A cation-pi binding interaction with a tyrosine in the binding site of the GABAC receptor

GABA(C) (rho) receptors are members of the Cys-loop superfamily of neurotransmitter receptors, which includes nicotinic acetylcholine (nACh), 5-HT(3), and glycine receptors. As in other members of this family, the agonist binding site of GABA(C) receptors is rich in aromatic amino acids, but while other receptors bind agonist through a cation-pi interaction to a tryptophan, the GABA(C) binding site has tyrosine at the aligning positions. Incorporating a series of tyrosine derivatives at position 198 using unnatural amino acid mutagenesis reveals a clear correlation between the cation-pi binding ability of the side chain and EC(50) for receptor activation, thus demonstrating a cation-pi interaction between a tyrosine side chain and a neurotransmitter. Comparisons among four homologous receptors show variations in cation-pi binding energies that reflect the nature of the cationic center of the agonist.     

A screened indicator of methyl orange with sulfonated copper phthalocyanine

Summary Copper phthalocyanine tetra sulfonate pottasium salt, has been found to be very useful as a screening-dye to improve methyl orange end-points.Mixtures of methyl orange and dye in varying proportions have been prepared and tested for their indicator-action. The transformation interval of the indicator is found to change as the concentration of the dye is varied in the mixture.The optimum concentration of the dye to be used with a certain amount of methyl orange is determined so as to give a mixed-indicator that functions most satisfactorily in all titrations where methyl orange is used.     

Electrically driven oscillations of a mercury-droplet electrode

The resonance frequencies of 13 polygonal vibrations plus 11 axisymmetric vibrations have been observed for a 4.0-mg sessile mercury droplet submerged in 0.10 N KCl solution. When an input voltage with suitable dc and ac components was applied between the mercury droplet and a Ag/AgCl counter electrode, the mercury droplet could be observed under a microscope to oscillate. The mechanism that drives this droplet into oscillation differs from past electrokinetic mechanisms. Basically, the oscillating input voltage causes periodic changes in the interfacial surface tension which, at specific input frequencies, induce resonant vibrations within the droplet by interacting with its expanding and contracting surface area. Because there are two cycles of surface-area variation and two cycles of surface-tension variation per cycle of droplet oscillation, the most effective driving frequency (but not the only driving frequency) is twice the frequency of the droplet oscillation. This work was performed at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee.     

Pulsed power modeling of very-large-aperture,transverse-discharge CO2 lasers

Discharge behavior of large-aperture (10–70 cm) CO₂ lasers is computed using a coupled particle kinetics-equivalent circuit model. Pulsed power systems that produce a single excitation pulse are only able to satisfy the preionization, ignition, and impedance matching conditions for interelectrode gaps 40–50 cm. Double-pulse systems are required for larger gaps, not only to optimize electrical efficiency, but to avoid oscillatory behavior which can lead to arc formation during the second cycle.     

Ion aging effects on the dissociative-attachment instability in CO2 lasers

Onset of the dissociative-attachment instability requires that the rate coefficient for electron detachment (k _d) from negative ions be below a critical value. The predominant negative and positive ions in a CO₂N₂He gas-discharge plasma are known to change with time. As secondary by-products form and the predominant negative-ion species changes from CO ₃ ^– to NO ₂ ^– , a decrease ink _d occurs destabilizing the discharge. Since NO ₂ ^– and NO ₃ ^– are largely unreactive with respect to associative detachment,k _d depends in a sensitive fashion on the concentration of certain minority negative ions (O^–, O ₂ ^– ) and neutrals (CO, O, N). The sufficient conditions for the dissociative-attachment instability are much less sensitive to changes in the electron-ion and ion-ion recombination rate coefficients resulting from the ion aging process.     

Solving second-order differential equations with variable coefficients

A method is developed in which an analytical solution is obtained for certain classes of second-order differential equations with variable coefficients. By the use of transformations and by repeated iterated integration, a desired solution is obtained. This alternative method represents a different way to acquire a solution from classic power series techniques and other approaches. It is, at times, more involved than traditional methods.     

The not-so-peculiar case of calcium oxide: a weakness in atomic natural orbital basis sets for calcium

Atomic natural orbital (ANO) basis sets for calcium may produce surprisingly poor atomic and molecular properties and energetics. The weaknesses in these basis sets may be traced primarily to deficiencies within the sets of d functions which are incapable of effectively correlating the 3s and 3p electrons. Examples are given which show that addition of tight d functions to the ANO basis is required to achieve qualitatively correct energetics and structures for conventionally bonded calcium compounds.