Mechanical properties of biological macromolecules

Our aims in this chapter are to introduce the principles underlying the methods based on delayed luminescence and other photophysical mechanisms, to describe the experimental designs enabling the measurement of rotational diffusion, and to illustrate applications in studies of the rotational properties of biological macromolecules. 

Alves, M.M., Antonov, Yu.A., Goii9alves, M.P. (2000). Phase equilibria and mechanical properties of gel-like water-gelatin-locust bean gum systems. International Journal of Biological Macromolecules, 27, 41 17. 

The radiation pressure exerted by light is very weak. A bright laser beam of several milliwatts of power can exert only a few piconewtons (pN) of force. However, a force of 10 pN is enough to pull a cell of E. coli through water ten times faster than it can swim.213 In about 1986, it was found that a laser beam focused down to a spot of - one K ( 1 pm for an infrared laser) can trap and hold in its focus a retractile bead of 1 pm diameter. This "optical tweezers" has become an important experimental tool with many uses.213 214 For example, see Fig. 19-19. Not only are optical tweezers of utility in studying biological motors but also mechanical properties of all sorts of macromolecules can be examined. For example, DNA can be stretched and its extensibility measured.215 Actin filaments have even been tied into knots 216... 

Cellulose, an important constituent of wood, has long chains of glucose molecules linked by glycoside bonds. These chains are cross-linked by hydrogen bonds. Many biological polymers have unusual mechanical properties, not at present matched by the properties of artificial macromolecules. For instance, arteries are... 

Photochromic control of the polymer properties leads to potential applications involving the mechanical properties of a solution (viscosity, photogelation), polymer fiber (extensibility, photomuscle ), or membrane (porosity). More important, however, the ability to control the activity of enzymes and other biologically important macromolecules leads to potential applications in clinical phototherapy. 

At the theoretical level, full quantum mechanical calculations on biologic macromolecules are not computationally feasible, nor would they be particularly helpful in understanding macro-molecular properties without proper inclusion of the solvent water or other biologic matrix on which these properties so intimately depend. However, ab initio quantum mechanical calculations on smaller systems that represent crucial steps in an enzymic reaction, for example, can be helpful in understanding specific processes within macromolecules or in estimating intermolecular forces and stereochemical effects in molecular mechanics simulations that are not experimentally accessible. 

Recently, our research attempted to find new materials based on blends of biological macromolecules, such as structural proteins and polysaccharides, and hydrophilic synthetic polymers, such as poly(vinyl alcohol) (PVA), in which the biocompatibility of the former is combined to the mechanical properties of the latter ((. ... 

Dong XM, Revol J-F, Gray DG (1998) Effect of microcrystallite preparation conditions on the formation of colloid crystals of cellulose. Cellulose 5 19-32 Dubief D, Samain E, Dufresne A (1999) Polysaccharide microcrystals reinforced amorphous poly (beta-hydroxyoctanoate) nanocomposite materials. Macromolecules 32 5765-5771 Dufresne A (2000) Dynamic mechanical analysis of the interphase in bacterial polyester/cellulose whiskers natural composites. Compos Interfaces 7 53-67 Dufresne A (2006) Comparing the mechanical properties of high performance polymer nanocomposites from biological sources. J Nanosci Nanotechnol 6 322-330 Dufresne A, Vignon MR (1998) Improvement of starch film performances using cellulose microfibrils. Macromolecules 31 2693-2696... 

Dufresne AJ (2006) Comparing the mechanical properties of high performance polymer nanocomposites from biological sources. J Nanosci Nanotechnol 6 322-330 Dufresne A (2008) Polysaccharide nano crystal reinforced nanocomposites. Can J Chem 86 484—494 Dufresne A, Vignon M (1998) Improvement of starch film performances using cellulose microfibrils. Macromolecules 31 2693-2696... 

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