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Fabrication of a reusable electrochemical platform based on acid-responsive host-guest interaction with β- cyclodextrin.

A reusable electrochemical glassy carbon electrode (GCE) platform based on the acid-responsive host-guest interaction between β-cyclodextrin (β-CD) and benzimidazole (BM) derivatives was developed. The β-CD can specifically recognize the BM derivative through the acid -responsive host-guest interaction. The electrode was first modified by eletrografting to immobilize a diamine linker (Boc-EDA), resulting in GCEBoc-EDA in which one amine was used for covalent immobilization to the electrode and another Boc protected amine was used to solid-phase synthesis on following step-by-step modifications on the electrode. After deprotection of the Boc group on the GCEBoc-EDA, carbonyldiimidazole (CDI)-activated β-CD was coupled with -NH2 on the electrode to result in GCEβ-CD. Due to the nonspecific interaction, we further improved the GCEβ-CD electrode by introducing immobilized poly(ethylene glycol) methyl ether (PEG-Me) to result in GCEβ-CD/PEG-Me, along with optimized procedures. CV, DPV, and EIS methods were applied for recording the electrochemistry signals. We utilized GCEβ-CD/PEG-Me to investigate the host-guest interaction and found the electrochemical signal exhibited dynamic behavior. The GCEβ-CD/PEG-Me was able to regenerate the β-CD surface more than 20 times after HCl acidic washes. We further investigated the interaction of carbendazim (CBZ), a commonly used fungicide in the agriculture and food industry, and observed a positive electrochemical response. The sensor design has potential applications in ensuring food safety.

Just Published
Oriented display of cello-oligosaccharides for pull-down binding assays to distinguish binding preferences of glycan binding proteins.

The production of biofuels from lignocellulosic biomass using carbohydrate-active enzymes like cellulases is key to a sustainable energy production. Understanding the adsorption mechanism of cellulases and associated binding domain proteins down to the molecular level details will help in the rational design of improved cellulases. In nature, carbohydrate-binding modules (CBMs) from families 17 and 28 often appear in tandem appended to the C-terminus of several endocellulases. Both CBMs are known to bind to the amorphous regions of cellulose non-competitively and show similar binding affinity towards soluble cello-oligosaccharides. Based on the available crystal structures, these CBMs may display a uni-directional binding preference towards cello-oligosaccharides (based on how the oligosaccharide was bound within the CBM binding cleft). However, molecular dynamics (MD) simulations have indicated no such clear preference. Considering that most soluble oligosaccharides are not always an ideal substrate surrogate to study the binding of CBMs to the native cell wall or cell surface displayed glycans, it is critical to use alternative reagents or substrates. To better understand the binding of type B CBMs towards smaller cello-oligosaccharides, we have developed a simple solid-state depletion or pull-down binding assay. Here, we specifically orient azido-labeled carbohydrates from the reducing end to alkyne-labeled micron-sized bead surfaces, using click chemistry, to mimic insoluble cell wall surface-displayed glycans. Our results reveal that both family 17 and 28 CBMs displayed a similar binding affinity towards cellohexaose-modified beads, but not cellopentaose-modified beads, which helps rationalize previously reported crystal structure and MD data. This may indicate a preferred uni-directional binding of specific CBMs and could explain their co-evolution as tandem constructs appended to endocellulases to increase amorphous cellulose substrate targeting efficiency. Overall, our proposed workflow can be easily translated to measure the affinity of glycan-binding proteins to click-chemistry based immobilized surface-displayed carbohydrates or antigens.

Open Access Just Published
Detailed investigation and influence of oxidation degree on synthesis, characterization and antibacterial activity of β- cyclodextrin.

Oxidation of β-cyclodextrin (β-CD) using varying molar ratios of sodium periodate (NaIO4) was investigated in detail on synthesis, characterization and antibacterial property. Synthesis and characterization results showed that Oxidized β-cyclodextrins (OX-β-CDs) were obtained and aldehyde (CHO) groups were successfully introduced. Our results demonstrated that aldehyde content and yield increased with increasing NaIO4 molar amount. However, the structure of β-CD was degraded as a result of glycosidic ring opening with increasing stoichiometric ratio of NaIO4/β-CD to 5/1 and 7/1. Aldehyde functional groups in OX-β-CDs were characterized by employing FTIR, 1H NMR, XRD, SEM techniques and confirmed by the detection of CHO peak at 1730 cm-1 in the FTIR and detection of the aldehyde H peak between 9 to 10ppm in the 1H NMR spectrum. In addition, SEM and XRD of OX-β-CDs showed alterations in the morphological and crystal structure (transforming from crystalline to amorphous) of β-CD as a result of increasing oxidation. Especially, antibacterial activity of OX-β-CDs was investigated against both Gram-negative and Gram-positive bacteria by using the minimal inhibitory concentration (MIC) and the Disk diffusion method. The results showed that OX-β-CDs possessed good antibacterial activity, which can destroy the bacterial cell wall, and may be used as an antibacterial agent.