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1.
Theodore D. Sideris Panayiotis V. Ioannou 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5):1017-1030
The scope of ascorbic acid/iodine and triphenylphosphine/iodine in methanol for the direct reduction of arsenic(V) compounds having the As[dbnd]O group has been investigated. Ascorbic acid/iodine reduces arsonic acids, diphenylarsinic acid (but not dimethylarsinic acid), and triphenylarsine oxide. The rates of reduction depend on the electronic effects of the ligands bound to arsenic and on the hydrogen-bonding strength of the species, when present. When the As(V) compound has an [sbnd]NH 2 or an [sbnd]NH 3 + group, the reduction product reacts with a ketonic form of dehydroascorbic acid, giving condensation product(s). Triphenylphosphine/iodine reduced slowly the zwitterionic o-aminophenylarsonic acid but reduced faster the hydrochloric acid salt of the same acid. It reduced dimethylarsinic acid as well because the powerful electron-withdrawing Ph 3 P +coordinated to As[dbnd]O seems to outweigh the electronic and hydrogen bonding effects. 相似文献
2.
Full NMR and ESI-MS spectra, and differential scanning calorimeter data are presented for 15 substituted phenylarsonic acids, including two new fluoro-substituted examples. X-ray crystal structure determinations of five examples (phenylarsonic acid and the 4-fluoro-, 4-fluoro-3-nitro-, 3-amino-4-hydroxy- and 3-amino-4-methoxy-substituted derivatives) were determined and the H-bonding crystal-packing patterns analysed. 相似文献
3.
Maryam Mirza‐Aghayan Rabah Boukherroub Mahshid Rahimifard Mohammad Bolourtchian 《应用有机金属化学》2010,24(6):477-480
Reduction of a variety of nitroaromatic compounds with triethylsilane in the presence of catalytic amounts of palladium chloride in ethanol resulted in the formation of the corresponding anilines in excellent yields. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
4.
Man-Yu Wang Hong-Ze Gang Lei Zhou Jin-Feng Liu Bo-Zhong Mu Shi-Zhong Yang 《国际化学动力学杂志》2020,52(2):99-108
The amidation of long-chain fatty acids is the key step for preparing surfactants with excellent interfacial activity. Gas chromatography–mass spectrometry was employed to detect the reactants and products in the direct amidation reactions. The conversion and the concentration of the amides in the reaction process were also investigated to determine the best catalyst, the reaction rate constants, and activation energy. It was identified that the amidation reaction of the long-chain phenyl fatty acid was a zero-order reaction and 3,4,5-trifluorophenylboronic acid was the most effective catalyst by which the activation energy reduced to 55.79 kJ/mol from 95.44 kJ/mol. The method can be applied to other long-chain fatty acids, saturated or unsatureated. The turning-over-temperature was 156°C, over which high yields can be achieved without any catalyst. These provide a reference for the preparation of long-chain fatty acid amides. 相似文献
5.
Maria-João R.P. Queiroz Elisabete M.S. Castanheira Ana S. Abreu Paula M.T. Ferreira Arzum Erdem 《Tetrahedron》2008,64(2):382-391
A benzothienoindole (BTIN) and a benzofuroindole (BFIN) were synthesized in high yields, as potential new DNA target compounds, using a metal-assisted intramolecular C-N cyclization of the methyl esters of N-(tert-butoxycarbonyl)-β,β-bis(dibenzothien-4-yl or dibenzofur-4-yl)dehydroalanines. The latter were obtained by a bis-Suzuki coupling of a β,β-dibromodehydroalanine with the corresponding heteroarylboronic acids. The absorption and fluorescence properties of the new tetracyclic compounds were studied in different solvents and in the presence of salmon sperm DNA. The results in several solvents show that either BTIN or BFIN can be used as fluorescence solvent sensitive probes. Spectroscopic studies of their interaction with dsDNA allowed to determine binding constant (Ki) values and binding site sizes (n). Fluorescence quenching experiments using iodide ion showed that intercalation is the preferred mode of binding to DNA. From the results obtained, BTIN is the more intercalative compound and has a higher affinity to DNA. The interaction of BTIN with DNA was also studied electrochemically, by using differential pulse voltammetry (DPV) in connection with disposable pencil graphite electrode (PGE). After the interaction of BTIN with DNA, the oxidation signals of BTIN and adenine strongly decreased. The latter result was attributed to the binding of BTIN to DNA and the former points to a possible damage of the oxidizable groups of BTIN after intercalation into DNA. The results of spectroscopic and electrochemical studies of BTIN interaction with DNA are in good agreement. 相似文献
6.
Successful separation of the six major hop bitter compounds by micellar electrokinetic chromatography depends critically on precise pH control. Any factor which can affect the actual in-column pH must, therefore, also be carefully controlled: it has been found that temperature-induced changes of the buffer pH can cause loss of resolution and even reversals in elution order. The pH level at which the effects occur suggests that the pKa values of the analytes are modified by the micellar medium. 相似文献
7.
Summary A method for the determination of 22 low relative molecular mass oxocarboxylic acids and carbonyl compounds in estuarine and
marine samples is described.
After derivatization of 5 ml samples with 2,4-dinitrophenylhydrazine separation is performed on a RP-18 column by gradient
elution and with UV-detection.
The detection limit ranges from 17 ngl−1 (glycolaldehyde) to 500 ngl−1 (cyclohexanone). The method was established for routine analysis of samples taken in an estuarine ecosystem but can be used
for other aqueous systems as well. 相似文献
8.
9.
Pablo M. Fidelibus Gustavo F. Silbestri María T. Lockhart Sandra D. Mandolesi Alicia B. Chopa Julio C. Podestá 《应用有机金属化学》2007,21(8):682-687
In this paper we describe a three‐step synthesis of aryldi‐ and triboronic acids starting from phenols. Several substituted phenols (I) were converted into the corresponding aryldiethylphosphates (II) in good to excellent yields. The latter, on reaction with sodium trimethylstannide in liquid ammonia, under irradiation, afforded the aryl‐ and heteroarylpoly(trimethylstannyl) derivatives in 65–90% yield. The third step is the reaction of the organotin compounds with borane in THF, which leads to the corresponding arylpolyboronic acids in around 80% yield. In order to confirm their structure, some of the diboronic acids were converted into the corresponding pinacol esters. The results obtained in a study on the synthesis of various terphenyls through double and triple Suzuki couplings catalyzed by palladium acetate between the obtained arylpolyboronic acids and various aryl halides are also reported. These reactions proceeded with an average 65% yield, and also enabled us to confirm the structures of some of the diboronic acids. The structure of the new compounds was determined by 1H, 13C and 119Sn NMR spectroscopy, mass spectrometry and IR spectroscopy. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
10.
Zwitterionic chiral stationary phases based on cinchona and chiral sulfonic acids for the direct stereoselective separation of amino acids and other amphoteric compounds
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Tong Zhang Emilie Holder Pilar Franco Wolfgang Lindner 《Journal of separation science》2014,37(11):1237-1247
An extensive series of free amino acids and analogs were directly resolved into enantiomers (and stereoisomers where appropriate) by HPLC on zwitterionic chiral stationary phases (Chiralpak ZWIX(+) and Chiralpak ZWIX(?)). The interaction and chiral recognition mechanisms were based on the synergistic double ion‐paring process between the analyte and the chiral selectors. The chiral separation and elution order were found to be predictable for primary α‐amino acids with apolar aliphatic side chains. A systematic investigation was undertaken to gain an insight into the influence of the structural features on the enantiorecognition. The presence of polar and/or aromatic groups in the analyte structure is believed to tune the double ion‐paring equilibrium by the involvement of the secondary interaction forces such as hydrogen bonding, Van der Waals forces and π–π stacking in concert with steric parameters. The ZWIX chiral columns were able to separate enantiomers and stereoisomers of various amphoteric compounds with no need for precolumn derivatization. Column switching between ZWIX(+) and ZWIX(?) is believed to be an instrumental tool to reverse or control the enantiomers elution order, due to the complementarity of the applied chiral selectors. 相似文献
11.
Piotr M?ynarz Agata Rydzewska Ziemowit Pok?adek 《Journal of organometallic chemistry》2011,696(2):457-460
Two groups of new boronic acids containing aminophosphonate functions were synthesized and characterized by NMR spectroscopy and ESI-MS. Both groups of compounds were obtained by simple reactions of prepared in situ tris(trimethylsilyl) phosphite with a corresponding imine. The synthesized compounds may serve as a potential new class of building blocks, BNCT agents and supramolecular host molecules. 相似文献
12.
13.
The intrinsic capacity (computed by ab initio molecular orbital techniques) of ethyl and methyl cations to bind to the anionic oxygens of the phosphate groups of the nucleic acids is found to be larger than their affinity for the carbonyl oxygens or for the nitrogens of the bases cytosine and guanine. Analysis of the components of the binding energies indicates that the preference of the ethyl cation for the oxygens of the phosphate or for those of the bases is due to different reasons. The results are discussed in connection with the available experimental observations. 相似文献
14.
《Journal of Chemical Sciences》2005,117(5):525-531
The silicon atom may increase its coordination number to values greater than four, to form pentacoordinated compounds. It
has been observed experimentally that, in general, pentacoordinated compounds show greater reactivity than tetracoordinated
compounds. In this work, density functional theory is used to calculate the global softness and the condensed softness of
the silicon atom for SiH
n
F4−n
and SiH
n
F
5−n
1−
. The values obtained show that the global and condensed softness are greater in the pentacoordinated compounds than in the
tetracoordinated compounds, a result that explains the enhanced reactivity. If the results are analysed through a local version
of the hard and soft acids and bases principle, it is possible to suggest that in nucleophilic substitution reactions, soft
nucleophiles preferably react with SiH
n
F
5−n
1−
, and hard nucleophiles with SiH
n
F4−n
. 相似文献
15.
31P nuclear magnetic resonance (NMR) spectroscopy was used to detect and quantify simultaneously a large number of phenolic compounds and the two triterpenic acids, ursolic acid and oleanolic acid, extracted from two oregano species Origanum onites and Origanum vulgare ssp. Hirtum using two different organic solvents ethanol and ethyl acetate. This analytical method is based on the derivatization of the hydroxyl and carboxyl groups of these compounds with the phosphorous reagent 2‐chloro‐4,4,5,5‐tetramethyl‐1,3,2‐dioxa phospholane and the identification of the phosphitylated compounds on the basis of the 31P chemical shifts. Unambiguous assignment of the 31P NMR chemical shifts of the dihydroxy‐ and polyhydroxy‐phenols in oregano species as well as those of the triterpenic acids was achieved upon comparison with the chemical shifts of model compounds assigned by using two‐dimensional NMR techniques. Furthermore, the integration of the appropriate signals of the hydroxyl derivatives in the corresponding 31P NMR spectra and the use of the phosphitylated cyclohexanol as an internal standard allowed the quantification of these compounds. The validity of this technique for quantitative measurements was thoroughly examined. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
16.
Chemistry and biology of the acylneuraminic acids 总被引:4,自引:0,他引:4
R Schauer 《Angewandte Chemie (International ed. in English)》1973,12(2):127-138
Acylneuraminic acids occupy an outstanding position both sterically and with respect to biological functions in gangliosides and in many glycoprotein molecules. Acylneuraminic acids are N-acylated and partly O-acylated derivatives of neuraminic acid, a polyhydroxyamino keto acid that has the properties of a carbohydrate and is therefore capable of forming a glycoside linkage. The present report provides a survey of our knowledge of the chemistry and biology of the acylneuraminic acids, which occur widely in particular in the animal kingdom. 相似文献
17.
Ekaterina V. MatveevaAnatoly E. Shipov Pavel V. PetrovskiiIrina L. Odinets 《Tetrahedron letters》2011,52(49):6562-6565
Application of water as a sole solvent promotes the aza-Michael reaction of diethyl vinylphosphonate and diphenylvinylphosphine oxide with α-substituted amino acid sodium salts generated in situ to afford the corresponding β-aminophosphonates and β-aminophosphine oxides in excellent yields and of high purity. The approach is equally suitable for the synthesis of both racemic and optically active compounds. In the case of glycine, the mono and bis(phosphonoethyl)-substituted products are formed in 6:4 ratio and when using a stoichiometric amount of the reactants, N,N-bis[2-(diethoxyphosphoryl)ethyl]glycine was the only product. In contrast, to perform the double phosphonoethylation of d,l-alanine, prolonged heating of the reaction mixture was required. 相似文献
18.
Summary At the present time the formation processes of clouds and precipitation are not totally understood. Because cloud- and raindroplets
are major sinks for chemical species in the atmosphere it is important to understand the physical and the chemical processes
which occur during precipitation. The development of models is hindered by the scarcity of information about the scavenging
of gases or aerosol particles by raindrops of different sizes. These processes can only be investigated by field experiments
using microanalytical methods and analysing single raindrops as well as size-classified raindrop samples. Raindrops were collected
according to their size by freezing them in liquid nitrogen (“Guttalgor” method). Sample volumes of the smallest raindrop
sizes (radius <200μm) were usually smaller than 2 μL. The analysis of microvolumina in the size range of μL down to pL required
the development of methods designed especially for this purpose. Analysis of rain samples was carried out by capillary electrophoresis.
Organic acids were determined using a new electrolyte system for indirect detection. With this system it was possible to determine
monocarboxylic acids (C1−C4) dicarboxylic acids (C2−C4, C9) and inorganic anions (Cl−, NO3
−, SO4
2−) in the rain samples. Carbonyl compounds were analysed after derivatisation with dansylhydrazine using direct UV-detection.
The system allows the identification of aliphatic carbonyl compounds (C1−C3, C5) as well as benzaldehyde. It was found that carbonyl compounds and carboxylic acids showed concentration maxima at different
raindrop radii. These concentration maxima are a consequence of particle scavenging. By using the results of a former experiment
we concluded that the two species are located on different aerosol particle sizes. Reasons for the different particle sizes
where these species are located are discussed.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996 相似文献
19.
20.
A. Stephen K. Hashmi Tanuja Dondeti Ramamurthi Frank Rominger 《Journal of organometallic chemistry》2009,694(4):592-1884
Organogold(I) phosphane complexes were prepared, their structure was investigated and their reactivity in reactions with Michael acceptors, sources of electrophilic halogens and protons were investigated. 相似文献