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The electronic absorption spectral characteristics of cycloimmonium ylids with a zwitterionic structure have been analyzed in forty-three solvents with different hydrogen bonding abilities. The two ylids lack fluorescence emission but are very dynamic in electronic absorption spectra. Using the maximum of the ICT band, the goal was to establish an accurate relationship between the shift of the ICT visible band and the solvent parameters and to estimate two of the descriptors of the first (the) excited state: the dipole moment and the polarizability. Two procedures were involved: the variational method and the relationships of the Abe model. The results indicate that the excited state dipole moment of the two methylids decreases in the absorption process in comparison with the ground state. The introduction of a correction term in the Abe model that neglects the intermolecular H-bonding interactions leads to a more accurate determination of the two descriptors. The strong solvatochromic response of both ylids has been further applied in distinguishing the solvents as a function of their specific parameters. Principal component analysis was applied to five selected properties, including the maximum of the charge transfer band. The results were further applied to discriminate several binary solvent mixtures. [ABSTRACT FROM AUTHOR]

Fluorescein sodium is a very important compound for a wide spectrum of applications, from which medical applications prevail. Despite this, there are very few studies in the literature related to the structure and fundamental properties of fluorescein sodium and its solutions, with most of the studies dealing with fluorescein. The purpose of the present article is to determine some parameters of the fluorescein sodium molecule approaching the quantum-mechanical modeling and experimental solvatochromism in both binary and ternary solutions. For data analysis, several theoretical models were applied. The results highlight the intermolecular interactions involved in the spectral shift of the electronic absorption band of fluorescein sodium when dissolved in different solvents or binary solvents and allowed the estimation of the difference between the interaction energy in molecular pairs of the type of fluorescein sodium − solvent 1 and fluorescein sodium − solvent 2. By applying a variational method, the dipole moment in the first excited state of the fluorescein sodium molecule and the angle between the dipole moments in the ground and excited states, respectively, were estimated. These results are useful for a better understanding of the behavior of fluorescein sodium when dissolved in different solvents or combinations of solvents, to develop new practical applications. [ABSTRACT FROM AUTHOR]

Investigation of chiroptical polymers in the solution phase is paramount for designing supramolecular architectures for photonic or biomedical devices. This work is devoted to the case study of poly(propylene oxide) (PPO) optical activity in several solvents: benzonitrile, carbon disulfide, chloroform, ethyl acetate, and p-dioxane. To attain information on the interactions in these systems, rheological testing was undertaken, showing distinct variations of the rheological parameters as a function of the solvent type. These aspects are also reflected in the refractive index dispersive behavior, from which linear and non-linear optical properties are extracted. To determine the circular birefringence and specific rotation of the PPO solutions, the alternative method of the channeled spectra was employed. The spectral data were correlated with the molecular modeling of the PPO structural unit in the selected solvents. Density functional theory (DFT) computational data indicated that the torsional potential energy—related to the O1-C2-C3-O4 dihedral angle from the polymer repeating unit—was hindered in solvation environments characterized by high polarity and the ability to interact via hydrogen bonding. This was in agreement with the optical characterization of the samples, which indicated a lower circular birefringence and specific rotation for the solutions of PPO in ethyl acetate and p-dioxane. Also, the shape of optical rotatory dispersion curves was slightly modified for PPO in these solvents compared with the other ones. [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate (PET) films are the subject of intensive research because of great interest in using them in applications, especially in medicine. From an optical point of view, PET films with a low degree of stretching can be considered uniaxial materials, for which the determination of the linear birefringence and its dispersion is very important. Two methods were applied here for the estimation of these parameters: the ellipsometric method and the channeled spectra method. The ellipsometric method uses monochromatic radiation; therefore, the linear birefringence of the PET films is determined for a given value of the radiation wavelength. The channeled spectra method allows for the estimation of the linear birefringence and its dispersion for a large range of wavelengths in the visible spectrum. A decrease in both parameters with the increase in the wavelength was recorded. To evidence the microstructure of PET films and the conformational changes induced by elongation and to evaluate the degree of orientation, a polarized infrared spectral study in attenuated total reflection (ATR-FTIR) mode was performed. The dichroic ratio (between the absorbance measured with linearly polarized radiation parallel and orthogonal relative to the stretching direction, respectively) and the ATR absorbance ratio for the machine direction (MD) and transversal direction (TD) configurations both for the stretched and unstretched PET samples were measured. [ABSTRACT FROM AUTHOR]

This article contains a comparative spectral analysis corroborated with the quantum mechanical computations of four cycloimmonium ylids. The spectral shift of the visible electronic absorption band of the studied molecules in 20 solvents with different empirical parameters is expressed by linear multi-parametric dependences that emphasize the intramolecular charge transfer (ICT) process. The nature of molecular interactions and their contribution to the spectral shift of the visible ICT band of solutes are also established in this manuscript. The results of the statistical analysis are used to estimate the cycloimmonium ylids' excited dipole moment by the variational method, using the hypothesis of McRae. The importance of the structure of both the heterocycle and carbanion substituents to the stability and reactivity of the studied cycloimmonium ylids is underlined by the quantum mechanical computations of the molecular descriptors. [ABSTRACT FROM AUTHOR]

The nature and strength of the molecular interactions were established by solvatochromic studies of 22 binary and 42 ternary diluted solutions of pyridinium–carbethoxy–anilidomethylid (PCAnM). The visible absorption band of PCAnM, due to an intramolecular charge transfer (ICT) from the carbanion towards the heterocycle, shows a great sensitivity to the solvent nature. The spectral data are analysed by linear energy relationship (LERS) and the contribution of each type of interaction to the total spectral shift is estimated. The results from the solvatochromic study and those obtained by quantum mechanical computations were correlated in order to estimate the excited state dipole moment of the studied methylid. The decrease of the dipole moment by excitation emphasized in this study corresponds to the ICT nature of the visible absorption band of the solute. The ternary solutions of PCAnM achieved in mixtures of water with primary alcohols (ethanol and methanol) show the dependence of the visible band on the molar fraction of water and give the difference between the interaction energies in molecular pairs of the type water–methylid and alcohol–methylid, computed based on the statistical cell model of ternary solutions. The decrease in strength of the hydrogen bond between PCAnM and the protic solvent molecules was estimated in the following order: water > methanol > ethanol. The results from this study can be utilized in Organic Chemistry to generate knowledge of the interactions with solvents when cycloimmonium methylids are used as precursors to obtain new heterocycles and also in Quantum Chemistry to obtain a better description of their excited electronic states. [ABSTRACT FROM AUTHOR]

Optical polymers are recognized for their high transparency, raised flexibility, low cost, and good film-forming ability; hence, they introduce a multitude of benefits in a wide range of devices, such as information storage, displays, optical communications, and filters. Among the optical properties, birefringence is an essential parameter in practical cases that demand the control of the state of polarization of light. This review is focused on describing some fundamental and applicative aspects concerning the optical birefringence of the polymer materials. First, elementary notions depicting the phenomenon of light double refraction in macromolecular media are provided. Furthermore, the most relevant optical techniques to determine birefringence are reviewed by highlighting the working principle and mathematical basis for computing this parameter. Then, a series of investigations of optically birefringent polymers are described, summarizing the most utilized approaches to induce light double refraction in such materials. The selected results are analyzed in relation to the pursued applications. In the end, the future of this scientific domain is briefly presented by establishing the research paths that need further exploration. Moreover, the novel directions that could be formulated and might contribute to certain considerable advancements in the materials employed in the modern optical technologies are mentioned. [ABSTRACT FROM AUTHOR]

The 1-dithiocarboxy-2-ethoxy-1-(isoquinolin-2-yl)-2-oxoethan-1-ylid (iQTCY) zwitterionic molecule has been studied by computational and spectral means in order to establish some of its structural parameters in the ground electronic state as well as the nature and the strength of its universal and specific interactions with different solvents. The prevalence of the orientation–induction interactions in the diluted solutions of iQTCY in aprotic solvents and the additional specific interactions by hydrogen bonds (HB) in the protic solvents were demonstrated. Three theoretical models were comparatively used to estimate the composition of the first solvation shell of the iQTCY molecule in ternary solutions. The difference between the interaction energies in molecular pairs solute–solvent was computed based on the statistical cell model of ternary solutions of iQTCY in mixtures of water–ethanol and water–methanol. Using the electro-optical parameters computed by the quantum-mechanical technique and the results of the solvatochromic study, the excited state dipole moment of iQTCY was estimated within the limit of the variational method applicable to molecules that show only an absorption electronic spectrum. [ABSTRACT FROM AUTHOR]

In a basic medium, 5-Mercapto-1,2,4-triazoles pass into the thiol form, allowing their transformation into sodium salts, which, in reaction with sodium monochloroacetate, lead to sodium 5-thioacetates of 1,2,4-triazoles-3,4-disubstituted. Sulfur derivatives converted to pivalic mixed anhydrides were used as active forms in the acylation of 6-amino penicillanic acid (6-AP) to obtain new semisynthetic penicillins. They contain in the molecule, together with the β-lactam ring, the nucleus 3-[(5-nitroindazol-1′-yl-methyl)]-4-aryl-5-mercapto-1,2,4-triazole, both contributing to an important antibacterial effect. The structure of the new antibiotics was confirmed by the results of elemental and spectral analysis (FT-IR, 1H- and 13C-NMR). The synthetic penicillins were tested for toxicological action and antibacterial activity and the obtained results were close to those for amoxicillin, the reference drug. [ABSTRACT FROM AUTHOR]

Four carbanion monosubstituted 4'-aryl-1,2,4-triazol-1-ium-4-R2-phenacylids, used as precursors in obtaining new heterocyclic compounds, and their corresponding derivatives belonging to the C2v point group of symmetry were studied by computational means in dimethylformamide (DMF) solutions compared with their isolated state. The changes in the computed parameters induced by the solvent compared with those of the isolated molecules were analyzed in this paper. The charge distribution and the molecular energies in the HOMO and LUMO, the electronic states responsible for the visible absorption band of 4'-aryl-1,2,4-triazol-1-ium-4-R2-phenacylids, in their isolated state and in solutions achieved in DMF were computed and compared with the visible electronic absorption spectra. The molecular descriptors of the studied compounds were computed, and the higher reactivity of the carbanion monosubstituted 4'-aryl-1,2,4-triazol-1-ium-4-R2-phenacylids compared with symmetric derivatives was established. The obtained results can help researchers to obtain new heterocycles with applications in the drug industry. [ABSTRACT FROM AUTHOR]

A simple method for determining the linear birefringence of the thin layers based on the determination of the orientation of the polarization ellipse of totally polarized light is proposed and it is applied to PVA thin foils. Theoretical notions and the experimental procedure are described. The linear birefringence of polymer thin foils with different degrees of stretching is determined and the applicability of the method is discussed. [ABSTRACT FROM AUTHOR]

Original results are presented in the field of research that addresses the extension of the reaction of residue of acyl-thiosemicarbazide fixation on the structure of 5-nitrobenzimidazole by a sulphonic group. The aim of the study is the increase of new thiosemicarbazide derivatives' applicative potential in the field of biochemistry, with a wide range of medical applications. The newly obtained compounds were characterized by using elemental analysis and spectral analysis (FT-IR and 1H NMR). A study regarding the optimization of the chemical reactions was made. The performed in vitro biological tests confirmed the tuberculostatic activity of three newly obtained compounds against Mycobacterium tuberculosis. [ABSTRACT FROM AUTHOR]

Four carbanion monosubstituted p-aryl-1,2,4-triazol-1-ium methylids are subjected to a comparative study between their spectral and quantum-mechanical parameters in order to obtain more information about their structural features in hydroxyl solvents as water and ethanol and also on the nature of electronic absorption transitions from the visible range. The quantum mechanical analysis, made by the Spartan'14 program, established a series of molecular parameters of the studied ylids important for their reactivity and for intermolecular interactions with hydroxyl liquids. An extensive solvatochromic study of 1,2,4-triazol-1-ium ylids is impossible due to their limited solubility in liquids. Binary solvent mixtures of water and ethanol with known solvent parameters from the literature were used for this study. The electronic absorption spectra in binary solvents water and ethanol were used to establish the influence of intermolecular interactions on the spectral characteristics of the studied methylids and also on the composition of their first solvation shell in ternary solutions. The difference between the interaction energies in molecular pairs ylid–water and ylid–ethanol was determined based on the statistical cell model applied to the ternary solutions of the type of ylid + water + ethanol. The obtained values are very small due to the hydroxylic nature of the two solvents. [ABSTRACT FROM AUTHOR]

Two 4-tolyl-1,2,4-triazol-1-ium methylids, namely 4-tolyl-1,2,4-triazol-1-ium-phenacylid and 4-tolyl-1,2,4-triazol-1-ium-4′-nitro-phenacylid, are studied from solvatochromic point of view in binary solvent mixtures of water with ethanol and water with methanol. The contributions (expressed in percent) of the universal and specific interactions are separated from the spectral shifts recorded in the visible range for each composition of the binary solvent mixture. The essential role of the orientation and induction interactions in the studied solutions was demonstrated. Based on the statistic cell model of the binary solvent mixture solutions, the difference between the formation energies of ylid-water and ylid-alcohol complexes is estimated. The composition of the ylid's first solvation shell was also established using the model of the binary solvent mixture solutions. The results obtained from the statistical cell model were compared with those obtained by using the Suppan's model, resulting a good agreement. [ABSTRACT FROM AUTHOR]

New di-(β-chloroethyl)-amides of some acids derived from 2-mercaptobenzoxazole were prepared by reaction of the corresponding pivalic mixed anhydrides with di-(β-chloroethyl)-amine. A study regarding the optimization of the chemical reactions was made for the case of di-(β-chloroethyl)-amines. The quantum chemical analysis by Spartan'14 was made in order to establish the most stable configuration of the ground electronic states for the obtained chemical structures and some physico-chemical parameters of N-mustards reported in this paper. Mercaptobenzoxazoles substituted in the side chain with the cytotoxic group show antitumor activity and they inhibit Ehrlich Ascites in an appreciable proportion compared to the drug I.O.B.-82, as our studies evidenced. [ABSTRACT FROM AUTHOR]

The results obtained both in quantum chemical computation and in solvatochromic study of pyridinium di-carbethoxy methylid (PCCM) are correlated in order to estimate the electric dipole moment in the excited state of this molecule. This estimation is made by a variational method in the hypothesis that the molecular polarizability does not change in time of the absorption process. Ternary solutions of PCCM in protic binary solvents are used here, both establishing the contribution of each type of interaction to the spectral shift and to characterize the composition of the first solvation shell of PCCM. Results are compared with those obtained before for other binary solvents. The difference between the interaction energies in molecular pairs of PCCM-active solvent and PCCM-less active solvent was also estimated based on the cell statistical model of the ternary solutions. [ABSTRACT FROM AUTHOR]

In this paper, poly(vinyl alcohol) (PVA) foils of comparable thickness were obtained by using 10 wt % PVA aqueous solutions exposed to microwave (MW) radiations for different times. The main goal of this paper is to identify the effects of MW irradiation on the induced optical birefringence of PVA stretched foils, since it is known that the changes in the chemical and physical properties of polymers induced by radiations can influence the asymmetry of their molecular structures from which the birefringence of polymers derives. The efficiency of the MW oven was estimated, and the contribution of sensible and latent heat and heat loss to the absorbed energy was discussed. The effects of MW irradiation, in terms of absorbed energy, were evidenced by using FTIR spectra analysis, contact angle measurements, scanning electron microscopy (SEM) images, and induced optical birefringence. The dehydration (cross-linking) of PVA in aqueous solution and the dependence of the anisotropy on the absorbed MW energy, stretching ratio, and the type of hydrogen bonds formed are discussed in this study. [ABSTRACT FROM AUTHOR]