Aggregation Number in Water/<i>n</i>‑Hexanol Molecular Clusters Formed in Cyclohexane at Different Water/<i>n</i>‑Hexanol/Cyclohexane Compositions Calculated by Titration ¹H NMR

Upon titration of <i>n</i>-hexanol/cyclohexane mixtures of different molar compositions with water, water/<i>n</i>-hexanol clusters are formed in cyclohexane. Here, we develop a new method to estimate the water and <i>n</i>-hexanol aggregation numbers in the clusters that combines integration analysis in one-dimensional ¹H NMR spectra, diffusion coefficients calculated by diffusion-ordered NMR spectroscopy, and further application of the Stokes–Einstein equation to calculate the hydrodynamic volume of the clusters. Aggregation numbers of 5–15 molecules of <i>n</i>-hexanol per cluster in the absence of water were observed in the whole range of <i>n</i>-hexanol/cyclohexane molar fractions studied. After saturation with water, aggregation numbers of 6–13 <i>n</i>-hexanol and 0.5–5 water molecules per cluster were found. O–H and O–O atom distances related to hydrogen bonds between donor/acceptor molecules were theoretically calculated using density functional theory. The results show that at low <i>n</i>-hexanol molar fractions, where a robust hydrogen-bond network is held between <i>n</i>-hexanol molecules, addition of water makes the intermolecular O–O atom distance shorter, reinforcing molecular association in the clusters, whereas at high <i>n</i>-hexanol molar fractions, where dipole–dipole interactions dominate, addition of water makes the intermolecular O–O atom distance longer, weakening the cluster structure. This correlates with experimental NMR results, which show an increase in the size and aggregation number in the clusters upon addition of water at low <i>n</i>-hexanol molar fractions, and a decrease of these magnitudes at high <i>n</i>-hexanol molar fractions. In addition, water produces an increase in the proton exchange rate between donor/acceptor molecules at all <i>n</i>-hexanol molar fractions

A New Methodology to Create Polymeric Nanocarriers Containing Hydrophilic Low Molecular-Weight Drugs: A Green Strategy Providing a Very High Drug Loading

To date, a large number of active molecules are hydrophilic and aromatic low molecular-weight drugs (HALMD). Unfortunately, the low capacity of these molecules to interact with excipients and the fast release when a formulation containing them is exposed to biological media jeopardize the elaboration of drug delivery systems by using noncovalent interactions. In this work, a new, green, and highly efficient methodology to noncovalently attach HALMD to hydrophilic aromatic polymers to create nanocarriers is presented. The proposed method is simple and consists in mixing an aqueous solution containing HALMD (model drugs: imipramine, amitriptyline, or cyclobenzaprine) with another aqueous solution containing the aromatic polymer [model polymer: poly(sodium 4-styrenesulfonate) (PSS)]. NMR experiments demonstrate strong chemical shifting of HALMD aromatic rings when interacting with PSS, evidencing aromatic-aromatic interactions. Ion pair formation and aggregation produce the collapse of the system in the form of nanoparticles. The obtained nanocarriers are spheroidal, their size ranging between 120 and 170 nm, and possess low polydispersity (≤0.2) and negative zeta potential (from -60 to -80 mV); conversely, the absence of the aromatic group in the polymer does not allow the formation of nanostructures. Importantly, in addition to high drug association efficiencies (≥90%), the formed nanocarriers show drug loading values never evidenced for other systems comprising HALMD, reaching ≈50%. Diafiltration and stopped flow experiments evidenced kinetic drug entrapment governed by molecular rearrangements. Importantly, the nanocarriers are stable in suspension for at least 18 days and are also stable when exposed to different high ionic strength, pH, and temperature values. Finally, they are transformable to a reconstitutable dry powder without losing their original characteristics. Considering the large quantity of HALMD with importance in therapeutics and the simplicity of the presented strategy, we envisage these results as the basis to elaborate a number of drug delivery systems with applications in different pathologies

Fibrous Materials Made of Poly(ε-caprolactone)/Poly(ethylene oxide)-b-Poly(ε-caprolactone) Blends Support Neural Stem Cells Differentiation

In this work, we design and produce micron-sized fiber mats by blending poly(&epsilon;-caprolactone) (PCL) with small amounts of block copolymers poly(ethylene oxide)m-block-poly(&epsilon;-caprolactone)n (PEOm-b-PCLn) using electrospinning. Three different PEOm-b-PCLn block copolymers, with different molecular weights of PEO and PCL, were synthesized by ring opening polymerization of &epsilon;-caprolactone using PEO as initiator and stannous octoate as catalyst. The polymer blends were prepared by homogenous solvent mixing using dichloromethane for further electrospinning procedures. After electrospinning, it was found that the addition to PCL of the different block copolymers produced micron-fibers with smaller width, equal or higher hydrophilicity, lower Young modulus, and rougher surfaces, as compared with micron-fibers obtained only with PCL. Neural stem progenitor cells (NSPC), isolated from rat brains and grown as neurospheres, were cultured on the fibrous materials. Immunofluorescence assays showed that the NSPC are able to survive and even differentiate into astrocytes and neurons on the synthetic fibrous materials without any growth factor and using the fibers as guidance. Disassembling of the cells from the NSPC and acquisition of cell specific molecular markers and morphology progressed faster in the presence of the block copolymers, which suggests the role of the hydrophilic character and porous topology of the fiber mats

Structural Insights into a Hemoglobin–Albumin Cluster in Aqueous Medium

A hemoglobin (Hb) wrapped covalently by three human serum albumins (HSAs) is a triangular protein cluster designed as an artificial O₂-carrier and red blood cell substitute. We report the structural insights into this Hb-HSA₃ cluster in aqueous medium revealed by 3D reconstruction based on cryogenic transmission electron microscopy (cryo-TEM) data and small-angle X-ray scattering (SAXS) measurements. Cryo-TEM observations showed individual particles with approximately 15 nm diameter in the vitrified ice layer. Subsequent image processing and 3D reconstruction proved the expected spatial arrangements of an Hb in the center and three HSAs at the periphery. SAXS measurements demonstrated the monodispersity of the Hb-HSA₃ cluster having a molecular mass of 270 kDa. The pair-distance distribution function suggested the existence of oblate-like particles with a maximum dimeter of ∼17 nm. The supramolecular 3D structure reconstructed from the SAXS intensity using an <i>ab initio</i> procedure was similar to that obtained from cryo-TEM data

Stability of Water/Poly(ethylene oxide)₄₃<i>-b-</i>poly(ε-caprolactone)₁₄/Cyclohexanone Emulsions Involves Water Exchange between the Core and the Bulk

The formation of emulsions upon reverse self-association of the monodisperse amphiphilic block copolymer poly­(ethylene oxide)₄₃<i>-<i>b</i>-</i>poly­(ε-caprolactone)₁₄ in cyclohexanone is reported. Such emulsions are not formed in toluene, chloroform, or dichloromethane. We demonstrate by magnetic resonance spectroscopy the active role of the solvent on the stabilization of the emulsions. Cyclohexanone shows high affinity for both blocks, as predicted by the Hansen solubility parameters, so that the copolymer chains are fully dissolved as monomeric chains. In addition, the solvent is able to produce hydrogen bonding with water molecules. Water undergoes molecular exchange between water molecules associated with the polymer and water molecules associated with the solvent, dynamics of major importance for the stabilization of the emulsions. Association of polymeric chains forming reverse aggregates is induced by water over a concentration threshold of 5 wt %. Reverse copolymer aggregates show submicron average hydrodynamic diameters, as seen by dynamic light scattering, depending on the polymer and water concentration