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991.
Austen Curtin Christine Austin Alessandro Giuliani Manuel Ruiz Marín Francheska Merced-Nieves Martha M. Tllez-Rojo Robert O. Wright Manish Arora Paul Curtin 《Entropy (Basel, Switzerland)》2021,23(12)
Metabolism and physiology frequently follow non-linear rhythmic patterns which are reflected in concepts of homeostasis and circadian rhythms, yet few biomarkers are studied as dynamical systems. For instance, healthy human development depends on the assimilation and metabolism of essential elements, often accompanied by exposures to non-essential elements which may be toxic. In this study, we applied laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to reconstruct longitudinal exposure profiles of essential and non-essential elements throughout prenatal and early post-natal development. We applied cross-recurrence quantification analysis (CRQA) to characterize dynamics involved in elemental integration, and to construct a graph-theory based analysis of elemental metabolism. Our findings show how exposure to lead, a well-characterized toxicant, perturbs the metabolism of essential elements. In particular, our findings indicate that high levels of lead exposure dysregulate global aspects of metabolic network connectivity. For example, the magnitude of each element’s degree was increased in children exposed to high lead levels. Similarly, high lead exposure yielded discrete effects on specific essential elements, particularly zinc and magnesium, which showed reduced network metrics compared to other elements. In sum, this approach presents a new, systems-based perspective on the dynamics involved in elemental metabolism during critical periods of human development. 相似文献
992.
993.
Manuel Snchez-Chaves Gerardo Martínez Enrique Lpez Madruga 《Journal of polymer science. Part A, Polymer chemistry》1999,37(15):2941-2948
2-Hydroxyethyl methacrylate (HEMA) and styrene (S) have been copolymerized in a 3 mol · L−1N,N′-dimethylformamide (DMF) solution using 2,2′azobis (isobutyronitrile) (AIBN) as an initiator over a wide composition and conversion range. From low-conversion experiments and 1H-NMR analysis, the monomer reactivity ratios were determined according to the Mayo–Lewis terminal model. The comparison of the obtained results with those previously reported for copolymerization in bulk and in toluene reveals a relatively small but noticeable solvent effect that can be qualitatively explained by the bootstrap model. Cumulative copolymer composition as a function of conversion is satisfactorily described by the integrated Mayo–Lewis equation; overall copolymerization rate increases with increasing the HEMA/S ratio, and individual monomer conversion is closely related to the monomer molar fraction in the feed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2941–2948, 1999 相似文献
994.
Manuel Martín Gemma Mas Flix Urpí Jaume Vilarrasa 《Angewandte Chemie (International ed. in English)》1999,38(20):3086-3089
The same precursor —namely, (2R)-2-ethyl-4-penten-1-ol—was used to obtain fragments C9–C13 and C1–C8 of 1 , the aglycon of Sch 38516 (which is active against Candida sp.) and fluvirucin B1 (which is active against influenza A virus). The key steps of the synthesis were the aldol-like reaction between the two fragments and the macrolactamization of a 13-azidotridecanoic acid derivative (see scheme). MOM=methoxymethyl, Py=2-pyridyl. 相似文献
995.
Christopher Knie Manuel Utecht Fangli Zhao Hannes Kulla Sergey Kovalenko Prof. Albert M. Brouwer Prof. Peter Saalfrank Prof. Stefan Hecht Dr. David Bléger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(50):16492-16501
Improving the photochemical properties of molecular photoswitches is crucial for the development of light‐responsive systems in materials and life sciences. ortho‐Fluoroazobenzenes are a new class of rationally designed photochromic azo compounds with optimized properties, such as the ability to isomerize with visible light only, high photoconversions, and unprecedented robust bistable character. Introducing σ‐electron‐withdrawing F atoms ortho to the N?N unit leads to both an effective separation of the n→π* bands of the E and Z isomers, thus offering the possibility of using these two transitions for selectively inducing E/Z isomerizations, and greatly enhanced thermal stability of the Z isomers. Additional para‐electron‐withdrawing groups (EWGs) work in concert with ortho‐F atoms, giving rise to enhanced separation of the n→π* transitions. A comprehensive study of the effect of substitution on the key photochemical properties of ortho‐fluoroazobenzenes is reported herein. In particular, the position, number, and nature of the EWGs have been varied, and the visible light photoconversions, quantum yields of isomerization, and thermal stabilities have been measured and rationalized by DFT calculations. 相似文献
996.
Cobas JC Tahoces PG Martin-Pastor M Penedo M Javier Sardina F 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,168(2):231-295
The application of a lossy data compression algorithm based on wavelet transform to 2D NMR spectra is presented. We show that this algorithm affords rapid and extreme compression ratios (e.g., 800:1), providing high quality reconstructed 2D spectra. The algorithm was evaluated to ensure that qualitative and quantitative information are retained in the compressed NMR spectra. Whilst the maximum compression ratio that can be achieved depends on the number of signals and on the difference between the most and the least intense peaks (dynamic range), a compression ratio of 80:1 is affordable even for the challenging case of homonuclear 2D experiments of large biomolecules. 相似文献
997.
Dr. Jesús A. Molina de la Torre Ignacio Pérez-Ortega Dr. Álvaro Beltrán Manuel R. Rodríguez Prof. Dr. M. Mar Díaz-Requejo Prof. Dr. Pedro J. Pérez Prof. Dr. Ana C. Albéniz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(2):556-563
Polynorbornenes prepared by vinyl addition polymerization and bearing pendant alkenyl groups serve as skeletons to support trispyrazolylborate ligands (Tpx) built at those alkenyl sites. Reaction with CuI in acetonitrile led to VA-PNB–TpxCu(NCMe) (VA-PBN=vinyl addition polynorbornene) with a 0.8–1.4 mmol incorporation of Cu per gram of polymer. The presence of tetracoordinated copper(I) ions was been assessed by FTIR studies on the corresponding VA-PNB-TpxCu(CO) adducts, in agreement with those on discrete TpxCu(CO). The new materials were employed as heterogeneous catalysts in several carbene- and nitrene-transfer reactions, showing a behavior similar to that of the homogeneous counterparts but also being recycled several times maintaining a high degree of activity and selectivity. This is the first example of supported Tpx ligands onto polymeric supports with catalytic applications. 相似文献
998.
Manuel G. Ricardo Javiel F. Marrrero Dr. Oscar Valdés Prof. Dr. Daniel G. Rivera Prof. Dr. Ludger A. Wessjohann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(3):769-774
The multicomponent backbone N-modification of peptides on solid-phase is presented as a powerful and general method to enable peptide stapling at the backbone instead of the side chains. This work shows that a variety of functionalized N-substituents suitable for backbone stapling can be readily introduced by means of on-resin Ugi multicomponent reactions conducted during solid-phase peptide synthesis. Diverse macrocyclization chemistries were implemented with such backbone N-substituents, including the ring-closing metathesis, lactamization, and thiol alkylation. The backbone N-modification method was also applied to the synthesis of α-helical peptides by linking N-substituents to the peptide N-terminus, thus featuring hydrogen-bond surrogate structures. Overall, the strategy proves useful for peptide backbone macrocyclization approaches that show promise in peptide drug discovery. 相似文献
999.
Otilia Mó M. Merced Montero-Campillo Ibon Alkorta José Elguero Manuel Yáñez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(50):11688-11695
High-level G4 calculations show that the strength of chalcogen interactions is enhanced dramatically if chalcogen compounds simultaneously form alkaline-earth bonds. This phenomenon is studied by exploring binary YX2⋅⋅⋅N-Base complexes and two types of ternary MCl2⋅⋅⋅YX2⋅⋅⋅N-Base, YX2⋅⋅⋅N-Base⋅⋅⋅MCl2 complexes, in which YX2 is a chalcogen compound (Y=S, Se; X=F, Cl), the N-Bases are sp, sp2, and sp3 bases (NCH, HN=CH2, NH3), and MCl2 are alkaline-earth BeCl2 or MgCl2 derivatives. Starting from the chalcogen-bonded complexes YX2⋅⋅⋅NH3 and YX2⋅⋅⋅HN=CH2, the binding site of a new incoming alkaline-earth bond is found, surprisingly, to depend on the nature of the halogen atom attached to the chalcogen. For the YF2 binary complexes the association site is the F atom of the YF2 subunit, whereas for YCl2 it is the N atom of the nitrogen base. Regarding YX2⋅⋅⋅NCH complexes, N is the most favorable site for an alkaline-earth interaction in ternary complexes, regardless of which YX2 derivative is used. The explanation relies on the interplay of all the noncovalent interactions involved: the strong cooperativity between chalcogen and alkaline-earth bonds, and the appearance of secondary noncovalent interactions in the form of hydrogen bonds. 相似文献
1000.
Dr. Manuel Souto Dr. Karol Strutyński Dr. Manuel Melle-Franco Prof. João Rocha 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(48):10912-10935
Electroactive organic molecules have received a lot of attention in the field of electronics because of their fascinating electronic properties, easy functionalization and potential low cost towards their implementation in electronic devices. In recent years, electroactive organic molecules have also emerged as promising building blocks for the design and construction of crystalline porous frameworks such as metal–organic frameworks (MOFs) and covalent-organic frameworks (COFs) for applications in electronics. Such porous materials present certain additional advantages such as, for example, an immense structural and functional versatility, combination of porosity with multiple electronic properties and the possibility of tuning their physical properties by post-synthetic modifications. In this Review, we summarize the main electroactive organic building blocks used in the past few years for the design and construction of functional porous materials (MOFs and COFs) for electronics with special emphasis on their electronic structure and function relationships. The different building blocks have been classified based on the electronic nature and main function of the resulting porous frameworks. The design and synthesis of novel electroactive organic molecules is encouraged towards the construction of functional porous frameworks exhibiting new functions and applications in electronics. 相似文献