Karl Maurer

Microelectrode Arrays and Ceric Ammonium Nitrate : A Simple Strategy for Developing New Site-Selective Synthetic Methods

Conditions for a site-selective ceric ammonium nitrate oxidation have been developed. The reactions proceed nicely on both 1K- and 12K-microelectrode arrays. The procedure for developing the reactions was very simple and demonstrated that the same reagents used for a solution-phase reaction can be used for a related site-selective reaction on a microelectrode array.

Building addressable libraries: site-selective Suzuki reactions on microelectrode arrays.

A site-selective Suzuki reaction has been developed for use on microelectrode arrays. The reaction conditions employed are similar to those used to achieve site-selective Heck reactions. The reaction can be run with either an aryliodide attached to the surface of the array and an arylboronic acid in solution or with an arylboronic acid attached to the surface of the array and an arylbromide in solution. Both allyl acetate and air are effective confining agents for the reaction. The reactions are compatible with arrays containing either 1024 microelectrodes cm(-2) or 12,544 microelectrodes cm(-2).

Moving known libraries to an addressable array: a site-selective hetero-Michael reaction.

A two-step, Michael reaction-based strategy for site-selectively placing molecules by unique electrodes in an addressable microelectrode array has been developed. The strategy is compatible with the use of polypeptide nucleophiles and works with microelectrode arrays having either 1024 electrodes/cm (2) or 12,544 electrodes/cm (2). The chemistry should allow for the transfer of existing molecular libraries to microelectrode array devices for analysis.

Use of a multiplexed CMOS microarray to optimize and compare oligonucleotide binding to DNA probes synthesized or immobilized on individual electrodes.

The CombiMatrix microarray with 12,544 electrodes supports in situ electrochemical synthesis of user-defined DNA probes. As an alternative, we immobilized commercially synthesized DNA probes on individual electrodes coated with electropolymerized polypyrrole (Ppy). Hybridization was measured using a biotinylated target oligonucleotide and either Cy5-streptavidin and fluorescence detection or horseradish peroxidase-streptavidin and enzyme-enhanced electrochemical detection. Detection efficiencies were optimized by varying the deposition of the Ppy, the terminal groups on the DNA probes, and other factors that impacted fluorescence quenching and electrical conductivity. Optimized results were compared against those obtained using a microarray with the same DNA sequences synthesized in situ. Immobilized probes produced higher fluorescence signals, possibly by providing a greater stand off between the Cy5 on the target oligonucleotide and the quenching effects of the Ppy and the platinum electrode.

Building addressable libraries: a site-selective click-reaction strategy for rapidly assembling mass spectrometry cleavable linkers

A click-reaction was site-selectively carried out on 1000 and 12,000 microelectrode arrays and characterized using TOF-SIMS.

Building addressable libraries: site-selective formation of an N-acyliminium ion intermediate.

A strategy for site-selectively generating reactive N-acyliminium ion intermediates on a microelectrode array has been developed. The route capitalizes on the use of an electroauxiliary for building a methoxylated amino acid substrate, and then the electrochemical generation and solution phase confinement of acid in order to form the N-acyliminium ion. Keys to this strategy were the stability of an N-alpha-methoxyalkyl amide to basic reaction conditions and the generality of the electrogenerated acid conditions for conducting microelectrode array reactions in a site-selective fashion.

Site-selectively functionalizing microelectrode arrays: the use of Cu(I)-catalysts.

Site-selective Cu(I)-catalyzed reactions have been developed on microelectrode arrays. The reactions are confined to preselected electrodes on the arrays using oxygen as the confining agent. Conditions initially developed for the Cu(I)-catalyzed click reaction have proven general for the coupling of amine, alcohol, and sulfur nucleophiles to both vinyl and aryl iodides. Differences between reactions run on 1-K arrays and reactions run on 12-K arrays can be attributed to the 1-K array reactions being divided cell electrolyses and the 12-K array reactions being undivided cell electrolyses. Reactions on the 12-K arrays benefit from the use of a non-sugar-derived porous reaction layer for the attachment of substrates to the surface of the electrodes. The reactions are sensitive to the nature of the ligand used for the Cu catalyst.

A new porous reaction layer for developing addressable molecular libraries.

A new diblock copolymer-derived porous reaction layer for microelectrode arrays has been tested for its stability and its compatibility with both site-selective synthesis and electrochemical signaling experiments. The diblock copolymer consisted of a cinnamoyl-substituted polymethacrylate block for attachment to the surface of the array and a bromo-substituted polystyrene block for selective functionalization of the surface proximal to microelectrodes in the array. Site-selective Suzuki, Heck, and Cu(I)-coupling reactions were all performed on the new reaction layer along with electrochemical impedance studies.

Stress responses of the industrial workhorse Bacillus licheniformis to osmotic challenges.

The Gram-positive endospore-forming bacterium Bacillus licheniformis can be found widely in nature and it is exploited in industrial processes for the manufacturing of antibiotics, specialty chemicals, and enzymes. Both in its varied natural habitats and in industrial settings, B. licheniformis cells will be exposed to increases in the external osmolarity, conditions that trigger water efflux, impair turgor, cause the cessation of growth, and negatively affect the productivity of cell factories in biotechnological processes. We have taken here both systems-wide and targeted physiological approaches to unravel the core of the osmostress responses of B. licheniformis. Cells were suddenly subjected to an osmotic upshift of considerable magnitude (with 1 M NaCl), and their transcriptional profile was then recorded in a time-resolved fashion on a genome-wide scale. A bioinformatics cluster analysis was used to group the osmotically up-regulated genes into categories that are functionally associated with the synthesis and import of osmostress-relieving compounds (compatible solutes), the SigB-controlled general stress response, and genes whose functional annotation suggests that salt stress triggers secondary oxidative stress responses in B. licheniformis. The data set focusing on the transcriptional profile of B. licheniformis was enriched by proteomics aimed at identifying those proteins that were accumulated by the cells through increased biosynthesis in response to osmotic stress. Furthermore, these global approaches were augmented by a set of experiments that addressed the synthesis of the compatible solutes proline and glycine betaine and assessed the growth-enhancing effects of various osmoprotectants. Combined, our data provide a blueprint of the cellular adjustment processes of B. licheniformis to both sudden and sustained osmotic stress.

Building Addressable Libraries: Site‐Selective Lewis Acid (Scandium(III)) Catalyzed Reactions

Microelectrode arrays 2] are potentially powerful tools for monitoring the binding of molecular libraries to biological receptors in “real time”. However, in order to capitalize on this potential, we must be able to synthesize the members of the molecular library in a manner that places each unique member of the library proximal to a unique, individually addressable microelectrode in the array. This is a daunting challenge because the arrays used for signaling contain 12544 microelectrodescm . With this in mind, we have been working to develop the synthetic methodology needed to site selectively conduct chemical reactions on micoelectrode arrays. In connection with these studies, the ability to employ a Lewis acid catalyst in a site-selective fashion would be particularly intriguing. Lewis acid catalysts are used to accelerate reactions, trigger cycloadditions, introduce stereocontrol elements into reaction transition states, and assemble reagents for multicomponent synthetic strategies. For example, Lavilla and co-workers recently demonstrated that a Sc species can be used as a Lewis acid to trigger multicomponent reactions that form tetrahydropyranring skeletons with three potential sites (R, R, R) for diversification (Scheme 1). Multicomponent reactions of