Selective cyclodimerization of epichlorohydrin to dioxane derivatives over MOFs

Glycerol can be converted to valuable products such as epichlorohydrin which is an important intermediate applied in various industries. For example, dioxane derivatives, which are important pharmaceuticals, can be obtained from epichlorohydrin. In the present study, ZIF-8, ZIF-67, MIL-100, and UiO-66 were applied for the direct cyclodimerization of epichlorohydrin. These MOFs were selected because they were already applied as active catalysts in ring opening of epoxides. Among them, ZIF-8 showed the highest activity and selectivity in the absence of any solvent or co-catalyst. Using ZIF-8 as a catalyst, the cyclodimer product (1,4-dioxane 2,5-bis-chloromethyl) was obtained in a yield of about 70% which was significantly superior to previous homo or heterogeneous catalysts for this reaction. Due to ZIF-8 structure and the proposed mechanism, the cyclodimerization reaction catalyzed either by the defects in the structure and/or on the surface. Furthermore, acidic-basic characteristics were also in play. The NH3 and CO2 temperature-programed desorption technique were utilized to identify the active sites and thereby reaction mechanism. Moreover, because of similar properties of ZIF-8 to zeolites, the activity of commercial ZSM-5 for the same reaction was also investigated in this work

Gold nanoparticles functionalised with stable, fast water exchanging Gd3+ chelates as high relaxivity contrast agents for MRI

Gold nanoparticles functionalized with Gd3+ chelates displaying fast water exchange, superb pH stability and inertness towards transmetalation with Zn2+ have been prepared and characterized as a new high relaxivity (29 mM-1s-1, 30 MHz, 25 ºC) Contrast Agent potentially safe for in vivo MRI applications. The Lipari-Szabo treatment for internal rotation was used to evaluate the effect of linker flexibility on the relaxivity of the gold nanoparticles. The relaxivity is limited by chelate flexibility. The effect of fast water exchange on the relaxivity of gold nanoparticles functionalized with Gd3+ chelates is also addressed in this communication.Fundação para a Ciência e TecnologiaProjecto PTDC/QUI/70063/2006PhD grant SFRH/BD/63994/2008 to Miguel FerreiraRede Nacional de RMN REDE/1517/RMN/2005 for the acquisition of the Varian VNMRS 600 NMR spectrometer in Coimbra and the Bruker Avance-3 400 Plus in BragaB. Mousavi and L. Helm acknowledge financial support by the Swiss National Science Foundation.COST D38 Actio

Gold nanoparticles functionalised with fast water exchanging Gd3+ chelates: linker effects on the relaxivity.

This is the accepted manuscript. The final version is available at http://dx.doi.org/10.1039/C4DT03210AThe relaxivity displayed by Gd(3+) chelates immobilized onto gold nanoparticles is the result of the complex interplay between the nanoparticle size, the water exchange rate and the chelate structure. In this work we study the effect of the length of ω-thioalkyl linkers, anchoring fast water exchanging Gd(3+) chelates onto gold nanoparticles, on the relaxivity of the immobilized chelates. Gold nanoparticles functionalized with Gd(3+) chelates of mercaptoundecanoyl and lipoyl amide conjugates of the DO3A-N-(α-amino)propionate chelator were prepared and studied as potential CA for MRI. High relaxivities per chelate, of the order of magnitude 28-38 mM(-1) s(-1) (30 MHz, 25 °C), were attained thanks to simultaneous optimization of the rotational correlation time and of the water exchange rate. Fast local rotational motions of the immobilized chelates around connecting linkers (internal flexibility) still limit the attainable relaxivity. The degree of internal flexibility of the immobilized chelates seems not to be correlated with the length of the connecting linkers. Biodistribution and MRI studies in mice suggest that the in vivo behavior of the gold nanoparticles was determined mainly by size. Small nanoparticles (HD = 3.9 nm) undergo fast renal clearance and avoidance of the RES organs while larger nanoparticles (HD = 4.8 nm) undergo predominantly hepatobiliary excretion. High relaxivities, allied to chelate and nanoparticle stability and fast renal clearance in vivo suggest that functionalized gold nanoparticles hold great potential for further investigation as MRI contrast agents. This study contributes to a better understanding of the effect of linker length on the relaxivity of gold nanoparticles functionalized with Gd(3+) complexes. It is a relevant contribution towards "design rules" for nanostructures functionalized with Gd(3+) chelates as Contrast Agents for MRI and multimodal imaging.This work was financially supported by Fundação para a Ciência e a Tecnologia, Portugal: PhD grant SFRH/BD/63994/2009 to Miguel Ferreira and Sabbatical Grant SFRH/BSAB/1328/2013 to José Martins at Bath University, UK; and Rede Nacional de NMR (REDE/1517/RMN/2005) for the acquisition of the Varian VNMRS 600 NMR spectrometer in Coimbra. T.B.R. was supported by a Marie Curie Fellowship (FP/- PEOPLE-2009-IEF 254380) and an EMBO Fellowship (ALTF 1145-2009). Financial support from Ministerio de Ciencia e Innovación, Spain, projects SAF2011-23622 (S.C.) and CTQ2010-20960-C02-02 (P.L.-L.), and Comunidad de Madrid, Spain, project S2010/BMD-2349 (S.C. and P.L.-L), is also acknowledged. B. Mousavi and L. Helm acknowledge financial support by the Swiss National Science Foundation. This work was carried out in the frame of the COST D38 Action “Metal Based Systems for Molecular Imaging” and COST TD1004 Action “Theranostics Imaging and Therapy”

Dinuclear Gd(III) Polyaminocarboxylates as Building Blocks for MRI Contrast Agents

Magnetic resonance imaging (MRI) technique is at the forefront of biomedical and clinical imaging. Its superb spatial resolution, noninvasive nature and use of benign radiation outweigh its intrinsic low detection sensitivity. However paramagnetic relaxers (called MRI contrast agents) can enhance dramatically the contrast between healthy and diseased tissues by shortening the relaxation times of the water protons in their vicinity. In recent years, extensive attempts have been applied towards new contrast agents with higher molar relaxivity and higher specificity. In this work with the aim of increasing relaxivity, several novel dinuclear Gd-based MRI contrast agents are synthesized. These systems possess two chelating groups per functional unit. An aromatic linker is used to join the chelating parts and the functional unit. This will increase the rigidity of systems and therefore their relaxivity. The functional units are chosen based on their application for different purposes. In all cases, the DTTA (H4DTTA = diethylenetriaminetetraacetic acid) was introduced as chelating ligand for Gd3+. This unit is fairly easy to synthesize and its Gd-complex has two inner sphere water molecules The second chapter deals with the development of a novel DTTA-based contrast agent which is capable of binding human serum albumin (HSA). Two DTTA chelators are bound to the rigid carbazole molecule as well as a biphenyl group which is aimed to bind to HSA. As a consequence of rigidity and the strong binding to the protein, a high relaxivity is obtained. The third chapter is aimed to synthesize two novel dinuclear surfactant molecules which possess again two DTTA as chelating units. Because of the long hydrophobic chain, depending on the concentration, they can aggregate into micellar form in aqueous solutions. Chapter IV is devoted to the synthesis and characterization of gold nanoparticles functionalized with Gd3+-DO3A-N-α-aminopropionate. This novel system with a fast water exchange is prepared and characterized as a new high relaxivity contrast agent potentially safe for in vivo application. In chapter V, compound [Gd4bipy(DTTA-derivative)4(H2O)8]4- is synthesized and characterized. This two-functionalities ligand contains four DTTA derivatives as chelating units for Gd3+, and a bipyridine unit for coordination to Fe2+. This self-assembly heterometallic compound could bring twelve Gd3+ ions together around one Fe2+ core

Carbazole as Linker for Dinuclear Gadolinium-Based MRI Contrast Agents

Ligands able to complex two gadolinium ions have been synthesized and characterized in view of the ability of the complexes to increase the spin relaxation of water protons. All ligands are based on the heptadentate diethylenetriaminetetraacetic acid (DTTA) chelator and carbazole as a rigid linker. Depending on the derivatization on the nitrogen atom of the five-membered ring, the compounds form small aggregates in aqueous solution, self-assemble to form micelles or bind to human serum albumin. In all cases, this leads to a marked increase in H-1 relaxivity at nuclear Larmor frequencies between 20 and 60 MHz. Water exchange on the gadolinium ions as measured by O-17 NMR relaxation is fast enough not to limit relaxivity. H-1 nuclear magnetic relaxation dispersion profiles were also measured and analyzed using Solomon-Bloembergen-Morgan theory including Lipari-Szabo treatment to include internal motion or anisotropic rotation

Two-Dimensional Zeolitic Imidazolate Framework ZIF-L: A Promising Catalyst for Polymerization

Here, for the first time, a 2D and leaf-like zeolitic imidazolate framework (ZIF-L) is reported for the synthesis of ultrahigh molecular weight (UHMW) poly(methyl methacrylate) (PMMA) with Mn up to 1390 kg mol−1. This synthesis method is a one-step process without any co-catalyst in a solvent-free medium. SEM, PXRD, FT-IR, TGA, and nitrogen sorption measurements confirmed the 2D and leaf-like structure of ZIF-L. The results of PXRD, SEM, TGA demonstrate that the catalyst ZIF-L is remarkably stable even after a long-time polymerization reaction. Zwitterionic Lewis pair polymerization (LPP) has been proposed for the catalytic performance of ZIF-L on methyl methacrylate (MMA) polymerization. This MMA polymerization is consistent with a living system, where ZIF-L could reinitiate the polymerization and propagates the process by gradually growing the polymer chains

One-step synthesis of stereo-pure L,L lactide from L-lactic acid

© 2018 Elsevier B.V. Poly (lactic acid) (PLA) is extensively used as an eco-friendly compound for many applications. The synthesis of stereo-pure lactide, specifically L,L-lactide which is the most desired isomer for the synthesis of high-quality PLA is very important. In this work, various materials including MOFs and simple bases have been applied as catalysts for the Lactide synthesis. Herein we report the one-step synthesis of L,L-lactide with high selectivity and yield (99%) in the absence of racemization by applying a cost-effective Cs2CO3 catalyst. The novel described procedure is even expected to be very efficient for industrial applications.status: publishe

Switching from linear to cyclic δ‐Polyvalerolactone synthesized via zeolitic imidazolate framework as a catalyst : a promising approach

A series of spray dried zeolitic imidazolate frameworks (ZIFs = ZIF-8, ZIF-67, and Zn/Co-ZIF) are used as a catalyst for the bulk ring-opening polymerization of delta-valerolactone without any co-catalyst to generate polyvalerolactone. Interestingly, using the same catalyst under the same reaction conditions could manipulate the structure of the product polymer, and thus its physical properties. Thus, using a dried substrate leads to the formation of the cyclic polymer while a linear polymer was formed on using the commercially available substrate. An activated monomer mechanism has been suggested where the propagating zinc alkoxide undergoes an intramolecular transesterification to release cyclic or linear polyvalerolactone. The ROP of delta-VL without drying shows that the polymeric zwitterions have little tendency to cyclize in the presence of moisture. At 140 degrees C, ZIF-8 shows a superior catalytic activity resulting in the production of cyclic polyvalerolactone having a high molecular weight as compared to ZIF-67 or Zn/Co-ZIF due to the presence of highly active sites. The catalyst could be recycled and reused without any significant loss of catalytic activity