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Scott A Trammell

Publications and source records attributed to Scott A Trammell.

12 recordsLinked to original sources
PubMed2007

Rapid proton-coupled electron-transfer of hydroquinone through phenylenevinylene bridges.

We describe the synthesis of two oligo(phenylene vinylene)s (OPVs) with a hydroquinone moiety and a thiol anchor group: 4-(2',5'-dihydroxystyryl)benzyl thioacetate and 4-[4'-(2' ',5' '-dihydroxystyryl)styryl]benzyl thioacetate. Monolayers on gold of these molecules were examined by electrochemical techniques to determine the electron transfer kinetics of the hydroquinone functionality (H2Q) through these delocalized tethers ("molecular wires") as a function of pH. Between pH 4 and 9, rate constants were ca. 100-fold faster than for the same H2Q functionality confined to the surface via alkane tethers. Also, in this same pH range rate constants were independent of the length of the OPV bridge. These new electroactive molecules in which the hydroquinone functionality is wired to the gold surface by means of OPV tethers should be useful platforms for constructing bioelectronic devices such as biosensors, biofuel cells, and biophotovoltaic cells with a fast response time.

Chemistry, Physical↗
PubMed2006

Conductive wiring of immobilized photosynthetic reaction center to electrode by cytochrome C.

The photosynthetic reaction center (RC) found in photosynthetic bacteria is one of the most advanced photoelectronic devices developed by nature. However, after immobilization on the electrode surface, the efficiency of electron transfer (ET) between the RC and the electrode is relatively low. This inefficiency has limited the possibility of using the RC for technological applications. Here we show that photoinduced electron transfer between the immobilized RC and a gold electrode can be increased by several tens-fold by incorporation of cytochrome c into the RC-self-assembled monolayer (SAM)-electrode complex. The effect does not depend on the initial redox state of the cytochrome and seems to be the result of the formation of a complex between the RC and the cytochrome c serving as an ET wire. This observation opens the possibility for electrochemical analysis of the special pair in the RC protein that is deeply buried inside the protein globe and is barely electrically addressable from the electrode surface.

Biosensing Techniques↗
PubMed2006

Electrochemical and ligand binding studies of a de novo heme protein.

Heme proteins can perform a variety of electrochemical functions. While natural heme proteins carry out particular functions selected by biological evolution, artificial heme proteins, in principle, can be tailored to suit specified technological applications. Here we describe initial characterization of the electrochemical properties of a de novo heme protein, S824C. Protein S824C is a four-helix bundle derived from a library of sequences that was designed by binary patterning of polar and nonpolar amino acids. Protein S824C was immobilized on a gold electrode and the formal potential of heme-protein complex was studied as a function of pH and ionic strength. The binding of exogenous N-donor ligands to heme/S824C was monitored by measuring shifts in the potential that occurred upon addition of various concentrations of imidazole or pyridine derivatives. The response of heme/S824C to these ligands was then compared to the response of isolated heme (without protein) to the same ligands. The observed shifts in potential depended on both the concentration and the structure of the added ligand. Small changes in structure of the ligand (e.g. pyridine versus 2-amino pyridine) produced significant shifts in the potential of the heme-protein. The observed shifts correlate to the differential binding of the N-donor molecules to the oxidized and reduced states of the heme. Further, it was observed that the electrochemical response of the buried heme in heme/S824C differed significantly from that of isolated heme. These studies demonstrate that the structure of the de novo protein modulates the binding of N-donor ligands to heme.

Binding Sites↗
PubMed2005

Ru2(ap)4(sigma-oligo(phenyleneethynyl)) molecular wires: synthesis and electronic characterization.

Reported in this contribution are the synthesis, characterization, and charge transport properties of wire-like Ru2(ap)4(OPEn), where ap is 2-anilinopyridinate and OPE is -(CCC6H4)nSCH2CH2SiMe3 with n = 1 (1) and 2 (2). Scanning tunneling microscopy (STM) measurements of compound 2 inserted into a SAM of C11 thiol reveal that molecule 2 exhibits (i) the stochastic switching characteristic of wire molecules embedded in insulating SAMs and (ii) higher conductivity than the C11 thiol SAM. More importantly, analysis of the molecular electronic decay constant (beta) exhibits a decrease of at least 15% as compared to purely organic molecular analogues. Hence, the transport characteristics of molecules can be significantly improved for nanoscale electronics through the incorporation of a Ru2 fragment into conjugated backbone.

Journal Article↗
PubMed2005

Probing pi-coupling in molecular junctions.

Charge transport characteristics for metal-molecule-metal junctions containing two structurally related pi-conjugated systems were studied to probe pi-pi interactions in molecular junctions. The first molecule contains a typical pi-conjugated framework derived from phenylene vinylene units, whereas the second has the phenylene vinylene structure interrupted by a [2.2]paracyclophane (pCp) core. Electrochemical investigations were used to characterize the defects and packing density of self-assembled monolayers of the two molecules on gold surfaces and to enable quantitative comparison of their transport characteristics. Current-voltage measurements across molecular junctions containing the two species demonstrate that the pCp moiety yields a highly conductive break in through-bond pi-conjugation. The observed high conductivity is consistent with density functional theory calculations, which demonstrate strong through-space pi-pi coupling across the pCp moiety.

Electrochemistry↗
PubMed2005

Effect of protein orientation on electron transfer between photosynthetic reaction centers and carbon electrodes.

A new type of monolayer of photosynthetic reaction centers (RC) with the primary donor facing the carbon electrode has been constructed using a new bifunctional linker and genetically engineered protein. Comparison of protein in two different orientations with linkers binding to the opposite sides of the protein demonstrates the possibility of utilizing the constructed surfaces as photoelectronic devices. The results show improvement of the electron transfer efficiency when RC is bound with the primary donor (P) facing the electrode (P-side). In either protein orientation, electron transfer within the protein is unidirectional and when applying a voltage RC operates as a photorectifier. Electron transfer between the protein and carbon electrodes in the constructed devices is most likely occurring by tunneling.

Carbon↗
PubMed2004

Orientated binding of photosynthetic reaction centers on gold using Ni-NTA self-assembled monolayers.

Coupling of photosynthetic reaction centers (RCs) with inorganic surfaces is attractive for the identification of the mechanisms of interprotein electron transfer (ET) and for possible applications in construction of photo- and chemosensors. Here we show that RCs from Rhodobacter sphaeroides can be immobilized on gold surfaces with the RC primary donor looking towards the substrate by using a genetically engineered poly-histidine tag (His(7)) at the C-terminal end of the M-subunit and a Ni-NTA terminated self-assembled monolayer (SAM). In the presence of an electron acceptor, ubiquinone-10, illumination of this RC electrode generates a cathodic photocurrent. The action spectrum of the photocurrent coincides with the absorption spectrum of RC and the photocurrent decreases in response to the herbicide, atrazine, confirming that the RC is the primary source of the photoresponse. Disruption of the Ni-NTA-RC bond by imidazole leads to about 80% reduction of the photocurrent indicating that most of the photoactive protein is specifically bound to the electrode through the linker.

Adsorption↗
PubMed2004

Electron conduction across electrode-immobilized neutravidin bound with biotin-labeled ruthenium pentaamine.

Voltammetry is reported here of a self-assembled redox-protein conjugate consisting of neutravidin conjugated with a biotin derivative redox probe, Ru(NH3)5(N-[(N-[(4-pyridyl)methyl]biotinamide], immobilized on gold electrodes modified by self-assembled monolayers of mercaptoundecanoic acid. This voltammetry indicates that self-assembly of the conjugate/electrode electronic interface, driven by electrostatic binding between the monolayer and a single redox probe, favors orientation of the conjugate, resulting in electronic accessibility of the remaining three redox probes.

Amines↗
PubMed2004

Reversible modulation of quantum dot photoluminescence using a protein- bound photochromic fluorescence resonance energy transfer acceptor.

Multiple copies ( approximately 20) of Escherichia coli maltose binding protein (MBP) were coordinated to luminescent semiconductor quantum dots (QDs) via a C-terminal oligohistidine segment. The MBP was labeled with a sulfo-N-hydroxysuccinimide-activated photochromic BIPS molecule (1',3-dihydro-1'-(2-carboxyethyl)-3,3-dimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-(2H)-indoline]) at two different dye-to-MBP ratios; D/P = 1 and 5. The ability of MBP-BIPS to modulate QD photoluminescence was tested by switching BIPS from the colorless spiropyran (SP) to the colored merocyanine (MC) using white light (>500 nm) or UV light ( approximately 365 nm), respectively. QDs surrounded by MBP-BIPS with D/P = 1 were quenched on average approximately 25% with consecutive repeated switches, while QDs surrounded by MBP-BIPS with D/P = 5 were quenched approximately 60%. This result suggests a possible use of BIPS-labeled proteins in QD-based nanostructures as part of a threshold switch or other biosensing device.

Benzopyrans↗
PubMed2003

A comparative study of electrochemically and fluorometrically addressed molecular reporter groups: effects of protein microenvironment.

To probe the effects of protein microenvironment on electrochemically and fluorometrically addressed molecular reporter groups, genetically engineered apo-cytochrome c peroxidase derivatives W51C, A174C, K243C, and S246C, each containing a single cysteine residue, were labeled at identical sites with two kinds of microenvironment sensitive reporters, either an electrochemically active sulfhydryl-reactive reagent, [Ru(II)(NH(3))(4)(1,10-phenanthroline-5-maleimide)](PF(6))(2) [RuPA4] or a fluorescent 6-acryloyl-2-dimethylaminonaphthalene [acrylodan] probe. Two types of sites were labeled with each probe based on their predicted solvent accessibilities from the known structure for holo-cytochrome c peroxidase. One set of sites (K243C and S246C) was selected to be completely solvent exposed, while the other two sites (W51C and A174C) were less accessible, residing in or near the heme binding site. Spectroscopic properties of the fluorescent probe were consistent with predictions for relative solvent accessibilities; however, even the less solvent accessible probes reported a quite polar environment, suggesting that this region of the apo-protein is either substantially solvent exposed or undergoes significant dynamic motion. A linear correlation was observed between the lambda(max) of the metal to ligand charge-transfer (MLCT) absorption band of the RuPA4 complex and the acrylodan emission maximum for the four labeled apo-protein variants. The same trend occurred for the formal potential of RuPA4 versus the acrylodan emission maximum, with the exception of electrochemical probe behavior at position 174, possibly due to specific probe-protein interactions.

2-Naphthylamine↗
PubMed2003

A reagentless electrochemical biosensor based on a protein scaffold.

Apo-myoglobin, labeled with the environmentally sensitive redox probe RuII(NH3)4(1,10-phenanthroline-5-maleimide)2+, was immobilized onto gold electrodes modified with 11-mercaptoundecanoic acid and subsequently labeled with biotin; avidin binding to the immobilized biotin was specifically and quantitatively detected by a change in cyclic voltammetry of the co-immobilized probe.

Animals↗