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1.
Experimental and Theoretical Studies on the Rearrangement of 2‐Oxoazepane α,α‐Amino Acids into 2′‐Oxopiperidine β2,3,3‐Amino Acids: An Example of Intramolecular Catalysis 下载免费PDF全文
Dr. Diego Núñez‐Villanueva Dr. M. Ángeles Bonache Laura Lozano Dr. Lourdes Infantes Prof. José Elguero Prof. Ibon Alkorta Prof. M. Teresa García‐López Dr. Rosario González‐Muñiz Dr. Mercedes Martín‐Martínez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2489-2500
Enantiopure β‐amino acids represent interesting scaffolds for peptidomimetics, foldamers and bioactive compounds. However, the synthesis of highly substituted analogues is still a major challenge. Herein, we describe the spontaneous rearrangement of 4‐carboxy‐2‐oxoazepane α,α‐amino acids to lead to 2′‐oxopiperidine‐containing β2,3,3‐amino acids, upon basic or acid hydrolysis of the 2‐oxoazepane α,α‐amino acid ester. Under acidic conditions, a totally stereoselective synthetic route has been developed. The reordering process involved the spontaneous breakdown of an amide bond, which typically requires strong conditions, and the formation of a new bond leading to the six‐membered heterocycle. A quantum mechanical study was carried out to obtain insight into the remarkable ease of this rearrangement, which occurs at room temperature, either in solution or upon storage of the 4‐carboxylic acid substituted 2‐oxoazepane derivatives. This theoretical study suggests that the rearrangement process occurs through a concerted mechanism, in which the energy of the transition states can be lowered by the participation of a catalytic water molecule. Interestingly, it also suggested a role for the carboxylic acid at position 4 of the 2‐oxoazepane ring, which facilitates this rearrangement, participating directly in the intramolecular catalysis. 相似文献
2.
Sergio Ayala‐Mar Javier Donoso‐Quezada Roberto C. Gallo‐Villanueva Victor H. Perez‐Gonzalez Jos Gonzlez‐Valdez 《Electrophoresis》2019,40(23-24):3036-3049
Exosomes are nanovesicles secreted by most cellular types that carry important biochemical compounds throughout the body with different purposes, playing a preponderant role in cellular communication. Because of their structure, physicochemical properties and stability, recent studies are focusing in their use as nanocarriers for different therapeutic compounds for the treatment of different diseases ranging from cancer to Parkinson's disease. However, current bioseparation protocols and methodologies are selected based on the final exosome application or intended use and present both advantages and disadvantages when compared among them. In this context, this review aims to present the most important technologies available for exosome isolation while discussing their advantages and disadvantages and the possibilities of being combined with other strategies. This is critical since the development of novel exosome‐based therapeutic strategies will be constrained to the effectiveness and yield of the selected downstream purification methodologies for which a thorough understanding of the available technological resources is needed. 相似文献
3.
4.
Ignacio Villanueva 《Mathematische Nachrichten》2003,250(1):98-103
We clarify and prove in a simpler way a result of Taskinen about symmetric operators on C(Kn), K an uncountable metrizable compact space. To do this we prove that, for any compact space K and any n ∈ ?, the symmetric injective n–tensor product of C(K), , is complemented in C(BC(K)*), a result of independent interest. The techniques we develop allow us to extend the result in several directions. We also show that the hypothesis of metrizability and uncountability cannot be removed. 相似文献
5.
Villanueva J Villegas V Querol E Avilés FX Serrano L 《Journal of mass spectrometry : JMS》2002,37(9):974-984
In the post-genomic era, several projects focused on the massive experimental resolution of the three-dimensional structures of all the proteins of different organisms have been initiated. Simultaneously, significant progress has been made in the ab initio prediction of protein three-dimensional structure. One of the keys to the success of such a prediction is the use of local information (i.e. secondary structure). Here we describe a new limited proteolysis methodology, based on the use of unspecific exoproteases coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), to map quickly secondary structure elements of a protein from both ends, the N- and C-termini. We show that the proteolytic patterns (mass spectra series) obtained can be interpreted in the light of the conformation and local stability of the analyzed proteins, a direct correlation being observed between the predicted and the experimentally derived protein secondary structure. Further, this methodology can be easily applied to check rapidly the folding state of a protein and characterize mutational effects on protein conformation and stability. Moreover, given global stability information, this methodology allows one to locate the protein regions of increased or decreased conformational stability. All of this can be done with a small fraction of the amount of protein required by most of the other methods for conformational analysis. Thus limited exoproteolysis, together with MALDI-TOF MS, can be a useful tool to achieve quickly the elucidation of protein structure and stability. 相似文献
6.
A. Fendler M. P. Villanueva E. Gimenez J. M. Lagarón 《Cellulose (London, England)》2007,14(5):427-438
The present work presents and discusses the interrelation between composition, morphology, thermal history, mechanical and
barrier properties to oxygen and limonene of composites of HDPE/MA-PE/cellulose fibers of significant interest in, among others,
food packaging applications. From the overall results, it was observed that increasing the loading of purified alpha-cellulose
fibers in the polyethylene matrix beyond 10 wt.% led to a decrease in the permeability coefficient of d-limonene, effect which was found to be primarily related to a decrease in the overall solubility of this strongly plasticizing
aroma component. On the other hand, the oxygen permeability was found to decrease to a significant extend with increasing
fiber content beyond 5 wt.%, but this effect was more strongly ascribed to a significant decrease in the diffusion coefficient.
Therefore, the fibers are thought to generate a more tortuous path for the non-interacting gas molecules to travel across
the composites thickness, even when tested at high relative humidity conditions. Optimum fiber loading levels in terms of
overall property balance were found to be around 20 wt.%. 相似文献
7.
Núñez Lisardo Fraga L. Núñez M. R. Villanueva M. Rial B. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):9-17
Curing reactions of the epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n=0) and m-xylylenediamine (m-XDA) were studied to calculate time-temperature-transformation (TTT) isothermal cure diagram for this system. Gel times were
measured as a function of temperature using solubility test. Differential scanning calorimetry (DSC) was used to calculate
the vitrification times. DSC data show a one-to-one relationship between T
g and fractional conversion, a independent of cure temperature. As a consequence, T
g can be used as a measure of conversion. The activation energy for the polymerization overall reaction was calculated from
the gel times obtained using the solubility test (41.5 kJ mol-1). This value is similar to the results obtained for other similar epoxy systems. Isoconversion contours were calculated by
numerical integration of the best fitting kinetic model.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Lisardo Núñez-Regueira M. Villanueva I. Fraga C. A. Gracia-Fernández S. Gómez-Barreiro 《Journal of Thermal Analysis and Calorimetry》2006,86(1):235-241
The thermal degradation
of an epoxy system consisting of a diglycidyl ether of bisphenol A (DGEBA, n=0) and m-xylylenediamine (m-XDA)
was studied by both thermogravimetric analysis (TG) and dielectric analysis
(DEA). It has been checked a deviation of the typical behaviour in the Arrhenius
plot expected for this kind of systems, owing to the thermal degradation.
Both, structural relaxation time and conductivity values, were represented
as a function of the mass loss, that allow a relationship to be obtained between
characteristic relaxation time and the degree of degradation at the beginning
of the degradation process. 相似文献
9.
Elucidation and identification of amino acid containing membrane lipids using liquid chromatography/high‐resolution mass spectrometry 下载免费PDF全文
10.
Pablo Salvador Julia Real Clara Zamorano Antonio Villanueva 《Mathematical and Computer Modelling》2011,53(1-2):42-54
In recent years, ground vibrations have become an important issue due to the growing awareness of the society about environmental living conditions. In this way, vibrations caused by trains running near houses or workplaces are considered disturbing for residents. Within this framework, this paper presents a procedure to estimate the vibration path caused by the passing of a train. In order to achieve this, the equations which describe the physical phenomenon are set in the frequency and wavenumber domain and solved by using the Fourier Transform. The obtained analytical solution is transformed back into the time and space domain by means of the Fourier series. The obtained theoretical results are compared with experimental measurements carried out in the Madrid–Barcelona High Speed Line in order to analyse the performance of this procedure. 相似文献