An overlooked UV spectroscopic tool for sensing coil-to-helix and helix-to-coil conformational transitions of proteins and peptides.

A simple spectrophotometric approach is proposed for sensing coil-to-helix and helix-to-coil conformational transitions of intrinsically disordered and folded peptide/protein sequences. Helix formation induced by a variety of physico-chemical factors results in a substantial intensity reduction (hypochromism) of the intense far-UV absorption band associated with the π-π* transition of amide chromophores. Conversely, the same band exhibits intensity increase (hyperchromism) as the consequence of unfolding events. This method, faded into obscurity several decades ago, may obtain widespread applications in the field of protein science.

Multicharged Phthalocyanines as Selective Ligands for G-Quadruplex DNA Structures.

The stabilization of G-Quadruplex DNA structures by ligands is a promising strategy for telomerase inhibition in cancer therapy since this enzyme is responsible for the unlimited proliferation of cancer cells. To assess the potential of a compound as a telomerase inhibitor, selectivity for quadruplex over duplex DNA is a fundamental attribute, as the drug must be able to recognize quadruplex DNA in the presence of a large amount of duplex DNA, in the cellular nucleus. By using different spectroscopic techniques, such as ultraviolet-visible, fluorescence and circular dichroism, this work evaluates the potential of a series of multicharged phthalocyanines, bearing four or eight positive charges, as G-Quadruplex stabilizing ligands. This work led us to conclude that the existence of a balance between the number and position of the positive charges in the phthalocyanine structure is a fundamental attribute for its selectivity for G-Quadruplex structures over duplex DNA structures. Two of the studied phthalocyanines, one with four peripheral positive charges (ZnPc1) and the other with less exposed eight positive charges (ZnPc4) showed high selectivity and affinity for G-Quadruplex over duplex DNA structures and were able to accumulate in the nucleus of UM-UC-3 bladder cancer cells.

Synthesis, CMC Determination, Antimicrobial Activity and Nucleic Acid Binding of A Surfactant Copper(II) Complex Containing Phenanthroline and Alanine Schiff-Base.

A new water-soluble surfactant copper(II) complex [Cu(sal-ala)(phen)(DA)] (sal-ala = salicylalanine, phen = 1,10-phenanthroline, DA = dodecylamine), has been synthesized and characterized by physico-chemical and spectroscopic methods. The critical micelle concentration (CMC) values of this surfactant-copper(II) complex in aqueous solution were obtained from conductance measurements. Specific conductivity data (at 303, 308, 313. 318 and 323 K) served for the evaluation of the temperature-dependent CMC and the thermodynamics of micellization (ΔG(0)m, ΔH(0)m and ΔS(0)m). The interaction of this complex with nucleic acids (DNA and RNA) has been explored by using electronic absorption spectral titration, competitive binding experiment, cyclic voltammetry, circular dichroism (CD) spectra, and viscosity measurements. Electronic absorption studies have revealed that the complex can bind to nucleic acids by the intercalative binding mode which has been verified by viscosity measurements. The DNA binding constants have also been calculated (Kb = 1.2 × 10(5) M(-1) for DNA and Kb = 1.6 × 10(5) M(-1) for RNA). Competitive binding study with ethidium bromide (EB) showed that the complex exhibits the ability to displace the DNA-bound-EB indicating that the complex binds to DNA in strong competition with EB for the intercalative binding site. The presence of hydrophobic ligands, alanine Schiff-base, phenanthroline and long aliphatic chain amine in the complex were responsible for this strong intercalative binding. The surfactant-copper (II) complex was screened for its antibacterial and antifungal activities against various microorganisms. The results were compared with the standard drugs, amikacin(antibacterial) and ketokonazole(antifungal).

Design, synthesis and DNA interaction studies of new fluorescent platinum complex containing anti-HIV drug didanosine.

Forming coordination complexes with nucleoside analogues may be helpful in studying anti-tumour activity of them. Therefore, to improve the clinical efficacy of nucleoside analogue and design new ones, a new fluorescent platinum (Pt) complex with anti-human immunodeficiency virus drug didanosine (ddI); K[PtCl(OCH3)2(ddI)]; was synthesized and characterized. The ultraviolet-visible (UV-vis) spectroscopy, infrared, thermogravimetric analysis, mass assignments and elemental analysis confirmed the preparation of the complex. The molecular ion peaks seen at the positive mass spectrum of Pt complex confirm coordination of the drug to metal centre. The interaction of this complex with calf thymus DNA (ct-DNA) was studied using several spectroscopic techniques such as UV absorption, fluorescence spectroscopy and dynamic viscosity measurements. Hyperchromism of the band in the UV-vis spectra and the intrinsic binding constant (0.56 ± 0.25) × 104 M-1, decreasing in Hoechst-DNA fluorescence by adding Pt complex concentration and also relatively small changes in DNA viscosity indicated that this complex could interact as a groove-binder. According to the UV spectra and the fluorescence quenching of the complex in our case seems to be primarily caused by complex formation between the Pt complex and DNA. The thermodynamic parameters showed that hydrogen bond and van der Waals interactions play main roles in the binding of Pt complex to ct-DNA. The free energy values are negative, showing the spontaneity of the Pt complex-DNA binding. The docking simulation was performed and the results confirm a preference of groove site of synthesized complex on DNA helix. The knowledge gained from this study will be helpful to further understand the DNA binding mechanism and can also provide much fruitful information for designing a new type of anti-cancer drugs.Communicated by Ramaswamy H. Sarma.

Thermal denaturation profile: A straightforward signature to characterize parallel G-quadruplexes.

G-quadruplexes (G4s) are fascinating non-canonical nucleic acid structures that attract broad attention due to their vital roles in gene expression and various applications. G4s exhibit high structural polymorphism and high resolution techniques (NMR, Crystallography) are often required to unambiguously determine G4 topology. Fast and handy techniques such as UV and CD provide interesting structural information. Here, we monitored the thermal denaturation profiles (TDPs) of various G4s at different wavelengths by UV, and confirmed that all G4 topologies (parallel, antiparallel and hybrid) exhibited hyperchromism at 243 nm and hypochromism at 295 nm. Furthermore, the absorption at 260 nm and 275 nm showed a remarkable topology-dependent behavior, and the hypochromism at 275 nm allows to discriminate parallel conformations from other G4 topologies. Therefore, this work provides a new inexpensive identification method for parallel G4 structures as well as a new perspective for the relationship between TDPs and G4 structures.

Insight into the binding of a non-toxic, self-assembling aromatic tripeptide with ct-DNA: Spectroscopic and viscositic studies.

The report describes the synthesis, self-association and DNA binding studies of an aromatic tripeptide H-Phe-Phe-Phe-OH (FFF). The peptide backbone adopts ß-sheet conformation both in solid and solution. In aqueous solution, FFF self-assembles to form nanostructured aggregates. Interactions of this peptide with calf-thymus DNA (ct-DNA) have been studied using various biophysical techniques including ultraviolet (UV) absorption spectroscopy, fluorescence spectroscopy and circular dichroism (CD) spectroscopy. The value of mean binding constant calculated from UV and fluorescence spectroscopic data is (2.914 ± 0.74) x 103 M-1 which is consistent with an external binding mode. Fluorescence intercalator displacement (FID) assay, iodide quenching study, viscosity measurement and thermal denaturation study of DNA further confirm the groove binding mode of peptide, FFF with ct-DNA. MTT cell survival assay reveals very low cytotoxicity of the peptide toward human lung carcinoma cell line A549.

Interaction of antihypertensive acetazolamide with nonsteroidal anti-inflammatory drugs.

The binding of antihypertensive acetazolamide with eleven nonsteroidal anti-inflammatory drugs (NSAIDs) was investigated at pH 3, 7 and 9.5 with the objective of monitoring their interactive pharmacokinetics during digestion and absorption in human body. The results of UV-Vis spectroscopy and cyclic voltammetry revealed two NSAIDs (acetaminophen and dichlofenic sodium) to interact with acetazolamide in stomach fluid conditions forming complexes of 1:1 and 1:2 stoichiometry. The complexation ratio was also verified by computational methods. The strong binding propensity of acetaminophen and dichlofenic sodium with acetazolamide prohibited their combined therapy. However, the poor binding affinity of aspirin and mefinamic acid suggested these drugs as preferred NSAIDs to be prescribed with acetazolamide.