Multiple Reactive Groups Research Articles

Effects of Hybrid POSS Nanoparticles on the Properties of Thermoplastic Elastomer-Toughened Polyamide 6.

In this study, polyamide 6 (PA6)/thermoplastic elastomer (TPE) blends were prepared to decrease the notch sensitivity of PA6 for automotive applications, and the morphological, rheological, mechanical, and thermal properties of PA6/TPE blends, which are partially miscible or immiscible depending on the TPE ratio, were significantly improved in the existence of polyhedral oligomeric silsesquioxane (POSS) nanoparticles with multiple reactive epoxy groups as compatibilizers. An unstable phase morphology was obtained with the addition of TPE into PA6 without POSS nanoparticles, whereas interfacial interactions between phases in the presence of POSS were enhanced as a result of a significant decrease in the average particle size from 1.39 to 0.41 μm. The complex viscosity value of the 70PA6/30TPE blend, which was 20 kPa/s-1 at 0.1 rad/s angular frequency, reached 380 kPa/s-1 with the addition of POSS due to the formation of long chains by the generation of graft and/or block copolymers, which resulted in a 65% increase in Young's modulus value. Most notably, the Izod impact strength of pure PA6, which was 10 kJ/m2, increased by 290% with the incorporation of POSS. It was confirmed by FTIR analysis that the reactive multiple epoxy groups of MultEpPOSS and EPPOSS nanoparticles react with the proper groups of PA6 and/or TPE, and also, a partial hydrogen bonding interaction occurs between PA6-TPE from the shifting of N-H and carbonyl peaks. In conclusion, it can be suggested that POSS nanoparticles can serve as highly effective compatibilizers for PA6/TPE blends and have potential commercial applications, especially in the automotive sector.

Multifunctional composite binder with synergistic transport mechanism to achieve high performance all-solid-state batteries

All-solid-state batteries (ASSBs) using solid polymer electrolytes (SPEs) show a wide range of prospects in many aspects, but they do not perform well at high current densities. In order to solve the above problems, much effort has been spent on the improvement of electrolyte materials, but there is a lack of research on binders. This paper emphasizes the critical role played by the binder in the positive plates without any liquid infiltration,and an aqueous composite binder (CB) is designed by utilizing the characteristics of polyethylene oxide (PEO) and carboxymethyl cellulose lithium (CMC-Li) in lithium-ions transport. Electrochemical and Fourier transform infrared spectrometer (FTIR) tests demonstrate that the two polymers in the CB build a high-speed channel for migrating lithium-ions through synergistic action. The binder containing multiple reactive groups is tested to be highly competitive in both mechanical and electrochemical properties, which creates sufficient conditions for achieving high-performance ASSBs. The cells with CB as the binder are assembled which show a capacity of 65.5 mAh·g−1 at a current density of 3C while PVDF-based ASSBs exhibit only 3.3 mAh·g−1, and exhibit a capacity retention of 86.7% after 700 charge/discharge cycles at 0.5C (for comparison, PVDF-based ASSBs exhibit only 42.5%). This novel composite binder provides guidance for the further development of solid polymer batteries.

Polymeric phase change material networks based on multi-telechelic polyethylene glycol-derived multimer structures for thermal energy storage

Multi-telechelic polyethylene glycol (PEG)-based multimers with multiple reactive groups at both ends of the molecular chains can be used to prepare solid–solid phase change materials (PCMs) networks with enhanced mechanical strength, shape stability, PEG weight and adjustability in crosslink density, denoted as multi-telechelic effect in this report. Herein, multi-telechelic PEG-based PCMs networks were synthesized via the crosslinking reactions between designed hydroxyl-terminated multi-telechelic PEG-based multimers and curing agents, whose parameters can be readily tuned by the structure of multi-telechelic PEG-based multimers, for example, the number of PEG-derived structural units and the functionality of curing agents. Compared to conventional di-telechelic diethanolamine (DEA)-cured PCMs (DPCMs), the multi-telechelic tri-hexamethylene diisocyanate-cured PCMs (TPCMs) increase to 8–50 times in the storage modulus while decreasing only by 9.4 % in melting latent heat (ΔHm). The ΔHm of TPCMs increases by 58.2 % from 77.0 J/g to 121.8 J/g with increasing the number of PEG-derived structural units (y) from 1 to 4 when PEG with a number-average molecular weight of 4 kDa was used. TPCMs possess fine shape and thermal stability as well as thermal reliability while the reprocessability of PCMs is endowed by introducing a transcarbamoylation catalyst. The multi-telechelic PEG-based multimers can provide an alternative approach towards high-performance PCMs networks.

Environmentally benign flame-retardant cotton fabric with superior anti-wrinkle performance and restorable flame retardancy

Flammability and wrinkling are major defects that enormously restrict its application of cotton fabric in daily life. Herein, a N-heterocyclic compound with ammonium phosphate ester groups (PNH) was synthesized and served as a cross-linking agent to simultaneously enhance the flame-retardant and anti-wrinkle properties of cotton fabric. Fabric treated by 20 wt% PNH solution (CT/PNH20) possessed a wrinkle recovery angle of 234.8° and an LOI value of 42.7 %. It still self-extinguished during combustion even after 50 washing times, and the deterioration in flame retardancy mainly resulted from the formation of sodium phosphates during washing. Its LOI value after 50 washing times restored to 37.8 % from 27.5 % by a facile ion exchange strategy, revealing remarkable flame-retardant restorability. This work provides new insights into simultaneously enhancing the flame-retardant, anti-wrinkle performances of cotton fabric and restoring the flame retardancy of treated fabric after washing via facile and eco-friendly approaches. • A N-heterocyclic compound with multiple reactive groups (PNH) was synthesized. • PNH conferred superior flame-retardant and anti-wrinkle properties to cotton fabric. • Treated cotton fabric showed remarkable flame-retardant durability and restorability.

Flame retardant polypropylene with a single molecule intumescent flame retardant based on chitosan

A single molecule intumescent flame retardant was synthesized through in-situ polymerization by chitosan-based ammonium polyphosphate microencapsulated by melamine-formaldehyde resin. The multiple reactive hydroxyl and amino groups in its molecular chain made it a positively charged polymer with excellent coordination. The decomposition of melamine-formaldehyde resin produced a large amount of incombustible gas, which reduced the heat absorption on the surface of the composite material and inhibited its decomposition. Through thermogravimetric analysis, it was found that its thermal stability was better at high temperatures. Due to the decomposition of melamine-formaldehyde resin, a large amount of incombustible gas was produced, which reduced the heat absorption on its surface and inhibited its decomposition, so that polypropylene composites containing the flame retardant had a smooth decomposition process. The burning results showed that the limiting oxygen index and vertical combustion grade of the polypropylene composites containing the flame retardant had been improved, which the vertical combustion rating was V-1, and the limiting oxygen index was 25.7%. At the same time, it was clearly observed that composites containing the single-molecule intumescent flame retardant had an excellent anti-dripping effect. The surface temperature of the composite material was greatly reduced during combustion, from 343.7 ℃ to 156.9 ℃. Raman spectra and SEM of the surface carbon layer of the burned spline revealed the composite containing the flame retardant with a lower ID/IG value, indicating that the carbon layer it formed had more excellent crystallinity. Therefore, its carbon layer had a better structure and stability. It could be borne out that our single-molecule intumescent flame retardant had a good flame retardant effect on PP.

Ultrasmall Superparamagnetic Iron Oxide Nanoparticles as Nanocarriers for Magnetic Resonance Imaging: Development and In Vivo Characterization.

Ultrasmall superparamagnetic iron oxide nanoparticles (uSPIOs) are attractive platforms for the development of smart contrast agents for magnetic resonance imaging (MRI). Oleic acid-capped uSPIOs are commercially available yet hydrophobic, hindering in vivo applications. A hydrophilic ligand with high affinity toward uSPIO surfaces can render uSPIOs water-soluble, biocompatible, and highly stable under physiological conditions. A small overall hydrodynamic diameter ensures optimal pharmacokinetics, tumor delivery profiles, and, of particular interest, enhanced T 1 MR contrasts. In this study, for the first time, we synthesized a ligand that not only fulfills the as-proposed properties but also provides multiple reactive groups for further modifications. The synthesis delivers a facile approach using commercially available reactants, with resultant uSPIO-ligand constructs assembled through a single-step ligand exchange process. Structural and molecular size analyses confirmed size uniformity and small hydrodynamic diameter of the constructs. On average, 43 reactive amine groups were present per uSPIO nanoparticle. Its r 1 relaxivity has been tested on a 7 Tesla MR instrument and is comparable to that of the clinically available T 1 gadolinium-based contrast agent GBCA (1 vs 3 mM-1 s-1, respectively). A significant decrease in tumor T1 (15%) within 1 h of injection and complete signal recovery after 2 h were detected with a dose of 7 μg Fe/g mouse. The agent also has high r 2 relaxivity and can be used for T 2 contrast-enhanced MRI. Taken together, good relaxation and delivery properties and the presence of multiple surface reactive groups can facilitate its application as a universal MRI-compatible nanocarrier platform.

Mussel-inspired polyphenol/polyethyleneimine assembled membranes with highly positive charged surface for unprecedented high cation perm-selectivity

Mono/multivalent cation separation techniques have shown increasing importance in diverse environmental and energy applications. The separation performance of emerging monovalent cation exchange membranes (MCEMs) is greatly determined by the architecture and charge property of MCEMs, which should be finely tuned for the energy efficiency applications. Herein, a series of mussel-inspired polyphenol/polyethyleneimine assembled membranes (PPAMs) with highly positively-charged surfaces were elegantly constructed through a facile layer-by-layer assembly method. Based on the synergetic reactions between polyphenols with multiple reactive groups and PEI with abundant amino groups, the denser membrane surfaces with a higher crosslinking degree and more positive charges were readily formed. As a result, the Na+/Mg2+ and Li+/Mg2+ perm-selectivities of PPAMs with such surface architecture and charge property followed the same order as gallic acid/polyethyleneimine membrane (M-GA/PEI) > pyrogallic/polyethyleneimine membrane (M-Pyrogallic/PEI) > protocatechuic acid/polyethyleneimine membrane (M-PA/PEI) > caffeic acid/polyethyleneimine membrane (M-CA/PEI). Most interestingly, the M-GA/PEI fabricated exhibited the unprecedented perm-selectivity (Na+/Mg2+) up to 180.4 with Na+ flux of 6.01 × 10−8 mol cm−2 s−1, which exceeded the current “Upper Bound” plot of MCEMs. The low membrane resistance and excellent separation performance of PPAMs brought great potential for resource recovery and environmental remediation.

Tyrosine-Based Dual-Functional Interface for Trapping and On-Site Photo-Induced Covalent Immobilization of Proteins.

Tyrosine, a simple and well-available natural amino acid, is featured by the small size of the compound that contains multiple reactive groups. This study developed an efficient bioconjugation strategy using tyrosine-based dual-functional interfaces. When tyrosine molecules are immobilized on the surface of a supporting material through amino groups, their carboxyl groups can function as an attracting trap due to their anionic nature at neutral pH and ability to chelate nickel(II) ions (Ni2+), allowing the capture and enrichment of cationic proteins and histidine (His)-tagged proteins on the surface. The trapped proteins can be further covalently immobilized on site through ruthenium-mediated photochemical cross-linking, which has been found to be highly efficient and can be completed within minutes. This strategy was successfully applied to two different material systems. We found that tyrosine-modified agarose beads had a binding capacity of the His-tagged enhanced green fluorescent protein comparable to that of commonly used nitrilotriacetic acid-based resins, and further covalent coupling via dityrosine cross-linking achieved a yield of 85% within 5 min, without compromising much on its fluorescence activity. On the surface of tyrosine-modified 316L stainless steel, lysozyme was captured through electrostatic interaction and further immobilized. The resultant surface exhibited remarkable antibacterial activity against both Staphylococcus aureus and Escherichia coli. Such a tyrosine-based capture-then-coupling method is featured by its simplicity, high coupling efficiency, and high utilization rate of target molecules, making it particularly suitable for the proteins that are highly priced or vulnerable to general immobilization chemistry.

Preparation of multiple-reactive-site and flexible crosslinking agent with transaconitic acid and acrylic acid and its application for three-dimensional crosslinking of cellulose

A novel multiple-reactive-site crosslinking agent, P(TAA‒AA), was developed from transaconitic acid and acrylic acid in this study. Cotton fabrics with durable wrinkle-resistant properties were obtained by crosslinking with P(TAA‒AA), which benefited from the multifunctional carboxyl groups of crosslinking agents and the three-dimensional crosslinking inside cotton fibers. The wrinkle-resistant properties of P(TAA‒AA)-modified fabrics were evaluated and compared with those of other polycarboxylic acid-treated fabrics, and the P(TAA‒AA)-modified fabrics showed a wrinkle recovery angle of 262° as high as the 1,2,3,4-butanetetracarboxylic acid-modified fabrics while maintaining nearly two-fold higher tearing strength retention (62.9%), and they showed a much higher value of whiteness index than the citric acid-modified fabrics. This demonstrated that the obtained P(TAA‒AA) is an ideal polycarboxylic acid already known to date simultaneously to realize the high wrinkle recovery angle and high tearing strength retention for treated cotton fabrics. The Raman depth mapping images and the scanning electron microscope images of P(TAA‒AA)-modified samples indicated that P(TAA‒AA) molecules can diffuse into the amorphous regions of the cellulose fibers and form crosslinking bridges between cellulose chains. The multiple reactive carboxyl groups in P(TAA‒AA) may form three or more ester bonds between the P(TAA‒AA) molecule and different cellulose chains, which were regarded as the main contribution to the high crosslinking effectiveness of the P(TAA‒AA)-modified fabrics.

Development of soybeans starch based tough, water resistant and mildew-proof adhesives through multiple cross linking cooperation strategy

The exploitation of the environment-friendly and renewable biomass adhesive is a promising alternative compared to petroleum-based ones in the wood industry. In this study, soybean flour (SF) was chosen as a renewable starting material for the preparation of the biomass adhesive. The soy protein structure was unfolded by the calcium hydroxide and multiple reactive groups (-COOH, –NH2, –OH, –SH) of the protein chain were exposed. Inspired by the marine mussel protein, tannic acid (TA) with many poly-catechol/pyrogallol groups was capable of interacting with protein molecules under the alkaline conditions and the strong metal coordination between Ca2+ and TA enable to reinforce the network structure of adhesive. Furthermore, the incorporation of 1,6-Hexanediol diglycidyl ether (HDE) into the pristine protein adhesive had reacted with protein molecules via chemical covalent bonds to form the stable and toughness cross-linking network. The as-obtained adhesive showed improved bonding strength and comparable water resistance. Notably, the enhanced adhesive showed an outstanding wet shear strength of 1.12 MPa, meeting China's interior furnishing requirements (≥0.7 MPa). Additionally, in contrast to unmodified adhesive, the mildew resistance of the cooperation modified adhesive was improved and the storage life extended. This research provides a novel and green way to develop a formaldehyde-free adhesive for the wood industry.

Preparation, characterization and testing of flame retardant cotton cellulose material: flame retardancy, thermal stability and flame-retardant mechanism

It is significant to treat cotton fabrics with flame retardant, which can effectively protect them from damage in the fire. A novel reactive flame retardant coating, ammonium salt of N,N-dimethylene-piperazine-(methylphosphonic acid) (ASNDP), was prepared and employed to enhance the anti-burning effect of pure cotton fabrics. Fourier transform infrared spectroscopy and nuclear magnetic resonance spectrum were used to analyze the chemical composition of the synthesized ASNDP. The combustion behavior and anti-burning performance of coated cotton fabrics were fully investigated with using cone calorimetry test, limited oxygen index (LOI) test and vertical flammability test. The total heat release value of the sample coated with ASNDP (450 g/L) decreased to 3.7 ± 0.1 MJ/m2 and the LOI value of the sample with a weight gain of 17.4 ± 0.3% raised to 29.5 ± 0.1%. The thermal and thermo-oxidative stability of coated cotton fabrics were researched with thermogravimetric analysis. The integral procedural decomposition temperature (IPDT) value of coated cotton fabrics in nitrogen atmosphere increased from 610.1 to 1402.8 °C, which proved that ASNDP inhibited the thermal degradation of fiber unit by promoting the growth of the char layer. Besides, the morphological structure of uncoated and coated samples before and after combustion was characterized by scanning electron microscopy. It can be observed that the fiber skeleton of the coated cotton fabrics was evenly distributed and remained intact after combustion. The conclusion was that ASNDP endowed cotton fabrics with good flame retardancy, and effectively performed the flame-retardant effect in both gas phase and the condensed phase. A novel phosphorus–nitrogen synergistic flame retardant containing multiple reactive groups was successfully synthesized and applied to improve the flame retardancy and thermal stability of pure cotton fabrics.

Semi‐Interpenetrating Polymer Electrolyte as a Coating Layer Constructed on Polyphenylene Sulfide Nonwoven to Afford Superior Stability and Performance for Lithium‐Ion Batteries

AbstractHigh power lithium‐ion battery (LIB) puts forward higher requirements for separator. In this study, a new composite separator (SIPN/PPS) with superior stability and improved electrochemical performance was fabricated by the construction of semi‐interpenetrating polymer network (SIPN) on polyphenylene sulfide (PPS) nonwoven substrate. In SIPN, branched polyethyleneimine (PEI) was selected as crosslinking points due to multiple reactive terminal groups −NH2. Meanwhile, PEI owned irregular topology structure, which would be beneficial to interrupt the crystallization of polymer matrix and increase electrolyte storage by swelling. Characterization results show that this designed composite separator can exhibit higher porosity, improved electrolyte wettability, enhanced electrolyte uptake and excellent electrochemical performance, thus endowing battery with superior discharge capacity even at 3 C. In addition, the introduction of SIPN is confirmed to increase mechanical strength more obviously than that of single cross‐linked network reported in previous study. Meanwhile, anode current begins to be detected for SIPN/PPS composite separator under higher applied voltage (4.6 V vs Li+/Li), indicating its broader electrochemical window. Moreover, SIPN/PPS composite separator is displayed satisfactory cycling stability with higher discharge capacity retention ratio (85.3 %). Consequently, this contribution opens a new avenue for separator applied in high power LIB.

Synthesis and Biopharmaceutical Characterization of Amphiphilic Squalenyl Derivative Based Versatile Drug Delivery Platform.

Limited drug loading capacity (LC), mostly below 5% w/w, is a significant drawback of nanoparticulate drug delivery systems (DDS). Squalenoylation technology, which employs bioconjugation of squalenyl moiety and drug, allows self-assemble of nanoparticles (NPs) in aqueous media with significantly high LC (>30% w/w). The synthesis and particle preparation of squalenoylated prodrugs are, however, not facile for molecules with multiple reactive groups. Taking a different approach, we describe the synthesis of amphiphilic squalenyl derivatives (SqDs) as well as the physicochemical and biopharmaceutical characterizations of their self-assembled NPs as DDSs. The SqDs included in this study are (i) cationic squalenyl diethanolamine (ii) PEGylated SqD (PEG 750 Da), (iii) PEGylated SqD (PEG 3,000 Da), and (iv) anionic squalenyl hydrogen sulfate. All four SqDs self-assemble into NPs in a size range from 100 to 200 nm in an aqueous solution. Furthermore, all NP derivatives demonstrate appropriate biocompatibility and adequate colloidal stability in physiological relevant pH environments. The mucoprotein binding of PEGylated NPs is reduced compared to the charged NPs. Most importantly, this technology allows excellent LC (at maximum of 45% w/w) of a wide range of multifunctional compounds, varying in physicochemical properties and molecular weight. Interestingly, the drug release profile can be tuned by different loading methods. In summary, the SqD-based NPs appear as versatile drug delivery platforms.

Improving the fracture toughness and flame retardant properties of epoxy thermosets by phosphaphenanthrene/siloxane cluster-like molecules with multiple reactive groups

To meet the increasingly stringent requirements for the fire safety and mechanical properties of epoxy thermoset (EP) in advanced manufacturing industry, two kinds of phosphaphenanthrene/siloxane cluster-like molecules with multiple reactive groups (TriDSi and TetraDSi) were synthesized, and then linked into the cross-linked network of epoxy thermoset, separately. The incorporated TriDSi and TetraDSi improved the fracture toughness and flame retardant performance of epoxy thermoset, simultaneously. The impact strength of 6%TriDSi/EP and 6%TetraDSi/EP both increased by more than 120%, compared with that of neat epoxy thermoset. Meanwhile, 6%TriDSi/EP and 6%TetraDSi/EP both passed UL94 V-0 rating with a limited oxygen index of 35.2% and 36.0%, respectively. Moreover, the heat release of burning thermoset was also suppressed significantly by incorporated cluster-like molecules. Through segmer-aggregation toughening effect and group-aggregation flame retardant effect, the cluster-like molecules TriDSi and TetraDSi endowed epoxy thermoset with superior fracture toughness and significantly lowered combustibility. This study provides a promising choice to manufacture advanced epoxy thermoset materials.

Synthesis of three novel amino acids-based flame retardants with multiple reactive groups for cotton fabrics

Three novel high efficient, halogen-free and formaldehyde-free flame retardants containing –P=O(O−NH4+)2 and –COO−NH4+ multiple reactive groups, ammonium salt of N,N-bis(phosphonomethyl) glycine (FR-G), ammonium salt of N,N-bis(phosphonomethyl) aspartic acid (FR-A) and ammonium salt of N,N,N,N-tetra(phosphonomethyl) lysine (FR-L), were synthesized for cotton fabric based on glycine, aspartic acid and lysine. The flame retardant properties and thermal stabilities of treated cotton fabrics were evaluated by limiting oxygen index (LOI), vertical flammability test, cone calorimetry test and thermogravimetric analysis (TG). The modifications and flame retardant mechanisms were investigated by TG-IR, FTIR, SEM, EDX. The comparison of three flame retardants was also investigated. The results reveal that flame retardants could graft on cotton fabric by the formation of P–O–C and C–O–C covalent bonds, the LOI value of cotton fabric treated by 30% FR-L could achieve 42.1%, which remained well after 40 laundering cycles with a LOI value of 27.1%. Vertical flammability test and cone calorimetry test also show that the flame retardancy of modified cotton fabrics was greatly improved. The results indicate that cellulose was phosphorylated by these flame retardants to prevent the formation of levoglucosan and promote the dehydration and charring. Moreover, the physical properties of treated cotton fabrics were maintained well.

Chemoselective Carbonyl Allylations with Alkoxyallylsiletanes.

Alkoxyallylsiletanes are capable of highly chemo- and diastereoselective carbonyl allylsilylations. Reactive substrates include salicylaldehydes and glyoxylic acids. Chemoselectivity in these reactions is thought to arise from a mechanism involving first exchange of the alkyoxy group on silicon with a substrate hydroxyl followed by activation of a nearby carbonyl by the Lewis acidic siletane and intramolecular allylation. In this way, substrates containing multiple reactive carbonyl groups (e.g., dialdehyde or triketone) can be selectively monoallylated, even overcoming inherent electrophilicity bias.

Sodium Hydroxide-Free Soy Protein Isolate-Based Films Crosslinked by Pentaerythritol Glycidyl Ether.

The soy protein isolate (SPI), sodium dodecylbenzenesulfonate (SDBS) and pentaerythritol glycidyl ether (PEGE) were used to make biodegradable films in this study. Unlike the usual method that adding sodium hydroxide (NaOH) during the SPI-based film casting, SDBS was used as a surfactant playing the similar role as NaOH. Since NaOH is a chemical with corrosiveness and toxicity, the replacing of NaOH by SDBS might reduce the hazard threat during the utilization of SPI-based films in food packing application. Furthermore, the presentation of SDBS helped dispersing the hydrophobic PEGE into the hydrophilic SPI. PEGE is a crosslinking agent with multiple reactive epoxy groups. The chemical structures and micro morphologies of the fabricated films were investigated by means of FTIR, XRD, and SEM. The thermal stabilities of the films were examined by means of the thermo-gravimetric analysis. After the chemical crosslinking, the ultimate tensile strength of the film was significantly increased, meanwhile, the water absorption was dramatically decreased. It was concluded that the SPI-based film containing 4% PEGE achieved the optimal performance.

DEVELOPMENT OF MUCOADHESIVE CHITOSAN-BASED DRUG DELIVERY SYSTEM

Chitosan is a highly versatile biopolymer characterised by low toxicity, biocompatibility, and slow but complete biodegradation in the human body, possessing multiple reactive groups. One of the most well-known properties of positively charged chitosan derivatives is their ability to bind mucous membranes. The aim of this work was the analysis of mucoadhesion of unmodified 20 kDa chitosan and its hydrophobic (HC) and hydrophobic quaternised (QHC) derivatives in vitro and ex vivo. Unmodified chitosan formed large aggregates in vitro in keratinocyte and colon cell cultures and ex vivo in murine small intestine and muscle explants. At the same time, HC and especially QHC bound cells in vitro and ex vivo in a fine dotted manner, as evidenced by confocal microscopy. Such a pattern of hydrophobic derivatives distribution provides the possibility to develop mucoadhesive drug delivery systems with increased local drug release and improved chitosan biodegradation.

A theoretical study on the antioxidant activity of Uralenol and Neouralenol scavenging two radicals

Uralenol and neouralenol are two typical licorice root extracts that presents multiple reactive hydroxyl groups, which are considered as good free radical scavengers. A theoretical study on the primary antioxidant activity of uralenol and neouralenol toward hydroxyl and hydroperoxyl radicals has been carried out using the density functional theory (DFT). A total of 10 reaction pathways of uralenol and neouralenol scavenging two radicals in gas phase and in water phase have been tracked. Neouralenol was found to be a better hydroxyl and hydroperoxyl scavenger than uralenol. In vivo, the more reactive sites in uralenol are U5 and U’1, respectively, for scavenging ·OH and ·OOH; and the more reactive sites in neouralenol are N4 and N’5 for scavenging ·OH and ·OOH, respectively.

Tunable, Chemo- and Site-Selective Nitrene Transfer Reactions through the Rational Design of Silver(I) Catalysts

Carbon-nitrogen (C-N) bonds are ubiquitous in pharmaceuticals, agrochemicals, diverse bioactive natural products, and ligands for transition metal catalysts. An effective strategy for introducing a new C-N bond into a molecule is through transition metal-catalyzed nitrene transfer chemistry. In these reactions, a metal-supported nitrene can either add across a C═C bond to form an aziridine or insert into a C-H bond to furnish the corresponding amine. Typical catalysts for nitrene transfer include Rh2Ln and Ru2Ln complexes supported by bridging carboxylate and related ligands, as well as complexes based on Cu, Co, Ir, Fe, and Mn supported by porphyrins and related ligands. A limitation of metal-catalyzed nitrene transfer is the ability to predictably select which specific site will undergo amination in the presence of multiple reactive groups; thus, many reactions rely primarily on substrate control. Achieving true catalyst-control over nitrene transfer would open up exciting possibilities for flexible installation of new C-N bonds into hydrocarbons, natural product-inspired scaffolds, existing pharmaceuticals or biorenewable building blocks. Silver-catalyzed nitrene transfer enables flexible control over the position at which a new C-N bond is introduced. Ag(I) supported by simple N-donor ligands accommodates a diverse range of coordination geometries, from linear to tetrahedral to seesaw, enabling the electronic and steric parameters of the catalyst to be tuned independently. In addition, the ligand, Ag salt counteranion, Ag/ligand ratio and the solvent all influence the fluxional and dynamic behavior of Ag(I) complexes in solution. Understanding the interplay of these parameters to manipulate the behavior of Ag-nitrenes in a predictable manner is a key design feature of our work. In this Account, we describe successful applications of a variety of design principles to tunable, Ag-catalyzed aminations, including (1) changing Ag/ligand ratios to influence chemoselectivity, (2) manipulating the steric environment of the catalyst to achieve site-selective C-H bond amination, (3) promoting noncovalent interactions between Ag/substrate or substrate/ligand to direct C-H functionalization, and (4) dictating the substrate's trajectory of approach to the Ag-nitrene. Our catalysts distinguish between the aminations of various types of C-H bonds, including tertiary C(sp3)-H, benzylic, allylic, and propargylic C-H bonds. Efforts in asymmetric nitrene transfer reactions catalyzed by Ag(I) complexes are also described.