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

Abstract

The zero-field splitting (ZFS) parameters of the [Mn(EDTA)(H2O)](2-)·2H2O and [Mn(MeNO2A)(H2O)]·2H2O systems were estimated by using DFT and ab initio CASSCF/NEVPT2 calculations (EDTA = 2,2',2″,2‴-(ethane-1,2-diylbis(azanetriyl))tetraacetate; MeNO2A = 2,2'-(7-methyl-1,4,7-triazonane-1,4-diyl)diacetate). Subsequent molecular dynamics calculations performed within the atom-centered density matrix propagation (ADMP) approach provided access to the transient and static ZFS parameters, as well as to the correlation time of the transient ZFS. The calculated ZFS parameters present a reasonable agreement with the experimental values obtained from the analysis of (1)H relaxation data. The correlation times calculated for the two systems investigated turned out to be very short (τc ∼ 0.02-0.05 ps), which shows that the transient ZFS is modulated by molecular vibrations. On the contrary, the static ZFS is modulated by the rotation of the complexes in solution, which for the small complexes investigated here is characterized by rotational correlation times of τR ∼ 35-60 ps. As a result, electron spin relaxation in small Mn(2+) complexes is dominated by the static ZFS.

Black Phosphorus Quantum Dots Encapsulated Biodegradable Hollow Mesoporous MnO2: Dual‐Modality Cancer Imaging and Synergistic Chemo‐Phototherapy

“…Under acidic conditions, MnO 2 would be decomposed to Mn 2+ with five unpaired 3d electrons, which was a T1-shortening agent in MR imaging. [44] The MR imaging and corresponding quantification analysis in Figure 6D,E showed that the T1-MR signals enhanced fourfold in the tumor at 24 h post-injection of nanoprobe, verifying the high tumor accumulation of nanoprobe, which was consistent with in vivo FLI results.…”

Understanding the Effect of the Electron Spin Relaxation on the Relaxivities of Mn(II) Complexes with Triazacyclononane Derivatives

“… 81 However, the [Mn(MeNO2A)(H 2 O)] complex, which is closely related to those investigated here, displays a positive D value according to CASSCF/NEVPT2 calculations (+0.045 cm –1 ). 34 These results highlight the difficulties of establishing relationships between the structure of Mn(II) complexes and the sign of D .…”

Hollow MnO2 as a tumor-microenvironment-responsive biodegradable nano-platform for combination therapy favoring antitumor immune responses

“…As Mn 2+ with five unpaired 3 d electrons is known to be a T1-shortening agent in MR imaging 42 , MR imaging of H-MnO 2 -PEG/C&D incubated in buffer solutions with different pHs (6 and 7.4) for 6 h was conducted. The significant concentration-dependent brightening effect of H-MnO 2 -PEG/C&D samples were found in T1-MR images at pH 6, whereas the signals of nanoparticles in the neutral buffer solution appeared to be much weaker (Fig.…”