Conformational analysis of mesocyclic polythioethers : Crystal and molecular structures of 1,4-dithiacycloheptane, 1,5-dithiacyclononane and 1,6-dithiacyclodecane

The crystal and molecular structures of 1,4-dithiacycloheptane (1,4-DTCH), 1,5-dithiacyclononane (1,5-DTCN), and 1,6-dithiacyclodecane (1,6-DTCD) have been determined by single crystal X-ray studies. These compounds crystallize in the space groups P2₁2₁2₁ (No. 19), P2₁/c (No. 14), and P2₁/n, respectively with a = 5.409(1), b = 10.883(2), c = 11.390(2) Å, Z = 4; a = 9.600(4), b = 12.378(8), c = 7.904(3) Å, /gb = 113.31(3)°, Z = 4; and a = 5.290(1), b = 12.853(3), c = 6.850(2) Å, β = 93.39(2)°, Z = 2, respectively. The nonhydrogen atoms were located using direct methods and the hydrogen atoms were found by Fourier difference maps. Full-matrix least-squares refinement led to conventional R factors of 0.0459, 0.0558 and 0.0314, respectively. The conformations adopted by 1,4-DTCH, 1,5-DTCN and 1,6-DTCD, in the crystalline slate, are twist chair (C₂ symmetry), twist boat chair (C₂ symmetry), and boat chair boat (C_2k symmetry), respectively. The transannular S-S distances are 3.583, 4.108 and 4.864 Å, respectively.     

New stereoselective intramolecular

Efficient 1,4-asymmetric induction has been achieved in the highly stereocontrolled intramolecular [2 + 2] cycloadditions between ketenimines and imines, leading to 1,2-dihydroazeto[2, 1-b]quinazolines. The chiral methine carbon adjacent to the iminic nitrogen controls the exclusive formation of the cycloadducts with relative trans configuration at C2 and C8. The stepwise mechanistic model, based on theoretical calculations, fully supports the stereochemical outcome of these cycloadditions.     

Experimental and Theoretical Study of the Electronic States and Spectra of BiNa

Gas-phase emission spectra of the hitherto unknown free radical BiNa have been measured in the NIR range with a Fourier transform spectrometer. The emissions were observed from a fast-flow system in which bismuth vapor in argon carrier gas was passed through a microwave discharge and mixed with sodium vapor in an observation tube. Two systems of blue-degraded bands observed in the ranges 8900-9800 and 7200-7800 cm(-1) were measured at high spectral resolution and vibrational and rotational analyses were performed. To aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain potential curves for the low-lying states of BiNa and also electric dipole transition moments connecting them. As in the isovalent BiH system, the ground state of BiNa is found to be X(3)Sigma(-) with a spin splitting of about 1769 cm(-1). The first excited state is A(3)Pi, and the observed band systems are assigned to the transitions A(3)Pi(A(2)0(+)) --> X(3)Sigma(-)(X(1)0(+), X(2)1). Comparison with earlier work on the isovalent BiH system emphasizes that the relative weakness of the varsigma MO in BiNa is responsible for qualitative differences in the electronic spectra of these two systems. Copyright 2000 Academic Press.     

The b1Sigma+(b0(+)) --> X3Sigma-(X10(+), X21) and a1Delta(a2) --> X21 Transitions of SbF, SbCl, SbBr, and SbI

Emission spectra of the a1Delta(a2) --> X21 and b1Sigma+(b0(+)) --> X3Sigma-(X10(+), X21) transitions of SbF, SbCl, SbBr, and SbI have been observed in the near-infrared spectral region. The antimony halide radicals were generated and excited in a fast-flow system by reaction of antimony vapor (Sbx) with the halides and microwave-discharged oxygen. The NIR chemiluminescence was measured with a Fourier-transform spectrometer equipped with Ge and InSb detectors. The spectra contain the known b1Sigma+(b0(+)) --> X3Sigma-(X10(+), X21) transitions in the range 730-910 nm and the hitherto unknown a1Delta(a2) --> X21 transitions in the range 1600-1900 nm. Vibrational analyses have yielded improved molecular constants for the X10(+), X21, and b0(+) states and the following constants of the a2 states (in cm-1): 121SbF: Te = 6815.6(5), omegae = 615.75(3), omegaexe = 2.62(1); 121Sb35Cl: Te = 6546.3(2), omegae = 379.8(1), omegaexe = 1.20(2); 121Sb79Br: Te = 6496.4(4), omegae = 265.9(2), omegaexe = 0.55(3); 121SbI: Te = 6366.7(3), omegae = 214.20(5), omegaexe = 0.430(9), where the numbers in parentheses are the standard deviations of the parameters. Copyright 1999 Academic Press.     

Monoterpenes and Sesquiterpenes of Essential Oils from Psidium Species and Their Biological Properties

Psidium (Myrtaceae) comprises approximately 266 species, distributed in tropical and subtropical regions of the world. Psidium taxa have great ecological, economic, and medicinal relevance due to their essential oils’ chemical diversity and biological potential. This review reports 18 Psidium species growing around the world and the chemical and biological properties of their essential oils. Chemically, 110 oil records are reported with significant variability of volatile constituents, according to their seasonality and collection sites. Monoterpenes and sesquiterpenes with acyclic (C₁₀ and C₁₅), p-menthane, pinane, bisabolane, germacrane, caryophyllane, cadinane, and aromadendrane skeleton-types, were the primary constituents. The essential oils showed various biological activities, including antioxidant, antifungal, antibacterial, phytotoxic, larvicidal, anti-inflammatory, and cytotoxic properties. This review contributes to the Psidium species rational and economic exploration as natural sources to produce new drugs.     

The influence of iron,fluorine and boron implantation on the magnetic properties of graphite

Iron, fluorine and boron ions were implanted into highly oriented pyrolytic graphite (HOPG). The samples were characterized before and after ion implantation as well as after heat treatments in vacuum by measurements of the magnetic moment and element analysis. Whereas the main magnetic contribution remains diamagnetic the paramagnetic one clearly increases with implantations and correlates with the amount of implanted ions. It is shown that a large part of the paramagnetic contribution is caused by the structural disorder created by particle bombardment using iron, fluorine or boron. All implanted HOPG samples show practically no change of the small ferromagnetic signal observed in their virgin state. No particular influence of iron on the ferromagnetic properties of HOPG is observed, up to ∼4000 μg/g Fe-concentration in the implanted region. For comparison, ferrous sulphates were added to ultra-clean graphite powder. This iron addition increases the number of paramagnetic spins proportional to the iron content in the untreated samples. In heat-treated samples however, a clear ferromagnetic behaviour is observed due to the formation of a ferromagnetic iron compound.     

Solid-state conformations of medium-sized-ring phosphorus heterocycles: Preparation and x-ray crystal structure of a benzo-fused 1,3,2-dioxaphosphepane in a twist conformation

The crystal and molecular structure of the benzo-fused seven-membered-ring phosphorus heterocycle, 2-phenyl-2-oxo-5,6-benzo-1,3,2-dioxaphosphepane, has been determined by single-crystal X-ray techniques. The compound crystallizes in the monoclinic space group P 2₁/c with four molecules per unit cell of dimensions a = 13.312(1) Å, b = 7.6132(8) Å, c = 12.119(2) Å, and β = 95.990(9)°. Full-matrix leastsquares refinement led to R = 4.4% and R_w = 5.9%. The conformation adopted by the 1,3,2-dioxaphosphepane ring is a twist with approximate C₂ symmetry.     

In Vitro Pharmacological Screening of Essential Oils from Baccharis parvidentata and Lippia origanoides Growing in Brazil

In this study, the in vitro antimicrobial, antiparasitic, antiproliferative and cytotoxic activities of essential oil from Baccharis parvidentata Malag. (EO-Bp) and Lippia origanoides Kunth (EO-Lo) were explored. The relevant effects were observed against the parasitic protozoans Plasmodium falciparum, Trypanosoma cruzi, Trypanosoma brucei and Leishmania amazonensis (ranging 0.6 to 39.7 µg/mL) and malignant MCF-7, MCF-7/HT, 22Rv1, and A431 cell lines (ranging 6.1 to 31.5 µg/mL). In parallel, EO-Bp showed better selective indexes in comparison with EO-Lo against peritoneal macrophages from BALB/c mice and MRC-5 cell line. In conclusion, EO-Lo is known to show a wide range of health benefits that could be added as another potential use of this oil with the current study. In the case of EO-Bp, the wide spectrum of its activities against protozoal parasites and malignant cells, as well as its selectivity in comparison with non-malignant cells, could suggest an interesting candidate for further tests as a new therapeutic alternative.     

Essential Oil Composition and DNA Barcode and Identification of Aniba species (Lauraceae) Growing in the Amazon Region

Lauraceae species are widely represented in the Amazon, presenting a significant essential oil yield, large chemical variability, various biological applications, and high economic potential. Its taxonomic classification is difficult due to the accentuated morphological uniformity, even among taxa from a different genus. For this reason, the present work aimed to find chemical and molecular markers to discriminate Aniba species collected in the Pará State (Brazil). The chemical composition of the essential oils from Aniba canelilla, A. parviflora, A. rosaeodora, and A. terminalis were grouped by multivariate statistical analysis. The major compounds were rich in benzenoids and terpenoids such as 1-nitro-2-phenylethane (88.34–70.85%), linalool (15.2–75.3%), α-phellandrene (36.0–51.8%), and β-phellandrene (11.6–25.6%). DNA barcodes were developed using the internal transcribed spacer (ITS) nuclear region, and the matK, psbA-trnH, rbcL, and ycf1 plastid regions. The markers psbA-trnH and ITS showed the best discrimination for the species, and the phylogenic analysis in the three- (rbcL + matK + trnH − psbA and rbcL + matK + ITS) and four-locus (rbcL + matK + trnH − psbA + ITS) combination formed clades with groups strongly supported by the Bayesian inference (BI) (PP:1.00) and maximum likelihood (ML) (BS ≥ 97%). Therefore, based on statistical multivariate and phylogenetic analysis, the results showed a significant correlation between volatile chemical classes and genetic characteristics of Aniba species.