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181.
The formation of complexes between 2-hydroxypropyl-β-cyclodextrin and monocarboxylic acids or cycloalkanols has been studied calorimetrically at 298 K in phosphate buffer, pH 11.3. The forces involved in the association process are discussed in the light of the signs and values of the thermodynamic parameters obtained: association enthalpy, binding constant, Gibbs free energy, and entropy.From this study it was inferred that (i) for monocarboxylic acids, hydrophobic interactions are the primary force determining complexation, as indicated by the small enthalpies and by the high and positive entropies. For the cycloalkanols, instead, enthalpies are negative and entropies positive or negative, depending on the solvent medium employed, namely water or phosphate buffer; (ii) the most important requirement for the formation of the complex is a good spatial fit between the two interacting molecules. A cavity elongation effect occurs because of the presence of the hydroxypropyl groups on the rim of the macrocycle. The relative contribution of hydrophobic and van der Waals interactions varies with the dimensions of the guest molecules; (iii) a linear correlation exists between enthalpy and entropy of complexation, underlying that inclusion is a process dominated by hydration phenomena and ascribed to the modifications experienced by the solvent in the hydration shells of the interacting substances. 相似文献
182.
Bartoli G Bosco M Carlone A Dalpozzo R Locatelli M Melchiorre P Sambri L 《The Journal of organic chemistry》2006,71(26):9580-9588
The reaction between alcohols and Boc2O leads to the formation of tert-butyl ethers and/or Boc-alcohols, depending on the nature of the Lewis acid catalyst. Product distribution is mainly tuned by the anionic part of the salt. Perchlorates and triflates, anions with highly delocalized negative charge, give prevalent or exclusive ether formation. On the other hand, Boc alcohols are the main or exclusive products with un-delocalized isopropoxide or low-delocalized acetate ions. The metal ion influences only the reaction rate, roughly following standard parameters for calculating Lewis acidity. A reaction mechanism is supposed, and a series of experimental evidences is reported to support it. These studies allowed us to conclude that, to synthesize tert-butyl ethers, in reactions involving aliphatic alcohols, Mg(ClO4)2 or Al(ClO4)3 represents the best compromise between costs and efficiency of the reaction, while, in reactions involving phenols, Sc(OTf)3 is the best choice, since aromatic tert-butyl ethers are not stable in the presence of perchlorates. 相似文献
183.
Microchips and single-photon avalanche diodes for DNA separation with high sensitivity 总被引:1,自引:0,他引:1
Modern techniques for DNA and protein analysis and separation rely on measurements of LIF and face a trend toward employing progressively smaller samples. The currently employed detectors that provide the required ultrahigh sensitivity, e.g. photomultiplier tubes (PMTs), are bulky and/or costly and delicate, whereas a key issue for the development of compact and economical instruments is the availability of miniaturized, inexpensive, and ultrasensitive photodetectors. The planar epitaxial silicon single-photon avalanche diodes (SPADs) combine the typical advantages of microelectronics (miniaturization, ruggedness, low voltage, low power, low cost, etc.) with high sensitivity, even better than that of PMTs. The suitability of such SPADs to microchip CE has been here ascertained by developing a new apparatus with dual-wavelength LIF detection. The apparatus has been experimented in studies on the EOF suppression and on the coating stability and tested in rapid sizing of DNA fragments. The experimental results obtained in the separation of Cy5-labeled oligonucleotide demonstrate sensitivity better than 3 pM, which corresponds to less than 100 fluorescent molecules in the 50 pL illuminated volume. 相似文献
184.
Bagno A Bonchio M Autschbach J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(33):8460-8471
The (183)W nuclear shielding in a variety of tungsten polyoxometalates (POM) (Lindqvist, Anderson, decatungstates, Keggin) of different shapes and charges has been modeled by DFT calculations that take into account relativistic effects, by means of the zero-order regular approximation (ZORA), and solvent effects, by the conductor-like screening model (COSMO) continuum method. The charge/surface area ratio (q/A) is proposed as an indicator of the charge density to which the solvation energies of all POMs are correlated in a satisfactory way. Among the various theoretical levels tested (ZORA scalar or spin-orbit, frozen-core or all-electron basis set, geometry optimization in the gas phase or in the continuum solvent, etc.), the best results are obtained when both geometry optimization in solvent and spin-orbit shielding are included (mean absolute error of delta=35 ppm). The quality of the computed chemical shifts depends systematically on the charge density as expressed by q/A; thus, POMs with low q/A ratios display the best agreement with experimental data. The performance of the method is such that computed values can aid the assignment of the (183)W NMR spectra of polyoxotungstates, as shown by the case of alpha-[PW(11)TiO(40)](5-), whose six signals are ranked computationally so as to almost reproduce the experimental ordering even though the signals are spaced by as little as 5 ppm. 相似文献
185.
Rodríguez-Fortea A Iannuzzi M Parrinello M 《The journal of physical chemistry. B》2006,110(8):3477-3484
The interaction between gas-phase nitric acid and the graphite surface is taken as a simple model of interactions occurring at the surface of atmospheric soot particles. In particular, we study the heterogeneous processes that lead to the dissociation of the nitric acid and the production of nitrous acid. The atomistic details of the reaction mechanisms are reproduced by use of the new metadynamics method. The binding interactions of the HNO3 molecule and its fragments with the graphite surface are calculated, and the role of the surface in catalyzing the reaction is taken into account. From the reactive trajectory generated by the metadynamics, it is seen that the path goes through several different intermediate states. We analyze in detail the electronic structures and spin density distributions of the relevant products and report on the mechanisms and the main features of the transition regions relative to all the activated processes observed. 相似文献
186.
Nelson DD McManus JB Herndon SC Shorter JH Zahniser MS Blaser S Hvozdara L Muller A Giovannini M Faist J 《Optics letters》2006,31(13):2012-2014
We report on power, spectral linewidth, and mode purity for a cw 5.3 microm quantum cascade laser operated on a thermo-electric cooler. A totally noncryogenic nitric oxide monitor was constructed by integrating this laser with an astigmatic multipass cell and a thermo-electrically cooled infrared detector. The resulting instrument is capable of continuous unattended monitoring of ambient, atmospheric nitric oxide for several weeks with no operator intervention. The detection method was rapid sweep, direct absorption spectroscopy. A detection sensitivity of 0.03 parts in 10(9) is achieved with 30 s averaging time with a path length of 210 m, corresponding to an absorbance path length product of 1.5 x 10(-10) cm(-1). 相似文献
187.
Bertolotti G Bersani D Lottici PP Alesiani M Malcherek T Schlüter J 《Analytical and bioanalytical chemistry》2012,402(4):1451-1457
Three bronze samples created by CNR-ISMN (National Research Council—Institute of Nanostructured Materials) to be similar to
Punic and Roman coins found in Tharros (OR, Sardinia, Italy) were studied to identify the corrosion products on their surfaces
and to evaluate the reliability of the reproduction process. Micro-Raman spectroscopy was chosen to investigate the corroded
surfaces because it is a non-destructive technique, it has high spatial resolution, and it gives the opportunity to discriminate
between polymorphs and to correlate colour and chemical composition. A significant amount of green copper hydroxychlorides
(Cu2(OH)3Cl) was detected on all the coins. Their discrimination by Raman spectroscopy was challenging because the literature on the
topic is currently confusing. Thus, it was necessary to determine the characteristic peaks of atacamite, clinoatacamite, and
the recently discovered anatacamite by acquiring Raman spectra of comparable natural mineral samples. Clinoatacamite, with
different degrees of order in its structure, was the major component identified on the three coins. The most widespread corrosion
product, besides hydroxychlorides, was the red copper oxide cuprite (Cu2O). Other corrosion products of the elements of the alloy (laurionite, plumbonacrite, zinc carbonate) and those resulting
from burial in the soil (anatase, calcite, hematite) were also found. This study shows that identification of corrosion products,
including discrimination of copper hydroxychlorides, could be accomplished by micro-Raman on valuable objects, for example
archaeological findings or works of art, avoiding any damage because of extraction of samples or the use of a destructive
analytical technique. 相似文献
188.
189.
Giovanni Ribaudo Enrico Zanforlin Marcella Canton Sergio Bova Giuseppe Zagotto 《Natural product research》2018,32(12):1395-1401
Parkinson’s disease (PD) is a neurodegenerative disorder bearing motor and nonmotor symptoms. The treatment today is symptomatical rather than preventive or curative and this leaves the field open for the search of both novel molecular targets and drug candidates. Interference with α-synuclein fibrillation, monoamine oxidase (MAO) inhibition, modulation of adenosine receptors and the inhibition of specific phosphodiesterase (PDE) isoforms are some of the currently pursued strategies. We synthesised and studied some semi-synthetic berberine derivatives using a set of in silico tools. We evaluated their drug-likeness and tested the compounds against a set of target proteins involved in the onset or progression of PD, with a particular attention to MAO-B. Preliminary in vitro assay on MAO-B confirmed our in silico predictions. 相似文献
190.
Berardi S La Ganga G Natali M Bazzan I Puntoriero F Sartorel A Scandola F Campagna S Bonchio M 《Journal of the American Chemical Society》2012,134(27):11104-11107
Isostructural cubane-shaped catalysts [Co(III)(4)(μ-O)(4)(μ-CH(3)COO)(4)(p-NC(5)H(4)X)(4)], 1-X (X = H, Me, t-Bu, OMe, Br, COOMe, CN), enable water oxidation under dark and illuminated conditions, where the primary step of photoinduced electron transfer obeys to Hammett linear free energy relationship behavior. Ligand design and catalyst optimization are instrumental for sustained O(2) productivity with quantum efficiency up to 80% at λ > 400 nm, thus opening a new perspective for in vitro molecular photosynthesis. 相似文献