Lothar Helm

Defect-induced magnetism in graphene

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 extended states has been observed. Calculated magnetic moments are equal to 1

Water exchange on metal ions: experiments and simulations

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Geometrical confinement of gadolinium-based contrast agents in nanoporous particles enhances T1 contrast

per hydrogen chemisorption defect and 1.12

Superparamagnetic gadonanotubes are high-performance MRI contrast agents

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Relaxivity of MRI contrast agents

1.53

The Chemistry of Contrast Agents in Medical Magnetic Resonance Imaging: Helm/The Chemistry of Contrast Agents in Medical Magnetic Resonance Imaging

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Gold nanoparticles functionalized with gadolinium chelates as high-relaxivity MRI contrast agents.

per vacancy defect depending on the defect concentration. The coupling between the magnetic moments is either ferromagnetic or antiferromagnetic, depending on whether the defects correspond to the same or to different hexagonal sublattices of the graphene lattice, respectively. The relevance of itinerant magnetism in graphene to the high-

Gadonanotubes as Ultrasensitive pH-Smart Probes for Magnetic Resonance Imaging

T_C

17O nuclear magnetic resonance in aqueous solutions of Cu2+ : The combined effect of Jahn–Teller inversion and solvent exchange on relaxation rates

magnetic ordering is discussed.

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

Abstract The water exchange reaction between coordination shells around metal ions in aqueous solution is a fundamental reaction in understanding the reactivity of these ions in chemical and biological systems. The results reviewed in this paper demonstrate the complementary of experimental studies and computer simulations or quantum chemical calculations performed on such systems. Due to the large range of exchange rate constants, a variety of experimental and different computer techniques have to be applied. Very fast exchange reactions between first and second coordination shell and between second shell and bulk solvent can be simulated by classical molecular dynamics technique. Reaction pathways for water exchange on metal ions with a less labile first coordination shell can be followed by calculation of clearly defined transition states. Success and shortcomings of the techniques are discussed by means of recent publications.