A Parallel Semisynthetic Approach for Structure–Activity Relationship Studies of Peptide YY

The gut hormone peptide YY (PYY) is postprandially secreted from enteroendocrine L cells and is involved in the regulation of energy homeostasis. The N‐terminal truncated version PYY(3–36) decreases food intake and has potential as an anti‐obesity agent. The anorectic effect of PYY(3–36) is mediated through Y₂ receptors in the hypothalamus, vagus, and brainstem regions, and it is well known that the C‐terminal tetrapeptide sequence of PYY(3–36) is crucial for Y₂ receptor activation. The aim of this work was to develop a semisynthetic methodology for the generation of a library of C‐terminally modified PYY(3–36) analogues. By using an intein‐based expression system, PYY(3–29) was generated as a C‐terminal peptide α‐thioester. Heptapeptides bearing an N‐terminal cysteine and modifications at one of the four C‐terminal positions were synthesized in a 96‐well plate by parallel solid‐phase synthesis. In the plate format, an array of [Ala30]PYY(3–36) analogues were generated by ligation, desulfurization, and subsequent solid‐phase extraction. The generated analogues, in which either Arg33, Gln34, Arg35, or Tyr36 had been substituted with proteinogenic or non‐proteinogenic amino acids, were tested in a functional Y₂ receptor assay. Generally, substitutions of Tyr36 were better tolerated than modifications of Arg33, Gln34, and Arg35. Two analogues showed significantly improved Y₂ receptor selectivity; therefore, these results could be used to design new drug candidates for the treatment of obesity.     

Morphology of pyrolysed polystyrene–isoprene–styrene and polystyrene–butadiene–styrene block copolymers

The surface morphology of thermooxidative degraded polystyrene–isoprene–styrene (SIS) and polystyrene–butadiene–styrene (SBS) thermoplastic block copolymers was studied by scanning electron microscopy. Surface changes caused by heating the samples in a pyrolyzer for 15 and 30 min were presented in different micrographs. The morphological changes occurring due to the formation of polar groups and their crosslinking during the thermooxidative degradation are discussed. Morphological study of these thermally degraded polymer samples shows very good correlation with the thermodegradation results. The rate of thermodegradation is fast in case of SBS when compared with SIS block copolymer. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 2549–2553, 2006     

Morphology of pyrolyzed polystyrene–isoprene–styrene and polystyrene–butadiene–styrene block copolymers

The surface morphology of thermooxidative‐degraded polystyrene–isoprene–styrene (SIS) and polystyrene–butadiene–styrene (SBS) thermoplastic block copolymers were studied by scanning electron microscopy. Surface changes caused by heating the samples in a pyrolizer for 15 and 30 min were presented in different micrographs. The morphological changes occurring due to the formation of polar groups and their crossing linking during the thermooxidative degradation are discussed. Morphological study of these thermally degraded polymer samples show very good correlation with the thermodegradation results. The rate of thermodegradation is fast in case of SBS compared with SIS block copolymer. ©2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Thermal behaviors and flame‐retardancy of styrene–ethylene–butadiene–styrene–block copolymer containing various additives

The thermal behaviors and the flame‐retardancy of styrene–ethylene–butadiene–styrene–block copolymer containing various additives were studied. The combustion was measured by the Underwriter laboratory (UL) test and cone calorimeter test and thermogravimetric analysis and program‐mass spectroscopy were applied to analyze the thermal behaviors. The blend with halogen additives showed the best result in the UL test. However, the blend with red‐phosphorous was the best in the cone calorimeter test. As the styrene sequence in the copolymer tended to degradate at a lower temperature, the major scission products spouted out from the polymer surface originated from polystyrene. The shorter the ignition times of the blends with red‐phosphorous were, the lower the peak heat release rates were. It was an interesting phenomenon because it suggested that the chemical structure of the residue changed to more stable polymers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 156–161, 2007     

Antibody–Bactericidal Macrocyclic Peptide Conjugates To Target Gram‐Negative Bacteria

To combat antimicrobial infections, new active molecules are needed. Antimicrobial peptides, ever abundant in nature, are a fertile starting point to develop new antimicrobial agents but suffer from low stability, low specificity, and off‐target toxicity. These drawbacks have limited their development. To overcome some of these limitations, we developed antibody–bactericidal macrocyclic peptide conjugates (ABCs), in which the antibody directs the bioactive macrocyclic peptide to the targeted Gram‐negative bacteria. We used cysteine S_NAr chemistry to synthesize and systematically study a library of large (>30‐mer) macrocyclic antimicrobial peptides (mAMPs) to discover variants with extended proteolytic stability in human serum and low hemolytic activity while maintaining bioactivity. We then conjugated, by using sortase A, these bioactive variants onto an Escherichia coli targeted monoclonal antibody. We found that these ABCs had minimized hemolytic activity and were able to kill E. coli at nanomolar concentrations. Our findings suggest macrocyclic peptides if fused to antibodies may facilitate the discovery of new agents to treat bacterial infections.     

Thermal behaviour of Cu–Mg–Mn and Ni–Mg–Mn layered double hydroxides and characterization of formed oxides

Thermal behaviour of synthetic Cu–Mg–Mn and Ni–Mg–Mn layered double hydroxides (LDHs) with M^II/Mg/Mn molar ratio of 1:1:1 was studied in the temperature range 200–1100 °C by thermal analysis (TG/DTA/EGA), powder X-ray diffraction (XRD), Raman spectroscopy, and voltammetry of microparticles. Powder XRD patterns of prepared LDHs showed characteristic hydrotalcite-like phases, but further phases were indirectly found as admixtures. The Cu–Mg–Mn precipitate was decomposed at temperatures up to ca. 200 °C to form an XRD-amorphous mixture of oxides. The crystallization of CuO (tenorite) and a spinel type mixed oxide of varying composition Cu_xMg_yMn_zO₄ with Mn⁴⁺ was detected at 300–500 °C. At high temperatures (900–1000 °C), tenorite disappeared and a consecutive crystallization of 2CuO·MgO (gueggonite) was observed. The high-temperature transformation of oxide phases led to a formation of Cu^I oxides accompanied by oxygen evolution. The DTA curve of Ni–Mg–Mn sample exhibited two endothermic effects characteristic for hydrotalcite-like compounds. The first one with minimum at 190 °C can be ascribed to a loss of interlayer water, the second one with minimum at 305 °C to the sample decomposition. Heating of the Ni–Mg–Mn sample at 300 °C led to the onset of crystallization of oxide phases identified as Ni_xMg_yMn_zO₄ spinel, (Ni,Mg)O oxide containing Mn⁴⁺ cations, and easily reducible XRD-amorphous species, probably free Mn^III,IV oxides. At 600 °C (Raman spectroscopy) and 700 °C (XRD), the (Ni,Mg)₆MnO₈ oxide with murdochite structure together with spinel phase were detected. Only spinel and (Ni,Mg)O were found after heating at 900 °C and higher temperatures. Temperature-programmed reduction (TPR) profiles of calcined Cu–Mg–Mn samples exhibited a single reduction peak with maximum around 250 °C. The highest H₂ consumption was observed for the sample calcined at 800 °C. The reduction of Ni–Mg–Mn samples proceeded by a more complex way and the TPR profiles reflected the phase composition changing depending on the calcination temperature.     

PEGylation of deuterohaemin–alanine–histidine–threonine–valine–glutamic acid–lysine and its influence on activity,stability, and aggregation

Deuterohaemin–alanine–histidine–threonine–valine–glutamic acid–lysine (DhHP‐6) is a synthetic heme‐containing peroxidase mimic that exhibits a high peroxidase enzyme activity. Compared to other microperoxidases, DhHP‐6 has a poor stability and tends to aggregate in aqueous solutions. In this study, poly(ethylene glycol) (PEG) was used to improve the properties of DhHP‐6. Factors that affected the PEGylation product yield were investigated. PEGylated DhHP‐6 (mPEG–DhHP‐6) was characterized by reversed‐phase high‐pressure liquid chromatography (RP‐HPLC), matrix‐assisted laser desorption/ionization time of flight mass spectra (MALDI‐TOF‐MS), and ultraviolet–visible (UV–vis) spectroscopy. The results show that the optimal PEGylation reaction conditions were achieved when the PEGylation was conducted in a borate buffer solution at pH 8.0 and 25°C for 4 h with a feeding ratio of 2 equiv of active PEG. After PEGylation, mPEG–DhHP‐6 showed a great improvement in its stability with little activity loss. The UV–vis spectra of DhHP‐6 and mPEG–DhHP‐6 in different pH solutions showed that the aggregation of DhHP‐6 was partly suppressed after PEGylation. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

On the effect of La–Cr–O– phase composition on diesel soot catalytic combustion

A series of samples of La–Cr–O– perovskites were designed as catalysts for diesel soot combustion. They were prepared by using co-precipitation method, at ambient temperature using ammonia followed by a hydrothermal treatment (T = 200 °C, P = 20 atm, t = 24 h). All the chromium-containing precursors were then calcined at high temperature to develop the oxide catalyst. Two phase composition 86%LaCrO₃–(14%) La₂CrO₆ or 94%LaCrO₃–6%La₂O₃ were formed depending on the atmosphere of calcination (oxygen or hydrogen respectively) used. Their respective BET surface areas were 1.1 and 6.5 m² g⁻¹. Highly crystalline, pure phase of LaCrO₃ and La₂CrO₆ powders were also prepared, with BET area of 4 and 3 m² g⁻¹, respectively. The crystalline structure and properties of all samples were characterised by X-ray diffraction (XRD), using Rietveld refinement, and temperature-programmed reduction (TPR) techniques. O₂-TPD measurements performed on all samples showed the presence of suprafacial, weakly chemisorbed oxygen only for LaCrO₃, which contributes actively to soot combustion. TPR study performed on all catalysts showed that while pure LaCrO₃ and La₂O₃ samples did not reduce, the biphasic catalysts showed the presence of oxygen depletion peaks characteristic of lattice oxygen mobility in the samples at ca. 665 °C. Catalytic combustion of diesel soot was studied over all catalysts. The results showed that pure LaCrO₃ exhibited significant catalytic activity which was sensitively affected by the modifier La₂CrO₆ or La₂O₃.     

Synthesis and properties of vinyltrimethoxysilane–EPDM–styrene graft terpolymer

The graft copolymerizations of vinyltrimethoxysilane (VTMO) and styrene (St) onto ethylene–propylene–diene terpolymer (EPDM) were carried out with benzoyl peroxide (BPO) as an initiator in toluene. The effects of EPDM concentration, mole ratio of VTMO to St, reaction time, reaction temperature, and initiator concentration on the graft copolymerizations were examined. The synthesized VTMO–EPDM–St graft terpolymers (VES) were confirmed by infrared and ¹H-NMR spectroscopies. The molecular weight, thermal stability, light resistance, and weatherability of the graft terpolymer were investigated by gel permeation chromatography, thermogravimetric analysis, and Fade-o-Meter. The number-average molecular weight was 109,000. It was found that the heat resistance and light resistance as well as weatherability of VES are considerably better than those of acrylonitrile–butadiene–styrene terpolymer. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1345–1352, 1998     

Magnetic Nanoparticle‐Supported Morita–Baylis–Hillman Catalysts

A magnetic nanoparticle‐supported quinuclidine was prepared and evaluated as a recoverable Morita–Baylis–Hillman catalyst. The supported catalyst 2 demonstrated comparable activity with that of DABCO and could be simply recycled with the assistance of an external magnet. The thus recycled catalyst could be reused for 7 times without significant loss of activity.     

Hydrothermal synthesis (200 °C) of Co–kaolinite and Al–Co–serpentine

In the systems CoO–Al₂O₃–SiO₂–H₂O and CoO–Al₂O₃–SiO₂–HCl–H₂O, at initial pH between 5.5 and 8.1 and temperature of 200 °C, kaolinite is unstable and the following phases form through a dissolution-precipitation process: a) kaolinite and Co-bearing kaolinite; b) Al–Co–serpentine; and c) poorly crystalline phases. Identification of the several phases was carried out from a combination of X-ray diffraction and transmission/analytical electron microscopy.Co–kaolinite shows variable morphologies: a) Platy lath-shaped particles with very low Co content; b) Spherical particles, with relatively constant Co contents (in the order of 0.10 apfu); c) Kaolinite stacks with very variable Co contents (up to 0.25 apfu). Analytical data indicate that the presence of Co(OH)₂ in the system favors the dissolution process as well as serpentine formation but it leads to the parallel formation of abundant poorly crystalline phases. The Co-content in kaolinite increased as a function of the Co(OH)₂/CoCl₂ ratio in the initial systems, and it is reflected by a parallel increase of the b-cell parameter of kaolinite. The average composition of the coexisting Al–Co–serpentine is: (Al_1.20Fe_0.11Co_1.27)(Si_1.64Al_0.36)O₅(OH,Cl)₂, with Cl contents in the order of 0.14 apfu.The assemblage Co–kaolinite + Al–Co–serpentine, which appears to be stable at 200 °C, has not been described in natural environments, probably because it requires unusual Al- and Co-rich chemical systems.     

Stability of polyaniline synthesized by a doping–dedoping–redoping method

Stability, including thermal stability, conductivity stability in air and after thermal treatment (100–200°C), of the polyaniline (PANI) films synthesized by a doping–dedoping–redoping method was investigated. It was found that thermogravimetric analysis (TGA) curves undergo three steps: loss of water or solvent, dedoping and decomposition, and those depend on the counterions. Compared with PANI films doped with camphor sulfonic acid (CSA) in m‐cresol, the thermal stability of the doped PANI films is improved by the new method, and thermal stability in the order of PANI–H₃PO₄ > PANI–p‐TSA > PANI–H₂SO₄ > PANI–HCl, PANI–HClO₄ > PANI–CSA was observed. The conductivity of the doped PANI films at room temperature was reduced after thermal treatment, and it is dependent of the counterions. It was found that the conductivity stability of PANI–p‐TSA and PANI–CSA is the best below 200°C. When the doped PANI films were placed in air, their conductivity decrease slowly with time due to deproton, and also depends on the counterions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 615–621, 1999     

Processing–morphology–property relationships of polypropylene–graphene nanoplatelets nanocomposites

Polypropylene (PP) nanocomposites reinforced with graphene nanoplatelets (GNPs) were prepared via melt extrusion. A special sheet die containing with two shunt plates was designed. The relationships among the flow field of the special die, exfoliation, and dispersion morphology of the GNPs in PP and the macroscopic properties of the nanocomposites were analyzed. Flow field simulation results show that the die with shunt plates provided a high shear stress, high pressure, and high velocity. The differential scanning calorimetry, X‐ray scattering, and electron microscopy results reveal that the nanocomposites prepared by the die with the shunt plates had higher crystallinity values and higher exfoliation degrees of GNPs. The orientation of the GNPs parallel with the extrusion direction was also observed. The nanocomposites prepared by the die with shunt plates showed a higher electrical volume conductivity, thermal conductivity, and tensile properties. This indicated that the high shear stress exfoliated the GNPs effectively to a thinner layer and then enhanced the electrical, thermal, and mechanical properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44486.     

W-promoted Co–Mo–K/γ–Al2O3 catalysts for water–gas shift reaction

The effects of incorporating tungsten into the traditional Co–Mo–K/γ–Al₂O₃ catalysts on the catalytic performances for water–gas shift reaction were investigated. Activity tests showed that W-promoted Co–Mo–K/γ–Al₂O₃ catalysts exhibited higher activity than W-free Co–Mo–K/γ–Al₂O₃ catalyst. Raman and H₂-TPR studies indicated that part of the octahedrally coordinated Mo–O species on Co–Mo–K catalysts transformed into tetrahedrally coordinated Mo–O species in the presence of W promoter.     

Prediction of aqueous phase pH for enzymatic synthesis of peptides in aqueous–organic biphasic systems

An approach has been developed for predicting the change of the aqueous phase pH due to the partition of amino acid substrates in aqueous–organic biphasic systems. In the model reaction of papain‐catalyzed synthesis of N‐benzyloxycarbonyl‐glycine‐L ‐phenylalanine methyl ester (ZGPM) in an aqueous–ethyl acetate system, the effects of the initial aqueous phase pH and phase volume ratio on the final aqueous phase pH, and the change of the final aqueous phase pH during the course of ZGPM synthesis, are investigated. The results suggest that the approach is useful for selecting optimum reaction conditions for peptide synthesis not only in the aqueous–organic biphasic systems with free or immobilized enzymes but also with an immobilized enzyme in an organic solvent. © 2001 Society of Chemical Industry     

Tunable Bifunctional Phosphine–Squaramide Promoted Morita–Baylis–Hillman Reaction of N‐Alkyl Isatins with Acrylates

A series of highly tunable bifunctional phosphine‐squaramide H‐bond donor organocatalysts 6 has been synthesized from inexpensive and commercially available β‐amino alcohols in moderate yields. Catalyst 6 f can efficiently promote the asymmetric Morita–Baylis–Hillman (MBH) reaction of N‐alkyl isatins with acrylate esters providing the chiral 3‐substituted 3‐hydroxy‐2‐oxindoles in good yields and enantioselectivities (up to 93 % yield and 95 % ee), in which the challenging substrate tert‐butyl acrylate 9 d , provided the best ee value to date. Moreover, this methodology was applied successfully in the synthesis of chiral cyclic spiropyrrolizidineoxindole and γ‐butyrolactone derivatives without enantioselectivity deterioration. The possible mechanism of this MBH reaction was also investigated by ³¹P NMR, ESI‐MS and KIE studies. The KIE experiments show that the electrophilic addition of N‐methyl isatin to the complex of acrylate ester and phophine‐squaramide is the rate‐determing step of the asymmetric MBH reaction.

     

Pt–Ru–Co catalysts for PEMFC synthesized by combustion

In this work the novel use of urea combustion synthesis as a straightforward method for the preparation of a trimetallic alloy, 60 Pt–30 Ru–10 Co (mol%) is described. A novel composition in the Pt–Ru–Co ternary system has been considered for a possible substitution of commercial anode catalysts in PEMFC. The specific surface area (102 m²/g) of the carbon supported catalysts produces anodes which gave power density stable values of 260 mW/cm². The XPS (X-ray Photoelectron Spectrometry) data showed that combustion synthesis produces Platinum and Cobalt segregated in the catalyst’s surface, these metals are layered structured and exhibit different oxidation states.     

Catalytic properties of Ni–B and Ni–P ultrafine materials

The ultrafine Ni–B and Ni–P amorphous alloy catalysts were prepared by the chemical reduction method. The catalysts were characterized with respect to ICP‐AES, XRD, nitrogen sorption, DSC, SEM, TEM and XPS. Nitrobenzene hydrogenation was used to compare their hydrogenation abilities. The different metalloids of boron and phosphorus bound to the nickel metal for the Ni–B and Ni–P catalysts result in the distinct different surface area, amorphous structure and hydrogenation activity of the catalysts. Ni–B had a larger surface area than Ni–P. The specific activity per surface area of Ni–P was greater than that of Ni–B. The different activities between the Ni–P and Ni–B can be attributed to the difference of the electron density on the nickel metal; boron donates electrons to the nickel metal and phosphorus accepts electrons from the nickel metal. The catalysts were easier to oxidize when they were exposed to air. This would result in the lower activity. However, the activity could be recovered in the reaction process due to the presence of hydrogen in the reaction system. © 2000 Society of Chemical Industry     

Modification of Acid Anhydride-cured Epoxy Resins By N-Phenyl- maleimide–Styrene Copolymers and N-Phenylmaleimide–Styrene– p-Hydroxystyrene Terpolymers

N-Phenylmaleimide–styrene copolymers (PMS) and reactive N-phenylmaleimide–styrene–p-hydroxystyrene (HSt) terpolymers (PMSH) containing p-hydroxyphenyl groups were used to improve the toughness of bisphenol A diglycidyl ether epoxy resin cured with methyl hexahydrophthalic anhydride. PMS and PMSH were effective modifiers for epoxies. The morphologies of the modified resins depended on modifier structure and content. The most effective modification for the cured resins was attained because of the co-continuous structure of the modified resins in both PMS and PMSH modification systems. When using 15wt% of PMS (M¯_w 125000), the fracture toughness, K_IC, for the modified resin increased by 230%, with retention of flexural modulus and glass transition temperature, but with a loss of flexural strength, compared with the values for the unmodified epoxy resin. When using PMSH as the reactive modifier, the efficiency decreased with increase in HSt content, because of the increasing extent of dispersion of the PMSH-rich continuous phases. In the modification with 10wt% PMSH (1·0mol% HSt unit, M¯_w 294000), the modified resin had balanced physical properties. © of SCI.