Photophysics and X-ray structure of crystalline 2-aminopurine.

To explore the effect of intermolecular interactions on the photophysics of 2-aminopurine (2AP) in a well-defined environment, we have investigated the fluorescence properties of single 2AP crystals, having determined their X-ray structure. In the crystal, 2AP is subject to base-stacking and hydrogen-bonding interactions similar to those found in DNA. The crystal shows dual fluorescence: pi-stacked molecules in the bulk of the lattice have redshifted excitation and emission spectra, while molecules at defect sites have spectra similar to those of 2AP in solution or in DNA. Heterogeneous intermolecular interactions in the crystal give rise to multiexponential fluorescence decay characteristics similar to those observed for 2AP-labelled DNA. The presence of about 13 % of the 7H tautomer in the crystal confirms that 9H-7H tautomerisation of 2AP occurs in the ground state. Long-wavelength excitation of a 2AP-labelled oligonucleotide duplex produced redshifted emission similar to that observed in the crystal, indicating that pi-stacking interaction of 2AP with nucleobases gives rise to a low energy excited state.     

1,3-Dipolar cycloadditions of 2-thio-3-chloroacrylamides with nitrile oxides and nitrones

1,3-Dipolar cycloadditions of 2-thio-3-chloroacrylamides with nitrile oxides and nitrones is described. A series of novel isoxazolines are isolated from the nitrile oxide cycloadditions, whilst the isoxazolines generated from the nitrone cycloadditions undergo further ring opening to yield piperidines.     

Selenodiazole-fused diacetamidopyrimidine, a selective fluorescence sensor for aliphatic monocarboxylates

A designed sensor, selenodiazole-fused pyrimidine ring having two acetylamino groups at 2,4-positions has been synthesized for selective recognition of aliphatic monocarboxylate anions over a wide range of other anions. The recognition study has been carried out by UV-vis and fluorescence methods. A significant bathochromic shift of the fluorescence intensity of the receptor in the presence of carboxylate makes the receptor a discriminating sensor for aliphatic monocarboxylates.     

Oxygen as a site specific probe of the structure of water and oxide materials

The method of oxygen isotope substitution in neutron diffraction is introduced as a site specific structural probe. It is employed to measure the structure of light versus heavy water, thus circumventing the assumption of isomorphism between H and D as used in more traditional neutron diffraction methods. The intramolecular and intermolecular O-H and O-D pair correlations are in excellent agreement with path integral molecular dynamics simulations, both techniques showing a difference of ?0.5% between the O-H and O-D intramolecular bond distances. The results support the validity of a competing quantum effects model for water in which its structural and dynamical properties are governed by an offset between intramolecular and intermolecular quantum contributions.     

Measuring the complete force field of an optical trap

The use of optical traps to measure or apply forces on the molecular level requires a precise knowledge of the trapping force field. Close to the trap center, this field is typically approximated as linear in the displacement of the trapped microsphere. However, applications demanding high forces at low laser intensities can probe the light-microsphere interaction beyond the linear regime. Here, we measured the full nonlinear force and displacement response of an optical trap in two dimensions using a dual-beam optical trap setup with back-focal-plane photodetection. We observed a substantial stiffening of the trap beyond the linear regime that depends on microsphere size, in agreement with Mie theory calculations. Surprisingly, we found that the linear detection range for forces exceeds the one for displacement by far. Our approach allows for a complete calibration of an optical trap.     

Minmax robustness for multi-objective optimization problems

In real-world applications of optimization, optimal solutions are often of limited value, because disturbances of or changes to input data may diminish the quality of an optimal solution or even render it infeasible. One way to deal with uncertain input data is robust optimization, the aim of which is to find solutions which remain feasible and of good quality for all possible scenarios, i.e., realizations of the uncertain data. For single objective optimization, several definitions of robustness have been thoroughly analyzed and robust optimization methods have been developed. In this paper, we extend the concept of minmax robustness (Ben-Tal, Ghaoui, & Nemirovski, 2009) to multi-objective optimization and call this extension robust efficiency for uncertain multi-objective optimization problems. We use ingredients from robust (single objective) and (deterministic) multi-objective optimization to gain insight into the new area of robust multi-objective optimization. We analyze the new concept and discuss how robust solutions of multi-objective optimization problems may be computed. To this end, we use techniques from both robust (single objective) and (deterministic) multi-objective optimization. The new concepts are illustrated with some linear and quadratic programming instances.     

Synthesis of spiroheterocycles derived from benzo[f]chromanone

The syntheses of an important class of hitherto unreported spiro derivatives containing benzo[f]chromanone moiety involving very simple cyclocondensation reactions are described. Installation of pharmacologically active moieties like thiazolidine and thiazolidinone is achieved by taking simple reagents like ethylchloroacetate, 1, 2‐dibromo ethane and thioglycollic acid. J. Heterocyclic Chem., (2011).     

Powder neutron diffraction of SrNbO2N at room temperature and 1.5 K

The structure of strontium niobium dioxygen nitride, SrNbO₂N, has been solved by powder neutron diffraction at room temperature and 1.5 K. SrNbO₂N crystallizes in the tetragonal space group I4/mcm, with a = 5.7056 (4) and c = 8.1002 (9) Å at room temperature, and a = 5.6938 (4) and c = 8.0974 (8) Å at 1.5 K. The crystal structure is derived from the cubic perovskite archetype by a slight rotation of the Nb(O,N)₆ octahedra with respect to the tetragonal axis. A partially ordered distribution of oxygen and nitrogen on the anionic sites was found.