CO2 Capture by Diamines in Dry and Humid Conditions: A Theoretical Approach.

This work is a mechanistic study of the CO2 reaction with diamines under both dry and wet conditions. All protic α,ω-diamines R1H1N1-(CH2)n-N2H2R2, with n = 1-5 and R1 and R2 = H and/or CH3, were investigated. Depending on the nature of the diamine, the reaction was found to follow one of two concerted asynchronous reaction mechanisms with a zwitterion hidden intermediate. Both mechanisms involved two processes. The first process consisted of a nucleophilic attack of the nitrogen N1 of the first amine group on the carbon of CO2, accompanied by the transfer of a hydrogen atom H1 from N1 to the nitrogen N2 of the second amine group, leading to the formation of a carbamate zwitterion. The subsequent process corresponds to the transfer of a hydrogen atom H2 from the second amine group N2 to an oxygen atom of CO2, thus ending the reaction by the formation of carbamic acid. The structure of the zwitterion hidden intermediate was determined using the reactive internal reaction coordinates (RIRC), a reaction pathway visualization tool, consisting of a 3D representation of the potential energy versus the internuclear distances N2-H1 and N2-H2, which correspond to the bond being formed and the bond being broken, respectively. The life span of the transitory species, i.e., the zwitterion, was found to depend on the nature of the second amine group. For primary amines, the life span of the zwitterion was "short", whereas for secondary amines, it was "long". The corresponding mechanisms were termed the "early" and "late" asynchronous mechanism, respectively. Regardless of the mechanism, the activation barriers were found to decrease with the length of the carbon chain linking the two amine groups, with an asymptotic behavior from n = 4. Involvement of a water molecule generates a significant catalytic effect for diamines with short carbon chains (n < 4), whereas for longer chain diamines, water has a slightly adverse effect.

In Search of Preferential Macrocyclic Hosts for Sulfur Mustard Sensing and Recognition: A Computational Investigation through the New Composite Method r2SCAN-3c of the Key Factors Influencing the Host-Guest Interactions.

Sulfur mustard (SM) is a harmful warfare agent that poses a serious threat to human health and the environment. Thus, the design of porous materials capable of sensing and/or capturing SM is of utmost importance. In this paper, the interactions of SM and its derivatives with ethylpillar[5]arene (EtP[5]) and the interactions between SM and a variety of host macrocycles were investigated through molecular docking calculations and non-covalent interaction (NCI) analysis. The electronic quantum parameters were computed to assess the chemical sensing properties of the studied hosts toward SM. It was found that dispersion interactions contributed significantly to the overall complexation energy, leading to the stabilization of the investigated systems. DFT energy computations showed that SM was more efficiently complexed with DCMP[5] than the other hosts studied here. Furthermore, the studied macrocyclic containers could be used as host-based chemical sensors or receptors for SM. These findings could motivate experimenters to design efficient sensing and capturing materials for the detection of SM and its derivatives.

Evaluation of a new series of pyrazole derivatives as a potent epidermal growth factor receptor inhibitory activity: QSAR modeling using quantum-chemical descriptors.

Pyrazole derivatives correspond to a family of heterocycle molecules with important pharmacological and physiological applications. At present, we perform a density functional theory (DFT) calculations and a quantitative structure-activity relationship (QSAR) evaluation on a series of 1-(4,5-dihydro-1H-pyrazol-1-yl) ethan-1-one and 4,5-dihydro-1H-pyrazole-1-carbothioamide derivatives as an epidermal growth factor receptor (EGFR) inhibitory activity. We thus propose a virtual screening protocol based on a machine-learning study. This theoretical model relates the studied compounds' biological activity to their calculated physicochemical descriptors. Moreover, the linear regression function is used to validate the model via the evaluation of Q2ext and Q2cv parameters for external and internal validations, respectively. Our QSAR model shows a good correlation between observed activities IC50 and predicted ones. Our model allows us to mitigate time-consuming problems and waste chemical and biological products in the preclinical phases.

A Unified Approach to CO2-Amine Reaction Mechanisms.

A unified CO2-amine reaction mechanism applicable to absorption in aqueous or nonaqueous solutions and to adsorption on immobilized amines in the presence of both dry and humid conditions is proposed. Key findings supported by theoretical calculations and experimental evidence are as follows: (1) The formation of the 1,3-zwitterion, RH2N+-COO-, is highly unlikely because not only the associated four-membered mechanism has a high energy barrier, but also it is not consistent with the orbital symmetry requirements for chemical reactions. (2) The nucleophilic attack of CO2 by amines requires the catalytic assistance of a BroÌ·nsted base through a six-membered mechanism to achieve proton transfer/exchange. An important consequence of this concerted mechanism is that the N and H atoms added to the C=O double bond do not originate from a single amine group. Using ethylenediamine for illustration, detailed description of the reaction pathway is reported using the reactive internal reaction coordinate as a new tool to visualize the reaction path. (3) In the presence of protic amines, the formation of ammonium bicarbonate/carbonate does not take place through the widely accepted hydration of carbamate/carbamic acid. Instead, water behaves as a nucleophile that attacks CO2 with catalytic assistance by amine groups, and carbamate/carbamic acid decomposes back to amine and CO2. (4) Generalization of the catalytic assistance concept to any BroÌ·nsted base established through theoretical calculations was supported by infrared measurements. A unified six-membered mechanism was proposed to describe all possible interactions of CO2 with amines and water, each playing the role of a nucleophile and/or BroÌ·nsted base, depending on the actual conditions.

LC-ESI-MS/MS profile of phenolic and glucosinolate compounds in samh flour (Mesembryanthemum forsskalei Hochst. ex Boiss) and the inhibition of oxidative stress by these compounds in human plasma.

Samh flour (Mesembryanthemum forsskalei) is a foodstuff with high protein content, which can be used as a replacement for wheat flour. It is often consumed by Bedouin tribes of northern Saudi Arabia. Very little is known about bioactive molecules present in samh flour, therefore we analyzed its extracts to evaluate the contents of secondary metabolites. A total of 43 secondary metabolites present in 60% MeOH extract of samh flour were tentatively identified using LC-ESI-MS/MS. These compounds represented five major categories: glucosinolates, sinapic acid and sinapoylglycosides, acylated flavonoids, flavonoids, and amide derivatives. Their effect on oxidative damage of proteins and lipids was determined in vitro by assessing levels of protein thiol groups and concentrations of thiobarbituric acid reactive species (TBARS) in human plasma. Obtained results indicated that samh flour is a rich source of compounds with antioxidant activity.