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Lothar Helm

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Related publications (91)

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

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

Speciation of aqueous tellurium(IV) in hydrothermal solutions and vapors, and the role of oxidized tellurium species in Te transport and gold deposition

Lothar Helm, Pascal Grundler

Despite the close association between tellurium (Te) and gold (Au) in many epithermal, orogenic, and intrusion-related hydrothermal ore deposits, the hydrothermal chemistry of Te remains poorly understood. We studied the protonation/ deprotonation and stru ...

Elsevier2013

Pyridine-Based Lanthanide Complexes Combining MRI and NIR Luminescence Activities

Sandrine Villette, Lothar Helm, Eva Jakab Toth, Jian Zhang

A series of novel triazole derivative pyridine-based polyaminopolycarboxylate ligands has been synthesized for lanthanide complexation. This versatile platform of chelating agents combines advantageous properties for both magnetic resonance (MR) and optica ...

2012

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

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

NMR and Electron Paramagnetic Resonance Studies of [Gd(CH3CN)(9)](3+) and [Eu(CH3CN)(9)](2+): Solvation and Solvent Exchange Dynamics in Anhydrous Acetonitrile

Lothar Helm, Gabriella Eva Bodizs

Homoleptic acetonitrile complexes [Gd(CH3CN)(9)]Al(OC(CF3)(3))(4) and [Eu(CH3CN)(9)]Al(OC(CF3)(3))(4) have been studied in anhydrous acetonitrile by N-14- and H-1 NMR relaxation as well as by X- and Q-band EPR. For each compound a combined analys ...

2012

New Bisaqua Picolinate-Based Gadolinium Complexes as MRI Contrast Agents with Substantial High-Field Relaxivities

Lothar Helm, Marinella Mazzanti

Two new tripodal heptadentate ligands, H4dpaba (N,N'-bis[(6-carboxypyridin-2-yl)methyl]aspartic acid) and H3mpatcn(1,4-bis(methoxycarbonyl)-7-[(6-carboxypyridin-2-yl)methyl]-1,4,7-triazacyclononane), which bear one or two picolinate pendant arms, have been ...

Wiley-Blackwell2012

Serum Albumin Targeted, pH-Dependent Magnetic Resonance Relaxation Agents

Loïck Moriggi, Lothar Helm

The objective of this work was the synthesis of serum albumin targeted, GdIII-based magnetic resonance imaging (MRI) contrast agents exhibiting a strong pH-dependent relaxivity. Two new complexes (Gd-glu and Gd-bbu) were synthesized based on the DO3A macro ...

2012

Hyperfine Coupling Constants on Inner-Sphere Water Molecules of Gd-III-Based MRI Contrast Agents

Lothar Helm

Herein we present a theoretical investigation of the hyperfine coupling constants (HFCCs) on the inner-sphere water molecules of Gd(H2O)(8) and different Gd-III-based magnetic resonance imaging contrast agents such as Gd(DOTA)(H2O), [Gd(DTPA)(H2 ...

Wiley-Blackwell2012

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

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

Isoquinoline-Based Lanthanide Complexes: Bright NIR Optical Probes and Efficient MRI Agents

Sandrine Villette, Lothar Helm, Eva Jakab Toth

In the objective of developing ligands that simultaneously satisfy the requirements for MRI contrast agents and near-IR emitting optical probes that are suitable for imaging, three isoquinoline-based polyaminocarboxylate ligands, L1, L2 and L3, have been s ...

2012

Mn2+ Complexes with 12-Membered Pyridine Based Macrocycles Bearing Carboxylate or Phosphonate Pendant Arm: Crystallographic, Thermodynamic, Kinetic, Redox, and 1H/17O Relaxation Studies

Lothar Helm, Eva Jakab Toth

Mn2+ complexes represent an alternative to Gd3+ chelates which are widely used contrast agents in magnetic resonance imaging. In this perspective, the authors studied the Mn2+ complexes of two 12-membered, pyridine-contg. macrocyclic ligands bearing one pe ...

2011

NMR Study of Ligand Exchange and Electron Self-Exchange between Oxo-Centered Trinuclear Clusters [Fe3(μ3-O)(μ-O2CR)6(4-R´py)3]+/0

André Merbach, Lothar Helm

The syntheses, single crystal X-ray structures, and magnetic properties of the homometallic mu(3)-oxo trinuclear clusters Fe-3(mu(3)-O)(mu-O2CCH3)(6)(4-Phpy)(3) (1) and F(e)3(mu(3)-O)(mu-O(2)CAd)(6)(4-Mepy)(3) (2) are reported (Ad = adamanta ...

American Chemical Society2011

Synthesis, complexation and NMR relaxation properties of Gd3+ complexes of Mes(DO3A)3

Hugues Jaccard, Lothar Helm, Pascal Miéville

Medium sized molecules endowed with multiple Gd3+ complexes are efficient high magnetic field MRI contrast agents. The novel ligand Mes(DO3A)3, presenting three DO3A (1,4,7,10-tetraazacyclododecane-N,N′,N′′-triacetatic acid) units grafted on the methyl pos ...

Royal Society of Chemistry2011

Kinetics of Yttrium-Ligand Complexation Monitored Using Hyperpolarized 89Y as a Model for Gadolinium in Contrast Agents

Geoffrey Bodenhausen, Lothar Helm, Sami Jannin, Pascal Miéville

Hyperpolarization by dissolution dynamic nuclear polarization (DNP) enhances Y-89 spin magnetization by 3 to 4 orders of magnitude and provides a way to monitor yttrium-ligand complexation "on the fly" by means of Y-89 NMR. In this communication, we show a ...

American Chemical Society2010

Optimization of gadolinium-based MRI contrast agents for high magnetic‑field applications

Lothar Helm

The search for higher spatial resolution and better sensitivity stimulates the development of high-field (3 T) and ultrahigh field (>3 T) MRI scanners. Gadolinium-based MRI contrast agents, commercial ones used in clinics, as well as recently developed mor ...

2010

Isomerization Mechanisms of Stereolabile tris- and bis-Bidentate Octahedral Cobalt(II) Complexes: X-ray Structure and Variable Temperature and Pressure NMR Kinetic Investigation

André Merbach, Lothar Helm, Rosario Scopelliti, Fabrice Riblet

The isomerization dynamics of five labile octahedral Co(II) compounds have been investigated by variable temperature and pressure 1H and 19F NMR spectroscopy in dichloromethane solution. The X-ray crystal structure of the two tris-chelates, [Co(HFA)2bpic] ...

American Chemical Society2010

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

Loïck Moriggi, Lothar Helm

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

2009

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

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