D3h-symmetrical hydrogen-bonding unit as a saccharide recognition and self-assembling module

A D(3h)-symmetrical triresorcinol module 1,3,5-tris(2,6-dihydroxy-4-pentylphenyl)benzene ( 3) was investigated in terms of its hydrogen-bonding ability for glycoside recognition and self-association. When 3 was treated with glycoside, corresponding changes were induced in (1)H NMR, UV, and CD spectra. The titration experiments indicated the participation of not only a 1:1 but also a 1:2 association of a glucosamine derivative guest. Self-association of 3 caused gelation with CDCl(3), and was studied by (1)H NMR and X-ray analysis.     

Long range influence of an excess proton on the architecture of the hydrogen bond network in large-sized water clusters

Infrared spectra of completely size-selected protonated water clusters H+(H2O)n are reported for clusters ranging from n=15 to 100. The behavior of the dangling OH stretch bands shows that the hydrogen bond structure in H+(H2O)n is uniquely different to that of (H2O)n up to the size of n=100, at least. This finding indicates that the presence of an excess proton creates a characteristic morphology in the hydrogen bond network architecture of more than 100 surrounding water molecules.     

Theoretical analyses of the morphological development of the hydrogen bond network in protonated methanol clusters

Extensive density functional theory (DFT) calculations are carried out on various structural isomers of protonated methanol clusters, H(+)(MeOH)n (n = 2-9), to analyze the morphological development of the hydrogen bond network in the clusters with an increase of the cluster size. Coexistence of multiple structural isomers is demonstrated by the nearly degenerated energies. Moreover, significant temperature dependence of the preferential isomer structure is shown by the calculated Gibbs free energies. The previously reported infrared spectra of H(+)(MeOH)n (J. Phys. Chem. A 2005, 109, 138) are revisited on the basis of the spectral simulations of the isomers by DFT calculations.     

InBr3-promoted divergent approach to polysubstituted indoles and quinolines from 2-ethynylanilines: switch from an intramolecular cyclization to an intermolecular dimerization by a type of terminal substituent group

Use of a 2-ethynylaniline having an alkyl or aryl group on the terminal alkyne selectively produced a variety of polyfunctionalized indole derivatives in moderate to excellent yields via indium-catalyzed intramolecular cyclization of the corresponding alkynylaniline. In contrast, employment of a substrate with a trimethylsilyl group or with no substituent group on the terminal triple bond, exclusively afforded polysubstituted quinoline derivatives in good yields via indium-promoted intermolecular dimerization of the ethynylaniline. This indium catalytic system successfully accommodated the intramolecular cyclization of other arylalkyne skeletons involving a carboxylic acid and an amide group.     

Tandem trimer pyrrole–imidazole polyamide probes targeting 18 base pairs in human telomere sequences

The binding of molecules to specific DNA sequences is important for imaging genome DNA and for studying gene expression. Increasing the number of base pairs targeted by these molecules would provide greater specificity. N-Methylpyrrole–N-methylimidazole (Py–Im) polyamides are one type of such molecules and can bind to the minor groove of DNA in a sequence-specific manner without causing denaturation of DNA. Our recent work has demonstrated that tandem hairpin Py–Im polyamides conjugated with a fluorescent dye can be synthesized easily and can serve as new probes for studying human telomeres under mild conditions. Herein, to improve their selectivities to telomeres by targeting longer sequences, we designed and synthesized a fluorescent tandem trimer Py–Im polyamide probe, comprising three hairpins and two connecting regions (hinges). The new motif bound to 18 bp dsDNA in human telomeric repeats (TTAGGG)_n, the longest sequence for specific binding reported for Py–Im polyamides. We compared the binding affinities and the abilities to discriminate mismatch, the UV-visible absorption and fluorescence spectra, and telomere staining in human cells between the tandem trimer and a previously developed tandem hairpin. We found that the tandem trimer Py–Im polyamide probe has higher ability to recognize telomeric repeats and stains telomeres in chemically fixed cells with lower background signal.     

Reaction pathway analysis for shuffle-set 60° perfect dislocation in Si

In this work, the EDIP potential is employed for representing silicon and the shuffle-set 60° perfect dislocation motion is investigated by reaction pathway analysis. There are three possible shuffle-set 60° perfect dislocation core structures named as S1, S2 and S3. The activation energy barriers of the kink migration and nucleation in S1and S2 types are calculated by CI-NEB method. The simulation results show that the critical resolved shear strain of the shuffle-set dislocation in S1 type is around 5%, and the S1 type is the dominate one in the shear strain region of 0 to 5%. During the shear strain from 5to 11.81%, the dislocation moves as the S1 core kink nucleation and migration, meanwhile the S1 dislocation core is in process of transforming into S2. More interestingly, both S1 and S2 dislocation core structures is observed along the dislocation line in this shear strain regime, which could response to the missing observation of long segment dislocation line in the experiment.     

Crystal structures of (azido)(pentamethylcyclopentadienyl)iridium(III) complexes containing various types of bidentate ligands

Several (azido)iridium(III) complexes having a pentamethylcyclopentadienyl (Cp∗) group, [Cp∗Ir(N₃)₂(Ph₂Ppy-κP)] (1: Ph₂Ppy = 2-diphenylphosphinopyridine), [Cp∗Ir(N₃)(Ph₂Ppy-κP,κN)]CF₃SO₃ (2), [Cp∗Ir(N₃)(dmpm)]PF₆ (3: dmpm = bis(dimethylphosphino)methane), [Cp∗Ir(N₃)(Ph₂Pqn)]PF₆·$·$CH₃OH (4·$·$CH₃OH: Ph₂Pqn = 8-diphenylphosphinoquinoline), and [Cp∗Ir(N₃)(pybim)] (5: Hpybim = 2-(2-pyridyl)benzimidazole) have been prepared and their crystal structures have been analyzed by X-ray diffraction. In complex 1, the Ph₂Ppy ligand is only coordinated via the P atom (-κP), while in 2 it acts as a bidentate ligand through the P and N atoms (-κP,κN) to form a four-membered chelate ring. Comparing the structural parameters of the chelate ring in 2 with those of a similar five-membered chelate ring formed by Ph₂Pqn in 4, it became apparent that the angular distortion in the Ph₂Ppy-κP,κN ring was remarkable, although the Ir–P and Ir–N bonds in the Ph₂Ppy-κP,κN ring were not elongated very much from the corresponding bonds in the Ph₂Pqn-κP,κN ring. In the pybim complex 5, the five-membered chelate ring was coplanar with the pyridine and benzimidazolyl rings. With the related (azido)iridium(III) complexes analyzed previously, comparison of the structural parameters of the Ir–N₃ moiety in [Cp∗Ir^III(N₃)(L–L′)]^+/0 complexes reveals an anomalous feature of the 2,2′-bipyridyl (bpy) complex, [Cp∗Ir(N₃)(bpy)]PF₆.     

Upgrading and expanding the scope of homogeneous transfer hydrogenation

Transfer hydrogenation using inexpensive and safe hydrogen sources of alcohols and formic acid has been studied thoroughly over the decades. In particular, the asymmetric version offers the state-of-the-art methods to obtain optically active alcohols and amines, which are valuable synthetic intermediates in the field of pharmaceutical and agrochemical industry. This digest paper highlights the recent notable advances in homogeneous transfer hydrogenation using transition metal complexes, especially in direction to establish practical greener processes by upgrading the catalyst performance or by expanding the scope of reducible functional groups.     

Highly enantioselective fluorescent recognition of mandelic acid derivatives by chiral salen macrocycles

Calixarene-like chiral salen macrocycles can be used for the enantioselective fluorescent recognition of mandelic acid derivatives. It was observed that one enantiomer of mandelic acid causes a 28-fold increase in the fluorescence intensity of a chiral salen macrocycle, whereas the other enantiomer causes only a 14-fold fluorescence enhancement. This highly enantioselective fluorescent response makes chiral salen macrocycles useful for the enantioselective fluorescent recognition of some mandelic acid derivatives.