1H NMR Self-Diffusion in Polymer-Surfactant Nanocapsules and Cryogels with Enzyme

Cryogels: morphological, structural and adsorption characterisation

Experimental results on polymer, protein, and composite cryogels and data treatment methods used for morphological, textural, structural, adsorption and diffusion characterisation of the materials are analysed and compared. Treatment of microscopic images with specific software gives quantitative structural information on both native cryogels and freeze-dried materials that is useful to analyse the drying effects on their structure. A combination of cryoporometry, relaxometry, thermoporometry, small angle X-ray scattering (SAXS), equilibrium and kinetic adsorption of low and high-molecular weight compounds, diffusion breakthrough of macromolecules within macroporous cryogel membranes, studying interactions of cells with cryogels provides a consistent and comprehensive picture of textural, structural and adsorption properties of a variety of cryogels. This analysis allows us to establish certain regularities in the cryogel properties related to narrow (diameter 0.4<d<2 nm), middle (2<d<50 nm) and broad (50<d<100 nm) nanopores, micropores (100 nm<d<100 μm) and macropores (d>100 μm) with boundary sizes within modified life science pore classification. Particular attention is paid to water bound in cryogels in native superhydrated or freeze-dried states. At least, five states of water - free unbound, weakly bound (changes in the Gibbs free energy-ΔG<0.5-0.8 kJ/mol) and strongly bound (-ΔG>0.8 kJ/mol), and weakly associated (chemical shift of the proton resonance δ(H)=1-2 ppm) and strongly associated (δ(H)=3-6 ppm) waters can be distinguished in hydrated cryogels using (1)H NMR, DSC, TSDC, TG and other methods. Different software for image treatment or developed to analyse the data obtained with the adsorption, diffusion, SAXS, cryoporometry and thermoporometry methods and based on regularisation algorithms is analysed and used for the quantitative morphological, structural and adsorption characterisation of individual and composite cryogels, including polymers filled with solid nano- or microparticles.

Evidence for domain motion in proteins affecting global diffusion properties: a nuclear magnetic resonance study

The rotational diffusion of proteins is an important hydrodynamic property. Compact protein structures were found previously to exhibit hydration layer viscosity, etaloc, higher than the viscosity of bulk water, eta. This implies an apparent activation energy for rotational diffusion higher than the activation energy of water viscosity, Eeta=15.4+/-0.3 kJ/mol. In this study we examine etaloc of internally mobile proteins using 15N spin relaxation methods. We also examine the activation enthalpy, DeltaH#, and activation entropy, DeltaS#, for rotational diffusion. Of particular relevance are internally mobile ligand-free forms and compact ligand-bound forms of multidomain proteins. Adenylate kinase (AKeco) and Ca2+-calmodulin (Ca2+-CaM) are typical examples. For AKeco (Ca2+-CaM) we find that DeltaH# is 14.5+/-0.5 (15.7+/-0.4) kJ/mol. For the complex of AKeco with the inhibitor AP5A (the complex of Ca2+-CaM with the peptide smMLCKp), we find that DeltaH# is 18.1+/-0.7 (18.2+/-0.5) kJ/mol. The internally mobile outer surface protein A has DeltaH#=12.6+/-0.8 kJ/mol, and the compact protein Staphylococcal nuclease has DeltaH#=18.8+/-0.6 kJ/mol. For the internally mobile and compact proteins studied, <|DeltaS(|> equals 62+/-7 J/(mol K) and 44+/-5 J/(mol K), respectively. The fact is that etaloc>eta (DeltaH#>Eeta) for compact proteins was ascribed previously to electrostatic interactions between surface sites and water rigidifying the hydration layer. We find herein that obliteration of these interactions by domain motion leads to etaloc approximately eta, DeltaH# approximately Eeta, and large activation entropy for internally mobile protein structures.

1H NMR Studies of Aqueous Micellar Solutions of N-Dodecyl- N,N-dimethyl-N-benzylammonium Chloride

(1)H NMR studies of the micellization process in N-dodecyl-N,N-dimethyl-N-benzylammonium chloride (DBeAC) were carried out. The spectra were measured at concentrations below and above the critical micelle concentration (CMC). The chemical shifts and Nuclear Overhauser Effect (NOE) measurements were analyzed as a function of the concentration. This allowed us to provide experimental evidence that the benzyl group of DBeAC changes its position during micellization and, as a consequence, is located inside the micelle. Copyright 1999 Academic Press.

1H NMR Self-diffusion Study of PVA Cryogels Containing Ethylene Glycol and Its Oligomers

The multicomponent self-diffusion of the PVA cryogels prepared by a freezing-thawing treatment of the water/oligooxyethylene glycol solutions of PVA has been studied with the NMR FT-PGSE method at various temperatures and compared with the diffusion of such systems without glycols. The evaluated apparent activation energies, E(a), of the self-diffusion for the PVA chains showed that entrapment of ethylene glycol, EG, and diethylene glycol, DEG, into cryogels made them more friable. These glycols acted as cryoprotectants. On the contrary, triethylene glycol, TEG, and, especially, PEG-400 made cryogels firmer. The E(a) values for the self-diffusion of oligooxyethylene glycols exceeded those for the water molecules in the same cryogel and increased along with the lengths of oligomers. These values are also above those obtained for the PVA chains in cryogels with EG, DEG, and TEG as well as without additives. This fact is in conformity with the mechanism of the phase separation of water and co-solvent by freezing the multicomponent system. It is expected that the presence of TEG and PEG-400 in cryogels leads to a decrease in dimensions of the solvent-filled pores and the PVA filaments like that which was found out earlier for DMSO containing cryogels. Such a compartmentation within cryogels depends mainly on the dimensions of ice and polymer microcrystallites formed by freezing the solution. Copyright 1999 Academic Press.

1H NMR Self-Diffusion Study of Morphology and Structure of Polyvinyl Alcohol Cryogels

The multicomponent self-diffusion of the polyvinyl alcohol (PVA) cryogels prepared by a freezing-thawing treatment of aqueous and water-DMSO solutions of PVA has been studied with the NMR FT-PGSE method. The temperature dependencies of the self-diffusion coefficients, Ds, for the PVA chains have a maximum at 45 degrees C due to the syneresis of cryogels. They are quite different from the monotonous increase of Ds for the aqueous solutions of PVA. Evaluated apparent activation energies, Ea, of the self-diffusion for the PVA chains in the PVA solutions and cryogels in D2O are practically the same and equal 22-24 kJ/mol below the crucial point. The proton spin-lattice relaxation times, T1, of the PVA chain also coincide with one another for solutions and cryogels. This means that molecular packing in cryogels depends mainly on the dimensions of the ice and polymer microcrystallites formed by freezing the solution. Above the crucial point polymer compartments become firmer, and the chain mobility somewhat reduces. The strength of cryogels also increases along with growing the DMSO contents and decreases by the BSA addition. For estimation of the cryogel morphology, effects of the restricted diffusion of both the water and PVA in a q-space have been taken into account. By the introduction of DMSO to cryogels the solvent filled pores become smaller, and channels become much shorter. The diameter of the PVA filaments is similar to those for all the cryogels, but the length of filaments with D2O is twice that for cryogels with a mixed solvent. Entrapment of BSA in the cryogel matrix by preparation leads to the increase of an average diameter of the water filled pores and destroys molecular packing the cryogel. Copyright 1999 Academic Press.