Photophysics and kinetics of naphthopyran derivatives,part 3: A general procedure to uniquely identify the kinetic and spectroscopic parameters of ABC(2k,2ϕ) systems and application to naphthopyran reactions

A new procedure has been developed with the aim of determining the kinetic and spectroscopic parameters of any photochemical systems of the generic ABC(2k,1?) and ABC(2k,2?) types. General expressions of the colorability and the equilibrium concentration ratio of two (of the three involved) species at a photostationary state or a state of thermal equilibrium have been derived. The procedure has been successfully applied to achieve unique identifiability for the seven sequences of the ABC(2k,1? and 2?) type that may represent naphthopyran dynamics. It is demonstrated that the reactivity of this particular compound is certainly described by a higher kinetic level than those (three or four reaction steps) considered in the present study. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 421–430, 2006     

A mathematical analysis and elucidation of AB(2k,1ϕ) thermophotochromic kinetics: Analytical solutions using pure kinetic data and considering as unknown the rate constants,quantum yield,and both species' spectra

A new spectrokinetic method is described that determines the absolute values of all five unknown parameters (ε_A, ε_B, ?_AB, k_AB, k_BA) of AB(2k,1?) thermophotoreactive chromic systems. For the first time, solely kinetic data are used to perform complete analytical elucidations. Also, the method addresses realistic situations by considering that both absorption spectra of the reactive species are unknown and partially or totally overlap, solving the identifiability problem, and using a single set of experimental data (for the thermal and photochemical reactions). The absolute values for the five unknown parameters that make up the true kinetic solution are readily obtained by the application of five analytically defined algebraic equations. The method is independent of experimental conditions relating to initial concentration, temperature, threshold of incident light intensity, and the wavelength at which the kinetic traces are measured. The detailed mathematical algorithm also allows the determination of the reaction quantum yield at any (isosbestic and nonisosbestic) irradiation wavelength and proposes a new colorability expression for these systems. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 255–264, 2009     

Photophysics and kinetics of naphthopyran derivatives,part 2: Analysis of diarylnaphthopyran kinetics. Degeneracy of the kinetic solution

The photocoloring and fading kinetics of the photochromic 3,3‐diphenyl‐3H‐naphtho[2,1‐b]pyran (NPY) have been analyzed using a kinetic treatment for three related species recently developed by us (Int J Chem Kinet 2005, 37(3), 162). The concepts of identifiability and distinguishability are developed with respect to the elucidation of the NPY kinetics. We find that neither set of kinetic data on its own, nor the two data sets combined, allow the true mechanism to be distinguished. In addition, even for a chosen mechanism, there exist degenerate sets of parameters i.e. the solutions are also unidentifiable. A discussion of the limits and uniqueness of the results' interpretation is presented. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 717–727, 2005     

An analytical solution for the kinetics of AB(1k,1ϕ) systems and its application to a spirobenzopyran

A new, rapid method is described which determines the absolute values of all the unknown parameters of an AB(1k,1?) reactive system from experimental information about the change of absorbance with time at any given wavelength. The mathematical algorithm is given for the case where the spectrum of the isomer B is not experimentally accessible and overlaps the spectrum of A. An example of its application to a photochromic spiropyran derivative is given. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 539–545, 2007     

Effect of magnetic exchange,double exchange,vibronic coupling,and asymmetry on magnetic properties in d2–d3 mixed‐valence dimers

The effect of magnetic exchange, double exchange, vibronic coupling, and asymmetry on magnetic properties of d²–d³ systems is discussed. The temperature‐dependent magnetic moment was calculated with the semiclassical adiabatic approach. The results show that the vibronic coupling from the out‐of‐phase breathing vibration on the metal sites (Piepho, Krausz, and Schatz [PKS] model) and the vibronic coupling from the stretching vibration between the metal sites (P model) favor the localization and delocalization of the “extra” electron in mixed‐valence dimers, respectively. The magnetic properties are determined by the interplay among magnetic exchange, double exchange, and vibronic coupling. The results obtained by analyzing d²–d³ systems can be generalized to other full delocalized dinuclear mixed valence systems with a unique transferable electron. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Inorganic–organic hybrids involving poly(ε‐caprolactone) and silica network: Hydrogen‐bonding interactions and isothermal crystallization kinetics

Inorganic–organic hybrids mediated by hydrogen‐bonding interactions involving silicon oxide network and poly(ε‐caprolactone) (PCL) were prepared via an in situ sol–gel process of tetraethoxysilane in the presence of PCL. Fourier transform infrared spectroscopy indicated that there were hydrogen‐bonding interactions between carbonyls of PCL and silanol hydroxyls that were formed by incomplete polycondensation in the sol–gel process. In terms of the frequency shift of the hydroxyl stretching vibration bands, it is concluded that the strength of the interassociation between PCL and silicon oxide networks is weaker than that of the self‐association in the control silica network. The phenomenon of equilibrium melting point depression was observed for the PCL/silica system. The hybridization of PCL with silica network causes a considerable increase in the overall crystallization rate and dramatically influences the mechanism of nucleation and growth of the PCL crystallization. The analysis of isothermal crystallization kinetic data according to the Hoffman‐Lauritzen theory shows that with increasing silica content in the hybrids, the surface energy of extremity surfaces increases dramatically for the hybrids. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2594–2603, 2005     

Phptotophysics and kinetics of naphthopyran derivatives,part 4: Investigation of [3H]‐naphthopyran kinetics considered as an ABC(2k, 6ϕ) system yielding a monoexponential trace

The elucidation of [3H]‐naphthopyran photochromic kinetics has been dealt with in this investigation by approximating the photocoloring traces as monoexponential. The experimental data have been analyzed, and 13 defining equations of the reactive dynamics have been established. These have been solved simultaneously as a system of nonlinear equations depending on the extinction coefficients and the six possible quantum yields of this ABC type system. The results of this new approach predict that both colored species are directly photochemically produced from the starting material. The most photochemically reactive photoisomer is the most thermally stable and is also the one characterized by the lowest extinction coefficient of the visible absorption band. The mechanism predicted for 3,3‐diphenyl‐3H‐naphtho[2,1‐b]pyran in toluene at 30°C obeys ABC(1k,6?) kinetics. © 2006 Wiley Periodicals, Inc. J Chem Kinet 38: 431–438, 2006     

Treatment of hydrogen bonding within CNDO/2 and MINDO/3: CNDO/2H and MINDO/3H

A formalism has been developed to treat hydrogen-bonded A—H…?B systems within the CNDO /2 and the MINDO /3 methodologies. In this formalism the interactions are divided into three distinct classes; those between (a) two hydrogen-bonded atoms, (b) one hydrogen-bonded and non-hydrogen-bonded atom, and (c) two non-hydrogen-bonded atoms. The last class of interactions is treated solely by the existing CNDO /2 or MINDO /3 method. For A –H…?B systems, the core resonance integrals are individually parametrized depending upon the class of the interaction. Three types of A—H…?B systems have been thus far parametrized. Nine hydrogen-bonded dimers have been studied using the new formalism and the current CNDO /2 and the MINDO /3 methods. MINDO /3 predicts very large interatomic (A –B) distances for the equilibrium geometry, and relatively small stabilization values for the hydrogen-bond energies. CNDO/2 predicts the reverse. The new formalism for both CNDO /2 and MINDO /3 predicts accurate geometries as well as energies for all nine dimers. The new formalisms are called CNDO /2H and MINDO /3H. A general discussion of the nature of hydrogen bonding as exhibited by CNDO /2H and MINDO /3H is presented.     

New Synthesis of Natural Carotene Isorenieratene (ϕ,ϕ‐Carotene) and its 3,3′‐Dimethoxy Analogue

The main pigments of Brevibacterium linens are the aromatic carotenoids 3,3′‐dihydroxyisorenieratene (φ,φ‐carotene‐3,3′‐diol), the corresponding monohydroxy compound, and the hydrocarbon isorenieratene. We report herein new syntheses of isorenieratene (?,?‐carotene) and its xanthophyll analogue, 3,3′‐dimethoxy‐?,?‐carotene, which may be considered a protected form of the natural xanthophyll, 3,3′‐dihydroxy‐?,?‐carotene.     

Nonisothermal crystallization kinetics of poly(ε‐caprolactone) blocks in double crystalline triblock copolymers containing poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) and poly(ε‐caprolactone) units

The poly(3‐hydroxbutyrate‐co‐3‐hydroxyvalerate)/poly(ε‐caprolactone) block copolymers (PHCLs) with three different weight ratios of PCL blocks (38%, named PHCL‐38; 53%, named PHCL‐53; and 60%, named PHCL‐60) were synthesized by using PHBV with two hydroxyl end groups to initiate ring‐opening polymerization of ε‐caprolactone. During DSC cooling process, melt crystallization of PHCL‐53 at relatively high cooling rates (9, 12, and 15 °C min^?1) and PHCL‐60 at all the selected cooling rates corresponded to PCL blocks so that PHCL‐53 and PHCL‐60 were used to study the nonisothermal crystallization behaviors of PCL blocks. The kinetics of PCL blocks in PHCL‐53 and PHCL‐60 under nonisothermal crystallization conditions were analyzed by Mo equation. Mo equation was successful in describing the nonisothermal crystallization kinetics of PCL blocks in PHCLs. Crystallization activation energy were estimated using Kissinger's method. The results of kinetic parameters showed that both blocks crystallized more difficultly than corresponding homopolymers. With the increase of PCL content, the crystallization rate of PCL block increased gradually. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Classic and multivariate modeling treatment of the kinetics and mechanism of isomerization of 5‐cholesten‐3‐one catalyzed by sodium ethoxide

A classic kinetic methodology including the treatment of the steady‐state method and a multivariate modeling kinetic treatment were applied to the kinetics and mechanism of the isomerization reaction of 5‐cholesten‐3‐one to 4‐cholesten‐3‐one catalyzed by EtO⁻ in ethanol absolute. The rate constants, thermodynamic parameters of activation, equilibrium constant, and the isomerization enthalpy were determined. The multivariate modeling kinetic treatment allows us to calculate the concentrations of the species, in which the 3,5‐dienolate is included as a highly reactive intermediate species and was able to discriminate among several applicable mechanisms validating the one comprising two reversible steps. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 38–47, 2006     

An Experimental Evidence of a Metal−Metal Bond in μ‐Carbonylhexacarbonyl[μ‐(5‐oxofuran‐2(5H)‐ylidene‐κC,κC)]‐dicobalt(Co−Co)[Co2(CO)6(μ‐CO)(μ‐C4O2H2)]

The orthorhombic crystal structure of [Co₂(CO)₆(μ‐CO)(μ‐C₄O₂H₂)] ( 1 ) was determined at 150 K (Fig. 1). Two C−H⋅⋅⋅O bonds connect the molecules, forming waving ribbons along the b axis. The experimental electron density, determined with the aspherical‐atom formalism, was analyzed with the topological theory of molecular structure. The presence of the Co−Co bond critical point indicates for the first time the existence of a metal−metal bond in a system with bridged ligands. The bond critical properties of the intramolecular bonds and of the intermolecular interactions show features similar to those found in [Mn₂(CO)₁₀], confirming our previously established bonding classification for organometallic and coordination compounds.     

New poly(oxyethylene) derivatives and their oligo analogues from Diels–Alder reactions of 5‐[methoxypoly(oxyethylene)]‐(3E)‐1, 3‐pentadiene and 5‐methoxyethoxy‐(3E)‐1,3‐pentadiene

Diels–Alder reactions of 5‐[methoxypoly(oxyethylene)]‐(3E)‐1,3‐pentadiene ( 1a ) with maleic anhydride, diethyl acetylenedicarboxylate (DADC), and acrolein were investigated for the synthesis of new poly(ethylene glycol) derivatives. To facilitate the characterization of the derivatives, Diels–Alder reactions of 5‐methoxyethoxy‐(3E)‐1,3‐pentadiene ( 1b ) with the aforementioned dienophiles were also studied. The reaction of o‐toluidine with the cycloaddition product from maleic anhydride and 1b resulted in the corresponding amide products. The reactions of 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone with cycloadducts derived from 1a and 1b with DADC resulted in the aromatization of the corresponding products. An NMR analysis of the adducts obtained from 1a and acrolein in water and from 1b and acrolein in water/acetonitrile (4:1 v/v) indicated a mixture of endo and exo, with the endo concentration being approximately 80%. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1895–1902, 2005     

Hydrolytic degradation of poly(ε‐caprolactone) with different end groups and poly(ε‐caprolactone‐co‐γ‐butyrolactone): characterization and kinetics of hydrocortisone delivery

Asymmetric telechelic α‐hydroxyl‐ω‐(carboxylic acid)‐poly(ε‐caprolactone) (HA‐PCL), α‐hydroxyl‐ω‐(benzylic ester)‐poly(ε‐caprolactone) (HBz‐PCL), and an asymmetric telechelic copolymer α‐hydroxyl‐ω‐(carboxylic acid)‐poly(ε‐caprolactone‐co‐γ‐butyrolactone) (HA‐PCB) were synthesized by ring‐opening polymerization of ε‐caprolactone (CL). CL and CL/γ‐butyrolactone mixture were used to obtain homopolymers and copolymer respectively at 150°C and 2 hr using ammonium decamolybdate (NH₄) [Mo₁₀O₃₄] (Dec) as a catalyst. Water (HA‐PCL and HA‐PCB) or benzyl alcohol (HBz‐PCL) were used as initiators. The three polylactones reached initial molecular weights between 2000 and 3000 Da measured by proton nuclear magnetic resonance (¹H‐NMR). Compression‐molded polylactone caplets were allowed to degrade in 0.5 M aqueous p‐toluenesulfonic acid at 37°C and monitored up to 60 days for weight loss behavior. Data showed that the copolymer degraded faster than the PCL homopolymers, and that there was no difference in the weight loss behavior between HA‐PCL and HBz‐PCL. Caplets of the three polylactones containing 1% (w/w) hydrocortisone were placed in two different buffer systems, pH 5.0 with citrate buffer and pH 7.4 with phosphate buffer at 37°C, and monitored up to 50 days for their release behavior. The release profiles of hydrocortisone presented two stages. The introduction of a second monomer in the polymer chain significantly increased the release rate, the degradation rate for HA‐PCB being faster than those for HBz‐PCL and HA‐PCL. At the pH studied, only slight differences on the liberation profiles were observed. SEM micrographs indicate that hydrolytic degradation occurred mainly by a surface erosion mechanism. Copyright © 2009 John Wiley & Sons, Ltd.     

Alternating copolymerization of N-benzylidine aniline (NBA) with α-haloacrylic acids (XAA). IV. Synthesis,characterization, and kinetics

This article describes a new, spontaneous, 1:1 alternating copolymerization between a Schiff base, N-benzylidine aniline (NBA), and α-haloacrylic acids (XAA) such as α-chloroacrylic acid (ClAA) and α-bromoacrylic acid (BrAA). The structure of the copolymers was identified by nuclear magnetic resonance (NMR) and infrared (IR) spectra. By using the isolation method we determined the order of each monomer. On the basis of kinetic studies, a mechanism that involves initiation, propagation, and termination by zwitterion is proposed. The effects of copolymerization under various conditions were studied and the intrinsic viscosity and number-average molecular weight were measured. The overall energy of activation, E_Rp, for the copolymerization was determined and thermal degradation studies were made.     

Monoaryloxo ytterbium(III) chlorides supported by β‐diketiminato ligands as novel initiators for the living ring‐opening polymerization of ε‐caprolactone

Ring‐opening polymerization of ε‐caprolactone (ε‐CL) was carried out using β‐diketiminato‐supported monoaryloxo ytterbium chlorides L¹Yb(OAr)Cl(THF) (1) [L¹ = N,N′‐bis(2,6‐dimethylphenyl)‐2,4‐pentanediiminato, OAr = 2,6‐di‐tert‐butylphenoxo‐], and L²Yb(OAr′)Cl(THF) (2) [L² = N,N′‐bis(2,6‐diisopropylphenyl)‐2,4‐pentanediiminato, OAr′ = 2,6‐di‐tert‐butyl‐4‐methylphenoxo‐], respectively, as single‐component initiator. The influence of reaction conditions, such as polymerization temperature, polymerization time, initiator, and initiator concentration, on the monomer conversion, molecular weight, and molecular weight distribution of the resulting polymers was investigated. Complex 1 was well characterized and its crystal structure was determined. Some features and kinetic behaviors of the CL polymerization initiated by these two complexes were studied. The polymerization rate is first order with respect to monomer. The M_n of the polymer increases linearly with the increase of the polymer yield, while polydispersity remained narrow and unchanged throughout the polymerization in a broad range of temperatures from 0 to 50 °C. The results indicated that the present system has a “living character”. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1147–1152, 2006     

Epoxy resin/poly(ϵ‐caprolactone) blends cured with 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane. I. Miscibility and crystallization kinetics

Crystalline thermosetting blends composed of 2,2′‐bis[4‐(4‐aminophenoxy)phenyl]propane (BAPP)‐cured epoxy resin (ER) and poly(?‐caprolactone) (PCL) were prepared via the in situ curing reaction of epoxy monomers in the presence of PCL, which started from initially homogeneous mixtures of diglycidyl ether of bisphenol A (DGEBA), BAPP, and PCL. The miscibility of the blends after and before the curing reaction was established with differential scanning calorimetry and dynamic mechanical analysis. Single and composition‐dependent glass‐transition temperatures (T_g's) were observed in the entire blend composition after and before the crosslinking reaction. The experimental T_g's were in good agreement with the prediction by the Fox and Gordon–Taylor equations. The curing reaction caused a considerable increase in the overall crystallization rate and dramatically influenced the mechanism of nucleation and the growth of the PCL crystals. The equilibrium melting point depression was observed for the blends. An analysis of the kinetic data according to the Hoffman–Lauritzen crystallization kinetic theory showed that with an increasing amorphous content, the surface energy of the extremity surfaces increased dramatically for DGEBA/PCL blends but decreased for ER/PCL blends. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1085–1098, 2003     

Cationic polymerizations by aromatic initiating systems. III. Model reactions for initiation and termination using the t-BuCl/ϕ3Al and Clt-R-Clt/ϕ3Al systems

Preparatory for the synthesis of terminally functional polyisobutylenes carrying one or two phenyl end groups, model experiments have been carried out using novel tert-butyl chloride/triphenylaluminum and 2,6-dichloro-2,6-dimethylheptane/triphenylaluminum initiating systems. As anticipated, t-BuCl was phenylated by ø₃Al and the product is tert-butylbenzene. The reaction is extremely rapid and temperature has little effect on it in the 0 to ?60°C range. The interaction between the 2,6-dichloro-2,6-dimethylheptane and ø₃Al was found to be complicated by a proximity effect which leads to proton elimination in addition to phenylation. The formation of the desired diterminally phenylated product is not quanititative even at ?60°C.