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Materials

2-D Organic Material Kills Bacteria

Materials: Electrostatic repulsions cause covalent framework-type compound to form ultrathin sheets

by Mitch Jacoby
February 26, 2016 | APPEARED IN VOLUME 94, ISSUE 8

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Credit: J. Am. Chem. Soc.
Weak stacking interactions cause this organic material to form robust 2-D sheets, not 3-D crystals. Carbon is gray, hydrogen is white, nitrogen is blue, oxygen is red, and chlorine is green.Weak stacking interactions cause this organic material (shown in two perspectives) to form robust 2-D sheets, not 3-D crystals.
 Carbon is gray, hydrogen is white, nitrogen is blue, oxygen is red, and chlorine is green.

Credit: J. Am. Chem. Soc.
Weak stacking interactions cause this organic material to form robust 2-D sheets, not 3-D crystals. Carbon is gray, hydrogen is white, nitrogen is blue, oxygen is red, and chlorine is green.Weak stacking interactions cause this organic material (shown in two perspectives) to form robust 2-D sheets, not 3-D crystals.
 Carbon is gray, hydrogen is white, nitrogen is blue, oxygen is red, and chlorine is green.


By incorporating a bonding weakness into an organic framework compound, researchers in India have devised a simple procedure for making two-dimensional materials that can be used to make membranes with antimicrobial properties (J. Am. Chem. Soc. 2016, DOI: 10.1021/jacs.5b13533). Covalent organic frameworks (COFs) are porous 3-D networks constructed of strong covalent bonds between light elements such as carbon, nitrogen, and oxygen. Researchers have tried delaminating COFs to make 2-D analogs, expecting that they would lead to novel applications in gas separation, electronics, and other areas. But those efforts have largely been thwarted because of strong π-π stacking interactions between adjacent layers. So Shouvik Mitra and Rahul Banerjee of the National Chemical Laboratory, in Pune, and coworkers made self-exfoliating materials based on guanidinium halides. They explain that repulsions between loosely bound chloride or other halide ions and between positively charged guanidinium units weaken π-π interactions, causing the material to spontaneously form micro­meter-sized 2-D flakes. Tests of the material in flake form and embedded in polysulfone films show that it exhibits potent antimicrobial properties. The team speculates that cell death is triggered by the material’s positively charged moieties disrupting the negatively charged phospholipid bilayer in cell membranes.

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