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A procedure has been developed for estimating the information content of retrieval systems with binary-coded mass spectra, as well as mass spectra coded by other methods, from the statistical properties of a reference file. For a reference file, binary-coded with a threshold of 1% of the intensity of the base peak, this results typically in an estimated information content of about 50 bits for 200 selected values. It is shown that, because of errors occurring in the binary-coded spectra, the actual information content is only about 12 bits. This explains the poor performance observed for retrieval systems with binary-coded mass spectra. 相似文献
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Zia‐ur‐ Rehman Muhammad Moazzam Naseer Afzal Shah Saqib Ali Auke Meetsma 《Heteroatom Chemistry》2015,26(2):123-133
A fascinating ligand, 4‐formylpiperazinium 4‐formylpiperazine‐1‐carbodithioate (L‐salt) has been reacted with two electronically and sterically different trimethyltin(IV) chloride and triphenyltin(IV) chloride. The complexes 1 and 2 were characterized by elemental analysis, spectroscopic techniques, and X‐ray single crystal analysis. The latter technique confirmed the polymeric and monomeric nature of 1 and 2 , respectively. Both 1 and 2 showed intriguing molecular packing properties in the solid state. However, the packing of 1 is more interesting and unique where one‐dimensional polymer chains self assemble in two‐over‐two saltire‐shaped fashion to provide an overall multilayered structure. The different behavior of L toward two different tin(IV) compounds can be attributed to different electronic and steric environments around metal center. 相似文献
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Shaukat Shujah Saqib Ali Nasir Khalid Mohammad Jane Alam Shabbir Ahmad Auke Meetsma 《Chemical Papers》2018,72(4):903-919
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Pim J. de Vink Auke A. Koops Giulia D'Arrigo Gabriele Cruciani Francesca Spyrakis Luc Brunsveld 《Chemical science》2022,13(9):2744
Nuclear Receptors (NRs) are highly relevant drug targets, for which small molecule modulation goes beyond a simple ligand/receptor interaction. NR–ligands modulate Protein–Protein Interactions (PPIs) with coregulator proteins. Here we bring forward a cooperativity mechanism for small molecule modulation of NR PPIs, using the Peroxisome Proliferator Activated Receptor γ (PPARγ), which describes NR–ligands as allosteric molecular glues. The cooperativity framework uses a thermodynamic model based on three-body binding events, to dissect and quantify reciprocal effects of NR–coregulator binding (KID) and NR–ligand binding (KIID), jointly recapitulated in the cooperativity factor (α) for each specific ternary ligand·NR·coregulator complex formation. These fundamental thermodynamic parameters allow for a conceptually new way of thinking about structure–activity-relationships for NR–ligands and can steer NR modulator discovery and optimization via a completely novel approach.A cooperativity framework describes the formation of nuclear receptor ternary complexes and deconvolutes ligand and cofactor binding into intrinsic affinities and a cooperativity factor, providing a conceptually new understanding of NR modulation. 相似文献
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van Delden RA Koumura N Schoevaars A Meetsma A Feringa BL 《Organic & biomolecular chemistry》2003,1(1):33-35
A newly designed donor-acceptor substituted molecular motor 1 allows unidirectional rotation driven by visible light and shows some unique photophysical properties. 相似文献
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The space group of alpha(')-NaV2O5 turns below T(c) = 34 K from Pmmn with all V sites equivalent, into Fmm2 with three independent vanadium sites per layer. This is incompatible with models of charge ordering into V4+ and V5+. Our structure determination indicates that the phase transition consists of a charge ordering with three distinct valence states, formally V4+, V4.5+, and V5+. The singlet formation is not associated with dimerization on the spin ladder, but with the formation of spin clusters. Finally, we ascribe the quadrupling of the c axis to the large polarizability of the V2O5 skeleton. 相似文献
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ter Wiel MK van Delden RA Meetsma A Feringa BL 《Journal of the American Chemical Society》2005,127(41):14208-14222
To investigate the unidirectional rotation of chiral overcrowded biphenanthrylidenes in more detail, the size of the substituent next to the double bond responsible for the unidirectionality of rotation was varied. The thermal and photochemical isomerization of three sterically overcrowded alkenes is described. The behavior of the biphenanthrylidenes with methyl and ethyl substituents is rather similar, and these compounds undergo a unidirectional 360 degrees rotation around the central double bond in a four-step sequence involving two photochemical cis-trans isomerizations and two thermal helix inversions. The only difference between these two true molecular motors was a small entropic effect, which causes the ethyl substituted molecular motor to rotate slightly faster. The behavior of the i-propyl substituted compound differs significantly from that of the other two. Although not all different isomers of the i-propyl substituted molecular motor were detected spectroscopically, experimental data led to the conclusion that this compound can also be considered as a molecular motor and is capable of performing a 360 degrees unidirectional rotation. (1)H NMR and X-ray analysis show a meso-like form as an intermediate in the unidirectional rotation, which proves that the thermal helix inversion is a stepwise process. 相似文献