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121.
The interaction of β‐peptides with the DNA duplexes of dA20dT20 and a GCN4‐binding CRE sequence was examined. To gauge the factors that govern these interactions, two β‐pentadecapeptides, 1 and 2 , a β‐dodecapeptide, 3 , three β‐decapeptides, 4 – 6 , three β‐heptapeptides, 7 – 9 , and β‐octaarginine 10 were designed and synthesized. The β‐peptides were conceived to adopt a β‐peptide 314 helix, in which the side chains at position i and i + 3 are aligned vertically along one side of the helix. The side chains of Lys, Asn, and Arg were positioned such that potential H‐bonding sites were created for a helical conformation to interact with the base pairs of DNA. CD Analysis showed that β‐peptides 1, 2 , and 10 interacted with dA20dT20. In addition, β‐peptides 1 and 2 showed significant interaction with a DNA‐duplex 20mer containing the ATF/CREB recognition sequence for the regulatory protein GCN4. It is impossible, at this stage of the investigation, to make a safe proposal about the actual nature of the interaction of the structures(s) of the complexes, the formation of which is suggested by the CD spectra reported herein.  相似文献   
122.
In a follow-up of the earlier characterisation of botulinum toxins type A and B (BTxA and BTxB) by mass spectrometry (MS), types C, D, E, and F (BTxC, BTxD, BTxE, BTxF) were now investigated. Botulinum toxins are extremely neurotoxic bacterial toxins, likely to be used as biological warfare agent. Biologically active BTxC, BTxD, BTxE, and BTxF are comprised of a protein complex of the respective neurotoxins with non-toxic non-haemagglutinin (NTNH) and, sometimes, specific haemagglutinins (HA). These protein complexes were observed in mass spectrometric identification. The BTxC complex, from Clostridium botulinum strain 003-9, consisted of a 'type C1 and D mosaic' toxin similar to that of type C strain 6813, a non-toxic non-hemagglutinating and a 33 kDa hemagglutinating (HA-33) component similar to those of strain C-Stockholm, and an exoenzyme C3 of which the sequence was in full agreement with the known genetic sequence of strain 003-9. The BTxD complex, from C. botulinum strain CB-16, consisted of a neurotoxin with the observed sequence identical with that of type D strain BVD/-3 and of an NTNH with the observed sequence identical with that of type C strain C-Yoichi. Remarkably, the observed protein sequence of CB-16 NTNH differed by one amino acid from the known gene sequence: L859 instead of F859. The BTxE complex, from a C. botulinum isolated from herring sprats, consisted of the neurotoxin with an observed sequence identical with that from strain NCTC 11219 and an NTNH similar to that from type E strain Mashike (1 amino acid difference with observed sequence). BTxF, from C. botulinum strain Langeland (NCTC 10281), consisted of the neurotoxin and an NTNH; observed sequences from both proteins were in agreement with the gene sequence known from strain Langeland. As with BTxA and BTxB, matrix-assisted laser desorption/ionisation (MALDI) MS provided provisional identification from trypsin digest peptide maps and liquid chromatography-electrospray (tandem) mass spectrometry (LC-ES MS) afforded unequivocal identification from amino acid sequence information of digest peptides obtained in trypsin digestion.  相似文献   
123.
A template synthesis procedure yielded [Ni(HL1)NH3]I, where HL1 is the monoanion of the terdentate ONN benzoylacetone S-methylisothiosemicarbazone ligand. The reaction of this complex with an excess of NH4NCS, pyridine, or hydrazine resulted in the complexes [Ni(HL1)(NH3)NCS] and [Ni(L1)A] (A = Py, N2H4). The monoanionic form of the ligand is obtained by deprotonation of the enolic form of the benzoylacetone moiety, whereas the dianion is formed by additional deprotonation of the terminal NH2 group. Finally, the reaction of [Ni(HL1)NH3]I with salicyladehyde produced the NiL2 complex in which L2 stands for the dianion of the ONNO ligand N(1)-2-butylidene-4-oxo-4-phenyl-N(4)-salicylidene-S-methylisothiosemicarbazide. All complexes are diamagnetic and have a square-planar configuration, except for [Ni(HL1)(NH3)NCS], for which te data of i.r. spectra suggest a square-pyramidal structure. The electronic absorption spectra of the ethanolic solutions of all complexes are characteristic of typical square-planar coordination of nickel(II).  相似文献   
124.
A frit restrictor interface for capillary column supercritical fluid chromatography/mass spectrometry (SFC/MS) has been constructed and used for the analysis of high boiling point alkanes. Packed column SFC/MS is described using both a moving belt liquid chromatographic/mass spectrometric interface and a thermospray source in the filament-on mode.  相似文献   
125.
Vanadate and vanadium compounds exist in many environmental, biological and clinical matrices, and despite the need only limited progress has been made on the analysis of vanadium compounds. The vanadium coordination chemistry of different oxidation states is known, and the result of the characterization and speciation analysis depends on the subsequent chemistry and the methods of analysis. Many studies have used a range of methods for the characterization and determination of metal ions in a variety of materials. One successful technique is high performance liquid chromatography (HPLC) that has been used mainly for measuring total vanadium level and metal speciation. Some cases have been reported where complexes of different oxidation states of vanadium have been separated by HPLC. Specifically reversed phase (RP) HPLC has frequently been used for the measurement of vanadium. Other HPLC methods such as normal phase, anion-exchange, cation-exchange, size exclusion and other RP-HPLC modes such as, ion-pair and micellar have been used to separate selected vanadium compounds. We will present a review that summarizes and critically analyzes the reported methods for analysis of vanadium salts and vanadium compounds in different sample matrices. We will compare various HPLC methods and modes including sample preparation, chelating reagents, mobile phase and detection methods. The comparison will allow us to identify the best analytical HPLC method and mode for measuring vanadium levels and what information such methods provide with regard to speciation and quantitation of the vanadium compounds.  相似文献   
126.
Preparation and Crystal Structure of the Pnictide Oxides Na2Ti2As2O and Na2Ti2Sb2O Na2Ti2As2O and Na2Ti2Sb2O were synthesized in form of very easily hydrolysed metallic-grey powders by reaction of Na2O and TiAs resp. TiSb in sealed tantalum tubes under argon. The tetrahedral bodycentered crystallizing compounds from a modified anti-K2NiF4 structure type [1] (also called Eu4As2O-type [2,3]), space group I4/mmm (no. 139), with the lattice constants for Na2Ti2As2O: a = 407.0(2) pm, c = 1528.8(4) pm and for Na2Ti2Sb2O: a = 414.4(0) pm, c = 1656.1(1) pm. Magnetic measurements of powder samples of Na2Ti2Sb2O show antiferromagnetic interaction within the Ti—O-layers. Superconductivity was not found by ac-shielding method down to 4 K.  相似文献   
127.
A sensitive and specific method was developed for the determination of sophoridine (SRI), sophocarpine (SC) and matrine (MT) in rabbit plasma by HPLC-MS. After an administration of Kuhuang by injection, blood samples were collected and extracted with methanol. The extract solutions were analysed by HPLC-MS method. The separation was performed on a ZORBAX Extend-C18 column using methanol/water/diethylamine (50:50:0.07, v/v/v) as mobile phase. The quinolizidine alkaloids were detected by using mass spectrometry in the SIM mode. There was a good linear relationship between peak area and concentration of analytes over the concentration range of 13.2–995.0 ng mL–1 for SRI, 7.0–530.0 ng mL–1 for SC and 8.8–655.0 ng mL–1 for MT, respectively. The absolute recovery of this method was more than 57% for SRI, 87% for SC and 91% for MT. The accuracy of assay was more than 90%. The limits of detection (LODs) were 6.8 ng mL–1 for SRI, 3.5 ng mL–1 for SC and 4.2 ng mL–1 for MT, respectively. The limits of quantitation (LOQs) were 13.2 ng mL–1 for SRI, 7.0 ng mL–1 for SC and 8.8 ng mL–1 for MT, respectively. The intra-day and inter-day coefficients of variation (RSDs) were less than 10.1, 6.3 and 5.8% for SRI, SC and MT, respectively. The developed method was applied to determine the concentration–time profiles of SRI, SC and MT in rabbit plasma after injection of Kuhuang.  相似文献   
128.
The highly sulfated gamma-CD (HS-gamma-CD) is a chiral selector widely used in CE for the enantioseparation of pharmaceutical compounds. This paper investigated different approaches to reduce the stereoselective analysis time of amphetamine (AT) derivatives according to the chiral selector concentration in the BGE. With high HS-gamma-CD concentration, tested analytes were separated in 3.5 min as anionic complexes with short-end injection technique in reversed polarity mode. However, this procedure presented some limitations in terms of efficiency and resolution, excessive Joule heating and poor compatibility with MS detection. With low HS-gamma-CD concentration, compounds were separated as cations. Conventional approaches to reduce CE analysis time demonstrated critical resolution between some analytes. Therefore, the use of the partial-filling technique compatible with MS detection was carried out. Under optimized conditions, the analysis time for the chiral separation of seven AT like compounds was reduced to 6 min. Moreover, sensitivity of CE-MS was sufficient for the determination of ATs in plasma following a simple liquid-liquid extraction.  相似文献   
129.
Zilpaterol, (±)‐trans‐4,5,6,7‐tetrahydro‐7‐hydroxy‐6‐(isopropylamino) imidazo [4,5,1‐jk]‐[1]benzazepin‐2(1H)‐one, is an adrenergic agonist drug licensed in Mexico and South Africa as feed additive for cattle at slaughter age. In contrast, the EU legislative framework prohibits the use of beta‐agonists as growth promoters to produce lean meat. In this study, the compound was quantified as its TMS derivative both by gas chromatography‐mass spectrometry (GC‐MS) with a quadrupole detector (QUADR) and by GC‐MS/MS with an ion trap detector (ITD), in Electron Impact (EI) ionization. Subsequently, an extraction and clean‐up procedure for the identification of Zilpaterol in commercial feeds was set up. Different extraction solvents and matrices were considered for their influence on Zilpaterol yield. The analytical method led to good recoveries and limits of detection and quantification in feeds well below the 5–20 μg/g dose proposed for animal nutrition.  相似文献   
130.
Inductively coupled plasma mass spectrometry (ICP-MS) was used in an isotope dilution mode to assay small-volume (0.25 ml) sediment pore waters for their uranium contents, using 236U as the spike. The only pretreatment required was a simple dilution by a factor of 20, which gave sufficient volume for three replicate analyses per sample. Rapid and accurate results were obtained for a variety of samples and standards, ranging in concentration from 0.05 to 10 ng U ml?1. A suite of 30 samples can be analysed in less than 6 h by this method. The relative standard deviation was better than 1.9%, with a detection limit, based on 3σ background, of 2 pg U ml?1 in solution (40 pg ml?1 in samples). Sea water is a difficult matrix for ICP-MS and thus the method is generally suitable for uranium determinations in many other sample solutions.  相似文献   
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