Hydrogen‐bonding interactions in (3,4‐dimethoxyphenyl)acetic acid monohydrate

The crystal structure of the title compound, C₁₀H₁₂O₄·H₂O, consists of (3,4‐dimethoxyphenyl)acetic acid and water molecules linked by O—H...O hydrogen bonds to form cyclic structures with graph‐set motifs R₁²(5) and R₄⁴(12). These hydrogen‐bond patterns result in a three‐dimensional network with graph‐set motifs R₄⁴(20) and R₄⁴(22), and the formation of larger macrocycles, respectively. The C—C bond lengths and the endocyclic angles of the benzene ring show a noticeable asymmetry, which is connected with the charge‐transfer interaction of the carboxyl or methoxy groups and the benzene ring. The title compound is one of the simple carboxylic acid systems that form hydrates. Thus, the significance of this study lies in the analysis of the interactions in this structure and the aggregations occurring via hydrogen bonds in two crystalline forms of (3,4‐dimethoxyphenyl)acetic acid, namely the present hydrate and the anhydrous form [Chopra, Choudhury & Guru Row (2003). Acta Cryst. E 59 , o433–o434]. The correlation between the IR spectrum of this compound and its structural data are also discussed.     

Thioacetanilide at 120 K

The title compound, C₈H₉NS, has four symmetry‐independent molecules in the asymmetric unit. These molecules link into two independent infinite N—H...S hydrogen‐bonded chains in the a‐axis direction with graph‐set notation C₂²(8). The NH—CS group adopts a trans conformation and forms a dihedral angle of about 50° with the phenyl ring. The intermolecular hydrogen‐bond energy calculated by the density functional theory (DFT) method is −14.95 kJ mol⁻¹. The correlation between the IR spectrum of this compound and the hydrogen‐bond energy is also discussed. This molecular system is of interest because of its biological function.     

Matrix-isolated diglycolic anhydride: vibrational spectra and photochemical reactivity

The structure of diglycolic anhydride (1,4-dioxane-2,6-dione; DGAn) isolated in a low-temperature argon matrix at 10 K was studied by means of FTIR spectroscopy. Interpretation of the experimental vibrational spectrum was assisted by theoretical calculations at the DFT(B3LYP)/aug-cc-pVTZ level. The optimized structure of the isolated DGAn molecule adopts an envelope conformation, which was found to resemble closely the structure of DGAn in a crystal. The UV-induced (lambda > 240 nm) photolysis of the matrix-isolated compound was also investigated. In order to identify the main species resulting from irradiation of the monomeric DGAn, a comparison between the DFT(B3LYP)/aug-cc-pVTZ calculated spectra of the putative products and the experimental data was carried out. The observed photoproducts can be explained by a model involving four channels: (a) 1,3-dioxolan-4-one + CO; (b) CO2 + CO + oxirane; (c) formaldehyde + ketene + CO2; (d) oxiran-2-one + oxiran-2-one. As a whole, the experiments indicated that the C-O-C bridge, connecting the two C=O groups, is the most reactive fragment in the molecule excited with UV light. This observation was confirmed by the natural bond orbital (NBO) analysis revealing that the most important NBO interactions are those between the carbonyl groups and the adjacent C-O and C-C bonds.     

Critical assessment of the elemental composition of Corning archeological reference glasses by LA-ICP-MS

Corning archeological reference glasses A, B, C, and D have been made to simulate different historic technologies of glass production and are used as standards in historic glass investigations. In this work, nanoseconds (193, 266 nm) and femtosecond (800 nm) laser ablation were used to study the elemental composition of Corning glasses using laser ablation inductively coupled plasma mass spectrometry. The determined concentrations of 26 oxides (Li₂O, B₂O₃, Na₂O, MgO, Al₂O₃, SiO₂, P₂O₅, K₂O, CaO, TiO₂, V₂O₅, Cr₂O₃, MnO, Fe₂O₃, CoO, NiO, CuO, ZnO, Rb₂O, SrO, ZrO₂, SnO₂, Sb₂O₅, BaO, PbO, Bi₂O₃) are compared with values reported in the literature. Results show variable discrepancies between the data, with the largest differences found for Cr₂O₃ in Corning A; Li₂O, B₂O₃, and Cr₂O₃ in Corning B; and MnO, Sb₂O₅, Cr₂O₃, and Bi₂O₃ in Corning C. The best agreement between the measured and literature values was found for Corning D. However, even for this reference, glass re-evaluation of the data was necessary and new values for PbO, BaO, and Bi₂O₃ are proposed.     

Analytic Features of Reproducing Groups for the Metaplectic Representation

We introduce the notion of admissible subgroup of relative to the (extended) metaplectic representation via the Wigner distribution. Under mild additional assumptions, it is shown to be equivalent to the fact that the identity holds (weakly) for all We use this equivalence to exhibit classes of admissible subgroups of We also establish some connections with wavelet theory, i.e., with curvelet and contourlet frames.     

Differences between surface and bulk refractive indices of a-InxSe1−x

Thin films of amorphous indium selenide compounds (a-In_xSe_1−x) are important, e.g. for photovoltaics. The feature of merit in such applications is also the real part of refractive index n of this material. The data on n in literature are divergent. In this paper, the results of investigations on n in the bulk as well as in the interface layers of thin films of a-In_xSe_1−x are presented. The measurements had been performed using optical transmittance and reflectance in spectral range from 1.24 to 1.96 eV of linear polarized radiation that hit the samples with angles of incidence from 0° to 80°. Investigations had been done for sample temperatures from 80 to 340 K. It was found that the refractive index for areas at the free surface n_f is bigger than the refractive index n_b at the interface of thin film-substrate. The averaged over thin film thickness value of real part refractive index have the biggest value in all spectral range. Values of these coefficients increase with increasing the temperature.     

Aggregates of rod-coil diblock copolymers adsorbed at a surface

The behavior of rod-coil diblock copolymers close to a surface is discussed by using extended scaling methods. The copolymers are immersed in selective solvent such that the rods are likely to aggregate to gain energy. The rods are assumed to align only parallel to each other, such that they gain a maximum energy by forming liquid crystalline structures. If an aggregate of these copolymers adsorbs with the rods parallel to the surface the rods shift with respect to each other to allow for the chains to gain entropy. It is shown that this shift decays with increasing distance from the surface. The profile of this decay away from the surface is calculated by minimization of the total free energy of the system. The stability of such an adsorbed aggregate and other possible configurations are discussed as well.     

Addition of difluorocarbene to 4',5'-unsaturated nucleosides: synthesis and deoxygenation reactions of difluorospirocyclopropane nucleosides

Synthetic routes to 4'-(2,2-difluorospirocyclopropane) analogues of adenosine, cytidine, and uridine are described. Treatment of 2',3'-O-isopropylidene-4',5'-unsaturated compounds derived from adenosine and uridine with difluorocarbene (generated from PhHgCF3 and NaI) gave diastereomeric mixtures of the 2,2-difluorospirocyclopropane adducts. Stereoselectivity resulting from hindrance by the isopropylidene group favored addition at the beta face. Removal of base and sugar protecting groups gave new difluorospirocyclopropane nucleoside analogues. The protected uridine analogue was converted into its cytidine counterpart via a 4-(1,2,4-triazol-1-yl) intermediate. Stannyl radical-mediated deoxygenation of the 3'-O-TBS-2'-thionocarbamate derivatives gave the 2'-deoxy products of direct hydrogen transfer. In contrast, identical treatment of the 2'-O-TBS-3'-thionocarbamate isomers resulted in opening of the vicinal difluorocyclopropane ring upon generation of a C3' radical followed by homoallylic hydrogen transfer to give 4'-(1,1-difluoroethyl)-3',4'-unsaturated nucleoside derivatives. Structural aspects and biological effect considerations are discussed.     

The divisor problem for d 4 (n) in short intervals

In this paper we establish an asymptotic formula for the sum