is an oral hypoglycemic agent of the sulfonylurea group used in the treatment of non-insulin-dependent diabetes. Crystalline GCM is characterized by low bioavailability, which is attributed to its poor dissolution properties. It prompted us to prepare this drug in its amorphous form as a means to enhance its dissolution characteristics. Two different methods were used to convert crystalline GCM into the glassy form: quench-cooling of the melt and cryogenic milling. To monitor solid-state properties of the amorphous samples, X-ray powder diffraction (XRD), infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), ultraperformance liquid chromatography (UPLC) and spectroscopy, and broadband dielectric spectroscopy (BDS) were applied. The results of UPLC separations along with associated infrared and NMR measurements unambiguously showed that the thermal degradation of the quenched GCM, as suggested in literature reports, does not occur. A similar analysis performed on the cryomilled material also did not indicate any chemical decomposition. On the other hand, both methods confirmed that the conversion to the amorphous form is connected with the amide-imidic acid tautomerism of the examined drug. Moreover it was shown that this transformation occurs regardless of the manner of amorphization. Finally, dielectric spectroscopy was employed to study the molecular dynamics of vitrified GCM. The analysis of the ε''(f) in terms of the KWW function from the dielectric measurements revealed the existence of an "excess wing" attributed to the true Johari-Goldstein process based on Ngai's coupling model. The dielectric properties of GCM obtained in the amorphous form both by rapid cooling of the melt and the cryogenic grinding of crystalline sample were also compared.

Observation of the dynamics of clusters in D-glucose with the use of dielectric spectroscopy.

Dielectric and FTIR measurements were performed on d-glucose in its supercooled liquid phase. The data obtained revealed that apart from the structural relaxation. a much slower relaxation mode exists in the liquid phase of d-glucose. Analysis of the dielectric data showed that this new mode exhibits features characteristic of the cluster relaxation process, i.e. the exponential relaxation function, as well as the equilibration time which is much longer than the relaxation time. Therefore we attributed this process to the long range correlation of density fluctuations (LRCDF). We also show that above T = 370 K the dielectric strength of the cluster relaxation starts to decrease rapidly. However FTIR measurements indicated that at T = 366 K reorganization of the liquid structure occurs. Combined dielectric and FTIR data showed that above T = 366 K clusters become less stable and probably disintegrate. Moreover the splitting temperature T(s) = 387 K was determined from the dielectric data. Its value corresponds to the temperature T = 385 K at which the change of dynamics of the hydroxyl group (hydrogen bonds) is observed. It can be assumed that the change of dynamics of the d-glucose (at T(s)) is related to the temperature at which LRCDF vanishes. It should be added that to the best of our knowledge this is the first dielectric study on dynamics of clusters in carbohydrates. Moreover, due to our studies the relaxation map of monosaccharides seems now to be complete.

Broadband dielectric relaxation study at ambient and elevated pressure of molecular dynamics of pharmaceutical: indomethacin.

Broadband dielectric measurements on the pharmaceutical indomethacin (IMC) were performed at ambient and elevated pressure. Data on molecular dynamics collected at ambient pressure are in good agreement with that published in the literature. In the glassy state, there is a well-resolved secondary relaxation with Arrhenius activation energy E(a) = 38 kJ/mol. This commonly observed relaxation process (labeled gamma) is of intramolecular origin because it is pressure-insensitive. Closer analysis of the ambient pressure dielectric spectra obtained in the vicinity of the T(g) indicated the presence of one more secondary relaxation (beta), which is slower than that commonly observed. Application of the CM predictions enabled us to classify it as a true JG relaxation. Pressure measurements confirmed our supposition concerning the origins of the two secondary relaxations in IMC. Moreover, we have found that IMC under pressure does not crystallize, even at very high temperatures of T > or = 372 K. This finding was discussed in the framework of the two-order parameter model proposed by Tanaka (Konishi, T.; Tanaka, H. Phys. Rev B 2007, 76, 220201), as well as the JG relaxation proposal by Oguni (Hikima T.; Hanaya M.; Oguni M. J. Mol Struct. 1999, 479, 245). We also showed that the shape of the alpha-relaxation loss peak is the same when comparing dielectric spectra with the same tau(alpha) but obtained at ambient and elevated pressure. Additionally, we found out that the fragility of IMC decreases with increasing pressure. In addition, the pressure coefficient of the glass transition temperature, dT(g)/dP, was determined, and it is 255 K/GPa. Finally, we discuss the possibility of preparation of the amorphous state with higher density than by cooling of the liquid.

Influence of the solvent on ultrasonically produced SbSI nanowires.

The influence of the substitution of methanol in place of ethanol during the ultrasonic production of antimony sulfoiodide (SbSI) nanowires is presented. The new technology is faster and more efficient at temperatures greater than 314 K. The products were characterized by using techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), optical diffuse reflection spectroscopy (DRS) and IR spectroscopy. The coexistence of Pna2(1) (ferroelectric) and Pnam (paraelectric) phases at 298 K was observed in the SbSI nanowires produced in methanol. The methanol decomposes during the sonication or due to the adsorption process on SbSI nanowires.

Tannic acid-stabilized pericardium tissue: IR spectroscopy, atomic force microscopy, and dielectric spectroscopy investigations.

Infrared (IR) spectroscopy, atomic force microscopy (AFM), and dielectric spectroscopy methods were employed to study structural and dynamic changes in the tannic acid (TA)-stabilized pericardium tissue. Chemically stabilized pericardium tissue is widely used in construction of the tissue derived bioprostheses. IR spectra recorded in the range 400-4000 cm-1 allowed us to recognize different types of TA-collagen interactions. Formation of hydrogen bonds between amine as well as amide NH groups from collagen and hydroxyl groups of TA was analyzed. The AFM imaging showed that the stabilization procedure with TA introduces considerable changes in both surface topography and thickness of collagen fibrils as well as in fibril arrangement on the tissue surface. It was found, that these structural changes have an impact on the dielectric behavior of the TA-stabilized tissue. The dielectric spectra for the native and TA-stabilized tissues were measured in the frequency and temperature ranges of 10(-1) -10(7) Hz and 120-270 K, respectively. The dielectric spectra revealed the relaxation process due to orientation of bound water supplemented by the fluctuation of collagen polar side groups. At the temperatures above approximately 210 K, the relaxation due to ion migration process was observed. It was found that both relaxation processes were influenced by the TA-collagen interaction.

Atomic force microscopy and FT-IR spectroscopy investigations of human heart valves.

Human aortic, mitral, tricuspid and pulmonary heart valves were investigated by the contact mode atomic force microscopy (AFM) in air, and using FT-IR spectroscopy in the frequency range 950-4000 cm(-1). Heart valves were collected post mortem from 65-78 years old patients who died from non-cardiac diseases. All of the examined valves showed considerable heterogeneity in the surface topography of collagen fibrils as well as in their organization on the tissue surface. The AFM images revealed areas with significantly different spatial organization of the collagen fibril bundles. We observed zones with multidirectional, stacked collagen fibrils as well as areas of thin fibrils packed regularly, densely and "in phase". The majority of the collagen fibrils reproduced the typical transverse D-banding pattern, with the band interval varying in rather wide range of 70-90 nm. Using AFM imaging, objects that correspond to some pathological states of heart valves at their early stages, i.e. some forms of mineral deposits, were observed. The FT-IR spectra allowed us to recognize main components, i.e. collagen and elastin, in di.erent layers (ventricularis, fibrosa) of the valve leaflets as well as they gave also support for the presence of mineral deposits on the valve surface. The presented results showed, that the AFM imaging and FT-IR spectroscopy can be applied as a complementary methods for structural characterization of heart valves at the molecular and supramolecular levels.

Infrared study of orientational order parameters of a ferroelectric liquid crystal.

A method of determining the set of four order parameters S , D , P , and C for a ferroelectric liquid crystal, using complementary results for different sample geometries, is presented. IR measurements have been performed for homeotropic, planar heterogeneous and, planar homogenous sample geometries. Orientational order parameters were determined in two frames of reference to obtain complete information on molecular arrangement. Results for the D , P , and C parameters indicate the importance of both the intrinsic and extrinsic biaxialities. The molecular rotation around the long molecular axis is not free, and the carbonyl dipole and plane of the central phenyl ring are oriented close to the tilt plane. It has been found that transition dipole moments show significant correlations, antiparallel for longitudinal dipoles and parallel for transversal ones.