William Morris

Nucleic acid-metal organic framework (MOF) nanoparticle conjugates

Nanoparticles of a metal-organic framework (MOF), UiO-66-N3 (Zr6O4OH4(C8H3O4-N3)6), were synthesized. The surface of the MOF was covalently functionalized with oligonucleotides, utilizing a strain promoted click reaction between DNA appended with dibenzylcyclooctyne and azide-functionalized UiO-66-N3 to create the first MOF nanoparticle-nucleic acid conjugates. The structure of the framework was preserved throughout the chemical transformation, and the surface coverage of DNA was quantified. Due to the small pore sizes, the particles are only modified on their surfaces. When dispersed in aqueous NaCl, they exhibit increased stability and enhanced cellular uptake when compared with unfunctionalized MOF particles of comparable size.

A two-dimensional zeolitic imidazolate framework with a cushion-shaped cavity for CO2 adsorption

A new two-dimensional zeolitic imidazolate framework (named as ZIF-L) was synthesized in zinc salt and 2-methylimidazole (Hmim) aqueous solution at room temperature. ZIF-L (Zn(mim)2·(Hmim)1/2·(H2O)3/2 or C10H16N5O3/2Zn) has unique cushion-shaped cavities and leaf-like crystal morphology, and exhibits excellent CO2 adsorption properties.

Large-area molecular patterning with polymer pen lithography

The challenge of constructing surfaces with nanostructured chemical functionality is central to many areas of biology and biotechnology. This protocol describes the steps required for performing molecular printing using polymer pen lithography (PPL), a cantilever-free scanning probe-based technique that can generate sub-100-nm molecular features in a massively parallel fashion. To illustrate how such molecular printing can be used for a variety of biologically relevant applications, we detail the fabrication of the lithographic apparatus and the deposition of two materials, an alkanethiol and a polymer onto a gold and silicon surface, respectively, and show how the present approach can be used to generate nanostructures composed of proteins and metals. Finally, we describe how PPL enables researchers to easily create combinatorial arrays of nanostructures, a powerful approach for high-throughput screening. A typical protocol for fabricating PPL arrays and printing with the arrays takes 48–72 h to complete, including two overnight waiting steps.

Surface-Specific Functionalization of Nanoscale Metal–Organic Frameworks

A method for modifying the external surfaces of a series of nanoscale metal-organic frameworks (MOFs) with 1,2-dioleoyl-sn-glycero-3-phosphate (DOPA) is presented. A series of zirconium-based nanoMOFs of the same topology (UiO-66, UiO-67, and BUT-30) were synthesized, isolated as aggregates, and then conjugated with DOPA to create stably dispersed colloids. BET surface area analysis revealed that these structures maintain their porosity after surface functionalization, providing evidence that DOPA functionalization only occurs on the external surface. Additionally, dye-labeled ligand loading studies revealed that the density of DOPA on the surface of the nanoscale MOF correlates to the density of metal nodes on the surface of each MOF. Importantly, the surface modification strategy described will allow for the general and divergent synthesis and study of a wide variety of nanoscale MOFs as stable colloidal materials.

Controlling Structure and Porosity in Catalytic Nanoparticle Superlattices with DNA

Herein, we describe a strategy for converting catalytically inactive, highly crystalline nanoparticle superlattices embedded in silica into catalytically active, porous structures through superlattice assembly and calcination. First, a body-centered cubic (bcc) superlattice is synthesized through the assembly of two sets of 5 nm gold nanoparticles chemically modified with DNA bearing complementary sticky end sequences. These superlattices are embedded in silica and calcined at 350 °C to provide access to the catalytic nanoparticle surface sites. The calcined superlattice maintains its bcc ordering and has a surface area of 210 m(2)/g. The loading of catalytically active nanoparticles within the superlattice was determined by inductively coupled plasma mass spectrometry, which revealed that the calcined superlattice contained approximately 10% Au by weight. We subsequently investigate the ability of supported Au nanoparticle superlattices to catalyze alcohol oxidation. In addition to demonstrating that calcined superlattices are effective catalysts for alcohol oxidation, electron microscopy reveals preservation of the crystalline structure of the bcc superlattice following calcination and catalysis. Unlike many bulk nanoparticle catalysts, which are difficult to characterize and susceptible to aggregation, nanoparticle superlattices synthesized using DNA interactions offer an attractive bottom-up route to structurally defined heterogeneous catalysts, where one has the potential to independently control nanoparticle size, nanoparticle compositions, and interparticle spacings.

Synthesis of (−)-Okilactomycin by a Prins-Type Fragment-Assembly Strategy†

Okilactomycin (1a) is a structurally interesting antitumor antibiotic that was isolated from Streptomyces griseoflavus in 1987.[1] In vitro studies have demonstrated that 1a exhibits significant antitumor and antiproliferative activity against both lymphoid leukemia L1210 cells and P388 leukemia cells with IC50 values of 216 nM and 89 nM, respectively.[1b] A closely related compound, chrolactomycin (1b), differs only in structure by the replacement of a methyl group with a methoxy moiety at the pyranone/lactone ring fusion and displays promising telomerase inhibition.[1c,d] In addition to their potent biological activity, these compounds posses a compact and intriguing architecture. The tricyclic core is characterized by a unique 6,5-fused tetrahydropyranone γ-lactone bicycle with a spiro fusion to a highly substituted cyclohexene. A strained deoxygenated dipropionate segment spans this unusual tricycle to generate a highly rigid tetracyclic topology. Despite the biological activity and structural complexity, there have been only limited reports on the synthesis of okilactomycin (1a) over the last two decades, namely from the laboratories of Takeda, Paquette, and Smith.[2] These synthetic efforts culminated in a total synthesis of unnatural enantiomer (−)-1 a and determination of the absolute configuration of the natural product by Smith et al. in 2007.[2d,e] There are no syntheses of chrolactomycin (1b) reported to date. We disclose herein a convergent synthesis of (−)-1 a utilizing a Prins-type Maitland–Japp cyclization strategy of two advanced fragments.

Role of Modulators in Controlling the Colloidal Stability and Polydispersity of the UiO-66 Metal–Organic Framework

Nanoscale UiO-66 Zr6(OH)4O4(C8O4H4)6 has been synthesized with a series of carboxylic acid modulators, R-COOH (where R = H, CH3, CF3, and CHCl2). The phase purity and size of each MOF was confirmed by powder X-ray diffraction, BET surface area analysis, and scanning transmission electron microscopy (STEM). Size control of UiO-66 crystals from 20 nm to over 1 μm was achieved, and confirmed by STEM. The colloidal stability of each MOF was evaluated by dynamic light scattering and was found to be highly dependent on the modulator conditions utilized in the synthesis, with both lower pKa and higher acid concentration resulting in more stable structures. Furthermore, STEM was carried out on both colloidally stable samples and those that exhibited a large degree of aggregation, which allowed for visualization of the different degrees of dispersion of the samples. The use of modulators at higher concentrations and with lower pKas leads to the formation of more defects, as a consequence of terephthalic acid ligands being replaced by modulator molecules, thereby enhancing the colloidal stability of the UiO-66 nanoparticles. These findings could have a significant impact on nanoscale MOF material syntheses and applications, especially in the areas of catalysis and drug delivery.

Exploring Prins Strategies for the Synthesis of Okilactomycin

Abstract This account describes the convergent synthesis of (−)-okilactomycin. The first-generation approach focused on the assembly of two complex fragments through a Prins reaction of a dioxinone and α-hydroxy aldehyde. While this route was not ultimately successful, a related Maitland–Japp process employing a β-keto ester in place of the dioxinone fragment provided the necessary union of functionalized intermediate, thereby establishing the full carbon framework of the natural product. The synthesis also employed a highly diastereoselective Lewis acid-promoted Diels–Alder reaction and an olefin ring-closing metathesis to close the strained 11-membered macrocycle of the natural product.

Utilization of Metal-Organic Frameworks for the Management of Gases Used in Ion Implantation

Metal-Organic Frameworks (MOFs) are porous extended crystalline structures comprised of organic ligands and metal units. By changing the identity of the organic ligand and metal unit utilized in the MOF synthesis, the structure, surface area, pore size, and reactivity of the MOF can be modulated. This structural flexibility means that MOFs can potentially be used in a wide range of storage, separation, and catalytic applications. There is a high level of interest in the storage, delivery, capture, and purification of ultra high-purity hazardous gases used in electronics manufacturing (electronic gases). This paper will discuss the use of MOFs as an ideal platform for product and process innovation in the electronic gas sector.