Caught in the Loop: Binding of the [Ru(phen)2(dppz)]2+ Light-Switch Compound to Quadruplex DNA in Solution Informed by Time-Resolved Infrared Spectroscopy

Ultrafast time-resolved infrared (TRIR) is used to report on the binding site of the [Ru(phen)₂(dppz)]²⁺ “light-switch” complex with both bimolecular (Oxytricha nova telomere) and intramolecular (human telomere) guanine-quadruplex structures in both K⁺ and Na⁺ containing solutions. TRIR permits the simultaneous monitoring both of the “dark” and “bright” states of the complex and of the quadruplex nucleobase bases, the latter via a Stark effect induced by the excited state of the complex. These data are used to establish the contribution of guanine base stacking and loop interactions to the binding site of this biologically relevant DNA structure in solution. A particularly striking observation is the strong thymine signal observed for the Na⁺ form of the human telomere sequence, which is expected to be in the anti-parallel conformation.     

Recognition and sensing of biologically relevant anions in alcohol and mixed alcohol-aqueous solutions using charge neutral cleft-like glycol-derived pyridyl-amidothiourea receptors

In this paper, the synthesis and the spectroscopic investigation of new colorimetric receptors for anions 3-6, possessing a glycol chain at the 4-position of the pyridyl ring, and 1 and 2, which lack such a chain, and the X-ray crystal structure of 2 is presented. Structures 3-6 are able to bind to anions in competitive media, such as alcohol or in a mixture of methanol and water, where the anion recognition gives rise to changes in the absorption spectra, which is red-shifted, in 1:1 or 1:2 (sensor/anion) stoichiometry. The anion recognition for 1 and 2 was also investigated in organic solvents and in a 4:1 mixture of DMSO/H(2)O. The binding of 1 to anions such as acetate, phosphate, and fluoride was also evaluated using (1)H NMR in DMSO-d(6).     

Synthesis and photophysical evaluation of a pyridinium 4-amino-1,8-naphthalimide derivative that upon intercalation displays preference for AT-rich double-stranded DNA

The synthesis, characterisation and solid state crystal structure of a cationic 4-amino-1,8-naphthalimide derivative (1) are described. The photophysical properties of 1 are shown to vary with the solvent polarity and H-bonding ability. The fluorescence of 1 is enhanced and blue-shifted in its 1:1 complex with 5'-adenosine-monophosphate while it is partially quenched and red-shifted in its complex with 5'-guanosine-monophosphate. Linear and circular dichroism measurements show that 1 binds to double-stranded DNA by intercalation. Comparative UV-visible and fluorescence studies with double stranded synthetic polynucleotides poly(dA-dT)(2) and poly(dG-dC)(2) show that 1 binds much more strongly to the AT polymer; 1 also has a strong preference for A-T rich sequences in natural DNA. Thermal denaturation measurements also reveal a much greater stabilisation of the double-stranded poly(dA-dT)(2) than of natural DNA.     

Lanthanide directed self-assembly synthesis and photophysical evaluation of chiral Eu(III) luminescent "half-helicates"

The reaction between the asymmetrical pyridyl ligands 3 (R) and 4 (S) and Eu(III) in CH(3)CN give rise to the formation of lanthanide luminescent 'half-helicates' in 1?:?3 (Ln:ligand) stoichiometry; the formation of which was observed by monitoring the changes in the ground and the excited state properties of the ligands, and in the time-resolved Eu-centred and the CPL emission.     

Selective and tuneable recognition of anions using C(3v)-symmetrical tripodal urea-amide receptor platforms

The synthesis and binding investigations of first generation C(3v)-symmetrical hydrogen bonding urea-amide based tripodal receptors, 1-6, with various anions such as acetate, phosphate, sulfate and chloride in DMSO-d(6) are presented. Analysis of the (1)H NMR titrations of 1-6 showed on all occasions the selective formation of 1?:?1 stoichiometries.     

Lanthanide directed self-assembly formations of Tb(III) and Eu(III) luminescent complexes from tryptophan based pyridyl amide ligands

The formation of self-assembly complexes between the ligands 1 (SS) and 2 (RR) and terbium or europium was undertaken and shown (using various spectroscopic titrations) to give rise to the exclusive formation of 2:1 (L:Ln) stoichiometry and not the anticipated 3:1 stoichiometry.     

Quaternarized pdppz: synthesis, DNA-binding and biological studies of a novel dppz derivative that causes cellular death upon light irradiation

The quaternarized pdppz derivative 1 was shown to bind strongly to DNA with concomitant changes in its ground and excited state photophysical properties. Furthermore, the compound also showed rapid cellular uptake, and induced apoptosis upon light irradiation in various cancer cell lines after 24 hours of incubation.