T. Randall Lee

Structural characterization and frictional properties of C60-terminated self-assembled monolayers on Au(111)

Abstract C60-terminated self-assembled monolayers (SAMs) were generated on the surface of Au(111) by the adsorption of unsymmetrical disulfides having saturated hydrocarbon backbone structures comprised of six (C-6) and eleven (C-11) carbon atoms. The formation of oriented monolayer films from these adsorbates was confirmed by ellipsometric thickness and contact angle measurements. The morphologies and frictional properties of the C60-terminated SAMs were examined using atomic force microscopy (AFM). The SAMs derived from the C-11 disulfides exhibited smooth morphologies and homogeneous frictional force distributions, which proved ideal for the study of intrinsic frictional properties. The SAMs derived from the C-6 disulfides, however, exhibited rough and inhomogeneous topographic and frictional force distributions. In addition, the shorter SAMs exhibited erratic frictional behavior and partial film delamination. The relative frictional forces observed on these immobilized C60 films were higher than those observed on normal methyl-terminated SAMs and on the surface of graphite.

Improved protein crystallization by vapor diffusion from drops in contact with transparent, self-assembled monolayers on gold-coated glass coverslips

The surfaces of glass coverslips of the type typically used for protein crystallization were modified with four types of transparent, chemically distinct self-assembled monolayers (SAMs). The SAM-functionalized surfaces exhibit a much higher degree of order and chemical uniformity than silanized glass, as judged by contact angle measurements. These characteristics lead to a marked increase in the range of solution conditions under which large crystals of lysozyme, α-lactalbumin, ribonuclease, hemoglobin, thaumatin, and catalase are observed to form. The results are rationalized in terms of a marked reduction in the rate of non-productive nucleation relative to the rate of crystal growth.

Synthesis, X-ray crystallographic, and reactivity studies of rhenium(V) alkyne complexes

Abstract [ReOMe 2 (bipy)(CH 3 CN)][PF 6 ], prepared in situ, reacted with alkynes (ethyne, propyne, 2-butyne, 3-hexyne, phenylacetylene, and diphenylacetylene) to give the cationic alkyne complexes trans -[ReOMe 2 (bipy)(alkyne)][PF 6 ] ( trans -Meue5f8Reue5f8Me). 1 H-NMR studies indicated that a cis isomer was formed initially. Kinetics studies showed that the isomerizations were first order in the alkyne complex. The observed rate constants depended on the steric bulk of the alkyne with bulkier alkynes producing smaller k obs values. An Eyring plot for the isomerization of [ReOMe 2 (bipy)(2-butyne)][PF 6 ] yielded Δ H ‡ =21(1) kcal mol −1 and Δ S ‡ =6(3) eu. The isomerization mechanism was proposed to involve the rearrangement of a five-coordinate intermediate formed by dissociation of a Reue5f8N bond. Treatment of [ReOMe 2 (bipy)(CH 3 CN)][PF 6 ] with dimethyl acetylenedicarboxylate afforded the metallacycle [ Re{C[C(O)OMe]C(Me)C(O )(OMe)}(O)Me(bipy)][PF 6 ] via insertion of the alkyne into a Reue5f8CH 3 bond. Trans -[ReOMe 2 (RCCH)(bipy)][PF 6 ] reacted with PMe 3 or PPh 3 to form the ylide complexes cis -[ReOMe 2 (bipy){C(R)CH(PR′ 3 )}][PF 6 ] (R=H, R′=Me or Ph; R=Ph, R′=Me). In each case, a trans isomer ( trans -Meue5f8Reue5f8Me) of the ylide complex was formed initially, which isomerized to the cis isomer. Spectroscopic and X-ray crystallographic studies suggest that the ylide complexes can be described as organometallic analogs of resonance-stabilized phosphonium ylides. The structures of trans -[ReOMe 2 (bipy)(PhCCPh)][PF 6 ], [ Re{C[C(O)OMe]C(Me)C(O )(OMe)}(O)Me(bipy)][PF 6 ], cis -[ReOMe 2 (bipy){C(H)CH(PPh 3 )}][PF 6 ] and cis -[ReOMe 2 (bipy){C(Ph)CH(PMe 3 )}][PF 6 ] were determined by X-ray crystallography.