SAMs capped

For transition and precious metals, thiols have been successfully employed as the stabilizing reagent (capping reagent) of metal nanoparticles [6]. In such cases, various functionalities can be added to the particles and the obtained nanoparticles may be very unique. It is well known that thiols provide good self-assembled monolayers (SAM) on various metal surfaces. When this SAM technique is applied to the nanoparticle preparation, nanoparticles can be covered constantly by functionalized moieties, which are connected to the terminal of thiol compounds. 

Important pathways requiring SAM include synthesis of epinephrine and of the 7-methylgua-nine cap on eukaryotic mRNA, Synthesis of SAM from methionine is shown in Figure T17-3. After donating the methyl group, SAM is converted to homocysteine and remethylated in a reaction catalyzed by N-methyl THF-homocysteine methyltransferase requirii both vitamin Bj2 and N-meth d-THF. The methionine produced is once again used to make SAM. 

An early nanopore study focused on an asymmetric Au-molecule-Ti junction based on thiol end-capped biphenyl 81b molecules [45], The asymmetry of the structure led to the observation of a prominent rectifying behavior with larger current when the Ti electrode was negatively biased. Recent work by Bao and coworkers [72] has shown that vapor deposition of Ti on SAMs results in penetration of the monolayer, thus destroying it. Similar observations were made using Au and A1 deposition. However, destruction of the monolayer could in this case be prevented if SAMs of dithiols were used, since the Au or A1 would react with the free thiol end. 

Thiol end-capped oligothiophenes 105a-c were used to form the SAMs between the electrodes. A series of distinct periodic steps in the conductance was observed for all samples at low temperature (<100 K). These features were suggested to originate from vibrational modes in the molecules. A (weakly coupled) gate potential could be applied to the molecular junction, which shifted the step position in the I(V) curves but not the step widths. This observation was taken as an indication that only a single molecule was electrically active in the molecular junction. 

Fig. 14.37. Speculative cartoon of cytochrome adsorbed c on a COOH-termi-nated self-assembled monolayer on gold. A crys-talline region for HS(CH2)15COOH SAM is depicted. Alkanethiol molecules are represented as end-capped cylinders with a COOH terminus (black) and a thiolate (gray) attachment to the gold electrode. Polypeptide line diagrams of cytochrome c molecule are shown in an electrostatically favored orientation. For clarity, the heme group has been blackened. (Reprinted from Bowden, "Wiring Mother Nature, Interface 6(4) 40-45, Fig. 2, 1997. Reproduced by permission of the Electrochemical Society, Inc.)...

Cn(hfac)2 (7b) °. The qnality of the copper fihns deposited on the SAM diffusion barrier was high regarding pnrity and nniformity, comparable to that of films deposited on Si(lOO) and traditional diffnsion barriers (TiN). Copper selenide binary phases can be grown from Cn(acac)2 (7a) and trioctylphosphine selenide. Depending on the techniques applied, tetragonal Cn2Se (aerosol-assisted CVD) or cnbic Cn2 xSe nanoparticles capped with hexadecylamine (liqnid deposition) are prodnced. ... 

Harry Ruben returned to New York because he could not earn a living in San Francisco making caps and doing small jobs. Meanwhile, Ida had a job in Berkeley. Freida, her son Sam, and her daughter Mae moved to Berkeley, where Ida supported them. Sam worked part time as a salesman at Call Me Joe s clothing store in Berkeley. 

Fig. 3 Structural features of methionine synthase. Methionine synthase is comprised of five domains, which bind homocysteine (HCY), methylfolate (5-methyl THF), cobalamin, and S-adenosylmethionine (SAM). The Cap domain restricts oxidation of cobalamin in its vulnerable Cbl(I) state. Strucmres from E.coli (Bandarian et al., 2002 Dixon et al. 1996) and T.maritima (Evans et al. 2004) (PDB codes 1Q8J, 1K98 and IMSK, respectively) were used to construct this composite model. An uncharacteiized linker segment between the folate and cap domains is absent...

While four domains of methionine synthase bind reaction components (HCY, SAM, cobalamin, and methylfolate), the fifth domain, known as the Cap domain, hovers above cobalamin while it is in its readily oxidized Cob(I) state, limiting access of reactive oxygen species or electrophilic substances. As such, the Cap domain restricts inactivation of methionine synthase and consequently promotes methylation over transsulfuration. In rt-PCR smdies using RNA from cultured human neuroblastoma cells, we found that the Cap sequence, corresponding to... 

Fig. 58 Schematic of inferred structure for CdSe nanocrystal infiltrated polymer brush photovoltaic device. From bottom to top ITO-coated glass slide modified by surface attachment of a bromine end-capped trichlorosilane self-assembled monolayer (SAM) (squares) polymer brushes grown from the SAM (lines) CdSe nanocrystals infiltrated into the brush network exhibiting some degree of phase separation in the plane of the film (small circles) and an aluminum cathode cap. (Reprinted with permission from [256], 2005, American Chemical Society)...

In another study, Liu et al. [66] used a PEM in place of an OTS SAM to create a new type of membrane for encapsulation of cultured cells. The PEM was composed of several alternating layers of poly(lysine) and alginate, capped with an amphiphilic terpolymer synthesized from yV,/V-dioctadecylcarbamoyl propionic acid, hydrox-yethylacrylate, and styrene sulfonate. The octadecyl chains provided a hydrophobic surface on which the acrylatePC was fused, then photopolymerized (Fig. 2). Coating alginate beads with the PEM/HBM multilayer significantly reduced the release... 

Capping of eukaryotic mRNA. (a) Enzymatic reactions required for 50 capping SAM is -S -adenosyl methionine and SAC is -S -adenosyl homocysteine, (b) Structure of 7-methylguanosine cap. 

The second method for capping mRNA takes advantage of the activity of the vaccinia virus capping enzyme, also known as guanylyltransferase. This enzyme is commercially available. In the presence of GTP and S-adenosyl methionine (SAM), it can add a natural Cap structure (7-methylguanosine) to the 5 triphosphate of a RNA molecule. As it is an enzymatic reaction, it can bring a correct Cap to all mRNA molecules, and thus, it is optimal compared with in vitro transcription in the presence of standard Cap but similar theoretically to in vitro transcription in the presence of ARCA Cap. 

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