Graphical Abstract: HCA 2/2003

The synthesis and antioxidant efficiencies of amphiphilic gallic acid derivatives are reported. To specify the impact of chemical structure on the antioxidant efficiency, several structural modifications of gallic acid were performed. The following structural features were chosen: i) introduction of hydrophobic or hydrophilic residues on the gallic acid and the type of their linkage, ii) the hydrophilic and/or lipophilic character of the whole molecule. The physico‐chemical studies of the different series prepared revealed that the antioxidant efficiency of this polyphenol depends clearly on the nature of the linkage with both hydrophilic and hydrophobic parts. A push‐pull effect is always necessary, and ester or amide bonds seem well adapted to increase the antioxidant efficiency. Second, under the oxidation conditions applied, it was observed that the hydrophilic and/or lipophilic character affects drastically the antioxidant activity of gallic acid derivatives. The results obtained are in accordance with the polar paradox, hydrophobic derivatives inhibit oxidation in an aqueous phase, whereas hydrophilic products are not efficient.     

Silver nanoparticles as antimicrobial agent: a case study on E. coli as a model for Gram-negative bacteria

The antimicrobial activity of silver nanoparticles against E. coli was investigated as a model for Gram-negative bacteria. Bacteriological tests were performed in Luria-Bertani (LB) medium on solid agar plates and in liquid systems supplemented with different concentrations of nanosized silver particles. These particles were shown to be an effective bactericide. Scanning and transmission electron microscopy (SEM and TEM) were used to study the biocidal action of this nanoscale material. The results confirmed that the treated E. coli cells were damaged, showing formation of "pits" in the cell wall of the bacteria, while the silver nanoparticles were found to accumulate in the bacterial membrane. A membrane with such a morphology exhibits a significant increase in permeability, resulting in death of the cell. These nontoxic nanomaterials, which can be prepared in a simple and cost-effective manner, may be suitable for the formulation of new types of bactericidal materials.     

New synthesis of 7-bromo-1, 3-dihydro-3-hydroxy-5-(2′-pyridyl)-2H-1,4-benzodiazepin-2-one

A new synthesis of 7-bromo-1,3-dihydro-3-hydroxy-5-(2′-pyridyl)-2H-1,4-benzodiazepin-2-one ( 5 ) is described. Starting from bromazepam ( 3 ), C(3) acylation with lead tetraacetate/potassium iodide in acetic acid affords 4 , while its mild hydrolysis according to our recently described method (5) gives 5 . Improved hexamine cyclization of 1 into 3 , via quaternary hexaminium salt 2 , is discussed, and identification of the intermediates 7 and 8 is performed. Compound 5 undergoes on melting, or on brief heating in glacial acetic acid, the thermal rearrangement into quinazolin-2-aldehyde ( 13 ), the structure of which is confirmed by oxidation into the ester 14 , which in turn was hydrolyzed to the acid 15 . The same compound ( 5 ) rearranges on heating with manganese(III) acetate in acetic acid into the 3-amino-2-quinolone derivative 6 . On heating in glacial acetic acid in the presence of lead tetraacetate/potassium iodide (or iodine), compound 4 , in addition to giving the aldehyde 13 , ester 14 and acid 15 rearrangement products, affords 1,2-dihydroquinazolin-2-carboxylic acid 16 .     

Photoelectron spectroscopy of natural products: terpenes

HeI photoelectron spectra of three terpenes: alpha-pinene, pulegone and cembrene have been measured. The analysis of their electronic structure is based on the comparison of measured spectra with those of related compounds and on the comparison with molecular structures of studied compounds. We discuss changes in ionization energies of C-C double bonds which are situated at different positions along the rings.     

Synthesis and crystal structure determination of the new ternary intermetallic phase Na17Cu6Ga46.5 (Na102Cu36Ga279)

Na₁₇Cu₆Ga_46.5 crystallizes in the trigonal system, space group with a = B = 16.183(6), C = 35.190(9) Å; Z = 6. Diffraction data were collected on a Nonius CAD 3 diffractometer within the octants hkl and of the corresponding A-centered monoclinic cell (a = 14.993(6), B = 16.184(7), C = 25.254(8) Å; β = 119.75(5)°). The 5091 reflections were transformed and averaged into 1216 observed (I> 3σ(I)) in the space group. The structure was solved by direct methods and refined by full-matrix least-squares to a final R(F) = 0.056. The structure of Na₁₀₂Cu₃₆Ga₂₇₉ contains icosahedra displaying two types of symmetry and a triply fused icosahedron which forms a very unusual polyhedral complex with a copper atom (M₂₈CuM₂₈). Clusters are linked to each other to form an intricated three-dimensional anionic lattice. Sodium cations lie inside 12-vertex (Friauf), 15-vertex, and 16-vertex polyhedral cavities. This stoichiometric phase has been interpreted in terms of electron-deficient bonding within clusters and localized (2c-2e) bonding between clusters. In association with the extended Hückel molecular orbital (EHMO) calculation, the Wade-Mingos electron counting procedure applies successfully.     

Water motion in reverse micelles studied by quasielastic neutron scattering and molecular dynamics simulations

Motion of water molecules in Aerosol OT [sodium bis(2-ethylhexyl) sulfosuccinate, AOT] reverse micelles with water content w(0) ranging from 1 to 5 has been explored both experimentally through quasielastic neutron scattering (QENS) and with molecular dynamics (MD) simulations. The experiments were performed at the energy resolution of 85 microeV over the momentum transfer (Q) range of 0.36-2.53 A(-1) on samples in which the nonpolar phase (isooctane) and the AOT alkyl chains were deuterated, thereby suppressing their contribution to the QENS signal. QENS results were analyzed via a jump-diffusion/isotropic rotation model, which fits the results reasonably well despite the fact that confinement effects are not explicitly taken into account. This analysis indicates that in reverse micelles with low-water content (w(0)=1 and 2.5) translational diffusion rate is too slow to be detected, while for w(0)=5 the diffusion coefficient is much smaller than for bulk water. Rotational diffusion coefficients obtained from this analysis increase with w(0) and are smaller than for bulk water, but rotational mobility is less drastically reduced than translational mobility. Using the Faeder/Ladanyi model [J. Phys. Chem. B 104, 1033 (2000)] of reverse micelle interior, MD simulations were performed to calculate the self-intermediate scattering function F(S)(Q,t) for water hydrogens. Comparison of the time Fourier transform of this F(S)(Q,t) with the QENS dynamic structure factor S(Q,omega), shows good agreement between the model and experiment. Separate intermediate scattering functions F(S) (R)(Q,t) and F(S) (CM)(Q,t) were determined for rotational and translational motion. Consistent with the decoupling approximation used in the analysis of QENS data, the product of F(S) (R)(Q,t) and F(S) (CM)(Q,t) is a good approximation to the total F(S)(Q,t). We find that the decay of F(S) (CM)(Q,t) is nonexponential and our analysis of the MD data indicates that this behavior is due to lower water mobility close to the interface and to confinement-induced restrictions on the range of translational displacements. Rotational relaxation also exhibits nonexponential decay. However, rotational mobility of O-H bond vectors in the interfacial region remains fairly high due to the lower density of water-water hydrogen bonds in the vicinity of the interface.     

Synthesis and Crystal Structure of M11X10 Compounds, M=Sr, Ba and X=Bi, Sb. Electronic Requirements and Chemical Bonding

The intermetallic compounds Sr₁₁Bi₁₀, Ba₁₁Bi₁₀, and (Sr₅Ba₆)Sb₁₀ have been obtained from melts of mixtures of the elements. They crystallize in the tetragonal system, space group I4/mmm, Ho₁₁Ge₁₀ structure type, tI84 Pearson symbol, Z=4, with cell parameters a=12.765(3), 13.230(3), 12.748(2) Å and c=18.407(3), 19.365(3), 18.761(2) Å, respectively. The structures were solved from single-crystal X-ray data and refined by full-matrix least-squares to R1=6.71, 5.44, and 5.73%. The structure of M₁₁X₁₀ contains three discrete anionic moieties: square rings X⁴⁻₄, dumbbells X⁴⁻₂, and isolated X³⁻. Using formal charges the unit cell of M₁₁X₁₀ may be described as containing 44 M²⁺, 2X⁴⁻₄, 8X⁴⁻₂, and 16X³⁻ ions. This structure is discussed in comparison with other Bi or Sb pnictide compounds. Bonding is analyzed therein using molecular orbital (EHMO) calculations for the anions (dumbbell and square units) and also the periodic tight-binding method. Lone pair repulsions inside and between the anionic units are evidenced; they are compensated by strong bonding cation-to-anion interactions. Interatomic distances along the series appear to be more dependent on packing than on electronic effects.     

Water/hydrocarbon interfaces: effect of hydrocarbon branching on single-molecule relaxation

Water/hydrocarbon interfaces are studied using molecular dynamics simulations in order to understand the effect of hydrocarbon branching on the dynamics of the system at and away from the interface. A recently proposed procedure for studying the intrinsic structure of the interface in such systems is utilized, and dynamics are probed in the usual laboratory frame as well as the intrinsic frame. The use of these two frames of reference leads to insight into the effect of capillary waves at the interface on dynamics. The systems were partitioned into zones with a width of 5 A, and a number of quantities of dynamical relevance, namely, the residence times, mean squared displacements, the velocity auto correlation functions, and orientational time correlations for molecules of both phases, were calculated in the laboratory and intrinsic frames at and away from the interface. For the aqueous phase, translational motion is found to be (a) diffusive at long times and not anomalous as in proteins or micelles, (b) faster at the interface than in the bulk, and (c) faster upon reduction of the effect of capillary waves. The rotational motion of water is (a) more anisotropic at the interface than in the bulk and (b) dependent on the orientation of the covalent O-H bond with respect to the plane of the interface. The effect of hydrocarbon branching on aqueous dynamics was found to be small, a result similar to the effect on the interfacial water structure. The hydrocarbon phase shows a larger variation for all dynamical probes, a trend consistent with their interfacial structure.