Publications de Lothar Helm | EPFL Graph Search

The Periodic Table and Kinetics?

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

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

Lothar Helm, Vassily Vorobiev

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

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

Self-Assembled Nanomicelles as MRI Blood-Pool Contrast Agent

Lothar Helm, Anne-Sophie Chauvin, Vassily Vorobiev

Gadolinium‐loaded nanomicelles show promise as future magnetic resonance imaging (MRI) contrast agents (CAs). Their increased size and high gadolinium (Gd) loading gives them an edge in proton relaxivity over smaller molecular Gd‐complexes. Their size and ...

2017

Carbazole as Linker for Dinuclear Gadolinium-Based MRI Contrast Agents

Loïck Moriggi, Lothar Helm, Anne-Sophie Chauvin, 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

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

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

Lothar Helm, Olivier Michielin, Pascal Miéville, Hikari Ananda Infinity Yoshihara

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

Evaluation of Water Exchange Kinetics on [Ln(AAZTAPh–NO2)(H2O)q]x Complexes Using Proton Nuclear Magnetic Resonance

Lothar Helm, Shima Karimi

Water exchange kinetics on [Ln(AAZTAPh–NO2)(H2O)q]− (Ln = Gd3+, Dy3+, or Tm3+) were determined by 1H nuclear magnetic resonance (NMR) measurements. The number of inner-sphere water molecules was found to change from two to one when going from Dy3+ to Tm3+. ...

American Chemical Society2016

Complexation of [Gd(DTTA–Me)(H2O)2]− by Fluoride and Its Consequences to Water Exchange

Loïck Moriggi, Lothar Helm, Shima Karimi, Gail Ruth Hunter

The displacement of water molecule(s) from the inner coordination sphere of [Gd(DTTA–Me)(H2O)2]− (DTTA = ethylenetriamine-N,N,N″,N″-tetraacetate) by fluoride has been studied by multinuclear NMR relaxation (1H, 17O, 19F) and DFT calculations. Fluoride anio ...

American Chemical Society2016

Transient versus Static Electron Spin Relaxation in Mn2+ Complexes Relevant as MRI Contrast Agents

Lothar Helm

The zero,-field splitting (ZFS) parameters of the Mn(EDTA)(H2O).2H(2)O. and [Mn(MeNO(2)A)(H2O)].2H(2)O systems were estimated by using DFT and ab initio CASSCF/NEVPT2 calculations (EDTA = (ethane-1,2-41bis(azanetriy1))tetraatetate; MeNO2A = 2,2'-(7-m ...

American Chemical Society2016

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

Geoffrey Bodenhausen, Lothar Helm, Pascal Miéville, Roberto Buratto, Daniele Mammoli, 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

Prototropic Exchange Governs T-1 and T-2 Relaxivities of a Potential MRI Contrast Agent Nanozeolite Gd-LTL with a High pH Responsiveness

Lothar Helm

Aqueous suspensions of lanthanide exchsanged zeolite LTL have been investigated by 1H, 17O NMR, and EPR relaxivity studies. Both the longitudinal and the transverse relaxivity of these Gd3+ loaded materials are strongly pH dependent and therefore, they hav ...

American Chemical Society2015

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

A Pyridine-Based Ligand with Two Hydrazine Functions for Lanthanide Chelation: Remarkable Kinetic Inertness for a Linear, Bishydrated Complex

Lothar Helm, Eva Jakab Toth

To study the influence of hydrazine functions in the ligand skeleton, we designed the heptadentate HYD ligand (2,2',2 '',2 ''-(2,2'-(pyridine-2,6-diyl)bis(2-methylhydrazine-2,1,1-triyl)) tetraacetic acid) and compared the thermodynamic, kinetic, and relaxa ...

American Chemical Society2015

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

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

Lothar Helm, Gabriella Eva Bodizs

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

Dinuclear DOTA-Based Gd-III Chelates - Revisiting a Straightforward Strategy for Relaxivity Improvement

Lothar Helm, Shima Karimi

The need for magnetic resonance imaging (MRI) contrast agents with improved relaxivity maintains the development of new Gd-III chelates as an intensive and demanding field of research. In this work, we introduce the new dimeric chelators bis{1,4,7,10-tetra ...

Wiley-Blackwell2015

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

Hugues Jaccard, Lothar Helm, Pascal Miéville

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

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

Lothar Helm

Amer Chemical Soc2014

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