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Lothar Helm

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Publications associées (91)

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Towards the Rational Design of MRI Contrast Agents: Electron Spin Relaxation Is Largely Unaffected by the Coordination Geometry of Gadolinium(III)-DOTA-Type Complexes

Lothar Helm, Alain Borel, Loïck Moriggi

Electron-spin relaxation is one of the determining factors in the efficacy of MRI contrast agents. Of all the parameters involved in determining relaxivity it remains the least well understood, particularly as it relates to the structure of the complex. On ...

2008

PEGylated DOTA-AHA-Based Gd-III Chelates: A Relaxometric Study

Lothar Helm, Shima Karimi

Three PEGylated derivatives of 6-amino-2-[4,7,10-tris(carboxymethyl)-1,4,7,10-tetrazacyclododec-1-yl]hexanoic acid (DOTA-AHA) with different molecular weights were prepared and characterized. Their Gd-III chelates were studied in aqueous solution through v ...

Wiley-Blackwell2015

O-17 NMR and Density Functional Theory Study of the Dynamics of the Carboxylate Groups in DOTA Complexes of Lanthanides in Aqueous Solution

Lothar Helm

The rotation of the carboxylate groups in DOTA (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) complexes of several lanthanide ions and Sc3+ was investigated with density functional theory (DFT) calculations and with variable temperature O-17 ...

2012

In-Vivo Detection and Tracking of T Cells in Various Organs in a Melanoma Tumor Model by F-19-Fluorine MRS/MRI

Lothar Helm, Hikari Ananda Infinity Yoshihara, Pascal Miéville

Background F-19-MRI and F-19-MRS can identify specific cell types after in-vitro or in-vivo F-19-labeling. Knowledge on the potential to track in-vitro F-19-labeled immune cells in tumor models by F-19-MRI/MRS is scarce. Aim To study F-19-based MR techniqu ...

Public Library of Science2016

Synthesis, structures and characterisations of truly homoleptic acetonitrile Ln3+ complexes in solid state and in solution

Rosario Scopelliti, Lothar Helm, Ines Raabe

Total halide abstraction from LnCl3 by Ag[Al(OC(CF3)3)4]/CH3CN has been confirmed for a series of lanthanide metal ions by the structural characterization of [Ln(CH3CN)n][Al(OC(CF3)3)4]3 (n = 9, Ln3+ = Nd, Eu, Gd, Dy; n = 8, Ln3+ = Tm) complexes. Evidence ...

2009

Collisional cross-section of water molecules in vapour studied by means of H-1 relaxation in NMR

Geoffrey Bodenhausen, Lothar Helm, Pascal Miéville, Daniele Mammoli, Roberto Buratto, Estel Canet Martinez

In gas phase, collisions that affect the rotational angular momentum lead to the return of the magnetization to its equilibrium (relaxation) in Nuclear Magnetic Resonance (NMR). To the best of our knowledge, the longitudinal relaxation rates R-1 = 1/T-1 of ...

Nature Research2016

Electronic fine structure calculation of [Gd(DOTA)(H2O)]- using LF-DFT: The zero field splitting

Lothar Helm, Alain Borel

Zerfo field splitting plays an important role in determining the electron spin relaxation of Gd(III) in solution. We understand the ZFS as an effect depending on the f electron structure and treat it in the framework of ligand field-density functional theo ...

2012

Ligand exchange and complex formation kinetics studied by NMR exemplified on fac-[(CO)3M(H2O)]+ (M = Mn, Tc, Re)

Lothar Helm

In this review ligand exchange and complex formation reactions on fac-[(CO)3M(H2O)3]+ (M = Mn, Tc, Re) and on fac-[(CO)2(NO)Re(H2O)3]2+ are presented. A variety of experimental NMR techniques are described and it is shown that sometimes combinations of tec ...

2008

Gadolinium complexes of monophosphinic acid DOTA derivatives conjugated to cyclodextrin scaffolds: efficient MRI contrast agents for higher magnetic fields

Lothar Helm

Middle-molecular-weight MRI contrast agents based on conjugates of a phosphinic acid DOTA analogue, 1,4,7,10-tetraazacyclododecane-4,7,10-triacetic-1-{methyl[(4-aminophenyl) methyl] phosphinic acid} (DO3AP(ABn)), with amino-substituted cyclodextrins were p ...

Royal Society of Chemistry2012

Gold nanoparticles functionalised with stable, fast water exchanging Gd3+ chelates as high relaxivity contrast agents for MRI

Lothar Helm, Bibimaryam Mousavi

Gold nanoparticles functionalized with Gd3+ chelates displaying fast water exchange, superb pH stability and inertness towards transmetalation with Zn2+ have been prepared and characterized as a new high relaxivity (29 mM(-1) s(-1), 30 MHz, 25 degrees C) c ...

Royal Society of Chemistry2012

Pharmacokinetics and biodistribution study of self-assembled Gd-micelles demonstrating blood-pool contrast enhancement for MRI

Lothar Helm, Yohan Van de Looij

Magnetic resonance angiography (MRA) requires the use of contrast agents (CAs) to enable accurate diagnosis. There are currently no CAs on the market with appropriate pharmacokinetic (PK) parameters, namely long persistence in the blood, that can be easily ...

2019

Gold Nanoparticles Functionalized with Gadolinium Chelates as High-Relaxivity MRI Contrast Agents

Lothar Helm, Loïck Moriggi

Functionalized nanoparticles (NPs) are presently under intensive study aimed at creating useful tools for molecular diagnosis, therapy, and biotechnology. ...

2009

Gd(DOTAlaP): Exploring the Boundaries of Fast Water Exchange in Gadolinium-Based Magnetic Resonance Imaging Contrast Agents

Lothar Helm, Shima Karimi

Here, we describe the synthesis of the single amino acid chelator DOTAlaP and four of its derivatives. The corresponding gadolinium(III) complexes were investigated for their kinetic inertness, relaxometric properties at a range of fields and temperatures, ...

American Chemical Society2014

A ruthenium-based metallostar: synthesis, sensitized luminescence and 1H relaxivity

Jean-Claude Bünzli, Lothar Helm, Alain Borel, Loïck Moriggi, Annina Aebischer

Ru-based metallostars Na4{Ru[Ln2bpy-DTTA2(H2O)4]3} (Ln = Y, Gd, and Eu) have been self-assembled in aqueous solution and their relaxivity and optical properties unravelled. The ynthesis and the purification of the new, highly stable heptametallic entities ...

2009

H-1 and O-17 NMR Relaxometric and Computational Study on Macrocyclic Mn(II) Complexes

Lothar Helm

Herein we report a detailed H-1 and O-17 relaxometric investigation of Mn(II) complexes with cyclenbased ligands such as 2-(1,4,7,10-tetraazacyclododecan-1-yl)acetic acid (DO IA), 2,2 '-(1,4,7,10-tetraazacyclododecane-1,4-diyI)diacetic acid (1,4-DO2A), 2,2 ...

American Chemical Society2013

Lanthanide chelates of (bis)-hydroxymethyl-substituted DTTA with potential application as contrast agents in magnetic resonance imaging

Lothar Helm

A novel bis-hydroxymethyl-substituted DTTA chelator N¢-Bz-C4,4¢-(CH2OH)2-DTTA (1) and its DTPA analogue C4,4¢-(CH2OH)2-DTPA (2) were synthesized and characterized. A variable-temperature 1H NMR spectroscopy study of the solution dynamics of their diamagnet ...

2009

Gadonanotubes as Ultrasensitive pH-Smart Probes for Magnetic Resonance Imaging

André Merbach, Lothar Helm, Sabrina Laus

With their nanoscalar, superparamagnetic Gd3+-ion clusters (1 ´ 5 nm) confined within ultrashort (20-80 nm) single- walled carbon nanotube capsules, gadonanotubes are high- performance T1-weighted contrast agents for magnetic resonance imaging (MRI). At 1. ...

American Chemical Society (ACS)2008

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 ...

IOP Publishing2007

Water Exchange on [Ln(DO3A)(H2O)2] and [Ln(DTTA–Me)(H2O)2]− Studied by Variable Temperature, Pressure, and Magnetic Field NMR

Lothar Helm, Shima Karimi

Water exchange kinetics of [Ln(L)(H2O)2]x complexes (Ln = Pr, Nd, Dy, Tm, and Yb; L = DO3A and DTTA–Me) were studied by 17O NMR spectroscopy as a function of temperature, pressure, and frequency and by 1H nuclear magnetic relaxation dispersion. Water excha ...

American Chemical Society2016

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

André Merbach, Lothar Helm

2006