NHEJ is promoted by the phosphorylation and phosphatase activity of PTEN via regulation of DNA-PKcs.

DNA double-strand breaks (DSBs) are considered one of the most harmful forms of DNA damage. These DSBs are repaired through non-homologous end joining (NHEJ) and homologous recombination (HR) pathways and defects in these processes can lead to genomic instability and promote tumorigenesis. Phosphatase and Tensin homolog (PTEN) are crucial in HR repair. However, its involvement in the NHEJ repair pathway has remained elusive. In this study, we investigate the function of epigenetic regulation of PTEN in the NHEJ repair pathway. Our findings indicate that both the phosphorylation and phosphatase activity of PTEN are required for efficient NHEJ-mediated DSB repair. During the DNA damage response, we observed a reduced expression and chromatin attachment of the key NHEJ proteins, including Ku70/80, DNA-PKcs, XRCC4, and XLF, in PTEN-null cells. This reduction was attributed to the instability of these NHEJ proteins, as confirmed by our protein half-life assay. We have demonstrated that the DNA-PKcs inhibitor, NU7026, suppresses the DNA damage-induced phosphorylation of the C-terminal of PTEN. Thus, our study indicates that PTEN could be a target of DNA-PKcs. Protein-protein docking analysis also shows that PTEN interacts with the C-terminal region of DNA-PKcs. PTEN null cells exhibit compromised DNA-PKcs foci after DNA damage as it is in a hyper-phosphorylated state. Phospho-PTEN assists in recruiting DNA-PKcs on the DNA damage site by maintaining its hypo-phosphorylated state which also depends on its phosphatase activity. Therefore, after DNA damage, crosstalk between PTEN and DNA-PKcs modulates the NHEJ pathway. Thus, during DNA damage, PTEN gets phosphorylated directly or indirectly by DNA-PKcs and attaches to chromatin, resulting in the dephosphorylation of DNA-PKcs and subsequently recruitment of other NHEJ factors on chromatin occurs for efficient execution of the NHEJ pathway. Thus, our research provides a molecular understanding of the epigenetic regulation of PTEN and its significant role in controlling the NHEJ pathway.

Multi-spectroscopic and thermodynamic profiles on HSA binding of Cassia fistula leaf based potential antibacterial and anticancer silver nanoparticles.

Here, a simple, one step, lucrative and green synthesis of Cassia fistula leaf extract inspired antibacterial silver nanoparticles (CF-SNPs) was provided. Characterization of these CF-SNPs were achieved by using various spectroscopic techniques for instance Ultraviolet Visible (UV-Vis) Spectroscopy, Fourier-Transform Infrared (FTIR) Spectroscopy, Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray (EDX). The effective antibacterial action of the CF-SNPs was checked against Escherichia coli (E. Coli) DH5-Alpha where MIC was 1.6 nM. Anticancer dynamism of the CF-SNPs was also tested in opposition to skin melanoma, A375 cell lines in which 4.4 nM was IC50. The binding proneness of HSA towards CF-SNPs was investigated by means of UV-Vis Spectroscopy, Fluorescence Spectroscopy, Time Resolved Fluorescence Spectroscopy, Circular Dichroism (CD) Spectroscopy, Dynamic Light Scattering, and Isothermal Titration Colorimetry (ITC). CD spectroscopy established minor secondary structural exchange of HSA in HSA-CF-SNPs complex. ITC and Time Resolved Fluorescence Spectroscopy verified the static type quenching mechanism involved in HSA-CF-SNPs complex. The binding constant was 3.45 × 108 M-1 at 298.15K from ITC study. The thermodynamic parameters showed that the interaction was occurred spontaneously by the hydrophilic forces and hydrogen bonding.Communicated by Ramaswamy H. Sarma.

Complete genome sequence of the multidrug-resistant clinical isolate Acinetobacter baumannii KBN10P05679: Insights into antimicrobial resistance genotype and potential virulence traits.

OBJECTIVES: Acinetobacter baumannii, a nosocomial pathogen, exhibits multidrug resistance and is a major concern worldwide. We therefore aimed to evaluate the genomic features of the clinical strain A. baumannii KBN10P05679 to elucidate its antibiotic resistance mechanisms and virulence factors. METHODS: In silico multilocus sequence typing, phylogenetic identification, genome annotation, genome analysis, antibiotic susceptibility testing, and biofilm formation assay were performed, and the expression levels of antibiotic resistance- and biofilm-related genes were investigated. RESULTS: The complete genome of KBN10P05679 comprises a circular chromosome of 3 990 428 bp and two plasmids (74 294 and 8731 bp) and was assigned to the ST451 sequence type. Clusters of Orthologous Gene annotation identified 3810 genes, including those involved in amino acid transport and metabolism, transcription, inorganic ion transport, energy production and conversion, replication, recombination and repair, and carbohydrate and protein metabolism. The antibiotic resistance genes were investigated by searching the Comprehensive Antibiotic Resistance Database, and the genome was found to harbour 30 different antibiotic resistance genes. Analysis of the Virulence Factor Database revealed 86 virulence factor genes in the KBN1005679 genome. The KBN10P05679 strain was found to have a higher capacity for biofilm formation and expressed biofilm-related genes at a higher level than the other tested strains. CONCLUSIONS: The antibiotic resistance genotype and potential virulence factor-related data obtained in this study would help direct future studies for developing the control measures for this multidrug-resistant pathogen.

Complete Genome Sequence of Acinetobacter baumannii Strain KBN10P04593, a Clinical Isolate from South Korea.

Acinetobacter baumannii is an opportunistic nosocomial pathogen that is responsible for various life-threating infections in immunocompromised hosts. We present the complete 3.93-Mb genome sequence of A. baumannii KBN10P04593, generated by combining PacBio and Illumina technologies.

A comparative study on DNA and protein binding properties of thymol and thymoquinone.

Two phytochemicals, thymol and thymoquinone obtained from thymes (Thymus vulgaris L., Lamiaceae etc.) and Nagila Sativa seed, respectively. Both the phytochemicals show several biochemical activities like anticancer, antimicrobial etc. In this paper, we studied the affinities of thymol and thymoquinone towards calf thymus DNA (CT-DNA) and protein (bovine serum albumin). Spectroscopic and molecular modelling studies revealed that both compounds have a high affinity toward both the receptors; DNA and protein. Both phytochemicals binds to the minor grooves of DNA and suitable pockets of protein. Several free energy function and hydrogen bonding play significant role during the binding phenomenon.Communicated by Ramaswamy H. Sarma.

DNA/Protein Binding and Apoptotic-Induced Anticancer Property of a First Time Reported Quercetin-Iron(III) Complex Having a Secondary Anionic Residue: A Combined Experimental and Theoretical Approach.

A new quercetin-based iron(III) cationic complex [Fe(Qr)Cl(H2O)(MeO)] (complex 1) is created in the current study by condensation of quercetin with ferric chloride in the presence of Et3N. Comprehensive spectroscopic analysis and conductometric measurement are used to pinpoint complex 1. The generated complex's +3-oxidation state has been verified by electron paramagnetic resonance (EPR) research. Density functional theory analysis was used to structurally optimize the structure of complex 1. Before biomedical use, a variety of biophysical studies are implemented to evaluate the binding capacity of complex 1 with DNA and human serum albumin (HSA) protein. The findings of the electronic titration between complex 1 and DNA, as well as the stunning fall in the fluorescence intensities of the HSA and EtBr-DNA/DAPI-DNA domain after complex 1 is gradually added, give us confidence that complex 1 has a strong affinity for both macromolecules. It is interesting to note that the displacement experiment confirms partial intercalation as well as the groove binding mechanism of the title complex with DNA. The time-dependent fluorescence analysis indicates that after interaction with complex 1, HSA will exhibit static quenching. The thermodynamic parameter values in the HSA-complex 1 interaction provide evidence for the hydrophobicity-induced pathway leading to spontaneous protein-complex 1 interaction. The two macromolecules' configurations are verified to be preserved when they are associated with complex 1, and this is done via circular dichroism spectral titration. The molecular docking investigation, which is a theoretical experiment, provides complete support for the experimental findings. The potential of the investigated complex to be an anticancer drug has been examined by employing the MTT assay technique, which is carried out on HeLa cancer cell lines and HEK-293 normal cell lines. The MTT assay results validate the ability of complex 1 to display significant anticancer properties. Finally, by using the AO/PI staining approach, the apoptotic-induced cell-killing mechanism as well as the detection of cell morphological changes has been confirmed.

Engineering of lysin by fusion of antimicrobial peptide (cecropin A) enhances its antibacterial properties against multidrug-resistant Acinetobacter baumannii.

Most clinical isolates of Acinetobacter baumannii, a nosocomial pathogen, are multidrug-resistant (MDR), fueling the search for alternative therapies. Bacteriophage-derived endolysins have potent antibacterial activities and are considered as alternatives to antibiotics against A. baumannii infection. Gram-negative bacteria possess outer lipid membrane that prevents direct contact between the endolysins and the cell wall. We hypothesized that the fusion of antimicrobial peptide (AMP) with endolysin could help to reduce bacterial endolysin resistance and increase antimicrobial activity by membrane permeability action. Accordingly, we fused cecropin A, a commonly used AMP, with the N-terminus of AbEndolysin, which enhances the bactericidal activity of the chimeric endolysin. The bactericidal activity of cecropin A-fused AbEndolysin increased by at least 2-8 fold for various MDR A. baumannii clinical isolates. The in vitro bactericidal activity results also showed higher bacterial lysis by the chimeric endolysin than that by the parental lysin. The engineered AbEndolysin (eAbEndolysin) showed synergistic effects with the beta-lactam antibiotics cefotaxime, ceftazidime, and aztreonam, and an additive effect with meropenem and imipenem. eAbEndolysin had no cytotoxic effect on A549 cell line and rescued mice (40% survival rate) from systemic A. baumannii infection. Together, these findings suggest the potential of lysin therapy and may prompt its use as an alternative to antibiotics.

Thermodynamic and structural profiles of multi-target binding of vinblastine in solution.

Structural information about drug-receptor interactions is paramount in drug discovery and subsequent optimization processes. Drugs can bind to multiple potential targets as they contain common chemical entities in their structures. Understanding the details of such interactions offer possibilities for repurposing and developing potent inhibitors of disease pathways. Vinblastine (VLB) is a potent anticancer molecule showing multiple receptor interactions with different affinities and degrees of structural perturbations. We have investigated the multi-target binding profile of VLB with DNA and human serum albumin (HSA) in a dynamic physiological environment using spectroscopic, molecular dynamics simulations, and quantum mechanical calculations to evaluate the structural features, mode, ligand and receptor flexibility, and energetics of complexation. These results confirm that VLB prefers to bind in the major groove of DNA with some inclination toward Thymidine residue and the TR-5 binding site in HSA with its catharanthine half making important contacts with both the receptors. Spectroscopic investigation at multiple temperatures has also proved that VLB binding is entropy driven indicating the major groove and TR-5 binding site of interaction. Finally, the overall binding is facilitated by van der Waals contacts and a few conventional H-bonds. VLB portrays reasonable conformational diversity on binding with multiple receptors.

Response of Ancillary Azide Ligand in Designing a 1D Copper(II) Polymeric Complex along with the Introduction of High DNA- and HAS-Binding Efficacy, Leading to Impressive Anticancer Activity: A Compact Experimental and Theoretical Approach.

A new versatile azide-bridged polymeric Cu(II) complex, namely, [Cu(L)(µ1,3-N3)]∞ (1), was synthesized utilizing an N,N,O-donor piperidine-based Schiff base ligand (E)-4-bromo-2-((2-(-1-yl)imino)methyl)phenol (HL), obtained via the condensation reaction of 1-(2-aminoethyl) piperidine and 5-bromo salicylaldehyde. The single-crystal X-ray diffraction analysis reveals that complex 1 consists of an end-to-end azido-bridged polymeric network, which is further rationalized with the help of a density functional theory (DFT) study. After routine characterization with a range of physicochemical studies, complex 1 is exploited to evaluate its biomedical potential. Initially, theoretical inspection with the help of a molecular docking study indicated the ability of complex 1 to effectively bind with macromolecules such as DNA and the human serum albumin (HSA) protein. The theoretical aspect was further verified by adopting several spectroscopic techniques. The electronic absorption spectroscopic analysis indicates a remarkable binding efficiency of Complex 1 with both DNA and HSA. The notable fluorescence intensity reduction of the ethidium bromide (EtBr)-DNA adduct, 4',6-diamidino-2-phenylindole (DAPI)-DNA adduct, and HSA after the gradual addition of complex 1 authenticates its promising binding potential with the macromolecules. The retention of the canonical B form of DNA and α form of HSA during the association of complex 1 was confirmed by implementing a circular dichroism spectral study. The association ability of complex 1 with macromolecules further inspired us to inspect its impact on different cell lines such as HeLa (cervical cancer cell), PA1 (ovarian cancer cell), and HEK (normal cell). The dose-dependent and time-dependent in vitro 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay suggests an effective antiproliferative property of complex 1 with low toxicity toward the normal cell line. Finally, the anticancer activity of complex 1 toward carcinoma cell lines was analyzed by nuclear and cellular staining techniques, unveiling the cell death mechanism.

A comparison on the biochemical activities of Fluorescein disodium, Rose Bengal and Rhodamine 101 in the light of DNA binding, antimicrobial and cytotoxic study.

Biochemical activities of Fluorescein, Rose Bengal and Rhodamine 101 were studied by DNA binding, antibacterial and cytotoxic studies. DNA binding studies were done using spectroscopic, thermodynamic and molecular modeling techniques. Antibacterial activities were investigated against a gram-negative bacteria Escherichia coli and a gram-positive bacteria Staphylococcus aureus. Cytotoxic activities were studied against Wi-38 cell line. We observed these dyes bound to minor groove of DNA and structural diversity of dyes affect the phenomenon. No significant antibacterial and cytotoxic activities of these dyes were found in our observations.

LeuO, a LysR-Type Transcriptional Regulator, Is Involved in Biofilm Formation and Virulence of Acinetobacter baumannii.

Acinetobacter baumannii is an important nosocomial pathogen that can survive in different environmental conditions and poses a severe threat to public health due to its multidrug resistance properties. Research on transcriptional regulators, which play an essential role in adjusting to new environments, could provide new insights into A. baumannii pathogenesis. LysR-type transcriptional regulators (LTTRs) are structurally conserved among bacterial species and regulate virulence in many pathogens. We identified a novel LTTR, designated as LeuO encoded in the A. baumannii genome. After construction of LeuO mutant strain, transcriptome analysis showed that LeuO regulates the expression of 194 upregulated genes and 108 downregulated genes responsible for various functions and our qPCR validation of several differentially expressed genes support transcriptome data. Our results demonstrated that disruption of LeuO led to increased biofilm formation and increased pathogenicity in an animal model. However, the adherence and surface motility of the LeuO mutant were reduced compared with those of the wild-type strain. We observed some mutations on amino acids sequence of LeuO in clinical isolates. These mutations in the A. baumannii biofilm regulator LeuO may cause hyper-biofilm in the tested clinical isolates. This study is the first to demonstrate the association between the LTTR member LeuO and virulence traits of A. baumannii.

Characterization of a Novel Phage ΦAb1656-2 and Its Endolysin with Higher Antimicrobial Activity against Multidrug-Resistant Acinetobacter baumannii.

Acinetobacter baumannii is a nosocomial pathogen, which is a problem worldwide due to the emergence of a difficult-to-treat multidrug-resistant A. baumannii (MDRAB). Endolysins are hydrolytic enzymes produced by a bacteriophage that can be used as a potential therapeutic agent for multidrug-resistant bacterial infection in replacing antibiotics. Here, we isolated a novel bacteriophage through prophage induction using mitomycin C from clinical A. baumannii 1656-2. Morphologically, ΦAb1656-2 was identified as a Siphoviridae family bacteriophage, which can infect MDRAB. The whole genome of ΦAb1656-2 was sequenced, and it showed that it is 50.9 kb with a G + C content of 38.6% and 68 putative open reading frames (ORFs). A novel endolysin named AbEndolysin with an N-acetylmuramidase-containing catalytic domain was identified, expressed, and purified from ΦAb1656-2. Recombinant AbEndolysin showed significant antibacterial activity against MDRAB clinical strains without any outer membrane permeabilizer. These results suggest that AbEndolysin could represent a potential antimicrobial agent for treating MDRAB clinical isolates.

Evidence for Dual Site Binding of Nile Blue A toward DNA: Spectroscopic, Thermodynamic, and Molecular Modeling Studies.

Binding of Nile Blue (NB) with calf thymus DNA has been studied using molecular modeling, spectroscopic, and thermodynamic techniques. Our study revealed that NB binds to the DNA helix by two types of modes (groove binding and intercalation) simultaneously. The thermodynamic study showed that the overall binding free energy is a combination of several negative and positive free energy changes. The binding was favored by negative enthalpy and positive entropy changes (due to the release of water from the DNA helix). The docking study validated all experimental evidence and showed that NB binds to a DNA minor groove at low concentrations and switches to intercalation mode at higher concentrations.

Biophysical insights into the interaction of human serum albumin with Cassia fistula leaf extracts inspired biogenic potent antibacterial and anticancerous gold nanoparticles.

In the present investigation, the characterization of Cassia fistula leaf extracts (CFLE) mediated gold nanoparticles (CF-GNPs) and its binding features with human serum albumin (HSA) through interaction have been probed. The results from UV-visible, TEM and EDX analysis proved the formation of CF-GNPs. The functional groups like OH, NH, CN etc present in the phytochemicals of CFLE were mainly acted as reducing and protecting agent which was confirmed by FTIR study. The zeta potential (-17.8 mV) and hydrodynamic size (20.4 nm) of the CF-GNPs were also measured by DLS. The microbicidal effect of the CF-GNPs was estimated against gram negative bacterium, Escherichia coli (DH5-Alpha) and MIC was found to be 2.8 nM. Anticancer activity of the CF-GNPs was also checked against A375 (skin melanoma) cell lines where IC50 was 6.5 nM. The interaction study of CF-GNPs with HSA and conformational alteration of HSA upon interaction were investigated by the fluorescence, lifetime, synchronous, circular dichroism spectrum and zeta potential measurement. The negative value of Gibb's free energy indicated spontaneity of the CF-GNPs-HSA complex formation. The fluorescence lifetime measurement confirmed the construction of ground state CF-GNPs-HSA complex passing through static quenching mechanism and determined the distance from donor to acceptor also. Circular dichroism spectroscopy signified unchangeable native structure of HSA with minor decrease of alpha helix structure (54.5% to 51.1%) upon interaction. The more negative zeta potential value (-25.9 mV) of CF-GNPs-HSA system than the CF-GNPs (-17.8 mV) proved the adsorption of HSA on the outer surface of CF-GNPs.Communicated by Ramaswamy H. Sarma.

Transcriptional Regulation of the Outer Membrane Protein A in Acinetobacter baumannii.

Acinetobacter baumannii is known for its virulence in severely ill, hospitalized patients and for exhibiting multidrug resistance. A. baumannii infection treatment poses a serious problem in clinical environments. The outer membrane protein A (OmpA) of the Acinetobacter genus is involved in bacterial virulence. Regulatory factors of OmpA in the post-transcriptional stage have been previously identified. However, the regulatory factors that act before the transcriptional stage remain unclear. We investigated the A1S_0316 gene that encodes a putative transcription factor for OmpA expression in A. baumannii. A1S_0316 was purified and examined using size-exclusion chromatography, which revealed that it forms an oligomer. The binding affinity of A1S_0316 to the OmpA promoter region was also examined. We compared the binding affinity to the OmpA promotor region between A1S_0316 and the AbH-NS protein. A1S_0316 showed higher binding affinity to the OmpA promotor region than did H-NS. We examined the regulatory effect of these proteins on OmpA expression in A. baumannii using real-time qPCR and various in vitro tools. Our results indicated that A1S_0316 acts as an anti-repressor on the promotor region of the OmpA gene by inhibiting the binding of the AbH-NS protein. This study was the first demonstration of the transcriptional regulation of OmpA expression.

Structures, Photoresponse Properties, and Biological Activity of Dicyano-Substituted 4-Aryl-2-pyridone Derivatives.

Described in this work is the synthesis of a novel dicyano-substituted N-2-aminoethyl-4-(3-pyridinyl)-2-pyridone organic compound (1) that is characterized by several spectroscopic methods. Compound (1) was utilized for the preparation of its perchlorate (2), chloride (3), and bromide (4) salts. Single-crystal X-ray structures of these three salts were determined, and noncovalent weak interactions involving the aromatic rings, anions, and water molecules in (2-4) were investigated in detail. Solid-state UV-vis spectrum of the reported compounds (1-4) was utilized to calculate their optical band gaps, which clearly indicated that they belong to the semiconductor family. Under illumination condition, the magnitudes of electrical properties of (1) and its salts (2-4) improve remarkably although the improvement differs from salt to salt and the result was analyzed theoretically. Salt (2) was tested for its DNA binding ability.

Binding interaction study on human serum albumin with bactericidal gold nanoparticles synthesized from a leaf extract of Musa balbisiana: a multispectroscopic approach.

This study describes the eco-friendly, low-cost and room-temperature synthesis of gold nanoparticles from Musa balbisiana leaf extract, which acts as both reducing and stabilizing agent, and characterized by ultraviolet-visible (UV-vis) light spectroscopy, fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FE-SEM), analytical transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDAX) and dynamic light scattering (DLS) instruments. These nanoparticles showed an average diameter of 33.83 ± 3.39 nm, which was confirmed from the size distribution histogram. The bactericidal activity of these nanoparticles was confirmed using bacteria Escherichia coli and Staphylococcus aureus at 1 and 2 nM minimum inhibitory concentrations, respectively. The interaction between nanoparticles and human serum albumin (HSA) was investigated, as this plays significant roles in biological systems. The nature of interaction, binding parameters and structural variation of HSA in the presence of these nanoparticles have been evaluated using several useful spectroscopic approaches such as UV-vis, FTIR, time-resolved and steady-state fluorescence, and circular dichroism in addition to the measurement of zeta potential. This interaction study revealed that static quenching occurs in this process with minimal alteration in the secondary structure, but the native structure of HSA remained unaltered. The binding constant and thermodynamic parameters of this interaction process were also evaluated.

Berberine derivatives as heteroatom induced hydrophobic sensor: An analytical approach for the selective and sensitive fluorometric detection and discrimination of serum albumins.

The detection and discrimination of serum albumins (SAs) has been transforming as a research work of keen interest to the scientists in recent times. This is in the root of foundation of more and more fluorescent probes to selectively identify and distinguish the SAs in the modern era of research. Fluorescence based sensors are preferably on high demand because of high sensitivity of fluorescence spectroscopy. Herein we have synthesized berberine derivatives with substitutions at two different positions (9 and 13) with the purpose of an analytical study to detect and differentiate the SAs. It was found that only the 9-O substituted derivatives showed a dramatic enhancement in their inherently weak fluorescence intensity after the addition of serum albumins (BSA and HSA) indicating the occurrence of heteroatom induced hydrophobic binding interaction. Lower value of detection limit, 6.8 nM and 6.1 nM for BSA and 17.8 nM and 16.3 nM for HSA respectively for the two compounds N1 and N2 and extended range of linearity for both the probes justify the fruitfulness of the research work. Moreover, the two effective 9-O substituted probes response differently in presence of the two SAs by the nature, intensity of the fluorescence spectra and position of wavelength maxima which enable us in deciphering the two essential proteins. All the results reveal how the presence of a heteroatom influences the hydrophobic sensing of the SAs and divulge the utility of the synthesized berberine derivatives in detection and distinction of two SAs successfully in the coming years.

Elucidating the chemical and biochemical applications of Citrus sinensis-mediated silver nanocrystal.

Synthesis of nanoparticles using biodegradable source is safer and echo-friendly. Here, we describe the synthesis of polycrystalline silver nanocrystals using Citrus sinensis acting as both reducing and capping agents. After exposing the silver ions to orange extract, rapid reduction of silver ions led to the formation of stable silver nanocrystals due to the reducing and stabilizing properties of orange fruit juice. The synthesized silver nanocrystals were characterized using various analytical techniques like UV-vis spectroscopy, X-ray diffraction (XRD), dynamic light scattering (DLS), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The biochemical activity of the synthesized nanocrystals was studied in the light of affinity to bovine serum albumin using several biophysical methods like absorbance, fluorescence and circular dichroism spectroscopy. Cytotoxic activity of these nanocrystals was also studied against Hep-2 cell line using fluorescence microscopy. It was also found that the synthesized nanocrystals can sense mercuric ion down to 50 µM in the presence of a number of cations. Furthermore, we established that the silver nanoparticles can effectively catalyse the reduction of methylene blue by ascorbic acid. The present study will enrich our knowledge on the chemical and biochemical activities of green-synthesized silver nanocrystals.

Structures, photoresponse properties and DNA binding abilities of 4-(4-pyridinyl)-2-pyridone salts.

Three salts [perchlorate (2), chloride (3) and tetrafluoroborate (4)] were synthesized from a 1-(2-aminoethyl)-6-hydroxy-2-oxo-1,2-dihydro-[4,4'-bipyridine]-3,5-dicarbonitrile compound (1) and characterized by spectroscopic and single crystal X-ray diffraction methods. Various noncovalent interactions (e.g., anion⋯π+, π⋯π, lp⋯π) are explored in the solid state crystal structure of the salts. Optical band gaps of all the four compounds were determined from their solid-state UV-vis spectrum. Electrical properties like electrical conductivity, photosensitivity, etc. were calculated and the results revealed that they have potential to act as optoelectronic devices. The values of the electrical parameters increase several times when they are exposed to visible light rather than in dark conditions. The light sensing properties of the salts (2-4) are enhanced compared to that of the mother organic compound 1 but the magnitude of this enhancement is not same for the three salts. This observation has been rationalized by theoretical considerations. Moreover, the DNA binding ability of one of the representative salts (compound 2) was examined to check the biological importance of the synthesized salts.