Iron(ii) and zinc(ii) monohelical binaphthyl salen complexes

Synthesis of amphiphilic chiral salen complexes and their conformational manipulation at the air-water interface

A series of amphiphilic salen complexes, [L1a,bM] and [L2a,bM], were designed and synthesized. These complexes consist of two or four hydrophilic triethylene glycol (TEG) chains and a hydrophobic π-extended metallosalen core based on naphthalene or phenanthrene. The obtained amphiphilic complexes, [L1bM] (M = Ni, Cu, Zn), formed a monolayer at the air-water interface, while the monocationic [L1bCo(MeNH₂)₂](OTf) did not form a well-defined monolayer. The number of hydrophilic TEG chains also had an influence on the monolayerformation behavior; the tetra-TEG derivatives, [L1bNi] and [L2bNi], showed a pressure rise at a less compressed region than the bis-TEG derivatives, [L1aNi] and [L2aNi]. In addition, the investigation of their compressibility and compression modulus suggested that the tetra-TEG derivatives, [L1bNi] and [L2bNi], are more flexible than the corresponding bis-TEG analogues, [L1aNi] and [L2aNi], and that the phenanthrene derivatives [L1a,bNi] were more rigid than the corresponding naphthalene analogues, [L2a,bNi]. The Langmuir-Blodgett (LB) films of one of the complexes, [L1bNi], showed CD spectra slightly different from that in solution, which may originate from the unique anisotropic environment of the air-water interface. Thus, we demonstrated the possibility of controlling the chiroptical properties of metal complexes by mechanical compression.

Dynamic Helicity Control of Oligo(salamo)-Based Metal Helicates

Much attention has recently focused on helical structures that can change their helicity in response to external stimuli. The requirements for the invertible helical structures are a dynamic feature and well-defined structures. In this context, helical metal complexes with a labile coordination sphere have a great advantage. There are several types of dynamic helicity controls, including the responsive helicity inversion. In this review article, dynamic helical structures based on oligo(salamo) metal complexes are described as one of the possible designs. The introduction of chiral carboxylate ions into Zn3La tetranuclear structures as an additive is effective to control the P/M ratio of the helix. The dynamic helicity inversion can be achieved by chemical modification, such as protonation/deprotonation or desilylation with fluoride ion. When (S)-2-hydroxypropyl groups are introduced into the oligo(salamo) ligand, the helicity of the resultant complexes is sensitively influenced by the metal ions. The replacement of the metal ions based on the affinity trend resulted in a sequential multistep helicity inversion. Chiral salen derivatives are also effective to bias the helicity; by incorporating the gauche/anti transformation of a 1,2-disubstituted ethylene unit, a fully predictable helicity inversion system was achieved, in which the helicity can be controlled by the molecular lengths of the diammonium guests.

A quantitative analysis of light-driven charge transfer processes using voronoi partitioning of time dependent DFT-derived electron densities

An analytical method is presented that provides quantitative insight into light-driven electron density rearrangement using the output of standard time-dependent density functional theory (TD-DFT) computations on molecular compounds. Using final and initial electron densities for photochemical processes, the subtraction of summed electron density in each atom-centered Voronoi polyhedron yields the electronic charge difference, QVECD . This subtractive method can also be used with Bader, Mulliken and Hirshfeld charges. A validation study shows QVECD to have the most consistent performance across basis sets and good conservation of charge between electronic states. Besides vertical transitions, relaxation processes can be investigated as well. Significant electron transfer is computed for isomerization on the excited state energy surface of azobenzene. A number of linear anilinepyridinium donor-bridge-acceptor chromophores was examined using QVECD to unravel the influence of its pi-conjugated bridge on charge separation. Finally, the usefulness of the presented method as a tool in optimizing charge transfer is shown for a homologous series of organometallic pigments. The presented work allows facile calculation of a novel, relevant quantity describing charge transfer processes at the atomic level. © 2017 Wiley Periodicals, Inc.

Zinc(II) silsesquioxane complexes and their application for the ring-opening polymerization of rac-lactide

In this Communication, we report the unprecedented solid-state structures for a series of zinc(II) silsesquioxane complexes. Initial catalytic data for the ring-opening polymerization of rac-lactide are also presented together with analogous heterogeneous species.

Iron(III)-salen complexes with less DNA cleavage activity exhibit more efficient apoptosis in MCF7 cells

To understand the relationship between DNA damage potential and biochemical activities, we synthesized nine different Fe(III)-salen derivatives with varying substituents, and analyzed their in vitro DNA cleavage properties and biochemical effects on cultured human cells. Our results demonstrated that Fe(III)-salen complexes affect cell viability, induce nuclear fragmentation, and activate caspases and apoptosis in cultured human cells. The nature and the position of the substituents in the Fe(III)-salen complexes play critical roles in determining their apoptotic efficiencies. Most importantly, our results demonstrated that the in vitro DNA cleavage activities of Fe(III)-salen complexes are not essential for their apoptotic activities in human cells. Instead, the lesser their DNA cleavage activity the greater is their apoptotic efficiency.

Dinuclear zinc(II) complexes of symmetric Schiff-base ligands with extended quinoline sidearms

The synthesis of two 2-formylquinolines is reported via the Skraup method followed by SeO(2) oxidation. Each aldehyde is condensed with (1R,2R)-diaminocyclohexane and (R)-BINAM, yielding four enantiomerically-pure bis(imine-quinoline) ligands. The neutral ligands are reacted with ZnCl(2) to give complexes with bis(bidentate) coordination of ZnCl(2) units. X-Ray structural characterization of three complexes shows them to have a single-stranded helical motif, with M helicity, except in one case where a 1:1 mixture of M and P helices is seen. The ligands and complexes are further characterized spectroscopically by solution (1)H and (13)C NMR, UV-vis and ECD.

Iron(ii) and zinc(ii) monohelical binaphthyl-salen complexes with overlapping benz[a]anthryl sidearms

The synthesis of the polyaromatic aldehyde 1-hydroxybenz[a]anthracene-2-carboxaldehyde is reported via a seven step protocol from 9,10-dihydroanthracene, with an overall yield of 30%. Two equivalents of the aldehyde are condensed with (R)-1,1'-binaphthyl-2,2'-diamine to produce a new binaphthyl-salen ligand, which is subsequently complexed to iron(II) and zinc(II) ions. The ligand and complexes are characterized by single-crystal X-ray crystallography. The complexes have distinct helical structures with overlapping benz[a]anthryl sidearms, and only M-helices are observed. The ligand and complexes are further characterized by solution (1)H and (13)C NMR spectroscopy as well as UV-visible and ECD spectroscopies. These studies indicate that there is a single component in solution, consistent with the solid state characterization.

Monohelical Iron(II) and Zinc(II) Complexes of a (1R,2R)-Cyclohexyl Salen Ligand with Benz[a]anthryl Sidearms

An enantiomerically pure C2-symmetric salen ligand with benz[a]anthracene siderams produces M helical complexes (FeII and ZnII) in solution. Interconversion to produce a 1:1 mixture of helical conformers in the solid state is possible, despite overlapped sidearms.