Antimicrobial Activity and Molecular Docking Studies of the Biotransformation of Diterpene Acanthoic Acid Using the Fungus Xylaria sp.

Biotransformations are reactions mediated by microorganisms, such as fungi. These bioreactions have high chemo- and stereoselectivity on organic substrates and can be applied in the search for new bioactive compounds. In this study, acanthoic acid (AA) was biotransformed using the fungus Xylaria sp., giving the novel compound 3ß,7ß-dihydroxyacanthoic acid (S1). Both the AA and the product S1 were tested against Gram-positive and Gram-negative bacteria. To identify and validate possible biological targets as enzymes or proteins involved in the activity observed in vitro, we used the molecular docking method. Hydroxylation at the C-3 and C-7 positions of the biotransformation product enhanced its activity against Escherichia coli as well as its binding affinity and interactions with superoxide dismutase 1 (SOD1; PDB ID 4A7G). Based on our results, the SOD1 enzyme was suggested to be a possible target for the antioxidant activity of product S1.

Photoinduced degradation of indigo carmine: insights from a computational investigation.

In this work, we present a computational investigation on the photoexcitation of indigo carmine (IC). Physical insights regarding IC photoexcitation and photolysis were obtained from a fundamental perspective through quantum chemistry computations. Density functional theory (DFT) was used to investigate the ground state while its time-dependent formalism (TD-DFT) was used for probing excited state properties, such as vertical excitation energies, generalized oscillator strengths (GOS), and structures. All the computations were undertaken using two different approaches: M06-2X/6-311+G(d,p) and CAM-B3LYP/6-311+G(d,p), in water. Results determined using both methods are in systematic agreement. For instance, the first singlet excited state was found at 2.28 eV (with GOS = 0.4730) and 2.19 eV (GOS = 0.4695) at the TD-DFT/CAM-B3LYP/6-311+G(d,p) and TD-DFT/M06-2X/6-311+G(d,p) levels of theory, respectively. Excellent agreement was observed between the computed and the corresponding experimental UV-Vis spectra. Moreover, results suggest IC undergoes photodecomposition through excited state chemical reaction rather than via a direct photolysis path. To the best of our knowledge, this work is the first to tackle the photoexcitation, and its potential connections to photodegradation, of IC from a fundamental chemical perspective, being presented with expectations to motivate further studies.

Probing structural properties and antioxidant activity mechanisms for eleocarpanthraquinone.

In this work, we present a computational investigation on the structure and energetics of eleocarpanthraquinone, a newly isolated polyphenolic anthrone-antraquinone. Properties such as bond lengths, angles, atomic charges, bond dissociation enthalpies (BDEs), and ionization potential (IP) were determined through the use of density functional theory (DFT). The B3LYP and M06-2X exchange-correlation functionals were employed along with the 6-31+G(d,p), 6-31+ +G(d,p), and 6-311+G(d,p) basis sets for performing computations in the gas-phase, water, methanol, and ethanol. The conformation presenting all the hydroxyl groups undergoing hydrogen-bond interactions with neighboring oxygen atoms (conformation 5) was assigned as the most stable structure while its counterpart presenting no hydrogen-bond interaction was found to be 36.45 kcal/mol less stable than conformation 5 in the potential energy surface probed at the B3LYP/6-311+G(d,p) level of theory in the gas-phase, for instance. More importantly, the lowest O-H bond dissociation enthalpy was determined to be 93.80 kcal/mol at the B3LYP/6-311+G(d,p) level of theory in water against the 146.58 kcal/mol regarding the IP computed at the same approach, suggesting the hydrogen atom transfer mechanism as being preferred over the single electron transfer mechanism in regards to the antioxidant potential for the case of eleocarpanthraquinone; the same conclusion was drawn from the outcomes of all the other approaches used.

A computational study on the reaction between fisetin and 2,2-diphenyl-1-picrylhydrazyl (DPPH).

The strategy of investigating the antioxidant potential of flavonols through the explicit modeling of chemical reactions (initiated to be employed in a previous work from our group) was taken further in this work. Therefore, a theoretical investigation on the reaction between fisetin and 2,2-diphenyl-1-picrylhydrazyl (DPPH) is presented. All the computations were performed using the density functional theory with the B3LYP functional along with the 6-31G(d,p) basis set. Structural, energetic quantities (ΔG and ΔG++), and reaction rates were probed in order to provide information on the antioxidant activity and to explore the contributions of each hydroxyl group to the referred property. According to the results obtained for the thermodynamic properties, fisetin presents antioxidant potential similar to quercetin (behavior that is also observed experimentally). In addition, the order of contribution of each OH group to the antioxidant potential was found to be 4'-ArOH (the most contributor, presenting ΔG = -5.17 kcal/mol) → 3'-ArOH (ΔG = -3.35 kcal/mol) → 3-ArOH (ΔG = -1.64 kcal/mol) → 7-ArOH (ΔG = 7.72 kcal/mol). These observations are in consistent agreement with the outcomes of other computational investigations performed using bond dissociation enthalpies (BDEs) as descriptors for the antioxidant activity. Therefore, the methodology employed in this work can be used as an alternative for probing antioxidant potential of compounds derived from fisetin. Graphical Abstract Illustrative scheme of the PES mapping in terms of hydrogen atom transfer from fisetin 3-ArOH to the nitrogen centered DPPH.

Natural products from Pluchea sagittalis act as inhibitors of photosynthesis in vitro.

Four compounds were isolated from roots and aerial parts of Pluchea sagittalis (Asteraceae), 3, 5-dihydroxy-6, 7, 3', 4'-tetramethoxiflavunol (1), 5-hydroxymethylfurfural (2), 3, 4-dimethoxybenzaldehyde (3) and 2, 3, 4-trihydroxybenzaldeyde (4). Their herbicidal potential was detected by polarographic techniques. All of them inhibited the non-cyclic electron transport on basal, phosphorylating and uncoupled conditions from H2O to methylviologen (MV); thus, they act as Hill reaction inhibitors. Studies on fluorescence of chlorophyll a (ChL a) indicated they have different modes of interaction and inhibition sites on the photosystem II electron transport chain; 1-3 have interacted with the acceptor side while 4 has interacted at the donor side.

Examining the reaction between antioxidant compounds and 2,2-diphenyl-1-picrylhydrazyl (DPPH) through a computational investigation.

In this work, we present a computational investigation on the reactions between two well-known antioxidants (quercetin and morin) and 2,2-diphenyl-1-picrylhydrazyl (DPPH). A density functional theory (DFT) approach with the B3LYP functional and the 6-31G(d,p) basis set was used for the simulations. The structural and energetic parameters (Gibbs free-energy, ΔG, and Gibbs free-energy of activation, ΔG++) were determined to provide information on the antioxidant activity as well as to evaluate the contributions of each hydroxyl group to the referred property. According to the results obtained, quercetin presented three hydroxyls as being thermodynamically spontaneous in the reaction with DPPH (4[Formula: see text]-ArOH, 3[Formula: see text]-ArOH, and 3-ArOH, with ΔG = -4.93 kcal/mol, -2.89 kcal/mol, and -1.87 kcal/mol, respectively) against only two in the case of morin (2[Formula: see text]-ArOH and 3-ArOH, with ΔG = -7.56 kcal/mol and -4.57 kcal/mol, respectively). Hence, quercetin was found to be a more efficient antioxidant, which is in agreement with different experimental and computational investigations of bond dissociation enthalpies (BDEs). However, the order of contribution of the OH groups of each compound to the antioxidant potential present some differences when compared to what was seen in the previous investigations, especially for morin. These findings are in contrast to what was observed in studies based on the determinations of BDEs. Therefore, experimental investigations on the hydrogen-atom transfer mechanism (HAT) for both compounds are encouraged in order to clarify these observations.

Cyanate as an Active Precursor of Ethyl Carbamate Formation in Sugar Cane Spirit.

The thermodynamic and kinetic aspects of ethyl carbamate (EC) formation through the reaction between cyanate and ethanol were investigated. The rate constant values for cyanate ion decay and EC formation are (8.0 ± 0.4) × 10(-5) and (8.9 ± 0.4) × 10(-5) s(-1), respectively, at 25 °C in 48% aqueous ethanolic solution at pH 4.5. Under the investigated experimental conditions, the rate constants are independent of the ethanol and cyanate concentrations but increase as the temperature increases (ΔH1(⧧) = 19.4 ± 1 kcal/mol, ΔS1(⧧) = −12.1 ± 1 cal/K, and ΔG1(⧧) = 23.0 ± 1 kcal/mol) and decrease as the solution pH increases. According to molecular modeling (DFT) that was performed to analyze the reaction mechanism, the isocyanic acid (HNCO) is the active EC precursor. The calculated ΔG1(⧧), ΔH1(⧧), and ΔS1(⧧) values are in very good agreement with the experimental ones.

Unexpected NO transfer reaction between trans-[Ru(II)(NO+)(NH3)4(L)]3+ and Fe(III) species: observation of a heterobimetallic NO-bridged intermediate.

The reaction between trans-[Ru(II)(NO(+))(NH3)4(L)](3+), L = ImN, IsN, Nic, P(OMe)3, P(OEt)3, and P(OH)(OEt)2, and the Fe(III) species [Fe(III)(TPPS)], metmyoglobin, and hemoglobin was monitored by UV-vis, EPR, and electrochemical techniques (DPV, CV). No reaction was observed when L = ImN, IsN, Nic, and P(OH)(OEt)2. However, when L = P(OMe)3 and P(OEt)3, the reaction was quantitative and the products were trans-[Ru(III)(H2O)(NH3)4(P(OR)3)](3+) and [Fe(II)(NO(+))] species. Reaction kinetics data and DFT calculations suggest a two-step reaction mechanism with the initial formation of a bridged [Ru-(µNO)-Fe] intermediate, which was confirmed through electrochemical techniques (E(0)' = -0.47 V vs NHE). The calculated specific rate constant values for the reaction were in the ranges k1 = 1.1 to 7.7 L mol(-1) s(-1) and k2 = 2.4 × 10(-3) to 11.4 × 10(-3) s(-1) for L = P(OMe)3 and P(OEt)3. The oxidation of the ruthenium center (Ru(II) to Ru(III)) containing the nitrosonium ligand suggests that NO can act as an electron transfer bridge between the two metal centers.

Methyl angolensate changes in Khaya ivorensis after fungal infection.

Khaya ivorensis with and without symptoms of stem and branch cankers, caused by Botryosphaeria rhodina were examined in order to determine whether the secondary metabolites in this plant were associated with a chemical defense response. This study provides evidence that the limonoid methyl angolensate (MA) is present at higher concentrations in K. ivorensis with symptoms of stem cankers rather than in the plants without symptoms. A rapid, sensitive and selective HPLC-ESI-MS/MS method (using selected reaction monitoring--SRM--mode) was developed for quantification of MA in all aerials parts of such plants, with a good linearity over a range of 0.1-20.0 g/kg, with r(2)>0.996+/-6.1%. The limits of detection (LOD) and quantification (LOQ) were less than 0.03 g/kg and 0.08 g/kg, respectively. Relative Standard Deviations (RSDs) ranged from 1.7% to 19.2% for all matrices. While the MA concentration did not change in the stem bark, its amounts increased nearly fourfold in stems and by 20% in leaves, when plants with symptoms were compared with those without symptoms. These data suggest that MA plays a role in plant-pathogen interactions, probably as a phytoanticipin.

Inhibition of photophosphorylation and electron transport chain in thylakoids by lasiodiplodin, a natural product from Botryosphaeria rhodina.

Four natural products were isolated from the fungus Botryosphaeria rhodina, and their effects on photosynthesis were tested. Only lasiodiplodin (1) inhibited ATP synthesis and electron flow from water to methylviologen; therefore, it acts as a Hill reaction inhibitor in freshly lysed spinach thylakoids. Photosystem I and II and partial reactions as well as ATPase were measured in the presence of 1. Three new different sites of 1 interaction and inhibition were found: one at CF1, the second in the water-splitting enzyme, and the third at the electron-transfer path between P680 and QA; these targets are different from that of the synthetic herbicides present. Electron transport chain inhibition by 1 was corroborated by fluorescence induction kinetics studies.

Ruthenium Nitrosyl Complexes with N-Heterocyclic Ligands.

A new route was developed for preparing a series of trans nitrosyl complexes of general formula trans-[Ru(NH(3))(4)L(NO)](BF(4))(3), where L = imidazole, L-histidine, pyridine, or nicotinamide. The complexes have been characterized by elemental analysis, molar conductance measurements, UV-visible, infrared, proton nuclear magnetic, and electron paramagnetic resonance spectroscopies, and electrochemical techniques. The compounds possess relatively high nu(NO) stretching frequencies indicating that a high degree of positive charge resides on the coordinated nitrosyl group. The nitrosyl complexes react with OH(-) according to the equation trans-[Ru(NH(3))(4)L(NO)](3+) + 2OH(-) right arrow over left arrow trans-[Ru(NH(3))(4)L(NO(2))](+) + H(2)O, with a K(eq) (at 25.0 degrees C in 1.0 mol/L NaCl) of 2.2 x 10(5), 5.9 x 10(7), 9.7 x 10(10), and 4.6 x 10(13) L(2) mol(-)(2) for the py, nic, imN, and L-hist complexes, respectively. Only one redox process attributed to the reaction [Ru(II)(NH(3))(4)L(NO(+))](3+) + e(-) right arrow over left arrow trans-[Ru(II)(NH(3))(4)L(NO(0))](2+) was observed in the range -0.45 to 1.20 V for all the nitrosyl complexes. Linear correlations are observed in plots of nu(NO) versus E(1/2) and of E(1/2) versus summation operatorE(L) showing that the oxidizing strength of the coordinated NO increases with increase in L pi-acidity. The crystal structure analysis of trans-[Ru(NH(3))(4)nicNO](2)(SiF(6))(3) shows that the mean Ru-N-O angle is very close to 180 degrees (177 +/- 1 degrees ) and the mean N-O distance is 1.17 +/- 0.02 Å, thus confirming the presence of the Ru(II)-NO(+) moiety in the nitrosyl complexes studied.