Publications by authors named "Jan Blahut"

12 Publications

  • Page 1 of 1

Maximizing efficiency of dipolar recoupling in solid-state NMR using optimal control sequences.

Sci Adv 2021 Oct 13;7(42):eabj5913. Epub 2021 Oct 13.

Bayerisches NMR Zentrum (BNMRZ) at Department Chemie, Technische Universität München (TUM), 85747 Garching, Germany.

[Figure: see text].
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http://dx.doi.org/10.1126/sciadv.abj5913DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8514097PMC
October 2021

Monitoring Dynamics, Structure, and Magnetism of Switchable Metal-Organic Frameworks via H-Detected MAS NMR.

Angew Chem Int Ed Engl 2021 Sep 2;60(40):21778-21783. Epub 2021 Sep 2.

Centre de Résonance Magnétique Nucléaire à Très Hauts Champs, UMR 5082 CNRS, ENS Lyon, UCBL), Université de Lyon, 69100, Villeurbanne, France.

We present a toolbox for the rapid characterisation of powdered samples of paramagnetic metal-organic frameworks at natural abundance by H-detected solid-state NMR. Very fast MAS rates at room and cryogenic temperatures and a set of tailored radiofrequency irradiation schemes help overcome the sensitivity and resolution limits often associated with the characterisation of MOF materials. We demonstrate the approach on DUT-8(Ni), a framework containing Ni paddle-wheel units which can exist in two markedly different architectures. Resolved H and C resonances of organic linkers are detected and assigned in few hours with only 1-2 mg of sample at natural isotopic abundance, and used to rapidly extract information on structure and local internal dynamics of the assemblies, as well as to elucidate the metal electronic properties over an extended temperature range. The experiments disclose new possibilities for describing local and global structural changes and correlating them to electronic and magnetic properties of the assemblies.
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http://dx.doi.org/10.1002/anie.202107032DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8519119PMC
September 2021

Spectroscopic Signature and Structure of the Active Sites in Ziegler-Natta Polymerization Catalysts Revealed by Electron Paramagnetic Resonance.

J Am Chem Soc 2021 Jul 25;143(26):9791-9797. Epub 2021 Jun 25.

Department of Chemistry and Applied Biosciences, ETH Zurich, Wolfgang-Pauli-Strasse 1-5, 8093 Zurich, Switzerland.

Despite decades of extensive studies, the atomic-scale structure of the active sites in heterogeneous Ziegler-Natta (ZN) catalysts, one of the most important processes of the chemical industry, remains elusive and a matter of debate. In the present work, the structure of active sites of ZN catalysts in the absence of ethylene, referred to as dormant active sites, is elucidated from magnetic resonance experiments carried out on samples reacted with increasing amounts of BCl so as to enhance the concentration of active sites and observe clear spectroscopic signatures. Using electron paramagnetic resonance (EPR) and NMR spectroscopies, in particular 2D HYSCORE experiments complemented by density functional theory (DFT) calculations, we show that the activated ZN catalysts contain bimetallic alkyl-Ti(III),Al species whose amount is directly linked to the polymerization activity of MgCl-supported Ziegler-Natta catalysts. This connects those spectroscopic signatures to the active species formed in the presence of ethylene and enables us to propose an ethylene polymerization mechanism on the observed bimetallic alkyl-Ti(III),Al species based on DFT computations.
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http://dx.doi.org/10.1021/jacs.1c02818DOI Listing
July 2021

Development of a Borane-(Meth)acrylate Photo-Click Reaction.

Angew Chem Int Ed Engl 2021 Jul 24;60(31):17037-17044. Epub 2021 Jun 24.

Université de Haute-Alsace, CNRS, IS2M UMR 7361, 68100, Mulhouse, France.

In the development of 3D printing fuels, there is a need for new photoinitiating systems working under mild conditions and/or leading to polymers with new and/or enhanced properties. In this context, we introduce herein N-heterocyclic carbene-borane complexes as reagents for a new type of photo-click reaction, the borane-(meth)acrylate click reaction. Remarkably, the higher bond number of boranes relative to thiols induced an increase of the network density associated with faster polymerization kinetics. Solid-state NMR evidenced the strong participation of the boron centers on the network properties, while DMA and AFM showed that the materials exhibit improved mechanical properties, as well as reduced solvent swelling.
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http://dx.doi.org/10.1002/anie.202103008DOI Listing
July 2021

Two-Photon Absorbing AIEgens: Influence of Stereoconfiguration on Their Crystallinity and Spectroscopic Properties and Applications in Bioimaging.

ACS Appl Mater Interfaces 2020 Dec 20;12(49):55157-55168. Epub 2020 Nov 20.

Univ. Lyon, ENS Lyon, CNRS, Université Lyon 1, Laboratoire de Chimie, UMR 5182, 46 Allée d'Italie, 69364 Lyon, France.

This paper aims at designing chromophores with efficient aggregation-induced emission (AIE) properties for two-photon fluorescence microscopy (2PFM), which is one of the best-suited types of microscopy for the imaging of living organisms or thick biological tissues. Tetraphenylethylene (TPE) derivatives are common building blocks in the design of chromophores with efficient AIE properties. Therefore, in this study, extended TPE AIEgens specifically optimized for two-photon absorption (2PA) are synthesized and the resulting (/) isomers are separated using chromatography on chiral supports. Comparative characterization of the AIE properties is performed on the pure () and () isomers and the mixture, allowing us, in combination with powder X-ray diffraction and solid-state NMR, to document a profound impact of crystallinity on solid-state fluorescence properties. In particular, we show that stereopure AIEgens form aggregates of superior crystallinity, which in turn exhibit a higher fluorescence quantum yield compared to diastereoisomers mixtures. Preparation of stereopure organic nanoparticles affords very bright fluorescent contrast agents, which are then used for cellular and intravital two-photon microscopy on human breast cancer cells and on zebrafish embryos.
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http://dx.doi.org/10.1021/acsami.0c15810DOI Listing
December 2020

Paramagnetic Cobalt(II) Complexes with Cyclam Derivatives: Toward F MRI Contrast Agents.

Inorg Chem 2020 Jul 7;59(14):10071-10082. Epub 2020 Jul 7.

Department of Inorganic Chemistry, Faculty of Science, Charles University, Hlavova 2030, 12843 Prague 2, Czech Republic.

In order to develop novel, more efficient, and/or selective contrast agents for magnetic resonance imaging (MRI), different are explored as alternatives to water-relaxation enhancement. In this work, cobalt(II/III) complexes of bis(-trifluoroethyl)cyclam derivatives with two acetate or two phosphonate pendant arms, H and H, were prepared and investigated. X-ray diffraction structures confirmed octahedral coordination with a very stable - cyclam conformation and with fluorine atoms located about 5.3 Å from the metal center. The Co(II) complexes are kinetically inert, decomposing slowly even in 1 M aqueous HCl at 80 °C. The Co(II) complexes exhibited well-resolved paramagnetically shifted NMR spectra. These were interpreted with the help of quantum chemistry calculations. The C NMR shifts of the -[Co()] complex were successfully assigned based on spin density delocalization within the ligand molecule. The obtained spin density also helps to describe -metal-induced NMR relaxation properties of F nuclei, including the contribution of a Fermi contact relaxation mechanism. The paramagnetic complexes show convenient relaxation properties to be used as F MRI contrast agents.
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http://dx.doi.org/10.1021/acs.inorgchem.0c01216DOI Listing
July 2020

Self-Assembled Thermoresponsive Polymeric Nanogels for F MR Imaging.

Biomacromolecules 2018 08 27;19(8):3515-3524. Epub 2018 Jul 27.

Institute of Macromolecular Chemistry AS CR , v.v.i., Heyrovského sq. 2 , Prague 6 162 06 , Czech Republic.

Magnetic resonance imaging using fluorinated contrast agents (F MRI) enables to achive highcontrast in images due to the negligible fluorine background in living tissues. In this pilot study, we developed new biocompatible, temperature-responsive, and easily synthesized polymeric nanogels containing a sufficient concentration of magnetically equivalent fluorine atoms for F MRI purposes. The structure of the nanogels is based on amphiphilic copolymers containing two blocks, a hydrophilic poly[ N-(2-hydroxypropyl)methacrylamide] (PHPMA) or poly(2-methyl-2-oxazoline) (PMeOx) block, and a thermoresponsive poly[ N(2,2difluoroethyl)acrylamide] (PDFEA) block. The thermoresponsive properties of the PDFEA block allow us to control the process of nanogel self-assembly upon its heating in an aqueous solution. Particle size depends on the copolymer composition, and the most promising copolymers with longer thermoresponsive blocks form nanogels of suitable size for angiogenesis imaging or the labeling of cells (approximately 120 nm). The in vitro F MRI experiments reveal good sensitivity of the copolymer contrast agents, while the nanogels were proven to be noncytotoxic for several cell lines.
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http://dx.doi.org/10.1021/acs.biomac.8b00812DOI Listing
August 2018

Paramagnetic F Relaxation Enhancement in Nickel(II) Complexes of N-Trifluoroethyl Cyclam Derivatives and Cell Labeling for F MRI.

Inorg Chem 2017 Nov;56(21):13337-13348

Department of Inorganic Chemistry, Faculty of Science, Charles University (Univerzita Karlova) , Hlavova 2030, 128 43 Prague 2, Czech Republic.

1,8-Bis(2,2,2-trifluoroethyl)cyclam (te2f) derivatives with two coordinating pendant arms involving methylenecarboxylic acid (Hte2f2a), methylenephosphonic acid (Hte2f2p), (2-pyridyl)methyl (te2f2py), and 2-aminoethyl arms (te2f2ae) in 4,11-positions were prepared, and their nickel(II) complexes were investigated as possible F MR tracers. The solid-state structures of several synthetic intermediates, ligands, and all complexes were confirmed by X-ray diffraction analysis. The average Ni···F distances were determined to be about 5.2 Å. All complexes exhibit a trans-III cyclam conformation with pendant arms bound in the apical positions. Kinetic inertness of the complexes is increased in the ligand order te2f2ae ≪ te2f < te2f2py ≈ Hte2f2p ≪ Hte2f2a. The [Ni(te2f2a)] complex is the most kinetically inert Ni(II) complex reported so far. Paramagnetic divalent nickel caused a shortening of F NMR relaxation time down to the millisecond range. Solubility, stability, and cell toxicity were only satisfactory for the [Ni(te2f2p)] complex. This complex was visualized by F MRI utilizing an ultrashort echo time (UTE) imaging pulse sequence, which led to an increase in sensitivity gain. Mesenchymal stem cells were successfully loaded with the complex (up to 0.925/5.55 pg Ni/F per cell).F MRI using a UTE pulse sequence provided images with a good signal-to-noise ratio within the measurement time, as short as tens of minutes. The data thus proved a major sensitivity gain in F MRI achieved by utilization of the paramagnetic (transition) metal complex as F MR tracers coupled with the optimal fast imaging protocol.
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http://dx.doi.org/10.1021/acs.inorgchem.7b02119DOI Listing
November 2017

A combined NMR and DFT study of conformational dynamics in lanthanide complexes of macrocyclic DOTA-like ligands.

Phys Chem Chem Phys 2017 Oct;19(39):26662-26671

Centro de Investigaciones Científicas Avanzadas (CICA) and Departamento de Química, Facultade de Ciencias, Universidade da Coruña, 15071 A Coruña, Galicia, Spain.

The solution dynamics of the Eu(iii) complexes of Hdota (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetracarboxylic acid) and Hdo3ap (1,4,7,10-tetraazacyclododecane-4,7,10-tris(carboxymethyl)-1-methylphosphonic acid, bound in both monoprotonated and fully deprotonated forms) were investigated by using a combination of NMR measurements and DFT calculations. In solution, an equilibrium between the square antiprismatic (SAP) and twisted-square antiprismatic isomers (TSAP) of these complexes is present. These two isomers interconvert by rotation of the pendant arms or inversion of the cyclen chelate rings. 1D EXSY NMR spectra were used to determine these exchange rates with unprecedented accuracy. It was found that the two processes occur at different rates. Additional variable-temperature measurements allowed determination of the corresponding activation parameters for the two processes. DFT calculations were then used to obtain mechanistic information at the molecular level. The results show that the cyclen inversion pathway involves stepwise inversion of the four chelate rings formed upon metal ion coordination. However, the arm rotation process may operate through a synchronous rotation of the pendant arms or a stepwise mechanism depending on the system. A mixed cluster-continuum approach was required to improve the agreement between experimental and calculated activation parameters for the arm rotation process. The obtained results will aid the design of MRI contrast agents. Furthermore, the methodology developed in this work can be further applied for the investigation of other dynamic paramagnetic systems, e.g. peptides with Ln(iii) probes or natively paramagnetic metalloproteins.
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http://dx.doi.org/10.1039/c7cp05296kDOI Listing
October 2017

A contactless positioning system for monitoring discontinuities in three dimensions with geological and geotechnical applications.

Rev Sci Instrum 2017 Jul;88(7):074501

IGS Research, Calle la Coma, Nave 8, 43140 La Pobla de Mafumet, Tarragona, Spain.

In this paper, a contactless positioning system is presented which has been designed to monitor the kinematic behavior of mechanical discontinuities in three dimensions. The positioning system comprises a neodymium magnet, fixed on one side of a discontinuity, and a magnetoresistive sensing array, fixed on the opposing side. Each of the anisotropic magnetoresistive sensors in the sensing array records the magnetic field along three orthogonal directions. The positioning system intrinsically generates compact data packages which are transmitted effectively using a range of standard wireless telecommunication technologies. These data are then modeled using a global least squares fitting procedure in which the adjustable parameters are represented by the position and orientation of the neodymium magnet. The instrumental resolution of the positioning system can be tuned depending on the strength of the magnetic field generated by the neodymium magnet and the distance between the neodymium magnet and the magnetoresistive sensing array. For a typical installation, the displacement resolution is shown to be circa 10 μm while the rotation resolution is circa 0.1°. The first permanently deployed positioning system was established in June 2016 to monitor the behavior of an N-S trending fault located at the contact between the eastern Alps and the Vienna Basin. The robust design of the positioning system is demonstrated by the fact that no interruptions in the broadcasted data streams have occurred since its installation. It has a range of potential applications in many areas of basic and applied research including geology, geotechnical engineering, and structural health monitoring.
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http://dx.doi.org/10.1063/1.4993925DOI Listing
July 2017

Eu(III) Complex with DO3A-amino-phosphonate Ligand as a Concentration-Independent pH-Responsive Contrast Agent for Magnetic Resonance Spectroscopy (MRS).

Inorg Chem 2017 Feb 7;56(4):2078-2091. Epub 2017 Feb 7.

Department of Inorganic Chemistry, Faculty of Science, Charles University , Hlavova 2030, Prague 2 128 43, Czech Republic.

A new DOTA-like ligand Hdo3aNP with a 2-[amino(methylphosphonic acid)]ethyl-coordinating pendant arm was prepared, and its coordinating properties were studied by NMR spectroscopy and potentiometry. The study revealed a rare slow exchange (on the H and P NMR time scale) between protonated and unprotonated complex species with a corresponding acidity constant pK ∼ 8.0. This unusually slow time scale associated with protonation is caused by a significant geometric change from square-antiprismatic (SA) arrangement observed for protonated complex SA-[Eu(Hdo3aNP)] to twisted-square-antiprismatic (TSA) arrangement found for deprotonated complex TSA-[Eu(do3aNP)]. This behavior results in simultaneous occurrence of the signals of both species in the P NMR spectra at approximately -118 and +70 ppm, respectively. Such an unprecedented difference in the chemical shifts between species differing by a proton is caused by a significant movement of the principal magnetic axis and by a change of phosphorus atom position in the coordination sphere of the central Eu(III) ion (i.e., by relative movement of the phosphorus atom with respect to the principal magnetic axis). It changes the sign of the paramagnetic contribution to the P NMR chemical shift. The properties discovered can be employed in the measurement of pH by MRS techniques as presented by proof-of-principle experiments on phantoms.
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http://dx.doi.org/10.1021/acs.inorgchem.6b02749DOI Listing
February 2017

Nickel(II) complexes of N-CH2CF3 cyclam derivatives as contrast agents for (19)F magnetic resonance imaging.

Dalton Trans 2016 Jan;45(2):474-8

Department of Inorganic Chemistry, Faculty of Science, Charles University (Univerzita Karlova), Hlavova 2030, 128 43 Prague 2, Czech Republic.

Kinetically inert Ni(ii) complexes of N(1),N(8)-bis(2,2,2-trifluoroethyl)cyclams with hydrogen atoms or phosphonic acid groups in the N(4),N(11)-positions show significant (19)F NMR relaxation rate enhancement useful for 19-fluorine MRI imaging.
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http://dx.doi.org/10.1039/c5dt04138dDOI Listing
January 2016
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