Surface confinement

Rasal, R.M. and Hirt, D.E. 2008. Toughness decrease of PLA-PHBHHx blend films upon surface-confined photopolymerization. Journal of Biomedical Materials Research Part A 88 1079-1086. 

SCHEME 3 The electrochemical gene sensing system based on the formation of complementary sandwich-type complex, (a) Target DNA combines the ferrocenyl ODN with the probe ODN on the electrode. Redox currents due to the surface-confined ferrocenyl units should reflect the concentration of the target, (b) Ferrocenyl units are not deposited onto the electrode using nontarget DNA. 

In neither case - Cr(CN-[P])g or Ni(CN-[P])4 - was a cyclic voltammetric response observed directly for the metal center at a Pt electrode, for either solution phase or surface-confined materials. The solution phase behavior in this respect is very similar to the situation encountered with many biological macromolecules (23). 

The [Co(terpy)2]+ ion (terpy = 2,2 6, 2"-terpyridine) has been found to catalyze the reduction of C02 when the divalent precursor is immobilized on electrode surfaces. The vinyl-substituted terpy analog was electropolymerized to give a film that reduced the overpotential for C02 reduction in DMF and MeCN by more than 1V.104 The activity of this surface-confined species was superior to that of the complexes in solution.105 Similarly, in water, the [Co(terpy)2]2+ ion immobilized and reduced in situ within a Nafion film also catalyzes the reduction of C02106 and H+ ions.107... 

In a specific example in the same paper [17], one polymer contained triphenyl-methane fragments and the other o-nitrophenol moieties (A and B, respectively, in Scheme 5.1). The triphenylmethane residues were reacted with an alkyllithium and converted to surface-confined trityllithium species. This derivatized polymer was then mixed with an excess of the second polymer and the combination was used in the stoichiometric benzoylation of y-butryrolactonc (Scheme 5.2) or of phenylace-tonitrile (Scheme 5.3). The procedure was also demonstrated successfully using solid sodium hydride instead of the lithiated polymer. 

Keywords zeolites, inner surfaces, confined phases. 

Mandal T. K., Fleming M. S., Walt D. R., Production of hollow polymeric microspheres by surface-confined living radical polymerization on silica templates, Chem. Mater. 2000 12 3481-7. 

The background problem can be further overcome when using a surface-confined fluorescence excitation and detection scheme at a certain angle of incident light, total internal reflection (TIR) occurs at the interface of a dense (e.g. quartz) and less dense (e.g. water) medium. An evanescent wave is generated which penetrates into the less dense medium and decays exponentially. Optical detection of the binding event is restricted to the penetration depth of the evanescent field and thus to the surface-bound molecules. Fluorescence from unbound molecules in the bulk solution is not detected. In contrast to standard fluorescence scanners, which detect the fluorescence after hybridization, evanescent wave technology allows the measurement of real-time kinetics (www.zeptosens.com, www.affinity-sensors.com). 

Similar to those observed with the cysteine-modified electrode in Cu, Zn-SOD solution [98], CVs obtained at the MPA-modified Au electrode in phosphate buffer containing Fe-SOD or Mn-SOD at different potential scan rates (v) clearly show that the peak currents obtained for each SOD are linear with v (not v 1/2) over the potential scan range from 10 to 1000 mVs-1. This observation reveals that the electron transfer of the SODs is a surface-confined process and not a diffusion-controlled one. The previously observed cysteine-promoted surface-confined electron transfer process of Cu, Zn-SOD has been primarily elucidated based on the formation of a cysteine-bridged SOD-electrode complex oriented at an electrode-solution interface, which is expected to sufficiently facilitate a direct electron transfer between the metal active site in SOD and Au electrodes. Such a model appears to be also suitable for the SODs (i.e. Cu, Zn-SOD, Fe-SOD, and Mn-SOD) with MPA promoter. The so-called... 

The second-generation 02" biosensors are mainly based on the electron transfer of SOD shuttled by surface-confined or solution-phase mediators, as shown in Scheme 2(b). In 1995, Ohsaka et al. found that methyl viologen could efficiently shuttle the electron transfer between SOD and the glassy carbon electrode and proposed that such a protocol could be useful for developing 02 biosensors [125], Recently, Endo et al. reported an 02, biosensor based on mediated electrochemistry of SOD [148], In that case, ferrocene-carboxaldehyde was used as the mediator for the redox process of SOD. The as-developed 02 biosensor showed a high sensitivity, reproducibility, and durability. A good linearity was obtained in the range of 0 100 pM. In the flow cell system, tissue-derived 02 was measured. 

Recently the wall-PRISM theory has been used to investigate the forces between hydrophobic surfaces immersed in polyelectrolyte solutions [98], Polyelectrolyte solutions display strong peaks at low wavevectors in the static structure factor, which is a manifestation of liquid-like order on long lengths-cales. Consequently, the force between surfaces confining polyelectrolyte solutions is an oscillatory function of their separation. The wall-PRISM theory predicts oscillatory forces in salt-free solutions with a period of oscillation that scales with concentration as p 1/3 and p 1/2 in dilute and semidilute solutions, respectively. This behavior is explained in terms of liquid-like ordering in the bulk solution which results in liquid-like layering when the solution is confined between surfaces. In the presence of added salt the theory predicts the possibility of a predominantly attractive force under some conditions. These predictions are in accord with available experiments [99,100]. 

N2, or CO2 when the proper enzyme is present as a catalyst.(53) The use of surface-confined, fast, one-electron, outer-sphere redox reagents like those derived from or III as redox mediators for biological reagents would seem to represent an excellent approach to the equilibration of the electrode with the biological reagents. 

Here, the overall absorbance change, A A, has two components, ai and a2, and the two second-order rate constants are k and K".The interpretation of this rate law is that electron injection leads to equal numbers of adsorbed M(III) complexes and injected electrons. Thus, the recombination process is first-order in [M(III)] and [n] where fri is the concentration of injected electrons. The concentration of M(III) is expressed in molecules cm-2 because the M(III) species are surface confined, while the concentration of injected electrons has units of electrons cm-3 these... 

The STM has also been used to follow the evolution of surface-confined reactions such as the oxidation of adsorbed sulfide to form adsorbed Sg and iodide to polyiodide [275,288,289]. The substrate exerts a strong influence on the dimensions and ordering of the adsorbed molecules, particularly the formation of the first monolayer. In a similar manner, studies of the impact of different adlayer structures on the electron transfer kinetics of various soluble redox species have been initiated [290]. 

The first report of surface-immobilized dendrimers was in 1994 [54]. Subsequently, our research group showed that the amine-terminated PAMAM and PPl dendrimers could be attached to an activated mercaptoimdecanoic acid (MUA) self-assembled monolayer (SAM) via covalent amide linkages [55, 56]. Others developed alternative surface immobilization strategies involving metal com-plexation [10] and electrostatic binding [57]. These surface-confined dendrimer monolayers and multilayers have found use as chemical sensors, stationary phases in chromatography, and catalytic interfaces [41,56,58,59]. Additional applications for surface-confined dendrimers are inevitable, and are dependent only on the synthesis of new materials and the development of clever, new immobilization strategies. 

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