Diazacoronand linked beta-cyclodextrin dimer complexes of Brilliant Yellow tetraanion and their sodium(I) analogues

Complexation of the Brilliant Yellow tetraanion, 3(4-), by two new diazacoronand linked beta-cyclodextrin (beta CD) dimers 4,13-bis(2-(6A-deoxy-beta-cyclodextrin-6A-yl)aminooctylamidomethyl- and 4,13-bis(8-(6A-deoxy-beta-cyclodextrin-6A-yl)aminooctylamidomethyl)-4,13- diaza-1,7,10-trioxacyclopentadecane, 1 and 2, respectively, has been studied in aqueous solution. UV-visible spectrophotometric studies at 298.2 K, pH 10.0 and I = 0.10 mol dm-3 (NEt4ClO4) yielded complexation constants for the complexes 1 x 3(4-) and 2 x 3(4-), K1 = (1.08 +/- 0.01) x 10(5) and (6.21 +/- 0.08) x 10(3) dm3 mol-1, respectively. Similar studies at 298.2 K, pH 10.0 and I = 0.10 mol dm-3 (NaClO4) yielded K3 = (4.63 +/- 0.09) x 10(5) and (3.38 +/- 0.05) x 10(4) dm3 mol-1 for the complexation of 3(4-) by Na+ x 1 and Na+ x 2 to give Na+ x 1 x 3(4-) and Na+ x 2 x 3(4-), respectively. Potentiometric studies of the complexation of Na+ by 1 and 2 by the diazacoronand component of the linkers to give Na+ x 1 and Na+ x 2 yielded K2 = (2.00 +/- 0.05) x 10(3) and (1.8 +/- 0.05) x 10(3) dm3 mol-1, respectively, at 298.2 K and I = 0.10 mol dm-3(NEt4ClO4). For complexation of Na+ by 1 x 3(4-) and 2 x 3(4-) to give Na+ x 1 x 3(4-) and Na+ x 2 x 3(4-) K2K3/K1 = K4 = 8.6 x 10(2) and 9.8 x 10(3) dm3 mol-1, respectively. The pKaS of 1H4(4+) are 7.63 +/- 0.01, 6.84 +/- 0.02, 5.51 +/- 0.04 and 4.98 +/- 0.03, and those of 2H4(4+) are 8.67 +/- 0.02, 8.11 +/- 0.02, 6.06 +/- 0.02 and 5.14 +/- 0.05. The larger magnitude of K1 for 1 by comparison with K1 for 2 is attributed to the octamethylene linkers of 2 competing with 3(4-) for occupancy of the annuli of the beta CD entities while the competitive ability of the dimethylene linkers of 1 is less. A similar argument applies to the relative magnitudes of K3 for Na+ x 1 and Na+ x 2. Increased electrostatic attraction probably accounts for K3 > K1 for Na+ x 1 x 3(4-) and 1 x 3(4-) and for Na+ x 2 x 3(4-) and 2 x 3(4-). The lesser magnitudes of K2 and K4 for Na+ x 1 and Na+ x 1 x 3(4-) compared with those for Na+ x 2 and Na+ x 2 x 3(4-) are attributed to the octamethylene linkers of 2 producing a more hydrophobic environment for the diazacoronand than that produced by the dimethylene linkers of 1. 1H NMR spectroscopic studies and the syntheses of 1 and 2 are described.     

Primary photophysical properties of ofloxacin

Steady-state fluorescence has been used to study the excited singlet state of ofloxacin (OFLX) in aqueous solutions. Fluorescence emission was found to be pH dependent, with a maximum quantum yield of 0.17 at pH 7. Two pKa*s of around 2 and 8.5 were obtained for the excited singlet state. Laser flash photolysis and pulse radiolysis have been used to study the excited states and free radicals of OFLX in aqueous solutions. OFLX undergoes monophotonic photoionization from the excited singlet state with a quantum yield of 0.2. The cation radical so produced absorbs maximally at 770 nm with an extinction coefficient of 5000 +/- 500 dm3 mol-1 cm-1. This is confirmed by one-electron oxidation in the pulse radiolysis experiments. The hydrated electron produced in the photoionization process reacts with ground state OFLX with a rate constant of 2.0 +/- 0.2 x 10(10) dm3 mol-1 s-1, and the anion thus produced has two absorption bands at 410 nm (extinction coefficient = 3000 +/- 300 dm3 mol-1 cm-1) and at 530 nm. Triplet-triplet absorption has a maximum at 610 nm with an extinction coefficient of 11,000 +/- 1500 dm3 mol-1 cm-1. The quantum yield of triplet formation has been determined to be 0.33 +/- 0.05. In the presence of oxygen, the triplet reacts to form both excited singlet oxygen and superoxide anion with quantum yields of 0.13 and < or = 0.2, respectively. Moreover, superoxide anion is also formed by the reaction of oxygen with the hydrated electron from photoionization. Hence the photosensitivity due to OFLX could be initiated by the oxygen radicals and/or by OFLX radicals acting as haptens.     

Cyclodextrin and modified cyclodextrin complexes of E-4-tert-butylphenyl-4'-oxyazobenzene: UV-visible, 1H NMR and ab initio studies

alpha-Cyclodextrin, beta-cyclodextrin, N-(6(A)-deoxy-alpha-cyclodextrin-6(A)-yl)-N'6(A)-deoxy-beta-cyclodextrin-6(A)-yl)urea and N,N-bis(6(A)-deoxy-beta-cyclodextrin-6(A)-yl)urea (alphaCD, betaCD, 1 and 2) form inclusion complexes with E-4-tert-butylphenyl-4'-oxyazobenzene, E-3(-). In aqueous solution at pH 10.0, 298.2 K and I = 0.10 mol dm(-3)(NaClO(4)) spectrophotometric UV-visible studies yield the sequential formation constants: K(11) = (2.83 +/- 0.28) x 10(5) dm(3) mol(-1) for alphaCD.E-(-), K(21) = (6.93 +/- 0.06) x 10(3) dm(3) mol(-1) for (alphaCD)(2).E-3(-), K(11) = (1.24 +/- 0.12) x 10(5) dm(3) mol(-1) for betaCD.E-(-), K(21) = (1.22 +/- 0.06) x 10(4) dm(3) mol(-1) for (betaCD)(2).E-(-), K(11) = (3.08 +/- 0.03) x 10(5) dm(3) mol(-1) for .E-3(-), K(11) = (8.05 +/- 0.63) x 10(4) dm(3) mol(-1) for .E-3(-) and K(12) = (2.42 +/- 0.53) x 10(4) dm(3) mol(-1) for .(E-3(-))(2). (1)H ROESY NMR studies show that complexation of E-3(-) in the annuli of alphaCD, betaCD, 1 and 2 occurs. A variable-temperature (1)H NMR study yields k(298 K)= 6.7 +/- 0.5 and 5.7 +/- 0.5 s(-1), DeltaH = 61.7 +/- 2.7 and 88.1 +/- 4.2 kJ mol(-1) and DeltaS = -22.2 +/- 8.7 and 65 +/- 13 J K(-1) mol(-1) for the interconversion of the dominant includomers (complexes with different orientations of alphaCD) of alphaCD.E-3(-) and (alphaCD)(2).E-3(-), respectively. The existence of E-3(-) as the sole isomer was investigated through an ab initio study.     

Ozonolysis of vinyl compounds,CH2=CH-X,in aqueous solution--the chemistries of the ensuing formyl compounds and hydroperoxides

Reactions of ozone with some vinyl compounds of the general structure CH2=CH-X were studied in aqueous solution. Rate constants (in brackets, unit: dm3 mol-1 s-1) were determined: acrylonitrile (670), vinyl acetate (1.6 x 10(5)), vinylsulfonic acid (anion, 8.3 x 10(3)), vinyl phenylsulfonate (ca. 200), vinyl diethylphosphonate (3.3 x 10(3)), vinylphosphonic acid (acid, 1 x 10(4); mono-anion, 2.7 x 10(4); di-anion, 1 x 10(5)), vinyl bromide (1 x 10(4)). The main pathway leads to the formation of HOOCH2OH and HC(O)X. As measured by stopped flow with conductometric detection, the latter one may undergo rapid hydrolysis by water, e.g. HC(O)CN (3 s-1). Other HC(O)X hydrolyse much slower, e.g. HC(O)PO3(Et)2 (7 x 10(-3) s-1) and HC(O)P(OH)O2- (too slow to be measured). The OH(-)-induced hydrolyses range from ca. 5 dm3 mol-1 s-1 [HC(O)PO(3)2-] to 3.8 x 10(5) dm3 mol-1 s-1 [HC(O)CN]. HC(O)Br mainly decomposes rapidly (too fast for the determination of the rate) into CO and Br- plus H+, and the competing hydrolysis is of minor importance (3.7%). The slow hydrolysis of HC(O)PO(3)2- at pH 10.2, where HOOCH2OH is rapidly decomposed into CH2O plus H2O2, allows an H2O2-induced decomposition (k = 260 dm3 mol-1 s-1) to take place. Formate and phosphate are the final products.     

Kinetics and thermodynamics of the reaction of deoxyhemerythrin with nitric oxide

Deoxyhemerythrin reacts with NO to form a 1:1 adduct shown spectrophotometrically. The kinetics of the formation have been studied directly by stopped-flow measurements at four different temperatures (0.0-23.6 degrees C). The kinetics of the dissociation have been studied, also by stopped-flow techniques, at five different temperatures (4.0-35.1 degrees C) using three different scavengers [Fe(II)(edta)2-, O2 and sperm whale deoxymyoglobin], which gave similar values. For the formation kf = (4.2 +/- 0.2) x 10(6) M-1 s-1, delta Hf not equal = 44.3 +/- 2.3 kJ mol-1, delta Sf not equal to = 30 +/- 8 J mol-1 K-1 and for the dissociation kd = 0.84 +/- 0.02 s-1, delta Hd not equal to 95.6 +/- 2.1 kJ mol-1 delta Sd not equal to = 74 +/- 7 J mol-1 K-1 (25 degrees C, I = 0.2 M and pH 7-8.1). From the kinetic data the thermodynamic data for the formation of HrNO were calculated: Kf = (5.0 +/- 0.3) x 10(6) M-1, delta H = -51.3 +/- 3.1 kJ mol-1 and delta S = -44 +/- 11 J mol-1 K-1 (25 degrees C). The kinetic data suggest that NO occupies the same iron(II) site in deoxyhemerythrin as oxygen does. The equilibrium constant for the formation of Fe(II)(edta)(NO)2- has been redetermined: K1 = (1.45 +/- 0.07) x 10(7) M-1, delta H = -77.5 +/- 1.5 kJ and mol-1 and delta S = -123.5 J mol-1 K-1 (25 degrees C).     

Determination of poorly fluorescent carbamate pesticides in water, bendiocarb and promecarb, using cyclodextrin nanocavities and related media

The effect of native cyclodextrins (alpha, beta, or gammaCD with six, seven and eight glucose units, respectively), hydroxypropyl-beta-cyclodextrin (HPCD), chitosan (CHT) and glucose in water solution or water with n-propylamine (PA) as co-solvent upon the UV-vis and fluorescence properties of poorly fluorescent N-methyl carbamates pesticides (C) as bendiocarb (2,2-dimethyl-1,3-benzodioxol-4-ol methylcarbamate, BC) and promecarb (3-methyl-5-(1-methylethyl)phenol methylcarbame, PC) was examined. Fluorescent enhancement was found for both substrates with all CDs in water or PA-water except from PC with alphaCD. The addition of CHT increases the fluorescence of BC but decreases the fluorescence of PC, and glucose addition gives in both cases no spectral changes. Host-guest interaction was clearly determined by fluorescence enhancement with betaCD and HPCD with a 1:1 stoichiometry for the complexes (C:CD). The values obtained for the association constants (K(A), M(-1)) were (6+/-2)x10(2) and (2.3+/-0.3)x10(2) for BC:betaCD and BC:HPCD complexes, respectively. For PC:betaCD and PC:HPCD the values of K(A) were (19+/-2)x10(2) and (21+/-2)x10(2), respectively. The ratio of the fluorescence quantum yields for the bound and free substrates (phi(CCD)/phi(C)) was in the range 1.74-3.8. The limits of detection (L(D), microg mL(-1)) for the best conditions were (0.57+/-0.02) for BC with HPCD and (0.091+/-0.002) for PC with betaCD in water. Application to the analysis in pesticide spiked samples of tap water and fruit yields satisfactory apparent recoveries (84-114%), and for the extraction procedure in fruits and a commercial formulation, recoveries were of 81-98% and 104%, respectively. The method is rapid, simple, direct, sensitive and useful for pesticide analysis.     

Kinetics of manganese(III) acetate in acetic acid: generation of Mn(III) with Co(III), Ce(IV), and dibromide radicals; reactions of Mn(III) with Mn(II), Co(II), hydrogen bromide,and alkali bromides

The reaction of cobalt(III) acetate with excess manganese(II) acetate in acetic acid occurs in two stages, since the two forms Co(IIIc) and Co(IIIs) are not rapidly equilibrated and thus react independently. The rate constants at 24.5 degrees C are kc = 37.1 +/- 0.6 L mol-1 s-1 and ks = 6.8 +/- 0.2 L mol-1 s-1 at 24.5 degrees C in glacial acetic acid. The Mn(III) produced forms a dinuclear complex with the excess of Mn(II). This was studied independently and is characterized by the rate constant (3.43 +/- 0.01) x 10(2) L mol-1 s-1 at 24.5 degrees C. A similar interaction between Mn(III) and Co(II) is substantially slower, with k = (3.73 +/- 0.05) x 10(-1) L mol-1 s-1 at 24.5 degrees C. Mn(II) is also oxidized by Ce(IV), according to the rate law -d[Ce(IV)]/dt = k[Mn(II)]2[Ce(IV)], where k = (6.0 +/- 0.2) x 10(4) L2 mol-2 s-1. The reaction between Mn(II) and HBr2., believed to be involved in the mechanism by which Mn(III) oxidizes HBr, was studied by laser photolysis; the rate constant is (1.48 +/- 0.04) x 10(8) L mol-1 s-1 at approximately 23 degrees C in HOAc. Oxidation of Co(II) by HBr2. has the rate constant (3.0 +/- 0.1) x 10(7) L mol-1 s-1. The oxidation of HBr by Mn(III) is second order with respect to [HBr]; k = (4.10 +/- 0.08) x 10(5) L2 mol-2 s-1 at 4.5 degrees C in 10% aqueous HOAc. Similar reactions with alkali metal bromides were studied; their rate constants are 17-23 times smaller. This noncomplementary reaction is believed to follow that rate law so that HBr2. and not Br. (higher in Gibbs energy by 0.3 V) can serve as the intermediate. The analysis of the reaction steps then requires that the oxidation of HBr2. to Br2 by Mn(III) be diffusion controlled, which is consistent with the driving force and seemingly minor reorganization.     

New functional model complexes of intradiol-cleaving catechol dioxygenases: properties and reactivity of CuII(L)(O2Ncat)

Complexes Cu(O2Ncat)(tbeda) (1) and Cu(O2Ncat)(tmeda) (2) (tbeda = N,N,N',N'-tetrabenzylethylenediamine, tmeda=N,N,N',N'-tetramethylethylenenediamine, O2NcatH2=4-nitrocatechol) have been prepared by the reaction of copper(II) perchlorate with 4-nitrocatechol in the presence of triethylamine and the appropriate bidentate ligand. These compounds represent structural and functional model systems for the copper-containing catechol 1,2-dioxygenase. Both complexes have been structurally characterized by X-ray crystallography and by UV-vis, IR, and EPR spectroscopies. Upon protonation of 1 and 2 with perchloric acid, the bidentate coordination of O2Ncat could be reversible converted to the monodentate coordination of O2NcatH. The equilibrium constants were found to be 4200 and 3500, respectively, by measuring the UV-vis spectra in DMF. Back-titration with morpholine proved the reversibility of both reactions. Kinetic data on the oxygenation of 1 and 2 revealed overall second-order rate equations with kinetic parameters: ktbeda=(4.63+/-0.23)x10(-2) mol-1 dm3 s-1, DeltaH=51+/-6 kJ mol-1, DeltaS=-137+/-16 J mol-1 K-1; ktmeda=(0.89+/-0.23) mol-1 dm3 s-1, DeltaH=85+/-7 kJ mol-1, DeltaS=-57+/-19 J mol-1 K-1 at 365.16 K. Oxygenation of 1, 2, and [Cu(O2NcatH)(L)]ClO4 (L=tbeda, tmeda) in DMF solution at ambient conditions gives the corresponding intradiol ring-cleaved (2-nitro-muconato)copper(II) complexes. These data support the assumption that the reaction of the differently coordinated catecholate ligand with dioxygen shows only 1,2-dioxygenase activity.     

NMR diffusion spectroscopy as a measure of host-guest complex association constants and as a probe of complex size

The complexes of cyclohexylacetic acid and cholic acid with beta-cyclodextrin were studied by NMR diffusion coefficient measurements. The diffusion coefficient of the 1:1 cyclohexylacetic acid/beta-cyclodextrin complex, K(a) = 1800 +/- 100 M(-1), is slightly slower (3.23 +/- 0.07 x 10(-6) cm(2) s(-1)) than that of beta-cyclodextrin (3.29 +/- 0.07 x 10(-6) cm(2) s(-1)). The diffusion coefficient of the 1:1 cholic acid/beta-cyclodextrin complex, K(a) = 5900 +/- 800 M(-1), is significantly slower (2.93 +/- 0.07 x 10(-6) cm(2) s(-1)) than that of beta-cyclodextrin. The results indicate that caution should be exercised when studying host-guest complexation by the so-called 'single point' technique. A novel data treatment is introduced which takes into account the diffusion behavior of all of the species when determining K(a). Experimentally determined diffusion coefficients of complexes are also a useful probe of the size of host-guest complexes.     

On the photochemistry of IONO2: absorption cross section (240-370 nm) and photolysis product yields at 248 nm

The absolute absorption cross section of IONO(2) was measured by the pulsed photolysis at 193 nm of a NO(2)/CF(3)I mixture, followed by time-resolved Fourier transform spectroscopy in the near-UV. The resulting cross section at a temperature of 296 K over the wavelength range from 240 to 370 nm is given by log(10)(sigma(IONO(2))/cm(2) molecule(-1)) = 170.4 - 3.773 lambda + 2.965 x 10(-2)lambda(2)- 1.139 x 10(-4)lambda(3) + 2.144 x 10(-7)lambda(4)- 1.587 x 10(-10)lambda(5), where lambda is in nm; the cross section, with 2sigma uncertainty, ranges from (6.5 +/- 1.9) x 10(-18) cm(2) at 240 nm to (5 +/- 3) x 10(-19) cm(2) at 350 nm, and is significantly lower than a previous measurement [J. C. M?ssinger, D. M. Rowley and R. A. Cox, Atmos. Chem. Phys., 2002, 2, 227]. The photolysis quantum yields for IO and NO(3) production at 248 nm were measured using laser induced fluorescence of IO at 445 nm, and cavity ring-down spectroscopy of NO(3) at 662 nm, yielding phi(IO) 相似文献   

Comparative study on the inclusion behavior between meso-tetrakis(4-N-ethylpyridiniurmyl)porphyrin and beta-cyclodextrin derivatives

5,10,15,20-Tetrakis(4-N-ethylpyridiniurmyl)porphyrin (TEPyP) formed 1:1 stoichiometry inclusion complexes with beta-cyclodextrin (beta-CD) and its derivatives including hydroxypropyl-beta-cyclodextrin (HP-beta-CD), sulfobutylether-beta-cyclodextrin (SBE-beta-CD) in basic aqueous solution. The supramolecular system was investigated by the methods of fluorescence, UV-vis absorption spectroscopy, nuclear magnetic resonance (NMR) technique. The inclusion ability of cyclodextrins exhibited remarkable difference for beta-CD, HP-beta-CD and SBE-beta-CD. Association constants as high as K=1.1 x 10(4) M(-1) in the case of HP-beta-CD/TEPyP and 2.0 x 10(5) M(-1) in the case of SBE-beta-CD/TEPyP complexes were determined, whereas a lower value (K=550 M(-1)) was given in the case of beta-CD/TEPyP. The results showed that hydrogen bonding and charge attraction play important roles in the processes of host-guest interaction. The interaction mechanism of inclusion processes could be explained by the analysis of NMR spectroscopy. The supramolecular assembly was formed. beta-CD and HP-beta-CD approached from the primary face of cavities of CDs.     

Unimolecular reactions of vibrationally excited CF2ClCHFCH3 and CF2ClCHFCD3: evidence for the 1,2-FCl interchange pathway

Chemically activated CF2ClCHFCH3 and CF2ClCHFCD3 molecules were prepared with 94 kcal mol-1 of vibrational energy by the recombination of CF2ClCHF and CH3(CD3) radicals at room temperature. The unimolecular reaction pathways were 2,3-FH(FD) elimination, 1,2-ClF interchange and 1,2-ClH elimination; the interchange produces CF3CHClCH3(CF3CHClCD3) with 105 kcal mol-1 of vibrational energy. Rate constants for CF2ClCHFCH3 [CF2ClCHFCD3] were (3.1+/-0.4)x10(6) s-1 [(1.0+/-0.1)x10(6) s-1] for 2,3-FH [FD] loss, (1.5+/-0.2)x10(6) s-1 [(8.3+/-0.9)x10(5) s-1] for 1,2-ClF interchange, and (8.2+/-1.0)x10(5) s-1 [(5.3+/-0.6)x10(5) s-1] for 1,2-ClH [DCl] loss. These correspond to branching fractions of 0.55+/-0.06 [0.43+/-0.04] for 2,3-FH [FD] loss, 0.29+/-0.03 [0.35+/-0.04] for 1,2-ClF interchange, and 0.16+/-0.02 [0.22+/-0.02] for 1,2-ClH [ClD] loss. Kinetic-isotope effects were 3.0+/-0.6 for 2,3-FH [FD] loss, 1.6+/-0.3 for 1,2-ClH loss, and 1.8+/-0.4 for 1,2-ClF interchange. The CF3CHClCH3 (CF3CHClCD3) molecules formed by 1,2-FCl interchange react by loss of HCl [DCl] with rate constants of (5.6+/-0.9)x10(7) s-1 [(2.1+/-0.4)x10(7)] s-1 for an isotope effect of 2.7+/-0.4. Density functional theory was employed to calculate vibrational frequencies and moments of inertia for the molecules and for the transition-state structures. These results were used with RRKM theory to assign threshold energies from comparison of computed and experimental unimolecular rate constants. The threshold energy for ClF interchange is 57.5 kcal mol-1, and those for HF and HCl channels are 2-5 kcal mol-1 higher. Experiments with vibrationally excited CF2ClCF2CF3, CF2ClCF2CF2Cl, and CF2ClCF2Cl, which did not show evidence for ClF interchange, also are reported.     

Measurement of sulfite at oxide-coated copper electrodes

The amperometric determination of sulfite was performed using copper electrodes in alkaline media. A mechanism for the oxidation of sulfite at these electrodes is suggested, based on the formation of superficial CuO(.OH), which acted as an electron transfer mediator to the analyte. At 0.5 V versus SCE in 1 M NaOH, sulfite could be calibrated at a sensitivity of 0.2 A l mol-1 cm-2, with a response time for the steady state of 30 s. The limit of detection (three times the signal-to-noise ratio) was 2.5 x 10(-6) M and the response was linear up to 5 x 10(-4) M (r2 = 0.9996, n = 15). The standard deviation (n = 10) at 1 x 10(-5) and 1 x 10(-4) M was 3.27 x 10(-7) A cm-2 (mean = 3.62 x 10(-6) A cm-2) and 1.07 x 10(-13) A cm-2 (mean = 2.25 x 10(-5) A cm-2), respectively.     

Formation of Metallo-6(A)-((2-(bis(2-aminoethyl)amino)ethyl)amino)-6(A)-deoxy-beta-cyclodextrins and Their Complexation of Tryptophan in Aqueous Solution

A pH titration study shows that 6(A)-((2-(bis(2-aminoethyl)amino)ethyl)amino)-6(A)-deoxy-beta-cyclodextrin (betaCDtren) forms binary metallocyclodextrins, [M(betaCDtren)](2+), for which log(K/dm(3) mol(-)(1)) = 11.65 +/- 0.06, 17.29 +/- 0.05, and 12.25 +/- 0.03, respectively, when M(2+) = Ni(2+), Cu(2+), and Zn(2+), where K is the stability constant in aqueous solution at 298.2 K and I = 0.10 mol dm(-)(3) (NaClO(4)). The ternary metallocyclodextrins [M(betaCDtren)Trp](+), where Trp(-) is the tryptophan anion, are characterized by log(K/dm(3) mol(-)(1)) = 8.2 +/- 0.2 and 8.1 +/- 0.2, 9.5 +/- 0.3 and 9.4 +/- 0.2, and 8.1 +/- 0.1 and 8.3 +/- 0.1, respectively, where the first and second values represent the stepwise stability constants for the complexation of (R)- and (S)-Trp(-), respectively, when M(2+) = Ni(2+), Cu(2+), and Zn(2+). From comparisons of stabilities and UV-visible spectra, the binary and ternary metallocyclodextrins appear to be six-coordinate when M(2+) = Ni(2+) and Zn(2+) and five-coordinate when M(2+) = Cu(2+). The factors affecting the stoichiometries and stabilities of the metallocyclodextrins, are discussed and comparisons are made with related systems.     

Kinetics and mechanism of the C6H5 + CH3CHO reaction: experimental measurement and theoretical prediction of the reactivity toward four molecular sites.

The kinetics and mechanism of the reaction of C6H5 with CH3CHO have been investigated experimentally and theoretically. The total rate constant for the reaction has been measured by means of the cavity ring-down spectrometry (CRDS) in the temperature range 299-501 K at pressures covering 20-75 Torr. The overall bimolecular rate constant can be represented by the expression k = (2.8 +/- 0.2) x 10(11) exp[-(700 +/- 30)/T] cm3 mol-1 s-1, which is slightly faster than for the analogous C6H5 + CH2O reaction determined with the same method in the same temperature range. The reaction mechanism for the C6H5 + CH3CHO reaction was also explored with quantum-chemical calculations at various hybrid density functional theories (DFTs) and using ab initio high-level composite methods. The theories predict that the reaction may occur by two hydrogen-abstraction and two addition channels with the aldehydic hydrogen-abstraction reaction being dominant. The rate constant calculated by the transition state theory for the aldehydic hydrogen-abstraction reaction is in good agreement with the experimental result after a very small adjustment of the predicted reaction barrier (+0.3 kcal mol-1). Contributions from other product channels are negligible under our experimental conditions. For combustion applications, we have calculated the rate constants for key product channels in the temperature range of 298-2500 K under atmospheric-pressure conditions; they can be represented by the following expressions in units of cm 3mol-1 s-1: k1,cho = 8.8 x 10(3)T2.6 exp(-90/T), k2,ch3 = 6.0 x 10(1)T3.3 exp(-950/T), k3a(C6H5COCH3 + H) = 4.2 x 10(5)T0.6 exp(-410/T) and k3b(C6H5CHO + CH3) = 6.6 x 10(9)T-0.5 exp(-310/T).     

A supramolecular receptor of diatomic molecules (O2, CO, NO) in aqueous solution

A per-O-methylated beta-cyclodextrin dimer, Py2CD, was conveniently prepared via two steps: the Williamson reaction of 3,5-bis(bromomethyl)pyridine and beta-cyclodextrin (beta-CD) yielding 2A,2'A-O-[3,5-pyridinediylbis(methylene)bis-beta-cyclodextrin (bisCD) followed by the O-methylation of all the hydroxy groups of the bisCD. Py2CD formed a very stable 1:1 complex (Fe(III)PCD) with [5,10,15,20-tetrakis(p-sulfonatophenyl)porphinato]iron(III) (Fe(III)TPPS) in aqueous solution. Fe(III)PCD was reduced with Na2S2O4 to afford the Fe (II)TPPS/Py2CD complex (Fe(II)PCD). Dioxygen was bound to Fe(II)PCD, the P(1/2)(O2) values being 42.4 +/- 1.6 and 176 +/- 3 Torr at 3 and 25 degrees C, respectively. The k(on)(O2) and k(off)(O2) values for the dioxygen binding were determined to be 1.3 x 10(7) M(-1) s(-1) and 3.8 x 10(3) s(-1), respectively, at 25 degrees C. Although the dioxygen adduct was not very stable (K(O2) = k(on)(O2)/k(off)(O2) = 3.4 x 10(3) M(-1)), no autoxidation of the dioxygen adduct of Fe(II)PCD to Fe(III)PCD was observed. These results suggest that the encapsulation of Fe (II)TPPS by Py2CD strictly inhibits not only the extrusion of dioxygen from the cyclodextrin cage but also the penetration of a water molecule into the cage. The carbon monoxide affinity of Fe(II)PCD was much higher than the dioxygen affinity; the P(1/2)(CO), k(on)(CO), k(off)(CO), and K(CO) values being (1.6 +/- 0.2) x 10(-2) Torr, 2.4 x 10(6) M(-1) s(-1), 4.8 x 10(-2) s(-1), and 5.0 x 10(7) M(-1), respectively, at 25 degrees C. Fe(II)PCD also bound nitric oxide. The rate of the dissociation of NO from (NO)Fe(II)PCD ((5.58 +/- 0.42) x 10(-5) s(-1)) was in good agreement with the maximum rate ((5.12 +/- 0.18) x 10(-5) s(-1)) of the oxidation of (NO)Fe(II)PCD to Fe(III)PCD and NO3(-), suggesting that the autoxidation of (NO)Fe(II)PCD proceeds through the ligand exchange between NO and O2 followed by the rapid reaction of (O2)Fe(II)PCD with released NO, affording Fe(II)PCD and the NO3(-) anion inside the cyclodextrin cage.     

Study on vitamin K3-cyclodextrin inclusion complex and analytical application

The inclusion interaction of the complexes between Vitamin K(3) (VK(3)) and beta-cyclodextrin (beta-CD), hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and sulfobutylether-beta-cyclodextrin (SBE-beta-CD) were studied by using steady-state fluorescence measurements. The various factors affecting the inclusion process were examined in detail. The formation constants and inclusion stoichiometry for VK(3)-CDs were determined. The results showed that the inclusion ability of beta-CD and its derivatives was the order: SBE-beta-CD>HP-beta-CD>beta-CD. The related inclusion mechanism is proposed to explain the inclusion process. A method of determining VK(3) was established with the linear range was 2.5 x 10(-6)-5.0 x 10(-4) M, and was used to determine the VK(3) tablets. The recoveries were in the range of 97.52-103.5%. The results were satisfactory.     

Differences of Eu(III) and Cm(III) chemistry in ionic liquids: investigations by TRLFS

In this study the coordination structure and chemistry of Eu(III) and Cm(III) in the ionic liquid C(4)mimTf(2)N (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) was investigated by time-resolved laser fluorescence spectroscopy (TRLFS). The dissolution of 1 x 10(-2) M Eu(CF(3)SO(3))(3) and 1 x 10(-7) M Cm(ClO(4))(3) in C(4)mimTf(2)N leads to the formation of two species for each cation with fluorescence emission lifetimes of 2.5 +/- 0.2 ms and 1.0 +/- 0.3 ms for the Eu-species and 1.0 +/- 0.3 ms and 300.0 +/- 50 micros for the Cm-species. The interpretation of the TRLFS data indicates a comparable coordination for both the lanthanide and actinide cation in this ionic liquid. The quenching influence of Cu(II) on the fluorescence emission of Eu(III) and Cm(III) was also measured by TRLFS. While Cu(ii) does not quench the Cm(III) fluorescence emission in C(4)mimTf(2)N the Eu(III) fluorescence emission lifetime for both Eu-species in C(4)mimTf(2)N decreases with increasing Cu(II) concentration. Stern-Volmer constants were calculated (k(SV) = 1.54 x 10(6) M(-1) s(-1) and k(SV) = 2.70 x 10(6) M(-1)). By contrast, the interaction of Cu(II) with Eu(III) and Cm(III) in water leads to a quenching of both the lanthanide and actinide fluorescence. The calculated Stern-Volmer constants are 1.20 x 10(4) M(-1) s(-1) for Eu(III) and 1.27 x 10(4) M(-1) s(-1) for Cm(III). The investigations show, while the chemistry of trivalent lanthanides and actinides is similar in an aqueous system it is dramatically different in ionic liquids. This difference in chemical behavior may provide the opportunity for a separation of lanthanides and actinides with regard to the reprocessing of nuclear fuel.     

Association interaction and voltammetric determination of 1-aminopyrene and 1-hydroxypyrene at cyclodextrin and DNA based electrochemical sensors

The aim of this work was voltammetric determination of 1-aminopyrene and 1-hydroxypyrene using carbon paste electrodes modified with cyclodextrin derivatives and double stranded deoxyribonucleic acid (dsDNA). The detection schemes based on a preconcentration and differential pulse voltammetric (DPV) determination at beta-cyclodextrin and gamma-cyclodextrin modified carbon paste electrode (beta-CD/CPE, gamma-CD/CPE), neutral beta-cyclodextrin polymer and carboxymethyl-beta-cyclodextrin polymer modified screen-printed electrode (beta-CDP/SPE, beta-CDPA/SPE) and dsDNA modified screen-printed electrode (DNA/SPE) are proposed for the trace determination of studied analytes within the concentration range from 2 x 10(-8) to 4 x 10(-7) mol dm(-3) and from 2 x 10(-7) to 4 x 10(-6) mol dm(-3) with the limits of quantification down to 10(-8) mol dm(-3). Depending on pH, 1-aminopyrene interacts with both surface attached CD and DNA by electrostatic bonds and supramolecular complexation while 1-hydroxypyrene associates with the CD hosts via complexation. The 1-aminopyrene interaction with dsDNA was confirmed by fluorimetric measurements in the solution phase using a competing DNA-TO-PRO-3 dye complex. In addition, the effect of temperature on this association was investigated using an electrically heated DNA-modified carbon paste electrode (DNA/CPE).     

Photophysics of melatonin in different environments

Melatonin (N-acetyl-5-methoxytryptamine) is a naturally occurring hormone with a structural resemblance to tryptophan. Its fluorescence is solvent dependent and strongly quenched in the presence of oxygen. Fluorescence quenching in aqueous and organic solutions have been studied in the presence of different quenchers. A 1: 1 inclusion complex formation between melatonin and different cyclodextrins in aqueous solution has been observed. The effects of microheterogeneous media provided by cyclodextrins, micelles and reverse micelles on the fluorescence characteristics of melatonin have been investigated. The water-soluble inorganic quenchers like KBr and KI were unable to quench the fluorescence of melatonin dissolved in a microemulsion consisting of surfactant + cyclohexane + 1-propanol + water, whereas the organic quenchers like CCl4 and CHCl3 were able to quench the fluorescence with a rate constant (on the order of 10(8) dm3 mol-1 s-1) quite similar to that in neat organic solvents.