Tanay Kundu

Helical Water Chain Mediated Proton Conductivity in Homochiral Metal–Organic Frameworks with Unprecedented Zeolitic unh-Topology

Four new homochiral metal-organic framework (MOF) isomers, [Zn(l-L(Cl))(Cl)](H(2)O)(2) (1), [Zn(l-L(Br))(Br)](H(2)O)(2) (2), [Zn(d-L(Cl))(Cl)](H(2)O)(2) (3), and [Zn(d-L(Br))(Br)](H(2)O)(2) (4) [L = 3-methyl-2-(pyridin-4-ylmethylamino)butanoic acid], have been synthesized by using a derivative of L-/D-valine and Zn(CH(3)COO)(2)·2H(2)O. A three-periodic lattice with a parallel 1D helical channel was formed along the crystallographic c-axis. Molecular rearrangement results in an unprecedented zeolitic unh-topology in 1-4. In each case, two lattice water molecules (one H-bonded to halogen atoms) form a secondary helical continuous water chain inside the molecular helix. MOFs 1 and 2 shows different water adsorption properties and hence different water affinity. The arrangement of water molecules inside the channel was monitored by variable-temperature single-crystal X-ray diffraction, which indicated that MOF 1 has a higher water holding capacity than MOF 2. In MOF 1, water escapes at 80 °C, while in 2 the same happens at a much lower temperature (∼40 °C). All the MOFs reported here shows reversible crystallization by readily reabsorbing moisture. In MOFs 1 and 2, the frameworks are stable after solvent removal, which is confirmed by a single-crystal to single-crystal transformation. MOFs 1 and 3 show high proton conductivity of 4.45 × 10(-5) and 4.42 × 10(-5) S cm(-1), respectively, while 2 and 4 shows zero proton conductivity. The above result is attributed to the fact that MOF 1 has a higher water holding capacity than MOF 2.

Mechanical Downsizing of a Gadolinium(III)-based Metal-Organic Framework for Anticancer Drug Delivery

A Gd(III) -based porous metal-organic framework (MOF), Gd-pDBI, has been synthesized using fluorescent linker pDBI (pDBI=(1,4-bis(5-carboxy-1H-benzimidazole-2-yl)benzene)), resulting in a three-dimensional interpenetrated structure with a one-dimensional open channel (1.9×1.2 nm) filled with hydrogen-bonded water assemblies. Gd-pDBI exhibits high thermal stability, porosity, excellent water stability, along with organic-solvent and mild acid and base stability with retention of crystallinity. Gd-pDBI was transformed to the nanoscale regime (ca. 140 nm) by mechanical grinding to yield MG-Gd-pDBI with excellent water dispersibility (>90 min), maintaining its porosity and crystallinity. In vitro and in vivo studies on MG-Gd-pDBI revealed its low blood toxicity and highest drug loading (12 wt %) of anticancer drug doxorubicin in MOFs reported to date with pH-responsive cancer-cell-specific drug release.

Correlation between coordinated water content and proton conductivity in Ca–BTC-based metal–organic frameworks

Proton conductivity of five Ca-based MOFs which depends on the amount of water molecules coordinated to the Ca-centres has been reported. These MOFs show high temperature proton conductivity due to the strong hydrogen bonding between the lattice and coordinated water molecules.

Crystalline metal-organic frameworks (MOFs): synthesis, structure and function

Metal-organic frameworks (MOFs) are a class of hybrid network supramolecular solid materials comprised of organized organic linkers and metal cations. They can display enormously high surface areas with tunable pore size and functionality, and can be used as hosts for a range of guest molecules. Since their discovery, MOFs have experienced widespread exploration for their applications in gas storage, drug delivery and sensing. This article covers general and modern synthetic strategies to prepare MOFs, and discusses their structural diversity and properties with respect to application perspectives.

Rapid microwave synthesis of fluorescent hydrophobic carbon dots

Fluorescent hydrophobic carbon dots (HCDs) have been fabricated from a poloxamer by a simple microwave assisted process within a few minutes for the first time. Small and distinct spherical HCDs emitted bright blue and green fluorescent light depending upon the excitation wavelength and were dispersed easily in a wide variety of organic solvents. HCDs exhibited excellent water resistant behavior with a contact angle of ∼122° enforcing good hydrophobic character which will be quite useful in potential surface applications.

A mechanochemically synthesized covalent organic framework as a proton-conducting solid electrolyte

Mechanochemistry has become an increasingly important synthetic tool for a waste-free environment. However, the poor quality of the so-derived materials in terms of their crystallinity and porosity has been their major drawback for any practical applications. In this report, we have for the first time successfully leveraged such characteristics to show that the mechanochemically synthesized bipyridine based covalent organic framework (COF) outperforms its conventional solvothermal counterpart as an efficient solid-state electrolyte in PEM fuel cells. Marking the first such attempt in COFs, a Membrane Electrode Assembly (MEA) fabricated using the mechanochemically synthesized COF was observed to inhibit the fuel crossover and build up a stable Open Circuit Voltage (OCV = 0.93 V at 50 °C), thereby establishing itself as an effective solid electrolyte material (with a proton conductivity of 1.4 × 10−2 S cm−1), while the solvothermally synthesized COF proved ineffective under similar conditions.

Targeted Drug Delivery in Covalent Organic Nanosheets (CONs) via Sequential Postsynthetic Modification

Covalent organic nanosheets (CONs) have emerged as a new class of functional two-dimensional (2D) porous organic polymeric materials with a high accessible surface, diverse functionality, and chemical stability. They could become versatile candidates for targeted drug delivery. Despite their many advantages, there are limitations to their use for target specific drug delivery. We anticipated that these drawbacks could be overturned by judicious postsynthetic modification steps to use CONs for targeted drug delivery. The postsynthetic modification would not only produce the desired functionality, it would also help to exfoliate to CONs as well. In order to meet this requirement, we have developed a facile, salt-mediated synthesis of covalent organic frameworks (COFs) in the presence of p-toluenesulfonic acid (PTSA). The COFs were subjected to sequential postsynthetic modifications to yield functionalized targeted CONs for targeted delivery of 5-fluorouracil to breast cancer cells. This postsynthetic modification resulted in simultaneous chemical delamination and functionalization to targeted CONs. Targeted CONs showed sustained release of the drug to the cancer cells through receptor-mediated endocytosis, which led to cancer cell death via apoptosis. Considering the easy and facile COF synthesis, functionality based postsynthetic modifications, and chemical delamination to CONs for potential advantageous targeted drug delivery, this process can have a significant impact in biomedical applications.

Relating pore hydrophilicity with vapour adsorption capacity in a series of amino acid based metal organic frameworks

A new Zn based porous homochiral metal–organic framework, ThrZnOAc, belonging to unh topology, has been synthesized using pyridyl functionalized threonine and Zn(OAc)2 as the metal precursor. Stepwise substitution of the homochiral MOF backbone by simply changing the sidearm of the amino acids (isopropyl in the case of valine, methyl in alanine and hydroxyethyl in threonine) resulted in increased water adsorption in ThrZnOAc compared to the previously reported ValZnOAc/AlaZnOAc. Extensive solvent sorption isotherms (water, methanol, isopropanol and toluene) have been carried out, which revealed high solvophilic interaction with polar solvents in ThrZnOAc due to the polar pore [2-hydroxyethyl {–CH(OH)CH3} sidearm of the amino acid], which is not prominent in the corresponding valine/alanine counterparts. The aforementioned functionalization in a series of isostructural amino acid based MOFs with the only difference being in the sidearm and their emergence as enhanced solvophilic materials is unprecedented in the MOF literature.

Phosphate enriched polyoxometalate based ionic salts for proton conduction

A series of [NiMo12O30(PO4)8]n− POM anion and organic cation based ionic composites have been prepared in hydrothermal conditions. The ionic composites with protonated ethylene diamine molecules have been tested for proton conductivity.

Catecholase and phenoxazinone synthase activities of a ferromagnetically coupled tetranuclear Cu(II) complex

A crystallographically characterized tetranuclear Cu(II) complex [CuII4(L)4] (1) [H2L = N-(2-hydroxyethyl)-3-methoxysalicylaldimine] is found to show overall ferromagnetic exchange coupling. Complex (1) mimics the catalytic activity of the plant enzyme catechol oxidase by oxidising 3,5-di-tert-butylcatechol to its corresponding quinone in methanol and dichloromethane medium in the presence of aerial oxygen. The reaction follows Michaelis–Menten enzymatic reaction kinetics with turnover numbers (Kcat) 6.99 × 103 and 1.85 × 103 h−1 in methanol and dichloromethane, respectively. 1 is also phenoxazinone synthase active in methanol medium with a turnover number of 1.21 × 105 h−1.