Development of an indole safety-catch linker using analytical constructs

The development, evaluation, and application of a novel safety-catch linker for solid-phase synthesis based on an N-tosylindole is reported. The development of this linker using analytical constructs to aid analysis is discussed.     

Minimum dissipative relaxed states in toroidal plasmas

Relaxation of toroidal discharges is described by the principle of minimum energy dissipation together with the constraint of conserved global helicity. The resulting Euler-Lagrange equation is solved in toroidal coordinates for an axisymmetric torus by expressing the solutions in terms of Chandrasekhar-Kendall (C-K) eigenfunctions analytically continued in the complex domain. The C-K eigenfunctions are obtained as hypergeometric functions that are solutions of scalar Helmholtz equation in toroidal coordinates in the large aspect-ratio approximation. Equilibria are constructed by assuming the current to vanish at the edge of plasma. For the m=0, n=0 (m and n are the poloidal and toroidal mode numbers respectively) relaxed states, the magnetic field, current, q (safety factor) and pressure profiles are calculated for a given value of aspect-ratio of the torus and for different values of the eigenvalue λ _{r 0}. The new feature of the present model is that solutions allow for both tokamak as well as RFP-like behaviour with increase in the values of λ _{r 0}, which is related directly to volt-sec in the experiment.     

Influence of oxygen on defect densities in nanocrystalline Si

A differential capacitance vs. frequency technique for determining trap densities as a function of energy in amorphous and nanocrystalline Si devices is presented. Through differential capacitance measurements, trap states can be accurately measured and profiled within the bandgap as a function of energy. Defects for amorphous silicon were shown to be Gaussian approximately 0.7 eV below the conduction band, on the order of 10¹⁵–10¹⁶ cm^? 3 depending on deposition. This agrees with both external a-Si measurements and C–V defect measurements. Defects in nano-crystalline silicon were studied as a function of oxygen present in the material. Five different depositions were carried out with varying amounts of oxygen. The defect densities of each device were then measured. A large increase in defect densities corresponding to an increase in oxygen content is observed.     

Steric control of lanthanide hydration state: fast water exchange at gadolinium in a mono-amide 'DOTA' complex

Detailed analyses of the solution structure and exchange dynamics of two sets of homologous mono-amide triacetate lanthanide complexes (Ln = Eu, Gd) of cyclen have been undertaken. The complex [LnL1], bearing an N-linked CH2CH2NHCO-pyridyl moiety, forms mono-aqua (q = 1) species in solution and the Gd complex undergoes rapid water exchange (k(ex)= 11 x 10(7) s(-1), 298 K) as a result of the steric destabilisation of the Ln-water binding interaction. The homologous complex with a C-3 spacing chain, [LnL2], forms a q = 0 species.     

An efficient method for the N-arylation of phenylurea via copper catalyzed amidation

The coupling reaction of phenylurea with different functionalized aryl halides in the presence of air stable CuI,N,N-dimethylethylenediamine as a ligand,and K₃PO₄ as a base gives symmetrical and unsymmetrical diarylureas in relatively high yields.This method is milder than the palladium catalyzed arylation and avoids the use of toxic phosphine ligands.     

Analytical construct resins for analysis of solid-phase chemistry

Rapid and unambiguous analysis of reactions performed on resin supports can be achieved by using "analytical constructs". These resins allow the synthesis of materials using solid-phase methods in the usual manner, but they also contain functionality enabling cleavage of analytically enhanced derivatives of the resin-bound products. This is possible due to the use of two linkers bound in series to the polymer. Cleavage at the first linker yields the products attached to an analytical enhancer that facilitates detection. Orthogonal cleavage at the second linker yields the desired products in the usual manner.