Corrosion inhibition in acidic environments: key interfacial insights with photoelectron spectroscopy.

In many engineering scenarios, surface-active organic species are added to acidic solutions to inhibit the corrosion of metallic components. Given suitable selection, such corrosion inhibitors are highly effective, preventing significant degradation even in highly aggressive environments. Nevertheless, there are still considerable gaps in fundamental knowledge of corrosion inhibitor functionality, severely restricting rational development.

Application of a peptide-based assay to characterize inhibitors targeting protein kinases from yeast.

Chemical molecules that inhibit protein kinase activity are important tools to assess the functions of protein kinases in living cells. To develop, test and characterize novel inhibitors, a convenient and reproducible kinase assay is of importance. Here, we applied a biotinylated peptide-based method to assess adenosine triphosphate-competitive inhibitors that target the yeast kinases Hog1, Elm1 and Elm1-as.

Determination of primary sequence specificity of Arabidopsis MAPKs MPK3 and MPK6 leads to identification of new substrates.

MAPKs (mitogen-activated protein kinases) are signalling components highly conserved among eukaryotes. Their diverse biological functions include cellular differentiation and responses to different extracellular stress stimuli. Although some substrates of MAPKs have been identified in plants, no information is available about whether amino acids in the primary sequence other than proline-directed phosphorylation (pS-P) contribute to kinase specificity towards substrates.

Functionalized nanostructures: redox-active porphyrin anchors for supramolecular DNA assemblies.

We have synthesized and studied a supramolecular system comprising a 39-mer DNA with porphyrin-modified thymidine nucleosides anchored to the surface of large unilamellar vesicles (liposomes). Liposome porphyrin binding characteristics, such as orientation, strength, homogeneity, and binding site size, was determined, suggesting that the porphyrin is well suited as a photophysical and redox-active lipid anchor, in comparison to the inert cholesterol anchor commonly used today. Furthermore, the binding characteristics and hybridization capabilities were studied as a function of anchor size and number of anchoring points, properties that are of importance for our future plans to use the addressability of these redox-active nodes in larger DNA-based nanoconstructs.

Positional scanning peptide libraries for kinase substrate specificity determinations: straightforward and reproducible synthesis using pentafluorophenyl esters.

An efficient method to synthesize positional scanning synthetic combinatorial libraries (PS-SCLs) for studying the specificity of protein kinases is presented. Isokinetic ratios for pentafluorophenyl esters were determined iteratively using a new approach incorporating high performance liquid chromatography (HPLC) quantification and statistical experimental design. In the development process a large amount of work was put in to find efficient ways of screening for new isokinetic mixtures and to optimize the process of PS-SCL synthesis.

Highly efficient incorporation of the fluorescent nucleotide analogs tC and tCO by Klenow fragment.

Studies of the mechanisms by which DNA polymerases select the correct nucleotide frequently employ fluorescently labeled DNA to monitor conformational rearrangements of the polymerase-DNA complex in response to incoming nucleotides. For this purpose, fluorescent base analogs play an increasingly important role because they interfere less with the DNA-protein interaction than do tethered fluorophores. Here we report the incorporation of the 5'-triphosphates of two exceptionally bright cytosine analogs, 1,3-diaza-2-oxo-phenothiazine (tC) and its oxo-homolog, 1,3-diaza-2-oxo-phenoxazine (tC(O)), into DNA by the Klenow fragment.

Membrane-anchored DNA assembly for energy and electron transfer.

In this work we examine the trapping and conversion of visible light energy into chemical energy using a supramolecular assembly. The assembly consists of a light-absorbing antenna and a porphyrin redox center, which are covalently attached to two complementary 14-mer DNA strands, hybridized to form a double helix and anchored to a lipid membrane. The excitation energy is finally trapped in the lipid phase of the membrane as a benzoquinone radical anion that could potentially be used in subsequent chemical reactions.

A membrane anchored DNA-based energy/electron transfer assembly.

In this work the trapping and conversion of visible light energy into chemical energy is examined using a supramolecular assembly. This consists of a light absorbing antenna and a porphyrin redox centre both covalently attached to a DNA strand, which in turn is bound to a lipid membrane. The excitation energy is finally trapped as a benzoquinone radical anion that could potentially be used in subsequent chemical reactions.

Charge recombination versus charge separation in donor-bridge-acceptor systems.

Optimizing the ratio of the rates for charge separation (CS) over charge recombination (CR) is crucial to create long-lived charge-separated states. Mastering the factors that govern the electron transfer (ET) rates is essential when trying to achieve molecular-scale electronics, artificial photosynthesis, and also for the further development of solar cells. Much work has been put into the question of how the donor-acceptor distances and donor-bridge energy gaps affect the electronic coupling, V(DA), and thus the rates of ET.

Triplet photophysics of gold(III) porphyrins.

Gold porphyrins are often used as electron-accepting chromophores in donor-acceptor complexes for the study of photoinduced electron transfer, and they can also be involved in triplet-triplet energy-transfer interactions with other chromophores. Since the lowest excited singlet state is very short-lived (240 fs), the triplet state is usually the starting point for the transfer reactions, and it is therefore crucial to understand its photophysics. The triplet state of various gold porphyrins has been reported to have a lifetime of around 1.

Triplet excitation energy transfer in porphyrin-based donor--bridge--acceptor systems with conjugated bridges of varying length: an experimental and DFT study.

A series of donor--bridge--acceptor (D--B--A) systems with varying donor-acceptor distances have been studied with respect to their triplet energy transfer properties. The donor and acceptor moieties, zinc(II), and free-base porphyrin, respectively, were separated by 2-5 oligo-p-phenyleneethynylene units (OPE) giving rise to edge-to-edge separations ranging between 12.7 and 33.

Solvent and base dependence of copper-free palladium-catalyzed cross-couplings between terminal alkynes and arylic iodides: development of efficient conditions for the construction of gold(III)/free-base porphyrin dimers.

In this paper, our attempts to optimize the Heck alkynylation (copper-free Sonogashira) reaction are presented. An efficient copper-free coupling protocol was needed for the synthesis of gold/zinc porphyrin dimers because previous methods had failed. Previous studies have usually focused on ligands, whereas this work focuses on the choice of solvent and base.

Interplay between barrier width and height in electron tunneling: photoinduced electron transfer in porphyrin-based donor-bridge-acceptor systems.

The rate of electron tunneling in molecular donor-bridge-acceptor (D-B-A) systems is determined both by the tunneling barrier width and height, that is, both by the distance between the donor and acceptor as well as by the energy gap between the donor and bridge moieties. These factors are therefore important to control when designing functional electron transfer systems, such as constructs for photovoltaics, artificial photosynthesis, and molecular scale electronics. In this paper we have investigated a set of D-B-A systems in which the distance and the energy difference between the donor and bridge states (DeltaEDB) are systematically varied.

Singlet energy transfer in porphyrin-based donor-bridge-acceptor systems: interaction between bridge length and bridge energy.

Singlet excitation energy transfer is governed by two donor-acceptor interactions, the Coulombic and exchange interactions giving rise to the Förster and Dexter mechanisms, respectively, for singlet energy transfer. In transfer between colliding molecules or between a donor (D) and acceptor (A) connected in donor-bridge-acceptor (D-B-A) system by an inert spacer (B), the distinction between these two mechanisms is quite clear. However, in D-B-A systems connected by a pi-conjugated bridge, the exchange interaction between the donor and acceptor is mediated by the virtual low-lying excited states (unoccupied orbitals) of that bridge and, as a consequence, becomes much more long-range in character.