Interaction of MRI Contrast Agent [Gd(DOTA)]- with Lipid Membranes: A Molecular Dynamics Study.

Contrast agents are important imaging probes in clinical MRI, allowing the identification of anatomic changes that otherwise would not be possible. Intensive research on the development of new contrast agents is being made to image specific pathological markers or sense local biochemical changes. The most widely used MRI contrast agents are based on gadolinium(III) complexes. Due to their very high charge density, they have low permeability through tight biological barriers such as the blood-brain barrier, hampering their application in the diagnosis of neurological disorders. In this study, we explore the interaction between the widely used contrast agent [Gd(DOTA)]- (Dotarem) and POPC lipid bilayers by means of molecular dynamics simulations. This metal complex is a standard reference where several chemical modifications have been introduced to improve key properties such as bioavailability and targeting. The simulations unveil detailed insights into the agent's interaction with the lipid bilayer, offering perspectives beyond experimental methods. Various properties, including the impact on global and local bilayer properties, were analyzed. As expected, the results indicate a low partition coefficient (KP) and high permeation barrier for this reference compound. Nevertheless, favorable interactions are established with the membrane leading to moderately long residence times. While coordination of one inner-sphere water molecule is maintained for the membrane-associated chelate, the physical-chemical attributes of [Gd(DOTA)]- as a MRI contrast agent are affected. Namely, increases in the rotational correlation times and in the residence time of the inner-sphere water are observed, with the former expected to significantly increase the water proton relaxivity. This work establishes a reference framework for the use of simulations to guide the rational design of new contrast agents with improved relaxivity and bioavailability and for the development of liposome-based formulations for use as imaging probes or theranostic agents.

Rational Design of Magnetic Nanoparticles as T1-T2 Dual-Mode MRI Contrast Agents.

Magnetic nanoparticles (MNPs), either paramagnetic or superparamagnetic depending on their composition and size, have been thoroughly studied as magnetic resonance imaging (MRI) contrast agents using in vitro and in vivo biomedical preclinical studies, while some are clinically used. Their magnetic properties responsible in some cases for high magnetization values, together with large surface area-to-volume ratios and the possibility of surface functionalization, have been used in MRI-based diagnostic and theranostics applications. MNPs are usually used as positive (T1) or negative (T2) MRI contrast agents, causing brightening or darkening of selected regions in MRI images, respectively. This review focusses on recent developments and optimization of MNPs containing Gd, Mn, Fe and other lanthanide ions which may function as dual-mode T1-T2 MRI contrast agents (DMCAs). They induce positive or negative contrast in the same MRI scanner upon changing its operational mode between T1-weighted and T2-weighted pulse sequences. The type of contrast they induce depends critically on their r2/r1 relaxivity ratio, which for DMCAs should be in the 2-10 range of values. After briefly discussing the basic principles of paramagnetic relaxation in MNPs, in this review, the basic strategies for the rational design of DMCAs are presented and typical examples are discussed, including in vivo preclinical applications: (1) the use of NPs with a single type of contrast material, Gd- or Mn-based NPs or superparamagnetic NPs with appropriate size and magnetization to provide T2 and T1 contrast; and (2) inclusion of both types of T1 and T2 contrast materials in the same nanoplatform by changing their relative positions.

Fluorinated Mn(III)/(II)-Porphyrin with Redox-Responsive 1 H and 19 F Relaxation Properties.

A new fluorinated manganese porphyrin, (Mn-TPP-p-CF3 ) is reported capable of providing, based on the Mn(III)/Mn(II) equilibrium, dual 1 H relaxivity and 19 F NMR response to redox changes. The physical-chemical characterization of both redox states in DMSO-d6 /H2 O evidenced that the 1 H relaxometric and 19 F NMR properties are appropriate for differential redox MRI detection. The Mn(III)-F distance (dMn-F =9.7-10 Å), as assessed by DFT calculations, is well tailored to allow for adequate paramagnetic effect of Mn(III) on 19 F T1 and T2 relaxation times. Mn-TPP-p-CF3 has a reversible Mn(II)/Mn(III) redox potential of 0.574 V vs. NHE in deoxygenated aqueous HEPES/ THF solution. The reduction of Mn(III)-TPP-p-CF3 in the presence of ascorbic acid is slowly, but fully reversed in the presence of air oxygen, as monitored by UV-Vis spectrometry and 19 F NMR. The broad 1 H and 19 F NMR signals of Mn(III)-TPP-p-CF3 disappear in the presence of 1 equivalent ascorbate replaced by a shifted and broadened 19 F NMR signal from Mn(II)-TPP-p-CF3 . Phantom 19 F MR images in DMSO show a MRI signal intensity decrease upon reduction of Mn(III)-TPP-p-CF3 , retrieved upon complete reoxidation in air within ~24 h. 1 H NMRD curves of the Mn(III)/(II)-TPP-p-CF3 chelates in mixed DMSO/water solvent have the typical shape of Mn(II)/Mn(III) porphyrins.

Contribution of non-ionic interactions on bile salt sequestration by chitooligosaccharides: Potential hypocholesterolemic activity.

Chitooligosaccharides have been suggested as cholesterol reducing ingredients mostly due to their ability to sequestrate bile salts. The nature of the chitooligosaccharides-bile salts binding is usually linked with the ionic interaction. However, at physiological intestinal pH range (6.4 to 7.4) and considering chitooligosaccharides pKa, they should be mostly uncharged. This highlights that other type of interaction might be of relevance. In this work, aqueous solutions of chitooligosaccharides with an average degree of polymerization of 10 and 90 % deacetylated, were characterized regarding their effect on bile salt sequestration and cholesterol accessibility. Chitooligosaccharides were shown to bind bile salts to a similar extent as the cationic resin colestipol, both decreasing cholesterol accessibility as measured by NMR at pH 7.4. A decrease in the ionic strength leads to an increase in the binding capacity of chitooligosaccharides, in agreement with the involvement of ionic interactions. However, when the pH is decreased to 6.4, the increase in charge of chitooligosaccharides is not followed by a significant increase in bile salt sequestration. This corroborates the involvement of non-ionic interactions, which was further supported by NMR chemical shift analysis and by the negative electrophoretic mobility attained for the bile salt-chitooligosaccharide aggregates at high bile salt concentrations. These results highlight that chitooligosaccharides non-ionic character is a relevant structural feature to aid in the development of hypocholesterolemic ingredients.

Elucidating the concentration-dependent effects of thiocyanate binding to carbonic anhydrase.

Many proteins naturally carry metal centers, with a large share of them being in the active sites of several enzymes. Paramagnetic effects are a powerful source of structural information and, therefore, if the native metal is paramagnetic, or it can be functionally substituted with a paramagnetic one, paramagnetic effects can be used to study the metal sites, as well as the overall structure of the protein. One notable example is cobalt(II) substitution for zinc(II) in carbonic anhydrase. In this manuscript we investigate the effects of sodium thiocyanate on the chemical environment of the metal ion of the human carbonic anhydrase II. The electron paramagnetic resonance (EPR) titration of the cobalt(II) protein with thiocyanate shows that the EPR spectrum changes from A-type to C-type on passing from 1:1 to 1:1000-fold ligand excess. This indicates the occurrence of a change in the electronic structure, which may reflect a sizable change in the metal coordination environment in turn caused by a modification of the frozen solvent glass. However, paramagnetic nuclear magnetic resonance (NMR) data indicate that the metal coordination cage remains unperturbed even in 1:1000-fold ligand excess. This result proves that the C-type EPR spectrum observed at large ligand concentration should be ascribed to the low temperature at which EPR measurements are performed, which impacts on the structure of the protein when it is destabilized by a high concentration of a chaotropic agent.

High spin Fe(III)-doped nanostructures as T1 MR imaging probes.

Magnetic Resonance Imaging (MRI) T1 contrast agents based on Fe(III) as an alternative to Gd-based compounds have been under intense scrutiny in the last 6-8 years and a number of nanostructures have been designed and proposed for in vivo diagnostic and theranostic applications. Excluding the large family of superparamagnetic iron oxides widely used as T2 -MR imaging agents that will not be covered by this review, a considerable number and type of nanoparticles (NPs) have been employed, ranging from amphiphilic polymer-based NPs, NPs containing polyphenolic binding units such as melanin-like or polycatechols, mixed metals such as Fe/Gd or Fe/Au NPs and perfluorocarbon nanoemulsions. Iron(III) exhibits several favorable magnetic properties, high biocompatibility and improved toxicity profile that place it as the paramagnetic ion of choice for the next generation of nanosized MRI and theranostic contrast agents. An analysis of the examples reported in the last decade will show the opportunities for relaxivity and MR-contrast enhancement optimization that could bring Fe(III)-doped NPs to really compete with Gd(III)-based nanosystems. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Diagnostic Tools > Diagnostic Nanodevices Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

MRI Contrast Agents in Glycobiology.

Molecular recognition involving glycoprotein-mediated interactions is ubiquitous in both normal and pathological natural processes. Therefore, visualization of these interactions and the extent of expression of the sugars is a challenge in medical diagnosis, monitoring of therapy, and drug design. Here, we review the literature on the development and validation of probes for magnetic resonance imaging using carbohydrates either as targeting vectors or as a target. Lectins are important targeting vectors for carbohydrate end groups, whereas selectins, the asialoglycoprotein receptor, sialic acid end groups, hyaluronic acid, and glycated serum and hemoglobin are interesting carbohydrate targets.

Elucidating the Nature of the External Acid Sites of ZSM-5 Zeolites Using NMR Probe Molecules.

The identification of acid and nonacid species at the external surface of zeolites remains a major challenge, in contrast to the extensively-studied internal acid sites. Here, it is shown that the synthesis of zeolite ZSM-5 samples with distinct particle sizes, combined with solid-state NMR and computational studies of trimethylphosphine oxide (TMPO) adsorption, provides insight into the chemical species on the external surface of the zeolite crystals. 1 H-31 P HETCOR NMR spectra of TMPO-loaded zeolites exhibit a broad correlation peak at δP ∼35-55 ppm and δH ∼5-12 ppm assigned to external SiOH species. Pore-mouth Brønsted acid sites exhibit 31 P and 1 H NMR resonances and adsorption energies close to those reported for internal acid sites interacting with TMPO. The presence of an external tricoordinate Al-Lewis site interacting strongly with TMPO is suggested, resulting in 31 P resonances that overlap with the peaks usually ascribed to the interaction of TMPO with Brønsted sites.

Modeling Gd3+ Complexes for Molecular Dynamics Simulations: Toward a Rational Optimization of MRI Contrast Agents.

The correct parametrization of lanthanide complexes is of the utmost importance for their characterization using computational tools such as molecular dynamics simulations. This allows the optimization of their properties for a wide range of applications, including medical imaging. Here we present a systematic study to establish the best strategies for the correct parametrization of lanthanide complexes using [Gd(DOTA)]- as a reference, which is used as a contrast agent in MRI. We chose the bonded model to parametrize the lanthanide complexes, which is especially important when considering the study of the complex as a whole (e.g., for the study of the dynamics of its interaction with proteins or membranes). We followed two strategies: a so-called heuristic approach employing strategies already published by other authors and another based on the more recent MCPB.py tool. Adjustment of the Lennard-Jones parameters of the metal was required. The final topologies obtained with both strategies were able to reproduce the experimental ion to oxygen distance, vibrational frequencies, and other structural properties. We report a new strategy to adjust the Lennard-Jones parameters of the metal ion in order to capture dynamic properties such as the residence time of the capping water (τm). For the first time, the correct assessment of the τm value for Gd-based complexes was possible by recording the dissociative events over up to 10 µs all-atom simulations. The MCPB.py tool allowed the accurate parametrization of [Gd(DOTA)]- in a simpler procedure, and in this case, the dynamics of the water molecules in the outer hydration sphere was also characterized. This sphere was divided into the first hydration layer, an intermediate region, and an outer hydration layer, with a residence time of 18, 10 and 19 ps, respectively, independent of the nonbonded parameters chosen for Gd3+. The Lennard-Jones parameters of Gd3+ obtained here for [Gd(DOTA)]- may be used with similarly structured gadolinium MRI contrast agents. This allows the use of molecular dynamics simulations to characterize and optimize the contrast agent properties. The characterization of their interaction with membranes and proteins will permit the design of new targeted contrast agents with improved pharmacokinetics.

Detection of glucose-derived D- and L-lactate in cancer cells by the use of a chiral NMR shift reagent.

BACKGROUND: Excessive lactate production, a hallmark of cancer, is largely formed by the reduction of pyruvate via lactate dehydrogenase (LDH) to L-lactate. Although D-lactate can also be produced from glucose via the methylglyoxal pathway in small amounts, less is known about the amount of D-lactate produced in cancer cells. Since the stereoisomers of lactate cannot be distinguished by conventional 1H NMR spectroscopy, a chiral NMR shift reagent was used to fully resolve the 1H NMR resonances of D- and L-lactate. METHODS: The production of L-lactate from glucose and D-lactate from methylglyoxal was first demonstrated in freshly isolated red blood cells using the chiral NMR shift reagent, YbDO3A-trisamide. Then, two different cell lines with high GLO1 expression (H1648 and H 1395) were selected from a panel of over 80 well-characterized human NSCLC cell lines, grown to confluence in standard tissue culture media, washed with phosphate-buffered saline, and exposed to glucose in a buffer for 4 h. After 4 h, a small volume of extracellular fluid was collected and mixed with YbDO3A-trisamide for analysis by 1H NMR spectroscopy. RESULTS: A suspension of freshly isolated red blood cells exposed to 5mM glucose produced L-lactate as expected but very little D-lactate. To evaluate the utility of the chiral NMR shift reagent, methylglyoxal was then added to red cells along with glucose to stimulate the production of D-lactate via the glyoxalate pathway. In this case, both D-lactate and L-lactate were produced and their NMR chemical shifts assigned. NSCLC cell lines with different expression levels of GLO1 produced both L- and D-lactate after incubation with glucose and glutamine alone. A GLO1-deleted parental cell line (3553T3) showed no production of D-lactate from glucose while re-expression of GLO1 resulted in higher production of D-lactate. CONCLUSIONS: The shift-reagent-aided NMR technique demonstrates that D-lactate is produced from glucose in NSCLC cells via the methylglyoxal pathway. The biological role of D-lactate is uncertain but a convenient method for monitoring D-lactate production could provide new insights into the biological roles of D- versus L-lactate in cancer metabolism.

Synthesis of a Novel Series of Cu(I) Complexes Bearing Alkylated 1,3,5-Triaza-7-phosphaadamantane as Homogeneous and Carbon-Supported Catalysts for the Synthesis of 1- and 2-Substituted-1,2,3-triazoles.

The N-alkylation of 1,3,5-triaza-7-phosphaadamantane (PTA) with ortho-, meta- and para-substituted nitrobenzyl bromide under mild conditions afforded three hydrophilic PTA ammonium salts, which were used to obtain a new set of seven water-soluble copper(I) complexes. The new compounds were fully characterized and their catalytic activity was investigated for the low power microwave assisted one-pot azide-alkyne cycloaddition reaction in homogeneous aqueous medium to obtain disubstituted 1,2,3-triazoles. The most active catalysts were immobilized on activated carbon (AC), multi-walled carbon nanotubes (CNT), as well as surface functionalized AC and CNT, with the most efficient support being the CNT treated with nitric acid and NaOH. In the presence of the immobilized catalyst, several 1,4-disubstituted-1,2,3-triazoles were obtained from the reaction of terminal alkynes, organic halides and sodium azide in moderate yields up to 80%. Furthermore, the catalyzed reaction of terminal alkynes, formaldehyde and sodium azide afforded 2-hydroxymethyl-2H-1,2,3-triazoles in high yields up to 99%. The immobilized catalyst can be recovered and recycled through simple workup steps and reused up to five consecutive cycles without a marked loss in activity. The described catalytic systems proceed with a broad substrate scope, under microwave irradiation in aqueous medium and according to "click rules".

What Is Being Measured with P-Bearing NMR Probe Molecules Adsorbed on Zeolites?

Elucidating the nature, strength, and siting of acid sites in zeolites is fundamental to fathom their reactivity and catalytic behavior. Despite decades of research, this endeavor remains a major challenge. Trimethylphosphine oxide (TMPO) has been proposed as a reliable probe molecule to study the acid properties of solid acid catalysts, allowing the identification of distinct Brønsted and Lewis acid sites and the assessment of Brønsted acid strengths. Recently, doubts have been raised regarding the assignment of the 31P NMR resonances of TMPO-loaded zeolites. Here, it is shown that a judicious control of TMPO loading combined with two-dimensional 1H-31P HETCOR solid-state NMR, DFT, and ab initio molecular dynamics (AIMD)-based computational modeling provides an unprecedented atomistic description of the host-guest and guest-guest interactions of TMPO molecules confined within HZSM-5 molecular-sized voids. 31P NMR resonances usually assigned to TMPO molecules interacting with Brønsted sites of different acid strength arise instead from both changes in the probe molecule confinement effects at ZSM-5 channel system and the formation of protonated TMPO dimers. Moreover, DFT/AIMD shows that the 1H and 31P NMR chemical shifts strongly depend on the siting of the framework aluminum atoms. This work overhauls the current interpretation of NMR spectra, raising important concerns about the widely accepted use of probe molecules for studying acid sites in zeolites.

Complexes of Bifunctional DO3A-N-(α-amino)propinate Ligands with Mg(II), Ca(II), Cu(II), Zn(II), and Lanthanide(III) Ions: Thermodynamic Stability, Formation and Dissociation Kinetics, and Solution Dynamic NMR Studies.

The thermodynamic, kinetic, and structural properties of Ln3+ complexes with the bifunctional DO3A-ACE4- ligand and its amide derivative DO3A-BACE4- (modelling the case where DO3A-ACE4- ligand binds to vector molecules) have been studied in order to confirm the usefulness of the corresponding Gd3+ complexes as relaxation labels of targeted MRI contrast agents. The stability constants of the Mg2+ and Ca2+ complexes of DO3A-ACE4- and DO3A-BACE4- complexes are lower than for DOTA4- and DO3A3-, while the Zn2+ and Cu2+ complexes have similar and higher stability than for DOTA4- and DO3A3- complexes. The stability constants of the Ln(DO3A-BACE)- complexes increase from Ce3+ to Gd3+ but remain practically constant for the late Ln3+ ions (represented by Yb3+). The stability constants of the Ln(DO3A-ACE)4- and Ln(DO3A-BACE)4- complexes are several orders of magnitude lower than those of the corresponding DOTA4- and DO3A3- complexes. The formation rate of Eu(DO3A-ACE)- is one order of magnitude slower than for Eu(DOTA)-, due to the presence of the protonated amine group, which destabilizes the protonated intermediate complex. This protonated group causes the Ln(DO3A-ACE)- complexes to dissociate several orders of magnitude faster than Ln(DOTA)- and its absence in the Ln(DO3A-BACE)- complexes results in inertness similar to Ln(DOTA)- (as judged by the rate constants of acid assisted dissociation). The 1H NMR spectra of the diamagnetic Y(DO3A-ACE)- and Y(DO3A-BACE)- reflect the slow dynamics at low temperatures of the intramolecular isomerization process between the SA pair of enantiomers, R-Λ(λλλλ) and S-Δ(δδδδ). The conformation of the Cα-substituted pendant arm is different in the two complexes, where the bulky substituent is further away from the macrocyclic ring in Y(DO3A-BACE)- than the amino group in Y(DO3A-ACE)- to minimize steric hindrance. The temperature dependence of the spectra reflects slower ring motions than pendant arms rearrangements in both complexes. Although losing some thermodynamic stability relative to Gd(DOTA)-, Gd(DO3A-BACE)- is still quite inert, indicating the usefulness of the bifunctional DO3A-ACE4- in the design of GBCAs and Ln3+-based tags for protein structural NMR analysis.

Inhibition of α-glucosidase by flavonoids of Cymbopogon citratus (DC) Stapf.

ETHNOPHARMACOLOGICAL RELEVANCE: Leaves extracts from Cymbopogon citratus (DC) Stapf. are widely used in traditional medicine exhibiting several in vivo biological activities, including antidiabetic. Several flavonoids, including aglycones and glycosides, were reported in this plant and previous studies suggested that flavonoids may interact with targets related to diabetes. AIM OF THE STUDY: Evaluated the hypoglycemic activity of C. citratus flavonoids through α-glucosidase inhibition and assess the structure-activity relationship using molecular docking studies. MATERIAL AND METHODS: An infusion of C. citratus leaves and its flavonoid-rich fraction were prepared. Five flavonoids from this fraction were isolated and structurally characterized by UV spectral analysis with shift reagents, HPLC-PDA-ESI/MSn and 1H NMR. The antidiabetic potential of C. citratus infusion, its flavonoid-rich fraction, glycosylated flavonoids and aglycones was evaluated trough the in vitro inhibition of yeast α-glucosidase. Posteriorly, molecular docking of the tested flavonoids was performed to investigate its possible interactions with the α-glucosidase pocket. RESULTS: The infusion of C. citratus, its flavonoid-rich fraction, luteolin and five flavone glycosides namely, luteolin 6-C-ß-glucopyranoside (isoorientin), luteolin 7-O-neohesperidoside (ionicerin), luteolin 7-O-ß-glucopyranoside (cynaroside), Luteolin 2″-O-rhamnosyl-C-(6-deoxy-ribo-hexos-3-ulosyl) (cassiaoccidentalin B), luteolin 6-C-α-arabinofuranosil-(1→2)-α-L-rhamnopyranoside (kurilesin A) showed higher inhibitory activity than the reference drug. This activity increased by the addition of a sugar moiety. However, the di-glycosides were less active than mono-glycosides. The docking studies showed interactions of sugar moieties and A or B rings with the catalytic pocket mainly through hydrogen bonds. CONCLUSIONS: Our results corroborate the potential of C. citratus as a medicinal plant for the treatment of diabetes and revealed that its flavonoid glycosides has hypoglycemic effect and can be explored as drug candidates to act as α-glucosidase inhibitors in the treatment of diabetes.

Concentration-Dependent Interactions of Amphiphilic PiB Derivative Metal Complexes with Amyloid Peptides Aß and Amylin*.

Metal chelates targeted to amyloid peptides are widely explored as diagnostic tools or therapeutic agents. The attachment of a metal complex to amyloid recognition units typically leads to a decrease in peptide affinity. We show here that by separating a macrocyclic GdL chelate and a PiB targeting unit with a long hydrophobic C10 linker, it is possible to attain nanomolar affinities for both Aß1-40 (Kd =4.4 nm) and amylin (Kd =4.5 nm), implicated, respectively in Alzheimer's disease and diabetes. The Scatchard analysis of surface plasmon resonance data obtained for a series of amphiphilic, PiB derivative GdL complexes indicate that their Aß1-40 or amylin binding affinity varies with their concentration, thus micellar aggregation state. The GdL chelates also affect peptide aggregation kinetics, as probed by thioflavin-T fluorescence assays. A 2D NMR study allowed identifying that the hydrophilic region of Aß1-40 is involved in the interaction between the monomer peptide and the Gd3+ complex. Finally, ex vivo biodistribution experiments were conducted in healthy mice by using 111 In labeled analogues. Their pancreatic uptake, ∼3 %ID g-1 , is promising to envisage amylin imaging in diabetic animals.

Concentration-Dependent Interactions of Amphiphilic PiB Derivative Metal Complexes with Amyloid Peptides Aß and Amylin*.

Invited for the cover of this issue are Jean-François Morfin and Éva Tóth at the CNRS in Orléans, and their collaborators from University of Debrecen, University of Coimbra and Université de Toulouse. The image depicts that when an amphiphilic compound is intravenously injected, monomer, pre-micellar and micellar forms can co-exist in the blood and have different affinities for amyloid peptides. Read the full text of the article at 10.1002/chem.202004000.

Introduction to Infrared and Raman-Based Biomedical Molecular Imaging and Comparison with Other Modalities.

Molecular imaging has rapidly developed to answer the need of image contrast in medical diagnostic imaging to go beyond morphological information to include functional differences in imaged tissues at the cellular and molecular levels. Vibrational (infrared (IR) and Raman) imaging has rapidly emerged among the molecular imaging modalities available, due to its label-free combination of high spatial resolution with chemical specificity. This article presents the physical basis of vibrational spectroscopy and imaging, followed by illustration of their preclinical in vitro applications in body fluids and cells, ex vivo tissues and in vivo small animals and ending with a brief discussion of their clinical translation. After comparing the advantages and disadvantages of IR/Raman imaging with the other main modalities, such as magnetic resonance imaging (MRI), computed tomography (CT), positron emission tomography/single-photon emission-computed tomography (PET/SPECT), ultrasound (US) and photoacoustic imaging (PAI), the design of multimodal probes combining vibrational imaging with other modalities is discussed, illustrated by some preclinical proof-of-concept examples.

Photophysical studies on lanthanide(III) chelates conjugated to Pittsburgh compound B as luminescent probes targeted to Aß amyloid aggregates.

The photophysical properties of Eu3+ and Tb3+ complexes of DOTAGA and DO3A-monoamide conjugates of the Pittsburgh compound B (PiB) chromophore, prepared using linkers of different lengths and flexibilities, and which form stable negatively charged (LnL1), and uncharged (LnL2) complexes, respectively, were studied as potential probes for optical detection of amyloid aggregates. The phenylbenzothiazole (PiB) moiety absorbs light at wavelengths longer than 330 nm with a high molar absorption coefficient in both probes, and acts as an antenna in these systems. The presence of the luminescent Ln3+ ion quenches the excited states of PiB through an energy transfer process from the triplet state of PiB to the metal centre, and structured emission is seen from Eu3+ and Tb3+. The luminescence study indicates the presence of a 5D4 → T1 back transfer process in the Tb3+ complexes. It also provides insights on structural properties of the Eu3+ complexes, such as the high symmetry environment of the Eu3+ ion in a single macrocyclic conformation and the presence of one water molecule in its inner coordination sphere. The overall quantum yield of luminescence of EuL1 is higher than for EuL2. However, their low values reflect the low overall sensitization efficiency of the energy transfer process, which is a consequence of the large distances between the metal center and the antenna, especially in the EuL2 complex. DFT calculations confirmed that the most stable conformation of the Eu3+ complexes involves a combination of a square antiprismatic (SAP) geometry of the chelate and an extended conformation of the linker. The large calculated average distances between the metal center and the antenna point to the predominance of the Förster energy transfer mechanism, especially for EuL2. This study provides insights into the behavior of amyloid-targeted Ln3+ complexes as optical probes, and contributes towards their rational design.

Supercritically dried superparamagnetic mesoporous silica nanoparticles for cancer theranostics.

Mesoporous silica nanoparticles with a superparamagnetic iron oxide core were prepared in this work, in order to obtain multifunctional platforms with adequate features for cancer theranostics. Three different core-shell nanocomplexes were obtained: IO-OAm/mSiO2, IO-APTES/mSiO2 and IO/SiO2/mSiO2. In the case of IO-OAm/mSiO2 and IO-APTES/mSiO2, iron oxide (IO) was obtained by thermal decomposition, having in this case a coating of oleylamine (OAm) that was in the second formulation exchanged by (3-aminopropyl)triethoxysilane ligand (APTES). Regarding the IO/SiO2/mSiO2 formulation, iron oxide was synthesized by microemulsion. The mesoporous silica shell (mSiO2) on the IO nanoparticles was obtained by sol-gel and the final materials were dried by supercritical fluids drying. VSM confirmed the superparamagnetic behaviour of the nanoparticles, leading to MS of 4.0, 1.8 and 10.2 emu·g-1, for IO-OAm/mSiO2, IO-APTES/mSiO2 and IO/SiO2/mSiO2, respectively. NMR relaxometry has shown the potential of these nanoparticles to be used as T2 contrast agents, with r2 values as high as 63.93 s-1·mM-1 Fe. The three types of nanoparticles exhibited loading contents of epirubicin of ~3% and drug release percentages of 19% for IO-OAm/mSiO2, 24% for IO-APTES/mSiO2 and 31% for IO/SiO2/mSiO2. The cytotoxicity of drug-loaded and non-loaded most promising nanoparticles was assessed, showing high potential of these platforms for application as anticancer drug carriers.

A Frequency-Selective pH-Responsive paraCEST Agent.

Paramagnetic chemical exchange saturation transfer (paraCEST) agents are well-suited for imaging tissue pH because the basis of CEST, chemical exchange, is inherently sensitive to pH. Several previous pH-sensitive paraCEST agents were based on an exchanging Ln3+ -bound water molecule as the CEST antenna but this design often added additional line-broadening to the bulk water signal due to T2 exchange. We report herein a pH-sensitive paraCEST agent that lacks an inner-sphere water molecule but contains one Ln-bound -OH group for CEST activation. The Yb3+ complex, Yb(1), displayed a single, highly shifted CEST peak originating from the exchangeable Yb-OH proton, the frequency of which changed over the biologically relevant pH range. CEST images of phantoms ranging in pH from 6 to 8 demonstrate the potential of this agent for imaging pH. Initial rodent imaging studies showed that Gd(1) remains in the vascular system much longer than anticipated but is cleared slowly via renal filtration.