148 research outputs found
Tops and Writhing DNA
The torsional elasticity of semiflexible polymers like DNA is of biological
significance. A mathematical treatment of this problem was begun by Fuller
using the relation between link, twist and writhe, but progress has been
hindered by the non-local nature of the writhe. This stands in the way of an
analytic statistical mechanical treatment, which takes into account thermal
fluctuations, in computing the partition function. In this paper we use the
well known analogy with the dynamics of tops to show that when subjected to
stretch and twist, the polymer configurations which dominate the partition
function admit a local writhe formulation in the spirit of Fuller and thus
provide an underlying justification for the use of Fuller's "local writhe
expression" which leads to considerable mathematical simplification in solving
theoretical models of DNA and elucidating their predictions. Our result
facilitates comparison of the theoretical models with single molecule
micromanipulation experiments and computer simulations.Comment: 17 pages two figure
Technical recommendations for clinical translation of renal MRI: a consensus project of the Cooperation in Science and Technology Action PARENCHIMA
Purpose The potential of renal MRI biomarkers has been increasingly recognised, but clinical translation requires more
standardisation. The PARENCHIMA consensus project aims to develop and apply a process for generating technical recommendations on renal MRI.
Methods A task force was formed in July 2018 focused on fve methods. A draft process for attaining consensus was distributed publicly for consultation and fnalised at an open meeting (Prague, October 2018). Four expert panels completed
surveys between October 2018 and March 2019, discussed results and refned the surveys at a face-to-face meeting (Aarhus,
March 2019) and completed a second round (May 2019).
Results A seven-stage process was defned: (1) formation of expert panels; (2) defnition of the context of use; (3) literature
review; (4) collection and comparison of MRI protocols; (5) consensus generation by an approximate Delphi method; (6)
reporting of results in vendor-neutral and vendor-specifc terms; (7) ongoing review and updating. Application of the process
resulted in 166 consensus statements.
Conclusion The process generated meaningful technical recommendations across very diferent MRI methods, while allowing for improvement and refnement as open issues are resolved. The results are likely to be widely supported by the renal
MRI community and thereby promote more harmonisation
Tautomerism of anthraquinones: IX. Protonated 1,5- and 1,8- dihydroxyanthraquinones
Fine structure of πl,π absorption of mono- and dications derived from 1,5- and 1,8-dihydroxyanthraquinones originates from their existence as dynamic equilibrium mixtures of isomers differing by position of the positive charge, double bond distribution, and number of intramolecular hydrogen bonds. Protonation is accompanied by displacement of isomeric equilibria. Isomeric transformations of protonated dihydroxyanthraquinones involve mainly excited states of their molecules. © 2009 Pleiades Publishing, Ltd
Proportional response method for the assignment of pi(1),pi* adsorption bands of ionized hydroxyanthraquinones
The proportional response method was proposed as a means of correctly assigning long-wavelength pi(1),pi* absorption bands of ionized hydroxyanthraquinones to their different ionization states and tautomer structures
Study of tautomeric transformations of 1,4,5,8-tetraaminoanthraquinone by electronic spectroscopy
Based on the example of 1,4,5,8-tetraamino-9,10-anthraquinone, a method is described for establishing the tautomeric compositions and sequences of tautomeric transformations that occur in known samples of quinones. An analysis of electronic absorption spectra shows that this substance is a dynamic equilibrium mixture of 4,5,8,9-tetraamino-1,10-anthraquinone and the imines tautomeric to it. The tautomeric compositions of different samples of matter differ and can contain 1,4,8-triamino-5-hydroxy-9,10- anthraquinone-10-imine, 4,8,9-triamino-10-hydroxy-1,5-anthraquinone-5-imine, 5,8-diamino-4,9-dihydroxy- 1,10-antraquinonediimine, and 8,10-diamino-5,9-dihydroxy-1,4- antraquinonediimine. Tautomeric equilibrium shifts can accompany not only chemical reactions but physical processes as well, so any investigation of the properties of substances without establishing their tautomeric compositions would be incorrect. © Pleiades Publishing, Ltd., 2013
Isomerism of 1-amino-4-hydroxy-9,10-anthraquinone
[No abstract available
Tautomerism of metal complexes with 1,8-dihydroxy-3-R1-6-R 2-9,10-anthraquinones
The structures of metal complexes with 1,8-dihydroxyanthraquinones studied by spectrophotometric, quantum-chemical, and correlation methods were found to be determined by tautomeric 9,10-1,10-anthraquinoid structures of the ligands and by the degree of the ligand ionization. Complex formation is accompanied by the shifts in tautomeric equilibria influencing both excited and ground states of the ligands. The 1,10-anthraquinoid forms of complexes are the most characteristic. The known complexes are classified in accordance with the ligand structures. © Pleiades Publishing, Inc., 2006
Competing tautomeric transformations and the structure of 1-(alkyl,aryl)amino-4-hydroxyanthraquinones
Keto-enol and amine-imine tautomerism and equilibria with trans-conformers are characteristic of 1-(alkyl,aryl)amino-4-hydroxy-9,10-anthraquinones. Amino forms possess 1,10- and 1,4-, but not 9,10-quinoid structure. Various tautomeric and conformeric transformations are in competition. The outcome of this competition may be studied by the correlation analysis of electron absorption spectra but it would be possible to understand the causes of changes in the direction of the competing transformation only in the case when each action on the substance would be accompanied with establishing the corresponding alterations in its tautomeric composition. © 2013 Pleiades Publishing, Ltd
Role of tautomerism and rotational isomerism in the interaction of α-hydroxyanthraquinones with boric acid
The products of reaction of α-hydroxyanthraquinones with boric acid are mixtures of 9,10-, 1,10 -, 1,4-and 1,5-quinoid tautomeric complexes of boric acid and borate esters differing by the coordination bonds with carbonyl groups existing in the dynamic equilibrium. The deepening of the reagents color in the presence of boron does not a result only of the complexation, but in the accompanying shift of the tautomeric equilibria. © Pleiades Publishing, Ltd., 2010
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