Gadolinium complexes of macrocyclic diethylenetriamine-N-oxide pentaacetic acid-bisamide as highly stable MRI contrast agents with high relaxivity

Fabrication of a novel graphene oxide based magnetic nanocomposite and its usage as a highly effectual catalyst for the construction of N,N'-alkylidene bisamides

At first, a novel graphene oxide-based magnetic nanocomposite namely Si-propyl-functionalized N 1,N 1,N 2,N 2-tetramethylethylenediamine-N 1,N 2-diium hydrogen sulfate anchored to graphene oxide-supported Fe3O4 (nano-[GO@Fe3O4@R-NHMe2][HSO4]) was fabricated. After full characterization of the nanocomposite, its catalytic performance was examined for the solvent-free construction of N,N'-alkylidene bisamides from aryl aldehydes (1 eq.) and primary aromatic and aliphatic amides (2 eq.), in which the products were acquired in short times (15-30 min) and high to excellent yields (89-98%). Nano-[GO@Fe3O4@R-NHMe2][HSO4] could be magnetically isolated form the reaction medium, and reused three times without remarkable loss of catalytic activity.

Theranostics Using MCM-41-Based Mesoporous Silica Nanoparticles: Integrating Magnetic Resonance Imaging and Novel Chemotherapy for Breast Cancer Treatment

Advanced breast cancer remains a significant oncological challenge, requiring new approaches to improve clinical outcomes. This study investigated an innovative theranostic agent using the MCM-41-NH2-DTPA-Gd3⁺-MIH nanomaterial, which combined MRI imaging for detection and a novel chemotherapy agent (MIH 2.4Bl) for treatment. The nanomaterial was based on the mesoporous silica type, MCM-41, and was optimized for drug delivery via functionalization with amine groups and conjugation with DTPA and complexation with Gd3+. MRI sensitivity was enhanced by using gadolinium-based contrast agents, which are crucial in identifying early neoplastic lesions. MIH 2.4Bl, with its unique mesoionic structure, allows effective interactions with biomolecules that facilitate its intracellular antitumoral activity. Physicochemical characterization confirmed the nanomaterial synthesis and effective drug incorporation, with 15% of MIH 2.4Bl being adsorbed. Drug release assays indicated that approximately 50% was released within 8 h. MRI phantom studies demonstrated the superior imaging capability of the nanomaterial, with a relaxivity significantly higher than that of the commercial agent Magnevist. In vitro cellular cytotoxicity assays, the effectiveness of the nanomaterial in killing MDA-MB-231 breast cancer cells was demonstrated at an EC50 concentration of 12.6 mg/mL compared to an EC50 concentration of 68.9 mg/mL in normal human mammary epithelial cells (HMECs). In vivo, MRI evaluation in a 4T1 syngeneic mouse model confirmed its efficacy as a contrast agent. This study highlighted the theranostic capabilities of MCM-41-NH2-DTPA-Gd3⁺-MIH and its potential to enhance breast cancer management.

Decoration of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) with N-oxides increases the T1 relaxivity of Gd-complexes

High complex stability and longitudinal relaxivity of Gd-based contrast agents are important requirements for magnetic resonance imaging (MRI) because they ensure patient safety and contribute to measurement sensitivity. Charged and zwitterionic Gd3+-complexes of the well-known chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) provide an excellent basis for the development of safe and sensitive contrast agents. In this report, we describe the synthesis of DOTA-NOx, a DOTA derivative with four N-oxide functionalities via "click" functionalization of the tetraazide DOTAZA. The resulting complexes Gd-DOTA-NOx and Eu-DOTA-NOx are stable compounds in aqueous solution. NMR-spectroscopic characterization revealed a high excess of the twisted square antiprismatic (TSAP) coordination geometry over square antiprismatic (SAP). The longitudinal relaxivity of Gd-DOTA-NOx was found to be r1=7.7 mm-1 s-1 (1.41 T, 37 °C), an unusually high value for DOTA complexes of comparable weight. We attribute this high relaxivity to the steric influence and an ordering effect on outer sphere water molecules surrounding the complex generated by the strongly hydrated N-oxide groups. Moreover, Gd-DOTA-NOx was found to be stable against transchelation with high excess of EDTA (200 eq) over a period of 36 h, and it has a similar in vitro cell toxicity as clinically used DOTA-based GBCAs.

Medicinal Chemistry of Drugs with N-Oxide Functionalities

Molecules with N-oxide functionalities are omnipresent in nature and play an important role in Medicinal Chemistry. They are synthetic or biosynthetic intermediates, prodrugs, drugs, or polymers for applications in drug development and surface engineering. Typically, the N-oxide group is critical for biomedical applications of these molecules. It may provide water solubility or decrease membrane permeability or immunogenicity. In other cases, the N-oxide has a special redox reactivity which is important for drug targeting and/or cytotoxicity. Many of the underlying mechanisms have only recently been discovered, and the number of applications of N-oxides in the healthcare field is rapidly growing. This Perspective article gives a short summary of the properties of N-oxides and their synthesis. It also provides a discussion of current applications of N-oxides in the biomedical field and explains the basic molecular mechanisms responsible for their biological activity.

Gd(III) and Yb(III) Complexes Derived from a New Water-Soluble Dioxopolyazacyclohexane Macrocycle

A new macrocyclic ligand was synthesized by a reaction between diethylenetriaminepentaacetic (DTPA) dianhydride and trans-1,4-diaminocyclohexane, and the Gd(III) and Yb(III) complexes were prepared. The compounds were characterized by spectroscopic methods. Structural calculation by DFT shows that the amide linkages are arranged in such a way that a conformational strain is minimized in the macrocyclic frame. The coordination modes of the ligand and water in the metal complexes were also determined by DFT. The longitudinal relaxation time T1 was measured for aqueous solutions of the Gd(III) complex. The T1 relaxivity arises from the structural feature that a water molecule coordinated to the paramagnetic metal is surrounded by a large open space, through which the exchange of water occurs readily to shorten the relaxation time of water in the entire region, as a result of the chelate conformation defined strictly by the amide groups and the cyclohexane ring.

Single-Atom Gadolinium Nano-Contrast Agents with High Stability for Tumor T1 Magnetic Resonance Imaging

Gadolinium chelates for tumor magnetic resonance imaging (MRI) face challenges such as inadequate sensitivity, lack of selectivity, and risk of Gd leakage. This study presents a single-atom Gd nano-contrast agent (Gd-SA) that enhances tumor MRI. Isolated Gd atoms coordinated by six N atoms and two O atoms are atomically dispersed on a hollow carbon nanosphere, allowing the maximum utilization of Gd atoms with reduced risk of toxic Gd ion leakage. Owning to the large surface area and fast exchange of relaxed water molecules, Gd-SA shows excellent T₁-weighted magnetic resonance enhancement with a r₁ value of 11.05 mM^-1 s^-1 at 7 T, which is 3.6 times that of the commercial gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA). In vivo MRI results show that the Gd-SA has a higher spatial resolution and a wider imaging time window for tumors than Gd-DTPA, with low hematological, hepatic, and nephric toxicities. These advantages demonstrate the great potential of single-atom Gd-based nanomaterials as safe, efficient, and long-term MRI contrast agents for cancer diagnosis.

The Potential of Gadolinium Ascorbate Nanoparticles as a Safer Contrast Agent

There have been health concerns raised against the use of gadolinium (Gd)-based magnetic resonance imaging contrast agents. The primary observation is that Gd ions are prone to leaking into the bloodstream, causing nephrogenic systemic fibrosis as one of the side effects. In addition, such leakage of the ions inhibits easy clearance from the body. Herein we propose that Gd-ascorbate nanoparticles could be one of the safer choices as they are rather stable in aqueous dispersion and they do not get affected by Zn or Fe ions in the medium. The magnetic properties of the ions are preserved in the nanoparticles, and particles when sufficiently small may be amenable to renal clearance from the human body. Thus, when an aqueous solution of Gd-acetate and ascorbic acid was left to evolve with time, a Gd-ascorbate complex was formed that led to the formation of nanoparticles with time. The sizes of the nanoparticles increased with time, and when the particles were sufficiently large, they precipitated out of the medium. In addition, smaller nanoparticles were consistently present at all times of observations. UV-vis, photoluminescence and FTIR spectroscopy, mass spectrometry, and transmission electron microscopy analyses confirmed the formation of nanoparticles of Gd-ascorbate complex. In addition, magnetic measurements confirmed the high relaxivity of the nanoparticles as compared to the parent salt, indicating the effectiveness of the nanoparticles as contrast agents. Density functional theory-based calculations of the molecular complex-based nanoparticles accounted for the experimental observations.

Preparation and MRI performance of a composite contrast agent based on palygorskite pores and channels binding effect to prolong the residence time of water molecules on gadolinium ions

Herein, gadolinium tannate was simply and conveniently coated on the surface of palygorskite by in situ reaction of a coordination polymer formed between tannic acid and Gd3+. The palygorskite-tannate gadolinium-polyvinyl alcohol integrated composite (PAL@Gd@PVA) is successfully prepared after the introduction of polyvinyl alcohol onto the palygorskite-tannate gadolinium. The structure is characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy analysis. The results show that TA-Gd and PVA are successfully loaded on the surface of palygorskite, and the rod crystal structure of palygorskite in the composite remains intact. Palygorskite fibres constitute the framework of the composite and play a key role in supporting and crosslinking the composite. The prepared compounds showed negligible cytotoxicity and low haemolysis rate, showing good biocompatibility. In vitro MRI results showed that the longitudinal and transverse relaxation rates of the composite are 59.56 and 340.81 mm-1 s-1, respectively.

[rac-1,8-Bis(2-carbamoyleth-yl)-5,5,7,12,12,14-hexa-methyl-1,4,8,11-tetra-aza-cyclo-tetra-deca-ne]copper(II) di-acetate tetra-hydrate: crystal structure and Hirshfeld surface analysis

The title CuII macrocyclic complex salt tetra-hydrate, [Cu(C22H46N6O2)](C2H3O2)2·4H2O, sees the metal atom located on a centre of inversion and coordinated within a 4 + 2 (N4O2) tetra-gonally distorted coordination geometry; the N atoms are derived from the macrocycle and the O atoms from weakly associated [3.2048 (15) Å] acetate anions. Further stability to the three-ion aggregate is provided by intra-molecular amine-N-H⋯O(carboxyl-ate) hydrogen bonds. Hydrogen bonding is also prominent in the mol-ecular packing with amide-N-H⋯O(amide) inter-actions, leading to eight-membered {⋯HNCO}2 synthons, amide-N-H⋯O(water), water-O-H⋯O(carboxyl-ate) and water-O-H⋯O(water) hydrogen bonds featuring within the three-dimensional architecture. The calculated Hirshfeld surfaces for the individual components of the asymmetric unit differentiate the water mol-ecules owing to their distinctive supra-molecular association. For each of the anion and cation, H⋯H contacts predominate (50.7 and 65.2%, respectively) followed by H⋯O/O⋯H contacts (44.5 and 29.9%, respectively).

Redetermination of the crystal structure of (2E,4Z,13E,15Z)-3,5,14,16-tetramethyl-2,6,13,17-tetraazatricyclo[16.4.0.07,12]docosa-1(22),2,4,7,9,11,13,15,18,20-decaene, C22H24N4

C22H24N4, triclinic, P 1 ‾ $P‾{1}$ (no. 2), a = 9.217(4) Å, b = 9.774(4) Å, c = 10.843(4) Å, α = 96.770(2)°, β = 101.791(5)°, γ = 105.873(3)°, V = 903.9(6) Å3, Z = 2, R gt (F) = 0.0391, wR ref (F 2) = 0.1069, T = 93(2) K.