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61.
Pittenauer E Zehl M Belgacem O Raptakis E Mistrik R Allmaier G 《Journal of mass spectrometry : JMS》2006,41(4):421-447
Various classes of polypeptide antibiotics, including blocked linear peptides (gramicidin D), side-chain-cyclized peptides (bacitracin, viomycin, capreomycin), side-chain-cyclized depsipeptides (virginiamycin S), real cyclic peptides (tyrocidin, gramcidin S) and side-chain-cyclized lipopeptides (polymyxin B and E, amfomycin), were investigated by low-energy collision induced dissociation (LE-CID) as well as high-energy CID (HE-CID). Ion trap (IT) based instruments with different desorption/ionization techniques such as electrospray ionization (ESI), atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI) and vacuum MALDI (vMALDI) as well as a vMALDI-time-of-flight (TOF)/curved field-reflectron instrument fitted with a gas collision cell were used. For optimum comparability of data from different IT instruments, the CID conditions were standardized and only singly charged precursor ions were considered. Additionally, HE-CID data obtained from the TOF-based instrument were acquired and compared with LE-CID data from ITs. Major differences between trap-based and TOF-based CID data are that the latter data set lacks abundant additional loss of small neutrals (e.g. ammonia, water) but contains product ions down to the immonium-ion-type region, thereby allowing the detection of even single amino-acid (even unusual amino acids) substitutions. For several polypeptide antibiotics, mass spectrometric as well as tandem mass spectrometric data are shown and discussed for the first time, and some yet undescribed minor components are also reported. De novo sequencing of unusually linked minor components of (e.g. cyclic) polypeptides is practically impossible without knowledge of the exact structure and fragmentation behavior of the major components. Finally, the described standardized CID condition constitutes a basic prerequisite for creating a searchable, annotated MS(n)-database of bioactive compounds. The applied desorption/ionization techniques showed no significant influence on the type of product ions (neglecting relative abundances of product ions formed) observed, and therefore the type of analyzer connected with the CID process mainly determines the type of fragment ions. 相似文献
62.
Akshay Kumar Hippolyte Durand Elisa Zeno Cyril Balsollier Bastien Watbled Cecile Sillard Sbastien Fort Isabelle Baussanne Naceur Belgacem Daniel Lee Sabine Hediger Martine Demeunynck Julien Bras Gaël De Paëpe 《Chemical science》2020,11(15):3868
Cellulose nanofibrils (CNF) are renewable bio-based materials with high specific area, which makes them ideal candidates for multiple emerging applications including for instance on-demand drug release. However, in-depth chemical and structural characterization of the CNF surface chemistry is still an open challenge, especially for low weight percentage of functionalization. This currently prevents the development of efficient, cost-effective and reproducible green synthetic routes and thus the widespread development of targeted and responsive drug-delivery CNF carriers. We show in this work how we use dynamic nuclear polarization (DNP) to overcome the sensitivity limitation of conventional solid-state NMR and gain insight into the surface chemistry of drug-functionalized TEMPO-oxidized cellulose nanofibrils. The DNP enhanced-NMR data can report unambiguously on the presence of trace amounts of TEMPO moieties and depolymerized cellulosic units in the starting material, as well as coupling agents on the CNFs surface (used in the heterogeneous reaction). This enables a precise estimation of the drug loading while differentiating adsorption from covalent bonding (∼1 wt% in our case) as opposed to other analytical techniques such as elemental analysis and conductometric titration that can neither detect the presence of coupling agents, nor differentiate unambiguously between adsorption and grafting. The approach, which does not rely on the use of 13C/15N enriched compounds, will be key to further develop efficient surface chemistry routes and has direct implication for the development of drug delivery applications both in terms of safety and dosage.DNP-enhanced solid-state NMR unravels the surface chemistry of functionalized nanocellulose. 相似文献
63.
Borges J. P. Godinho M. H. Martins A. F. Trindade A. C. Belgacem M. N. 《Mechanics of Composite Materials》2001,37(3):257-264
The mechanical and optical properties of cellulose-based composite films are investigated.It is shown that the use of toluene diisocyanate as a coupling agent and Avicel fibers as reinforcing elements give films with the highest mechanical characteristics. Using differential scanning calorimetry, it is also found that the glass transition temperature T
g of all the materials studied is below the room temperature and that the T
g increased with cross-linking and introduction of Avicel. 相似文献
64.
Thermodynamic irreversibilities generated by the combustion process are evaluated and analyzed numerically. The numerical simulation is performed for a reference case study for which experimental data are available in the literature: diffusion flame properties in a common burner configuration are studied by the Fluent software with the standard k–ε turbulence model and two-step chemical reaction. The study quantifies the contribution of each mechanism to entropy generation, i.e., friction, heat conduction, species diffusion, and chemical reaction. The chemical reaction and heat conduction are found to be the major sources of entropy production. Preheating of air reduces thermodynamic irreversibilities within the combustor. 相似文献
65.
The Ramanujan Journal - In this paper, we establish a distributional Rodrigues formula for non-symmetric Dunkl-classical orthogonal polynomial sequences. Then, we use this formula to determine,... 相似文献
66.
Russian Journal of Applied Chemistry - In this paper, we investigate the exergy analysis of the combustion chamber supplied by different fuel compositions based mainly on methane and/or hydrogen in... 相似文献
67.
Belgacem Balsam Leveneur Sébastien Chlendi Mohamed Estel Lionel Bagane Mohamed 《Journal of Thermal Analysis and Calorimetry》2019,135(3):1891-1898
Journal of Thermal Analysis and Calorimetry - Phosphoric acid, a non-renewable chemical, is used in different industries. Production of this chemical from natural phosphate can be done by two... 相似文献
68.
Barhoumi E. M. Okonkwo P. C. Zghaibeh Manaf Belgacem I. Ben Alkanhal Tawfeeq Abdullah Abo-Khalil A. G. Tlili Iskander 《Journal of Thermal Analysis and Calorimetry》2020,141(1):221-230
Journal of Thermal Analysis and Calorimetry - Energy is linked to the most economic and social issues which affect sustainable development of countries. To diversify its economy sources, Saudi... 相似文献
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In this paper, the problem of internal finite‐time stabilization for 1‐D coupled wave equations with interior point mass is handled. The nonlinear stabilizing feedback law leads, in closed‐loop, to nonlinear evolution equations where Kato theory is used to prove the well‐posedness. In addition, it is showed that in some cases, the solution of this hybrid system is constant in finite‐time if we use Neumann boundary conditions. This result can be improved (in complete finite‐time stability sense) if we change the above feedback. 相似文献