RESUMO
A novel rotary switch, overcoming the disadvantages of hydrazone based switches with competitive proton acceptor sub-rotors, has been designed. The new compound contains a pyridyl ring and a COOH group as sub-rotors, which provides engagement of the pyridyl nitrogen atom and leads to the existence of a single isomer in the ground state. The availability of acidic functionality in the rotor creates conditions for excited state intramolecular proton transfer (ESIPT), which exhibits anti-Kasha behavior.
RESUMO
The concept for sensing systems using the tautomerism as elementary signaling process has been further developed by synthesizing a ligand containing 4-(phenyldiazenyl)naphthalene-1-ol as a tautomeric block and an amide group as metal capturing antenna. Although it has been expected that the intramolecular hydrogen bonding (between the tautomeric hydroxy group and the nitrogen atom from the amide group) could stabilize the pure enol form in some solvents, the keto tautomer is also observed. This is a result from the formation of intramolecular associates in some solvents. Strong bathochromic and hyperchromic effects in the visible spectra accompany the 1:1 formation of complexes with some alkaline earth metal ions.
RESUMO
The keto-enol tautomeric equilibrium in two newly developed molecular switches was studied by using various mass spectral techniques. In these two compounds, namely 4-(phenyldiazenyl)-2-(piperidin-1- ylmethyl)naphthalen-1-ol and 2-[(1,4,7,10-tetraoxa-13-azacyclopentadecan-13-yl)methyl]-4- (phenyldiazenyl)naphthalen-1-ol, the switching on/off states are achieved by a controlled shift of the tautomeric equilibrium. In the first compound, electron impact-mass spectrometry confirms that the unprotonated dye exists as an enol tautomer, while the electrospray ionization tandem mass spectrometry (ESI-MS/MS) experiment proves the clear shift to the keto tautomeric form under switching with acid addition. In the second compound, the addition of the alkali metal ions causes transition of the tautomeric equilibrium from the pure enol to the pure keto form. The ESI-MS study demonstrated better sensitivity towards lithium ions.
RESUMO
The tautomeric constants of a series of azo dyes were estimated in the gas phase by using electron ionization mass spectrometry. It was shown that the relative amount of the keto tautomer increases from 4-phenylazo-1-phenol to 4-phenylazo-anthracen-1-ol, thus confirming the quantum-chemical predictions. The existence of the enol tautomer of 4-phenylazo-anthracen-1-ol is shown for the first time by mass spectrometry in the gas phase. This finding is supported by flash photolysis measurements in solution.
RESUMO
Gas-phase tautomerism in 1-phenylazonaphthalene-4-ol (1) was studied by using electron ionization (EI) mass spectrometry on the basis of the fragmentations of the model enol and keto tautomers, where the movable proton is replaced by a methyl group. These fixed tautomers were obtained as an easy separable mixture by simple methylation of the cheap and easily accessible diazene (1). It was found that their EI mass spectral fragmentations are in full congruence with the already published theoretical predictions. The relative energies required for bond cleavage in 1 and its fixed tautomers were estimated by stepwise increasing of the electron energy of the ion source of the mass spectrometer. A simple equation for the approximate estimation of the molar fractions of the individual tautomers was suggested. It was shown that the enol form is dominant in the temperature range of 200-300 degrees C.
RESUMO
The possibility of applying near-infrared (NIR) spectroscopy to monitor 13 active components (phenolic acids, flavonoids, and sesquiterpene lactones) in Arnicae flos was studied. The preprocessing of the spectra were performed by using the conventional Golay-Savitzky procedure and the newly developed step-by-step filter. The results obtained show that the step-by-step filter derivatives provide a better signal-to-noise ratio at a lower convolution window. Better calibration for the content of protocatechuic acid, chlorogenic acid, caffeic acid, p-cumaric acid, ferulic acid, isoquercitrin, and quercetin were obtained by step-by-step filter derivatives, compared to the direct raw spectra processing and the Golay-Savitzky approach. Although the step-by-step filter substantially reduces the spectral distortion, the convolution procedure leads to loss of spectral points in the red end of the spectral curve. Probably for this reason this approach shows better calibration only in seven of the monitored 13 active components.