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Tetranuclear copper(II) complexes are of paramount importance in structural biology, and they are potential materials for magnetism and catalysis. To develop such a system, a new 6-aminoazouracil ligand, 1,3-dimethyl-5-(o-phenolate-azo)-6-aminouracil (H2L, 1) with a NuNaO (Nu, uracil-N and Na, azo-N) chromophore was synthesized and used to generate a noble discrete doubly opened Cu4O4 cubane-like cluster ([CuL]4·2H2O, 2.2H2O) for studying magnetism. The coordination environment of Cu(II) is distorted square planar linked through phenolate-μ2-O bridges. The ligand crystallizes in the monoclinic space group P121/c1 and the complex is in the tetragonal I41/a space group with an S4 symmetry. The ligand has two dissociable hydrogen atoms in the solution with pK1 4.91 (hydrazone proton) and pK2 9.68 (phenolic proton). In the solid state, the ligand exhibits displaced stacking (energy, −69.5 and −77.3 kJ mol−1 for the molecules A and B, respectively) and tetrel bonding interactions (energy, −43.8 kJ mol−1). In 2.2H2O, the symmetrical units are stacked to show weak noncovalent interactions. The magnetic property of 2.2H2O was investigated based on the cubane [Cu4O4] core and discussed in detail, resulting in the exchange coupling parameter [(J1 (short Cu⋯Cu distances) = −110.1(1) cm−1, J2 (long Cu⋯Cu distances) = −27.1(2) cm−1)] that indicate a strong antiferromagnetic interaction between tetranuclear copper(II) ions through μ-phenolate linkers, which is a result of the interaction of dx2−y2 orbitals in the square plane. The EPR study is concomitant with the results of magnetism. Thus, it could be a potential material in the field of antiferromagnetic spintronics as well. [ABSTRACT FROM AUTHOR]

Three new coordination polymers, [NaI(H2L)(H2O)3]n (1), {[KI(H2L)(H2O)]8·13H2O}n (2), and {[NiIINaI2(HL)2(H2O)8]·6H2O}n (3), were assembled from 1,3-dimethyl-5-(p-sulfonic-phenylazo)-6-aminouracil (H3L) as a versatile building block. Although azo-coupling reactions generally result in simple azo-compounds, the presence of the sulfonate (–SO3−) group at the ligand frame led to the formation of the NaI-1D (1) or KI-3D (2) homometallic coordination polymer with different ligand coordination modes. Moreover, the heterometallic NiII/NaI-1D (3) coordination polymer was obtained while carrying the reaction of 2 with NiCl2·6H2O. The structures of the obtained products were fully established by single crystal X-ray diffraction and confirmed by standard methods. Compounds 1 and 3 possess 1D metal–organic chains with the 2C1 topology, whereas 2 features a very complex 3D metal–organic architecture with an unprecedented topology. The computational study for molecular electrostatic potential (MEP) surface energies revealed an important finding, namely a decrease of the π-acidity of the uracil ring upon coordination and a consequent increase of the π-basicity of the phenyl-sulfonate ring, resulting in effective anti-parallel π–π stacking interactions in 1 and 2. Finally, a semi-conductive behavior of the obtained compounds was explored using impedance spectroscopy, revealing the very remarkable conductive properties of 1 (2.2 × 10−4 S cm−1), which is a far better conductive material than 2 (7.2 × 10−6 S cm−1) and 3 (4.8 × 10−7 S cm−1). The obtained products represent the first coordination compounds derived from H3L. This study contributes to the design of functional coordination polymers driven by still poorly explored 6-aminouracil building blocks. [ABSTRACT FROM AUTHOR]

Graphical abstract Two new 1D coordination polymers were assembled and fully characterized; their structural, spectroscopic, magnetic, theoretical and antimicrobial features are discussed in detail. Highlights • Base assisted tuning of coordination polymer. • Structures and C/H-Ni(II) Agostic interaction. • Disaggregation of polymeric structures in solution. • Zero-field splitting effect on Ni(II)-magnetism. • Potential pyocyanin production inhibitor. Abstract A new azo-ligand, 1,3-dimethyl-5-(p -carboxy-phenylazo)-6-aminouracil (H 3 L) containing 6-aminouracil (a biomolecule) and a carboxylic function (a potential linker) was synthesized. This ligand was then employed for complexation with Ni(II), resulting in the Ni(II)/Na(I) heterometallic {[NiNa 2 (μ-HL) 2 (μ-H 2 O) 2 (H 2 O) 6 ]·6H 2 O} n (1) and Ni(II) homometallic {[Ni 2 (μ-HL) 2 (H 2 O) 4 ]·5·.5H 2 O} n (2) 1D coordination polymers. These were obtained from similar reaction mixtures and conditions, except the type of the base (NaOH for 1 or KOH/Et 3 N for 2). Compounds 1 and 2 were characterized by single-crystal X-ray diffraction, UV-vis, NMR, and IR spectroscopy. Both the coordination polymers 1 and 2 show resembling zigzag chains that are topologically classified as 2-connected underlying nets with the 2C1 topology. In 1 , the 1D metal-organic chains are further extended by intermolecular H-bonds, giving rise to a 3D H-bonded net; it is topologically described as a uninodal 6-connected net with the pcu topology. In solution, the 1D polymeric structures of both compounds disaggregate into monomeric Ni(II)-square-planar complex units [Ni(HL) 2 ]2−, as evidenced by NMR and UV-vis spectroscopy studies. The magnetic properties of 2 were also investigated, indicating a dominant zero field splitting parameter D of the Ni(II) center. The type of the base is important for tuning the selective formation of the desired product 1 or 2. Density functional theory (DFT) study justifies the experimental findings for a base-assisted selectivity between the compounds 1 or 2 by optimizing their structures at the PBE-D/DNP level of theory. The existence of agostic interactions between the C H bonds of the methyl groups of the coordinated HL2− moieties and the Ni centers in both structures is suggested by natural bond orbital (NBO) calculations at the M06-2X/6-31 + G∗ level of theory. The compound 1 proves to be a potential inhibitor of a bacterial virulence factor, pyocyanin. [ABSTRACT FROM AUTHOR]

N -(1-Naphthly)ethylenediammonium cations (NEDA 2 + ) stabilized silver nanoparticles (NEDA-Ag-NPs) were synthesized and explored their potential use for a chemo-sensor probe. The NEDA 2 + cations being fluorescent active make the particles functionalized as well. They physically adsorb (adsorption constant (K ads ), 2.65 × 10 9 M − 1 ) onto the surface of Ag-NPs and make them cationic with zeta potential value of 23 ± 2 mV. TEM image shows that particles are indeed spherical in shape. Monitoring SPR band (extinction coefficient (ε), 5.3 × 10 8 M − 1 cm − 1 ) the potencies of particles for sensing pH and citrate anions have been explored. The citrate anions interact with the surface adsorbed NEDA 2 + cations and form association complex, NEDA 2 + ‐‐‐citrate 3‐ , leading aggregation which is a kinetic effect. The aggregation kinetics was thus monitored for evaluating the association constant (K asso ) by studying UV–vis and fluorescence spectroscopic tools. The critical coagulation concentrations (CCC) for both the methods are considered to be the detection limit for citrate anions. [ABSTRACT FROM AUTHOR]

The (arylazo-6-aminouracil)nickel(II) derivatives [NiII(DMA3U)2] [HDMA3U = 1,3-dimethyl-5-(arylazo)-6-aminouracil; arylazo = phenylazo ( 1), p-Me-phenylazo ( 2), p-Cl-phenylazo ( 3)] have been synthesized and isolated in crystalline form. Single-crystal X-ray diffraction study of [Ni( 1)2] reveals that, in the complex, the metal center has a square-planar environment. The intramolecular N-H/π and C-H/π interactions hold in the solid state as well as in poor hydrogen-bond acceptor (HBA) solvents, but are disrupted in good HBA solvents. Crystal-structure analysis further shows that the NH groups of the coordinated ligands are not available for hydrogen-bonding interactions in the solid state, and this conclusion is corroborated by DFT calculations. Complexes exhibit multiple absorption bands in the UV/Vis region and TDDFT studies were performed to understand the origin of the ground-state electronic absorptions. The complexes exhibit intense emission spectra in poor HBA solvents rather than in good HBA solvents. The association constant ( Kasso) values for complex HBA solvents, which were determined UV/Vis spectrophotometrically, range from 1.18 to 2.51 m-1. [ABSTRACT FROM AUTHOR]

In this report, we have studied the recognition of citrate anions adsorbed on the surface of silver nanoparticles (cit-Ag-NPs), by macrocyclic polyammonium cations (MCPACs): Me6[14]ane-N4H84+ (Tet-A/Tet-B cations) and [32]ane-N8H168+, which are well reputed anion recognizers and are treated as to mimic of biological polyamines. The study was monitored on ultraviolet-visible spectroscopy by performing a titration of the aqueous dispersion of the cit-Ag-NPs by the aqueous solution of MCPACs. The ultraviolet-visible time-scan plots over the reduction of the absorption band of surface plasmon resonance of cit-Ag-NPs at 390 nm are well fitted with fourth-order polynomial equation and are employed to determine the initial aggregation rate constants. It has been stated that the aggregation is the result in electrostatic attraction followed by H-bond formation between the surface-adsorbed citrate anions and added MCPACs. The atomic force microscopy results have evidenced aggregation of cit-Ag-NPs in presence of MCPACs. The evaluated H-bonded association constant (Kasso) using Benesi-Hildebrand method reveals that [32]ane-N8H168+ cations form stronger association complex, as expected, with the citrate anions than the Me6[14]ane-N4H84+ cations. The study would thus provide the insight of molecular interactions involved in nanoparticle surface-adsorbed anions with biological polyamines. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The study of inter-conversion between molecules, especially biologically and pharmaceutically important molecules, is extremely important. This study reports the inter-conversion between two azo-derivtives: azo-6-aminouracils to azo-barbituric acids. We successfully converted the 1,3-dimethyl-5-(arylazo)-6-aminouracils ( Uazo-1 to Uazo-4) to 1,3-dimethyl-5-(arylazo)-barbituric acids ( BAazo-1 to BAazo-4) (where aryl⇒C6H5-( 1); p-MeC6H4-( 2), p-ClC6H4-( 3), and p-NO2C6H4-( 4)) following an acid-hydrolysis path. The products were characterized using spectroscopic tools like UV-vis, IR, and NMR spectroscopy. UV-vis spectra of the as-prepared dyes reveal that in contrast to the azo-6-aminouracils they are hardly responsive towards solvatochromism. IR spectra exhibit three characteristic >CO frequencies for as-prepared azobarbituric acids instead of two for mother azo-6-aminouracils. 1H NMR spectra which reflect the existence of solution species evidence the absence of >CNH group (characteristic imido-H at the 6-position of hydrazone species of azo-6-aminouracils) and consequence presence of >CO group at the same position in as-prepared azobarbituric acids. They exhibit structural emissions in the range of 400-440 nm upon excitation at 360 nm. The determined acid dissociation constant (pKa) values of BAazos increase according to the following sequence: BAazo- 2> 1> 3> 4. [ABSTRACT FROM AUTHOR]

Some of our group recently demonstrated combining theory and a statistical survey of the Cambridge Structural Database (CSD) that the interaction between the π-holes of nitro groups and electron-rich atoms is somewhat directional (Chem. Commun., 2015, 51, 1491–1493). In this communication, we present a joint experimental and theoretical study on a novel cadmium(ii) complex, [Cd(C7H3N2O6)2(C12H8N2)2]·H2O·DMF (1) [where C7H4N2O6 = 3,5-dinitrobenzoic acid and C12H8N2 = 1,10-phenanthroline] to unravel the important role of this π-hole interaction. [ABSTRACT FROM AUTHOR]