Hybrid, dual visible and near-infrared fluorescence emission of (6,5) single-walled carbon nanotubes modified with fluorescein through aryl diazonium salt chemistry.

The aryl diazonium salt chemistry offers enhancement of near-infrared (NIR) emission of single-walled carbon nanotubes (SWCNTs), although, the attachment of functional molecules which could bring hybrid properties through the process is underdeveloped. In this work, we utilize aryl diazonium salt of fluorescein to createsp3defects on (6,5) SWCNTs. We study the influence of pH on the grafting process identifying that pH 5-6 is necessary for a successful reaction. The fluorescein-modified (6,5) SWCNTs (F-(6,5) SWCNTs) exhibit red-shiftedE11* emission in the NIR region attributed to luminescentsp3defects, but also visible (Vis) fluorescence at 515 nm from surface-attached fluorescein molecules. The fluorescence in both Vis and NIR regions of F-(6,5) SWCNTs exhibit strong pH-dependency associated with the dissociation of fluorescein molecules with an indication of photoinduced-electron transfer quenching the Vis emission of fluorescein dianion. The F-(6,5) SWCNTs could potentially be used for dual-channel medical imaging as indicated by our preliminary experiments. We hope that our research will encourage new, bold modifications of SWCNTs with functional molecules introducing new, unique hybrid properties.

Oxygen Functional Groups on MWCNT Surface as Critical Factor Boosting T2 Relaxation Rate of Water Protons: Towards Improved CNT-Based Contrast Agents.

PURPOSE: Salicyl (Sal) - among other oxygen functionalities - multi-walled carbon nanotubes (MWCNTs) and their nanohybrids are investigated as promising contrast agents (CA) in magnetic resonance imaging (MRI) or drug delivery platforms, due to their unique properties. The preliminary results and the literature reports were the motivation to endow high r2 relaxivities, excellent dispersibility in water, and biocompatibility to superparamagnetic MWCNTs nanohybrids. It was hypothesized that these goals could be achieved by, not described in the literature yet, two-stage oxygen functionalization of MWCNTs. RESULTS: Two structurally different MWCNT materials differing in diameters (44 and 12 nm) and the iron content (4.7% and 0.5%) are studied toward the functionalization effect on the T2 relaxometric properties. MWCNT oxidation is typically the first step of functionalization resulting in "first generation" oxygen functional groups (OFGs) on the surface. Until now, the impact of OFGs on the relaxivity of MWCNT was not truly recognized, but this study sheds light on this issue. By follow-up functionalization of oxidized MWCNT with 4-azidosalicylic acid through [2+1] cycloaddition of the corresponding nitrene, "second generation" of oxygen functional groups is grafted onto the nanohybrid, ie, Sal functionality. CONCLUSION: The introduced OFGs are responsible for an almost 30% increase in the relaxivity, which leads to remarkable r2 relaxivity of 951 mM-1s-1 (419 (mg/mL)-1s-1), the unprecedented value reported to date for this class of CAs. Also, the resulting nanohybrids express low cytotoxicity and superb diffusion after subcutaneous injection to a mouse.

Unprecedented Water Effect as a Key Element in Salicyl-Glycine Schiff Base Synthesis.

Salens, as chelating, double Schiff base ligands, are an important group utilized in transition metal catalysis. They have been used to build interesting functional metal-organic frameworks (MOFs). However, salens interacting with amino acids have also found applications in receptors. Here, we intended to form a "green" glycine-derived salen fragment, but the available literature data were contradictory. Therefore, we optimized the synthetic conditions and obtained the desired product as two different crystallographic polymorphs (orthorhombic Pcca and monoclinic P21/c space groups). Their structures differ in conformation at the glycine moiety, and the monoclinic form contains additional, disordered water molecules. Despite the high stability of Schiff bases, these newly obtained compounds hydrolyze in aqueous media, the process being accelerated by metal cations. These studies, accompanied by mechanistic considerations and solid-state moisture and thermal analysis, clarify the structure and behavior of this amino acid Schiff base and shed new light on the role of water in its stability.

Multiwalled carbon nanotube hybrids as MRI contrast agents.

Magnetic resonance imaging (MRI) is one of the most commonly used tomography techniques in medical diagnosis due to the non-invasive character, the high spatial resolution and the possibility of soft tissue imaging. Contrast agents, such as gadolinium complexes and superparamagnetic iron oxides, are administered to spotlight certain organs and their pathologies. Many new models have been proposed that reduce side effects and required doses of these already clinically approved contrast agents. These new candidates often possess additional functionalities, e.g., the possibility of bioactivation upon action of particular stimuli, thus serving as smart molecular probes, or the coupling with therapeutic agents and therefore combining both a diagnostic and therapeutic role. Nanomaterials have been found to be an excellent scaffold for contrast agents, among which carbon nanotubes offer vast possibilities. The morphology of multiwalled carbon nanotubes (MWCNTs), their magnetic and electronic properties, the possibility of different functionalization and the potential to penetrate cell membranes result in a unique and very attractive candidate for a new MRI contrast agent. In this review we describe the different issues connected with MWCNT hybrids designed for MRI contrast agents, i.e., their synthesis and magnetic and dispersion properties, as well as both in vitro and in vivo behavior, which is important for diagnostic purposes. An introduction to MRI contrast agent theory is elaborated here in order to point to the specific expectations regarding nanomaterials. Finally, we propose a promising, general model of MWCNTs as MRI contrast agent candidates based on the studies presented here and supported by appropriate theories.