Towards understanding the crystallization of photosystem II: influence of poly(ethylene glycol) of various molecular sizes on the micelle formation of alkyl maltosides

The influence of poly(ethylene glycol) (PEG) polymers H-(O-CH2-CH2)p-OH with different average molecular sizes p on the micelle formation of n-alkyl-β-D-maltoside detergents with the number of carbon atoms in the alkyl chain ranging from 10 to 12 is investigated with the aim to learn more about the detergent behavior under conditions suitable for the crystallization of the photosynthetic pigment-protein complex photosystem II. PEG is shown to increase the critical micelle concentration (CMC) of all three detergents in the crystallization buffer in a way that the free energy of micelle formation increases linearly with the concentration of oxyethylene units (O-CH2-CH2) irrespective of the actual molecular weight of the polymer. The CMC shift is modeled by assuming for simplicity that it is dominated by the interaction between PEG and detergent monomers and is interpreted in terms of an increase of the transfer free energy of a methylene group of the alkyl chain by 0.2 kJ mol-1 per 1 mol L-1 increase of the concentration of oxyethylene units at 298 K. Implications of this effect for the solubilization and crystallization of protein-detergent complexes as well as detergent extraction from crystals are discussed.

Refined definition of the critical micelle concentration and application to alkyl maltosides used in membrane protein research

The critical micelle concentration (CMC) of nonionic detergents is defined as the breaking point in the monomer concentration as a function of the total detergent concentration, identified by setting the third derivate of this function to zero. Combined with a mass action model for micelle formation, this definition yields analytic formulae for the concentration ratio of monomers to total detergent at the CMC and the relationship between the CMC and the free energy of micellization g mic. The theoretical breaking point is shown to coincide with the breaking point of the experimental titration curve, if the fluorescence enhancement of 8-anilino-1-naphthalene-sulfonic acid (ANS) or a similar probe dye is used to monitor micelle formation. Application to a series of n-alkyl-β-d-maltosides with the number of carbon atoms in the alkyl chain ranging from 8 to 12 demonstrates the good performance of a molecular thermodynamic model, in which the free energy of micellization is given by g mic = σΦ + g pack + g st. In this model, σ is a fit parameter with the dimension of surface tension, Φ represents the change in area of hydrophobic molecular surfaces in contact with the aqueous phase, and g pack and g st are contributions, respectively, from alkyl chain packing in the micelle interior and steric repulsion of detergent head groups. The analysis of experimental data from different sources shows that varying experimental conditions such as co-solutes in the aqueous phase can be accounted for by adapting only σ, if the co-solutes do not bind to the detergent to an appreciable extent. The model is considered a good compromise between theory and practicability to be applied in the context of in vitro investigations of membrane proteins.

Improved Core Viscosity Achieved by PDLLA10kCo-Incorporation Promoted Drug Loading and Stability of mPEG2k-b-PDLLA2.4k Micelles

PURPOSE

This study aims to investigate the effect of poly(D, L-lactic acid)10K (PDLLA10K) incorporation on the drug loading and stability of poly(ethylene glycol)2K-block-poly(D, L-lactide)2.4K (mPEG2k-b-PDLLA2.4k) micelles. In addition, a suitable lyophilization protector was screened for this micelle to obtain favorable lyophilized products.

METHODS

The incorporation ratios of PDLLA10k were screened based on the particle size and drug loading. The dynamic stability, core viscosity, drug release, stability in albumin, and in vivo pharmacokinetic characteristics of PDLLA10k incorporated micelles were compared with the original micelles. In addition, the particle size variation was used as an indicator to screen the most suitable lyophilization protectant for the micelles. DSC, FTIR, XRD were used to illustrate the mechanism of the lyophilized protectants.

RESULTS

After the incorporation of 5 wt% PDLLA10K, the maximum loading of mPEG2k-b-PDLLA2.4k micelles for TM-2 was increased from 26 wt% to 32 wt%, and the in vivo half-life was increased by 2.25-fold. Various stability of micelles was improved. Also, the micelles with hydroxypropyl-β-cyclodextrin (HP-β-CD) as lyophilization protectants had minimal variation in particle size.

CONCLUSIONS

PDLLA10k incorporation can be employed as a strategy to increase the stability of mPEG2k-b-PDLLA2.4k micelles, which can be attributed to the viscosity building effect. HP-β-CD can be used as an effective lyophilization protectant since mPEG and HP-β-CD form the pseudopolyrotaxanesque inclusion complexes.

Effect of Spacer Structures on the Interfacial Adsorption and Micelle Properties of Quaternary Ammonium Salt-Based Gemini Surfactants

In this study, we synthesized quaternary ammonium salt-based gemini surfactants, 2C₁₂(Spacer), with different spacer structures using ethylenediamine derivatives, and investigated their adsorption and aggregation properties by measuring their electrical conductivity, surface tension, fluorescence, and viscosity in conjunction with dynamic light scattering and small-angle X-ray scattering studies to investigate the effect of spacer structures on the properties of the gemini surfactants. The gemini surfactants with spacers containing nitrogen and oxygen atoms were highly soluble in water, whereas those with rigid spacers containing diethylene and triethylene chains exhibited low water solubility. The adsorption and orientation of the gemini surfactants at the air/water interface were significantly affected by the spacer length. Among the synthesized gemini surfactants, the one with the N,N'-dimethylpiperazine spacer showed the highest surface activity. In contrast, the gemini surfactant with the 1-methyl-4-[2-(N,N-dimethylammonio)ethyl]piperazin-1-ium spacer containing an ethylene chain attached to the amino group in the N,N'-dimethylpiperazine spacer (2C₁₂(2/2-N-2)) adsorbed efficiently. However, due to the increased spacer length, this surfactant was unable to orient efficiently at the air/water interface.