Spectrophotometric determination of lithium ion using a water-soluble octabromoporphyrin in aqueous solution

A water-soluble porphyrin, (2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin; H(2)obtpps(4-)) was synthesized and developed for the determination of lithium ion in aqueous solution. The octabromo groups lower the basicity of the porphyrin by their electron-withdrawing effect, and enable the porphyrin to react with the lithium ion in alkaline solution to form the lithium complex along with a shift of absorption maximum: lambda max/nm (logepsilon/mol(-1) dm(3) cm(-1)) of the lithium porphyrin are 490.5 nm (5.31) and 734 nm (4.36). Sodium and potassium ions did not react with the porphyrin. The equilibrium constant for the reaction Li(+)+Hobtpps(5-)right harpoon over left harpoon[Li(obtpps)](5-)+H(+) was found to be 10(-8.80) and the conditional formation constant of the [Li(obtpps)](5-) at pH 13 is 10(4.21). The above results were applied to the determination of lithium ion in aqueous solution. The interference from transition and heavy metal ions was masked by using N,N'-1,2-ethanediylbis[N(carboxylmethy)glycinato]magnesium(II) ([Mg(edta)](2-)) solution. Absorbance at 490 nm was measured against a blank solution. A calibration graph was linear over the range of 0.007-0.7 mug cm(-3) (1x10(-6)-1x10(-4) mol dm(-3)) of lithium(I) with a correlation factor of 0.967. Lithium ion less than ppm level was determined spectrophtometrically in aqueous solution. The proposed method was applied to the determination of lithium in human serum and sea water samples.     

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.     

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.     

Kinetics and mechanism of the interaction of pentaammine(pyridine-2-carboxylato)cobalt(III) ions with hexaaquanickel(II) and nickel(II) complexes: the role of chelating ligands

The reversible complexation of the pentaammine(pyridine-2-carboxylato)cobalt(III) ion [N5Co{O2C-(2)-C5H4 N}]2+ [N5=5HN3 and tetraethylenepentaammine (tetren)] with NiIIL(OH2)6-n [L=H2O (N5=tetren); L=bipy, ida2- (iminodiacetate) and nta3- (nitrilotriacetate), N5=5NH3 and tetren] has been investigated by the stopped-flow technique at 20-40 degC, and I= 0.3mol dm-3. At 25degC, the rate constants, kf(dm3 mol-1s-1), DeltaH(kJmol-1) and DeltaS(JK-1mol-1) for the formation of the ternary complexes [(tetren)-CoIII{O2C-(2)-C5H4N} NiIIL(OH2)6-n] are as follows: L=H2O, 530+9, 53+2, -15+7, respectively; L=bipy, 640+30, 37+3, -65+9; L=ida2-, 3900+100, 47+3, -18+11; L=nta3-, 10200+400, 49+1, −2+2. Nickel(II), in the ternary complexes, is chelated by the free pyridyl-N and the carboxylato moiety of the pyridine-2-carboxylate bound to the cobalt centre. The formation rate constant (kf) and the associated activation parameters are relatively insensitive to the N5 moieties for a given ligand L; kf increased in the order: Ni(OH2)62+Ni(bipy)(OH2)42+ Ni(ida)(OH2)3 (nta)(OH2)2-. Data analysis indicated that the mechanism shifted from the dissociative interchange (Id) to the chelation-controlled one, with the decrease of the available sites for coordination in NiIIL(OH2)6−n. The rate constants (kr) for the dissociation of [N5CoIII{O2C-(2)-C5 H4N}NiIIL(OH2) 6-(n+2)] to the parent reactants indicated steric acceleration [krL(5NH3) <krL(tetren)] and followed the trend: krNi(nta)->kr Ni(ida) >krNi(bipy)2+ for both pentaammine substrates. The chelate ring opening rate constants for the ternary complexes were estimated, from which it was apparent that the tetren envelope of cobalt(III) exerted relatively greater steric pressure as compared with 5NH3 in favouring opening up of the chelate ring. This revised version was published online in June 2006 with corrections to the Cover Date.     

Cu(II)氧化抗坏血酸的动力学和机理

本文在总离子强度I=1.00mol.dm^-^3、[Cu^2^+]>>[H2A]、[H^+]>>[H2A]、无氧及无缓冲剂存在的条件下, 研究Cu(II)氧化抗坏血酸(H2A)的动力学和机理. 发现Cu(II)与H2A不发生配位反应, 但以Cl^-存在的情况下, 确有Cu(II)的H2A配合物生成, Cu(II)氧化H2A反应的速率方程为r={a+b[Cl^-]}[Cu^2^+]{[H+]+Ka}^-^2, 25℃时a和b值分别为4.08×10^-^4s^-^1和0.555dm^3.s^-^1.mol^-^1. Cu(II)氧化H2A反应的表观活化能为68.1KJ.mol^-^1. 根据动力学结果, 提出了反应机理, 并给出了配合物ClCuHA的结构形式.     

Rigidity and/or flexibility of calixarenes. effect of the p-sulfonatocalix[n]arenes (n = 4, 6, and 8) on the electron transfer process [Ru(NH3)5pz]2+ + Co(C2O4)3(3-)

The reaction [Ru(NH3)5pz]2+ + Co(C2O4)33- has been studied in aqueous solutions of p-sulfonatocalix[n]arene (n = 4, 6, and 8). The results are interpreted by using the pseudophase model. Results show that the rigidity and/or flexibility of the assembled rings have a great effect on the thermodynamics of inclusion of the guest into the host and, therefore, on the kinetics of the electron transfer processes that take place in these media. The obtained results are discussed from the viewpoint of two types of interactions: electrostatic and nonelectrostatic. From surface potential measurements, the guest-host interactions have been demonstrated to be mainly due to nonelectrostatic interactions, although the species are charged. So, the nonelectrostatic contribution to the equilibrium constant in all the calixarenes studied is 1 order of magnitude higher than the electrostatic one (Knel = 144 and 884 mol-1 dm3 for p-sulfonatocalix[n]arene (n = 4 and 6, respectively) and Kel approximately 10 mol-1 dm3). Electrostatic interactions also affect the kinetic results.     

水合偏硼酸钾的热化学研究

Hydrated potassium monoborate(KBO₂·4/3H₂O) was obtained from an aqueous solution in a mole ratio of K₂O∶B₂O₃=2∶1 and characterized by powder X-ray diffraction(XRD)， infrared spectroscopy(FT-IR) and Raman spectroscopy. The enthalpy of solution of hydrated potassium monoborate， KBO₂·4/3H₂O， in approximately 1mol·dm^-3 aqueous hydrochloric acid was determined. Together with the previously determined enthalpies of so-lution of H₃BO₃ in approximately 1mol·dm^-3 HCl(aq) ，and of KCl in aqueous(hydrochloric acid+boric acid)， the standard molar enthalpy of formation of -(1411.11±0.84)kJ·mol^-1 for KBO₂·4/3H₂O was obtained from the standard molar enthalpies of formation of KCl(s)， H₃BO₃(s)， and H₂O(l). The standard molar entropy of formation of -422.94J·K^-1·mol^-1 and standard molar entropy of 163.47J·K^-1·mol^-1 for KBO₂·4/3H₂O were calculated from the thermodynamic relations. A group contribution method is applicable to KBO₂·4/3H₂O.     

Allosteric Binding of an Ag+ Ion to Cerium(IV) Bis-porphyrinates Enhances the Rotational Activity of Porphyrin Ligands

A series of cerium(IV) bisporphyrinate double-deckers [Ce(bbpp)2] (BBPP = 5,15-bis(4-butoxyphenyl) porphyrin dianion), [Ce(tmpp)2] (TMPP = 5,10,15,20-tetrakis(4-methoxyphenyl)-porphyrin dianion), [Ce(tfpp)2] (TFPP = 5,10,15,20-tetrakis(4-fluorophenyl)porphyrin dianion), [Ce(tmcpp)2] (TMCPP = 5,10,15,20-tetrakis(4-methoxycarbonylphenyl)porphyrin dianion), and [Ce(tmpp)(tmcpp)] was prepared. They bind three Ag+ ions to their concave porphyrin pi subunits (pi-clefts) according to a positive homotropic allosteric mechanism with Hill coefficients (nH) of 1.7-2.7. The rotation rates of the porphyrin ligands in [Ce(bbpp)2] were evaluated to be 200 s-1 at 20 degrees C (delta G++293 = 14.1 kcal mol-1) and 220 s-1 at -40 degrees C (delta G++233 = 11.0 kcal mol-1) without and with Ag+ ions, respectively. These results consistently support our unexpected finding that Ag+ binding can accelerate rotation of the porphyrin ligand. On the basis of UV-visible, 1H NMR, and resonance Raman spectral measurements, the rate enhancement of the rotational speed of the porphyrin ligands is attributed to conformational changes of the porphyrin in cerium(IV) bis-porphyrinate induced by binding of Ag+ guest ions in the clefts. This novel concept of positive homotropic allosterism is applicable to the molecular design of various supramolecular and switch-functionalized systems.     

Kinetics of base hydrolysis of [Co(tetren)dmf]3+ and [Co(tetren)-dmso]3+ (tetren=1,11-diamino-3,6,9-triazaundecane)

The complexes [Co(tetren)dmf](ClO4)3 and [Co(tetren)-dmso](ClO4)3 have been prepared from alpha alpha-[Co(tetren)-Cl](ClO4)Cl (tetren=1,11-diamino-3,6,9-triazaundecane). 1H-n.m.r. and i.r. measurements confirm that the complexes contain O-bonded dmf and dmso. A biphasic reaction is observed in the base hydrolysis of the dmf derivative, monitored by the pH-stat method, with the fast reaction having kOH=1.2*104dm3mol-1s-1 and the slower reaction kOH=1.9*102dm3mol-1s-1 at 25degC and I=0.1moldm3. The fast reaction is assigned to the hydrolysis of the alpha beta(R)-[Co(tetren)dmf]3+ and the slower reaction to that of the alpha The reaction appears to proceed predominantly by a DCB pathway without parallel hydrolysis of coordinated dmf, which has been observed in the hydrolysis of [Co-(NH3)5dmf]3+. Base hydrolysis of [Co(tetren)dmso]3+ was monitored spectrophotometrically over the pH range 4.2 to 5.0. A single reaction was observed with kOH=1.9*106dm3mol-1 s-1 at 25°C and I=0.1 moldm-3. The rapid base hydrolysis is attributed to hydrolysis of the alpha beta(R)- or the alpha beta(S)-[Co(tetren)-dmso]3+ isomer rather than the alpha alpha-isomer. This revised version was published online in June 2006 with corrections to the Cover Date.     

Fe(III)与2,3-二羟基苯甲酸配位反应的动力学和机理

研究了水溶液中三价铁与2,3-二羟基苯甲酸络合反应的机理与动力学. 测定并计算了络合作用的反应速度常数. 活性 和活性焓随氢离子浓度增加而降低, 指明了FeCH2(3+)的缔合机理和FeOH(2+)与Fe2(OH)2(4+)的解离活化机理, 反应速率方程表明氢离子浓度的依赖关系对Fe(III)络合作用是典型的. 但是在[Fe(III)]的二级反应动力学则有一个反常贡献.     

Ionic association of hydroperoxide anion HO2- in the binding mean spherical approximation. Spectroscopic study of hydrogen peroxide in concentrated sodium hydroxide solutions

The ultraviolet-visible (UV-vis) spectroscopy of hydrogen peroxide in concentrated sodium hydroxide solutions was studied. The peroxide band in the UV range shifts from approximately 214 nm to approximately 236 nm as the NaOH concentration increases from 0.338 mol dm-3 to 13.1 mol dm-3. The band originates from an intramolecular electronic transition of the hydroperoxide anion HO2-, as indicated by the negligible temperature effect on the band position and confirmed by ab initio quantum mechanical calculations. It is postulated that the bathochromic shift of the peroxide band that accompanies the increase in NaOH concentration originates from the formation of the ion pair (Na+HO2-). The equilibrium constant for the ion association reaction (0.048 mol-1 dm3) and the characteristics of the individual absorption bands of the hydroperoxide anion and its associate with Na+ were determined from the numerical modeling of the absorbance data, using the binding mean spherical approximation (BIMSA).     

Gas phase generation of the neutrals H2CCCCO, HCCCCDO and CCCHCHO from anionic precursors. Rearrangements of HCCCCDO and CCCHCHO. A joint experimental and theoretical study

The reaction between O-. and MeO-CH2-C identical to C-CDO in the ion source of a VG ZAB 2HF mass spectrometer gives a number of product anions including [H2CCCCO]-. and [HCCCCDO]-. (in the ratio 1:5). Neutralisation-reionisation (NR+) of [H2CCCCO]-. results in the sequential two-electron vertical oxidation [H2CCCCO]-.-->H2CCCCO-->[H2CCCCO](+.). Singlet H2CCCCO lies 158 kJ mol-1 below the triplet [at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory]. The majority of neutrals H2CCCCO are stable for the microsecond duration of the NR experiment, but some are energized and decompose to give H2CCC and CO. A similar NR+ experiment with [HCCCCDO]-. yields neutrals HCCCCDO, some of which are excited and rearrange. Calculations show that it is the singlet form of HCCCCHO which rearranges (the singlet lies 36 kJ mol-1 above the ground state triplet): the rearrangement occurs by the sequential H transfer process, HCCCCHO-->HCC(CH)CO<--H2CCCCO. Neutral HCCCCHO needs an excess energy of only 43 kJ mol-1 to effect this reaction, which is exothermic by 230 kJ mol-1. Both HCC(CH)CO and H2CCCCO formed in this way should have sufficient excess energy to cause some loss of CO. The anions [CC(CH)CHO]-. and [CC(CD)CHO]-. are formed in the ion source of the mass spectrometer by the reactions of HO- with Me3SiC identical to C-CH = CHOMe and Me3SiC identical to C-CD = CHOMe respectively. NR+ of these anions indicate that energized forms of CC(CH)CHO and CC(CD)CHO may rearrange to isomer(s) which decompose by loss of CO. Singlet CC(CH)CHO rearranges to HCC(CH)CO and H2CCCCO, both of which are energized and fragment by loss of CO.     

二(氢过碘酸)合银(III)配离子氧化愈创甘油醚的反应动力学及机理

在碱性介质中, 用传统的分光光度法研究了Ag(III)配离子, 即[Ag(HIO6)2]5-, 氧化药物分子愈创甘油醚的动力学及其机理. 用质谱鉴定了氧化产物；反应对Ag(III) 和愈创甘油醚均为一级；在温度25.0-40.0 ℃范围内, 通过分析[OH-]和[IO-4]tot对反应速率的影响, 二级速率常数有以下表达式：k′=(ka+kb[OH-])K1/{f([OH-])[IO-4]tot+K1}, 在25.0 ℃及离子强度0.30 mol·L-1时, 对此反应有ka=(2.6±1.2)×10-2 mol-1·L·s-1, kb=(2.8±0.1) mol-2·L2·s-1, 及K1=(4.1±0.4)×10-4 mol·L-1, 求出了涉及ka, kb的活化参数, 并据此推出反应机理为反应体系中的[Ag(HIO6)2]5-配离子在前期平衡后, 反应活性中心与药物分子形成Ag(III)-过碘酸-愈创甘油醚分子三元配合物, 配位甘油醚分子通过两个平行途径将两电子传递给中心原子Ag：一个途径无OH-离子参与, 另一途径有OH-参与完成.     

5-[2-(对苯偶氮苯氧基)丁氧基]苯基-10,15,20-三[(对甲氧基苯基)]卟啉及其金属配合物的合成

以5-[2-(4-溴丁氧基)苯基]-10,15,20-三(对甲氧基苯基)卟啉和对羟基偶氮苯为原料,经取代反应合成新化合物5-[2-(对苯偶氮苯氧基)丁氧基]苯基-10,15,20-三[(对甲氧基苯基)]卟啉(2),2经配位反应合成了金属铜,锌配合物(2a)和(2b),其结构经UV-Vis,1H NMR,IR和元素分析表征。     

Structural, redox, and photophysical studies of the tetra(pyridyl)porphyrin complex containing four (2,2'-bipyridine)(2,2':6',2"-terpyridine)ruthenium(II) groups

New hybrid complexes of polypyridyl ruthenium and pyridylporphyrins have been prepared by the coordination of pyridyl nitrogens to the ruthenium centers. A 1:4 hybrid complex, [{Ru(bpy)(trpy)}4(mu4-H2Py4P)]8+ ([1]8+) (bpy = 2,2'-bipyridine; trpy = 2,2':6',2"-terpyridine; H2Py4P = 5,10,15,20-tetra(4-pyridyl)porphyrin), has been characterized by the single-crystal X-ray diffraction method. A 1:1 complex, [{Ru(bpy)(trpy)}(H2PyT3P)]2+ ([2]2+) (H2PyT3P = 5-(4-pyridyl)tritolylporphyrin) has also been prepared. The Soret band of the porphyrin ring shifts to longer wavelength with some broadening, the extent of the shift being larger for [1]8+. Cyclic voltammograms of the two complexes show simple overlap of the component redox waves. The complexes are weakly emissive at room temperature, which becomes stronger at lower temperatures. While [1]8+ at >140 K and [2]2+ at 77-280 K show only porphyrin fluorescence, [1]8+ at <140 K shows ruthenium and porphyrin phosphorescence, in addition to the porphyrin fluorescence.     

Hydroxypropyl-beta-cyclodextrin enhanced fluorimetric method for the determination of melatonin and 5-methoxytryptamine

The effects of native cyclodextrins (alpha, beta or gamma), hydroxypropyl-beta-cyclodextrin, beta-cyclodextrin solubilized in urea, soluble starch and glucose in water solution on the fluorescence behaviour of melatonin (N-acetyl-5-methoxytryptamine) (M) and 5-methoxytryptamine [5-methoxy-3-(2-aminoethyl)indole] (5M) were determined. In addition, the effect of methanol and propanol with and without beta-cyclodextrin or hydroxypropyl-beta-cyclodextrin was assessed. From the fluorescence changes with pH, the values of the pKa for the ground (9.9 +/- 0.2) and the excited state (7.7 +/- 0.2) for 5M were determined. From the fluorescence changes with beta-cyclodextrin or hydroxypropyl-beta-cyclodextrin, the association constants of M, 5MH [5-methoxy-3-(2-ammoniumethyl)indole] and 5M with the two hosts were determined. The values with beta-cyclodextrin were KAssoc5MH = (1.4 +/- 0.4) x 10(2) mol-1 dm3, KAssoc5M = (1.6 +/- 0.1) x 10(2) mol-1 dm3 and KAssocM = (1.1 +/- 0.2) x 10(2) mol-1 dm3, and with hydroxypropyl-beta-cyclodextrin KAssoc5MH = (1.1 +/- 0.3) x 10(2) mol-1 dm3, KAssoc5M = (2.5 +/- 0.1) x 10(2) mol-1 dm3 and KAssocM = (1.51 +/- 0.07) x 10(2) mol-1 dm3. The ratios of the fluorescence quantum yields for the bound and free substrate (phi b/phi f) were in the range 1.15-1.48. The detection limits under the optimum conditions were 0.381 +/- 0.001 ng cm-3 for the complex 5MH-hydroxypropyl-beta-cyclodextrin in water and 0.290 +/- 0.001 ng cm-3 for the complex M-hydroxypropyl-beta-cyclodextrin in water with 5% of methanol. The recovery of melatonin from pharmaceutical preparations was 98-103% with an RSD of 2%. The recovery from rat pineals was also good. The method is direct, simple and accurate.     

Solvent effects on the oxidation of RuIV=O to O=RuVI=O by MnO4-. hydrogen-atom versus oxygen-atom transfer

The kinetics of the oxidation of trans-[RuIV(tmc)(O)(solv)]2+ to trans-[RuVI(tmc)(O)2]2+ (tmc is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane, a tetradentate macrocyclic tertiary amine ligand; solv = H2O or CH3CN) by MnO4- have been studied in aqueous solutions and in acetonitrile. In aqueous solutions the rate law is -d[MnO4]/dt = kH2O[RuIV][MnO4-] = (kx + (ky)/(Ka)[H+])[RuIV][MnO4-], kx = (1.49 +/- 0.09) x 101 M-1 s-1 and ky = (5.72 +/- 0.29) x 104 M-1 s-1 at 298.0 K and I = 0.1 M. The terms kx and ky are proposed to be the rate constants for the oxidation of RuIV by MnO4- and HMnO4, respectively, and Ka is the acid dissociation constant of HMnO4. At [H+] = I = 0.1 M, DeltaH and DeltaS are (9.6 +/- 0.6) kcal mol-1 and -(18 +/- 2) cal mol-1 K-1, respectively. The reaction is much slower in D2O, and the deuterium isotope effects are kx/kxD = 3.5 +/- 0.1 and ky/kyD = 5.0 +/- 0.3. The reaction is also noticeably slower in H218O, and the oxygen isotope effect is kH216O/kH218O = 1.30 +/- 0.07. 18O-labeled studies indicate that the oxygen atom gained by RuIV comes from water and not from KMnO4. These results are consistent with a mechanism that involves initial rate-limiting hydrogen-atom abstraction by MnO4- from coordinated water on RuIV. In acetonitrile the rate law is -d[MnO4-]/dt = kCH3CN[RuIV][MnO4-], kCH3CN = 1.95 +/- 0.08 M-1 s-1 at 298.0 K and I = 0.1 M. DeltaH and DeltaS are (12.0 +/- 0.3) kcal mol-1 and -(17 +/- 1) cal mol-1 K-1, respectively. 18O-labeled studies show that in this case the oxygen atom gained by RuIV comes from MnO4-, consistent with an oxygen-atom transfer mechanism.     

Reduction and adduct formation from electrosprayed solutions of porphyrin salts

The solutions of four meso-tetrakis(N-alkylpyridinium-4-yl)porphyrin salts and of the p-toluenesulfonate salt of meso-tetrakis(4-trimethylammoniumphenyl)porphyrin, in methanol, were studied by electrospray mass spectrometry, in order to investigate the influence of the type of counter ion, the length of the substituent N-alkyl groups of the four (N-alkylpyridinium-4-yl)porphyrins and the presence of an aromatic (alkylpyridinium) or aliphatic (trimethylammonium) nitrogen, in ion formation.In our experimental conditions, adducts with the counter ions were formed only for the meso-tetrakis(4-trimethylammoniumphenyl)porphyrin and were not observed for the other porphyrins, even when the counter ion was the same. In contrast, formation of reduced species, such as the [M(4+) + e(-)]3+, [M(4+) + 2e(-)]2+, [M(4+) + 4e(-) + 2H(+)]2+, and [M(4+) + 5e(-) + 2H(+)]+ ions was observed only for the (N-alkylpyridinium-4-yl)porphyrins and the appearance of these species is apparently solvent related and may occur via counter ion/solvent adducts.