Development of Poly(sorbitol adipate)-g-poly(ethylene glycol) Mono Methyl Ether-Based Hydrogel Matrices for Model Drug Release

Hydrogels were prepared by Steglich esterification and by crosslinking pre-synthesized poly(sorbitol adipate)-graft-poly(ethylene glycol) mono methyl ether (PSA-g-mPEG) using different-chain-length-based disuccinyl PEG. PSA and PSA-g-mPEG were investigated for polymer degradation as a function of time at different temperatures. PSA-g-mPEG hydrogels were then evaluated for their most crucial properties of swelling that rendered them suitable for many pharmaceutical and biomedical applications. Hydrogels were also examined for their Sol-Gel content in order to investigate the degree of cross-linking. Physical structural parameters of the hydrogels were theoretically estimated using the modified Flory-Rehner theory to obtain approximate values of polymer volume fraction, the molecular weight between two crosslinks, and the mesh size of the hydrogels. X-ray diffraction was conducted to detect the presence or absence of crystalline regions in the hydrogels. PSA-g-mPEG hydrogels were then extensively examined for higher and lower molecular weight solute release through analysis by fluorescence spectroscopy. Finally, the cytotoxicity of the hydrogels was also investigated using a resazurin reduction assay. Experimental results show that PSA-g-mPEG provides an option as a biocompatible polymer to be used for pharmaceutical applications.

A Living Topochemical Ring-Opening Polymerization of Achiral Amino Acid N-Carboxy-Anhydrides in Single Crystals

A living topochemical ring-opening polymerization (ROP) of achiral amino-acid N-carboxyanhydrides (NCAs) is reported. Single crystals of the NCAs of α-aminoisobutyric acid (Aib) and 1-aminocyclohexanecarboxylic acid (ACHC) were grown, allowing a ring-opening polymerization macroscopically induced by amines. The single crystals could be polymerized at temperatures from 25-50 °C after physically contacting the amine-based initiator with the crystals. Topochemical polymerization of the crystals was proven by MALDI-ToF MS and XRD, generating polymers with chain lengths of up to 40 units and a complete affixation of the initiating amine at the polymer's head. Due to the proper alignment of the reacting groups in the crystal, longer polymer chains with improved purities can be reached, as chain-transfer is reduced as compared to solution polymerization. Simple purification of the polymers can be achieved by separation of the unreacted NCA via dispersion in acetonitrile. Overall, this method enables the preparation of polymers with higher chain length and purities at mild conditions, finally demonstrating a crystal-based ring opening polymerization.

Synthesis and Characterization of Dimeric Artesunate Glycerol Monocaprylate Conjugate and Formulation of Nanoemulsion Preconcentrate

Malaria is one of the major life-threatening health problems worldwide. Artesunate is the most potent antimalarial drug to combat severe malaria. However, development of drug resistance, short plasma half-life, and poor bioavailability limit the efficacy of this drug. Here, we applied the dimerization concept to synthesize dimeric artesunate glycerol monocaprylate conjugate (D-AS-GC) by conjugating artesunate (AS) with glycerol monocaprylate (GC) via esterification reaction. D-AS-GC conjugate, AS, and GC were well characterized by ¹H NMR, attached proton test (APT) ¹³C NMR and 2D NMR spectroscopy. D-AS-GC conjugate was further analyzed by ESI-TOF MS. Finally, a series of nanoemulsion preconcentrate (F1-F6) of D-AS-GC was prepared by mixing different ratios of oil and surfactant/cosurfactant and evaluated after dilution with an aqueous phase. The optimized formulation (F6) exhibits a clear nanoemulsion and the hydrodynamic diameter of the dispersed phase was determined by DLS and DOSY NMR spectroscopy. The morphology of the nanoemulsion droplets of F6 was investigated by AFM, which revealed the formation of tiny nanoemulsion droplets on a hydrophilic mica substrate. Moreover, using a less polar silicon wafer led to the formation of larger droplets with a spherical core shell-like structure. Overall, the rational design of the dimeric artesunate-based nanoemulsion preconcentrate could potentially be used in more efficient drug delivery systems.

Graphene Oxide-Grafted Hybrid Diblock Copolymer Brush (GO-graft-PEG6k-block-P(MA-POSS)) as Nanofillers for Enhanced Lithium Ion Conductivity of PEO-Based Nanocomposite Solid Polymer Electrolytes

Nanocomposite solid polymer electrolytes (NSPEs) with PEO as the matrix and (i) GO or (ii) GO-graft-PEG_6k or (iii) GO-graft-PEG_6k-block-P(MA-POSS) as nanofillers have been fabricated to elucidate the impact of the filler morphology on the lithium ion conductivity. GO-graft-PEG_6k was obtained by grafting PEG_6k onto GO via esterification. GO-graft-PEG_6k-block-P(MA-POSS) was prepared via surface-initiated atom transfer radical polymerization. Fourier-transform infrared spectroscopy revealed enhanced salt dissociation and complexation between the filler and PEO host that could be attributed to Lewis acid-base interactions. Electrochemical impedance spectroscopy revealed the improved ion conductivity of the fabricated NSPEs as compared with the pristine PEO-LiClO₄. As an example, at 50 °C, the ion conductivity increased to 4.01 × 10^-5 and 6.31 × 10^-5 S cm^-1 with 0.3% GO and 0.3% GO-graft-PEG_6k, respectively, from 2.36 × 10^-5 S cm^-1 of PEO-LiClO₄, suggesting that the filler with brush-like architecture (GO-graft-PEG_6k) is more efficient in enhancing the ion conductivity. Further increase in filler content resulted in lowering of the ion conductivity that could be ascribed to aggregation of the filler. The most dramatic impact on conductivity was observed with the incorporation of brush-like GO-graft-PEG_6k-block-P(MA-POSS) as a nanofiller (3.0 × 10^-4 S cm^-1 at 50 °C with 1.0 wt % filler content). The increase in ion conductivity in the current systems, as opposed to the conventional view, could not be correlated with the content of the amorphous phase of the matrix. The conduction mechanism is still unclear; nevertheless, it could be assumed that in addition to the ion conduction through the PEO matrix, the filler forms additional low-energy ion conducting channels at its interface with the matrix. The pendent POSS nanocages of GO-graft-PEG_6k-block-P(MAPOSS) might probably increase the free volume at the interface with the matrix that is associated with higher chain and ion mobility, thus further enhancing the ion conductivity as compared with GO and GO-graft-PEG_6k. The faster ion dynamics in 1.0 wt % GO-graft-PEG_6k-block-P(MAPOSS) NSPEs has also been verified by the dielectric relaxation studies. Thus, integration of both the PEG and POSS nanocages into GO-grafted brush-like architecture offers a new tool for tuning the lithium ion conductivity for potential Li ion battery applications.

Comparing C2=O and C2=S Barbiturates: Different Hydrogen-Bonding Patterns of Thiobarbiturates in Solution and the Solid State

Carbonyl-centered hydrogen bonds with various strength and geometries are often exploited in materials to embed dynamic and adaptive properties, with the use of thiocarbonyl groups as hydrogen-bonding acceptors remaining only scarcely investigated. We herein report a comparative study of C2=O and C2=S barbiturates in view of their differing hydrogen bonds, using the 5,5-disubstituted barbiturate B and the thiobarbiturate TB as model compounds. Owing to the different hydrogen-bonding strength and geometries of C2=O vs. C2=S, we postulate the formation of different hydrogen-bonding patterns in C2=S in comparison to the C2=O in conventional barbiturates. To study differences in their association in solution, we conducted concentration- and temperature-dependent NMR experiments to compare their association constants, Gibbs free energy of association ∆Gassn., and the coalescence behavior of the N-H‧‧‧S=C bonded assemblies. In Langmuir films, the introduction of C2=S suppressed 2D crystallization when comparing B and TB using Brewster angle microscopy, also revealing a significant deviation in morphology. When embedded into a hydrophobic polymer such as polyisobutylene, a largely different rheological behavior was observed for the barbiturate-bearing PB compared to the thiobarbiturate-bearing PTB polymers, indicative of a stronger hydrogen bonding in the thioanalogue PTB. We therefore prove that H-bonds, when affixed to a polymer, here the thiobarbiturate moieties in PTB, can reinforce the nonpolar PIB matrix even better, thus indicating the formation of stronger H-bonds among the thiobarbiturates in polymers in contrast to the effects observed in solution.

Formation of Surface Wrinkles in Collapsed Langmuir Films of a Polyhedral Oligomeric Silsesquioxane Containing Diblock Copolymer

Surface pressure versus mean molecular area isotherms of Langmuir films of a hybrid diblock copolymer of poly(ethylene glycol) (PEG) and poly(methacrylo polyhedral oligomeric silsesquioxane) P(MA-POSS) together with Brewster angle microscopy reveal details of the phase transitions. The formation of a periodic wrinkling pattern in collapsed films is observed by epifluorescence microscopy after applying several compression-expansion cycles above the surface pressure of ≈18 mN/m. The wrinkle formation is reversible upon compression and expansion of the Langmuir films. Two distinct orientations of POSS molecules are assumed in Langmuir films upon compression, vertically for chains close to the water surface and horizontally orientated upper layers with significant amounts of PEG in between them. Thus, the wrinkling forms mainly in the top stiffer MA-POSS blocks above a certain compressional stress. The wrinkles disappear during the Langmuir-Blodgett (LB) transfer. Nevertheless, atomic force microscopy and grazing incidence wide-angle X-ray scattering experiments reveal the formation of highly ordered POSS molecules in LB films.

Polymer Networks Synthesized from Poly(Sorbitol Adipate) and Functionalized Poly(Ethylene Glycol)

Polymer networks were prepared by Steglich esterification using poly(sorbitol adipate) (PSA) and poly(sorbitol adipate)-graft-poly(ethylene glycol) mono methyl ether (PSA-g-mPEG12) copolymer. Utilizing multi-hydroxyl functionalities of PSA, poly(ethylene glycol) (PEG) was first grafted onto a PSA backbone. Then the cross-linking of PSA or PSA-g-mPEG12 was carried out with disuccinyl PEG of different molar masses (Suc-PEGn-Suc). Polymers were characterized through nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). The degree of swelling of networks was investigated through water (D2O) uptake studies, while for detailed examination of their structural dynamics, networks were studied using 13C magic angle spinning NMR (13C MAS NMR) spectroscopy, 1H double quantum NMR (1H DQ NMR) spectroscopy, and 1H pulsed field gradient NMR (1H PFG NMR) spectroscopy. These solid state NMR results revealed that the networks were composed of a two component structure, having different dipolar coupling constants. The diffusion of solvent molecules depended on the degree of swelling that was imparted to the network by the varying chain length of the PEG based cross-linking agent.

Crystallization of Poly(ethylene)s with Regular Phosphoester Defects Studied at the Air-Water Interface

Poly(ethylene) (PE) is a commonly used semi-crystalline polymer which, due to the lack of polar groups in the repeating unit, is not able to form Langmuir or Langmuir-Blodgett (LB) films. This problem can be solved using PEs with hydrophilic groups arranged at regular distances within the polymer backbone. With acyclic diene metathesis (ADMET) polymerization, a tool for precise addition of polar groups after a certain interval of methylene sequence is available. In this study, we demonstrate the formation of Langmuir/LB films from two different PEs with regular phosphoester groups, acting as crystallization defects in the main chain. After spreading the polymers from chloroform solution on the water surface of a Langmuir trough and solvent evaporation, the surface pressure is recorded during compression under isothermal condition. These π-A isotherms, surface pressure π vs. mean area per repeat unit A, show a plateau zone at surface pressures of ~ (6 to 8) mN/m, attributed to the formation of crystalline domains of the PEs as confirmed by Brewster angle and epifluorescence microscopy. PE with ethoxy phosphoester defects (Ethoxy-PPE) forms circular shape domains, whereas Methyl-PPE-co-decadiene with methyl phosphoester defects and two different methylene sequences between the defects exhibits a film-like morphology. The domains/films are examined by atomic force microscopy after transferring them to a solid support. The thickness of the domains/films is found in the range from ~ (2.4 to 3.2) nm depending on the transfer pressure. A necessity of chain tilt in the crystalline domains is also confirmed. Grazing incidence X-ray scattering measurements in LB films show a single Bragg reflection at a scattering vector qxy position of ~ 15.1 nm-1 known from crystalline PE samples.

Dissolving Cellulose in 1,2,3-Triazolium- and Imidazolium-Based Ionic Liquids with Aromatic Anions

We present 1,2,3-triazolium- and imidazolium-based ionic liquids (ILs) with aromatic anions as a new class of cellulose solvents. The two anions in our study, benzoate and salicylate, possess a lower basicity when compared to acetate and therefore should lead to a lower amount of N-heterocyclic carbenes (NHCs) in the ILs. We characterize their physicochemical properties and find that all of them are liquids at room temperature. By applying force field molecular dynamics (MD) simulations, we investigate the structure and dynamics of the liquids and find strong and long-lived hydrogen bonds, as well as significant π-π stacking between the aromatic anion and cation. Our ILs dissolve up to 8.5 wt.-% cellulose. Via NMR spectroscopy of the solution, we rule out chain degradation or derivatization, even after several weeks at elevated temperature. Based on our MD simulations, we estimate the enthalpy of solvation and derive a simple model for semi-quantitative prediction of cellulose solubility in ILs. With the help of Sankey diagrams, we illustrate the hydrogen bond network topology of the solutions, which is characterized by competing hydrogen bond donors and acceptors. The hydrogen bonds between cellulose and the anions possess average lifetimes in the nanosecond range, which is longer than found in common pure ILs.

Monolayer behavior of pure F-DPPC and mixed films with DPPC studied by epifluorescence microscopy and infrared reflection absorption spectroscopy

The monolayer behavior of a l-DPPC derivative with a single fluorination in one of its terminal methyl groups (F-DPPC) at air-water interface was investigated by epifluorescence microscopy and infrared reflection absorption spectroscopy (IRRAS). Epifluorescence microscopy was utilized to study the shape and morphology of liquid-condensed (LC) domains observed upon compression of the film. IRRAS was employed for the determination of chain order and orientation. The shapes of LC-domains in a monolayer of F-DPPC are more dependent on the rate of compression than those of DPPC. The LC domains of F-DPPC display pronounced fractal growth patterns depending on the compression speed. The evolution of LC domain occurs under dominating electrostatic dipolar forces in F-DPPC. IRRAS measurements with the analysis of the frequency of the methylene stretching vibrations as a function of film compression show that the acyl chains in an F-DPPC monolayer in the LE-phase are more disordered than those in a DPPC film. The reason for the higher chain disorder in LE phase F-DPPC monolayers is a back folding of the fluorinated sn-2 chain terminus towards the air-water interface leading to larger molecular area requirement. Angular dependent IRRA spectra of monolayers at a surface pressure of 30 mN m^-1 show that in the LC phase DPPC and F-DPPC exhibit a similar tilt of the acyl chains of ca. 28-30 ° relative to the surface normal. F-DPPC is ideally miscible with l-DPPC-d₆₂ having the same chirality, as indicated by epifluorescence images and by IRRAS. However, the LC domains in an equimolar mixture of d-DPPC and F-DPPC having opposite chirality show multi-lobed complex domain patterns indicating chiral phase separation within LC domains.

Conjugation of Amine-Functionalized Polyesters With Dimethylcasein Using Microbial Transglutaminase

Protein-polymer conjugates have been used as therapeutics because they exhibit frequently higher stability, prolonged in vivo half-life, and lower immunogenicity compared with native proteins. The first part of this report describes the enzymatic synthesis of poly(glycerol adipate) (PGA(M)) by transesterification between glycerol and dimethyl adipate using lipase B from Candida antarctica. PGA(M) is a hydrophilic, biodegradable but water insoluble polyester. By acylation, PGA(M) is modified with 6-(Fmoc-amino)hexanoic acid and with hydrophilic poly(ethylene glycol) side chains (mPEG12) rendering the polymer highly water soluble. This is followed by the removal of protecting groups, fluorenylmethyloxycarbonyl, to generate polyester with primary amine groups, namely PGA(M)-g-NH₂-g-mPEG12. ¹H NMR spectroscopy, FTIR spectroscopy, and gel permeation chromatography have been used to determine the chemical structure and polydispersity index of PGA(M) before and after modification. In the second part, we discuss the microbial transglutaminase-mediated conjugation of the model protein dimethylcasein with PGA(M)-g-NH₂-g-mPEG12 under mild reaction conditions. SDS-PAGE proves the protein-polyester conjugation.

Crystallization of Poly(ethylene oxide) on the Surface of Aqueous Salt Solutions Studied by Grazing Incidence Wide-Angle X-ray Scattering

We report the thin layer crystallization of high-molar mass poly(ethylene oxide) (PEO) on a liquid support using a 4 M K₂CO₃ aqueous solution as a subphase. Because of the Hofmeister effect, PEO does not dissolve and remains at the surface during compression on a Langmuir trough. The transition from the flat pancake conformation upon compression of the spread polymer film to an entangled monolayer results in a plateau region of the Langmuir isotherm. Using grazing incidence wide-angle X-ray scattering, the final crystallization of PEO was observed, and the crystal orientation was determined. The fold surface was (209̅), that is, the helix axis has a tilt angle of 2.9° to the normal vector of the water surface.

Ion Transport Properties and Ionicity of 1,3-Dimethyl-1,2,3-Triazolium Salts with Fluorinated Anions

1,2,3-Triazolium salts are an important class of materials with a plethora of sophisticated applications. A series of three novel 1,3-dimethyl-1,2,3-triazolium salts with fluorine, containing anions of various size, is synthesized by methylation of 1,2,3-triazole. Their ion conductivity is measured by impedance spectroscopy, and the corresponding ionicities are determined by diffusion coefficients obtained from ¹H and 19F pulsed field gradient nuclear magnetic resonance (PFG NMR) spectroscopy data, revealing that the anion strongly influences their ion conductive properties. Since the molar ion conductivities and ionicities of the 1,3-dimethyl-1,2,3-triazolium salts are enhanced in comparison to other 1,2,3-triazolium salts with longer alkyl substituents, they are promising candidates for applications as electrolytes in electrochemical devices.

Polyphilicity-An Extension of the Concept of Amphiphilicity in Polymers

Recent developments in synthetic pathways as simple reversible-deactivation radical polymerization (RDRP) techniques and quantitative post-polymerization reactions, most notoriously 'click' reactions, leading to segmented copolymers, have broadened the molecular architectures accessible to polymer chemists as a matter of routine. Segments can be blocks, grafted chains, branchings, telechelic end-groups, covalently attached nanoparticles, nanodomains in networks, even sequences of random copolymers, and so on. In this review, we describe the variety of the segmented synthetic copolymers landscape from the point of view of their chemical affinity, or synonymous philicity, in bulk or with their surroundings, such as solvents, permeant gases, and solid surfaces. We focus on recent contributions, current trends, and perspectives regarding polyphilic copolymers, which have, in addition to hydrophilic and lipophilic segments, other philicities, for example, towards solvents, fluorophilic entities, ions, silicones, metals, nanoparticles, and liquid crystalline moieties.

Indomethacin functionalised poly(glycerol adipate) nanospheres as promising candidates for modified drug release

The linear polyester poly(glycerol adipate) (PGA) with its free pendant hydroxyl groups was covalently grafted with indomethacin which yields polymeric prodrugs. It was possible to produce nanospheres with narrow particle size distribution of these polymer-drug conjugates with an optimized interfacial deposition method. Nanospheres were characterized by zeta potential measurements, dynamic light scattering, electron microscopy and nanoparticle tracking analysis. Moreover, cell viability studies and cytotoxicity tests in three different cell lines were carried out showing low toxicity for three different degrees of grafting. In addition, the nanospheres had (in contrast to the free drug) low hemolytic activity in vitro. Release studies of nanodispersions are challenging. The use of a specially developed setup with highly porous aluminum oxide membranes enabled us to overcome problems associated with other setups (e.g. dialysis membranes). A slow and controlled release profile without any burst was observed over 15 days. The results indicate that indomethacin-PGA conjugates can be formulated successfully as nanospheres with the desired characteristics of small size with narrow distribution, controlled drug release and low toxicity. The newly developed particles have the potential to improve the therapy of inflammation and associated diseases.

Intended and Unintended Targeting of Polymeric Nanocarriers: The Case of Modified Poly(glycerol adipate) Nanoparticles

Biodegradable nanoparticles based on stearic acid-modified poly(glycerol adipate) (PGAS) are promising carriers for drug delivery. In order to investigate the impact of the particle interface characteristics on the biological fate, PGAS nanoparticles are covalently and noncovalently coated with N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers. HPMA copolymer-modified PGAS nanoparticles have similar particle sizes, but less negative zeta-potentials. Nanoparticles are double labeled with the fluorescent dyes DiR (noncovalently) and DYOMICS-676 (covalently bound to HPMA copolymer), and their biodistribution is investigated noninvasively by multispectral optical imaging. Both covalent and noncovalent coatings cause changes in the pharmacokinetics and biodistribution in healthy and tumor-bearing mice. In addition to the intended tumor accumulation, high signals of both fluorescent dyes are also observed in other organs, including liver, ovaries, adrenal glands, and bone. The unintended accumulation of nanocarriers needs further detailed and systematic investigations, especially with respect to the observed ovarian and adrenal gland accumulation.

Chain Tilt and Crystallization of Ethylene Oxide Oligomers with Midchain Defects

Many text books and publications do not focus on the necessity of chain tilting in crystalline lamellae of oligomers and polymers, a fundamental aspect of their crystallization already discussed by Flory. Herein we investigate the chain tilt of ethylene oxide oligomers (EOs) containing various midchain defects by WAXS, SAXS and solid state ¹³C MAS NMR spectroscopy. At low temperatures, one out of the two EO chains of EO₉-meta-EO₉ and EO₁₁-TR-EO₁₁ containing a 1,3-disubstituted benzene or a 1,4-disubstituted 1,2,3-triazole defect in central position of the oligomer chain forms crystals and the other EO chain as well as the defect remain in the amorphous phase. The aromatic midchain defect of these two oligomers can be incorporated into the crystalline lamella upon heating below T_m. Then, the adjoining amorphous EO chain crosses from the lamellae to the amorphous regions at an angle ξ, which is preordained by the substitution pattern of the aromatic defect, revealing that the chain tilt angle ranges between 36° ≤ ϕ ≤ 60°.

Effect of Perfluoroalkyl Endgroups on the Interactions of Tri-Block Copolymers with Monofluorinated F-DPPC Monolayers

We studied the interaction of amphiphilic and triphilic polymers with monolayers prepared from F-DPPC (1-palmitoyl-2-(16-fluoropalmitoyl)-sn-glycero-3-phosphocholine), a phospholipid with a single fluorine atom at the terminus of the sn-2 chain, an analogue of dipalmitoyl-phosphatidylcholine (DPPC). The amphiphilic block copolymers contained a hydrophobic poly(propylene oxide) block flanked by hydrophilic poly(glycerol monomethacrylate) blocks (GP). F-GP was derived from GP by capping both termini with perfluoro-n-nonyl segments. We first studied the adsorption of GP and F-GP to lipid monolayers of F-DPPC. F-GP was inserted into the monolayer up to a surface pressure Π of 42.4 mN m⁻¹, much higher than GP (32.5 mN m⁻¹). We then studied isotherms of lipid-polymer mixtures co-spread at the air-water interface. With increasing polymer content in the mixture a continuous shift of the onset of the liquid-expanded (LE) to liquid-condensed (LC) transition towards higher molecular and higher area per lipid molecule was observed. F-GP had a larger effect than GP indicating that it needed more space. At a Π-value of 32 mN m⁻¹, GP was excluded from the mixed monolayer, whereas F-GP stayed in F-DPPC monolayers up to 42 mN m⁻¹. F-GP is thus more stably anchored in the monolayer up to higher surface pressures. Images of mixed monolayers were acquired using different fluorescent probes and showed the presence of perfluorinated segments of F-GP at LE-LC domain boundaries.

Molecular Dynamics in the Crystalline Regions of Poly(ethylene oxide) Containing a Well-Defined Point Defect in the Middle of the Polymer Chain

The chain mobility in crystals of a homopolymer of poly(ethylene oxide) (PEO) with 22 monomer units (PEO₂₂) is compared with that of a PEO having the identical number of monomer units but additionally a 1,4-disubstituted 1,2,3-triazole (TR) point defect in the middle of the chain (PEO₁₁-TR-PEO₁₁). In crystals of PEO₂₂, the characteristic α_c-relaxation (helix jumps) is detected and the activation energy of this process is calculated from the pure crystalline ¹H FIDs to 67 kJ/mol. PEO₁₁-TR-PEO₁₁ exhibits a more complex behavior, i.e. a transition into the high temperature phase HTPh is noticed during heating in the temperature range between -5 and 10 °C which is attributed to the incorporation of the TR ring into the crystalline lamellae. The crystal mobility of the low temperature phase LTPh of PEO₁₁-TR-PEO₁₁ is in good agreement with PEO₂₂ since helical jump motions could also be detected by analysis of the ¹H FIDs and the corresponding values of their second moments M₂. In contrast, the high temperature phase of PEO₁₁-TR-PEO₁₁ shows a completely different behavior of the crystal mobility. The crystalline PEO chains are rigid in this HTPh on the time scale of both, the ¹H time-domain technique and in ¹³C MAS CODEX NMR spectroscopy, i.e. the α_c-mobility of PEO in the HTPh of PEO₁₁-TR-PEO₁₁ is completely suppressed and the PEO₁₁ chains are converted into a crystal-fixed polymer due to the incorporation of the TR rings into the crystal structure. However, the TR defect of PEO₁₁-TR-PEO₁₁ shows in the HTPh characteristic π-flip motions with an Arrhenius type activation energy of 223 kJ/mol measured by dielectric relaxation spectroscopy. This motion cannot be observed by corresponding ¹³C MAS CODEX NMR measurements due to an interfering spin-dynamic effect.

The annular tautomerism of lithium 1,2,3-triazolate

The tautomeric equilibrium of 1-lithium-1,2,3-triazolate (1Li-TR) and 2-lithium-1,2,3-triazolate (2Li-TR) is studied by X-ray diffraction, NMR spectroscopy and molecular dynamics simulations.

Perfluorinated Moieties Increase the Interaction of Amphiphilic Block Copolymers with Lipid Monolayers

The interaction of amphiphilic and triphilic block copolymers with lipid monolayers has been studied. Amphiphilic triblock copolymer PGMA20-PPO34-PGMA20 (GP) is composed of a hydrophobic poly(propylene oxide) (PPO) middle block that is flanked by two hydrophilic poly(glycerol monomethacrylate) (PGMA) side blocks. The attachment of a perfluoro-n-nonyl residue (F9) to either end of GP yields a triphilic polymer with the sequence F9-PGMA20-PPO34-PGMA20-F9 (F-GP). The F9 chains are fluorophilic, i.e., they have a tendency to demix in hydrophilic as well as in lipophilic environments. We investigated (i) the adsorption of both polymers to differently composed lipid monolayers and (ii) the compression behavior of mixed polymer/lipid monolayers. The lipid monolayers are composed of phospholipids with PC or PE headgroups and acyl chains of different length and saturation. Both polymers interact with lipid monolayers by inserting their hydrophobic moieties (PPO, F9). The interaction is markedly enhanced in the presence of F9 chains, which act as membrane anchors. GP inserts into lipid monolayers up to a surface pressure of 30 mN/m, whereas F-GP inserts into monolayers at up to 45 mN/m, suggesting that F-GP also inserts into lipid bilayer membranes. The adsorption of both polymers to lipid monolayers with short acyl chains is favored. Upon compression, a two-step squeeze-out of F-GP occurs, with PPO blocks being released into the aqueous subphase at 28 mN/m and the F9 chains being squeezed out at 48 mN/m. GP is squeezed out in one step at 28 mN/m because of the lack of F9 anchor groups. The liquid expanded (LE) to liquid condensed (LC) phase transition of DPPC and DMPE is maintained in the presence of the polymers, indicating that the polymers can be accommodated in LE- and LC-phase monolayers. These results show how fluorinated moieties can be included in the rational design of membrane-binding polymers.

Enzymatic Synthesis and Characterization of Hydrophilic Sugar Based Polyesters and Their Modification with Stearic Acid

Biodegradable and hydrophilic functional polyesters were synthesized enzymatically using xylitol or d-sorbitol together with divinyl adipate and lipase B from Candida antartica (CAL-B). The resulting polyesters had pendant OH-groups from their sugar units which were esterified to different degrees with stearic acid chloride. The structure and the degrees of polymerization of the resulting graft copolymers based on poly(xylitol adipate) and poly(d-sorbitol adipate) were characterized by ¹H NMR spectroscopy and SEC. DSC, WAXS and SAXS measurements indicated that a phase separation between polymer backbone and stearoyl side chains occurred in the graft copolymers, and, additionally, the side chains were able to crystallize which resulted in the formation of a lamellar morphology. Additionally, nanoparticles of the graft copolymers in an aqueous environment were studied by DLS and negative stain TEM.

Proton conductivity and phase transitions in 1,2,3-triazole

1,2,3-Triazole (TR) is a good proton conductor which is tidely related to formation of a hydrogen bond network along the N-HN trajectory and its self-dissociation into diH-1,2,3-triazolium and 1,2,3-triazolate. To gain a deeper understanding, the proton conductivity of TR is measured by impedance spectroscopy (IS) across its melting temperature and an additionally discovered solid-solid phase transition. The orthorhombic high temperature phase and the monoclinic low temperature modification are investigated by polarized optical microscopy, DSC- and WAXS measurements. Furthermore, the diffusion coefficients of TR are determined from IS data and measured by (1)H PFG NMR spectroscopy in the melt which allows for separate evaluation of contributions of proton hopping across the hydrogen bond network and the vehicle mechanism to the proton conductivity where the vehicles are defined as charged species generated by TR self-dissociation. Finally, the degree of dissociation of TR is calculated and the influence of the self-dissociation of TR on the proton conductivity is discussed in the context of the dielectric constant.

Unusual triskelion patterns and dye-labelled GUVs: consequences of the interaction of cholesterol-containing linear-hyperbranched block copolymers with phospholipids

Cholesterol (Ch) linked to a linear-hyperbranched block copolymer composed of poly(ethylene glycol) (PEG) and poly(glycerol) (hbPG) was investigated for its membrane anchoring properties. Two polyether-based linear-hyperbranched block copolymers with and without a covalently attached rhodamine fluorescence label (Rho) were employed (Ch-PEG30-b-hbPG23 and Ch-PEG30-b-hbPG17-Rho). Compression isotherms of co-spread 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) with the respective polymers were measured on the Langmuir trough and the morphology development of the liquid-condensed (LC) domains was studied by epi-fluorescence microscopy. LC domains were strongly deformed due to the localization of the polymers at the domain interface, indicating a line activity for both block copolymers. Simultaneously, it was observed that the presence of the fluorescence label significantly influences the domain morphology, the rhodamine labelled polymer showing higher line activity. Adsorption isotherms of the polymers to the water surface or to monolayers of DPPC and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), respectively, were collected. Again the rhodamine labelled polymer showed higher surface activity and a higher affinity for insertion into lipid monolayers, which was negligibly affected when the sub-phase was changed to aqueous sodium chloride solution or phosphate buffer. Calorimetric investigations in bulk confirmed the results found using tensiometry. Confocal laser scanning microscopy (CLSM) of giant unilamellar vesicles (GUVs) also confirmed the polymers' fast adsorption to and insertion into phospholipid membranes.

Conjugates of degraded and oxidized hydroxyethyl starch and sulfonylureas: synthesis, characterization, and in vivo antidiabetic activity

Orally administered drugs usually face the problem of low water solubility, low permeability, and less retention in bloodstream leading to unsatisfactory pharmacokinetic profile of drugs. Polymer conjugation has attracted increasing interest in the pharmaceutical industry for delivering such low molecular weight (Mw) drugs as well as some complex compounds. In the present work, degraded and oxidized hydroxyethyl starch (HES), a highly biocompatible semisynthetic biopolymer, was used as a drug carrier to overcome the solubility and permeability problems. The HES was coupled with synthesized N-arylsulfonylbenzimidazolones, a class of sulfonylurea derivatives, by creating an amide linkage between the two species. The coupled products were characterized using GPC, FT-IR, (1)H NMR, and (13)C NMR spectroscopy. The experiments established the viability of covalent coupling between the biopolymer and N-arylsulfonylbenzimidazolones. The coupled products were screened for their in vivo antidiabetic potential on male albino rats. The coupling of sulfonylurea derivatives with HES resulted in a marked increase of the hypoglycemic activity of all the compounds. 2,3-Dihydro-3-(4-nitrobenzensulfonyl)-2-oxo-1H-benzimidazole coupled to HES10100 was found most potent with a 67% reduction in blood glucose level of the rats as compared to 41% reduction produced by tolbutamide and 38% by metformin.

Effects of circuit resistance training and timely protein supplementation on exercise-induced fat oxidation in tetraplegic adults

BACKGROUND

Substrate utilization during exercise in persons with spinal cord injury (SCI) remains poorly defined.

PURPOSE

To investigate effects of circuit resistance training (CRT) and timing of protein supplementation (PS) on fuel utilization in persons with tetraplegia.

METHODS

Eleven individuals with chronic tetraplegia underwent 6 months of CRT 3 times weekly. Five randomly assigned participants received immediate PS (iPS) administered in split doses prior to and following all exercise sessions. Other participants consumed a matched dose of PS that was delayed until 24 hours post-exercise (dPS). Participants underwent a maximal graded exercise test (GXT) to volitional exhaustion at 4 conditioning time points: 3 months before (-3mo), at the beginning of (0mo), 3 months into (3mo), and 6 months following (6mo) the CRT conditioning program. Respiratory measures were continuously obtained throughout the GXT via open-circuit spirometry. Fuel utilization and energy expenditure were computed from the respiratory data.

RESULTS

The differences in changes in substrate utilization between the PS groups were not significant as determined by the interaction of PS group and conditioning time point, F (3, 27) = 2.32, P = .098, η(2) P = .205. Maximal absolute fat oxidation did not change significantly from 0 to 6mo (mean difference, 0.014 ± 0.031 g/min; P = .170), and fat oxidation remained low never exceeding an average of 0.10 ± 0.09 g/min for any given exercise intensity.

CONCLUSION

Maximum fat utilization during exercise and fat utilization at matched exercise intensities were not increased in persons with tetraplegia, independent of PS, and levels of fat oxidation remained low after training.

Binding of amphiphilic and triphilic block copolymers to lipid model membranes: the role of perfluorinated moieties

A novel class of symmetric amphi- and triphilic (hydrophilic, lipophilic, fluorophilic) block copolymers has been investigated with respect to their interactions with lipid membranes. The amphiphilic triblock copolymer has the structure PGMA(20)-PPO(34)-PGMA(20) (GP) and it becomes triphilic after attaching perfluoroalkyl moieties (F9) to either end which leads to F(9)-PGMA(20)-PPO(34)-PGMA(20)-F(9) (F-GP). The hydrophobic poly(propylene oxide) (PPO) block is sufficiently long to span a lipid bilayer. The poly(glycerol monomethacrylate) (PGMA) blocks have a high propensity for hydrogen bonding. The hydrophobic and lipophobic perfluoroalkyl moieties have the tendency to phase segregate in aqueous as well as in hydrocarbon environments. We performed differential scanning calorimetry (DSC) measurements on polymer bound lipid vesicles under systematic variation of the bilayer thickness, the nature of the lipid headgroup, and the polymer concentration. The vesicles were composed of phosphatidylcholines (DMPC, DPPC, DAPC, DSPC) or phosphatidylethanolamines (DMPE, DPPE, POPE). We showed that GP as well as F-GP binding have membrane stabilizing and destabilizing components. PPO and F9 blocks insert into the hydrophobic part of the membrane concomitantly with PGMA block adsorption to the lipid headgroup layer. The F9 chains act as additional membrane anchors. The insertion of the PPO blocks of both GP and F-GP could be proven by 2D-NOESY NMR spectroscopy. By fluorescence microscopy we show that F-GP binding increases the porosity of POPC giant unilamellar vesicles (GUVs), allowing the influx of water soluble dyes as well as the translocation of the complete triphilic polymer and its accumulation at the GUV surface. These results open a new route for the rational design of membrane systems with specific properties.