Formation and characterization of thioglycolic acid–silver cluster complexes

Gas phase reactivity observed in an ion trap was used to produce silver clusters protected with thioglycolic acid. Fragmentation pathways as well as optical properties were explored experimentally and theoretically. Sequential losses of SCH2 and CO2 in the ion trap lead to redox reactions with charge transfers between the metal part and the carboxylate and thiolate groups. This allows us to control the number of electrons in the metallic subunit and thus optical properties of the complexes. The presented formation process can be used as a prototype for tuning optical and chemical properties of ligated metal clusters by varying the number of confined electrons within the metallic subunit

Interplay between chromophore binding and domain assembly by the B₁₂-dependent photoreceptor protein, CarH.

From Europe PMC via Jisc Publications RouterHistory: ppub 2021-05-01, epub 2021-05-05Publication status: PublishedFunder: Biotechnology and Biological Sciences Research Council; Grant(s): BB/L002655/1, BB/L016486/1, BB/M011208/1Organisms across the natural world respond to their environment through the action of photoreceptor proteins. The vitamin B12-dependent photoreceptor, CarH, is a bacterial transcriptional regulator that controls the biosynthesis of carotenoids to protect against photo-oxidative stress. The binding of B12 to CarH monomers in the dark results in the formation of a homo-tetramer that complexes with DNA; B12 photochemistry results in tetramer dissociation, releasing DNA for transcription. Although the details of the response of CarH to light are beginning to emerge, the biophysical mechanism of B12-binding in the dark and how this drives domain assembly is poorly understood. Here - using a combination of molecular dynamics simulations, native ion mobility mass spectrometry and time-resolved spectroscopy - we reveal a complex picture that varies depending on the availability of B12. When B12 is in excess, its binding drives structural changes in CarH monomers that result in the formation of head-to-tail dimers. The structural changes that accompany these steps mean that they are rate-limiting. The dimers then rapidly combine to form tetramers. Strikingly, when B12 is scarcer, as is likely in nature, tetramers with native-like structures can form without a B12 complement to each monomer, with only one apparently required per head-to-tail dimer. We thus show how a bulky chromophore such as B12 shapes protein/protein interactions and in turn function, and how a protein can adapt to a sub-optimal availability of resources. This nuanced picture should help guide the engineering of B12-dependent photoreceptors as light-activated tools for biomedical applications

Heteroatom Donor‐Decorated Polymer‐Immobilized Ionic Liquid Stabilized Palladium Nanoparticles : Efficient Catalysts for Room‐Temperature Suzuki‐Miyaura Cross‐Coupling in Aqueous Media

Palladium nanoparticles stabilized by heteroatom donor‐modified polystyrene‐based polymer immobilized ionic liquids (PdNP@HAD‐PIILP; HAD‐PPh2, OMe, NH2, CN, pyrrolidone) are highly efficient catalysts for the Suzuki‐Miyaura cross‐coupling in aqueous media under mild conditions. Catalyst modified with phosphine was consistently the most efficient as it gave high yields across a range of substrates under mild conditions at low catalyst loadings. Incorporation of polyethylene glycol into the phosphine modified immobilised ionic liquid support improved catalyst efficacy by improving dispersibility and facilitating access to the active site. Moreover, each of the heteroatom modified catalysts was more active than the corresponding unsubstituted imidazolium‐based polystyrene benchmark as well as commercial samples of Pd/C. Catalyst generated in situ from either [PdCl4]@PPh2‐PIILP or its PEGylated counterpart [PdCl4]@PPh2‐PEGPIILP, by reduction with phenylboronic acid, outperformed their pre‐formed counterparts for the vast majority of substrates examined. The turnover frequency of 16,300 h−1 obtained at room temperature is one of the highest to be reported for palladium nanoparticle‐catalysed Suzuki‐Miyaura cross‐coupling between 4‐bromoacetophenone and phenylboronic acid in aqueous media under such mild conditions

Optical and infrared spectroscopy on biomolecules and metal-molecule complex in the gas phase

Les différents travaux présentés dans ce mémoire de thèse regroupent des études de spectroscopie en phase gazeuse de biomolécules et de systèmes molécule-agrégats métalliques. Le couplage de la spectroscopie de masse avec la spectroscopie laser UV/Visible et IR permet de réaliser de la spectroscopie d’action sur des ions et des complexes ioniques sélectionnés en masse et isolés dans un piège ionique. Les mesures renseignent sur les caractéristiques intrinsèques du système étudié permettant d’obtenir ses propriétés vibrationnels et électroniques. La principale partie de ce travail est axée sur l’étude des protéines et des processus chimiques mis en jeu dans leurs sous-parties essentielles, les acides aminés. Nous avons ainsi pu obtenir le spectre d’absorption optique en phase gazeuse de protéines entières. L’étude des systèmes radicalaires et notamment les propriétés du tryptophane radicalaire ont permis d’établir des signatures spectroscopiques pour diagnostiquer ces états réactifs. Les différents sites de complexation d’un cation métallique dans une séquence peptidique modèle ont permis d’illustrer la complémentarité des informations obtenues en regroupant les techniques de spectroscopie infrarouge et UV/Visible avec la mobilité ionique. Des approches ont été réalisées sur la synthèse de systèmes modèles en phase gazeuse et l’étude des précurseurs observés lors de la synthèse de nanoparticules en solution. Nous avons notamment pu synthétiser par collision en piège ionique et isoler un agrégat d’argent Ag42+ stabilisé. Le rôle des ligands dans les propriétés optiques des nanoparticules stabilisées par des molécules de type thiols a ainsi également été étudiéThe Different works presented in this thesis include studies of gas phase spectroscopy of biomolecules and metal-molecule complex. Coupling mass spectrometry and laser spectroscopy in the UV/Visible and IR range allows for action spectroscopy of mass-selected and isolated ions in ion trap. Measures provide information on intrinsic characteristics of the system and informs on vibrational and electronic properties. The main part of this work focuses on the study of proteins and chemical processes involved in their subparts, amino acids. We were able to obtain optical absorption spectrum of entire proteins in the gas phase. The studies of radical systems incuding tryptophan radical properties have established spectroscopic signatures of these reactive states. Different sites of a metal cation, silver, in a model peptide sequence were used to illustrate the complementarity of infrared spectroscopy and UV/Visible with ion mobility to get information resolve preferential metal binding site. Others approaches have been done on the synthesis of model systems in the gas phase concerning the study of precursors observed during the synthesis of nanoparticles. In particular, we could synthesize collision in ion trap and isolate an Ag42+ stabilized cluster. The role of ligands on the optical properties of nanoparticles stabilized by thiol-type molecules has also been studie

Using Collision Cross Section Distributions to Assess the Distribution of Collision Cross Section Values

In this study we explore the use of collision cross section distributions to allow comparability of IM-MS data for proteins on different instruments. We present measurements on seven standard proteins across three IM-MS configurations, namely an Agilent 6560 IM QToF, a Waters Synapt G2 possessing a TWIMS cell and a modified Synapt G2 possessing an RF confining linear field drift cell. Mobility measurements were taken using both He and N2 as the drift gases. To aid comparability across instruments and best assess the corresponding gas-phase conformational landscapes of the protein ‘standards’ we present the data in the form of averaged collision cross section distributions

Initial protein unfolding events revealed by 213 nm UVPD coupled to IM-MS

In this work we couple UVPD with activated ion mobility mass spectrometry to measure how three model proteins start to unfold. Ubiquitin, cytochrome c and myoglobin ions produced via nESI from salty solutions are subjected to UV irradiation pre-mobility separation, experiments are conducted with a range of source conditions which alter the conformation of the precursor ion as shown by the drift time profiles. For all three proteins the compact structures result in less fragmentation than more extended structures which emerge following progressive in-source activation. Cleavage sites are found to differ between conformational ensembles, for example, for the dominant charge state of cytochrome c [M+7H]7+, cleavage at Phe10, Thr19 and Val20 was only observed in activating conditions while cleavage at Ala43 is dramatically enhanced. Mapping the photo-cleaved fragments onto crystallographic structures provides insight into the local structural changes that occur as protein unfolding progresses, which is coupled to global restructuring observed in the drift time profiles

Quantification of Protein Glycation Using Vibrational Spectroscopy

Glycation is a protein modification prevalent in the progression of diseases such as Diabetes and Alzheimer's, as well as a byproduct of therapeutic protein expression, notably for monoclonal antibodies (mAbs). Quantification of glycated protein is thus advantageous in both assessing the advancement of disease diagnosis and for quality control of protein therapeutics. Vibrational spectroscopy has been highlighted as a technique that can easily be modified for rapid analysis of the glycation state of proteins, and requires minimal sample preparation. Glycated samples of lysozyme and albumin were synthesised by incubation with 0.5 M glucose for 30 days. Here we show that both FTIR-ATR and Raman spectroscopy are able to distinguish between glycated and non-glycated proteins. Principal component analysis (PCA) was used to show separation between control and glycated samples. Loadings plots found specific peaks that accounted for the variation - notably a peak at 1027 cm-1 for FTIR-ATR. In Raman spectroscopy, PCA emphasised peaks at 1040 cm-1 and 1121 cm-1. Therefore, both FTIR-ATR and Raman spectroscopy found changes in peak intensities and wavenumbers within the sugar C-O/C-C/C-N region (1200-800 cm-1). For quantification of the level of glycation of lysozyme, partial least squares regression (PLSR), with statistical validation, was employed to analyse Raman spectra from solution samples containing 0-100% glycated lysozyme, generating a robust model with R2 of 0.99. We therefore show the scope and potential of Raman spectroscopy as a high throughput quantification method for glycated proteins in solution that could be applied in disease diagnostics, as well as therapeutic protein quality control