KU Researcher worked with NYUAD to create the first woven calixarene-based covalent organic framework (COF) with plenty of tunable pores for adsorption applications

Synthetic dyes are common ingredients in the textile industry, but because of their general use, they often find their way into waterbodies from industrial wastewater, where they pollute the water and threaten water security.

Removing these polluting dyes can be achieved through adsorption, where the dyes are collected in the pores of highly porous materials that scoop the pollutants from water and trap them in the pores.

Dr. Dinesh Shetty, Assistant Professor of Chemistry, has created a tunable, two-dimensional polymeric network from an organic macrocycle called calixarenes that can selectively adsorb toxic dyes from wastewater.

Dr. Shetty is a member of the Khalifa University Center for Catalysis and Separation (CeCaS), one of KU’s 18 specialized research centers. CeCaS research aims at developing practical solutions to chemical engineering challenges faced by several industries today. In collaboration with researchers from New York University Abu Dhabi, Dr. Shetty has developed a novel structure using calixarenes to remove dyes selectively and efficiently from wastewater. Their work was recently published in the and appeared as a cover article.

Calixarenes are bowl-shaped organic molecules that consist of defined hydrophobic cavities. This unique feature allows host-guest chemistry where calixarenes play the host for small molecules and/or ions.

“Calixarene molecules have been extensively exploited as versatile supramolecular building blocks,” explained Dr. Shetty. “This is due to their ability to adopt different conformations, which refers to the spatial arrangement of atoms in a molecule, and the relative ease with which they can be functionalized, which refers to how easily a calixarene can take on new functions, features, capabilities, or properties by changing its surface chemistry.”

This is particularly true of calixarenes where the ring consists of four aromatic rings. Calixarenes work as excellent adsorbers, but in the monomer form, they can be dissolved in some solvents, which would hinder their practical use.

In a macroscopic architecture, however, calixarenes become insoluble in almost every solvent, especially in water.

To create calixarenes with a macroscopic architecture, Dr. Shetty and his team turned to covalent organic frameworks, or COFs. COFs are a class of materials that form two- or three-dimensional structures through reactions between their organic components, resulting in strong, covalent bonds that create porous, crystalline materials.  

“COFs have proven to be an important class of porous materials on account of their well-defined structures, tuneable pore functionality, and good chemical stability,” explained Dr. Shetty.

Giving calixarenes a macroscopic architecture is very challenging but if successful could allow them to be incorporated into practical platforms such as powders in cartridges or membranes.

While few researchers have attempted to build COFs with multiple ringed, or macrocyclic molecules, like calixarenes, Dr. Shetty’s team realized that a calixarene-based COF would be an ideal way to remove toxic dyes from industrial wastewater.

Dr. Shetty, along with Trabolsi research group at NYUAD, developed the first woven structures of calixarene-based COFs, making a 2D network that can be delicately tuned for each application. They joined calixarenes by creating covalent bonds between the organic molecules to link them together, then these calixarene chains were interwoven by slotting one calixarene into the bowl-shape of another, effectively stacking the chains.

The synthesized COFs showed well-defined lattice structures, indicating a highly crystalline nature for both COFs, with plenty of pores for adsorption applications. By varying the concentration of calixarene units in the solution, the stacking orientation in the COFs can be altered, meaning researchers can create both interpenetrated (meaning catenated) and non-interpenetrated frameworks. The resulting COFs featured wavy layers containing the calixarene cavities, making them attractive candidates for adsorbing small molecules.

The researchers validated the materials ability by using them for selective removal of cationic-dyes from aqueous mixtures.

Importantly, creating a structure with organized pores increases the number of molecular interactions between pollutant molecules and adsorbent. Interestingly, the COFs developed by the research team were exceptionally selective for the cationic dyes in the test mixtures without depending on the size of the molecules. The COFs also demonstrated a highly negative surface charge, allowing charge-selective removal of the dye molecules.

“With the inherently hydrophobic cavity, anionic surface, and possibility to develop these COFs in a membrane, our work has the potential to bring calixarene chemistry to an exciting materials science horizon,” said Dr. Shetty.

Jade Sterling
Science Writer
20 April 2021

The post A Tunable 2D Covalent Network for Charge-selective Removal of Toxic Dyes from Wastewater appeared first on Khalifa University.

[vc_row][vc_column][vc_column_text]Mollusks Dosed with Amantadine Reveals Intracellular Trafficking Pathway

A paper published by Khalifa university faculty has enhanced understanding of nanoparticle toxicity, specifically which uptake pathway contributes most to the damaging effects of silver on a cellular level.
Nanoparticles are defined as materials that are between 1 and 100 nanometers. Metal and metal oxide nanoparticles (NPs) are used in many different kinds applications and products – like deodorants,
sunblock, electronics and even clothing, for their known and beneficial functions on macro scale. The Global Nanomaterials market was valued at USD7.3 billion in 2016 and is growing at a rate of 15%
annually, with a projected value of USD16.8 billion by 2022. However, how they behave on the nanoscale is not as well known, resulting in unplanned and unwanted impacts to plants and animals in
our environment.

“There is a growing body of literature to which I and my collaborators have contributed, that many nanoparticles cause oxidative stress because they stimulate production of reactive oxygen species. We
have found that this damages proteins in the cell by oxidizing them directly. It is unclear presently why some nanoparticles are very toxic while others are not,” said Dr. David Sheehan, Professor of Chemistry
and Dean of the College of Arts and Sciences.

Dr. Sheehan recently coauthored a paper titled “Redox proteomic insights into involvement of clathrin-mediated endocytosis in silver nanoparticle toxicity to Mytilus galloprovincialis” in the journal PLoS One
in collaboration with a research group at the University of Carthage in Tunisia.

Mollusks, as filter-feeders, are particularly sensitive to metallic micro-pollutants, as they extract and concentrate metals in their tissues. This makes them an ideal organism to study to research the impact
of nanoparticles.

“Bivalves like mollusks can be seen as a type of lab rat to assess aspects of nanoparticle toxicology, which is also relevant to human health. The idea was to selectively block uptake of the silver
nanoparticles by inhibiting each of the two main uptake mechanisms. In this way we could assess which was contributing most to protecting against toxicity,” explained Dr. David Sheehan, Professor of
Chemistry and Dean of the College of Arts and Sciences.

The silver nanoparticle is mainly absorbed by the mollusk through clathrin-mediated endocytosis – which is a cellular process where a eukaryotic cell absorbs proteins and fats through its membranes. In
their experiment, the team selectively blocked the clathrin-mediated uptake pathway with an inhibitor, the Parkinson’s Disease drug amantadine. Clathrin is a protein that plays a major role in the formation of
the large coated large structures within a cell that are made up of a liquid enclosed by a lipid bilayer, known as vesicles.

“This resulted in reduced toxicity of the silver nanoparticles, thus showing that this uptake pathway facilitates NP toxicity. Our study really just wanted to ask the question, which uptake pathway
contributes most to NP toxicity and was not primarily intended to point to prevention of NP toxicity,” Dr. Sheehan added.

He explained that this points future research to exploring the fate of clathrin-coated pits within the cell in assessing the role of intracellular trafficking in nanoparticle toxicity.

“We would like to generalize this study to see if other nanoparticles are taken up in the same way. In particular, I want to study iron NPs because iron is a toxic chemical that triggers production of “reactive
oxygen species” but also, iron is magnetic. In preliminary work with cultured human cells, I have found the cells become magnetized once iron NPs are taken up. This would, in principle, mean that we could
select subcellular organelles as the NPS are trafficked through the cell towards lysosomes and build up a picture of the trafficking process and how it contributes to toxicity,” Dr. Sheehan concluded.

Zarina Khan
Senior Editor
24 December 2018[/vc_column_text][/vc_column][/vc_row]

The post Cellular Uptake of Silver Nanoparticles Explored appeared first on Khalifa University.