New Insights on Solvent-Induced Changes in Refractivity and Specific Rotation of Poly(propylene oxide) Systems Extracted from Channeled Spectra.

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.

Optical Anisotropy of Polyethylene Terephthalate Films Characterized by Spectral Means.

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.

Review on Optical Methods Used to Characterize the Linear Birefringence of Polymer Materials for Various Applications.

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.

New Semisynthetic Penicillins Obtained by Coupling of the 6-Aminopenicillanic Acid with 5-Mercapto-1,2,4-triazoles-3,4-disubstituted.

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 ß-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.

Birefringence of Thin Uniaxial Polymer Films Estimated Using the Light Polarization Ellipse.

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.

Optimized Synthesis of New Thiosemicarbazide Derivatives with Tuberculostatic Activity.

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.

Solvatochromic Study of Two Carbanion Monosubstituted 4-Tolyl-1,2,4-triazol-1-ium Phenacylids in Binary Hydroxyl Solvent Mixtures.

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.

Optimized Synthesis of New N-Mustards Based on 2-Mercaptobenzoxazole Derivatives with Antitumor Activity.

New di-(ß-chloroethyl)-amides of some acids derived from 2-mercaptobenzoxazole were prepared by reaction of the corresponding pivalic mixed anhydrides with di-(ß-chloroethyl)-amine. A study regarding the optimization of the chemical reactions was made for the case of di-(ß-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.

Anisotropy of Thin Foils Obtained from Microwave-Irradiated Poly(Vinyl Alcohol) Aqueous Solutions.

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.

Specific and universal interactions in Benzo-[f]-Quinolinium Acetyl-Benzoyl Methylid (BQABM) solutions; excited state dipole moment of BQABM.

The zwitterionic molecule Benzo-[f]-Quinolinium Acetyl Benzoyl Methylid (BQABM) is studied in this paper from quantum mechanical and solvatochromic point of view. The nature and contribution of each type of intermolecular interaction to the spectral shifts in different solvents were estimated based on solvatochromic analyze of BQABM visible absorption band. The correlation coefficients for the dependence of the wavenumber in the maximum of BQABM visible band vs. the solvent parameters were computed by Linear Energy Relationships Simulation (LERS). The optimized geometry of BQABM and some physical and chemical parameters for isolated molecule in its ground electronic state were obtained with Spartan'14 programs. The results obtained in quantum mechanical analysis and also LERS correlation coefficients were used to determine the excited state dipole moment of BQABM by a Variational method in McRae and Kawschi hypothesis that the molecular polarizability does not change in the visible absorption process. An increase in the BQABM electric dipole moment by excitation resulted in our study.

Computational and solvatochromic study of pyridinium-acetyl-benzoyl-methylid (PABM).

Pyridinium-acetyl-benzoyl-methylid is a cycloimmonium ylid studied here from structural and spectral point of view. Quantum mechanical analysis offers information about the most stable spatial structure, the electro-optical properties in the ground electronic state as well as the QSAR parameters of PABM. The solvatochromic study of the visible absorption band of PABM was made in order to establish the electro-optical features of the ylid in the excited electronic state and also to approximate the contribution of different types of intermolecular interactions in solutions with different solvents. The ternary solutions of PABM were used to estimate the difference between the interaction energies in molecular pairs of the types: ylid-inactive solvent and ylid-active solvent from interaction point of view.

Spectral study of specific interactions between zwitterionic compounds and protic solvents.

The zwitterionic compounds, like ylids, can interact both by universal and specific forces with the protic solvents. Ylids have a visible electronic absorption band with intramolecular charge transfer (ICT), very sensitive to the solvent nature and considered as an indicator of their stability. Two zwitterionic compounds: pyridinium dicarbethoxy methylid and iso-quinolinium dicarbethoxy methylid were studied from solvatochromic point of view and the contribution of solute-solvent specific interactions to the total spectral shift of the visible ICT band was established. Ternary solutions of the studied ylids were used to estimate the difference of interaction energies in molecular pairs ylid-protic solvent and ylid-aprotic solvent in the limits of the cell model of three component solutions.

Solvent scales used to study the intermolecular interactions in binary solutions of two p-aryl-pyridazinium methylids.

The visible electronic absorption band with intramolecular charge transfer of two pyridazinium ylids having common carbanion and different heterocycles is recorded in solutions and its position is correlated to parameters of some empirical scales of solvents. The nature of the intermolecular interactions in pyridazinium ylid solutions is discussed and the supply of each type of interaction is established based on solvatochromic study.

About intermolecular interactions in binary and ternary solutions of some azo-benzene derivatives.

The nature and strength of the intermolecular interactions in the solutions of three azo-benzene derivatives (ADi, i=1, 2, 3) were established by solvatochromic effects in solvents with different electric permittivities, refractive indices and Kamlet-Taft constants. A quantum mechanical analysis corroborated with spectral data offered information about the excited state dipole moments and polarizabilities of the studied compounds. The separation of the supply of universal and specific interactions to the total spectral shift was made based on the regression coefficients from the equations describing the solvatochromic effect. Supplementary information about the composition of the first solvation shell and the energy in the solute-solvent molecular pairs were obtained analyzing the ternary solutions of ADi, i=1, 2, 3 compounds in solvent mixture Methanol (M)+n-Hexane (H).

New method to determine the optical rotatory dispersion of inorganic crystals applied to some samples of Carpathian Quartz.

A new method to determine the optical rotatory dispersion (ORD) in the visible range, based on a channeled spectrum obtained with a uniax inorganic crystal introduced between two crossed polarizers with its optical axis parallel to the light propagation direction is detailed in this paper. When the studied inorganic crystals are transparent, this method permits the estimation of the optical rotatory dispersion in the visible range, for which the cheap polarizers are available. The speed of the measurements is very high, because the estimations are made from the channeled spectrum obtained for a single arrangement of the optical components. By using a computer, ORD is quickly determined for the visible range. The results obtained by this method for some Carpathian Quartz samples are consistent with those from literature. The proposed method can be also applied in UV and IR spectral ranges, when the anisotropic layers are transparent and the linearly polarized radiations can be obtained.

Intermolecular interactions in binary and ternary solutions of two cycloimmonium-carboethoxy-anilido-methylids.

Two cycloimmonium ylids with pyridinium and iso-quinolinium as heterocycle and having common carbanion were studied from the point of view of the solvent influence on electronic absorption spectra in binary and ternary solutions. The supplies of the universal and specific interactions to the spectral shifts in the electronic absorption spectra of hydroxyl solutions were separated. The strength of the specific interactions of the ylid molecules with octanol was estimated by using ternary solutions in binary solvent Octanol+Dichloroethane, in which the universal interactions have similar strengths. Quantum mechanical calculations and also the solvatochromic effect allowed us estimating the values of the molecular dipole moments in the excited state of the studied ylids. The conclusions showed that by excitation the molecular dipole moment of the studied ylids decreases or changes its sense, due to the electronic charge transport from the carbanion towards the heterocycle.

Computational and spectral studies of 1,6-diphenyl-1,3,5-hexatriene (DPH) multicomponent solutions.

The multicomponent 1,6-diphenyl-1,3,5-hexatriene+tetrahydrofuran+water+ethanol (DPH+THF+W+E) solutions with variable content in water were studied by computational and spectral means. The computational results that indicate micelle formation in multicomponent solutions at high water content were correlated by the independence of the wavenumber in the maximum of the fluorescence on the solvent composition.

Solvent influence on the electronic absorption spectra (EAS) of 1,6-diphenyl-1,3,5-hexatriene (DPH).

The electronic absorption spectra of 1,6-diphenyl-1,3,5-hexatriene (DPH) were recorded in a great number of solvents with various physico-chemical properties. The dependence of the wavenumber in the maximum of the DPH vibronic bands on the solvent dispersion function demonstrates the prevalence of the dispersion interactions in the studied solutions. Some electro-optical parameters of DPH molecule were computed by HyperChem and were correlated with the results obtained from the solvatochromic effects on DPH. The polarizability in the electronic excited state of DPH has been estimated from the solvatochromic effect.

Birefringence and dichroism of poly(vinyl-alcohol) foils containing phthalazinium ylids.

Pure and colored with phthalazinium ylids poly(vinyl-alcohol) (PVA) foils were stretched under gentile heating. The birefringence of the thin foils was determined with a Babinet compensator standardized for yellow radiation of a Sodium lamp. The determined birefringence of the colored PVA foils is higher than that of the pure PVA foils. This fact indicates that the phthalazinium ylids facilitate the increase in the anisotropy of the stretched foils. The visible absorption electronic band of phthalazinium ylids was used to estimate the dichroic ratio and the degree of order of the ylid molecules in the stretched PVA foils. An increase in dichroism and birefringence with the degree of stretching has been evidenced for uncolored and colored PVA foils.