Enantioselective Synthesis of α‐Amino‐γ‐sulfonyl Phosphonates with a Tetrasubstituted Chiral α‐Carbon via Quinine‐Squaramide‐Catalyzed Michael Addition of Nitrophosphonates to Vinyl Sulfones

α‐Nitro‐γ‐sulfonyl phosphonates with a key tetrasubstituted chiral α‐carbon center have been synthesized for the first time in high yield and enantioselectivity through a quinine‐squaramide‐catalyzed conjugate addition of α‐nitro phosphonates to aryl vinyl sulfones. Representative examples presented here for the transformation of nitrosulfonyl phosphonates to aminosulfonyl phosphonates, alkylation at the α‐position of the sulfonyl group followed by desulfonation and scale‐up of the conjugate addition highlight the practical applications of the methodology.     

Retracted: Copper‐Catalyzed Cascade Reaction for Practical and Efficient Synthesis of Alkyl 2H‐Isoindole‐1‐carboxylates

The copper‐catalyzed cascade reaction comprising the condensation/α‐arylation between 2‐halobenzaldehydes and α‐amino acid esters provides a straightforward methodology for the efficient synthesis of alkyl 2H‐isoindole‐1‐carboxylates.     

Preparation and characterization of chitosan/α‐zirconium phosphate nanocomposite films

Nano‐fillers play an important role in the final structure and properties of nanocomposites. The objective of the work presented here was to prepare nanocomposite films of chitosan/α‐zirconium phosphate using a casting process, with α‐zirconium phosphate (α‐ZrP) as nano‐filler and chitosan as matrix. The effects of α‐ZrP on the structure and properties of the nanocomposites were investigated. X‐ray diffraction patterns showed that α‐ZrP crystals were intercalated by n‐butylamine. The results from scanning electron microscopy and transmission electron microscopy indicated that α‐ZrP could be uniformly dispersed in the chitosan matrix when α‐ZrP loading in the composites was less than 2 wt%. A strong interaction between α‐ZrP and chitosan formed during the film‐forming process. Tensile testing showed that the tensile strength and elongation at break of nanocomposite films achieved maximum values of 61.6 MPa and 58.1%, respectively, when α‐ZrP loading was 2 wt%. The parameter B calculated from tensile yield stress according to the Pukanszky model was used to estimate the interfacial interaction between the chitosan matrix and α‐ZrP. Films with a loading of 2 wt% α‐ZrP had the highest B value (3.2), indicating the strongest interfacial interaction. The moisture uptake of the nanocomposites was reduced with addition of α‐ZrP. It can be concluded that α‐ZrP as nano‐filler in a chitosan matrix can enhance the mechanical properties of nanocomposites due to the strong interactions between α‐ZrP and chitosan. Copyright © 2010 Society of Chemical Industry     

Preparation and properties of castor oil‐based polyurethane/α‐zirconium phosphate composite films

Novel castor oil‐based polyurethane/α‐zirconium phosphate (PU/α‐ZrP) composite films with different α‐ZrP loading (0–1.6 wt %) and different NCO/OH molar ratios were synthesized by a solution casting method. The characteristic properties of the PU/α‐ZrP composite films were examined by Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and tensile testing. The results from Fourier transform infrared spectroscopy indicated that strong intermolecular hydrogen bonding formed between α‐ZrP and PU, XRD and SEM results revealed that the α‐ZrP particles were uniformly distributed in the PU matrix at low loading, and obvious aggregation existed at high loading. Because of hydrogen bonding interactions, the maximum values of tensile strength were obtained with 0.6 wt % α‐ZrP loading and 1.5 of NCO/OH molar ratio in the matrix. Evidence proved that the induced α‐ZrP used as a new filler material can affect considerably the mechanical and thermal properties of the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of Chiral N‐Sulfonyl and N‐Phosphinoyl α‐Halo Aldimine Precursors

α‐Halogenated aldimines have emerged as an important class of synthetic intermediates. The stability and reactivity of α‐halo aldimines can vary greatly depending on the nitrogen protecting group. A general synthesis of stable, chiral α‐halo‐N‐sulfonyl and N‐phosphinoyl aldimine precursors is presented (42–96% yield). The corresponding α‐halo aldimines can be isolated upon treatment with a mild base. Enantioenriched α‐chloro aldehydes can be employed to afford aldimine precursors with no erosion of optical purity. Both the enantioenriched aldimine precursor and the isolated aldimine can react with an alkynyllithium nucleophile to give trans‐β‐chloroamine products with excellent dr. Ring closure affords the enantioenriched trans‐aziridine, demonstrating the potential for this approach in complex molecule synthesis.     

2,2′‐Bis(monoacylglycero) PO4 (BMP), but Not 3,1′‐BMP,Increases Membrane Curvature Stress to Enhance α‐Tocopherol Transfer Protein Binding to Membranes

Previous work revealed that α‐tocopherol transfer protein (α‐TTP) co‐localizes with bis(monoacylglycero)phosphate (BMP) in late endosomes. BMP is a lipid unique to late endosomes and is believed to induce membrane curvature and support the multivesicular nature of this organelle. We examined the effect of BMP on α‐TTP binding to membranes using dual polarization interferometry and vesicle‐binding assay. α‐TTP binding to membranes is increased by the curvature‐inducing lipid BMP. α‐TTP binds to membranes with greater affinity when they contain the 2,2′‐BMP versus 3,1′‐BMP isomers.     

Antioxidant α‐tocopherol/γ‐cyclodextrin–inclusion complex encapsulated poly(lactic acid) electrospun nanofibrous web for food packaging

α‐Tocopherol (α‐TC) and α‐TC/cyclodextrin (CD)–inclusion complex (IC) incorporated electrospun poly(lactic acid) (PLA) nanofibers (NF) were developed via electrospinning (PLA/α‐TC–NF and PLA/α‐TC/γ‐CD–IC–NF). The release of α‐TC into 95% ethanol (fatty food simulant) was much greater from PLA/α‐TC/γ‐CD–IC–NF than from PLA/α‐TC–NF because of the solubility increase in α‐TC; this was confirmed by a phase‐solubility diagram. 2,2‐Diphenyl‐1‐picrylhydrazyl radical‐scavenging assay shows that PLA/α‐TC–NF and PLA/α‐TC/γ‐CD–IC–NF had 97% antioxidant activities; this value was expected to be high enough to inhibit lipid oxidation. PLA/α‐TC–NF and PLA/α‐TC/γ‐CD–IC–NF were tested directly on beef with the thiobarbituric acid reactive substance (TBARS) method, and the nanofibers displayed a lower TBARS content than the unpackaged meat sample. Thus, active packaging significantly enhanced the oxidative stability of the meat samples at 4 °C. In conclusion, PLA/α‐TC/γ‐CD–IC–NF was shown to be promising as an active food‐packaging material for prolonging the shelf life of foods. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44858.     

Directional Interactions of α‐Particles with FOX‐7. A DFT Study

FOX‐7 is exposed to the effects of α‐particles from selected directions of approach. Various energies and properties of these composite FOX‐7 systems (FOX‐7+α‐particle) are obtained. The effect of α‐particles on FOX‐7 is drastic. The CC double bond turns into a single bond and one of the C NO₂ bonds highly elongates. The approach from the side of amino groups results more stable composite system compared to the approach from the side of nitro groups.     

Single‐Molecule FRET Reveals Structural Heterogeneity of SDS‐Bound α‐Synuclein

SDS‐concentration‐dependent α‐synuclein structure : Upon interaction with SDS, αSyn folds into a structure with two antiparallel α‐helices. We show from single‐molecule FRET that αSynn adopts this conformation in an all‐or‐none fashion below the SDS critical micelle concentration. Population of the folded species is directly coupled to an increase in α‐helix content; this suggests that the entire N terminus is involved in the transaction.

     

Enhanced Heat Stability of α‐Chymotrypsin through Single‐Enzyme Confinement in Attoliter Liposomes

The entrapment of α‐chymotrypsin (α‐CT) within 70–140 nm liposomes formed from POPC (1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphocholine) leads to an unexpected and remarkable increase in the thermal stability of the enzyme. This finding is based on the observation that heating aqueous suspensions of α‐CT‐containing POPC liposomes to 80 °C for 30 minutes resulted in partial enzyme inactivation, whereas the same treatment of aqueous solutions of free α‐CT inactivated the enzyme completely. The stabilizing effect of enzyme confinement in the attoliter volumes of the liposomes was found to increase with decreasing numbers of α‐CT molecules per liposome. Single‐enzyme confinement was particularly effective, as intermolecular interactions between heat‐denatured α‐CT molecules (causing irreversible inactivation) are not possible.     

Enantioselective α‐Alkylation of Benzylideneamino tert‐Butyl Malonates by Phase‐Transfer Catalysis

A new enantioselective synthetic method for the synthesis of α,α‐dialkylmalonates with a quaternary carbon center was developed via α‐alkylation of prochiral malonates by phase‐transfer catalysis (PTC). Asymmetric α‐alkylation of benzylideneamino tert‐butyl α‐methylmalonates under phase‐transfer catalytic conditions in the presence of (S,S)‐3,4,5‐trifluorophenyl‐NAS bromide afforded the corresponding α,α‐dialkylmalonates in high yields (up to 97%) with excellent enantioselectivities (up to 98% ee). The products were then selectively hydrolyzed to chiral malonic monoacids under basic, acidic, or catalytic hydrogenation conditions.

     

Toughening modification of (Acrylonitrile‐styrene‐acrylic copolymer)/(α‐Methylstyrene‐acrylonitrile copolymer) binary blend via using different impact modifiers

In this work, different impact modifiers such as acrylic resin impact modifier, chlorinated polyethylene (CPE), nitrile rubber, powdered nitrile rubber, and hydrogenated nitrile rubber, were chosen to improve the toughness of (acrylonitrile‐styrene‐acrylic copolymer)/(α‐methylstyrene‐acrylonitrile copolymer) (ASA/α‐MSAN) binary blend. The blend ratios of the ASA/(α‐MSAN)/(impact modifier) ternary system were 30/70/20 and 70/30/20 by mass, respectively. The results showed that the impact strength significantly increased, nearly 30 times (22.59 kJ·m^?2, 22.26 kJ·m^?2, and 25.24 kJ·m^?2) compared with that of control samples (0.80 kJ·m^?2) when nitrile rubber, powdered nitrile rubber, or hydrogenated nitrile rubber was added to the ASA/(α‐MSAN) (30/70) matrix, respectively. Moreover, the impact strength of ASA/(α‐MSAN) (70/30) was dramatically enhanced to 46 kJ·m^?2 with the addition of 20 parts by weight per hundred parts of resin of chlorinated polyethylene. The toughness of ASA/(α‐MSAN) with or without impact modifiers was also characterized via fracture energy calculated from stress‐strain curves. The results were perfectly consistent with that of impact strength. The results of dynamic mechanical analysis demonstrated the existence of α‐MSAN (glass transition temperature at approximately 140°C). The heat distortion temperature was barely changed, indicating the addition of impact modifiers barely affects the heat resistance. J. VINYL ADDIT. TECHNOL., 22:326–335, 2016. © 2014 Society of Plastics Engineers     

Influence of α′‐/α‐crystal polymorphism on properties of poly(l‐lactic acid)

Poly(l ‐lactic acid) (PLLA) is a biodegradable and biocompatible thermoplastic polyester produced from renewable sources, widely used for biomedical devices, in food packaging and in agriculture. It is a semicrystalline polymer, and as such its properties are strongly affected by the developed semicrystalline morphology. As a function of the crystallization temperature, PLLA can form different crystal modifications, namely α′‐crystals below about 120 °C and α‐crystals at higher temperatures. The α′ modification is therefore of special importance as it may be the preferred polymorph developing at processing‐relevant conditions. It is a metastable modification which typically transforms into the more stable α‐crystals on annealing at elevated temperature. The structure, kinetics of formation and thermodynamics of α′‐ and α‐crystals of PLLA are reviewed in this contribution, together with the effect of α′‐/α‐crystal polymorphism on the properties of PLLA. © 2018 Society of Chemical Industry     

Evaluation of β‐Amino Acid Replacements in Protein Loops: Effects on Conformational Stability and Structure

β‐Amino acids have a backbone that is expanded by one carbon atom relative to α‐amino acids, and β residues have been investigated as subunits in protein‐like molecules that adopt discrete and predictable conformations. Two classes of β residue have been widely explored in the context of generating α‐helix‐like conformations: β³‐amino acids, which are homologous to α‐amino acids and bear a side chain on the backbone carbon adjacent to nitrogen, and residues constrained by a five‐membered ring, such the one derived from trans‐2‐aminocyclopentanecarboxylic acid (ACPC). Substitution of α residues with their β³ homologues within an α‐helix‐forming sequence generally causes a decrease in conformational stability. Use of a ring‐constrained β residue, however, can offset the destabilizing effect of α→β substitution. Here we extend the study of α→β substitutions, involving both β³ and ACPC residues, to short loops within a small tertiary motif. We start from previously reported variants of the Pin1 WW domain that contain a two‐, three‐, or four‐residue β‐hairpin loop, and we evaluate α→β replacements at each loop position for each variant. By referral to the ?,ψ angles of the native structure, one can choose a stereochemically appropriate ACPC residue. Use of such logically chosen ACPC residues enhances conformational stability in several cases. Crystal structures of three β‐containing Pin1 WW domain variants show that a native‐like tertiary structure is maintained in each case.     

Multi‐Enzymatic Synthesis of Optically Pure β‐Hydroxy α‐Amino Acids

A novel enzymatic production system of optically pure β‐hydroxy α‐amino acids was developed. Two enzymes were used for the system: an N‐succinyl L ‐amino acid β‐hydroxylase (SadA) belonging to the iron(II)/α‐ketoglutarate‐dependent dioxygenase superfamily and an N‐succinyl L ‐amino acid desuccinylase (LasA). The genes encoding the two enzymes are part of a gene set responsible for the biosynthesis of peptidyl compounds found in the Burkholderia ambifaria AMMD genome. SadA stereoselectively hydroxylated several N‐succinyl aliphatic L ‐amino acids and produced N‐succinyl β‐hydroxy L ‐amino acids, such as N‐succinyl‐L ‐β‐hydroxyvaline, N‐succinyl‐L ‐threonine, (2S,3R)‐N‐succinyl‐L ‐β‐hydroxyisoleucine, and N‐succinyl‐L ‐threo‐β‐hydroxyleucine. LasA catalyzed the desuccinylation of various N‐succinyl‐L ‐amino acids. Surprisingly, LasA is the first amide bond‐forming enzyme belonging to the amidohydrolase superfamily, and has succinylation activity towards the amino group of L ‐leucine. By combining SadA and LasA in a preparative scale production using N‐succinyl‐L ‐leucine as substrate, 2.3 mmol of L ‐threo‐β‐hydroxyleucine were successfully produced with 93% conversion and over 99% of diastereomeric excess. Consequently, the new production system described in this study has advantages in optical purity and reaction efficiency for application in the mass production of several β‐hydroxy α‐amino acids.

     

α‐cyclodextrin assisted self‐assembly of poly(ethylene glycol)‐block‐poly(N‐isopropylacrylamide) in aqueous media

Poly(ethylene glycol)‐block‐poly(N‐isopropylacrylamide) (PEG‐b‐PNIPAM) block copolymers were synthesized by atom transfer radical polymerization, and the α‐cyclodextrin (α‐CD) induced self‐assembly characteristics of the system were elucidated. Below the lower critical solution temperature (LCST) of PNIPAM, CD threaded onto the PEG segments and induced micellization to form rod‐shaped nanostructures comprising of a PEG/α‐CD condensed phase and a PNIPAM shell. Increasing the temperature of system above the LCST caused the PNIPAM segments to collapse, which resulted in the dethreading of the CD. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Organocatalytic Enantioselective Sulfenylation of β‐Keto Phosphonates: A Convenient Approach to Construct Hetero‐ Quaternary Stereocenters

The highly effective and enantioselective sulfenylation of β‐keto phosphonates catalyzed by α,α‐diaryl‐L ‐prolinols has been developed. The optically active α‐sulfenylated β‐keto phosphonates could be obtained under mild reaction conditions in good yields (up to 92%) and with excellent enantioselectivities (up to 92% ee).     

Acetylcholine Promotes Binding of α‐Conotoxin MII at α3β2 Nicotinic Acetylcholine Receptors

α‐Conotoxin MII (α‐CTxMII) is a 16‐residue peptide with the sequence GCCSNPVCHLEHSNLC, containing Cys2–Cys8 and Cys3–Cys16 disulfide bonds. This peptide, isolated from the venom of the marine cone snail Conus magus, is a potent and selective antagonist of neuronal nicotinic acetylcholine receptors (nAChRs). To evaluate the impact of channel–ligand interactions on ligand‐binding affinity, homology models of the heteropentameric α₃β₂‐nAChR were constructed. The models were created in MODELLER with the aid of experimentally characterized structures of the Torpedo marmorata‐nAChR (Tm‐nAChR, PDB ID: 2BG9) and the Aplysia californica‐acetylcholine binding protein (Ac‐AChBP, PDB ID: 2BR8) as templates for the α₃‐ and β₂‐subunit isoforms derived from rat neuronal nAChR primary amino acid sequences. Molecular docking calculations were performed with AutoDock to evaluate interactions of the heteropentameric nAChR homology models with the ligands acetylcholine (ACh) and α‐CTxMII. The nAChR homology models described here bind ACh with binding energies commensurate with those of previously reported systems, and identify critical interactions that facilitate both ACh and α‐CTxMII ligand binding. The docking calculations revealed an increased binding affinity of the α₃β₂‐nAChR for α‐CTxMII with ACh bound to the receptor, and this was confirmed through two‐electrode voltage clamp experiments on oocytes from Xenopus laevis. These findings provide insights into the inhibition and mechanism of electrostatically driven antagonist properties of the α‐CTxMIIs on nAChRs.     

Synergistic effect on flame retardancy and thermal behavior of polycarbonate filled with α‐zirconium phosphate@gel‐silica

A new kind of flame retardant (ZS) with layered α‐zirconium phosphate disks (α‐ZrP) as the core and inorganic flame retardant (gel‐silica, GS) to shield solid acid sites on the surface of α‐ZrP as the shell, was synthesized via a facile method. The incorporation effects of ZS with silicone resin on the thermal properties and flame retardance of PC composites were investigated. The presence of ZS could improve the thermal stability of PC matrix. With the addition of ZS contents increased to 3 wt %, the limiting oxygen index (LOI) of the composite was 32.3% and the vertical burning (UL‐94) test reached a V‐0 rating. However, with more contents of ZS, the LOI value decreased, and without the GS layer, the LOI value was decreased significantly as well. The synergism between the α‐ZrP core and gel‐silica shell, also with the silicone resin were found. Based on these results, the flame‐retardant mechanism was proposed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44829.     

Crystallization behavior of α‐cellulose short‐fiber reinforced poly(lactic acid) composites

The isothermal crystallization behavior of α‐cellulose short‐fiber reinforced poly(lactic acid) composites (PLA/α‐cellulose) was examined using a differential scanning calorimeter and a petrographic microscope. Incorporating a natural micro‐sized cellulose filler increased the spherulite growth rate of the PLA from 3.35 μm/min for neat PLA at 105°C to a maximum of 5.52 μm/min for the 4 wt % PLA/α‐cellulose composite at 105°C. In addition, the inclusion of α‐cellulose significantly increased the crystallinities of the PLA/α‐cellulose composites. The crystallinities for the PLA/α‐cellulose composites that crystallized at 125°C were 48–58%, higher than that of the neat PLA for ～13.5–37.2%. The Avrami exponent n values for the neat and PLA/α‐cellulose composites ranged from 2.50 to 2.81 and from 2.45 to 3.44, respectively, and the crystallization rates K of the PLA/α‐cellulose composites were higher than those of the neat PLA. The activation energies of crystallization for the PLA/α‐cellulose composites were higher than that of the neat PLA. The inclusion of α‐cellulose imparted more nucleating sites to the PLA polymer. Therefore, it was necessary to release additional energy and initiate molecular deposition. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013