Substituent effects on non-covalent interactions with aromatic rings: insights from computational chemistry

Non-covalent interactions with aromatic rings pervade modern chemical research. The strength and orientation of these interactions can be tuned and controlled through substituent effects. Computational studies of model complexes have provided a detailed understanding of the origin and nature of these substituent effects, and pinpointed flaws in entrenched models of these interactions in the literature. Here, we provide a brief review of efforts over the last decade to unravel the origin of substituent effects in π-stacking, XH/π, and ion/π interactions through detailed computational studies. We highlight recent progress that has been made, while also uncovering areas where future studies are warranted.     

A Convenient Preparation of (R)-7-(3-Benzothienylglycylamido)deacetoxycephalosopranic Acid

An efficient synthesis of (R)-7-(3-benzothienylamido)deacetoxy-cephalosporanic acid (1) is described beginning from (R)-alpha-aminobenzo[b]thiophene-3- acetic acid (2) and 7-amino-3-methyl-3-cephem-4-carboxylic acid (7-ADCA). Good yields were obtained and the procedure is amenable to multikilogram preparations.     

Lipid bilayer templated gold nanoparticles nanoring formation using zirconium ion coordination chemistry

We used positively charged lipids to prepare lipid bilayer assemblies (LBAs) upon which we assembled negatively charged gold nanoparticles (AuNPs). Treatment of the assembly with zirconium chloride resulted in the formation of nanorings of the diameters inversely related to the zirconium ion concentration. The nanorings were attributed to the zirconium ion coordinated AuNPs formed during the lipid bilayer budding process promoted by the acid effect of zirconium chloride. Nanoring organization was also dependent on the fluidity of lipid bilayers, an indication of LBA-assisted nanomaterials organization. We suggest that such bioorganic-inorganic hybrid assemblies coupled to unique topological and morphological variations might be useful as stimuli-responsive sensors or storage compartments for proteins or drugs.     

A new angle on pluronic additives: advancing droplets and understanding in digital microfluidics

Biofouling in microfluidic devices limits the type of samples which can be handled and the duration for which samples can be manipulated. Despite the cost of disposing fouled devices, relatively few strategies have been developed to tackle this problem. Here, we have analyzed a series of eight amphiphilic droplet additives, Pluronic coblock polymers of poly(propylene oxide) (PPO) and poly(ethylene oxide) (PEO), as a solution to biofouling in digital microfluidics using serum-containing cell culture media as a model fluid. Our analysis shows that species with longer PPO chains are superior for enabling droplet motion and reducing biofouling. Two of the tested species, L92 and P105, were found to lengthen device lifetimes by 2-3 times relative to additives used previously when used at optimal concentrations. Pluronics with low PEO content such as L92 were found to be cytotoxic to an immortalized mammalian cell line, and therefore we recommend that Pluronic additives with greater or equal to 50% PEO composition, such as P105, be used for digital microfluidic applications involving cells. Finally, contact angle measurements were used to probe the interaction between Pluronic-containing droplets and device surfaces. Strong correlations were found between various types of contact angle measurements and the capacity of additives to reduce biofouling, which suggests that contact angle measurements may be useful as a tool for rapidly screening new candidates for the potential to reduce biofouling. We propose that this study will be useful for scientists and engineers who are developing digital microfluidic platforms for a wide range of applications involving protein-containing solutions, and in particular, for applications involving cells.     

Weyl geometry

We develop the properties of Weyl geometry, beginning with a review of the conformal properties of Riemannian spacetimes. Decomposition of the Riemann curvature into trace and traceless parts allows an easy proof that the Weyl curvature tensor is the conformally invariant part of the Riemann curvature, and shows the explicit change in the Ricci and Schouten tensors required to insure conformal invariance. We include a proof of the well-known condition for the existence of a conformal transformation to a Ricci-flat spacetime. We generalize this to a derivation of the condition for the existence of a conformal transformation to a spacetime satisfying the Einstein equation with matter sources. Then, enlarging the symmetry from Poincaré to Weyl, we develop the Cartan structure equations of Weyl geometry, the form of the curvature tensor and its relationship to the Riemann curvature of the corresponding Riemannian geometry. We present a simple theory of Weyl-covariant gravity based on a curvature-linear action, and show that it is conformally equivalent to general relativity. This theory is invariant under local dilatations, but not the full conformal group.     

Polyamides incorporating phosphine oxide groups. III. Polymerisation of bis[4-(2-aminoethyl)aminophenyl]-phenylphosphine oxide with dicarboxylic acids

The new polymerisation monomer bis[4-(2-aminoethyl)aminophenyl]-phenylphosphine oxide (p-BAPPO) was prepared in good yield by the nucleophilic substitution reaction between bis(4-fluorophenyl)phenylphosphine oxide and a large excess of 1,2-diaminoethane. Five novel polyamides, incorporating phosphine oxide groups within the polymer backbone were synthesised by the condensation reaction of p-BAPPO with a series of aromatic and aliphatic dicarboxylic acids. The thermal properties of these polymers were investigated by differential scanning calorimetry and thermogravimetric analysis. Glass transition temperatures in the 180–215°C range were recorded. Although we observed their thermooxidative stabilities (5% weight loss > 345°C) to be lower by 40–70°C than those previously found for wholly aromatic polyamides with phosphine oxide groups within the parent chain, char yields upon prolonged heating at 650°C were still excellent (26–38%). Also, good solubility in aprotic polar solvents was observed for all polyamides synthesised. The new polyamides clearly represent significant progress in the quest for processible fire retardant materials. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2865–2870, 1997