I. G. Panova

Noncovalent columnar structures based on β-cyclodextrin

A new method for the synthesis of associates of cyclodextrins (CDs) of the columnar type consisting of the precipitation of CDs from aqueous solutions into acetone at lowered temperatures is developed. It is shown that columnar structures exist in both a crystalline state and in aqueous solutions. Hydrodynamic radii and molecular masses of noncovalent columnar structures (NCSs) in aqueous solutions are determined by the dynamic and static light scattering methods. The degree of association of noncovalent columnar polymers is ∼40. It is revealed the NCS associates based on β-CD are stable and their hydrodynamic radius Rh is equal to 100 ± 10 nm. The kinetics of interactions of initial β-CD and NCS with poly(propylene oxide) (PPO) is studied. The pattern of kinetic curves of Rh growth upon interaction between NCS and PPO indicates that the aggregation of the particles of polymer inclusion complex proceeds in the regime of reaction-limited cluster-cluster aggregation. Kinetic curves describing the interaction processes between β-cyclodextrin and PPO are characterized by the presence of induction period t0. At t > t0, Rh ∞ t0.56 which is typical for the diffusion-limited cluster-cluster aggregation. Schemes of the formation of polymer inclusion complexes between initial β-CD or NCS and poly(propylene oxide) are proposed. Comparison of kinetic data on the complexation of β-CD in solution in the form of associates of two types with PPO demonstrates that columnar forms of associates are reactive species acting as macroreceptors.

Non-covalent columnar cyclodextrin-based structures

Examples of the formation of ordered ensembles of α-, β-, and γ-cyclodextrins (CDs) molecules with a columnar packing of macrocycles are reported. These ensembles are formed by (1) the supramolecular dissociation of polymer inclusion complexes under the action of organic solvents that are selective with respect to a polymer guest and (2) the fixation of columnar CD aggregates self-organized in aqueous solutions at high temperatures upon the precipitation from water into organic solvents. Specific features of the organization of cyclodextrins in the thus-synthesized structures are studied by X-ray diffraction. Preliminarily oriented polymer inclusion complexes based on corresponding CDs are used as a model with the columnar arrangement of macrocycles.

Payload release by liposome burst: Thermal collapse of microgels induces satellite destruction

Abstract We present a smart liposome carrier system for stimulated release, consisting of cationic, thermo-responsive microgels. At low temperature, the swollen microgels adsorb about 200 anionic liposomes, 50 nm in diameter, per microgel. When heated from 39 °C to 41 °C, the microgel–liposome complex particles collapse from approx. 370 nm down to approx. 270 nm. Upon the thermo-induced collapse, the adsorbed liposome satellite layer is squeezed until the initially spherical liposomes explode and release their payload (antitumor drug doxorubicin) into the surrounding. This burst release mechanism, taking place over a narrow temperature range, is newly reported and of possible biomedical importance.

Aggregation of Inclusion Complexes Formed by Noncovalent Columnar Structures Based on α- and γ-Cyclodextrins and Poly(alkylene glycols)

Kinetic analysis of the aggregation of complexes formed by columnar types of α- and γ-cyclodextrins (α-CDcol and γ-CDcol) and poly(alkylene glycols) is performed by the dynamic light scattering method. For comparison, analogous studies were conducted for systems containing initial α- and γ-cyclodextrins (α-CD and γ-CD). Upon the aggregation of systems containing α-CD, the number of nuclei with critical sizes slowly increases at the initial part of kinetic curve throughout the solution bulk; when some limiting concentration and sizes of formed aggregates are achieved, the system is transformed into the gel-like state. The aggregation of γ-CDcol-poly(ethylene glycol) system proceeds into two stages. At the first fast stage, aggregates are formed by particles representing single-strand inclusion complexes composed of one γ-CDcol molecule and two units of ethylene oxide. At the second, much slower stage, aggregates are formed by two-strand complexes composed of one γ-CDcol molecule and four units of ethylene oxide. It follows from the comparison of aggregative properties of γ-CDcol-poly(ethylene glycol) and γ-CDcol-poly(propylene glycol) systems that the rate of aggregation is much higher in the second case.

The one-step synthesis of polymer-based magnetic γ-Fe2O3/carboxymethyl cellulose nanocomposites

A novel one-step procedure is described for synthesizing water soluble biocompatible nanocomposites from maghemite nanoparticles and carboxymethyl cellulose (CMC). The procedure allows the magneto-sensitive nanocomposites with a controlled content of the inorganic phase. The maghemite formation has been proved by X-ray diffraction analysis and Mossbauer spectroscopy. An average diameter of the maghemite nanoparticles is equal to 11nm according to transmission electron microscopy. As shown by FTIR spectroscopy, the nanoparticles bind to the polymer matrix via electrostatic and coordination interactions. The diameter of the nanocomposites in dilute aqueous solutions vary from 50nm at the iron content of 2-4.3wt.% to 140nm at the iron content of 5.2-8.6wt.%. The study of specific magnetization of the nanocomposites vs. applied magnetic field indicates their ferromagnetic properties. The saturation magnetization and coercive force of the sample with the maximum maghemite content (8.6wt.%) are 11.5emu/g and 30.08Oe, respectively. The nanocomposite motion has been shown to be controlled by an external magnetic field. The biocompartible maghemite-CMC nanocomposites seem to be promising for encapsulation and delivery of biologically active compounds.

Supramolecular Dissociation of Polymeric Inclusion Complexes Containing Cyclodextrins as a Method of Preparing New Columnar Structures

Polymeric inclusion complexes formed from cyclodextrins (CDs) and linear polymers are molecular necklaces (MNs), structures in which dozens of CD molecules are tightly thread onto a polymer chain [1]. These systems clearly exemplify the significance of the geometric match between the size of the CD cavity and the cross section of the polymer. For example, α -CD forms complexes with poly(ethylene oxide) (PEO) but not with poly(propylene oxide) (PPO); β -CD forms complexes with PPO but not with PEO; and γ -CD interacts either with one PPO molecule or with two PEO molecules [2]. In crystals of MNs, CD molecules are arranged in channels, forming a columnar structure. The question arises as to whether this structure will survive after removal of the thread polymer. Similar structures are of interest as new crystalline CD modifications with a common extended channel and, hence, exhibiting new properties. The resolution of the problem calls for a method of removing the polymer from the MN cavity that would leave the type of crystal lattice unaltered. In this paper, we describe a new property of MNs, namely, their ability to dissociate under the action of an organic solvent, selective to the thread polymer but inert to the macrocycle, to produce a new ordered CD form, a columnar CD structure (CD column ). The synthesis of complexes and their properties are described elsewhere [3‐5]. Previously, we studied the formation, composition, and structure of MNs based on α -, β - , and γ -CDs. These MNs are precipitated on mixing water solutions of a CD and a poly(alkylene oxide) (PAO) complementary in size to the CD. The complexes contain one macrocyclic molecule per two monomeric units of PAO (except the γ -CD‐PEO, which contains a double amount of the polymer). As a third component, MNs also include water, which is involved in the formation of intermolecular hydrogen bonds between hydroxyls of neighboring CD molecules. Therefore, we obtained the complexes α - CD‐PEO, γ -CD‐PEO, and β -CD‐PPO, composed of macrocycles threaded on polymer chains and characterized by a lack of covalent bonds between cyclic and thread molecules. To selectively extract the polymers from MNs, we used both polar (acetone, THF) and nonpolar (chloroform, carbon tetrachloride, benzene, tert -butylbenzene, Tetralin) organic solvents inert to CDs. A solvent was added to a MN powder, stirred for several hours, and then the organic phase was separated. For all three types of complexes, the corresponding polymer was identified in the solution within several hours. The polymer content of the β -CD‐PPO-3500 complexes was quantitatively assessed by IR spectroscopy [6].

Water-Soluble Magnetic Nanocomposites Based on Carboxymethyl Cellulose and Iron(III) Oxide

The one-step synthesis of water-soluble composites from maghemite (γ-Fe2O3) nanoparticles with a diameter of 12 ± 4 nm and a biocompatible polysaccharide, namely, sodium salt of carboxymethyl cellulose, is described. The role of the polymer matrix consists in stabilization of the resulting nanoparticles by the electrostatic interaction of polymer carboxyl groups with the surface atoms of iron in the (3+) oxidation state. The dissolution of the composites in water affords aggregatively stable dispersions responding to the external magnetic field. The content of the magnetic phase (iron oxide) in the formulation of the maghemite–carboxymethyl cellulose composite is defined by the ratio of components during the synthesis.

Inhibitory effect of polyethylene oxide and polypropylene oxide triblock copolymers on aggregation and fusion of atherogenic low density lipoproteins

Triblock copolymers of poly(ethylene oxide) and poly(propylene oxide) (so-called pluronics) were shown to influence the aggregation and fusion of atherogenic low density lipoproteins (atLDL) and be able to inhibit these processes. The character of the influence and the degree of the stabilizing effect depended on the structure, relative hydrophobicity, and concentration of the copolymer. Pluronics L61, P85, and L64 characterized by the hydrophilic–lipophilic balance (HLB) value from 3 to 16 had the greatest ability to suppress the aggregation of atLDL. Pluronic L81 with the higher hydrophobicity (HLB = 2) partially inhibited atLDL aggregation at low concentrations but stimulated it at high concentrations. The influence of pluronics did not have a direct connection with their ability for micelle formation, but it was realized through individual macromolecules. We suppose that effects of pluronics could be due to their interaction with the lipid component of LDL and to a possible influence of these copolymers on the structure and hydrophilic–lipophilic characteristics of lipoproteins.

Receptor properties of nanoporous structures based on β-cyclodextrin

A columnar modification of β-cyclodextrin (β-CDcol) has been synthesized using self-assembly and self-organization processes. It is shown that the obtained macrocycle assemblies in the solid state are highly ordered structures with through cylindrical pores with an average diameter of ∼0.7 nm and a length of about 60 nm. These structures can be of interest as a new type of macroreceptors for the inclusion of molecules with diameters not exceeding 0.7 nm belonging to various chemical classes. The abilities of the common cage structure of β-CD and the β-CDcol modification to bind low-molecular-weight volatile organic compounds have been compared. The dependence of the composition, structure, and thermal stability of the inclusion complexes on the ligand nature and geometry is analyzed. The absence of any specificity in the adsorption of ligands on β-CDcol and the possibility of using this structure as a stable nanocontainter for the storage of volatile compounds is demonstrated.

Iron-containing nanoparticles based on the 2-hydroxypropyl-β-cyclodextrin in aqueous solutions

The water-soluble hybrid nanoparticles based on high-substituted 2-hydroxypropyl-β-cyclodextrin were formed in situ during the reduction of iron(+2) salts by hypophosphite ion in alkaline medium. These nanoparticles are high sensitive to temperature and ultrasonication. It was established that the temperature and ultrasonication time of exposure increase leads to the successive dissociation of the nanoparticles.