Crystalline inclusion compounds of lower rim propyl substituted calix[4]arenes featuring different number and positions of the modifying groups

Three lower rim n-propyl substituted calix[4]arenes (1–3) with varied number and position of the modifying groups have been prepared. Inclusion compounds (five species) involving different kinds of guest solvents have been isolated. Their X-ray crystal structures were determined and comparatively discussed using isostructurality calculations. Two of the inclusion compounds obtained (1a and 1b) are polymorphs containing the same host and guest molecules in equal stoichiometric ratio but different Z′ values caused by a phase transition around 140 K. The inclusion compounds 2a and 2b refer to the interesting case of a mixed solvent complex while 3a allows studying the effect of full lower rim n-propyl substitution.     

Empirical entropic contributions in computational docking: evaluation in APS reductase complexes

The results from reiterated docking experiments may be used to evaluate an empirical vibrational entropy of binding in ligand-protein complexes. We have tested several methods for evaluating the vibrational contribution to binding of 22 nucleotide analogues to the enzyme APS reductase. These include two cluster size methods that measure the probability of finding a particular conformation, a method that estimates the extent of the local energetic well by looking at the scatter of conformations within clustered results, and an RMSD-based method that uses the overall scatter and clustering of all conformations. We have also directly characterized the local energy landscape by randomly sampling around docked conformations. The simple cluster size method shows the best performance, improving the identification of correct conformations in multiple docking experiments.     

Surface charging of layered double hydroxides during dynamic interactions of anions at the interfaces

In this research, we investigated the effect of dynamic anion adsorption/exchange on the surface charging property of Mg(2)AlClLDH and Mg(2)AlCO(3)LDH particles that show the average zeta potential of 41 and 34 mV in the as-prepared suspension, respectively. The addition of NaCl up to 3x10(-3) M in the suspension does not obviously affect the zeta potential of both LDHs, which can be attributed to the less affinity of Cl(-) to LDH. The introduction of Na(2)CO(3) severely reduces the zeta potential at the CO(3)(2-) concentration higher than 1x10(-4) M, and to the negative value in both LDH systems at ca. 2x10(-3) M, which is presumably resulted from the exchange and the re-orientation of CO(3)(2-) in a tilt/vertical style on the surface. All four organic anions (dodecyl sulfate, folate, citrate and polyacrylate) also significantly affect the zeta potential of the LDH particles. At the lower concentrations of organic anionic groups (<1x10(-4) M), the zeta potential was slightly affected, i.e. limited exchange/adsorption. However, the concentration increasing to some point suddenly decreases and reverses the zeta potential of the LDH particles, which is presumably caused by the hydrophobic interactions that bind the hydrophobic hydrocarbon chains (especially in dodecyl sulfate) into the micelle-like bilayer bunches on the LDH surface. In addition, the effect of pH in 5.5-11.0 on the LDH particle surface charging is mainly reflected through the conversion of CO(3)(2-) to HCO(3)(-)/H(2)CO(3) when pH decreases from ca. 11 to 6, with limited contribution from protonation/deprotonation and exchange/adsorption.     

Experimental and theoretical study of the carbon-13 and deuterium kinetic isotope effects in the Cl and OH reactions of CH3F

A laser flash photolysis-resonance fluorescence technique has been employed to determine absolute rate coefficients for the CH3F + Cl reaction in N2 bath gas in the temperature range of 200-700 K and pressure range of 33-133 hPa. The data were fitted to a modified Arrhenius expression k(T) = 1.14 x 10(-12) x (T/298)2.26 exp{-313/T}. The OH and Cl reaction rates of (13)CH3F and CD3F have been measured by long-path FTIR spectroscopy relative to CH3F at 298 +/- 2 K and 1013 +/- 10 hPa in purified air. The FTIR spectra were fitted using a nonlinear least-squares spectral fitting method including line data from the HITRAN database and measured infrared spectra as references. The relative reaction rates defined by alpha = k(light)/k(heavy) were determined to be k(OH+CH3F)/k(OH+CD3F) = 4.067 +/- 0.018, k(OH+CH3F)/k(OH+(13)CH3F) = 1.067 +/- 0.006, k(Cl+CH3F)/k(Cl+CD3F) = 5.11 +/- 0.07, and k(Cl+CH3F)/k(Cl+(13)CH3F) = 1.016 +/- 0.006. The carbon-13 and deuterium kinetic isotope effects in the OH and Cl reactions of CH3F have been further investigated by quantum chemistry methods and variational transition state theory.     

The scanned nanopipette: a new tool for high resolution bioimaging and controlled deposition of biomolecules

The boundary between the physical and biological sciences has been eroded in recent years with new physical methods applied to biology and biological molecules being used for new physical purposes. We have pioneered the application of a form of scanning probe microscopy based on a scanned nanopipette, originally developed by Hansma and co-workers, for reliable non-contact imaging over the surface of a live cell. We have found that the nanopipette can also be used for controlled local voltage-driven application of reagents or biomolecules and this can be used for controlled deposition and the local delivery of probes for mapping of specific species. In this article we review this progress, focussing on the physical principles and new phenomena that we have observed, and then outline the future applications that are now possible.     

Recycling of homogeneous Pd catalysts using superparamagnetic nanoparticles as novel soluble supports for Suzuki, Heck, and Sonogashira cross-coupling reactions

Recycling of homogeneous catalysts could be achieved by using magnetic nanoparticles and solid-phase beads, but nanoparticle-supported catalysis proceeded much faster than its counterpart on resins.     

A diode laser system for long-path,automatic monitoring of SO2

A diode laser system for automatic monitoring of SO₂ along a 60 m atmospheric path is reported. The laser is wavelength modulated and is used to obtain i.r. absorption spectra from the measurement path. These spectra are automatically correlated with reference spectra obtained simultaneously from a calibration cell. The minimum detectable SO₂ concentration is at present around 100 ppb.