Home

Person

Lothar Helm

About
Privacy
Disclaimer

Graph Chatbot

Related publications (91)

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, Loïck Moriggi, Lothar Helm, Alain Borel

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

Early stages of radiation damage in graphite and carbon nanostructures: A first-principles molecular dynamics study

Lothar Helm, Ursula Röthlisberger, Ivano Tavernelli, Oleg Yazyev

Understanding radiation-induced defect formation in carbon materials is crucial for nuclear technology and for the manufacturing of nanostructures with desired properties. Using first-principles molecular dynamics, we perform a systematic study of the none ...

2007

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

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, Eva Jakab Toth, Petra Lebduskova

2007

Gadolinium(III) ion in liquid water: structure, dynamics and magnetic interactions from first principles

Lothar Helm, Oleg Yazyev

We applied first principles molecular dynamics (MD) technique to study structure, dynamics, and magnetic interactions of the

Gd^{3+}

aqua ion dissolved in liquid water, a prototypical system for Gd-based complexes used as contrast agents for magnetic res ...

2007

Multiple-frequency EPR spectra of two aqueous Gd3+ polyaminopolypyridinecarboxylate complexes: a study of high field effects

Lothar Helm, Alain Borel, Sabrina Laus, Marinella Mazzanti

In the search for highly efficient magnetic resonance imaging contrast agents, polyaminopolypyridinecarboxylate complexes of Gd3+ have shown unusual properties with both very rapid and very slow electron spin relaxation in solution observed by electron par ...

2007

Understanding Paramagnetic Relaxation Phenomena for Water-Soluble Gadofullerenes

André Merbach, Lothar Helm, Eva Jakab Toth, Sabrina Laus

2007

Magnetism induced by single-atom defects in nanographites

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 magnetism due to the defect-induced extended sta ...

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

Relaxivity in paramagnetic systems: Theory and mechanisms

Lothar Helm

2006

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

Positively Charged GdIII Cryptates: Slow, Associative Water Exchange

André Merbach, Lothar Helm, Eva Jakab Toth

A combined variable-temp. and multiple field 17O NMR, EPR and NMRD study was performed for the 1st time on Gd(III) complexes of cryptand ligands, L1 and L2, where L1 contains three 2,2'-bipyridine units ([bpy.bpy.bpy]) and L2 is the disubstituted Me ester ...

2006

Hyperfine interactions in aqueous solution of Cr3+: an ab initio molecular dynamics study

Lothar Helm, Oleg Yazyev

We performed an ab initio mol. dynamics simulation of the paramagnetic transition metal ion Cr3+ in aq. soln. Isotropic hyperfine coupling consts. between the electron spin of the chromium ion and nuclear spins of all water mols. have been detd. for instan ...

2006

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

Kinetic studies on the first dihydrogen aquacomplex, [Ru(H2)(H2O)5]2+: Formation under H2 pressure and catalytic H/D isotope exchange in water

Gabor Laurenczy, André Merbach, Lothar Helm, Pascal Grundler, Oleg Yazyev

The ruthenium(II) hexaaqua complex [Ru(H2O)6]2+ reacts with dihydrogen under pressure to give the h2-dihydrogen ruthenium(II) pentaaqua complex [Ru(H2)(H2O)5]2+.The complex was characterized by 1H, 2H and 17O NMR: d H = -7.65 ppm, J HD = 31.2 Hz, d O = -80 ...

2006

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

First in vivo MRI assessment of a self-assembled metallostar compound endowed with a remarkable high field relaxivity

André Merbach, Lothar Helm, Eva Jakab Toth, Joao Bruno Livramento Fig.

{Fe[Gd2bpy(DTTA)2(H2O)4]3}4- is a self-assembled, metallostar-structured potential MRI contrast agent, with six efficiently relaxing Gd3+ centers confined into a small mol. space. Its proton relaxivity is particularly remarkable at very high magnetic field ...

2006

Phosphinic derivative of DTPA conjugated to a G5 PAMAM dendrimer: an 17O and 1H relaxation study of its Gd(III) complex

André Merbach, Lothar Helm, Eva Jakab Toth, Petra Lebduskova

A DTPA-based chelate containing one phosphinate group was conjugated to a generation 5 polyamidoamine (PAMAM) dendrimer via a benzylthiourea linkage. The Gd(III) complex of this novel conjugate has potential as a contrast agent for magnetic resonance imagi ...

2006

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

Unexpected Aggregation of Neutral, Xylene-Cored Dinuclear GdIII Chelates in Aqueous Solution

André Merbach, Lothar Helm, Eva Jakab Toth, Jéröme Costa

2006

Page 4 of 5