Synthesis and characterization of alkyl-, alkenyl-, acyl- and nitrogen-substituted derivatives of the potent phototoxin α-terthiophene

Some alkyl-, alkenyl-, acyl- and nitrogen- derivatives of α-terthienyl 1 have been synthesized in an effort to expand the potential insecticidal activity profile of this compound. The introduction of substituents was carried out directly on the α-terthienyl molecule. Three compounds were isolated in the nitration reaction and the compounds have been identified as 5-nitro-2,2′:5′,2″-terthiophene 5 , 3′-nitro-2,2′:5′,2″-terthiophene 6 and 3-nitro-2,2′:5′,2″-terthiophene 7 respectively. Preliminary results of biological acitivity are reported.     

Photoelectrochemical oxidation of water at transparent ferric oxide film electrodes

The fabrication of thin-film Fe(2)O(3) photoanodes from the spray pyrolysis of Fe(III)-containing solutions is reported along with their structural characterization and application to the photoelectrolysis of water. These films combine good performance, measured in terms of photocurrent density, with excellent mechanical stability. A full investigation into the effects that modifications of the spray-pyrolysis method, such as the addition of dopants or structure-directing agents and changes in precursor species or carrier solvent, have on the performance of the photoanodes has been realized. The largest photocurrents were obtained from photoanodes prepared from ferric chloride precursor solutions, simultaneously doped with Ti(4+) (5%) and Al(3+) (1%). Doping with Zn(2+) also shows promise, cathodically shifting the onset potential by approximately 0.22 V.     

A new biotinylated tris bipyridinyl iron(II) complex as redox biotin-bridge for the construction of supramolecular biosensing architectures

The bioaffine immobilization of several avidin layers on an electrode modified by a biotinylated polymer was accomplished by the first biotinylated redox bridge consisted of a tris(bipyridyl)iron(II) complex bearing six pre-oriented biotin groups.     

Quantum chemistry and Dick Stufkens photochemistry

A survey of the quantum chemical results obtained for several MLCT complexes studied in Amsterdam is presented in order to illustrate the progress made in this field from the beginning of the 1980s when excited states properties were analyzed in terms of bonding and antibonding molecular orbitals (MO). Nowadays the photoactive states and the main features of the absorption spectra can be determined without any ambiguity. The time scales of elementary processes such as direct ultra-fast dissociations or intersystem crossing processes, are also readily available.     

Sidnyaxanthin,a new carotenoid from the tunicate, Sidnyum argus.

A new carotenoid, Sidnyaxanthin, was isolated from the Tunicate: Sidnyum argus. The structure was elucidated by spectral analysis and chemical transformation     

Recentered Importance Sampling With Applications to Bayesian Model Validation

Since its introduction in the early 1990s, the idea of using importance sampling (IS) with Markov chain Monte Carlo (MCMC) has found many applications. This article examines problems associated with its application to repeated evaluation of related posterior distributions with a particular focus on Bayesian model validation. We demonstrate that, in certain applications, the curse of dimensionality can be reduced by a simple modification of IS. In addition to providing new theoretical insight into the behavior of the IS approximation in a wide class of models, our result facilitates the implementation of computationally intensive Bayesian model checks. We illustrate the simplicity, computational savings, and potential inferential advantages of the proposed approach through two substantive case studies, notably computation of Bayesian p-values for linear regression models and simulation-based model checking. Supplementary materials including the Appendix and the R code for Section are available online.     

Spectroscopy of Ru(II) polypyridyl complexes used as intercalators in DNA: Towards a theoretical study of the light switch effect

The absorption spectroscopy of [Ru(phen)₂dppz]²⁺ and [Ru(tap)₂dppz]²⁺ (phen = 1,10-phenanthroline, tap = 1,4,5,8-tetraazaphenanthrene; dppz = dipyridophenazine) complexes used as molecular light switches by intercalation in DNA has been analysed by means of Time-Dependent Density Functional Theory (TD-DFT). The electronic ground state structures have been optimized at the DFT (B3LYP) level of theory. The absorption spectra are characterized by a high density of excited states between 500 nm and 250 nm. The absorption spectroscopy of [Ru (phen)₂dppz]²⁺ in vacuum is characterized by metal-to-ligand-charge-transfer (MLCT) transitions corresponding to charge transfer from Ru(II) either to the phen ligands or to the dppz ligand with a strong MLCT () absorption at 411 nm. In contrast, the main feature of the lowest part of the vacuum theoretical spectrum of [Ru(tap)₂dppz]²⁺ between 522 nm and 400 nm is the presence of various excited states such as MLCT (), ligand-to-ligand-charge-transfer LLCT () or intra-ligand IL () states. When taking into account solvent corrections within the polarizable continuum model (PCM) approach (H₂O, CH₃CN) the absorption spectrum of [Ru(tap)₂dppz]²⁺ is dominated by a strong absorption at 388 nm (CH₃CN) or 390 nm (H₂O) assigned to a ¹IL () corresponding to a charge transfer from the outside end of the dppz ligand to the site of coordination to Ru(II). These differences in the absorption spectra of the two Ru(II) complexes have dramatic effects on the mechanism of deactivation of these molecules after irradiation at about 400 nm. In particular, the electronic deficiency at the outside end of the dppz ligand created by absorption to the ¹IL state will favour electron transfer from the guanine to the Ru(II) complex when it is intercalated in DNA.     

Photoactivity and UV absorption spectroscopy of RCo(CO)4 (R = H, CH3) organometallic complexes

The photoactivity of RCo(CO)4 (R = H, CH3) complexes has been investigated and compared by means of state correlation diagrams connecting the low-lying singlet (1)E (d(Co) --> sigma*(Co-R) and d(Co) --> pi*(CO)) and (1)A1 (d(Co) --> pi*(CO)) electronic states accessible through UV irradiation, and the low-lying triplet states ((3)E and (3)A1), to the corresponding states of the primary products R + Co(CO)4 and CO(ax) + RCo(CO)3. The electronic absorption spectra have been calculated by time-dependent wave packet propagations on two-dimensional potential energy surfaces describing both channels of dissociation, namely the homolysis of the R-Co and the CO(ax)-Co bonds. It is shown that the absorption spectrum of HCo(CO)4 is characterized by two peaks; the most intense peaks for each set are located respectively at 42,659 and 45,001 cm(-1). The CH(3)Co(CO)4 absorption spectrum also gives two sets of signals with maximum intensities found at 42,581 and 51,515 cm(-1). These bands for both molecules are assigned to the two metal-to-ligand-charge-transfer (MLCT; d(Co) --> pi*(CO)) states. Three photoactive states have been determined in both molecules, namely the singlet metal-to-sigma-bond-charge-transfer (MSBCT) states (a(1)E and b(1)E), simultaneously dissociative for both the homolysis of CO and the R-Co bond, and the (3)A1 (sigma(Co-R) --> sigma*(Co-R)), dissociative along the R-Co bond.