L-ribose specific recognition surface constructed by pillar[5]arene-based host-guest interaction

In living organisms, chiral molecules have specific chiral conformations that produce different physiological effects. Ribose is one of the components of RNA, which mainly plays a role in regulating biological activity. Inspired by the biological recognition of sugars, functional chiral surfaces for recognizing L-ribose through non-covalent interactions were constructed. In the strategy of this study, a functional chiral gold surface based on host-guest interactions was constructed through the assembly of the host molecule single-function alynyl pillar[5]arene(SAP5) and the guest molecule (S) -mandelate-violet (SMV). The association constant of SMV and SAP5 was calculated to be 2.95×104 M-1, with a binding ratio of 1:1. By impedance and contact angle detection, the constructed functional interface has good detection effect on L-ribose in the range of 1×10-7 M to1× 10-2 M. In addition, CV was disassembled from the aromatic cavity of pillar[5]arene after adding zinc powder and it can repeat five times with good recyclability, thus achieving the organic combination of interface recognition and intelligence.

Recent advances in chiral discrimination on host-guest functionalized interfaces

Chiral discrimination has gained much focus in supramolecular chemistry, since it is one of the fundamental processes in biological systems, enantiomeric separation and biochemical sensors. Though most of the biochemical processes can routinely recognize biological enantiomers, enantioselective identification of chiral molecules in artificial systems is currently one of the challenging topics in the field of chiral discrimination. Inaccuracy, low separation efficiency and expensive instrumentation were considered typical problems in artificial systems. Recently, chiral recognition on the interfaces has been widely used in the fields of electrochemical detection and biochemical sensing. For the moment, a series of macrocyclic host functionalized interfaces have been developed for use as chiral catalysts or for enantiomeric separation. Here, we have briefly exposited the most recent advances in the fabrication of supramolecular functionalized interfaces and their application for chiral recognition.

Ultrasound enhanced the binding ability of chitinase onto chitin: From an AFM insight

In order to evaluate the effect of ultrasound to chitinase from a molecular level, atomic force microscopy (AFM) was employed to investigate the interaction force of chitinase binding onto chitin surface. In the measurement of force-distance curve, a series of pull-off events were discovered using the immobilized AFM tips with chitinase either treated by ultrasound or not, whereas no interaction peak was observed by the AFM tips without chitinase, indicating that the obtained adhesion forces were coming from the binding functions between chitinase and chitin. Through the analysis of these force curves, at the loading velocity of 0.3 μm/s, the maximum binding force of the chitinase treated by ultrasound for 20 min onto chitin was measured to be 105.33 ± 23.51 pN, while the untreated onto chitin was 71.05 ± 12.73 pN, suggesting the stronger binding force between ultrasonic treated chitinase and chitin substrate. Therefore, AFM has provided a useful method to directly and quantitatively characterize the interactions between chitinase and chitin, and successfully proved that ultrasound could activate chitinase by enhancing the binding ability of chitinase onto chitin.

Hydration Effects Turn a Highly Stretched Polymer from an Entropic into an Energetic Spring

Polyethylene glycol (PEG) is a structurally simple and nontoxic water-soluble polymer that is widely used in medical and pharmaceutical applications as molecular linker and spacer. In such applications, PEG's elastic response against conformational deformations is key to its function. According to text-book knowledge, a polymer reacts to the stretching of its end-to-end separation by a decrease in entropy that is due to the reduction of available conformations, which is why polymers are commonly called entropic springs. By a combination of single-molecule force spectroscopy experiments with molecular dynamics simulations in explicit water, we show that entropic hydration effects almost exactly compensate the chain conformational entropy loss at high stretching. Our simulations reveal that this entropic compensation is due to the stretching-induced release of water molecules that in the relaxed state form double hydrogen bonds with PEG. As a consequence, the stretching response of PEG is predominantly of energetic, not of entropic, origin at high forces and caused by hydration effects, while PEG backbone deformations only play a minor role. These findings demonstrate the importance of hydration for the mechanics of macromolecules and constitute a case example that sheds light on the antagonistic interplay of conformational and hydration degrees of freedom.

Direct comparison between chemisorption and physisorption: a study of poly(ethylene glycol) by means of single-molecule force spectroscopy

Chemisorption on an AFM-tip is the most promising protocol, if a functionalized polymer sample is available.