Comparison between biokinetics of inhaled plutonium nitrate and gadolinium oxide in humans and animals

Due to the paucity of human data after inhalation of different chemical forms of radionuclides, the implications for human exposure are often based on animal studies. This paper describes biokinetic studies of plutonium nitrate and gadolinium oxide in human volunteers and rats. The results, together with information from other studies with radionuclides, suggests that animal studies can be used with advantage for assessing the biokinetic behavior in humans, and for providing guidance on the assessment of intake and optimal monitoring regimens.     

Functional Rotaxanes in Catalysis

Mechanically interlocked molecules (MIMs) have gained attention in the field of catalysis due to their unique molecular properties. Central to MIMs, rotaxanes are highly promising and attractive supramolecular catalysts due to their unique three-dimensional structures and the flexibility of their subcomponents. This Minireview discusses the use of rotaxanes in organocatalysis and transition-metal catalysis.     

Mapping chemical exchange in proteins with MW > 50 kD

Chemical exchange reveals motions in proteins that are critical for ligand binding, catalysis, and allosteric regulation at the microsecond to millisecond time scale. The detection of chemical exchange is inherently difficult in large proteins because of the fast transverse relaxation rate (R2) and spectral overlap. Here we report novel pulse sequences for the rapid identification of chemical exchange applicable to large deuterated proteins with MW greater than 30 kD. The success of our method is demonstrated in triosephosphate isomerase (TIM, MW = 54 kD).     

Functionalized fullerenes in self-assembled monolayers

Anisotropy of intermolecular and molecule-substrate interactions holds the key to controlling the arrangement of fullerenes into 2D self-assembled monolayers (SAMs). The chemical reactivity of fullerenes allows functionalization of the carbon cages with sulfur-containing groups, thiols and thioethers, which facilitates the reliable adsorption of these molecules on gold substrates. A series of structurally related molecules, eight of which are new fullerene compounds, allows systematic investigation of the structural and functional parameters defining the geometry of fullerene SAMs. Scanning tunnelling microscopy (STM) measurements reveal that the chemical nature of the anchoring group appears to be crucial for the long-range order in fullerenes: the assembly of thiol-functionalized fullerenes is governed by strong molecule-surface interactions, which prohibit formation of ordered molecular arrays, while thioether-functionalized fullerenes, which have a weaker interaction with the surface than the thiols, form a variety of ordered 2D molecular arrays owing to noncovalent intermolecular interactions. A linear row of fullerene molecules is a recurring structural feature of the ordered SAMs, but the relative alignment and the spacing between the fullerene rows is strongly dependent on the size and shape of the spacer group linking the fullerene cage and the anchoring group. Careful control of the chemical functionality on the carbon cages enables positioning of fullerenes into at least four different packing arrangements, none of which have been observed before. Our new strategy for the controlled arrangement of fullerenes on surfaces at the molecular level will advance the development of practical applications for these nanomaterials.     

Effect of monovalent ion binding on molecular dynamics of the S100-family calcium-binding protein calbindin D9k

Calbindin D_9k is a member of the S100 subfamily of EF-hand calcium binding proteins, and has served as an important model system for biophysical studies. The fast timescale dynamics of the calcium-free (apo) state is characterized using molecular dynamics simulations. Order parameters for the backbone NH bond vectors are determined from the simulations and compared with experimentally derived values, with a focus on the dynamics of calcium-binding site I. There is a significant discrepancy between simulated and experimental order parameters for site I residues in the case of no ion bound in site I. However, it was found in the simulations that a Na⁺ ion can bind in site I, and the resulting order parameters determined from the simulations are in excellent agreement with experiment. Comparisons are made to X-ray structures of other S100 family members in which Na⁺ ions were observed or suggested to be bound in site I. © 2019 Wiley Periodicals, Inc.     

Comparison of the stability of multiwalled carbon nanotube dispersions in water

Continuous real-time monitoring of the nanotube concentration in aqueous solution using UV-Vis spectroscopy allows quantitative comparison of the stability of different types of nanotube dispersions. Systematic investigation of the effects of nanotube length and functionalisation for thin multiwalled carbon nanotubes (MWNT) has revealed that shorter MWNT form more stable dispersions than longer nanotubes of the same diameter. MWNT shortened to an average length of approximately 1 microm form stable dispersions in water with concentrations up to 0.013 mg ml(-1) in the absence of surfactants or solubilising functional groups. The introduction of carboxylic or thiol groups on the surface of shortened nanotubes further increases the stability of MWNT dispersions (up to 0.24 mg ml(-1)). The introduction of surfactant or surface charge on MWNT has contrasting effects on functionalised and non-functionalised nanotubes, destabilising and stabilising their dispersions, respectively.     

Shedding Light on the Interactions of Hydrocarbon Ester Substituents upon Formation of Dimeric Titanium(IV) Triscatecholates in DMSO Solution

The dissociation of hierarchically formed dimeric triple lithium bridged triscatecholate titanium(IV) helicates with hydrocarbyl esters as side groups is systematically investigated in DMSO. Primary alkyl, alkenyl, alkynyl as well as benzyl esters are studied in order to minimize steric effects close to the helicate core. The ¹H NMR dimerization constants for the monomer–dimer equilibrium show some solvent dependent influence of the side chains on the dimer stability. In the dimer, the ability of the hydrocarbyl ester groups to aggregate minimizes their contacts with the solvent molecules. Due to this, most solvophobic alkyl groups show the highest dimerization tendency followed by alkenyls, alkynyls and finally benzyls. Furthermore, trends within the different groups of compounds can be observed. For example, the dimer is destabilized by internal double or triple bonds due to π–π repulsion. A strong indication for solvent supported London dispersion interaction between the ester side groups is found by observation of an even/odd alternation of dimerization constants within the series of n-alkyls, n-Ω-alkenyls or n-Ω-alkynyls. This corresponds to the interaction of the parent hydrocarbons, as documented by an even/odd melting point alternation.     

NMR R1 rho rotating-frame relaxation with weak radio frequency fields

NMR spin relaxation in the rotating frame (R(1 rho)) is one of few methods available to characterize chemical exchange kinetic processes occurring on micros-ms time scales. R(1 rho) measurements for heteronuclei in biological macromolecules generally require decoupling of (1)H scalar coupling interactions and suppression of cross-relaxation processes. Korzhnev and co-workers demonstrated that applying conventional (1)H decoupling schemes while the heteronuclei are spin-locked by a radio frequency (rf) field results in imperfect decoupling [Korzhnev, Skrynnikov, Millet, Torchia, Kay. J. Am. Chem. Soc. 2002, 124, 10743-10753]. Experimental NMR pulse sequences were presented that provide accurate measurements of R(1 rho) rate constants for radio frequency field strengths > 1000 Hz. This paper presents new two-dimensional NMR experiments that allow the use of weak rf fields, between 150 and 1000 Hz, in R(1 rho) experiments. Fourier decomposition and average Hamiltonian theory are employed to analyze the spin-lock sequence and provide a guide for the development of improved experiments. The new pulse sequences are validated using ubiquitin and basic pancreatic trypsin inhibitor (BPTI). The use of weak spin-lock fields in R(1 rho) experiments allows the study of the chemical exchange process on a wider range of time scales, bridging the gap that currently exists between Carr-Purcell-Meiboom-Gill and conventional R(1 rho) experiments. The new experiments also extend the capability of the R(1 rho) technique to study exchange processes outside the fast exchange limit.     

Microbore liquid chromatography coupled to a flow fast atom bombardment probe for the on-line detection of the Tyr-Pro cleavage of a nonapeptide by recombinant HIV-1 protease

The nonapeptide Val-Ser-Gln-Asn-Tyr-Pro-Ile-Val-Gln has been reported as a model substrate for an aspartyl protease produced by the human immunodeficiency virus (HIV-1). Cleavage of this peptide at the Tyr-Pro linkage to produce tetra- and pentapeptide fragments is the basis of high-performance liquid chromatographic assays to detect HIV-1 protease activity. Confirmation of the cleavage site has been proved by using microbore liquid chromatography coupled to a dynamic fast atom bombardment interface. Comparison with fortified control incubates indicates that an approximate stoichiometric amount of the tetrapeptide was formed from the nonapeptide, confirming that the cleavage of the substrate by HIV-1 protease is both specific and quantitative.