Self-assembly initial monomer concentration

Although the self-assembly of polymeric structures can involve nucleation and elongation steps (See Actin Assembly Kinetics Microtubule Assembly Kinetics), one can simplify the assembly process through what is known as seeded assembly. At an initial monomer concentration [M], seeded assembly is induced by the addition of pre-assembled polymeric structures consequently the polymer number concentration must remain constant. The rate of monomer incorporation into indefinite length polymers can be written as follows ... 

Provided that Eq. 22 holds, the next question regards the monomer concentration at which self-assembly becomes significant. This is the so-called lower self-assembly concentration (Isac), that is the initial monomer concentration at which half of the monomer is assembled into the cyclic -mer (Eq. 24). 

At first, the native S-layer protein of S. ureae ATCC 13881 is investigated. In vitro recrystallization smdies in solution and on a silicon wafer are performed. The influence of several factors such as initial monomer concentration on the self-assembly process is discussed. 

To investigate the influence of initial monomer concentration on the self-assembly properties of the S-layer of S. ureae ATCC 13881, in vitro recrystaUization experiments in solution at two different protein concentrations were conducted. In particular, 4.5 and 0.38 mg/ml initial monomer concentrations (concentration in dialysis) were chosen. 

Figure 3.7 shows S-layer patches that have formed during dialysis at different initial monomer concentrations. These patches are different in number and size depending on the protein concentration brought into the self-assembly reaction. At high initial monomer concentration (4.5 mg/ml) a large number of patches can... 

Influence of Initial monomer concentration on the self-assembly. 

In order to further monitor the self-assembly process, samples from the recrystallization solution were taken after 1 week as well, adsorbed onto a Si substrate, stained with uranyl acetate and imaged by SEM. Images in Figure 3.7c and f show that in this time tubes were formed no matter whether the initial monomer concentration was low or high. 

MIP films, applied to a QCM transducer, have been employed for chiral recognition of the R- and 5-propranolol enantiomers [107]. MIP films were prepared for that purpose by surface grafted photo-radical polymerization. First, a monolayer of 11-mercaptoundecanoic acid was self-assembled on a gold electrode of the quartz resonator. Then, a 2,2 -azobis(2-amidinopropane) hydrochloride initiator (AAPH), was attached to this monolayer. Subsequently, this surface-modified resonator was immersed in an ACN solution containing the MAA functional monomer, enantiomer template and trimethylolpropane trimethacrylate (TRIM) cross-linker. Next, the solution was irradiated with UV light for photopolymerization. The resulting MIP-coated resonator was used for enantioselective determination of the propranolol enantiomers under the batch [107] conditions and the FIA [107] conditions with an aqueous-ACN mixed solvent solution as the carrier. The MIP-QCM chemosensor was enantioselective to 5-propranolol at concentrations exceeding 0.38 mM [107]. 

Considerations of the packing parameter concept of Israelachvili et al. [1] suggest that double-chain surfactants, which form the basis of measurements described in this article, cannot readily form spherical micelles. With double-chain surfactants, a more likely aggregate structure is the formation of bilayer vesicles, which can be also thought of as a dispersed lamellar phase (La) as such the vesicular dispersed form is likely to be preferentially formed at low concentrations ( 1 mmol dm-3) of surfactant. Furthermore, it is necessary to consider the possibility, unlike in the case of micelles, that such vesicles, formed by self-assembly of surfactant monomers, will not be thermodynamically stable. The instability is then likely to be in the direction of growth to a thermodynamically-stable lamellar phase from the vesicles. This process will be driven, at least initially, by fusion of two vesicles. 

In contrast, recent kinetic investigation of the polymerization of spacerless G2 dendron-substi-tuted styrene and methylmethacrylate, respectively, in solution lead to the unexpected conclusion that above a certain critical monomer concentration a strong increase in the rate of the free radical polymerization is observed [21]. The results can be explained by self-organization of the growing polymer chain to a spherical or columnar superstructure in solution, depending on the degree of polymerization (DP, Fig. 2). The rate constants and low initiator efficiency lead one to conclude that the self-assembled... 

Although the earher treatment for self-assembly refers to a monomer of the type A—B, Eqs [19] and [25] also hold for the case A—A 4- B—B provided that the concentrations of the two monomen are exactly equal and the total monomer concentration is taken as the sum of the initial concentrations of the two monomers. It must be noted that in the case A—A + B—B, only assembhes in which n is an even number are allowed. 

The protein concentration in this case was 1 mg/ml and the self-assembly is initiated in the presence of Ca ions and Tris/HCl buffer having pH 9. At this pH, the protein carries an overall net negative charge and repulsion from the substrate and buffer molecules in this case is diminished, therefore monomers can nucleate on the silicon substrate (heterogeneous nucleation) and grow into large crystalline layers. With further optimization of the recrystallization reaction, a total coverage of the Si surface can be foreseen. 

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