Hg(ii) interactions with T-rich regions in oligonucleotides: effects of positional variations on the electrochemical properties.

Hg(ii) binding to thymine-rich oligonucleotides (ODNs) is investigated electrochemically. The focus of this study is to probe the effects of position on the electrochemical response. For this purpose, three oligonucleotides were investigated in which the position of a hexa-thymine repeat is varied within a surface-supported oligonucleotide. The hexa repeats were placed in the top, middle, and bottom positions within the strand with respect to the gold surface. The effects were monitored by electrochemical impedance spectroscopy and scanning electrochemical microscopy. Using charge transfer resistance (RCT) and tip current (I) as a measure, it was possible to monitor the effects of Hg(ii) binding to the ds-oligonucleotide. The extent of film resistance reduces as the T-rich region moves from the bottom to top position within the film. The T-rich region closer to the gold surface probably builds less flexible and more rigid T-Hg(ii)-T basepairs compared to the other two positions and is expected to stay in the upright orientation on the surface. This in turn results in significant differences in the electrochemical readout, demonstrating that the position of T-rich sequences within an oligonucleotide strand matters.

Advances in the synthesis, molecular architectures and potential applications of gemini surfactants.

Gemini surfactants have been the subject of intensive scrutiny by virtue of their unique combination of physical and chemical properties and being used in ordinary household objects to multifarious industrial processes. In this review, we summarize the recent developments of gemini surfactants, highlighting the classification of gemini surfactants based on the variation in headgroup polarity, flexibility/rigidity of spacer, hydrophobic alkyl chain and counterion along with potential applications of gemini surfactants, depicting the truly remarkable journey of gemini surfactants that has just come of age. We have focused on those objectives which will act as suitable candidates to take the field forward. The preceding information will permit us to estimate the effect of structural variation on the aggregation behavior of gemini surfactants for nanoscience and biological applications like antimicrobial, anti-fungal agent, better gene and drug delivery agent with low cytotoxicity and biodegradability, which makes them more advantageous for a number of technological processes and hence reduces the impact of these gemini surfactants on the environment.

DNA Films Containing the Artificial Nucleobase Imidazole Mediate Charge Transfer in a Silver(I)-Responsive Way.

The first sequence-dependent study of DNA films containing metal-mediated base pairs was performed to investigate the charge transfer resistance (RCT ) of metal-modified DNA. The imidazole (Im) deoxyribonucleoside was chosen as a highly AgI -specific ligandoside for the formation of Im-AgI -Im complexes within the duplexes. This new class of site-specifically metal-modified DNA films was characterized by UV, circular dichroism (CD), and X-ray photoelectron spectroscopy (XPS). The electrochemical properties of these systems were investigated by means of electron impedance spectroscopy and scanning electrochemical microscopy. Taken together, these experiments indicated that the incorporation of AgI ions into the DNA films leads to reduced electron transfer through the DNA films. A simple device was proposed that can be switched reversibly between two distinct states with different charge transfer resistance.

Interactions of Hg(ii) with oligonucleotides having thymine-thymine mispairs. Optimization of an impedimetric Hg(ii) sensor.

The present work describes the effect of the number of thymine-thymine mispairs in single strand DNA probes on Hg(ii) interactions and further to develop a highly sensitive DNA based impedimetric sensor for Hg(ii) detection. To achieve this goal, the influence of the number of T-T mispairs on the signal response prompted by DNA-Hg(ii) binding interactions was examined on three designed DNA probes: 5'-OH-(CH2)6-S-S-(CH2)6-AGTCCACACGTTCCTTACGC-3', 5'-OH-(CH2)6-S-S-(CH2)6-AGTCCACATTTTCCTTTTGC-3', 5'-OH-(CH2)6-S-S-(CH2)6-AGTCCATTTTTTCCTTTTTT-3' having 2T-T, 4T-T and 6T-T mispairs with identical length, respectively. This study revealed that the number of T-T mispairs plays a critical role in maximizing the signal intensity of DNA-Hg(ii) binding interactions. Based on these results, DNA comprising maximum number of T-T mispairs was further utilized for construction of the Hg(ii) sensor, which exhibited a linear correlation between the change in charge transfer resistance (ΔRCT) and the concentration of Hg(ii) over the range of 1.0 × 10-5 M to 1.0 × 10-10 M with a lower detection limit of 3.2 × 10-11 M. The selectivity was tested against 12 different metal ions including Hg(ii). The ΔRCT response from Hg(ii) is 3 times higher than the nearest competitor Pb(ii) and approximately 10 times than other ions. The potential application of such a robust and label-free DNA sensor was demonstrated by analyzing environmental samples collected from Lake Ontario.

Detection of the Lipopeptide Pam3CSK4 Using a Hybridized Toll-like Receptor Electrochemical Sensor.

Electrochemical detection of Pam3CSK4, a synthetic triacylated lipopeptide that mimics the structural moieties of its natural Gram negative bacterial pathogen-associated molecular pattern (PAMP) counterpart, has been achieved using hybridized toll-like receptors (TLR) combining TLR1 and TLR2 onto a single sensor surface. These sensors represent the first hybridized TLR sensors. The limit of detection for Pam3CSK4 attained was 7.5 µg/mL, which is within the same order of magnitude for that of the more labor-intensive and time-consuming cell-assay technique, 2.0 µg/mL. The results gathered in these electrochemical experiments show that sensors fabricated by immobilizing a mixture of cooperative TLR1 and -2 generate higher responses when exposed to the analyte in comparison to the control sensors fabricated using pure TLR1 or -2 standalone. A PAMP selectivity test was carried out in line with our inspiration from the mammalian innate immune response. TLRs1-5 as standalone biorecognition elements and the hybridized "TLR1 and 2" sensor surface were investigated, understanding the known TLR-PAMP interactions, through the exploitation of this electrochemical sensor fabrication technique. The experimental result is consistent with observations from previously published in vivo and in vitro studies, and it is the first demonstration of the simultaneous evaluation of electrochemical responses from multiple, unique fabricated TLR sensor surfaces against the same analyte.

A quantitative appraisal of the binding interactions between an anionic dye, Alizarin Red S, and alkyloxypyridinium surfactants: a detailed micellization, spectroscopic and electrochemical study.

The interactions of an anionic redox-active dye Alizarin Red S (ARS) with novel N-hydroxyethyl-3-alkyloxypyridinium surfactants 1-(2-hydroxyethyl)-3-(tetradecyloxy)pyridinium bromide, [HEC14OPyBr], and 1-(2-hydroxyethyl)-3-(hexadecyloxy)pyridinium bromide, [HEC16OPyBr], were investigated in an aqueous solution for the first time with an attempt to obtain comprehensive knowledge of oppositely charged dye-surfactant mixed systems. Different state-of-the-art techniques viz. conductivity, surface tension (ST), UV-visible spectroscopy, cyclic voltammetry (CV), linear sweep voltammetry (LSV), potentiometry, dynamic light scattering (DLS) and (1)H-NMR analysis have been employed. The presence of ARS decreases the critical micelle concentration (cmc) of alkyloxypyridinium surfactants as the ARS monomers behave as aromatic counterions. A combined analysis of the techniques revealed the existence of cation-π, π-π stacking, H-bonding, electrostatic and hydrophobic interactions among ARS and alkyloxypyridinium surfactants. A quantitative appraisal of the process of interaction among ARS and alkyloxypyridinium surfactants has been made in terms of various micellar, binding and electrochemical parameters evaluated using ST, UV-visible and voltammetric measurements. Also, the results extracted from (1)H-NMR and voltammetric measurements indicate that the catechol moiety of ARS is involved in the binding mechanism among ARS and alkyloxypyridinium surfactants.

Interactional behavior of the polyelectrolyte poly sodium 4-styrene sulphonate (NaPSS) with imidazolium based surface active ionic liquids in an aqueous medium.

The present study aims to develop an understanding of the interactions between an anionic polyelectrolyte, poly sodium 4-styrene sulphonate (NaPSS), and cationic surface active imidazolium based ionic liquids (SAILs), [Cnmim][Cl] (n = 10, 12, 14) using a multi-technique approach. Various physicochemical and electrochemical techniques such as surface tension, conductivity, fluorescence, isothermal titration calorimetry (ITC), dynamic light scattering (DLS), turbidity, potentiometry, cyclic voltammetry (CV), and differential pulse voltammetry (DPV) are employed to obtain comprehensive information about NaPSS-SAIL interactions. Different stages of interaction, corresponding to the critical aggregation concentration (cac), critical saturation concentration (Cs) and critical micelle concentration (cmc) have been observed owing to the strong electrostatic and hydrophobic interactions, and the results obtained from different techniques complement each other very well. The results extracted from DLS and turbidity measurements clearly indicated that the size of the micelle like aggregates first decreases and then increases in the presence of polyelectrolyte. The binding isotherms obtained using potentiometry show a concentration dependence and the highly co-operative nature of the interactions which is attributed to aggregation of the polyelectrolyte-SAIL complexes. The diffusion coefficients (Dm) of the electroactive probe in the pure and NaPSS-SAIL mixed systems were obtained, which were further used to obtain the values of the micellar self-diffusion coefficients (D) and inter-micellar interaction parameters (kd).

Electrochemical sensing of iron (III) by using rhodamine dimer as an electroactive material.

The voltammetric and potentiometric sensors based on a novel electroactive rhodamine dimer (RD) have been developed for the determination of Fe (III) ions. The RD exhibits two anodic peaks at 0.5 V and 0.7 V vs. Ag/Ag(+) within the potential range of 0.2-1.2V, which on addition of Fe (III) ions get converted to single anodic peak with a shift toward more positive potential of 0.9 V vs. Ag/Ag(+) due to the formation of Fe (III)-RD complex. The voltammetric sensor has been found to work well in the concentration range of 1.5 × 10(-5)-3.5 × 10(-4)M with the detection limit of 3.3 × 10(-6)M. Further, the potentiometric response of proposed PVC based solid contact coated graphite electrode (CGE-1) was linear for Fe (III) ions in the concentration range of 1.0 × 10(-1)-1.0 × 10(-7)M. The electrode showed a slope of 18.8 mV/decade with a detection limit of 4.68 × 10(-8)M for Fe (III) ions. Both of the sensors revealed good selectivity towards Fe (III) ions in comparison to various diverse metal ions. The analytical utility of the proposed sensors has been confirmed by the estimation of the Fe (III) content in different sample matrices.

Selective sensing of mercury(II) using PVC-based membranes incorporating recently synthesized 1,3-alternate thiacalix[4]crown ionophore.

The construction and electrodes characteristics of poly(vinylchloride) (PVC)-based polymeric membrane electrode (PME) and coated graphite electrode (CGE), incorporating 1,3-alternate thiacalix[4]crown as ionophore for estimation of Hg(II) ions, are reported here. The best potential response was observed for PME-1 having membrane composition of: ionophore (6.2 mg), PVC (100.0 mg), 2-nitrophenyl octyl ether (2-NPOE; 200.0 mg), and sodium tetraphenyl borate (NaTPB; 2.0 mg); for CGE-1 with the membrane composition: ionophore (3.5 mg), PVC (40.0 mg), 2-NPOE (80.0 mg), and NaTPB (2.0 mg). The electrodes exhibits Nernstian slope of 29.16 mV/decade with PME-1 and 30.39 mV/decade with CGE-1 for Hg(II) ions over wide concentration range, i.e., 1.0 × 10(-1) to 5.0 × 10(-6) M with PME-1 and 1.0 × 10(-1) to 5.0 × 10(-7) M with CGE-1. Lower detection limits were found to be 9.77 × 10(-6) M for PME-1 and 7.76 × 10(-7) M for CGE-1 with response time varying from 10 to 20 s. Also, these electrodes work within pH range of 2.0-6.0 for PME-1 and 1.5-6.5 for CGE-1. Overall, CGE-1 has been found to be better than PME-1. CGE-1 has been used as indicator electrode for the potentiometric titration of Hg(II) ions with EDTA as well as successfully applied for determination of Hg(II) content in wastewater, insecticide, dental amalgam, and ayurvedic medicines samples with very good performance (0.9974 correlation coefficient in the comparison against volumetric method).