Integrating CuO−Fe2O3 Nanocomposites and Supramolecular Assemblies of Phenazine for Visible‐Light Photoredox Catalysis

A photoredox catalytic ensemble consisting of CuO‐Fe₂O₃ nanocomposites and oligomeric derivative of phenazine has been developed. The prepared system acts as an efficient photoredox catalyst for C?N bond formation reaction via SET mechanism under ‘green’ conditions (aerial environment, mixed aqueous media, recyclable), requiring less equivalents of base and amine substrate. The present study demonstrates the significant role of supramolecular assemblies as photooxidants and reductants upon irradiation and their important contribution towards the activation of the metallic centre through energy transfer and electron transfer pathways. The potential of oligomer 4 : CuO‐Fe₂O₃ has also been explored for C?C bond formation reactions via the Sonogashira protocol.     

MD simulations of spontaneous membrane protein/detergent micelle formation

The in vitro study of membrane proteins for the purpose of physicochemical analysis or structure determination often relies upon successful reconstitution into detergent micelles. Moreover, a number of biological processes such as membrane protein folding and transport rely on lipid interactions which may resemble the micellar environment. Little is known about the structures of these micelles or the processes which lead to their formation. We therefore present two 50 ns all-atom molecular dynamics simulations of spontaneous dodecylphosphocholine micelle formation around representatives of the two major families of membrane proteins, a small beta-barrel protein, OmpA, and a model alpha-helical protein, glycophorin A. Despite differences in protein architecture, we highlight common mechanistic pathways in micelle formation, which are consistent with experimental studies. We characterize the exponential kinetics of detergent-protein adsorption and suggest a simple model which may explain the aggregation process. We also compare the results with 25 and 50 ns simulations of preformed micelles containing the same proteins. We confirm that the end structures of the self-assembled micelles are similar to those from their preformed counterparts, with each micelle presenting a bilayerlike environment to the enclosed protein.     

Acid/Base‐Triggered Switching of Circularly Polarized Luminescence and Electronic Circular Dichroism in Organic and Organometallic Helicenes

Electronic circular dichroism and circularly polarized luminescence acid/base switching activity has been demonstrated in helicene‐bipyridine proligand 1 a and in its “rollover” cycloplatinated derivative 2 a . Whereas proligand 1 a displays a strong bathochromic shift (>160 nm) of the nonpolarized and circularly polarized luminescence upon protonation, complex 2 a displays slightly stronger emission. This strikingly different behavior between singlet emission in the organic helicene and triplet emission in the organometallic derivative has been rationalized by using quantum‐chemical calculations. The very large bathochromic shift of the emission observed upon protonation of azahelicene‐bipyridine 1 a has been attributed to the decrease in aromaticity (promoting a charge‐transfer‐type transition rather than a π–π* transition) as well as an increase in the HOMO–LUMO character of the transition and stabilization of the LUMO level upon protonation.     

Molecular dynamics simulations of GlpF in a micelle vs in a bilayer: conformational dynamics of a membrane protein as a function of environment

Octyl glucoside (OG) is a detergent widely employed in structural and functional studies of membrane proteins. To better understand the nature of protein-OG interactions, molecular dynamics simulations (duration 10 ns) have been used to explore an alpha-helical membrane protein, GlpF, in OG micelles and in DMPC bilayers. Greater conformational drift of the extramembraneous protein loops, from the initial X-ray structure, is seen for the GlpF-OG simulations than for the GlpF-DMPC simulation. The mobility of the transmembrane alpha-helices is approximately 1.3x higher in the GlpF-OG than the GlpF-DMPC simulations. The detergent is seen to form an irregular torus around the protein. The presence of the protein leads to a small perturbation in the behavior of the alkyl chains in the OG micelle, namely an approximately 15% increase in the trans-gauche(-)-gauche(+) transition time. Aromatic side chains (Trp, Tyr) and basic side chains (Arg, Lys) play an important role in both protein-detergent (OG) and protein-lipid (DMPC) interactions.     

Nucleophilic addition of β-amino carbanions to arynes: one-pot synthesis of 4-aryl-N-methyl-1,2,3,4-tetrahydroisoquinolines

A novel approach for the direct C-4 arylation of N-methyl-1,2,3,4-tetrahydroisoquinolines by nucleophilic addition of β-aminocarbanions to benzynes is described which provides a one-pot procedure for synthesis of the title compounds.     

Lipid/protein interactions and the membrane/water interfacial region

Despite the importance of lipid/protein interactions in the folding, assembly, stability, and function of membrane proteins, information at an atomic level on how such proteins interact with the lipids that surround them remains sparse. The dynamics and flexible nature of the protein/bilayer interaction make it difficult to study, for example, by crystallographic means. However, based on recent progress in molecular simulations of membranes it is possible to address this problem computationally. This communication reports one of the first attempts to use multiple ns molecular simulations to establish a qualitative picture of the intermolecular interactions between the lipids of a bilayer and two topologically different membrane proteins for which a high resolution (2 A or better) X-ray structure is available.