Thermochemical Transition in Low Molecular Weight Substances: The Example of the Silybin Flavonoid.

Silybin is a complex organic molecule with high bioactivity, extracted from the plant Silybum. As a pharmaceutical substance, silybin's bioactivity has drawn considerable attention, while its other properties, e.g., thermodynamic properties and thermal stability, have been less studied. Silybin has been reported to exhibit a melting point, and values for its heat of fusion have been provided. In this work, differential scanning calorimetry, thermogravimetry including derivative thermogravimetry, infrared spectroscopy, and microscopy were used to provide evidence that silybin exhibits a thermochemical transition, i.e., softening occurring simultaneously with decomposition. Data from the available literature in combination with critical discussion of the results in a general framework suggest that thermochemical transition is a broad effect exhibited by various forms of matter (small molecules, macromolecules, natural, synthetic, organic, inorganic). The increased formation of hydrogen bonding contributes to this behavior through a dual influence: (a) inhibition of melting and (b) facilitation of decomposition due to weakening of chemical bonds.

Thermodynamics of the Glassy Polymer State: Equilibrium and Non-Equilibrium Aspects.

This work examines, first, the non-equilibrium character of the glassy state of polymer systems and its significance in the development of novel materials for important technological applications. Subsequently, it summarizes the essentials of the generalized lattice fluid approach for the description of this highly complex non-equilibrium behavior with an approximate and simple, yet analytically powerful formalism. The working equations are derived in a straightforward and consistent manner by clearly defining the universal and specific variables needed to describe the discussed properties. The role of the non-random distribution of molecular species and free volume in the glassy system is also examined, as is the role of strong specific interactions, such as hydrogen-bonding networks. This work also reports examples of applications in a variety of representative systems, including glass densification, retrograde vitrification, increase in glass-transition temperature in hydrogen-bonded polymer mixtures, and hysteresis phenomena in sorption-desorption from glassy polymer matrices.

Thermal Behavior of Poly(vinyl alcohol) in the Form of Physically Crosslinked Film.

Evaluation and understanding of the thermal behavior of polymers is crucial for many applications, e.g., polymer processing at relatively high temperatures, and for evaluating polymer-polymer miscibility. In this study, the differences in the thermal behavior of poly(vinyl alcohol) (PVA) raw powder and physically crosslinked films were investigated using various methods, such as thermogravimetric analysis (TGA) and derivative TGA (DTGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Various strategies were adopted, e.g., film casting from PVA solutions in H2O and D2O and heating of samples at carefully selected temperatures, in order to provide insights about the structure-properties relationship. It was found that the physically crosslinked PVA film presents an increased number of hydrogen bonds and increased thermal stability/slower decomposition rate compared to the PVA raw powder. This is also depicted in the estimated values of specific heat of thermochemical transition. The first thermochemical transition (glass transition) of PVA film, as for the raw powder, overlaps with mass loss from multiple origins. Evidence for minor decomposition that occurs along with impurities removal is presented. The overlapping of various effects (softening, decomposition, and evaporation of impurities) has led to confusion and apparent consistencies, e.g., from the XRD, it is derived that the film has decreased crystallinity, and apparently this is in agreement with the lower value of heat of fusion. However, the heat of fusion in this particular case has a questionable meaning.

Redefining solubility parameters: the partial solvation parameters.

The present work reconsiders a classical and universally accepted concept of physical chemistry, the solubility parameter. Based on the insight derived from modern quantum chemical calculations, a new definition of solubility parameter is proposed, which overcomes some of the inherent restrictions of the original definition and expands its range of applications. The original single solubility parameter is replaced by four partial solvation parameters reflecting the dispersion, the polar, the acidic and the basic character of the chemical compounds as expressed either in their pure state or in mixtures. Simple rules are adopted for the definition and calculation of these four parameters and their values are tabulated for a variety of common substances. In contrast, however, to the well known Hansen solubility parameters, their design and evaluation does not rely exclusively on the basic rule of "similarity matching" for solubility but it makes also use of the other basic rule of compatibility, namely, the rule of "complementarity matching". This complementarity matching becomes particularly operational with the sound definition of the acidic and basic components of the solvation parameter based on the third σ-moments of the screening charge distributions of the quantum mechanics-based COSMO-RS theory. The new definitions are made in a simple and straightforward manner, thus, preserving the strength and appeal of solubility parameter stemming from its simplicity. The new predictive method has been applied to a variety of solubility data for systems of pharmaceuticals and polymers. The results from quantum mechanics calculations are critically compared with the results from Abraham's acid/base descriptors.

Selective extraction of oxygenated compounds from oregano with sub-critical water.

BACKGROUND: The essential oil of oregano is composed of numerous substances that exhibit various properties (e.g. antioxidants). The innovative and promising method of extraction with sub-critical water (subcH2O) has been applied to the Greek oregano. RESULTS: The sub-critical water extraction experiments were performed at various conditions of pressure, temperature and water flow rate. Extracts collected at different extraction times were examined by gas chromatography. The oil has been processed by super-critical carbon dioxide (scCO2) followed by steam distillation or sub-critical water extraction. The conventional method of steam distillation was also performed. The main component of the plant is carvacrol. The favourable oxygenated compounds (carvacrol, thymol, borneol and thymoquinone) have been extracted preferentially and faster with sub-critical water. This method was selective for thymoquinone, which was not present in the oil from steam distillation. The oil yield obtained was much higher in the case of sub-critical water extraction compared to the one of super-critical carbon dioxide. The latter method resulted in oil with the highest concentration in carvacrol. CONCLUSION: Compared to the classical steam distillation, the sub-critical water extraction is superior in terms of higher yields, less energy consumption (as it was a faster process), and better composition/selectivity of the extracts controlled by the extraction parameters.

HPLC-DAD-MS analysis of dyes identified in textiles from Mount Athos.

Organic colorants contained in 30 textiles (16th to early 20th century) from the monastery of Simonos Petra (Mount Athos) have been investigated using high-performance liquid chromatography equipped with diode-array detection and mass spectrometry (HPLC-DAD-MS). The components of natural dyes identified in samples treated by the standard HCl dyestuff extraction method were: alizarin, apigenin, butein, carminic acid, chrysoeriol, dcII, dcIV, dcVII, ellagic acid, emodin, fisetin, flavokermesic acid, fustin, genistein, haematein derivative (Hae'), indigotin, indirubin, isoliquiritigenin, isorhamnetin, kaempferide, kaempferol, kermesic acid, luteolin, naringenin, purpurin, quercetin, rhamnazin, rhamnetin, sulfuretin, and type B and type C compounds (last two are markers for Caesalpinia trees). Early, semi-synthetic dyes, for example indigo carmine, fuchsin components, and rhodamine B were identified in objects dated late 19th to early 20th century. A dyestuff extraction method which involves use of TFA, instead of HCl, was applied to selected historical samples, showing that the mild method enables efficient extraction of weld (Reseda luteola L.) and dyer's broom (Genista tinctoria L.) glycosides. The marker compound (Hae') for logwood (Haematoxylum campechianum L.) identification after treatment with HCl was investigated by liquid chromatography coupled to mass spectrometry (LC-MS) in negative electrospray ionization (LC-MS-ESI(-)) mode. LC-MS in negative atmospheric pressure chemical ionization (LC-MS-APCI(-)) mode was used, probably for the first time, to investigate cochineal (Dactylopius coccus Costa) samples. Positive electrospray ionization (LC-MS-ESI(+)) mode was used for identification of fuchsin components. Detailed HPLC-DAD studies were performed on young fustic (Cotinus coggygria Scop.) and Persian berries (Rhamnus trees).

Equation-of-state modeling of mixtures with ionic liquids.

A non-electrolyte equation-of-state model was used to describe the phase behavior of binary systems containing alkyl-methyimidazolium bis(trifluoromethyl-sulfonyl)imide ionic liquids. A methodology is suggested for modeling this phase behavior by using the Non-Random Hydrogen-Bonding (NRHB) model. According to this methodology, the scaling constants of the ionic liquid are calculated using limited available experimental data on liquid densities and Hansen's solubility parameters, while all electrostatic interactions (polar, hydrogen bonding and ionic) are treated as strong specific interactions. Using the aforementioned methodology, the model is applied to describe the vapor-liquid and the liquid-liquid equilibria in mixtures of ionic liquids with various polar or quadrupolar solvents at low and high pressures. In all cases, one temperature-independent binary interaction parameter was used. Accurate correlations were obtained for the majority of the systems, both, for vapor-liquid and liquid-liquid equilibria.

Partial Solvation Parameters of Drugs as a New Thermodynamic Tool for Pharmaceutics.

Partial solvation parameters (PSP) have much in common with the Hansen solubility parameter or with a linear solvation energy relationship (LSER), but there are advantages based on the sound thermodynamic basis. It is, therefore, surprising that PSP has so far not been harnessed in pharmaceutics for the selection of excipients or property estimation of formulations and their components. This work introduces PSP calculation for drugs, where the raw data were obtained from inverse gas chromatography. It was shown that only a few probe gases were needed to get reasonable estimates of the drug PSPs. Interestingly, an alternative calculation of LSER parameters in silico did not reflect the experimentally obtained activity coefficients for all probe gases as well, which was attributed to the complexity of the drug structures. The experimental PSPs were proven to be helpful in predicting drug solubility in various solvents and the PSP framework allowed calculation of the different surface energy contributions. A specific benefit of PSP is that parameters can be readily converted to either classical solubility or LSER parameters. Therefore, PSP is not just about a new definition of solvatochromic parameters, but the underlying thermodynamics provides a unified approach, which holds much promise for broad applications in pharmaceutics.

Fractionation of a hydrocolloid emulsifier reclaimed from winery waste.

Complex hydrocolloids have been isolated and fractionated using a consecutive elution process, starting from winery waste. These extracts consist mainly of polysaccharidic populations and of smaller protein molecules and they exhibit emulsifying, thickening and texture-modifying activity. This work is a systematic study of these individual populations, as fractionated with preparative size exclusion chromatography (Prep-SEC) in terms of their chemical identity, surface properties, and emulsification behavior. The fractions have been characterized via SEC-MALLS, FTIR, DLS, zeta potential, and interfacial tension measurements. The results highlight the antagonistic and synergistic effects of the individual components of the above-mentioned complex natural material (winery waste extract) towards its emulsifying behavior, and provide a model for the kinetics of the evolution of a Pickering interfacial layer.

Synthesis of caffeic acid and p-hydroxybenzoic acid molecularly imprinted polymers and their application for the selective extraction of polyphenols from olive mill waste waters.

Using caffeic acid and p-hydroxybenzoic acid as templates, two molecularly imprinted polymers (MIPs) were prepared that were used for isolation of polyphenols from olive mill waste water samples (OMWWs) without previous pre-treatment. For the preparation of the caffeic acid MIPs 4-vinylpyridine, allylurea, allylaniline and methacrylic acid were tested as functional monomers, ethylene glycol dimethylacrylate (EDMA), pentaerythritol trimethylacrylate (PETRA) and divinylbenzene 80 (DVB80) as cross-linkers and tetrahydrofuran as porogen. For p-hydroxybenzoic acid 4-vinylpyridine, allylurea and allylaniline were tested as functional monomers, EDMA and PETRA as cross-linkers and acetonitrile as porogen. The performance of the synthesized polymers was evaluated against seven structurally related compounds by means of polymer-based HPLC. The two polymers that presented the most interesting properties were further evaluated by batch rebinding and from the derived isotherms their capacity and binding strength were determined. Using solid-phase extraction (SPE), their ability to recognize and bind the template molecule from an aqueous solution as well as the pH dependence of the binding strength were explored. After establishing the best SPE protocol, an aqueous model mixture of compounds and a raw OMWWs sample were loaded on the two best polymers. The result of the consecutive use of the two polymers on the same sample was explored. It was concluded that acidic conditions favour the recognition abilities of both polymers and that they can be used for a quick and efficient isolation of the polyphenol fraction directly from raw OMWW.

Biodegradable polymer nanocomposites: the role of nanoclays on the thermomechanical characteristics and the electrospun fibrous structure.

Polymer nanocomposites, based on poly(e-caprolactone) (PCL) and organically modified montmorillonite, were prepared by the solution intercalation technique. The thermal stability of the prepared materials was analyzed by thermogravimetric analysis. Investigation of their mechanical properties revealed that incorporation of the high aspect ratio montmorillonite sheets into the matrix significantly enhanced the polymer stiffness without sacrificing its ductility. Fibrous membranes of neat and nanocomposite PCL were fabricated by electrospinning. The effect of the applied voltage, the solution concentration and the clay content of the nanocomposite materials on the final fibrous structure was investigated. The results showed that the introduction of the inorganic filler and the increase in the applied voltage from 7.5 to 15 kV facilitated the formation of fine fibers with fewer bead defects. The presence of nanoclay resulted in narrower fiber size distributions, although the mean fiber diameter was not significantly altered. The increase in the solution concentration led to the formation of more uniform fiber structures and to a slight increase in the mean fiber diameter. Furthermore, the electrospinning process affected significantly the structure of the nanocomposite material by increasing the interlayer spacing of the inorganic mineral.

Enhanced adsorption of phenolic compounds, commonly encountered in olive mill wastewaters, on olive husk derived activated carbons.

Olive husk was used for the preparation of activated carbon by chemical activation with KOH. The effects of carbonization and activation time on carbon properties were evaluated. The surface area of the produced carbons was measured by means of N(2) adsorption at 77K. The carbons with the highest surface area were further characterized by means of elemental analysis, particle size measurement, Boehm titration, zeta potential measurement, and temperature programmed desorption (TPD). Subsequently they were used for adsorption of a mixture of polyphenols consisting of caffeic acid, vanillin, vanillic acid, pi-hydroxybenzoic acid and gallic acid at two temperatures, and their adsorptive capacity was compared to a commercial carbon Acticarbon CX and found to be higher enough. The role of the porosity and surface groups are discussed in relation to the adsorption forces and the properties of the adsorbed substances. A thermodynamic interpretation of the results is also attempted.

Investigation of the Cross-Section Stratifications of Icons Using Micro-Raman and Micro-Fourier Transform Infrared (FT-IR) Spectroscopy.

The cross-section stratifications of samples, which were removed from six icons, are studied using optical microscopy, micro-Raman spectroscopy, and micro-Fourier transform infrared (FT-IR) spectroscopy. The icons, dated from the 14th to 19th centuries, are prominent examples of Byzantine painting art and are attributed to different artistic workshops of ​​northern Greece. The following materials are identified in the cross-sections of the icon samples using micro-Raman spectroscopy: anhydrite; calcite; carbon black; chrome yellow; cinnabar; gypsum; lead white; minium; orpiment; Prussian blue; red ochre; yellow ochre; and a paint of organic origin which can be either indigo ( Indigofera tinctoria L. and others) or woad ( Isatis tinctoria L.). The same samples are investigated using micro-FT-IR which leads to the following identifications: calcite; calcium oxalates; chrome yellow; gypsum; kaolinite; lead carboxylates; lead sulfate (or quartz); lead white; oil; protein; Prussian blue; saponified oil; shellac; silica; and tree resin. The study of the cross-sections of the icon samples reveals the combinations of the aforementioned inorganic and organic materials. Although the icons span over a long period of six centuries, the same stratification comprising gypsum ground layer, paint layers prepared by modified "egg tempera" techniques (proteinaceous materials mixed with oil and resins), and varnish layer is revealed in the investigated samples. Moreover, the presence of three layers of varnishes, one at the top and other two as intermediate layers, in the cross-section analysis of a sample from Virgin and Child provide evidence of later interventions.

Dimerization of Carboxylic Acids: An Equation of State Approach.

The association term of the nonrandom hydrogen bonding theory, which is an equation of state model, is extended to describe the dimerization of carboxylic acids in binary mixtures with inert solvents and in systems of two different acids. Subsequently, the model is applied to describe the excess enthalpies and the vapor-liquid equilibrium of relevant binary mixtures containing low molecular weight organic acids. The model sheds light on the interplay of intermolecular interactions through the calculation of the various contributions to the mixing enthalpies, namely from hydrogen bonding and non-hydrogen bonding (dipolar, induced polar or dispersive) interactions. According to model predictions, the acid molecules are so strongly associated that the addition of inert solvents to carboxylic acids with small carbon numbers at ambient temperature does not dramatically alter their degree of association. Consequently, the observed endothermic dissolution process is mainly attributed to the hindering of polar interactions. Furthermore, upon mixing of two carboxylic acids, the rearrangement of hydrogen bonds due to the formation of cross associating species results in an insignificant contribution to the heats of mixing due to the rather constant dimerization enthalpy that is revealed by the available experimental data for low molecular weight compounds.

Interfacial tension and interfacial profiles: an equation-of-state approach.

A quasi-thermodynamic approach of inhomogeneous systems is used for modeling the fluid-fluid interface. It is based on the recently introduced QCHB (quasi-chemical hydrogen bonding) equation-of-state model of fluids and their mixtures, which is used for the estimation of the Helmholtz free energy density difference, Deltapsi(0), between the system with interface and another system of the same constitution but without interface. Consistent expressions for the interfacial tension and interfacial profiles for various properties are presented. The interfacial tension is proportional to the integral of Deltapsi(0) along the full height of the system, the proportionality constant being equal to 1, when no density gradient contributions are taken into consideration, 2, when the Cahn-Hilliard approximation is adopted, and 4, when the full density gradient contributions are taken into consideration. A satisfactory agreement is obtained between experimental and calculated surface tensions. Extension of the approach to mixtures is examined along with the associated problems for the numerical calculations of the interfacial profiles. A new equation is derived for the chemical potentials in the interfacial region, which facilitates very much the calculation of the composition profiles across the interface.

Assessment of the thermodynamic properties of poly(2,2,2-trifluoroethyl methacrylate) by inverse gas chromatography.

The thermodynamic properties of poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) were determined by the aid of the inverse gas chromatography technique (IGC), at infinite dilution. The interactions between the polymer and 15 solvents were examined in the temperature range of 120-150 °C via the estimation of the thermodynamic sorption parameters, the parameters of mixing at infinite dilution, the weight fraction activity coefficients and the Flory-Huggins interaction parameters. Additionally, the total and the partial solubility parameters of PTFEMA were estimated. The findings of this work indicate that the type and strength of the intermolecular interactions between the polymer and the solvents are strongly depended on the functional groups of the polymer and the solvents. The proton acceptor character of the polymer is responsible for the preferential solubility of PTFEMA in chloroform which acts as a proton donor solvent. The results also reveal that the polymer is insoluble in alkanes and alcohols whereas it presents good miscibility with polar solvents, especially with 2-butanone, 2-pentanone and 1,4-dioxane. Furthermore, the total and dispersive solubility parameters appear diminishing upon temperature rise, whereas the opposite behavior is noticed for the polar and hydrogen bonding solubility parameters. The latter increase with temperature, probably, due to conformational changes of the polymer on the solid support. Finally, comparison of the solubilization profiles of fluorinated methacrylic polymers studied by IGC, leads to the conclusion that PTFEMA is more soluble compared to polymers with higher fluorine content.

Partial solvation parameters and mixture thermodynamics.

The recently introduced partial solvation parameters (PSPs) are molecular descriptors that combine elements from quantum mechanics with the QSPR/LSER/solvatochromic and solubility parameter approaches. Basic regularities and universalities exhibited by PSPs are examined in this work and the concepts of homosolvation, heterosolvation and solvation energy density are quantified. A simple consistent thermodynamic framework is developed, through which the validity of the PSP approach is tested. The predictions are compared with experimental phase equilibrium data that span the full composition range from the pure fluid state to infinite dilution. They include vapor-liquid equilibria of fluids interacting with strong specific forces, dissolution of solids/liquids in various solvents and probe/oligomer or probe/polymer interactions as typically determined by inverse gas-chromatography. These applications show the potential of the PSP approach not only to reasonably predict a variety of properties of classes of complex systems but, also, to shed light to challenging aspects of intermolecular interactions. The perspectives of this unified approach to solution thermodynamics are discussed.

Inverse gas chromatography and partial solvation parameters.

Inverse gas chromatography (IGC) is widely used for the characterization of polymers and surfaces. The present work describes a novel method for this characterization through the recently introduced partial solvation parameters (PSPs). PSPs are molecular descriptors that combine elements from Quantum Mechanics with the QSPR/LSER/solvatochromic and solubility parameter approaches. A simple coherent thermodynamic framework is presented, through which IGC experimental measurements are used to determine the dispersion, polarizability, and Lewis acid/base interactions of the studied polymers and surfaces. The role or usefulness of various classes of probes for this characterization is critically examined. Emphasis is given on the hydrogen-bonding features of polymers and on the way IGC may be used to extract reliable information on hydrogen-bond formation constants and on the related energy-, entropy-, and free-energy changes. The new method has been used for the characterization of a number of common polymers and one hyperbranched structure. Extension to materials surface characterization, determination of partial surface tensions, and other perspectives of the new method are discussed. The new approach establishes a thermodynamically consistent, coherent, and straightforward method for the integral characterization of polymers as regards their cohesion (partial solubility parameters), solvation (partial solvation parameters), and surface (partial surface tensions) features.

A new expanded solubility parameter approach.

The partial or Hansen solubility parameters (HSP) are important properties of the various substances and very useful tools for the selection of their solvents or the prediction of their behaviour in numerous applications. Their design and evaluation relies on the basic rule of "similarity matching" for solubility. The present work attempts to enhance the capacity of HSPs by incorporating into their evaluation the other basic rule of solubility, namely, the rule of "complementarity matching". This is done in a simple and straightforward manner by splitting the hydrogen bonding HSP into its acidic or proton donor component and its basic or proton acceptor one. The splitting is based on the third σ-moments of the screening charge distributions or sigma profiles of the quantum-mechanics based COSMO-RS theory. The whole development and application does not involve any sophisticated calculations or any strong specific background. The new method has been applied to a variety of solubility data for systems of pharmaceutical interest in order to verify the significant improvement over the classical HSP approach. The application of the new method requires, of course, the knowledge of the HSPs. For this reason, in Appendix A is presented an updated version of a robust and reliable group-contribution method for the calculation of the HSPs. The key features of this combined tool are critically discussed.

Thermodynamic characterization of poly(1,1,1,3,3,3-hexafluoroisopropyl methacrylate) by inverse gas chromatography.

The thermodynamic characterization of a fluorinated methacrylic homopolymer was conducted by means of inverse gas chromatography (IGC) at infinite dilution. The polymer under study, poly(1,1,1,3,3,3-hexafluoroisopropyl methacrylate) (PHFIMA) was synthesized via a free radical polymerization reaction and was properly characterized prior to IGC measurements. The IGC characterization encompassed the calculation of the thermodynamic sorption parameters, the parameters of mixing at infinite dilution, the weight fraction activity coefficients and the Flory-Huggins interaction parameters of 15 probes. Moreover, the total and partial solubility parameters of the polymer were determined. The impact of the temperature and the chemical nature of the probes on the aforementioned thermodynamic parameters are discussed. Results demonstrate that PHFIMA is insoluble in almost every tested solvent, with the exception of chloroform, due to its proton donor character which is favorable for the formation of hydrogen bonds with the fluorine groups and the oxygen atoms of the carbonyl groups (proton acceptors) of the polymer. Furthermore, the total and dispersive solubility parameters descend in a linear manner with the increase of temperature, whereas the polar and hydrogen bonding solubility parameters increase when temperature rises, probably due to the conformational changes of the polymer on the solid support.