Globular macromolecules

Materials have many properties that are important, scientifically and teclmologically, that do not depend on the details of long-range stnicture. For example, consider a solution of globular macromolecules in a solvent... 

The recommendations embodied in this document are concerned with the terminology relating to the structure of crystalline polymers and the process of macromolecular crystallization. The document is limited to systems exhibiting crystallinity in the classical sense of three-dimensionally periodic regularity. The recommendations deal primarily with crystal structures that are comprised of essentially rectilinear, parallel-packed polymer chains, and secondarily, with those composed of so-called globular macromolecules. Since the latter are biological in nature, they are not covered in detail here. In general, macromolecular systems with mesophases are also omitted, but crystalline polymers with conformational disorder are included. 

One of the possible alternative to micelles are spherical dendrimers of diameter generally ranging between 5 and 10 nm. These are highly structured three-dimensional globular macromolecules composed of branched polymers covalently bonded to a central core [214]. Therefore, dendrimers are topologically similar to micelles, with the difference that the strnctnre of micelles is dynamic whereas that of dendrimers is static. Thus, unlike micelles, dendrimers are stable nnder a variety of experimental conditions. In addition, dendrimers have a defined nnmber of fnnctional end gronps that can be functionalized to prodnce psendostationary phases with different properties. Other psendostationary phases employed to address the limitations associated with the micellar phases mentioned above and to modnlate selectivity include water-soluble linear polymers, polymeric surfactants, and gemini snrfactant polymers. 

Bharathi P, Zhao H, Thayumanavan S. Toward globular macromolecules with functionahzed interiors design and synthesis of dendrons with an interesting twist. Org Lett 2001 3 1961-1964. 

Dendrimers are three-dimensional hyperbranched, globular macromolecules that are capable of condensing DNA into small complexes, and thereby increase plasmid transfection efficiency (14). Dendrimers are typically stable in serum and not temperature sensitive, but are also non-biodegradable and cause significant cytotoxicity. 

Dendrimers and hyperbranched polymers are globular macromolecules having a highly branched structure, in which all bonds converge to a focal point or core, and a multiplicity of reactive chain ends. Because of the obvious similarity of their building blocks, many assume that the properties of these two families of dendritic macromolecules are almost identical and that the terms dendrimer and hyperbranched polymer can be used interchangeably. These assumptions are incorrect because only dendrimers have a precise end-group multiplicity and functionality. Furthermore, they exhibit properties totally unlike that of other families of macromolecules. 

Proteins are globular macromolecules, with a radius smaller and much better defined than the average size of a random coil. Thus, Eq. 5.8a should give excellent results. It does not because these molecules are surrounded by a hydration shell, which increases their effective diameter. Yormg et al. [17] have derived a correlation for proteins... 

Recently the development of dendritic and hyperbranched polymers (HBPs) has attracted much attention (Tomalia, 1985, Newkome et al, 1985, Webster, 1991, Chu and Hawker, 1993, Wooley et al, 1994, Feast and Stanton, 1995, Malmstrom et al, 1995, Kim, 1998). The key features of the macromolecular architecture of dendrimers and HBPs are given in Section 1.2, and their synthesis by stepwise polymerization is discussed in Section 1.2.1. Dendrimers and HBPs are globular macromolecules that have a highly branched structure with multiple reactive chain ends (shell), which converge to a central focal point (core) see Figure 5.1, where I is the core, 11 is the structure and 111 is the shell. 

One of the most widely used methods of preparing biomolecules and other small specimens for shadowcasting is to apply an aerosol of the specimen dissolved in a glycerol solution to the surface of freshly cleaved mica (117, 118). An especially facile and reliable method is to use an artists airbrush, suitably modified to hold a microliter pipet tip filled with the specimen solution. While this method was originally proposed for extended macromolecules, it works well for a range of subjects from globular macromolecules to viruses. 

HigMy branched polymeric materials with large number of end groups can offer unique physical properties. Dendrimers (described in Chap. 1) differ from linear polymers in viscosity and thermal behavior. A variety of applications have been forecast for these highly branched globular macromolecules. One early approach to dedrimer synthesis relied upon the Michael reaction using repeated sequential additions of an amine to a,(3-unsaturated ester [248] ... 

Pendant hydroxamate groups of water-soluble globular macromolecules possessing considerable internal cross-linking show enhanced reactivity (> 1000-fold) compared with the monomer species in reaction with a series of 4-nitrophenyl esters. ... 

The globular macromolecules contribute less to non-ideality of a solution than the asymmetric rods or random colls because the permutations and combination of arrangements possible in a solution for the latter are always less in number than the former. 

How these techniques have been used in several exchange experiments involving water, nonelectrolytes, polyphenolics, peptides, globular macromolecules, and surfactants will now be described. 

---