Carbohydrate-based polyamides and polyesters: an overview illustrated with two selected examples

An overview on the synthesis, structure and properties of polyamides and aromatic copolyesters produced by using monomers derived from carbohydrates is provided. Two examples are selected for illustration: (a) aliphatic polyamides prepared from aldaric acids and (b) aromatic copolyesters containing alditols units. Polycondensation in solution of n-alkanediamines (n taking even values from 6 to 12) with activated pentaric (L-arabino and xylo) and hexaric (galacto and D-manno) acids bearing the secondary hydroxyl groups protected as methyl ether, afforded linear polyaldaramides PA-nSu with Mw oscillating between 25 000 and 150 000 g mol 1. They are stable above 300 C and are semicrystalline even so only PA-nMn are stereoregular. Melting temperatures of PA-nSu range between 140 and 230 C and most of them are able to crystallize from the melt at a rate that increases with the length of the polymethylene segment. Both melting and glass transition temperatures decrease with the content in sugar units. Spherulitic films, oriented fibers and lamellar single crystals could be obtained from PA-nSu. All these polyamides seem to adopt a common crystal structure made of hydrogen-bonded sheets with the sugar residue skewed to attain an efficient side-by-side packing of the polymer chains. Aromatic homopolyesters and copolyesters derived from terephthalic acid and mixtures of butylene glycol and O-methylated alditols were prepared by polycondensation in the melt with Mw in the 20 000–50 000 g mol 1 range and a random microstructure. The thermal properties of PBT containing alditols units are very depending on the sugar constitution and copolyester composition. In general they are thermally stable above 300 C and display crystallinity for contents in alditols up to 30%. Melting temperatures decrease with the content in alditols whereas an opposite trend is observed for glass transition temperatures. The crystalline structure of PBT is preserved in the crystalline copolyesters whereas a different crystal lattice is adopted by homopolyesters entirely made of alditol units. In general, polyamides and polyesters containing sugar derived units are widely soluble in organic solvents, markedly hydrophilic and more susceptible to hydrolysis than their parent polymers.Postprint (published version

Validation of smart nanoparticles as controlled drug delivery systems: loading and pH-dependent release of pilocarpine

Micelles are good devices for use as controlled drug delivery systems because they exhibit the ability to protect the encapsulated substance from the routes of degradation until they reach the site of action. The present work assesses loading kinetics of a hydrophobic drug, pilocarpine, in polymeric micellar nanoparticles (NPs) and its pH-dependent release in hydrophilic environments. The trigger pH stimulus, pH 5.5, was the value encountered in damaged tissues in solid tumors. The new nanoparticles were prepared from an amphiphilic block copolymer, [(HEMA19%-DMA31%)-(FMA5%-DEA45%)]. For the present research, three systems were validated, two of them with cross-linked cores and the other without chemical stabilization. A comparison of their loading kinetics and release profiles is discussed, with the support of additional data obtained by scanning electron microscopy and dynamic light scattering. The drug was loaded into the NPs within the first minutes; the load was dependent on the degree of cross-linking. All of the systems experienced a boost in drug release at acidic pH, ranging from 50 to 80% within the first 48 h. NPs with the highest degree (20%) of core cross-linking delivered the highest percentage of drug at fixed times. The studied systems exhibited fine-tuned sustained release features, which may provide a continuous delivery of the drug at specific acidic locations, thereby diminishing side effects and increasing therapeutic rates. Hence, the studied NPs proved to behave as smart controlled drug delivery systems capable of responding to changes in pH.Peer ReviewedPostprint (published version

The mere sight of loved ones does not inhibit psychophysiological defense mechanisms when threatened

Open Access funding enabled and organized by Projekt DEAL.Looking at pictures of loved ones, such as one’s romantic partner or good friends, has been shown to alleviate the experience of pain and reduce defensive reactions. However, little is known about such modulatory effects on threat and safety learning and the psychophysiological processes involved. Here, we explored the hypothesis that beloved faces serve as implicit safety cues and attenuate the expression of fear responses and/or accelerate extinction learning in a threatening context. Thirtytwo participants viewed pictures of their loved ones (romantic partner, parents, and best friend) as well as of unknown individuals within contextual background colors indicating threat-of-shock or safety. Focusing on the extinction of non-reinforced threat associations (no shocks were given), the experiment was repeated on two more test days while the defensive startle-EMG, SCR, and threat ratings were obtained. Results confirmed pronounced defensive responding to instructed threatof- shock relative to safety context (e.g., threat-enhanced startle reflex and SCR). Moreover, threatpotentiated startle response slowly declined across test days indicating passive extinction learning in the absence of shocks. Importantly, neither a main effect of face category (loved vs. unknown) nor a significant interaction with threat/safety instructions was observed. Thus, a long-term learning history of beneficial relations (e.g., with supportive parents) did not interfere with verbal threat learning and aversive apprehensions. These findings reflect the effects of worries and apprehensions that persist despite the repeated experience of safety and the pictorial presence of loved ones. How to counter such aversive expectations is key to changing mal-adaptive behaviors (e.g., avoidance or stockpiling), biased risk perceptions, and stereotypes.Projekt DEA

Contextual information resolves uncertainty about ambiguous facial emotions: Behavioral and magnetoencephalographic correlates

We are grateful to Karin Wilken for her assistance in data collection.Environmental conditions bias our perception of other peoples’ facial emotions. This becomes quite relevant in potentially threatening situations, when a fellow’s facial expression might indicate potential danger. The present study tested the prediction that a threatening environment biases the recognition of facial emotions. To this end, low- and medium-expressive happy and fearful faces (morphed to 10%, 20%, 30%, or 40% emotional) were presented within a context of instructed threat-of-shock or safety. Self-reported data revealed that instructed threat led to a biased recognition of fearful, but not happy facial expressions. Magnetoencephalographic correlates revealed spatio-temporal clusters of neural network activity associated with emotion recognition and contextual threat/safety in early to mid-latency time intervals in the left parietal cortex, bilateral prefrontal cortex, and the left temporal pole regions. Early parietal activity revealed a double dissociation of face–context information as a function of the expressive level of facial emotions: When facial expressions were difficult to recognize (lowexpressive), contextual threat enhanced fear processing and contextual safety enhanced processing of subtle happy faces. However, for rather easily recognizable faces (medium-expressive) the left hemisphere (parietal cortex, PFC, and temporal pole) showed enhanced activity to happy faces during contextual threat and fearful faces during safety. Thus, contextual settings reduce the salience threshold and boost early face processing of lowexpressive congruent facial emotions, whereas face-context incongruity or mismatch effects drive neural activity of easier recognizable facial emotions. These results elucidate how environmental settings help recognize facial emotions, and the brain mechanisms underlying the recognition of subtle nuances of fear.German Research Foundation (DFG) BU 3255/1-1 Ju2/024/15 SF58C0

Sugar-based bicyclic monomers for aliphatic polyesters: a comparative appraisal of acetalized alditols and isosorbide

Three series of polyalkanoates (adipates, suberates and sebacates) were synthesized using as monomers three sugar-based bicyclic diols derived from D-glucose (Glux-diol and isosorbide) and D-mannose (Manx-diol). Polycondensations were conducted in the melt applying similar reaction conditions for all cases. The aim was to compare the three bicyclic diols regarding their suitability to render aliphatic polyesters with enhanced thermal and mechanical properties. The ensuing polyesters had molecular weights (Mw) in the 25,000–50,000 g mol-1 range with highest values being attained for Glux-diol. All the polyesters started to decompose above 300 °C and most of them did not display perceivable crystallinity. On the contrary, they had glass transition temperatures much higher than usually found in homologous polyesters made of alkanediols, and showed a stress– strain behavior consistent with their Tg values. Glux-diol was particularly effective in increasing the Tg and to render therefore polyesters with high elastic modulus and considerable mechanical strength.Peer ReviewedPostprint (published version

Triblock copolyesters derived from lactic acid and glucose: synthesis, nanoparticle formation and simulation

ABA triblock copolyesters were synthesized by ring-opening polymerization (ROP) of l-lactide in solution initiated by a telechelic d-glucose-based polyester macroinitiator. The macroinitiator with a number-average molecular weight about 2500 g mol-1 was synthesized by non-stoichiometric polycondensation in the melt of 2,4:3,5-di-O-methylene-d-glucitol and dimethyl succinate. Two triblock copolyesters of Mn ranging between ~6000 and ~9000 g mol-1, and differing in the length of the polylactide blocks were prepared. These copolyesters started to decompose when heated at ~220 °C and degraded slowly upon aqueous incubation under physiological conditions. They did not display any perceivable crystallinity and showed a single glass transition temperature (Tg) around 60 °C with the higher value corresponding to the larger content in glucitol units. The copolyesters were able to form nanoparticles with average diameters of ~100–130 nm and satisfactory dispersity. The effect of the block lengths on size, ¿-potential values and physical stability of the nanoparticles was evaluated. A molecular dynamics simulation study allowed modelling the two-phase structure of the nanoparticles and evidenced the preference of the glucose-based block to be peripherally located.Peer ReviewedPostprint (author's final draft

Crystalline structure and thermotropic behavior of alkyltrimethylphosphonium amphiphiles

Quaternary organophosphonium salts bearing long alkyl chains are cationic surfactants of interest owing to their physical and biological properties. In the present work, the crystal structure and thermotropic behavior of the homologous series of alkyltrimethylphosphonium bromides (nATMP·Br), with the alkyl chain containing an even number (n) of carbon atoms from 12 to 22, have been examined within the 0–300 °C range of temperatures. These compounds were shown to be resistant to heat up to ~390 °C. The phases adopted at different temperatures were detected by DSC, and the structural changes involved in the phase transitions have been characterized by simultaneous WAXS and SAXS carried out in real-time, and by polarizing optical microscopy as well. Three or four phases were identified for n = 12 and 14 or n = 16, respectively, in agreement with the heat exchange peaks observed by DSC. The phase existing at room temperature (Ph-I) was found to be fully crystalline and its crystal lattice was determined by single-crystal X-ray diffraction methods. Ph-II consisted of a semicrystalline structure that can be categorized as Smectic-B with the crystallized ionic pairs hexagonally arranged in layers and the molten alkyl chain confined in the interlayer space. Ph-II of 12ATMP·Br and 14ATMP·Br directly isotropicized upon heating at ~220 °C, whereas for n = 16, it converted into a Smectic-A phase (Ph-III) that needed to be heated above ~240 °C to become isotropic (Ph-Is). The correlation existing between the thermal behavior, phase structure and length of the alkyl side chain has been demonstrated.Peer ReviewedPostprint (published version

Isohexide and sorbitol-derived, enzymatically synthesized renewable polyesters with enhanced Tg

Sugar-based polyesters derived from sorbitol and isohexides were obtained via solvent-free enzymatic catalysis. Pendant hydroxyl groups, coming from the sorbitol units, were present along the polyester backbone, whereas the two isohexides, namely, isomannide and isoidide dimethyl ester monomers, were selected to introduce rigidity into the polyester chains. The feasibility of incorporating isomannide as a diol compared to the isoidide dimethyl ester as acyl-donor via lipase-catalyzed polycondensation was investigated. The presence of bicyclic units resulted in enhanced Tg with respect to the parent sorbitol-containing polyester lacking isohexides. The different capability of the two isohexides to boost the thermal properties confirmed the more flexible character provided by the isoidide diester derivative. Solvent-borne coatings were prepared by cross-linking the sugar-based polyester polyols with polyisocyanates. The increased rigidity of the obtained sugar-based polyester polyols led to an enhancement in hardness of the resulting coatings.Peer ReviewedPostprint (author's final draft

Fully bio-based aromatic–aliphatic copolyesters: poly(butylene furandicarboxylate-co-succinate)s obtained by ring opening polymerization

Poly(butylene 2,5-furandicarboxylate-co-succinate) copolyesters (coPBFxSy) have been synthesized by ring opening polymerization (ROP). Cyclic butylene 2,5-furandicarboxylate and butylene succinate oligomer mixtures, to be used as monomers for ROP, were prepared by high dilution condensation and enzymatic cyclization reactions, respectively. Two different catalytic systems, tin dioctanoate and supported Candida antarctica lipase B (CALB), were used for polymerization. Thus two series of copolyesters covering the whole range of compositions were prepared and their properties comparatively examined. In both cases, random copolyesters with compositions close to those used in their respective feeds were obtained. The influence of composition on reaction kinetics with respect to time and temperature was evaluated for the two series. Chemically catalyzed ROP rendered copolyesters with Mw in the ~50 000–65 000 g mol-1 range, whereas values between 15 000 and 45 000 g mol-1 were attained when the ROP reaction was assisted by CALB. The thermal behavior of coPBFxSy obtained by ROP was similar to that reported for such copolymers prepared by melt polycondensation. They all start to decompose above 300 °C and display melting enthalpy and temperatures that decrease with copolymerization, attaining minimum values when the comonomer contents are approximate to balance. On the contrary, the glass-transition temperature increased almost linearly with the content of butylene furandicarboxylate units, covering the whole range of values between those of the two parent homopolyesters. Small deviations in thermal properties observed between the two series could be attributed to their differences in molecular weights. Hydrolytic and enzymatic degradation studies revealed that coPBFxSy became more degradable with increasing content of succinic units, whereas the homopolyester PBF remained practically unaffected when incubated under similar conditions.Peer ReviewedPostprint (author's final draft