Rational design of a chromo- and fluorogenic hybrid chemosensor material for the detection of long-chain carboxylates

A strategy for the rational design of a new optical sensor material for the selective recognition of long-chain carboxylates in water is presented. The approach relies on the combination of structure-property relationships to single out the optimal molecular sensor unit and the tuning of the sensing characteristics of an inorganic support material. A spacer-substituted 7-urea-phenoxazin-3-one was employed as the signaling moiety and a mesoporous trimethylsilylated UVM-7 (MCM-41 type) material served as the solid support. The sensor material shows the advantageous features of both modules that is absorption and emission in the visible spectral range, a fluorescence red-shift and enhancement upon analyte coordination, and the amplification of noncovalent (binding) and hydrogen-bonding (recognition) interactions in the detection event. Besides these basic results that are related to the design and performance of the sensor material, the paper discusses general aspects of amido-substituted phenoxazinone photophysics and addresses some general features of molecular anion recognition chemistry in aqueous vs nonaqueous media, utilizing steady-state and time-resolved optical as well as NMR spectroscopies. Detailed studies on potentially competing biochemical species and a first access to the schematic model of the response of the sensor material as obtained by a combination of fluorescence lifetime distribution analysis and Langmuir-type fitting of the gross binding constants complement the key issues of the paper.     

Fractal geometry of surface areas of sand grains probed by pulsed field gradient NMR

Pulsed field gradient NMR self-diffusion studies of water were used to determine surface-to-volume ratios and specific surface areas of the grains forming a glacial sand deposit. Both quantities exhibit a noninteger power-law dependence as a function of the diameters of the grains. The associated fractal dimensions of the surface area ( D(s)) and of the pore volume ( D(v)) are found to be D(s)-D(v) = -0.70+/-0.05 and D(s) = 2.20+/-0.05. The results demonstrate that NMR studies with native pore fluids are suitable to investigate the fractal nature of natural, unconsolidated porous materials.     

Half-moufang generalized hexagons

If Γ is a half-Moufang generalized hexagon, then Γ is Moufang. We also give a very short proof that a generalized hexagon admitting a split BN-pair is a Moufang hexagon. Supported by a Heisenberg-Stipendium.     

Investigations on structure of regioselectively functionalized celluloses ID solution exemplified by using 3-β-alkyl ethers and light scattering

Regioselectively functionalized 3--alkyl ethers of cellulose (alkyl =-pentyl, isopentyl, dodecyl) can be synthesized using 2,6-di--thexyldimethylsilyl cellulose as a protected intermediate. ID comparison to the corresponding 2,3,6-tri--alkyl ethers, the dissolution behavior and the structure ID solution of the 3--alkyl ethers were investigated using light scattering. The aim of the paper ID to present the first experimental and systematic work on specific properties of regioselectively modified celluloses. The results of structure investigation ID solution are discussed ID detail and lead to a primary understanding of interactions of this type of cellulosics on a molecular and supramolecular level.     

RNA: primed for packing?

How does RNA's seemingly subtle 2'-hydroxyl group contribute to its diverse biological functions? Using quantitative structure-activity relationship (QSAR) analysis, Piccirilli and colleagues find that the 2'-OH fosters van der Waals and hydrophobic interactions that play underappreciated roles in RNA structure and molecular recognition.     

The effect of cross-channel synchrony on the perception of temporal regularity

Temporal models of pitch are based on the assumption that the auditory system measures the time intervals between neural events, and that pitch corresponds to the most common time interval. The current experiments were designed to test whether time intervals are analyzed independently in each peripheral channel, or whether the time-interval analysis in one channel is affected by synchronous activity in other channels. Regular and irregular click trains were filtered into narrow frequency bands to produce target and flanker stimuli. The threshold for discriminating a regular target from an irregular distracter click train was measured in the presence of an irregular masker click train in the target band, as a function of the frequency separation between the target band and a flanker band. The flanker click train was either regular or irregular. The threshold for detecting the regular target was 5-7 dB lower when the flanker was regular. The data indicate that the detection of temporal regularity (and thus, pitch) involves cross-channel processes that can operate over widely separated channels. Model simulations suggest that these cross-channel processes occur after the time-interval extraction stage and that they depend on the similarity, or consistency, of the time-interval patterns in the relevant channels.     

Mirror Symmetry on Kummer Type <Emphasis Type="Italic">K</Emphasis>3 Surfaces

We investigate both geometric and conformal field theoretic aspects of mirror symmetry on N=(4,4) superconformal field theories with central charge c=6. Our approach enables us to determine the action of mirror symmetry on (non-stable) singular fibers in elliptic fibrations of _N orbifold limits of K3. The resulting map gives an automorphism of order 4,8, or 12, respectively, on the smooth universal covering space of the moduli space. We explicitly derive the geometric counterparts of the twist fields in our orbifold conformal field theories. The classical McKay correspondence allows for a natural interpretation of our results.