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991.
Highly Stereoselective [4+2] and [3+2] Spiroannulations of 2‐(2‐Oxoindolin‐3‐ylidene)acetic Esters Catalyzed by Bifunctional Thioureas
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Prof. Magda Monari Dr. Elisa Montroni Andrea Nitti Prof. Marco Lombardo Prof. Claudio Trombini Dr. Arianna Quintavalla 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(31):11038-11049
A new Michael–Michael cascade reaction between 2‐(2‐oxoindolin‐3‐ylidene)acetic esters 1 and nitroenoates 2 , catalyzed by bifunctional thioureas, is investigated. The combination of the two Michael reactions results in a novel and facile [4+2] or [3+2] spiroannulation process, which is characterized by the following features: 1) two carbon–carbon bonds and four stereocenters, including a quaternary spiro carbon, are formed under mild conditions; 2) an unprecedented and stereochemically defined substitution pattern on the spirocarbocyclic unit is obtained; 3) the double‐bond configuration of the donor–acceptor nitroenoate 2 determines the absolute configuration of the spiro center, whereas the remaining stereocenters are formed under control of the catalyst. The effect on the final stereochemical outcome of structural variations of each starting material, catalyst, and experimental conditions is analyzed in detail. In particular, the use of specifically designed chiral nitroenoates enables diverse polyfunctional spirocyclohexane derivatives containing six consecutive stereogenic centers to be constructed. To our knowledge, this is the first asymmetric organocatalytic strategy enabling both five‐ and six‐membered β‐nitro spirocarbocyclic oxindoles. 相似文献
992.
Prof. Claudio Toniolo Dr. Marco Crisma Prof. Alessandro Moretto Dr. Cristina Peggion Prof. Fernando Formaggio Prof. Carlos Alemán Prof. Carlos Cativiela Prof. Chandrasekharan Ramakrishnan Prof. Padmanabhan Balaram 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(40):13866-13877
Among the various types of α‐peptide folding motifs, δ‐turn, which requires a central cis‐amide disposition, has been one of the least extensively investigated. In particular, this main‐chain reversal topology has been studied in‐depth neither in linear/cyclic peptides nor in proteins. This Minireview article assembles and critically analyzes relevant data from a literature survey on the δ‐turn conformation in those compounds. Unpublished results from recent conformational energy calculations and a preliminary solution‐state analysis on a small model peptide, currently ongoing in our laboratories, are also briefly outlined. 相似文献
993.
Prof. Steven V. Ley Daniel E. Fitzpatrick Dr. Rebecca M. Myers Dr. Claudio Battilocchio Dr. Richard. J. Ingham 《Angewandte Chemie (International ed. in English)》2015,54(35):10122-10136
In this Review we describe how the advent of machines is impacting on organic synthesis programs, with particular emphasis on the practical issues associated with the design of chemical reactors. In the rapidly changing, multivariant environment of the research laboratory, equipment needs to be modular to accommodate high and low temperatures and pressures, enzymes, multiphase systems, slurries, gases, and organometallic compounds. Additional technologies have been developed to facilitate more specialized reaction techniques such as electrochemical and photochemical methods. All of these areas create both opportunities and challenges during adoption as enabling technologies. 相似文献
994.
Enhancement of Photophysical and Photosensitizing Properties of Flavin Adenine Dinucleotide by Mutagenesis of the C‐Terminal Extension of a Bacterial Flavodoxin Reductase
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Dr. Lorena Valle Dr. Inés Abatedaga Dr. Faustino E. Morán Vieyra Dr. Ana Bortolotti Prof. Dr. Néstor Cortez Prof. Dr. Claudio D. Borsarelli 《Chemphyschem》2015,16(4):872-883
The role of the mobile C‐terminal extension present in Rhodobacter capsulatus ferredoxin–NADP(H) reductase (RcFPR) was evaluated using steady‐state and dynamic spectroscopies for both intrinsic Trp and FAD in a series of mutants in the absence of NADP(H). Deletion of the six C‐terminal amino acids beyond Ala266 was combined with the replacement A266Y to emulate the structure of plastidic reductases. Our results show that these modifications of the wild‐type RcFPR produce subtle global conformational changes, but strongly reduce the local rigidity of the FAD‐binding pocket, exposing the isoalloxazine ring to the solvent. Thus, the ultrafast charge‐transfer quenching of 1FAD* by the conserved Tyr66 residue was absent in the mutant series, producing enhancement of the excited singlet‐ and triplet‐state properties of FAD. This work highlights the delicate balance of the specific interactions between FAD and the surrounding amino acids, and how the functionality and/or photostability of redox flavoproteins can be modified. 相似文献
995.
Differences in Dynamics between Crosslinked and Non‐Crosslinked Hyaluronates Measured by using Fast Field‐Cycling Relaxometry
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Enrico Ravera Marco Fragai Giacomo Parigi Prof. Claudio Luchinat 《Chemphyschem》2015,16(13):2803-2809
The dynamic properties of water molecules in gels containing linear and crosslinked hyaluronic acid polymers are investigated by using an integrated approach that includes relaxometry, solid‐state NMR spectroscopy, and scanning electron microscopy. A model‐free analysis of field‐dependent nuclear relaxation is applied to obtain information on mobility and the population of different pools of water molecules in the gels. Differences between linear and crosslinked hyaluronic acid polymers are observed, indicating that crosslinking increases both the fraction and the correlation time of water molecules with slow dynamics. 相似文献
996.
Faramarz S. Gard Diego M. Santos María B. Daizo José L. Mijares Patricia B. Bozzano Claudio A. Danón María Reinoso Emilia B. Halac 《Surface and interface analysis : SIA》2020,52(11):755-769
Raman spectroscopy, optical microscopy, scanning electron microscopy (SEM), and electron probe microanalysis (EPMA) were used to study pigments on an Egyptian cartonnage from the Ptolemaic period (305–30 bc ). The surface morphology of each color region was examined using backscattering (BS) and secondary electron imaging. SEM X-ray energy dispersive spectrometry and EPMA wavelength dispersive spectroscopy provided semiquantitative chemical analysis of each pigment. Raman spectroscopy was used to identify the minerals associated with the pigments. This technique confirmed the presence of cinnabar (α-HgS) in the red part of the fragments. A mixture of orpiment (As2S3) and bonazziite (β-As4S4) and/or alacránite (As8S9) was detected in the yellow regions of the fragments. The orange pigment was confirmed to be a mixture of orpiment, uzonite (χ-As4S5), and pararealgar (As4S4). Egyptian blue (CaCuSi4O10) and Egyptian green ((Cu,Ca)SiO3) pigments were detected from blue/green dark-colored regions of the fragments. 相似文献
997.
Giuseppe Buscarnera Giuseppe Dattola Claudio di Prisco 《International Journal of Solids and Structures》2011,48(13):1867-1878
In this paper the onset of instabilities in elastoplastic materials is theoretically studied and a conceptual basis for understanding the physical implications of a loss of uniqueness and/or existence of the incremental response is provided. For this purpose, the concept of test controllability is reinterpreted and mixed stress–strain loading programmes are accounted for. A set of scalar indices, the moduli of instability, related with the inception of an unstable response is introduced and their dependency on the loading programme is explicitly illustrated. The paper shows that the use of these newly defined scalar measures provides support for an alternative definition for mechanical stability, which is closely related with the mathematical notions of existence and uniqueness of the predicted incremental response. In the final section, some mathematical properties of the moduli of instability are discussed, suggesting a novel reinterpretation of other well established theories and providing additional tools for the future application of the proposed framework. 相似文献
998.
We consider a suitable scaling, called the slow Markov walk limit, for a risk process with shot noise Cox claim number process and reserve dependent premium rate. We provide large deviation estimates for the ruin probability. Furthermore, we find an asymptotically efficient law for the simulation of the ruin probability using importance sampling. Finally, we present asymptotic bounds for ruin probabilities in the Bayesian setting. 相似文献
999.
Claudio Storck Raphael Gehrer Claude Fischer Markus Wolfensberger Flurin Honegger Gerhard Friedrich Markus Gugatschka 《Journal of voice》2011,25(5):632-637
Objectives/Hypothesis
Cricothyroid approximation (CTA) surgery aims at raising the voice pitch in male-to-female transsexuals. However, 30% of the patients are not satisfied with the result. The purpose of our study was to examine the cricothyroid joint (CTJ) biomechanics and to analyze if (and how) the CTJ anatomy influences the movement of the cricoid and, consequently, the elongation of the vocal fold and the voice pitch after CTA.Methods
Twenty-four cadaver larynges were examined with high-resolution computerized tomography and MIMICS three-dimensional imaging software (Materialise Interactive Medical Image Control System, Leuven, Belgium). After superimposing the two scans taken in “neutral” and in “CTA” positions, vector geometrical analysis was used to determine the effective rotation axis of the CTJ and to calculate the elongation of the vocal folds after CTA.Results
Our results showed that the cricoid rotates around an axis, the position of which depends on the anatomical structure of the CTJ. Based on the location of this effective rotation axis, we could distinguish three groups. In group I (N = 13), the rotation axis was located in the lower third; in group II (N = 5), it was located in the middle third; and in group III (N = 6), it was located in the upper third of the cricoid. The elongations of the vocal fold were 12%, 8%, and 3%, in groups I, II, and III, respectively.Conclusions
The anatomical structure of the CTJ influences directly (1) the position of the effective rotation axis and (2) the elongation of the vocal folds. 相似文献1000.
Assessing the optical changes in dissolved organic matter in humic lakes by spectral slope distributions 总被引:1,自引:0,他引:1
Galgani L Tognazzi A Rossi C Ricci M Galvez JA Dattilo AM Cozar A Bracchini L Loiselle SA 《Journal of photochemistry and photobiology. B, Biology》2011,102(2):132-139
The impact of photodegradation and mixing processes on the optical properties of dissolved organic matter (DOM) was examined using a distribution of absorption spectral slopes and fluorescence measurements in two Argentine lakes. By examining the variability of the absorption spectral slopes throughout the ultraviolet and visible wavelengths, it was possible to determine which wavelength intervals were most sensitive to dominant loss processes. For DOM photodegradation, results show that increases in the absorption spectral slope between 265 and 305 nm were highly sensitive to increased exposure to solar ultraviolet radiation. A slightly larger wavelength range (265-340 nm) was found to be influenced when both mixing and photodegradation processes were considered, in terms DOM residence time, DOM absorption and UV diffuse attenuation coefficients. This same interval of spectral slopes (265-340 nm) was found to highly correlate with changes in fluorescence emission/excitation in wavelengths that are typically associated with terrestrial humic-like DOM. The identification of specific wavelength intervals, rather than the use of standard wavelength intervals or ratios, improved our ability to identify the dominant dissolved organic matter (humic-like) and major loss mechanisms (photodegradation) in these lakes. 相似文献