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The azo-derivative, 1,3-dimethyl-5-(p-sulfonamide-phenylazo)-6-aminouracil (HL) containing 6-aminouracil (a biomolecule) and sulfonamide functionality (commonly found in sulfa-drugs), and its Ni(II) complex, NiIIL2 were synthesized. Single-crystal X-ray diffraction studies show that the ligand (HL) consists of an E conformation about the azo-linkage with a nearly planar geometry and the complex possesses distorted square planar geometry. The H-bonded underlying networks of HL and NiIIL2 were topologically classified revealing distinct topological types, namely tts and hxl, respectively. Moreover, topology of molecular packings in HL and NiIIL2 has also been discussed. Density functional theory (DFT) calculations, at the M06-2X/def2TZVP level of theory, are employed to characterize a great variety of non-covalent interactions that explicitly show the importance of antiparallel stacking interactions established by π−–π+ interactions and H-bonds in the self-assembled dimmers in HL and lp–π/C–H⋯π interactions in NiIIL2. The results of NMR and UV–vis spectroscopies evidence that the ligand exists in hydrazone-imine-keto (B) tautomeric form in solution. The ligand absorption bands consist of the overlapping bands of π→π* and n→π* transitions. The complex experiences electronic transitions that consist of basically ILCT in character with some sort of participation of the atomic d-orbitals of the nickel. The pKa value of the ligand is found to be 4.09. © 2017 Elsevier B.V.

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Journal of Molecular Structure

Synthesis and structure of 1,3-dimethyl-5-(p-sulfonamide-phenylazo)-6-aminouracil and its Ni(II) complex: Topological insights and investigation for noncovalent interactions

In this study, unique methyl-functionalized derivatives (T∗PP+) of the drug carrier triphenylphosphonium (TPP+) that exhibit significant enhancement of the accumulation of both the cation and its conjugated cargo in cell mitochondria are designed. We show that the presence of methyl group(s) at key positions within the phenyl ring results in an increase in the hydrophobicity and solvent accessible surface area of T∗PP+. In particular, when the para position of the phenyl ring in T∗PP+ is functionalized with a methyl group, the cation is most exposed to the surrounding environment, leading to a large decrease in water entropy and an increase in the level of van der Waals interaction with and partition into a nonpolar solvent. Therefore, stronger binding between the hydrophobic T∗PP+ and mitochondrial membrane occurs. This is exemplified in a (hexachloro-fluorescein)-TPP+ conjugate system, where an ∼12 times increase in the rate of mitochondrial uptake and a 2 times increase in photodynamic therapy (PDT) efficacy against HeLa and FU97 cancer cells are achieved when TPP+ is replaced with T∗PP+. Importantly, nearly all the FU97 cells treated with the (hexachloro-fluorescein)-T∗PP+ conjugate are killed as compared to only half the population of cells in the case of the (hexachloro-fluorescein)-TPP+ conjugate at a similar PDT light dosage. This study thus forms a platform for the healthcare community to explore alternative TPP+ derivatives that can act as optimal drug transporters for enhanced mitochondrially targeted therapies. © 2017 American Chemical Society.

Bioconjugate Chemistry

Unique Triphenylphosphonium Derivatives for Enhanced Mitochondrial Uptake and Photodynamic Therapy

In this work, strategic enhancement of electrophilicity of phosphenium cations for the purpose of small-molecule activation was described. Our synthetic methodology for generation of novel two-coordinate phosphorus(III)-based compounds [{C6H4(MeN)2C}2C·PR]2+ ([2a]2+, R = NiPr2; [2b]2+, R = Ph) was based on the exceptional electron-donating properties of the carbodicarbene ligand (CDC). The effects of P-centered substituent exchange and increase in the overall positive charge on small substrate activation were comparatively determined by incorporating the bis(amino)phosphenium ion [(iPr2N)2P]+ ([1]+) in this study. Implemented structural and electronic modifications of phosphenium salts were computationally verified and subsequently confirmed by isolation and characterization of the corresponding E-H (E = B, Si, C) bond activation products. While both phosphenium mono- and dications oxidatively inserted/cleaved the B-H bond of Lewis base stabilized boranes, the increased electrophilicity of doubly charged species also afforded the activation of significantly less hydridic Si-H and C-H bonds. The preference of [2a]2+ and [2b]2+ to abstract the hydride rather than to insert into the corresponding bond of silanes, as well as the formation of the carbodicarbene-stabilized parent phosphenium ion [{C6H4(MeN)2C}2C·PH2]+ ([2·PH2]+) were experimentally validated. © 2017 American Chemical Society.

Inorganic Chemistry

E-H (E = B, Si, C) Bond Activation by Tuning Structural and Electronic Properties of Phosphenium Cations

Abstract: Nickel(II) complex, [NiII(L)2] of the ligand 1,3-dimethyl-5-(p-Cl-phenylazo)-6-aminouracil (HL) was isolated in the form of single crystals and characterized by single-crystal X-ray diffraction. The complex possesses square planar geometry with molecular formula C24H22Cl2N10NiO4. The atomic arrangements about the Ni(II) are in trans-square planar fashion where the Ni(II) ion lies on an inversion centre. It crystallizes in the orthorhombic system, space group Pbca, with lattice parameters: a = 11.9282(7) Å, b = 11.2222(6) Å, c = 19.9242(12) Å and α = β = γ = 90°. The complex is stable in neutral to basic buffer solution region and dissociates to its anionic hydrazone form followed by the hydrazone in acidic buffer solution. The dissociation process was studied kinetically and is described as “acid-limiting” or “saturation kinetics”, in which the rate becomes independent of the hydrogen ion concentration at high acid concentration. The process involves rapid protonation pre-equilibrium (constant, K) followed by rate-determining dissociation (constant, k) step and these constants are found to be 3.41 × 10−6 M−1 and 8.37 × 10− M−1s−1, respectively. The interaction of the complex with different anions like F−, Cl−, Br−, AcO−, NO3 − or HSO4 − was studied and found quite different results. With fluoride ions the complex using its –NH- fragments, forms H-bonded association complex whereas in presence of HSO4 − the complex like in acidic buffer solution, dissociates to form (kd = 1.28 M−1s−1) the hydrazone form of the ligand. Graphical Abstract: The square planar nickel(II) complex of the ligand 1,3-dimethyl-5-(p-Cl-phenylazo)-6-aminouracil forms association complex with F− ions and dissociates to form the hydrazone form of the ligand in acidic buffer solution and in presence of HSO4 −.[Figure not available: see fulltext.]. © 2017, Springer Science+Business Media, LLC.

Journal of Chemical Crystallography

Nickel(II) Square-Planar Complex of 1,3-Dimethyl-5-(p-Cl-phenylazo)-6-aminouracil: Crystal Structure, Dissociation Kinetics and Anion Interaction

6-Aminouracils have extensively been used as precursors for synthesizing numerous uracil derivatives of biological and pharmaceutical significance. This study describes an application of 1,3-dimethyl-5-(arylazo)-6-aminouracils (Uazo: Uazo1-Uazo4, precursors) for an efficient synthesis of a series of 8-substituted-azapurins (AP), namely 1,3-dimethyl-8-(aryl)-azapurin-2,6-diones (aryl = p-HC6H4 (AP1), -MeC6H4 (AP2), –ClC6H4 (AP3), and –SO2NH2C6H4 (AP4)) following an oxidation method in the presence of copper (II) nitrate and in alkaline medium. The obtained compounds were isolated in good yields as crystalline air-stable products and have been fully characterized in the solution by UV–vis and NMR spectroscopy, as well as in the solid state by FT-IR spectroscopy, elemental analysis, and single-crystal X-ray diffraction (for AP2 and AP4). UV–vis study evidences that the conversion of the 6-aminouracil precursors occurs via an intermediate, Cu(II)-complex and a plausible mechanism for the formation of AP1-AP4 has been proposed. Unlike AP2 the crystal structure of AP4 reveals the formation of interdigitated 1D H-bonded chains that has been topologically classified within the 2C1 type. The 1H NMR spectra of the products have proton signals that completely devoid of hydrazone (–NH–) and imine (=NH) signals of their parent Uazo derivatives, thus confirming their full conversion and a stability of the AP1-AP4 in solution. The excitation and emission spectra of AP1-AP4 were also recorded in solution, revealing electronic transitions between similar vibrational energy levels of S0 (singlet ground state) and S1 (singlet first excited state). © 2017 Elsevier B.V.

Study of an efficient conversion of 1,3-dimethyl-5-(Arylazo)-6-Amino-Uracils to 1,3-dimethyl-8-(Aryl)-Azapurin-2,6-Diones

The synthesis and characterization of complex [Cu(dppo)2] (dppo = 1,3-diphenylpropane-1,3-dione) is reported. The complex has been fully characterized by FT-IR, UV–vis, elemental analysis and Cyclic Voltammetry. The paramagnetic nature of the complex was confirmed by magnetic measurement and the square planar geometry was ascertained by single crystal X-ray determination. The complex has been found to be a good homogeneous catalyst for the synthesis of 1,2,3-triazole derivatives via one-pot reaction of arylboronic acids, sodium azide and alkynes in DMF. © 2016 Elsevier B.V.

Inorganica Chimica Acta

Synthesis, characterization and crystal structure of a diketone based Cu(II) complex and its catalytic activity for the synthesis of 1,2,3-triazoles

Photovoltaics with dye-sensitized solar cells have been recognized as being promising for the utilization of sunlight to produce electricity and 'solar chemicals'. One of the remaining unsolved challenges is the development of an affordable, robust dye that has a panchromatic light harvesting range and efficiently provides separated charges for the desired photochemistry. The most commonly employed molecular photosensitizers include the noble metal-based ruthenium and iridium complexes, synthetically challenging porphyrin derivatives, and expensive, functionalized polypyridine compounds. Here, we describe the development of Cu(i) dyes supported by bis(arylimino)acenaphthene (Ar-BIAN) ligands, which can be synthesized in fewer than three steps from affordable, commercially available reagents. The diamagnetic, homoleptic complexes have been characterized by a suite of spectroscopic and analytical methods and exhibit panchromatic light absorption extending to the near infrared (NIR) region. Remarkably, the crystal structure of a complex bearing an ortho-iodoarylimino substituent displays a unique, rhombically distorted square planar geometry around the Cu(i) center, for crystals isolated from two disparate solvent combinations. Density functional theory (DFT) calculations were performed to provide insights into the spectroscopic features and the unusual coordination sphere around the metal center, and allude to non-covalent interactions between the aromatic groups and among the iodide atoms. Preliminary studies were conducted to explore the application of these copper photosensitizers in dye-sensitized solar cells. © 2016 the Partner Organisations.

Fulltext

Inorganic Chemistry Frontiers

Development of bis(arylimino)acenaphthene (BIAN) copper complexes as visible light harvesters for potential photovoltaic applications

The first example of a phosphenium trication has been prepared by using the exceptional nucleophilic properties of a carbodicarbene ligand. According to theoretical investigations the trication contains quite polarized P-C bonds suggesting a substantial contribution from the dative bond model. As one of the resonance forms for the title compound depicted a hypervalent phosphoranide we also showed that phosphoranides, in general, do not contain a hypervalent P centre. © The 2016 The Royal Society of Chemistry.

Chemical Communications

Bis(carbodicarbene)phosphenium trication: The case against hypervalency

In this research, we successfully synthesized and fully characterized the new compound 5,8,13,16,21,24-hex-(triisopropylsilyl)ethynyl)-6,23-dihydro-6,7,14,15,22,23-hexaza-trianthrylene (HHATA, brown color in a mixed solvent of CH2Cl2/CH3CN 1:1, v/v, weakly blue fluorescent), which can be easily oxidized to 5,8,13,16,21,24-hex-(triisopropylsilyl)ethynyl)-6,7,14,15,22,23-hexazatrianthrylene (HATA) (yellow color in CH2Cl2/CH3CN 1:1, v/v), red fluorescent) by Cu2+ ions. This reaction only proceeds efficiently in the presence of Cu2+ ions when compared with other common metal ions such as Fe3+, Co2+, Mn2+, Hg2+, Ni2+, Pb2+, Ag+, Mg2+, Ca2+, K+, Na+, and Li+. Our result suggests that this reaction can be developed as an effective method for the detection of Cu2+ ions. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chemistry - An Asian Journal

A Colorimetric and Fluorimetric Chemodosimeter for Copper Ion Based on the Conversion of Dihydropyrazine to Pyrazine

3,4-dihydro-2H-1,2,4,3-triazaborol-3-yl-lithium 3 was synthesized and fully characterized. The 11B NMR spectrum, X-ray diffraction analysis, and computational studies revealed the ionic nature of the B-Li bond, and indeed 3 displays nucleophilic property which allowed preparation of a series of 1,2,4,3-triazaborol-3-yl-metal complexes (Al; 5, Au; 6, Zn; 7, Mg; 8, Sb; 9, and Bi; 10). 3 reacted with CO (1 atm) and various isonitriles under ambient condition, and mechanistic study suggests that the reactions with CO and aryl isonitriles proceed via an insertion of CO and isonitrile carbon into the B-Li bond followed by isomerization to yield transient carbene species, one of which was confirmed by trapping with S8. With PhNC, compounds 5 and 7·(thf) underwent exchange of THF molecule coordinating to the metal center with isonitrile, whereas insertion of isonitrile carbon occurred at the B-Bi bond in 10 which afforded stable bismuth (boryl)iminomethane 20. © 2016 American Chemical Society.