Publications by André Merbach

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An Ia mechanism was assigned for water exchange on the hexaaquaions Rh(OH2)63+ and Ir(OH2)63+ on the basis of negative ΔV⧧ experimental values (−4.2 and −5.7 cm3 mol-1, respectively). The use of ΔV⧧ as a mechanistic criterion was open to debate primarily because ΔV⧧ could be affected by extension or compression of the nonparticipating ligand bond lengths on going to the transition state of an exchange process. In this paper, volume and energy profiles for two distinct water exchange mechanisms (D and Ia) ha

Recent neutron-diffraction studies on dilute solutions have shown that a change in coordination numbers from nine to eight water molecules in the first hydration sphere occurs when going from the light to the heavy lanthanide (III) ions. To acquire a deeper insight into the structure of the first coordination sphere of these ions Monte Carlo and molecular-dynamics computer simulations were performed. The initial results will be compared with neutron-diffraction data and solid-state structures. Recently ther

The syntheses and single crystal X-ray structural analysis of five novel hetero- and homometallic μ3-oxo trinuclear cluster with the formula [FeIII2MII(μ3-O)(μ-O2CCH3)6(4-Rpy)3] · x(4-Rpy) · y(CH3CN) where R ) Ph for 1(Fe2Mn),2(Fe2Fe), 3(Fe2Co), 4(Fe2Ni) a ...

Multiple experiments (17O NMR, 1H NMR, and EPR) have been performed in the past to understand the microscopic parameters that control the magnetic relaxation rate enhancement induced by paramagnetic molecules on neighboring water protons, the so-called relaxivity. The generally accepted theories of the electron spin relaxation of S = 7/2 ions such as Gd3+ (Solomon-Bloembergen-Morgan or simplified Hudson-Lewis) are unsatisfactory for a simultaneous analysis. Recently, an improved theory, where the electron s

A combined variable-temp. and multiple field 17O NMR, EPR and NMRD study was performed for the 1st time on Gd(III) complexes of cryptand ligands, L1 and L2, where L1 contains three 2,2'-bipyridine units ([bpy.bpy.bpy]) and L2 is the disubstituted Me ester ...

We determined the structure of the hydrated Cu(II) complex by both neutron diffraction and first-principles molecular dynamics, In contrast with the generally accepted picture, which assumes an octahedrally solvated Cu(II) ion, our experimental and theoretical results favor fivefold coordination. The simulation reveals that the solvated complex undergoes frequent transformations between square pyramidal and trigonal bipyramidal configurations. We argue that this picture is also consistent with experimental

An Electron Paramagnetic Resonance (EPR) study of glasses and magnetically dilute powders of [Gd(DTPA)(H2O)]2−, [Gd(DOTA)(H2O)]-, and macromolecular Gd-P792 complexes was carried out at X-, Q-band and 240 GHz DTPA=diethylenetriaminepentaacetato; DOTA=1,4,7 ...

The increasing use of contrast agents in magnetic resonance imaging (MRI) for medical diagnosis is due to the ability, called relaxivity, of these paramagnetic compounds to accelerate the relaxation of the surrounding water proton spins. A new classical force field for molecular dynamics simulations of Gd3+ polyaminocarboxylates has recently been published, which allows the study of the chelate internal mobility. We present two selected examples where such motions can affect relaxivity. Knowing the relation

{Fe[Gd2bpy(DTTA)2(H2O)4]3}4- is a self-assembled, metallostar-structured potential MRI contrast agent, with six efficiently relaxing Gd3+ centers confined into a small mol. space. Its proton relaxivity is particularly remarkable at very high magnetic field ...

Previous studies of cyanide exchange on square planar tetracyanoplatinate complex [Pt(CN)4]2- have been undertaken only at a high pH. For a more complete fundamental understanding of this system we extended the investigations of these exchanges over a large pH range. NMR kinetics methods (magnetisation transfer, isotopic exchange) proved to be very useful for obtaining quantitative rate data of the cyanide exchange on this complex. In fact it is quite significant that the reactivity of this metal center spa

In this paper, the authors will describe an acidic sulfate medium in which various concentrations of the possible Ce(IV) species can be prescribed. Secondly, they present the computations-based on simultaneous solutions of various equilibrium of the concentration distributed of the sulfato and hydroxo species of Ce(IV). Lastly, the optimum planning of a kinetic study of a Ce(IV)-reductant system, based on the quantitative description of the medium is suggested.

The water-soluble endohedral gadofullerene derivatives, Gd@C60(OH)x and Gd@C60[C(COOH)2]10, have been characterized with regard to their MRI contrast agent properties. Water-proton relaxivities have been measured in aqueous solution at variable temperature ...

Since the first facile synthesis of Ru(H2O)(6)(2) was published at the beginning of the eighties, several Ru-II aqueous inorganic and organometallic complexes were described, showing the increasing interest in this kind of compound due to potential applications in catalysis and medicine. To understand what governs the reactivity of the ligands in the first coordination sphere of the Ru-II center. we discuss its solution behavior, starting with the simplest aqueous species Ru(H2O)(6) and moving

he structure and dynamics of the surrounding water were studied through molecular dynamics (MD) simulations for several GdIII polyaminocarboxylate and polyaminophosphonate complexes in aqueous solution. The radial distribution functions (rdf) show that a few water molecules are bonded to the ligand through hydrogen bonds to hydrophilic groups such as carboxylates and phosphonates. Residence times are of the order of 20-25 ps for the polyaminocarboxylate and 56 ps for the polyaminophosphonate chelates. No pr

The structures and intramolecular dynamics of [Ln(EGTA)(H2O)]- (Ln = La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+, Lu3+ and EGTA4- = 3,12-bis(carboxymethyl)-6,9-dioxa-3,12-diazatetradecanedioate(4-)) in aqueous solution have been investigated by variable temperature 1H and 13C NMR. The quantitative analysis of the proton hyperfine shifts and considerations about the stereochemical nonrigidity indicate the occurrence of a structural change along the lanthanide series with the

The EPTPA5- chelate, which ensures fast water exchange in GdIII complexes, has been coupled to three different generations (5, 7, and 9) of polyamidoamine (PAMAM) dendrimers through benzylthiourea linkages (H5EPTPA=ethylenepropylenetriamine-N,N,N,N,N-penta ...

We performed variable temperature (0–100°C), concentration and frequency (9.425, 75, 150 and 225 GHz) continuous wave electron paramagnetic resonance (EPR) measurements on three different Gd(III) compounds: [Gd(H2O)8]3+, [Gd(DOTA)(H2O)]− (DOTA: 1,4,7,10-tetrakis(carboxymethyl)-1,4,7,10-tetraazacyclododecane) and [Gd(DTPA-BMA)(H2O)] (DTPA-BMA: 1,5-[bis(N-methylcarbamoyl)methyl]-1,3,5-tris(carboxymethyl)-1,5-diamino-3-azapentane) in aqueous solution. A simultaneous analysis of peak-to-peak widths and dynamic

The study of electron spin relaxation in aqueous Gd(III) complexes is the source of new insights into the physics and chemistry of magnetic resonance imaging (MRI) contrast agents. The coupling of the seven unpaired electrons of the Gd(III) ion with the surrounding water protons observed in MRI is the basis of the contrast agent effectiveness. Therefore, understanding the behavior of the electron spin system can provide valuable information for the development of new compounds. The availability of high freq

In the recent years Magnetic Resonance Imaging has evolved into one of the most powerfuldiagnostic techniques in medicine, in part thanks to the application of suitable contrastagents. The design of new, more efficient MRI contrast media requires the complete under-standing of all factors and mechanisms that influence proton relaxivity, hence efficiency ofGd(III) complexes. In this chapter we give an overview of our current knowledge in this fieldby shortly surveying theory and citing the most illustrative

André Merbach

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Calculated Volume and Energy Profiles for Water Exchange on t2g6 Rhodium(III) and Iridium(III) Hexaaquaions: Conclusive Evidence for an Ia Mechanism

Structure and dynamics of lanthanide ions and lanthanide complexes in solution

Mechanism of Pyridine-Ligand Exchanges at the Different Labile Sites of 3d Heterometallic and Mixed Valence μ3-oxo Trinuclear Clusters

Multiexponential Electronic Spin Relaxation and Redfield's Limit in Gd(III) Complexes in Solution: Consequences for 17O/1H NMR and EPR Simultaneous Analysis

Positively Charged GdIII Cryptates: Slow, Associative Water Exchange

First solvation shell of the Cu(II) aqua ion: Evidence for fivefold coordination

Multiple Frequency and Variable Temperature EPR study of Gd(III) polyaminocarboxylates: analysis and comparison of the magnetically dilute powder and the frozen solution spectra

Molecular dynamics simulations of the internal mobility of Gd3+-based MRI contrast agents: consequences for water proton relaxivity

First in vivo MRI assessment of a self-assembled metallostar compound endowed with a remarkable high field relaxivity

High Pressure Cyanide Exchange Study on Square-planar Tetracyanometalate Complex of Pt(II)

Planning a kinetic and mechanistic study with cerium(IV)

Water-Soluble Gadofullerenes: Toward High-Relaxivity, pH-Responsive MRI Contrast Agents

Aspects of aqueous ruthenium(II) chemistry

Molecular dynamics simulations of MRI-relevant GdIII chelates: direct access to outer-sphere relaxivity

A Multinuclear NMR Study on the Structure and Dynamics of Lanthanide(III) Complexes of the Poly(amino carboxylate) EGTA4- in Aqueous Solution

Rotational Dynamics Account for pH-Dependent Relaxivities of PAMAM Dendrimeric, Gd-Based Potential MRI Contrast Agents

EPR on aqueous Gd3+ complexes and a new analysis method considering both line widths and shifts

Molecular dynamics of Gd(III) complexes in aqueous solution by HF EPR

Reactivity of the novel organometallic aqua-ion [(CO)2(NO)Re(H2O) 3]2+: Kinetics of H2O substitution and 17O exchange of CO ligands

Relaxivity of MRI contrast agents