Syntheses, crystal structures, reactivity, and photochemistry of gold(III) bromides bearing N-heterocyclic carbenes

Gold(I) complexes bearing N-heterocyclic carbenes (NHC) of the type (NHC)AuBr (3a/3b) [NHC = 1-methyl-3-benzylimidazol-2-ylidene (= MeBnIm), and 1,3-dibenzylimidazol-2-ylidene (= Bn(2)Im)] are prepared by transmetallation reactions of (tht)AuBr (tht = tetrahydrothiophene) and (NHC)AgBr (2a/2b). The homoleptic, ionic complexes [(NHC)(2)Au]Br (6a/6b) are synthesized by the reaction with free carbene. Successive oxidation of 3a/3b and 6a/6b with bromine gave the respective (NHC)AuBr(3) (4a/4b) and [(NHC)(2)AuBr(2)]Br (7a/7b) in good overall yields as yellow powders. All complexes were characterized by NMR spectroscopy, mass spectrometry, elemental analysis and single crystal X-ray diffraction. Reactions of the Au(III) complexes towards anionic ligands like carboxylates, phenolates and thiophenolates were investigated and result in a complete or partial reduction to a Au(I) complex. Irradiation of the Au(III) complexes with UV light yield the Au(I) congeners in a clean photo-reaction.     

An antimicrobial zinc based molecule for cross linking poly-acrylic acid

A system for incorporating antimicrobial zinc into polymeric materials, in particular hydrogel type polymers has been developed. Zn(Bipy-(MMOES)₂) a zinc carboxylate monomer was designed with the purpose of mimicking commercial cross linking agents such as ethylene glycol diacrylate, as well as containing antimicrobial zinc ions (Zn²⁺), with the intention that it can be used to cross link into any polymeric material, the example here being polyacrylic acid. Two systems were studied: a homopolymer of the Zn(Bipy-(MMOES)₂) and copolymers of Zn(Bipy-(MMOES)₂) with acrylic acid (AA). The AA – Zn(Bipy-(MMOES)₂) produced water swellable polymers which retained antimicrobial activity. The ability of the polymers to release the zinc ions was shown to be pH responsive and the leachate analysed to give a proposed mechanism of action. The Zn(Bipy-(MMOES)₂) monomer and polymers have shown antibacterial activity against both gram positive Methicillin susceptible staphylococcus aureus (MSSA 476) and gram negative Pseudomonas aeruginosa (PA01).     

Determination of the binding sites for oxaliplatin on insulin using mass spectrometry-based approaches

Using insulin as a model protein for binding of oxaliplatin to proteins, various mass spectrometric approaches and techniques were compared. Several different platinum adducts were observed, e.g. addition of one or two diaminocyclohexane platinum(II) (Pt(dach)) molecules. By top-down analysis and fragmentation of the intact insulin–oxaliplatin adduct using nano-electrospray ionisation quadrupole time-of-flight mass spectrometry (nESI-Q-ToF-MS), the major binding site was assigned to histidine5 on the insulin B chain. In order to simplify the interpretation of the mass spectrum, the disulphide bridges were reduced. This led to the additional identification of cysteine6 on the A chain as a binding site along with histidine5 on the B chain. Digestion of insulin–oxaliplatin with endoproteinase Glu-C (GluC) followed by reduction led to the formation of five peptides with Pt(dach) attached. Identification of several of the binding sites was obtained using matrix-assisted laser desorption/ionization (MALDI)-ToF-ToF-MS and liquid chromatography-nESI-Q-ToF-MS. Upon comparing the top-down and bottom-up approaches, the suitability of the bottom-up approach for determining binding sites was questioned, as the release and possible re-association of Pt(dach) were demonstrated upon enzymatic digestion. The associated advantages and disadvantages of ESI and MALDI were also pointed out.     

Challenges and strategies in the preparation of large‐volume polymer‐based monolithic chromatography adsorbents

To date, the number of published reports on the large‐volume preparation of polymer‐based monolithic chromatography adsorbents is still lacking and is of great importance. Many critical factors need to be considered when manufacturing a large‐volume polymer‐based monolith for chromatographic applications. Structural integrity, validity, and repeatability are thought to be the key factors determining the usability of a large‐volume monolith in a separation process. In this review, we focus on problems and solutions pertaining to heat dissipation, pore size distribution, “wall channel” effect, and mechanical strength in monolith preparation. A template‐based method comprising sacrificial and nonsacrificial techniques is possibly the method of choice due to its precise control over the porous structure. However, additional expensive steps are usually required for the template removal. Other strategies in monolith preparation are also discussed.     

Structural and photophysical studies of phenanthrene adducts involving C6F5HgCl and [o-C6F4Hg]3

Both pentafluorophenylmercury chloride and trimeric perfluoro-ortho-phenylene mercury interact with phenanthrene to form phosphorescent adducts which exhibit extended binary stacks in the solid state.     

Experimental and Computational Probes of the Nature of Halogen Bonding: Complexes of Bromine‐Containing Molecules with Bromide Anions

The nature of halogen bonding is examined via experimental and computational characterizations of a series of associates between electrophilic bromocarbons R? Br (R? Br=CBr₃F, CBr₃NO₂, CBr₃COCBr₃, CBr₃CONH₂, CBr₃CN, etc.) and bromide anions. The [R? Br, Br^?] complexes show intense absorption bands in the 200–350 nm range which follow the same Mulliken correlation as those observed for the charge‐transfer associates of bromide anions with common organic π‐acceptors. For a wide range of the associates, intermolecular R? Br???Br^? separations decrease and intramolecular C? Br bond lengths increase proportionally to the Br^?→R? Br charge transfer; and the energies of R? Br???Br^? bonds are correlated with the linear combination of orbital (charge‐transfer) and electrostatic interactions. On the whole, spectral, structural and thermodynamic characteristics of the [R? Br, Br^?] complexes indicate that besides electrostatics, the orbital (charge‐transfer) interactions play a vital role in the R? Br???Br^? halogen bonding. This indicates that in addition to controlling the geometries of supramolecular assemblies, halogen bonding leads to electronic coupling between interacting species, and thus affects reactivity of halogenated molecules, as well as conducting and magnetic properties of their solid‐state materials.     

Ansa‐Bridged Bis(benzene) Titanium Complexes

Taking advantage of an improved synthesis of [Ti(η⁶‐C₆H₆)₂], we report here the first examples of ansa‐bridged bis(benzene) titanium complexes. Deprotonation of [Ti(η⁶‐C₆H₆)₂] with nBuLi in the presence of N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (pmdta) leads to the corresponding 1,1′‐dilithio salt [Ti(η⁶‐C₆H₅Li)₂] ? pmdta that enables the preparation of the first one‐ and two‐atom‐bridged complexes by simple salt metathesis. The ansa complexes were fully characterized (NMR spectroscopy, UV/Vis spectroscopy, elemental analysis, and X‐ray crystallography) and further studied electrochemically and computationally. Moreover, [Ti(η⁶‐C₆H₆)₂] is found to react with the Lewis base 1,3‐dimethylimidazole‐2‐ylidene (IMe) to give the bent sandwich complex [Ti(η⁶‐C₆H₆)₂(IMe)].     

Strategies for electrooptic film fabrication. Influence of pyrrole-pyridine-based dibranched chromophore architecture on covalent self-assembly, thin-film microstructure, and nonlinear optical response

The new dibranched, heterocyclic "push-pull" chromophores bis{1-(pyridin-4-yl)-2-[2-(N-methylpyrrol-5-yl)]ethane}methane (1), 1-(pyrid-4-yl)-2-(N-methyl-5-formylpyrrol-2-yl)ethylene (2), {1-(N-methylpyridinium-4-yl)-2-[2-(N-methylpyrrol-5-yl)]ethane}{(1-(pyridin-4-yl)-2-[2-(N-methylpyrrol-5-yl)]ethane}methane (3), N-methyl-2-[1-(N-methylpyrid-4-yl)ethen-2-yl]-5-[pyrid-4-yl]ethen-2-yl]pyrrole iodide (4), bis{1-(N-methyl-4-pyridinio)-2-[2-(N-methylpyrrol-5-yl)]ethane}methane iodide (5), and N-methyl-2,5-[1-(N-methylpyrid-4-yl)ethen-2-yl]pyrrole iodide (6) have been synthesized and characterized. The neutral (1 and 2) and monomethyl salts (3 and 4) undergo chemisorptive reaction with iodobenzyl-functionalized surfaces to afford chromophore monolayers SA-1/SA-2 and SA-3/SA-4, respectively. Molecular structures and other physicochemical properties have been defined by (1)H NMR, optical spectroscopy, and XRD. Thin-film characterization by a variety of techniques (optical spectroscopy, specular X-ray reflectivity, atomic force microscopy, X-ray photoelectron spectroscopy, and angle-dependent polarized second harmonic generation) underscore the importance of the chromophore molecular architecture as well as film growth method on film microstructure and optical/electrooptic response.     

Probing hemoglobin structure by means of traveling-wave ion mobility mass spectrometry

Hemoglobin (Hb) is a tetrameric noncovalent complex consisting of two α- and two β-globin chains each associated with a heme group. Its exact assembly pathway is a matter of debate. Disorders of hemoglobin are the most common inherited disorders and subsequently the molecule has been extensively studied. This work attempts to further elucidate the structural properties of the hemoglobin tetramer and its components. Gas-phase conformations of hemoglobin tetramers and their constituents were investigated by means of traveling-wave ion mobility mass spectrometry. Sickle (HbS) and normal (HbA) hemoglobin molecules were analyzed to determine whether conformational differences in their quaternary structure could be observed. Rotationally averaged collision cross sections were estimated for tetramer, dimer, apo-, and holo-monomers with reference to a protein standard with known cross sections. Estimates of cross section obtained for the tetramers were compared to values calculated from X-ray crystallographic structures. HbS was consistently estimated to have a larger cross section than that of HbA, comparable with values obtained from X-ray crystallographic structures. Nontetrameric species observed included apo- and holo- forms of α- and β-monomers and heterodimers; α- and β-monomers in both apo- and holo- forms were found to have similar cross sections, suggesting they maintain a similar fold in the gas phase in both the presence and the absence of heme. Heme-deficient dimer, observed in the spectrum when analyzing commercially prepared Hb, was not observed when analyzing fresh blood. This implies that holo-α-apo-β is not an essential intermediate within the Hb assembly pathway, as previously proposed.