On the symmetry of the xyz vibration in the photochemistry of Pt(II) D4h complexes

A symmetry concept is proposed that links the presence of vibronic structure in UV-visible spectra in d-systems, with the identification of a single photochemical reaction pathway. It is shown that the vibronic structure on some bands of the Pt(II) D_4h complexes is due to the non- degenerate, ungerade b_1u (xyz) vibration that points on an intramolecular twisting process for the photochemical cis-trans isomerization. The reaction coordinate is unambiguously defined in a coordinate system where x and y bisect the metal-ligand ML₂ angle.     

End‐group modification of poly(2,6‐dimethyl‐1,4‐phenylene ether) and in situ synthesis of poly(2,6‐dimethyl‐1,4‐phenylene ether)‐b‐poly(ethylene terephthalate) block copolymer

The preparation of poly(2,6‐dimethyl‐1,4‐phenylene ether)‐b‐poly(ethylene terephthalate) block copolymer was performed by the reaction of the 2‐hydroxyethyl modified poly(2,6‐dimethyl‐1,4‐phenylene ether) (PPE‐EtOH) with poly(ethylene terephthalate) (PET) by an in situ process, during the synthesis of the polyester. The yield of the reaction of the 2‐hydroxyethyl functionalized PPE‐EtOH with PET was close to 100%. A significant proportion of the PET‐b‐PPE‐EtOH block copolymer was found to have short PET block. Nevertheless, the copolymer structured in the shape of micelles (20 nm diameter) and very small domains with 50–200 nm diameter, whereas unmodified PPE formed much larger domains (1.5 μm) containing copolymer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3985–3991, 2008     

Real time study of hybrid sol-gel photopolymerization by UV light

Polycrystalline La_0.67 (Sr_1-x Cd _x )_0.33MnO₃ (LSCMO x = 0, 1/8, 2/8, 3/8, 4/8) films were fabricated on Si(100) single crystal substrates by the sol–gel and the rapid annealing process. According to the field-emission scan electron microscopy (FE-SEM) observation and X-ray (XRD) diffraction studies, all the samples are single phase. We also prepared a series of samples by fixing the ratio of La at 0.67. It is shown that with increase of the doping amount x in La_0.67(Sr_1-x Cd _x )_0.33MnO₃, the average A-site cation radius 〈A〉 decreases, the temperature of metal-insulator transition (T_MI) decreases monotonically, ρ and magnetoresistance (MR) values increase dramatically, which can be explained by the lattice effects. The enhanced MR effect at low temperature for the LSCMO film is attributed to the suppression of the spin dependent scattering of polarized electrons at the grain boundaries. The low-field magnetoresistance values under 0.3 T are observed to be 2.48% (x = 0) at 300 K and 37.5% (x = 4/8) at 85 K, respectively.     

Comparative conformational analysis between an undecamer of DNA and its apurinic homologue

Molecular modeling of a DNA undecamer and a corresponding DNA apurinic undecamer (d(CGCACXCACGC) d(GCGTGTGTGCG), X = A or apurinic site) has been performed using the jumna program. Among the possible structures, several are slightly distorted and correctly fit the experimental data obtained from NMR measurements. In these structures, the thymine base that faces the apurinic site lies inside the double helix.     

Protection and Labelling of Thymidine by a Fluorescent Photolabile Group

A fluorescent photolabile group including coumarin and MeNPOC moieties was synthesized to protect 5′‐OH terminal function of thymidine (T). Its photochemical and photophysical properties were studied, in particular the photocleavage (photodeprotection under a 365‐nm irradiation) is only lowered by a factor of two by addition of the fluorophore. Fluorescence properties of the coumarin probe are not changed upon irradiation, which is satisfactory for the application required, i.e., in situ synthesis of DNA microarrays.     

Amide‐Based Oligocatenanes by an Iterative Template Strategy

A new pathway for the supramolecular synthesis of oligocatenanes is developed. It is based on a combination of most suitable macrocyclic structural units, obtained from tert‐butyl‐substituted isophthalic acid and terephthalic acid building blocks. These structural parts guarantee, on the one hand, the solubility of the catenanes and their intermediates, and, on the other hand, the preferred formation of larger ring sizes of the macrocycles to be intertwined. Acting as monotopic and ditopic concave templates, the tetra‐ and octalactam macrocycles were submitted to threading procedures to yield higher‐order catenanes of the amide type. By repetition of the threading steps, it was possible to isolate multiply mechanically connected [n]catenanes up to n=4 composed of various macrocyclic units.