Structure, stability, and nature of bonding between high energy water clusters confined inside cucurbituril: A computational study

An "on-off" fluorescent probe based on cucurbit[7]uril for highly sensitive determination of ammonia nitrogen in aquaculture water

A novel "on-off" fluorescent probe was synthesized for highly sensitive and ultra-trace determination of ammonia nitrogen in aquaculture water. Ammonium can react with formaldehyde and sodium hydroxide to form a ring substance (urotropine), which shows no fluorescence signal. Palmatine hydrochloride (PAL) can enter the hydrophobic cavity of cucurbit[7]uril (CB[7]), eventually forming a 1 : 1 host guest complex called PAL@CB[7] under neutral or acidic conditions, which has strong green fluorescence with the maximum excitation (λ_ex) wavelength at 343 nm, and the maximum emission (λ_em) wavelength at 500 nm, while urotropine has a fluorescence quenching effect on the fluorescence enhancement system of PAL@CB[7]. Therefore, a fluorescent chemosensor based on PAL@CB[7] and the reaction of ammonia nitrogen with formaldehyde was developed. The results indicate that the linearity range and the limit of detection of the proposed method are 1-300 μg L^-1 with a good correlation coefficient (r² = 0.9966) and 1.8 × 10^-2 μg L^-1, respectively. Under the optimal conditions, the method was employed for the detection of ammonia nitrogen in real aquaculture water samples, revealing high selectivity and sensitivity. In the future, the combination of the "on-off" fluorescence method, a portable hardware system and intelligent algorithms will provide technology support for the design of on-line sensors for measuring ammonia nitrogen in aquaculture water.

Possible pre-phase transition of the α-HMX crystal observed by the variation of hydrogen-bonding network under high pressures

The variation of non-covalent interactions in the HMX crystal under high pressures was investigated through disassembling the hydrogen-bonding network.

Experimental and theoretical study of the role of CH/π interactions in the aminolysis reaction of acetyl galactoside

Molecular recognition of saccharides is a growing field, which has many implications in cancer therapy, drug discovery, and cellular communication among others. The participation of CH/π interactions in this event is well known. Nevertheless, the intrinsic role of CH/π for modulating chemical reactions is still far from being applicable. In this experimental and computational work we have evaluated the participation of CH/π interactions in the aminolysis reaction of acetyl galactoside promoted with different 6-substituted 2(1H)-pyridones. Two features have been incorporated to the promoter molecular structure, on one end the promoting pyridone group and on the other end the recognition moiety, joined together by an alkyne spacer. The small increment in the observed pseudo-first-order rate constant values (k_obs) was related to the stability of the transition state provided by noncovalent interactions, including CH/π interactions. A longer alkyne spacer was necessary to improve the molecular recognition of the galactoside substrate. The trend of the calculated activation energy values (ΔE_RTS) was in good accordance with the experimental rate constant values.