Metallation-Induced Heterogeneous Dynamics of DNA Revealed by Single-Molecule FRET

The metallation of nucleic acids is key to wide-ranging applications, from anticancer medicine to nanomaterials, yet there is a lack of understanding of the molecular-level effects of metallation. Here, we apply single-molecule fluorescence methods to study the reaction of an organo-osmium anticancer complex and DNA. Individual metallated DNA hairpins are characterised using Förster resonance energy transfer (FRET). Although ensemble measurements suggest a simple two-state system, single-molecule experiments reveal an underlying heterogeneity in the oligonucleotide dynamics, attributable to different degrees of metallation of the GC-rich hairpin stem. Metallated hairpins display fast two-state transitions with a two-fold increase in the opening rate to ≈2 s⁻¹, relative to the unmodified hairpin, and relatively static conformations with long-lived open (and closed) states of 5 to ≥50 s. These studies show that a single-molecule approach can provide new insight into metallation-induced changes in DNA structure and dynamics.     

Two‐Photon‐Induced Fluorescence of Isomorphic Nucleobase Analogs

Five isomorphic fluorescent uridine mimics have been subjected to two‐photon (2P) excitation analysis to investigate their potential applicability as non‐perturbing probes for the single‐molecule detection of nucleic acids. We find that small structural differences can cause major changes in the 2P excitation probability, with the 2P cross sections varying by over one order of magnitude. Two of the probes, both thiophene‐modified uridine analogs, have the highest 2P cross sections (3.8 GM and 7.6 GM) reported for nucleobase analogs, using a conventional Ti:sapphire laser for excitation at 690 nm; they also have the lowest emission quantum yields. In contrast, the analogs with the highest reported quantum yields have the lowest 2P cross sections. The structure‐photophysical property relationship presented here is a first step towards the rational design of emissive nucleobase analogs with controlled 2P characteristics. The results demonstrate the potential for major improvements through judicious structural modifications.     

Analysis of t-butylphenol acetylene condensed resin with methyl-methine linkages in vulcanized rubber by pyrolysis-gas chromatography/mass spectrometry

Methyl-methine linkages of Novolac, a commercially available t-butylphenol acetylene condensed (TBPA) resin, have been identified by recognition of pyrolysis pathways using pyrolysis-gas chromatography/mass spectrometry (Py-GC/mS) in vulcanized rubber. The diagnostic mass spectrum of t-butylphenol with methyl-methine linkages between phenolic rings was observed at m/z 192, corresponding to 4-t-butyl-2-ethyl-6-methylphenol. Other molecular ions were observed at m/z 178, 164, and 150 in the characteristic pyrolyzates. The ion at m/z 192 in the TBPA resin was observed to be characteristic for methyl-methine linkages between the phenolic groups, and the analytical pyrolysis-GC/mS method was thus able to identify the resin at low levels in vulcanized rubber. Copyright 1999 John Wiley & Sons, Ltd.     

The microwave-assisted Dötz benzannulation process

Chromium carbene-mediated D?tz benzannulation has been shown to proceed remarkably rapidly and with enhanced efficiency under developed microwave-assisted conditions.     

Assembly of hydrophobic shells and shields around lanthanides

Luminescent lanthanide complexes have been developed, based on the assembly of bulky ligands around the lanthanide ion, to provide shell-type protection of the ion from coordinated solvent molecules. Aryl-functionalised imidodiphosphinate ligands (tpip and Metpip) provide a bidentate anionic site that leads to hexa-coordinate lanthanide complexes in which the aryl groups surround the ion. There are twelve phenyl groups around the lanthanide that act as "remote" (from the binding site) sensitisers for the metal ion. It is shown that these ligands are suitable for sensitising luminescence for all the lanthanides that emit in the visible range, namely, SmIII, EuIII, TbIII, DyIII. A "builtin" shield on the ligand is designed to provide a complete block of the approach of water to the lanthanide ion. The synthesis of the ligands and their lanthanides complexes as well as detailed photophysical studies of the complexes in solution and in the solid-state are presented.     

Probing the Liquid-State Structure and Dynamics of Aqueous Solutions by Fluorescence Spectroscopy

Time-resolved fluorescence spectroscopy of the solvent-sensitive molecule 1,8-anilinonaphthalene sulfonate (ANS) is used to probe the structure and dynamics of an aqueous methanol solution (mole fraction = 0.5). The intensity decay of ANS in the mixed solvent displays single exponential kinetics under ambient conditions. At low temperature, a simple two-state solvent relaxation model describes the fluorescence decay for ANS in both methanol and the mixed solvent. The temperature dependence of ANS fluorescence in the mixed solvent is attributed to the onset of glassy dynamics in the aqueous component at higher temperature, implying a partial demixing of the water and methanol due to self-association. We discuss the absence of more complicated fluorescence decays in such a heterogeneous solvent system.