In vivo magnetic resonance spectroscopy measurement of gray-matter and white-matter gamma-aminobutyric acid concentration in sensorimotor cortex using a motion-controlled MEGA point-resolved spectroscopy sequence

Gamma-aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the brain. Understanding the GABA concentration, in vivo, is important to understand normal brain function. Using MEGA point-resolved spectroscopy sequence with interleaved water scans to detect subject motion, GABA level of sensorimotor cortex was measured using a voxel identified from a functional magnetic resonance imaging scan. The GABA level in a 20×20×20-mm³ voxel consisting of 37%±7% gray matter, 52%±12% white matter and 11%±8% cerebrospinal fluid in the sensorimotor region was measured to be 1.43±0.48 mM. In addition, using linear regression analysis, GABA concentrations within gray and white matter were calculated to be 2.87±0.61 and 0.33±0.11 mM, respectively.     

Effects of the Berry phase and instantons in one-dimensional Kondo-Heisenberg model

Motivated by the global phase diagram of antiferromagnetic heavy-fermion metals, we study the Kondo effect from the perspective of a nonlinear sigma model in the one-dimensional Kondo-Heisenberg model away from half-filling. We focus on the effects of the instanton configurations of the sigma-model field and the associated Berry phase. Guided by the results derived using bosonization methods, we demonstrate that the Kondo-singlet formation is accompanied by an emergent Berry phase. This Berry phase also captures the competition between the Kondo-singlet formation and spin-Peierls correlations. Related effects are likely to be realized in Kondo lattice systems in higher dimensions.     

Green fluorescent protein for in situ synthesis of highly uniform Au nanoparticles and monitoring protein denaturation

Purified recombinant green fluorescent protein (GFP) expressed in E. coli was used for single-step synthesis of gold nanoparticles (Au NPs) with extraordinary size specificity in aqueous medium. The fluorescence of GFP offered a probe for concomitant changes in the protein during the course of synthesis, in addition to the monitoring of the time-dependent formation of Au NPs by the surface plasmon resonance. Reaction of AuCl⁻₄ with the protein produced spherical Au NPs having diameters ranging from 5–70 nm. Remarkably, addition of 1.0×10⁻⁵ M AgNO₃ in the medium produced uniform spherical Au NPs with particle diameter of 2.2±0.5 nm. Fluorescence spectroscopic measurements suggest that during synthesis of Au NPs in absence of AgNO₃, partial denaturation of the protein occurred resulting in the lowering of fluorescence intensity. On the other hand, when the NPs were synthesized in the presence of AgNO₃ complete denaturation of the protein with complete loss of fluorescence could be observed, which was further confirmed by native and sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE). However, use of AgNO₃ only resulted neither in the formation of NPs nor had any significant effect on the fluorescence of GFP.     

Synthesis,structure and magnetic properties of mono- and di-nuclear nickel(II) thiocyanate complexes with tridentate N3 donor Schiff bases

The 1:1 condensation of N-methyl-1,3-diaminopropane and N,N-diethyl-1,2-diminoethane with 2-acetylpyridine, respectively at high dilution gives the tridentate mono-condensed Schiff bases N-methyl-N′-(1-pyridin-2-yl-ethylidene)-propane-1,3-diamine (L¹) and N,N-diethyl-N′-(1-pyridin-2-yl-ethylidene)-ethane-1,2-diamine (L²). The tridentate ligands were allowed to react with methanol solutions of nickel(II) thiocyanate to prepare the complexes [Ni(L¹)(SCN)₂(OH₂) (1) and [{Ni(L²)(SCN)}₂] (2). Single crystal X-ray diffraction was used to confirm the structures of the complexes. The nickel(II) in complex 1 is bonded to three nitrogen donor atoms of the ligand L¹ in a mer orientation, together with two thiocyanates bonded through nitrogen and a water molecule, and it is the first Schiff base complex of nickel(II) containing both thiocyanate and coordinated water. The coordinated water initiates a hydrogen bonded 2D network. In complex 2, the nickel ion occupies a slightly distorted octahedral coordination sphere, being bonded to three nitrogen atoms from the ligand L², also in a mer orientation, and two thiocyanate anions through nitrogen. In contrast to 1, the sixth coordination site is occupied by a sulfur atom from a thiocyanate anion in an adjacent molecule, thus creating a centrosymmetric dimer. A variable temperature magnetic study of complex 2 indicates the simultaneous presence of zero-field splitting, weak intramolecular ferromagnetic coupling and intermolecular antiferromagnetic interactions between the nickel(II) centers.