Synthesis of 2,5-disubstituted thienosultines and their thermal reactions with dienophiles and nucleophiles

The 2,5-disubstituted thienosultines (5,7-disubstituted 1,4-dihydro-1H-3lambda(4)-thieno[3,4-d][2,3]oxathiin-3-oxides) 5a-d were prepared from the corresponding dichlorides 4a-d with the commercially available Rongalite (sodium formaldehyde sulfoxylate) in 17-60% yields. When heated in the presence of electron-poor dienophiles, sultines 5a-d underwent elimination of SO(2), and the resulting non-Kekulé biradicals 7a-d were intercepted as the 1:1 adducts 8-12 in good to excellent yields. The pyrolysis of sultines and sulfolenes with different concentrations of dienophiles revealed that either a preequilibrium between starting reagents and biradical species or Diels-Alder and retro-Diels-Alder reaction mechanisms may be involved; however, more work is necessary to establish the proposed mechanisms. Reaction of sultine 5b with nBuLi was found to undergo a nucleophilic ring-opening reaction to give sulfinyl alcohol 17 after H(2)O workup. When sultine 5a was heated in benzene in a sealed tube in the presence of methanol, methanol-d(4), or 2-mercaptoethanol, the respective 1:1 trapping adducts 19-21 as well as the rearranged sulfolene 6a were isolated in similar amounts. The isolation of adducts 19-21 may be explained by the involvement of either biradical or ionic intermediates during the pyrolysis.     

Epoxidation of cycloolefins with hydrogen peroxide in the presence of heteropoly acids combined with phase transfer catalyst

Oxidation of cycloolefins (cyclohexene, cyclooctene, and cyclododecene) with a 30% solution of hydrogen peroxide at 65 °C in the presence of heteropoly acids (HPA) H₃PW_12–x Mo _x O₄₀ (x = 0—12), which are precursors of active peroxo complexes, and phase transfer catalysts Q⁺Cl^–, where Q⁺ is the quaternary ammonium cation containing C₄—C₁₈ alkyl groups or [C₅H₅NC₁₆H₃₃]⁺, was studied. The catalytic activity decreases in the HPA series: H₃PW₁₂O₄₀ > H₃PW₉Mo₃O₄₀ > H₃PW₆Mo₆O₄₀ > H₃PW₃Mo₉O₄₀ > H₃PMo₁₂O₄₀. The state of the H₃PW₁₂O₄₀—I₂I₂ system was studied using UV, IR, and ³¹P NMR spectroscopies with variation of the [H₂O₂] : [HPA] ratio from 2 to 200 during cyclohexene epoxidation. Despite different catalytic precursors, the reaction proceeds through the same peroxo complex.     

Thermal polymerization of acrylamide in the solid state

The role of imperfections in thermal polymerization of acrylamide in the solid state was studied. The polymer yield and the degree of polymerization are highly dependent on the particle size and on the pressure to which the monomer is subjected prior to polymerization reaction. There is an enhancement in the rate of polymerization in air unlike in the case of radiation-induced polymerization. Thermal polymerization of acrylamide in pelletized form results in the formation of water-soluble linear polymer and water-insoluble cross-linked product with the evolution of ammonia. The activation energy (E) values obtained in the present investigation reveal that basically there are two processes taking place, one with E = 34–36 kcal/mole, corresponding to the initiation process, and the other with E = 19 ± 3 kcal/more for the propagation process.     

Optimization of sample stacking for the simultaneous determination of nonsteroidal anti-inflammatory drugs with a wall-coated histidine capillary column

A wall-coated histidine capillary column was developed for the on-line preconcentration of nonsteroidal anti-inflammatory drugs (NSAIDs) in capillary electrochromatography (CEC). A wide variety of experimental parameters, such as the sample buffer, background electrolyte (BGE) composition, concentration, sample plug lengths, water plug, and the effect of organic modifiers were studied. The relationship between peak height and injection times for the NSAIDs by variation of sample and BGE buffer concentration was investigated. On addition of sodium chloride (0.3-0.6%) to the sample zone, the stacking efficiency was increased. With acetate buffer (100 mM, pH 5.0)/ethanol (20% v/v) as BGE and sample solution in acetate buffer (0.2 mM, pH 5.0)/ethanol (20% v/v)/NaCl (0.3% w/v), NSAIDs could be determined at low microM levels without sample matrix removal. The detection limit was 0.096 microM for indoprofen, 0.110 microM for ketoprofen, 0.012 microM for naproxen, 0.023 microM for ibuprofen, 0.110 microM for fenoprofen, 0.140 microM for flurbiprofen, and 0.120 microM for suprofen. The method could be successfully applied to the simultaneous determination of NSAIDs in urine. The recoveries were better than 82% for all the analytes. The present method enables simple manipulation with UV detection for the determination of NSAIDs at low concentration levels in complex matrix samples.     

Micropallet arrays with poly(ethylene glycol) walls

Arrays of releasable micropallets with surrounding walls of poly(ethylene glycol) (PEG) were fabricated for the patterning and sorting of adherent cells. PEG walls were fabricated between the SU-8 pallets using a simple, mask-free strategy. By utilizing the difference in UV-transmittance of glass and SU-8, PEG monomer was selectively photopolymerized in the space surrounding the pallets. Since the PEG walls are composed of a cross-linked structure, the stability of the walls is independent of the pallet array geometry and the properties of the overlying solution. Even though surrounded with PEG walls, the individual pallets were detached from the array by the mechanical force generated by a focused laser pulse, with a release threshold of 6 microJ. Since the PEG hydrogels are repellent to protein adsorption and cell attachment, the walls localized cell growth to the pallet top surface. Cells grown in the microwells formed by the PEG walls were released by detaching the underlying pallet. The released cells/pallets were collected, cultured and clonally expanded. The micropallet arrays with PEG walls provide a platform for performing single cell analysis and sorting on chip.     

Dispersion-convolution model for simulating peaks in a flow injection system

A dispersion-convolution model is proposed for simulating peak shapes in a single-line flow injection system. It is based on the assumption that an injected sample plug is expanded due to a "bulk" dispersion mechanism along the length coordinate, and that after traveling over a distance or a period of time, the sample zone will develop into a Gaussian-like distribution. This spatial pattern is further transformed to a temporal coordinate by a convolution process, and finally a temporal peak image is generated. The feasibility of the proposed model has been examined by experiments with various coil lengths, sample sizes and pumping rates. An empirical dispersion coefficient (D*) can be estimated by using the observed peak position, height and area (tp*, h* and At*) from a recorder. An empirical temporal shift (Phi*) can be further approximated by Phi*=D*/u2, which becomes an important parameter in the restoration of experimental peaks. Also, the dispersion coefficient can be expressed as a second-order polynomial function of the pumping rate Q, for which D*(Q)=delta0+delta1Q+delta2Q2. The optimal dispersion occurs at a pumping rate of Qopt=sqrt[delta0/delta2]. This explains the interesting "Nike-swoosh" relationship between the peak height and pumping rate. The excellent coherence of theoretical and experimental peak shapes confirms that the temporal distortion effect is the dominating reason to explain the peak asymmetry in flow injection analysis.     

Quantifying the intrinsic effects of two point mutation models of pro-pro-pro triamino acid diamide. A first-principle computational study

Stabilities and conformational properties of two Pro --> Thr point mutation models were computed at the B3LYP/6-31G(d) level of theory for the parent triamino acid diamide Pro-Pro-Pro (HCO-Pro-Pro-Pro-NH2). Geometrical parameters for the amino acid sequences, used in the molecular orbital computations for Pro-Pro-Thr and Pro-Thr-Pro, were retrieved from the Protein Data Bank. Thermodynamic functions (S, H, G) were computed for the fully optimized geometries. To assess the stabilization energetics of these mutant models, relative to the parent Pro-Pro-Pro reference conformer epsilon(L) epsilon(L) gamma(L), isodesmic reactions were constructed to calculate DeltaS, DeltaH, and DeltaG. The importance of intramolecular hydrogen bonds involving the -OH group of the Thr side chain, which emerged after the point mutations, was also examined to determine the internal stabilization of these peptide models. This study describes an approach to analyzing a point mutation at the center of a peptide chain and compares its stability to that of a point mutation at a terminal end in a small peptide model.     

Transition state infrared spectra for the trans-->cis isomerization of a simple peptide model

Trans-->cis isomerization of N-methylacetylamide (MeCO-NHMe) has been studied at the G3MP2B3 level of theory and the vibration spectrum has been calculated as a function of the torsional mode of motion along the peptide bond. Noticeable spectral differences have been observed for the transition state interconnecting the cis and trans isomers.     

A cross-sectional scanning tunneling microscopy study of IrO2 rutile single crystals

Rutile iridium dioxide (IrO₂) surfaces were studied by cross-sectional scanning tunneling microscopy (XSTM). Atomically flat surfaces prepared by in situ ultra high vacuum cleaving of crystalline platelets of thicknesses <50 μm were successfully demonstrated. In addition to (1 1 0) surface, several vicinal planes, e.g., (1 2 0), (1 3 0) and , were also examined. The cleaved planes are close to bulk-terminated surfaces with predominant [0 0 1]-oriented bridge oxygen rows. Unlike TiO₂, bright oxygen rows are imaged and oxygen defects appear as dim species. Our studies show that XSTM is a viable technique to study oxide surfaces that are otherwise difficult to prepare.     

Junceols D-H, new polyoxygenated briaranes from sea whip gorgonian coral Junceella juncea (Ellisellidae)

Chemical investigations on the sea whip gorgonian coral Junceella juncea have led to the isolation of five new 8-hydroxybriarane diterpenoids, junceols D-H (1-5). The structures of briaranes 1-5 were determined on the basis of spectroscopic methods and the methylenecyclohexane rings were found to exist in boat form in these new diterpenoids. Junceols D (1) and F-H (3-5) exhibited cytotoxicity toward CCRF-CEM and DLD-1 tumor cells and junceols E-H (2-5) displayed weak inhibitory effects on superoxide anion generation by human neutrophils.