Ivânia T.A. Schuquel

Solvent effects on the miscibility of PMMA/PVAc blends: II. Using two-dimensional NMR method, NOESY

The influence of solvent on the miscibility of poly(methyl methacrylate)/poly(vinyl acetate), PMMA/PVAc, and the interpolymer interactions responsible for their miscibility were investigated. 2D nuclear overhauser effect spectroscopy, NOESY, experiments were performed with pure polymers and also with 50/50 blend. Under conditions of blend miscibility, chloroform at 40°C and toluene at 30°C, NOESY results indicated the presence of two different types of intermolecular interactions between (i) methoxy protons of PMMA and methyne protons of PVAc; (ii) methoxy protons of PMMA and methyl protons of PVAc. In immiscible conditions, in DMF and in benzene, both at 40°C, only type (ii) interactions were detected. These results indicate that intermolecular interactions between the methoxy protons of PMMA and the methyne protons of PVAc are responsible for the miscibility of the blends in chloroform and toluene. The interactions between the methoxy protons of PMMA and the methyl protons of PVAc do not contribute to the miscibility of the blend and were explained as originating from contacts of unlike polymers in the interphase.

Semiempirical and ab initio calculations versus dynamic NMR on conformational analysis of cyclohexyl-N,N-dimethylcarbamate

Axial-equatorial conformational proportions for cyclohexyl-N,N-dimethyl carbamate have been measured, for the first time, by the Eliel method, 1H and 13C dynamic nuclear magnetic resonance (DNMR). The results were compared against those determined by theoretical calculations. By the Eliel method at least five experimentally independent measureables were used in CCl4, CDCl3 and CD3CN. The 1H and 13C low temperature experiments were performed in CF2Br2/CD2Cl2 . Semiempirical methods MNDO, AM1 and PM3 and ab initio molecular orbital calculations at the HF/STO-3G and HF/6-31G(d,p) levels have been performed on the axial and equatorial conformers populations. All applied methods correctly predict the equatorial conformer preference over the axial one. The resulting equatorial preferences determined by NMR data and theoretical calculations are in good agreement.

A urethane-based multimethacrylate mixture and its use in dental composites with combined high-performance properties

OBJECTIVES To synthesize and characterize different molar weight urethane multimethacrylates with a single stage (one-pot) procedure. To prepare and characterize the properties of related composites. METHODS Two methacrylate precursors were initially synthesized. Then, these precursors and the multimethacrylate system formed by their coupling were characterized by FTIR and (1)H NMR. The final product was used as a matrix (with TEGDMA and SiO2 silanized microparticles) in the preparation of composites and their physical and mechanical properties were compared to those of a bis-GMA-based resin. Water sorption and solubility measurements of the composites were also performed. RESULTS FTIR and NMR suggested that the proposed synthesis route yields a mixture of mainly urethane-di, -tri, and tetramethacrylates. The composites presented low polymerization shrinkage (e.g. 1.88±0.08% for a resin with 70% of SiO2) and high flexural strength (e.g. 124.74±9.68 MPa for a resin with 65% of SiO2) when compared to the bis-GMA based resin and other composites found to date. Water sorption and solubility results show that the composites were deemed compliant with ISO 4049 requirements. SIGNIFICANCE The mixture containing different molar weight of urethane multimethacrylates showed to be an excellent substitute for bis-GMA, achieving an equilibrium of properties (unlike reports elsewhere which show the enhancement of some parameters in detriment to others) and composites with low polymerization shrinkage, suitable microhardness and degree of conversion, and up to standard water sorption/solubility and flexural strength.

A tetrahydro β-carboline trisaccharide from Palicourea coriacea (Cham.) K. Schum

A new tetrahydro beta-carboline alkaloid that has an oligosaccharide unit was isolated from the root extracts of the Palicourea coriacea. The structure was elucidated using spectral methods, including 2D NMR: COSY, HMQC, HMBC and NOESY.

Iridoid glucosides from Bouchea fluminensis

Abstract From the aerial parts of Bouchea fluminensis , a new iridoid glucoside, named boucheoside, along with four known iridoid glucosides, lamiide, lamiidoside, durantoside II, and duranterectoside C, were isolated. The structure of the new compound was elucidated based on the spectroscopic evidence.

Atribuição inequívoca de deslocamentos químicos de RMN de ¹H e 13C de plumierídeo isolado da Allamanda cathartica

There are NMR data of 1H and 13C of the iridoid plumieride, but controversy related to the assignments of the protons H-3 or H-10 and carbons C-6 or C-7 and C-3 or C-10 are described in the literature. There are a little discussion regarding to the resonance assignment of protons of the glycoside unity. Analysis based on 2D shift correlated NMR spectra (COSY, HETCOR, HETCORLR) and NOE difference 1H NMR spectra allowed to assign unambigously the chemical shift of 1H and 13C of plumieride which has been found in the literature with non coincident values.

Ixorine, a New Cyclopeptide Alkaloid from the Branches of Ixora brevifolia

The isolation and structure determination of new cyclic peptide alkaloid ixorine, along with five known constituents frangulanine, syringaresinol, cinnamtannin B-1, daucosterol and mannitol from the branches of Ixora brevifolia are described. The cyclic peptide frangulanine is being described for the first time in the Rubiaceae family. The structures were elucidated on their spectral data basis, mainly one- (1H, 13C, DEPT) and two-dimensional (COSY, NOESY, HSQC and HMBC) nuclear magnetic resonance (NMR) and by comparison with data from the literature. The mixture of two cyclopeptide alkaloids showed weak activity against Leishmania amazonensis.

Constituintes químicos das folhas e avaliação da atividade anti-inflamatória de extratos das raízes e folhas de Guettarda pohliana Müll. Arg. (Rubiaceae)

This phytochemical investigation of Guettarda pohliana leaves led to the isolation of the triterpenes pomolic acid, rotundic acid, 3β,6α,19α,23-tetrahydroxyurs-12-en-28-oic acid, clethric acid, ursolic acid and oleanolic acid, the monoterpenoids loliolide and secoxyloganin, besides daucosterol and steroids. The structures of the isolated compounds were assigned on the basis of NMR data, including two-dimensional NMR methods. The anti-inflammatory activity of the crude methanolic extracts from leaves and roots, as well as of their fractions, was evaluated.

β-Carboline alkaloids from Galianthe ramosa inhibit malate synthase from Paracoccidioides spp.

As part of our continuing chemical and biological analyses of Rubiaceae species from Cerrado, we isolated novel alkaloids 1 and 2, along with known compounds epicatechin, ursolic acid, and oleanolic acid, from Galianthe ramosa. Alkaloid 2 inhibited malate synthase from the pathogenic fungus Paracoccidioides spp. This enzyme is considered an important molecular target because it is not found in humans. Molecular docking simulations were used to describe the interactions between the alkaloids and malate synthase.

Chemical constituents of Machaerium hirtum Vell. (Fabaceae) leaves and branches and its anti-inflammatory activity evaluation

Leaves and branches of Machaerium hirtum Vell. (Fabaceae), native to South America, were subjected to phytopharmacological investigation in order to identify its major chemical constituents and evaluate its extracts, fractions and isolated compounds in assays for anti-inflammatory activities. These were performed using mouse ear edema model, pleurisy and myeloperoxidase activity assays. Six compounds were isolated and identified as the flavanones swertisin and isovitexin, the alkaloid 4-hydroxy-N-methylproline, the triterpenes friedelin and lupeol, and the steroids sitosterol and stigmasterol. These compounds were identified by nuclear magnetic resonance of 1H and 13C data, in comparison with literature.