Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was employed to characterize the polygalloyl polyflavan-3-ols (PGPF) in grape seed extracts. Masses corresponding to a series of PGPF units inclusive of nonamers were observed in the positive-ion reflectron mode. Masses of PGPF inclusive of undecamers were observed in the positive-ion linear mode, providing the first known evidence of PGPF of this size. Soluble PGPF of grape seed extracts were precipitated by complexation with Yb(3+). The PGPF were then recovered by dissolving the precipitate in water and removing the Yb(3+) by a weakly acidic cation-exchange resin (Amberlite IRP-64). Comparisons of HPLC chromatograms of the crude grape seed extract prior to precipitation with Yb(3+) and after recovery of the PGPF indicated that 96% of the phenolic compounds were precipitated and 99% of the precipitated PGPF were recovered by cation-exchange resin. These results indicate that MALDI-TOF MS is able to determine the mass distribution of complex mixtures of oligomeric PGPF and that precipitation of PGPF by Yb(3+) is useful for isolation and quantification.

Isotope effects were measured for all the atoms at the reactive center of formamide during hydrolysis in dilute alkaline solution. Most of the reaction proceeds by a pathway that is first-order in hydroxide, although a small amount proceeds by a pathway that is second-order in hydroxide. For alkaline hydrolysis at 25 °C the carbonyl carbon isotope effect is 13 k obs = 1.0321, the carbonyl oxygen isotope effect is 18 k obs(C  O) = 0.980, the formyl hydrogen isotope effect is D k obs = 0.80, and the nitrogen leaving group isotope effect is 15 k obs = 1.0040. The ratio of the rate of hydrolysis to the rate of exchange for the alkaline hydrolysis of formamide was shown to be linearly dependent on the hydroxide concentration, ranging from an extrapolated value of k h/k ex = 2.1 at very low hydroxide concentrations to k h/k ex = 8.4 at 1.5 M hydroxide. This is consistent with a mechanism in which an increasing fraction of the tetrahedral intermediate pool is trapped as a dianion at high pH, effectively lowering the rate of exchange. These results also indicate that the transition states leading into and out of the tetrahedral intermediate are of comparable energy for the pathway which is first-order in hydroxide. The solvent nucleophile isotope effect is 18 k obs(nuc) = 1.022 for water as the attacking nucleophile or 18 k obs(nuc) = 0.982 for hydroxide as the attacking nucleophile. These results strongly suggest that one of the water molecules hydrating the hydroxide ion is the actual attacking nucleophile instead of hydroxide ion itself.

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The trimethylsilanethiolate complexes of the platinum triad metals (dppe)M(SSiMe 3 ) 2 (M ) Ni, Pd, Pt) and (COD)Pt(SSiMe 3 ) 2 were prepared by the reaction of NaSSiMe 3 with (dppe)-MCl 2 or (COD)PtI 2 . These complexes are water-sensitive. New, sulfido-bridged heterobimetallic complexes L 2 M(µ 3 -S) 2 {Ru(N)Me 2 } 2 resulted from the reactions of (dppe)Pt(SSiMe 3 ) 2 , (COD)Pt(SSiMe 3 ) 2 , or (dppe)Pd(SSiMe 3 ) 2 with [PPh 4 ][Ru(N)Me 2 Cl 2 ]. The reaction between (dppe)Pt(SSiMe 3 ) 2 and [Os(N)(CH 2 SiMe 3 ) 2 (NCMe) 2 ][BF 4 ] produced (dppe)Pt(µ 3 -S) 2 {Os(N)-(CH 2 SiMe 3 ) 2 } 2 . All new compounds have been characterized through spectroscopic techniques and elemental analysis. The molecular structures of (dppe)Pt(µ 3 -S) 2 {Ru(N)Me 2 } 2 and (dppe)-Pt(µ 3 -S) 2 {Os(N)(CH 2 SiMe 3 ) 2 } 2 were determined by single-crystal X-ray diffraction.

Mass spectrometry is a widely used and versatile tool for scientists in many different fields. Soft ionization techniques such as matrix-assisted laser desorption/ionization (MALDI) allow for the analysis of biomolecules, polymers, and clusters. This article describes a MALDI mass spectrometry experiment designed for students in introductory courses that provides hands-on experience with research instrumentation and reinforces the course concepts of isotopes, molecular masses, and molecular formulas. The students prepare peptide samples for mass analysis and then collect and analyze mass spectral data. This experiment could easily be adapted to an instructor's available or preferred soft ionization technique.

The laser desorption/ionization (LDI) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectra of trinuclear Cs(3)Re(3)Cl(12) and Cs(3)Re(3)Br(12) and dinuclear (Bu(4)N)(2)[Re(2)Cl(8)] are reported. In each case, characteristic fragments due to the loss of halogen atoms give ion signals that can be used to identify the number of rhenium atoms and the identity of ligands bound to the cluster. The ion signals are identified by both m/z values and distinctive isotope patterns. The results presented here illustrate the usefulness of MALDI-TOF mass spectrometry in the characterization of metal atom clusters.

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