Ammonium and imidazolium-based amphiphilic tetramethoxy resorcinarenes: Adsorption, micellization, and protein binding

Inhibition of Polyphenol Oxidase Activity by Mesoporous Silica Nanoparticles and Multiwalled Carbon Nanotubes Modified with Surfactants

Polyphenol oxidase (PPO) is the culprit behind the browning of fruits and vegetables. Therefore, how to reduce the thermal deactivation temperature of PPO or use as few safe reagents as possible to inhibit enzymatic browning has practical significance. Mesoporous silica nanoparticles (MSNs) and multiwalled carbon nanotubes (MWCNTs) are stable and have high biosafety. In the present study, efficient PPO inhibitors were developed based on MSNs and MWCNTs. It is found that after modification with a very small amount of dodecyl trimethylammonium bromide (DTAB, ≥60 μg/mL), MSNs can significantly inhibit the activity of PPO although single MSNs and single DTAB show very limited effect on PPO activity. After modification with a very small amount of sodium dodecyl sulfate (SDS, 5.7-9.5 μg/mL), MWCNTs almost completely inactivate PPO. However, SDS@MSN and DTAB@MWCNT cannot decrease PPO activity significantly.

Improvement effect of p-sulfonatocalix[4]arene on the performance of the PEG/salt aqueous two-phase system

The PEG/salt aqueous two-phase system (ATPS) is the most common ATPS, but its application is still limited due to the restricted polarity difference between the two phases and the poor enhancement effect of adjuvants on ATPS performance so far. Unlike the adjuvants used so far, calixarenes can bind ions and molecules via multiple noncovalent interactions. In the present study, a water-soluble calixarene, p-sulfonatocalix[4]arene (SC[4]), was used for the first time as the adjuvant to improve the performance of the PEG 600/(NH₄)₂SO₄ ATPS through multiple interactions. It is found that when the SC[4] and the SC[4]/imidazole ionic liquid ([C_nmim]Br) complex were used as the adjuvants, the formation of PEG 600/(NH₄)₂SO₄ ATPS was enhanced, and the transfer of the extracts (including S-mandelic acid, L-tryptophan, and L-phenylalanine) into the PEG phase was promoted. Moreover, although the single [C_nmim]Br, a commonly used adjuvant, does not promote the migration of the target molecules into the polymer phase, the SC[4]/[C_nmim]Br complex is superior to SC[4] in enhancing the performance of the ATPS because the SC[4]/[C_nmim]Br aggregates enable more binding sites to combine with the extract. Besides, the partition coefficient of SC[4] in the PEG/trisodium citrate ATPS is much smaller than that in the PEG/(NH₄)₂SO₄ ATPS, which is helpful for the recovery of extracts into the citrate phase.

Recognition of Heavy Metals by Using Resorcin[4]arenes Soluble in Water

The complexing properties of two water-soluble resorcin[4]arenes (tetrasodium 5,11,17,23-tetrakissulfonatemethylen 2,8,14,20-tetra(butyl)resorcin[4]arene, Na₄BRA, and tetrasodium 5,11,17,23-tetrakissulfonatemethylen-2,8,14,20-tetra(2-(methylthio)ethyl)resorcin[4]arene, Na₄SRA) with polluting heavy metals such as Cu²⁺, Pb²⁺, Cd²⁺ and Hg²⁺ were studied by conductivity, and the findings were confirmed by using other techniques to try to apply this knowledge to removing them. The results indicate that Na₄BRA is able to complex Cu²⁺ in a 1:1 ratio and Pb²⁺ in a 1:2 ratio, while Na₄SRA complexes Hg²⁺ in a 1:1 ratio. On the contrary, no indications have been observed that either of the resorcin[4]arenes studied complexes the Cd²⁺ ions. The results suggest that the bonds established between the sulfur atoms located at the lower edge of the SRA^4- and the solvent hydrogens could prevent the entry of the guest into the host cavity. However, in the case of Hg²⁺ ions, the entry is favoured by the interactions between the sulfur donor atoms present on the lower edge of Na₄SRA and the Hg²⁺ ions. Therefore, it can be said that Na₄BRA is selective for Cu²⁺ and Pb²⁺ ions and Na₄SRA is selective for Hg²⁺ ions.