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<P class=MsoNormal style="MARGIN: 0cm 2.2pt 0pt 0cm; TEXT-ALIGN: center"
align=center><SPAN><STRONG><FONT face="Times New Roman">Aula Dr. Venancio
Deulofeu<o:p></o:p></FONT></STRONG></SPAN></P>
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face="Times New Roman">Departamento de Química
Orgánica<o:p></o:p></FONT></STRONG></SPAN></P>
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align=center><SPAN lang=ES-AR
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face="Times New Roman">Ciudad Universitaria, Pab. II, Piso
3<o:p></o:p></FONT></STRONG></SPAN></P>
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align=center><SPAN lang=ES-AR
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face="Times New Roman">Lunes 25 de Septiembre, 11.30
hs<o:p></o:p></FONT></STRONG></SPAN></P>
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align=center><SPAN lang=ES-AR
style="FONT-SIZE: 18pt; COLOR: black; FONT-FAMILY: Arial; mso-ansi-language: ES-AR"><STRONG>Alfred
D. French<o:p></o:p></STRONG></SPAN></P>
<P class=MsoBodyText2 style="MARGIN: 6pt 27.1pt 0pt 36pt; TEXT-ALIGN: center"
align=center><SPAN lang=EN-US
style="FONT-SIZE: 13pt; COLOR: black; FONT-FAMILY: Arial; mso-ansi-language: EN-US"><STRONG>USDA
- SRRC (United States Department of Agriculture - Southern <st1:place
w:st="on"><st1:PlaceName w:st="on">Regional</st1:PlaceName> <st1:PlaceName
w:st="on">Research</st1:PlaceName> <st1:PlaceType
w:st="on">Center</st1:PlaceType></st1:place>), Nueva
Orleáns<o:p></o:p></STRONG></SPAN></P>
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align=center><SPAN lang=EN-US
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<P class=MsoBodyText2 style="MARGIN: 6pt 27.1pt 0pt 36pt; TEXT-ALIGN: center"
align=center><SPAN> <STRONG>Modeling of cellobiose- the shortest cellulose
chain<o:p></o:p></STRONG></SPAN></P>
<P class=MsoBodyText2 style="MARGIN: 6pt 27.1pt 0pt 36pt; TEXT-ALIGN: left"
align=left><SPAN lang=EN-US
style="FONT-SIZE: 14pt; FONT-FAMILY: Arial; mso-ansi-language: EN-US; mso-bidi-font-style: italic"><o:p><STRONG> </STRONG></o:p></SPAN></P>
<P class=MsoNormal
style="MARGIN: 0cm 27.1pt 0pt 36pt; mso-layout-grid-align: none"><SPAN
lang=EN-US
style="FONT-SIZE: 12pt; FONT-FAMILY: TimesNewRoman; mso-ansi-language: EN-US; mso-bidi-font-family: TimesNewRoman"><FONT
face="Times New Roman">Cellulose is important in many aspects of biology as well
as being an important industrial molecule. It is the main component of plant
cell walls, and is used in paper, textiles and building materials. In
particular, it is the primary molecule in cotton fiber, the reason for our
continuing interest at the U. S. Department of Agriculture’s Southern Regional
Research Center. The relation between cotton fiber and moisture is currently an
interesting topic because the moisture affects the mechanical and other
properties related to fiber quality. For example, cotton is an unusual
carbohydrate because it is stronger when it is wet! Like other polysaccharides,
cellulose is often crystalline, but it appears that non-crystalline components
are more interesting. The noncrystalline components are very difficult to
characterize experimentally, so molecular modeling is an appropriate tool for
study.<o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal
style="MARGIN: 0cm 27.1pt 0pt 36pt; mso-layout-grid-align: none"><SPAN
lang=EN-US
style="FONT-SIZE: 12pt; FONT-FAMILY: TimesNewRoman; mso-ansi-language: EN-US; mso-bidi-font-family: TimesNewRoman"><FONT
face="Times New Roman">Among our approaches, we have made Ramachandran energy
surfaces with quantum mechanics to study the shortest cellulose chain,
cellobiose. This was a massive study, involving some 15,000 energy minimizations
that each took several hours of cpu time. More than 100 different arrangements
of the primary and secondary groups were considered, and the results were
examined in some detail to understand the contributions of these groups to the
energy surface.<o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal
style="MARGIN: 0cm 27.1pt 0pt 36pt; mso-layout-grid-align: none"><SPAN
lang=EN-US
style="FONT-SIZE: 12pt; FONT-FAMILY: TimesNewRoman; mso-ansi-language: EN-US; mso-bidi-font-family: TimesNewRoman"><FONT
face="Times New Roman">The final map was quite predictive of crystal structures,
somewhat to our surprise, because similar surfaces made with molecular mechanics
require elevated dielectric constants to provide predictive maps. Still, the
work confirmed earlier reports that the global energy minimum for cellobiose is
for a structure that is not near the structures observed by diffraction, as
proposed by Strati et al. Although 24 different “starting geometries”
contributed to the central 81 point portion of the map, the low energies were
often obtained by distortions of several low energy structures. Using only the
starting geometry that gave the lowest overall energy would give discrepancies
of up to 6 kcal/mol with the final adiabatic map. Probing the high-energy
regions showed that the maximum energy was about 30
kcal/mol.<o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal
style="MARGIN: 0cm 27.1pt 0pt 36pt; mso-layout-grid-align: none"><SPAN
lang=EN-US
style="FONT-SIZE: 12pt; FONT-FAMILY: TimesNewRoman; mso-ansi-language: EN-US; mso-bidi-font-family: TimesNewRoman"><FONT
face="Times New Roman">For comparison we have made new energy surfaces with MM3,
MM4 and AMBER/GLYCAM-<o:p></o:p></FONT></SPAN></P>
<P class=MsoNormal
style="MARGIN: 0cm 27.1pt 0pt 36pt; mso-layout-grid-align: none"><SPAN
lang=EN-US style="FONT-SIZE: 12pt; mso-ansi-language: EN-US"><FONT
face="Times New Roman">04 for both cellobiose and its analog based on
tetrahydropyran. Hybrid QM/MM methods can be used, given the MM disaccharide and
analog maps and QM analog maps. These will also be discussed.</FONT></SPAN><SPAN
lang=EN-US
style="FONT-SIZE: 12pt; FONT-FAMILY: TimesNewRoman; mso-ansi-language: EN-US; mso-bidi-font-family: TimesNewRoman"><o:p></o:p></SPAN></P>
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