Fluorescence Spectroscopic Studies Research Articles

Study of A Tridentate Schiff-Base as A Highly Selective Fluorescent Sensor for Detection of Copper and Chromium Ions

A simple and easily synthesized fluorescent sensor, Schiff base sensor (SBS), produced by condensation reaction of equal amounts of anthranilic acid and salicyladehyde. It was synthesized and characterized systemically. Both UV-vis and fluorescence spectroscopic studies indicated that the SBS sensor showed good selectivity toward the studied ions: Na+, K+, Cu2+, Co2+, Fe3+ , Al3+ and Cr3+. Whereas, chromium (III) and copper (II) exhibited the largest fluorescence enhancement over the other investigated ions. Chelation-enhanced fluorescence were shown upon the interaction of SBS sensor with some metal ions studied forming inclusion complexes. The fluorescent sensor in aqueous ethanolic solution exhibited high selectivity towards Cu2+ and Cr3+ ions, forming 2 : 1 (L : M) complex as determined by Job’s plot. The formation constants of the inclusion complexes (Mn+/SBS) were measured via spectrofluorometric method applying Benesi-Hildebrand equation.

Hemin protects against Zika virus infection by disrupting virus-endosome fusion

Zika virus (ZIKV) is a flavivirus that causes severe neuropathology in newborns and adults. There is no ZIKV-specific treatment or preventative. Therefore, it is urgent to develop safe and effective anti-ZIKV agents. Hemin, an iron-binding porphyrin, has been authorized by FDA to treat acute porphyria since the 1970s. Here, we aim to evaluate the anti-ZIKV effect of hemin in SNB-19 cells (a human glioma cell line) and explore the underlying mechanism based on the virus life cycle and functions of the host cell. Our study found that hemin has a strong activity to protect SNB-19 cells from ZIKV infection presented by decreased expression of viral proteins and virus yield. Meanwhile, ZIKV infection caused STAT1/IRF1 signaling activation and induced inflammatory responses in SNB-19 cells, which was relieved by hemin treatment. HO-1 has been reported to be potently induced by hemin and play a broad-spectrum antiviral effect. Intriguingly, hemin could still exert anti-ZIKV activity upon HO-1 siRNA treatment. Then, we conducted a time-of-addition assay, the result indicated hemin works mainly by interfering with the virus entry process. Further experiments excluded the effects of hemin on AXL-dependent viral adsorption and clathrin-mediated endocytosis processes. Subsequently, by fluorescence spectroscopy studies, intracellular fusion assay and syncytia formation assay, we revealed that hemin acts on the process of virus-endosome fusion. This study elaborated that hemin could play anti-ZIKV activity by disrupting the virus-endosome fusion process and shed new light on developing novel agents against ZIKV infection.

Mononuclear cobalt(II) complexes with polypyridyl ligands: Synthesis, characterization, DNA interactions and in vitro cytotoxicity towards human cancer cells

Mononuclear cobalt(II) complexes [CoII(L1)Cl2]; 1, [CoII(L1)(bpy)Cl]PF6; 2, [CoII(L1)(phen)Cl]PF6; 3 and [CoII(L2)Cl2]; 4 (where L1 = N,N-bis(pyridin-2-ylmethyl)aniline, L2 = (2,4,6-trimethyl-N,N-bis(pyridin-2-ylmethyl)aniline, bpy = 2,2/−bipyridine, phen = 1,10-phenanthroline) were synthesized and characterized by different analytical and spectroscopic methods. All the complexes were structurally identified by single-crystal X-ray crystallography. Penta-coordinated complex 1 adopted distorted trigonal bipyramidal and hexacoordinated complexes 2 and 3 having distorted octahedral geometry whereas tetra-coordinated complex 4 has distorted tetrahedral geometry. The interactions of salmon sperm DNA (ss-DNA) with complexes (1-4) were investigated by absorbance, fluorescence spectroscopy and molecular docking studies. All the complexes are very susceptible to DNA binding and the binding affinity (Kb) follows the order 3 (2.05 × 104 M −1) > 4 (1.40 × 104 M −1) > 2 (1.36 × 104 M −1) > 1 (1.34 × 104 M −1) indicating they have superior DNA binding ability. The Stern-Volmer constant (Ksv) ranges from 1.10 × 104 M −1 to 1.95 × 104 M −1 suggesting weak or moderate binding with DNA. DNA cleavage study in plasmid DNA reveals very efficient DNA cleavage factors even in the absence of any external agents. Using multiple biochemical assays, we have demonstrated that 1–4 induces apoptosis of human cancer cells with IC50 values of 26.48 ± 1.45 μM, 10.89 ± 0.55 μM, 7.63 ± 0.4 μM and 37.67 ± 2.06 μM, respectively in A549 lung adenocarcinoma cells and 14.45 ± 0.73 μM, 1.97 ± 0.1 μM, 0.98 ± 0.05 μM and 24.43 ± 1.22 μM, respectively in MDA-MB-231 breast adenocarcinoma cells.

Integrated Approach to Interaction Studies of Pyrene Derivatives with Bovine Serum Albumin: Insights from Theory and Experiment.

This work aimed to investigate the interaction of bovine serum albumin with newly synthesized potent new pyrene derivatives (PS1 and PS2), which might prove useful to have a better antibacterial character as found for similar compounds in the previous report [Low et al. Bioconjugate Chemistry2014, 12, 2269−2284]. However, to date, binding studies with plasma protein are still unknown. Steady-state fluorescence spectroscopy and lifetime fluorescence studies show that the static interaction binding mode and binding constants of PS1 and PS2 are 7.39 and 7.81 [Kb × 105 (M–1)], respectively. The experimental results suggest that hydrophobic forces play a crucial role in interacting pyrene derivatives with BSA protein. To verify this, molecular docking and molecular dynamics simulations were performed to predict the nature of the interaction and the dynamic behavior of the two compounds in the BSA complex, PS1 and PS2, under physiological conditions of pH = 7.1. In addition, the free energies of binding for the BSA-PS1 and BSA-PS2 complexes were estimated at 300 K based on the molecular mechanics of the Poisson–Boltzmann surface (MMPBSA) with the Gromacs package. PS2 was found to have a higher binding affinity than PS1. To determine the behavior of the orbital transitions in the ground state geometry, we found that both compounds have similar orbital transitions from HOMO–LUMO via π → π* and HOMO–1–LUMO+1 via n → π*, which was included in the FMO analysis. A cytotoxicity study was performed to determine the toxicity of the compounds. Based on the MD study, the stability of the compounds with BSA and the dynamic binding modes were further revealed, as well as the nature of the binding force components involved and the important residues involved in the binding process. From the binding energy analysis, it can be assumed that PS2 may be more active than PS1.

Very rapid synthesis of highly efficient and biocompatible Ag2Se QD phytocatalysts using ultrasonic irradiation for aqueous/sustainable reduction of toxic nitroarenes to anilines with excellent yield/selectivity at room temperature

There are many problems associated with the synthesis of nanocatalysts and catalytic reduction of nitroarenes - e.g., high temperatures, costs, long reaction/synthesis process times, the toxicity of chemicals/solvents, undesirable byproducts, the toxic/harmful wastes, low efficiency/selectivity, etc. This study represents an attempt to overcome these challenges. To this purpose, biocompatible and highly efficient Ag2Se quantum dots (QDs) catalysts with antibacterial activity were synthesized in a very rapid (30 sec, rt), simple, inexpensive, sustainable/green, and one-pot strategy in water using ultrasonic irradiation. Characterization of the QDs was performed using different techniques. UV–Vis absorption and fluorescence spectroscopic studies showed an absorption peak at 480–550 nm and a maximum emission peak around 675 nm, which confirmed the successful synthesis of Ag2Se QDs via the applied biosynthetic method. Subsequently, catalytic reduction of nitroarenes by them was carried out under safe conditions (H2O, rt, air atmosphere) in ∼ 60 min with excellent yield and selectivity (>99%). Their catalytic activity in the reduction of various toxic nitroarenes to aminoarenes under green conditions was investigated. Thus, a rapid and safe ultrasound-based method was employed to prepare stable and green Ag2Se QDs phyto-catalysts with unique properties, including exquisite monodispersity in shape (orthorhombic) and size (∼7 nm), air-stability, and good purity and crystallinity. Importantly, instead of various toxic chemicals, the plant extract obtained by rapid ultrasonic method (10 min, rt) was used as natural reducing, capping, and stabilizing agents. Moreover, antibacterial assays results showed that Ag2Se-QDs catalysts at low concentrations (ppm) have high activity against all tested bacteria, especially E. coli (MIC:31.25 ppm, MBC:125 ppm) which were significantly different from those of Fig extract (MIC = MBC:500 ppm). The data reflect the role of these bio-synthesized Ag2Se-QDs catalysts in the development of versatile and very safe catalysts with biomedical properties.

Nano-Sized Polyelectrolyte Complexes Formed between Poly(vinyl benzyl trimethyl ammonium chloride) and Insulin

Novel biohybrid homo-polyelectrolyte-based nanocarriers were formed by the complexation of insulin (INS) with a biocompatible and cationic polyelectrolyte, namely, poly(vinyl benzyl trimethylammonium chloride) (PVBTMAC). According to light-scattering techniques, the hydrophilic PVBTMAC homo-polyelectrolyte forms single chains in aqueous media. The resulting biohybrid PVBTMAC/INS nanocarriers were formed via electrostatic co-assembly. The effects of polyelectrolyte structure and content on the characteristics of the formed PVBTMAC/INS complexes were studied. A significant aggregation tendency of the PVBTMAC/INS complexes was observed, based on the physicochemical results, especially at high protein concentration, corroborating the effective electrostatic interaction of INS with the cationic polyelectrolyte. The physicochemical properties of the formed PVBTMAC/INS nanocarriers depended on the concentration of the stock polymer and INS solutions. A neat PVBTMAC homo-polymer and PVBTMAC/INS nanocarriers demonstrated good serum stability in the presence of fetal bovine serum (FBS) proteins. Fluorescence spectroscopy (FS) studies revealed no INS conformational changes after its complexation with the cationic PVBTMAC polyelectrolyte. The obtained PVBTMAC/INS complexes demonstrated considerable and promising characteristics for potential use as insulin delivery systems.

Synthesis, characterization, DNA interactions and biological activity of new palladium(II) complexes with some derivatives of 2-aminothiazoles

Newly palladium(II) complexes (C1, C2) with derivatives of 2-aminothiazoles (L1 = 2-amino-6-methylbenzothiazole, L2 = 2-amino-6-chlorobenzothiazole), general formula [PdL2Cl2] were synthesized and characterized by elemental microanalyses, IR, NMR spectroscopy and X-ray spectroscopy in case of [Pd(L2)2Cl2]. The kinetic of the substitution reactions of complexes and the nucleophiles, such as guanosine-5′-monophosphate (5’-GMP), tripeptide glutathione (GSH) and amino acid L-methionine (L-Met), were studied by stopped-flow technique. The complex C2 was always more reactive, while the order of the reactivity of the nucleophiles, due to the associative mode of the reaction, was L-Met > GSH > 5’-GMP. In order to determine the type of interactions between palladium(II) complexes and calf thymus DNA (CT-DNA), we used electronic absorption spectroscopy, viscosity measurements, and fluorescence spectroscopic studies, while interactions with bovine serum albumin (BSA) were determined only with fluorescence spectroscopic studies. The observed results confirmed that both complexes bound to DNA by groove binding. The significantly strong interaction with BSA, especially for complex C2, was also observed. In vitro cytotoxic activity was evaluated against four tumor cell lines, 4 T1, CT26, MDA-MB-468, HCT116 and mesenchymal stem cells (mMSC). C1 complex showed higher cytotoxic activity against CT26 cell line. Flow cytometry analysis showed that C1 stimulated apoptosis of tumor cells via inhibition of expression of antiapoptotic Bcl-2 molecule and decelerated proliferation by decreasing Cyclin-D and increasing expression of P21. In vitro antimicrobial activity for ligands and corresponding palladium(II) complexes was investigated by microdilution method and minimum inhibitory concentration (MIC) and minimum microbicidal concentration (MMC) were determined. Tested compounds exhibited selective and moderate activity.

Design of variants of human fibroblast growth factor 1 with enhanced stability and cell proliferation activity

Human Fibroblast growth factor 1 (hFGF1) is a member of FGF1 subfamily which play significant biological roles, including cell proliferation, cell differentiation, and wound healing. Under physiological temperatures, hFGF1 has low thermodynamic stability and susceptible to the action of proteases. Circular dichroism, fluorescence spectroscopy, and other related studies reveal that reversal of charge on R136 by acidic amino acids (Glu) drastically increases the enzymatic resistance to thrombin, thermal stability, and cell proliferation activity of the growth factor. Interestingly, introduction of R136D mutation shows that the protein stability and cell proliferation activity is similar to the wild‐type protein. Microsecond molecular dynamics studies suggest that length of the side chain of acidic amino acid at position 136 is critical to confer stability to the protein. Detailed analysis of the results will be presented.

Ultrafast Collective Excited-State Dynamics of a Virus-Supported Fluorophore Antenna.

Radiation brightening was recently observed in a multifluorophore-conjugated brome mosaic virus (BMV) particle at room temperature under pulsed excitation. On the basis of its nonlinear dependence on the number of chromophores, the origins of the phenomenon were attributed to a collective relaxation. However, the mechanism remains unknown. We present ultrafast transient absorption and fluorescence spectroscopic studies which shed new light on the collective nature of the relaxation dynamics in such radiation-brightened, multifluorophore particles. Our findings indicate that the emission dynamics is consistent with a superradiance mechanism. The ratio between the rates of competing radiative and nonradiative relaxation pathways depends on the number of chromophores per virus. The findings suggest that small icosahedral virus shells provide a unique biological scaffold for developing nonclassical, deep subwavelength light sources and may open new avenues for the development of photonic probes for medical imaging applications.

Preventive Effects of Anthocyanins from Lyciumruthenicum Murray in High-Fat Diet-Induced Obese Mice Are Related to the Regulation of Intestinal Microbiota and Inhibition of Pancreatic Lipase Activity.

Lyciumruthenicum Murray (L. ruthenicum) has been used both as traditional Chinese medicine and food. Recent studies indicated that anthocyanins are the most abundant bioactive compounds in the L. ruthenicum fruits. The purpose of this study was to investigate the preventive effects and the mechanism of the anthocycanins from the fruit of L. ruthenicum (ACN) in high-fat diet-induced obese mice. In total, 24 male C57BL/6J mice were divided into three groups: control group (fed a normal diet), high-fat diet group (fed a high-fat diet, HFD), and HFD +ACN group (fed a high-fat diet and drinking distilled water that contained 0.8% crude extract of ACN). The results showed that ACN could significantly reduce the body weight, inhibit lipid accumulation in liver and white adipose tissue, and lower the serum total cholesterol and low-density lipoprotein cholesterol levels compared to that of mice fed a high-fat diet. 16S rRNA gene sequencing of bacterial DNA demonstrated that ACN prevent obesity by enhancing the diversity of cecal bacterial communities, lowering the Firmicutes-to-Bacteroidota ratio, increasing the genera Akkermansia, and decreasing the genera Faecalibaculum. We also studied the inhibitory effect of ACN on pancreatic lipase. The results showed that ACN has a high affinity for pancreatic lipase and inhibits the activity of pancreatic lipase, with IC50 values of 1.80 (main compound anthocyanin) and 3.03 mg/mL (crude extract), in a competitive way. Furthermore, fluorescence spectroscopy studies showed that ACN can quench the intrinsic fluorescence of pancreatic lipase via a static mechanism. Taken together, these findings suggest that the anthocyanins from L. ruthenicum fruits could have preventive effects in high-fat-diet induced obese mice by regulating the intestinal microbiota and inhibiting the pancreatic lipase activity.

Tunning of Optoelectronic Properties in Nanohybrids of Peptide-Appended Perylenebisimides and Carbon Nanodots

Two hybrid materials based on carbon dots (C-dots) and two perylenebisimide (PBI)-linked peptides with different functionality have been fabricated. These hybrids are designed to facilitate the electronic interaction between the electron donor C-dots and acceptor PBI-appended peptides, and the optoelectronic properties of these nanohybrids are compared. Amazingly, it is observed that the C-dots have exhibited favorable interactions with the PBI molecule (P1) bearing a similar charge (both negative) and have not shown any electronic interaction with the PBI molecule having opposite charges at their termini (P2). The pH of the medium has been found to be the limiting factor that has inhibited the electronic interaction between C-dots and P2. The interaction between C-dots and P1 has been attributed to the noncovalent complex formation. UV–visible and fluorescence spectroscopic study, field emission gun transmission electron microscopy, and time-correlated single-photon counting studies are made for this purpose. This nanohybrid material shows the emergence of good photoswitching behavior with the highest photocurrent gain of 5.14 (Ion/Ioff) compared to that of only P1 or C-dots. The increase in the photoswitching property is attributed to efficient charge (electron–hole) separation and holds a future promise for fabricating a new nanohybrid material with a high photocurrent conversion efficiency.

Truncation of C-terminal amino acids of GH26 endo-mannanase (ManB-1601) affects biochemical properties and stability against anionic surfactants

Hitherto, the contribution of C-terminal amino acids in structure, stability and function of GH26 endo-mannanases has not been demonstrated. Semi-logarithmic plot of endo-mannanase activity showed a progressive decline with increase in the number of truncated amino acids [ManB-CΔ5 (129 U/mL), ManB-CΔ10 (47 U/mL), ManB-CΔ15 (0.05 U/mL) and ManB-CΔ20 (0.02 U/mL)]. ManB-CΔ5 and ManB-CΔ10 exhibited similar temperature and pH optima and product profile but biochemical properties (kinetic constants, mannan hydrolysis, response to metal ions and enzyme inhibitors) and stability (in presence of commercial detergents, anionic surfactants and organic solvents and half-life) were markedly affected. Interaction of truncated proteins with anionic surfactants was probed using intrinsic, Nile red, acrylamide quenching, resonance light scattering and synchronous fluorescence spectroscopy studies. Truncation of ten amino acids increased vulnerability to anionic surfactants as conformational changes, exposure of the hydrophobic core and susceptibility to unfolding process were observed. The microenvironment around Trp residues was affected more with surfactants as compared to Tyr residues in truncated proteins. Zn2+ coordination might not play a role in providing stability against SDS. MD simulation studies corroborated that C-terminal amino acids (327−336) helps in structure stabilization, regulating flexibility of loops around the active site and preventing denaturation in the presence of SDS.

Phosphodiesterase-3 Enzyme Inhibitor Drug Milrinone Interaction with DNA and HSA: Electrochemical, Spectroscopic and Molecular Docking

In this study, the interaction between the phosphodiesterase-3 enzyme inhibitor drug milrinone and biomolecules was investigated by electrochemical, fluorescence spectroscopy, and molecular docking studies for the first time. The interaction between milrinone and biomolecules was investigated according to the decrease in deoxyguanosine oxidation signals of milrinone and calf thymus double-stranded deoxyribonucleic acid (ct-dsDNA) by cyclic voltammetry and differential pulse voltammetry. In fluorescence spectroscopy studies, a competitive study was conducted on ct-dsDNA by adding a well-known fluorescent methylene blue and ct-dsDNA solution. The fluorescent results showed that milrinone had a higher affinity for ct-dsDNA binding compared to methylene blue. Interaction studies show that milrinone binds to ct-dsDNA via a groove-binding mode, and the binding constant values ​​were calculated as 4.27 × 106 M−1 and 6.03 × 104 M−1 at 25 °C, based on cyclic voltammetry and spectroscopic results, respectively. As a result of the interaction of human serum albumin and milrinone, the binding coefficient was calculated as 4.11 × 106 M−1 by cyclic voltammetry. In addition, experimental results were confirmed by obtaining information about the possible spatial structure of the aggregate formed through theoretical calculations based on energy minimization for milrinone- ct-dsDNA and milrinone-human serum albumin mixtures with molecular insertion.

Homocysteine-Thiolactone Modulates Gating of Mitochondrial Voltage-Dependent Anion Channel (VDAC) and Protects It from Induced Oxidative Stress.

The gating of the Voltage-Dependent Anion Channel (VDAC) is linked to oxidative stress through increased generation of mitochondrial ROS with increasing mitochondrial membrane potential (ΔΨm). It has been already reported that H2O2 increases the single-channel conductance of VDAC on a bilayer lipid membrane. On the other hand, homocysteine (Hcy) has been reported to induce mitochondria-mediated cell death. It is argued that the thiol-form of homocysteine, HTL could be the plausible molecule responsible for the alteration in the function of proteins, such as VDAC. It is hypothesized that HTL interacts with VDAC that causes functional abnormalities. An investigation was undertaken to study the interaction of HTL with VDAC under H2O2 induced oxidative stress through biophysical and electrophysiological methods. Fluorescence spectroscopic studies indicate that HTL interacts with VDAC, but under induced oxidative stress the effect is prevented partially. Similarly, bilayer electrophysiology studies suggest that HTL shows a reduction in VDAC single-channel conductance, but the effects are partially prevented under an oxidative environment. Gly172 and His181 are predicted through bioinformatics tools to be the most plausible binding residues of HTL in Rat VDAC. The binding of HTL and H2O2 with VDAC appears to be cooperative as per our analysis of experimental data in the light of the Hill-Langmuir equation. The binding energies are estimated to be - 4.7kcalmol-1 and - 2.8kcalmol-1, respectively. The present in vitro studies suggest that when mitochondrial VDAC is under oxidative stress, the effects of amino acid metabolites like HTL are suppressed.

Probing multifunctional azure B conjugated gold nanoparticles with serum protein binding properties for trimodal photothermal, photodynamic, and chemo therapy: Biophysical and photophysical investigations

Multimodal or combination therapy has been considered as a powerful approach for treatment of complex diseases like cancer. The fascinating physicochemical and optoelectronic properties of gold nanoparticles make them potential candidate for cancer therapeutic and diagnostic applications. Herein, we design a multifunctional nanosystem by conjugating a photosensitizer, Azure B (AB) with citrate reduced gold nanoparticles (CI-Au NPs) through non-covalent interactions. The conjugation of AB with CI-Au NPs was confirmed through UV–Visible absorption spectroscopy and Fourier Transform Infra-red (FT-IR) spectroscopy. The morphology, size, and charge of the prepared nano-conjugates (AB@CI-Au NPs) were determined by transmission electron microscopy (TEM), Dynamic light scattering (DLS), and zeta potential measurements. The proficiency of AB@CI-Au NPs for cancer photo-therapies was demonstrated by evaluating their potential for photothermal heating and singlet oxygen generation in solution upon Visible laser (635 nm, 500 mW/cm2) irradiation. The AB@CI-Au NPs display superior heating efficiency than CI-Au NPs alone or free AB, and offer better photostability as well as singlet oxygen generation rate compared to free photosensitizer. The interaction of AB@CI-Au NPs with Calf thymus DNA (Ct-DNA) and transport protein Bovine Serum Albumin (BSA) were studied using various biophysical techniques including Circular dichroism, UV–Visible and fluorescence spectroscopic studies. AB@CI-Au NPs show intercalative binding with Ct-DNA by inducing local perturbations in double helical structure and hence can exert chemotherapeutic action by targeting DNA. AB@CI-Au NPs also display moderate binding with BSA without any adverse effect on BSA structure, which is desirable for significant biodistribution and pharmacokinetics of AB@CI-Au NPs. Also, in vitro cytotoxicity of the AB@CI-Au NPs with and without laser irradiation (635 nm, 500 mW/cm2) was demonstrated using the hepatocellular carcinoma (HepG2) cell lines. Our findings through photophysical and biophysical studies strongly recommend the exploitation of AB@CI-Au NPs nanoconjugates as a multifunctional probe for trimodal anticancer therapy.

2-Amino-5-substituted-1,3,4-oxadiazole as chemosensor for Ni(II) ion detection: antifungal, antioxidant, DNA binding, and molecular docking studies.

An oxadiazole derivative 2 was prepared by condensation reaction through cyclization of semicarbazone in the presence of bromine; the structural confirmation was supported by 1 H and 13 C nuclear magnetic resonance (NMR) spectroscopy, Fourier transform-infrared spectroscopy, and liquid chromatography-mass spectrometry. Its sensing ability towards Ni2+ ion was examined showing a binding constant of 1.04 × 105 compared with other suitable metal cations (Ca2+ , Co2+ , Cr3+ , Ag+ , Pb2+ , Fe3+ , Mg2+ , and K+ ) using ultraviolet-visible (UV-vis) and fluorescence spectroscopic studies. The minimum concentration of Ni2+ ions and limit of detection was found to be 9.4 μM. A job's plot gave the binding stoichiometry ratio of oxadiazole derivative 2 vs Ni2+ ions as 2:1. Furthermore, the intercalative binding mode of oxadiazole derivative 2 with calf thymus DNA was supported by ultraviolet-visible (UV-vis) and fluorescent light, viscosity, cyclic voltammetry, time-resolved fluorescence, and circular dichroism measurements. The molecular docking result gave the binding score for oxadiazole derivative 2 as -6.5 kcal/mol, which further confirmed the intercalative interaction. In addition, the antifungal activity of oxadiazole derivative 2 was also screened against several fungal strains (C. albicans, C. glabrata, and C. tropicalis) by broth dilution and disc diffusion methods. In antioxidant studies, the oxadiazole derivative 2 showed potential scavenging activity against 2,2-diphenyl-1-picrylhydrazyl and H2 O2 free radicals.

N-OH-AABP Modifications in Human DNA May Lead to Auto-Antibodies in Bladder Cancer Subjects.

4-Aminobiphenyl (4-ABP) and other related arylamines have emerged to be responsible for human urinary bladder tumors and cancers. Hemoglobin-ABP adducts have been recognized in the blood of smokers, and it builds up in the circulatory system over the period of years that might lead to a bladder tumor. N-hydroxy-Acetyl 4-Aminobiphenyl (N-OH-AABP) is one of the reactive forms of 4-ABP which has a potential to initiate tumor growth and causes cancer rapidly. In the present study, commercially available human DNA was modified by N-OH-AABP, and its modifications were analyzed biophysically from fluorescence spectroscopy and thermal denaturation studies. Further, Sera and IgG from bladder cancer patients’ blood were assessed for affinity to native and N-OH-AABP modified human DNA using ELISA. The study showed N-OH-AABP caused damage in the structure of the DNA macromolecule and the perturbations resulting from damage leads to change in the Tm of the DNA molecule. Bladder cancer auto-antibodies, particularly in smoker group, showed preferential binding to N-OH-AABP modified human DNA. This study shows that N-OH-AABP modified DNA could be an antigenic stimulus for the generation of autoantibodies in the sera of bladder cancer patients.

Study on the interaction of ethylene glycol with trypsin: Binding ability, activity, and stability

The study of the structural changes and thermal stabilities of proteins in the presence of various co-solutes is a critical element of basic research, drug discovery, and development. Ethylene glycol (EG) is typically known to be poisonous and teratogenic, causing skeletal and external abnormalities as well as other disorders. At pH 8, the influence of EG on the structure and thermal stability of trypsin was investigated using a variety of spectroscopic techniques. Spectroscopic techniques, fluorescence spectroscopy, circular dichroism (CD), and molecular dynamics simulation studies were used to evaluate the binding reaction between ethylene glycol and trypsin in the current study. Circular dichroism, Trp fluorescence, and absorption tests demonstrated that EG has an effect on secondary and tertiary structures of trypsin, and it boosts the protein's thermal stability, which increases with increasing EG concentration. This contact occurs through a static quenching process, according to fluorescence spectroscopy data, and van der Waals contributions and hydrogen bonds were also important in binding ethylene glycol to trypsin. The ethylene glycol binding constant (Kb) and the number of binding sites (n) were calculated using fluorescence quenching data. Kinetic technique analysis displayed a decrease in trypsin activity in the presence of ethylene glycol. Also, circular dichroism results confirmed the conformation changes resulting from the binding of ethylene glycol to trypsin. Molecular dynamics simulation using RMSD was used to test the stability of the trypsin-ethylene glycol complex in this study. Molecular docking research revealed that EG interacts with trypsin amino acid residues via hydrogen bonding and van der Waals interactions.

Spectroscopic Characterization of Mitochondrial G-Quadruplexes.

Guanine quadruplexes (G4s) are highly polymorphic four-stranded structures formed within guanine-rich DNA and RNA sequences that play a crucial role in biological processes. The recent discovery of the first G4 structures within mitochondrial DNA has led to a small revolution in the field. In particular, the G-rich conserved sequence block II (CSB II) can form different types of G4s that are thought to play a crucial role in replication. In this study, we decipher the most relevant G4 structures that can be formed within CSB II: RNA G4 at the RNA transcript, DNA G4 within the non-transcribed strand and DNA:RNA hybrid between the RNA transcript and the non-transcribed strand. We show that the more abundant, but unexplored, G6AG7 (37%) and G6AG8 (35%) sequences in CSB II yield more stable G4s than the less profuse G5AG7 sequence. Moreover, the existence of a guanine located 1 bp upstream promotes G4 formation. In all cases, parallel G4s are formed, but their topology changes from a less ordered to a highly ordered G4 when adding small amounts of potassium or sodium cations. Circular dichroism was used due to discriminate different conformations and topologies of nucleic acids and was complemented with gel electrophoresis and fluorescence spectroscopy studies.

Augmented Self-Association by Electrostatic Forces in Thienopyrrole-Fused Thiadiazoles that Contain an Ester instead of an Ether Linker.

During the self-assembly of π-conjugated molecules, linkers and substituents can potentially add supportive noncovalent intermolecular interactions to π-stacking interactions. Here, we report the self-assembly behavior of thienopyrrole-fused thiadiazole (TPT) fluorescent dyes that possess ester or ether linkers and dodecyloxy side chains in solution and the condensed phase. A comparison of the self-association behavior of the ester- and ether-bridged compounds in solution using detailed UV-vis, fluorescence, and NMR spectroscopic studies revealed that the subtle replacement of the ether linkers by ester linkers leads to a distinct increase in the association constant (ca. 3-4 fold) and the enthalpic contribution (ca. 3 kcal mol-1 ). Theoretical calculations suggest that the ester linkers, which are in close proximity to one another due to the π-stacking interactions, induce attractive electrostatic forces and augment self-association. The self-assembly of TPT dyes into well-defined 1D clusters with high aspect ratios was observed, and their morphologies and crystallinity were investigated using SEM and X-ray diffraction analyses. TPTs with ester linkers exhibit a columnar liquid crystalline mesophase in the condensed phase.