Experimental and Computational Study of Novel Pyrazole Azo Dyes as Colored Materials for Light Color Paints

This paper presents the synthesis of eight new pyrazole azo dyes using ethyl 5-amino-3-methyl-1H-pyrazole-4-carboxylate as the diazotization component and various active methylene derivatives as coupling components. These new azo dyes were characterized by spectroscopic (FT-IR, UV-VIS), and spectrometric (¹H NMR, ¹³C NMR, MS) analyses. The dye structures were modeled by the MMFF94s force field and quantum chemical density functional theory (DFT) calculations using the B3LYP functional and the 6-311G(d,p) basis set, in the gas phase. Weak electrostatic hydrogen bonds for the azo and hydrazo dye tautomers were found in the ground state. The CIS, TD (using the B3LYP and M06-2X functionals), and ZINDO methods were used to estimate the dye UV-VIS spectra in ethanol, which were compared with the experimental ones. The anti-configuration arrangement of the π-bonds and the presence of the prevalent hydrazo dye tautomer were supported by the computed ¹H NMR and ¹³C NMR spectra. A good accordance between the experimental and predicted absorption maxima and chemical shifts was observed. Color investigations using the CIEL*a*b* space were conducted for all dyes in powder and for their mixtures in water-based acrylic resins. The results confirm the newly synthesized dyes' color properties and that they might be used for light color paints in the varnishes industry.

High pressure Raman investigation on trans-urocanic acid

Trans-urocanic acid (t-UCA) is an important epidermal UV protector predominantly found in human skin. Exposure of UV radiation triggers photoisomerization of t-UCA into its other conformer, cis-urocanic acid (cis-UCA), which has been shown to be a mediator of UV-induced immune-suppression leading to skin cancer. In this report, we present the investigation of molecular changes of t-UCA under high pressures by in-situ high pressure Raman spectroscopy. The study indicates onset of ring opening polymerization of t-UCA at pressure above 1.4 GPa. At pressures beyond 5 GPa, a well discernible characteristic vibrational mode (CC stretch) accompanied by several other spectral features such as δ CO₂^- and δ NH modes of cis-UCA point towards the isomerization of residual t-UCA monomers into cis-UCA. The content of cis-UCA gradually increased with increase in pressure. On release to ambient conditions, the spectrum of the quenched sample showed Raman modes of polymer and cis-UCA indicating that the changes are irreversible.

Vibrational and conformational analysis of structural phase transition in Estradiol 17β valerate with temperature

Estradiol 17β valerate (E2V) is a hormonal medicine widely used in hormone replacement therapy. E2V undergoes a reversible isosymmetric structural phase transition at low temperature (̴ 250 K) which results from the reorientation of the valerate chain. The reversible isosymmetric structural phase transition follows Ehrenfest's classification when described as first-order and Buerger's classification when classified as order-disorder. The conformational difference also induces changes in molecular torsional angles and on the hydrogen bond pattern. In combination with density functional theory (DFT) calculations, vibrational spectroscopy has been used to correlate the valerate chain modes with the modifications of the dihedral angles on phase transition. We are expecting improvement in our understanding of the phase transition mechanism driven by the temperature. The Conformational analysis reveals the feasible structures corresponding to changes in the dihedral angles associated with the valerate chain. The infrared spectra of calculated conformers are in good agreement with the experimental spectra of E2V structure recorded at room temperature revealing that the changes in valerate chain modes at 1115 cm^-1, 1200 cm^-1and 1415 cm^-1 fingerprint the molecular conformation. An investigation made to determine the ligand-protein interaction of E2V through docking against estrogen receptor (ER) reveals the inhibitive and agonist nature of E2V.

Phase transition-induced changes in the Raman properties of DMSO/benzene binary systems

The Raman spectra of dimethylsulfoxide (DMSO)/benzene binary mixtures were studied by decreasing the temperature from 333 K to 263 K with the aim to reveal the molecular interaction properties during phase transition. The intensity of the Raman band for benzene at 992 cm-1 showed an increasing trend in the liquid and solid phases, while it exhibited a highly decreasing trend during the liquid-solid phase transition. The potential energy was calculated to study the effect of intermolecular interaction distance between DMSO and benzene on Raman intensity. The observations indicated that the blueshift of the low-frequency bands of DMSO was significantly different from the redshift of its high-frequency bands. The hydrogen bond generated between DMSO and benzene was well formed in the binary systems. This interaction inducing an enhanced hydrogen bond between the binary systems and attenuated C-H bonds led to opposite Raman shift variations with decreasing temperature. The Raman bands of DMSO at 1425 cm-1, 2899 cm-1, and 2992 cm-1 each split into two peaks after phase transition. The splitting of the Raman bands of DMSO at 1417 cm-1, 2895 cm-1, and 2982 cm-1 cropped up as the temperature dropped to the transformation point of 288 K. This is attributed to the phase transition-induced latent def.(C7) atomic vibrations corresponding to the individual methyl groups of DMSO. The implications of these analyses are expected to be helpful to understand the effect of phase transition on the Raman properties of binary solutions.

The structural properties of a ZnCl2-ethylene glycol binary system and the peculiarities at the eutectic composition

ATR-FTIR spectroscopy was performed on a series of ZnCl2-ethylene glycol (EG) mixtures with a wide-range of compositions (1 : 1.5-1 : 14 in molar ratios), involving the stable ZnCl2-4EG deep-eutectic solvent (DES) composition, to explore the spectral variations, structural heterogeneity, and hydrogen bonding (H-bonding) properties. To enhance the resolution of the spectra, excess absorption and two-dimensional correlation spectroscopies were employed. In the initial IR spectra, a quasi-isosbestic point was identified, signaling that the major disturbance on EG microstructures by adding ZnCl2 is to form a distinct complex. Further analysis uncovered the main transformation process to be from the EG tetramer to the ZnCl2-4EG complex. It was also found that as the EG content increases, negative charge increasingly transfers to ZnCl2, resulting in the strengthening of the Zn ← O coordination bonds and the weakening and finally dissociation of Zn-Cl bonds. Regarding the ZnCl2-4EG DES, several incomparable specificities were observed. It was found that ZnCl2 destructed the H-bonding network of pure EG to the largest extent, resulting in the highest production of the dimer and trimer of EG. Moreover, in comparison with other compositions, the ZnCl2-4EG DES showed abrupt increases in the negative charge of the salt, the length of the Zn-Cl bond, and the strength of the Zn ← O coordination bond. All these imply the strongest intermolecular interactions and the highest solvation of ZnCl2 in EG at the eutectic composition compared to those of other mixtures, resulting in a super-stable liquid mixture. The work provides physical insights into the structural and interactive properties of deep-eutectic solvents.

Molecular Dynamics Simulation of Polyacrylamide Adsorption on Cellulose Nanocrystals

Classical molecular dynamics simulations of polyacrylamide (PAM) adsorption on cellulose nanocrystals (CNC) in a vacuum and a water environment are carried out to interpret the mechanism of the polymer interactions with CNC. The structural behavior of PAM is studied in terms of the radius of gyration, atom–atom radial distribution functions, and number of hydrogen bonds. The structural and dynamical characteristics of the polymer adsorption are investigated. It is established that in water the polymer macromolecules are mainly adsorbed in the form of a coil onto the CNC facets. It is found out that water and PAM sorption on CNC is a competitive process, and water weakens the interaction between the polymer and CNC.

Impact of alkyl chain length and water on the structure and properties of 1-alkyl-3-methylimidazolium chloride ionic liquids

Conformational isomerism in C_nmim Cl (n = 2, 4, 6, 8, and 10) is identified by marker IR bands for the first time.

Synthesis of zwitterionic acrylamide copolymers for biocompatible applications

In order to prepare acrylamide copolymers with non-toxicity for environment-friendly materials, a series of zwitterionic acrylamide copolymers with varying acrylamide content were synthesized with DMAPS (3-dimethyl (methacryloyloxyethyl) ammonium propane sulfonate) and acrylamide via free radical polymerization. The structural properties and cytotoxicity are carefully investigated. The results demonstrate that DMAPS- co-acrylamide copolymers contain DMAPS and acrylamide segments that form a matrix consisting of strong electrostatic interactions as well as strong hydrogen bonding. DMAPS segments exhibit negligible influence on the glass phase transition behavior, yet affect the composite’s water-contact angle. The optimum hydrophilic properties are obtained by adjusting the acrylamide content to 50 wt%. All DMAPS- co-acrylamide copolymers are measured to be non-toxic. The DMAPS segments allow for suitable contribution to the biocompatibility of the synthesized copolymer, in which copolymers containing higher DMAPS content demonstrate better biocompatibility.

Raman and NMR kinetics study of the formation of amidoamines containing N-hydroxyethyl groups and investigations on their Cu(II) complexes in water

Three amidoamines containing the N-hydroxyethyl group (^HOEt), namely (^HOEt)₂N(CH₂)₂C(O)NH₂ (1), [(^HOEt)₂N(CH₂)₂C(O)NH]₂CH₂ (2) and ^HOEtN[(CH₂)₂C(O)NH₂]₂ (3) have been synthesized by reacting diethanolamine ^HOEt₂NH with acrylamide and N,N'-methylenebisacrylamide (respectively 1 and 2) and ethanolamine ^HOEtNH₂ with acrylamide (3). Four other compounds corresponding to 1 and 2, but derived from sec-amines Me₂NH (4 and 5) and Et₂NH (6 and 7) have been prepared for the sake of comparison of the spectroscopic features. All compounds have been obtained by the well-known aza-Michael addition between an N-nucleophile and an activated vinyl group. The reaction in water between diethanolamine and acrylamide leading to 1 has been monitored in situ by Raman and NMR spectroscopy, both techniques confirming second order kinetics and giving values for kinetic constants in excellent agreement. The coordination ability of 1 and 2 towards Cu²⁺ in water has been studied by the Job's plot method. Spectroscopic data indicate that ligand 1 prevalently forms a 4:1 Ligand/Metal complex with a (N,O₃) coordination set on the equatorial plane of Cu²⁺, whereas ligand 2, containing two amide functionalities bridged by a methylene group, appears able to form a 1:1 Ligand/Metal chelate species, again with a (N,O₃) donor set around copper.

Monitoring potential molecular interactions of adenine with other amino acids using Raman spectroscopy and DFT modeling

We report on the modes of inter-molecular interaction between adenine (Ade) and the amino acids: glycine (Gly), lysine (Lys) and arginine (Arg) using Raman spectroscopy of binary mixtures of adenine and each of the three amino acids at varying molar ratios in the spectral region 1550-550 cm(-1). We focused our attention on certain specific changes in the Raman bands of adenine arising due to its interaction with the amino acids. While the changes are less apparent in the Ade/Gly system, in the Ade/Lys or Ade/Arg systems, significant changes are observed, particularly in the Ade Raman bands that involve the amino group moiety and the N7 and N1 atoms of the purine ring. The ν(N1-C6), ν(N1-C2), δ(C8-H) and δ(N7-C8-N9) vibrations at 1486, 1332, 1253 and 948 cm(-1) show spectral changes on varying the Ade to amino acid molar ratio, the extent of variation being different for the three amino acids. This observation suggests a specific interaction mode between Ade and Lys or Arg, which is due to the hydrogen bonding. The measured spectral changes provide a clear indication that the interaction of Ade depends strongly on the structures of the amino acids, especially their side chains. Density functional theory (DFT) calculations were carried out to elucidate the most probable interaction modes of Ade with the different amino acids.