Multimetallic Complexes and Functionalized Gold Nanoparticles Based on a Combination of d- and f-Elements

Smart magnetic resonance imaging-based theranostics for cancer

Smart theranostics are dynamic platforms that integrate multiple functions, including at least imaging, therapy, and responsiveness, in a single agent. This review showcases a variety of responsive theranostic agents developed specifically for magnetic resonance imaging (MRI), due to the privileged position this non-invasive, non-ionising imaging modality continues to hold within the clinical imaging field. Different MRI smart theranostic designs have been devised in the search for more efficient cancer therapy, and improved diagnostic efficiency, through the increase of the local concentration of therapeutic effectors and MRI signal intensity in pathological tissues. This review explores novel small-molecule and nanosized MRI theranostic agents for cancer that exhibit responsiveness to endogenous (change in pH, redox environment, or enzymes) or exogenous (temperature, ultrasound, or light) stimuli. The challenges and obstacles in the design and in vivo application of responsive theranostics are also discussed to guide future research in this interdisciplinary field towards more controllable, efficient, and diagnostically relevant smart theranostics agents.

A Single-Pot Template Reaction Towards a Manganese-Based T1 Contrast Agent

Manganese-based contrast agents (MnCAs) have emerged as suitable alternatives to gadolinium-based contrast agents (GdCAs). However, due to their kinetic lability and laborious synthetic procedures, only a few MnCAs have found clinical MRI application. In this work, we have employed a highly innovative single-pot template synthetic strategy to develop a MnCA, MnLMe , and studied the most important physicochemical properties in vitro. MnLMe displays optimized r1 relaxivities at both medium (20 and 64 MHz) and high magnetic fields (300 and 400 MHz) and an enhanced r1b =21.1 mM-1  s-1 (20 MHz, 298 K, pH 7.4) upon binding to BSA (Ka =4.2×103  M-1 ). In vivo studies show that MnLMe is cleared intact into the bladder through renal excretion and has a prolonged blood half-life compared to the commercial GdCA Magnevist. MnLMe shows great promise as a novel MRI contrast agent.

A Single-Pot Template Reaction Towards a Manganese-Based T1 Contrast Agent

Manganese-based contrast agents (MnCAs) have emerged as suitable alternatives to gadolinium-based contrast agents (GdCAs). However, due to their kinetic lability and laborious synthetic procedures, only a few MnCAs have found clinical MRI application. In this work, we have employed a highly innovative single-pot template synthetic strategy to develop a MnCA, MnLMe, and studied the most important physicochemical properties in vitro. MnLMe displays optimized r 1 relaxivities at both medium (20 and 64 MHz) and high magnetic fields (300 and 400 MHz) and an enhanced r 1 b=21.1 mM-1 s-1 (20 MHz, 298 K, pH 7.4) upon binding to BSA (K a=4.2×103 M-1). In vivo studies show that MnLMe is cleared intact into the bladder through renal excretion and has a prolonged blood half-life compared to the commercial GdCA Magnevist. MnLMe shows great promise as a novel MRI contrast agent.

Preparation, Functionalization, Modification, and Applications of Nanostructured Gold: A Critical Review

Gold nanoparticles (Au NPs) play a significant role in science and technology because of their unique size, shape, properties and broad range of potential applications. This review focuses on the various approaches employed for the synthesis, modification and functionalization of nanostructured Au. The potential catalytic applications and their enhancement upon modification of Au nanostructures have also been discussed in detail. The present analysis also offers brief summaries of the major Au nanomaterials synthetic procedures, such as hydrothermal, solvothermal, sol-gel, direct oxidation, chemical vapor deposition, sonochemical deposition, electrochemical deposition, microwave and laser pyrolysis. Among the various strategies used for improving the catalytic performance of nanostructured Au, the modification and functionalization of nanostructured Au produced better results. Therefore, various synthesis, modification and functionalization methods employed for better catalytic outcomes of nanostructured Au have been summarized in this review.

Metallostar Assemblies Based on Dithiocarbamates for Use as MRI Contrast Agents

Two different octadentate gadolinium chelates based on DO3A and DOTAGA chelates (hydration number q = 1) have been used to prepare a series of bi-, tri-, and tetrametallic d-f mixed-metal complexes. The piperazine-based dithiocarbamate linker ensures that rotation of the gadolinium chelates is restricted, leading to enhanced relaxivity (r₁) values, which increase with the overall mass and number of gadolinium units. The r₁ value (at 10 MHz, 25 °C) per gadolinium unit rises from 5.0 mM^-1 s^-1 for the Gd-DO3A-NH₂ monogadolinium chelate to 9.2 mM^-1 s^-1 in a trigadolinium complex with a ruthenium(III) core. Using a 1.5 T clinical scanner operating at 63.87 MHz (25 °C), an 86% increase in the relaxivity per gadolinium unit is observed for this multimetallic compound compared to clinically approved Dotarem. The gadolinium complexes based on the DOTAGA chelate also performed well at 63.87 MHz, with a relaxivity value of 9.5 mM^-1 s^-1 per gadolinium unit being observed for the trigadolinium d-f mixed-metal complex with a ruthenium(III) core. The versatility of dithiocarbamate coordination chemistry thus provides access to a wide range of d-f hybrids with potential for use as high-performance MRI contrast agents.

Combined Magnetic Resonance Imaging and Photodynamic Therapy Using Polyfunctionalised Nanoparticles Bearing Robust Gadolinium Surface Units

A robust dithiocarbamate tether allows novel gadolinium units based on DOTAGA (q=1) to be attached to the surface of gold nanoparticles (2.6-4.1 nm diameter) along with functional units offering biocompatibility, targeting and photodynamic therapy. A dramatic increase in relaxivity (r₁ ) per Gd unit from 5.01 mm^-1  s^-1 in unbound form to 31.68 mm^-1  s^-1 (10 MHz, 37 °C) is observed when immobilised on the surface due to restricted rotation and enhanced rigidity of the Gd complex on the nanoparticle surface. The single-step synthetic route provides a straightforward and versatile way of preparing multifunctional gold nanoparticles, including examples with conjugated zinc-tetraphenylporphyrin photosensitizers. The lack of toxicity of these materials (MTT assays) is transformed on irradiation of HeLa cells for 30 minutes (PDT), leading to 75 % cell death. In addition to passive targeting, the inclusion of units capable of actively targeting overexpressed folate receptors illustrates the potential of these assemblies as targeted theranostic agents.

Functionalization of Gold Nanoparticles by Inorganic Entities

The great affinity of gold surface for numerous electron-donating groups has largely contributed to the rapid development of functionalized gold nanoparticles (Au-NPs). In the last years, a new subclass of nanocomposite has emerged, based on the association of inorganic molecular entities (IME) with Au-NPs. This highly extended and diversified subclass was promoted by the synergy between the intrinsic properties of the shell and the gold core. This review-divided into four main parts-focuses on an introductory section of the basic notions related to the stabilization of gold nanoparticles and defines in a second part the key role played by the functionalizing agent. Then, we present a wide range of inorganic molecular entities used to prepare these nanocomposites (NCs). In particular, we focus on four different types of inorganic systems, their topologies, and their current applications. Finally, the most recent applications are described before an overview of this new emerging field of research.

Gold nanomaterials functionalised with gadolinium chelates and their application in multimodal imaging and therapy

An overview of recent progress in the design of gadolinium-functionalised gold nanoparticles for use in MRI, multimodal imaging and theranostics.

Polyfunctionalised Nanoparticles Bearing Robust Gadolinium Surface Units for High Relaxivity Performance in MRI

The first example of an octadentate gadolinium unit based on DO3A (hydration number q=1) with a dithiocarbamate tether has been designed and attached to the surface of gold nanoparticles (around 4.4 nm in diameter). In addition to the superior robustness of this attachment, the restricted rotation of the Gd complex on the nanoparticle surface leads to a dramatic increase in relaxivity (r₁ ) from 4.0 mm^-1  s^-1 in unbound form to 34.3 mm^-1  s^-1 (at 10 MHz, 37 °C) and 22±2 mm^-1  s^-1 (at 63.87 MHz, 25 °C) when immobilised on the surface. The one-pot synthetic route provides a straightforward and versatile way of preparing a range of multifunctional gold nanoparticles. The incorporation of additional surface units for biocompatibility (PEG and thioglucose units) and targeting (folic acid) leads to little detrimental effect on the high relaxivity observed for these non-toxic multifunctional materials. In addition to the passive targeting attributed to gold nanoparticles, the inclusion of a unit capable of targeting the folate receptors overexpressed by cancer cells, such as HeLa cells, illustrates the potential of these assemblies.

Heteromultimetallic compounds based on polyfunctional carboxylate linkers

Polyfunctional linkers bearing carboxylate, bipyridine and alkyne functionalities allow the stepwise construction of multimetallic assemblies incorporating redox and photophysical properties.

The stepwise generation of multimetallic complexes based on a vinylbipyridine linkage and their photophysical properties

The versatile rhenium complex [ReCl(CO)₃(bpyC[triple bond, length as m-dash]CH)] (HC[triple bond, length as m-dash]Cbpy = 5-ethynyl-2,2'-bipyridine) is used to generate a series of bimetallic complexes through the hydrometallation of [MHCl(CO)(BTD)(PPh₃)₂] (M = Ru, Os; BTD = 2,1,3-benzothiadiazole). The ruthenium complex [Ru{CH[double bond, length as m-dash]CH-bpyReCl(CO)₃}Cl(BTD)(CO)(PPh₃)₂] was characterised structurally. Ligand exchange reactions with bifunctional linkers bearing oxygen and sulfur donors provide access to tetra- and pentametallic complexes such as [{M{CH[double bond, length as m-dash]CH-bpyReCl(CO)₃}(CO)(PPh₃)₂}₂(S₂CNC₄H₈NCS₂)] and Fe[C₅H₄CO₂M{CH[double bond, length as m-dash]CH-bpyReCl(CO)₃}(CO)(PPh₃)₂]₂. The effect of the group 8 metal on the photophysical properties of the rhenium centre was investigated using the complexes [Ru{CH[double bond, length as m-dash]CH-bpyReCl(CO)₃}Cl(BTD)(CO)(PPh₃)₂] and [M{CH[double bond, length as m-dash]CH-bpyReCl(CO)₃}{S₂P(OEt)₂}(CO)(PPh₃)₂] (M = Ru, Os). This revealed the quenching of the rhenium-based emission in favour of weak radiative processes based on the Ru and Os centres. The potential for exploiting this effect is illustrated by the reaction of [Ru{CH[double bond, length as m-dash]CH-bpyReCl(CO)₃}Cl(CO)(BTD)(PPh₃)₂] with carbon monoxide, which results in a 5-fold fluorescence enhancement in the dicarbonyl product, [Ru{CH[double bond, length as m-dash]CH-bpyReCl(CO)₃}Cl(CO)₂(PPh₃)₂], as the quenching effect is disrupted.

Complications in complexation kinetics for lanthanides with DTPA using dye probe molecules in aqueous solution

Dye probe molecules were used to investigate lanthanide complexation and verify the viability of the ligand displacement methodology for measuring DTPA complexation rate constants. Results showed that dye probes underestimate the rate constants.

Gd(III)-Dithiolane Gold Nanoparticles for T1-Weighted Magnetic Resonance Imaging of the Pancreas

Pancreatic adenocarcinoma has a 5 year survival of approximately 3% and median survival of 6 months and is among the most dismal of prognoses in all of medicine. This poor prognosis is largely due to delayed diagnosis where patients remain asymptomatic until advanced disease is present. Therefore, techniques to allow early detection of pancreatic adenocarcinoma are desperately needed. Imaging of pancreatic tissue is notoriously difficult, and the development of new imaging techniques would impact our understanding of organ physiology and pathology with applications in disease diagnosis, staging, and longitudinal response to therapy in vivo. Magnetic resonance imaging (MRI) provides numerous advantages for these types of investigations; however, it is unable to delineate the pancreas due to low inherent contrast within this tissue type. To overcome this limitation, we have prepared a new Gd(III) contrast agent that accumulates in the pancreas and provides significant contrast enhancement by MR imaging. We describe the synthesis and characterization of a new dithiolane-Gd(III) complex and a straightforward and scalable approach for conjugation to a gold nanoparticle. We present data that show the nanoconjugates exhibit very high per particle values of r1 relaxivity at both low and high magnetic field strengths due to the high Gd(III) payload. We provide evidence of pancreatic tissue labeling that includes MR images, post-mortem biodistribution analysis, and pancreatic tissue evaluation of particle localization. Significant contrast enhancement was observed allowing clear identification of the pancreas with contrast-to-noise ratios exceeding 35:1.

Organically-modified magnesium silicate nanocomposites for high-performance heavy metal removal

A disulfide-grafted polyethyleneimine (PES)@Mg₂SiO₄composite was synthesized, characterized, and used successfully to remove heavy metals from wastewater.

Gold nanostars co-coated with the Cu(II) complex of a tetraazamacrocyclic ligand

The twelve-membered tetraazamacrocyclic ligand L1 bears an appended lipoic acid unit, whose disulphide ring is an efficient grafting moiety for the surface of gold nanostars (GNS). The GNS that were used featured a localized surface plasmon resonance (LSPR) absorption at ∼800 nm, i.e. in the near infrared (NIR). We investigated different approaches for coating them with the Cu(2+) complex of L1. While the direct reaction of [CuL1](2+) with as-prepared GNS led to aggregation, an initial coating step with polyethyleneglycol-thiol (PEG-SH) was found to be advantageous. Displacement reactions were carried out on pegylated GNS either with [CuL1](2+), directly generating [Cun(L1@GNS)](2n+), or with void L1, thus obtaining @GNS that coordinates Cu(2+) in a second step. In both cases, even with a large excess of the competing disulphide moiety, only partial displacement of PEG-SH is observed, obtaining ca. 500-1500 [CuL1](2+) per GNS depending on the conditions, with PEG-SH remaining in the [Cun(L1@GNS)](2n+) hybrids and imparting them with remarkable stability. Comparison of the photothermal and two-photon luminescence (TPL) properties of the GNS between the pegylated GNS and [Cun(L1@GNS)](2n+) revealed that the grafted copper complex does not change them to any extent. Finally, the stability against demetallation and transmetallation of the complexes, as well as the fast kinetics of complexation of the monodispersed macrocycle and of L1@GNS, have been examined, suggesting [Cun(L1@GNS)](2n+) as a device capable of TPL optical tracking and NIR photothermal therapy and as a possible agent for PET imaging.

Long N. Towards understanding the design of dual-modal MR/fluorescent probes to sense zinc ions

A series of new gadolinium complexes have been synthesised to test the design of dual-modal probes that can display a change in fluorescence or relaxivity response upon zinc binding. By an iterative change in parameters of the probes, the compounds give insight into the design protocols required for successful imaging of zinc ions.

On the interaction of copper(II) with disulfiram

In combination with copper(II) ions, disulfiram (DSF) has been reported to be a potentially potent anticancer agent based on in vitro results. The interaction of DSF with copper(II) chloride in solution has been studied using a range of spectroscopic techniques. There is strong evidence for the rapid formation of the bis(N,N-diethyl dithiocarbamato)copper(II) complex in situ. Kinetic experiments were used to determine rate laws for the reaction that give insight into the mechanism of the process which may help to explain the observed in vitro cytotoxicity.