Molecular organization in two-dimensional films of liquid II. Langmuir and Langmuir-Blodgett films of a perylene-like dye mixed with liquid crystals having a terminal cyano group crystalline mixtures

Langmuir and Langmuir-Blodgett (LB) films of a perylene-like compound and its binary mixtures with 4-octyl-4'-cyanobiphenyl (8CB) and 4-pentyl-4"-cyano-p-terphenyl (5CT) have been studied. On the basis of the surface pressure-area isotherms, the molecular organization on the air-water interface has been estimated. Information about the miscibility or the phase separation of components in the binary mixtures has been obtained. The spectroscopic study of the LB films has allowed conclusions to be drawn about the arrangement of the molecules on the quartz slides. The fluorescence spectra of the LB films of the perylene-like compound have revealed the formation of self-aggregates.     

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.     

Chemoselective Removal of Protecting Groups from O-Glycosyl Amino Acid and Peptide (Methoxyethoxy)ethyl Esters Using Lipases and Papain

The selective C-terminal deprotection of O-glycopeptide (methoxyethoxy)ethyl esters is achieved under mild conditions (pH 6.6, 37 degrees C) by enzymatic hydrolysis using papain or lipase M from Mucor javanicus to give building blocks useful for chain-extending glycopeptide synthesis. On the other hand, the selective removal of acetyl protecting groups from the saccharide portion of glycopeptides is accomplished by alternative enzymatic hydrolysis with lipase WG from wheat germ to furnish model substrates for enzymatic glycosyl transfer reactions in order to extend the carbohydrate side chain of these conjugates.     

Alignment of liquid crystal and dichroic dye molecules in mixed Langmuir and Langmuir-Blodgett films

A study of dichroic dye-liquid crystal mixtures (guest-host systems) in monolayers formed at a gas-liquid interface (Langmuir films) and at a solid surface (Langmuir-Blodgett films) has been made. As a host 4- n -octyl-4'-cyanobiphenyl (8CB) or 4- n -pentyl-4"-cyano- p -terphenyl (5CT) were chosen, while three dichroic azo dyes with various molecular structures were used as guest species. The dyes were added to the liquid crystal matrices at a concentration corresponding to the whole range of molar fractions and the surface pressure-mean molecular area isotherms for Langmuir films were recorded. On the basis of the isotherms, conclusions about the molecular organization and the miscibility of the components in the ultrathin films were drawn. The Langmuir films were transferred onto the quartz plates at surface pressures below the collapse point. The polarized absorption spectra of the Langmuir-Blodgett films were recorded and information about the alignment and intermolecular interactions in the mixtures of the non-amphiphilic dichroic dyes and the liquid crystals with strongly polar terminal groups were obtained.     

Application of carbon nanotubes as solid-phase extraction sorbent for analysis of chlorophenols in water samples

The aim of this work was to investigate the efficiency of various MWCNTs as SPE materials for the preconcentration of chlorophenols. The COOH-functionalized MWCNTs and MWCNTs were used as SPE sorbents. To evaluate the capability of MWCNTs for the preconcentration of chlorophenols from water samples, 2,4-chlorophenol, 4-chlorophenol, 2,4,6-chlorophenol, 2,6-chlorophenol, 3,4-chlorophenol, and 2-chlorophenol were used as model compounds. Chlorophenols were extracted with acetone, methanol, ethanol, and dichloromethane, and determined by gas chromatography–mass spectrometry. COOH-functionalized MWCNTs <8 nm were found to be the best sorbent for the tested chlorophenols. For COOH-functionalized MWCNTs <8 nm, the recovery rates for all chlorophenols were higher than 50% when acetone or ethanol was used as eluents. In the case of dichloromethane elution, recovery rates for chlorophenols were from 62.0% for 2,6-DCP to 116.8% for 2,4-DCP; only for 2,4,6-TCP was the recovery rate 30.6%. Similar percentage recoveries were achieved with methanol as the eluent.     

Reliability in reconstruction of the axisymmetric refractive index profiles from transverse interferograms. Accurate versus approximate methods: A comparative study

A mathematical formalism related to the approximate as well as the accurate interferometric data reduction schemes is briefly outlined and subsequently applied in the reconstruction of the assumed (Luneburg) axisymmetric refractive index distribution. The presented comparative analysis confirms the generally held opinion that the approximate methods (“straight-line” and Kokubun-Iga approaches) may provide quite reasonable results in the examination of refractively inhomogeneous disturbances characterized by weak gradient and moderate index variation. On the other hand, the accurate scheme for transverse interferometric data interpretation and reduction, based on the close-form correlation between the fringe shift and the deflection function, [1] remains the only method for reliable reconstruction of strongly refracting index profiles, independently of magnitude of refraction and ambiguity of the fringes. This fact is of considerable importance for transverse interferometry of fibers (preform rods) and/or GRIN-rod lenses characterized by high numerical apertures.     

Conformations of 2-C:1-N-carbonyl-2-deoxy-d-glycopyranosylamines

Geometry and molecular conformation of theN-toluenesulfonyl1 andN-acetyl-2 derivatives of peracetylated 2-C:1-N-carbonyl-2-deoxy--d-glucopyranosylamine were investigated with the use of X-ray diffraction methods. Compound1 (C₂₀H₂₃NSO₁₀) crystallizes in the monoclinic P2₁ space group, withZ=2 anda=8.238(1),b=7.988(1),c=16.928(2)Å, =99.12(1)°. Compound2 (C₁₅H₁₉NO₉) crystallizes in orthorhombic P2₁2₁2₁ space group withZ=4 anda=8.385(1),b=8.550(1),c=24.000(2) Å. Analysis of differences in bond lengths and angles between compounds1 and2 and other compounds of this class showed that the electronwithdawing effect by the residue located at the nitrogen atom can be manifested by lengthening of the -lactam C-N bonds, with simultaneous shortening of the distance between two carbon atoms at the ring fusion. Semi-empirical calculations suggested that the title compounds displayed two positively charged centers, susceptible for attack of nucleophiles, one at the carbonyl group of -lactam and the second at the anomeric carbon atom. Atomic charges, however, calculated for compounds1 and2 did not explain their different reaction directions during alcoholysis.Part 3. For part 1 and 2, see Refs. 5 and 6.     

Intermolecular interactions in mixtures of dichroic dyes with n-alkyl-4-(4-isothiocyanatophenyl)bicyclo[2,2,2]octanes

On the basis of the polarized absorption spectra, the guest order parameter as a function of temperature for five dichroic azo dyes dissolved in four members (pentyl to octyl) of the homologous series of n-alkyl-4-(4-isothiocyanatophenyl)bicyclo[2,2,2]octanes has been evaluated. Moreover, the influence of the dichroic dye addition on the nematic-isotropic phase transition temperature has been examined. The relation between the molecular geometry of the guest, its orientation efficiency in the nematic host and the clearing temperature of the azo dye-liquid crystal mixtures has been determined. The experimental results have been compared in some detail with calculations performed on the basis of the mean field theory for binary mixtures.     

Influence of substituent length in dichroic dye molecules on the orientational properties of guest-host liquid crystal mixtures

The polarized absorption spectra of eight dichroic dyes, alkyl derivatives of 4-amino-(N-ethylnaphthalimide) dissolved in the nematic liquid crystals 5CB and 6CHBT have been measured as a function of temperature. On the basis of these spectra, the guest order parameter has been evaluated. The influence of the alkyl chain length of the dye molecule on the molecular orientation has been examined. Moreover, the nematic-isotropic transition temperatures for the dye-liquid crystal mixtures have been determined. The experimental results have been compared in some detail with calculations made on the basis of the mean field theory for binary mixtures.