Cucurbituril binding of trans-[{PtCl(NH3)2}2(micro-NH2(CH2)8NH2)]2+ and the effect on the reaction with cysteine

The effect of encapsulation by cucurbiturils Q[7] and Q[8] on the rate of reaction of the anti-cancer dinuclear platinum complex trans-[{PtCl(NH3)2}2(micro-NH2(CH2)8NH2)]2+ with the model biological nucleophiles glutathione and cysteine has been examined by NMR spectroscopy. It was expected that the octamethylene linking chain would fold inside the cucurbituril host and hence position the reactive platinum centres close to the cucurbituril portals, and thereby, confer resistance to degradation by biological nucleophiles. The upfield shifts of the resonances from the methylene protons in the linking ligand observed in 1H NMR spectra of the platinum complex upon addition of either Q[7] or Q[8] indicate that the cucurbituril is positioned over the linking ligand, with the Pt(II) centres projecting out of the portal. Furthermore, the relative changes in chemical shift of the methylene resonances suggest that the octamethylene linking chain folds within the cucurbituril cavity, particularly in Q[8]. Simple molecular models, based on the observed relative changes in chemical shift, could be constructed that were consistent with the proposed folding of the linking ligand within the cucurbituril cavity. Encapsulation by Q[7] was found to reduce the rate of reaction of the platinum complex with glutathione. Encapsulation by Q[7] and Q[8] was also found to reduce the rate of reaction of the platinum complex with cysteine, with Q[8] slowing the reaction to a greater extent than Q[7], consistent with the inferred encapsulation geometries. Encapsulation of dinuclear platinum complexes within the cucurbituril cavity may provide a novel way of reducing the reactivity and degradation of these promising chemotherapeutic agents with blood plasma proteins.     

Configurational analysis of cyclopropyl fatty acids isolated from Escherichia coli

[reaction: see text] The absolute configuration of methyl lactobacillate and its 9,10 homologue, both isolated from Escherichia coli B-ATCC 11303, was found to be 11R,12S and 9R,10S, respectively.     

A Theorem on Homogeneous Differential Polynomials

We substantially strengthen an unpublished result of Whitehead from his PhD thesis (Whitehead, A.: Differential equations and differential polynomials in the complex. PhD thesis, University of Nottingham, 2002) using a refinement of his techniques.     

A Dual Threat: Redox-Activity and Electronic Structures of Well-Defined Donor–Acceptor Fulleretic Covalent-Organic Materials

The effect of donor (D)–acceptor (A) alignment on the materials electronic structure was probed for the first time using novel purely organic porous crystalline materials with covalently bound two- and three-dimensional acceptors. The first studies towards estimation of charge transfer rates as a function of acceptor stacking are in line with the experimentally observed drastic, eight-fold conductivity enhancement. The first evaluation of redox behavior of buckyball- or tetracyanoquinodimethane-integrated crystalline was conducted. In parallel with tailoring the D-A alignment responsible for “static” changes in materials properties, an external stimulus was applied for “dynamic” control of the electronic profiles. Overall, the presented D–A strategic design, with stimuli-controlled electronic behavior, redox activity, and modularity could be used as a blueprint for the development of electroactive and conductive multidimensional and multifunctional crystalline porous materials.     

Anion‐Mediated Effects on the Size and Mechanical Properties of Enzymatically Crosslinked Suckerin Hydrogels

The suckerin family of proteins, identified from the squid sucker ring teeth assembly, offers unique mechanical properties and potential advantages over other natural biomaterials. In this study, a small suckerin isoform, suckerin‐12, is used to create enzymatically crosslinked, macro‐scale hydrogels. Upon exposure to specific salt conditions, suckerin‐12 hydrogels contracted into a condensed state where mechanical properties are found to be modulated by the salt anion present. The rate of contraction is found to correlate well with the kosmotropic arm of the Hofmeister anion series. However, the observed changes in hydrogel mechanical properties are better explained by the ability of the salt to neutralize charges in suckerin‐12 by deprotonization or charge screening. Thus, by altering the anions in the condensing salt solution, it is possible to tune the mechanical properties of suckerin‐12 hydrogels. The potential for suckerins to add new properties to materials based on naturally‐derived proteins is highlighted.     

A sodium atom in a large water cluster: electron delocalization and infrared spectra

Ab initio molecular dynamics simulations modeling low-energy collisions of a sodium atom with a cluster with more than 30 water molecules are presented. We follow the dynamics of the atom-cluster interaction and the delocalization of the valence electron of sodium together with the changes in the electron binding energy. This electron tends to be shared by the nascent sodium cation and the water cluster. IR spectra of the sodium-water cluster are both computationally and experimentally obtained, with a good agreement between the two approaches.     

Density functional theory and CCSD(T) evaluation of ionization potentials,redox potentials,and bond energies related to zirconocene polymerization catalysts

Quantum-mechanical-based computational design of molecular catalysts requires accurate and fast electronic structure calculations to determine and predict properties of transition-metal complexes. For Zr-based molecular complexes related to polyethylene catalysis, previous evaluation of density functional theory (DFT) and wavefunction methods only examined oxides and halides or select reaction barrier heights. In this work, we evaluate the performance of DFT against experimental redox potentials and bond dissociation enthalpies (BDEs) for zirconocene complexes directly relevant to ethylene polymerization catalysis. We also examined the ability of DFT to compute the fourth atomic ionization potential of zirconium and the effect the basis set selection has on the ionization potential computed with CCSD(T). Generally, the atomic ionization potential and redox potentials are very well reproduced by DFT, but we discovered relatively large deviations of DFT-calculated BDEs compared to experiment. However, evaluation of BDEs with CCSD(T) suggests that experimental values should be revisited, and our CCSD(T) values should be taken as most accurate.     

Emergence of charge-transfer-to-solvent band in the absorption spectra of hydrogen halides on ice nanoparticles: spectroscopic evidence for acidic dissociation

Extensive ab initio calculations complemented by a photodissociation experiment at 193 nm elucidate the nature of hydrogen halide molecules bound on free ice nanoparticles. Electronic absorption spectra of small water clusters (up to 5 water molecules) and water clusters doped with hydrogen fluoride, hydrogen chloride and hydrogen bromide were calculated. The spectra were modeled at the time-dependent density functional (TDDFT) level of theory with the BHandHLYP functional using the reflection principle. We observe the emergence of a charge-transfer-to-solvent (CTTS) band in the absorption spectra upon the acidic dissociation of the hydrogen halides. The CTTS band provides a spectroscopically observable feature for the acidic dissociation. The calculated spectra were compared with our new experimental photodissociation data for larger water clusters doped with HCl and HBr. We conclude that HCl and HBr dissociate to a large extent on the surface of ice nanoparticles at temperatures near 120 K and photoactive products are formed. The acidic dissociation of HX leads to an enhancement by about 4 orders of magnitude of the HCl photolysis rate in the 200-300 nm region, which is potentially relevant for the halogen budget in the atmosphere.     

Preparation, separation, and characterization of ruthenium(II) thiocyanate linkage isomers

The reaction of [(p-cym)Ru(bpy)Cl](+) (p-cym = eta(6)-p-cymene; bpy = 2,2'-bipyridine) with SCN(-) gives a mixture of the linkage isomers [(p-cym)Ru(bpy)(SCN)](+) and [(p-cym)Ru(bpy)(NCS)](+). The linkage isomers were efficiently separated by column chromatography on Hg(NO3)2-coated Al2O3. Both isomers were fully characterized by elemental analysis, (1)H NMR and IR spectroscopy, and X-ray crystallography. The equilibrium constant for the conversion of the S-bound to the N-bound isomer was determined to be 0.29(4) in methanol-d4 and 0.74(7) in acetone-d6, respectively, at 50 degrees C. Kinetic data for the linkage isomerization reaction are also reported.     

Total synthesis of isoprekinamycin: structural evidence for enhanced diazonium ion character and growth inhibitory activity toward cancer cells

The structurally novel diazobenzo[a]fluorene antibiotic isoprekinamycin (IPK) has been synthesized for the first time employing a Suzuki coupling of a brominated AB ring synthon with a boronate ester representing the D ring, followed by anionic cyclization and appropriate functional group manipulations. The first indication that the diazobenzo[a]fluorene system exhibits in vitro anticancer activity is provided and X-ray crystallographic evidence for enhancement of diazonium ion character as a consequence of intramolecular H-bonding is described.