Pyridinium Boranephosphonate Modified DNA Oligonucleotides.

The synthesis of previously unknown derivatives of boranephosphonate that contain amine substitutions at boron and the incorporation of these derivatives into the backbone of DNA oligonucleotides is described. These derivatives result from iodine-mediated replacement of one BH3 hydride of a boranephosphonate linkage by pyridine, various substituted pyridines, other aromatic amines, and certain unsaturated amines. Oligonucleotides containing these backbone modifications show enhanced uptake, relative to unmodified DNA, in mammalian cells. The redox behavior of the boranephosphonate and pyridinium boranephosphonate conjugated linkages has also been studied.

Doping Engineering in Electrode Material for Boosting the Performance of Sodium Ion Batteries.

In recent years, sodium ion batteries (SIBs) emerged as promising alternative candidates for lithium ion batteries (LIBs) due to the high abundance and low cost of sodium resources. However, their commercialization has been hindered by inherent limitations, such as low energy density and poor cycling stability. To address these issues, doping methodology is one of the most promising approaches to boosting the structural and electrochemical properties of SIB electrodes. This review provides a comprehensive overview of recent advancements in doping strategies, focusing on the improvement of the performance of SIBs. Various dopants including s- and p-block elements, transition metals, oxides, carbonaceous materials, and many more dopants are discussed in terms of their effects on enhancing the electrochemical properties of SIBs. Furthermore, the mechanisms responsible for the improvement in the performance of doped SIBs materials are also discussed. It also highlights the importance of doping sites in the crystal lattice, which also play a crucial role in doping in optimizing electrode structure, enhancing ion diffusion kinetics, and stabilizing electrode/electrolyte interfaces. The review ends by looking at the recent studies in simultaneous multiple heteroatom doping, offering valuable perspectives for a high performance SIB. This study provides valuable insight into the researchers and battery industries striving for advancements in energy storage technologies.

Triazolyl donor/acceptor chromophore decorated unnatural nucleosides and oligonucleotides with duplex stability comparable to that of a natural adenine/thymine pair.

We report the design and synthesis of triazolyl donor/acceptor unnatural nucleosides via click chemistry and studies on the duplex stabilization of DNA containing two such new nucleosides. The observed duplex stabilization among the self-pair/heteropair has been found to be comparable to that of a natural A/T pair. Our observations on the comparable duplex stabilization has been explained on the basis of possible π-π stacking and/or charge transfer interactions between the pairing partners. The evidence of ground-state charge transfer complexation came from the UV-vis spectra and the static quenching of fluorescence in a heteropair. We have also exploited one of our unnatural DNAs in stabilizing abasic DNA.

Highly solvatochromic fluorescent naphthalimides: design, synthesis, photophysical properties and fluorescence switch-on sensing of ct-DNA.

We report the design, synthesis and photophysical properties of highly solvatochromic donor/acceptor substituted naphthalimide based fluorophores. The synthesized naphthalimides containing propargyl ends showed highly solvatochromic intramolecular charge transfer (ICT) feature as was revealed from the UV-visible, fluorescence photophysical properties of these fluorophores and DFT/TDDFT calculation. Fluorescence life times for the imide fluorophores were also measured in different solvents. The solid state photophysical property of donor substituted naphthalimide 1 showed promising for future application in material sciences. Furthermore, both the donor/acceptor substituted naphthalimide fluorophores 1-2 were exploited in sensing calf-thymus DNA via switch-on fluorescence response. The propargyl linker containing naphthalimides can further be exploited for the synthesis of labeled biomolecular building blocks.

Sensing of micellar microenvironment with dual fluorescent probe, triazolylpyrene (TNDMBPy).

We report a dual fluorescent triazolylpyrene ((TNDMB) Py) as an efficient fluorescent light-up probe of various micellar microenvironments. The absorption spectra of (TNDMB) Py in an aqueous solution of varying surfactant concentration, CTAB, SDS and TX-100 showed that as the surfactant concentration was increased the absorbance increased with no shift in wavelength maxima. The increase of absorbance in each surfactant solution with increase in surfactant concentration was due to the enhanced solubilization of (TNDMB) Py in surfactant solutions. Our investigations based on steady state and time resolved fluorescence techniques showed that the probe reports the microenvironment of ionic surfactant solutions (CTAB and SDS) via dual emission (LE and ICT) at low surfactant concentration. The ICT band showed a blue shifting pattern with enhanced intensity that disappeared as the concentration of surfactant increases (> 1 mM for CTAB and > 3 mM for SDS). In non-ionic surfactant (Triton X-100) solution, the fluorophore showed dual emission with dominant ICT behaviour over LE emission at low concentration (up to 0.35 mM). In reverse micelle we observed a blue shifted ICT band with no LE band with increasing molar concentration of water. We found 100 nm blue shifting when we moved from R = 0 to R = 7, where R is the molar ratio of water to TX-100 (R = [H2O]/[TX-100]). The blue shifting of ICT band is because of the movement of the probe from hydrophilic core to hydrophobic core (surface) of the reverse micelle. Thus from the steady-state fluorescence study it was observed that the ICT band of the probe, (TNDMB) Py was more influenced by the micellar environment in comparison to the LE band. This difference in behaviour of the fluorophore is probably because of varying extent of hydrophobic/hydrogen bonding interactions experienced by the probe and its relative disposition inside the various micellar nanocores.

Installation/modulation of the emission response via click reaction.

We have demonstrated the installation of a fluorescence property into a nonfluorescent precursor and modulation of an emission response of a pyrene fluorophore via click reaction. The synthesized fluorophores show different solvatochromicity and/or intramolecular charge transfer (ICT) feature as is revealed from the UV-visible, fluorescence photophysical properties of these fluorophores, and DFT/TDDFT calculation. We observed that some of the synthesized fluorophores showed purely ICT character while emission from some of them arose from the LE state. A structureless and solvent polarity-sensitive dual emission behavior was observed for one of the triazolylpyrene fluorophores that contains an electron-donating -NMe(2) substituent (fluorophore, 7a). Conversely, triazolylpyrene with an electron-withdrawing -CN group (fluorophore, 7b) showed a solvent polarity-independent vibronic emission. The effect of ICT on the photophysical properties of these fluorophores was studied by fluorescence emission spectra and DFT/TDDFT calculations. Fluorescence lifetimes were also measured in different solvents. All of our findings revealed the delicate interplay of structure and emission properties and thus having broader general utility. As the CT to LE intensity ratio can be employed as a sensing index, the dual emissive fluorophore can be utilized in designing the molecular recognition system too. We envisage that our investigation is of importance for the development of new fluorophores with predetermined photophysical properties that may find a wide range of applications in chemistry, biology, and material sciences.

Click-reagent version of Sonogashira coupling protocol to conjugated fluorescent alkynes with no or reduced homocoupling.

A click-reagent version of the Sonogashira-coupling protocol has been developed. Diarylalkynes with donor and/or acceptor substituents have been synthesized via this protocol at moderate to excellent yields and with no or drastically reduced quantities of undesired homocoupled side products. This protocol is green-solvent compatible, air-insensitive, and effective under microwave conditions.

Singly and doubly labeled base-discriminating fluorescent oligonucleotide probes containing oxo-pyrene chromophore.

We have developed new oxo-pyrene labeled fluorescent nucleoside, (Oxo-Py)U which showed a strong fluorescence dependency on solvent polarity at long wavelength. The designed singly and doubly (Oxo-Py)U labeled fluorescent oligonucleotide probes were found highly efficient for the discrimination of A and consecutive AA bases of target DNA opposite to the labeled base via generation of enhanced fluorescence signal.

Cationic Amphiphilic Peptides: Synthetic Antimicrobial Agents Inspired by Nature.

Antimicrobial peptides are ubiquitous in multicellular organisms and have served as defense mechanisms for their successful evolution and throughout their life cycle. These peptides are short cationic amphiphilic polypeptides of fewer than 50 amino acids containing either a few disulfide-linked cysteine residues with a characteristic ß-sheet-rich structure or linear α-helical conformations with hydrophilic side chains at one side of the helix and hydrophobic side chains on the other side. Antimicrobial peptides cause bacterial cell lysis either by direct cell-surface damage via electrostatic interactions between the cationic side chains of the peptide and the negatively charged cell surface, or by indirect modulation of the host defense systems. Electrostatic interactions lead to bacterial cell membrane disruption followed by leakage of cellular components and finally bacterial cell death. Because of their unusual mechanism of cell damage, antimicrobial peptides are effective against drug-resistant bacteria and may therefore prove more effective than classical antibiotics in certain cases. Currently, around 3000 natural antimicrobial peptides from six kingdoms (bacteria, archaea, protists, fungi, plants, and animals) have been isolated and sequenced. However, only a few of them are under clinical trials and/or in the commercial development stage for the treatment of bacterial infections caused by antibiotic-resistant bacteria. Moreover, high structural complexity, poor pharmacokinetic properties, and low antibacterial activity of natural antimicrobial peptides hinder their progress in drug development. To overcome these hurdles, researchers have become increasingly interested in modification and nature-inspired synthetic antimicrobial peptides. This review discusses some of the recent studies reported on antimicrobial peptides.

Stabilization of an abasic site paired against an unnatural triazolyl nitrobenzene nucleoside.

An abasic site is the most frequently observed among the various forms of DNA lesions in genomic DNA. If left unrepaired, an abasic site might turn out to be a principle cause for deleterious mutations and can be threat to cellular survival. Thus, to keep cellular integrity and measure the extent of DNA damage, recognition and stabilization of the abasic sites (apurinic/apyrimidinic site = Ap) are essential. Further, it is crucial to detect and stabilise the abasic site for towards the development of new diagnostics and chemotherapeutics. Herein, we report the stabilization of an abasic DNA duplex wherein the abasic site paired against a novel unnatural nucleoside, triazolylnitrobenzene (TNBBAc). This nucleoside is bulky and exhibits, high polarizability and good stacking propensity. Robust hetero-pair stabilization is another feature of it. Therefore, it is interesting to study the stabilization of an abasic DNA containing a synthesized triazolylnitrobenzene nucleoside TNBBAc We planned to study the thermal as well as the thermodynamic origin of abasic DNA stabilization by our synthesized oligonucleotide probe containing TNBBAc nucleoside. We observed that the nucleoside TNBBAc offered good thermal stabilization of a TNBBAc-Φ duplex via strong intercalative stacking interaction alongside an abasic site. The UV-visible spectroscopic study supported the intercalative stacking interaction. The stabilization though is marginal, but it would shed light on the design of bases of significant volume to stabilise abasic DNA to a greater extent.

G-Tetraplex-Induced FRET within Telomeric Repeat Sequences Using (Py) A-(Per) A as Energy Donor-Acceptor Pair.

G-tetraplex induced fluorescence resonance energy transfer (FRET) within telomeric repeat sequences has been studied using a nucleoside-tethered FRET pair embedded in the human telomeric G-quadruplex forming sequence (5'-A GGG TT(Py) A GGG TT(Per) A GGG TTA GGG-3', Py=pyrene, Per=perylene). Conformational change from a single strand to an anti-parallel G-quadruplex leads to FRET from energy donor ((Py) A) to acceptor ((Per) A). The distance between the FRET donor/acceptor partners was controlled by changing the number of G-quartet spacer units. The FRET efficiency decreases with increase in G-quartet units. Overall findings indicate that this could be further used for the development of FRET-based sensing and measurement techniques.

Dual door entry to exciplex emission in a chimeric DNA duplex containing non-nucleoside-nucleoside pair.

Dual door entry to exciplex formation was established in a chimeric DNA duplex wherein a fluorescent non-nucleosidic base surrogate () is paired against a fluorescent nucleosidic base surrogate (). Packing of the nucleobases via intercalative stacking interactions led to an exciplex emission either via FRET from the donor or direct excitation of the FRET acceptor .

Suppressed beta-effect of silicon in 3-silylated monocyclic beta-lactams: the role of antiaromaticity.

The beta-stabilizing effect of silicon substituent at C-3 on a C-4 cation and a radical in the 2-azetidinone systems is studied using NMR kinetics. While the beta-effect is virtually nonexistent in the case of a cation, a foiled beta-effect (only a 3-fold rate enhancement) is observed for a radical intermediate. From both the experimental and theoretical studies, it is demonstrated that antiaromaticity is playing the prime role in suppressing the beta-stabilizing effect of silicon.