Cellulose computer modeling

In 1960, D.W. Jones supplemented fiber diffraction data from cellulose with a computer model, a list of proposed atomic coordinates that was stored in a digital con uter 3). He then... 

Alfred D. French and John W. Brady, Computer Modeling of Carbohydrate Molecules. Developed from a symposium by the ACS Divisions of Carbohydrate Chemistry, Cellulose, Paper, and Textile Chemistry and Computers in Chemistry, at the 197th National Meeting, Dallas, Texas, April 9-14, 1989, in ACS Symposium Series 430, American Chemical Society, Washington, DC, 1990. 

One way to study the shapes of cellulose chains is to construct models that accommodate the available experimental data. There are many approaches to modeling, and comprehensive studies require extensive computations. The first computer model of a carbohydrate was a part of the experimental diffraction studies of cellulose [176]. Since then, there have been substantial improvements in both computers and their representations of molecules. 

Chain Conformation. From computer modeling studies of cellulose ( ), we know that the cellulose molecule has limited flexibility. Only a few regular (Internally symmetric) conformations are allowed for cellulose, a beta 1,4-llnked glucan, and structures similar to the traditional 2-fold helix are the only ones In accord with the observed z axis spacing. Such chains resemble flat ribbons. 

Matthews JE, Himmel ME, Brady JW. (2010). Simulations of the structure of cellulose. In Nimlos MR, Crowley MF, editors. Computational Modeling in Lignocellulosic Biofuel Production, Vol. 1052 ACS Symposium Series. American Chemical Society, pp. 17-53. 

Five articles on polysaccharide helices solved prior to 1979 have appeared in the volumes published between 1967 and 1982.2-6 The first was a review on X-ray fiber diffraction and its application to cellulose, chitin, amylose, and related structures, and the rest were bibliographic accounts. Since then, X-ray structures of several new polysaccharides composed of simple to complex repeating units have been successfully determined, thanks to technological advances in fiber-diffraction techniques, the availability of fast and powerful computers, and the development of sophisticated software. Also, some old models have been either re-... 

Finally, the question of the ability of the modeling methods to predict the crystal lattice (i.e., the unit cell) from the conformation of the chain should be addressed, despite the expected computational difficulties. Based on previous work, in which the prediction of the unit cells of all four cellulose polymorphs in both parallel and antiparallel chain packing polarities was... 

Our initial, small models of an isolated cellulose chain ranged from the dimer (cellobiose) to the octamer. The dynamics of these fragments have thus far been simulated only in vacuum, using different potential energy functions such as those of MM2(85) (9) and AMBER (10), with and without contributions from electrostatic terms and hydrogen bonds, etc. (The program DISCOVER, customized for carbohydrates and for operation on the Alliant FX/80 computer, has been used (12).) Generally, the time span for the simulations has been of the order of several hundred picoseconds to 1 nanosecond. 

Our efforts were supported by three divisions of the American Qiem-ical Society Carbohydrate Qiemistry Cellulose, Paper, and Textiles and Computers in Chemistry. Additional financial support was provided by Polygen Corporation, suppliers of the Quanta Modeling System, and Chemical Design, developers and distributors of CHEM-X. 

Model building in the computer is used to compare the influence of remote contacts on the stereochemistry and properties of P-1,2-, p-1,3-, and P-1,4-glucans, including their optical rotation behavior, and to explore the possibility of chain folding in cellulose, chltin, and xylan derivatives. 

To control the complex process of cooking by the sulfate process cellulose, by means of a computer, it is necessary to have a mathematical model of the process. To obtain this model for the process of cooking by the sulfate process cellulose from a mixture of soft and hardwood and deciduous trees, we have used a fractional factorial experiment. It included these seven factors xi consumption of active lye, % Na20 on completely dry wood X2 cooking temperature, °C ... 

Aspergillus nidulans (biA-1 sorA-2) germination time and hyphae growth rate as a function of NMR and NMR T2 relaxation times of cellulose (c), sorbose (s), and orange serum broth solids with different s c ratios at 25°C. (Source From Brown, D. and Rothery, P. Models in Biology-Mathematics, Statistics and Computing, Wiley, Chichester, UK, 1993. With permission.)... 

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