Reiko Kuroda

A solid-state dedicated circular dichroism spectrophotometer: Development and application

A solid-state dedicated circular dichroism (CD) spectrophotometer (J-800KCM) was designed and constructed. As a CD spectrophotometer is a polarization–modulation instrument, CD spectra are necessarily accompanied by artifacts due to macroscopic anisotropies such as linear birefringence (LB) and linear dichroism (LD) which are unique to the solid state. A photomultiplier with the least polarization characteristics and a photoelastic modulator (PEM) with the least residual static birefringence were selected for the new instrument, which was based on the electrical and optical systems of a commercially available spectrophotometer. A phased-locked loop circuit was introduced to a PEM driver, and a sample rotation holder, a stage controller, and an analyzer were installed. We have designed and built a special solid-state sample holder to enable the cancellation of artifact CD, and a lens unit for smaller samples. A set of procedures for obtaining true CD has been devised based on the Mueller matrix method, and...

Facile Synthetic Route to Highly Luminescent Sila[7]helicene

A facile synthetic route to dimethylsila[7]helicene by using a Lewis acid catalyzed double-cyclization reaction for construction of the twisted two phenanthrene moieties is described. Sila[7]helicene exhibited a high fluorescence quantum yield and a realatively large g value (dissymmetric factor) of circularly polarized luminencence (CPL) for small molecules.

1,1′-Binaphthyl-2,2′-diol and 2,2′-diamino-1,1′-binaphthyl: versatile frameworks for chiral ligands in coordination and metallosupramolecular chemistry

Abstract This review covers the use of chiral 1,1′-binaphthyl-2,2′-diol and 2,2′-diamino-1,1′-binaphthyl frameworks for the construction of ligands for coordination and metallosupramolecular chemistry. The 1,1′-binaphthyl-2,2′-diol unit is readily functionalised with ligating groups at both the diol oxygen atoms and at a variety of positions on the binaphthyl rings. This has allowed the synthesis of a wide range of ligands which, in combination with metal ions, has given rise to an array of chiral coordination compounds and supramolecular complexes. This review details polynuclear complexes prepared in this manner. 2,2′-Diamino-1,1′-binaphthyl has been used as a ligand in a number of complexes. Also, ligating groups have been attached to the 2,2′-diamino-1,1′-binaphthyl framework via its amine nitrogen atoms, usually by formation of a Schiff base. The coordination chemistry of both the parent 2,2′-diamino-1,1′-binaphthyl compound and of its derivatives are covered by this review.

Chiral blastomere arrangement dictates zygotic left–right asymmetry pathway in snails

Most animals display internal and/or external left–right asymmetry. Several mechanisms for left–right asymmetry determination have been proposed for vertebrates and invertebrates but they are still not well characterized, particularly at the early developmental stage. The gastropods Lymnaea stagnalis and the closely related Lymnaea peregra have both the sinistral (recessive) and the dextral (dominant) snails within a species and the chirality is hereditary, determined by a single locus that functions maternally. Intriguingly, the handedness-determining gene(s) and the mechanisms are not yet identified. Here we show that in L. stagnalis, the chiral blastomere arrangement at the eight-cell stage (but not the two- or four-cell stage) determines the left–right asymmetry throughout the developmental programme, and acts upstream of the Nodal signalling pathway. Thus, we could demonstrate that mechanical micromanipulation of the third cleavage chirality (from the four- to the eight-cell stage) leads to reversal of embryonic handedness. These manipulated embryos grew to ‘dextralized’ sinistral and ‘sinistralized’ dextral snails—that is, normal healthy fertile organisms with all the usual left–right asymmetries reversed to that encoded by the mothers’ genetic information. Moreover, manipulation reversed the embryonic nodal expression patterns. Using backcrossed F7 congenic animals, we could demonstrate a strong genetic linkage between the handedness-determining gene(s) and the chiral cytoskeletal dynamics at the third cleavage that promotes the dominant-type blastomere arrangement. These results establish the crucial importance of the maternally determined blastomere arrangement at the eight-cell stage in dictating zygotic signalling pathways in the organismal chiromorphogenesis. Similar chiral blastomere configuration mechanisms may also operate upstream of the Nodal pathway in left–right patterning of deuterostomes/vertebrates.

Body Handedness Is Directed by Genetically Determined Cytoskeletal Dynamics in the Early Embryo

Although substantial progress has been made recently in understanding the establishment of left-right asymmetry in several organisms, little is known about the initial step for any embryo. In gastropods, left-right body handedness is determined by an unknown maternally inherited single gene or genes at closely linked loci and is associated with the sense of spiral cleavage in early embryos. Contrary to what has been believed, we show that temporal and spatial cytoskeletal dynamics for the left- and right-handed snails within a species are not mirror images of each other. Thus, during the third cleavage of Lymnaea stagnalis, helical spindle inclination (SI) and spiral blastomere deformation (SD) are observed only in the dominant dextral embryos at metaphase-anaphase, whereas in the recessive sinistral embryos, helicity emerges during the furrow ingression. Actin depolymerization agents altered both cleavages to neutral. Further, we found a strong genetic linkage between the handedness-specific cytoskeletal organization and the organismal handedness, using backcrossed F4 congenic animals that inherit only 1/16 of dextral strain-derived genome either with or without the dextrality-determining gene(s). Physa acuta, a sinistral-only gastropod, exhibits substantial SD and SI levotropically. Thus, cytoskeletal dynamics have a crucial role in determination of body handedness with further molecular, cellular, and evolutionary implications.

CD spectra of solid-state samples

Solid-state CD spectroscopy can provide valuable information on conformation, intermolecular interactions, including chirality induction, and enantioselective reactions which occur specifically in the solid state. The technique can, however, suffer from serious artifacts. Some examples of solid-state CD are given and potential artifacts are discussed. Copyright 2000 Wiley-Liss, Inc.

Anion-Directed Formation and Degradation of an Interlocked Metallohelicate

Although there are many examples of catenanes, those of more complex mechanically interlocked molecular architectures are rare. Additionally, little attention has been paid to the degradation of such interlocked systems into their starting complexes, although formation and degradation are complementary phenomena and are equally important. Interlocked metallohelicate, [(Pd(2)L(4))(2)](8+) (2(8+)), is a quadruply interlocked molecular architecture consisting of two mechanically interlocked monomers, [Pd(2)L(4)](4+) (1(4+)). 2(8+) has three internal cavities, each of which encapsulates one NO(3)(-) ion (1:3 host-guest complex, 2⊃(NO(3)|NO(3)|NO(3))(5+)) and is characterized by unusual thermodynamic stability. However, both the driving force for the dimerization and the origin of the thermodynamic stability remain unclear. To clarify these issues, BF(4)(-), PF(6)(-), and OTf(-) have been used to demonstrate that the dimerization is driven by the anion template effect. Interestingly, the stability of 2(8+) strongly depends on the encapsulated anions (2⊃(NO(3)|NO(3)|NO(3))(5+) ≫ 2⊃(BF(4)|BF(4)|BF(4))(5+)). The origins of this differing thermodynamic stability have been shown through detailed investigations to be due to the differences in the stabilization of the interlocked structure by the host-guest interaction and the size of the anion. We have found that 2-naphthalenesulfonate (ONs(-)) induces the monomerization of 2⊃(NO(3)|NO(3)|NO(3))(5+) via intermediate 2⊃(ONs|NO(3)|ONs)(5+), which is formed by anion exchange. On the basis of this finding, and using p-toluenesulfonate (OTs(-)), the physical separation of 2⊃(NO(3)|NO(3)|NO(3))(5+) and 1(4+) as OTs(-) salt was accomplished.

Chain-Terminus Triggered Chiral Memory in an Optically Inactive 310-Helical Peptide

A new optically inactive 3(10)-helical peptide with a side-chain cross-linking was found to exhibit chiral memory stored in the peptide backbone, whose chirality was induced by a noncovalent interaction of a chiral molecule at the N-terminal end of the peptide.

Formation of 1 D and 3 D Coordination Polymers in the Solid State Induced by Mechanochemical and Annealing Treatments: Bis(3‐cyano‐pentane‐2,4‐dionato) Metal Complexes

Bis(3-cyano-pentane-2,4-dionato) (CNacac) metal complex, [M(CNacac)(2)], which acts as both a metal-ion-like and a ligand-like building unit, forms supramolecular structures by self-assembly. Co-grinding of the metal acetates of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with CNacacH formed a CNacac complex in all cases: mononuclear complex was formed in the cases of Mn(II), Cu(II) and Zn(II), whereas polymeric ones were formed in the cases of Fe(II), Co(II) and Ni(II). Subsequent annealing converted the mononuclear complexes of Mn(II), Cu(II) and Zn(II) to their corresponding polymers as a result of dehydration of the mononuclear complexes. The resultant Mn(II), Fe(II), Co(II), Ni(II) and Zn(II) polymeric complexes had a common 3 D structure with high thermal stability. In the case of Cu(II), a 1 D polymer was obtained. The Mn(II), Cu(II) and Zn(II) polymeric complexes returned to their original mononuclear complexes on exposure to water vapour but they reverted to the polymeric complexes by re-annealing. Co-grinding of metal chlorides with CNacacH and annealing of the mononuclear CNacac complexes prepared from solution reactions were also examined for comparison. [Mn(CNacac)(2)(H(2)O)(2)], [M(CNacac)(2)(H(2)O)] (M=Cu(II) and Zn(II)) and [M(CNacac)(2)](infinity) (M=Mn(II), Fe(II) and Zn(II)) are new compounds, which clearly indicated the power of the combined mechanochemical/annealing method for the synthesis of varied metal coordination complexes.

Annealing assisted mechanochemical syntheses of transition-metal coordination compounds and co-crystal formation

This article focuses on heating or annealing process in the mechanochemical preparation of coordination compounds in the solid state. Heating of metal complexes often promotes the liberation of weakly coordinated ligands and results in the complex with its coordination geometry unsaturated. Such “activated” complexes can be used as the building blocks of coordination polymers in the solid state. As one example, our recent work on [M(CNacac)2]∞ (CNacac = 3-cyano-pentane-2,4-dionato, M = MnII, FeII, CoII, NiII, CuII and ZnII) is presented. Further, co-grinding and annealing treatments of an enantiomeric pair of chiral crystals of [M(phen)3](PF6)2 (M = RuII and OsII, phen = 1,10-phenanthoroline) afford diffusion and rearrangement of transition metal complex ions to form co-crystal phases of racemic or quasi-racemic compounds by way of recognizing chirality. Our latest result of co-crystal formation via chirality transfer between optically stable and labile metal complexes is also briefly introduced.