Search results for "Spectral data"
showing 10 items of 56 documents
Sesquiterpenoids in subtribe Centaureinae (Cass.) Dumort (tribe Cardueae, Asteraceae): distribution, (13)C NMR spectral data and biological propertie…
2012
Asteraceae Bercht. & J. Presl is one of the biggest and most economically important plant families. The taxonomy and phylogeny of Asteraceae is rather complex and according to the latest and most reliable taxonomic classification of Panero & Funk, based on the analysis of nine chloroplast regions, the family is divided into 12 subfamilies and 35 tribes. One of the largest tribes of Asteraceae is Cardueae Cass. with four subtribes (Carlininae, Echinopinae, Carduinae and Centaureinae) and more than 2500 species. Susanna & Garcia-Jacas have organized the genera of Centaureinae (about 800 species) into seven informal groups, which recent molecular studies have confirmed: 1. Basal genera; 2. Vol…
Stereoselective synthesis of the published structure of feigrisolide A. Structural revision of feigrisolides A and B.
2006
The total synthesis of the proposed structure of feigrisolide A is reported. Ethyl (S)-3-hydroxybutyrate was the chiral starting material. A Brown asymmetric allylation and an Evans aldol reaction were key steps of the synthesis. The NMR data of the synthetic product are different from those of the natural product. The published structure of feigrisolide A is therefore erroneous. A subsequent comparison of spectral data strongly suggests that feigrisolides A and B are identical with (-)-nonactic acid and (+)-homononactic acid, respectively.
Recognition and classification of external skin damage in citrus fruits using multispectral data and morphological features
2009
The computer vision systems currently used for the automatic inspection of citrus fruits are normally based on supervised methods that are capable of detecting defects on the surface of the fruit but are unable to discriminate between different types of defects. identifying the type of the defect affecting each fruit is very important in order to optimise the marketing profit and to be able to take measures to prevent such defects from occurring in the future. In this paper, we present a computer vision system that was developed for the recognition and classification of the most common external defects in citrus. in order to discriminate between 11 types of defects, images of the defects we…
Diepoxyrollin and Diepomuricanin B: Two New Diepoxyacetogenins from Rollinia membranacea Seeds
1997
Diepoxyrollin (1) and diepomuricanin B (2), two new Annonaceous acetogenins were isolated from the cytotoxic MeOH extract of the seeds of Colombian Rollinia membranacea. Five others known acetogenins were also isolated, dieporeticanin 1, dieporeticanin 2, diepomuricanin A, rollinone, and sylvaticin. Their structures were elucidated on the basis of spectral data. Compounds 1 and 2 belong to the rare type of diepoxyacetogenins, which are probably precursors of the mono-tetrahydrofuran acetogenins.
Synthesis of chlorinated alkylbibenzyls and 9-chlororetene
1995
Abstract The synthesis of chlorinated alkylbibenzyls and 9-chlororetene is described. These compounds were synthesized for use as model compounds in analytical and toxicological characterization. The structures of the synthesized model compounds found to be very similar to those identified in pulp mill effluent and products. The 1H NMR and mass spectral data for the compounds are also reported.
Multidimensional Borg–Levinson theorems for unbounded potentials
2018
We prove that the Dirichlet eigenvalues and Neumann boundary data of the corresponding eigenfunctions of the operator $-\Delta + q$, determine the potential $q$, when $q \in L^{n/2}(\Omega,\mathbb{R})$ and $n \geq 3$. We also consider the case of incomplete spectral data, in the sense that the above spectral data is unknown for some finite number of eigenvalues. In this case we prove that the potential $q$ is uniquely determined for $q \in L^p(\Omega,\mathbb{R})$ with $p=n/2$, for $n\geq4$ and $p>n/2$, for $n=3$.
Tripoxyrollin, a New Epoxy Acetogenin from the Seeds ofRollinia membranacea1
1993
Abstract A new epoxy acetogenin, tripoxyrollin (1), has been isolated from the seeds of the Colombian Annonaceae, Rollinia membranacea. Its structure was elucidated on the basis of spectral data. Biomimetic synthesis of isodesacetyluvaricin (2) from tripoxyrollin (1) suggests its key role in the biogenesis of the adjacent bis-tetrahydrofuran acetogenins.
Optimization criteria in sample selection step of local regression for quantitative analysis of large soil NIRS database
2012
International audience; Large soil spectral libraries compiling thousands of NIR (Near Infrared) reflectance spectra have been created encompassing a wide diversity and heterogeneity of spectra. Among the many chemometric approaches to the calibration of chemical and physical properties from these large libraries, local calibrations have the advantage of being able to select the most similar spectra to the spectrum of a target sample. This is particularly relevant when dealing with highly heterogeneous media such as soils, where the mineral matrix has a strong influence on spectral features. A crucial step in the implementation of local calibration procedures is the construction of local ne…
<b>ANTIMICROBIAL DITERPENOID ALKALOIDS FROM <i>ERYTHROPHLEUM SUAVEOLENS</i> (GUILL. & PERR.) BRENAN</b>
2005
An investigation of the stem bark of Erythrophleum suaveolens (Guill. & Perr.) Brenan yielded the known amide norcassaide ( 1 ) and a new diterpenoid alkaloid named norerythrosuaveolide ( 2 ) which was characterized as 7β-hydroxy-7-deoxo-6-oxonorcassaide. The structures were established on the basis of one and two-dimensional 1 H and 13 C NMR spectral data. The compounds showed potent antimicrobial activities against bacteria and yeasts. KEY WORDS: Erythrophleum suaveolens (Guill. & Perr.) Brenan, Norcassaide, Diterpenoid alkaloid, Norerythrosuaveolide, Antimicrobial activities, Bacteria, Yeasts Bull. Chem. Soc. Ethiop. 2005, 19(2), 221-226.
Specificity of 15N NMR chemical shifts to the nature of substituents and tautomerism in substituted pyridine N-oxides
2012
1H, 13C, and 15N NMR chemical shifts have been measured for 2-aminopyridine N-oxide (1), its eleven derivatives (2–10, 13, 14), and 3-Cl and 3-Br substituted 4-nitropyridine N-oxides (11, 12). δ(15N) of pyridine ring nitrogen in 2-acetylaminopyridine N-oxides are 5.9–11.5 ppm deshielded from those in 2-aminopyridine N-oxides. When amino and acetylamino substituents are in 4-position, δ(15N) of ring nitrogen is 21.3 ppm deshielded in the acetylated derivative. The strong resonance interaction between 2-amino and 5-nitro groups reflects in the decrease of amino nitrogen shielding about 5.3–17.9 ppm. Also, 1H and 13C NMR spectral data are in agreement with 15N NMR results reflected as deshield…