Interactions of glutathione tripeptide with gold cluster: influence of intramolecular hydrogen bond on complexation behavior

Understanding the nature of the interaction between metal nanoparticles and biomolecules has been important in the development and design of sensors. In this paper, structural, electronic, and bonding properties of the neutral and anionic forms of glutathione tripeptide (GSH) complexes with a Au(3) cluster were studied using the DFT-B3LYP with 6-31+G**-LANL2DZ mixed basis set. Binding of glutathione with the gold cluster is governed by two different kinds of interactions: Au-X (X = N, O, and S) anchoring bond and Au···H-X nonconventional hydrogen bonding. The influence of the intramolecular hydrogen bonding of glutathione on the interaction of this peptide with the gold cluster has been investigated. To gain insight on the role of intramolecular hydrogen bonding on Au-GSH interaction, we compared interaction energies of Au-GSH complexes with those of cystein and glycine components. Our results demonstrated that, in spite of the ability of cystein to form highly stable metal-sulfide interaction, complexation behavior of glutathione is governed by its intramolecular backbone hydrogen bonding. The quantum theory of atom in molecule (QTAIM) and natural bond orbital analysis (NBO) have also been applied to interpret the nature of interactions in Au-GSH complexes. Finally, conformational flexibility of glutathione during complexation with the Au(3) cluster was investigated by means of monitoring Ramachandran angles.     

Does gold cluster promote or scavenge radicals? A controversy at DFT

Anticancer character of gold cluster has been indicated through its free radical scavenging properties. This is in contrast to its free radical promoting ability suggested by other workers. Here, we address this controversy by probing the stabilizing effects of Au₃ cluster on RO^? vs its impacts on RO–H bond dissociation enthalpy, at B3LYP/ LACVP+* level (R═H, methyl, ethyl, n‐propyl, i‐propyl, n‐butyl, t‐butyl, and phenyl). In the presence of Au₃ cluster, bond dissociation enthalpy of O–H bond and the spin density at the RO^? oxygen are reduced dramatically. These are clear evidences for both the Au₃ facilitation of the RO–H bond breakage and its scavenging of RO^? radical. Since O–Au anchoring bond is responsible for the interaction of Au₃ cluster and ROH (or RO^?), its nature was interpreted by means of the quantum theory of atoms in molecules and the natural bond orbital. The results indicate that O–Au bond is stronger and has more covalent character in RO^?–Au₃ than in ROH–Au₃. The interaction of Au₃ cluster with RO^? is 1.5 to 3 times more than that with ROH. As a result, gold cluster scavenging property appears more prominent than its free radical initiation activity.     

DNA as a Target for Anticancer Phen-Imidazole Pd(II) Complexes

Imidazole ring is a known structure in many natural or synthetic drug molecules and its metal complexes can interact with DNA and do the cleavage. Hence, to study the influence of the structure and size of the ligand on biological behavior of metal complexes, two water-soluble Pd(II) complexes of phen and FIP ligands (where phen is 1,10-phenanthroline and FIP is 2-(Furan-2-yl)-1H–Imidazo[4,5-f][1, 10]phenanthroline) with the formula of [Pd(phen)(FIP)](NO₃)₂ and [Pd(FIP)₂]Cl₂, that were activated against chronic myelogenous leukemia cell line, K562, were selected. Also, the interaction of these anticancer Pd(II) complexes with highly polymerized calf thymus DNA was extensively studied by means of electronic absorption, fluorescence, and circular dichroism in Tris-buffer. The results showed that the binding was positive cooperation and [Pd(phen)(FIP)](NO₃)₂ (K _f = 127 M^-1 G = 1.2) exhibited higher binding constant and number of binding sites than [Pd(FIP)₂]Cl₂ (K _f = 13 M^-1 G = 1.03) upon binding to DNA. The fluorescence data indicates that quenching effect for [Pd(phen)(FIP)](NO₃)₂ (K _SV = 58 mM^?1) was higher than [Pd(FIP)₂]Cl₂ (K _SV = 12 mM^?1). Also, [Pd(FIP)₂]Cl₂ interacts with ethidium bromide-DNA, as non-competitive inhibition, and can bind to DNA via groove binding and [Pd(phen)(FIP)](NO₃)₂ can intercalate in DNA. These results were confirmed by circular dichroism spectra. Docking data revealed that longer complexes have higher interaction energy and bind to DNA via groove binding.

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Graphical Abstract Two anticancer Pd(II) complexes of imidazole derivative have been synthesized and interacted with calf thymus DNA. Modes of binding have been studied by electronic absorption, fluorescence, and CD measurements. [Pd(FIP)₂]Cl₂ can bind to DNA via groove binding while intercalation mode of binding is observed for [Pd(phen)(FIP)](NO₃)₂.

     

Improving activity of anticancer oxalipalladium analog by the modification of oxalate group with isopentylglycine

In this article, we describe the influence of structure on biological behavior of amino acid-Pd complex and compare it with oxalipalladium. A new water-soluble oxalipalladium analog with formula of [Pd(DACH)(isopentylgly)](NO₃), where DACH is 1R,2R-diaminocyclohexane, has been synthesized and characterized by elemental analysis, conductivity measurements, IR, UV–Vis, and ¹H NMR spectroscopies. The interactions of oxalipalladium and its amino acid derivative with highly polymerized calf-thymus DNA have been extensively studied by spectroscopic methods. The high binding constants of oxalipalladium (0.38 × 10⁴ M^?1) and new amino acid-Pd complex (0.65 × 10⁴ M^?1) were determined using absorption measurements. Also circular dichroism (CD) studies show that Pd complex causes more disturbances on DNA structure rather than oxalipalladium. The experimental results proposed that [Pd(DACH)(isopentylgly)](NO₃) is bound to DNA by groove-binding mode as well as partially covalent interaction, while oxalate analog binds covalently to DNA after hydrolysis. Interaction of the two metal derivative complexes was studied by molecular docking simulation. The results showed that amino acid-Pd complex has higher negative docking energy and higher tendency for interaction with DNA, and exert more structural change on DNA. Finally, the anticancer and growth inhibitory activities of synthesized complexes were investigated against human colon cancer cell line of HCT116 after 24 h incubation time using MTT assay. Results show that the complex [Pd(DACH)(isopentylgly)](NO₃) showed enhanced anticancer and growth inhibitory activities against human colon can cell line HCT116.     

Efficient Acetylation of Alcohols,Phenols, and Amines Catalyzed by Melamine Trisulfonic Acid (MTSA)

Melamine trisulfonic acid (MTSA) was easily prepared by the reaction of melamine with neat chlorosulfonic acid at room temperature. This reagent can be used as an efficient catalyst for the acetylation of alcohols, phenols, and amines with Ac₂O under mild and completely heterogeneous reaction conditions.     

Synthesis of Mn3O4 Nanorods by Solid-State Thermal Decomposition of Manganese(III) Schiff Base Complex [Mn(Brsal-mepn)(μ1,3-N3)]n

Hausmannite Mn₃O₄ nanorods were successfully prepared via solid-state thermal decomposition route with manganese(III) Schiff base complex [Mn(Brsal-mepn)(μ_1,3-N₃)]_n as manganese source in air at 400 °C for 4 h. Powder X-ray diffraction, Fourier transform infrared spectrometry and scanning electron microscopy were used to characterize Mn₃O₄ nanoparticles. These results confirm that the resulting manganese oxide was pure single-phase Mn₃O₄ nanoparticles. Using the present method, Mn₃O₄ nanorods can be product without expensive organic solvent and complicated equipment.     

Wells–Dawson tungsten heteropolyacid-catalyzed reactions of benzylic alcohols, influence of the structure of the substrate

Heterolytic cleavage of the C–OH bond of various benzylic alcohols has been catalyzed with H₆P₂W₁₈O₆₂. Alkenes or symmetric ethers are produced, depending on the structure of the substrate.     

Diminishing vortex intensity and improving heat transfer by applying magnetic field on an injectable slip microchannel containing FMWNT/water nanofluid

In this study, heat transfer and entropy generation were investigated in a microchannel containing FMWNT/water nanofluids given the slip condition. The main focus was on utilizing injection technique in the presence of the magnetic field. The injection from the upper high-temperature wall was incorporated into the flow field. Injection at high Reynolds number causes vortex formation, which ultimately reduces local heat transfer in the adjacent injection zone. By applying the magnetic field, the vortex intensity as well as boundary layer thickness was diminished which in turn improved the heat transfer. Based on numerical results, at higher nanoparticle volume fraction, the effect of the magnetic field on heat transfer enhancement was amplified. Moreover, at higher Reynolds numbers, the magnetic field efficacy is more obvious. The highest heat transfer occurred at the highest values of the Hartmann and Reynolds numbers and eventually the nanoparticle volume fraction. Owing to applying the magnetic field on the injectable microchannel containing nanofluid, heat transfer improvement can reach up to 79%. From the second law prospective, the entropy generation intensified by 82.8%.