Unsymmetrical 1λ3-1,2,4,6-thiatriazinyls with aryl and trifluoromethyl substituents: synthesis, crystal structures, EPR spectroscopy, and voltammetry

A general synthetic route to 3-trifluoromethyl-5-aryl-1λ(3)-1,2,4,6-thiatriazinyl radicals was developed. X-ray structures were obtained for all five neutral radicals and show that they exist in the solid state as cofacial dimers linked by S···S contacts. X-ray structures were also obtained for two of the precursor chlorothiatriazines along with several aryl N-imidoylamidines, p-methoxybenzamidine, and N-chlorosulfonyl-N,N'-benzamidine. Cyclic voltammetric studies were performed on the [R(2)C(2)N(3)S](?) radicals in CH(3)CN and CH(2)Cl(2) with [(n)Bu(4)N][PF(6)] as the supporting electrolyte under vacuum conditions in an all-glass electrochemical cell. The results provide quasi-reversible formal potentials for the [R(2)C(2)N(3)S](-/0) process in the range of -0.61 to -0.47 V, irreversible peak potentials for the [R(2)C(2)N(3)S](0/+) process from 0.59 to 0.91 V at lower concentrations, and the appearance of a second, reversible oxidation process from 0.69 to 0.94 V at higher concentrations (versus the Fc(0/+) couple; Fc = ferrocene). This behavior was indicative of monomer-dimer equilibrium in solution, as ascertained from digital models of the voltammograms. There is a small but measurable trend in both the oxidation and reduction potentials with varying remote aryl substituents. EPR spectra were obtained for all five neutral radicals in CH(2)Cl(2) solutions, which confirm the concentration of the unpaired electron density on the heterocyclic core. Trends were also seen in the hyperfine splitting constants a(N) with varying remote aryl substituents. Calculations were performed for all three oxidation states of the [R(2)C(2)N(3)S](-/?/+) monomeric rings; the resulting theoretical redox energies correlate well with solution phase voltammetric data.     

Integration of a macro/micro architectured compartmentalised neuronal culture device using a rapid prototyping moulding process

The rapid prototyping of a reversible and one step moulded compartmentalised neuron glass/PDMS device with a thin wall barrier directly adjacent to the reservoirs is presented. A simple moulding technique to produce these devices results in a barrier of 560 μm where the 3 μm deep by 8 μm wide channels can be reversibly fabricated in either the glass base or PDMS compartmentalised mould depending on the type of application required. Using glass substrates with commercially laser engraved microchannels, both the PDMS planar and PDMS channelled device can be easily fabricated in a standard laboratory. The compartmentalised device has several advantages including good experimental accessibility and versatility with a variety of end user applications.     

Studies of Specific Adsorption Sites for Sodium Ion and Water on the Interface of Mixed Micelles of Novel Type II Lyomesophases

Novel aqueous type II lyotropic mesophases that align in magnetic fields have been synthesized for binary and ternary mixtures of amphiphiles. A system in which major components of the micelle bilayer are decyltrimethylammonium and dodecanoate ions is an aligning mesophase from 100% to 35% dodecanoate, but replacement of the cationic amphiphile with hexadecyltrimethylammonium facilitates the extension to aligning mesophases up to 100% replacement of the dodecanoate ions. A study of sodium and deuterium quadrupole splittings observed in their nuclear magnetic resonance spectra, confirms and extends a three site adsorption theory for sodium ion in the mixed head group interface. The first site is associated with more strongly hydrated ions and head groups and involves adjacent dodecanoate head groups, the second is not so strongly hydrated and involves one dodecanoate group while the third is a weakly bound water at - N(CH₃)⁺ groups and a sodium remote from the interface layer in close to average isotropic motion.

Mixed detergent mesophases of type II, which spontaneously align in the field, have also been synthesized from variable mixtures of hexadecyltrimethylammonium bromide and decylammonium chloride and from mixtures of potassium dodecanoate and sodium decylsulphate. In the mixed cationic system the sodium quadrupole splittings are always low but water is tightly bound to the -NH₃ ⁺ head group. In the anionic detergent mixture sodium appears about as strongly bound to dodecanoate and decylsulphate head groups. In most of the mixed mesophases some decanol is required (maximum 25% of the bilayer) in order to render the desired type II mesophase stable over a range of mixtures of the charged detergents. Specific site adsorption for sodium and water, peculiar to different head groups renders the effect of the added decanol as primarily a convenient diluent in the bilayer to preserve mesophase integrity.     

Solid-phase synthesis of 2,3-diphenylpropionic acid library as VLA-4 antagonists

2,3-Diphenylpropionic acid library for VLA-4 antagonist was synthesized on solid-phase. Comparison of the two synthetic routes via an orthogonal generation of two aromatic amino functional groups are discussed. From this work, several compounds were identified as potent VLA-4 antagonists.     

14N nuclear quadrupole resonance in nicotinic acid derivatives

Nitrogen-14 nuclear quadrupole resonance (NQR) spectra of nicotinic acid derivatives, known as antitumor agents, are reported and analyzed in the framework of the Townes and Dailey theory. A strong correlation exists between the charge difference σ_NC ? π at the pyridinic nitrogen and the inhibition of acetylcholinesterase by nicotinic acid derivatives, in which the inhibition potency (pI₅₀) increases as the charge difference σ_NC ? π increases. There are significant differences between ¹⁴N NQR spectra for the pyridinic nitrogen sites of nicotinic acid and nicotinamide; these can be explained in terms of the differences in hydrogen bond lengths.     

Raman probe studies of Nd: YAlG laser generated non-equilibrium excitations in GaAs

A survey is presented of the non-equilibrium excitations in GaAs that can be probed by Raman scattering. Intense Q-switched Nd:YAlG laser pulses are used both for generating the non-equilibrium excitations at low temperature, and for in-situ Raman scattering probe measurements. Particular emphasis is placed on the search for non-equilibrium, zone-edge slow TA phonons. We discovered that the difference frequency combination spectrum involving slow TA phonons is surprisingly coincident with the acceptor excitation line spectrum for the Zn impurity. The discrimination between the non-equilibrium phonon population and a non-equilibrium hole population on minority acceptors in n-GaAs is discussed.     

On the thermal conductivity of diamond under changes to its isotopic character

We show that the 50% increase of the room-temperature thermal conductivity of single-crystal diamond [1] upon increasing its isotopic purity is unlikely to be due to a decrease in phonon-isotope scattering alone. In addition, removal of the¹³C isotope can sharpen the phonon dispersion in a heretofore unappreciated way and thereby decrease the phonon-phonon Umklapp scattering enough to cause the observed results. In addition, the order-of-magnitude increase [1] in the UV damage threshold in the isotopically purer diamond is probably caused by similar effects. In fact, all physical processes wherein phonon wave-vector or energy thresholds are important should be affected by this mechanism.     

14N nuclear quadrupole resonance in N-acetyl amino acids

¹⁴N Nuclear quadrupole resonance (NQR) spectra of several N-acetyl amino acids and related compounds are reported and analyzed within the framework of the Townes and Dailey theory. The inductive effect of the chloroacetyl group on the nitrogen is discussed. A positive correlation between the π-σ_NC electron density at the nitrogen and the Taft inductive parameter σ* is observed, suggesting that the nitrogen π-charge density in the N-acetyl amino acids does not vary appreciably. NQR data for hippuric acid are compared to the ¹⁴N quadrupole parameters extracted from ENDOR data reported for X-irradiated hippuric acid.