The effect of initiators and oxidants on the morphology of poly [(±)‐2‐(sec‐butyl) aniline] a chiral bulky substituted polyaniline derivative

The nano and micro sphere synthesis of chiral bulky substituted polyaniline from monomer (±)‐2‐sec‐butylaniline in bulk and template‐free method (rapid mixing) was done successfully using ammonium peroxydisulfate (APS) and FeCl₃·6H₂O as oxidants. The effect of initiators such as p‐phenylendiamine and 1,4‐benzenediamine, temperature and concentration of monomer on morphology is demonstrated by scanning electron microscopy (SEM) images. The nano and micro sphere morphology was obtained using initiators. Smallest particles were achieved when 1,4‐benzenediamine was used as initiator in the presence of FeCl₃·6H₂O as oxidant. By increasing the concentration of monomer more uniform spheres were obtained. Characterization was made via FT‐IR, UV–Vis, ¹H and ¹³C‐NMR spectroscopy. Elemental analysis and electrical conductivity of products are also presented. All analysis data are in good agreement with nigraniline oxidation state of polyaniline. Copyright © 2015 John Wiley & Sons, Ltd.     

Probing the Conformational Changes in the Enzymatic Hydrolysis of 2‐Acetamido‐2‐deoxy‐β‐D‐glucopyranosides

The isoquinuclidines 7 and 8 were synthesised and tested as inhibitors of hexosaminidases from jack beans and from bovine kidney. These isoquinuclidines mimick the ^1,4B‐conformer of a N‐acetyl‐glucosamine‐derived β‐d‐ glucopyranoside; they are competitive inhibitors with K_i values from 0.014 to 0.30 μM . The strong inhibition of these enzymes agrees with the hypothesis that the enzymatic hydrolysis of 2‐acetamido‐2‐deoxy‐β‐d‐ glucopyranosides proceeds via a boat‐like conformer with a pseudo‐axial scissile glycosidic bond and a pseudo‐axial acetamido substituent optimally oriented to effect an intramolecular substitution of the aglycon.     

Synthesis and polymerization of 5‐(methacrylamido)tetrazole,a water‐soluble acidic monomer

The reaction of methacryloyl chloride with 5‐aminotetrazole gave the polymerizable methacrylamide derivative 5‐(methacrylamido)tetrazole ( 4 ) in one step. The monomer had an acidic tetrazole group with a pK_a value of 4.50 ± 0.01 in water methanol (2:1). Radical polymerization proceeded smoothly in dimethyl formamide or, after the conversion of monomer 4 into sodium salt 4‐Na , even in water. A superabsorbent polymer gel was obtained by the copolymerization of 4‐Na and 0.08 mol % N,N′‐methylenebisacrylamide. Its water absorbency was about 200 g of water/g of polymer, although the extractable sol content of the gel turned out to be high. The consumption of 4‐Na and acrylamide (as a model compound for the crosslinker) during a radical polymerization at 57 °C in D₂O was followed by ¹H NMR spectroscopy. Fitting the changes in the monomer concentration to the integrated form of the copolymerization equation gave the reactivity ratios r _4‐Na = 1.10 ± 0.05 and r_acrylamide = 0.45 ± 0.02, which did not differ much from those of an ideal copolymerization. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4333–4343, 2002     

Anilinolysis of reactive aryl 2,4‐dinitrophenyl carbonates: Kinetics and mechanism

The reactions of a series of anilines with phenyl 2,4‐dinitrophenyl ( 1 ), 4‐nitrophenyl 2,4‐dinitrophenyl ( 2 ), and bis(2,4‐dinitrophenyl) ( 3 ) carbonates are subjected to a kinetic investigation in 44 wt% ethanol–water, at 25.0 ± 0.1°C and an ionic strength of 0.2 M. Under amine excess pseudo‐first‐order rate coefficients (k_obs) are obtained. Plots of k_obs against free amine concentration at constant pH are linear, with slopes k_N. The Brønsted plots (log k_N vs. anilinium pK_a) for the anilinolysis of 1 – 3 are linear, with slope (β) values of 0.52, 0.61, and 0.63, respectively. The values of these slopes and other considerations suggest that these reactions are ruled by a concerted mechanism. For these reactions, the k_N values follow the reactivity sequence: 3 > 2 > 1 . Namely, the reactivity increases as the number of nitro groups attached to the nonleaving group increases. Comparison of the reactions of this work with the stepwise pyridinolysis of carbonates 1 – 3 indicates that the zwitterionic tetrahedral intermediate (T^±) formed in the pyridinolysis reactions is destabilized by the change of its pyridino moiety by an isobasic anilino group. This is attributed to the superior leaving ability from the T^± intermediate of anilines, relative to isobasic pyridines, which destabilize kinetically this intermediate. The k_N values for the anilinolysis of carbonates 1 – 3 are similar to those found in the reactions of these carbonates with secondary alicyclic amines. With the kinetic data for the anilinolysis of the title substrates and 4‐methylphenyl and 4‐chlorophenyl 2,4‐dinitrophenyl carbonates, a multiparametric equation is derived for log k_N as a function of the pK_a of the conjugate acids of anilines and nonleaving groups. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 191–197, 2011     

Synthesis of a soluble conjugated cumulene polymer: poly(biphenyl‐4,4′‐diyl‐1,4‐bis(4‐dodecyloxyphenyl)‐buta‐1,2,3‐triene‐1,4‐diyl)

A conjugated polymer with a butatriene segment in the main chain, poly(biphenyl‐4,4′‐diyl‐1,4‐bis(4‐dodecyloxyphenyl)buta‐1,2,3‐triene‐1,4‐diyl), was synthesized from 1,4‐bis(4‐bromophenyl)‐1,4‐bis(4‐dodecyloxyphenyl)buta‐1,2,3‐triene by dehalogenative polycondensation using Ni(cod)₂. The polymer was well soluble in usual organic solvents such as CHCl₃ and THF. Structural analyses and characterizations were carried out by IR, NMR, UV‐Vis, PL, and Raman spectroscopy, as well as electrical conductivity. It is suggested that π‐conjugation is extended to some degree through biphenylylene and butatrienylene linkages.     

Synthesis and pH‐Dependent Spectroscopic Behavior of 2,4,6‐Trisubstituted Pyridine Derivatives

Seven 2,4,6‐trisubstituted pyridine derivatives with N,N‐diethylaniline substituents at the 4‐position were synthesized, and their spectroscopic properties in the absence and presence of acid were studied. The spectral effects of protonation, molar absorptivities, pK_a values, and the structural origins of the observed spectral behavior were ascertained. The pyridine nitrogen was found to be more basic than the diethylamino nitrogen atom. Protonation of the pyridine ring nitrogen is associated with the appearance of a red‐shifted intramolecular charge transfer peak in the UV‐visible spectra. Favorable color indicating properties result from electron‐donating substitution at the 2 and 6 positions of pyridine, which provide a greater absorptivity of the red‐shifted peak associated with protonation of the pyridine nitrogen. These findings will assist in the design and optimization of these compounds for ion‐indicating and pH‐sensing applications.     

Azulene‐1‐azo‐2′‐thiazoles. Synthesis and properties

Several derivatives belonging to a new compound class, namely azulene‐1‐azo‐2′‐thiazoles, were prepared by the diazotization of 2‐aminothiazoles in the presence of HNO₃/H₃PO₄ followed by the coupling of diazonium salts with azulenes in buffered medium. The reactions proved to be general for this class, the yields are, however, considerably influenced by the substituents at thiazole moiety. For the first time a N‐oxide provided from an amino substituted five‐member nitrogenous heterocycle was diazotized and coupled. The structure of the obtained compounds was assigned and their physico‐chemical properties were discussed. The new azulene azo derivatives exhibit a strong bathochromic shift in UV‐Vis due to the intense push‐pull effect of aromatic system and to the intrinsic properties of thiazole moiety.     

Combined Experimental and Computational Studies on the Physical and Chemical Properties of the Renewable Amide, 3‐Acetamido‐5‐acetylfuran

The pK_a of 3‐acetamido‐5‐acetylfuran (3A5AF) was predicted to be in the range 18.5–21.5 by using the B3LYP/6‐311+G(2d,p) method and several amides as references. The experimental pK_a value, 20.7, was determined through UV/Vis titrations. Its solubility was measured in methanol‐modified supercritical CO₂ (mole fraction, 3.23×10^?4, cloud points 40–80 °C) and it was shown to be less soluble than 5‐hydroxymethylfurfural (5‐HMF). Dimerization energies were calculated for 3A5AF and 5‐HMF to compare hydrogen bonding, as such interactions will affect their solubility. Infrared and ¹H nuclear magnetic resonance spectra of 3A5AF samples support the existence of intermolecular hydrogen bonding. The highest occupied molecular orbital, lowest unoccupied molecular orbital, and electrostatic potential of 3A5AF were determined through molecular orbital calculations using B3LYP/6‐311+G(2d,p). The π–π* transition energy (time‐dependent density functional theory study) was compared with UV/Vis data. Calculated atomic charges were used in an attempt to predict the reactivity of 3A5AF. A reaction between 3A5AF and CH₃MgBr was conducted. As 3A5AF is a recently developed renewable compound that has previously not been studied extensively, these studies will be helpful in designing future reactions and processes involving this molecule.     

Conformational polymorphism of (E,E)‐N,N′‐bis(4‐nitrobenzylidene)benzene‐1,4‐diamine

Two polymorphs of (E,E)‐N,N′‐bis(4‐nitrobenzylidene)benzene‐1,4‐diamine, C₂₀H₁₄N₄O₄, (I), have been identified. In each case, the molecule lies across a crystallographic inversion centre. The supramolecular structure of the first polymorph, (I‐1), features stacking based on π–π interactions assisted by weak hydrogen bonds involving the nitro groups. The second polymorph, (I‐2), displays a perpendicular arrangement of molecules linked via the nitro groups, combined with weak C—H...O hydrogen bonds. Both crystal structures are compared with that of the carbon analogue (E,E)‐1,4‐bis[2‐(4‐nitrophenyl)ethenyl]benzene, (II).     

β,β‐(1,4‐Dithiino)subporphyrin Dimers Capturing Fullerenes with Large Association Constants

β,β‐(1,4‐Dithiino)subporphyrin dimers 7‐syn and 7‐anti were synthesized by the nucleophilic aromatic substitution reaction of 2‐bromo‐3‐(4‐methoxyphenylsulfonyl)subporphyrin 4 with 2,3‐dimercaptosubporphyrin 5 under basic conditions followed by axial arylation. Additions of C₆₀ or C₇₀ to a dilute solution of 7‐anti (ca. 10^?6 m ) in toluene did not cause appreciable UV/Vis spectral changes, while similar additions to a concentrated solution (ca. 10^?3 m ) resulted in precipitation of complexes. In contrast, dimer 7‐syn captured C₆₀ and C₇₀ in different complexation stoichiometries in toluene; a 1:1 manner and a 2:1 manner, respectively, with large association constants; K_a=(1.9±0.2)×10⁶ m ^?1 for C₆₀@ 7‐syn , and K₁=(1.6±0.5)×10⁶ and K₂=(1.8±0.9)×10⁵ m ^?1 for C₇₀@( 7‐syn )₂. These association constants are the largest for fullerenes‐capture by bowl‐shaped molecules reported so far. The structures of C₆₀@ 7‐anti , C₇₀@ 7‐anti , C₆₀@ 7‐syn , and C₇₀@ 7‐syn have been determined by single‐crystal X‐ray diffraction analysis.     

Efficient Light‐Induced pKa Modulation Coupled to Base‐Catalyzed Photochromism

Photoswitchable acid–base pairs, whose pK_a values can be reversibly altered, are attractive molecular tools to control chemical and biological processes with light. A significant, light‐induced pK_a change of three units in aqueous medium has been realized for two thermally stable states, which can be interconverted using UV and green light. The light‐induced pK_a modulation is based on incorporating a 3‐H‐thiazol‐2‐one moiety into the framework of a diarylethene photoswitch, which loses the heteroaromatic stabilization of the negatively charged conjugate base upon photochemical ring closure, and hence becomes significantly less acidic. In addition, the efficiency of the photoreactions is drastically increased in the deprotonated state, giving rise to catalytically enhanced photochromism. It appears that protonation has a significant influence on the shape of the ground‐ and excited‐state potential energy surfaces, as indicated by quantum‐chemical calculations.     

Poly­[[μ2‐aqua‐bis­[(1,10‐phenanthro­line)nickel(II)]]‐di‐μ2,μ4‐5‐nitro‐1,3‐benzene­di­carboxyl­ato]

The reaction of Ni(CH₃COO)₂·4H₂O, 5‐nitro‐1,3‐benzene­di­carboxylic acid (H₂nmbdc), 1,10‐phenanthroline and water under hydro­thermal conditions yields the first reported two‐dimensional nickel coordination polymer with water‐ and carboxyl­ate‐bridged dimeric units, viz. [Ni₂(C₈H₃NO₆)₂(C₁₂H₈N₂)₂(H₂O)]_n. The coordination polyhedron of the Ni^II ion in the title structure is an octahedron defined by an N₂O₄ donor set. The water mol­ecule is positioned on a mirror plane and the 5‐nitro‐1,3‐benzene­di­carboxylate group is located on a twofold axis. Two types of nmbdc²⁻ coordination mode are observed: one is a bis‐monodentate mode, μ₂‐nmbdc²⁻, and the other is a bis‐bridging mode, μ₄‐nmbdc²⁻. The dimeric unit in the title compound is similar to the structural moiety in urease. In the two‐dimensional framework in the title compound, strong stacking interactions between benzene rings (μ₂‐nmbdc²⁻ and μ₄‐nmbdc²⁻) and 1,10‐phenanthroline ligands are observed.     

A two‐dimensional manganese(II) coordination polymer: poly­[[di­aqua­manganese(II)]‐μ‐4,4‐bi­pyridine‐κ2N:N′‐μ‐(p‐phenyl­ene­dioxy­diacetato)‐κ2O:O′]

In the title two‐dimensional coordination polymer, [Mn(1,4‐BDOA)(4,4‐bipy)(H₂O)₂]_n [1,4‐BDOA²⁻ is the p‐phenyl­ene­dioxy­di­acetate dianion (C₁₀H₈O₆) and 4,4‐bipy is 4,4‐bi­pyridine (C₁₀H₈N₂)], each Mn^II atom displays octahedral coordination by two O atoms of the 1,4‐BDOA²⁻ groups, two N atoms of the 4,4‐bipy ligands and two solvent water mol­ecules. The Mn^II atom, 4,4‐bipy ligand and 1,4‐BDOA²⁻ group occupy different inversion centres. Adjacent Mn^II atoms are bridged by 1,4‐BDOA²⁻ groups and 4,4‐bipy ligands, forming a two‐dimensional network with Mn⋯Mn separations of 11.592 (2) and 11.699 (2) Å. Hydro­gen bonds from a water O—H group link the layers in the third dimension.     

Wurster’s Blue‐type Cation Radicals Framed in a 5,10‐Dihydrobenzo[a]indolo[2,3‐c]carbazole (BIC) Skeleton: Dual Electrochromism with Drastic Changes in UV/Vis/NIR and Fluorescence

Electron‐donating dihydrobenzindolocarbazoles (BICs) 1 a – c , which adopt planar disk‐shaped geometries, were prepared by gold(I)‐catalyzed cyclization as a key step. Due to the presence of a 1,4‐phenylenediamine (PD) moiety in the framework, they undergo reversible one‐electron oxidation to the corresponding Wurster’s Blue (WB)‐type species that exhibits NIR absorptions up to λ=1200 nm. In the case of the N,N′‐dimethyl derivative, cation radical 1 c ^+. is stable enough to be isolated as a salt and X‐ray analysis indicated paraquinoid‐type bond alternation in the WB core unit, whereas the bond lengths in the peripheral benzene rings are identical to those in the neutral donor. Upon electrochemical interconversion, the redox pairs of 1 a – c and 1 a – c ^+. exhibited an electrochromic response in the UV/Vis/NIR region, which was accompanied by a drastic change in the fluorescence spectrum because only neutral donors 1 a – c are highly emissive (Φ_F: 0.7–0.8).     

Unexpected Formation of 5‐Nitro‐1H‐benzimidazoles by Nucleophilic Recyclization of 1‐Methyl‐5‐nitropyridinium Salts

The synthesis of substituted 5‐nitro‐2‐phenyl‐1H‐benzimidazoles has been described via domino anionic process rearrangement of 3‐benzoylamino‐1,2‐dimethyl‐5‐nitropyridinium salts in the presence of NaOH water–alcohol solution. Substituted N‐benzoyl‐o‐phenylenediamines was obtained via recyclization of 3‐benzoylamino‐1,2‐dimethyl‐5‐nitropyridinium salts in the presence of aqueous methylamine solution.     

A Practical One‐Step Synthesis of 1,2‐Oxazoline Derivatives from Unprotected Sugars and Its Application to Chemoenzymatic β‐N‐Acetylglucosaminidation of Disialo‐oligosaccharide

A facile and practical method for synthesis of sugar oxazolines (=dihydrooxazoles) from the corresponding N‐acetyl‐2‐amino sugars has been developed by using 2‐chloro‐1,3‐dimethyl‐1H‐benzimidazol‐3‐ium chloride (CDMBI) as a dehydrative condensing agent. The intramolecular dehydrative reaction between the 2‐acetamido group and the anomeric OH group of unprotected N‐acetyl‐2‐amino sugars took place smoothly in H₂O, leading to the formation of a 1,2‐oxazoline (=4,5‐dihydrooxazole) moiety in good yield. Since the reaction proceeds in H₂O without using any protecting groups, the resulting oxazolines can be utilized as effective glycosyl donors for the subsequent enzymatic glycosylation. We have successfully demonstrated a highly efficient chemoenzymatic transglycosylation of a disialo‐oligosaccharide moiety to p‐nitrophenyl N‐acetylglucosaminide catalyzed by a mutant endo‐N‐acetylglucosaminidase without isolating disialo‐oligosaccharide oxazoline as synthetic intermediate.     

Synthesis of ω‐fluorenyl‐functionalized soluble polyphenylene: influence of polymer chain structure on photoluminescence quenching

The influence of the polymer chain structure of soluble polyphenylene (SPP) on the photoluminescence (PL) quenching of fluorene is strongly affected by the 1,2‐phenylene (1,2‐Ph)/1,4‐phenylene (1,4‐Ph) unit molar ratios of SPP, and the amount of 1,4‐Ph units is a major factor for PL quenching. The addition of the fluorenyl group by the formation of carbon–carbon bond at the polymer chain end of SPP is also an important factor for PL quenching of fluorene. Charge (electron) transfer from the fluorenyl end‐group to the main chain of ω‐fluorenyl‐functionalized SPP (FL‐SPP) was very efficient. UV/Vis and PL spectra suggested that this FL‐SPP may be useful for preparing an effective polymer photocell. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and asymmetric anionic polymerization of substituted 7‐aryl‐2,6‐dimethyl‐1,4‐benzoquinone methides

Substituted 7‐aryl‐2,6‐dimethyl‐1,4‐benzoquinone methides which have an electron‐donating methoxy substituent at the para‐position (p‐OMe, 2a ) or an electron‐withdrawing chloro one at the para‐ (p‐Cl, 2b ), meta‐ (m‐Cl, 2c ) , and ortho‐positions (o‐Cl, 2d ) of the benzene ring were synthesized, and their asymmetric anionic polymerizations using the complex of lithium 4‐isopropylphenoxide with (?)‐sparteine were carried out in toluene at 0 °C. The polymers with negative specific rotation were obtained for all of four monomers, and the polymer obtained from 2a showed smaller specific rotation value than that of polymer having no substituent (p‐H, 1 ) on the phenyl group and the polymers obtained from 2b–d showed larger ones. It was found that the kind of a substituent and its substitution position on the phenyl group affect significantly the optical activity of polymers. The largest specific rotation value of [α]₄₃₅= ?153.2° was obtained in the polymerization of 2d with an ortho‐chloro substituent. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 437–444     

Amido‐3‐hydroxypyridin‐4‐ones as Iron(III) Ligands

The synthesis and physicochemical properties of a range of 2‐ and 6‐amido‐3‐hydroxypyridin‐4‐ones are described. All the amido‐substituted 3‐hydroxypyridin‐4‐ones have lower pK_a values than 1,2‐dimethyl‐3‐hydroxypyridin‐4‐one (deferiprone). This is due to the inductive effect of the amido group. Furthermore, the pK_a values of the 3‐hydroxy group in 1‐nonsubstituted pyridinones are dramatically lower than those of the corresponding 1‐alkyl analogues, indicating that a strong hydrogen bond exists between the 2‐amido function and the 3‐oxygen anion, which stabilises the anion. As a result of the decreased competition with protons, the pFe³⁺ values of this group of molecules are higher than that of deferiprone. The distribution coefficients of these molecules are also increased despite the lack of a hydrophobic 1‐alkyl substituent and this is ascribed to the intramolecular hydrogen bond. X‐ray diffraction studies confirm the existence of the intramolecular hydrogen bond.