Zeeman effect of chlorine nuclear quadrupole resonance and hydrogen bonding in 2,6-, 2,5- and 3,5-dichlorophenols

The Zeeman effect of chlorine nuclear quadrupole resonance in polycrystalline samples of 2,6-, 2,5 and 3,5-dichlorophenol has been investigated at room temperature in order to study the effect of hydrogen bonding on the electric field gradient asymmetry parameter n. While the two n.q.r. lines in 3,5-dichlorophenol gave an asymmetry parameter of 10%, those in 2,6- and 2,5-dichlorophenol gave different values of n for the two chlorines. The chlorine atom which is ortho to the OH group and involved in hydrogen bonding (i.e., corresponding to the low frequency line) gave an asymmetry parameter of 0.21 in 2,6-dichlorophenol and 0.17 in 2,5-dichlorophenol while the other chlorine (i.e., corresponding to the high frequency line) gave a lower value of 0.12 in 2,6-dichlorophenol and 0.11 in 2,5-dichlorophenol. These values of n are discussed in terms of hydrogen bonding and bond parameters.

Photodegradation of dichloroacetic acid and 2,4-dichlorophenol by ferrioxalate/H2O2 system

The photo-Fenton process using potassium ferrioxalate as a mediator in the photodegradation reaction of organochloride compounds in an aqueous medium was investigated. The influence of parameters such as hydrogen peroxide and ferrioxalate concentrations and initial pH, was evaluated using dichloroacetic acid (DCA) as a model compound under black-light lamp irradiation. An upflow annular photoreactor, operating in a single pass or recirculating mode was used during photodegradation experiments with artificial light. The extent of the release of chloride ions was used to evaluate the photodegradation reaction. The optimum pH range observed was 2.5-2.8. The efficiency of DCA dechlorination increased with increasing concentrations of H2O2 and potassium ferrioxalate, reaching a plateau after the addition of 6 and 1.5 mmol/L of those reagents, respectively. The total organic carbon (TOC) content in DCA and 2,4-dichlorophenol (DCP) solutions was compared with the chloride released after photodegradation. The influence of natural solar light intensity, measured at 365 nm, was evaluated for the dechlorination of DCA on typical summer's days showing a linear dependency. The photodegradation of DCA using black-light lamp and solar irradiation was compared.

Solar photodegradation of dichloroacetic acid and 2,4-dichlorophenol using an enhanced photo-Fenton process

The photo-Fenton process using potassium ferrioxalate as a mediator was investigated for the photodegradation of dichloracetic acid (DCA) and 2,4-dichlorophenol (DCP) in aqueous medium using solar light as source of irradiation. The influence of the solution depth, the light intensity and the effect of stirring the solution during irradiation process were evaluated using DCA as a model compound. A negligible influence of stirring the solution was observed when the concentration of ferrioxalate (FeOx) was 0.8 mM and solution depth was 4.5 or 14 cm. The optimum FeOx concentration determined for solution depths between 4.5 and 14 cm was 0.8 mM considering total organic carbon (TOC) removal during DCA irradiation. The high efficiency of the photo-Fenton process was demonstrated on summer days, when only 10 min of exposition (around noon) were sufficient to completely destroy the organic carbon of a 1.0 mM DCA solution in the presence of 0.8 mM FeOx and 6.0 mM H2O2 using a solution depth of 4.5 cm. It was observed that the photodegradation efficiency increases linearly with the solar light intensity up to values around 15 Wm-2 but this linear relationship does not hold above this value showing a square root dependence. The photodegradation of a solution of DCP/FeOx showed a lower TOC removal rate than that observed for DCA/FeOx, achieving ∼90% after 35 min irradiation under 19 Wm-2, while under this light intensity, the same TOC removal of DCA/FeOx was achieved in only 10 min irradiation. © 2002 Elsevier Science Ltd. All rights reserved.

rac-3-exo-Ammonio-7-anti-carboxytricyclo-[2.2.10.2,6]heptane-3-endo-carboxylate

The racemic title compound, C9H11NO4 . H2O, a tricyclic rearranged aminonorbornane dicarboxylic acid is a conformationally rigid analogue of glutamic acid and exists as an ammonium-carboxylate zwitterion, with the bridghead carboxylic acid group anti-related. In the crystal, intermolecular N-H...O and O-H...O hydrogen-bonding interactions involving the ammonium, carboxylic acid and water donor groups with both water and carboxyl O-atom acceptors give a three-dimensional framework structure.

1,3-Dimethyl-2,6-diphenylpiperidin-4-one

In the title moleclue, C19H21NO, the 4-piperidone ring adopts a chair conformation in which the two benzene rings and the methyl group attached to C atoms all have equatorial orientations. In the crystal structure, centrosymmetric dimers are formed through weak intermolecular C-H center dot center dot center dot O hydrogen bonds [the dihedral angle between the aromatic rings is 58.51 (5)degrees].

DC-SIGN and alpha 2,6-sialylated IgG Fc interaction is dispensable for the anti-inflammatory activity of IVIg on human dendritic cells

Intravenous immunoglobulin (IVIg) is widely used to treat autoimmune diseases. Several mutually nonexclusive mechanisms are proposed to explain the beneficial effects of IVIg in patients (1, 2). Lately, Ravetch and colleagues (3) demonstrate that anti-inflammatory activity of IVIg is mediated mainly by antibodies that contain terminal _2,6-sialic acid linkages at the Asn297-linked glycan of Fc region.

A thermal molecular migration in the solid-state - structures of isomeric 5-amino-4-(2,6-dichlorophenyl)-1-(2-nitrophenyl)-1h-1,2,3-triazole (yellow form i) and 4-(2,6-dichlorophenyl)-5-(2-nitroanilino)-2h-1,2,3-triazole (red form-ii), c14h9cl2n5o2

Yellow form (I): Mr= 350.09, monoclinic, P2Jn, Z--4, a=9.525(1), b=14.762(1), c= 11.268(1),/t, fl= 107.82 (1) o , V= 1508.3 A 3 , Din(flotation in aqueous KI)= 1.539 (2), D x= 1.541 (2) g cm -3, #(Cu Ka, 2 = 1.5418 A) = 40.58 cm -~, F(000) = 712, T= 293 K, R = 8.8% for 2054 significant refections. Red form (II): Mr= 350.09, triclinic, Pi, Z=2, a=9.796(2), b= 10.750 (2), c= 7.421 (1)A, a= 95.29 (2), fl= 0108-2701/84/111901-05501.50 70.18 (1), y = 92-.76 (2) °, V= 731.9 A 3, Din(flotation in KI) = 1.585 (3), D x = 1.588 (3) g cm -3, ~t(Cu Ka, 2 = 1.5418/~) = 40.58 cm -1, F(000) = 356, T=293 K, R = 5.8% for 1866 significant reflections. There are no unusual bond distances or angles. The triazole and two phenyl rings are planar. On the basis of packing considerations the possibility of intermolecular interactions playing a role in the reactivity of the starting material is ruled out.

Acid-catalysed cyclisations: structures of novel products isolated in the reaction of 2-[3-(2,6-dimethoxyphenyl)but-2-enyl]-2-methylcyclopentane-1,3-dione with MeOH-HCl

Reaction of the title compound (1a) with anhydrous MeOH-HCl gave 2-endo-(2,6-dimethoxyphenyl)-2-exo-methyl-5-methylbicyclo[3.2.1]octane-6,8-dione (3a), 1,5,14-timethoxy-5,8-seco-6,7-dinorestra-1,3,5(10),9(11)-tetraen-17-one (4), 1,5-dimethoxy-5,8-seco-6,7-dinorestra-1,3,5(10),8,14-pentaen-17-one (5), and 3,4,5,6-tetrahydro-2,7-dimethoxy-3,6-dimethyl-3,2,6-(13-oxopropan[1]yI[3]ylidene)-2H-1-benzoxocin (6). Structures assigned to compounds (3a), (4), and (6) are based on spectral data. The exo-tricyclic acetal structure (6) was further confirmed by the analysis of the 1H n.m.r. spectra of the isomeric alcohols (11) and (12), obtained by sodium borohydride reduction of (6).

Stabilization of the Alleged 'Bishomoaromatic' Bicyclo[3.2.l]octa-2,6-dienyl Anion by Counterion Interactions and by Hyperconjugation

Hyperconjugation and inductive effects, rather than homoaromaticity, are responsible for the stabilization of the title anion in the gas phase; interaction of the double bond with the Li+ gegenion in the endo geometry contributes additionally in solution.

Temperature dependence of 35Cl NQR in 2,6-dichloropyridine

Chlorine NQR in 2,6-dichloropyridine has been investigated in the temperature range 77 K to room temperature and a single resonance line has been observed throughout. Using this data, torsional frequencies of the molecule have been evaluated on the basis of both the Bayer theory and the modified Bayer theory incorporating Tatsuzaki correction.

4-(4-Methoxyphenyl)-1-phenylpyridine-2,6(1H,3H)-dione

In the title compound, C18H15NO3, the pyridine-2,6-dione ring adopts an envelope conformation. The phenyl ring lies approximately perpendicular to the mean plane of the pyridine-2,6-dione ring [dihedral angle =81.5 (1)degrees], while the methoxyphenyl ring is tilted to the same plane by a dihedral angle of 34.8 (1)degrees. Intermolecular C-H center dot center dot center dot O interactions link the molecules into chains along [100].

Structure of 2-(2,6-dimethoxyphenyl)-2,5- dimethylbicyclo[3.2.1]octane-6,8-dione

C18H2204, orthorhombic, P212~21, a = 7.343 (4), b = 11.251 (4), c = 19.357 (4)A, Z = 4, Dr, ' = 1.20, D e = 1.254 g cm -3, F(000) = 648, p(MoKa) = 0.94 cm -~. X-ray intensity data were collected on a Nonius CAD-4 diffractometer and the structure was solved by direct methods. Full-matrix least-squares refinement gave R = 0.052 (R w = 0.045) for 1053 observed reflections. The stereochemical configuration at C(2) has been shown to be 2-exo-methyl-2-endo-(2,6-dimethoxyphenyl), i.e. (3) in contrast to the structure (2) assigned earlier based on its ~H NMR data.

1-Benzoyl-3-methyl-2,6-diphenyl-4-piperidone

In the title moleclue, C25H23NO2, the 4-piperidone ring adopts a boat conformation. The molecular conformation is stabilized by an intramolecular C-H center dot center dot center dot O hydrogen bond. In the crystal, molecules are connected through weak intermolecular C-H center dot center dot center dot O hydrogen bonds.