There is robust evidence of the hypochlorous acid (HClO)-mediated damage in biomolecules, and nicotine boosts the chlorination potency of HClO. We present experimental and theoretical evidence of the mechanism by which nicotine catalyzes the chlorination of pyranine. The rate constants for chlorination of pyranine by HClO were measured in the presence (5.3 × 105 mol 1 L s-1) and absence of nicotine (4.2 × 103 mol-1 L s-1), revealing the catalytic effect of the alkaloid. Density functional theory (DFT) calculations, based on B3LYP-GD3(BJ)/6-311++G(3df,2p)/SMD(Water)//B3LYP-GD3(BJ)/6-311++G(2d,p)/SMD(Water) level of theory, were performed and showed a decreased activation energy for chlorine transfer and hydrogen abstraction when nicotine chloramine intermediated the reaction. The atomic polar tensor (APT) charges on the chlorine atom of HClO (+0.084) were lower than the chlorine of nicotine chloramine (+0.149), revealing the higher electrophilic character of nicotine chloramine. In conclusion, the increased electrophilic nature of HClO provoked by nicotine explains its catalytic effect.

Imiquimod (IMQ), an immune response modifier, is used for topical treatment of basal cell carcinoma and actinic keratosis. The very poor aqueous solubility of imiquimod gives rise to difficulties in designing aqueous formulations with this drug. One approach that is widely used to enhance drug solubility is complexation with cyclodextrins. The formation of the inclusion complex between IMQ and β-cyclodextrin was investigated in solution and in solid state. IMQ aqueous solubility was improved in the presence of citric acid. The experimental results and molecular modeling indicated the formation of the inclusion complex in aqueous solution of citric acid pH 3.0; however, the low apparent stability constant suggested weak interaction between β-cyclodextrin and IMQ which hampered the use of this approach to improve imiquimod aqueous solubility and the development of an aqueous formulation containing IMQ in the same concentration as in the commercial product.

Benzbromarone (BZB) is a drug that has diuretic activity and is used in the gout treatment. Its therapeutic efficiency is decreased by its low water solubility (11.8 mg L-1) and highly hydrophobic aspect (logP 2.7), which are responsible for affecting its intestinal absorption and bioavailability. BZB inclusion complex (IC) aims at increasing the drug solubility in water and reduce adverse effects resulting in more efficient formulations. The coprecipitation encapsulating method was used to obtain the IC of BZB in β-cyclodextrin (β-CD) and the complex (BZB@β-CD) was characterized via physical-chemical analysis. A comparative study of time-dependent density functional theory (TD-DFT) and configuration interaction singles (CIS), along with “our own N-layered integrated molecular orbital and molecular mechanics” (ONIOM) method, has been carried out on the UV-Vis absorption of BZB and BZB@β-CD. The qualitative description of the simulated spectrum, given by ONIOM(CIS:PM6), is in accord with the formation of BZB@β-CD. It only became possible when phosphate buffer (pH 7.4) was used to prepare the solutions, since the complex formation did not occur in deionized water or buffered acid. Furthermore, by using the Job plot, the Scatchard method and fluorescence, it was possible to conclude that the complex molecular stoichiometry was 1:1 (1 BZB to 1 β-CD).

The fact that the dissymmetry lgeb (g-factor) of camphor is large has been known for decades, and the interpretation of the observed data has also been known for a long time. However, due to the ability of quantum chemical methods to describe chiroptical phenomena more appropriately, additional approaches based on these methods have been successful employed. The g-factor lgebra in S-camphor and L-tryptophan have been investigated by UV-Vis and electronic circular dichroism (ECD) spectroscopies of the n ® p* electronic transition. Time-dependent density functional theory (TD-DFT) calculations at CAM-B3LYP/6-311++G(3df,2p)//B3LYP/6-311++G(2d,p) level of theory including Grimme’s dispersion effects have been performed. The lgebra effect was added using solvation model based on density (SMD) approach in solvation environment. The results permit insights into the ground and excited states electronic properties associated with the g-factor. The theoretical spectra showed good similarity with the experimental ones. The theoretical ECD of camphor was found at 282 nm, whereas the experimental shows its maximum at 290 nm. Regarding the maximum value of the molar absorptivity lgebrante, the theoretical and experimental values were 16.2 and 30.2 M-1 cm-1, respectively. The same concordance was obtained for g-factor, as follows: -0.0445 and -0.0886, for experimental and theoretical results, respectively.

The effect of selenate and selenite enrichment on mineral composition of a red type of lettuce cv. “Veneza roxa” was evaluated using inductively coupled plasma-optical emission spectroscopy (ICP OES), molecular modeling and principal component analysis (PCA). Both Se species did not show toxicity, while selenate promoted the greatest Se accumulation by the plant. There was an increase of 886 µg of Se per 100 g of fresh sample at different concentrations of selenate, but for selenite the maximum variation was only of 114 µg per 100 g. Selenate promoted the absorption of Mo and S and the reduction of K, Mn and P, meanwhile selenite increased Mn and decreased Mo accumulation. Copper and Fe absorption was negatively affected, Ca and Mg showed a slight increase, and Na and Zn were not affected by Se species. Despite the changes in the nutritional balance, Se-enriched lettuce can still be considered a potential dietary source of this essential element.

One of the goals of this manuscript is to celebrate the forty years of the SBQ (Sociedade Brasileira de Química). We believe using historical analysis could benefit our researchers to overcome the challenges ahead, look into the future, to the scientific progress and the way science increases its problem-solving ability. There are several topics covered by the challenges in Physical Chemistry: nanoscience and nanotechnology, single molecule studies, gas phase photochemistry and photophysics, molecular structure, spectroscopy, reaction dynamics, interfacial phenomena, energy, and so on. However, the critical challenge for our Division still is to create a desired link between experimental approaches and theoretical knowledge.

<p>The molecular geometries of boraphosphabenzene (BP-benzene) and boron phosphorus coronene (BP-coronene) can be misinterpreted when they are obtained from density functional theory (DFT) calculations. In this study, we found that some exchange-correlation (XC) functionals yielded a distorted geometry of the above molecules when P atoms are present in their resonance structures. This phosphorus pyramidalization may be due to spurious errors caused by using these functionals. To verify this behavior, the electronic structures of BP-benzene and BP-coronene were studied using sixteen functionals (B3LYP, B97D, BHLYP, BP96, PBE, PBE0, PWLDA, Slater-Dirac-exchange, TPSS, M05, M06, M062X, M08HX, M11, wB97 and wB97X-D) with the SVP or TZVPP basis sets. The calculations were carried out using the TURBOMOLE and GAMESS programs. The geometry optimization calculations were carried out for each functional using both of the basis sets. Two different initial geometries, plane (D_3h symmetry) and distorted (C1 symmetry) were considered. The optimized geometries of the BP-systems obtained at the MP2/TZVPP and CC2/TZVPP levels of theory exhibited D_3h symmetry. These calculations were used as a reference and compared with those obtained from DFT. The optimized geometries obtained from DFT were found to exhibit C₁ symmetry for the majority of the XC functionals.</p>

In this study we examine the electronic and molecular structures of the [51 knot···(PF6)10]+ pentafoil knot system and report calculated interaction energies that result from halides (X = F, Cl, Br, and I) localized at the center of the [51knot···(PF6)9]X molecular structure. The equilibrium geometries were fully optimized at the ONIOM(M06/6-31G(2d,p):PM6) level of theory, starting from an initial geometry for the pentafoil knot obtained from experimental X-ray data. The molecular systems were divided into two layers, for which the M06/6-31G(2d,p) level of theory was used to describe the high layer ([C4H6]5X- structure) and the PM6 semiempirical method was employed for the low layer. The calculated electronic energies show that the interaction between the fluorine anion and the pentafoil knot produces the most stable structure, whereas an unfavorable interaction is observed for iodide due to the diffuse character of its electronic cloud. Using basis set superposition error (BSSE) correction techniques, the observed values of the interaction are -0.201 hartrees for the fluoride ion and -0.100 hartrees for iodide.