Leucine zipper motif inspiration: a two-dimensional leucine Velcro-like array in peptide coordination polymers generates hydrophobicity.

Here, we show that the well-known hydrophobic leucine (Leu) zipper motif (also known as the coiled-coil or Leu scissors motif), typically found in proteins, can be used as a source of inspiration in coordination polymers built from Leu-containing dipeptides or tripeptides. We demonstrate that this motif can be extended to form Velcro-like layers of Leu, and that the hydrophobicity of these layers is transferred to coordination polymers, thereby enabling the development of a new type of hydrophobic materials.

Femtolitre chemistry assisted by microfluidic pen lithography.

Chemical reactions at ultrasmall volumes are becoming increasingly necessary to study biological processes, to synthesize homogenous nanostructures and to perform high-throughput assays and combinatorial screening. Here we show that a femtolitre reaction can be realized on a surface by handling and mixing femtolitre volumes of reagents using a microfluidic stylus. This method, named microfluidic pen lithography, allows mixing reagents in isolated femtolitre droplets that can be used as reactors to conduct independent reactions and crystallization processes. This strategy overcomes the high-throughput limitations of vesicles and micelles and obviates the usually costly step of fabricating microdevices and wells. We anticipate that this process enables performing distinct reactions (acid-base, enzymatic recognition and metal-organic framework synthesis), creating multiplexed nanoscale metal-organic framework arrays, and screening combinatorial reactions to evaluate the crystallization of novel peptide-based materials.

Cycloaddition reactivity studies of first-row transition metal-azide complexes and alkynes: an inorganic click reaction for metalloenzyme inhibitor synthesis.

The studies described herein focus on the 1,3-dipolar cycloaddition reaction between first-row transition metal-azide complexes and alkyne reagents, i.e. an inorganic variant of the extensively used "click reaction". The reaction between the azide complexes of biologically-relevant metals (e.g., Fe, Co and Ni) found in metalloenzyme active sites and alkyne reagents has been investigated as a proof-of-principle for a novel method of developing metalloenzyme triazole-based inhibitors. Six Fe, Co and Ni mono-azide complexes employing salen- and cyclam-type ligands have been synthesized and characterized. The scope of the targeted inorganic azide-alkyne click reaction was investigated using the electron-deficient alkyne dimethyl acetylenedicarboxylate. Of the six metal-azide complexes tested, the Co and Ni complexes of the 1,4,8,11-tetrametyl-1,4,8,11-tetraazacyclotetradecane (Me(4)cyclam) ligand showed a successful cycloaddition reaction and formation of the corresponding metal-triazolate products, which were crystallographically characterized. Moreover, use of less electron deficient alkynes resulted in a loss of cycloaddition reactivity. Analysis of the structural parameters of the investigated metal-azide complexes suggests that a more symmetric structure and charge distribution within the azide moiety is needed for the formation of a metal-triazolate product. Overall, these results suggest that a successful cycloaddition reaction between a metal-azide complex and an alkyne substrate is dependent both on the ligand and metal oxidation state, that determine the electronic properties of the bound azide, as well as the electron deficient nature of the alkyne employed.

Comparative study of the phototoxicity of long-wavelength photosensitizers targeted by the MornigaG lectin.

Morniga G is a plant lectin selective for high density of tumor-associated carbohydrate T and Tn antigens on the surface of cells. The interaction of the protein with Tn induces its cell penetration. This property was used for targeting photosensitizers (consisting of the porphyrins TrMPyP and TPPS, the Al(III)-phthalocyanin AlPcS(4), and the chlorin e6) against leukemic Jurkat T cells after covalent coupling to the protein. The control of MornigaG/photosensitizer loading allowed the comparison of the toxicity of the different photosensitizer conjugates. Conjugate including a single AlPcS(4) per protein appeared promising, since it is poorly toxic when irradiated under white light, while it shows a strong phototoxicity (LD(50) = 4 nM) when irradiated in the therapeutic window, it preferentially kills cancerous lymphocytes, and the sugar binding specificity of the lectin part of the molecule remains unaltered.

Coexistence of two thermally induced intramolecular electron transfer processes in a series of metal complexes [M(Cat-N-BQ)(Cat-N-SQ)]/[M(Cat-N-BQ)2] (M = Co, Fe, and Ni) bearing non-innocent catechol-based ligands: a combined experimental and theoretical study.

The different thermally induced intermolecular electron transfer (IET) processes that can take place in the series of complexes [M(Cat-N-BQ)(Cat-N-SQ)]/[M(Cat-N-BQ)(2)], for which M = Co (2), Fe (3) and Ni(4), and Cat-N-BQ and Cat-N-SQ denote the mononegative (Cat-N-BQ(-)) or dinegative (Cat-N-SQ(2-)) radical forms of the tridentate Schiff-base ligand 3,5-di-tert-butyl-1,2-quinone-1-(2-hydroxy-3,5-di-tert-butylphenyl)imine, have been studied by variable-temperature UV/Vis and NMR spectroscopies. Depending on the metal ion, rather different behaviors are observed. Complex 2 has been found to be one of the few examples so far reported to exhibit the coexistence of two thermally induced electron transfer processes, ligand-to-metal (IET(LM)) and ligand-to-ligand (IET(LL)). IET(LL) was only found to take place in complex 3, and no IET was observed for complex 4. Such experimental studies have been combined with ab initio wavefunction-based CASSCF/CASPT2 calculations. Such a strategy allows one to solicit selectively the speculated orbitals and to access the ground states and excited-spin states, as well as charge-transfer states giving additional information on the different IET processes.

Morphological investigation of Mn12 single-molecule magnets adsorbed on Au(111).

We report on the adsorption of Mn(12) single-molecule magnets bearing external biphenyl groups on Au(111) surfaces after a simple dipping procedure. Topographic AFM images confirm that the biphenyl groups favor the adsorption of the molecules without the need of functionalization with thiols or thioether groups. The first formed molecular layer covers homogenously the whole surface, whereas further growth takes place mostly in the form of molecular wires (or aggregates) and, occasionally, as molecular islands. Interestingly, the Mn(12) core is preserved for all the cases, although its aggregation state appears to influence significantly the rigidity of the molecular aggregates. Force-volume imaging experiments have demonstrated that molecules at the second layer are stiffer, that is, more rigid, than the molecules lying at the background layer. This fact clearly reveals that the interplay of attractive and repulsive forces between molecules and the molecule-surface interaction modulate the mechanical properties of the Mn(12) single-molecule magnets upon grafting. These results are very important to understand how surface-induced morphological deformations can modify the magnetic properties of these molecular systems on the translation from the macroscopic to a surface.