Monodisperse Au(25)L(18)(0) (L = S(CH(2))(2)Ph) and [n-Oct(4)N(+)][Au(25)L(18)(-)] clusters were synthesized in tetrahydrofuran. An original strategy was then devised to oxidize them: in the presence of bis(pentafluorobenzoyl) peroxide, the neutral or the negatively charged clusters react as efficient electron donors in a dissociative electron-transfer (ET) process, in the former case yielding [Au(25)L(18)(+)][C(6)F(5)CO(2)(-)]. As opposed to other reported redox methods, this dissociative ET approach is irreversible, easily controllable, and clean, particularly for NMR purposes, as no hydrogen atoms are introduced. By using this approach, the -1, 0, and +1 charge states of Au(25)L(18) could be fully characterized by (1)H and (13)C NMR spectroscopy, using one- and two-dimensional techniques, in various solvents, and as a function of temperature. For all charge states, the NMR results and analysis nicely match recent structural findings about the presence of two different ligand populations in the capping monolayer, each resonance of the two ligand families displaying distinct NMR patterns. The radical nature of Au(25)L(18)(0) is particularly evident in the (1)H and (13)C NMR patterns of the inner ligands. The NMR behavior of radical Au(25)L(18)(0) was also simulated by DFT calculations, and the interplay between theory and experiments revealed a fundamental paramagnetic contribution coming from Fermi contact shifts. Interestingly, the NMR patterns of Au(25)L(18)(-) and Au(25)L(18)(+) were found to be quite similar, pointing to the latter cluster form as a diamagnetic species.

Synthesis of Octapeptide 3Boc-Ser(Al)-OH 1 : NaH (2.44 g of a 60% oil dispersion, 1.46 g, 0.061 mol) was suspended in 20 mL of DMF and cooled to 0 °C in a flask fitted with a dropping funnel. Boc-Ser-OH (5.0 g, 0.024 mol) was dissolved in 40 mL of DMF and the resulting solution was transferred to the dropping funnel. This solution was added drop-wise to the NaH solution over a period of 30 minutes. Allyl bromide (2.0 mL, 0.024 mol) was added and the flask contents warmed to room temperature and stirring was continued for 3 hours. The reaction was quenched by the slow addition of 12 mL of water. The solvents were then removed on the rotary evaporator and the residue dissolved in water (40 mL), which was washed with two 20 mL portions of ethyl acetate. The aqueous phase was acidified to pH 2 with the addition of 6 M HCl and extracted with two 40 mL portions of ethyl acetate. The organic phases were combined and dried over anhydrous magnesium sulfate. After filtration, the solvent was evaporated to yield a viscous oil (4.8 g, 82%) which was found to be of sufficient purity to be used in subsequent reactions.1 H NMR (400 MHz, CDCl 3 ): δ 9.1 (1H br s), 5.85 (1H, m), 5.41 (1H, d, J = 8.4 Hz), 5.25 (1H, dq, J = 17.2, 1.5 Hz), 5.19 (1H, dq, J = 10.4, 1.5 Hz), 4.45 (1H, d, J = 8.5 Hz), 4.00 (2H, dt, J = 5.7, 1.5 Hz), 3.90 (1H, dd, J = 9.5, 3.0 Hz), 3.67 (1H, dd, J = 9.5, 3.6 Hz), 1.45 (9H, s).13 C NMR (100 MHz, CDCl 3 ): δ 175. 96, 156.15, 134.25, 118.21, 80.77, 72.80, 69.96, 54.16, 28.70

The use of a single crystal gold bead electrode is demonstrated for characterization of self-assembled monolayers (SAM)s formed on the bead surface expressing a complete set of face centered cubic (fcc) surface structures represented by a stereographic projection. Simultaneous analysis of many crystallographic orientations was accomplished through the use of an in situ fluorescence microscopic imaging technique coupled with electrochemical measurements. SAMs were prepared from different classes of molecules, which were modified with a fluorescent tag enabling characterization of the influence of electrical potential and a direct comparison of the influence of surface structure on SAMs adsorbed onto low index, vicinal and chiral surfaces. The assembly of alkylthiol, Aib peptide and DNA SAMs are studied as a function of the electrical potential of the interface revealing how the organization of these SAMs depend on the surface crystallographic orientation, all in one measurement. This approach allows for a simultaneous determination of SAMs assembled onto an electrode surface onto which the whole fcc stereographic triangle can be mapped, revealing the influence of intermolecular interactions as well as the atomic arrangement of the substrate. Moreover, this method enables study of the influence of the Au surface atom arrangement on SAMs that were created and analyzed, both under identical conditions, something that can be challenging for the typical studies of this kind using individual gold single crystal electrodes. Also demonstrated is the analysis of a SAM containing two components prepared using thiol exchange. The two component SAM shows remarkable differences in the surface coverage, which strongly depends on the surface crystallography enabling estimates of the thiol exchange energetics. In addition, these electrode surfaces enable studies of molecular adsorption onto the symmetry related chiral surfaces since more than one stereographic triangle can be imaged at the same time. The ability to observe a SAM modified surface that contains many complete fcc stereographic triangles will facilitate the study of the single and multicomponent SAMs, identifying interesting surfaces for further analysis.

We synthesized two series of compounds in which a nitroxide radical and a fullerene C 60 moiety were kept separated by a 3 10 -helical peptide bridge containing two intramolecular CO···H−N hydrogen bonds. The direction of the resulting molecular dipole moment could be reversed by switching the position of fullerene and nitroxide with respect to the peptide nitrogen and carbon termini. The resulting fullerene−peptide−radical systems were compared to the behaviors of otherwise identical peptides but lacking either C 60 or the free radical moiety. Electrochemical analysis and chemical nitroxide reduction experiments show that the dipole moment of the helix significantly affects the redox properties of both electroactive groups. Besides providing evidence of a folded helical conformation for the peptide bridge, IR and NMR results highlight a strong effect of peptide orientation on the spectral patterns, pointing to a specific interaction of one of the helical orientations with the C 60 moiety. Time-resolved EPR spectra show not only that for both systems triplet quenching by nitroxide induces spin polarization of the radical spin sublevels, but also that the coupling interaction can be either weak or strong depending on the orientation of the peptide dipole. As opposed to the concept of dyads, the molecules investigated are thus better described as fullerene−peptide−radical systems to stress the active role of the bridge as an important ingredient capable of tuning the system's physicochemical properties. ■ INTRODUCTIONSince its discovery in 1985, 1 the properties of the C 60 fullerene have been extensively investigated. Thorough understanding of its chemical reactivity has led to the synthesis of a large number of fullerene derivatives whose properties and applications have been studied from many viewpoints.2 Among them, interesting molecular systems are featured by fullerene−radical dyads where C 60 is covalently linked, through formation of fulleropyrrolidines, 3 either directly or via a molecular spacer to a free radical function. 4,5 Besides interest in synthesis and properties of C 60 and its derivatives, endohedral fullerenes 6 in which atom or small molecule is encapsulated in the C 60 nano cavity have become a field that attracts more attention due to their potential applications in medicine and biology. 7,8 In particular, the recently successful synthesis 9 of H 2 @C 60 by the molecular surgery method makes the material available in quantities from tens to hundreds of milligrams. Therefore, to probe the interactions of the motion of the endohedral molecule with the outside environment, 10 a series of H 2 @C 60 derivatives covalently linked to a nitroxide radical has been synthesized in which the nitroxide moiety acts as a relaxation agent, and the effect of the nitroxide radical on proton nuclear spin relaxation of the endohedral molecule has been investigated. 11In this Article, we describe properties and compare the behavior of compounds in which a free radical and a fullerene C 60 moiety are...