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71.
Zully A. Benzo Manuelita Velosa Claudio Ceccarelli Miguel Guardia Amparo Salvador 《Fresenius' Journal of Analytical Chemistry》1991,339(4):235-239
Summary The literature on the application of the slurry technique to biological materials is reviewed. It is obvious from the various applications that the most frequently employed atomization method for slurry analysis in biological materials is electrothermal atomization using either graphite tube or platform atomizers. The slurry technique is particularly useful when certified reference materials are not available and when the standard addition method is to be avoided. The literature survey revealed that this technique compares favourably with other methods for the determination of trace metals in biological materials. 相似文献
72.
Anaí Duarte Wilson Cunico Claudio M.P. Pereira Alex F.C. Flores Rogério A. Freitag Geonir M. Siqueira 《Ultrasonics sonochemistry》2010,17(2):281-283
An ultrasound-enhanced method has been developed for the synthesis of a variety of thioesters from benzoyl chlorides and 2-mercaptobenzoxa(thia)zoles. Applying this methodology, 14 compounds were synthesized in excellent yields. 相似文献
73.
Dalvit C Flocco M Veronesi M Stockman BJ 《Combinatorial chemistry & high throughput screening》2002,5(8):605-611
High-throughput ligand-based NMR screening with competition binding experiments is extended to (19)F detection. Fluorine is a favorable nucleus for these experiments because of the significant contribution of the Chemical Shift Anisotropy (CSA) to the (19)F transverse relaxation of the ligand signal when bound to a macromolecular target. A low to moderate affinity ligand containing a fluorine atom is used as a reference molecule for the detection and characterization of new ligands. Titration NMR experiments with the selected reference compound are performed for finding the optimal set-up conditions for HTS and for deriving the binding constants of the identified NMR hits. Rapid HTS of large chemical mixtures and plant or fungi extracts against the receptor of interest is possible due to the high sensitivity of the (19)F nucleus and the absence of overlap with the signals of the mixtures to be screened. Finally, a novel approach for HTS using a reference molecule in combination with a control molecule is presented. 相似文献
74.
Alpha-amino acids are soluble in acetonitrile when treated with phosphazene bases. As a result, the protection/deprotection events that are usually required for peptide coupling reactions can be minimized. This is illustrated in the synthesis of the important angiotensin-converting enzyme (ACE) inhibitor enalapril. [reaction: see text] 相似文献
75.
Pau Bernadó Renato Barbieri Esteve Padrós Claudio Luchinat Miquel Pons 《Journal of the American Chemical Society》2002,124(3):374-375
Addition of Tb3+ to purple membrane (PM) suspensions changes the orientation of the menbrane normal from parallel to perpendicular with respect to the magnetic field. Residual dipolar couplings measured in protein L in the presence of PM are scaled by a factor of -1/2. NMR line broadening and cross-correlation effects induced by the addition of PM are partially reversed by Tb3+ but not by Tm3+ that has no effect on the orientation of PM. This is interpreted as the result of anisotropically restricted motion of protein L in the transiently PM-bound form. 相似文献
76.
JPC – Journal of Planar Chromatography – Modern TLC - 相似文献
77.
Combined Experimental and Multivariate Model Approaches for Glycoalkaloid Quantification in Tomatoes
Gabriella Tamasi Alessio Pardini Riccardo Croce Marco Consumi Gemma Leone Claudia Bonechi Claudio Rossi Agnese Magnani 《Molecules (Basel, Switzerland)》2021,26(11)
The intake of tomato glycoalkaloids can exert beneficial effects on human health. For this reason, methods for a rapid quantification of these compounds are required. Most of the methods for α-tomatine and dehydrotomatine quantification are based on chromatographic techniques. However, these techniques require complex and time-consuming sample pre-treatments. In this work, HPLC-ESI-QqQ-MS/MS was used as reference method. Subsequently, multiple linear regression (MLR) and partial least squares regression (PLSR) were employed to create two calibration models for the prediction of the tomatine content from thermogravimetric (TGA) and attenuated total reflectance (ATR) infrared spectroscopy (IR) analyses. These two fast techniques were proven to be suitable and effective in alkaloid quantification (R2 = 0.998 and 0.840, respectively), achieving low errors (0.11 and 0.27%, respectively) with the reference technique. 相似文献
78.
Saad Sene Marc Reinholdt Dr. Guillaume Renaudin Dr. Dorothée Berthomieu Prof. Claudio M. Zicovich‐Wilson Prof. Christel Gervais Dr. Philippe Gaveau Prof. Christian Bonhomme Dr. Yaroslav Filinchuk Prof. Mark E. Smith Prof. Jean‐Marie Nedelec Dr. Sylvie Bégu Dr. P. Hubert Mutin Dr. Danielle Laurencin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(3):880-891
Boronic acids (R‐B(OH)2) are a family of molecules that have found a large number of applications in materials science. In contrast, boronate anions (R‐B(OH)3?) have hardly been used so far for the preparation of novel materials. Here, a new crystalline phase involving a boronate ligand is described, Ca[C4H9‐B(OH)3]2, which is then used as a basis for the establishment of the spectroscopic signatures of boronates in the solid state. The phase was characterized by IR and multinuclear solid‐state NMR spectroscopy (1H, 13C, 11B and 43Ca), and then modeled by periodic DFT calculations. Anharmonic OH vibration frequencies were calculated as well as NMR parameters (by using the Gauge Including Projector Augmented Wave—GIPAW—method). These data allow relationships between the geometry around the OH groups in boronates and the IR and 1H NMR spectroscopic data to be established, which will be key to the future interpretation of the spectra of more complex organic–inorganic materials containing boronate building blocks. 相似文献
79.
Quassinoids from Picrasma crenata 总被引:1,自引:0,他引:1
From woods of Picrasma crenata, a new stereoisomer dihydronorneoquassin was obtained together with others well knowns dihydronorneoquassin, parain, alpha-neoquassin, beta-neoquassin and quassin. The structures were determined by spectroscopic data and chemical evidence. 相似文献
80.
Methyl or silyl dissociation in the CH(2)=CHCH(2)-XH(3) (a-XH(3)(*)(+)) and CH(2)=CHCH=CHCH(2)-XH(3) (p-XH(3)(*) (+)) radical cations (X = C, Si) yields a(+) or p(+) and XH(3)(*). Similarly, the radical anions a-CH(3)(*) (-) and p-CH(3)(*) (-) give the pi-delocalized anion and CH(3)(*) preferentially. In contrast, a-SiH(3)(*) (-) and p-SiH(3)(*-) prefer to dissociate into the pi-delocalized radical and silide. All reactions are endoergic: by 43-50 kcal mol(-)(1) in the radical cations, and easier to some extent in the radical anions, that require 29-33 (X = C) and 13-14 kcal mol(-)(1) (X = Si). The fragmentation energy profiles do not present significant barriers for the backward process in the case of the radical cations. All radical anions exhibit an energy maximum along the dissociation pathway, but the barrier is lower than the dissociation limit. Fragmentation is "activated" more in the anions than in the cations with respect to homolysis in the corresponding neutrals (that requires 72-81 kcal mol(-)(1)). Wave function analysis indicates that the C-X bond cleavage in the hydrocarbon radical ions, although formally comparable to a homolytic process, is at variance with this model, due to the spin recoupling of one of the two C-X bond electrons with the originally unpaired electron. This is basically true also for the silyl-substituted radical anions, in which the initial more delocalized charge distribution might suggest some heterolytic character of the bond cleavage. 相似文献