Charge regulation enables anionic hydroxypropyl guar-borate adsorption onto anionic and cationic polystyrene latex

Reported are adsorption isotherms for guar and hydroxypropyl guar (HPG), with and without the presence of borate ions, onto surfactant free anionic polystyrene latex. Guar and HPG formed adsorbed monolayers on the hydrophobic latex. The presence of borate ions converted the nonionic guar and HPG into an anionic polyelectrolyte. However, there was no measurable influence of bound borate ions on the adsorption of guar or HPG onto anionic, hydrophobic latex. To underscore the unusual behavior of HPG-borate, a sample of HPG was oxidized to introduce carboxyl groups, and the adsorption of the carboxylated HPG onto anionic polystyrene was measured. Unlike HPG-borate, oxidized HPG did not adsorb onto negative polystyrene latex at neutral pH because of electrostatic repulsion. To explain the adsorption of negative HPG-borate onto negative latex, we proposed that as HPG-borate segments approach the latex surface, the negative electrostatic potential near the latex surface induces the detachment of the labile borate groups from HPG.     

Ionic diamine rhodium complex catalyzed reductive N-heterocyclization of 2-nitrovinylarenes

Ionic diamine rhodium complex (1) catalyzes the reductive N-cyclization of 2-vinylnitroarenes using carbon monoxide as a reducing agent to afford functionalized indoles. The catalytic system allows direct access to indoles with ester and ketone groups at the 2- or 3-position, in good yields.     

Structures, energetics and vibrational frequency shifts of hydrated pyrimidine

More than 70 unique micro-hydrated structures of pyrimidine, ranging in size from 1 to 7 water molecules, have been characterized with the B3LYP density functional and the 6-311++G(2df,2pd) triple-ζ split-valence basis set. Explicitly correlated MP2-F12 single-point computations were performed on each structure with a correlation consistent triple-ζ basis set to estimate the relative and dissociation energies at the MP2 complete basis set (CBS) limit. Many of these new structures have significantly lower energies than those previously reported (by as much as 12.66 kcal?mol(-1)). For clusters with 1 and 2 water molecules, the MP2-F12 relative and dissociation energies are virtually identical to the corresponding CCSD(T)-F12 values. As the number of hydrating waters increases, the structures in which the water molecules are clustered together at one of the N atoms have lower energies than those where the water molecules are more distributed around the pyrimidine ring. Micro-hydrated structures that effectively extend the low-energy hydrogen-bonding motifs to both sides of the ring, as would be expected in the bulk phase, reproduce the experimentally observed vibrational frequency shifts of ν(1) and ν(8b) in very dilute aqueous pyrimidine solutions to within 1 cm(-1) . Micro-hydrated structures of pyrimidine in which water molecules are clustered together have lower energies than structures in which the water molecules are more evenly spread around the pyrimidine ring.     

Experimental charge density study into C-C σ-interactions in a Binor-S rhodium complex

Transition-metal complexes containing (C-C)→M σ-interactions have potential applications in both catalysis and the activation and cleavage of C-C bonds. Fully characterising the bonding and interactions in complexes containing such (C-C)→M σ-interactions is vital to understand their chemical behaviour. As a result a high-resolution experimental X-ray charge density study has been undertaken on [Rh(Binor-S)(PCy(3))][HCB(11)Me(11)] (Binor-S = 1,2,4,5,6,8-dimetheno-s-indacene) which contains a (C-C)→Rh interaction. The data are analysed using Bader's "Atoms in Molecules" (AIM) approach with particular attention paid to the interactions around the rhodium centre. The results provide clear evidence for the σ(C-C)→Rh interaction in the solid-state which is classified as a weak covalent interaction. These results are supported by theoretical calculations.     

Surface-assisted laser desorption and ionization mass spectrometry using low-cost matrix-free substrates

Surface-assisted laser desorption/ionization (SALDI) substrates have been fabricated using nanospiked polyurethane (PU) substrates that are replicated by a low-cost soft nanolithography method from silicon nanospike structures formed with femtosecond laser irradiations. The strongest mass spectrometry (MS) signal of Angiotensin II was obtained on 45-nm Au-coated nanospiked PU substrates. The effective ionization appears to be due to surface plasmon excitation. Such low-cost and identical SALDI substrates can be used for MS analysis of various molecules with high reproducibility.     

DFT and AIM study of the protonation of nitrous acid and the pKa of nitrous acidium ion

The gas phase and aqueous thermochemistry, NMR chemical shifts, and the topology of chemical bonding of nitrous acid (HONO) and nitrous acidium ion (H(2)ONO(+)) have been investigated by ab initio methods using density functional theory. By the same methods, the dissociation of H(2)ONO(+) to give the nitrosonium ion (NO(+)) and water has also been investigated. We have used Becke's hybrid functional (B3LYP), and geometry optimizations were performed with the 6-311++G(d,p) basis set. In addition, highly accurate ab initio composite methods (G3 and CBS-Q) were used. Solvation energies were calculated using the conductor-like polarizable continuum model, CPCM, at the B3LYP/6-311++G(d,p) level of theory, with the UAKS cavity model. The pK(a) value of H(2)ONO(+) was calculated using two different schemes: the direct method and the proton exchange method. The calculated pK(a) values at different levels of theory range from -9.4 to -15.6, showing that H(2)ONO(+) is a strong acid (i.e., HONO is only a weak base). The equilibrium constant, K(R), for protonation of nitrous acid followed by dissociation to give NO(+) and H(2)O has also been calculated using the same methodologies. The pK(R) value calculated by the G3 and CBS-QB3 methods is in best (and satisfactory) agreement with experimental results, which allows us to narrow down the likely value of the pK(a) of H(2)ONO(+) to about -10, a value appreciably more acidic than literature values.     

Intercalating oleylamines in graphite oxide

Graphite oxide has been synthesized from raw graphite particles and been treated with various mass amounts of oleylamine as intercalants to form intercalation compounds. X-ray diffraction patterns reveal that the inter-sheet distances strongly depend on the graphite oxide to oleylamine mass ratios. The equilibrium-like behavior implies diffusion-dominated oleylamine adsorption on graphite oxide in solution and excluded volume intercalations among oleylamine-adsorbed graphite oxide during restacking. The intercalation compounds are soluble in organic solvents, and their applications in the fabrication of transparent and conductive coatings have been demonstrated.     

Palladium-catalyzed intermolecular cyclocarbonylation of 2-iodoanilines with the Michael acceptor, diethyl ethoxycarbonylbutendienoate

Palladium-catalyzed intermolecular cyclocarbonylation of 2-iodoanilines with diethyl ethoxycarbonylbutendienoate produces 2,3,3-triethoxycarbonyl-2,3-dihydro-4(1H)-quinolinone derivatives in moderate to good yields. This protocol involves Michael addition and subsequent carbonylation.