Of macromolecules

We also attempt to distinguish between surface physical chemistry and colloid and polymer physical chemistry. This distinction is not always possible, and clearly many of the features of physical chemistry of surfaces, such as the electrostatic interactions and adsorption of macromolecules, have a significant... 

Tao T 1969 Time-dependent fluorescence depolarization and Brownian rotational diffusion coefficients of macromolecules Biopolymers 8 609-32... 

Grosberg A Y and Khokhlov A R 1994 Statistical Physics of Macromolecules (AlP Series in Polymers and Complex Materials) (New York AlP)... 

Freed K F 1987 Renormalization Group Theory of Macromolecules (New York Wiley-Interscience)... 

Asakura S and Oosawa F 1954 On interaction between two bodies immersed in a solution of macromolecules J. Chem. Phys. 22 1255-6... 

B. R. Brooks and M. Karplus. Normal modes for specific motions of macromolecules Application to the hinge-bending mode of lysozyme. Proc. Natl. Acad. Sci. USA, 82 4995-4999, 1985. 

Among the main theoretical methods of investigation of the dynamic properties of macromolecules are molecular dynamics (MD) simulations and harmonic analysis. MD simulation is a technique in which the classical equation of motion for all atoms of a molecule is integrated over a finite period of time. Harmonic analysis is a direct way of analyzing vibrational motions. Harmonicity of the potential function is a basic assumption in the normal mode approximation used in harmonic analysis. This is known to be inadequate in the case of biological macromolecules, such as proteins, because anharmonic effects, which MD has shown to be important in protein motion, are neglected [1, 2, 3]. 

For a given potential energy function, one may take a variety of approaches to study the dynamics of macromolecules. The most exact and detailed information is provided by MD simulations in which one solves the equations of motion for the atoms constituting the macromolecule and any surrounding environment. With currently available techniques and methods it is possible... 

Watanabe, M., Karplus, M. Dynamics of Molecules with Internal Degrees of Freedom by Multiple Time-Step Methods. J. Chem. Phys. 99 (1995) 8063-8074 Figueirido, F., Levy, R. M., Zhou, R., Berne, B. J. Large Scale Simulation of Macromolecules in Solution Combining the Periodic Fast Multiple Method with Multiple Time Step Integrators. J. Chem. Phys. 106 (1997) 9835-9849 Derreumaux, P., Zhang, G., Schlick, T, Brooks, B.R. A Truncated Newton Minimizer Adapted for CHARMM and Biomolecular Applications. J. Comp. Chem. 15 (1994) 532-555... 

The CIF file format was quickly and widely adopted by the scientific community for at least two reasons [165J it was, and still is, endorsed by the lUCr and submission of data to the journal Acta Ciystallographka, Section C in a form conforming to CI F assures faster processing and hence faster publication of accepted papers. The current CIF file dictionary defines about 1200 data names, but it is still unable to represent all the details of the crystallographic measurements of macromolecules. Thus, yet another STAR-based data format is needed. 

D structures of macromolecules, especially proteins and nudeic adds, are found in the Protein Data Bank (PDB) [27]. 

The PDB contains 20 254 experimentally determined 3D structures (November, 2002) of macromolecules (nucleic adds, proteins, and viruses). In addition, it contains data on complexes of proteins with small-molecule ligands. Besides information on the structure, e.g., sequence details (primary and secondary structure information, etc.), atomic coordinates, crystallization conditions, structure factors. 

Bovey, F. A., High Resolution NMR of Macromolecules, Academic, New York, 1972. 

Tanford, C.,PhysicalChemistry of Macromolecules, Ii ey,Ne N York, 1961. Tompa, H., Po/jgmer Butterworths, London, 1956. 

Tanford, C., Physical Chemistry of Macromolecules, Wiley, New York, 1961. 

J. Clausen, Immunochemical Techniques for the Identification and Estimation of Macromolecules, 3rd ed., Elsevier, Amsterdam, the Netherlands, 1988. A. Kawamura, Jr., ed.. Fluorescent Mntibody Techniques and Their Applications, University of Tokyo Press, Baltimore, 1977. 

A key factor determining the performance of ultrafiltration membranes is concentration polarization due to macromolecules retained at the membrane surface. In ultrafiltration, both solvent and macromolecules are carried to the membrane surface by the solution permeating the membrane. Because only the solvent and small solutes permeate the membrane, macromolecular solutes accumulate at the membrane surface. The rate at which the rejected macromolecules can diffuse away from the membrane surface into the bulk solution is relatively low. This means that the concentration of macromolecules at the surface can increase to the point that a gel layer of rejected macromolecules forms on the membrane surface, becoming a secondary barrier to flow through the membrane. In most ultrafiltration appHcations this secondary barrier is the principal resistance to flow through the membrane and dominates the membrane performance. 

The phenomenon of concentration polarization, which is observed frequently in membrane separation processes, can be described in mathematical terms, as shown in Figure 30 (71). The usual model, which is weU founded in fluid hydrodynamics, assumes the bulk solution to be turbulent, but adjacent to the membrane surface there exists a stagnant laminar boundary layer of thickness (5) typically 50—200 p.m, in which there is no turbulent mixing. The concentration of the macromolecules in the bulk solution concentration is c,. and the concentration of macromolecules at the membrane surface is c. 

Arsenic. Arsenic is under consideration for inclusion as an essential element. No clear role has been estabHshed, but aresenic, long thought to be a poison, may be involved in methylation of macromolecules and as an effector of methionine metaboHsm (158,160). Most research has focused on the toxicity or pharmaceutical properties of arsenic (158). 

The nomenclature of macromolecules can be compHcated when there is Httle or no regularity in the molecules for such molecules, the stmctural details may also be uncertain. In cases where the macromolecule is a polymeric chain with some uncertainties about regularity in its stmcture, a simple expedient is to name the polymer after the monomer that gave rise to it. Thus there are source-based names such as poly(vinyl chloride). 

The compositional distribution of ethylene copolymers represents relative contributions of macromolecules with different comonomer contents to a given resin. Compositional distributions of PE resins, however, are measured either by temperature-rising elution fractionation (tref) or, semiquantitatively, by differential scanning calorimetry (dsc). Table 2 shows some correlations between the commercially used PE characterization parameters and the stmctural properties of ethylene polymers used in polymer chemistry. 

Processes for HDPE with Broad MWD. Synthesis of HDPE with a relatively high molecular weight and a very broad MWD (broader than that of HDPE prepared with chromium oxide catalysts) can be achieved by two separate approaches. The first is to use mixed catalysts containing two types of active centers with widely different properties (50—55) the second is to employ two or more polymerization reactors in a series. In the second approach, polymerization conditions in each reactor are set drastically differendy in order to produce, within each polymer particle, an essential mixture of macromolecules with vasdy different molecular weights. Special plants, both slurry and gas-phase, can produce such resins (74,91—94). 

The advantage of the LB technique is that it allows systematic studies of 2-D organization, both before and after transfer from the air—water interface onto a soHd substrate. However, the coupling of 3-D self-organization of macromolecules in solution with organization at a soHd surface may best be achieved using the self-assembly technique. 

Laue Method for Macromolecule X-Ray Diffraction. As indicated above it is possible to determine the stmctures of macromolecules from x-ray diffraction however, it normally takes a relatively long period of data collection time (even at synchrotrons) to collect all of the data. A new technique, the Laue method, can be used to collect all of the data in a fraction of a second. Instead of using monochromated x-rays, a wide spectmm of incident x-rays is used. In this case, all of the reflections that ate diffracted on to an area detector are recorded at just one setting of the detector and the crystal. By collecting many complete data sets over a short period of time, the Laue method can be used to foUow the reaction of an enzyme with its substrate. This technique caimot be used with conventional x-ray sources. 

J. Vinograd and J. E. Hearst, Equilibrium Separation of Macromolecules and Viruses in a Density Gradient, Springer-Vedag, Wien, Austna, 1962. 

Early efforts to develop molecular models emphasized ways of representing three-dimensional aspects in two-dimensional projections. Some of the problems addressed were the folding of macromolecules (43,44) and two-dimensional projections with hidden surfaces (45,46). The state of the art in the early 1970s has been reviewed (47). 

J. Kleia, Molecular Conformation and Dynamics of Macromolecules in Condensed Systems, Elsevier, Amsterdam, 1988, p. 333. 

Reverse Osmosis and Ultrafiltration. Reverse osmosis (qv) (or hyperfiltration) and ultrafilttation (qv) ate pressure driven membrane processes that have become well estabUshed ia pollution control (89—94). There is no sharp distinction between the two both processes remove solutes from solution. Whereas ultrafiltration usually implies the separation of macromolecules from relatively low molecular-weight solvent, reverse osmosis normally refers to the separation of the solute and solvent molecules within the same order of magnitude in molecular weight (95) (see also Membrane technology). 

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