1,720,962 research outputs found
Orthogonal synthesis of a heterodimeric ligand for the development of the Gd(III)/Ga(III) ditopic complex as potential pH-sensitive MRI/PET probe
No full textHyperfine Coupling Constants on Inner-Sphere Water Molecules of a TACN-based Mn(II) Complex and Related Systems Relevant as MRI Contrast Agents
No full textWe report the synthesis of the ligand H2MeNO2A
(1,4-bis(carboxymethyl)-7-methyl-1,4,7-triazacyclononane) and a
detailed experimental and computational study of the hyperfine coupling constants (HFCCs) on the inner-sphere water molecules of [Mn(MeNO2A)] and related Mn2+ complexes relevant as
potential contrast agents in magnetic resonance imaging (MRI). Nuclear magnetic relaxation dispersion (NMRD) profiles, 17O NMR chemical shifts, and transverse relaxation rates of aqueous
solutions of [Mn(MeNO2A)] were recorded to determine the
parameters governing the relaxivity in this complex and the 17O and 1H HFCCs. DFT calculations (TPSSh model) performed in aqueous solution (PCM model) on the [Mn(MeNO2A)(H2O)]·xH2O and [Mn(EDTA)(H2O)]2−·xH2O (x = 0−4) systems were used to determine theoretically the 17O and 1H HFCCs responsible for the 17O NMR chemical shifts and the scalar contributions to 17O and 1H NMR relaxation rates. The use of a mixed cluster/continuum approach with the explicit inclusion of a few second sphere water molecules is critical for an accurate calculation of HFCCs of coordinated water molecules. The impact of complex dynamics on the calculated HFCCs was evaluated with the use of molecular dynamics simulations within the atom-centered density matrix propagation (ADMP) approach. The 17O and 1H HFCCs calculated for these complexes and related systems show an excellent agreement with the experimental data. Both the 1H and 17O HFCCs (Aiso values) are dominated by the spin
delocalization mechanism. The Aiso values are significantly affected by the distance between the oxygen atom of the coordinated water molecule and the Mn2+ ion, as well as by the orientation of the water molecule plane with respect to the Mn−O vector
One-pot synthesis of a piperidine-based rigidified DTPA analogue and its bifunctional chelating agent
No full textThe core structure of cis-3,5-diaminopiperidine was N-alkylated with excess t-butylbromoacetate in order to exploit the successive N-quaternarization and Stevens rearrangement to access the pentaalkylated product and the bifunctional chelating agent containing a N-butanedioic acid pendant arm at the same time. The relaxometric properties of the Gd III complexes with these ligands were studied also in terms of pH and serum stabilities
Scaling laws at the nanosize: the effect of particle size and shape on the magnetism and relaxivity of iron oxide nanoparticle contrast agents
No full textThe magnetic properties of iron oxide nanoparticles govern their relaxivities and efficacy as contrast agents
for MRI. These properties are in turn determined by their composition, size and morphology. Herein we present a systematic study of the effect of particle size and shape of magnetite nanocrystals synthesized
by thermal decomposition of iron salts on both their magnetism and longitudinal and transverse relaxivities, r1 and r2, respectively. Faceted nanoparticles demonstrate superior magnetism and relaxivities to spherical nanoparticles of similar size. For faceted nanoparticles, but not for spherical ones, r1 and r2 further increase with increasing particle size up to a size of 18 nm. This observation is in accordance with increasing saturation magnetization for nanoparticles increasing in size up to 12 nm, above which a plateau is observed. The NMRD (Nuclear Magnetic Resonance Dispersion) profiles of MIONs (Magnetic Iron Oxide Nanoparticles) display an increase in longitudinal relaxivity with decreasing magnetic field strength with a plateau below 1 MHz. The transverse relaxivity shows no dependence on the magnetic field strength between 20 MHz and 500 MHz. These observations translate to phantom MR images: in T1-weighted SWIFT (SWeep Imaging with Fourier Transform) images MIONs have a
positive contrast with little dependence on the particle size, whereas in T2-weighted gradient-echo images MIONs create a negative contrast which increases in magnitude with increasing particle size.
Altogether, these results will enable the development of particulate MRI contrast agents with enhanced efficacy for biomedical and clinical applications
Comparative in vitro studies of MR imaging probes for metabotropic glutamate subtype-5 receptor targeting
No full textA series of magnetic resonance imaging probes has been evaluated to target selectively the metabotropic glutamate receptor subtype 5 (mGluR5). Eight imaging probes based on the contrast agent [Gd·DOTA], previously derived by linking it to a series of specific and selective mGluR5 antagonists, have been extensively tested for their functionality in vitro. The Nuclear Magnetic Relaxation Dispersion (NMRD) profiles of selected probes have been examined via field-cycling relaxometry in the presence and absence of a model protein. The properties of the targeted contrast agents were evaluated using a primary astrocyte model, as these cells mimic the in vivo situation effectively. The probes were non-toxic (up to 200 μM) to these mGluR5 expressing primary cells. Cellular proton longitudinal relaxation rate enhancements of up to 35 were observed by MRI at 200 μM of probe concentration. The antagonistic effect of all compounds was tested using an assay measuring changes of intracellular calcium levels. Furthermore, treatment at two different temperatures (4 °C vs. 37 °C) and of an mGluR5-negative cell line provided further insight into the selectivity and specificity of these probes towards cell surface mGluR5. Finally, two out of eight probes demonstrated an antagonistic effect as well as significant enhancement of receptor mediated cellular relaxation rates, strongly suggesting that they would be viable probes for the mapping of mGluR5 by MRI in vivo
Paramagnetic Solid Lipid Nanoparticles as a novel platform for the development of molecular MRI probes
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Responsive Mn(II) complexes for potential applications in diagnostic Magnetic Resonance Imaging
No full textThe investigation of new Mn(II)-based MRI/Molecular Imaging probes responsive to the enzyme tyrosinase for potential diagnostic applications is herein described. The expression of the enzyme tyrosinase, an oxidoreductase, is up-regulated in melanoma cancer cells. Three novel ligands (L1, L2 and L3) were designed as modified acyclic polyaminocarboxylate chelates by introducing an l-tyrosine residue in place of an aminoacetate unit. The corresponding Mn(II) complexes were fully characterised by 1H NMR relaxometric techniques in aqueous media. The responsive activity towards the expression of tyrosinase was then assessed by monitoring the 1H 1/T1 relaxivity changes during incubation experiments in buffered solutions containing tyrosinase at different concentrations and in B16F10 melanoma cell homogenate. New insight on the mechanism of action of these systems was gained by measuring the magnetic field dependence of the relaxivity and ESR spectra of the incubated solutions. The systems developed showed responsive activity to tyrosinase with a relaxation enhancement spanning from 50% (MnL1) to 350% (MnL3) which augurs well for the development of diagnostic probes to detect melanoma cancer
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