排序方式: 共有45条查询结果,搜索用时 15 毫秒
1.
Maria De Fenza Anna Esposito Daniele DAlonzo Annalisa Guaragna 《Molecules (Basel, Switzerland)》2021,26(6)
The de novo synthesis of piperidine nucleosides from our homologating agent 5,6-dihydro-1,4-dithiin is herein reported. The structure and conformation of nucleosides were conceived to faithfully resemble the well-known nucleoside drugs Immucillins H and A in their bioactive conformation. NMR analysis of the synthesized compounds confirmed that they adopt an iminosugar conformation bearing the nucleobases and the hydroxyl groups in the appropriate orientation. 相似文献
2.
A new cryostat for Mössbauer spectroscopic measurements has been developed around a cryogenerator of the Gifford McMahon type operating with helium gas in a closed circuit. Both source and absorber can be cooled to about 30K and the unwanted vibrations caused by the helium compression/expansion cycle have been limited to approximately 0.05–0.06 mms?1. 相似文献
3.
We analyze the influence of residual two-photon excitation (2PE) in two-color (two-photon) optical beam induced current (2CE-OBIC) generation in wide band gap semiconductor samples. 2CE-OBIC generation is accomplished with two confocal excitation beams of separation angle θ and wavelengths λ1 and λ2 where , λe = hc/Eb, h is the Planck’s constant, c is speed of light in vacuum, and Eb is the energy band gap. Because the conduction band of the sample is a continuum, at least one excitation beam would also contribute an undesirable 2PE-OBIC signal that degrades the signal-to-noise ratio of the measured 2CE-OBIC response and broadens the effective OBIC distribution in the sample particularly when θ ≠ 0 or π. We show that the deleterious effects of crosstalk are reduced by a careful selection of λ1 and λ2 and the relative excitation beam intensities. λ1 and λ2 should be chosen to minimize the ratio of the two-photon absorption coefficients (β1, β2) to the 2CE absorption coefficient β12 or at least satisfy the constraint: β1 + β2 β12. Keeping the two excitation intensities equal is beneficial only when β1 = β2. Otherwise, it is advantageous to bias the intensity ratio towards the wavelength with a lower 2PE absorption coefficient. 相似文献
4.
Conte P Mineo V Bubici S De Pasquale C Aboud F Maccotta A Planeta D Alonzo G 《Analytical and bioanalytical chemistry》2011,400(5):1443-1450
A number of pistachio oils were selected in order to test the efficacy of nuclear magnetic resonance relaxation dispersion (NMRD) technique in the evaluation of differences among oils (1) obtained from seeds subjected to different thermal desiccation processes, (2) retrieved from seeds belonging to the same cultivar grown in different geographical areas and (3) produced by using seed cultivars sampled in the same geographical region. NMRD measures relaxation rate values which are related to the dynamics of the chemical components of complex food systems. Results not only allowed to relate kinematic viscosity to relaxometry parameters but also were successful in the differentiation among the aforementioned oils. In fact, from the one hand, the larger the kinematic viscosity, the faster the rotational motions appeared as compared to the translational ones. On the other hand, relaxation rate curves (NMRD) varied according to the oxidative stresses and chemical composition of each sample. The present study showed for the first time that NMRD is a very promising technique for quick evaluations of pistachio oil quality without the need for time-consuming chemical manipulations. 相似文献
5.
1H longitudinal relaxation time profiles (T1) at different proton Larmor frequencies were registered for a solid-state plant tissue by using fast field cycling (FFC) nuclear magnetic resonance (NMR) spectroscopy. T1 distributions were obtained and the curves deconvoluted in order to differentiate among the different T1 components. Among the components, two were assigned to hydrophobic (e.g., fatty acid) and hydrophilic (e.g., saccharide) molecular systems, whereas the others were attributed to bulk and bound water. This paper shows for the first time solid-state FFC-NMR spectroscopy applied to plant tissue and reveals that relaxometry is a very promising technique for studying plant systems. 相似文献
6.
G. C. Stocco G. Alonzo A. Silvestri N. Bertazzi L. Pellerito R. Barbieri 《无机化学与普通化学杂志》1974,409(2):248-256
The configuration in the solid state and in solution phase of complexes of SuIV wit,li tridentate “planar” ligands, Sn(trid)2 and HNEt3Cl3 Sntrid, have been investigated by infrared and MÖSSBAUER spectroscopy, as well as by osmometry, conductivity, and electronic and PMR spectroscopy. The presence of monomeric Sn(trid)2 and ionic [HNEt] [Cl3Sn trid?] species has been inferred. Octahedral type configurations are advanced for both classes of compounds. 相似文献
7.
Dayonna P. Park Kevin Davis Samid Gilani Christal-Anne Alonzo Danil Dobrynin Gary Friedman Alexander Fridman Alexander Rabinovich Gregory Fridman 《Current Applied Physics》2013
Water quality, mineralization, and chemical composition, particularly pH and nitrogen compounds each, play a crucial role in plant development and growth. Treatment of water with non-equilibrium discharges results in the change of its properties and chemical composition, which in turn may affect plant growth process and subsequently agriculture produce quality. Both thermal and non-thermal discharges generated in air or in water produce a number of reactive neutral and charged species, electric fields, and ultraviolet radiation. Plasma treatment of water results in significant change of its properties like pH, oxidation–reduction potential (ORP), conductivity, and concentration of reactive oxygen and reactive nitrogen species (ROS and RNS). Here we report the results of an experimental study of the effect of water treated with different atmospheric plasmas on germination, growth rates, and overall nutritional value of various plants. In the study we have used three types of plasmas: thermal spark discharge, gliding arc discharge, and transferred arc discharge. It is shown that the effects of these plasmas on chemical composition of various types of water are qualitatively different. Non-thermal gliding arc discharge plasma results in lower (acidic) pH, and production of significant amount of oxidizing species (e.g. H2O2). Gliding arc discharge also causes significant acidification of water, but it is accompanied by production of reactive nitrogen species (NO, NO2? and NO3?). Spark discharge treatment results in neutral or higher (basic) pH depending on initial water composition, and production of RNS. 相似文献
8.
Franco Benetollo Gabriella Bombieri Giuseppe Alonzo Nuccio Bertazzi 《Journal of chemical crystallography》1995,25(2):89-92
The synthesis and the crystal and molecular structure of the difluoro(hydroxodi-2-pyridylmethoxo-NNO) antimony(III) compound determined by single crystal X-ray diffraction analysis are reported. Crystals are orthorhombic, space group Pbcn,a=12.732(2),b=12.165(2),c=15.936(2) Å. Refinement based on 1516 observed reflections led to a finalR value of 0.025 (Rw=0.028). In the crystal the di-2-pyridyl ketone behaves asfacial-(NNO)-terdentate in the Sb coordination, the square pyramid geometry around the metal is completed by the coordination of two fluorine atoms. 相似文献
9.
Hind A. Maouel Vronique Alonzo Thierry Roisnel Houria Rebbah Eric Le Fur 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(7):i36-i38
The title synthesized hypophosphite has the formula V(H2PO2)3. Its structure is based on VO6 octahedra and (H2PO2)− pseudo‐tetrahedra. The asymmetric unit contains two crystallographically distinct V atoms and six independent (H2PO2)− groups. The connection of the polyhedra generates [VPO6H2]6− chains extended along a, b and c, leading to the first three‐dimensional network of an anhydrous transition metal hypophosphite. 相似文献
10.
Gabriella Butera Claudio De Pasquale Antonella Maccotta Giuseppe Alonzo Pellegrino Conte 《Cellulose (London, England)》2011,18(6):1499-1507
Use of crude oil derivatives such as diesel and gasoline is becoming unsuitable due to their detriment to environment and
to the increasing worldwide energy demand which is driving crude oil reservoirs towards exhaustion. Replacement of diesel
and gasoline with biofuels (i.e. biodiesel and bioethanol, respectively) is very desirable. In fact, biofuels are not only
environmentally sustainable, but also potentially inexhaustible due to the large amounts of waste biomasses from which they
can be retrieved. In the present study, a model compound (micro-crystalline cellulose) was dissolved in phosphoric acid and
converted at 80 °C to glucose, thereby providing the possible substrate for fermentation to bioethanol. Results revealed that
after 1 h heating, the reaction had the largest glucose yield as compared to similar studies done by using other acid catalysts.
In addition, the temperature applied here was from 40 to 60 °C lower than those already reported in literature for acid-driven
cellulose degradations. Phosphoric acid allowed both glucose and levulinic acid achievement. The latter is usually used to
synthesize fuel additives, catalysts, solvents and herbicides, thereby enhancing the added value of the conversion of cellulose
to glucose in phosphoric acid. Finally, 1H T1 NMR relaxometry showed its suitability to monitor cellulose degradation. The advantages of relaxomety are its quickness since
only few minutes are needed to obtain relaxograms, and the possibility to use raw mixtures without the needing of sample preparation. 相似文献