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141.
Helmut Simon Johann Bader Helmut Günther Stefan Neumann Jordanes Thanos 《Angewandte Chemie (International ed. in English)》1985,24(7):539-553
It has been known for many decades that chiral compounds can be obtained by stereospecific biocatalytic reduction. Further significant methodological developments in this field have, however, only been made during the past ten years; they include the application of previously unused microorganisms and electron donors, the discovery of additional substrates for the known reductases, the development of methods for regenerating reduced pyridine nucleotides, and the discovery of new reductases which were sought for specific preparative purposes. Many chiral compounds can now be synthesized by microbial hydrogenation using H2 and hydrogenase-containing microorganisms as well as by electromicrobial or electroenzymatic reduction. In the two latter methods, anaerobic or aerobic organisms are supplied with electrons from electrochemically reduced, artificial mediators, e.g., methyl viologen. Reductases that do not require pyridine nucleotides and can accept electrons directly from reduced viologens are especially useful. Two examples of this type of enzyme are described which are of preparative interest. Many cells contain methyl viologen-dependent NAD(P) reductases, a large number of which have still not been characterized. A productivity number is proposed which allows different methods of bioconversion with microorganisms to be compared. The productivity numbers of compounds synthesized by the methods described in this review are often 10- to 100-fold higher than those of substances obtained by conventional techniques. 相似文献
142.
Abstract— Absorbance changes were monitored from 250 to 650 nm during the first microsecond after photolysis of detergent suspensions of bovine rhodopsin at 20°C. Global analysis of the resulting data produced difference spectra for bathorhodopsin, BSI and lumirhodopsin which give the change in absorbance of the aromatic amino acid side chains in these photointermediates relative to rhodopsin. These spectra show that the significant bleaching of absorbance near 280 nm, which has been seen previously for the lumirhodopsin, metarhodopsin I and metarhodopsin II intermediates, extends to times as early as bathorhodopsin. Because no corresponding absorbance increase is observed in the 250-275 nm region, the earliest bleaching of the 280 nm absorbance in rhodopsin is attributed to disruption of a hyperchromic interaction affecting Trp265 . Partial decay of this 280 nm bleaching as bathorhodopsin converts to BSI takes place maximally near 290 nm, where Trp265 has been shown to absorb, and could be due to the ring of the retinylidene chromophore resuming a position at the BSI stage that reestablishes the hyperchromic interaction with Trp265 . A subsequent change in the 250-300 nm region, which has no counterpart in the visible chromophore bands, indicates the possible presence of a protein-localized process as lumirhodopsin is formed. 相似文献
143.
Synthesis of 6-O-(2-amino-2-deoxy--D-glucopyranosyl)-D-myo-inositol 1-phosphate, an inner core structure found in various glycosylphosphatidylinositols, and the corresponding 1,2-cyclic phosphate, proposed as part of an insulin second messenger glycosylinositol phosphate, is described. Chirality in the inositol part of the molecule was achieved by the use of a known D-camphor acetal intermediate. The glycosylation used 4-O-allyl-2-azido-3,6-di-O-benzyl-2-deoxy--D-glucopyranosyl fluoride as glycosyl donor. The allyl group can be chemoselectively removed, opening a route to oligosaccharides bound to the 4-position of the glucosamine unit. The phosphorylation was accomplished by the phosphoramidate procedure. 相似文献
144.
E. Anklam Maria Rosa Bassani Thomas Eiberger Stefan Kriebel Markus Lipp Reinhard Matissek 《Analytical and bioanalytical chemistry》1997,357(7):981-984
Pyrolysis Mass Spectrometry (Py-MS) was used for the discrimination of cocoa butters from other vegetable fats. Mass spectra
ranging from 50 amu to 250 amu were analyzed by principal component analysis (PCA) and with neural nets. The application of
neural nets leads to a good discrimination between the two classes. Detailed analysis of the nets revealed that only the first
60 masses were used within the net. The use of PCA requires a careful selection of the number of masses included in the calculation.
Canonical variance analysis was applied to determine the significant masses. Optimal performance of PCA was observed only
using the first 22 significant masses. Most of these masses were different from the ones used by the neural net. It seems
that the mass spectra obtained by Py-MS contain sufficient information for the discrimination of pure cocoa butter from other
vegetable fats, but none of the methods seems to be able to extract all information available. Neural net provides a very
robust method for this task and no prior data selection was necessary.
Received: 13 May 1996 / Revised: 7 August 1996 / Accepted: 7 August 1996 相似文献
145.
Prof. Dr. Tunga Salthammer Friederike Monegel Nicole Schulz Dr. Erik Uhde Prof. Dr. Stefan Grimme Jakob Seibert Prof. Dr. Uwe Hohm Dr. Wolf-Ulrich Palm 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(3):1046-1056
The chemical background of olfactory perception has been subject of intensive research, but no available model can fully explain the sense of smell. There are also inconsistent results on the role of the isotopology of molecules. In experiments with human subjects it was found that the isotope effect is weak with acetone and D6-acetone. In contrast, clear differences were observed in the perception of octanoic acid and D15-octanoic acid. Furthermore, a trained sniffer dog was initially able to distinguish between these isotopologues of octanoic acid. In chromatographic measurements, the respective deuterated molecule showed weaker interaction with a non-polar liquid phase. Quantum chemical calculations give evidence that deuterated octanoic acid binds more strongly to a model receptor than non-deuterated. In contrast, the binding of the non-deuterated molecule is stronger with acetone. The isotope effect is calculated in the framework of statistical mechanics. It results from a complicated interplay between various thermostatistical contributions to the non-covalent free binding energies and it turns out to be very molecule-specific. The vibrational terms including non-classical zero-point energies play about the same role as rotational/translational contributions and are larger than bond length effects for the differential isotope perception of odor for which general rules cannot be derived. 相似文献
146.
Panagiotis Kl. Barkoutsos Fotios Gkritsis Pauline J. Ollitrault Igor O. Sokolov Stefan Woerner Ivano Tavernelli 《Chemical science》2021,12(12):4345
The development of tailored materials for specific applications is an active field of research in chemistry, material science and drug discovery. The number of possible molecules obtainable from a set of atomic species grow exponentially with the size of the system, limiting the efficiency of classical sampling algorithms. On the other hand, quantum computers can provide an efficient solution to the sampling of the chemical compound space for the optimization of a given molecular property. In this work, we propose a quantum algorithm for addressing the material design problem with a favourable scaling. The core of this approach is the representation of the space of candidate structures as a linear superposition of all possible atomic compositions. The corresponding ‘alchemical’ Hamiltonian drives the optimization in both the atomic and electronic spaces leading to the selection of the best fitting molecule, which optimizes a given property of the system, e.g., the interaction with an external potential as in drug design. The quantum advantage resides in the efficient calculation of the electronic structure properties together with the sampling of the exponentially large chemical compound space. We demonstrate both in simulations and with IBM Quantum hardware the efficiency of our scheme and highlight the results in a few test cases. This preliminary study can serve as a basis for the development of further material design quantum algorithms for near-term quantum computers.‘Alchemical’ quantum algorithm for the simultaneous optimisation of chemical composition and electronic structure for material design. By exploiting quantum mechanical principles this approach will boost drug discovery in the near future. 相似文献
147.
Alexander Aster Christopher Rumble Anna-Bea Bornhof Hsin-Hua Huang Naomi Sakai Tom olomek Stefan Matile Eric Vauthey 《Chemical science》2021,12(13):4908
1,4,5,8-Naphthalenediimides (NDIs) are widely used motifs to design multichromophoric architectures due to their ease of functionalisation, their high oxidative power and the stability of their radical anion. The NDI building block can be incorporated in supramolecular systems by either core or imide functionalization. We report on the charge-transfer dynamics of a series of electron donor–acceptor dyads consisting of a NDI chromophore with one or two donors linked at the axial, imide position. Photo-population of the core-centred π–π* state is followed by ultrafast electron transfer from the electron donor to the NDI. Due to a solvent dependent singlet–triplet equilibrium inherent to the NDI core, both singlet and triplet charge-separated states are populated. We demonstrate that long-lived charge separation in the triplet state can be achieved by controlling the mutual orientation of the donor–acceptor sub-units. By extending this study to a supramolecular NDI-based cage, we also show that the triplet charge-separation yield can be increased by tuning the environment.Ultrafast electron transfer from singlet and triplet excited states in equilibrium results in the population of both singlet and triplet charge-separated states. 相似文献
148.
Stefan Sander Dr. Robert Müller Dr. Mike Ahrens Prof. Dr. Martin Kaupp Prof. Dr. Thomas Braun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(57):14287-14298
The reaction of [PtCl2(COD)] (COD=1,5-cyclooctadiene) with diisopropyl-2-(3-methyl)indolylphosphine (iPr2P(C9H8N)) led to the formation of the platinum(ii ) chlorido complexes, cis-[PtCl2{iPr2P(C9H8N)}2] ( 1 ) and trans-[PtCl2{iPr2P(C9H8N)}2] ( 2 ). The cis-complex 1 reacted with NEt3 yielding the complex cis-[PtCl{κ2-(P,N)-iPr2P(C9H7N)}{iPr2P(C9H8N)}] ( 3 ) bearing a cyclometalated κ2-(P,N)-phosphine ligand, while the isomer 2 with a trans-configuration did not show any reactivity towards NEt3. Treatment of 1 or 3 with (CH3)4NF (TMAF) resulted in the formation of the twofold cyclometalated complex cis-[Pt{κ2-(P,N)-iPr2P(C9H7N)}2] ( 4 ). The molecular structures of the complexes 1–4 were determined by single-crystal X-ray diffraction. The fluorido complex cis-[PtF{κ2-(P,N)-iPr2P(C9H7N)}{iPr2P(C9H8N)}] ⋅ (HF)4 ( 5 ⋅ (HF)4) was formed when complex 4 was treated with different hydrogen fluoride sources. The Pt(ii ) fluorido complex 5 ⋅ (HF)4 exhibits intramolecular hydrogen bonding in its outer coordination sphere between the fluorido ligand and the NH group of the 3-methylindolyl moiety. In contrast to its chlorido analogue 3 , complex 5 ⋅ (HF)4 reacted with CO or the ynamide 1-(2-phenylethynyl)-2-pyrrolidinone to yield the complexes trans-[Pt(CO){κ2-(P,C)-iPr2P(C9H7NCO)}{iPr2P(C9H8N)}][F(HF)4] ( 7 ) and a complex, which we suggest to be cis-[Pt{C=C(Ph)OCN(C3H6)}{κ2-(P,N)-iPr2P(C9H7N)}{iPr2P(C9H8N)}][F(HF)4] ( 9 ), respectively. The structure of 9 was assigned on the basis of DFT calculations as well as NMR and IR data. Hydrogen bonding of HF and NH to fluoride was proven to be crucial for the existence of 7 and 9 . 相似文献
149.
Grégoire Sieg Quentin Pessemesse Sascha Reith Stefan Yelin Prof. Dr. Christian Limberg Prof. Dr. Dominik Munz Dr. C. Gunnar Werncke 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(67):16760-16767
Carbonyl and iminyl based radical anions are reactive intermediates in a variety of transformations in organic synthesis. Herein, the isolation of ketyl, and more importantly unprecedented ketiminyl and aldiminyl radical anions coordinated to cobalt and iron complexes is presented. Insights into the electronic structure of these unusual metal bound radical anions is provided by X-Ray diffraction analysis, NMR, IR, UV/Vis and Mössbauer spectroscopy, solid and solution state magnetometry, as well as a by a detailed computational analysis. The metal bound radical anions are very reactive and facilitate the activation of intra- and intermolecular C−H bonds. 相似文献
150.
Bumhee Lim Yangyang Cheng Takehiro Kato Anh-Tuan Pham Eliott Le Du Abhaya Kumar Mishra Elija Grinhagena Dimitri Moreau Naomi Sakai Jerome Waser Stefan Matile 《Helvetica chimica acta》2021,104(8):e2100085
Thiol-mediated uptake is emerging as method of choice to penetrate cells. This study focuses on irreversible covalent inhibitors of thiol-mediated uptake. High-content high-throughput screening of the so far largest collection of hypervalent iodine reagents affords inhibitors that are more than 250 times more active than Ellman’s reagent and rival the best dynamic covalent inhibitors. Comparison with other irreversible reagents reveals that inhibition within one series follows reactivity, whereas inhibition across series deviates from reactivity. These trends support that molecular recognition, besides dynamic covalent exchange, contributes significantly to thiol-mediated uptake. The most powerful inhibitors besides the best hypervalent iodine reagents were Fukuyama’s nosyl protecting group and super-cinnamaldehydes that have been introduced as irreversible activators of the pain receptor TRPA1. Considering that several viruses use different forms of thiol-mediated uptake to enter cells, the identification of new irreversible inhibitors of thiol-mediated uptake is of general interest for the discovery of new antivirals. 相似文献