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.

Versatile anti-infective properties of pyrido- and dihydropyrido[2,3-d]pyrimidine-based compounds

A series of 1H-indeno[2',1':5,6]dihydropyrido[2,3-d]pyrimidine and 1H-indeno[2',1':5,6]pyrido[2,3-d]pyrimidine derivatives was prepared and screened for antiparasitic and viral RNase H inhibitory activity. Several compounds showed considerable activity against Toxoplasma gondii parasites and Leishmania major amastigotes, which warrants further investigation. Based on the structural similarities of certain derivatives with common viral RNase H inhibitors, a HIV-1 RNase H assay was used to study the RNase H inhibition by selected test compounds. Docking of active derivatives into the active site of the HIV-1 RNase H enzyme was carried out. The new compound 2a, inactive in the antiparasitic tests, showed distinct HIV-1 RNase H inhibition. Thus, ring substitution determines antiparasitic or HIV-1 RNase H inhibitory activity of this promising compound class.

Evaluation of the Antiparasitic and Antifungal Activities of Synthetic Piperlongumine-Type Cinnamide Derivatives: Booster Effect by Halogen Substituents

A series of synthetic N-acylpyrrolidone and -piperidone derivatives of the natural alkaloid piperlongumine were prepared and tested for their activities against Leishmania major and Toxoplasma gondii parasites. Replacement of one of the aryl meta-methoxy groups by halogens such as chlorine, bromine and iodine led to distinctly increased antiparasitic activities. For instance, the new bromo- and iodo-substituted compounds 3 b/c and 4 b/c showed strong activity against L. major promastigotes (IC50 =4.5-5.8 μM). Their activities against L. major amastigotes were moderate. In addition, the new compounds 3 b, 3 c, and 4 a-c exhibited high activity against T. gondii parasites (IC50 =2.0-3.5 μM) with considerable selectivities when taking their effects on non-malignant Vero cells into account. Notable antitrypanosomal activity against Trypanosoma brucei was also found for 4 b. Antifungal activity against Madurella mycetomatis was observed for compound 4 c at higher doses. Quantitative structure-activity relationship (QSAR) studies were carried out, and docking calculations of test compounds bound to tubulin revealed binding differences between the 2-pyrrolidone and 2-piperidone derivatives. Microtubules-destabilizing effects were observed for 4 b in T. b. brucei cells.

Fingerprinting of two an acylated polyoxypregnane glycosides from Caralluma quadrangula (Forssk.) N.E.Br. using UPLC-ESI-Q-TOF and computational study

The present study has tentatively elucidated the structure of two acylated polyoxypregnane glycosides from Caralluma quadrangula (Forssk.) N.E.Br. (CQ). The analyses were performed using an electrospray-ionization quadrupole time-of-flight (ESI-Q-TOF) mass spectrometer in positive ionization modes to explore fragmentation pathways. The used ionization mode provided consistent and/or complementary information for most of the pregnane glycosides, their fragmentation sequences, and their aglycones. Presumably, this is due to higher efficiency, sensitivity, and better selectivity of the mass spectrometry-based method. The present experimental and theoretical report deals with the characteristic fragmentation behaviors of two acylated polyoxypregnane glycosides CQ1 and CQ2 from the aerial parts of C. quadrangular. A DFT Study was performed to elucidate the position of ikemoyl, and benzoyl residues in compounds CQ1 and CQ2, respectively.

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.

Comprehensive polyoxypregnane glycosides report in Caralluma quadrangula using UPLC-ESI-Q-TOF and their antioxidant effects in human plasma

ETHNOPHARMACOLOGICAL RELEVANCE

Caralluma quadrangula (Forssk.) N.E.Br. (Syns: = Stapelia quadrangula Forssk. = Monolluma quadrangula Forssk.) is an indigenous member of the genus Caralluma and it is a rather common species on rocky hillsides in the southwestern part of Saudi Arabia. Several members of this genus have found medicinal uses in the treatment of rheumatism, diabetes, leprosy and as antiseptics and disinfectants. All parts are edible but rather more bitter and can cause diarrhea.

AIM OF THE STUDY

The present report was tentatively elucidated the structure of acylated and non-acylated polyoxypregnane glycosides from Caralluma quadrangula.

MATERIALS AND METHODS

The analyses were performed using an electrospray-ionization quadrupole time-of-flight (ESI-Q-TOF) mass spectrometer in both positive and negative ionization modes to explore fragmentation pathways. The antioxidant and prooxidant properties of the different mobility portions of human plasma were evaluated in vitro using thiobarbituric acid reactive substance assay (TBARS).

RESULTS

The analyses showed sixty-five characteristic ion peaks which could be more efficient to assignment the aglycones and fragmentation sequences of sugar moieties. The used ionization modes provided consistent and/or complementary information for most of the pregnane glycosides, their fragmentation sequences, and their aglycones. A DFT Study was performed to elucidate the neutral loss of H₂O molecules sequences from aglycones and the esterification linkage.

CONCLUSIONS

This report could be useful to reduce material consuming and time in phytochemistry analysis of the different medicinal plants. The two portions significantly depleted TBARS were subjected to autoperoxidation assay in the presence of hydrogen peroxide.

A Computational Approach to Nontraditional Intrinsic Luminescence: Vibrationally Resolved Absorption and Fluorescence Spectra of DABCO

Recently, so-called "nontraditional intrinsic luminescence" has been reported in several macromolecular systems. Although DABCO (1,4-diazabicyclo[2.2.2]octane) is the first system in which the effect was observed, a thorough analysis of the optical properties of the molecule, which would reveal the origin of this mysterious effect, is still pending. We perform an advanced post-Hartree-Fock treatment of the low-lying electronic states of this molecule, which need to be described with care because of their pronounced Rydberg character. We take a deeper look into the low-lying electronic transitions of DABCO targeting the explanation of the complex vibronic structures of its absorption and fluorescence spectra. Two electronic states, the ¹E'(n₊3p_xy) and ¹A₂^″(n₊3p_z) states, contribute to the absorption spectrum in the 39000-46000 cm^-1 spectral range. We also reveal the spectroscopic signature of the ¹A₂^″(n₊3p_z) state. The analyses of the contributions of individual vibrational normal modes allowed the identification of those giving rise to the complex vibronic structures of the spectra. Fluorescence emission arises from the vibronic coupling of the one-photon forbidden transition between the ¹A₁^'(n₊3s) state and the electronic ground state. The spectrum, which can be interpreted in terms of populating a few vibrational normal modes, is shifted toward visible wavelengths mostly due to the forced interaction of the lone pair electrons of the two nitrogen atoms. Our work on DABCO may help to rationalize the luminescence of more complex systems containing tertiary amine groups.

Carbon dioxide adsorption and activation on ionic liquid decorated Au(111) surface: A DFT study

We use first principle approaches to study the adsorption and catalytic activation mechanism of CO₂ on ionic liquids (ILs, [C_nMIm]⁺[Cl]^- (n = 0-6)) attached to a Au(111) surface. The adsorption of CO₂ at this liquid-solid model interface occurs via either (i) parallel π-stacking mode or (ii) CO₂ oxygen lone pair (lp)···π interaction. These CO₂ physisorption modes, which depend on the CO₂ landing angle at this interface, are identified as an efficient way to activate CO₂ and its further conversion into value-added products. For illustration, we discuss the conversion of CO₂ into formic acid where the ILs@Au(111) decorated interface allows reduction of the activation energy for the CO₂ + H₂ → HCOOH reaction. In sum, our electrode/electrolyte based interface model provides valuable information to design novel heterogeneous catalysts for CO₂ conversion. Indeed, our work establishes that a suitable interface material is enough to activate CO₂.

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 Q² _ext and Q² _cv 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.

S2O2q+ (q = 0, 1, and 2) Molecular Systems: Characterization and Atmospheric Planetary Implications

We use accurate ab initio methodologies at the coupled cluster level ((R)CCSD(T)) and its explicitly correlated version ((R)CCSD(T)-F12) to investigate the electronic structure, relative stability, and spectroscopy of the stable isomers of the [S₂O₂] system and of some of its cations and dications, with a special focus on the most relevant isomers that could be involved in terrestrial and planetary atmospheres. This work identifies several stable isomers (10 neutral, 8 cationic, and 5 dicationic), including trigonal-OSSO, cis-OSSO, and cyc-OSSO. For all these isomers, we calculated geometric parameters, fragmentation energies, and simple and double ionization energies of the neutral species. Several structures are identified for the first time, especially for the ionic species. Computations show that in addition to cis-OSSO and trans-OSSO proposed for the absorption in the near-UV spectrum of the Venusian atmosphere other S₂O₂, S₂O₂⁺, and S₂O₂²⁺ species may contribute. Moreover, the characterization of the stability of singly and doubly charged S₂O₂ entities can also be used for their identification by mass spectrometry and UV spectroscopy in the laboratory or in planetary atmospheres. In sum, the quest for the main UV absorber in Venus' atmosphere is not over, since the physical chemistry of sulfur oxides in Venus' atmosphere is far from being understood.

Structural, QSAR, machine learning and molecular docking studies of 5-thiophen-2-yl pyrazole derivatives as potent and selective cannabinoid-1 receptor antagonists

We performed a structural study followed by theoretical analysis of the chemical descriptors and biological activity of a series of 5-thiophen-2-yl pyrazole derivatives as potent and selective cannabinoid-1 (CB1) receptor antagonists.

Theoretical Characterization of the Structure and Spectroscopy of HCNO2 Isomers and Applications

We carried out a theoretical, fully ab initio, investigation of the stable forms of the [H,C,N,O,O] pentatomic molecular system, whose isomers are involved in fundamental combustion and atmospheric processes and are of potential interest for astrophysics. By adopting the MP2 and CCSD(T) electronic structure methods, combined with extrapolations to the complete basis set (CBS) limit, we characterized 20 low-energy isomers, excluding weak van der Waals complexes. For these molecules, we determined a set of geometrical parameters, relative energies, anharmonic vibrational frequencies, IR intensities, and fragmentation/formation energies from various atomic and/or molecular fragments. We discuss the relevance of the present findings for the search of new molecular species in astrophysical and atmospheric media and give suggestions for their possible detection in laboratory experiments. The set of data provided by the present work should facilitate the identification of these species from their gas-phase and low-temperature solid matrix spectra, whenever measured.

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 Bro̷nsted 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 Bro̷nsted 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 Bro̷nsted base, depending on the actual conditions.

Electrospray ionization mass spectrometry characterization of ubiquitous minor lipids and oligosaccharides in milk of the camel (Camelus dromedarius) and their inhibition of oxidative stress in human plasma

The aim of this study was to characterize minor lipids in methanol fraction extracted from raw camel milk after loading it on a water-preconditioned short C18 open column and fractionating with a gradient of methanol/water. The C18 column showed high fractionation efficiency of minor lipids, such as glycosphingolipids, lipopolysaccharides, or oligosaccharides, when compared with other constituents, in particular polysaccharides, proteins, and free fatty acids. Liquid chromatography electrospray ionization tandem mass spectrometry in negative ion mode was used to identify 21 new glycosphingolipids, lipopolysaccharides, and oligosaccharides. Electrospray ionization tandem mass spectrometry was qualified to provide relevant data for recognizing the molecular mass, glycosylation sequences, and structure of saccharide moieties for the revealed compounds. The sequence of combinations of one selected lipopolysaccharide, which was considered the backbone of the remaining lipopolysaccharides, was confirmed in a density functional theory study. The obtained results showed that the tested fraction is a rich source of glycosphingolipids, lipopolysaccharides, and oligosaccharides with antioxidant activity.

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.

Synthesis and characterization of new thiazolidinones containing coumarin moieties and their antibacterial and antioxidant activities

New coumarin derivatives, namely (2-(4-methyl-2-oxo-2H-chromen-7-yloxy)-N-(4-oxo-2-phenylthiazolidin-3-yl)acetamide, N-(2-(3-methoxyphenyl)-4-oxothiazolidin-3-yl)-2-(4-methyl-2-oxo-2H-chromen-7-yloxy)acetamide, 2-(4-methyl-2-oxo-2H-chromen-7-yloxy)-N-(4-oxo-2-(2,3,4trimethoxyphenyl)thiazolidin-3-yl)acetamide and N-(2-(4-bromophenyl)-4-oxothiazolidin-3-yl)-2-(4-methyl-2-oxo-2H-chromen-7-yloxy)acetamide) were synthesized starting from 4-methyl-7-hydroxycoumarin. The structures of the obtained compounds were confirmed by analytical IR and NMR spectra to elucidate the different positions of protons and carbons and as well as theoretical studies (DFT/B3LYP). The new compounds were screened for antibacterial activity. Most of them are more active against E. coli S. aureus and B. subtilis than standard references.