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Lothar Helm

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Publications associées (91)

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H5EPTPACH2OH: Synthesis, Relaxometric Characterization and 1H NMR Spectroscopic Studies on the Solution Dynamics of Its LnIII Complexes

Lothar Helm

The synthesis and characterization of a new metal chelator, 4-(S)-hydroxymethyl-3,6,10-tri(carboxymethyl)-3,6,10-triazadodecanedioic acid (H5EPTPACH2OH), is reported. Protonation constants for the ligand H5EPTPACH2OH and for the previously reported H5EPTPA ...

2007

Design of Gd(III)-Based Magnetic Resonance Imaging Contrast Agents: Static and Transient Zero-Field Splitting Contributions to the Electronic Relaxation and Their Impact on Relaxivity

André Merbach, Lothar Helm, Alain Borel, Loïck Moriggi

A multiple-frequency (9.4-325 GHz) and variable-temperature (276-320 K) electron paramagnetic resonance (EPR) study on low molecular weight gadolinium(III) complexes for potential use as magnetic resonance imaging (MRI) contrast agents has been performed. ...

2007

17O nuclear quadrupole coupling constants of water bound to a metal ion: A gadolinium(III) case study

Lothar Helm, Oleg Yazyev

Rotational correlation times of metal ion aqua complexes can be detd. from 17O NMR relaxation rates if the quadrupole coupling const. of the bound water oxygen-17 nucleus is known. The rotational correlation time is an important parameter for the efficienc ...

2006

Defect-induced magnetism in graphene

Lothar Helm, Oleg Yazyev

We study from first principles the magnetism in graphene induced by single carbon atom defects. For two types of defects considered in our study, the hydrogen chemisorption defect and the vacancy defect, the itinerant magnetism due to the defect-induced ex ...

2007

Tellurium speciation under hydrothermal conditions

Lothar Helm, Pascal Grundler

Tellurium is the only element which forms a variety of minerals with gold as principal component (e.g. calaverite AuTe2, krennerite (AuAg)Te2, petzite Ag3AuTe2 and sylvanite AgAuTe4). These minerals have been known for a long time and are of economic value ...

2009

Aqueous solubility and speciation of Te(IV) at elevated temperatures

Lothar Helm, Pascal Grundler

2009

Core spin-polarization correction in pseudopotential-based electronic structure calculations

Ursula Röthlisberger, Lothar Helm, Oleg Yazyev, Ivano Tavernelli

A simple scheme for the evaluation of the core spin-polarization contribution within pseudopotential electronic structure methods is proposed. The method uses a reconstruction of the all-electron wave functions and the frozen valence spin-d. approxn. to so ...

2005

Quantum Chemical Investigation of Hyperfine Coupling Constants on First Coordination Sphere Water Molecule of Gadolinium(III) Aqua Complexes

Lothar Helm, Oleg Yazyev

2005

Relevance of the Ligand Exchange Rate and Mechanism of fac-[(CO)3M(H2O)3]+ (M = Mn, Tc, Re) Complexes for New Radiopharmaceuticals

André Merbach, Lothar Helm, Pascal Grundler

2006

Solvent Exchange and Electron-Spin Relaxation on Homoleptic Acetonitrile Complexes of Trivalent Lanthanides

Lothar Helm

Homoleptic acetonitrile complexes [Nd(CH3CN)(9)]Al(OC(CF3)(3))(4), [Dy(CH3CN)(9)]Al(OC(CF3)(3))(4), and [Tm(CH3CN)(8)]Al(OC(CF3)(3))(4) have been studied in anhydrous acetonitrile by 14N and 1H NMR relaxation. Solvent-exchange rate constants ...

American Chemical Society2015

Spectroscopic investigation of Tellurium in chloride brines

Lothar Helm, Pascal Grundler

2008

Carbazole as Linker for Dinuclear Gadolinium-Based MRI Contrast Agents

Lothar Helm, Anne-Sophie Chauvin, Loïck Moriggi, Bibimaryam Mousavi

Ligands able to complex two gadolinium ions have been synthesized and characterized in view of the ability of the complexes to increase the spin relaxation of water protons. All ligands are based on the heptadentate diethylenetriaminetetraacetic acid (DTTA ...

Wiley-V C H Verlag Gmbh2017

A High-Frequency EPR Study of Frozen Solutions of Gd(III) Complexes: Straightforward Determination of the Zero-Field Splitting Parameters and Simulation of the NMRD Profiles

André Merbach, Lothar Helm, Alain Borel

Gd(III) (S = 7/2) polyaminocarboxylates, used as contrast agents for Magnetic Resonance Imaging (MRI), were studied in frozen solutions by High-Frequency-High-Field Electron Paramagnetic Resonance (HF-EPR). EPR spectra recorded at 240 GHz and temperatures ...

2006

MRI micelles self-assembled from synthetic gadolinium-based nano building blocks

Lothar Helm

A synthetic nano building block endowed with amphiphilic properties and chelated gadoliniumis presented. Spontaneous self-assembly into small 12 nm corona-core stealth Gd-micelles with inherently high gadolinium loading occurs in water. Gd-Micelles are a n ...

Royal Society of Chemistry2019

High relaxivity MRI contrast agents for high magnetic field - challenges and pitfalls

Lothar Helm

Amer Chemical Soc2014

Gadolinium(III) complexes of mono-and diethyl esters of monophosphinic acid analogue of DOTA as potential MRI contrast agents: solution structures and relaxometric studies

André Merbach, Lothar Helm

2007

Isomerization mechanisms of a labile Co(II) octahedral complex

André Merbach, Lothar Helm, Fabrice Riblet

The labile cobalt (II) complex [Co(TUF)2(Pic)2] with 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (TUF) bidentate and 4-methylpyridine (Pic) monodentate ligands was studied by variable temp. (VT) 19F NMR from 184 to 312 K. In contrast to the solid state, ...

2006

Physicochemical and MRI characterization of Gd3+-loaded polyamidoamine and hyperbranched dendrimers

André Merbach, Lothar Helm, Loïck Moriggi

Springer2007

Rigid M(II)L2Gd(III)2 (M=Fe, Ru) Complexes of a Terpyridine-Based Heteroditopic Chelate: A Class of Candidates for MRI Contrast Agents

André Merbach, Lothar Helm

2005

Water-Exchange Study Revealed Unexpected Substitution Behavior of [(CO)2(NO)Re(H2O)3]2+ in Aqueous Media

André Merbach, Lothar Helm, Pascal Grundler, Marie-Line Lehaire

The pH-dependent water-exchange rates of [(CO)2(NO)Re(H2Ocis)2(H2Otrans)]2+ (1) in aq. media were investigated by means of 17O NMR spectroscopy at 298 K. Because of the low pKa value found for 1 (pKa = 1.4 ± 0.3), the water-exchange rate const. kobsH2Otran ...

2006