Efficient rate enhancement due to intramolecular general base (IGB) assistance in the hydrolysis of N-(o-hydroxyphenyl)phthalimide

The rates of the hydrolyses of N-(o-hydroxyphenyl)phthalimide (1) and N-(o-methoxyphenyl)phthalimide (2), studied at different pH, show that the hydrolysis of 1 involves intramolecular general base (IGB) assistance where the o-O- group of ionized 1 acts as IGB and H2O as the reactant. The rate enhancement due to the IGB-assisted reaction of H2O with ionized 1 is>8x10(4)-fold. Pseudo-first-order rate constant for the reaction of water with 2 is approximately 2x10(3)-fold smaller than the first-order rate constant (0.10 s-1) for pH-independent hydrolysis of 1 within the pH range of 9.60-10.10. Second-order rate constants (kOH) for hydroxide ion-assisted hydrolysis of ionized 1 and 2 are 3.0 and 29.1 M-1 s-1, respectively. The solvent deuterium kinetic isotope effect (dKIE) on the rate of alkaline hydrolysis of 1 and 2 reveals that the respective values of kOH/kOD are 0.84 and 0.78, where kOD represents the second-order rate constant for DO--assisted cleavage of these imides (1 and 2). The value of kwH2O/kdD2O is 2.04, with kwH2O and kdD2O representing pseudo-first-order rate constants for the reactions of ionized 1 with H2O and D2O, respectively.     

Kinetic evidence for the formation of monocationic N,N'-disubstituted phthalamide in tertiary amine-catalyzed hydrolysis of N-substituted phthalimides

A kinetic study on the aqueous cleavage of N-(2-methoxyphenyl)phthalimide (1) and N-(2-hydroxyphenyl)phthalimide (2), under the buffers of N-methylmorpholine, reveals the equilibrium presence of monocationic amide (Ctam) formed due to nucleophilic reactions of N-methylmorpholine with 1 and 2. Pseudo-first-order rate constants for the reactions of water and HO- with Ctam (formed through nucleophilic reaction of N-methylmorpholine with 1) are 4.60 x 10(-5) s-1 and 47.9 M-1 s-1, respectively. But the cleavage of Ctam, formed through nucleophilic reaction of N-methylmorpholine with 2, involves intramolecular general base (2'-O- group of Ctam)-assisted water attack at carbonyl carbon of cationic amide group of Ctam in or before the rate-determining step.     

Kinetic coupled with UV spectral evidence for near-irreversible nonionic micellar binding of N-benzylphthalimide under the typical reaction conditions: an observation against a major assumption of the pseudophase micellar model

Pseudo-first-order rate constants (k(obs)) for alkaline hydrolysis of N-benzylphthalimide (1) show a nonlinear decrease with the increase in [C(m)E(n)]T (total concentration of Brij 58, m = 16, n = 20 and Brij 56, m = 16, n = 10) at constant [CH(3)CN] and [NaOH]. These nonionic micellar effects, within the certain typical reaction conditions, have been explained in terms of the pseudophase micellar (PM) model. The values of micellar binding constants (KS) of 1 are 1.04 x 10(3) M(-1) (at 1.0 x 10(-3) M NaOH) and 1.08 x 10(3) M(-1) (at 2.0 x 10(-3) M NaOH) for C(16)E(20) as well as 600 M(-1) (at 7.6 x 10(-4) M NaOH) and 670 M(-1) (at 1.0 x 10(-3) M NaOH) for C(16)E(10) micelles. The pseudo-first-order rate constants (kM) for hydrolysis of 1 in C(16)E(20) micellar pseudophase are approximately 90-fold smaller than those (kW) in water phase. The values of kM for hydrolysis of 1 in C(16)E(10) micelles are almost zero. Kinetic coupled with UV spectral data reveals significant irreversible nonionic micellar binding of 1 molecules in the micellar environment of nearly zero hydroxide ion concentration at >or=0.14 M C(16)E(20) and 1.0 x 10(-3) M NaOH while such observations could not be detected at or=3 x 10(-3) M C(16)E(10) and 7.6 x 10(-4) M NaOH, while the rate of hydrolysis of 1 is completely ceased at >or=0.05 M C(16)E(10) and 7.6 x 10(-4) M NaOH. The rate of hydrolysis of 1 at 5.0 x 10(-2) and 8.8 x 10(-2) M C(16)E(10) and 1.0 x 10(-3) M NaOH reveals the formation of presumably phthalic anhydride, whereas such observation was not observed in the C(16)E(20) micellar system under similar experimental conditions.     

Butylated hydroxytoluene analogs: synthesis and evaluation of their multipotent antioxidant activities

A computer-aided predictions of antioxidant activities were performed with the Prediction Activity Spectra of Substances (PASS) program. Antioxidant activity of compounds 1, 3, 4 and 5 were studied using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and lipid peroxidation assays to verify the predictions obtained by the PASS program. Compounds 3 and 5 showed more inhibition of DPPH stable free radical at 10?? M than the well-known standard antioxidant, butylated hydroxytoluene (BHT). Compound 5 exhibited promising in vitro inhibition of Fe2?-induced lipid peroxidation of the essential egg yolk as a lipid-rich medium (83.99%, IC?? 16.07 ± 3.51 μM/mL) compared to α-tocopherol (α-TOH, 84.6%, IC?? 5.6 ± 1.09 μM/mL). The parameters for drug-likeness of these BHT analogues were also evaluated according to the Lipinski’s “rule-of-five” (RO5). All the BHT analogues were found to violate one of the Lipinski’s parameters (LogP > 5), even though they have been found to be soluble in protic solvents. The predictive polar surface area (PSA) and absorption percent (% ABS) data allow us to conclude that they could have a good capacity for penetrating cell membranes. Therefore, one can propose these new multipotent antioxidants (MPAOs) as potential antioxidants for tackling oxidative stress and lipid peroxidation processes.     

Modified Baptista type chaotic cryptosystem via matrix secret key

In 1998, M.S. Baptista proposed a chaotic cryptosystem using the ergodicity property of the simple low-dimensional and chaotic logistic equation. Since then, many cryptosystems based on Baptista's work have been proposed. However, over the years research has shown that this cryptosystem is predictable and vulnerable to attacks and is widely discussed. Among the weaknesses are the non-uniform distribution of ciphertexts and succumbing to the one-time pad attack (a type of chosen plaintext attack). In this Letter, our objective is to modify the chaotic cryptographic scheme proposed previously. We use a matrix secret key such that the cryptosystem would no longer succumb to the one-time pad attack.     

Synchronization in coupled Ikeda delay systems

In this work, we demonstrate the use of a Field Programmable Gate Array (FPGA) as a physical platform for realizing chaotic delay differential equations (DDE). Moreover, using our platform, we also experimentally study the synchronization between two time delayed systems. We illustrate two different experimental approaches – one is hardware co-simulation (using a Digilent Atlys with a Xilinx Spartan-6 FPGA) and the other is analog output (using a Terasic DE2-115 with an Altera Cyclone IV E FPGA).     

Cyclization vs. cyclization/dimerization in o-amidostilbene radical cation cascade reactions: the amide question

The n-butyramido, isobutyramido, benzamido, and furancarboxamido functions profoundly modulate the electronics of the stilbene olefinic and NH groups and the corresponding radical cations in ways that influence the efficiency of the cyclization due presumably to conformational and stereoelectronic factors. For example, isobutyramido- stilbene undergoes FeCl(3) promoted cyclization to produce only indoline, while n-butyramidostilbene, under the same conditions, produces both indoline and bisindoline.     

Effects of nonionic micelles on the rate of alkaline hydrolysis of N-(2'-methoxyphenyl)phthalimide (1): kinetic and rheometric evidence for a transition from spherical to rodlike micelles under the typical reaction conditions

Pseudo-first-order rate constants (k(obs)) for alkaline hydrolysis of N-(2'-methoxyphenyl)phthalimide (1) decrease nonlinearly with increasing total concentration of nonionic surfactant C(m)E(n) (i.e. [C(m)E(n)](T) where m and n represent the respective number of methyl/methylene units in the tail and polyoxyethylene units in the headgroup of a surfactant molecule and m/n=16/20, 12/23 and 18/20) at constant 2% v/v CH(3)CN and 1.0 mM NaOH. The k(obs)vs. [C(m)E(n)](T) data follow the pseudophase micellar (PM) model at ≤ 50 mM C(16)E(20), ≤ 1.4 mM C(12)E(23) and ≤ 2.0 mM C(18)E(20) where rate of hydrolysis of 1 in micellar pseudophase could not be detected. The values of k(obs) fail to follow the PM model at > ～50 mM C(16)E(20), > ～1.4 mM C(12)E(23) and > ～2.0 mM C(18)E(20) which has been attributed to a micellar structural transition from spherical to rodlike which in turn increases C(m)E(n) micellar binding constant (K(S)) of 1 with increasing values of [C(m)E(n)](T). Rheological measurements show the presence of spherical micelles at ≤ 50 mM C(16)E(20), ≤ 1.4 mM C(12)E(23) and ≤ 3.0 mM C(18)E(20). The presence of rodlike micelles is evident from rheological measurements at > ～50 mM C(16)E(20), > ～1.4 mM C(12)E(23) and > ～3.0 mM C(18)E(20).     

Highly selective transformation of poly[(R)-3-hydroxybutyric acid] into trans-crotonic acid by catalytic thermal degradation

Highly selective transformation of poly[(R)-3-hydroxybutyric acid] (PHB) into trans-crotonic acid was achieved by thermal degradation using Mg compounds: MgO and Mg(OH)₂ as catalysts. Through catalytic action, not only the temperature and E_a value of degradation were lowered by 40-50 °C and 11-14 kJ mol⁻¹, respectively, but also significant changes in the selectivity of pyrolyzates were observed. Notably, Mg(OH)₂ showed nearly complete selectivity (∼100%) to trans-crotonic acid. Kinetic analysis of TG profiles revealed that the catalytic thermal degradation of PHB was initiated by some random degradation reactions, followed by the unzipping β-elimination from crotonate chain-ends as a main process. It was suggested that the Mg catalysts promote the totality of the β-elimination reactions by acting throughout the beginning and main processes, resulting in a lowering in the degradation temperature and the completely selective transformation of PHB.     

Effects of mixed aqueous‐organic solvents on the rate of intramolecular carboxylic group‐catalyzed cleavage of N‐(4′‐methoxyphenyl)phthalamic acid

Kinetic study on the cleavage of N‐(4′‐methoxyphenyl)phthalamic acid (NMPPAH) in mixed H₂O‐CH₃CN and H₂O‐1,4‐dioxan solvents containing 0.05 M HCl reveals the formation of phthalic anhydride (PAn)/phthalic acid (PA) as the sole or major product. Pseudo first‐order rate constants (k₁) for the conversion of NMPPAH to PAn decrease nonlinearly from 60.4 × 10^?5 to 2.64 × 10^?5 s^?1 with the increase in the contents of 1,4‐dioxan from 10 to 80% v/v in mixed aqueous solvents. The rate of cleavage of NMPPAH in mixed H₂O‐CH₃CN solvents at ≥50% v/v CH₃CN follows an irreversible consecutive reaction path: NMPPAH PA. The values of k₁ are larger in H₂O‐CH₃CN than in H₂O‐1,4‐dioxan solvents. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 316–325, 2004