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51.
Addition of aldehydes to the P-anion derivatives of chiral phosphorous acid diamides (1S,2S,1′S,1″S)-2 and (1R, 2R,1′S,1″S)-2 in THF gave α-hydroxyphosphonamides in good yield (64-100%) and moderate diastereoselectivities. 相似文献
52.
We present a systematic study of the electrophoretic migration of 10-200 kDa protein fragments in dilute-polymer solutions using microfluidic chips. The electrophoretic mobility and dispersion of protein samples were measured in a series of monodisperse polydimethylacrylamide (PDMA) polymers of different molecular masses (243, 443, and 764 kDa, polydispersivity index <2) of varying concentration. The polymer solutions were characterized using rheometry. Prior to loading onto the microchip, the polymer solution was mixed with known concentrations of SDS (SDS) surfactant and a staining dye. SDS-denatured protein samples were electrokinetically injected, separated, and detected in the microchip using electric fields ranging from 100 to 300 V/cm. Our results show that the electrophoretic mobility of protein fragments decreases exponentially with the concentration c of the polymer solution. The mobility was found to decrease logarithmically with the molecular weight of the protein fragment. In addition, the mobility was found to be independent of the electric field in the separation channel. The dispersion is relatively independent of polymer concentration and it first increases with protein size and then decreases with a maximum at about 45 kDa. The resolution power of the device decreases with concentration of the PDMA solution but it is always better than 10% of the protein size. The protein migration does not seem to correspond to the Ogston or the reptation models. A semiempirical expression for mobility given by van Winkle fits the data very well. 相似文献
53.
A quantitative determination method of formic acid in apple juices is proposed by means of the proton nuclear magnetic resonance (1H NMR) technique. Formic acid gives a singlet signal at the 8.2-8.4 ppm interval of the spectrum, and its area is used to determine the concentration of the acid. 1,3,5-Benzenetricarboxylic acid is added to the juice as an internal standard. Since the chemical shift of both species varies with the pH, ascorbic acid is also added to adjust it at 2.74 and to avoid the overlapping of the signals. Recoveries between 95 and 109% are obtained when the standard addition method is applied to the juices of five different cider apple varieties. The coefficient of variation obtained is 3.9% for intra-day repeatability (n = 5), and 4.6% for inter-day repeatability (n = 10). The limit of detection is 1.49 mg/l, calculated from “3Sy/x + intercept”. The described method is direct and no previous derivatization is needed. 相似文献
54.
55.
Elisabetta Ranucci Gloria Spagnoli Paolo Ferruti 《Macromolecular rapid communications》1999,20(1):1-6
A novel activated derivative of methacrylic acid, namely 2‐[(1‐imidazolyl)formyloxy]ethyl methacrylate was synthesized and homopolymerized. The resulting polymer was used in exchange reactions with alcohols and amines, thus showing a potential for the synthesis of multifunctional polymers. All reactions, expecially those carried out in the presence of amines, proceeded under mild conditions. 2‐[(1‐Imidazolyl)formyloxy]ethyl methacrylate can also be regarded as a valuable precursor for the preparation of new and easily polymerizable functional monomers. 相似文献
56.
Stefano Gialanella Fabrizio Girardi Gloria Ischia Ivan Lonardelli Maurizio Mattarelli Maurizio Montagna 《Journal of Thermal Analysis and Calorimetry》2010,102(3):867-873
This study deals with some microstructural and crystallographic aspects of the thermally induced transformation of goethite
(α-FeOOH) into hematite (α-Fe2O3), occurring at about 300 °C. Powder specimens of goethite have been annealed in air at different temperatures, ranging from
200 °C up to 1,000 °C. The resulting products have been analyzed for a complete characterization of the changes brought about
by the thermal treatments, using a multianalytical approach, based on: thermogravimetry, differential thermal analysis, transmission
electron microscopy, Raman spectroscopy, and X-ray diffraction. At lower temperatures, the transition to hematite produces
no important changes in size and shape of the original goethite grains. Recrystallization, and partial sintering, occurs only
at temperatures in excess of 800 °C. The relevant evolution of pores present in both phases has been also considered, as it
may provide important indications on the actual formation mechanism of hematite. 相似文献
57.
Mario Bianchi Gloria Menchi Franco Francalanci Franco Piacenti Ugo Matteoli Piero Frediani Carlo Botteghi 《Journal of organometallic chemistry》1980,188(1):109-119
Saturated monocarboxylic acids up to C6, several bicarboxylic acids and some of the corresponding anhydrides are hydrogenated in the homogeneous phase with H4Ru4(CO)8(PBu3)4 as catalyst to give the corresponding alcohols (present among the reaction products as esters) or lactones at 100–200°C under a pressure of 100–200 atm of hydrogen. Anhydrides react at temperatures lower than those needed for acids. Esters are not reduced. Only δ-valerolactone is hydrogenated to 1,5-pentanediol. Ruthenium carbonyl carboxylates have been recovered at the end of the reaction and appear to be catalytically active intermediates. 相似文献
58.
Luo Z Oki A Carson L Adams L Neelgund G Soboyejo N Regisford G Stewart M Hibbert K Beharie G Kelly-Brown C Traisawatwong P 《Chemical physics letters》2011,513(1-3):88-93
The thermal stability of funtionalized carbon nanotubes (CNTs) has been studied experimentally by direct in-situ observations using a heating stage in a transmission electron microscope, from room temperature (RT) to about 1000 °C. It was found that the thermal stability of the functionalized CNTs was significantly reduced during the in-situ heating process. Their average diameter dramatically expanded from RT to about 500 °C, and then tended to be stable until about 1000 °C. The X-ray energy dispersive spectroscopy analysis suggested that the diameter expansion was associated with coalescence of the carbon structure instead of deposition with additional foreign elements during the heating process. 相似文献
59.
60.
Violeta Yeguas Gloria Inés Cárdenas-Jirón María Isabel Menéndez Ramón López 《Journal of mathematical chemistry》2010,48(1):137-144
The B3LYP density functional theory methodology in conjunction with the 6-31G(d,p) basis set has been used to characterize
triply N-confused meso-tetraphenylporphyrins. According to our computations, there is no a direct correlation between stability and aromaticity
as already found for non-substituted confused porphyrins. The inclusion of these substituents in the calculations provokes
a decrease of the planarity and aromaticity of these macrocycles along with a notable rise of their relative stability with
respect to the non-substituted case. Steric repulsions, both among phenyl rings and β atoms in the pyrrolic rings, and among H atoms in the core of the macrocycles, dominate over aromaticity in the establishment
of the most stable conformation of each isomer. 相似文献