Long bonds in radical cations of sorbitol and mannitol

The quantum chemical analysis (RM1 semiempirical method) of sorbitol and mannitol in their radical cation states reveals C-C long bonds with lengths around 2.1 or 2.2 Å. In some cases, the stabilities of these long bonds appear to be related with the intensities of the corresponding peaks found in the mass spectra of these hexitols

Semi-empirical proof of long bond states as intermediates in mass spectrometry fragmentation of aldohexofuranose derivatives

Following the observation that the m/z 101 peak is usually the base peak in the electron ionization mass spectra of di-O-isopropylidenated aldohexofuranose derivatives, quantum chemical calculations were carried out in order to provide a judicious explanation for the preference of these derivatives towards the cleavage of the exocyclic dioxolane moiety. It was also established that geminal electron donor functional groups play an important part in the stabilization of the radical cation generated during the loss of one electron from these compounds (the ionization process). In this paper, by using the PM7 semi-empirical method we show that the radical character is preferentially located between the C4-C5 carbon atoms from the di-O-isopropylidenated derivatives, which is why the C4-C5 bond becomes elongated, thus justifying the cleavage that produces the high intensity peak at m/z 101

Use of some natural supports for the adsorption of theophylline from aqueous solutions

In this work, the interaction of Theophylline with lemon peel and olive leaves (two natural solid supports) was studied at 25, 35 and 45 oC in order to identify the most appropriate theoretical adsorption model, as well as the corresponding thermodynamic parameters (free energy of Gibbs, enthalpy and entropy) of the adsorption process. In the first stage, the time necessary for attaining the equilibrium was established in a series of preliminary experiments, which indicated periods of time ranging from 182 to 356 minutes. The experimental data obtained from the adsorption process was fitted to the Freundlich and Langmuir classical adsorption models by linear regression analysis. The obtained results indicate that for both studied systems, the Langmuir model described better the interaction of Theophylline with the solid supports taken in work

Preliminary TLC studies on Posidonia oceanica seagrass

Several photosynthetic pigments, i.e. chlorophylls and carotenoids, belonging to Posidonia oceanica seagrass, were separated by thin-layer chromatography (TLC) using a hexane/acetone solvent mixture. Additionally, densitometric measurements and spectral scanning of the TLC plates were performed using the Camag TLC Scanner 3 together with the WinCATS software

TLC-Densitometric investigation of bioactive components from Mediterranean algae

Several photosynthetic pigments from two algae, namely Padina pavonica and Codium fragile, were extracted in different solvents and subsequently analyzed through TLC. The optimization of the separation parameters led to the choosing of the optimum eluent (hexane/acetone mixture) for polar silica gel plates. The isolated compounds were evaluated through densitometric measurements and by the acquisition of their UV-Vis spectra. While xanthophylls, chlorophyll a and pheophytin a were the most typical pigments of Padina pavonica, chlorophyll a and b, xanthophyll and β-carotene were the most characteristic pigments for Codium fragile

Characterization by soft ionization mass spectrometry methods of mono- and oligosaccharides functionalized at the anomeric center

In order to obtain oligosaccharides functionalized with amine groups, aliphatic diamines and polyamines were coupled with maltose by using reductive amination reactions. The synthesized compounds were characterized through electrospray ionization mass spectrometry (ESI-MS), while finer structural details were obtained by using MS

DFT study of long bonds in radical cations of sugar derivatives

We have performed DFT computations on radical cations of several monosaccharide derivatives, using the STO-3G and 3-21G basis sets. The obtained long bond lengths were compared with the values we have previously obtained using the RM1 and PM7 semi-empirical methods. The applied DFT methods offered smaller values for the long bond lengths, attaining only 1.6÷1.7 Å. Also, in contrast with the simple STO-3G basis set, which shows some exceptions, the more advanced 3-21G basis set always places the long bond in the correct C4-C5 position, as suggested by the EI-MS analyses