Rodica Bandula

Synthesis of some new solvatochromic 1(4)-substituted Pyrazol-5-one Azo derivatives

Abstract New 1-(2′-benzthyazolyl)-3-methyl-pyrazol-5-one-4-substituted azo derivatives have been prepared and characterised by elemental analysis, IR, 1 H-NMR and UV-VIS. The solvatochromic behaviour was investigated and their ionisation constants were determined. These dyes generally absorb near-infrared light at around 11,000 cm −1 and this is the most favourable wavelength region for semiconductor laser optical recording dye medium. ©

A TDDFT study of the fluorescence properties of three alkoxypyridylindolizine derivatives.

The fluorescence properties of three pyridylindolizine derivatives (one tricarbomethoxy-7-pyridyl-pyrrolopyridine and two dicarboethoxy-3-bromobenzoyl-7-pyridyl-pyrrolopyridines) have been investigated by applying density functional theory (DFT) and the time-dependent DFT (TDDFT). Performances of two hybrid-type functionals (BH&HLYP and B3LYP) and one generalized gradient approximation (GGA) functional (PBE) as well as three basis sets (SV(P), DZP, and TZVP) have been assessed. The solvent environment has been modeled with the conductor-like screening model (COSMO). Of the three functionals only BH&HLYP is able to yield reasonable estimates for all the studied indolizine derivatives whereas the success of the PBE and B3LYP functionals is highly dependent on the structure of the studied molecule. The SV(P) basis set provides geometrical changes as well as fluorescence maxima and Stokes shifts that agree with those obtained with DZP and TZVP. When a nonpolar solvent is used, COSMO is able to reproduce the experimental fluorescence maxima and Stokes shifts well. However, the agreement between the calculations and experiments is not as good when a solvent with higher polarity is used.

Polarity profiles in reverse micelles of Triton X-100, as studied by spin probe and absorption probe techniques

The microenvironment characteristics — polarity, viscosity and order degree - in Triton X-100 reverse micelles (RM) in cyclohexane and benzene — n-hexane 30 : 70 (v/v), were investigated with the aid of a homologous series of cationic spin probes, CAT n, of 5- and 16-doxyl stearic acids and of a new absorption probe, 4-nitropyridine-N-oxide (NP). The spectral parameters were related to local hydration values by means of a series of poly(oxyethylene) (PEO)/water calibration mixtures. All results regarding the polarities in RM and calibration mixtures have been expressed in terms of Kosowers Z values, by determining the linear dependence of the transition energies of NP, ENP, on Z, for a series of polar solvents: Z = 3.008ENP − 178.4 (in kcal mol−1). This way the relative radial positioning of all probes was established and could be compared with those of 1-methyl-8-oxyquinolinium betaine (QB) and methyl orange (MO), previously used in the same systems. A continuous variation of the polarity in the RM was evidenced with different probes, from the most polar region in the center, with the polarity of ethanol/water mixtures (CAT 1, CAT 4 and QB) to a region corresponding to tetraethylene glycol (TG)/water mixtures and triethylene glycol monoethyl ether (TGME)/water mixtures (NP and CAT 8), to a region at the limits of the core, with the polarities of the triethylene glycol dimethyl ether (TGDE)/water mixtures (MO) and to still lower values, found with the 16-doxyl probe, in the corona. At the same time, the different hydration dynamics at various depths in the micelles were followed showing earlier saturation in the outer regions of the core as compared to the central regions. The spin probes evidenced the compacting and ordering effects of water on the surfactant chains in the polar core and corona. From this point of view the RM in benzene-hexane appear to have a much lower viscosity in the polar core (over the whole range of water contents) as compared to those in cyclohexane. The order degree of the surfactant chains is lower too and the corona appears to be penetrable by an oil-soluble Cu complex, at variance with the cyclohexane system. All this data can be consistently explained by the loosening effect of benzene, solvating the surfactant chains in the corona.

Spectrophotometric Characteristics of New Pyridylindolizine Derivatives Solutions

Three new pyridylindolizine derivatives, 1, 2, 3-tricarbometoxi-7-(4-pyridyl)-pyrrolo[1, 2-a]pyridine (I), 1,2-dicarboethoxy-3-(4-bromobenzoyl)-7-(4-pyridyl)-pyrrolo[1,2-a]pyridine (II) and its isomer 1,2-dicarboethoxy-3- (4-bromobenzoyl) -5- (2-pyridyl) -pyrrolo[1, 2-a]pyridine (III) have been investigated in different solutions by UV-VIS absorption, steady-state, and time-resolved fluorescence methods. The effects of the substituent and solvent on the spectroscopic properties have been demonstrated. The fluorescence decay data could be fitted to a single-exponential function. The lifetime values are higher in protic polar than in aprotic apolar solvents for compound I. In the case of compounds II and III the fluorescence intensities and lifetimes are very low, with the exception of III in aprotic solvents. The absorption and fluorescence properties of the compounds showed a solvent dependence.

3,6-diHydroxyflavone/bovine serum albumin interaction in cyclodextrin medium: Absorption and emission monitoring

Photophysical properties of a bioactive flavonol which can be used as a model for polyhydroxylated natural flavonols, 3,6-diHydroxyflavone (3,6-diHF) in cyclodextrins (CDs)/bovine serum albumin (BSA) systems have been studied by absorption and fluorescence spectroscopy. The influence of CDs nature and of the different molar ratios BSA/CDs on the fluorescent characteristics of 3,6-diHF, and on the excited - state intramolecular proton transfer (ESIPT) process were studied. Quantitative information on the interaction between 3,6-diHF and BSA in CDs medium, were estimated. The influence of temperature (25-60°C range) on the intrinsic fluorescence of BSA in 3,6-diHF/BSA/CDs systems, was investigated. The results are discussed with relevance to 3,6-diHF as a potential sensitive fluorescence probe in the systems of biological interest.

Microstructure of polyelectrolyte nanoaggregates studied by fluorescence probe method.

The microstructure of water soluble nanoaggregates based on polyelectrolyte complex formed by the cationic comb-type copolymer poly(acrylamide -co-[3- (methacryloyl-amino)propyl] trimethylammonium chloride)-graft- polyacrylamide [P(AM-co-MAPTAC)-g-PAM] and the anionic linear polyelectrolyte sodium polyacrylate (NaPA) was investigated using the fluorescence probe technique. The fluorescence probe were 1-anilinonaphthalene-8-sulfonic acid (ANS), pyrene (Py) and 1,10-bis(1-pyrene) decane (PD). The fluorescence properties in polyelectrolyte complex solutions, which are sensitive to either micropolarity (ANS, Py) or microviscosity (PD), were related to the quantities obtained in different pure or mixed solvents. Micropolarities were quantified utilizing the polarity common index (Reichardt) ET(30). ANS and Py showed a variation of the micropolarity with the charge ratio of the two polymers, with the lowest polarity reached at the complex neutralization. The PD probe, by its excimer-to-monomer fluorescence intensities ratio, enabled us to evidence the effect of the composition and the comb-type copolymer grafting density on the microviscosity of the interpolyelectrolytes aggregates. It has been found that the microviscosity increased with the density of the grafting PAM chains.