These long-range correlations lead to significant deviations of polymer size from ideal with mean square end-to-end distance hR2i. These findings are explained by a fine interplay of polymer connectivity and the non-zero range of monomer interactions. Moreover, this effect is not specific for dilute q-solutions and exists in semidilute solutions and melts of polymers.
Our theory is in good agreement with the experimental data on Flory characteristic ratio, as well as with results of computer simulations. On surfaces, brush-like macromolecules were visualized by the atomic force microscopy AFM. In order to quantitatively analyze conformations of visualized molecules we developed the corresponding algorithms and software.
This software enables detection of the molecular contour, measurement of molecule size, area, orientational and nematic order parameters, etc. In addition, the automated procedure of molecular detection reduced the time and improved the quality of analysis of image series. Using our method we have studied the molecular weight and polydispersity of linear and multi-arm molecular brushes, the spontaneous curvature of grafted molecules, which is caused by competition of conformational entropy of side chains and elasticity of backbone, behavior of brushes in a matrix of linear polymer, the effect of structure of multi-armed brushes on their 2d orientational order, the dynamics and conformational transitions of individual molecules in the precursor layer of spreading droplet, the spontaneous scission of grafted molecules with long side-chains.
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Natural polymers do occur. The most familiar is natural rubber , also known as latex.
Hydrodynamics of Macromolecules: Conformation Zoning for General Macromolecules
It has been used for the production of tires after vulcanization , paint, and even by the clothing industries. Natural rubber is an elastic and has been artificially created by polymerization of isoprene. A byproduct of the research into these industrial rubbers was Silly Putty. Most artificial plastics are made from refined crude oil.
Because they are hard to produce otherwise, their continued availability is tied to petroleum security. However, some newer biological process, such as polylactide production, and Dupont's biological polyethylene glycol monomer synthesis route, use biological feed-stocks instead. Simple polymers are the products of polymerization reactions.
Polymerization reactions are known for their exothermic nature their ability to release energy in the form of heat and their fast kinetics. They continue until one of the reactants has been used, as for instance in the formation of polyurethane. As demonstrated in many high school classes, adding small amounts of ethene and urea to an acidic solution of water results in a high volume polymer in a seemingly never ending process. A very well known biological polymer is starch.
Starch is a complex carbohydrate that contains two molecules: amylose and amylopectin, both of which are large polymers of glucose. Starch is soluble in water, and is used as a way of storing excess glucose by plants; it is mainly found in their fruit, seed rhizomes or tubers. Starch also plays a role in storing energy in the bodies of animals, although the two kinds of starch differ in composition.
Some artificial polymers exhibit behavior not seen in other materials; for example, kevlar is a composite material that is stronger than steel but which weighs very little in comparison and is very flexible. Such materials have found many uses, from bullet-proof vests to enforcing more rigidity in the hull of aeroplanes. Another polymer of importance is silicone , famous by now for its application in the building industry as well as in medicine, reconstructive surgery as well as cosmetic surgery.
Silicone is a polymer with a repetitive siloxane group as the backbone. The behavior of a large group of polymers can be divided in two groups, the thermoplasts and the thermoharders. Thermoplasts respond to heat by becoming more fluid in their behavior, enabling them to be molded to any desired shape.
This behavior can also be achieved by adding substances to the polymer or plastic called weakeners. Thermoharders are characterized by responding with a more crystalline structure upon heating, ultimately creating a granular resulting material. Many composite materials use these two behaviors in making plastics for special purposes.
The thermoplastic behavior of polymers used for clothing, nylon, polyester makes them easier to wash and handle, but also introduces a danger.
Chain structure and conformation of macromolecules
When heated extendedly they turn into a very hot liquid state, some to the point of burning. If they catch fire while being worn, severe injuries can occur as the materials melt get very sticky and burn into the skin. One of the first artificial polypeptides made was nylon. Most nylons are condensation copolymers formed by reacting equal parts of a diamine and a dicarboxylic acid , so that amide bonds form at both ends of each monomer in a process analogous to polypeptide biopolymers.
Because the reaction also produces H 2 O the reaction is called a condensation. The most common variant is nylon , which refers to the fact that the diamine hexamethylene diamine and the diacid adipic acid each donate six carbons to the polymer chain the numerical suffix specifies the numbers of carbons donated by the monomers; the diamine first and the diacid second. As with other regular copolymers, like polyesters and polyurethanes, the 'repeating unit' consists of one of each monomer, so that they alternate in the chain.
In the laboratory, nylon 6,6 can also be made using adipoyl chloride instead of adipic acid. The best known biological macromolecules are deoxyribonucleic acid DNA , ribonucleic acid RNA , proteins and polysaccharides. There is a huge diversity of these molecules in living organisms, and not all of their functions are completely known.
All of them have a polarity and are synthesised by condensation reactions that add monomers to a defined end of the polymer. The biological chemistry and chemical functions of biological macromolecules are discussed further in Biochemistry. While nylon is a famous example of a synthetic polypeptide, in a biological context this class of macromolecules is generally referred to as "proteins". In proteins, the amide bond is known as a peptide bond and consists of the following pairing: left-chain -CO-NH- right chain the C and the O are bound by a double bond, the N and H with a single bond, the combination is a carbonyl group.
The amino acid residues that repeat to make large polypeptides are all linked by peptide bonds to form the primary sequence of the protein. The first amino acid in a polypeptide sequence is at the carboxy-terminal and the amino acid monomers are added to the amino-terminal using the messenger RNA molecules as a template to ensure the correct sequence. This transfer of information from the RNA molecule to synthesise the polypeptide is catalysed by the ribosome. It must be pointed out that enzymes are a class of proteins with a catalytic function. Some other proteins have a more structural role, forming the ropes and tubes that are the framework of a cell cytoskeleton and the basis for locomotion in muscles.
Plant proteins are also used for the storage of food in some seeds maize and soyabean and are a staple food group for most vegetarians. The macromolecule has a repeating backbone of ribose sugars that are joined by phosphodiester O-P-O bonds. The sequence of these four nucleotides is the chemical basis for the genetic code.
Because the exact sequence must be conserved for the code to be maintained these macromolecules are synthesised by copying a template. Polysaccharides are the simplest biological macromolecules, often consisting of only one repeating glucose unit joined by glycosidic bonds. In animals, these macromolecules are primarily for storage, but they have an important structural role in plants, as cellulose is the primary component of their cell walls. In the form of cotton fibers, cellulose is an important textile raw material.
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Ruminants , such as cows, can digest cellulose in their second stomach by co-opting bacteria to digest the cellulose. A lipid is synthesized by adding two fatty acid chains polyhydrocarbons to a three carbon backbone. In cells, the third carbon is often a polar head group, linked by a phosphate, such that these phospholipids have a hydrophobic fatty acid tail and a hydrophilic head. In an aqueous environment the most stable conformation for the phospholipids is to form a bilayer with the hydrocarbon tails interacting with each other and the polar head group interacting with the surrounding water.
Phospholipid bilayers are the basis for cellular life, as the double layer of lipids is the key component of cell membranes that compartmentalize cellular metabolism in a controlled environment.
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Cell membranes are also integrally associated with proteins, some of which pass directly through the membrane. The function of the whole membrane structure is diverse and includes signaling, transport and metabolism, all of which depend on the fluidity of the proteins and lipids in the membrane. Their movement reaching up to speeds of ms -1 over a broad range of temperatures is made possible by cholesterol , a substance needed to make the membrane more fluid-like at low temperatures and yet less fluid-like at high temperatures.
The physical properties of a macromolecule depend largely upon its composition. The simplest hydrocarbon is methane CH 4 ; methane is a greenhouse gas , and is highly inflammable and explosive. As can be deduced from their composition, hydrocarbons with longer chains than butane tend to be liquid at room temperature, and very high chain length hydrocarbons are solids. Because of the simple composition of the first four hydrocarbons and their small molecular sizes, the lack of any significant internal polarity makes it hard for these molecules to interact either with one another or with the molecules of a solvent.
In water, therefore, these molecules will escape from solution and diffuse into the air. Larger hydrocarbon molecules will shy away from the solvent water and will form a double layer system of water and oil. The thorough mixing of these two layers with the help of an emulsifier into a stable emulsion is a basic ingredient of cooking and many cosmetic products. Anyone who has tried to mix an oily ingredient with a watery ingredient will know of the separation of phases for instance when trying to make mayonnaise , but easy home experiments better known as cooking can solve that problem of phase separation.
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Any charged polyelectrolyte can be treated like a usual ionic electrolyte. When the macromolecule is acidic, the polymeric acid can be titrated using a litmus test to determine its "concentration".
Biological Molecules – Concepts of Biology – 1st Canadian Edition
In this case, the "concentration" is now somewhat of a statistical answer, as the weight of the molecule and its molecular weight are only known within statistical limits. The concentration of macromolecules is also a statistical mean value for that reason. Like a simple solution, macromolecules dissolve in the right solvent and show the same interactions with the solvent. In an aqueous solution, the hydrophilic parts of a macromolecule will be - on average - more exposed to the aqueous solvent than its hydrophobic parts. Using these hydrophilic and hydrophobic qualities DNA gets transcribed by transcriptases binding to the DNA in electrodynamical ways, partly hydrogen bonding plays a role as well as local substrate concentration.
A functioning DNA molecule reacts in a way that chemists can describe relatively simply, such as by its kinetics, reactivity and physico-chemical behavior. However, the biological implications may not always be easy to understand. Macromolecules do exhibit different behaviour as well. Physical chemists use light diffraction direct and indirect - or first- and second-order light diffraction to determine the shape of a molecule, just as a rotating cigar will diffract light differently to a rotating ball. Shape can be a clue to the functionality of a molecule in vivo.