Two-dimensional Fourier transform spectroscopy in the pump-probe geometry

Two-dimensional (2D) Fourier transform (FT) infrared spectroscopy is performed by using a collinear pulse-pair pump and probe geometry with conventional optics. Simultaneous collection of the third-order response and pulse-pair timing permit automated phasing and rapid acquisition of 2D absorptive spectra. To demonstrate the ability of this method to capture molecular dynamics, couplings and structure found in the conventional boxcar 2D FT spectroscopy, a series of 2D spectra of a metal carbonyl, and a beta-sheet protein are acquired.     

Three-dimensional chemical concentration maps in a microfluidic device using two-photon absorption fluorescence imaging

Two-photon absorption fluorescence is employed within a microfluidic device to create a three-dimensional chemical concentration map for mixing uniformity characterization. This multiphoton technique images fluorescence intensity directly and provides a simple, rapid, and readily employed route to composition characterization within microfluidic systems.     

Interaction of oleic acid with dipalmitoylphosphatidylcholine (DPPC) bilayers simulated by molecular dynamics

The fatty acid oleic acid (OA) is known to modulate the structure of membranes, which forms the basis for a number of its important applications including its use as a therapeutic supplement to reduce the risk of cardiovascular disease, in molecule delivery systems such as liposomes, and as a skin permeability enhancer. While a number of studies have investigated the effect of OA on lipid membranes, our understanding of its mechanisms of action at the molecular level remains rudimentary. We have carried out molecular dynamics simulations using coarse-grained models to investigate the interactions of OA at a range of concentrations with a dipalmitoylphosphatidylcholine (DPPC) bilayer in the liquid-crystalline phase. We have also investigated the relative permeability of the bilayers to model hydrophilic and hydrophobic penetrants by means of chemical potential calculations. The results indicate that OA is able to disperse homogeneously into the bilayer at all concentrations without much perturbation. OA appears to slightly weaken the lateral forces between lipid headgroups, and as the concentration of OA increases this manifests itself as a slight decrease in the area compressibility modulus and a minor increase in the diffusion rate of the OA molecules. While the chemical potential profiles showed little or no variation as a function of OA concentration, the frequency of water permeation events was found to double, indicating some OA-induced permeability enhancement. The study suggests that physiological effects of OA are probably more subtle rather than via gross perturbation of the structure, or that its significant effects are restricted to more condensed membrane structures such as the gel phase.     

Linear, redox modified DNA probes as electrochemical DNA sensors

We show here that hybridization-linked changes in the dynamics of a redox-modified, electrode-bound linear (as opposed to stem-loop) probe DNA produce large changes in Faradaic current, allowing for the ready detection of target oligonucleotides.     

Fluorous tagged small molecule microarrays

The affinity fluorous interaction between fluorous tagged small molecules and a fluoroalkyl modified glass surface was shown to facilitate the detection of protein-ligand binding interactions in the fabrication and screening of small molecule microarrays.     

Theory, measurements, and modeling of OH and HO2 formation in the reaction of cyclohexyl radicals with O2

The production of OH and HO(2) in Cl-initiated oxidation of cyclohexane has been measured using pulsed-laser photolytic initiation and continuous-laser absorption detection. The experimental data are modeled by master equation calculations that employ new G2(MP2)-like ab initio characterizations of important stationary points on the cyclo-C(6)H(11)O(2) surface. These ab initio calculations are a substantial expansion on previously published characterizations, including explicit consideration of conformational changes (chair-boat, axial-equatorial) and torsional potentials. The rate constants for the decomposition and ring-opening of cyclohexyl radical are also computed with ab initio based transition state theory calculations. Comparison of kinetic simulations based on the master equation results with the present experimental data and with literature determinations of branching fractions suggests adjustment of several transition state energies below their ab initio values. Simulations with the adjusted values agree well with the body of experimental data. The results once again emphasize the importance of both direct and indirect components of the kinetics for the production of both HO(2) and OH in radical + O(2) reactions.     

Using in situ Raman monitoring as a tool for rapid optimisation and scale-up of microwave-promoted organic synthesis: esterification as an example

Microwave-promoted esterification reactions have been monitored using in situ Raman spectroscopy. Having optimised a reaction on a 23 mmol scale, it was transferred to a larger reaction vessel and scaled up to 0.26 mol, again with Raman monitoring. With conditions in hand, an automated stop-flow apparatus was used to prepare 5.7 moles of product.