COOH-terminated surfaces

The C. hydrogenoformans CODH can catalyze CO oxidation with a turnover number of 39 000 s and a of over 10 M s. The first step in the CODH reaction is binding of substrates, CO and H2O or CO2 and protons to Cluster C. Dobbek et al. described a hydrophobic CO channel in the COOH-terminal domain of ACS and a hydrophihc positively charged water channel that connects the surface and the C-Cluster in the C. hydrogenoformans CODH 11. ... 

Fig. 4.4 F-d curves recorded with a silicon nitride tip in ambient on (a) CH3 and (b) COOH terminated areas of a patterned SAM model surface, (c) Pull-off force histogram calculated from 4096 individual f-d curves, (d) Corresponding quantitative pull-off force map [22]...

Fig. 4.8 (a) Histograms of pull-off force values obtained with an unmodified Si3N4 tip on untreated and oxyfluorinated iPP films in ethanol. The total surface free energy y of the polymer film is shown, (b) Mean values of pull-off force measured with COOH-terminated tips on modified polyolefin surfaces (iPP, isotactic polypropylene LDPE, low-density polyethylene) in ethanol (top) and with OH-terminated tips on oxyfluorinated iPP in water (pH 3.8, bottom) as a function of cos 0 (contact angle measured with water). (Reprinted in part/adapted with permission from [26, 27]. Copyright 1998, 2000, American Chemical Society.)... 

Finally, the selective growth of inorganic crystals was demonstrated on a SAM-templated silver surface. Hsu and coworkers [58] preferentially grew zinc oxide (ZnO) from an aqueous solution on silver surfaces. The silver surface was patterned by 4CP with a carboxyl acid (-COOH)-terminated SAM to inhibit ZnO growth. Figure 5.5.9(b) and (c) contain micrographs that demonstrate ZnO growth only... 

SAMs with COOH-terminated alkanethiols (HS-CCH j -COOH) immobilize cytochrome c in a stable, electroactive state. With n > 8 the standard electron-transfer rate depends exponentially on n and electron-transfer occurs by tunneling. The electron transfer rate is increased by a factor of >1000 the COOH-thiol monolayer is coassembled with OH-thiols. The mixed monolayer obviously allows direct contact with the heme edge, which does not occur in the pure COOH-thiol monolayer. Furthermore the surface pk of 8 of the pure monolayer shifts to more acidic values in the co-assembly. The monolayer may thus contain more negative charges to allow the higher binding of cytochrome c (El Kasmi et al., 1998). 

Immobile trypsin-Sepharose and anti-small subunits IgG-Sepharose can fully interact with the large subunits, but not the small subunits, because the long COOH-terminal extensions of the large subunits run between and above small subunits. The small subunits appear largely covered by the large subunits. Perhaps the carboxyl-terminal tail of the small subunit is slightly exposed to the molecular surface, so the small subunits separated from the large subunit core can enter into solution when immobile holoenzyme is dissociated by 2 M urea. 

Fujihira and coworkers extended PFM-AFM to adhesive force mapping on a patterned SAM [356-358]. In this mode of PFM-AFM, difference in the adhesive force between the —CH3 and —COOH terminated regions on the (xCP patterned SAM was mapped simultaneously with its topographic image. To achieve the quantitative analyses of the adhesive forces for chemical differentiation on the patterned surface by PFM-AFM, accurate information about the tip and substrate geometries [359, 360] and chemical modification of the tip surfaces [361] as well as the precise environmental control, such as electrolyte concentrations [292, 362, 363], and humidity [364] are indispensable. Recently, Bohn and coworkers used PFM-AFM to map the adhesion force between an AFM tip and samples of -substituted alkanethiol monolayer terminated with —CH3 and —COOH prepared by gCP... 

Although not completely known, the amino acid sequence of the rabbit muscle aldolase subunit is largely elucidated. (A more detailed description on protein structure appears in the chapter on inborn errors of metabolism.) The molecule contains 364 amino acids with a proline NH2-terminal, a tyrosine in the COOH-terminal position, and 8 cysteine residues. A critical residue is the lysine 221 which is believed to form a Schiff base with dihydroxyacetone phosphate. (The role of Schiff bases in enzymic reactions is discussed in more detail in the section devoted to transaminases.) In the model proposed by Lai und Horecker [51], this lysine is near the center of the molecule. If one follows the contour of the molecule from this critical residue 221, which must be at the active center, toward the tyrosine carboxy terminal, three SH groups are well exposed on the surface of the molecule. They occupy positions 193, 171, and 143. 

Azurine has been immobilized on the hydrophobic surfaces (methyl terminated) of alkanethiol SAMs on Au. Reversible charge transfer from the Cu redox centers to the Au surface becomes more difficult as the length of the hydrocarbon chains is increased. Laccase has also been immobilized on COOH-terminated thiol SAM on Au(lll). The enzyme shows a good catalytic activity for oxygen electroreduction. 

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