Improved Lignin Polyurethane Properties with Lewis Acid Treatment

Chemical modification strategies to improve the mechanical properties of lignin-based polyurethanes are presented. We hypothesized that treatment of lignin with Lewis acids would increase the concentration of hydroxyl groups available to react with diisocyanate monomers. Under the conditions used, hydrogen bromide-catalyzed modification resulted in a 28% increase in hydroxyl group content. Associated increases in hydrophilicity of solvent-cast thin films were also recorded as evidenced by decreases in water contact angle. Polyurethanes were then prepared by first preparing a prepolymer based on mixtures of toluene-2,4-diisocyanate (TDI) and unmodified or modified lignin, then polymerization was completed through addition of polyethylene glycol (PEG), resulting in mass ratios of TDI:lignin:PEG of 43:17:40 in the compositions investigated here. The mixture of TDI and unmodified lignin resulted in a lignin powder at the bottom of the liquid, suggesting it did not react directly with TDI. However, a homogeneous solution resulted when TDI and the hydrogen bromide-treated lignin were mixed, suggesting demethylation indeed increased reactivity and resulted in better integration of lignin into the urethane network. Significant improvements in mechanical properties of modified lignin polyurethanes were observed, with a 6.5-fold increase in modulus, which were attributed to better integration of the modified lignin into the covalent polymer network due to the higher concentration of hydroxyl groups. This research indicates that chemical modification strategies can lead to significant improvements in the properties of lignin-based polymeric materials using a higher fraction of an inexpensive lignin monomer from renewable resources and a lower fraction an expensive, petroleum-derived isocyanate monomer to achieve the required material properties

Functionalized polyolefin graft copolymers via transition metal-catalyzed C--H activation and controlled radical polymerization

Polyolefin is the most widely used commercial polymer in the world. Currently, approximately 60% of total volume of polymer production is based on polyolefin materials because of their good mechanical, chemical properties, as well as low production cost. However, poor compatibility with polar materials (metals, ceramics, and polar polymers) remains a problem that limits further application of this indispensable material. Introduction of the polar group into the polyolefin has been suggested as the best way to overcome this drawback. However, the inherent inertness of polyolefin has made the introducing polar group difficult. Although free radical modification of commercial polyolefin, copolymerization with protected polar vinyl monomer and subsequent deprotection, and copolymerization using oxophilic late transition metal have been adopted to introduce polar groups on polyolefins, these methods still displayed serious shortcomings in terms of controlling polymer structures, molecular weights, and concentrations of polar groups; We report a novel approach that allows us to introduce polar groups into a commercial polyolefin, isotactic poly(1-butene), while maintaining original properties of the polymer: regioselective rhodium catalyzed C-H borylation of side chains of poly(1-butene) and the subsequent oxidation of the boronic ester to hydroxyl group. (Abstract shortened by UMI.)

Rapidly Cross-Linkable DOPA Containing Terpolymer Adhesives and PEG-Based Cross-Linkers for Biomedical Applications

A new three-component bio-inspired adhesive was synthesized that is a terpolymer composed of a water-soluble segment, an interfacial adhesion segment, and a cross-linking segment. Strong wet adhesion properties are obtained utilizing a 3,4-dihydroxy-l-phenylalanine (DOPA) moiety. Poly(acrylic acid) provides high water solubility due to strong ionic interactions with water. An acrylic acid N-hydroxysuccinimide ester (NHS) was included in the adhesive polymer to allow rapid cross-linking with thiol-terminated, 3-armed poly(ethylene glycol) cross-linking agents. The thiol terminal poly(ethylene glycol) was designed to be bulky to avoid possible penetration of molecules to the cell and tissue. The NHS and thiol groups react within 30 s to form covalent bonds. This design allows for rapid optimization of properties for specific applications. Lap shear strength tests on wet porcine skin demonstrated a 190% increased value in adhesion strength for adhesives having the DOPA moiety. After cross-linking, adhesion was enhanced by 450% over poly(acrylic acid-co-acrylic acid NHS) and was 240% higher than un-cross-linked poly(acrylic acid-co-acrylic acid NHS-co-N-methacryloyl-3,4-dihydroxyl-l-phenylalanine). Rheology studies show adhesive viscosity drops significantly at high shear rates, demonstrating its potential to be injected via syringe. The cross-linked adhesive displayed much stronger mechanical properties and higher elastic and viscous moduli than an un-cross-linked adhesive model. Furthermore, the cross-linked adhesive has enhanced moduli near body temperature (38 °C) as compared to room temperature (23 °C), increasing the applications as a biomedical adhesive

Rapidly crosslinkerable bio-inspired adhesives for biomedical applications

A new three component bio-inspired adhesive was synthesized. The new adhesive is a terpolymer composed of water sol. segment, interfacial segment and crosslinking segment. Strong wet adhesion properties are obtained utilizing 3,4-dihydroxy-L-phenylalanine (DOPA) moiety as the interfacial segment. Polyacrylic acid provides high water soly., thanks to strong ionic interactions with water. Acrylic acid N-hydroxysuccinimide ester (NHS) was included in the adhesive polymer to allow rapid crosslinking with thiol terminated, 3-armed polyethylene glycol crosslinking agents. Thiol terminal PEG was designed to have bulky vol. to avoid possible penetration of mols. to the cell and tissue. NHS and thiol group react very rapidly within 30 s to form covalent bonds. This rapid NHS-thiol group reaction formed mech. stable crosslinked adhesives which have strong wet adhesion properties. Lap shear strength test on wet porcine skin demonstrated a 190 % increased value in adhesion strength for adhesives having the DOPA moiety. After crosslinking, adhesion enhanced by 450 % over poly(acrylic acid-co-acrylic acid NHS) and 240 % higher than uncrosslinked poly(acrylic acid-co-acrylic acid NHS-co-DOPA)

Visible-Light Induced Thiol–Ene Reaction on Natural Lignin

The current use of lignin as a raw material is very limited and focused only on cheap and poorly defined nonfunctional materials mainly due to challenges in synthetic modification of lignin. Herein, we report a new low energy and environmentally friendly lignin modification method induced by visible blue light. The key modification reaction is a photoredox catalyzed thiol–ene reaction. The lignin was modified to possess alkenes for the thiol–ene reaction. Three photochemical reagentsRu­(bpy)₃Cl₂, Eosin Y, and 2,2-dimethoxy-2-phenylacetophenonewere tested to determine the best thiol–ene modification method. The thiol–ene reaction between lignin–alkene and 1-decanethiol revealed that Ru­(bpy)₃Cl₂ was the most efficient, resulting in conversions of 97% with 2.5 mol % catalyst loading. The Ru­(bpy)₃Cl₂ was further investigated with diverse thiol compounds. All tested thiol–ene reactions showed excellent efficiencies, with conversions of 93–97% under low-energy 3W blue LED light. In particular, thiol terminal poly­(ethylene glycol) also displayed 94% conversion after 80 min of irradiation. The developed photoredox catalyzed thiol–ene modification of lignin was very conveniently controlled by simply turning the light source on and off. Excellent conversion, 95%, of lignin thiol–ene modification was achieved even by natural sunlight after 4 h of irradiation

Fear conditioning and extinction distinctively alter bidirectional synaptic plasticity within the amygdala of an animal model of post-traumatic stress disorder

Synaptic plasticity in the amygdala plays an essential role in the formation and inhibition of fear memory; however, this plasticity has mainly been studied in the lateral amygdala, making it largely uninvestigated in other subnuclei. Here, we investigated long-term potentiation (LTP) and long-term depression (LTD) in the basolateral amygdala (BLA) to the medial division of the central amygdala (CEm) synapses of juvenile C57BL/6N (B6) and 129S1/SvImJ (S1) mice. We found that in naïve B6 and S1 mice, LTP was not induced at the BLA to CEm synapses, whereas fear conditioning lowered the threshold for LTP induction in these synapses of both B6 and S1 mice. Interestingly, fear extinction disrupted the induction of LTP at the BLA to CEm synapses of B6 mice, whereas LTP was left intact in S1 mice. Both low-frequency stimulation (LFS) and modest LFS (mLFS) induced LTD in naïve B6 and S1 mice, suggesting that the BLA to CEm synapses express bidirectional plasticity. Fear conditioning disrupted both types of LTD induction selectively in S1 mice and LFS-LTD, presumably NMDAR-dependent LTD was partially recovered by fear extinction. However, mLFS-LTD which has been known to be endocannabinoid receptor 1 (CB1R)-dependent was not induced after fear extinction in both mouse strains. Our observations suggest that fear conditioning enhances LTP while fear extinction diminishes LTP at the BLA to the CEm synapses of B6 mice with successful extinction. Considering that S1 mice showed strong fear conditioning and impaired extinction, strong fear conditioning in the S1 strain may be related to disrupted LTD, and impaired extinction may be due to constant LTP and weak LFS-LTD at the BLA to CEm synapses. Our study contributes to the further understanding of the dynamics of synaptic potentiation and depression between the subnuclei of the amygdala in juvenile mice after fear conditioning and extinction

Improved Lignin Polyurethane Properties with Lewis Acid Treatment

Chemical modification strategies to improve the mechanical properties of lignin-based polyurethanes are presented. We hypothesized that treatment of lignin with Lewis acids would increase the concentration of hydroxyl groups available to react with diisocyanate monomers. Under the conditions used, hydrogen bromide-catalyzed modification resulted in a 28% increase in hydroxyl group content. Associated increases in hydrophilicity of solvent-cast thin films were also recorded as evidenced by decreases in water contact angle. Polyurethanes were then prepared by first preparing a prepolymer based on mixtures of toluene-2,4-diisocyanate (TDI) and unmodified or modified lignin, then polymerization was completed through addition of polyethylene glycol (PEG), resulting in mass ratios of TDI:lignin:PEG of 43:17:40 in the compositions investigated here. The mixture of TDI and unmodified lignin resulted in a lignin powder at the bottom of the liquid, suggesting it did not react directly with TDI. However, a homogeneous solution resulted when TDI and the hydrogen bromide-treated lignin were mixed, suggesting demethylation indeed increased reactivity and resulted in better integration of lignin into the urethane network. Significant improvements in mechanical properties of modified lignin polyurethanes were observed, with a 6.5-fold increase in modulus, which were attributed to better integration of the modified lignin into the covalent polymer network due to the higher concentration of hydroxyl groups. This research indicates that chemical modification strategies can lead to significant improvements in the properties of lignin-based polymeric materials using a higher fraction of an inexpensive lignin monomer from renewable resources and a lower fraction an expensive, petroleum-derived isocyanate monomer to achieve the required material properties

Selectively Impaired Endocannabinoid-Dependent Long-Term Depression in the Lateral Habenula in an Animal Model of Depression

Abnormal potentiation in the lateral habenula (LHb) has been suggested to mediate depression-like behaviors. However, the underlying mechanisms of the synaptic efficacy regulation of LHb synapses and the potential for their modulation are only poorly understood. Here, we report that long-term synaptic depression (LTD) occurs in the LHb upon both low-frequency stimulation (LFS) and moderate-frequency stimulation (MFS). LFS-induced LTD (LFS-LTD) is accompanied by a reduction in presynaptic release probability, which is endocannabinoid (eCB) signaling dependent. Surprisingly, exposure to an acute stressor completely masks the induction of LFS-LTD in the LHb while leaving the MFS-induced LTD intact. Pharmacological activation of cannabinoid receptor 1 (CB1R) or blockade of αCaMKII successfully restored LTD in the LHb in an animal model of depression. Thus, our findings reveal a form of synaptic strength regulation and a stress-induced shift of synaptic plasticity in the LHb

Rapidly Cross-Linkable DOPA Containing Terpolymer Adhesives and PEG-Based Cross-Linkers for Biomedical Applications

A new three-component bio-inspired adhesive was synthesized that is a terpolymer composed of a water-soluble segment, an interfacial adhesion segment, and a cross-linking segment. Strong wet adhesion properties are obtained utilizing a 3,4-dihydroxy-l-phenylalanine (DOPA) moiety. Poly­(acrylic acid) provides high water solubility due to strong ionic interactions with water. An acrylic acid <i>N</i>-hydroxysuccinimide ester (NHS) was included in the adhesive polymer to allow rapid cross-linking with thiol-terminated, 3-armed poly­(ethylene glycol) cross-linking agents. The thiol terminal poly­(ethylene glycol) was designed to be bulky to avoid possible penetration of molecules to the cell and tissue. The NHS and thiol groups react within 30 s to form covalent bonds. This design allows for rapid optimization of properties for specific applications. Lap shear strength tests on wet porcine skin demonstrated a 190% increased value in adhesion strength for adhesives having the DOPA moiety. After cross-linking, adhesion was enhanced by 450% over poly­(acrylic acid-<i>co</i>-acrylic acid NHS) and was 240% higher than un-cross-linked poly­(acrylic acid-<i>co</i>-acrylic acid NHS-<i>co</i>-<i>N</i>-methacryloyl-3,4-dihydroxyl-l-phenylalanine). Rheology studies show adhesive viscosity drops significantly at high shear rates, demonstrating its potential to be injected via syringe. The cross-linked adhesive displayed much stronger mechanical properties and higher elastic and viscous moduli than an un-cross-linked adhesive model. Furthermore, the cross-linked adhesive has enhanced moduli near body temperature (38 °C) as compared to room temperature (23 °C), increasing the applications as a biomedical adhesive