Density functional theory (DFT) was used to calculate the properties of a set of molecular descriptors for 14 fluoroquinolone with anti-Pseudomonas aeruginosa activity. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were employed in order to reduce dimensionality and investigate the effectiveness of variables, i. e., which subset of variables should be more effective for classifying fluoroquinolones according to their antibacterial activities against P. aeruginosa. The PCA results showed that the variables ELUMO, ΔEHL, Q5, Q6, logP, MR, and MP are responsible for the separation between compounds with higher and lower anti-P. aeruginosa activity. The HCA results were similar to those obtained using PCA. By using the chemometric results, four synthetic compounds were analyzed through the PCA and HCA. Two of them are proposed as active molecules against P. aeruginosa. The result is consistent with the observations of clinic experiments. The methodologies of PCA and HCA provide a reliable rule for classifying new fluoroquinolones with anti-P. aeruginosa activity.

The S–NO bond dissociation energies (BDEs) for S-nitrosothiols (RSNO) compounds are computed using the DFT (B3LYP, B3PW91 and B3P86) with the 6-31g∗∗ and 6-311g∗∗ basis set. By comparing the computed energies and experimental results, we find that the B3PW91/6-31g∗∗ and B3P86/6-311g∗∗ method can give good results of BDE, which have the mean absolute deviations of 7.39 and 7.57 kJ/mol, respectively. Considering the smaller maximum difference, we recommend the B3PW91 method combined with 6-31g∗∗ basis set, as a satisfactory method of computing the BDEs for removal of the NO group in RSNO compounds. In addition, we find that the mean absolute deviation reduces from 9.07 to 7.39 kJ/mol when the 6-311g∗∗ basis set in the B3PW91 model is replaced by 6-31g∗∗ basis set, which proves that B3PW91 DFT method is sensitive to the basis sets.

The heats of formation of several nitroester compounds have been calculated at the levels of B3LYP, B3PW91 and B3P86 theories in conjunction with the 6-31g∗, 6-31g∗∗, 6-311g∗ and 6-311g∗∗ basis sets. Isodesmic reactions of seven nitroester compounds were selected in order to study their heats of formation at 298.15 K. The heats of formation obtained from the isodesmic reaction at the B3P86/6-31g∗∗ level are in reasonable agreement with the experimental results. But the heats of formation obtained from the atomization reaction at these levels are much too lower. Using B3P86/6-31g∗∗ method, the heats of formation of other five nitroesters are computed. In addition, it is noted that the computed heat of formation increases when the number of methylene group increases for normal chain alkyl nitrate and nitrite and the average increment of heat of formation is about 3.7 kcal/mol.