Theoretical and experimental studies of enflurane. Infrared spectra in solution, in low-temperature argon matrix and blue shifts resulting from dimerization

Theoretical studies are performed on enflurane (CHFCl-CF(2)-O-CHF(2)) to investigate the conformational properties and vibrational spectra. Calculations are carried out at the B3LYP/6-31G(d) level along with a natural bond orbital (NBO) analysis. Experimental infrared spectra are investigated in carbon tetrachloride solution at room temperature and in argon matrix at 12 K. In agreement with previously reported data (Pfeiffer, A.; Mack, H.-G.; Oberhammer, H. J. Am. Chem. Soc. 1998, 120, 6384), it is shown that the four most stable conformers possess a trans configuration of the C-C-O-C skeleton and a gauche orientation of the CHF(2) group (with respect to the central C-O bond). These conformations are favored by electrostatic interaction between the H atom of the CHF(2) group and the F atoms of the central CF(2) group. Hyperconjugation effects from the O lone pairs to the antibonding orbitals of the neighboring C-H and C-F bonds also contribute to the stability of the four conformers. The vibrational frequencies, infrared intensities, and potential energy distributions are calculated at the same level of theory for the most stable conformers. On the basis of the theoretical results, these conformers are identified in an argon matrix. The influence of the concentration on the nu(CH) vibrations suggests the formations of higher aggregates in solution. Theoretical calculations are carried out on the enflurane dimer. The results show that the dimer is formed between two enflurane conformers having the largest stability. The dimer has an asymmetric cyclic structure, the two enflurane molecules being held together by two nonequivalent C-H...F hydrogen bonds, the C-H bond of the CHFCl group acting as a proton donor, and one of the F atoms of the CHF(2) groups acting as a proton acceptor. The theory predicts a contraction of 0.0014-0.0025 A of the two CH bonds involved in the interaction along with a blue shift of 30-38 cm(-1) of the corresponding nu(C-H) bands, in good agreement with the blue shifts of 35-39 cm(-1) observed in an argon matrix.     

Application of solid-phase microextraction to monitoring indoor air quality

Practical application of Solid-Phase Microextraction (SPME) for the assessment of the quality of indoor air is presented. SPME was used to sample selected organic pollutants (carbon tetrachloride, benzene, toluene, chlorobenzene, p-xylene and n-decane). An SPME fiber was coated with a 100 μm film of polydimethylsiloxane. The analytes extracted were analysed with a gas chromatograph directly coupled with a mass spectrometer (GC-MS). The method was used to assess the indoor air quality in a few selected flats. The concentrations ranged from below detection limits to 6.9 mg/m³ for benzene depending on the flat; they were relatively high for newly built or freshly renovated flats. Received: 14 July 1998 / Revised: 17 November 1998 / Accepted: 21 November 1998     

Capillary electrophoretic separation of N-acetylcysteine and its impurities as a method for quality control of pharmaceuticals.

Capillary electrophoresis has been applied to separate and determine N-acetylcysteine (NAC) and related impurities. Determination conditions were found to be optimum with 100 mmol/l borate as the buffer, pH 8.40. The limit of detection was established for each substance examined. The method has been validated by examining linearity ranges, precision and repeatability. The method was used to determine the content of NAC in, and purity of, pharmaceutical preparations. The major impurities (N,N-diacetylcystine, N,S-diacetylcysteine and cystine) were determined at levels of 0.1%.     

Growth of thin polymer films containing side-chain azo-dye analyzed by atomic force microscopy

Thin films containing both the azo-dye disperse red 1 (DR1) and the poly(methylmetacrylate) (PMMA) or the poly(phenylenevinylene) (PPV) are deposited by Langmuir-Blodgett and spin coating techniques on various substrates. The morphology, surface structure and growth pattern of the azo-dye-polymers were studied by atomic force microscopy. Nucleation and growth processes are responsible for the generation of different structures. The spin coated films were additionally oriented using the electric field poling method (corona poling). The film homogeneity is improved by this method in all cases. Due to the polar character of DR1 molecules, rod-like sub-structures are observed after the corona poling process in DR1-MMA films. The indium tin oxide surface enhances reorientation of the azo-dye-polymer molecules during corona poling and results in a significant reduction of the surface roughness.     

Synthesis, spectroscopic characterization, X-ray structure and DFT calculations of [Re(CO)3L2Cl] (L = 1,2,4-triazolo-[1,5-a]pyrimidine)

The paper presents a combined experimental and computational study of novel tricarbonyl complex – fac-[Re(CO)₃(tp)₂Cl] (tp = 1,2,4-triazolo-[1,5-a]pyrimidine). The compound has been characterized spectroscopically and structurally (by single-crystal X-ray diffraction). The absorption and emission spectra of the complex have been discussed on the basis of DFT and time-dependent (TD)DFT calculations.     

Diaquadichloridobis(1H‐imidazole)manganese(II) at 100 K

The mononuclear title complex, [MnCl₂(C₃H₄N₂)₂(H₂O)₂], is located on a crystallographic inversion center. The Mn^II ion is coordinated by two imidazole ligands [Mn—N = 2.2080 (9) Å], two Cl atoms [Mn—Cl = 2.5747 (3) Å] and two water molecules [Mn—O = 2.2064 (8) Å]. These six monodentate ligands define an octahedron with almost ideal angles: the adjacent N—Mn—O, N—Mn—Cl and O—Mn—Cl angles are 90.56 (3), 92.04 (2) and 90.21 (2)°, respectively. Hydrogen bonds between the coordinated water molecules and Cl atoms form a two‐dimensional network parallel to (100) involving R₄²(8) rings. The two‐dimensional networks link into a three‐dimensional framework through weaker N—H...Cl interactions. Thermogravimetric analysis results are in accordance with the water‐coordinated character of the substance and its dehydration in two successive steps.     

The chemical composition of the essential oils of Cirsium palustre and C. rivulare and their antiproliferative effect

The composition of the essential oils of Cirsium palustre and C. rivulare and their antiproliferative activity against breast adenocarcinoma cells (MCF-7 and MDA-MBA-231) were investigated. The essential oils obtained by hydro-distillation from the roots (yield 0.2 and 0.1% v/w, respectively), leaves and inflorescences (yield below 0.01%), were analyzed by gas chromatography coupled with mass spectrometry (GC-MS). The composition of the essential oils in the respective organs of each plant differed considerably. On the other hand, similarities were observed in the composition of root and leaf oils. In C. palustre and C. rivulare root oil, 50 and 39 constituents were identified, accounting for 95.3% and 92.4% of the total content. The main components were aplotaxene and its derivatives, representing 78.6% and 46.6% of the total content. In leaf oils of both species, 59 and 49 compounds, respectively, were identified, representing 67.4% and 78.3% of the total content. The major constituents were beta-damascenone (4.1% and 13.4%, respectively) and beta-ionone (6.7% and 5.3%, respectively). Short-chain saturated and unsaturated aliphatic alcohols and aldehydes constituted another important group of compounds (17.7% and 9.0%, respectively). The essential oils of the roots have moderate anti-proliferative activity, with IC50 values ranging from 110 to 140 microg/mL. These concentrations were below the level able to inhibit the proliferation of healthy cells.     

Antimicrobial Activity of Geranium Oil against Clinical Strains<em> </em>of <em>Staphylococcus aureus</em>

The aim of this work was to investigate the antibacterial properties of geranium oil obtained from Pelargonium graveolens Ait. (family Geraniaceae), against one standard S. aureus strain ATCC 433000 and seventy clinical S. aureus strains. The agar dilution method was used for assessment of bacterial growth inhibition at various concentrations of geranium oil. Susceptibility testing of the clinical strains to antibiotics was carried out using the disk-diffusion and E-test methods. The results of our experiment showed that the oil from P. graveolens has strong activity against all of the clinical S. aureus isolates-including multidrug resistant strains, MRSA strains and MLS_B-positive strains-exhibiting MIC values of 0.25-2.50 μL/mL.