Boron-diindomethene (BDI) dyes and their tetrahydrobicyclo precursors--en route to a new class of highly emissive fluorophores for the red spectral range

The X-ray crystallographic, optical spectroscopic, and electrochemical properties of a newly synthesized class of boron-diindomethene (BDI) dyes and their tetrahydrobicyclo precursors (bc-BDP) are presented. The BDI chromophore was designed to show intensive absorption and strong fluorescence in an applicationary advantageous spectral range. Its modular architecture permits fusion of a second subunit, for example, a receptor moiety to the dye's core to yield directly linked yet perpendicularly prearranged composite systems. The synthesis was developed to allow facile tuning of the chromophore platform and to thus adjust its redox properties. X-ray analysis revealed a pronounced planarity of the chromophore in the case of the BDIs, which led to a remarkable close packing in the crystal of the simplest derivative. On the other hand, deviation from planarity was found for the diester-substituted bc-BDP benzocrown that exhibits a "butterfly"-like conformation in the crystal. Both families of dyes show charge- or electron-transfer-type fluorescence-quenching characteristics in polar solvents when equipped with a strong donor in the meso-position of the core. These processes can be utilized for signaling purposes if an appropriate receptor is introduced. Further modification of the chromophore can invoke such a guest-responsive intramolecular quenching process, also for receptor groups of low electron density, for example, benzocrowns. In addition to the design of various prototype molecules, a promising fluoroionophore for Na+ was obtained that absorbs and emits in the 650 nm region and shows a strong fluorescence enhancement upon analyte binding. Furthermore, investigation of the remarkable solvatokinetic fluorescence properties of the "butterfly"-like bc-BDP derivatives suggested that a second intrinsic nonradiative deactivation channel can play a role in the photophysics of boron-dipyrromethene dyes.     

Molecular geometry and tautomerism of 2-carboxymethylamido-3(4H)-quinoxalone

2-Carboxymethylamido-3(4H)-quinoxalone cyrstallizes in the triclinic space group P1 with four molecules per unit cell (a = 8.797, b = 11.240, c = 11.099 Å, α = 85.62, β = 67.75, γ = 67.35°). The structure was solved by direct methods and refined by fullmatrix least squares calculations to the final R-value of 0.042. The tautomeric equilibrium of the compound is discussed in connection with the molecular conformation and the ability to form intramolecular hydrogen bonds. Evidence is given that the oxo form of 2-hydroxyquinoxalines largely dominates and that 5-membered intramolecular chelates involving H-bonds of the type (N, O) H…(N, O) are so weak that they usually do not govern conformational equilibria.     

The crystal and molecular structure of hydrazine-N,N′-dicarbonic-acid-di-(4-chlorophenyl)-ester Dihydrate,C14H10Cl2N2O4 · 2 H2O

The crystal and molecular structure of the title compound has been determined by X-ray diffraction techniques. It crystallizes in the monoclinic space group C2/c with cell parameters a = 30.719(8), b = 5.016(3), c = 10.946(8) Å, and β = 106.08(3)°. The structure was solved by direct methods and refined to R = 0.038. The drug molecule consists of two chemically identical parts, symmetry related by a two-fold axis coinciding with that of the space group. Hydrogen bonds connect water and drug molecules forming infinite layers parallel to the y, z-plane.     

L-alpha-lyxopyranosyl (4'-->3') oligonucleotides: a base-pairing system containing a shortened backbone

[formula: see text] The L-alpha-lyxopyranosyl (4'-->3') oligonucleotide system shows cooperative base-pairing in spite of containing only five instead of the usual six covalent bonds per repetitive backbone unit. In contrast, corresponding D-beta-ribofuranosyl (4'-->3') oligonucleotides do not show adenine-thymine pairing under comparable conditions. The difference in pairing behavior relates to the conformation of the two systems' vicinal 3',4'-phosphodiester substituents, which is diaxial in the lyxopyranosyl system and 3'-axial-4'-equatorial in the ribopyranosyl system.     

Three-dimensional localization of sperm whales using a single hydrophone

A three-dimensional localization method for tracking sperm whales with as few as one sensor is demonstrated. Based on ray-trace acoustic propagation modeling, the technique exploits multipath arrival information from recorded sperm whale clicks and can account for waveguide propagation physics like interaction with range-dependent bathymetry and ray refraction. It also does not require ray identification (i.e., direct, surface reflected) while utilizing individual ray arrival information, simplifying automation efforts. The algorithm compares the arrival pattern from a sperm whale click to range-, depth-, and azimuth-dependent modeled arrival patterns in order to estimate whale location. With sufficient knowledge of azimuthally dependent bathymetry, a three-dimensional track of whale motion can be obtained using data from a single hydrophone. Tracking is demonstrated using data from acoustic recorders attached to fishing anchor lines off southeast Alaska as part of efforts to study sperm whale depredation of fishing operations. Several tracks of whale activity using real data from one or two hydrophones have been created, and three are provided to demonstrate the method, including one simultaneous visual and acoustic localization of a sperm whale actively clicking while surfaced. The tracks also suggest that whales' foraging is shallower in the presence of a longline haul than without.     

Structure and high-pressure behavior of 2,5-di-(4-aminophenyl)-1,3,4-oxadiazole

The crystalline structures of two modifications of a compound containing the oxadiazole ring, 2,5-di-(4-aminophenyl)-1,3,4-oxadiazole (DAPO) were determined. One of these modifications contains water molecules in the crystal structure, which is observed for the first time for an oxadiazole crystal. Both crystals show an orthorhombic structure. The water free modification, DAPO I, belongs to the space group Pbca (61) and has the lattice parameters: a=13.461(5), b=7.937(3) and c=22.816(8) Å (CCDC 246608). The water containing pseudo-polymorph, DAPO II, has the space group Cmcm (63) and the lattice parameters: a=16.330(5), b=12.307(2) and c=6.9978(14) Å (CCDC 246609). To gain information on the inter molecular interactions within the crystals, X-ray experiments under compression at ambient temperature and under heating at vacuum conditions were performed. Neither DAPO I nor DAPO II undergo phase transitions in the ressure range up to 5 GPa, as could be concluded from X-ray and Raman experiments. X-ray and calorimetric studies indicate that DAPO II dehydrates into DAPO I under increasing temperature. Structural considerations suggest a two-stage process. The compression behavior of both substances is well described by the Murnaghan equation of state (MEOS) and the values of the bulk modulus and its pressure derivative are determined for these crystals. Additionally, in the case of DAPO I, also the thermal expansion coefficient α₀ was measured.