Armando Ariza-Castolo

Molecular structure of di-aryl-aldimines by multinuclear magnetic resonance and X-ray diffraction

Abstract The complete 1H, 13C and 15N NMR analyses for a series of 25 diaryl-aldimines containing phenyl, pyridyl, pyrazolone and furanyl moieties are described herein. Detailed evaluation of substituent chemical shift and coupling constant effects showed that interaction between the lone pair of the pyrazolone carbonyl group or the nitrogen of 2-substitued pyridines with the aldimine hydrogen increases the 1 J CH value and shifts the resonance signal for this hydrogen to high frequency, in the 1H NMR spectra. The X-ray crystal structure analysis of pyrazolone substituted aldimines evidenced the planarity of the aryl groups which are conjugated with the CN double bond. In the case of the N-(2-pyridinemethylene)-1,5-dimethyl-2-phenyl-1,2-dihydro-pyrazol-3-one, two rotamers were observed in the same unit cell.

Versatile behavior of 2‐guanidinobenzimidazole nitrogen atoms toward protonation, coordination and methylation

The structure, dynamic behavior, protonation, methylation, and coordination sites of 2-guanidinobenzimidazole la were investigated. Structures of compounds [2-guanidinium-1,3,10-trihydrobenzimidazole]sulfate lb, [2-guanidinium-l,3-dihydro-benzimidazole]sulfate lc-ld, [2-guanidinium-l,3-dihydro-benzimidazole]tetrafluoroborate le, [2-guanidinium-l,3-dihydro-benzimidazole]chbride If, [2-guanidinium-1,3dihydro-benzimidazole] perchlorate 1% 2-guanidinoI-methyl-benzimidazole 2a, [2-guanidinium-l,3-dimethyl-benzimidazole]iodide 2b, [2-guanidinium-1methyl-3-hydro-benzimidazole]chloride 2c, [2

1 H, 13C, 15N, 2D and variable temperature NMR study of the role of hydrogen bonding in the structure and conformation of oxamide derivatives

The structure and conformation of N,N′-bis[(2-hydroxy)phenyl]oxamide (1); N,N′-bis[(2-methoxy)-phenyl]oxamide (2); N,N′-bis(phenyl)oxamide (3); N,N′-bis[(1R,2S)-(–)-norephedrine]oxamide (4); N,N′-bis[(1R,2R)-(–)-norpseudoephedrine]oxamide (5); N-[(2-hydroxy)phenyl]methylamide (6); N-[(2-methoxy)phenyl]methylamide (7); N-phenylmethylamide (8); N-[(–)-norephedrine]-methylamide (9) and N-[(–)-norpseudoephedrine]methylamide (10) were unambiguously established by 1H, 13C, 15N, 2D and variable temperature NMR spectroscopy. A careful NMR investigation of the conformational behaviour in these systems was relevant. It has been found that the dicarbonylic group in compounds 1–5 has a trans geometry, stabilized by intramolecular hydrogen bonding and that they possess a C2 axis. Compounds 1 and 2 are planar and compounds 1, 2, 4 and 5 present the amidic proton coordinated by two oxygen atoms.

Biopesticides from plants: Calceolaria integrifolia s.l.

The effects of persistent organic pollutants (POPs) on humans and biodiversity are multiple and varied. Nowadays environmentally-friendly pesticides are strongly preferred to POPs. It is noteworthy that the crop protection role of pesticides and other techniques, i.e. biopesticides, plant extracts, prevention methods, organic methods, evaluation of plant resistance to certain pests under an integrated pest management (IPM), could improve the risks and benefits which must be assessed on a sound scientific basis. For this directive it is crucial to bring about a significant reduction in the use of chemical pesticides, not least through the promotion of sustainable alternative solutions such as organic farming and IPM. Biopesticides are derived from natural materials such as animals, plants, bacteria, and certain minerals. Most of them are biodegradable in relatively short periods of time. On this regard, substances from Calceolaria species emerge as a strong alternative to the use of POPs. The American genus Calceolaria species are regarded both as a notorious weeds and popular ornamental garden plants. Some have medicinal applications. Other taxa of Calceolaria are toxic to insects and resistant to microbial attack. These properties are probably associated with the presence of terpenes, iridoids, flavonoids, naphthoquinones and phenylpropanoids previously demonstrated to have interesting biological activities. In this article a comprehensive evaluation of the potential utilization of Calceolaria species as a source of biopesticides is made. The chemical profile of selected members of the Chilean Calceolaria integrifolia sensu lato complex represents a significant addition to previous studies. New secondary metabolites were isolated, identified and tested for their antifeedant, insect growth regulation and insecticidal activities against Spodoptera frugiperda and Drosophila melanogaster. These species serve as a model of insect pests using conventional procedures. Additionally, bactericidal and fungicidal activity were determined. Dunnione mixed with gallic acid was the most active fungistatic and fungicidal combination encountered. Several compounds as isorhamnetin, combined with ferulic and gallic acid quickly reduced cell viability, but cell viability was recovered quickly and did not differ from that of the control. The effect of these mixtures on cultures of Aspergillus niger, Fusarium moniliforme, Fusarium sporotrichum, Rhizoctonia solani, and Trichophyton mentagrophytes, was sublethal. However, when fungistatic isorhamnetin and dunnione were combined with sublethal amounts of both ferulic and gallic acid, respectively, strong fungicidal activity against theses strains was observed. Thus, dunnione combined with gallic acid completely restricted the recovery of cell viability. This apparent synergistic effect was probably due to the blockade of the recovery process from induced-stress. The same series of phenolics (iridoids, flavonoids, naphthoquinones and phenylpropanoids) were also tested against the Gram-negative bacteria Escherichia coli, Enterobacter agglomerans, and Salmonella typhi, and against the Gram-positive bacteria Bacillus subtilis, Sarcinia lutea, and Staphylococcus aureus and their effects compared with those that of kanamycin. Mixtures of isorhamnetin/dunnione/kaempferol/ferulic/gallic acid in various combinations were found to have the most potent bactericidal and fungicidal activity with MFC between 10 and 50 μg/ml. Quercetin was found to be the most potent fungistatic single compound with an MIC of 15 µg/ml. A time-kill curve study showed that quercetin was fungicidal against fungi assayed at any growth stage. This antifungal activity was slightly enhanced by combination with gallic acid. The primary antifungal action of the mixtures assayed likely comes from their ability to act as nonionic surfactants that disrupt the function of native membrane-associated proteins. Hence, the antifungal activity of isorhamnetin and other O-methyl flavonols appears to be mediated by biophysical processes. Maximum activity is obtained when the balance between hydrophilic and hydrophobic portions of the molecules of the mixtures becomes the most appropriate. Diterpenes, flavonoids, phenylpropanoids, iridoids and phenolic acids were identified by chromatographic procedures (HPLC-DAD), ESI-MS, and NMR hyphenated techniques.

NMR Structural Study of the Prototropic Equilibrium in Solution of Schiff Bases as Model Compounds

An NMR titration method has been used to simultaneously measure the acid dissociation constant (pKa) and the intramolecular NHO prototropic constant ΔKNHO on a set of Schiff bases. The model compounds were synthesized from benzylamine and substituted ortho-hydroxyaldehydes, appropriately substituted with electron-donating and electron-withdrawing groups to modulate the acidity of the intramolecular NHO hydrogen bond. The structure in solution was established by 1H-, 13C- and 15N-NMR spectroscopy. The physicochemical parameters of the intramolecular NHO hydrogen bond (pKa, ΔKNHO and ΔΔG°) were obtained from 1H-NMR titration data and pH measurements. The Henderson–Hasselbalch data analysis indicated that the systems are weakly acidic, and the predominant NHO equilibrium was established using Polster–Lachmann δ-diagram analysis and Perrin model data linearization.

seco-Briarellinone and Briarellin S, Two New Eunicellin-Based Diterpenoids from the Panamanian Octocoral Briareum asbestinum

Two new eunicellin-based diterpenes, seco-briarellinone (1) and briarellin S (2), and a known seco-asbestinin (3) have been isolated from the methanolic extract of the common octocoral Briareum asbestinum collected in Bocas del Toro, Caribbean of Panama. The structures and relative stereochemistry of the compounds were defined using extensive spectroscopic analysis including 1D, 2D-nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS). compounds 1 and 2 displayed anti-inflammatory properties inhibiting nitric oxide (NO) production induced by lipopolisacharide (LPS) in macrophages with an Inhibitory concentration 50% (IC50) of 4.7 μM and 20.3 μM, respectively. This is the first report of briarellin diterpenes containing a ketone group at C-12.

Small Molecules Derived from Thieno[3,4-c]pyrrole-4,6-dione (TPD) and Their Use in Solution Processed Organic Solar Cells

In this work, microwave synthesis, chemical, optical and electrochemical characterization of three small organic molecules, TPA-TPD, TPA-PT-TPD and TPA-TT-TPD with donor-acceptor structure and their use in organic photovoltaic cells are reported. For the synthesis, 5-(2-ethylhexyl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione was used as electron withdrawing fragment while the triphenylamine was used as electron donating fragment. Molecular electronic geometry and electronic distribution density were established by density functional theory (DFT) calculations and confirmed by optical and chemical characterization. These molecules were employed as electron-donors in the active layer for manufacturing bulk heterojunction organic solar cells, where [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) was used as electron-acceptor. As cathode, Field′s metal (FM), an eutectic alloy (Bi/In/Sn: 32.5%, 51%, and 16.5%, respectively) with a melting point above 62 °C, was easily deposited by drop casting under vacuum-free process and at air atmosphere. Prepared devices based on TPA-TPD:PC71BM (1:4 w/w ratio) presented a large VOC = 0.97 V, with JSC = 7.9 mA/cm2, a FF = 0.34, then, a power conversion efficiency (PCE) of 2.6%.

Conformational and structural analysis of exocyclic olefins and ketimines by multinuclear magnetic resonance

The 1H, 13C, and 15N NMR spectra of 5 exocyclic alkenes and 15 different ketimines obtained from cyclohexanone and derivatives using benzyl bromide and primary amines—are analyzed. Relative stereochemical and preferential conformations are determined by analyzing both the homonuclear coupling and the chemical shifts of the protons and carbon atoms in the aliphatic rings, which are directly related to the geometry of the double bond and the steric and electronic effects of the exocyclic group. In addition, the racemic mixture of the N‐(4‐methylcyclohexylidene)pyridine‐3‐amine derivative is resolved. Copyright

Synthesis and characterization of tetracarbonyl complexes of molybdenum and tungsten with functionalized imines. Crystal structure of cis-Mo(CO)4[CH3)(C6H5) C=N (CH)2)]2

Abstract A series of octahedral cis -iminetetracarbonyl molybdenum and tungsten complexes of the general formula [M(CO) 4 L 2 , where These imine chelates complexes of molybdenum and tungsten have exocyclic double bonds. A consistent structural feature of these complexes appears to be the chelate bonding of the imine ligand with consequent rotation around the carbon-nitrogen bond. This phenomenon leads to isomeric compounds: 4 and 5; 8 and 9; 11 and 12 . NMR data analysis established unambigously the configuration of the following nine complexes: confirmed the configuration and chemical shifts assignments for complexes 11 and 12 . The 13 C chemical shifts of the carbonyl groups are particularly useful in the characterization of the molybdenum compounds. Single-crystal X-ray diffraction studies of 4 confirm the formation of the nonsymmetric complex cis -[ trans -2,7-diphenyl-3,6-diaza-2,6-octadiene]tetracarbonylmolybdenum. The complex crystallizes in the space group P 2 1 / n with the unit cell paramters full-matrix least-squares techniques to R and R w values of 0.052 and 0.064, respectively, for 4706 observed reflections. The data obtained show that the structure has been solvated with half a molecule of benzene. Evidence of monocoordination of imine 1 to Mo(CO) 4 (NBD) has been obtained by 13 C NMR spectroscopy and some insight into the mechanism of complex formation is provided.

Stereochemical arrangement of spiro[4.5]decane derivatives by 15N and 17O NMR spectroscopy

The relative axial–equatorial position of spiro[4.5]decanes substituted in the 1,4‐positions by oxygen or nitrogen were assigned by 15N and 17 O NMR spectroscopy. The substituent, chemical exchange and steric effects upon the chemical shifts are discussed. A linear relationship between 15N and 17O was found and the relative configuration of the chiral spiro atom was determined. Copyright