Reaction of Au(55)(PPh(3))(12)Cl(6) with thiols yields thiolate monolayer protected Au(75) clusters

This paper describes the reaction of the phosphine-protected Au nanoparticle Au(55)(PPh(3))(12)Cl(6) (1, "Au55") with hexanethiol (2) and other thiols. The voltammetry of the reaction product 2 displays a well-defined pattern of peaks qualitatively reminiscent of Au(38) nanoparticles, but with quite different spacing (0.74 +/- 0.01 V) between the potentials of initial oxidation and reduction steps (electrochemical gap). Correction of this "molecule-like" gap for charging energy indicates a HOMO-LUMO gap energy of about 0.47 V. Voltammetry of the products (3 and 4) of reaction of 1 with C(3)H(7)SH and PhC(2)H(4)SH, respectively, is similar. Laser desorption/ionization mass spectrometry (LDI-MS) shows that 2 contains a high proportion of a core mass in the 14-15 kDa range, which is proposed to be Au(75). UV-vis spectra of 2-4 are relatively featureless, similar to previous reports of thiolate-protected Au(75) nanoparticles. HPLC analysis of 2 shows a Au(75) content of ca. 73%; the electrochemical purity estimate is also high, about 55%. Combining the mass spectrometric result with thermogravimetric analysis of 2 leads to a preliminary formulation Au(75)(SC(6)H(13))(40). This Au(75) synthesis complements a previous Brust-type synthesis and is unusual in the apparent provocation in the reaction of an increase in core size.     

Dimethylmetal(III) pyrazolides

The complexes Me₂Au(R₂pz) (R = H, Me; pzH = pyrazole) are formed on reaction of dimethylgold(III) nitrate with 3,5-disubstituted pyrazoles, R₂pzH, in water, but a similar procedure with Ph₂pzH followed by recrystallization from CHCl₃/CCl₄ gives [Me₂Au(Ph₂pzH)₂]NO₃ · ca.$\text{3}\text{4}$CCl₄. The complexes Me₂(Ph₂pz) (M = Au, Tl), Me₂In(Ph₂pz)·$\text{1}\text{2}$CH₂Cl₂, and Me₂Tl(Me₂pz) are formed on reaction of Me₂MI (M = Au, Tl) or Me₂InCl with Ag(R₂pz) in nonaqueous solvents. The complexes Me₂Au(R₂pz) (R = H, Me, Ph) are dimeric in chloroform and Me₂Tl(Me₂pz) is dimeric in benzene, but osmometric data for Me₂Tl(Ph₂pz) in benzene indicate presence of a monomer—dimer equilibrium.     

Interlaboratory GC/MS response factor precision

A quality control procedure for Fused Silica Capillary Column Gas Chromatography/Mass Spectroscopy (FSCC GC/MS) was tested and shown to produce similar response factors at five Spectroscopy (FSCC GC/MS) was tested and shown to produce similar response factors at five laboratories. The average relative standard deviation (RSD) of interlaboratory response factors for fifty three compounds of environmental interest determined at each laboratory at nominal injected weights of 20, 100, and 200 ng was found to be 18.9% for four of the five laboratories which participated in this work. These data demonstrate that similar response factors can be attained in routine GC/MS measurements when adequate quality control is maintained.     

Semicommuting and Commuting Operators for the Heun Family

We derive the most general families of first- and second-order differential operators semicommuting with the Heun class differential operators. Among these families, we classify all the families that commute with the Heun class. In particular, we find that a certain generalized Heun equation commutes with the Heun differential operator, which allows constructing a general solution of a complicated fourth-order linear differential equation with variable coefficients whose solution cannot be obtained using Maple 16.