Interfacial Synthesis,Vol. Ill,Recent Advances,Charles E. Carraher,Jr. and Jack Preston,editors, Marcel Dekker,Inc., New York and Basel, 1982, $65.00

Hydrolyses of p‐nitrophenyl picolinate (PNPP) and p‐nitrophenyl acetate (PNPA) mediated by the micellar catalytic systems of two types of cationic surfactants [cetyltrimethylammonium bromide (CTAB), Gemini dimethylene‐1,2‐bis(cetyltrimethylammonium bromide) (16‐2‐16, 2Br^?)] were investigated spectrophotometrically in the pH range of 7.0–9.0 and 25°C. Also, the effects of several kinds of additives, such as ethanol, cyclodextrins (CDs), on the hydrolytic reactions of PNPP and PNPA were studied systematically. It is noteworthy that: (1) double chain Gemini surfactant micellar system enhanced the hydrolyses of carboxylic acid esters notably compared with single chain surfactant (CTAB) micellar solutions under the same reaction conditions; (2) the apparent rate constants (k _obsd) of PNPP and PNPA hydrolyses increased with the increasing in pH values of reaction media; (3) as additives, ethanol has effect on both PNPP and PNPA hydrolyses, and moreover, the k _obsd for hydrolyses decreased with the increasing contents of ethanol (≤5%) at 25°C and pH 9.00; (4) the presence of CDs [α‐cyclodextrin (α‐CD), β‐cyclodextrin (β‐CD), γ‐cyclodextrin (γ‐CD)], as additives, showed different effects on PNPP and PNPA hydrolyses in different reaction systems.     

On the Kinetics of Heterogeneous Free Radical Crosslinking Polymerization1)

Abstract

In this paper, two oximato complexes, mononuclear [Cu(Hdmg)₂] and binuclear [Cu₂(Hdmg)₂(H₂dmg)]ClO₄ · H₂O (H₂dmg: dimethylglyoxime), were synthesized and characterized. Hydrolyses of carboxyl acid esters, p‐nitrophenyl picolinate (PNPP) and p‐nitrophenyl acetate (PNPA), catalyzed by these two complexes were investigated in different micellar systems in the pH range from 6.58–8.65 at 25°C. The results obtained indicate that these two complexes exhibit good catalytic function. It also appears that both complexes accelerate the hydrolytic cleavage of PNPP and PNPA in cationic CTAB micellar solution faster than that in nonionic Brij35 micellar solution, which may be due to the different coordinating ability of substrates to complexes and electrostatic interaction between micelles and complexes. For binuclear Cu(II), the rate constant (k _N) for the hydrolysis of PNPA is about two times larger than that for PNPP in CTAB micellar solution, while in Brij35 micellar solution, the k _N values for PNPA and PNPP are roughly the same. This small difference may be ascribed to the configurations of intermediates formed during the reaction and electrostatic interaction between micelles and reactants.     

Investigation Micellar Catalysis of p-Nitrophenyl Acetate Hydrolysis with Mn(Niten)2H2O Complex

In this article, a mononuclear Mn(Niten)2H₂O complex was prepared to catalyze hydrolysis of p-nitrophenyl acetate (PNPA) in presence of Cetyltrimethylammonium bromide (CTAB) micellar system in different pH range from 6.5–10 at 25°C. These results obtained indicate that the complex exhibits good catalytic function. It also appears the complex accelerates the hydrolytic cleavage of PNPA in cationic CTAB micellar solution which may be due to coordinating ability of substrate to complex, electrostatic interaction between micelles and complex and due to electrostatic interaction between micelles with reactant.     

Carboxyester hydrolysis promoted by novel nano‐sized macrocyclic Zn(II) complexes

A novel series of nano‐sized Zn(II) macrocyclic complexes has been synthesized using the template method, i.e. by the in situ reaction of Schiff bases (derived from 1,4‐bis(4‐amino‐5‐mercapto‐1,2,4‐triazol‐3‐yl)alkanes/phenylene with salicylaldehyde/2‐hydroxyacetophenone) and 1,4‐dibromobutane in the presence of zinc(II) acetate dihydrate in ethanol. The complexes have been characterized using elemental analysis, infrared and NMR spectroscopies, scanning electron microscopy and thermal analysis. The catalytic properties of these complexes have been investigated kinetically for the hydrolysis of p‐nitrophenylacetate (PNPA) at 25°C in aqueous dimethylsulfoxide using phosphate buffer (pH = 7.0–8.5). During the reaction, absorbance of p‐nitrophenolate increases linearly with time (i.e. increase of p‐nitrophenolate concentration) which indicates that the rate of the reaction increases linearly with time. On the basis of these results, a plausible mechanism for the hydrolysis of PNPA is proposed. It is shown that coordinated water may serve as a good nucleophile that effectively catalyses PNPA hydrolysis. Therefore, these complexes may serve as model compounds for hydrolytic enzymes. Copyright © 2014 John Wiley & Sons, Ltd.     

Interaction between primary aliphatic amines and carboxylic acid esters in aqueous micellar solutions of cationic surfactants

The effects of cetylpyridinium bromide (CPB) on the acid-base equilibria of primary aliphatic amines and on the kinetics of reactions of the amines withp-nitrophenyl acetate (PNPA) andp-nitrophenyl caprylate (PNPC) were studied by potentiometric titration and UV spectroscopy. The values of apparent pK _a of the amines in the micellar phase, binding constants of their neutral forms, and the surface potentials of micelles were determined. Cetylpyridinium bromide accelerates the aminolysis of PNPA by factors of 3 to 8 by forming mixed micellar aggregates with the amines. The shift of pK _a values of the amines in micellar solutions is not the only factor that enhances their reactivity. The substrate specificity was found: in contrast to the reaction with PNPA, CPB accelerates (by factors of 15 to 65) or retards (by factors of 4 to 6) the aminolysis of PNPA depending on the hydrophobicity of the nucleophilic reagent. The binding constants of substrates, the rate constants in the micellar phase, and the critical concentrations of micellization were determined from the data obtained. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1333–1338, July, 1998.     

Activity of α‐Chymotrypsin in Cationic and Nonionic Micellar Media: Ultraviolet and Fluorescence Spectroscopic Approach

α‐Chymotrypsin (α‐CT) activity was measured in aqueous buffer with the following alkyltriphenylphosphonium bromide surfactants in the series cetyl, tetradecyl, and dodecyl as a tail length. For the sake of comparison with mixed micellar investigation on activity of α‐CT, cationic cetyltriphenylphosphonium bromide (CTPB) and nonionic surfactant Triton X‐100, Brij‐56, Brij‐35, Tween 20, and Igepal Co‐210 have been used. The p‐nitrophenyl acetate (PNPA) hydrolysis rate was determined at the surfactant concentration of both cationic and mixed micellar systems by a UV–vis spectrophotometer. The catalytic reaction follows the Michaelis–Menten mechanism, and the catalytic efficiency (k_cat/K_M) was evaluated for both homogeneous and mixed‐micellar media. The maximum catalytic efficiency was observed at 5 mM concentration of CTPB, but the highest catalytic efficiency, 572 M^?1 s^?1, was measured in the presence of mixed micellar (7.5 mM CTPB + 2.5 mM Tween‐20). The fluorescence (FL) spectra showed the differences of α‐CT conformations in the presence of cationic surfactants. The FL results suggest that the influence of cationic surfactant on proteolysis arises from the interaction with the α‐CT. The binding constant, k_sv, of α‐CT with cationic aggregates was determined in the buffer using the Stern–Volmer equation by the fluorescence spectroscopic approach.     

Kinetic study of the reactions of p‐nitrophenyl acetate and p‐nitrophenyl benzoate with oximate nucleophiles

The reactions of p‐nitrophenyl acetate (PNPA) and p‐nitrophenyl benzoate (PNPB) with α‐nucleophile oximates, that is, butane 2,3‐dione monoximate, pralidoximate, and other oximates have been studied in the presence of different cationic surfactants. The first‐order rate constant increases with increasing surfactant concentration. The extent of acceleration is dependent on the head group structure of surfactants. The PNPA is more reactive than PNPB toward all the nucleophiles at higher concentration of surfactants. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 57–64, 2009     

Micellar‐accelerated hydrolysis of organophosphate and thiophosphates by pyridine oximate

Rate constants for the hydrolysis reaction of phosphate (paraoxon) and thiophosphate (parathion, fenitrothion) esters by oximate (pyridinealdoxime 2‐PyOx⁻ and 4‐PyOx⁻) and its functionalized pyridinium surfactants 4‐(hydroxyimino) methyl)‐1‐alkylpyridinium bromide ions (alkyl = C_nH_2n+1, n = 10, 12, 14, 16) have been measured kinetically at pH 9.5 and 27°C in micellar media of cationic surfactants cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB). Acid dissociation constant, pK_a, of oximes has also been determined by spectrophotometric, kinetic, and potentiometric methods. The rate acceleration effects of cationic micelles have been explored. Cationic micelles of the pyridinium head group (CPB) showed a large catalytic effect than the ammonium head group (CTAB). The effects of pH, oximate concentration, and surfactants have been discussed.     

Influence of Amine‐Based Cationic Gemini Surfactants on Catalytic Activity of α‐Chymotrypsin

The α‐chymotrypsin activity was tested in aqueous media with the presence of novel cationic amine–based gemini surfactant, with different spacer chain lengths and head group size, and also compared with the cationic cetyltrimethylammonium bromide (CTAB) and cetyltriphenylphosphonium bromide (CTPB) surfactants and aqueous buffer only. The p‐nitrophenyl acetate (PNPA) hydrolysis rate was monitored in the presence of the surfactant concentration at 30°C. Most of these gemini surfactants gave higher catalytic activity as compared to cationic CTAB and CTPB. The highest superactivity was measured in the presence of gemini 16‐12‐16, [dodecanediyl‐1,12‐bis(cetyldimethylammonium bromide)] surfactant at pH 7.5. The catalytic reaction follows the Michaelis–Menten mechanism. The catalytic rate constants, k_cat, show the same profile that the catalytic affinity; K_M being enhanced with increasing space chain length. The results are favorable for considering that the amine‐based gemini surfactant influences more than both the aqueous and cationic micellar media.     

Effect of cationic gemini surfactants on the hydrolysis of carboxylate and phosphate esters using hydroxamate ions

The kinetics of the hydrolysis of p-nitrophenyl acetate (PNPA) and p-nitrophenyl diphenyl phosphate (PNPDPP) by hydroxamate ions mediated by gemini surfactants with quaternary ammonium bromide (16-n-16,2Br⁻, n = 3, 4, 6, 12) and pyridinium chloride (12py-n-py12,2Cl⁻, n = 3, 4) head group have been investigated at 27 °C. The gemini surfactant with the pyridinium head group, 12-py-4-py12,2Cl⁻ (tetramethylene-1,4 bis dodecylpyridinium chloride) shows a large rate acceleration effect than that with an ammonium head group, 16-12-16,2Br⁻, relative to those in water. The apparent pK _a of the hydroxamic acids have been determined in the presence of gemini surfactants. Catalytic system N-phenylbenzohydroxamate/12py-4-py12,2Cl⁻ demonstrated over ~1,590-fold and ~255-fold rate enhancement in the hydrolysis of PNPA and PNPDPP, respectively, for the identical reaction performed in buffer aqueous media at 27 °C. The second order rate constant and binding constants for reactions were determined employing pseudophase model for micellar catalysis.     

The α‐effect in micelles: Nucleophilic substitution reaction of p‐nitrophenyl acetate with N‐phenylbenzohydroxamate ion

Pseudo‐first‐order rate constants have been determined for the nucleophilic substitution reactions of p‐nitrophenyl acetate with p‐chlorophenoxide (4‐ClC₆H₄O^?) and N‐phenylbenzohydroxamate (C₆H₅CON(C₆H₅)O^?) ions in phosphate buffer (pH 7.7) at 27°C. The effect of cationic, (CTAB, TTAB, DTAB), anionic (SDS), and nonionic (Brij‐35) surfactants has been studied. The k_obs value increases upon addition of CTAB and TTAB. The effect of DTAB and other surfactants on the reaction is not very significant. The micellar catalysis and α‐effect shown by hydroxamate ion have been explained. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 26–31, 2006     

Influence of pyridine oximate and quaternized pyridinium oximate ions on the hydrolysis of phosphate esters in cationic microemulsions

Kinetic studies have been performed to understand the hydrolytic potencies of oximate (2- and 4-pyridinealdoxime) and its functionalized oximate (4-(hydroxyiminomethyl)-1-alkylpyridinium bromide) ions (alkyl?=?C₁₀H₂₁ (4-C₁₀PyOx^-); alkyl?=?C₁₂H₂₅ (4-C₁₂PyOx^-)) in the cleavage of phosphate esters, diethyl p-nitrophenylphosphate (Paraoxon) and p-nitrophenyl diphenyl phosphate (PNPDPP) in a cationic (O/W) microemulsion system (ME) over a pH range 7.5 to 11.0 at 300?K. The k_obs values for the reaction of paraoxon with oximate and its functionalized oximate were determined in different microemulsion composition and the kinetic rate data shows that k_obs values increases with increasing water content. The specificity of different chain length of alcohols (n-butanol, n-pentanol, n-hexanol and n-octanol) was also investigated in hydrolytic reactions of paraoxon for different microemulsion composition.     

O‐Nucleophilicity of Hydroxamate Ions for Cleavage of Carboxylate and Phosphate Esters in Cationic Micelles

The nucleophilic reactivities of hydroxamate ( HA^? ) ions of the structure RCONHO^? [R = CH₃ (acetohydroxamate, AHA^? ), C₆H₅ (benzohydroxamate, BHA^? ), 2‐OHC₆H₄ (salicylhydroxamate, SHA^? ), and 4‐CH₃OC₆H₄ (4‐methoxbenzohydroxamate, MBHA^? )] for the hydrolysis of p‐nitrophenyl benzoate ( PNPB ), tris(3‐nitrophenyl) phosphate ( TRIS ), and bis(2,4‐dinitrophenyl) phosphate ( BDNPP ) have been examined kinetically. Over the pH range of 6.7–11.4, the α‐nucleophile ( HA^? ) accelerates deacylation of PNPB and dephosphorylation of TRIS (in cetyltrimethylammonium bromide (CTAB) micelle, 2.0 × 10^?3 M). The salicylhydroxamate ion encountered effective catalysis than AHA^? , BHA^? , and MBHA^? ions. The monoanionic SHA^? and dianionic SA^2? forms of salicylhydroxamic acid are the reactive species. The hydroxamic acid concentration–dependent critical micelle concentration (cmc) and fractional ionization constant ( α ) and of CTAB provide qualitative information for the micellar incorporation of the hydroxamate ion. The ab initio calculations performed on the hydroxamate ions at restricted Hartree–Fock using the 6‐311G (d,p) basis set revealed the O‐nucleophilicity of hydroxamate ions toward C=O and P=O centers. On the basis of ab initio calculation, it has been concluded that hydroxamic acids can exist into E‐amide and Z‐amide forms. The large stable amide or imide anions of hydroxamate are strong nucleophilic for the esterolytic cleavage of carboxylate and phosphate esters.     

Bioaffinitive and Nanosized Polymeric Micelles Based on a Reactive Block Copolymer

Summary: Bio‐affinitive, nanosized polymeric micelles with glucosamine in their corona have a specific interaction with Concanavalin A. They are prepared by a substitution reaction of p‐nitrophenol groups in the poly(p‐nitrophenyl acrylate) (PNPA) corona of stable micelles with glucosamine. The nanosized, stable, and reactive micelles are formed by self‐assembly of the diblock copolymer, poly(p‐nitrophenyl acrylate)‐block‐polystyrene (PNPA‐b‐PSt) in nitromethane, followed by a shell cross‐linking reaction. This method may be useful in the preparation of targeted drugs.

A schematic of the formation of stable glucosamine‐carrying micelles from the diblock copolymer, PNPA‐b‐PSt.     

Reversible addition–fragmentation transfer polymerization of p‐nitrophenyl acrylate and synthesis of diblock copolymers poly(p‐nitrophenyl acrylate)‐b‐polystyrene

Poly(p‐nitrophenyl acrylate)s (PNPAs) with different molecular mass and narrow polydispersity were successfully synthesized for the first time by reversible addition–fragmentation transfer (RAFT) polymerization with azobisisobutyronitrile (AIBN) as an initiator and [1‐(ethoxy carbonyl) prop‐1‐yl dithiobenzoate] as the chain‐transfer agent. Although the molecular mass of PNPAs can be controlled by the molar ratio of NPA to RAFT agent and the conversion, a trace of homo‐PNPA was found, especially at the early stage of polymerization. The dithiobenzoyl‐terminated PNPA obtained was used as a macro chain‐transfer agent in the successive RAFT block copolymerization of styrene (St) with AIBN as the initiator. After purification by two washings with cyclohexane and nitromethane to remove homo‐PSt and homo‐PNPA, the pure diblock copolymers, PNPA‐b‐PSt's, with narrow molecular weight distribution were obtained. The structural analysis of polymerization products by ¹H NMR and GPC verified the formation of diblock copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4862–4872, 2004     

Superoxide Dismutase Activity of the Naturally Occurring Human Serum Albumin–Copper Complex without Hydroxyl Radical Formation

The superoxide radical anion (O₂^.?) is biologically toxic and contributes to the pathogenesis of various diseases. Here we describe the superoxide dismutase (SOD) activity of human serum albumin (HSA) complexed with a single Cu^II ion at the N‐terminal end (HSA–Cu complex). The structure of this naturally occurring copper‐coordinated blood serum protein has been characterized by several physicochemical measurements. The O₂^.? dismutation ability of the HSA–Cu (1:1) complex is almost the same as that of the well‐known SOD mimics, such as Mn^III‐tetrakis(N‐methylpyridinium)porphyrin. Interestingly, the HSA–Cu complex does not induce a subsequent Fenton reaction to produce the hydroxyl radical (OH^.), which is one of the most harmful reactive oxygen species.     

Study of the reaction Fe(CN)4(bpy)2− + S2O82− in Sulfobetaine Aqueous Micellar Solutions

The reaction Fe(CN)₄(bpy)^2? + S₂O₈^2? has been studied in aqueous micellar solutions of N‐tetradecyl‐N,N‐dimethyl‐3‐ammonio‐1‐propanesulfonate, SB3‐14. The influence of changes in the surfactant concentration as well as in the peroxodisulfate ions concentration on k_obs was investigated. Spectroscopic and conductivity measurements have given information about the distribution of both anionic reagents between the aqueous and micellar pseudophases of the SB3‐14 micellar solutions. A discussion about the adequacy of various equations based on the pseudophase model to rationalize kinetic micellar effects for anion‐anion reactions in sulfobetaine micellar solutions has been done. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 225–231, 2001     

Visible‐Light‐Mediated Generation of Nitrogen‐Centered Radicals: Metal‐Free Hydroimination and Iminohydroxylation Cyclization Reactions

The formation and use of iminyl radicals in novel and divergent hydroimination and iminohydroxylation cyclization reactions has been accomplished through the design of a new class of reactive O‐aryl oximes. Owing to their low reduction potentials, the inexpensive organic dye eosin Y could be used as the photocatalyst of the organocatalytic hydroimination reaction. Furthermore, reaction conditions for a unique iminohydroxylation were identified; visible‐light‐mediated electron transfer from novel electron donor–acceptor complexes of the oximes and Et₃N was proposed as a key step of this process.     

Carbon–carbon coupling reactions catalyzed by supported Pd porphyrins

The tetrakis(4‐N‐methylpyridinium)porphyrinatopalladium(II) iodide, [Pd(TMPyP)]I₄, supported on Dowex 50WX8 and Amberlite IR‐120 ion‐exchange resins, was used as heterogeneous, recyclable and active catalyst for the Suzuki–Miyaura and Heck cross‐coupling reactions. These catalysts were applied to coupling of various aryl halides with phenylboronic acid and styrene in Suzuki and Heck reactions, respectively, and the corresponding products were obtained in excellent yields and short reaction times. The catalysts could be recovered easily by simple filtration and reused several times without significant loss of their catalytic activity. The catalysts were characterized by diffuse‐reflectance UV–visible spectroscopy and scanning electron microscopy, and their stability was confirmed by TGA. Copyright © 2014 John Wiley & Sons, Ltd.     

Esterolytic activity of imidazole-containing polymers. Synthesis and characterization of copoly[1-alkyl-4- or 5-vinylimidazole/4(5)-vinylimidazole] and its catalytic activity in the hydrolysis of p-nitrophenyl acetate

The water-soluble monomers, 1-methyl-4-vinylimidazole, 1-methyl-5-vinylimidazole, 1-ethyl-5-vinylimidazole, and 1-propyl-5-vinylimidazole have been synthesized, polymerized, and copolymerized with 4(5)-vinylimidazole. The copolymers were characterized by ¹⁴C-labeling, NMR, pK_a determination and viscosity measurements. The monomer reactivity ratios determined by ¹⁴C counting are r₁ = 1.04; r₂ = 0.94 [M₁ = 4(5)-vinylimidazole, M₂ = 1-methyl-4-vinylimidazole] and r₁ = 1.01; r₂ = 0.86 [M₁ = 4(5)-vinylimidazole, M₂ = 1-methyl-5-vinylimidazole]. The esterolytic activity of the copolymers for the hydrolysis of p-nitrophenyl acetate (PNPA) at pH 7–8 in 28.5% ethanol–water was higher than that of the mixtures of homopolymers. At pH 5–6 the esterolytic activities of the copolymers and the mixtures were similar. The most efficient esterolytic activity for PNPA hydrolysis at pH 7.11 in 28.5% ethanol–water occurred for copolymers containing 75 mole % 4(5)-vinylimidazole and for copolymers containing 1-methyl-4-vinylimidazole rather than 1-methyl-5-vinylimidazole.