The first photocrystallographic evidence for light-induced metastable linkage isomers of ruthenium sulfur dioxide complexes

Light-induced metastable linkage isomers of trans-[Ru(NH(3))(4)Cl(SO(2))]Cl and trans-[Ru(NH(3))(4)(H(2)O)(SO(2))](C(6)H(5)SO(3))(2) have been identified for the first time using photocrystallographic methods. In both linkage isomers the SO(2) ligand is side bound, but the Ru-O and Ru-S distances are considerably longer and almost equal in the trans-H(2)O isomer. DFT calculations confirm that both isomers correspond to minima on the ground-state potential energy surface and also predict the existence of a second oxygen-bound isomer for both compounds. The decay of the light-induced species has been studied by both DSC and IR. Activation energies for the thermal back-reaction, as derived from the temperature-dependent disappearance of light-induced IR bands, are 50.0 and 58.4 kJ/mol for the two isomers, which is larger than the corresponding numbers for photoinduced side-bound nitrosyl linkage isomers.     

Synthesis of Functionalized o‐, m‐, and p‐Terphenyl Derivatives by Consecutive Cross‐Coupling Reactions of Triazene‐Substituted Arylboronic Esters

Triazene‐substituted arylboronic esters were prepared readily from the corresponding aryl magnesium derivatives and shown to function as a new class of donor–acceptor‐substituted coupling reagents. The selective functionalization of these aromatic derivatives led to a wide variety of terphenyl derivatives in which the original bifunctional unit (often further substituted with another functional group) formed the central aromatic ring. The functionalized terphenyl derivatives were formed in two efficient cross‐coupling steps from the triazene‐substituted boronic esters: Suzuki cross‐coupling with an aryl halide was followed by BF₃?OEt₂‐induced palladium‐catalyzed coupling of the diazonium salt generated in situ from the triazene with an arylboronic acid.     

Micellization and catalytic activity of the cetyltrimethylammonium bromide-Brij 97-water mixed micellar system

Surface tension measurements and the kinetic study of the basic hydrolysis of ethyl p-nitrophenyl chloromethyl phosphonate were used to examine the structural behavior and catalytic activity of the cethyltrimethylammonium bromide (CTAB)-polyoxyethylene (10) oleyl ether, C(18)H(35)(OCH(2)CH(2))(10)OH (Brij 97)-water mixed micellar system. Application of the regular solution model to the experimental data yields the value of the interaction parameter beta as -4.6, which indicates an attractive interaction of the surfactants in the mixed micelle and reflects synergistic solution behavior of the mixture. The mixed micellar composition is found to be enriched in the surfactant with the lower critical micelle concentration (cmc). In the kinetic study a nonmonotonic change in the pseudo-first-order rate constant of basic hydrolysis of the substrate is observed with increasing mole fraction of nonionic surfactant. The pseudophase micellar model reveals that the concentration factor mainly contributes to the catalytic effect, while the microenvironmental factor plays a negative role.     

An evaluation of analytical techniques for determination of lead, cadmium, chromium, and mercury in food-packaging materials

Closed microwave digestion and a high-pressure asher have been evaluated for wet-oxidation and extraction of lead, cadmium, chromium, and mercury from a range of typical packaging materials used for food products. For the high-pressure asher a combination of nitric and sulfuric acids was efficient for destruction of a range of packaging materials; for polystyrene, however, nitric acid alone was more efficient. For microwave digestion, a reagent containing nitric acid, sulfuric acid, and hydrogen peroxide was used for all materials except polystyrene. Use of the high-pressure asher resulted in the highest recoveries of spiked lead (median 92%), cadmium (median 92%), chromium (median 97%), and mercury (median 83%). All samples were spiked before digestion with 40 microg L(-1) Cd, Cr, and Pb and 8 microg L(-1) Hg in solution. The use of indium as internal standard improved the accuracy of results from both ICP-MS and ICP-AES. Average recovery of the four elements from spiked packaging materials was 92 +/- 14% by ICP-MS and 87 +/- 15% (except for mercury) by ICP-AES. For mercury analysis by CVAAS, use of tin(II) chloride as reducing agent resulted in considerably better accuracy than use of sodium borohydride reagent.     

Hydration and dielectric properties of aqueous solutions of protonated diallylmethylammonium polymer: transition from monomer to polymer

Abstract

The high-frequency dielectric relaxation of aqueous solutions of protonated diallylammonium polyelectrolyte, namely poly(diallylmethylammonium trifluoroacetate) has been studied at the maximum water dispersion frequencies, 7.5–25?GHz, and temperatures of 288, 298, and 308?K. Dielectric relaxation parameters have been calculated and compared with similar characteristics of aqueous solutions of monomer, diallylmethylammonium trifluoroacetate, and pyrrolidinium trifluoroacetate salt simulated structure of pyrrolidinium polymer link. It has been concluded that although the monomer features hydrophobic hydration, its polymer exhibits hydrophilic hydration properties. This change is related to conformation of hydrophilic-hydrophobic polycations in aqueous solutions and the change in the structure of polymer links.     

Synthesis and use of alpha-silyl-substituted alpha-hydroxyacetic acids

[reaction: see text] Rhodium-catalyzed oxygen transfer was used to generate benzyl 2-silyl-2-oxoacetates in good yields. The hydrogenation of these compounds led to chiral alpha-silyl-substituted alpha-hydroxyacetic acids. Resolution by means of HPLC using a chiral stationary phase afforded an enantiomerically pure representative of this class of compounds, which was successfully applied as a chiral ligand in an asymmetric aldol-type reaction.     

In situ determination of orientational distributions in Langmuir monolayers by total internal reflection fluorescence

A new application of the polarized total internal reflection fluorescence (PTIRF) technique to study the orientation distribution of a fluorophore within a Langmuir monolayer in situ on an aqueous subphase is described. The technique utilizes the measurement of polarized fluorescence, excited by the evanescent field appearing upon total internal reflection. The excitation by the evanescent field is achieved by launching the beam into a prism that is brought into contact with the monolayer from above. We also show here that a combination of PTIRF of monolayers on water and those freshly deposited onto the prism by horizontal lift in the same experiment provide enough data to determine the dielectric constant of the actual local environment of the fluorophore in the monolayer to eliminate the ambiguity of the orientation determination, arising from uncertainty in the normal component of excitation field. The new technique was applied to several model systems: fatty acid monolayers containing amphiphilic dyes DiI or BODIPY and also a monolayer of a synthetic amphiphilic porphyrin-binding peptide AP0. This technique is more accurate than polarized epifluorescence (PEF) in determining the fluorophore orientation distribution due to the much higher normal component of the excitation, achievable in the evanescent field, and to the lack of surface vibrations caused by capillary waves. Comparison of the new PTIRF approach with PEF shows that the monolayer structure is not disturbed by weak van der Waals attachment to the hydrophobic substrate.     

Functionalized nanodiamonds part I. An experimental assessment of diamantane and computational predictions for higher diamondoids

The structures, strain energies, and enthalpies of formation of diamantane 1, triamantane 2, isomeric tetramantanes 3-5, T(d)-pentamantane 6, and D(3d)-hexamantane 7, and the structures of their respective radicals, cations, as well as radical cations, were computed at the B3LYP/6-31G* level of theory. For the most symmetrical hydrocarbons, the relative strain (per carbon atom) decreases from the lower to the higher diamondoids. The relative stabilities of isomeric diamondoidyl radicals vary only within small limits, while the stabilities of the diamondoidyl cations increase with cage size and depend strongly on the geometric position of the charge. Positive charge located close to the geometrical center of the molecule is stabilized by 2-5 kcal mol(-1). In contrast, diamondoid radical cations preferentially form highly delocalized structures with elongated peripheral C-H bonds. The effective spin/charge delocalization lowers the ionization potentials of diamondoids significantly (down to 176.9 kcal mol(-1) for 7). The reactivity of 1 was extensively studied experimentally. Whereas reactions with carbon-centered radicals (Hal)(3)C(*) (Hal=halogen) lead to mixtures of all possible tertiary and secondary halodiamantanes, uncharged electrophiles (dimethyldioxirane, m-chloroperbenzoic acid, and CrO(2)Cl(2)) give much higher tertiary versus secondary selectivities. Medial bridgehead substitution dominates in the reactions with strong electrophiles (Br(2), 100 % HNO(3)), whereas with strong single-electron transfer (SET) acceptors (photoexcited 1,2,4,5-tetracyanobenzene) apical C(4)-H bridgehead substitution is preferred. For diamondoids that form well-defined radical cations (such as 1 and 4-7), exceptionally high selectivities are expected upon oxidation with outer-sphere SET reagents.     

Sulfonated and sulfoacylated poly(styrene-divinylbenzene) copolymers as packing materials for cation chromatography

Three different types of cation exchangers were produced from four basic poly(styrene-divinylbenzene) substrates with different properties. Porous PS-DVB resin beads were functionalized by sulfonation and sulfoacylation under various conditions to produce sulfonated resins with exchange capacities of 0.03-1.80 mM g(-1). The matrix with 50% of cross-linking is most suitable for updating by the proposed technique. Sulfuric and chlorosulfonic acids were used as the reagents for sulfonation. The sulfonating conditions, capacities, and the technique of the synthesis are given. The effects of parameters of the sulfonation reaction and the composition of the reactionary mixture on ion-exchange capacity of the sorbents were investigated. Selectivity and efficiency of the separation of some inorganic cations and derivatives of amines and hydrazines on the resins obtained are compared by ion chromatography with conductometric detection. As a result, the sulfoacylated resin was proved more efficient for the separation of these analytes. The resolution of the analytes strongly depends on the degree of functionalization. The best performance about 19,000 plates m(-1) was obtained using the sulfopropionylated beads with an ion-exchange capacity of 0.3 mM g(-1). The prepared sulfoacylated cation exchanger was compared with the commercially available Dionex CS-12 packing material. It was found that the separation of alkaline ions and 1,1-dimethylhydrazine (UDMH) were much better that those for the commercial material.     

Single-molecule magnets constructed from cyanometalates: {[Tp*Fe(III)(CN)3M(II)(DMF)4]2[OTf]2} x 2DMF (M(II) = Co, Ni)

Treatment of several divalent transition-metal trifluoromethanesulfonates [M(II)(OTf)2; M(II) = Mn, Co, Ni] with [NEt4][Tp*Fe(III)(CN)3] [Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate] in DMF affords three isostructural rectangular clusters of {[Tp*Fe(III)(CN)3M(II)(DMF)4]2[OTf]2} x 2DMF (M(II) = Mn, 3; Co, 4; Ni, 5) stoichiometry. Magnetic studies of 3-5 indicate that the Tp*Fe(CN)3(-) centers are highly anisotropic and exhibit antiferromagnetic (3 and 4) and ferromagnetic (5) exchange to afford S = 4, 2, and 3 spin ground states, respectively. ac susceptibility measurements suggest that 4 and 5 exhibit incipient single-molecule magnetic behavior below 2 K.