Brent R. Stranix

A RATIONAL APPROACH TO SELECTIVE RECOGNITION OF NH4+ OVER K+

An ion-selective electrode (ISE) based on receptor 1 is highly selective for binding NH(4)(+) over K(+) (lg K(NH(4)(+)/K(+))=-2.6); the three imine nitrogen atoms in 1 are ideally positioned for hydrogen bonding with the tetrahedral NH(4)(+) ion. This selectivity is considerably greater than that found for commercial ISEs based on nonactin (lg K(NH(4)(+)/K(+))=-1.0).

Effect of temperature and viscosity on intramolecular charge-transfer fluorescence of a 4-p-dimethylaminostyrylpyridinium salt in protic solvents

The steady-state fluorescence of a 4-p-dimethylaminostyrylpyridinium salt (1) has been studied in aqueous solutions. An orange emission band close to 600 nm arose from two excitation bands, at 360 and 469 nm. Possible origins of species responsible for the red-side emission are discussed: (i) excitation at 360 nm, followed by twisted intramolecular charge transfer (TICT) and (ii) excitation at 469 nm of a different ground state with intramolecular charge transfer (ICT).The effect of temperature and solvent viscosity on the fluorescence quantum yield of both charge transfer (CT) bands of 1 has been investigated. The Debye–Stokes–Einstein hydrodynamic model gave an accurate description of the reorientation dynamics of the fluorescent probe. At low viscosities, the quantum yield of the charge transfer fluorescence was linear with solvent viscosity. The activation energy of the thermally activated reorientation relaxation for both CT bands corresponds to the viscosity energy of activation of the medium. Nearly identical activation energies for both CT bands suggest that the corresponding emitting species have the same origin.

Substituted 4-[4-(dimethylamino)styryl]pyridinium salt as a fluorescent probe for cell microviscosity

In aqueous solution, 4-[4-(dimethylamino)styryl]pyridine (DMASP) derivatives displayed dual fluorescence, in which excitation at either 469 or 360 nm produced an emission band near 600 nm. Increasing the viscosity of the environment intensified the fluorescence emission obtained at the longer wavelength of excitation, whereas the emission at the lower wavelength of excitation showed little change in intensity. Thus, using the ratio of the 600 nm emission obtained by exciting at 469 nm to that obtained with 360 nm excitation, it is possible to obtain a value related to the local viscosity that does not depend on the system parameters. The fluorescence emission of the dye in aqueous solution, as well as in living cells, is well suited for use with visible fluorescence spectroscopy. The N-carboxymethyl butyl ester DMASP derivative (1) was found to be irreversibly loaded into living smooth muscle cells, presumably because it is hydrolyzed by cellular esterases, transforming it into a membrane-impermeable fluorescent carboxylate DMASP derivative. (2) After calibrating 2 against glycerol/water and sucrose/water mixtures of known viscosity, the fluorescence ratio generated from cultured smooth muscle cells in dual-excitation mode gave an average intracellular viscosity of 4.5 cP. This value corresponds to those reported in the literature.

EIN RATIONALER ANSATZ ZUR SELEKTIVEN ERKENNUNG VON NH4+ GEGENUBER K+

Eine ionenselektive Elektrode (ISE) auf der Grundlage des Rezeptors 1 weist eine hohe Selektivitat fur NH4+ im Vergleich zu K+ auf (lg K=−2.6); die drei Imin-Stickstoffatome von 1 sind ideal positioniert, um uber Wasserstoffbrucken an das tetraedrische NH4+-Ion zu binden. Diese Selektivitat ist betrachtlich hoher als die der herkommlichen ISEs auf Nonactin-Basis (lg K=−1.0).

Functional polymers from (vinyl)polystyrene. Enzyme immobilization through a cysteinyl-S-ethyl spacer

By radical-catalyzed addition to residual vinyl groups, cysteine was S-linked to porous beads of divinylbenzene/ethylstyrene copolymer. Subsequent treatment with acetic anhydride gave polystyrene-supported azlactone groups able to covalently bind enzymes out of aqueous solution under mild conditions. Pseudomonas cepacia lipase thus immobilized remained active for the hydrolysis of esters, even after storage and/or several cycles of use and recovery.