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Title: NEUTRON AND SYNCHROTRON X-RAY FIBER DIFFRACTION STUDIES OF CELLULOSE POLYMORPHS

Abstract

No abstract prepared.

Authors:
Publication Date:
Research Org.:
Los Alamos National Lab., NM (US)
Sponsoring Org.:
US Department of Energy (US)
OSTI Identifier:
789006
Report Number(s):
LA-UR-01-6470
TRN: US200202%%323
DOE Contract Number:
W-7405-ENG-36
Resource Type:
Conference
Resource Relation:
Conference: Conference title not supplied, Conference location not supplied, Conference dates not supplied; Other Information: PBD: 1 Nov 2001
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CELLULOSE; NEUTRON DIFFRACTION; SYNCHROTRON RADIATION; X-RAY DIFFRACTION; ISOMERS

Citation Formats

P. A. LANGAN. NEUTRON AND SYNCHROTRON X-RAY FIBER DIFFRACTION STUDIES OF CELLULOSE POLYMORPHS. United States: N. p., 2001. Web.
P. A. LANGAN. NEUTRON AND SYNCHROTRON X-RAY FIBER DIFFRACTION STUDIES OF CELLULOSE POLYMORPHS. United States.
P. A. LANGAN. Thu . "NEUTRON AND SYNCHROTRON X-RAY FIBER DIFFRACTION STUDIES OF CELLULOSE POLYMORPHS". United States. doi:. https://www.osti.gov/servlets/purl/789006.
@article{osti_789006,
title = {NEUTRON AND SYNCHROTRON X-RAY FIBER DIFFRACTION STUDIES OF CELLULOSE POLYMORPHS},
author = {P. A. LANGAN},
abstractNote = {No abstract prepared.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Nov 01 00:00:00 EST 2001},
month = {Thu Nov 01 00:00:00 EST 2001}
}

Conference:
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  • Although the crystalline nature of cellulose has been one of most studied structural problems in polymer science there remain many open questions. Cellulose is a polymer formed by (1-4)-linked {beta}-D-glucosyl residues that are alternately rotated by 180o along the polymer axis to form flat ribbon-like chains. Each glucosyl unit bears three hydroxyl groups, one an hydroxymethyl group. It has been long recognized that these hydroxyl groups and their ability to bond via hydrogen bonding not only play a major role in directing how the crystal structure of cellulose forms but also in governing important physical properties of cellulose materials. Throughmore » the development of new techniques we have been able to prepare fiber samples of cellulose with exceptionally high order. The quality of these samples is allowing us to exploit the unique properties of synchrotron X-ray and neutron sources in order to collect diffraction data to near atomic resolution. Synchrotron X-rays are used to provide accurate crystallographic parameters for C and O atoms. However, because of the relatively weak scattering power of H atoms for X-rays, neutrons are used to determine H atom parameters. We have developed methods for replacing labile H atoms with D, without any loss in crystalline perfection. Deuterated fibers can diffract neutrons with intensities that are substantially different from the intensities diffracted from hydrogenated fibers. These differences, along with the phases calculated from the C and O positions determined in our X-ray studies, are used to calculate Fourier difference syntheses in which density associated with labile hydrogen atoms is imaged. The unprecedented high resolution of these data is revealing new information on cellulose structure and hydrogen bonding.« less
  • Different extended packing motifs of dichloro-[2-(pyridin-2-yl)-1,10-phenanthroline]copper(II), CuCl2 (C17H11N3Cl2) are obtained depending on the crystallization conditions. A triclinic form (I) is obtained from dimethylformamide-diethyl ether or methanol whereas crystallization from dimethylformamide-water yields a monoclinic form (II). In each case, the CuII center is in a 5-coordinate, distorted square-pyramidal geometry. The extended packing for both forms can be described as a highly-offset π stacking arrangement with interlayer distances of 3.674 (3) and 3.679 (3) Å for (I) and (II), respectively. The reaction of diprotonated Pt(tmpip2NCN)Cl (tmpip2NCN = 2,6-bis(2,2,6,6-tetramethylpiperidylmethyl)- benzyl) with AgPF6 under acidic conditions followed by the addition of 2-(pyridin-2-yl)-1,10-phenanthroline, results inmore » a hydrogen bonded co-crystal, 2,2,6,6-tetramethyl-4-oxopiperidinium hexafluorophosphate- 2-(pyridin-2-yl)-1,10-phenanthroline (1/1),C9H18NO+.PF6-.C17H11N3.(III). The extended packing maximizes π-π interactions in a parallel, faceto-face arrangement with an interlayer stacking distance of 3.4960 (14) Å.« less
  • The structure of cellulose I{alpha} has been examined by electron diffraction methods and linked-atom least-squares modeling methods. Only a single chain passes through the triclinic unit cell insuring that all chains are parallel. The unit cell parameters are a = 0.674, b = 0.593 and c = 1.036 mn with {alpha} = 117.{degrees}, {beta}=113.{degrees} and {gamma} = 81.{degrees} which forces adjacent chains to be staggered with respect to one another by approximately c/4. The major difference between the molecular conformation and that previous reported for cellulose I is the existence of different conformations for successive hydroxymethl groups along the backbone.more » The structure of the other polymorph, I{beta}, does not differ significantly from that proposed for cellulose I.« less
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