Copper(II) complexes (1–4) of tri‐ or tetradentate bis(2‐methylbenzimidazolyl)amine ligands (L1–L4) have been prepared and characterized by spectroscopic methods in solution, as well as in the solid state by X‐ray crystallography. The ligands act as tridentate donors towards the cupric ions through one central amine and two benzimidazole N atoms in the solid state; a water ligand and a bridging perchlorate group define the distorted octahedral environments of 2 and 3. Complex 4 has square‐pyramidal coordination geometry, with an additional thioether donor attached to the central N atom in the axial position. Electrospray mass spectrometry characterized the complexes as monomeric in acetonitrile solution. Cyclic voltammetry studies established that amine N benzyl‐containing 3 has the highest half‐wave redox potential of all of these complexes at –0.08 V (vs. Fc+/Fc) for the Cu2+/Cu+ couple. The complexes display dose‐dependent cytotoxicity against one human and four murine cancer cell lines. Complexes 3 and 4 have good antiproliferative activity against the human chronic leukemia cell line K562. Moreover, for 3 the proliferation of all malignant cell lines decreases at concentrations lower than the IC50 for healthy bone marrow cells.

Photoinduced charge separation and transport through photosystem I (PSI) is an essential part of the photosynthetic electron transport chain. To investigate charge exchange processes mediated by the P700 reaction center of PSI, we have developed a strategy to functionalize gold electrodes with PSI complexes that orients and exposes their luminal side to the electrolyte. Bulk photoelectrochemical measurements demonstrate that PSI remains functional in a wide sample potential range around 0 mV/SSC. Electrochemical scanning tunneling microscopy (ECSTM) imaging of individual complexes shows lateral sizes in agreement with the dimensions of PSI and an apparent height that is gated by the probe potential of ECTSM as reported for smaller globular redox proteins. This experimental setup enables ECSTM current-distance spectroscopic measurements that unequivocally correspond to the P700 side of PSI. In these conditions, we observe that the spatial span of the current is enhanced (the distance-decay rate β is reduced) through the solution at sample potential 0 mV/SSC and probe potential 400 mV/SSC. This process corresponds to hole injection into an electronic state that is available in the absence of illumination. We propose that a pair of tryptophan residues located near P700 and known to integrate the hydrophobic recognition site for plastocyanin may have an additional role as hole exchange mediator involved in charge transport through PSI.<br>

The transport of electrons along photosynthetic and respiratory chains involves aseries of enzymatic reactions that are coupled through redoxm ediators,i ncluding proteins and small molecules.The use of native and synthetic redoxprobes is key to understanding charge transport mechanisms and to the design of bioelectronic sensors and solar energy conversion devices.H owever,r edoxp robes have limited tunability to exchange charge at the desired electrochemical potentials (energy levels) and at different protein sites.H erein, we take advantage of electrochemical scanning tunneling microscopy (ECSTM) to control the Fermi level and nanometric position of the ECSTM probe in order to study electron transport in individual photosystem I( PSI) complexes.C urrent-distance measurements at different potentiostatic conditions indicate that PSI supports long-distance transport that is electrochemically gated near the redoxp otential of P700, with current extending farther under hole injection conditions. Photosynthesis is an essential process for plants,a lgae,a nd bacteria since it converts light energy,C O 2 ,a nd water into carbohydrate molecules.A lthough the identity and structure of the main proteins and complexes involved in photosynthesis have been extensively characterized, [1] the underlying electron transport pathways,their mechanisms and regulation are not fully understood at the nanometer scale.P rogress in this direction would enable the rational design of bioelectronic nanodevices based on photosynthetic complexes for solar energy applications like hydrogen production [2] and photocurrent generation in photovoltaic cells. [3]

Preparation of bis(1-tert-butoxycarbonyl-2-benzimidazolylmethyl)amines from N-tert-butoxycarbonyl-protected 2-chloromethylbenzimidazole is described. The reaction with primary amines containing several functional groups afforded bis(1-tertbutoxycarbonyl-2-benzimidazolylmethyl)amines in good yields. Hydrogenolysis of bis(2-benzimidazolylmethyl)benzylamine, catalyzed by Pd(OH) 2 /C, cleaved the benzyl group, leaving the tertbutoxycarbonyl and 2-benzimidazolylmethyl groups intact. The product of the latter reaction, bis(1-tert-butoxycarbonyl-2-benzimidazolylmethyl)amine, was thus obtained in 56% yield; the presence of the tert-butoxycarbonyl groups at the N-benzimidazole positions makes it amenable to further functionalization at the central nitrogen atom.

<p>The transport of electrons along photosynthetic and respiratory chains involves a series of enzymatic reactions that are coupled through redox mediators, including proteins and small molecules. The use of native and synthetic redox probes is key to understand charge transport mechanisms, and to design bioelectronic sensors and solar energy conversion devices. However, redox probes have limited tunability to exchange charge at the desired electrochemical potentials (energy levels) and at different protein sites. Here, we take advantage of electrochemical scanning tunneling microscopy (ECSTM) to control the Fermi energy and nanometric position of the ECSTM probe in order to study electron transport in individual photosystem I (PSI) complexes. Current-distance measurements at different potentiostatic conditions indicate that PSI supports long-distance transport that is electrochemically gated near the redox potential of P700, with current extending farther under hole injection conditions.</p>