Fluorimetric detection of tautomeric equilibria in 8-aminoquinolines

The 1-methylquinolinium cations derived from 8-aminoquinoline and 8-amino-6-methoxyquinoline were prepared by methylation of the corresponding nitroquinolines and reduction of the nitro-compounds. The dissociation constants of the protonated species of these compounds are almost identical to those of doubly-protonated 8-aminoquinoline and 8-amino-6-methoxyquinoline, respectively, suggesting that the parent quinolines are exclusively first protonated at the ring nitrogen atom. However, the molar absorptivities of the 1-methyl derivatives at their longest-wavelength absorption maxima are substantially greater than the corresponding absorptivities of the unmethylated aminoquinolines, a result which suggests tautomerism of the singly-protonated parent quinolines, with a proportion of the population protonated at the amino group. Fluorescence spectroscopy reveals a single emission from the 8-amino-6-methoxy-1-methylquinolinium ion and two excitation-wavelength-dependent fluorescences from the 8-amino-6-methoxyquinolinium ion, confirming the occurrence of tautomerism and supporting choice of the absorptiometric approach rather than the titrimetric approach as the preferred method for the detection of tautomerism and the calculation of tautomeric equilibrium constants.     

Narrow band quantitative and multivariate electroencephalogram analysis of peri-adolescent period

ABSTRACT: BACKGROUND: The peri-adolescent period is a crucial developmental moment of transition from childhood to emergent adulthood. The present report analyses the differences in Power Spectrum (PS) of the Electroencephalogram (EEG) between late childhood (24 children between 8 and 13 years old) and young adulthood (24 young adults between 18 and 23 years old). RESULTS: The narrow band analysis of the Electroencephalogram was computed in the frequency range of 0--20 Hz. The analysis of mean and variance suggested that six frequency ranges presented a different rate of maturation at these ages, namely: low delta, delta-theta, low alpha, high alpha, low beta and high beta. For most of these bands the maturation seems to occur later in anterior sites than posterior sites. Correlational analysis showed a lower pattern of correlation between different frequencies in children than in young adults, suggesting a certain asynchrony in the maturation of different rhythms. The topographical analysis revealed similar topographies of the different rhythms in children and young adults. Principal Component Analysis (PCA) demonstrated the same internal structure for the Electroencephalogram of both age groups. Principal Component Analysis allowed to separate four subcomponents in the alpha range. All these subcomponents peaked at a lower frequency in children than in young adults. CONCLUSIONS: The present approaches complement and solve some of the incertitudes when the classical brain broad rhythm analysis is applied. Children have a higher absolute power than young adults for frequency ranges between 0-20 Hz, the correlation of Power Spectrum (PS) with age and the variance age comparison showed that there are six ranges of frequencies that can distinguish the level of EEG maturation in children and adults. The establishment of maturational order of different frequencies and its possible maturational interdependence would require a complete series including all the different ages.     

The vibrational force field of halogenated aromatic molecules: II. Out-of-plane vibrations of fluoroaromatics

A general quadratic force field is determined for the out-of-plane vibrations of florobenzenes. The force constants for the out-of-plane wagging of both CH and CF bonds decrease by about 10 % for each ortho fluorine substituent. No significant meta dependence could be detected. It is shown that the present field is in excellent accord with the chlorobenzene field of Scherer and with the benzene fields of Whiffen and of Kydd when due allowance is made for differences in coordinate definitions.     

Strong field dual-pulse excitation of Ag<Subscript>N</Subscript>

The ionization of silver clusters exposed to pairs of intense femtosecond laser pulses strongly depends on the optical delay. Enhanced production of a certain atomic charge state z is obtained by a z-dependent delay. This may open a possible route to control the excitation process and populate specific charge states. The optimum pulse separation which maximizes the generation of highly ionized species varies by more than one order of magnitude when the mean size of the clusters increases from to . Semiclassical Vlasov simulations applied to a model system reveal the importance of the initial ionic motion in the ionization process.     

Integral equation formulation for buoyancy-driven convection problems

An integral equation formulation for buoyancy-driven convection problems is developed and illustrated. Buoyancy-driven convection in a bounded cylindrical geometry with a free surface is studied for a range of aspect ratios and Nusselt numbers. The critical Rayleigh number, the nature of the cellular motion, and the heat transfer enhancement are computed using linear theory. Green's functions are used to convert the linear problem into linear Fredholm integral equations. Theorems are proved which establish the properties of the eigenvalues and eigenfunctions of the linear integral operator which appears in these equations.     

57Fe Mössbauer Spectroscopic Investigation of Low-Iron Coals and Their Flyash

Trends in the speciation of iron and sulfur in high iron/sulfur coals are well-established. Less is known concerning iron and sulfur speciation in low sulfur coals such as those investigated in this study. Low sulfur coals and their flyash from Thunder Bay, Ontario, Canada and Atikokan, West Virginia, U.S.A. have been investigated by means of ⁵⁷Fe Mössbauer spectroscopy, X-ray diffraction and X-ray fluorescence. Virgin coals, containing approximately 0.1% Fe, exhibited Mössbauer spectra too low in intensity to characterize the phases present. The flyash exhibited well-resolved, simple doublets with ΔE_Q=1.16 mm s^?1 (Canada) and 1.26 mm s^?1 (U.S.A.) and isomer shift values (w.r.t. Fe) of 0.22 mm s^?1 and 0.23 mm s^?1, respectively, characteristic of Fe³⁺. The linewidths of ～0.80 mm s^?1 are unusually large. Treatment of the flyash with cold, hydrofluoric acid resulted in a sample that exhibited very little absorption in its ⁵⁷Fe Mössbauer spectrum. This result, in conjunction with the linewidths, indicates that the Fe is present in the flyash mainly as a silicate glass.