Preparation and UV/Vis Spectroscopic Characterization of N,N‐Disubstituted 2‐Amino‐5‐arylazoselenazoles and Some of Their Carbocyclic and Heterocyclic Analogues

By coupling of aryldiazonium salts 5 with N,N‐disubstituted 2‐amino‐5H‐selenazoles 4 deeply coloured 5‐arylazo‐substituted 2‐amino‐selenazoles 6a—6l have been prepared and their solvatochromic properties determined by means of UV/Vis spectroscopy, and compared with the ones of several other arylazosubstituted N,N‐dialkylanilines 7a—7d , 2‐(N,N‐dialkylamino)‐thiophenes 8a—8e , and 2‐(N,N‐dialkylamino)‐thiazoles 9a—9c .     

The photosensitive properties of polysiloxane acrylate resin containing tertiary amine groups

The photosensitive properties of a novel oligomer, di (N,N‐diacrylolyl)‐α, ω‐diaminopolysiloxane (ANS) with tertiary amine groups and acryloyl groups in its molecular structure were investigated using FTIR and gel yield method. It was noted that the ANS system showed a notable photosensitive property and its photosensitivity in air could be up to16.3 mJ/cm². The UV‐curing behavior of the ANS was studied by electron spin resonance (ESR). The results showed that amino‐alkyl radicals can be formed by excited BP abstracting hydrogen at a‐carbon bonded with nitrogen in the ANS molecule under UV irradiation, which can mitigate the oxygen inhibition in radical polymerization. It is proven that tertiary amine groups introduced into ANS could boost photosensitivity of the photopolymerization system. The oligomer ANS may find application in photopolymerization to improve the properties of UV‐curing coating materials. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Aggregation in Organic Solutions of Malonamides: Consequences for Water Extraction

The molecular organization of N,N′‐dimethyl‐N,N′‐dioctylhexylethoxymalonamide (DMDOHEMA), the current reference extractant for the DIAMEX (DIAMide EXtraction) process, is correlated with its water extraction properties from neutral media. The aggregation of DMDOHEMA in n‐heptane was investigated by vapor pressure osmometry (VPO) and the aggregate speciation characterized by combined small‐angle neutron and X‐ray scattering (SANS and SAXS, respectively). Two approaches were taken to model the aggregation of the diamide and the water extraction as a function of the diamide concentration by taking into account a single aggregation equilibrium with an average aggregation number N equal to 4.28 ± 0.05; and a competition between two types of aggregates in the organic phase, namely, aggregates of the reverse micelle type with 4 diamides per aggregate, and an oligomeric structure composed of about 10 diamide molecules which appears at high extractant concentration (>1 mol/L). In both cases, the supramolecular speciation representing the monomers/aggregates distribution was determined, and for each supramolecular organization, a solubilization parameter was calculated using the Sergievskii‐Dannus relationship. Thus, the correlation between the two types of micellization of the diamide and the extraction of water into the organic phase was demonstrated. The larger aggregates can extract about five times more water than monomers.     

Low molecular weight water‐soluble chitosans: Preparation with the aid of cellulase,characterization, and solubility

Preparation of water‐soluble chitosan (WSC) was made by treating partially N‐deacetylated chitosan with acetic anhydride in aqueous acetic acid. The optimal conditions of preparing WSC were determined on the basis of orthogonal tests. Low molecular weight WSC with broad molecular weight (600–1.5 kDa) were obtained by the depolymerization of WSC using cellulase at optimum condition of pH 4.5 and 60°C. The solubility of WSC in water and aqueous organic solvents was investigated in detail. Weight–average molecular weight (M_w) and molecular weight distribution (M_w/M_n) of samples were measured by gel permeation chromatography. The structure of WSC and its degraded products were characterized by XRD, FTIR, and MALDI‐TOF MS. The decrease of molecular weight led to transformation of crystal structure and the increase of solubility, but the chemical structures of residues were not modified compared to WSC, which was not hydrolyzed. The solubility of the WSC in water and aqueous organic solvents increased with the decrease of molecular weight. The solubility of the WSC with low molecular weight was rather high even in aqueous dimethylacetamide and dimethylsulfoxide. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1098–1105, 2006     

Incorporation of manganese complexes into xylanase: new artificial metalloenzymes for enantioselective epoxidation

Here we report the best artificial metalloenzyme to date for the selective oxidation of aromatic alkenes; it was obtained by noncovalent insertion of Mn^III‐meso‐tetrakis(p‐carboxyphenyl)porphyrin [Mn(TpCPP), 1 ‐Mn] into a host protein, xylanase 10A from Streptomyces lividans (Xln10A). Two metallic complexes—N,N′‐ethylene bis(2‐hydroxybenzylimine)‐5,5′‐dicarboxylic acid Mn^III [(Mn‐salen), 2 ‐Mn] and 1 ‐Mn—were associated with Xln10A, and the two hybrid biocatalysts were characterised by UV–visible spectroscopy, circular dichroism and molecular modelling. Only the artificial metalloenzyme based on 1 ‐Mn and Xln10A was studied for its catalytic properties in the oxidation of various substituted styrene derivatives by KHSO₅: after optimisation, the 1 ‐Mn ‐ Xln10A artificial metalloenzyme was able to catalyse the oxidation of para‐methoxystyrene by KHSO₅ with a 16 % yield and the best enantioselectivity (80 % in favour of the R isomer) ever reported for an artificial metalloenzyme.     

Synthesis of pentavalent imidovanadium complexes and their catalyses for the polymerization of ethylene and propylene

Imidovanadium complexes with cyclopentadienyl (Cp) ligands—(Cp)V(?NC₆H₄Me‐4)Cl₂ (1), (Cp)V(?N^tBu)Cl₂ (2), and (^tBuCp)V(?N^tBu)Cl₂ (3; ^tBuCp = tert‐butylcyclopentadienyl)—were synthesized through the reaction of imidovanadium trichloride with (trimethylsilyl)cyclopentadiene derivatives. The molecular structure of 3 was determined by X‐ray crystallography. The monocyclopentadienyl complex 1 exhibited moderate activity in combination with methylaluminoxane [MAO; 10.3 kg of polyethylene (mol of V)^?1 h^?1 atm^?1], whereas similar complexes with bulky ^tBu groups, 2 and 3, were less active. (2‐Methyl‐8‐quinolinolato)imidovanadium complexes, V(?NR)(O ?N)Cl₂ (R = C₆H₃ⁱPr₂‐2,6 (4) or n‐hexyl (5), O ?N = 2‐methyl‐8‐quinolinolato), were obtained from the reaction of imidovanadium trichloride with 2‐methyl‐8‐quinolinol. Upon activation with modified MAO, complex 4 showed moderate activities for the polymerization of ethylene at room temperature. The complex 5/MAO system also exhibited moderate activity at 0°C. The polyethylenes obtained by these complexes had considerably high melting points, which indicated the formation of linear polyethylene. Moreover, the 5/dried MAO system showed propylene polymerization activities and produced polymers with considerably high molecular weights and narrow molecular weight distributions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1008–1015, 2005     

Copper(II)‐bis‐Histidine Coordination Structure in a Fibrillar Amyloid β‐Peptide Fragment and Model Complexes Revealed by Electron Spin Echo Envelope Modulation Spectroscopy

Truncated and mutated amyloid‐β (Aβ) peptides are models for systematic study—in homogeneous preparations—of the molecular origins of metal ion effects on Aβ aggregation rates, types of aggregate structures formed, and cytotoxicity. The 3D geometry of bis‐histidine imidazole coordination of Cu^II in fibrils of the nonapetide acetyl‐Aβ(13–21)H14A has been determined by powder ¹⁴N electron spin echo envelope modulation (ESEEM) spectroscopy. The method of simulation of the anisotropic combination modulation is described and benchmarked for a Cu^II‐bis‐cis‐imidazole complex of known structure. The revealed bis‐cis coordination mode, and the mutual orientation of the imidazole rings, for Cu^II in Ac‐Aβ(13–21)H14A fibrils are consistent with the proposed β‐sheet structural model and pairwise peptide interaction with Cu^II, with an alternating [‐metal‐vacancy‐]_n pattern, along the N‐terminal edge. Metal coordination does not significantly distort the intra‐β‐strand peptide interactions, which provides a possible explanation for the acceleration of Ac‐Aβ(13–21)H14A fibrillization by Cu^II, through stabilization of the associated state and low‐reorganization integration of β‐strand peptide pair precursors.     

Effect of Glycosylation on the Biocatalytic Properties of Hydroxynitrile Lyase from the Passion Fruit,Passiflora edulis: A Comparison of Natural and Recombinant Enzymes

A hydroxynitrile lyase from the passion fruit Passiflora edulis (PeHNL) was isolated from the leaves and showed high stability in biphasic co‐organic solvent systems for cyanohydrin synthesis. Cyanohydrins are important building blocks for the production of fine chemicals and pharmaceuticals. Thus, to enhance production yields of PeHNL for industrial applications, we cloned and expressed recombinant PeHNL in Escherichia coli BL21(DE3) and Pichia pastoris GS115 cells without a signal peptide sequence. The aim of this study is to determine the effect of N‐glycosylation on enzyme stability and catalytic properties in microbial expression systems. PeHNL from leaves (PeHNL‐N) and that expressed in P. pastoris (PeHNL‐P) were glycosylated, whereas that expressed in E. coli (PeHNL‐E) was not. The enzymes PeHNL‐N and PeHNL‐P showed much better thermostability, pH stability, and organic solvent tolerance than the deglycosylated enzyme PeHNL‐E and the deglycosylated mutant N105Q from P. pastoris (PeHNL‐P‐N105Q). The glycosylated PeHNL‐P also efficiently performed transcyanation of (R)‐mandelonitrile with a 98 % enantiomeric excess in a biphasic system with diisopropyl ether. These data demonstrate the efficacy of these methods for improving enzyme expression and stability for industrial application through N‐glycosylation.     

Synthesis and Characterization of Octapeptide Somatostatin Analogues with Backbone Cyclization: Comparison of Different Strategies,Biological Activities and Enzymatic Stabilities

Somatostatin octapeptide analogues of the general sequence DPhe⁵‐Phe ⁶‐Tyr⁷‐DTrp⁸‐Lys⁹‐Val¹⁰‐Ph ¹¹‐Thr¹²‐NH₂ containing two types of backbone cyclization have been synthesized by the solid phase methodology. Backbone cyclization in these peptides was achieved via N‐modified phenylalanines in position 6 and 11. The N‐modified amino acids were incorporated as dipeptide building units which have been prepared in solution prior to the solid phase synthesis. Two dipeptide units of structure a) Fmoc‐aa ₁ ψ[CO—N((CH₂)_n‐X)]Phe—OH or b) Fmoc‐aa₁ ψ[CH₂—N(COlpar;CH₂)_n‐X)]Phe—OH have been introduced into the peptide sequence. Different resins and linkers were examined for an optimized peptide assembly and monitoring. The synthesized somatostatin analogues are highly resistant against enzymatic degradation as determined in vitro by incubation with rat liver homogenate. The biological activity was determined in binding experiments to the somatostatin receptors expressed in CHO‐ or BON‐1 cells. Most analogues show moderate activity without differentiation between the receptor subtypes.     

Synthesis of 20‐O‐linked 20(S)‐Camptothecin Glycoconjugates: Impact of the Side Chain of the Ester‐linked Amino Acid on Epimerization During the Acylation Reaction and on Hydrolytic Stability of the Final Glycoconjugates

To improve solubility and tumor selectivity of 20(S)‐camptothecin the synthesis of 20‐O‐linked glycoconjugates 11A — G is described. Particular focus of the paper is the utilization of N‐tert‐butoxycarbonyl protected amino acid N‐carboxy anhydrides (UNCAs) 2a — f for an efficient acylation of the sterically hindered and deactivated tertiary 20‐hydroxy group of 20(S)‐camptothecin 1 . Depending on the solvent and on the side chain of the amino acid different extents of epimerization of the amino acids during the coupling reaction are observed; however, the epimers can easily be separated after removal of the tert‐butoxycarbonyl protecting group and camptothecin amino acid conjugates 4B — E with L‐ and D‐ configured amino acids, respectively, are obtained. Particularly, bulky and β‐branched amino acids can be attached to camptothecin in high yields and with low epimerization. Starting from the camptothecin amino acid conjugates 4B — E the synthesis of the glycoconjugates 11A — G is straightforward following standard procedures. The glycoconjugate hydrochlorides 11A — G show good water solubility (> 5mg‐ ml) and hydrolytic stability of the ester bond which again depends on the side chain of the amino acid residue linked to camptothecin. Particularly, glycoconjugates 11B — E with a bulky and β‐branched amino acid at the ester linkage show high hydrolytic stability in aqueous solutions with less than 2.5% of 20(S)‐camptothecin cleaved within 24 h. These results provide a basis for the selection of appropriate spacer groups for delivery systems of 20(S)‐camptothecin for therapeutic use.     

Substituent effects on the photofading of disperse azo dyes on poly(ethylene terephthalate) substrate

The relationships between the chemical structures and oxidative fading of the disperse azo dyes, p‐nitrophenylazo‐ and benzothiazoleazo‐anilines, on poly(ethylene terephthalate) substrate are discussed in terms of the parameters k_0,i (rate constants of reaction towards ¹O₂) and f_i (photosensitivity), the molecular parameters of molecular orbital theory and substituents in the diazo and coupling components, on the assumption that the initial rates of oxidative fading are proportional to the product of k_0,i and f_i. 2‐Methoxy‐5‐acetylamino‐N‐substituted aniline couplers exhibited large f_i values. 2‐Chloro and 4‐nitro substituents of aniline diazo components exhibited small f_i values or high quantum yields of internal conversion, while 4‐nitro substituent did not. A close correlation between N‐substituents and light fastness, proposed by Müller and supplemented by Dawson, demonstrates the applicability of frontier orbital theory, through the highest occupied molecular orbital (HOMO) energy of the dyes, to the analysis of oxidative fading. Dyes with N‐2‐cyanoethyl substituents, which gave a lower HOMO energy, also exhibited superior light fastness compared with N‐2‐hydroxyethyl substituents.     

Modulating the Substrate Specificity of LTA4H Aminopeptidase by Using Chemical Compounds and Small‐Molecule‐Guided Mutagenesis

Leukotriene A₄ hydrolase (LTA4H) is a bifunctional zinc‐containing enzyme with an epoxide hydrolase activity and an aminopeptidase activity of unclear function. The two activities occupy different, but overlapping sites. In this study we have focused on the non‐overlapping regions of these sites and have found that a series of previously reported compounds—diphenyl ether, 4‐phenoxyphenol, and their derivatives—can change the substrate specificity of LTA4H aminopeptidase, from arginyl peptide to alanyl peptide. The possible substrate specificity alteration mechanism was studied with the aid of molecular modeling and site‐directed mutagenesis. Furthermore, several mutants that show different substrate specificity, such as F314E and V367W, were successfully designed by using the proposed small‐molecule binding site as a model. F314E behaves as a highly selective aminopeptidase towards arginyl peptides with a selectivity increase of 850‐fold, whereas V367W prefers alanyl peptides over arginyl peptides, just as the organic modulators do.     

Impact of a Stereocentre Inversion in Cyclic Lipodepsipeptides from the Viscosin Group: A Comparative Study of the Viscosinamide and Pseudodesmin Conformation and Self‐Assembly

The viscosin group covers a series of cyclic lipodepsipeptides (CLPs) produced by Pseudomonas bacteria, with a range of biological functions and antimicrobial activities. Their oligopeptide moieties are composed of both L ‐ and D ‐amino acids. Remarkably, the Leu5 amino acid—centrally located in the nonapeptide sequence—is the sole residue found to possess either an L or D configuration, depending on the producing strain. The impact of this D /L switch on the solution conformation was investigated by NMR‐restrained molecular modelling of the epimers pseudodesmin A and viscosinamide A. Although the backbone fold remained unaffected, the D /L switch adjusted the segregation between hydrophobic and hydrophilic residues, and thus the amphipathicity. It also influenced the self‐assembly capacity in organic solvents. Additionally, several new minor variants of viscosinamide A from Pseudomonas fluorescens DR54 were identified, and an NMR assay is proposed to assess the presence of either an L ‐ or D ‐Leu5.     

Modification of preparation method for polymer inclusion membrane (PIM) to produce hollow fiber PIM

A new preparation method for polymer inclusion membrane (PIM) was developed. The preparation method—called post‐treatment method—is very convenient to prepare a hollow fiber PIM. Using this method, a commercial cellulose triacetate (CTA) hollow fiber membrane can be easily converted into a hollow fiber PIM. Thus, a CTA hollow fiber membrane was allowed to swell in 2‐nitrophenyl‐n‐octyl ether (NPOE) in the presence of chloroform as a solvent for CTA and N,N,N′,N′‐tetraoctyl‐3‐oxapentane diamide (TODGA) as a carrier. After evaporating chloroform, a hollow fiber PIM containing NPOE and TODGA was obtained. The result of the transport experiment of cerium(III) ions using the hollow fiber PIM showed that cerium ions were effectively transported from the feed solution to the strip solution through the hollow fiber PIM, indicating that the hollow fiber PIM was successfully prepared using the post‐treatment method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4372–4377, 2006     

Eine neue,breit anwendbare Synthese für aromatische Aldehyde

Diformamide ( 1 ) reacts with activated aromatic compounds like toluene, anisole, m‐xylene, 1,2‐dimethoxybenzene in the presence of AlCl₃ to give N‐(diarylmethyl)‐formamides 2a—d , the corresponding aromatic aldehydes 3—6 are formed as by‐products in low yields. From N,N‐dimethylaniline and 1 /AlCl₃ the triphenylmethane derivative 7 can be obtained. The reaction of anisole with N‐methyl‐diformamide ( 9 ) affords the formamide 10 . The mixture of formamide, P₄O₁₀ and AlCl₃ reveals to be a reagent which is capable to formylate toluene and anisole, resp. Triformamide ( 14 )/AlCl₃ is an effective formylating system which allows the preparation of aromatic aldehydes (e.g. 3,4,17—32 ) from the corresponding aromatic hydrocarbons. Aluminiumchloride can be replaced by borontrichloride. The yields of the formylation reactions depend strongly from the reaction conditions (molar ratio: aromatic hydrocarbon/AlCl₃/ 14 ; solvent, reaction temperature). The scope of the reaction covers nearly complete those of the Gattermann‐Koch‐, Gattermann‐ and Vilsmeier—Haack‐reaction.     

Atom transfer radical polymerization of acrylonitrile

Iron(II) chloride coordinated by succinic acid was first used as the catalyst in 2‐chloropropionitrile‐initiated atom transfer radical polymerization (ATRP) of acrylonitrile. N,N‐dimethylformamide was used as a solvent to improve the solubility of the ligand. An iron(II) chloride to succinic acid ratio of 0.5 not only gives the best control of molecular weight and its distribution but also provides rather rapid reaction rate. Effects of solvent on polymerization of acrylonitrile were also investigated. The induction period is shorter in N,N‐dimethylformamide than in propylene carbonate and toluene and the rate of the polymerization in N,N‐dimethylformamide is fastest. The molecular weight of polyacrylonitrile agrees reasonably well with the theoretical molecular weight of N,N‐dimethylformamide. The rate of polymerization increases and the induction period becomes shorter with increasing polymerization temperature, and the apparent activation energy was calculated to be 56.5 kJ mol^?1. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1050–1054, 2006     

Synthesis of a branched photosensitive copolymer and its application for negative‐type photoresists

Novel branched copolymers, poly(styrene‐alt‐maleic anhydride) (BPSMA), were synthesized through mercapto chain‐transfer polymerization with styrene, maleic anhydride (MA), and 4‐vinyl benzyl thiol (VBT). Then, the hydroxyl of hydroxyethyl methacrylate was reacted with MA to synthesize branched photosensitive copolymers, p‐BPSMAs. Fourier transform IR spectroscopy and ¹H‐NMR indicated that the synthesis was successful. Gel permeation chromatography indicated that the molecular weight decreased with increasing content of VBT. The thermal properties were characterized by thermogravimetric analysis; the results show that the thermal decomposition temperature of the BPSMAs was greatly enhanced. Real‐time IR was used to evaluate the UV‐curable kinetics of the p‐BPSMAs; the results show that the p‐BPSMAs could rapidly photopolymerize under UV irradiation in the presence of photoinitiators. Moreover, the photoresist based on the p‐BPSMAs exhibited improved photosensitivity when the VBT content increased, and the photoresist with 12 mol % VBT content had a low value of the dose that retained 50% of the original film thickness (10 mJ/cm²), and a 50‐μm resolution could be achieved compared to a linear photoresist. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42838.     

High‐molecular‐weight polyacrylonitrile by atom transfer radical polymerization

A single‐pot atom transfer radical polymerization was used for the first time to successfully synthesize polyacrylonitrile with a molecular weight higher than 80,000 and a narrow polydispersity as low as 1.18. This was achieved with CuBr/isophthalic acid as the catalyst, 2‐bromopropionitrile as the initiator, and N,N‐dimethylformamide as the solvent. The effects of the solvent on the polymerization of acrylonitrile were also investigated. The induction period was shorter in N,N‐dimethylformamide than in propylene carbonate and toluene, and the rate of the polymerization in N,N‐dimethylformamide was fastest. The molecular weight of polyacrylonitrile agreed reasonably well with the theoretical molecular weight in N,N‐dimethylformamide. When chlorine was used in either the initiator or the catalyst, the rate of polymerization showed a trend of decreasing, and the molecular weight deviated from the theoretical predication significantly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3372–3376, 2006     

Synthesis and characterization of negative‐type photosensitive polyimides based on cyclobutane‐1,2,3,4‐tetracarboxylic dianhydride

A series of negative‐type photosensitive polyamic acids (PAAs) with various molecular weights was synthesized from cyclobutane‐1,2,3,4‐tetracarboxylic dianhydride, 2‐(methacryloyloxy)ethyl‐3,5‐diaminobenzoate, and 2‐(methacryloyloxy)ethyl‐4‐aminobenzoate in N‐methyl‐2‐pyrrolidone. We investigated the degree of planarity, transmittance, and thermal stability for the PAAs after the photoirradiation reaction at an exposure dose of 200 mJ/cm². The films prepared from the PAA with the lowest molecular weight (PAA‐1) exhibited a higher degree of planarity and transmittance compared with those of the film prepared from the PAA with the highest molecular weight (PAA‐4). The initial decomposition temperatures of the cured PAAs with different molecular weights were similar and were stable up to around 300°C. Further, the photosensitivity and transmittance of PAA‐1 were investigated in the presence of photoinitiators at 365–400 nm with a high‐pressure mercury lamp. The resolution of the photocured film was about 50 μm. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2300–2308, 2005     

Effect of water‐miscible solvents on the organic solvent‐resistant tyrosinase from Streptomyces sp. REN‐21

The effect of various water‐miscible organic solvents (ethanol, methanol, acetone, acetonitrile, N,N‐dimethylformamide (DMF) and dimethylsulfoxide (DMSO)) on the kinetics of 4‐tert‐butylcatechol (tBC) oxidation in the presence of different samples of organic solvent‐resistant tyrosinase (OSRT) has been studied. In contrast to mushroom tyrosinase the enzyme shows a high relative stability in solutions of organic solvents and increased activity toward the bulky and hydrophobic substrate, tBC, in respect to catechol. Rates of the studied OSRT‐catalyzed reactions are however reduced by the presence of organic solvents and for all studied samples of OSRT decrease exponentially with the content of an organic solvent. The effect has been satisfactorily described by the effect of organic solvents on the thermodynamic activity of tBC. The correlation of the inhibition parameters with the hydrophobicity of a particular solvent (log P), its intrinsic molar volume, V_i, and the Dimroth–Reichardt parameter, E_T(30), are shown. The results allow also the prediction of OSRT activity in aqueous solutions of water‐miscible organic solvents. Copyright © 2003 Society of Chemical Industry