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1.
M. L. Ostrofsky 《Hydrobiologia》2012,696(1):199-203
Several methods are in use to measure total phosphorus in lake sediments making cross-study comparisons tenuous, and may lead to potential errors in calculating other phosphorus fractions. Four methods in common use in the limnological literature were compared using sediments spanning a range of organic content from 2 to 35% C. No significant differences were found in within-lake comparisons, although a method using persulfate oxidation was highly variable, and this variability was correlated with organic content suggesting inconsistent oxidation. The other methods (combustion, acid digestion with HClO4, H2SO4 + H2O2) gave uniformly small variances. 相似文献
2.
L. A. Stetsenko V. Yu. Rakitin N. I. Shevyakova Vl. V. Kuznetsov 《Russian Journal of Plant Physiology》2009,56(6):808-813
The content of free and conjugated polyamines (PA) was studied in the leaves of secondary shoots and in roots of the facultative
halophyte Mesembryanthemum crystallinum L. under salinity. Plants were grown in water culture and at the age of 10 weeks were subjected to salinity stress by a single
introduction of NaCl into nutrient medium to a final concentration of 400 mM. In 0, 6, 24, and 48 h, the content of free,
HClO4-soluble, and HClO4-insoluble conjugates of PA were measured in leaves and roots. The levels of free and conjugated PA in the roots of control
plants and plants subjected to salinity stress were higher than in the leaves. In response to salinity shock, the content
of all forms of spermine (Spm), particularly its HClO4-soluble conjugates, increased in roots and leaves. In contrast, the content of Spm precursors, putrescine (Put) and spermidine
(Spd), as well as their HClO4-soluble conjugates, decreased. Salinity treatment elevated the content of free cadaverine both in roots and leaves, whereas
the content of its conjugated forms decreased, which might suggest transition of conjugated forms of cadaverine into the free
form. The product of oxidative degradation of Spm and Spd, 1,3-diaminopropane (Dap), was absent in leaves, whereas the content
of free and conjugated forms of this diamine in roots increased under salinity conditions. The obtained data indicate organ
specificity for the content of free and conjugated forms of PA, as well as their active role in adaptation of Mesembryanthemum crystallinum to salinity shock. 相似文献
3.
Frank J. Koppenhagen Gert Storm Willy J. M. Underberg 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1998,716(1-2)
This paper describes the development of an isocratic reversed-phase high-performance liquid chromatographic method for the routine analysis of recombinant interleukin-2 (rIL-2) in liposome samples. The chromatographic system employed a C4 column maintained at 30°C eluted with 52.5% (w/w) acetonitrile in water, containing 100 mM NaClO4 and 10 mM HClO4. To remove phospholipid interference the chromatographic method was combined with a lipid-extraction procedure. No significant loss of rIL-2 was noted upon inclusion of this extraction step. The protein eluted from the column with a capacity factor (k′) of 5.8. The method was validated for robustness, linearity, precision and reproducibility. It was shown that the method was linear over a sample concentration range of 1–100 μg/ml. Upon assessment of the intra-day and inter-day precision, the relative standard deviations (RSD) were within the range of the methodical error (approximately 5%), except at the lower concentration of 10 μg/ml, where the intra-day RSD was relatively high (17.8%). The recovery of rIL-2 upon liposome preparation and subsequent analysis of the samples was in the range 94±9%. The results indicate that the method is suitable for routine quantitation of rIL-2 in liposomal samples. 相似文献
4.
The selenium determination in biological materials by the classical fluorometric method (FM) is time-consuming and also hazardous,
as it requires the destruction of the organic matrix samples with hot HNO3/HClO4 mixtures prior to analysis. Accordingly, commercial analytical laboratories are increasingly using faster instrumental methods;
for sample digestion, avoid using HClO4. Because of these procedural changes, the results obtained by commercial laboratories may be unreliable, especially for samples
containing Se in organic forms. One such “difficult” substrate is Se yeast, which contains most of its Se as selenomethionine.
To establish which methods for Se analysis and sample digestion are applicable, samples of Se yeast and of selenomethionine
standards were sent to laboratories employing either flame atomic absorption spectrometry (FAAS), inductively coupled plasma-mass
spectrometry (ICP-MS), or hydride generation atomic absorption spectrometry (HGAAS). The result were compared with those obtained
by FM and non-destructive instrumental neutron activation analysis (INAA). ICP-MS, after microwave digestion of sample with
HNO3/H2O2, produced results within 5% of the expected values, as did those obtained by FM and INAA. With FAAS, acceptable results were
obtained after digestion with HNO3/HCl. With HGAAS, sample digestion with HNO3/H2O2 produced values that were systematically elevated by about 10% and exhibited standard deviations of ≥10%. Thus, current methods
of sample digestion are applicable for Se yeast analysis by ICP-MS and FAAS, but not by HGAAS. 相似文献
5.
《Inorganica chimica acta》1988,141(2):211-220
The reaction of CrCl3 · 6H2O (dehydrated in DMSO) with 1,5,9-triazanonane (3,3-tri) gives mer- CrCl3(3,3-tri), the configuration being established by isomorphism with the corresponding Co(III) complex. This non-electrolyte is hydrolyzed in aqueous acidic solution and mer-[CrCl2(3,3-tri)- (OH2)]ClO4 can be isolated by anation with HCl in the presence of HClO4. Reaction of mer-CrCl3- (3,3-tri) in DMF with diamines produces complexes of the type [CrCl(diamine)(3,3-tri)] Cl2 [diamine= 1,2-diaminoethane (en), 1.2-diaminopropane (pn), 1,3-diaminopropane (tn), 2,2-dimethyl-1,3-diaminopropane (Me2tn) and cyclohexanediamine (chxn, cis plus trans mixture; two isomers A and B)] and these have been characterized as the ZnCl42− salts. The configuration of the triamine ligand in these complexes has been established as mer-(H↓)- by a single crystal X-ray analysis of [CrCl(en)(3,3-tri)]- ZnCl4, monoclinic, P21, a=7.932, b= 14.711, c= 8.312 Å, β=104.6° and Z=2, refined to a conventional R factor of 0.034. The kinetics of the Hg2+- assisted chloride release from [CrCl(diamine)(3,3- tri)]ZnCl4 salts were measured spectrophotometrically (μ=1.0 M HClO4 or HNO3) over 15 K temperature ranges to give, in order, 104kHg (298.2 K) (M−1 s−1), Ea(kJ mol−1), ΔS# (J K−1 mol−1): en- (HClO4): 5.95, 78.1, -53; pn(HClO4); 5.24, 81.2; -44; tn(HClO4): 26.7, 85.6, -15; Me2tn(HClO4): 21.8, 78.6, -40; A-chxn(HNO3): 7.60, 81.0,-41; B-chxn(HNO3): 18.3, 56.8, -115. A ‘non-replaced ligand effect’ on the rate is observed for the first time in this series of homologous Cr(III) complexes. The kinetics of the thermal aquation (kH, 0.1 M HClO4) were measured titrimetrically for CrCl(diamine) (3,3-tri)2+ to give the following kinetic parameters: diamine=en: 107 kH (298.2)=5.34 s−1, Ea=99.2 kJ mol−1, ΔS#=-40 J K−1 mol-1; diamine =tn: 107 kH (298.2)=5.04 s−1, Ea= 82.8, ΔS#= -96. 相似文献
6.
The complexation of Al3+, Zn2+, Cd2+ and Pb2+ by the 3-hydroxyflavones: 3-hydroxy-2-(2-methoxyphenyl)-4H-1-benzopyran-4-one (H1) and 3-hydroxy-2-(4-methoxyphenyl)-4H-1-benzopyran-4-one (H2), and by the 3-methoxythioflavone: 3-hydroxy-2-(2-methoxyphenyl)-4H-1-benzopyran-4-thione (H3) have been studied spectrophotometrically and fluorimetrically to determine the corresponding complexation constants, Ksp and Kfl, in 5:95 water:ethanol (v/v) solution for which [HClO4] was either 10−2 or 10−5 mol dm−3 and I = 0.10 mol dm−3 (NaClO4) at 298.2 K. Complexation occurs dominantly through the deprotonated ligand for [Al(1)]2+ and [Al(2)]2+ for which log Ksp = 4.51 and 4.73, respectively, in 10−2 mol dm−3 HClO4 and 4.21 and 4.61 in 10−5 mol dm−3 HClO4. For Pb2+ complexation by H1, H2 and H3 is characterized by log Ksp = 2.20, 2.57 and 3.22, respectively, in 10−2 mol dm−3 HClO4 and 4.70, 5.38 and 5.74 in 10−5 mol dm−3 HClO4. Equilibrium mixtures of [Pb(H1)]2+ and [Pb1]+, [Pb(H2)]2+ and [Pb2]+, and [Pb(H3)]2+ and [Pb3]+ appear to be formed. Complexation of Zn2+ and Cd2+ by all three ligands was only detected in 10−5 mol dm−3 HClO4. For Zn2+ complexation by H1, H2 and H3 log Ksp = 3.22, 3.74 and 4.46 and for Cd2+ the corresponding values are 2.39, 2.40 and 3.72 for Cd2+. Only [Al1]2+ and [Al2]2+ show significant fluorescence and are characterized by log Kfl = 6.30 and 7.49 in 10−2 mol dm−3 HClO4. 相似文献
7.
Jitendra N. Tiwari Ahmad M. Harzandi Miran Ha Siraj Sultan Chang Woo Myung Hyo Ju Park Dong Yeon Kim Pandiarajan Thangavel Aditya Narayan Singh Pankaj Sharma Selvaraj Selva Chandrasekaran Foad Salehnia Ji‐Wook Jang Hyeon Suk Shin Zonghoon Lee Kwang S. Kim 《Liver Transplantation》2019,9(26)
The most efficient electrocatalyst for the hydrogen evolution reaction (HER) is a Pt‐based catalyst, but its high cost and nonperfect efficiency hinder wide‐ranging industrial/technological applications. Here, an electrocatalyst of both ruthenium (Ru) single atoms (SAs) and N‐doped‐graphitic(GN)‐shell‐covered nitrided‐Ru nanoparticles (NPs) (having a Ru‐Nx shell) embedded on melamine‐derived GN matrix { 1 : [Ru(SA)+Ru(NP)@RuNx@GN]/GN}, which exhibits superior HER activity in both acidic and basic media, is presented. In 0.5 m H2SO4/1 m KOH solutions, 1 shows diminutive “negative overpotentials” (?η = |η| = 10/7 mV at 10 mA cm?2, lowest ever) and high exchange current densities (4.70/1.96 mA cm?2). The remarkable HER performance is attributed to the near‐zero free energies for hydrogen adsorption/desorption on Ru(SAs) and the increased conductivity of melamine‐derived GN sheets by the presence of nitrided‐Ru(NPs). The nitridation process forming nitrided‐Ru(NPs), which are imperfectly covered by a GN shell, allows superb long‐term operation durability. The catalyst splits water into molecular oxygen and hydrogen at 1.50/1.40 V (in 0.1 m HClO4/1 m KOH), demonstrating its potential as a ready‐to‐use, highly effective energy device for industrial applications. 相似文献
8.
《Carbohydrate research》1986,154(1):127-144
The synthesis of all four deoxyfluoro-α-d-glucopyranosyl phosphates is described. Rate constants for their acid-catalyzed hydrolysis were determined, and fluorine substitution was shown to have a significant effect in lowering the rate, particularly when the substitution is adjacent to the anomeric center. Relative rate-constants measured in m HClO4 at 25° are 60.30:1.00:7.05:3.97:16.5 for α-d-glucopyranosyl phosphate and the 2-, 3-, 4- and 6-deoxyfluoro derivatives, respectively. The hydrolysis of 2-deoxy-2-fluoro-α-d-glucopyranosyl phosphate was studied in more detail, and an activation entropy and enthalpy of 4.1 e.u. (m reactant) and 113.5 kJ.mol−1, respectively, were determined for hydrolysis in m HClO4 at 60° The pH dependence of its hydrolysis was investigated, and rate constants for hydrolysis of the monoanion (kM = 1.88 × 10−6 s−1) and neutral (kN = 6.23 × 10−5 s−1) species were thus extracted. Hydrolysis of the monoanion is not significantly affected by fluorine substitution, as expected. The ability or inability of several mechanistically distinct enzymes to utilize these fluorinated substrates is rationalized in the light of these findings. 相似文献
9.
László Sipos István Ilisz Anita Aranyi Zsanett Gecse Melinda Nonn Ferenc Fülöp Myung Ho Hyun Antal Péter 《Chirality》2012,24(10):817-824
The enantiomers of four unusual isoxazoline‐fused 2‐aminocyclopentanecarboxylic acids were directly separated on chiral stationary phases containing (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid as chiral selector. The nature of the alcoholic modifier (MeOH, EtOH, IPA) exerted a great effect on the retention, whereas the selectivity and resolution did not change substantially. Two types of dependence of retention on alcohol content were detected: k1 increased continuously with increasing alcohol content or a U‐shaped retention curve was observed. A comparison of the chromatographic data obtained with HCOOH, AcOH, TFA, HClO4, H2SO4, or H3PO4 as acidic modifier at a constant concentration demonstrated that in most cases, larger k values were obtained on the application of AcOH or HCOOH, and an increase of the acid content resulted in a decrease of retention. Some mechanistic aspects of the chiral recognition process are discussed with respect to the structures of the analytes and selector. The sequence of elution of the enantiomers was determined in all cases. Chirality 24:817‐824, 2012. © 2012 Wiley Periodicals, Inc. 相似文献
10.
Olaf R. Ludek 《Carbohydrate research》2010,345(14):2074-2383
Obtaining high stereoselectivity in glycosylation reactions is often challenging in the absence of neighboring group participation. In this study, we demonstrate that activation of glycosyl trichloroacetimidate donors with immobilized perchloric acid on silica (HClO4-SiO2) provides higher α-selectivity than trimethylsilyl triflate (TMSOTf) for reactions that do not involve neighboring group participation. 相似文献
11.
The transformation of acetonides into acetates is frequently required in synthetic chemistry. An efficient procedure for direct conversion of acetonides into acetates in the presence of HClO4-SiO2 under mild conditions was developed. The acetonides of primary hydroxy groups are directly converted to diacetates, and the anomeric acetonides of furanosides are stereoselectively transformed into the corresponding acetyl β-d-furanosides with a 2-acetoxyisopropyl group. 相似文献
12.
The kinetics of oxidation of sunset yellow (SY) by sodium-N-chloro-p-toluenesulfonamide or chloramine-T (CAT) was studied spectrophotometrically in HClO4 and NaOH media with Os(VIII) as a catalyst in the latter medium at 298 K and 303 K, respectively. In acid medium, the experimental rate law is −d[CAT]/dt = k[CAT]0[SY]0[HClO4]−0.46. Alkali accelerates the rate of reaction and the rate law takes the form −d[CAT]/dt = k[CAT]0[SY]0[NaOH]0.23[OsO4]0.84. The solvent isotope effect was studied using D2O. Benzenesulfonic acid and 1,2-naphthoquinone-6-sulfonic acid were characterized as the oxidation products of SY. Under identical set of experimental conditions in alkaline medium, Os(VIII) catalyzed reaction is about seven-fold faster than the uncatalyzed reaction. Activation parameters for the overall reaction and also with respect to catalyst have been evaluated. The observed results have been explained by plausible mechanisms and the related rate laws have been deduced. 相似文献
13.
I. N. Valassis M. Parissi-Poulou P. Macheras 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1999,721(2):79
An isocratic reversed-phase HPLC method was developed to determine cefepime levels in plasma and vitreous fluid. Cefepime and the internal standard cefadroxil were separated on a Shandon Hypersil BDS C18 column by using a mobile phase of 25 mM sodium dihydrogen phosphate monohydrate (pH 3) and methanol (87:13, v/v). Ultraviolet detection was carried out at 270 nm. The retention times were 4.80 min for cefepime and 7.70 min for cefadroxil. This fast procedure which involves an efficient protein precipitation step (addition of HClO4), allows a quantification limit of 2.52 μg ml−1 and a detection limit of 0.83 μg ml−1. Recoveries and absolute recoveries of cefepime from plasma were 96.13–99.44% and 94–102.5% respectively. The intra-day and inter-day reproducibilities were less than 2% for cefepime at 10, 30, 50 μg ml−1 (n=10).The method was proved to be suitable for determining cefepime levels in human plasma and was modified to measure vitreous fluid samples. 相似文献
14.
Orientation Regulation of Phenylethylammonium Cation Based 2D Perovskite Solar Cell with Efficiency Higher Than 11%
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Xinqian Zhang Gang Wu Weifei Fu Minchao Qin Weitao Yang Jielin Yan Zhongqiang Zhang Xinhui Lu Hongzheng Chen 《Liver Transplantation》2018,8(14)
Increasing the power conversion efficiency (PCE) of the two‐dimensional (2D) perovskite‐based solar cells (PVSCs) is really a challenge. Vertical orientation of the 2D perovskite film is an efficient strategy to elevate the PCE. In this work, vertically orientated highly crystalline 2D (PEA)2(MA)n–1PbnI3n+1 (PEA= phenylethylammonium, MA = methylammonium, n = 3, 4, 5) films are fabricated with the assistance of an ammonium thiocyanate (NH4SCN) additive by a one‐step spin‐coating method. Planar‐structured PVSCs with the device structure of indium tin oxide (ITO)/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate)/(PEA)2(MA)n–1PbnI3n+1/[6,6]‐phenyl‐C61‐butyric acid methyl ester/bahocuproine/Ag are fabricated. The PCE of the PVSCs is boosted from the original 0.56% (without NH4SCN) to 11.01% with the optimized NH4SCN addition at n = 5, which is among the highest PCE values for the low‐n (n < 10) 2D perovskite‐based PVSCs. The improved performance is attributed to the vertically orientated highly crystalline 2D perovskite thin films as well as the balanced electron/hole transportation. The humidity stability of this oriented 2D perovskite thin film is also confirmed by the almost unchanged X‐ray diffraction patterns after 28 d exposed to the moisture in a humidity‐controlled cabinet (Hr = 55 ± 5%). The unsealed device retains 78.5% of its original PCE after 160 h storage in air atmosphere with humidity of 55 ± 5%. The results provide an effective approach toward a highly efficient and stable PVSC for future commercialization. 相似文献
15.
An improved method for the preparation of chromosomes from the male gametophyte of the alga Laminaria japonica Aresch. was described. The male gametophyte was pretreated with pDB (p-dichlorobenzene) and 8-hydroxyquinoline in order to clear cell wall and soften cytoplasm. The samples were treated by mordant iron alum [FeNH4 (SO4)2⋅6H2O] followed by staining with haemotoxylin. Well-spread and highly stained chromosomes were observed without precipitation. The chromosome number of male gametophyte of L. japonica was estimated to be 31. %
相似文献16.
Rapid sampling of yeast cells and automated assays of adenylate, citrate, pyruvate and glucose-6-phosphate pools 总被引:7,自引:0,他引:7
A sampling technique for yeast cells with a very short interval between harvesting and inactivation of the cells is described. HClO4 serves as inactivating agent. Optimal extraction is achieved by three freeze-thaw cycles of the acidic solution followed by neutralization with 2 m KHCO3 to pH 7.5. Methods are presented for the automated fluorometric analyses of ATP, ADP, AMP, glucose-6-phosphate, pyruvate and citrate, as well as for the preparation of crude cell extracts. 相似文献
17.
《Inorganica chimica acta》1988,145(2):299-302
The reactions of dirhodium(II) aquo cation {Rh2(aq)4+} with dioxygen were examined. It has been found that the nature of the oxidation product depends upon the concentration of dioxygen in the solution. The dimeric or polymeric Rh(III)(aq) cationic species with a charge of greater than +3 is formed when air oxygen slowly diffuses into a solution containing Rh2(aq)4+. The paramagnetic cation of proposed formula [(H2O)4Rh(O2−)(OH)2Rh(H2O)4]3+ is formed when molecular oxygen is bubbled through a 2–3 M HClO4 solution of Rh2(aq)4+. This species has been isolated and characterized in solution. 相似文献
18.
Davide Menga Francisco Ruiz‐Zepeda Lonard Moriau Martin ala Friedrich Wagner Burak Koyutürk Marjan Bele Ura Petek Nejc Hodnik Miran Gaber
ek Tim‐Patrick Fellinger 《Liver Transplantation》2019,9(43)
Atomically dispersed Fe–N–C catalysts are considered the most promising precious‐metal‐free alternative to state‐of‐the‐art Pt‐based oxygen reduction electrocatalysts for proton‐exchange membrane fuel cells. The exceptional progress in the field of research in the last ≈30 years is currently limited by the moderate active site density that can be obtained. Behind this stands the dilemma of metastability of the desired FeN4 sites at the high temperatures that are believed to be a requirement for their formation. It is herein shown that Zn2+ ions can be utilized in the novel concept of active‐site imprinting based on a pyrolytic template ion reaction throughout the formation of nitrogen‐doped carbons. As obtained atomically dispersed Zn–N–Cs comprising ZnN4 sites as well as metal‐free N4 sites can be utilized for the coordination of Fe2+ and Fe3+ ions to form atomically dispersed Fe–N–C with Fe loadings as high as 3.12 wt%. The Fe–N–Cs are active electocatalysts for the oxygen reduction reaction in acidic media with an onset potential of E0 = 0.85 V versus RHE in 0.1 m HClO4. Identical location atomic resolution transmission electron microscopy imaging, as well as in situ electrochemical flow cell coupled to inductively coupled plasma mass spectrometry measurements, is employed to directly prove the concept of the active‐site imprinting approach. 相似文献
19.
A technique to measure the activity of pyruvate carboxylase spectrophotometrically in crude liver homogenates is described. The assay is based on the transformation of oxaloacetate, which is formed during the carboxylation reaction, into citrate in the presence of excess acetyl CoA and citrate synthase. After removal of pyruvate with KBH4 and of protein with HClO4, citrate is cleaved with citrate lyase into oxaloacetate and acetate, and oxaloacetate then is measured spectrophotometrically. Optimal concentrations of pyruvate, Mg2+, ATP, and KHCO3 for the carboxylation reaction and the Vmax were in good correlation with the data found by others using [14C]pyruvate. 相似文献
20.
An enzymatic method for the measurement of ethanol has been developed to permit analyses with unneutralized acid extracts of blood, liver, cell suspensions, or other biological materials. Components of the assay mixture include NAD, yeast alcohol dehydrogenase, tris(hydroxymethyl)aminomethane (Tris), and lysine. Tris is a trapping agent for the reaction product, acetaldehyde. Lysine is used to maintain the pH at 9.7 where oxidation of ethanol is quantitative and most rapid, even when as much as 0.2 ml of 0.5 n HClO4 is added. Lysine also causes the reaction to be 2 to 4 times faster than it is when either glycine or 2-amino-2-methyl-1-propanol is used as the buffer. The assay is linear up to an ethanol concentration of 0.125 mm in the reaction mixture and is complete by 4 min. By substituting ethanol for NAD in the reagents, the assay performs equally well in measuring NAD. 相似文献