Synthesis and electrochemical properties of environmental free l-glutathione grafted graphene oxide/ZnO nanocomposite for highly selective piroxicam sensing

A simple and reliable strategy was proposed to engineer the glutathione grafted graphene oxide/ZnO nanocomposite (glutathione-GO/ZnO) as electrode material for the high-performance piroxicam sensor. The prepared glutathione-GO/ZnO nanocomposite was well characterized by X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). The novel nanocomposite modified electrode showed the highest electrocatalytic activity towards piroxicam (oxidation potential is 0.52 V). Under controlled experimental parameters, the proposed sensor exhibited good linear responses to piroxicam concentrations ranging from 0.1 to 500 μM. The detection limit and sensitivity were calculated as 1.8 nM and 0.2 μA/μM·cm2, respectively. Moreover, it offered excellent selectivity, reproducibility, and long-term stability and can effectively ignore the interfering candidates commonly existing in the pharmaceutical tablets and human fluids even at a higher concentration. Finally, the reported sensor was successfully employed to the direct determination of piroxicam in practical samples.

A novel isatin-based probe for ratiometric and selective detection of Hg2+ and Cu2+ ions present in aqueous and environmental samples

A novel isatin derivative (1) is UV-Visible active and displays about 90 nm bathochromic shift upon interaction with only Hg²⁺ and Cu²⁺, but not with other common metal ions. Also, the colorless probe 1 turns to brick-red and yellow in the presence of Hg²⁺ and Cu²⁺, respectively. Addition of increasing amounts of Hg²⁺ or Cu²⁺ to 1 leads to the emergence of a new absorption at ~470 nm (due to LMCT), with a concomitant decrease in the intensity of absorption of 1 at ~380 nm, and thereby provides a ratiometric response. Common metal ions and anions do not interfere with the interactions of 1 with Hg²⁺or Cu²⁺ ions. Probe 1 shows very high sensitivity and selectivity towards Hg²⁺ and Cu²⁺ as revealed by their very low detection limits 0.95 × 10^-9 M and 1.5 × 10^-9 M, respectively. Formation of 1:1 complex with Hg²⁺ and 2:1 complex with Cu²⁺ is confirmed using NMR, ESI-MS and FT-IR techniques, Job plot and DFT calculations. Selective detection of Hg²⁺ from Cu²⁺ is established from the ratiometric response caused by β-mercaptoethanol. Advantages of the probe 1 in terms of high sensitivity, stability in the physiological pH and suitability for dual detection are presented. Probe impregnated silica plates for onsite detection of Hg²⁺ and Cu²⁺ present in environmental samples is also demonstrated.

Ultra sensitive detection of Cd (II) using reduced graphene oxide/carboxymethyl cellulose/glutathione modified electrode

The present work describes the electrochemical detection of Cd²⁺ using reduced graphene oxide (rGO), carboxymethyl cellulose (CMC) and glutathione (GSH) modified glassy carbon electrode (GCE) by Square Wave Anodic Stripping Voltammetry (SWASV). The prepared nanocomposite was characterized by X-ray diffraction (XRD), RAMAN, Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR) and X-ray photoelectron spectroscopy (XPS), Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). The influence of experimental parameters such as effect of pH, choice of supporting electrolyte, deposition time and deposition potential, were optimized. Under the optimized conditions, the linear relationship between the current intensity and Cd²⁺ concentration (2-20 nM) was I (μA) = -6.78 (c/nM) + 4.547 (R² = 0.996). The detection limit and sensitivity achieved for the modified electrode were 0.05 nM and 4.5 μA/nM respectively. Finally, rGO/CMC/GSH/GCE was successfully demonstrated for the detection of Cd²⁺ in real samples, and the results were compared with AAS analysis.

Ethyl 7-oxo-3,5-diphenyl-1,4-diazepane-2-carboxyl-ate

The title compound, C₂₀H₂₂N₂O₃, crystallizes with two independent mol­ecules in the asymmetric unit. In both mol­ecules, the diazepane rings adopt chair conformations. The mean planes of the diazepane rings in the two molecules form dihedral angles of 71.6 (4)/40.3 (5) and 75.9 (5)/58.6 (7)° with the neighbouring benzene rings. The carbonyl-group O atoms deviate significantly from the diazepane rings, by 0.685 (14) and 0.498 (13) Å. The eth­oxy­carbonyl groups show conformational difference between two mol­ecules, as reflected in the orientation of the carbonyl O atoms and the C—C—O—C torsion angle of −179.0 (2)° in one mol­ecule and 73.2 (2)° in the other. In one molecule there is a short N—H⋯O contact that generates an S(5) ring motif. In the crystal, N—H⋯O inter­actions generate R₂²(8) graph-set motifs and C—H⋯O inter­actions generate R₂²(10) and R₂²(14) graph-set motifs. C—H⋯π inter­actions also occur.

Ethyl 2-(7-oxo-3,5-diphenyl-1,4-diazepan-2-yl)acetate

In the title compound, C21H24N2O3, the diazepane ring adopts a chair conformation. The central diazepane ring forms dihedral angles 67.80 (7) and 72.29 (5)° with the two benzene rings. The ethoxycarbonyl group is disordered over two conformations with site-occupancy factors of 0.643 (5) and 0.357 (5). In the crystal, inversion dimers linked by pairs of N—H...O hydrogen bonds generateR22(8) loops.

Cloning and sequencing of Indian water buffalo (Bubalus bubalis) interleukin-3 cDNA

Full-length cDNA (435 bp) of the interleukin-3(IL-3) gene of the Indian water buffalo was amplified by reverse transcriptase-polymerase chain reaction and sequenced. This sequence had 96% nucleotide identity and 92% amino acid identity with bovine IL-3. There are 10 amino acid substitutions in buffalo compared with that of bovine. The amino acid sequence of buffalo IL-3 also showed very high identity with that of other ruminants, indicating functional cross-reactivity. Structural homology modelling of buffalo IL-3 protein with human IL-3 showed the presence of five helical structures.

N-[1-(5-Acetamido-3-acetyl-2-methyl-2,3-dihydro-1,3,4-thia-diazol-2-yl)-2-phenyl-ethyl]acetamide

In the title compound, C(17)H(22)N(4)O(3)S, the dihedral angle between the planes of the thia-diazole and phenyl rings is 63.47 (7)°. The dihedral angle between the thia-diazole ring and the acetamide side chain is 7.72 (9)°. Mol-ecules related by a 2(1) screw axis along the a axis are linked by inter-molecular N-H⋯O hydrogen bonds generating a supra-molecular chain.

5-[Acetamido(phenyl)methyl]-5-methylimidazolidine-2,4-dione

The title compound, alternatively named N-[(4-methyl-2,5-dioxoimidazolidin-4-yl)(phenyl)methyl]acetamide, C(13)H(15)N(3)O(3), crystallizes in the centrosymmetric space group P2(1)/c with one molocule in the asymmetric unit. The imidazolidine-2,4-dione system is essentially planar, as evidenced by NMR studies. The dihedral angle between the planes of the imidazolidine and phenyl rings is 23.3 (1) degrees, while the dihedral angle between the acetamide side chain and the imidazolidine ring is 60.7 (1) degrees. The molecular structure and packing is stabilized by C-H.O and N-H.O interactions. Intermolecular hydrogen bonds form cyclic dimers, with graph-set descriptor R(2)(2)(8), and a chain of C(7).

An Efficient Preparation of 1,2-Diamino-1-phenylheptane

A convenient four-step method for the preparation of the lipophilic vicinal diamine 1,2-diamino-1-phenylheptane is described. Condensation involving octan-2-one, benzaldehyde and ammonia is reported. Regioselective Schmidt rearrangement of 2,6-diphenyl-3-pentyl-piperidin-4-one (1) to 2,7-diphenyl-3-pentyl hexahydrodiazapin-5-one (3) is presented. Hydrolysis of 2,7-diphenyl-3-pentyl hexahydrodiazapin-5-one to 1,2-diamino-1-phenylheptane (4) is also reported for the first time.

Effects of salt and denaturant on structure of the amino terminal alpha-helical segment of an antibacterial peptide dermaseptin and its binding to model membranes

The amino terminal 1-18 domain of dermaseptin s is an important determinant of its structure as well as the antibacterial activity. A thorough investigation on the structure of the 18-residue peptide (D18) and its binding to model membranes in presence of salt and denaturant guanidinium chloride has been carried out. In presence of salt, there is an increase in the fraction of peptide molecules in helical conformation. In presence of the denaturant, D18 is unordered, but addition of the structure-promoting solvent trifluoroethanol results in a transition to the helical conformation. In presence of denaturant, the peptide is unordered, but binding to lipid vesicles is not abolished. Investigation of model membrane permeabilizing ability of the peptide in solutions containing various proportions of sodium chloride and guanidinium chloride indicates that vesicle permeabilization parallels extent of binding. The peptide thus binds to lipid vesicles in an unfolded state. Since the peptide has propensity to fold into a helical conformation, lipid induced transition to a helical structure occurs, followed by membrane permeabilization as a result of pore formation.

Synthetic peptides corresponding to the beta-hairpin loop of rabbit defensin NP-2 show antimicrobial activity

Mammalian defensins, a class of antibacterial peptides, are composed of 29-35 amino acids with six cysteines which form three disulfide bonds. Structural studies indicate a triple stranded beta-sheet structure with a well defined beta-hairpin loop at the C-terminal region. It is demonstrated in this report that 18 and 26 residue synthetic peptides corresponding to the beta-hairpin region, constrained by a single disulfide bond, have potent antimicrobial activity without hemolytic activity. Circular dichroism spectroscopy indicates that the single S-S bridge appears to constrain the peptides to a beta-structure. Peptides corresponding to the beta-hairpin region of defensins could thus be attractive candidates as therapeutic agents as well as good model compounds for investigation of the various physiological actions of defensins.

Solution conformations of peptides representing the sequence of the toxin pardaxin and analogues in trifluoroethanol-water mixtures: analysis of CD spectra

The cytolytic activities and conformational properties of pardaxin (GFFALIPKIISSPLFKTLLSAVGSALSSSGEQE), a 33-residue linear peptide that exhibits unusual shark repellent and cytolytic activities, and its analogues have been examined in aqueous environment and trifluoroethanol (TFE) using CD spectroscopy. A peptide corresponding to the 1-26 segment and an analogue where P7 has been changed to A show greater hemolytic activity than pardaxin. While the peptide corresponding to the N-terminal 18-residue segment does not exhibit hemolytic activity, its analogue where P7 is replaced by A is hemolytic. The secondary structural propensities of the peptides were inferred by deconvolution of the experimental spectra into pure components. Pardaxin, its variant where proline at position 7 was replaced by alanine, and shorter peptides corresponding to N-terminal segments exist in multiple conformations in aqueous medium that are comprised of beta-turn, beta-sheet, and distorted helical structures. With increasing proportions of TFE, while helical conformation predominates in all the peptides, both distorted and the regular alpha-helices appear to be populated. Analysis of CD spectra by deconvolution methods appears to be a powerful tool for delineating multiple conformations in peptides, especially membrane-active peptides that encounter media of different polarity ranging from aqueous environment to one of low dielectric constant in the hydrophobic interior of membranes. Our study provides further insights into the structural requirements for the biological activity of pardaxin and related peptides.

Specific antimicrobial and hemolytic activities of 18-residue peptides derived from the amino terminal region of the toxin pardaxin

Peptides are part of the host defense system against bacteria and fungi in species right across the evolutionary scale. However, endogenous antibacterial peptides are often composed of 25 residues or more and, therefore, are not ideal for therapeutic use. Hence it is of considerable interest to design and engineer short peptides having antimicrobial activity. Peptides composed of 18 amino acids, derived from the N-terminal region of the 33-residue toxin pardaxin (PX), GFFALIPKIISSPLFKTLLSAVGSALSSSGEQE, were synthesized and examined for biological activities. Peptide corresponding to the 1-18 stretch of PX exhibited antimicrobial activity only against Escherichia coli and not against Gram-positive microorganisms. The peptide also did not possess hemolytic activity. Replacement of P7 by A resulted in a peptide possessing both antibacterial and hemolytic activity. Substitution of both K residues by Q in the 'A' analog resulted in a peptide having only hemolytic activity. Conformational analysis of these peptides and investigation of their model membrane permeabilizing activities indicated that selective activity can be explained by their biophysical properties. Hence, by a rational design approach based on biophysical principles, it should be possible to generate short peptides having specific biological activity.

Granulocytes from chronic myeloid leukemia (CML) patients show differential response to different chemoattractants

Binding of chemoattractant to polymorphonuclear leukocytes (PMNL) triggers a series of events like polymerization of actin and tubulin, orientation of cells, chemotaxis, increase in fluid pinocytosis and phagocytosis, and stimulation of microbicidal pathways which includes lysosomal degranulation and generation of reactive oxygen species. Earlier studies from our laboratory have shown that stimulation of chemotaxis, fluid pinocytosis, and actin polymerization of CML PMNL in response to a synthetic chemotactic peptide formyl-methionyl-leucyl-phenylalanine (fMLP) is significantly lower than that in normal PMNL. It is not known whether this lower response of CML PMNL to fMLP is a global phenomenon involving different chemoattractant receptors or is restricted to the fMLP pathway. We have evaluated chemoattractant induced degranulation process in normal and CML PMNL to fMLP, platelet activating factor (PAF), leukotriene B4 (LTB4), and an analogue of fMLP viz formyl-methionine-1 aminocyclooctane 1 carboxylic acid-phenylalanine-O-methionine (FACC8) using release of lysozyme as a parameter. We find that after stimulation with fMLP and FACC8, the mean percent release of lysozyme was significantly lower in CML PMNL as compared to that in normal cells (P < 0.001). There was no significant difference between the two after stimulation with PAF and LTB4. The results indicate that the fMLP pathway is suppressed in CML granulocytes whereas PAF and LTB4 pathways appear unaltered in these cells. We therefore also studied the kinetics of peptide-receptor interaction with a labelled hexapeptide fNLPNTL which binds to the fMLP receptor. Our results show that the number of fMLP receptors/cell is significantly lower in CML PMNL (P < 0.05) than in normal PMNL, while their affinity constants and dissociation constants were comparable.

Design of 16-residue peptides possessing antimicrobial and hemolytic activities or only antimicrobial activity from an inactive peptide

We have explored the possibility of generating peptides having antimicrobial and hemolytic activities or only antimicrobial activity, from a 16-residue peptide, GFFALIPKIISSPLFK, corresponding to the N-terminal region of the toxin pardaxin. This peptide does not exibit these activities, although it can permeabilize model membranes. Peptides were synthesized wherein either A4 or P7 were substituted by K and S11 replaced by K. Peptides in which P7 and S11 were replaced with K, (AK) and A4 and S11 replaced with K and A instead of P at position 7, (KA) showed potent antimicrobial and hemolytic activities. However, the peptide where S11 and A4 were replaced with K, (KP) showed pronounced antimicrobial activity with very weak hemolytic activity. Circular dichroism studies indicated that peptides AK and KA had a strong propensity to occur in a helical conformation, whereas KP did not. Peptides AK and KA were very effective in permeabilizing model membranes, whereas KP was relatively ineffective. Our studies thus suggest the requirements for a peptide to have only antimicrobial activity and also that selectivity in activity can be rationalized on the basis of biophysical principles. Thus, by judicious positioning of amino acids, especially positively charged ones, it should be possible to generate biologically active peptides without taking recourse to a combinatorial approach.