QSAR models for the ozonation of diverse volatile organic compounds at different temperatures.

In order to assess the fate and persistence of volatile organic compounds (VOCs) in the atmosphere, it is necessary to determine their oxidation rate constants for their reaction with ozone (kO3). However, given that experimental values of kO3 are only available for a few hundred compounds and their determination is expensive and time-consuming, developing predictive models for kO3 is of great importance. Thus, this study aimed to develop reliable quantitative structure-activity relationship (QSAR) models for 302 values of 149 VOCs across a broad temperature range (178-409 K). The model was constructed based on the combination of a simplified molecular-input line-entry system (SMILES) and temperature as an experimental condition, namely quasi-SMILES. In this study, temperature was incorporated in the models as an independent feature. The hybrid optimal descriptor generated from the combination of quasi-SMILES and HFG (hydrogen-filled graph) was used to develop reliable, accurate, and predictive QSAR models employing the CORAL software. The balance between the correlation method and four different target functions (target function without considering IIC or CII, target function using each IIC or CII, and target function based on the combination of IIC and CII) was used to improve the predictability of the QSAR models. The performance of the developed models based on different target functions was compared. The correlation intensity index (CII) significantly enhanced the predictability of the model. The best model was selected based on the numerical value of Rm2 of the calibration set (split #1, Rtrain2 = 0.9834, Rcalibration2 = 0.9276, Rvalidation2 = 0.9136, and calibration = 0.8770). The promoters of increase/decrease for log kO3 were also computed based on the best model. The presence of a double bond (BOND10000000 and $10 000 000 000), absence of halogen (HALO00000000), and the nearest neighbor codes for carbon equal to 321 (NNC-C⋯321) are some significant promoters of endpoint increase.

Electronic structure of some thymol derivatives correlated with the radical scavenging activity: theoretical study.

Molecules acting as antioxidants capable of scavenging reactive oxygen species (ROS) are of upmost importance in the living cell. Thymol derivatives exhibit various antioxidant activities and potential health benefits. Exploration of structure-radical scavenging activity (SAR) was approached with a wide range of thymol derivatives. To accomplish this task, the DPPH experimental assay along with quantum-chemical calculations were also employed for these compounds. By comparing the structural properties of the derivatives of interest, their antioxidant activity was explained by the formation of an intramolecular hydrogen bond and the presence of unsaturated double bond (-CHCH substituent) in their radical spices. Moreover, the delocalization of odd electrons in these radicals has been investigated by natural bond orbital analysis and interpretation of spin density maps. Reactivity order of the compound towards the ROS: HO, HOO, and O2(-) was found to be as HO>HOO >> O2(-).

Theoretical investigation on antioxidant activity of bromophenols from the marine red alga Rhodomela confervoides: H-atom vs electron transfer mechanism.

Bromophenols are known as antioxidant radical scavengers for some biomolecules such as those in marine red alga. Full understanding of the role played by bromophenols requires detailed knowledge of the radical scavenging activities in probable pathways, a focus of ongoing research. To gain detailed insight into two suggested pathways, H-atom transfer and electron transfer, theoretical studies employing first principle quantum mechanical calculations have been carried out on selected bromophenols. Detailed investigation of the aforementioned routes revealed that upon H-atom abstraction or the electron transfer process, bromophenols cause an increase in radical species in which the unpaired electron appears to be delocalized as much as possible over the whole aromatic ring, especially in the bromine substituent. The O-H bond dissociation energies (BDEs) and ionization potential energies (IPs) are reported at the B3LYP level of theory, providing the first complete series of BDEs and IPs for bromophenols. The observations are compared to those of other antioxidants for which BDEs and IPs have been previously obtained.

Interactions of coinage metal clusters with histidine and their effects on histidine acidity; theoretical investigation.

Understanding the nature of interaction between metal nanoparticles and biomolecules such as amino acids is important in the development and design of biosensors. In this paper, binding of M(3) clusters (M = Au, Ag and Cu) with neutral and anionic forms of histidine amino acid was studied using density functional theory (DFT-B3LYP). It was found that the interaction of histidine with M(3) clusters is governed by two major bonding factors: (a) the anchoring N-M and O-M bonds and (b) the nonconventional N-H···M and O-H···M hydrogen bonds. The nature of these chemical bonds has been investigated based on quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. In the next step, the effects of Au, Ag and Cu metal clusters on the gas-phase acidity of weak organic acid (histidine) have been explored. The acidity of isolated histidine was compared with the acidity of its Au(3)-, Ag(3)- and Cu(3)-complexed species. Results indicate that upon complexation with M(3) clusters (at 298 K), the gas-phase acidity (GPA) of histidine varies from 339.5 to 312.3, 315.0, and 313.7 kcal mol(-1) for Au(3)-, Ag(3)- and Cu(3)-His complexes, respectively (i.e., its dissociation becomes much less endothermic). These values indicate that a weak organic acid can be converted to a super acid when it is complexed with metal clusters. Also, in order to investigate the acidity value of the imidazole moiety in histidine, histidine methyl ester (His-OMe) was selected. Similarly, the acidity of this compound was compared with the acidity of their Au(3), Ag(3) and Cu(3)-complexed species. After complexation with M(3) clusters at 298 K, the gas-phase acidity (GPA) of His-OMe varies from 333.0 to 280.0, 304.2 and 291.5 kcal mol(-1), respectively. Moreover, pK(a) values were determined in water for isolated and complexed species of His and His-OMe. The resulting pK(a) values were found to decrease upon complexation with M(3) clusters.