Improving resins for solid phase synthesis: incorporation of 1-[2-(2-methoxyethoxy)ethoxy]-4-vinyl-benzene

The preparation, characterisation and application of a series of non-grafted polystyrene (PS) resins containing a styrenic methoxypoly(ethylene glycol) (MPEG) derivative is presented. These novel PS-MPEG resins were designed to balance swelling and solvation with improved handling. The monomer, 1-[2-(2-methoxyethoxy)ethoxy]-4-vinyl-benzene, contained an inert phenyl ether linkage designed to provide broad chemical compatibility and stability, yet imparting all the favourable properties of the PEG group into the new resin, whilst maintaining a high loading capacity. The synthetic performance of the new resins compared very favourably to those of TentaGel™, ArgoGel™ and aminomethyl PS.     

The use of comet assay data with a simple reaction mechanism to evaluate the relative effectiveness of free radical scavenging by quercetin, epigallocatechin gallate and N-acetylcysteine in UV-irradiated MRC5 lung fibroblasts

Comet assay data (tail DNA %) have been gathered for the concentration dependent role of three antioxidants (AOs); quercetin (Q), epigallocatechin gallate (EGCG) and N-acetylcysteine (NAC) in reducing UV-induced damage to DNA in normal fetal lung fibroblasts (MRC5). All three compounds demonstrate a concentration dependent reduction maximum with a pro-oxidant effect at higher (though not cytotoxic) concentrations. Manipulation of a simple 4-step reaction mechanism for free radical (FR) scavenging by AOs produced rate constant ratios which allowed the relative effectiveness (Q > EGCG > NAC) of the AOs to be evaluated.     

Alkyl radical adducts of aromatic N-oxides as hydrogen-abstracting agents: The reactivity of phenazine-N,N′-dioxide-methyl radical adduct

An O-methylated analog of protonated phenazine-di-N-oxide radical anion abstracts hydrogen from primary and secondary alcohols in a slow (k ₁ < 500 M⁻¹ s⁻¹) bimolecular reaction. No kinetic evidence has been found for the unimolecular release of free methoxyl radicals through the homolytic N-OMe bond cleavage in these species. DFT calculations at the UB3LYP 6-31G(d) level indicate that protonated and O-alkylated radical anions of pyrazine, quinoxaline and phenazine di-N-oxides are close analogues of aromatic nitroxyl radicals with the highest spin density localized on the oxygen and nitrogen of the nitrone moiety.     

Push-pull effects and emission from ternary complexes of platinum(II), substituted terpyridines, and the strong-field cyanide ion

As part of an effort to develop new lumaphors involving late transition metal ions, this report describes the synthesis and characterization of the first platinum(II) derivatives containing 2,2':6',2'-terpyridine (trpy) and cyanide as co-ligands. According to existing models, including cyanide in the coordination sphere should raise the energies and minimize the influence of short-lived d-d excited states that otherwise compromise the excited-state lifetime. Both [Pt(trpy)(CN)]+ and the 4'-cyano-2,2':6',2'-terpyridine analogue [Pt(CN-T)(CN)]+ are emissive in dichloromethane solution, but the signals are weak. Part of the problem is that the d-pi* charge-transfer excited states also rise in energy, so that the emission actually originates from a (3)pi-pi* state with a relatively low radiative rate constant. However, another member of the series, the 4'-dimethylamino-2,2':6',2'-terpyridine (dma-T) derivative [Pt(dma-T)(CN)]+, proves to be a very promising platform with an emission quantum yield of phi= 0.26 and an excited-state lifetime of tau = 22 micros in room-temperature, deoxygenated dichloromethane solution. In the dma-T complex the electron-rich dimethylamino substituent provides the basis for an emissive, but largely ligand-based, charge-transfer excited state. The orbital parentage is such that the photoluminescence persists in donating solvents like dimethylformamide, which ordinarily quenches d-pi* excited states in complexes of this type.     

Magnetic properties of cyano-bridged Ln3+-M3+ complexes. Part I: trinuclear complexes (Ln3+ = La, Ce, Pr, Nd, Sm; M3+ = FeLS, Co) with bpy as blocking ligand

The reaction of Ln(NO3)3(aq) with K3[Fe(CN)6] or K3[Co(CN)6] and 2,2'-bipyridine in water/ethanol led to eight trinuclear complexes: trans-[M(CN)4(mu-CN)2{Ln(H2O)4(bpy)2}2][M(CN)6].8H2O (M = Fe3+ or Co3+, Ln = La3+, Ce3+, Pr3+, Nd3+, and Sm3+). The structures for the eight complexes [La2Fe] (1), [Ce2Fe] (2), [Pr2Fe] (3), [Nd2Fe] (4), [Ce2Co] (5), [Pr2Co] (6), [Nd2Co] (7), and [Sm2Co] (8) have been solved; they crystallize in the triclinic space group P and are isomorphous. They exhibit a supramolecular 3D architecture through hydrogen bonding and pi-pi stacking interactions. A stereochemical study of the nine-vertex polyhedra of the lanthanide ions, based on continuous shape measures, is presented. No significant magnetic interaction was found between the lanthanide(III) and the iron(III) ions.     

Nitric oxide photorelease from ruthenium salen complexes in aqueous and organic solutions

The complexes [Ru(salen)(NO)Cl] and [Ru(salen)(NO)(H(2)O)](+) were shown to release the nitrosyl ligand as nitric oxide upon exposure to visible light in organic and aqueous solutions respectively, by means of UV-visible, EPR, and FTIR spectroscopies. The former was prepared by a new synthetic route and had its structure determined by single-crystal X-ray diffraction. A crystal of the dichloromethane solvate is orthorhombic, space group Fdd2 (No. 43) and formula C(16)H(14)ClN(3)O(3)Ru.CH(2)Cl(2), with Z = 16 and cell parameters a = 25.489(4), b = 33.435(4), and c = 9.3716(9) A. The electronic absorption spectra of the complexes were calculated using the INDO/S method. The water-soluble complex is a potential drug for antitumoral phototreatment.     

Enthalpies of transfer of 2-methyl-2-propanol from water to mixtures of water with methanol,ethanol and 1,4-dioxane

The enthalpies of transfer of 2-methyl-2-propanol (TBA) from water to mixtures of water with methanol, ethanol and 1,4-dioxane have been measured. The data are considered in terms of recently developed theory, and it is found that the enthalpies of transfer can be reproduced quantitatively over most of the composition range in each solvent system. The parameters recovered from the analyses indicate that the net effect of TBA on the solvent structure is a breaking of solvent-solvent bonds and that TBA is preferentially hydrated in the aqueous alcohol systems, but randomly solvated in the water+1,4-dioxane system. It is also found that the model parameters for TBA solvation in the alcohol systems are independent of the alcohol.     

Infrared spectra of bis(aniline) and bis (p-toluidine) metal(II) isothiocyanate complexes

The infrared spectra of eight complexes of general formula [ML₂(NCS)₂] (M = Co, Ni, Cu, Zn; L = aniline or p-toluidine) have been determined over the range 4000–4150 cm^?1. Colour, magnetic moments and IR spectra are consistent with polymeric octahedral coordination in the Co(II) and Ni(II) complexes and polymeric tetragonal coordination in the Cu(II) complexes, while the Zn(II) complexes are assigned polymeric octahedral (L = aniline) and tetrahedral (L = p-toluidine) structure on the basis of their IR spectra. Independent ¹⁵N-labelling of the nitrogen atoms of the amino and isothiocyanate groups yields assignments for the internal vibrations of both groups and enables the metal-amine and metal—isothiocyanate stretching vibrations (vM-NH₂ and vM-NCS) to be distinguished. Both vM-NH₂ and vM-NCS are metal ion dependent in the Irving-Williams sequence (Co < Ni < Cu > Zn) expected from their proposed structures while the vN-H and vN-CS vibrations are inversely related to the masses of the coordinated metal ions.     

First-order semidefinite programming for the direct determination of two-electron reduced density matrices with application to many-electron atoms and molecules

Direct variational calculation of two-electron reduced density matrices (2-RDMs) for many-electron atoms and molecules in nonminimal basis sets has recently been achieved through the use of first-order semidefinite programming [D. A. Mazziotti, Phys. Rev. Lett. (in press)]. With semidefinite programming, the electronic ground-state energy of a molecule is minimized with respect to the 2-RDM subject to N-representability constraints known as positivity conditions. Here we present a detailed account of the first-order algorithm for semidefinite programming and its comparison with the primal-dual interior-point algorithms employed in earlier variational 2-RDM calculations. The first-order semidefinite-programming algorithm, computations show, offers an orders-of-magnitude reduction in floating-point operations and storage in comparison with previous implementations. We also examine the ability of the positivity conditions to treat strong correlation and multireference effects through an analysis of the Hamiltonians for which the conditions are exact. Calculations are performed in nonminimal basis sets for a variety of atoms and molecules and the potential-energy curves for CO and H(2)O.     

Use of mobile phase 18-crown-6 to improve peak resolution between mono- and divalent metal and amine cations in ion chromatography

It is difficult to quantify NH4+ by ion chromatography in the presence of high concentrations of Na+ due to peak overlap. The Dionex IonPac CS15 column, which contains phosphonate, carboxylate, and 18-crown-6 functional groups, was originally developed to overcome this problem. We have found that the addition of 18-crown-6 to the eluent promotes improved peak resolution between Na+ and NH4+ even at concentrations as high as 60,000 to 1 using this column. Its use also improves the separation of alkali and alkaline earth metal and amine cations. Mobile phase 18-crown-6 increased the retention times of CH3NH3+, NH4+, and K+, and decreased the retention time of Sr2+. The retention times of Li+, Na+, Mg2+, Ca2+, (CH3)2NH2+, and (CH3)3NH+ were not affected. This method makes possible the direct analysis of ammonia from nitrogenase, the enzyme responsible for biological nitrogen fixation. The resolution of the NH4+ peak from the Na+ and Mg2+ peaks improved from zero resolution to values of 6.19 and 5.65, respectively. This technique considerably reduces the analysis time of NH4+ in the presence of high concentrations of Mg2+ and Na+ over traditional indophenol measurements.