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91.
Artificial Neural Networks for Guest Chirality Classification through Supramolecular Interactions 下载免费PDF全文
Jarosław M. Granda Prof. Janusz Jurczak 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(39):12368-12372
A novel strategy for classification of guest chirality based on the combination of artificial neural networks and anion‐receptor chemistry is reported. The receptor reported herein forms supramolecular complexes with a variety of biologically important carboxylates, in which the chemical shift changes during addition of anions result in complex guest‐stereochemistry‐dependent patterns as followed by 1H NMR spectroscopy. The neural network had learnt these patterns from a training set of 12 anions, and successfully identified the “unknown” chirality of 14 guests present in the test set. Additionally, principal component analysis could discriminate most of the guests studied (26) and allowed for identification of the receptor protons, which are responsible for information transfer of guest chirality. 相似文献
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Joanna Bojarska Milan Remko Izabela D. Madura Krzysztof Kaczmarek Janusz Zabrocki Wojciech M. Wolf 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(4):328-345
Recently, fluorenylmethoxycarbonyl (Fmoc) amino acids (e.g. Fmoc–tyrosine or Fmoc–phenylalanine) have attracted growing interest in biomedical research and industry, with special emphasis directed towards the design and development of novel effective hydrogelators, biomaterials or therapeutics. With this in mind, a systematic knowledge of the structural and supramolecular features in recognition of those properties is essential. This work is the first comprehensive summary of noncovalent interactions combined with a library of supramolecular synthon patterns in all crystal structures of amino acids with the Fmoc moiety reported so far. Moreover, a new Fmoc‐protected amino acid, namely, 2‐{[(9H‐fluoren‐9‐ylmethoxy)carbonyl](methyl)amino}‐3‐{4‐[(2‐hydroxypropan‐2‐yl)oxy]phenyl}propanoic acid or N‐fluorenylmethoxycarbonyl‐O‐tert‐butyl‐N‐methyltyrosine, Fmoc‐N‐Me‐Tyr(t‐Bu)‐OH, C29H31NO5, was successfully synthesized and the structure of its unsolvated form was determined by single‐crystal X‐ray diffraction. The structural, conformational and energy landscape was investigated in detail by combined experimental and in silico approaches, and further compared to N‐Fmoc‐phenylalanine [Draper et al. (2015). CrystEngComm, 42 , 8047–8057]. Geometries were optimized by the density functional theory (DFT) method either in vacuo or in solutio. The polarizable conductor calculation model was exploited for the evaluation of the hydration effect. Hirshfeld surface analysis revealed that H…H, C…H/H…C and O…H/H…O interactions constitute the major contributions to the total Hirshfeld surface area in all the investigated systems. The molecular electrostatic potentials mapped over the surfaces identified the electrostatic complementarities in the crystal packing. The prediction of weak hydrogen‐bonded patterns via Full Interaction Maps was computed. Supramolecular motifs formed via C—H…O, C—H…π, (fluorenyl)C—H…Cl(I), C—Br…π(fluorenyl) and C—I…π(fluorenyl) interactions are observed. Basic synthons, in combination with the Long‐Range Synthon Aufbau Modules, further supported by energy‐framework calculations, are discussed. Furthermore, the relevance of Fmoc‐based supramolecular hydrogen‐bonding patterns in biocomplexes are emphasized, for the first time. 相似文献
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Headspace solid phase microextraction (headspace SPME) has been demonstrated to be an excellent solvent-free sampling method. One of the major factors contributing to the success of headspace SPME is the concentrating effect of the fiber coating toward organic compounds. The affinity of the fiber coating toward very volatile analytes, such as chloromethane, may, however, not be large enough for detection at the parts per trillion concentration level. Static headspace analysis, on the other hand, is very effective for these very volatile compounds. As analyte volatility decreases, the sensitivity of static headspace analysis drops. The complementary nature of these two sampling methods can be exploited by combining the SPME device with a gastight syringe. The sensitivity of the new sampling device is better than that of SPME for very volatile compounds or that of static headspace analysis for less volatile compounds. This new method can sample a wide range of compounds from chloromethane (b.p. −24°C) to bromoform (b.p. 149°C) with estimated limits of detection at the low parts per trillion level. 相似文献
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Air sampling of aromatic hydrocarbons in the presence of ozone by solid-phase microextraction 总被引:3,自引:0,他引:3
Effects of ozone on air sampling of standard gas mixtures of aromatic hydrocarbons were tested using solid-phase microextraction (SPME). Standard concentrations of ozone ranging from 10 ppb (v/v) to 6400 ppm (v/v) were generated using an in-house built ozone generator based on corona discharge. Effects of temperature, discharge voltage, and oxygen flow on the ozone generation were tested. The working dc voltage had the greatest effect on generated ozone concentration and was proportional to the ozone concentration. Generation temperature and oxygen flow rate were inversely proportional to ozone concentrations. Produced ozone was mixed with standard benzene, toluene, ethylbenzene, and xylenes (BTEX) gas at less than 100 ppb (v/v). Air samples were collected with poly(dimethylsiloxane) (PDMS) 100 microm SPME fibers and analyzed by gas chromatography (GC)-flame ionization detection (FID) and GC-MS. Significant reductions of BTEX concentrations were observed. In addition, some products of BTEX-ozone-oxygen reactions were identified. SPME worked well as a rapid sampler for BTEX and BTEX-ozone-oxygen reaction products. No significant deterioration of the PDMS coating and no significant reduction of absorption capacity were observed after repeated exposure to ozone. 相似文献
96.
Extraction of formic and acetic acids from aqueous solution by dynamic headspace-needle trap extraction temperature and pH optimization 总被引:1,自引:0,他引:1
A combined method of dynamic headspace-needle trap sample preparation and gas chromatography for the determination of formic and acetic acids in aqueous solution was developed in this study. A needle extraction device coupled with a gas aspirating pump was intended to perform sampling and preconcentration of target compounds from aqueous sample before gas chromatographic analysis. The needle trap extraction (NTE) technique allows for the successful sampling of short chain fatty acids under dynamic conditions while keeping the headspace (HS) volume constant. Two important parameters, including extraction temperature and effect of acidification, have been optimized and evaluated using the needle trap device. The method detection limits for the compounds estimated were 87.2microg/L for acetic acid and 234.8microg/L for formic acid in spite of the low flame ionization detection response for formic acid and its low Henry's law constant in aqueous solution. Precision was determined based on the two real samples and ranged between 4.7 and 10.7%. The validated headspace-needle trap extraction method was also successfully applied to several environmental samples. 相似文献
97.
Simple-structured, well-functioned disposable poly(dimethylsiloxane) (PDMS) microchips were developed for capillary isoelectric focusing with whole column imaging detection (CIEF-WCID). Side-by-side comparison of the developed microchips with well-established commercial capillary cartridges demonstrated that the disposable microchips have comparable performance as well as advantages such as absence of lens effect and possibility of high-aspect-ratio accompanied with a dramatic reduction in cost. 相似文献
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