摘要:

AbstractContemporary progress regarding guest/host types of excited‐state double proton transfer has been reviewed, among which are the biprotonic transfer within doubly H‐bonded host/guest complexes, the transfer through a solvent bridge relay, the intramolecular double proton transfer and solvation dynamics coupled proton transfer. Of particular emphases are the photophysical and photochemical properties of excited‐state double proton transfer (ESDPT) in 7‐azaindole and its corresponding analogues. From the chemical aspect, two types of ESDPT reaction, namely the catalytic and non‐catalytic types of ESDPT, have been classified and reviewed separately. For the case of static host/guest hydrogen‐bonded complexes both hydrogen‐bonding strength and configuration (i.e. geometry) play key roles in accounting for the reaction dynamics. In addition to the dynamical concern, excited‐state thermodynamics are of importance to fine‐tune the proton transfer reaction in the non‐catalytic host/guest type of ESDPT. The mechanisms of protic solvent assisted ESDPT, depending on host molecules and proton‐transfer models, have been reviewed where the plausible resolution is deduced. Particular attention has been given to the excited‐state proton transfer dynamics in pure water, aiming at its future perspective in biological applications. Finally, the differentiation in mechanism between solvent diffusive reorganization and solvent relaxation to affect the host/guest ESPT dynamics is made a

ISSN:0009-4536    

DOI:10.1002/jccs.200100097

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractEquilibrium constants are deter mined for the protonation and metal complexation of the nickel(II) complexes with 4‐methyl‐4,7‐diazadecanediamide (4‐Me‐L‐2,2,2), 4,7‐dimethyl‐4,7‐diazadecanediamide (4,7‐N,N′‐Me2‐L‐2,2,2), 4‐ethyl‐4,7‐diazadecanediamide (4‐Et‐L‐2,2,2), and 4‐methyl‐4,8‐ diazaundecane diamide (4‐Me‐L‐2,3,2), in 0.10 M KCl at 25.0°C. The formation kinetics of these nickel (II) complexes have been studied under the same conditions with use of the stopped‐flow technique. The possible path ways for the complexation reaction of nickel (II) with these ligands are discussed. The first metal‐nitrogen bond formation is proposed as the rate‐determining step for the reactions of nickel (II) with the unprotonated ligands; proton loss is the rate‐limiting step in the reactions of nickel (II) with the monoprotonated ligands. Similarly, in dissociation reactions of these nickel (II) complexes, the rate‐determining step for the water dissociation pathway is the break age of the second nickel‐nitrogen bond; the rate‐determining step for the proton‐assisted path way is the protonation of the released amino group. The important factors determining the reactivity of these complexes are considered. The kinetic results of the formation and dissociation rea

ISSN:0009-4536    

DOI:10.1002/jccs.200100098

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractIn aqueous dioxane containing triethylamine the title 3‐chloroformazans1are converted into the corresponding 1,4‐bis(arylazo)‐3,6‐diaryl‐1,2,4,5‐tetrazines3via head‐to‐tail dimerization of the intitially formed 1,3‐dipolar ions 2. The kinetics of triethylamine‐catalyzed dehydrochlorination of1in 70% dioxane at 27°C and ionic strength of 0.1 were studied. The rate data were linearly correlated with enhanced Hammett substituent constants σx−and an overall ρ value of 0.2 was determined for the variation of the N‐aryl substituent. These results were interpreted in terms of a two‐step mechanism. Also, the mechanisms of the unimolecular fragmentation of1and3in the mas

ISSN:0009-4536    

DOI:10.1002/jccs.200100099

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThe total capability of an atom attracting valence electrons can be measured by the sum of ionization energies of valence electron in a ground‐state free atom plus its electron affinity called Total Attracting Energy, TAE = ΣniEi+ EA, where, Eiis the ionization energy of theith valence‐shell electron in a ground‐state free atom, niis the number of valence‐shell electron bearing energy Ei, and EA is the electron affinity. And the electronegativity χCLis proportional to the average of TAE, AAE = TAEav, divided by Σni, the number of atomic valence‐shell electrons. χCL= 0.1813 TAEav= 0.1813 AAE = 0.1813 TAE/Σni, = 0.1813 (ΣniEI+ EA)/Σni. Further, the atomic valence orbital electronegativity can be also obtained from the TAE value of an atom. Some discussions were made on several special aspects such as scale of rare gases, comparisons with Pauling's and All

ISSN:0009-4536    

DOI:10.1002/jccs.200100100

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThe phase behavior and motional mobility in binary blends of poly(4‐methylstyrene) (P4MS) and poly(cyclohexyl methacrylate) (PCHMA) have been examined by13C solid state NMR techniques. The blend miscibility was studied by measuring the1H spin‐relaxation times in the laboratory frame (T1H) and in the rotating frame (T1ρH), respectively. Although intermolecular spin diffusion contributes to the proton relaxations in accordance with homogeneity,T1ρHdata shows signs of in complete averaging. TheT1ρHrelaxation behavior indicates the existence of heterogeneous do mains with shortest dimensions in the nanometer range, which is also sup ported by the intermolecular cross polarization experiments with variable contact times. In addition, according to the resuits of carbon T1ρrelaxation time measurements, it is concluded that mixing is intimate some what enough to cause a reduction in local chain mobility for P4MS and vice versa fo

ISSN:0009-4536    

DOI:10.1002/jccs.200100101

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractZnCl2(NIT‐pPy)1, (NIT‐pPy = 2‐(4‐pyridyl)‐4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazolyl‐1‐oxyl‐3‐oxide) crystallizes in the orthorhombic space groupPnn2 with the cell parametersa= 9.4083(9),b= 39.686(3),c= 7.4417(14) Å. ZnCl2(NIT‐6M‐oPy)2, (NIT‐6M‐oPy = 2‐(6‐methyl‐2‐pyridyl)‐4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazolyl‐1‐oxyl‐3‐oxide) crystallizes in the monoclinic space groupPn witha= 7.377(2),b= 19.096(4),c= 11.853(2) Å, β = 95.65(3)°. The temperature dependence magnetic susceptibility of complex1revealed an intermolecular ferromagnetic exchange interaction. A simple spin‐polarization model has been used to justify the observed ferromagnetic excha

ISSN:0009-4536    

DOI:10.1002/jccs.200100102

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractA new biradical of nitronyl nitroxide, 1,3‐[di‐2‐(4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazolyl‐1‐oxyl‐3‐oxide) phenoxy]propane [BNITPhOPr (1)], was prepared and characterized. The temperature dependence of the magnetic susceptibility values were observed for1in the range of 2–300 K. The observed data was successfully simulated giving the exchange integralJ= −0.47 cm−1, θ = −0.94 K. This result indicates a weak antiferromagnetic spin exchange in

ISSN:0009-4536    

DOI:10.1002/jccs.200100103

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractLithium‐7 NMR spectrometry was used to study the complexation reaction between lithium ions and several 12‐, 15‐ and 18‐membered crown ethers in a number of binary acetonitrile‐nitrobenzene mixtures. Formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift‐mole ratio data. There is an inverse relationship between the complex stability and the amount of acetonitrile in the mixed solvent. Among different sized crown ethers used, 15‐crowns were found to form the most stable Li+complexes in the series. The influence of substitution on the macrocyclic rings on the stability of the resulting complexes

ISSN:0009-4536    

DOI:10.1002/jccs.200100104

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractAn ion‐selective electrode using ionophore 2′‐picolylsym‐dibenzo‐16‐crown‐5 ether as membrane carrier, sodium tetraphenylborate (NaTPB) as an anion excluder, and 2‐nitrophenyl‐octyl ether (NOPE) as the plasticing solvent mediator has been successfully developed. This electrode exhibits al in ear response with a slope of 42 mV/decade in concentration ranging from 10−5molL−1to 10−1molL−1, slightly larger than the 30 mV expected from the one‐to‐one complex. The reason for the super‐Nernstain slope is the partial dimmer formation in side the membrane of the electrode, because this dimmer [Cu(C25H27NO6)2(H2O)2] 2ClO4, has been isolated and confirmed by single crystal X‐ray crystallography. The detection limit for the cop per (II) ion was estimated to be 1 × 10−6molL−1. Electrades composed of other plasticing solvent mediators such as tris(2‐ethylhexyl) phosphate (TOP), bis (2‐ethylhexyl) sebacate (DOS) and dibutyl phthalate (DBP) were also investigated. Stability constants (logKs) of the two to one and the one to one 2‐picolylsym‐dibenzo‐16‐crown‐5 ether‐Cu (II) complexes have b

ISSN:0009-4536    

DOI:10.1002/jccs.200100105

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractA wavelet neural network (WNN) is employed to create a quantitative structure‐retention index relationship, which correlates the novel molecular distance edge vector (MDEV)‐consisting of ten elements to Gas Chromatographic retention indexes (RIGC) of Alkanes. TheRIGChas been calculated by the WNN from the molecular topological descriptors of examined alkanes. In this work, theRIGCestimated and predicted by conventional neural networks (say back propagation neural networks, BP) has also been provided. The excellent predicted results with a correlation of 0.9996 and standard deviation of 5.0598 suggest that the WNN technique is a powerful tool in QSAR/QSPR modeling and superior to the BP neural netwo

ISSN:0009-4536    

DOI:10.1002/jccs.200100106

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY