An insight into the effect of interaction with protein on antibacterial activity of chitosan derivatives.

Antimicrobial activity of chitosan in protein-rich media is of a particular interest for various protein-based drug delivery and other systems. For the first time, bacteriostatic activity of chitosan derivatives in the presence of caseinate sodium (CAS) was studied and discussed. Complexation of chitosan derivatives soluble in acidic (CH and RCH) or alkalescent (RCH) media with CAS was confirmed by fluorescent spectroscopy, turbodimetry, light scattering data and measurement of electrical potentials of CAS/chitosan derivative complexes. An addition of CH and RCH caused a static quenching of CAS. Binding constants Kb determined for CH/CAS and RCH/CAS complexes at pH 6.0 were equal to 29.8 × 106 M-1 and 8.9 × 106 M-1, respectively. Kb value of RCH/CAS complex at pH 7.4 was equal to 1.1 × 105'M-1. The poisoned food method was used for counting the number and the direct measurement of the size of bacterial colonies on the surfaces of turbid agar media containing CAS/chitosan derivative complexex. Complete suppression of E. coli cells growth and restriction of S. aureus cells growth were observed on the surface of acidic media. A high concentration of CAS reduced the activity. The activity of RCH in alkalescent media is low or absent. These results can be promising for preparation of microbiologically stable protein-based drug delivery systems.

Effect of Soft Preheating of Bovine Serum Albumin on the Complexation with Oligochitosan: Structure and Conformation of BSA in the Complex.

Phase analysis, spectroscopic, and light scattering methods are applied to investigate the peculiarities of the interaction of oligochitosan (OCHI) with native and preheated bovine serum albumin (BSA) as well as the conformational and structural changes of BSA in BSA/OCHI complex. As shown, untreated BSA binds with OCHI mainly forming soluble electrostatic nanocomplexes, with the binding causing an increase in BSA helicity without a change in the local tertiary structure and thermal stability of BSA. In contrast, soft preheating at 56 °C enhances the complexation of BSA with OCHI and slightly destabilizes the secondary and local tertiary structures of BSA within the complex particles. Preheating at 64 °C (below the irreversible stage of BSA thermodenaturation) leads to further enhancement in the complexation and formation of insoluble complexes stabilized by both Coulomb forces and hydrophobic interactions. The finding can be promising for the preparation of biodegradable BSA/chitosan-based drug delivery systems.

Complexation of oligochitosan with sodium caseinate in alkalescent and weakly acidic media.

Сomplexation of oligochitosan (OCHI) having the degree of acetylation (DA 26 %) with sodium caseinate (SC) at pH 5.8 and 7.2 is described and compared with the complexation of OCHI (DA 2 %) at pH 5.8. In the alkalescent medium, the complexation of OCHI (DA 26 %) is weaker and dualistic depending on SC concentration in the system. In the diluted alkalescent system, the formation of only soluble complexes is observed at OCHI/SC ratio ≤0.9. In the semi diluted one, the complexation results in the formation of insoluble complexes those composition changes symbatically with the OCHI/SC ratio in the system. At pH 5.8, OCHI/SC ratio in insoluble complexes remains the same regardless of OCHI/SC ratio in the solution. At pH 5.8, the electrostatic complexation weakens with an increase in DA and is completely suppressed at a high ionic strength. These results can be promising for construction of biodegradable protein/chitosan drug delivery systems.

A feasible approach to tune the interaction of chitosan with sodium dodecyl sulfate.

Interaction of binary chitosan/nonionic surfactant (NIS) system with sodium dodecyl sulfate (SDS) in aqueous solution is described using turbodimetry, light scattering, electophoretic mobility and cryogenic electron microscopy. The formation of insoluble CHI/SDS complexes is weakened with a decrease in molecular weight of chitosan and critical micelle concentration of NIS as well as with an increase in NIS concentration. Soluble chitosan/NIS complexes absorb SDS molecules until the charge of mixed chitosan/NIS/SDS complexes reaches a critical value that depends on chitosan molecular weight followed by aggregation of primary electrostatic complexes via hydrogen bonding to complex nanoparticles. In contrast to formation of asymmetric swarm-like structures in the binary chitosan/SDS system, the aggregation of complex nanoparticles in the ternary chitosan/NIS/SDS system occurs by a head-to-tail binding mechanism with formation of elongated filamentous microstructures. The finding can be promising for preparation of microbiologically stable pharmaceutical and cosmetic compositions and drug delivery systems containing mixed surfactants.

Macromolecular complexes of BSA with gelatin.

This work studies the effect of the helix-coil transition in gelatin on the structure development in the complex forming water-gelatin-BSA system using dynamic light scattering, environment scanning electron microscopy, rheometry, differential scanning microcalorimetry, circular dichroism, fluorescence, and absorption measurements. It was established that the structure of the complexes formed and the mechanism of intermacromolecular interaction are different in the case of two conformation states of gelatin. Above the temperature of the conformational transition (40 °C) intermacromolecular interaction leads to collapse gelatin macromolecules and formation compact (30 nm in radius) BSA-gelatin complexes (∼6:1, mole/mole), partial stabilization of the secondary structure (increase the mean helix content), and stabilization of BSA molecules against thermo aggregation. At the same time it does not leads to an appreciable change in the thermodynamic parameters of the thermal transitions for BSA and gelatin. Below the temperature of the conformation transition (at 18 °C) the interaction results in formation of the large (600-1000 nm in radius) complex particles due to trapping BSA molecules into the meshes of the gelatin network and, as consequence, a substantial increase in the storage and loss moduli of the system.