Data_Huntingtin_Profilin.zip

All experimental CPMG and exchange-induced shift data, as well as Matlab scripts used to globally fit the experimental data, presented in the following paper published in Proc. Natl. Acad. Sci. U.S.A.Ceccon, A., Tugarinov, V., Ghirlando, R and Clore, G.M. (2020) Abbrigation of prenucleation, transient oligomerization of the Huntingtin exon 1 protein by human profilin I. Proc. Natl. Acad. Sci. U.S.A. epub ahead of print doi: http://www.pnas.org/cgi/doi/10.1073/pnas.1922264117</div

Improved Detection and Quantification of Cyclopropane Fatty Acids via Homonuclear Decoupling Double Irradiation NMR Methods

Over the years, NMR spectroscopy has become a powerful analytical tool for the identification and quantification of a variety of natural compounds in a broad range of food matrices. Furthermore, NMR can be useful for characterizing food matrices in terms of quality and authenticity, also allowing for the identification of counterfeits. Although NMR requires minimal sample preparation, this technique suffers from low intrinsic sensitivity relative to complementary techniques; thus, the detection of adulterants or markers for authenticity at low concentrations remains challenging. Here, we present a strategy to overcome this limitation by the introduction of a simple band-selective homonuclear decoupling sequence that consists of double irradiation on 1H during NMR signal acquisition. The utility of the proposed method is tested on dihydrosterculic acid (DHSA), one of the cyclopropane fatty acids (CPFAs) shown to be a powerful molecular marker for authentication of milk products. A quantitative description of how the proposed NMR scheme allows sensitivity enhancement yet accurate quantification of DHSA is provided

Global Dynamics and Exchange Kinetics of a Protein on the Surface of Nanoparticles Revealed by Relaxation-Based Solution NMR Spectroscopy

The global motions and exchange kinetics of a model protein, ubiquitin, bound to the surface of negatively charged lipid-based nanoparticles (liposomes) are derived from combined analysis of exchange lifetime broadening arising from binding to nanoparticles of differing size. The relative contributions of residence time and rotational tumbling to the total effective correlation time of the bound protein are modulated by nanoparticle size, thereby permitting the various motional and exchange parameters to be determined. The residence time of ubiquitin bound to the surface of both large and small unilamellar liposomes is ∼20 μs. Bound ubiquitin undergoes internal rotation about an axis approximately perpendicular to the lipid surface on a low microsecond time scale (∼2 μs), while simultaneously wobbling in a cone of semiangle 30–55° centered about the internal rotation axis on the nanosecond time scale. The binding interface of ubiquitin with liposomes is mapped by intermolecular paramagnetic relaxation enhancement using Gd³⁺-tagged vesicles, to a predominantly positively charged surface orthogonal to the internal rotation axis

Dynamics of a Globular Protein Adsorbed to Liposomal Nanoparticles

A solution-state NMR method is proposed to investigate the dynamics of proteins that undergo reversible association with nanoparticles (NPs). We applied the recently developed dark-state exchange saturation transfer experiment to obtain residue-level dynamic information on a NP-adsorbed protein in the form of transverse spin relaxation rates, <i>R</i>₂^bound. Based on dynamic light scattering, fluorescence, circular dichroism, and NMR spectroscopy data, we show that the test protein, human liver fatty acid binding protein, interacts reversibly and peripherally with liposomal NPs without experiencing significant structural changes. The significant but modest saturation transfer from the bound state observed at 14.1 and 23.5 T static magnetic fields, and the small determined <i>R</i>₂^bound values were consistent with a largely unrestricted global motion at the lipid surface. Amino acid residues displaying faster spin relaxation mapped to a region that could represent the epitope of interaction with an extended phospholipid chain constituting the protein anchor. These results prove that atomic-resolution protein dynamics is accessible even after association with NPs, supporting the use of saturation transfer methods as powerful tools in bionanoscience

Heterobimetallic Indenyl Complexes. Kinetics and Mechanism of Substitution and Exchange Reactions of <i>trans</i>-[Cr(CO)₃-indenyl-Rh(CO)₂] with Olefins

The trans coordination of the benzene ring of the indenyl-Rh(CO)2 complex with tricarbonylchromium strongly enhances the rate of substitution of CO's with bidentate olefins, 1,5-cyclooctadiene (COD) and norbornadiene (NBD) (“extra-indenyl effect”). The activation parameters suggest an associative reaction pathway assumed to proceed via the intermediacy of a nonisolable low-hapticity species, η1-indenyl-Rh(CO)2(L2). In addition, the rate of exchange of the Cr(CO)3 group of the complexes trans-[Cr(CO)3-indenyl-Rh(CO)2], 3, and trans-[Cr(CO)3-indenyl-Rh(COD)], 3a, and suitable acceptors (hexamethylbenzene and cycloheptatriene) is markedly increased with respect to that measured for the same reaction in the monometallic complex η-naphthalene-Cr(CO)3 (“extra-naphthalene effect”). These mutual effects of the Cr(CO)3 and RhL2 units are transmitted through the 10 π electron indenyl framework, and the results obtained are in agreement with the existence of an haptomeric ground-state equilibrium between the two isomers trans-[Cr(CO)3-μ,η6:η3-indenyl-RhL2], I, and trans-[Cr(CO)3-μ,η4:η5-indenyl-RhL2], II

Single Two-Electron Transfers and Successive One-Electron Transfers in Biferrocenyl−Indacene Isomers

Novel biferrocenyl complexes of s- and as-dihydroindacenes have been prepared and the charge transfer properties of their mono- and dicationic derivatives, selectively generated by one-electron and two-electron oxidation, have been investigated. Mixed-valence cations are generated by chemical oxidation using acetylferricinium as an oxidant agent and monitored in the visible, IR, and near-IR regions. The IT bands in the near-IR spectra are rationalized in the framework of Marcus−Hush theory. The rigid and planar indacene platform bonded to two terminal redox groups displays a redox chemistry that can be switched from single two-electron transfers to two successive one-electron transfers by changing the supporting electrolyte from nBu4NPF6 to nBu4NB(C6F5)4

Single Two-Electron Transfers and Successive One-Electron Transfers in Biferrocenyl−Indacene Isomers

Novel biferrocenyl complexes of s- and as-dihydroindacenes have been prepared and the charge transfer properties of their mono- and dicationic derivatives, selectively generated by one-electron and two-electron oxidation, have been investigated. Mixed-valence cations are generated by chemical oxidation using acetylferricinium as an oxidant agent and monitored in the visible, IR, and near-IR regions. The IT bands in the near-IR spectra are rationalized in the framework of Marcus−Hush theory. The rigid and planar indacene platform bonded to two terminal redox groups displays a redox chemistry that can be switched from single two-electron transfers to two successive one-electron transfers by changing the supporting electrolyte from nBu4NPF6 to nBu4NB(C6F5)4

Heterobimetallic Indenyl Complexes. Mechanism of Cyclotrimerization of Dimethyl Acetylenedicarboxylate (DMAD) Catalyzed by <i>trans</i>-[Cr(CO)₃(Heptamethylindenyl)Rh(CO)₂ ]^†

The complex trans-[Cr(CO)3(heptamethylindenyl)Rh(CO)2] (II) is a very efficient catalyst precursor in the cyclotrimerization reaction of dimethyl acetylenedicarboxylate (DMAD) to hexacarbomethoxybenzene. The formation of the “true” catalyst, likely to be the complex trans-[Cr(CO)3−Ind*−Rh(DMAD)2], is the slow step of the reaction and takes place during the induction period, the length of which is temperature dependent. After total consumption of the monomer two organometallic complexes were isolated from the inorganic residue, viz., the catalyst precursor II and the complex trans-[Cr(CO)3−Ind*−Rh(CO)(FADE)] (III; FADE = fumaric acid dimethyl ester), which turns out to be active in the trimerization reaction as II. The hydrogenation of DMAD to FADE is probably occurring via C−H bond activation of the solvent cyclohexane

Intervalence Charge Transfer in Cationic Heterotrinuclear Fe(III)−Rh(I)−Cr(0) Triads of the Polyaromatic Cyclopentadienyl−Indenyl Ligand

The challenge to realize polymetallic assemblies of unambiguous structure and stereochemistry, in which the nature of the intervalence transition (IT) is rationalized, has been faced by investigating the syn and anti isomers of η6-Cr(CO)3{η5-[(2-ferrocenyl)indenyl]Rh(CO)2} and their mixed-valence cations. Crystallographic studies and DFT calculations provide a detailed description of the structural and electronic features of these complexes, evidencing a significant difference in geometrical distortions and frontier MO composition between syn and anti isomers. Mixed-valence cations are generated and monitored by low-temperature spectroelectrochemistry in the visible, IR, and near-IR regions. The IT bands in the near-IR spectra are rationalized in the framework of Marcus−Hush theory and at quantum chemistry level by density functional theory. Noteworthy, the results reported provide rare experimental evidence that the presence of a third metal center (Rh) increases the metal−metal (Fe−Cr) interaction with respect to the structurally correlated binuclear system