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31.
Mohammadreza Shariatgorji Zdenek Spacil Gianluca Maddalo Lourdes B. Cardenas Leopold L. Ilag 《Rapid communications in mass spectrometry : RCM》2009,23(23):3655-3660
Quaternary protoberberine alkaloids belong to a pharmaceutically important class of isoquinoline alkaloids associated with bactericidal, fungicidal, insecticidal and antiviral activities. As traditional medicine gains wider acceptance, quick and robust analytical methods for the screening and analysis of plants containing these compounds attract considerable interest. Thin‐layer chromatography (TLC) combined with matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) is a powerful technique but suffers from dilution of the TLC bands resulting in decreased sensitivity and masking of signals in the low‐mass region both due to addition of matrix. This study integrates for the first time conventional silica gel TLC and laser desorption ionization mass spectrometry (LDI‐MS) thus eliminating the need for any external matrix. Successful separation of berberine (Rf = 0.56) and palmatine (Rf = 0.46) from Berberis barandana including their identification by MS are demonstrated. Furthermore, a robust electrospray ionization (ESI)‐MS method utilizing residual sample from TLC for quantification of berberine applying selected reaction monitoring and standard addition method is presented. The amount of berberine in the plant root prepared for the study was determined to be 0.70% (w/w). Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Ciro Ciliberto Thomas Dedieu Concettina Galati Andreas Leopold Knutsen 《Mathematische Nachrichten》2023,296(2):574-587
We prove that certain Severi varieties of nodal curves of positive genus on general blow-ups of the twofold symmetric product of a general elliptic curve are nonempty and smooth of the expected dimension. This result, besides its intrinsic value, is an important preliminary step for the proof of nonemptiness of Severi varieties on general Enriques surfaces. 相似文献
34.
A simple and sensitive method was developed using hydrophilic interaction liquid chromatography coupled to tandem mass spectrometry
for determination of monosaccharides liberated from marine polysaccharides by acidic hydrolysis. Optimal separation of diastereomeric
monosaccharides including hexoses, pentoses, and deoxyhexoses was achieved using an aminopropyl bonded column with mobile
phase containing ternary solvents (acetonitrile/methanol/water) in conjunction with MS/MS in SRM mode. Mechanisms for fragmentation
of deprotonated monosaccharides with regard to cross-ring cleavage were proposed. Matrix effects from coeluting interferences
were observed and isotopic-labeled internal standard was used to compensate for the signal suppression. The method demonstrated
excellent instrumental limits of detection (LOD), ranging from 0.7 to 4.2 pg. Method LODs range from 0.9 to 5.1 nM. The proposed
method was applied to the analysis of polysaccharides in seawater collected from the open leads of the central Arctic Ocean
in the summer of 2008. 相似文献
35.
Szabó L Herman K Leopold N Buzumurgă C Chiş V 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,79(1):226-231
The surface-enhanced Raman scattering (SERS) spectra of Eriochrome Black T (EBT) and its Cu(II), Fe(III), Mn(II) and Pb(II) complexes were recorded using a hydroxylamine reduced silver colloid. Molecular geometry optimization, molecular electrostatic potential (MEP) distribution and vibrational frequencies calculation were performed at B3LYP/6-31G(d) level of theory for the EBT molecule and its Cu(EBT), Fe(EBT) and Mn(EBT) metal complexes. Differentiation between EBT complexes of Cu(II), Fe(III), Mn(II) and Pb(II) is shown by the SERS spectral features of each complex. 相似文献
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Leopold Halpern 《General Relativity and Gravitation》1977,8(8):623-630
A gravitational law is proposed on a De Sitter covariant space. Dirac's De Sitter covariant spinning electron equation is generalized to the presence of gravitational fields. The resulting equation differs from the generally covariant Dirac equation by a mass renormalization. The last result is a generalization of that of Gürsey and Lee [2] in case of the homogenous De Sitter metric, and it gives a wider outlook on the significance of this result from the point of view of gauge theory.Dedicated to Achille Papapetrou on the occasion of his retirement. 相似文献