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61.
Condensation of 1,4-dimethoxybenzene with 1,1-cyclopentane dicarboxylic acid or 1,1-indan dicarboxylic acid derivatives led to the title compounds. 相似文献
62.
Francesco Pergola Maria R. Moncelli Rolando Guidelli 《Journal of Electroanalytical Chemistry》1980,107(2):295-306
A polarographic investigation of CuII electroreduction from solutions of benzotriazole (BTA) of pH from 1 to 3 at a dropping mercury electrode shows the presence of two successive adsorption waves of equal height (waves Ic and IIIc) due, respectively, to the formation and to the subsequent dissolution of an adsorbed film of a CuI compound. The dependence of the half-wave potential of wave IIIc, which is polarographically reversible, upon pH and BTA concentration indicates that the adsorbed film has the composition [CuI(BTA?)], where BTA? denotes the deprotonated anionic form of benzotriazole. Moreover, the maximum height of wave IIIc indicates that this film is one monolayer thick. A third cathodic wave (wave IIc), lying between waves Ic and IIIc, stems from the reduction to the metal state of the CuII ions diffusing from the bulk solution. Copper(0) oxidation at dropping amalgam electrodes in BTA solutions yields two successive adsorption waves (waves Ia and IIa). Wave Ia is due to the same electrode process, Cu0 (Hg)+BTA?CuI(BTA?)+H++e, responsible for the cathodic wave IIIc. On the other hand, wave IIa is due to the formation of roughly two adsorbed monolayers of [CuI(BTA?)] upon that formed along wave Ia. 相似文献
63.
β-Alkoxyalkylmercury(II) acetates have been symmetrised in situ with alkaline sodium stannite to afford good yields of bis(β-alkoxyalkyl)mercurials, [R1R2C(OR)CHR3]2 Hg. 相似文献
64.
The thermal stability and folding kinetics of a 15-residue beta-hairpin (SESYINPDGTWTVTE) have been studied by using infrared (IR) spectroscopy coupled with laser-induced temperature-jump (T-jump) technique for rapid folding-unfolding initiation. An alternative method based on analyzing IR difference spectra was also introduced to obtain thermodynamic properties of beta-sheets, which complements the commonly used circular dichroism (CD) and fluorescence techniques. Equilibrium IR measurements indicate that the thermal unfolding of this beta-hairpin is fairly broad. However, it can be described by a two-state transition with a thermal melting temperature of approximately 29 degrees C. Time-resolved IR measurements following a T-jump, probed at 1634 cm(-1), indicate that the folding of this beta-hairpin follows first-order kinetics and is amazingly fast. At 300 K, the folding time is approximately 0.8 micros, which is only 2-3 times slower than that of alpha-helix formation. Additionally, the energetic barrier for folding is small (approximately 2 kcal mol(-1)). These results, in conjunction with results from other studies, support a view that the details of native contacts play a dominant role in the kinetics of beta-hairpin folding. 相似文献
65.
Giovanni Piccardi Francesco Pergola Maria Luisa Foresti Rolando Guidelli 《Journal of Electroanalytical Chemistry》1977,84(2):235-253
Polarographic current-potential characteristics and current-time curves for the reduction of methylene blue (MB) to methylene blue leucoform (MBL) in a pH 7.9 aqueous phosphate buffer have been examined in detail over a wide concentration range. It has thus been shown that the so called “normal” or “main” reduction wave of MB actually consists of two separate steps, the former with a half-wave potential practically coinciding with the formal potential E0=?0.250 V/SCE of the MB/MBL couple and the latter with a half-wave potential of about ?0.310 V/SCE. As soon as the well-known MB adsorption prewave has attained its maximum height (which occurs at a MB bulk concentration c0*?5×10?5M), a further slight increase in c0* causes the appearance of the wave with E1/2=?0.310 V. The height of the linear potential-sweep voltammetric peak corresponding to the latter wave increases proportionally to the sweep rate, thus revealing the “adsorption” nature of this wave. A comparison with a previous chronocoulometric investigation of the MB/MBL system has permitted us to conclude that the wave with E1/2=?0.310 V is due to reduction of the MB molecules which, after having reached the surface of the dropping electrode by diffusion, are adsorbed at the top of the adsorbed monolayer of MBL in direct contact with the electrode and remain in this adsorbed state after reduction. For c0*>7×10?5M the wave with E1/2?E0=?0.250 V starts to develop. This wave is due to the electroformation of MBL molecules which diffuse back into the solution. The shape of polarographic current-potential characteristics and current-time curves has been accounted for semiquantitatively through an approximate solution of the corresponding diffusional problem. 相似文献
66.
Magnani A Barbucci R Lamponi S Chiumento A Paffetti A Trabalzini L Martelli P Santucci A 《Electrophoresis》2004,25(14):2413-2424
Plasma protein adsorption patterns on surfaces may give vital information to evaluate biocompatibility of biomaterials designed for direct blood-contacting applications or tissue integration. Adsorption of human serum proteins on four different types of biomaterials (glass, aminosilanized glass, hyaluronan and sulfated hyaluronan) was analyzed by two-dimensional electrophoresis. Desorption of proteins from the surfaces was first classically achieved by sodium dodecyl sulfate (SDS) elution. We introduced a second elution step (by use of isoelectric focusing (IEF) sample buffer consisting of urea, 3-[(3-cholamidopropyl)dimethylammonio]-1-propansulfonate, and dithioerythritol) which allows more stringent elution conditions and is a tool to evaluate the protein adsorption strength to biomaterials. Moreover, the two-step elution may discriminate between irreversible and reversible adsorption of plasma proteins for biomaterials, thus helping to elucidate the structure of protein multilayers which form a complex system at the surfaces. The IEF sample buffer proved not to alter the biomaterial structure and integrity. Hydrophobic bonds resulted to be the main strength driving protein adsorption onto our biomaterials. Apolipoproteins were the most important proteins interacting with the surfaces suggesting that high-density lipoprotein (HDL) particles could play a role in biocompatibility due to their beneficial effects on endothelial cells. 相似文献
67.
Rubn D. Santiago-Acosta Ernesto M. Hernndez-Cooper Rolando Prez-lvarez Jos A. Otero 《Molecules (Basel, Switzerland)》2022,27(7)
The Stefan problem regarding the formation of several liquid–solid interfaces produced by the oscillations of the ambient temperature around the melting point of a phase change material has been addressed by several authors. Numerical and semi-analytical methods have been used to find the thermal response of a phase change material under these type of boundary conditions. However, volume changes produced by the moving fronts and their effects on the thermal performance of phase change materials have not been addressed. In this work, volume changes are incorporated through an additional equation of motion for the thickness of the system. The thickness of the phase change material becomes a dynamic variable of motion by imposing total mass conservation. The modified equation of motion for each interface is obtained by coupling mass conservation with a local energy–mass balance at each front. The dynamics of liquid–solid interface configurations is analyzed in the transient and steady periodic regimes. Finite element and heat balance integral methods are used to verify the consistency of the solutions to the proposed model. The heat balance integral method is modified and adapted to find approximate solutions when two fronts collide, and the temperature profiles are not smooth. Volumetric corrections to the sensible and latent heat released (absorbed) are introduced during front formation, annihilation, and in the presence of two fronts. Finally, the thermal energy released by the interior surface is estimated through the proposed model and compared with the solutions obtained through models proposed by other authors. 相似文献
68.
Miguel A. D. Gonçalves Virgínia D. Pinto Rolando C. S. Dias Mário Rui P. F. N. Costa 《Macromolecular Symposia》2011,302(1):179-190
Summary : Experimental and theoretical studies concerning the suspension copolymerization of styrene with divinylbenzene are reported. Experiments were carried out in a batch stirred reactor, at 1.2 dm3 scale, and extended beyond gelation in order to synthesize insoluble material. Looking for real time information concerning the building process of such materials, these polymerizations were In-line monitored using a FTIR-ATR immersion probe. Polymer samples collected before and after gelation were Off-line characterized using a SEC/RI/MALLS system allowing the measurement of monomer conversion, average molecular weights, MWD and also the z-average radius of gyration. The weight fraction of insoluble material (gel) was measured for samples with different reaction times. The experimental program has included the study of the influence of key polymerization parameters on the dynamics of gelation and some properties of the resulting networks, namely the initial mole fraction of crosslinker and the initial proportions between monomers and inert diluent. Variable n-heptane/toluene mixtures were used within this purpose. These experimental observations were complemented with theoretical studies using a general kinetic approach allowing the prediction of MWD and z-average radius of gyration before and also after gelation. Comparison of the experimental measurements with these predictions is being exploited to develop modeling tools useful for the design of operating conditions allowing the improvement of the performance of the final products. 相似文献
69.
Theories of monochromatic high-frequency electromagnetic fields have been designed by Felsen, Kravtsov, Ludwig and others
with a view to portraying features that are ignored by geometrical optics. These theories have recourse to eikonals that encode
information on both phase and amplitude — in other words, are complex-valued. The following mathematical principle is ultimately
behind the scenes: any geometric optical eikonal, which conventional rays engender in some light region, can be consistently
continued in the shadow region beyond the relevant caustic, provided an alternative eikonal, endowed with a non-zero imaginary
part, comes on stage.
In the present paper we explore such a principle in dimension 2. We investigate a partial differential system that governs
the real and the imaginary parts of complex-valued two-dimensional eikonals, and an initial value problem germane to it. In
physical terms, the problem in hand amounts to detecting waves that rise beside, but on the dark side of, a given caustic.
In mathematical terms, such a problem shows two main peculiarities: on the one hand, degeneracy near the initial curve; on
the other hand, ill-posedness in the sense of Hadamard.We benefit from using a number of technical devices: hodograph transforms,
artificial viscosity, and a suitable discretization. Approximate differentiation and a parody of the quasi-reversibility method
are also involved.We offer an algorithm that restrains instability and produces effective approximate solutions. 相似文献
70.
Becucci L León RR Moncelli MR Rovero P Guidelli R 《Langmuir : the ACS journal of surfaces and colloids》2006,22(15):6644-6650
The channel-forming peptide melittin was incorporated into a biomimetic membrane consisting of a mercury electrode coated with a thiolipid monolayer, with a lipid monolayer self-assembled on top of it. The thiolipid consisted of a hydrophilic tetraethyleneoxy chain terminated at one end with a disulfide group, for anchoring to the mercury surface, and covalently linked at the other end to two diphytanyl chains, which formed a lipid bilayer with the overhanging lipid monolayer. The conductance of the lipid bilayer in contact with aqueous 0.1 M KCl was measured by electrochemical impedance spectroscopy over a frequency range from 1 x 10(-2) to 1 x 10(5) Hz and a potential range of 0.7 V for different compositions of the outer lipid monolayer. The conductance increases abruptly above the background level at sufficiently negative applied potentials, attaining a maximum value that increases with the composition of the outer monolayer in the order PC/chol (60:40) < PC < PC/SM/chol (59:15:26) < PS, with PC = phosphatidylcholine, chol = cholesterol, SM = sphingomyelin, and PS = phosphatidylserine. The higher the maximum conductance, the less negative the applied potential at which it is attained. This behavior is also discussed using a model of the electrified interphase. 相似文献