Temperature-Responsive Chiral (A)6B Supramolecular Cages Based on Conformational Preferences.

Two chiral (A)6B-typed supramolecular cages were constructed from hydrogen-bonded C6 -symmetric zinc porphyrin hexamers and chiral C3-symmetric pyridyl hexadentates with a core of 1,3,5-triphenylbenzene. Circular dichroism and molecular simulations revealed that the symmetry of the supramolecular cages switched from pseudo-C3v to C3 with the rotational confinement of the biphenyl backbones at low temperatures, which generated conformationally chiral transfer and amplification. This unique phenomenon suggests a new strategy to develop smart materials with high sensitivity and excellent reversibility.

Folding-induced folding: the assembly of aromatic amide and 1,2,3-triazole hybrid helices.

Folding-induced folding for the construction of artificial hybrid helices from two different kinds of aromatic sequences is described. Linear compounds 1 a, 1 b, and 2, containing one aromatic amide trimer or pentamer and one or two aromatic 1,2,3-triazole tetramers, have been designed and synthesized. The trimeric and pentameric amide segments are driven by intramolecluar N-H⋅⋅⋅F hydrogen bonding to adopt a folded or helical conformation, whereas the triazole segment is intrinsically disordered. In organic solvents of low polarity, the amide foldamer segment induces the attached triazole segment(s) to fold through intramolecular stacking, leading to the formation of hybrid helices. The helical conformation of these hybrid sequences has been confirmed by (1)H and (19)F NMR spectroscopy, UV/Vis spectroscopy, circular dichroism (CD) experiments, and theoretical calculations. It was found that the amide pentamer exhibits a stronger ability to induce the folding of the attached triazole segment(s) compared with that of the shorter trimer. Enantiomers (R)-3 and (S)-3, which contain an R- or S-(1-naphthyl)ethylamino group at the end of a tetraamide segment, have also been synthesized. CD experiments showed that introduction of a chiral group caused the whole framework to produce a strong helicity bias. Density-functional-theory calculations on (S)-3 suggested that this compound exists as a right-handed (P) helix.

Self-resistance to an antitumor antibiotic: a DNA glycosylase triggers the base-excision repair system in yatakemycin biosynthesis.

Resistance is (not) futile: The yatakemycin biosynthetic gene cluster involves the ytkR2 gene, which encodes a protein with homology to a recently discovered bacterial DNA glycosylase. Genetic validation in vivo, biochemical assays, and in vitro mutagenesis studies revealed that YtkR2 confers resistance for the bacteria by specifically recognizing and cleaving the YTM-modified base (see scheme).

Studies on CH3CN-assisted decomposition of 1st Grubbs catalyst by electrospray ionization tandem mass spectrometry.

The CH(3)CN-assisted decomposition reaction of the 1(st) Grubbs catalyst (1) was studied using electrospray ionization tandem mass spectrometry (ESI-MS/MS). We detected a series of Ru-intermediates and decomposition products by off-line and on-line ESI-MS(/MS) monitoring of the decomposition process. In particular, an on-line microreactor method was applied with ESI-MS/MS to profile the change and relationship of various Ru-intermediates by controlling the reaction within the first 30 s of its time scale. The main fast decomposition mechanism of Ru-catalyst 1 in the presence of CH(3)CN was similar to that proposed by Grubbs, and this was confirmed by detecting the (PhCH(2)PCy(3))(+) ion at m/z 371 as the major decomposition products with ESI-MS. We also studied the time evolution of the transient reactive Ru-intermediate ions step by step with ESI-MS/MS and detected the C-H bond activation products of toluene--dehydrogenated PCy(3), such as P(Cy)(2)(C(6)H(9)), P(Cy)(2)Ph--by analyzing the decomposition reaction solution by gas chromatography (GC)/MS. The mechanism of another minor decomposition pathway involving the phosphine activation of catalyst 1 was proposed on the basis of the ESI-MS(/MS) interception and characterization of the transient reactive Ru-species in the decomposition reaction solution. Finally the coordination effect of the CH(3)CN in assisting the decomposition and stabilizing the transient Ru-complexes is discussed.

Analysis of low molecular weight compounds by MALDI-FTICR-MS.

This review focuses on recent applications of matrix-assisted laser desorption ionization-Fourier-transform ion cyclotron resonance mass spectrometry (MALDI-FTICR-MS) in qualitative and quantitative analysis of low molecular weight compounds. The scope of the work includes amino acids, small peptides, mono and oligosaccharides, lipids, metabolic compounds, small molecule phytochemicals from medicinal herbs and even the volatile organic compounds from tobacco. We discuss both direct analysis and analysis following derivatization. In addition we review sample preparation strategies to reduce interferences in the low m/z range and to improve sensitivities by derivatization with charge tags. We also present coupling of head space techniques with MALDI-FTICR-MS. Furthermore, omics analyses based on MALDI-FTICR-MS were also discussed, including proteomics, metabolomics and lipidomics, as well as the relative MS imaging for bio-active low molecular weight compounds. Finally, we discussed the investigations on dissociation/rearrangement processes of low molecular weight compounds by MALDI-FTICR-MS.

Gas-phase synthesis of hydrodiphenylcyclopropenylium via nonclassical Favorskii rearrangement from alkali-cationized alpha,alpha'-dibromodibenzyl ketone.

The gas-phase synthesis of hydrodiphenylcyclopropenylium from alkali-cationized alpha,alpha'-dibromodibenzyl ketone (1) via nonclassical Lewis-acid-induced Favorskii rearrangement has been studied by electrospray ionization/tandem mass spectrometry (ESI-MS/MS) and theoretical methods, showing that cations [1-Br](+) by debromination from 1 and 1.M(+)(M = Li or Na) by alkali-metal cationization of 1 could convert into the protonated diphenylcyclopropenone 2.H(+) by collision-induced dissociation in the gas phase. A concerted mechanism for the Lewis-acid-induced Favorskii rearrangement from alkali-metal-cationized alpha,alpha'-dibromodibenzyl ketone was proposed and studied, based on mass spectrometric results and theoretical methods.