Andrea Centrone

Cooperative Nanoparticles for Tumor Detection and Photothermally Triggered Drug Delivery

The ability of one structural type to perform multiple medical diagnostic or therapeutic functions is often cited as an advantageous characteristic of nanomaterials that cannot be achieved with organic small molecules.[1–3] Although there are now many examples of nanosystems that integrate multiple functions into a single structure, the designs can reduce the efficacy of the individual functions due to space and surface-chemistry limitations in the tiny platforms. For example, magnetic nanoparticles and drug molecules can be co-encapsulated in liposomes to simultaneously perform multiple functions, such as magnetic resonance imaging, magnetic drug delivery and hyperthermia,[4] but the loading capacity and the stability are typically compromised relative to a single-component liposome. There has been some effort to develop intrinsically multifunctional nanomaterials such as magnetic nanocapsules and luminescent porous silicon nanoparticles to overcome such problems,[5,6] although these more complicated structures may lose versatility in terms of the types of payloads they can carry. Access to the payloads can also be limited, reducing the ability to control their release. Separating functions into two or more nanoparticle formulations is one means to simplify the problem. If two separate nanomaterials can be engineered to synergistically cooperate in their diagnostic or therapeutic functions, it is possible that the overall dosage can be reduced, minimizing side effects and providing a safer transition to the clinic.

Growth of Metal−Organic Frameworks on Polymer Surfaces

Polymer substrates have been functionalized with a MOF material (MIL-47) synthesized directly on polyacrylonitrile using in situ microwave irradiation. The growth of MIL-47 on these substrates was studied as a function of microwave irradiation time using scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The conversion of nitrile to carboxylic acid groups on the PAN surface was necessary for the growth of MIL-47 on the substrate. MIL-47 crystals grew over time at the expense of a related disordered precursor phase, which lacks the long-range order of MIL-47. This work paves the way for the development of a new class of hybrid MOF-polymer materials that will extend the applications of MOFs to fields such as membrane separations, filtration, and protective textiles.

Formation of nanosized organic molecular crystals on engineered surfaces.

The pharmaceutical industry has great interest in organic molecular nanosized crystals because their enhanced solubility and dissolution rate can potentially enhance drug bioavailability. In this work, patterned engineered surfaces were used to crystallize glycine with a lateral dimension below 200 nm in a confined volume while controlling supersaturation. Bifunctional patterned surfaces with hydrophilic islands, as small as 500 nm, surrounded by hydrophobic regions were prepared using lithography and self assembled monolayers. Individual glycine crystals under 200 nm were formed from the confined solutions wetting each hydrophilic island, while supersaturation was controlled by slow antisolvent diffusion. Individual crystals were characterized with AFM and Raman spectroscopy and determined to be the metastable beta form. The solubility enhancement as a function of crystal size was measured, and the solubility of crystals with a radius of 100 nm or less was estimated.

Facile Synthesis of Vanadium Metal–Organic Frameworks and their Magnetic Properties

Metal–organic frameworks (MOFs) are materials obtained by the assembly of small inorganic clusters and organic linkers to form one-, two-, or three-dimensional (3D) crystalline networks. The synthesis of 3D porous MOFs with large surface area and pore volume and chemical stability, coupled with the ability to tailor pore sizes and functionality during the synthesis step, makes these materials promising in hydrogen storage, separation, sequestration of carbon dioxide or harmful gases, and catalysis. When transition metal ions are incorporated in the MOF structures, these materials show interesting optical, ionic conductivity, and magnetic properties that, combined with their exceptional porous characteristics, provide the opportunity to develop new low-density multifunctional materials. In this Communication, we present the facile and fast microwave synthesis of MIL-47, one of the most studied MOF materials, and 6 new vanadium MOFs obtained under similar conditions using different organic building blocks. We show that these different organic building blocks affect the interactions between V ions, and, consequently, the magnetic properties of the MOF. Furthermore, we studied the effect on the magnetic properties when guest molecules were removed from the MIL-47 pores. It was suggested that changes in the magnetic properties upon guest-molecule desorption are due to a change in the vanadium oxidation state from V3þ to V4þ. In this Communication, we will show that the changes in the material magnetic properties are due to

Separation of Chemical Reaction Intermediates by Metal–Organic Frameworks

HPLC columns custom-packed with metal-organic framework (MOF) materials are used for the separation of four small intermediates and byproducts found in the commercial synthesis of an important active pharmaceutical ingredient in methanol. In particular, two closely related amines can be separated in the methanol reaction medium using MOFs, but not with traditional C18 columns using an optimized aqueous mobile phase. Infrared spectroscopy, UV-vis spectroscopy, X-ray diffraction, and thermogravimetric analysis are used in combination with molecular dynamic simulations to study the separation mechanism for the best-performing MOF materials. It is found that separation with ZIF-8 is the result of an interplay between the thermodynamic driving force for solute adsorption within the framework pores and the kinetics of solute diffusion into the material pores, while the separation with Basolite F300 is achieved because of the specific interactions between the solutes and Fe(3+) sites. This work, and the exceptional ability to tailor the porous properties of MOF materials, points to prospects for using MOF materials for the continuous separation and synthesis of pharmaceutical compounds.

Montmorillonite Functionalized with Pralidoxime As a Material for Chemical Protection against Organophosphorous Compounds

Montmorillonite K-10 functionalized with α-nucleophilic 2-pralidoxime (PAM) and its zwitterionic oximate form (PAMNa) is introduced as a versatile material for chemical protection against organophosphorous (OP) compounds such as pesticides and chemical warfare agents (CWA). Upon inclusion into the montmorillonite interlayer structure, the pyridinium group of PAMNa is strongly physisorbed onto acidic sites of the clay, leading to shrinking of the interplanar distance. Degradation of diethyl parathion by PAMNa-functionalized montmorillonite in aqueous-acetonitrile solutions occurred primarily via hydrolytic conversion of parathion into diethylthio phosphoric acid, with the initial stages of hydrolysis observed to be pseudo-first-order reactions. Hydrolysis catalyzed by the clay intercalated by PAMNa was 10- and 17-fold more rapid than corresponding spontaneous processes measured at 25 and 70 °C, respectively. Hydrolytic degradation of diisopropyl fluorophosphate (DFP), a CWA simulant, was studied on montmorillonite clay functionalized by PAMNa and equilibrated with water vapor at 100% relative humidity by ³¹P high-resolution magic angle spinning NMR and was observed to be rather facile compared with the untreated montmorillonite, which did not show any DFP hydrolysis within 24 h. The incorporation of the functionalized clay particles into elastomeric film of polyisobutylene was shown to be a means to impart DFP-degrading capability to the film, with clay particle content exceeding 18 wt %.

Polymorphism control of nanosized glycine crystals on engineered surfaces

Crystallization in a constrained environment was used to prepare organic molecular nanocrystals of glycine. Bifunctional patterned surfaces, with hydrophilic islands as small as 1 µm surrounded by hydrophobic regions, were prepared by photolithography. Individual nanosized glycine crystals were formed from the confined solution droplets on each hydrophilic island. Supersaturation was controlled by slow cooling or by slow evaporation. Individual crystals were characterized with AFM and Raman spectroscopy. Slow cooling produced the least stable β-form except for the slowest cooling rate (0.001 °C min−1) which produced both α- and β-form. Slow evaporation (100 hours) resulted in the concomitant nucleation of all three glycine forms.

Controlling thermochromism in a photonic block copolymer gel.

The tunable properties of stimulus-responsive materials attract great interest in a variety of technological applications. Photonic gels are a new class of these materials, which can be tuned to reflect different wavelengths of light. Controlling this reflected color via temperature-induced changes of self-assembled photonic materials is important for their application in sensors and displays. In this work, the thermochromic behavior of a PS-P2VP photonic gel was found to originate from a temperature-induced change in the pK(a) of the P2VP blocks. Control was obtained through the manipulation of the solution pH. The findings of this work provide the basis for understanding and controlling the properties of thermochromic block copolymers fostering their use in technologically relevant applications.

Chains of divalent gold nanoparticles

We discuss our recently developed method to selectively functionalize mixed ligand gold nanoparticles at two specific defect points in the ligand shell and to join the nanoparticles together into chains by placing reactive molecules at those two points. Here we use infrared spectroscopy to confirm that the process of functionalizing those defect points rapidly reaches equilibrium. In addition, we demonstrate the quantitative reproducibility of the chaining reaction, and we discuss the case in which we perform the same functionalization procedure on homoligand nanoparticles.