Studies on metal-organic framework (MOF) nanomedicine preparations of sildenafil for the future treatment of pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) is an incurable disease, although symptoms are treated with a range of dilator drugs. Despite their clinical benefits, these drugs are limited by systemic side-effects. It is, therefore, increasingly recognised that using controlled drug-release nanoformulation, with future modifications for targeted drug delivery, may overcome these limitations. This study presents the first evaluation of a promising nanoformulation (highly porous iron-based metal-organic framework (MOF); nanoMIL-89) as a carrier for the PAH-drug sildenafil, which we have previously shown to be relatively non-toxic in vitro and well-tolerated in vivo. In this study, nanoMIL-89 was prepared and charged with a payload of sildenafil (generating Sil@nanoMIL-89). Sildenafil release was measured by Enzyme-Linked Immunosorbent Assay (ELISA), and its effect on cell viability and dilator function in mouse aorta were assessed. Results showed that Sil@nanoMIL-89 released sildenafil over 6 h, followed by a more sustained release over 72 h. Sil@nanoMIL-89 showed no significant toxicity in human blood outgrowth endothelial cells for concentrations up to100µg/ml; however, it reduced the viability of the human pulmonary artery smooth muscle cells (HPASMCs) at concentrations > 3 µg/ml without inducing cellular cytotoxicity. Finally, Sil@nanoMIL-89 induced vasodilation of mouse aorta after a lag phase of 2-4 h. To our knowledge, this study represents the first demonstration of a novel nanoformulation displaying delayed drug release corresponding to vasodilator activity. Further pharmacological assessment of our nanoformulation, including in PAH models, is required and constitutes the subject of ongoing investigations.

First example of solid-state luminescent borasiloxane-based chiral helices assembled through N-B bonds.

The reaction between differently substituted borasiloxanes and 2,5-bis(3-pyridylethynyl)thiophene provided the first example of luminescent borasiloxane-based chiral helices held together by N-B bonds. The starting building blocks and the helices were fully characterized, and the nature of the N-B bond rationalized by means of theoretical calculations.

Stable metal-organic frameworks with low water affinity built from methyl-siloxane linkers.

A tetracarboxylic acid with a methyl-substituted siloxane core (L-H4) has been prepared and applied in the construction of water stable MOFs with low water affinity. L-H4 itself crystallizes as an interpenetrated 3D hydrogen-bonded network. Reaction of L-H4 with ZrIV/HfIV gave IMP-32-Zr/Hf - both 3D MOFs of scu topology.

Internalization of Metal-Organic Framework Nanoparticles in Human Vascular Cells: Implications for Cardiovascular Disease Therapy.

Abstract: Cardiovascular diseases (CVDs) are the leading cause of morbidity and mortality worldwide. Alteration of endothelial cells and the underlying vasculature plays a central role in the pathogenesis of various CVDs. The application of nanoscale materials such as nanoparticles in biomedicine has opened new horizons in the treatment of CVDs. We have previously shown that the iron metal-organic framework nanoparticle, Materials Institut Lavoisier-89 (nanoMIL-89) represents a viable vehicle for future drug delivery of pulmonary arterial hypertension. In this study, we have assessed the cellular uptake of nanoMIL-89 in pulmonary artery endothelial and smooth muscle cells using microscopy imaging techniques. We also tested the cellular responses to nanoMIL-89 using molecular and cellular assays. Microscopic images showed cellular internalization of nanoMIL-89, packaging into endocytic vesicles, and passing to daughter cells during mitosis. Moreover, nanoMIL-89 showed anti-inflammatory activity without any significant cytotoxicity. Our results indicate that nanoMIL-89 formulation may offer promising therapeutic opportunities and set forth a new prototype for drug delivery not only in CVDs, but also for other diseases yet incurable, such as diabetes and cancer.

Biomimetic peptide enriched nonwoven scaffolds promote calcium phosphate mineralisation.

Cell-free translational strategies are needed to accelerate the repair of mineralised tissues, particularly large bone defects, using minimally invasive approaches. Regenerative bone scaffolds should ideally mimic aspects of the tissue's ECM over multiple length scales and enable surgical handling and fixation during implantation in vivo. Leveraging the knowledge gained with bioactive self-assembling peptides (SAPs) and SAP-enriched electrospun fibres, we presented a cell free approach for promoting mineralisation via apatite deposition and crystal growth, in vitro, of SAP-enriched nonwoven scaffolds. The nonwoven scaffold was made by electrospinning poly(ε-caprolactone) (PCL) in the presence of either peptide P11-4 (Ac-QQRFEWEFEQQ-Am) or P11-8 (Ac QQRFOWOFEQQ-Am), in light of the polymer's fibre forming capability and its hydrolytic degradability as well as the well-known apatite nucleating capability of SAPs. The 11-residue family of peptides (P11-X) has the ability to self-assemble into ß-sheet ordered structures at the nano-scale and to generate hydrogels at the macroscopic scale, some of which are capable of promoting biomineralisation due to their apatite-nucleating capability. Both variants of SAP-enriched nonwoven used in this study were proven to be biocompatible with murine fibroblasts and supported nucleation and growth of apatite minerals in simulated body fluid (SBF) in vitro. The fibrous nonwoven provided a structurally robust scaffold, with the capability to control SAP release behaviour. Up to 75% of P11-4 and 45% of P11-8 were retained in the fibres after 7 day incubation in aqueous solution at pH 7.4. The encapsulation of SAP in a nonwoven system with apatite-forming as well as localised and long-term SAP delivery capabilities is appealing as a potential means of achieving cost-effective bone repair therapy for critical size defects.

Enhancing bond strength on demineralized dentin by pre-treatment with selective remineralising agents.

Bonding to demineralized dentin of a diseased tooth has shown to be a significant clinical issue. This study evaluated the effect of 0.2% NaF-(NaF), MI Paste™-(CPP-ACP) and the self-assembling peptide 'P11-4' (Ace-QQRFEWEFEQQ-NH2) contained in Curodont™ Repair, have on microtensile bond strength-(µTBS) of two different adhesive systems (Adper™ Single Bond-(SB) or Clearfil™ SE Bond (CSE)) and wettability of demineralized dentin slices after remineralising agents were applied. The highest µTBS were found for the demineralized dentin-(DD) treated with CPP-ACP; both adhesives systems (p < 0.05) did not significantly difference from P11-4 treatment associated with SB, and also presented higher values than sound dentin-(SD/SB) (p < 0.01). DD treated with P11-4 associated with CSE did not differ from DD/CSE (p > 0.05). The NaF treatment associated with CSE recovered the bond strength values of SD/CSE and associated with CSE demonstrated lower µTBS than other groups, although significantly higher than DD (p < 0.05). P11-4 and CPP-ACP increased significantly the wettability of demineralized dentin (p < 0.05); etching acid improved wettability for all groups (p < 0.05), whilst NaF did not affect the wettability of demineralized dentin (p > 0.05). Morphological analysis of the dentin surface and dentin-resin interface revealed unique features of the applied remineralizing agent. The results indicated that self-assembling peptide P11-4 associated with SB and CPP-ACP associated with SB or CSE significantly enhanced the bond strength to demineralized dentin (p < 0.05). We conclude that by modifying the dentine surface and restoring conditions found on sound dentin, this can enhance the interfacial bonding.

Encapsulation of Crabtree's Catalyst in Sulfonated MIL-101(Cr): Enhancement of Stability and Selectivity between Competing Reaction Pathways by the MOF Chemical Microenvironment.

Crabtree's catalyst was encapsulated inside the pores of the sulfonated MIL-101(Cr) metal-organic framework (MOF) by cation exchange. This hybrid catalyst is active for the heterogeneous hydrogenation of non-functionalized alkenes either in solution or in the gas phase. Moreover, encapsulation inside a well-defined hydrophilic microenvironment enhances catalyst stability and selectivity to hydrogenation over isomerization for substrates bearing ligating functionalities. Accordingly, the encapsulated catalyst significantly outperforms its homogeneous counterpart in the hydrogenation of olefinic alcohols in terms of overall conversion and selectivity, with the chemical microenvironment of the MOF host favouring one out of two competing reaction pathways.

Siloxane-based linkers in the construction of hydrogen bonded assemblies and porous 3D MOFs.

A siloxane-based hexacarboxylic acid (L1-H6) has been prepared and applied in MOF construction. L1-H6 itself crystallizes as an unusual interpenetrated 3D hydrogen-bonded framework. Reaction of L1-H6 with Zn(ii) gave IMP-18 - a 3D MOF incorporating Si-O-Si functionality. Cleavage of L1-H6 gives a silanol-based triacid which is shown to give a coordination polymer (IMP-19) with Zn(ii).

Peptide strand length controls the energetics of self-assembly and morphology of ß-sheet fibrils.

Self-assembling peptides can be used as versatile, natural, and multifunctional building blocks to produce a variety of well-defined nanostructures, materials and devices for applications in medicine and nanotechnology. Here, we concentrate on the 1D self-assembly of de novo designed Px-2 peptide ß-strands into anti-parallel ß-sheet tapes and higher order aggregates. We study six members of the Px-2 family, ranging from 3 amino acids (aa) to 13 aa in length, using a range of complementary experimental techniques, computer simulation and theoretical statistical mechanics. The critical concentration for self-assembly (c*) is found to increase systematically with decreasing peptide length. The shortest peptide found to self-assemble into soluble ß-tapes in water is a 5 amino acid residue peptide. These investigations help decipher the role of the peptide length in controlling self-assembly, aggregate morphology, and material properties. By extracting free energies from these data using a statistical mechanical analysis and combining the results with computer simulations at the atomistic level, we can extract the entropy of association for individual ß-strands.

Poly(amino acid)-polyester graft copolymer nanoparticles for the acid-mediated release of doxorubicin.

Biodegradable polymers have emerged as highly effective drug delivery vehicles. We combine N-carboxyanhydride and O-carboxyanhydride ring opening polymerisations to synthesise a poly(amino acid)-polyester graft copolymer capable of encapsulating, and subsequently releasing doxorubicin via acid-mediated hydrolysis. Consequently, the nanoparticles detailed are extremely promising vehicles for the controlled delivery of chemotherapeutic agents.

Chemical and biological assessment of metal organic frameworks (MOFs) in pulmonary cells and in an acute in vivo model: relevance to pulmonary arterial hypertension therapy.

Pulmonary arterial hypertension (PAH) is a progressive and debilitating condition. Despite promoting vasodilation, current drugs have a therapeutic window within which they are limited by systemic side effects. Nanomedicine uses nanoparticles to improve drug delivery and/or reduce side effects. We hypothesize that this approach could be used to deliver PAH drugs avoiding the systemic circulation. Here we report the use of iron metal organic framework (MOF) MIL-89 and PEGylated MIL-89 (MIL-89 PEG) as suitable carriers for PAH drugs. We assessed their effects on viability and inflammatory responses in a wide range of lung cells including endothelial cells grown from blood of donors with/without PAH. Both MOFs conformed to the predicted structures with MIL-89 PEG being more stable at room temperature. At concentrations up to 10 or 30 µg/mL, toxicity was only seen in pulmonary artery smooth muscle cells where both MOFs reduced cell viability and CXCL8 release. In endothelial cells from both control donors and PAH patients, both preparations inhibited the release of CXCL8 and endothelin-1 and in macrophages inhibited inducible nitric oxide synthase activity. Finally, MIL-89 was well-tolerated and accumulated in the rat lungs when given in vivo. Thus, the prototypes MIL-89 and MIL-89 PEG with core capacity suitable to accommodate PAH drugs are relatively non-toxic and may have the added advantage of being anti-inflammatory and reducing the release of endothelin-1. These data are consistent with the idea that these materials may not only be useful as drug carriers in PAH but also offer some therapeutic benefit in their own right.

A New NO-Releasing Nanoformulation for the Treatment of Pulmonary Arterial Hypertension.

Pulmonary arterial hypertension (PAH) is a chronic and progressive disease which continues to carry an unacceptably high mortality and morbidity. The nitric oxide (NO) pathway has been implicated in the pathophysiology and progression of the disease. Its extremely short half-life and systemic effects have hampered the clinical use of NO in PAH. In an attempt to circumvent these major limitations, we have developed a new NO-nanomedicine formulation. The formulation was based on hydrogel-like polymeric composite NO-releasing nanoparticles (NO-RP). The kinetics of NO release from the NO-RP showed a peak at about 120 min followed by a sustained release for over 8 h. The NO-RP did not affect the viability or inflammation responses of endothelial cells. The NO-RP produced concentration-dependent relaxations of pulmonary arteries in mice with PAH induced by hypoxia. In conclusion, NO-RP drugs could considerably enhance the therapeutic potential of NO therapy for PAH.

Encapsulation of an organometallic cationic catalyst by direct exchange into an anionic MOF.

Metal-Organic Frameworks (MOFs) are porous crystalline materials that have emerged as promising hosts for the heterogenization of homogeneous organometallic catalysts, forming hybrid materials which combine the benefits of both classes of catalysts. Herein, we report the encapsulation of the organometallic cationic Lewis acidic catalyst [CpFe(CO)2(L)]+ ([Fp-L]+, Cp = η5-C5H5, L = weakly bound solvent) inside the pores of the anionic [Et4N]3[In3(BTC)4] MOF (H3BTC = benzenetricarboxylic acid) via a direct one-step cation exchange process. To conclusively validate this methodology, initially [Cp2Co]+ was used as an inert spatial probe to (i) test the stability of the selected host; (ii) monitor the stoichiometry of the cation exchange process and (iii) assess pore dimensions, spatial location of the cationic species and guest-accessible space by single crystal X-ray crystallography. Subsequently, the quasi-isosteric [Fp-L]+ was encapsulated inside the pores via partial cation exchange to form [(Fp-L)0.6(Et4N)2.4][In3(BTC)4]. The latter was rigorously characterized and benchmarked as a heterogeneous catalyst in a simple Diels-Alder reaction, thus verifying the integrity and reactivity of the encapsulated molecular catalyst. These results provide a platform for the development of heterogeneous catalysts with chemically and spatially well-defined catalytic sites by direct exchange of cationic catalysts into anionic MOFs.

A structurally self-assembled peptide nano-architecture by one-step electrospinning.

Self-assembling peptides (SAPs) have been shown to offer great promise in therapeutics and have the ability to undergo self-assembly and form ordered nanostructures. However SAP gels are often associated with inherent weak and transient mechanical properties and incorporation of them into polymeric matrices is a route to enhance their mechanical stability. The aim of this work was to incorporate P11-8 peptide (CH3COQQRFOWOFEQQNH2) within poly(ε-caprolactone) (PCL) fibrous webs via one-step electrospinning, aiming to establish the underlying relationships between spinning process, molecular peptide conformation, and material internal architecture. Electrospinning of PCL solutions (6% w/w) in hexafluoro-2-propanol (HFIP) containing up to 40 mg mL-1 P11-8 resulted in the formation of fibres in both nano- (10-100 nm) and submicron range (100-700 nm), in contrast to PCL only webs, which displayed a predominantly submicron fibre distribution. FTIR and CD spectroscopy on both PCL/peptide solutions and resulting electrospun webs revealed monomeric and ß-sheet secondary conformation, respectively, suggesting the occurrence of peptide self-assembly during electrospinning due to solvent evaporation. The peptide concentration (0 → 40 mg mL-1) was found to primarily affect the internal structure of the fabric at the nano-scale, whilst water as well as cell culture medium contact angles were dramatically decreased. Nearly no cytotoxic response (>90% cell viability) was observed when L929 mouse fibroblasts were cultured in contact with electrospun peptide loaded samples. This novel nanofibrous architecture may be the basis for an interesting material platform for e.g. hard tissue repair, in light of the presence of the self-assembled P11-8 in the PCL fibrous structure.

Synthesis, characterisation and reactivity of copper(I) amide complexes and studies on their role in the modified Ullmann amination reaction.

A series of copper(I) alkylamide complexes have been synthesised; copper(I) dicyclohexylamide (1), copper(I) 2,2,6,6-tetramethylpiperidide (2), copper(I) pyrrolidide (3), copper(I) piperidide (4), and copper(I) benzylamide (5). Their solid-state structures and structures in [D6 ]benzene solution are characterised, with the aggregation state in solution determined by a combination of DOSY NMR spectroscopy and DFT calculations. Complexes 1, 2 and 4 are shown to exist as tetramers in the solid state by X-ray crystallography. In [D6 ]benzene solution, complexes 1, 2 and 5 were found by using (1) H DOSY NMR to exist in rapid equilibrium between aggregates with average aggregation numbers of 2.5, 2.4 and 3.3, respectively, at 0.05 M concentration. Conversely, distinct trimeric, tetrameric and pentameric forms of 3 and 4 were distinguishable by one-dimensional (1) H and (1) H DOSY NMR spectroscopy. Complexes 3-5 are found to react stoichiometrically with iodobenzene, in the presence or absence of 1,10-phenanthroline as an ancillary ligand, to give arylamine products indicative of their role as potential intermediates in the modified Ullmann reaction. The role of phenanthroline has also been explored both in the stoichiometric reaction and in the catalytic Ullmann protocol.

Lithium heterocuprates: the influence of the amido group on organoamidocuprate structures.

Lithium organoamidocuprates of the general stoichiometry LiCuR(NR) are an important class of organocopper reagents and have found widespread application in conjugate addition and other bond-forming reactions. The dependence of the structures and equilibrium of these species on the steric and electronic properties of the amido group is reported in both the solid state and in solution. Three different cuprate complexes have been crystallographically characterized: the organoamidocuprate [Cu2Li2Mes2TMP2] (2) (TMP = 2,2,6,6-tetramethylpiperidide) which is shown to adopt a head-to-tail conformation; [Cu2Li2(N(CH2Ph)CH2CH2NMe2)4] (3 ) which is a homoamidocuprate and contains additional coordination of the lithium centres from intra-molecular tertiary amine groups; and the diastereomeric organoamidocuprate [Cu2Li2Mes2(N(R-CH(Ph)Me)(CH2CF3))2] (4) which adopts a head-to-head conformation. Complex 4 is unique in being the first crystallographically characterised example of a head-to-head isomer of a heterocuprate, and its structure also has implications for the use of scalemic amidocuprates in asymmetrically induced conjugate addition. The solution equilibria of all new complexes have also been studied using (7)Li NMR spectroscopy, and in each case the species observed in the crystal structure was shown to also be the predominant isomer in solution.

Organosilicon linkers in metal organic frameworks: the tetrahedral tetrakis(4-tetrazolylphenyl)silane ligand.

Formal substitution of the central carbon by silicon within the tetrahedral tetrakis(4-tetrazolylphenyl)methane linker in a copper-based MOF is shown to uniquely influence the structure of the resultant MOF, affecting the orientation of the metal-based nodes and leading to an increase in unit-cell volume and solvent accessible void space.

Preparations of metal trichalcogenophosphonates from organophosphonate esters.

A new method for the preparation of metal trichalcogenophosphonates is presented wherein organophosphonate esters are first reduced with LiAlH(4) and subsequently treated with an organometallic reagent and elemental sulfur or selenium to give the desired trichalcogenophosphonate complex. Using this synthetic protocol with (n)BuLi as the organometallic reagent, the lithium trithiophosphonate complexes [Li(2)(S(3)PCH(2)Ph)(THF)(TMEDA)](2) (1) and [Li(4)(S(3)P(n)Pr)(2)(TMEDA)(3)](∞) (3), where THF = tetrahydrofuran and TMEDA = N,N,N',N'-tetramethylethylenediamine, have been prepared. In both cases, the formation of byproducts is also evident, including, for 1, the tetrathiohypodiphosphonate complex [(PhCH(2)P(S(2)))(2)Li(2)(THF)(4)] (2), which has been structurally characterized. Replacement of (n)BuLi with (n)Bu(2)Mg as the metallating agent led to much cleaner products and improved yields, with the new trithio- and triselenoorganophosphonate complexes [Mg(S(3)PCH(2)Ph)(TMEDA)](2) (4) and [Mg(Se(3)P(n)Pr)(TMEDA)](2) (5) reported. All trichalcogenophosphonate complexes have been structurally characterized in the solid state: 1 adopts a dimer structure in which the [PhCH(2)PS(3)](2-) ligand exhibits a unique µ(3)-η(2),η(2),η(2)-coordination mode; 3 is polymeric comprising of [Li(4)(S(3)P(n)Pr)(2)(TMEDA)(2)] dimers linked via additional bridging bis(monodentate) TMEDA molecules; 4 and 5 both adopt dimeric motifs with µ(2)-η(2),η(2) coordination of the magnesium centers.

Facile synthesis of bis(dichalcogenophosphinate)s and a remarkable [Li8(OH)6]2+ polyhedron.

The synthesis and characterization of three lithium complexes of novel bis(dichalcogenophosphinate) ligands are reported: (PhP(S)(2)CH(2)CH(2)P(S)(2)Ph)Li(2)(THF)(4) (2), (PhP(Se)(2)CH(2)CH(2)P(Se)(2)Ph)Li(2)(THF)(4).(PhP(Se)(2)CH(2)CH(2)P(Se)(2)Ph)Li(2)(THF)(6) (3), and [PhP(Te)(2)CH(2)CH(2)P(Te)(2)Ph][Li(8)(OH)(6)(THF)(8)] (4). The synthetic route to these complexes proceeds via the insertion reaction of elemental chalcogens into the phosphorus-lithium bonds of 1,2-dilithio-1,2-di(phenylphosphine)ethylene (1). X-ray analysis of 2 revealed isobidentate coordination of the lithiums by the dithiophosphinate groups. In contrast, the diselenophosphinate groups in 3 coordinate the lithium centers in both isobidentate and monodentate modes, and the ditellurophosphinate groups in 4 form non-coordinate separate ion pairs. The countercation in 4 is shown to be a unique [Li(8)(OH)(6)](2+) rhombic dodecahedral polyhedron, putatively formed from the capping of a hexameric [Li(OH)](6) aggregate with lithium cations on its open faces.

The influence of tetrahydrofuran on the structures and reactivities of lithium organo-amidocuprates.

The organo-amidocuprate [Cu(2)Li(2)Mes(2)(N(CH(2)Ph)(2))(2)] is solvated by thf to yield the monomeric contact ion pair complex [MesCuN(CH(2)Ph)(2).Li(thf)(3)] in which the Li cation is bound to the amido nitrogen; this behaviour differs significantly from that observed in diorganocuprates which favour solvent separate ion pairs.