Electron transport through self-assembled monolayers of tripeptides

We report how the electron transport through a solid-state metal/Gly-Gly-His tripeptide (GGH) monolayer/metal junction and the metal/GGH work function are modified by the GGH complexation with Cu2+ ions. Conducting AFM is used to measure the current-voltage histograms. The work function is characterized by combining macroscopic Kelvin probe and Kelvin probe force microscopy at the nanoscale. We observe that the Cu2+ ions complexation with the GGH monolayer is highly dependent on the molecular surface density and results in opposite trends. In the case of a high density monolayer the conformational changes are hindered by the proximity of the neighboring peptides, hence forming an insulating layer in response to copper-complexation. Whereas the slightly lower density monolayers allow for the conformational change to a looped peptide wrapping the Cu-ion, which results in a more conductive monolayer. Copper-ion complexation to the high- and low-density monolayers systematically induces an increase of the work functions. Copper-ion complexation to the low-density monolayer induces an increase of electron transport efficiency, while the copper-ion complexation to the high-density monolayer results in a slight decrease of electron transport. Both of the observed trends are in agreement with first-principle calculations. Complexed copper to low density GGH-monolayer induces a new gap state slightly above the Au Fermi energy that is absent in the high density monolayer.Comment: Full paper with supporting informatio

The Breaking Beads Approach for Photocleavage from Solid Support

Photocleavage from polystyrene beads is a pivotal reaction for solid phase synthesis that relies on photolabile linkers. The photocleavage, usually performed by batch irradiation, suffers from incomplete and slow cleavage. To overcome these issues, continuous flow and high-energy lamps are frequently used, but these setups are hazardous, technically challenging, and expensive. We developed a photocleavage approach that relies on a benchtop LED lamp and magnetic stirring. In this approach, we crush the beads instead of keeping their integrity to increase the yield of photocleavage. This approach proved very efficient for photocleavage of protected oligosaccharides

pH Controlled Impedimetric Sensing of Copper(II) Ion Using Oxytocin as Recognition Element

We report the modulation of the specific metal gation properties of a peptide and demonstrate a highly selective sensor for copper(II) ion. The neuropeptide oxytocin (OT) is reported for its high affinity towards Zn2+ and Cu2+ at physiological pH. The binding of the metal ions to OT is tuned by altering the pH of the medium. OT was self-assembled on glassy carbon electrode using surface chemistry, and electrochemical impedance spectroscopy (EIS) was used to probe the binding of Cu2+. Our results clearly indicate that at pH 10.0, the binding of Cu2+ to OT is increased compared to that at pH 7.0, while the binding to Zn2+ becomes almost negligible. This proves that the selectivity of OT towards each of the ions can be regulated simply by controlling the pH of the medium and hence allows the preparation of a sensing device with selectivity to Cu2+

Stirring Peptide Synthesis to a New Level of Efficiency

In this work, a new setup that relies on fast stirring and heating was used to increase the diffusion of both reagents and solid support. we show that the combination of fast mixing and elevated temperature enables the acceleration of solid-phase peptide synthesis without using a large excess of reagents, providing a greener and accessible alternative to the state-of-the-art.<br /

Diffusion Enhanced Amide Bond Formation on Solid Support

Performing amino acids coupling reactions on solid support using fast overhead stirring is far more efficient than the common shaking mixing methods. Stirring does not harm the polystyrene beads and allows to decrease dramatically the amount of reagents used and wasted in these transformations

Using Photoactive N-Heterocyclic Carbenes Monolayers to Identify the Influence of Surface Proximity on Photoswitching Activity

Self-assembly of photoresponsive molecules is a robust technology for reversibly tuning the chemical and electronic properties of functional materials. In most systems the photoactive group is separated from the surface by a spacer and thus the photo-responsiveness does not benefit from interactions with the metal. Herein, the impact of metal photoactive-group interactions on photoswitchability and surface potential were probed by self-assembly of N-heterocyclic carbene molecules (NHCs) that were functionalized with stilbene group directly on their imidazole ring. Stilbene-NHCs that were adsorbed on weakly interacting Au surface accumulated a vertical orientation, as identified by FTIR measurements. This positioning enabled structural flexibility and high photoisomerization efficiency that induced reversible changes in surface potential. Stilbene-NHCs that were anchored on Pt film accumulated flat-lying adsorption geometry due to strong metal-adsorbate interactions. These interactions limited the structural flexibility of the stilbene groups and induced deteriorated photoswitchability that led to lower photoinduced changes in surface potential. While stronger metal-adsorbate interactions hindered the photo-induced isomerization yield of stilbene, these interactions prompted the cis-to-trans thermal-induced isomerization rate, which was an order of magnitude higher on Pt than on Au. </p

Accelerated Solid Phase Glycan Synthesis ASGS

Solid phase synthesis is the most dominant approach for the synthesis of biological oligomers as it enables the introduc-tion of monomers in an iterative, reproducible manner. Solid phase synthesis of oligosaccharides is crucial for the devel-opment of glycobiology. Accelerated solid phase synthesis of biological oligomers is crucial for chemical biology, but its application to the synthesis of oligosaccharide is not trivial. Solid phase oligosaccharide synthesis is performed in a variety of conditions and temperatures, requires inert gas atmosphere, and demand high excess of glycosyl donors. The reactions are usually very long, and the poor mixing of the solid support increases the risk of diffusion-independent hydrolysis of the activated donor. The entire process is slow and done mostly in special synthesizers. High shear stirring is a new con-cept in solid phase that enables shortening the synthesis time. The efficient mixing makes sure that reactive intermedi-ates can diffuse faster to and into the solid support thereby increase the kinetics of the reactions. We report the first stir-ring-based accelerated solid-phase oligosaccharide synthesis. We harnessed high shear mixing to promote diffusion-dependent glycosylation over diffusion-independent side reactions resulting in high conversion in short reaction time. We eliminated the need for high excess of glycosyl donors and overcame the need to use inert atmosphere. We showed that by tailoring the deprotection and glycosylation conditions to the same temperature, all steps are performed continuously and full glycosylation cycles is completed in few minute