MOLECULAR MODELING OF HUMAN HAIR 475 molecules bound to a UHSP cause 18-MEA to straighten out to approach its full length on a protein backbone that we have calculated at more than 2.5 nm, in reasonable agree- ment with TEM measurements of the upper beta layer of human hair by Swift and Holmes (20) of 2.5 nm and by Swift (14) of 3 nm. NEXT STEPS IN MOLECULAR MODELING OF HUMAN HAIR Our next steps involve constructing a molecular model of the virgin keratin fi ber surface to build on this molecular model by adding free lipids to the existing model to determine if free lipids can cause 18-MEA to stretch out to its full length and approach the length found for the upper beta layer of keratin fi bers. We hope at some time to construct models to simulate the lower layer(s) of the epicuticle by adding a second layer of proteins to provide an overall thickness of the epicuticle layer of approximately 13 nm, as reported by Swift and Smith (8). This will require new software to allow us to increase the number of atoms so that we can test the inclusion of KAP-5 and KAP-10 proteins (10,11) includ- ing disulfi de and/or isopeptide cross-links in either one or both, or between protein lay- ers. We also intend to develop different damaged hair models, working from our current virgin keratin fi ber surface molecular model. ACKNOWLEDGMENT The authors thank the Polymer Chemistry Division of the National Chemical Laboratory, Pune 411 008, India, where the modeling part of this project was carried out. GLOSSARY OF TERMS USED FOR MOLECULAR MODELING IN THIS PAPER Dreiding II force fi eld: A versatile force fi eld that contains the parameters and mathematical functions for describing the interatomic potential energy of interaction between atoms that are either bonded to each other or non-bonded (dispersion, van der Waals, electrostatic, and hydrogen bonding terms). Dreiding II force fi eld is useful for predicting structures and dynamics of organic, biological, and main-group inorganic molecules. Details are given in the following reference: S. L. Mayo, B. D. Olafson, and W. A. Goddard III, Dreiding: A generic force fi eld for molecular simulations, J. Phys. Chem., 94, 8897–8909 (1990). Energy minimization procedure: A mathematical procedure for fi nding minimum values of the interatomic thermodynamic potential energy function that is continuous in spatial dimensions, specifi cally using gradient-based (derivative) methods. Examples are the Newton-Raphson methods and their variants such as conjugate gradient, Fletcher- Powell, etc. The x,y,z coordinates of atoms taking part in this process is obtained from this procedure. Molecular dynamics simulations (MD): A theoretical method to track the motion of atoms and molecules in space and time coordinates, by numerical integration of the equations of motion. MD can be used to calculate equilibrium thermodynamic properties.

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