Optimization of preparation of thermally stable cellulose nanofibrils via heat‐induced conversion of ionic bonds to amide bonds

Improving the thermal stability of nanocelluloses is important for practical applications such as melt compounded nanocellulose‐reinforced polymer composites and flexible substrates for nanocellulose‐containing electronic devices. Here, we report optimum conditions for a straightforward surface modification strategy for improving the thermal stability of 2,2,6,6‐tetramethypiperidine‐1‐oxyl (TEMPO)‐oxidized cellulose nanofibrils (TOCNs); the heat‐induced conversion of TOCN alkyl ammonium carboxylates to amides. Different amine‐terminated compounds (R‐NH₂) were grafted onto the surface of TOCNs under aqueous conditions. The influences of R‐NH₂ molecular weight, R‐NH₂/TOCN‐COOH molar ratio, and thermal stability of R‐NH₂ on the properties of the grafted TOCN films were investigated through infrared spectroscopy and thermogravimetric analysis. For maximum thermal improvement of up to 90 °C, complete ionic bonding of TOCN carboxy groups with R‐NH₂ was required, as well as proper selection of the R‐NH₂ compound. A controlled heating process was also needed to achieve effective ionic‐to‐amide bond conversion. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1750–1756     

Scalable synthesis of ionic liquids: comparison of performances of microstructured and stirred batch reactors

A range of alkylpyridinium bromide ionic liquids have been synthesized in a stirred reactor at multigram scale and characterized by physical methods (viscosity, conductivity, melting point, electrochemical window, and water content). One ionic liquid, octylpyridinium bromide, was chosen to be synthesized in both macro and reduced scale reactors, in order to compare its performance and to afford evidence of the advantages of a cross channel micro reactor (channel width = 1 mm) compared to a stirred reactor.     

Biodegradable photocrosslinkable poly(depsipeptide‐co‐ε‐caprolactone) for tissue engineering: Synthesis,characterization, and In vitro evaluation

Stereolithography has become increasingly popular in scaffold fabrication due to automation and well‐controlled geometry complexity, and consequently, there is a great need for new suitable biodegradable photocrosslinkable polymers. In this study, a new type of photocrosslinkable poly(ester amide) was synthesized based on ε‐caprolactone and l ‐alanine‐derived depsipeptide and was applied to fabrication of three‐dimensional (3D) scaffolds by stereolithography. ¹H nuclear magnetic resonance and Fourier transform infra‐red analysis confirmed the formation of new bonds during the polymer synthesis. Incorporation of depsipeptide increased the glass transition temperature and hydrophilicity of the polymer and accelerated hydrolytic degradation compared with the poly(ε‐caprolactone) homopolymer. The compressive strength of the 3D scaffolds increased with the increasing depsipeptide content. This work demonstrated that incorporation of depsipeptide into photocrosslinkable polyesters resulted in excellent cytocompatibility and tunable degradation rates and mechanical properties and thus expanded the repertoire of biomaterials suitable for 3D photofabrication of high‐resolution tissue engineering scaffolds. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3307–3315     

Nutation frequency modulation on NMR signal of nuclear spins in chemical exchange with solvent water under the BEST conditions

Solvent exchange properties of protein backbone amide protons provide valuable residue‐specific information on protein solvent accessibility, structure stability and flexibility and hence are of significant interest in structural biology. NMR has served as a unique means for the characterization of chemical exchange including proton amide exchange with solvent water at residue‐specific levels across a broad range of exchange rates. One of the methods used for the characterization of protein backbone amide exchange by NMR involves the use of progressive selective irradiation of the water resonance. Here, we report the experimental observation of the nutation frequency (strength of RF field used for the irradiation of water resonance) modulation on amide proton signals for those in exchange with the solvent water under the band‐selective excitation short transient (BEST) conditions. Compared with conventional saturation transfer of water magnetization experiments, this nutation frequency modulation observed on signal of nuclear spins under the BEST conditions potentially offers a quick identification of protein backbone amides in rapid exchange with solvent water. Copyright © 2014 John Wiley & Sons, Ltd.     

Solid‐Phase Synthesis of N‐Aryl‐N′‐Carboalkoxy Guanidines by the Mitsunobu Reaction of Fmoc‐Guanidines

Abstract

A new method for the solid‐phase synthesis of N‐aryl‐N′‐carboalkoxy guanidines is described. Aromatic amines were reacted with Fmoc‐isothiocyanate to provide Fmoc‐thioureas, which were coupled with Rink amide resin to provide the corresponding resin‐bound Fmoc‐guanidines. Subsequent Mitsunobu alkylation with a variety of alcohols delivered N‐aryl‐N′ carboalkoxy guanidines in good to high purity after resin cleavage.     

Facile One-Pot Conversion of Aldehydes into Amides

A facile one-pot synthesis of amides from aldehydes has been developed. This tandem process involves the formation of a nitrile intermediate obtained from the reaction of an aldehyde with hydroxylamine hydrochloride in dimethylsulfoxide at 100°C and the subsequent treatment of the nitrile with basic hydrogen peroxide. The resulting amide products were produced in good yields (67–95%) and purity (>95%).     

Short,Efficient Syntheses of Pyrrole α-Amides

We report an inexpensive method for producing a diverse array of pyrrole amides on a large scale and in good yield. The synthetic sequence allows for the preparation of a number of pyrrole amide derivatives in excellent to moderate yields from commercially available compounds. The diketene adduct, in the presence of an amine nucleophile, provides an excellent method for acetoacetylation. For diversity and versatility, a second method utilizing Meldrum's acid was successfully employed for the preparation of additional acetoacetamide derivatives. Using the Knorr pyrrole synthesis, pyrrole amides were readily prepared from the oxime of the acetoacetamides.     

Platinum(II)-Catalyzed Novel Synthesis of 3,4-Fused Furans

A novel synthesis of 3,4-fused furans (both tricyclic and bicyclic) through platinum-catalyzed cyclization of 3-(2-formylcycloalkenyl)-acrylic amides 2 in methanol is described (up to 90% yield). Tricyclic 3,4-fused dihydrofuran derivatives were also obtained via reductive cyclization of 2. The substrates 2 were obtained from β- bromovinyl aldehydes by a Pd-catalyzed Heck reaction.     

Novel Synthesis of Optically Active 2‐Ethylhexanoic Acid, 2‐Ethylhexanol,and 2‐Ethylhexylamine via the Asymmetric Favorskii Rearrangement

The asymmetric Favorskii rearrangement of optically active α‐haloketones, which are easily prepared from chiral menthyl‐4‐toluenesulfoxide in several steps using primary or secondary amines, yields their corresponding secondary or tertiary chiral amides. The secondary chiral amides were converted to acids or amines using acylation followed by hydrolysis or reduction. In addition, the tertiary amides were directly reduced to alcohol with Super‐Hydride^®.     

Synthesis of nitrocyclopropyl peptidomimetics

Nitrocyclopropanation of amino-acid derived enones has led to a series of cyclopropyl peptidomimetics suitable for further elaboration to compounds with the potential for biological activity.