The 143 and 300 K polymorphs of hexa­methyl­enetetraminium 2,4-di­nitro­phenolate monohydrate

The title compound, 3,5,7-tri­aza-1-azoniatri­cyclo­[3.3.1.1^3,7]­decane 2,4-di­nitro­phenolate monohydrate, C₆H₁₃N₄⁺·C₆H₃N₂O₅⁻·H₂O, the 1:1 hydrate adduct of hexa­methyl­enetetr­amine (HMT) and 2,4-di­nitro­phenol, undergoes a temperature phase transition. In the room-temperature phase, the adduct crystallizes in the monoclinic P2₁/m space group, whereas in the low-temperature phase, the adduct crystallizes in the triclinic P space group. This phase transition is reversible, with the transition temperature at 273 K, and the phase transition is governed by hydrogen bonds and weak interactions. In both these temperature-dependent polymorphs, the crystal structure is alternately layered with sheets of hexa­methyl­enetetr­amine and sheets of di­nitro­phenol stacked along the c axis. The hexa­methyl­enetetr­amine and di­nitro­phenol moieties are linked by intermolecular hydrogen bonds. The water mol­ecule in the adduct plays an important role, forming O—H⋯O hydrogen bonds which, together with C—H⋯O hydrogen bonds, bridge the adducts into molecular ribbons. Extra hydrogen bonds and weak interactions exist for the low-temperature polymorph and these interconnect the molecular ribbons into a three-dimensional packing structure. Also in these two temperature-dependent polymorphs, di­nitro­phenol acts as a hydrogen-bond acceptor and HMT acts as a hydrogen-bond donor.     

(2‐Methyl­quinolin‐8‐olato)­iron(III) and ‐copper(II) complexes

The crystal structures of tris(2‐methyl­quinolin‐8‐olato‐N,O)­iron(III), [Fe­(C₁₀­H₈­NO)₃], (I), and aqua­bis(2‐methyl­quinolin‐8‐olato‐N,O)­copper(II), [Cu­(C₁₀­H₈NO)₂­(H₂O)], (II), have been determined. Compound (I) has a distorted octahedral configuration, in which the central Fe atom is coordinated by three N atoms and three O atoms from three 2‐methylquinolin‐8‐olate ligands. The three Fe—O bond distances are in the range 1.934 (2)–1.947 (2) Å, while the three Fe—N bond distances range from 2.204 (2) to 2.405 (2) Å. In compound (II), the central Cu^II atom and H₂O group lie on the crystallographic twofold axis and the coordination geometry of the Cu^II atom is close to trigonal bipyramidal, with the three O atoms in the basal plane and the two N atoms in apical positions. The Cu—N bond length is 2.018 (5) Å. The Cu—O bond length in the basal positions is 1.991 (4) Å, while the Cu—O bond length in the apical position is 2.273 (6) Å. There is an intermolecular OW—H?O hydrogen bond which links the mol­ecules into a linear chain along the b axis.     

Coordination of Deprotonated Saccharin in Copper(II) Complexes. Structural Role of the Saccharinate Directed by the Ancillary N‐heterocyclic Ligands

Four different coordination patterns were observed following the partial or complete thermodynamically‐controlled ligand substitution of the hydrated tetraaquabis(o‐sulfobenzimidato‐N)copper(II) complex with heterocyclic bases as examined by X‐ray diffraction. The N‐heterocycle directs the o‐sulfobenzimidate (saccharinate) anion into the immediate coordination polyhedron of the metal by any of the imido, carbonyl or sulfonyl functionalities, or as a lattice counter‐ion in the crystal lattice. Aqua(o‐sulfobenzimidato‐O)tetrakis(4‐methylpyridine)copper(II) o‐sulfobenzimidate hemihydrate ( 1 ) crystallizes in the monoclinic space group P2₁/n [a = 14.7858(2), b = 16.9090(1), c = 26.2350(2)Å; β = 92.861(1)°], aquadi(o‐sulfobenzimidato‐N)bis(4‐propylpyridine)copper(II) ( 2 ) in the tetragonal space group P4₂/n [a = 15.4127(1), c = 13.4604(1)Å], diaquatetrakis(3‐(2‐propenyl)imidazole)copper(II) di‐o‐sulfobenzimidate ( 3b ) in the monoclinic space group P2₁/c [a = 9.3959(5), b = 28.029(2), c = 8.8763(3)Å; β = 111.175(1)°] and di(o‐sulfobenzimidato)tetra(isoquinoline)copper(II) ( 4b ) in the orthorhombic space group Pna2₁ [a = 23.2132(6), b = 11.5760(2), c = 17.6297(4)Å]. The copper atom in 1 is six‐coordinate in a distorted trans‐N₄O₂Cu octahedron with elongated copper—oxygen bonds [Cu—O_water = 2.462(3), Cu—O_sulfonyl = 2.567(3)Å]. This adduct represents the first example of a combined O_sulfonyl/ionic coordination of the o‐sulfobenzimidate ion in the same crystal. The copper atom in 2 is five‐coordinate in the form of a N₄OCu square pyramid [Cu—O_water = 2.238(5)Å]. In 3 , the o‐sulfobenzimidate anions are linked to the copper atom through the coordinated water molecule forming a distorted octahedral N₄O₂Cu environment. In 4 , the copper atom is nearly octahedrally coordinated by four nitrogen atoms and a pair of o‐sulfobenzimidate carbonyl oxygen atoms. The structural details of the o‐sulfobenzimidate coordination pattern correspond well with the 298 and 77 K FT IR spectra of the adducts. The structures of two other solid adducts, tris(3‐(2‐propenyl)imidazole)copper(II) di‐o‐sulfobenzimidate trihydrate ( 3a ) and diaquabis(o‐sulfobenzimidato‐N)bis(isoquinoline)copper(II) ( 4a ) have been predicted by their spectral features. Alteration of the o‐sulfobenzimidate coordination mode upon changing the heterocycle ligand shows that this moiety is as a convenient polyfunctional structural tool for the construction of functional solids.     

Polymeric structure of (ethyl­ene­diamine)silver(I) 3‐nitro­benzoate monohydrate

In the ternary title compound, catena‐poly­[[silver(I)‐μ‐ethylenedi­amine‐κ²N:N′] 3‐nitro­benzoate monohydrate], {[Ag(C₂H₈N₂)](C₇H₄NO₄)·H₂O}_n, the Ag atom is bicoordinated in a linear configuration by two different N atoms from two symmetry‐related ethyl­enedi­amine ligands, thus giving linear polymeric chains with an [–Ag—N—C—C—N–]_n backbone running parallel to the a axis. In the crystal packing, these linear chains are interconnected by N—H⃛O and O—H⃛O hydrogen bonds to form layers parallel to the ab plane.     

gem-Diethyl Pyrroline Nitroxide Spin Labels: Synthesis,EPR Characterization,Rotamer Libraries and Biocompatibility

The availability of bioresistant spin labels is crucial for the optimization of site-directed spin labeling protocols for EPR structural studies of biomolecules in a cellular context. As labeling can affect proteins’ fold and/or function, having the possibility to choose between different spin labels will increase the probability to produce spin-labeled functional proteins. Here, we report the synthesis and characterization of iodoacetamide- and maleimide-functionalized spin labels based on the gem-diethyl pyrroline structure. The two nitroxide labels are compared to conventional gem-dimethyl analogs by site-directed spin labeling (SDSL) electron paramagnetic resonance (EPR) spectroscopy, using two water soluble proteins: T4 lysozyme and Bid. To foster their use for structural studies, we also present rotamer libraries for these labels, compatible with the MMM software. Finally, we investigate the “true” biocompatibility of the gem-diethyl probes comparing the resistance towards chemical reduction of the NO group in ascorbate solutions and E. coli cytosol at different spin concentrations.     

A Dendritic Macrocyclic Organic Polyradical with a Very High Spin of S=10

Designed as a ferromagnetically coupled spin pentamer , the macrocyclic polyradical 1 possesses an average spin of S=10 in the ground state. This is the highest spin quantum number that has yet been measured for an organic molecule. Ar=tBuC₆H₄.     

Chemical-Genetic Interactions of Bacopa monnieri Constituents in Cells Deficient for the DNA Repair Endonuclease RAD1 Appear Linked to Vacuolar Disruption

Colorectal cancer is a common cancer worldwide and reduced expression of the DNA repair endonuclease XPF (xeroderma pigmentosum complementation group F) is associated with colorectal cancer. Bacopa monnieri extracts were previously found to exhibit chemical-genetic synthetic lethal effects in a Saccharomyces cerevisiae model of colorectal cancer lacking Rad1p, a structural and functional homologue of human XPF. However, the mechanisms for B. monnieri extracts to limit proliferation and promote an apoptosis-like event in RAD1 deleted yeast was not elucidated. Our current analysis has revealed that B. monnieri extracts have the capacity to promote mutations in rad1∆ cells. In addition, the effects of B. monnieri extracts on rad1∆ yeast is linked to disruption of the vacuole, similar to the mammalian lysosome. The absence of RAD1 in yeast sensitizes cells to the effects of vacuole disruption and the release of proteases. The combined effect of increased DNA mutations and release of vacuolar contents appears to induce an apoptosis-like event that is dependent on the meta-caspase Yca1p. The toxicity of B. monnieri extracts is linked to sterol content, suggesting saponins may be involved in limiting the proliferation of yeast cells. Analysis of major constituents from B. monnieri identified a chemical-genetic interaction between bacopasaponin C and rad1∆ yeast. Bacopasaponin C may have potential as a drug candidate or serve as a model for the development of analogs for the treatment of colorectal cancer.     

Electroanalysis of tetracycline using nickel-implanted boron-doped diamond thin film electrode applied to flow injection system.

The electrochemical analysis of tetracycline was investigated using nickel-implanted boron-doped diamond thin film electrode by cyclic voltammetry and amperometry with a flow injection system. Cyclic voltammetry was used to study the electrochemical oxidation of tetracycline. Comparison experiments were carried out using as-deposited boron-doped diamond thin film electrode (BDD). Nickel-implanted boron-doped diamond thin film electrode (Ni-DIA) provided well-resolved oxidation irreversible cyclic voltammograms. The current signals were higher than those obtained using the as-deposited BDD electrode. Results using nickel-implanted boron-doped diamond thin film electrode in flow injection system coupled with amperometric detection are presented. The optimum potential for tetracycline was 1.55 V versus Ag/AgCl. The linear range of 1.0 to 100 microM and the detection limit of 10 nM were obtained. In addition, the application for drug formulation was also investigated.     

Synthesis, structure, and conformation of aza[1n]metacyclophanes

N-Benzyl substituted aza[1n]metacyclophanes (n = 4, 6, 8, and 10) were prepared in overall 40% isolated yields via Pd-catalyzed aminations. Analyses of the reaction mixtures showed that aza[14]metacyclophane and the related polymer were the primary products ( approximately 60% overall yield); aza[1n]metacyclophanes up to n = 14 and linear oligomers with up to 20 nitrogen atoms (with at least three types of end groups) were detected. Macrocyclic structures for n = 4, 6, and 10 were confirmed by X-ray crystallography. 1,3-Alternate (D(2d)) and 1,3,5-alternate (S(6)) conformations in solution on NMR time scale at low temperatures were found for macrocycles with n = 4 and n = 6, respectively; the barrier for ring inversion was considerably lower for the larger macrocycle.