Femtosecond dynamics of the ring closing process of diarylethene: a case study of electrocyclic reactions in photochromic single crystals

The cyclization reaction of the photochromic diarylethene derivative 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene was studied in its single crystal phase with femtosecond transient absorption spectroscopy. The transient absorption measurements were performed with a robust acquisition scheme that explicitly exploits the photoreversibility of the molecular system and monitors the reversibility conditions. The crystalline system demonstrated 3 × 10(4) repeatable cycles before significant degradation was observed. Immediately following photoexcitation, the excited state absorption associated with the open-ring conformation undergoes a large spectral shift with a time constant of approximately 200 fs. Following this evolution on the excited state potential energy surface, the ring closure occurs with a time constant of 5.3 ps, which is significantly slower than previously reported measurements for similar derivatives in the solution phase. Time resolved electron diffraction studies were used to further demonstrate the assignment of the transient absorption dynamics to the ring closing reaction. The mechanistic details of the ring closing are discussed in the context of prior computational work along with a vibrational mode analysis using density functional theory to give some insight into the primary motions involved in the ring closing reaction.     

Interactions of single-stranded DNA on microcantilevers

The microcantilever approach has attracted considerable attention in recent years as a means of label-free detection of a variety of biomolecular and chemical reactions. The underlying physics of the intermolecular interactions that result in mechanical motions is yet to be fully explored, but it seems both rich in science and of technological importance. This paper presents an overview of experiments and theories related to interactions of single-stranded DNA immobilized on microcantilevers. Experiments and theories show that, at high grafting density, hydration forces are the dominant factor determining cantilever deflections, not electrostatics or conformational entropy.     

Label-free fluorescent detection of Cu(II) ions based on DNA cleavage-dependent graphene-quenched DNAzymes

We developed a novel and general methodology to design a label-free fluorescent Cu(II) sensor based on internal DNA cleavage and an extrinsic fluorophore in a graphene/DNAzymes complex with high sensitivity and selectivity.     

Optically pure bulky (hetero)arylalkyl carbinols via kinetic resolution

Planar chiral nucleophilic catalyst Fc-PIP was employed in the kinetic resolution of bulky (hetero)arylalkyl carbinols delivering unreacted alcohols with extremely high enantiomeric excess (>99.0% ees) in ideal conversions ranging from 50.4-56.7%.     

FITC-modified PPy nanotubes embedded in nanoporous AAO membrane can detect trace PCB20 via fluorescence ratiometric measurement

A highly sensitive and selective fluorescence ratiometric sensor membrane for 2,3,3'-trichlorobiphenyl has been achieved, via depositing polypyrrole nanotubes (PPyNTs, the fluorescence indicator) in nano-porous anodic aluminium oxide (NPAAO) template and subsequently immobilizing fluorescein isothiocyanate (as an internal reference) onto the inner walls of the PPyNTs embedded in the NPAAO.     

Nucleic acids determination using the complex of eriochrome black T and silver nanoparticles in a resonance light scattering technique

A novel method for the determination of nucleic acids by using silver nanoparticle (AgNPs)-eriochrome black T (EBT) as a resonance light scattering (RLS) probe has been developed. Under optimum conditions, there are linear relationships between the quenching extent of RLS intensity and the concentration of nucleic acids in the range of 4.0×10(-9)-4.0×10(-7), 4.0×10(-7)-1.6×10(-6) g mL(-1) for fish sperm DNA (fsDNA) and 4.0×10(-8)-2.0×10(-6) g mL(-1) for yeast RNA (yRNA). Their detection limits (S/N=3) are 2.0 ng mL(-1) and 21 ng mL(-1), respectively. The results indicate that AgNPs can form wirelike aggregates and nanoslices in the presence of the EBT. Whereas, when nucleic acids are added into the AgNPs-EBT system, the dynamic balance of AgNPs-EBT system is destroyed and the nanoparticles undergo dispersion again, leading to the RLS intensity of AgNPs-EBT system quenching. Meanwhile, the conformation of fsDNA is changed by the synergistic effect of AgNPs and EBT.     

Facile synthesis of water-soluble multi-wall carbon nanotubes and polyaniline composites and their application in detection of small metabolites by matrix assisted laser desorption/ionization mass spectrometry

Multi-wall carbon nanotubes and polyaniline composites were synthesized via a simple hydrothermal reaction, and the as-made composites were successfully applied in the analysis of small molecular-weight metabolites as a novel matrix by matrix assisted laser desorption/ionization mass spectrometry.     

Ag nanosheet-assembled micro-hemispheres as effective SERS substrates

Large-scale Ag nanosheet-assembled micro-hemispheres, with sufficient hot spots on their surfaces, have been achieved on an indium tin oxide substrate via electrodeposition. Surface-enhanced Raman scattering (SERS) measurements demonstrate that the Ag nanosheet-assembled micro-hemispheres can serve as sensitive and reproducible SERS substrates.     

Tin (IV) chloride-promoted one-pot synthesis of novel tacrine analogues

A facile synthesis of potential acetylcholinesterase (AChE) inhibitors, the tacrine analogues 3a-p, has been accomplished by direct cyclocondensation of 1-aryl-4-cyano-5-aminopyrazole with β-ketoesters using tin(IV) chloride as catalyst. The structures of all the compounds have been confirmed by IR, 1H- and 13C-NMR.     

Occurrence and estimation of trans-resveratrol in one-year-old canes from seven major Chinese grape producing regions

The concentration of trans-resveratrol in 165 grape cane samples from three major grape production regions and four large distribution centers of Chinese wild Vitis species were determined by reversed-phase high-performance liquid chromatography (HPLC). Among the different genotype groups and purpose of uses, cultivars of V. vinifera had much higher amounts of trans-resveratrol than did the cultivars of both V. labrusca or V. labrusca and V. vinifera hybrids, and within the V. vinifera species, significantly higher amounts of trans-resveratrol were found in wine grapes compared to table ones. No significant differences were observed between V. labrusca and its hybrids from crosses with V. vinifera, and between red cultivars and white ones (P < 0.05 or P < 0.01). The contents of trans-resveratrol, as a normal constituent occurring in grape canes, in Chinese wild species of V. amurensis, V. pentagona, and V. davidii from their native habitats were also relatively high.