Aromatic amines and their derivatives,Part 2. Synthesis,spectroscopic properties,and molecular and crystal structure ofN-acetyl-4,N-dimethyl-6-(N-acetyl-p-toluidinomethyl)aniline

The synthesis and selected aspects of the UV, IR, and¹H NMR spectra of the title compound are described. The crystals of the title compound are triclinic witha=12.999(9),b=8.911(4),c=9.199(5) Å;=105.56(3),=113.50(4), =92.53(3)°;Z=2; space groupP¯1. Its X-ray crystal structure analysis provides information regarding the conformational features of the amide linkage when no intermolecular hydrogen bonding involving this group is present. The X-ray study shows that the C-N bond is longer [1.363(4) Å] than that found normally in peptide molecules. The compound shows a peculiar disorder involving one of the two amide groups present in the molecule. The conformation of theN-methyl acetanilide moiety and its relation to the¹H NMR spectrum of the compound are discussed.     

Microfluidic patterning of nanodisc lipid bilayers and multiplexed analysis of protein interaction

We report a microfluidic method for precisely patterning lipid bilayers and a multiplexed assay to examine the interaction between the lipids and protein analytes. The lipids were packaged into nanoscale lipid bilayer particles known as Nanodiscs and delivered to surfaces using microfluidic channels. Two types of lipids were used in this study: biontinylated lipids and phosphoserine lipids. The deposition of biotinylated lipids on a glass surface was confirmed by attaching streptavidin coated quantum dots to the lipids, followed by fluorescent imaging. Using this multiplexed grid assay, we examined binding of annexin to phosphoserine lipids, and compared these results to similar analysis performed by surface plasmon resonance.     

Determination of plasma topiramate concentration using LC-MS/MS for pharmacokinetic and bioequivalence studies in healthy Korean volunteers

A rapid, simple and validated liquid chromatography coupled to tandem mass spectrometric method (LC-MS/MS) for topiramate analysis in human plasma has been applied to pharmacokinetic and bioequivalence studies in 24 healthy male Korean volunteers. The procedure involves a simple liquid extraction of topiramate and prednisone (internal standard) with acetonitrile and separation by HPLC equipped with a Capcell Pak C18 column using acetonitrile-0.1% triethylamine (80:20, v/v) as a mobile phase. Detection was carried out on an API 2000 MS system by multiple reactions monitoring mode. The ionization was optimized using ESI(-) and selectivity was achieved by MS/MS analysis, m/z 338.0 --> 77.5 and m/z 357.1 --> 327.2 for topiramate and prednisone, respectively. The method had a total run time of 2.5 min and showed good linearity over a working range of 20-5000 ng/mL in human plasma with a lower limit of quantification of 20 ng/mL. No metabolic compounds were found to interfere with the analysis. The inter-day and intra-day accuracy were in the ranges of 99.24-116.63 and 93.45-108.68%, respectively, and inter-day and intra-day precisions were below 6.24 and 5.25%, respectively. This method was successfully applied for pharmacokinetic and bioequivalence studies by analysis of blood samples taken up to 96 h after an oral administration of 100 mg of topiramate in 24 healthy Korean volunteers.     

Structural evolution of a recoverable rhodium hydrogenation catalyst

A recoverable, water soluble, hydrogenation catalyst was synthesized by reacting poly-N-isopropylacrylamide containing a terminal amino group (H₂N-CH₂CH₂-S-pNIPAAm) with [Rh(CO)₂Cl]₂ in organic solvents to form the square planar rhodium complex (Rh(CO)₂Cl(H₂N-CH₂CH₂-S-pNIPAAm)). The catalyst-ligand structure was characterized using in situ multinuclear NMR, XAFS and IR spectroscopic methods. Model complexes containing glycine (H₂NCH₂COOH), cysteamine (H₂NCH₂CH₂SH) and methionine methyl ester (H₂NCH(CH₂CH₂SCH₃)COOCH₃) ligands were studied to aid in the interpretation of the coordination sphere of the rhodium catalyst. The spectroscopic data revealed a switch in ligation from the amine bound (Rh-NH₂-CH₂CH₂-S-pNIPAAm) to the thioether bound (Rh-S(-CH₂CH₂NH₂)(-pNIPAAm)) rhodium when the complex was dissolved in water. The evolution of the structure of the rhodium complex dissolved in water was followed by XAFS. The structure changed from the expected monomeric complex to form a rhodium cluster of up to four rhodium atoms containing one SRR′ ligand and one CO ligand per rhodium center. No metallic rhodium was observed during this transformation. The rhodium-rhodium interactions were disrupted when an alkene (3-butenol) was added to the aqueous solution. The kinetics of the hydrogenation reaction were measured using a novel high-pressure flow-through NMR system and the catalyst was found to have a TOF of 3000/Rh/h at 25 °C for the hydrogenation of 3-butenol in water.     

Using a two-step hydride transfer to achieve 1,4-reduction in the catalytic hydrogenation of an acyl pyridinium cation

The stoichiometric reduction of N-carbophenoxypyridinium tetraphenylborate (6) by CpRu(P-P)H (Cp = eta(5)-cyclopentadienyl; P-P = dppe, 1,2-bis(diphenylphosphino)ethane, or dppf, 1,1'-bis(diphenylphosphino)ferrocene), and Cp*Ru(P-P)H (Cp* = eta(5)-pentamethylcyclopentadienyl; P-P = dppe) gives mixtures of 1,2- and 1,4-dihydropyridines. The stoichiometric reduction of 6 by Cp*Ru(dppf)H (5) gives only the 1,4-dihydropyridine, and 5 catalyzes the exclusive formation of the 1,4-dihydropyridine from 6, H(2), and 2,2,6,6-tetramethylpiperidine. In the stoichiometric reductions, the ratio of 1,4 to 1,2 product increases as the Ru hydrides become better one-electron reductants, suggesting that the 1,4 product arises from a two-step (e(-)/H(*)) hydride transfer. Calculations at the UB3LYP/6-311++G(3df,3pd)//UB3LYP/6-31G* level support this hypothesis, indicating that the spin density in the N-carbophenoxypyridinium radical (13) resides primarily at C4, while the positive charge in 6 resides primarily at C2 and C6. The isomeric dihydropyridines thus result from the operation of different mechanisms: the 1,2 product from a single-step H(-) transfer and the 1,4 product from a two-step (e(-)/H(*)) transfer.     

Spectroscopic studies on the effect of temperature on pH-induced folded states of human serum albumin

Human serum albumin (HSA) is a very important multi-domain transporter protein in the circulatory system responsible for carriage of various kinds of ligands within the physiological system. HSA is also known to undergo conformational transformation at different pH(s) and temperatures. In this report we have studied the binding interactions of a photosensitizing drug, protoporphyrin IX (PPIX) with various conformers of HSA at different temperatures using picosecond time-resolved fluorescence spectroscopy. Also, using dynamic light scattering (DLS) and circular dichroism (CD) spectroscopy we have followed the structural transition of various conformers of HSA at different temperatures. Ensuring the intact binding of PPIX to various conformers of HSA at different temperatures as revealed through time-resolved fluorescence anisotropy decay and significant spectral overlap of emission of Trp214 residue (donor) in domain-IIA and absorption of PPIX (acceptor) bound to domain-IB of HSA, we have applied F?rster's resonance energy transfer (FRET) technique to determine the interdomain separation under various environmental conditions. The alkali-induced conformer of HSA shows almost no change in donor-acceptor distance in contrast to the native and acid-induced conformers of HSA, which show a decrease in distance with increase in temperature. Through this study the non-covalently bound PPIX is shown to be an efficient FRET probe in reporting the different temperature-induced folded states of HSA in buffer solutions of widely differing pH values.     

Molecular structure and dynamics in the low temperature (orthorhombic) phase of NH3BH3

Variable temperature 2H NMR experiments on the orthorhombic phase of selectively deuterated NH3BH3 spanning the static to fast exchange limits of the borane and amine motions are reported. New values of the electric field gradient (EFG) tensor parameters have been obtained from the static 2H spectra of V(zz) = 1.652 (+/-0.082) x 10(21) V/m(2) and eta = 0.00 +/- 0.05 for the borane hydrogens and V(zz) = 2.883 (+/-0.144) x 10(21) V/m(2) and eta = 0.00 +/- 0.05 for the amine hydrogens. The molecular symmetry inferred from the observation of equal EFG tensors for the three borane hydrogens and likewise for the three amine hydrogens is in sharp contrast with the C(s) symmetry derived from diffraction studies. The origin of the apparent discrepancy has been investigated using molecular dynamics methods in combination with electronic structure calculations of NMR parameters, bond lengths, and bond angles. The computation of parameters from a statistical ensemble rather than from a single set of atomic Cartesian coordinates gives values that are in close quantitative agreement with the 2H NMR electric field gradient tensor measurements and are more consistent with the molecular symmetry revealed by the NMR spectra.     

A chiral pinwheel supramolecular network driven by the assembly of PTCDI and melamine

The mixing of perylene-3,4,9,10-tetracarboxylic diimide (PTCDI) and 1,3,5-triazine-2,4,6-triamine (melamine) at room temperature in a ratio of 3 : 4 on Au(111) leads to the formation of a new chiral "pinwheel" structure.     

Isolation and characterization of a neutral imino-semiquinone radical

The neutral imino-semiquinone, 4,6-di-tert-butyl-2-tert-butylimino-semiquinone (isqH.), can be prepared by a conproportionation of the parent aminophenol and iminoquinone compounds. The neutral radical species has been characterized in the solid state by X-ray diffraction and in solution by EPR and UV-vis absorption spectroscopy. The stability of the open-shell radical is derived from the basicity of the tert-butylimino group and the intramolecular hydrogen bond.