Padmaja P. Mishra

Chlorin p6 as a fluorescent probe for the investigation of surfactant–cyclodextrin interactions

Cyclodextrins (CD) are often proposed as potential vehicles in targeted drug delivery. However, if the membrane structure is disrupted by CD, then it cannot be considered to be a good drug delivery vehicle. When an extrinsic fluorescence probe is used to monitor such interactions, there are no less than three possible equilibria that can operate simultaneously: surfactant–cyclodextrin, surfactant–fluorophore and cyclodextrin–fluorophore. The fluorescence intensity/lifetime might be affected by all these and so, the results depend strongly on the fluorophore used as well as the nature of the surfactant. This aspect highlights the importance of the suitability of the fluorescence probe to be used to study complicated systems and interaction. In the present work, chlorin p6, prepared from chlorophyll from spinach leaves, has been used as the fluorescence probe to investigate the interaction between α-CD and β-CD with the neutral surfactants Triton X 100 (TX 100) and cetyl trimethyl ammonium bromide (CTAB). The fluorophore is found to be a sensitive one for the study of the interaction of α, β and γ-CD with the surfactants TX 100 and CTAB. It is found that contrary to earlier reports, a complex between α-CD and TX 100 is formed, even though the binding constant is not very high. This observation can be obtained with chlorin p6, which does not bind to the CDs, but not with a fluorophore, which binds to the CD as well and thus complicates the situation as the binding with CD is stronger than that between TX 100 and α-CD as compared to that between TNS and CD.

Conformational Changes Followed by Complete Unzipping of DNA Double Helix by Charge-Tuned Gold Nanoparticles

The complete unzipping of DNA double helix by small size gold nanoparticles having weakly positive surface charge has been monitored using ensemble and single molecule fluorescence resonance energy transfer (smFRET) techniques. We believe, as the gold nanoparticles have positive charge on the surface, the DNA and nanoparticles were pulled together to form two single strands. The positively charged ligands on the nanoparticles attached to the DNA, and the hydrophobic ligands of the nanoparticles became tangled with each other, pulling the nanoparticles into clusters. At the same time, the nanoparticles pulled the DNA apart. The conformational changes followed by unzipping have been investigated for long DNA (calf thymus DNA) as well as for short DNA (∼40 base pair) using ensemble methods like circular dichroism (CD) spectroscopy, fluorescence intercalation assay, viscometric method, and single molecule FRET imaging. This observation not only reveals a new aspect in the field of nano-bio interface but also provides additional information about DNA dynamics.

Chlorin p 6 as a fluorescent probe for the investigation of surfactant-cyclodextrin interactions

Cyclodextrins (CD) are often projected as potential vehicles in targeted drug delivery. However, if the membrane structure is disrupted by CD, then it cannot be considered to be a good drug delivery vehicle. When an extrinsic fluorescence probe is used to monitor such interactions, there are no less than three possible equilibria that can operate simultaneously: surfactant-cyclodextrin, surfactant-fluorophore and cyclodextrin-fluorophore. The fluorescence intensity / lifetime might be affected by all these and so, the results depend strongly on the fluorophore used as well as the nature of the surfactant. This aspect highlights the importance of the suitability of the fluorescence probe to be used to study complicated systems and interaction. In the present work, chlorin p6, prepared from chlorophyll from spinach leaves, has been used as the fluorescence probe to investigate the interaction between α-CD and β-CD with the neutral surfactants TX 100 and CTAB. The fluorophore is found to be a sensitive one for the study of the interaction of α- and β-CD with the surfactants Tritron X 100 (TX 100) and cetyl trimethyl ammonium bromide (CTAB). It is found that contrary to earlier reports, a complex between α-CD and TX 100 is formed, even though the binding constant is not very high. This observation can be obtained with chlorin p6, which does not bind to the CDs, but not with a fluorophore like TNS, which binds to the CD as well and thus complicates the situation as the binding with CD is stronger than that between TX 100 and α-CD as compared to that between TNS and CD.