Electronic Structure of Solvent-Polarity Indicators. Solvatochromism and Tautomeric Epuilibria of Styryl-Merocyanines

AbstractSolvatochromic and halochromic behaviour of two unsymmetrical merocyanine-type dyes, namely 2-[2′- and 4′-hydroxystyryl]-pyridinium methiodide, are studied.In alcoholic and hydrogen-bond-acceptor (HBA) solvents their visible absorption spectra exhibit an additional long-wavelength band suggesting the existence of tautomeric equilibria in their solutions. The tautomeric equilibrium constants in triethanolamine-acetone mixed solvents are determined.Quantum mechanical MO method PPP-π-SCF-CI is used to calculate the electronic spectra and the underlying keto-enol-tautomeric stability. Deprotonation of the OH group is shown to provide destabilization in binding energy in excess of 5 eV in agreement with the experimental results indicating that these indicators exist mainly as protonated species (enol form) in their solutions.Furthermore, solvent-induced changes in the ground-state electronic structures are examined by means of 1H-NMR spectroscopy and the PPP calculations

Synthesis of Some Pyrimidine, Pyrazole, and Pyridine Derivatives and Their Reactivity Descriptors

A series of novel pyrimidine (2, 3), pyrazole (4, 5), and pyridine (6) derivatives were synthesized using a chalcone-bearing thiophene nucleus (1). The target compounds were synthesized by reaction of compound (1) with urea, thiourea, malononitrile, hydrazine hydrate, and 2,4-dinitrophenyl hydrazine, respectively. Molecular electronic structures have been modeled within density functional theory framework (DFT). Reactivity indices and electrostatic surface potential maps (ESP maps) allow us to establish trends that enable making predictions about chemical characteristics of the newly synthesized molecules and their proton transfer tautomers. Proton transfer is generally more favored in solution than in the gas phase. In acetonitrile, keto-form tautomers and thione-form tautomers become more energetically stable than the corresponding enol or thiol tautomers due to solvent-induced enhancement in the molecular polarity identified by computed dipole moment

Phycoremediation of contaminated water by cadmium (Cd) using two cyanobacterial strains (Trichormus variabilis and Nostoc muscorum)

Background Water pollution with heavy metals is a severe dilemma that concerns the whole world related to its risk to natural ecosystems and human health. The main objective was to evaluate the removal efficiency of Cd of various concentrations from contaminated aqueous solution by use of two cyanobacterial strains (Nostoc muscorum and Trichormus variabilis). For this purpose, a specially designed laboratory pilot-scale experiment was conducted using these two cyanobacterial strains on four different initial concentrations of Cd (0, 0.5, 1.0 and 2.0 mg L−1) for 21 days. Results N. muscorum was more efficient than T. variabilis for removing Cd (II), with the optimum value of residual Cd of 0.033 mg L−1 achieved by N. muscorum after 21 days with initial concentration of 0.5 mg L−1, translating to removal efficiency of 93.4%, while the residual Cd (II) achieved by T. variabilis under the same conditions was 0.054 mg L−1 (89.13% removal efficiency). Algal growth parameters and photosynthetic pigments were estimated for both cyanobacterial strains throughout the incubation period. Conclusions High Cd concentration had a more toxic impact on algal growth. The outcomes of this study will help to produce treated water that could be reused in agrarian activities.Validerad;2022;Nivå 2;2022-01-01 (johcin)</p