Lithium ion induced stabilization of the liquid crystalline DNA

A comparative study of the effects of alkali metal ions Li(+), Na(+), K(+), Rb(+), and Cs(+) on the liquid crystalline organization of high-molecular-weight calf thymus DNA using polarized light microscopy was performed. Major differences in the behavior of Li(+) as compared to the other ions were found. Critical DNA concentration expected to exhibit anisotropic behavior was found to be the same for all the monovalent ions, except for Li(+). DNA initially showed cholesteric textures, which later changed to higher ordered columnar phase for all ions, with the cholesteric-columnar transition facilitated upon increasing the size of the counterion. For Li(+) ion, a nematic schlieren-like texture was formed initially, which after a few days changed to a highly stable (for more than 2 months) biphasic cholesteric-columnar arrangement. The observed differences between Li(+) and other alkali metal ions could be rationalized on the basis of the higher number of hydration water molecules of Li(+) and its complexation behavior. Highly stable DNA mesophases may find applications in the field of nanoelectronics, in designing biosensing units, and in DNA chips.     

Designed alpha-helical barrels for charge-selective peptide translocation

Synthetic alpha-helix based pores for selective sensing of peptides have not been characterized previously. Here, we report large transmembrane pores, pPorA formed from short synthetic alpha-helical peptides of tunable conductance and selectivity for single-molecule sensing of peptides. We quantified the selective translocation kinetics of differently charged cationic and anionic peptides through these synthetic pores at single-molecule resolution. The charged peptides are electrophoretically pulled into the pores resulting in an increase in the dissociation rate with the voltage indicating successful translocation of peptides. More specifically, we elucidated the charge pattern lining the pore lumen and the orientation of the pores in the membrane based on the asymmetry in the peptide-binding kinetics. The salt and pH-dependent measurements confirm the electrostatic dominance and charge selectivity in controlling target peptide interaction with the pores. Remarkably, we tuned the selectivity of the pores to charged peptides by modifying the charge composition of the pores, thus establishing the molecular and electrostatic basis of peptide translocation. We suggest that these synthetic pores that selectively conduct specific ions and biomolecules are advantageous for nanopore proteomics analysis and synthetic nanobiotechnology applications.

Synthetic alpha-helix based pores for selective sensing of peptides have not been characterized previously.     

Ruthenium hydrazone complexes with 1:1 and 1:2 metal–ligand stoichiometry: a comparison of biomolecular interactions and in vitro cytotoxicities

Transition Metal Chemistry - Two ruthenium(II) complexes [RuIICl(PPh3)2(L)] (1) and [RuII(L)2] (2) were synthesized by reacting [RuCl2(PPh3)3] and thiophene-2-carboxylic acid...     

Organoruthenium (II) complexes featuring pyrazole‐linked Schiff base ligands: Crystal structure,DNA/BSA interactions,cytotoxicity and molecular docking

Half‐sandwiched ruthenium (II) arene complexes with piano stool‐like geometry with the general formula [(p‐cymene)RuClL¹] and [(p‐cymene)RuClL²] [where L¹ = (Z)‐N′‐((1,3‐diphenyl‐1H‐pyrazol‐4‐yl)methylene)furan‐2‐carbohydrazide and L² = (Z)‐N′‐((1,3‐diphenyl‐1H‐pyrazol‐4‐yl)methylene)thiophene‐2‐carbohydrazide] were synthesized and characterized. The single crystal X‐ray data revealed that the complexes belong to the same crystal system (monoclinic) with octahedral geometry, where the ruthenium atom is surrounded by hydrazone ligand coordinated through ON atoms, one chloride labile co‐ligand and the remaining three coordination sites covered by an electron cloud of p‐cymene moiety. The interaction between the complexes and DNA/bovine serum albumin (BSA) was evaluated using absorption and emission titration methods showing intercalative modes of interaction. The DNA cleavage ability of the complexes was checked by agarose gel electrophoresis method exhibiting the destruction of DNA duplex arrangement. To understand the interaction between ruthenium complex and DNA/BSA molecule, molecular docking studies were performed. In vitro cytotoxicity of the complexes was examined by the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay on human lung cancer cell line, A549, and found that at lower IC₅₀, cell growth inhibition has occurred. Similarly, the IC₅₀ values of the complexes treated with cancerous cell lines have produced a significant amount of lactase dehydrogenase and nitrite content in the culture medium, which were evaluated as apoptosis‐inducing factors, suggesting that the ruthenium (II) arene hydrazone complexes with pyrazole ligands have promising anticancer activities.     

Role of Mg2+ and Ca2+ in DNA bending: evidence from an ONIOM-based QM-MM study of a DNA fragment

The binding of hydrated Mg2+ and Ca2+ ions with a DNA fragment containing two phosphate groups, three sugar units, and a G.C base pair is modeled in the anion and dianion states using a three-layer ONIOM approach. A monodentate binding mode was the most stable structure observed for both the ions in the anion model. However, the interactions of Mg2+ and Ca2+ with the dianion model of the DNA fragment gave rise to a large structural deformation at the base pair region, leading to the formation of "ring" structures. In both anion and dianion models, Mg2+-bound structures were considerably more stable than the corresponding Ca2+-bound structures. This feature and the formation of ring structures in the dianion models strongly supported the higher coordination power of the Mg2+ toward DNA systems for its compaction. The charge of the DNA fragment appeared to be crucial in deciding the binding strength as well as the binding mechanism of the metal ions. To the best of our knowledge, this is the first theoretical investigation of the interaction of a comparatively larger DNA model system with the biologically important Mg2+ and Ca2+ ions.     

Excited-state intramolecular proton transfer driven by conical intersection in hydroxychromones

Nonradiative decay pathways associated with vibronically coupled S₁(ππ*)–S₂(nπ*) potential energy surfaces of 3- and 5-hydroxychromones are investigated by employing the linear vibronic coupling approach. The presence of a conical intersection close to the Franck–Condon point is identified based on the critical examination of computed energetics and structural parameters of stationary points. We show that very minimal displacements of relevant atoms of intramolecular proton transfer geometry are adequate to drive the molecule toward the conical intersection nuclear configuration. The evolving wavepacket on S₁(ππ*) bifurcates at the conical intersection: a part of the wavepacket moves to S₂(nπ*) within a few femtoseconds while the other decays to S₁ minimum. Our findings indicate the possibility of forming the proton transfer tautomer product via S₂(nπ*), competing with the traditional pathway occurring on S₁(ππ*).     

Investigations on the liquid crystalline phases of cation-induced condensed DNA

Viral and nonviral condensing agents are used in gene therapy to compact oligonucleotides and plasmid DNA into nanostructures for their efficient transport through the cell membranes. Whereas viral vectors are best by the toxic effects on the immune system, most of the nonviral delivery vehicles are not effective for use in clinical system. Recent investigations indicate that the supramolecular organization of DNA in the condensed state is liquid crystalline. The present level of understanding of the liquid crystalline phase of DNA is inadequate and a thorough investigation is required to understand the nature, stability, texture and the influence of various environmental conditions on the structure of the phase. The present study is mainly concerned with the physicochemical investigations on the liquid crystalline transitions during compaction of DNA by cationic species such as polyamines and metallic cations. As a preliminary to the above investigation, studies were conducted on the evolution of mesophase transitions of DNA with various cationic counterion species using polarized light microscopy. These studies indicated significant variations in the phase behaviour of DNA in the presence of Li and other ions. Apart from the neutralization of the charges on the DNA molecule, these ions are found to influence selectively the hydration sphere of DNA that in turn influences the induction and stabilization of the LC phases. The higher stability observed with the liquid crystalline phases of Li-DNA system could be useful in the production of nanostructured DNA. In the case of the polyamine, a structural specificity effect depending on the nature, charge and structure of the polyamine used has been found to be favoured in the crystallization of DNA.     

Molybdenum Incorporated Strontium-Iron and Strontium-Cobalt (SrBMoO3−δ; B=Fe & Co) Perovskites: Preparation and Their Application on Oxidation of Iso-Eugenol into Vanillin

SrBO_3−δ (B=Fe & Co) type perovskite oxides and their 25 % molybdenum doped counterparts, SrFe_0.75Mo_0.25O_3−δ (SFMO) and SrCo_0.75Mo_0.25O_3−δ (SFCO) are synthesized by the conventional solid-state method and systematically characterized using Fourier transfer infrared spectroscopy, powder X-ray diffraction, thermo-gravimetric analysis, nitrogen sorption, and temperature-programmed reduction. The powder X-ray diffraction patterns and FTIR spectral analysis evident the formation of the pure cubic phase and the doping of molybdenum into the perovskite crystal lattice. The variable oxidation states of iron and cobalt and the formation of oxygen vacancies are apparent from the TPR-H₂ and TGA curves, respectively. All of the samples have a lower surface area than porous materials, which is typical of the bulk oxide character. The iron-based perovskite demonstrated superior activity to the cobalt-based one for the oxidation of iso-eugenol to 4-hydroxy-3-methoxybenzaldehyde (vanillin) when employing aqueous H₂O₂ as the oxidant. The maximum conversion of 73 % with 63 % selectivity for vanillin was obtained within 1.5 h at 60 °C over the SFMO catalyst. The catalytic conversion was almost similar upon re-use of the catalyst.