MPA SAM

Campuzano et al. [39] Soft drinks Glucose oxidase (GOx)/ cross-linked with glutaraldehyde Mercaptopropionic acid (MPA)-SAM-modified gold electrode/+0.2 V vs. Ag/AgCl Tetrathiafulvalene (TTF) (also cross-linked with glutaraldehyde)... 

TTF-GADH-MPA-SAM-coated BAS gold disk (3-mm 0) as working electrode BAS MF-2063Ag AgCl KCl 3M reference electrode Pt wire counter electrode and 10-mL glass electrochemical cell. 

Immerse the clean AuE in a 40 mmol L 1 MPA solution in EtOH/ H202 (75/25, v/v) for at least 15 h to form the MPA-SAM. Rinse the modified electrode with deionized water and dry with an argon stream. 

Fig. 5. (Left) SEIRAS of NaHA and DNA on PAMAM dendrimer SAMs after adsorption for 30 min from aqueous solutions. Dendrimer SAMs were prepared by the amide bond formation of dendrimers with active ester groups of 3-mercapto-propionic acid (MPA) SAMs on CaF2 substrates. Infrared absorption spectra of NaHA, DNA, and PAMAM dendrimer are also included. (Right) Schematic illustration of the interactions between polyelectrolytes and dendrimer SAMs. Reprinted from Ref. [110].

Figure 8-12. Left Monolayer protein voltammetry of P. furiosus ferredoxin on an Au(lll)-electrode modified by a mercaptopropionic acid (MPA) SAM, cf, Fig. 8-lOC 5 mM phosphate buffer, pH 7.9. Scan rate 5 mV s . Middle In situ STM image of P. furiosus ferredoxin molecules in electron transport action on the same MPA-modified Au(lll)-electrode surface Ar-atmosphere. Working electrode potential -0.35 V (SCE), bias voltage -0.35 V. Tunneling current 0.10 nA. Right Schematic view of the P. furiosus ferredoxin molecule on the MPA-modified Au( 111 )-surface. From ref. 137 with permission.

By using this selective replacement technique, artificially phase-separated SAMs can be prepared. For example, MUA and UT form a homogeneously mixed SAM when they are made to be coadsorbed from a bathing solution. MPA domains of phase-separated UT-MPA SAM can... 

SAM of MPA. Interestingly, the electron transfer of Fe-SOD and Mn-SOD could not be facilitated by the SAM of cysteine even though the SAM of cysteine could be used for promoting the electron transfer of Cu, Zn-SOD [98], as described above. This again suggests the promoter-dependent nature of the electron transfer properties of the SODs. 

In a scheme complementary to the one just presented where thiols are removed by reductive desorption of thiols, molecules can also be removed during stripping of a UPD layer. This was demonstrated by Shimazu et al. [221] where an alkane thiol SAM was deposited onto a Au(l 11) that had been modified with Pb. Oxidative stripping of the lead also caused thiols to be removed. The empty sites were then subsequently filled with mercaptopropionic acid (MPA). A remarkable result is that the binary SAMs exhibit only one desorption peak. From this it was concluded that a well-mixed layer forms that is very different from the mixed SAM obtained by adsorption from solution containing both types of thiols. In this case the layer exhibits singlecomponent domains that are refiected by two desorption peaks. 

Fig. 10.2. Cu(II) coverage (T) of Gly-Gly-His modified gold electrodes on mixed SAMs of MPA and MP, determined by integration of CV peaks. Mixed SAMs comprising MPA and MP were prepared by immersing the gold-coated substrates in solutions of mixtures of MPA and MP of a given fraction. In all cases, Cu(II) was accumulated at the Gly-Gly-His modified electrode at open circuit for 10 min in a 0.05 M ammonia acetate buffer solution (pH 7.0) containing 0.1 iM copper nitrate, removed, rinsed and then placed in a copper-free ammonium acetate buffer solution. Scan rate 100 mV s-1. Reproduced with permission of The Royal Society of Chemistry from Ref. [6], Copyright, Royal Society of Chemistry (2003).

Hybridization and one-base mismatch detection was performed by using self-assembled monolayer (SAM) on gold electrodes in the presence of MB indicator first time [61]. 14-mer short oligonucleotides were immobilized onto Au electrode surface by using alkanethiol monolayer coupling at surface. Mercaptopropionic acid (MPA) was used for monolayer production. Voltammetric reduction signal of MB was monitored for hybridization and mismatch detection. 

Mycophenolic acid (MPA) is being used as an immunosuppressant in patients undergoing kidney, heart, and liver transplants. The final step in the biosynthesis of MPA involves the transfer of a methyl group from SAM to the demethylmycophenolic acid (Figure 1.5b) [3]. 

Transfer-molding pressure n. The pressure applied to the cross-sectional area of the material pot or cylinder (MPa or kpsi). Pittance JC (ed) (1990) Engineering plastics and composites. SAM International, Materials Park, OH. 

Various pieces of information on the SAM and/or SAM/solution interfaces can be obtained from the mpe values. On the basis of the mpe for the reductive desorption of mercaptoalkanoic acid SAMs of various chain lengths (mercaptopropi-onic acid (MPA) to mercaptoundecanoic acid (MUA)), for example, Shimazu and coworkers concluded in the same paper [32] that the terminal carboxylate of a SAM is associated with the solvated cation (the solvation numbers are 1.6, 2.4-3.0 and 0.2 for li+, K" " and Cs+, respectively). 

Totally different results were obtained by Shimazu and coworkers for the titrations of the SAMs of mercaptoalkanoic acids of different chain lengths (MPA, MHA=mercaptohexanoic acid, MU A, and MHDA) [42-44]. The resonance frequency of the QCM was continuously monitored when the pH of an unbuffered 0.1 M NaCl solution was increased by adding 0.1 M NaOH at a constant flow rate (Fig. 5). The frequency decreased by ca. 

In contrast, in the case of the binary SAM of MPA and HDT, two peaks appear in the voltammograms at the positions near the EpS for singlephase-separated two domains in the SAM. This phase separation forming nanometer-scale domains can be directly seen in the STM images of the SAM [17, 42). This binary SAM is a typical example of the case when the interaction between A-A or B-B pairs is stronger than that of A-B pairs. 

From a detailed comparison of the peak areas and the STM images, the minimum size of the domain that behaves as a two-dimensional bulk phase is about 15 nm or 50 thiolate molecules in the case of binary SAM of HDT and MPA [17]. A domain that consists of less than 50 molecules has a desorption potential in the middle of the two peaks corresponding to the desorption of phase-separated two types of domains. 

Figure 17 shows voltammograms of phase-separated HDT-MPA binary SAM before the selective desorption (a), after the selective desorption of the MPA-rich domains (b), and after the immersion of selectively removed substrate into an ethanol solution of MPA (c) [56]. It is possible to introduce different thiol molecules... 

Fig. 17 Cyclic voltammograms for the reductive desorption of various SAMs in 0.5 M KOH solution (a) original phase-separated binary SAM of MPA and HDT where the surface mole fraction of MPA is 0.49 (b) SAM after the selective desorption of MPA (c) regenerated binary SAM of MPA and HDT (d) binary SAM of MUAand HDT after the selective replacement of M PA with MUA. Initial potential, —0.2 V scan rate, 20 mV s electrode area,...

---