The thermodynamics and kinetics of adsorption of the redox-active dendrimers diaminobutane-dend-(NHCOFc)8, (dendrimer-Fc8), diaminobutane-dend-(NHCOFc)16, (dendrimer-Fc16), diaminobutane-dend-(NHCOFc)32, (dendrimer-Fc32), and diaminobutane-dend-(NHCOFc)64, (dendrimer-Fc64) containing 8, 16, 32, and 64 ferrocenyl moieties on the periphery, respectively, have been studied using electrochemical and electrochemical quartz crystal microbalance (EQCM) techniques. All of these materials adsorb onto a Pt electrode surface. At an applied potential of 0.0 V (vs SSCE), where the ferrocenyl sites are in the reduced form and the dendrimers are neutral, the adsorption thermodynamics are well-characterized by the Langmuir adsorption isotherm. The kinetics of adsorption were activation-controlled and the rate constant decreased with decreasing size of the dendrimer. Potential scanning past +0.60 V, where the ferrocenyl sites are oxidized, gave rise to the electrodeposition of multilayer equivalents of the dendrimers. The additional material gradually desorbed upon rereduction, so only a monolayer equivalent remained on the electrode surface. Impedance analysis of the resonator response suggests that at multilayer equivalent coverages, the adsorbed dendrimers do not behave as rigid films and that incorporation of significant amounts of solvent and/or salt accompany the adsorption of these materials at such high coverages. On the other hand, at monolayer coverages, the adsorbed films appear to exhibit rigid film behavior. Using tapping mode atomic force microscopy we have been able to image dendrimer-Fc64 adsorbed onto a Pt(111) surface. The images reveal that the apparent size of the dendrimer adsorbed on the surface is significantly larger than estimated values based on calculations, which is ascribed to a flattening of the dendrimer upon adsorption.

Polyamidoamine dendrimers have been surface-modified via peptide coupling with pyridyl, bipyridyl, and terpyridyl ligands to give the analogous polypyridyl dendrimer ligands in high yield. Complexation of the pendant chelating groups with appropriate ruthenium(II) precursor complexes yielded dendrimers surface-functionalized with tris(bipyridyl)ruthenium(II) or bis(terpyridyl)ruthenium(II) pendant complexes. Electrochemical studies of the dendrimer complexes show metal-centered and ligand-centered redox couples. These molecules also adsorb onto platinum electrodes, and the deposition process and the properties of the resulting films have been investigated with the electrochemical quartz crystal microbalance. The resulting films exhibit morphological changes with potential that can be attributed to the deposition or dissolution of the dendrimer and/or to ejection or incorporation of counterions and/or solvent into the film. A number of the electrodeposited films exhibited charge trapping peaks. Dendrimers containing terminal tris(bipyridyl)ruthenium(II) complexes exhibited room-temperature luminescence, while these and dendrimers with terminal bis(terpyridyl)ruthenium(II) complexes exhibited luminescence in a rigid butyronitrile matrix at 77 K.

Although important roles of receptor activator of NF-kappaB ligand (RANKL) and its receptor (RANK) have been established for osteoclastogenesis and bone resorption, their expression and roles during physiological root resorption remain uncertain. Physiological root resorption for shedding of human deciduous teeth is mediated by osteoclast-like cells (odontoclasts). In this study, we examined the expression of RANKL and osteoprotegerin (OPG), a decoy receptor that prevents RANKL from binding to RANK in human periodontal ligament (PDL) cells during physiological root resorption using immunocytochemistry and reverse transcriptase polymerase chain reaction. The effect of RANKL on root resorbing activity of odontoclasts was evaluated by measuring the size of dissolved area on calcium phosphate-coated coverslips. The PDL cells isolated from either non-resorbing deciduous teeth or permanent teeth abundantly expressed OPG, but not RANKL. In contrast, PDL cells derived from resorbing deciduous teeth dominantly expressed RANKL. Human odontoclasts derived from resorbing deciduous teeth expressed both RANKL and RANK. It was observed that RANKL increased odontoclast actin ring formation and resorbing activity in a dose-dependent manner. These results indicate that PDL cells during the root-resorbing state express RANKL but decrease OPG expression. Expression of RANKL likely participates in odontoclastogenesis and activates physiological root resorption.

Exposure of gold surfaces to solutions of dithiobis N-succinimidyl propionate (DTSP) gives rise to the modification of the surface with N-succinimidyl-3-thiopropionate (NSTP) which can, in turn, react with amino groups allowing for the covalent immobilization of enzymes such as horseradish peroxidase (HRP). The coverage of NSTP has been estimated to be of the order of 1.3 x 10(-10) from the charge consumed during its reductive desorption. The binding reaction of HRP with NSTP modified gold surfaces has been studied with the quartz crystal microbalance, and the results suggest that the immobilization process involves two steps in which the first (faster) appears to correspond to the rapid incorporation of the enzyme whereas the second is likely due to the slow incorporation of additional enzyme and/or reorganization of the immobilized layer. Spectrophotometric and electrochemical assays indicate that the immobilized HRP retains its enzymatic activity after immobilization onto the DTSP modified gold surface. The amount of immobilized (and active) HRP was estimated from QCM and spectrophotometric measurements to be of the order of 1.5 x 10(-11) mol/cm2. A peroxide biosensor was developed making use of a gold surface modified with DTSP and HRP employing Os and Ru complexes of 1,10-phenanthroline 5,6-dione (phen-dione) of the type [M(phendione)x(L)3-x]+2 (where L = 1,10-phenanthroline or 2,2'-bipyridine, x = 1-3) as mediators with the quinone moieties being the active component. The efficiency of the mediators increased with increasing number of phendione ligands.