Amphiphilic polycations

Fig. 21 (a-f) Amphiphilic polycations amphiphilic polymers and lipopolymers not forming micelles after addition to DNA... 

The pioneering work on amphiphilic polyelectrolytes goes back to 1951, when Strauss et al. [25] first synthesized amphiphilic polycations by quaternization of poly(2-vinylpyridine) with n-dodecyl bromide. They revealed that the long alkyl side chains attached to partially quaternized poly(vinylpyridine)s tended to aggregate in aqueous solution so that the polymers assumed a compact conformation when the mole fraction of the hydrophobic side chains exceeded a certain critical value. Thus, Strauss et al. became the first to show experimentally the intramolecular micellation of amphiphilic polymers and the existence of a critical content of hydrophobic residues which may be compared to the critical micelle concentration of ordinary surfactants. They called such amphiphilic polyelectrolytes polysoaps [25],... 

EFFECT OF POLYCATION IN SUBPHASE ON AGGREGATION STRUCTURE OF MONOLAYER OF ANIONIC AMPHIPHILE... 

Sinani VA, Gheith MK, Yaroslavov AA, Rakhnyanskaya AA, Sun K, Mamedov AA, Wicksted JP, Kotov NA (2005) Aqueous dispersions of single-wall and multiwall carbon nanotubes with designed amphiphilic polycations. Journal ofthe American Chemical Society 127 3463-3472. 

It was also observed that nonionic amphiphilic ABA polymers (e.g., PEO-PPO-PEO) [200,205], polycations (e.g., quaternized poly(4-vinylpyridine) [214] and hydrophobically modified poly(N-isopropylacrylamide) [204] are able to accelerate translocation from the inside leaflet to the outside leaflet ( flip-flop ) within... 

A series of antimicrobial polymethacrylates (PMA) containing quaternary ammonium cations (QUAT) has been synthesised via the N-alkylation of thiazole and triazole pendent groups using butyl iodide (Bui), and the chemical composition and distribution of amphiphilic polycations was characterised by nuclear magnetic resonance spectroscopy [13]. The correlation between their structure and antibacterial properties are presented in Figure 8.1, and clearly indicates that polyelectrolytes are responsible for their excellent selective toxicity against bacteria. 

If the concentration of the amphiphilic polymer in the sample is above its CMC, there are two cases to consider the micellar solution is added to the DNA solution or the DNA solution is added to a micellar solution. In the first case, where the micellar solution of polycation is added to DNA, the micelles are immediately diluted in the DNA solution, which on one hand can mean that the polymer concentration is under its CMC and therefore that the polymer is only present as individual chains in solution (unimers), on the other hand, that there is concurrence between self-assembly of micelles versus electrostatic interactions with a large quantity of negatively charged material. In this case, the micelles are usually destabilized as soon as they reach the DNA solution (Scheme 11, case 1). 

In the case of DNA added to a micellar solution of polycation, the micelles can stay stable in some cases (it depends on the hydrophobicity of the micellar core and strength of the electrostatic interactions). This can be proven if pyrene or other hydrophobic molecules entrapped in the hydrophobic interior are not released even after addition of DNA [77]. It has to be noted that micelles are in thermodynamic equilibrium with unimers and that both species can form electrostatic interactions with DNA. When the micelles do not undergo a strucmral change, no rearrangement into a scrambled eggs structure takes place between the amphiphilic polycation and DNA, and because DNA is in minority, it adds to the positive shell of the structure until neutralization (Scheme 11, case 2). 

Fig. 20 (a-g) Amphiphilic polycations strong polyelectrolytes with alkyl chains... 

Figure 15.4 Illustration of different subclasses of biocidal polymers (a) amphiphilic polycations, (b) telechelic biocidal polymers, and (c) hydrophilic...

Basically, all amphiphilic polycations are mimics of magainin, with the restriction that they often do not contain a stiff backbone, which results in the fact that the hydrophilic and hydrophobic regions of the macromolecules are not as efficiently separated as they are in magainin. Therefore, synthetic biocidal polymers are not as active as AMPs in most cases. ... 

The balance between hydrophilic and hydrophobic moieties was found to be a very important parameter for the preparation of antimicrobial amphiphilic polycations. On the one hand, the cationic part of the macromolecule is the main reason for electrostatic interactions with the anionic components of the bacterial cell surface.On the other hand, the mode of action of amphiphilic polycations calls for a certain hydrophobicity otherwise, the amphiphilic polycations would not be able to penetrate the bacterial cell membrane.However, it has been pointed out in various investigations that the higher the hydrophobic part, the higher the hemolysis rate will be. This means that there has to be an optimum value for an amphiphilic polymer system that offers maximum efficacy against bacteria and, simultaneously, minimal hemolytic activity. As pointed out by Palermo and Kuroda, there are mainly three different strategies used to tune the balance between the... 

So far, a number of highly active antimicrobial polymers have been developed following the biomimetic concept. They disrupt bacterial cell membranes selectively, because they are negatively charged on the outside. However, amphiphilic antimicrobial polymers are also able to destroy mammalian and human cell membranes due to their amphiphilic character. The tendency of membrane disruption is much lower, because the latter membranes have a neutral surface net charge at the outside and, additionally, contain stabilizing cholesterol. However, amphiphilic polycations are, to some extent, cytotoxic towards mammalian and human cells. So far, selectivity values of hemotoxicity (HCsoj/antimicrobial activity (MIC) of more than 500 have been achieved. 

Different investigations concerning the mode of action of hydrophilic polycations have been performed. All results have in common that the polymers are located in the surroundings of the phosphate ions of the cytoplasmic membrane, lipopolysaccharides, or the peptidoglycan components of the cell wall. ° ° This results in a displaeement of Ca ions, which has also been observed for the amphiphilie polyeations discussed in Section 2.2.1.4.1. Because of this, it was concluded that the mode of action could be similar to that of amphiphilic polyeations. However, because of their low toxicity, the mode of action has to differ from that of amphiphilic polycations in some way, especially due to the lack of hydrophobic domains. 

A method for preparation of a composite based on the three-dimensional nanosized copolymer template has been discussed [118]. The IPEC of the metallo-containing PEI-Ag polycation with the ionic amphiphilic diblock copolymer PS-h-PAA was obtained for further synthesis of encapsulated metal NPs. The silver NPs with diameter 20-40 nm were successfully synthesized in coronas of micelles (Fig. 24). In this case, PEI was used as both reducing and stabdizing agent. The cryo-TEM images suggest that the Ag content determines the size and spatial distribution of silver NPs. 

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