Publications by Lothar Helm | EPFL Graph Search

Related publications (91)

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

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

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

Rosario Scopelliti, André Merbach, Lothar Helm, 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

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

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

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

In vivo MRI assessment of a novel GdIII-based contrast agent designed for high magnetic field applications

André Merbach, Lothar Helm, Joao Bruno Livramento Fig.

Gd3L is a trinuclear Gd3R complex of intermediate size, designed for contrast agent applications in high field magnetic resonance imaging (H12L is based on a trimethylbenzene core bearing three methylene-diethylenetriamine-N,N,N00,N00-tetraacetate moieties ...

2008

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

Lothar Helm, Loïck Moriggi

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

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

Lothar Helm, Marinella Mazzanti, Alain Borel, Sabrina Laus

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

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

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

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

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

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

Dynamic aggregation of the mid-sized gadolinium complex {Ph-4[Gd(DTTA)(H2O)(2)](-)(3)}

Lothar Helm, Pascal Miéville, Hugues Jaccard

A compound binding three Gd3+ ions, {Ph-4Gd(DTTA)(H2O)(2) (3)} (where H(5)DTTA is diethylenetriaminetetraacetic acid), has been synthesized around a hydrophobic center made up of four phenyl rings. In aqueous solution the molecules start to self-aggre ...

Springer2014

Pyridine-Based Lanthanide Complexes Combining MRI and NIR Luminescence Activities

Lothar Helm, 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

The effect of pyridinecarboxylate chelating groups on the stability and electronic relaxation of gadolinium complexes

André Merbach, Lothar Helm, Marinella Mazzanti, Alain Borel

The ligand N,N'-bis[6-carboxy-2-pyridylmethyl]ethylenediamine-N,N'-diacetic acid (H4bpeda) was synthesized using an improved procedure which requires a reduced no. of steps and leads to a higher yield with respect to the published procedure. It was obtaine ...

2005

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

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

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

Gold nanoparticles functionalised with fast water exchanging Gd3+ chelates: linker effects on the relaxivity

Lothar Helm, Bibimaryam Mousavi

The relaxivity displayed by Gd3+ chelates immobilized onto gold nanoparticles is the result of the complex interplay between the nanoparticle size, the water exchange rate and the chelate structure. In this work we study the effect of the length of omega-t ...

Royal Society of Chemistry2015

The Periodic Table and Kinetics?

André Merbach, Lothar Helm

Mendeleev in his first publication ordered the chemical elements following an apparent periodicity of properties such as atomic volume and valence. The reactivity of the elements was only studied systematically many years later. To illustrate the systemati ...

2019

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

Physicochemical Properties of the High-Field MRI-Relevant [Gd(DTTA-Me)(H2O)2]− Complex

Lothar Helm, Loïck Moriggi

To study the physicochemical properties of the DTTA chelating moiety (H4DTTA = diethylenetriaminetetraacetic acid = N,N′-[iminobis(ethane-2,1-diyl)]bis[N-(carboxymethyl)glycine]), used in several compounds proposed as magnetic resonance imaging (MRI) contr ...

2008

Comparison of different methods for calculating the paramagnetic relaxation enhancement of nuclear spins as a function of the magnetic field

Lothar Helm

The enhancement of the spin-lattice relaxation rate for nuclear spins in a ligand bound to a paramagnetic metal ion [known as the paramagnetic relaxation enhancement (PRE)] arises primarily through the dipole-dipole (DD) interaction between the nuclear spi ...

2008