Effects of Si−Al composition on the fluorescence spectra of 1-naphthol during the sol-gel-xerogel transitions

A systematic study has been carried out on the characteristic changes in the fluorescence spectra of 1-naphthol doped in the sol-gel-xerogel transition systems comprised of tetraethyl orthosilicate and diisobutoxyaluminium triethylsilicate catalyzed by a small amount of HCl, NH₄OH, as well as under uncatalyzed conditions. In the systems containing large amounts of silicon, the fluorescence of 1-naphthol shifts to the red (a predominant emission from the ¹L_a state) during the first stage of the reaction. This red shift indicates an increase in the polarity of the matrix surrounding 1-naphthol. In the second stage of the reaction, the spectrum shifts to the blue (a predominant emission from the ¹L_b state), reflecting an increase in the micro-viscosity around 1-naphthol. In the systems containing relatively large amounts of aluminum, however, the spectrum just after mixing shows a larger red shift than that originating from the ¹L₂ emission. This large red-shifted fluorescence reflects the formation of a complex between 1-naphthol and the −O−Al−O−Si−O-network. The spectrum then shifted to the blue. The spectral behaviours observed indicate that there is a large and dynamic molecular-level change in the physicochemical properties of the matrix surrounding the 1-naphthol molecules during the sol-gel-xerogel transitions of the systems while the gelation phenomenon reflects macroscopic inflexibility although it is completely different from the restriction of movement at the molecular level.     

Features of diffusion-controlled bimolecular reaction of fluorescence quenching in sol-gel-xerogel transitions

Reaction kinetics have been investigated in the diffusion-controlled quenching of pyrene fluorescence by N,N-dimethylaniline in a medium that gradually changes from homogeneous to heterogeneous as a result of solution-sol-gel-xerogel transitions. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 2, pp. 122–125, March–April, 1998.     

Rapid simultaneous analysis of 1-naphthol and 2-naphthol in water samples by derivative variable-offset synchronous fluorescence spectroscopy

Derivative variable-offset synchronous fluorescence spectroscopy is developed to improve the spectral resolution and the selectivity of fluorescence measurements. 1-naphthol and 2-naphthol are employed to evaluate the proposed coupled technique and the various spectral comparisons are conducted. Second derivative variable-offset synchronous scanning permits the rapid simultaneous identification and quantitative determination of 1-naphthol and 2-naphthol in a mixture from a single spectrum. 6.7-2000 ng/ml 1-naphthol and 3.6-500 ng/ml 2-naphthol can be quantified with 1-naphthol and 2-naphthol ratios of 40: 1-1: 10. The determination of 1-naphthol and 2-naphthol in various spiked water samples gave a mean recovery of 100.7% with a relative standard deviation of 2.8% for 1-naphthol and mean recovery of 99.7% with a relative standard deviation (RSD of 2.6% for 2-naphthol, respectively.     

pH-induced changes in electronic absorption and fluorescence spectra of phenazine derivatives

The visible electronic absorption and fluorescence spectra as well as fluorescence polarization degrees of imidazo-[4,5-d]-phenazine (F1), 2-methylimidazo-[4,5-d]-phenazine (F2), 2-trifluoridemethylimidazo-[4,5-d]-phenazine (F3), 1,2,3-triazole-[4,5-d]-phenazine (F4) and their glycosides, imidazo-[4,5-d]-phenazine-N1-beta-D-ribofuranoside (F1rib), 1,2,3-triazole-[4,5-d]-phenazine-N1-beta-D-glucopyranoside (F4gl), were investigated in aqueous buffered solutions over the pH range of 0-12, where the spectral transformations were found to be reversible. The effects of protonation and deprotonation on spectral properties of these dyes were studied. We have determined the ranges of pH, where individual ionic species are predominant. In aqueous buffered solutions the fluorescence was found only for neutral species of F1, F1rib, F2, and F4gl dyes, whereas for the ionic forms of these dyes, as well as for F3 and F4 ones, the fluorescence has not been detected. The concentrational deprotonation pKa values were evaluated from experimental data. It was shown that donor-acceptor properties of the substituent group in the second position of the pentagonal ring substantially affect the values of the deprotonation constants and the character of protonation for chromophore. The substitution of a hydrogen atom in the NH-group by the sugar residue blocks the formation of the anionic species, and results in enhancement of the dye emission intensity. The steep emission dependence for F1 and F1rib over pH range of 0-7 with intensities ratio of IpH 7/IpH 1=60 allows us to propose them as possible indicator dyes in luminescence based pH sensors for investigation of processes accompanied by acidification, e.g. as gastric pH-sensors. A comparative analysis of the studied dyes has shown that F4gl is the most promising compound to be used as a fluorescent probe for investigation of molecular hybridization of nucleic acids.     

Theoretical studies on fluorescence of phenol and 1-naphthol in both acid and alkali solutions

The molecular structures of the ground state and the first singlet excited state for , C₆H₅OH, C₆H₅O⁻, , C₁₀H₇OH and C₁₀H₇O⁻, the forms of phenol and 1-naphthol in acid and alkali solutions, were optimized by ab initio HF and configuration interaction with singlet excitations (CIS) method, respectively. Their fluorescent spectra were obtained by the time-dependent density functional theory (TD-DFT) using the B3LYP method with the 6-31+G (d) basis set. The frontier molecular orbital characteristics, fluorescent spectrum and proton affinities had been analyzed systematically in order to study different fluorescence of phenol and 1-naphthol in acid and alkali solutions. It was found that C₆H₅OH and are the main forms of phenol in acid solution, but C₆H₅O⁻ in alkali solution; C₁₀H₇OH and C₁₀H₇O⁻ are the main forms of 1-naphthol in alkali solution, but in acid solution. The calculated results are in good agreement with the experimental data.     

Metastable transitions in the mass spectra of fluoro-ethylenes

Metastable transitions in the mass spectra of six fluoroethylenes are reported. In several cases in which HF is the neutral species lost, 0.4 to 0.7 eV of kinetic energy is liberated. In two fragmentations, it is shown that the kinetic energy release is only about half the minimum energy of activation of the back reaction calculated from thermochemical data. Evidence is presented to support the view that in some cases at least, fragmentation occurs from two or more electronic states of the molecular ion.     

MR spectra and azo-quinonehydrazone tautomerism in 4-arylazo-1-naphthol derivatives,without intramolecular proton transfer

Conclusions Using¹³C-NMR spectroscopy conditions have been elucidated under which 4-R-azo-1-naphthol derivatives containing carbo- and heterocyclic functional groups R exist in solution predominantly in azo- or quinonehydrazone tautomeric forms, respectively. A mechanism has been proposed to account for azo-quinonehydrazone tautomerism; this mechanism would be expected to be valid in aprotic meida for hydroxyazo compounds which do not contain intramolecular hydrogen bonds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1292–1298, June, 1988.The authors wish to thank S. I. Dvoskin for submitting samples of compounds (Ia) and (Ic).     

Fluorimetric determination of 1-naphthol and mixtures of carbaryl and 1-naphthol in micellar media

Summary The interaction of 1-naphthol with different types of anionic, cationic and non-ionic surfactants has been studied spectrofluorimetrically in order to obtain a sensitivity enhancement in the determination of this compound. At neutral pH, cetyl trimethyl ammonium bromide (CTAB) provides a 2-fold sensitivity enhancement of 1-naphthol and exhibits a weak interaction with carbaryl. In strong alkaline medium carbaryl is hydrolyzed to 1-naphthol and in the presence of CTAB micells, a 5-fold sensitivity enhancement and a limit of detection of 0.2 g·ml^–1 with a 101±3% percentage of recovery is obtained. These facts permit the development of an accurate method for the fluorimetric analysis of 1-naphthol and carbaryl mixtures, comprising the determination of the sum of both compounds (pH 12, 0.1% w/v CTAB, _em=449 nm, _ex=341 nm) and of the concentration of 1-naphthol (neutral pH, 0.4% w/v CTAB, _em=449 nm, _ex=312 nm).     

Broadening of electronic spectra at the critical point of a binary polar mixture

It is shown that in the vicinity of the critical point of a binary polar mixture the electronic spectral linewidth increases when approaching the critical point. The linewidth obeys the law of A_o[(T-T_c)/T_c]^?γ, where γ is the universal critical index of dispersion of concentration fluctuations.     

Radiolysis of 1-naphthol in aqueous solutions

The effects of absorbed doses, initial pH and 1-naphthol concentration onto its radiolysis in aqueous sulphuric and hydrochloric acids by gamma rays from ⁶⁰Co were investigated. Under the experimental conditions, 1-naphthol degradation yields increased with increasing the absorbed doses (0.3–3.0 kGy) and with decreasing the initial 1-naphthol concentration (20–1 ppm). It was found out that the hydrated electrons did not play any significant roles in 1-naphthol radiolysis, as the degradation yields were higher at pH₀ ~ 0.46 compared to those at pH₀ ~ 2.0–5.0. The corresponding radiolytic yields G(−1-naphthol) were (6.13 ± 1.00)) × 10⁻² and (5.11 ± 0.22) × 10⁻² μmol/J in sulphuric acids, (15.61 ± 3.85) × 10⁻² and (4.76 ± 0.48) × 10⁻² μmol/J in hydrochloric acids. 1-Naphthol degradation rates could be described by the kinetic equations of pseudo-first-order reactions. An empirical relation between the observed reaction constants k _D and the initial 1-naphthol concentrations was established, enabling to predict the absorbed doses required for a given treatment efficiency. Three products of 1-naphthol degradation were revealed using an HPLC/UV procedure.     

Characteristic frequencies in the infrared spectra of pyrazolines

Pyrazolines are characterized by valence vibrations at the following frequencies: C=N (1580–1627 cm^–1), H-C³=N (3040–3063 cm^–1), H-N (3270–3305 cm^–1) and CH₃-N (2780–2805 cm^–1). Lowering of the frequencies of the valence vibrations of C=N in pyrazolines, when compared with the magnitudes characteristic of alkyledene amines and oximes, is regarded as a consequence of coupling with the unshared electron pair of the neighboring nitrogen atom. By means of the IR spectra, it is possible to determine the position of the double bonds in the pyrazoline ring, to distinguish between pyrazolines substituted and nonsubstituted in positions 1 and 3, and to establish the presence of geminate (twin) methyl groups and methyl groups in position 1.     

Charge-transfer transitions in the vacuum-ultraviolet of protein circular dichroism spectra

Circular dichroism (CD) is widely used in the structural characterization and secondary structure determination of proteins. The vacuum UV region (below 190 nm), where charge-transfer transitions have an influence on the CD spectra, can be accessed using synchrotron radiation circular dichroism (SRCD) spectroscopy. Recently, charge-transfer transitions in a conformationally diverse set of dipeptides have been characterized ab initio using complete active space self-consistent field calculations, and the relevant charge distributions have been parametrized for use in the matrix method for calculations of protein CD. Here, we present calculations of the vacuum UV CD spectra of 71 proteins, for which experimental SRCD spectra and X-ray crystal structures are available. The theoretical spectra are calculated considering charge-transfer and side chain transitions. This significantly improves the agreement with experiment, raising the Spearman correlation coefficient between the calculated and the experimental intensity at 175 nm from 0.12 to 0.79. The influence of the conformation on charge-transfer transitions is analyzed in detail, showing that the n --> pi* charge-transfer transitions are most important in alpha-helical proteins, whereas in beta strand proteins the pi --> pi* charge-transfer transition along the chain in the amino- to carboxy-end direction is most dominant.     

溶液中溶菌酶的荧光光谱研究

本文采用荧光分析法(荧光光谱、荧光偏振度)结合内源荧光探针色氨酸残基对溶菌酶及其在不同条件下的构象变化进行了研究。结果表明,利用荧光光谱可对溶菌酶溶液构象进行有效的分析,能够较直观地表征色氨酸残基在溶菌酶分子中的微环境及其在不同条件下构象的变化,得出了一些较有价值的结果。     

Semi-empirical AM1 calculation of the solvent effect on the fluorescence spectra of some dihydroquinolinones

The COnductor-like Screening MOdel of solvent-solute interactions of Klamt and Schüürmann, COSMO, at the semiempirical AM1 level of MO calculations, augmented by limited singles and doubles configuration interaction, proves useful for the study of solvent induced shifts of fluorescence spectra. Optimization of geometry of ground S0 and excited S1 states for each solvent separately provides estimates of the changes of solvation energy accompanying the electron transition process and helps the understanding of the related solvent-solute reorganization and fluorescence mechanisms.     

Identification of conjugate electron transitions in X-ray photoelectron spectra

The regularities of the electron energy dissipation found in the subsurface atomic layer are valid in the bulk of a solid, too. On the example of model graphite-based materials it is shown that energy losses in X-ray photoelectron spectra agree with the calculated valence electron excitation spectra in analogous unit cells. The control of conjugate electron transitions opens the way to gain new data on the geometry, character, and order of bonding between atoms in the sample by the conventional electron spectroscopy and quantum chemistry methods.     

Laser induced fluorescence bands in the FT-Raman spectra of bioceramics

A new fluorescence band at about 1930cm-1 has been observed in the FT-Raman spectra of some bioceramics. While a fluorescence band at about 760cm-1 has been already reported in the FT-Raman spectra of hydroxyapatite and related calcium phosphates, this new band is observed for the first time. This strong band is totally absent in the anti-Stokes side of the FT-Raman spectra and therefore has been assigned as a laser induced fluorescence band. It has been concluded that in recording FT-Raman spectra of minerals, all precautions about fluorescence bands should be considered, otherwise the FT-Raman spectra may well be misinterpreted.     

Reversible resonant hole burning in the fluorescence spectra of protochlorophyll

Hole burning at a resonance frequency wthin the S₁-S₀ fluorescence band of protochlorophyll in ether, ether-butanol glass and n-heptane was observed at temperatures of 1.8–30 K. Both triplet-state population and photochemical burning mechanisms were found. Besides narrow lines (0.3 cm^?1 wide), distinct broad phonon wings werc detected in the hole-burning spectra. The photochemical phase was shown to consist of light-induced reversible site interconversions.     

Dynamics of radiationless transitions in large molecules: 1. Absorption spectra of adjoin reservoir states

The dynamics of radiationless transitions in large molecules interacting with the surroundings is determined by the dense discrete spectrum of final states {R _n }, close in energy to the initial state s, and by the sets of SR-coupling matrix elements and the decay rate constants of S and {R _n }. It has been shown that the shape and the fine structure of the absorption band of the optical transition from the ground to the initial state S ← S ₀ makes it possible to find the characteristic function of these three distributions. The transformation of the regular spectrum into the stochastic one has been considered.