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1.
Simone Schiesel Michael Lämmerhofer Wolfgang Lindner 《Analytical and bioanalytical chemistry》2010,397(1):147-160
In the present paper, we report on the development of a straightforward reversed-phase liquid chromatography–electrospray
ionization–tandem mass spectrometry method for the determination of the most abundant fatty acids; α-tocopherol and cephalosporin
P1 in fermentation broths. Using this method, fatty acids could be successfully determined in extracts of fermentation broths
from penicillin and cephalosporin production without prior derivatization. Matrix effects were investigated in detail, and
various kinds of calibrations (i.e., by use of neat standard solutions as well as by matrix-matched calibration employing
standard addition each with and without internal standards) were comparatively assessed. The optimized and validated method
was employed for the analysis of extracts of fermentation broths and nutrition media. 相似文献
2.
This study reports in detail the results of systematic large-scale theoretical investigations of the acidic dimeric structural
units (D–E, E–F, F–G, and G–H) and pentamer D–E–F–G–H (fondaparinux) of the glycosaminoglycan heparin, and their anionic forms.
The geometries and energies of these oligomers have been computed using HF/6–31G(d), Becke3LYP/6–31G(d), and Becke3LYP/6–311+G(d,p)
methods. The optimized geometries indicate that the most stable structure of these units in the neutral state is stabilized
via a system of intramolecular hydrogen bonds. The equilibrium structure of these species changed appreciably upon dissociation.
Water has a remarkable effect on the geometry of the anions studied. Because of high negative charge, the solvent effect also
resulted in an appreciable energetic stabilization of biologically active anionic forms of these glycosaminoglycans. The stable
energy conformations around glycosidic bonds found for dimers and pentamer investigated are compared and discussed with the
available experimental X-ray structural data for the structurally related heparin-derived pentasaccharides in cocrystals with
proteins. 相似文献
3.
A simple and direct spectrophotometric method is developed for the determination of some cephalosporin group antibiotic drugs
such as Loracarbef (Lora), Ceftazidime (Ceft), and Cefaclor (Cefa) in bulk and pharmaceutical formulations. The optimum conditions
for the analysis of aqueous solutions of drugs are studied. Under the optimum conditions, the three drugs could be assayed
in the concentration range 2–9 × 10−5, 2–6 × 10−5, and 3–9 × 10−5 M for Lora, Ceft and Cefa, respectively. Detection and quantification limits are calculated. The obtained results showed
good recoveries of 100.4, 107.4, and 100.7% for Lora, Ceft, and Cefa, respectively. The results obtained are compared favorably
with those given by literature methods. 相似文献
4.
V. N. Emel’yanenko S. P. Verevkin E. N. Burakova G. N. Roganov M. K. Georgieva 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2009,83(8):1271-1279
The enthalpies of formation of δ-hexanolactone and δ-nonanolactone were determined by combustion calorimetry. Conformational
analysis and quantum-chemical calculations of equilibrium structures, fundamental vibrations, moments of inertia, and total
energies were performed for δ-pentanolactone (I), δ-hexanolactone (II), and δ-nonanolactone (III) by the B3LYP/6-311G(d,p), B3LYP/6-311++G(d,p), and G3MP2 methods. The experimental IR spectra and calculated vibrational frequencies were used to suggest the assignment
of vibrational frequencies of stable conformations. The thermodynamic properties of I–III in the ideal gas state were determined over the temperature range 0–1500 K. A thermodynamic analysis of mutual isomerization
in the gas and liquid phases over the temperature range 298.15–900 K and liquid-phase polymerization of γ- and δ-pentanolactones
and 4-pentenoic acid over the temperature range 298.15–500 K was performed. 相似文献
5.
Huachuan Cao Yinsheng Wang 《Journal of the American Society for Mass Spectrometry》2009,20(4):611-617
The collision-induced dissociation pathways of isomeric cytosine-guanine and cytosine-adenine intrastrand crosslink-containing
dinucleoside monophosphates were investigated with the stable isotope-labeled compounds to gain insights into the effects
of chemical structure on the fragmentation pathways of these DNA modifications. A Dimroth-like rearrangement, which was reported
for protonated 2′-deoxycytidine and involved the switching of the exocyclic N4 with the ring N3 nitrogen atom, was also observed
for the cytosine component in the protonated ions of C[5–8]G, C[5–2]A, and C[5–8]A, but not C[5-N
2]G or C[5-N
6]A. In these two sets of crosslinks, the C5 of cytosine is covalently bonded with its neighboring purine base via a carbon
atom on the aromatic ring and an exocyclic nitrogen atom, respectively. On the contrary, the rearrangement could occur for
the deprotonated ions of C[5-N
2]G, C[5-N
6]A, and unmodified cytosine, but not C[5–8]G, C[5–2]A, or C[5–8]A. In addition, ammonia could be lost more readily from C[5-N
2]G and C[5-N
6]A than from C[5–8]G, C[5–2]A, and C[5–8]A. The results from the present study afforded important guidance for the application
of mass spectrometry for the structure elucidation of other intrastrand/interstrand crosslink lesions. 相似文献
6.
Khaled Bahgat 《Central European Journal of Chemistry》2006,4(4):773-785
The solid phase FT-IR and FR-Raman spectra of acetyl coumarin have been recorded in the regions 4000–50 cm−1. The spectra were interpreted with the aid of normal coordinate analysis following full structure optimization and force
field calculations based on density functional theory (DFT) and Hartree-Fock (HF) at 6–31G* and 6–311++G** basis sets. The
resulting force fields were transformed to internal coordinates, the calculated vibrational frequencies and normal modes were
utilized in the assignment of the observed vibrational fundamentals. The measured spectral data were used to refine the vibrational
force constants by means of a small number of scaling factors. 相似文献
7.
Bhagwant S. Despande Sudha S. Ambedkar Jaiprakash G. Shewale 《Applied biochemistry and biotechnology》1996,60(3):245-250
A simple method based on Schiff’s base formation betweenp-dimethylaminobenzaldehyde and cephalosporin C is developed for estimation of cephalosporin C. The calibration curve was linear
up to 500 μg of cephalosporin C. The application of the method in monitoring bioconversion of cephalosporin C to glutaryl-7-amino
cephalosporanic acid is described. 相似文献
8.
Use of some organic dyes in gamma irradiation dose determination 总被引:1,自引:0,他引:1
In the present work, the radiation-induced color bleaching of Remazol brilliant blue (RBB), Wegocet orange (WO), Methyl green
(Me G) and Thioflavine S (Th S) dyes solutions was studied. Solutions of these dyes in different solvents were found to obey
Beer’s law within certain concentration levels. The % color bleaching occurring in different dye solutions on using different
gamma irradiation doses was determined and the data obtained showed the existence of good linear relationships among them
in the four dye systems used. The linear sections lines were used as calibration curves for evaluating unknown gamma irradiation
doses. From the obtained results, it was concluded that RBB in water, WO in ethanol, Me G in butanol and Th S in 60% ethanol–water
mixture could be used for dose evaluation within the dose ranges 5–25 kGy for RBB, 20–90 kGy for WO, 10–70 kGy for Me G and
5–160 kGy for Th S. The sensitivity of the systems towards gamma radiations has been also reported. 相似文献
9.
Summary The possibility of determination of four cephalosporin antibiotics in clinical samples by capillary electrophoresis has been
investigated. The separation conditions for capillary zone electrophoresis (CZE) were studied in detail. The precision of
migration times measured by use of the optimized method was satisfactory (RSD<1%) and response was linearly dependent on concentration
over the approximate range 2–150 mg L−1 for all the compounds studied (cefuroxime, cefotaxime, ceftriaxone, and ceftazidime). Complete separation could be achieved
within 5 min. The CZE method was found to be highly suitable for direct determination of the antibiotics in clinical samples
such as wound drainage, cerebrospinal fluid, and urine; for serum, however, the use of micellar electrokinetic capillary chromatography
(MECC) was more advantageous.
Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001 相似文献
10.
Clavijo CF Hoffman KL Thomas JJ Carvalho B Chu LF Drover DR Hammer GB Christians U Galinkin JL 《Analytical and bioanalytical chemistry》2011,400(3):715-728
Opioids such as morphine are the cornerstone of pain treatment. The challenge of measuring the concentrations of morphine
and its active metabolites in order to assess human pharmacokinetics and monitor therapeutic drugs in children requires assays
with high sensitivity in small blood volumes. We developed and validated a semi-automated LC-MS/MS assay for the simultaneous
quantification of morphine and its active metabolites morphine 3β-glucuronide (M3G) and morphine 6β-glucuronide (M6G) in human
plasma and in dried blood spots (DBS). Reconstitution in water (DBS only) and addition of a protein precipitation solution
containing the internal standards were the only manual steps. Morphine and its metabolites were separated on a Kinetex 2.6-μm
PFP analytical column using an acetonitrile/0.1% formic acid gradient. The analytes were detected in the positive multiple
reaction mode. In plasma, the assay had the following performance characteristics: range of reliable response of 0.25–1000 ng/mL
(r
2 > 0.99) for morphine, 1–1,000 ng/mL (r
2 > 0.99) for M3G, and 2.5–1,000 ng/mL for M6G. In DBS, the assay had a range of reliable response of 1–1,000 ng/mL (r
2 > 0.99) for morphine and M3G, and of 2.5–1,000 ng/mL for M6G. For inter-day accuracy and precision for morphine, M3G and
M6G were within 15% of the nominal values in both plasma and DBS. There was no carryover, ion suppression, or matrix interferences.
The assay fulfilled all predefined acceptance criteria, and its sensitivity using DBS samples was adequate for the measurement
of pediatric pharmacokinetic samples using a small blood of only 20–50 μL. 相似文献
11.
Calculation of the hydrogen binding energies of complexes between formamide and adenine-thymine pair
Chun-sheng Duan Hui Fu Jin-mao You Ke-sheng Ma Zheng-yu Zhou 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(13):2300-2305
The hydrogen bonding of complexes formed between formamide and adenine-thymine base pair has been completely investigated
in the present study. In order to gain deeper insight into structure, charge distribution, and energies of complexes, we have
investigated them using density functional theory at 6–311++G(d, p), 6–31G, 6–31+G(d), and 6–31++G(d, p) level. Seven stable cyclic structures (ATF1–ATF7) being involved in the interaction has been found on the potential energy
surface. In addition, for further correction of interaction energies between adenine—thymine and formamide, the basis set
superposition error associated with the hydrogen bond energy has been computed via the counterpoise method using the individual
bases as fragments. The infrared spectrum frequencies, IR intensities and the vibrational frequency shifts are reported. 相似文献
12.
The molecular and electronic structure of the ground state of peroxyacetyl nitrate (PAN) was calculated by the unrestricted
Hartree-Fock-Roothaan method with the use of the standard 3–21G and 6–31G basis set. The potential curve of the internal rotation
about the peroxide bond of PAN was calculated with the 6–31G basis set. The curve contains two maxima. The ground state of
PAN is characterized by a structure in which groups of atoms adjacent to the peroxide bond lie in planes that are perpendicular
to each other (the dihedral angle ϱ(COON) is 89.9°). The calculated barriers to rotation are 19.6 and 66.8 kJ mol−1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 600–604, April, 1998. 相似文献
13.
Bernardino Susana Estrela Nídia Ochoa-Mendes Vanessa Fernandes Pedro Fonseca Luís P. 《Journal of Sol-Gel Science and Technology》2011,58(2):545-556
Biocatalysis presents a sound alternative to chemical synthesis in the field of drug production, given the highly selective
nature of biological catalysts. Penicillin G Acylase (PGA) from E. coli is currently used to hydrolyze penicillin G (PG) and catalyzes the synthesis of β-lactam antibiotics. In this work, particular
emphasis is given to recent developments in penicillin G acylase immobilization, by entrapment simultaneously with nano-magnetic
particles in a silica matrix. The sol–gel biocatalytic particles were prepared either by a conventional method (crushed powder)
or by a more recent approach, based in an emulsion system using 150 mM AOT/isooctane, which allowed for the formation of spherical
micro- and nanobeads. The effects on PGA activity of different sol–gel precursors, additives, enzyme concentration, aging,
drying conditions and mechanical stability were evaluated. After these optimization studies, a mechanically stable carrier
based on porous xerogels silica matrixes, starting from tetramethoxysilane (TMOS) with 65–67% PGA activity yield in these
carriers allowed an immobilization yield of 74 mg protein gdry sol–gel−1 and 930 Ugdry sol–gel−1 for specific activity were obtained. 相似文献
14.
A new affinity adsorbent, using D-alanyl-D-alanine as ligand, has been prepared. The dipeptide immobilized on Activated CH-Sepharose
4B (D-Ala-D-Ala-AGA) bioselectively binds the glycopeptide antibiotics teicoplanin, vancomycin, ristocetin A (vancomycinlike
group of antibiotics) while it does not bind other antibiotics equally active on cell wall biosynthesis but with different
target sites, such as penicillin G, cephalosporin C, gardimycin, and bacitracin. Teicoplanin, vancomycin, and ristocetin A
have similar binding characteristics for the immobilized dipeptide, as indicated by equilibrium binding experiments. The affinity
constants of the three antibiotics for D-Ala-D-Ala-AGA is of the same order of magnitude (105 L mol-1) and the number of effective binding sites is similar for each antibiotic (6–7 μEq/mL of gel). The adsorption is biospecific
as no binding has been observed to immobilized L-alanyl-L -alanine.
D-Ala-D-Ala-AGA has been successfully used to purify teicoplanin from mixtures of different complexity and for concomitant
extraction and purification from fermentation liquors by both batch adsorption and column chromatography. The antibiotic can
be recovered from the resin in high yields by elution at pH 11. 相似文献
15.
The direct molecular structure implementations of the gage-including atomic orbital (GIAO), individual gages for atoms in
molecules (IGAIM) and continuous set of gage transformations (CSGT) methods for calculating nuclear magnetic shielding tensors
at both the Hartree-Fock (HF) and density functional (B3LYP) levels of theory with 6-31G(d), 6-311G(d), 6-31++G(d,p), 6-311++G(d,p),
and 6-311++G(df,pd) basis sets are presented. Dependence on the 1H and 13C NMR chemical shifts on the choice of method and basis set have been investigated. Also, these chemical shifts of 2-aryl-1,3,4-oxadiazoles
5a–g have been performed related to dihedral angles (C4–C3–C2–O) of two conformers. The optimized molecular geometries and 1H and 13C chemical shift values of 2-aryl-1,3,4-oxadiazoles 5a–g in the ground state have been obtained. The linear correlation coefficients of 13C NMR chemical shifts for these molecules were given. The new nuclear magnetic shielding tensors of tetramethylsilane (TMS)
were calculated. The data of 2-aryl-1,3,4-oxadiazole derivatives display significant molecular structure and NMR analysis.
Also, these provide the basis for future design of efficient materials having the 1,3,4-oxadiazole core. 相似文献
16.
The DFT-B3LYP and G3X model chemistry were used to predict the cation structures and energetics of fluorinated, chlorinated,
and brominated methanes. Ion–complex structures between methylene cations and HX (X = F, Cl, Br) were found for all H-containing
cations, and [CHF–FH]+, [CF2–FH]+, [CCl2–ClH]+, and [CCl2–FH]+ structures are more stable than their normal tetravalent structures. Several cations should also be better described as ion–complex
structures between methyl cations and halogen atoms, e.g., [CF3–Br]+. Transition states connecting normal and ion–complex structures were also located, and potential energy diagrams were constructed
for decomposition of methane cations and to predict the fragmentation pathways. The G3X energies were used to predict the
adiabatic ionization energies (IEas) and ion fragment appearance energies (AEs) from methanes. Many of the experimental AEs correspond to the energies of transition
states instead of the thermodynamic dissociation limits.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
17.
Equilibrium ground state geometry configurations and their relevant electronic properties of four experimentally reported
asymmetric spirosilabifluorene derivatives are calculated by the HF(DFT)/6-31G(d) method. Their excited state geometries are
investigated using the CIS/6-31G(d) method. The absorption and emission spectra are evaluated using the TD-B3LYP/6-31G(d)
and TD-PBE0/6-31+G(d) levels both in gas phase and CHCl3 solvent. Our results show an excellent agreement with the experimental data on their optical properties. To predict the substitution
effect, the H/R (R = –NO2, –CN, –NH2 and –OCH3) substituted symmetric and asymmetric spirosilabifluorene derivatives are also investigated, and the optical properties of
H/R substituted derivatives are predicted in gas phase and CHCl3 solvent. In comparison with the parent compound, significant red-shift is predicted for the emission spectra of the di-substituted
symmetric derivatives with –NH2 (96 nm), –OCH3 (61 nm) and the push–pull (containing both –NH2 and –NO2) derivative (56 nm). It is found that the performance and the optical properties of these derivatives can be improved by
adding push–pull substitutents. The largest change in the electronic and optical properties of this system can be obtained
upon symmetric di-substitution among mono-, di-, tri- and tetra-substitutions.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
18.
Salt ions were found to have an influence on template binding to two model molecularly imprinted polymers (MIPs), targeted
to penicillin G and propranolol, respectively, in water–acetonitrile mixtures. Water was detrimental to rebinding of penicillin
G whereas propranolol bound in the entire water–acetonitrile range tested. In 100% aqueous solution, 3-M salt solutions augmented
the binding of both templates. The effects followed the Hofmeister series with kosmotropic ions promoting the largest increase.
Binding was mainly of a non-specific nature under these conditions. In acetonitrile containing low amounts of water, the specific
binding to the MIPs increased with the addition of salts. Binding of penicillin G followed the Hofmeister series while an
ion-exchange mechanism was observed for propranolol. The results suggest that hydration of kosmotropic ions reduces the water
activity in water-poor media providing a stabilizing effect on water-sensitive MIP–template interactions. The effects were
utilized to develop a procedure for molecularly imprinted solid-phase extraction (MISPE) of penicillin G from milk with a
recovery of 87%. 相似文献
19.
The conformational composition of gaseous MTMNB and the molecular structures of the rotational forms have been studied by
electron diffraction at 130∘C aided by results from ab initio and density functional theory calculations. The conformational potential energy surface
has been investigated by using the B3LYP/6-31G(d,p) method. As a result, six minimum-energy conformers have been identified.
Geometries of all conformers were optimized using MP2/6-31G(d,p), B3LYP/6-31G(d,p), and B3LYP/cc-pVTZ methods. These calculations
resulted in accurate geometries, relative energies, and harmonic vibrational frequencies for all conformers. The B3LYP/cc-pVTZ
energies were then used to calculate the Boltzmann distribution of conformers. The best fit of the electron diffraction data
to calculated values was obtained for the six conformer model, in agreement with the theoretical predictions. Average parameter
values (ra in angstroms, angle α in degrees, and estimated total errors given in parentheses) weighted for the mixture of six conformers
are r(C–C) = 1.507(5), r(C–C)ring, av = 1.397(3), r(C–S)av = 1.814(4), r(C–N) = 1.495(4), r(N–O)av = 1.223(3), ∠(C–C–C)ring = 116.0–122.5, ∠ C6–C4–C7 = 118.2(4), ∠ C–C–S = 113.6(6), ∠ C–S–C = 98.5(12), ∠ N–C–C4 = 121.9(3), ∠(O–N–C)av = 116.8(3), ∠ O–N–O = 127.0(4). Torsional angles could not be refined. Theoretical B3LYP/cc-pVTZ torsional angles for the
rotation about C–N bond, φC−N, were found to be 30.5–36.5∘ for different conformers. As to internal rotation about C–C and C–S bonds, values of φC−C = 68–118∘ and φC−S = 66–71∘ were obtained for the three most stable conformers with gauche orientation with respect to these bonds.
Some conclusions of this work were presented in a short communication in Russ. J. Phys. Chem. 2005, 79, 1701. 相似文献
20.
M. Z. Kassaee M. R. Momeni F. A. Shakib M. Ghambarian S. M. Musavi 《Structural chemistry》2009,20(3):517-524
Biologically important bicyclic species, including 6H-, 6H-6-aza-, and 6-oxabenzocycloheptatrienes (in which the benzene moiety is fused meta with respect to the tetrahedral constituents: –CH2–, –NH–, and –O–, respectively), show strong shifts of tautomerizations in favor of the corresponding tricyclic benzonorcaradienes
(with ΔH values of −11.49, −14.55, and −19.20 kcal mol−1, respectively), at B3LYP/6-311++G**//B3LYP/6-31G*, and MP2/6-311++G**//MP2/6-31G* levels, and at 298 K. In contrast, such
shifts are strongly disfavored by the isomeric bicyclic species in which the benzene moieties are fused ortho or para with respect to –CH2–, –NH–, and –O–, respectively. Hence for species with ortho benzene rings including 5H-, 5H-5-aza- and 5-oxabenzocycloheptatrienes, tautomerization ΔH values are 30.76, 31.89, and 25.27 kcal mol−1, respectively, while for species with para fused benzene moieties including 7H-, 7H-7-aza-, and 7-oxabenzocycloheptatrienes, tautomerization ΔH values are 24.12, 26.00, and 19.55 kcal mol−1, respectively. NICS calculations are successfully used to rationalize these results. The calculated energy barriers for inversion
of the seven-membered rings of bicyclic species predict a dynamic nature for all the structures except for the virtually planar
6H-6-aza- and 6-oxabenzocycloheptatrienes. Finally, our theoretical data are compared to the experimental results where available.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献