The rate of base-mediated ester hydrolysis in monolayers of 11-mercaptoundecyl isonicotinate on gold is monitored by infrared spectroscopy and cyclic voltammetry. The hydrolysis product, a surface-confined alcohol, can be converted to a trifluoroacetate, increasing the sensitivity of infrared monitoring. Pentaammineruthenium(II) can be attached to the pendant isonicotinate either prior to or after monolayer assembly, leading to monolayers with a highly-charged monolayer/solution interface and a built-in electrochemical probe. The rate of ester hydrolysis within the monolayer is controlled by steric factors associated with monolayer packing and by the amount of charge at the monolayer/solution interface. The stability of the pendant Ru(III) complex is very sensitive to pH and interfacial charge. These results are correlated with Gouy-Chapman double-layer theory.

The application of boron neutron capture therapy to rheumatoid arthritis requires the selective delivery of the boron-10 isotope to the synovitic tissue. The use of liposomes as a boron delivery method has been explored through the measurement of the time course biodistribution of boron in rats with collagen-induced arthritis (CIA). In an attempt to increase the synovium͞blood boron ratio by lowering the blood boron concentration, a liposomal formulation characterized by a shorter blood clearance time was examined. Thus, the biodistribution of liposomes with additional K[nido-7-CH 3 (CH 2 ) 15 -7,8-C 2 B 9 H 11 ] incorporated in the vesicle membrane not only demonstrated more rapid blood clearance and slightly higher synovium͞blood boron ratios but also exhibited reduced boron uptake in synovial tissue. These studies with boron neutron capture therapy for CIA suggest that this form of therapy may be feasible in the treatment of rheumatoid arthritis.

The apical−apical isomer of the polyhedral borane anion [a 2-B20H18]4- reacts with various proton sources in dichloromethane to produce the protonated species [a 2-B20H19]3- in high yield. The mixed tetraethylammonium−pyridinium salt of [a 2-B20H19]3- crystallizes in the monoclinic space group P21/n with a = 11.223(3) Å, b = 10.970(3) Å, c = 15.328(4) Å, β = 106.06(1)°, V = 1819 Å3, and Z = 2. Data were collected on a Syntex P1̄ diffractometer using Cu Kα radiation, to a maximum 2θ = 115°, giving 2359 unique reflections, and the structure was solved by direct methods (SHELX86). The final discrepancy indices were R = 0.062 and R w = 0.086 for 1967 independent reflections with I > 3σ(I). The structure of the [a 2-B20H19]3- anion is similar to that of its apical−apical [a 2-B20H18]4- precursor with the addition of a hydrogen bridge connecting the two 10-boron atom cages. The boron−hydrogen−boron bond forms an angle of 91(3)° although the component B10H9 cages share a common axis through their B(1)−B(10) vertices.

The apical-apical (a2) isomer of [Et4N]4[B20H18] reacts with oxalyl chloride in dichloromethane to produce a protonated bis-substituted carbonyl species, [Et4N][a2-B20H17(CO)2] ([Et4N][H1]), in 60% yield. Removal of the bridging hydrogen of the [H1]- anion in aprotic media results in rearrangement to form the equatorial-equatorial [e2-B20H16(CO)2]2- anion ([e2-1]2-). The reaction of [Et4N][H1] with sodium azide in acetonitrile produces [Et4N]3- [a2-B20H17(NCO)2] ([Et4N]3[H2]) in 53% yield, which subsequently reacts with isopropylamine in acetonitrile to provide the urea derivative [a2-B20H16(NH2C(O)NH(i-Pr))2]2- ([Et4N]2[4]) in 89% yield. The [H1]- ion is hydrolyzed in aqueous acetonitrile to give a protonated [a2-B20H17(CO2H)2]3- ion ([H3]3-) in 61% yield. The a2 isomers of the bis-substituted species [B20H16(CO2H)2]4- ([3]4-), [B20H16(NCO)2]4- ([2]4-), and [B20H16(NH2C(O)NH(i-Pr))2]2- ([4]2-), formed by the removal of the bridging proton from their protonated precursors, rearrange to form a mixture of ae isomers in solution.

The possible utilization of organic oxidizing agents in polyhedral borane anion redox chemistry was examined by using the synthesis of the well-characterized [B20H18]2- anion as a model system. The [B20H18]2- anion was synthesized in high yield from the polyhedral borane anion [closo-B10H10]2- by using tetrachlorobenzoquinone in acetonitrile. Benzoquinone reacted with the polyhedral borane anions [e 2 -B20H18]4- and [a 2 -B20H18]4- to give the [B20H18]2- anion but did not react with the [closo-B10H10]2- anion. Weaker oxidizing agents, such as azobenzene, nitrobenzene, and benzophenone, failed to react with either the [e 2 -B20H18]4- or the [closo-B10H10]2- anion.