高效毛细管电泳分析羊栖菜多糖对肿瘤机体红细胞合淌度的影响

为了分析羊栖菜多糖（SFPS）对肿瘤机体红细胞合淌度的影响,建立了肿瘤动物模型,分高、中、低剂量腹腔给予羊栖菜多糖7 d,采集并制备红细胞悬液,应用高效毛细管电泳法检测红细胞的合淌度。实验条件:毛细管为75 μm×50 cm,电泳缓冲液为含2 g/L羟丙基甲基纤维素的磷酸盐溶液(0.1 mol/L,pH 7.4),压力进样为3.448 kPa×10 s,分离电压为20 kV,柱温为25 ℃,电渗淌度为2.16×10-4 cm2·V-1·s-1。实验结果表明：羊栖菜多糖能降低肿瘤机体红细胞的电泳迁移时间(阴性对照组为15.76 min,SFPS低剂量组为13.96 min,SFPS中剂量组为12.90 min,SFPS高剂量组为13.51 min,正常对照组为11.51 min),增加红细胞的合淌度(阴性对照组为1.06×10-4 cm2·V-1·s-1,SFPS低剂量组为1.19×10-4 cm2·V-1·s-1,SFPS中剂量组为1.29×10-4 cm2·V-1·s-1,SFPS高剂量组为1.23×10-4 cm2·V-1·s-1,正常对照组为1.45×10-4 cm2·V-1·s-1),SFPS 3个剂量组红细胞的合淌度与阴性对照组比较均有非常显著的差异(P＜0.01)。羊栖菜多糖能够改变肿瘤机体红细胞的合淌度,并使之趋向于正常机体水平,这可能与其改变红细胞表面的电荷密度有关。高效毛细管电泳法可以作为检测红细胞生理状态和功能的一种辅助工具。     

Dynamics for reaction of an ion pair in aqueous solution: reactivity of carboxylate anions in bimolecular carbocation-nucleophile addition and unimolecular ion pair collapse

[reaction: see text]. The sum of the rate constants for solvolysis and 18O-scrambling of 4-MeC6H4(13)CH(Me)18OC(O)C6F5 in 50/50 (v/v) trifluoroethanol/water, k(solv) + k(iso) = 1.22 x 10(-5) s(-1), is larger than k(solv) = 1.06 x 10(-5) s(-1) for solvolysis of the unlabeled ester. This shows that the ion pair intermediate undergoes significant internal return. The data give k(-1) = 7 x 10(9) s(-1) for internal return by unimolecular collapse of the ion pair, which is significantly larger than k(Nu) = 5 x 10(8) M(-1) x s(-1) for bimolecular nucleophilic addition of carboxylate anions to 4-MeC6H4CH(Me)+.     

Suggested Improvement in the Ing-Manske Procedure and Gabriel Synthesis of Primary Amines: Kinetic Study on Alkaline Hydrolysis of N-Phthaloylglycine and Acid Hydrolysis of N-(o-Carboxybenzoyl)glycine in Aqueous Organic Solvents

A slight modification of the Gabriel synthesis of primary amines is suggested on the basis of the observed and reported values of rate constants for the alkaline and acid hydrolyses of phthalimide, phthalamic acid, benzamide, and their N-substituted derivatives. The suggested procedure requires shorter reactions time and milder acid-base reaction conditions compared with the conventional acid-base hydrolysis in the Gabriel synthesis. A slight modification in the Ing-Manske procedure is also suggested. Pseudo-first-order rate constants, k(obs), for hydrolysis of N-phthaloylglycine, NPG, decrease from 24.1 x 10(-3) to 7.72 x 10(-3) and 6.12 x 10(-3) s(-1) with increasing acetonitrile and 1,4-dioxan contents, respectively, from 2 to 50% v/v (all the percentages given in the paper are vol %), while increasing the organic cosolvents content from 50 to 80% increases k(obs) from 7.72 x 10(-3) to 19.7 x 10(-3) s(-1) for acetonitrile and from 6.12 x 10(-3) to 52.8 x 10(-3) s(-1) for 1,4-dioxan, in aqueous organic solvents containing 0.004 M NaOH at 35 degrees C. The rate constants for NPG hydrolysis decrease from 2.11 x 10(-2) to 1.19 x 10(-4) s(-1) with increasing MeOH content from 2 to 84%, in aqueous organic solvents containing 2% MeCN and 0.004 M NaOH at 35 degrees C.     

Preparations and electrochemical properties of pyrazine-bridged ruthenium-binuclear complexes exhibiting molecular hysteresis

Three binuclear Ru complexes cis-,cis-[(NH3)4(L)Ru-pz-Ru(NH3)4(dmso)](PF6)4 (L = NH3 (4), pyridine (5), benzonitrile (6); dmso = dimethyl sulfoxide) have been prepared, and their electrochemical behavior, exhibiting molecular hysteresis, is reported. Simulations of cyclic voltammograms and thin-layer cyclic voltammograms have provided redox potentials, isomerization rates, and interconversion rates of the complexes. The rates of the conversions between two isomeric intermediate states have been determined to be5 x 10(-6) and 4 x 10(-4) s(-1) for the complex 4, 4 x 10(-5) and 4 x 10(-4) s(-1) for the complex 5, and 2 x 10(-4) and 5 x 10(-5) s(-1) for the complex 6. The equilibrium parameters between these states are discussed in relation to the redox potentials of the complexes.     

Atmospheric chemistry of perfluorinated aldehyde hydrates (n-C(x)F(2x+1)CH(OH)2, x = 1, 3, 4): hydration, dehydration, and kinetics and mechanism of Cl atom and OH radical initiated oxidation

Smog chamber/Fourier transform infrared (FTIR) techniques were used to measure k(Cl+C(x)F(2x+1)CH(OH)(2)) (x = 1, 3, 4) = (5.84 +/- 0.92) x 10(-13) and k(OH+C(x)F(2x+1)CH(OH)(2)) = (1.22 +/- 0.26) x 10(-13) cm(3) molecule(-1) s(-1) in 700 Torr of N(2) or air at 296 +/- 2 K. The Cl initiated oxidation of CF(3)CH(OH)(2) in 700 Torr of air gave CF(3)COOH in a molar yield of 101 +/- 6%. IR spectra of C(x)F(2x+1)CH(OH)(2) (x = 1, 3, 4) were recorded and are presented. An upper limit of k(CF(3)CHO+H(2)O) < 2 x 10(-23) cm(3) molecule(-1) s(-1) was established for the gas-phase hydration of CF(3)CHO. Bubbling CF(3)CHO/air mixtures through liquid water led to >80% conversion of CF(3)CHO into the hydrate within the approximately 2 s taken for passage through the bubbler. These results suggest that OH radical initiated oxidation of C(x)F(2x+1)CH(OH)(2) hydrates could be a significant source of perfluorinated carboxylic acids in the environment.     

Low temperature NH(X 3sigma-) radical reactions with NO, saturated, and unsaturated hydrocarbons studied in a pulsed supersonic laval nozzle flow reactor between 53 and 188 K

The reactions of ground-state imidogen radicals (NH(X 3sigma-)) with NO and select saturated and unsaturated hydrocarbons have been measured in a pulsed supersonic expansion Laval nozzle flow reactor in the temperature range 53-188 K. The rate coefficients for the NH + NO system display negative temperature dependence in the temperature regime currently investigated and a global temperature-dependent fit is best represented in a modified power law functional form, with k1(NH + NO) = (4.11 +/- 0.31) x 10(-11) x (T/300)(-0.30+/-0.17) x exp(77+/-21/T) cm3/s. The reactions of NH with ethylene, acetylene, propene, and diacetylene were measured over the temperature range 53-135 K. In addition, the reactions of NH with methane and ethane were also measured at 53 K, for reasons discussed later. The temperature dependence of the reactions of NH with the unsaturated hydrocarbons are fit using power law expressions, k(T) = A(T/300)(-n), and are as follows: k4 = (2.3 +/- 1.2) x 10(-12) x (T/300)(-1.09+/-0.33) cm3/s, k5 = (4.5 +/- 0.3) x 10(-12) x (T/300)(-1.07+/-0.04) cm3/s, k6 = (5.6 +/- 1.9) x 10(-12) x (T/300)(-1.23+/-0.21) cm3/s, and k7 = (7.4 +/- 1.8) x 10(-12) x (T/300)(-1.23+/-0.15) cm3/s for ethylene, acetylene, propene, and diacetylene, respectively. The rate for NH + ethane at 53 K is measured to be k3 = (6.8 +/- 1.7) x 10(-12) cm3/s, while that for methane at the same temperature represents an upper bound of k2 < or = (1.1 +/- 4.3) x 10(-12) cm3/s, as this is at the limits of measurement with our current technique. The behavior of these systems throughout the temperature range explored indicates that these reactions occur over a potential energy surface without an appreciable barrier through a complex formation mechanism. Implications for chemistry in low temperature environments where these species are found are briefly discussed.     

A pulse radiolysis investigation of the reactions of tributyl phosphate with the radical products of aqueous nitric acid irradiation

Tributyl phosphate (TBP) is the most common organic compound used in liquid-liquid separations for the recovery of uranium, neptunium, and plutonium from acidic nuclear fuel dissolutions. The goal of these processes is to extract the actinides while leaving fission products in the acidic, aqueous phase. However, the radiolytic degradation of TBP has been shown to reduce separation factors of the actinides from fission products and to impede the back-extraction of the actinides during stripping. As most previous investigations of the radiation chemistry of TBP have focused on steady state radiolysis and stable product identification, with dibutylphosphoric acid (HDBP) invariably being the major product, here we have determined room temperature rate constants for the reactions of TBP and HDBP with the hydroxyl radical [(5.00 +/- 0.05) x 10(9), (4.40 +/- 0.13) x 10(9) M(-1) s(-1)], hydrogen atom [(1.8 +/-0.2) x 10(8), (1.1 +/- 0.1) x 10(8) M(-1) s(-1)], nitrate radical [(4.3 +/- 0.7) x 10(6), (2.9 +/- 0.2) x 10(6) M(-1) s(-1)], and nitrite radical (<2 x 10 (5), <2 x 10(5) M(-1) s(-1)), respectively. These data are used to discuss the mechanism of TBP radical-induced degradation.     

Photodissociation of p-xylene in polar and nonpolar solutions

The photodissociation of p-xylene at 266 nm in n-heptane and acetonitrile has been studied with use of nanosecond fluorescence and absorption spectroscopy. The p-methylbenzyl radical was identified in n-heptane and acetonitrile by its fluorescence, which was induced by excitation at 308 nm. The p-xylene radical cation was observed in acetonitrile by its absorption. In n-heptane, the decay rate of the S(1) state of p-xylene ((3.2 +/- 0.2) x 10(7) s(-1)) is equal to the growth rate of the p-methylbenzyl radical ((2.7 +/- 0.4) x 10(7) s(-1)), showing that the molecule dissociates via the S(1) state into the radical by C-H bond homolysis (quantum efficiency approximately 5.0 x 10(-3)). In acetonitrile, the formation of the p-xylene radical cation requires two 266 nm photons, and the decay rate of the radical cation ((1.6 +/- 0.2) x 10(6) s(-1)) equals the growth rate of the p-methylbenzyl radical ((2.0 +/- 0.2) x 10(6) s(-1)). This shows that the radical cation dissociates into the radical by deprotonation (quantum efficiency approximately 8.9 x 10(-2)).     

旋转圆盘电极体系上的非稳态电极过程

本文用Laplace变换和正则摄动法求解旋转圆盘电极体系的对流扩散方程, 得到精确的级数解, 并拟合得到近似公式。从该公式出发, 经Laplace变换运算, 本文得到了大幅度电位阶跃过程的电流公式和脉冲电流过程的极限电流公式。     

Aminocyclodextrins to facilitate the deprotonation of 4-tert-butyl-alpha-nitrotoluene

6A-Amino-6A-deoxy-beta-cyclodextrin enhances the rate of the deprotonation of 4-tert-butyl-alpha-nitrotoluene. The rate constants for reaction of the cyclodextrin-bound species, kinc = 4 x 10(-3), 9 x 10(-3) and 19 x 10(-3) s(-1), at pH 6.0, 6.5 and 7.0, respectively, in 0.1 mol dm(-3) aqueous phosphate buffer containing 1% methanol at 298 K. These rate constants correspond to a rate acceleration (kinc/kun) of ca. 10 times at each pH. Under the same conditions, 6A-dimethylamino-6A-deoxy-beta-cyclodextrin and 6A-(2-aminoethylamino)-6A-deoxy-beta-cyclodextrin are more effective; at pH 6.0, 6.5 and 7.0, for the former, kinc = 3 x 10(-2), 7 x 10(-2) and 12 x 10(-2) s(-1), whilst for the latter, kinc = 4 x 10(-2), 5 x 10(-2) and 9 x 10(-2) s(-1), respectively. Each cyclodextrin also decreases the pKa of the nitrotoluene, from 6.8 in free solution, to 6.2 when bound. The accelerated deprotonation by 6A-amino-6A-deoxy-beta-cyclodextrin is reflected in the enhanced rates of hydrogen-deuterium exchange of the nitrotoluene in deuterium oxide, and in the conjugate addition of the nitrotoluene to methyl vinyl ketone in aqueous solution.     

Hypohalite ion catalysis of the disproportionation of chlorine dioxide

The disproportionation of chlorine dioxide in basic solution to give ClO2- and ClO3- is catalyzed by OBr- and OCl-. The reactions have a first-order dependence in both [ClO2] and [OX-] (X = Br, Cl) when the ClO2- concentrations are low. However, the reactions become second-order in [ClO2] with the addition of excess ClO2-, and the observed rates become inversely proportional to [ClO2-]. In the proposed mechanisms, electron transfer from OX- to ClO2(k1OBr- = 2.05 +/- 0.03 M(-1) x s(-1) for OBr(-)/ClO2 and k1OCl-= 0.91 +/- 0.04 M(-1) x s(-1) for OCl-/ClO2) occurs in the first step to give OX and ClO2-. This reversible step (k1OBr-/k(-1)OBr = 1.3 x 10(-7) for OBr-/ClO2, / = 5.1 x 10(-10) for OCl-/ClO2) accounts for the observed suppression by ClO2-. The second step is the reaction between two free radicals (XO and ClO2) to form XOClO2. These rate constants are = 1.0 x 10(8) M(-1) x s(-1) for OBr/ClO2 and = 7 x 10(9) M(-1) x s(-1) for OCl/ClO2. The XOClO2 adduct hydrolyzes rapidly in the basic solution to give ClO3- and to regenerate OX-. The activation parameters for the first step are DeltaH1(++) = 55 +/- 1 kJ x mol(-1), DeltaS1(++) = - 49 +/- 2 J x mol(-1) x K(-1) for the OBr-/ClO2 reaction and DeltaH1(++) = 61 +/- 3 kJ x mol(-1), DeltaS1(++) = - 43 +/- 2 J x mol(-1) x K(-1) for the OCl-/ClO2 reaction.     

Through-bond excited energy transfer mediated by an amidinium-carboxylate salt bridge in Zn-porphyrin free-base porphyrin dyads

Excited energy-transfer processes were investigated for a supramolecular Zn-porphyrin free-base porphyrin dyad, ZnPA-2 x FbPC-2, in which beta-octaalkylated meso-diarylporphyrins are connected through an amidinium-carboxylate salt bridge. The rate of energy transfer in the dyad (1.3 x 10(9) s(-1)) is substantially slower than that in the previously reported dyad, ZnPA-1FbPC-1 (4.0 x 10(9) s(-1)), in which meso-tetraarylporphyrins are connected through the same amidinium-carboxylate salt bridge. The F?rster-type mechanism can explain only minor parts of these rates (3.3 x 10(8) and 5.1 x 10(8) s(-1), respectively). Thus, Dexter-type through-bond energy transfer may be invoked. Indeed, bridge-mediated electronic processes would be favored in ZnPA-1 x FbPC-1 over ZnPA-2 x FbPC-2 on the basis of steric and electronic factors. Sterically, the phenyl groups in ZnPA-2 and FbPC-2 are more closely perpendicular to the porphyrin planes than those in ZnPA-1 and FbPC-1. Electronically, the energy and symmetry of the occupied frontier orbitals should favor ZnPA-1 x FbPC-1 over ZnPA-2 x FbPC-2 in terms of electronic interactions through the bridge. Therefore, the observed trend (ZnPA-1 x FbPC-1>ZnPA-2 x FbPC-2), consistent with these considerations, lends further support to the through-bond mechanism. Thus, the amidinium-carboxylate salt bridge is effective in mediating through-bond energy transfer even though the bond is noncovalent.     

Examination of cucurbit[7]uril and its host-guest complexes by diffusion nuclear magnetic resonance

The self-diffusion of cucurbit[7]uril (CB[7]) and its host-guest complexes in D2O has been examined using pulsed gradient spin-echo nuclear magnetic resonance spectroscopy. CB[7] diffuses freely at a concentration of 2 mM with a diffusion coefficient (D) of 3.07 x 10(-10) m(2) s(-1). At saturation (3.7 mM), CB[7] diffuses more slowly (D = 2.82 x 10(-10) m(2) s(-1)) indicating that it partially self-associates. At concentrations between 2 and 200 mM, CsCl has no effect on the diffusion coefficient of CB[7] (1 mM). Conversely, CB[7] (2 mM) significantly affects the diffusion of 133Cs+ (1 mM), decreasing its diffusion coefficient from 1.86 to 0.83 x 10(-9) m(2) s(-1). Similar changes in the rate of diffusion of other alkali earth metal cations are observed upon the addition of CB[7]. The diffusion coefficient of 23Na+ changes from 1.26 to 0.90 x 10(-9) m(2) s(-1) and 7Li+ changes from 3.40 to 3.07 x 10(-9) m(2) s(-1). In most cases, encapsulation of a variety of inorganic and organic guests within CB[7] decreases their rates of diffusion in D2O. For instance, the diffusion coefficient of the dinuclear platinum complex trans-[[PtCl(NH3)2}2mu-dpzm](2+) (where dpzm is 4,4'-dipyrazolylmethane) decreases from 4.88 to 2.95 x 10(-10) m(2) s(-1) upon encapsulation with an equimolar concentration of CB[7].     

Geminate proton recombination at the surface of SDS and CTAC micelles probed with a micelle-anchored anthocyanin

The functionalized flavylium salt 6-hexyl-7-hydroxy-4-methyflavylium chloride (HHMF) was employed to probe some of the fundamental features of proton transfer reactions at the surface of anionic sodium dodecyl sulfate (SDS) and cationic hexadecyltrimethylammonium chloride (CTAC) micelles. In contrast to most ordinary flavylium salts, HHMF is insoluble in water, but readily incorporates into SDS and CTAC micelles. In the ground state, the rate constant for deprotonation of the acid form (AH+) of HHMF decreases 100-fold upon going from CTAC (kd = 3.0 x 10(6) s(-1)) to SDS (kd = 1.4 x 10(4) s(-1)), consistent with the presence of an activation barrier for proton transfer in the ground state and reflecting, respectively, stabilization or destabilization of the AH+ cation by the micelle. Reprotonation of A is diffusion-controlled in both micelles (kp(SDS) = (2.1 x 10(11))[H+]aq s(-1) and kp(CTAC) = (3.7 x 10(8))[H+]aq s(-1)), the difference reflecting the rate of proton entry into the micelles. In the excited singlet state, the rate constants for deprotonation of the AH+* form of HHMF are similar in the two micelles (2.4 x 10(10) s(-1)), consistent with activationless proton transfer. Reprotonation of the excited A is dominated by fast geminate recombination of the photogenerated (A*-H+) pair at the micelle surface (k(rec)(SDS) = 6.1 x 10(9) s(-1) and k(rec)(CTAC) = 3.4 x 10(10) s(-1)) and the net efficiencies of geminate recombination are quite similar in SDS (0.89) and CTAC (0.86).     

Rates of electronic excitation hopping in anisotropic ionic crystals of [Ru(2,2'-bipyridine)3]X2 (X = ClO4-, PF6-, SbF6-); Monte Carlo simulation of single- and multi-exponential emission decays

Emission decays of triplet metal-to-ligand charge transfer states in anisotropic crystals of [Ru(1 - x)Os(x)(bpy)(3)]X(2) (bpy = 2,2'-bipyridine, X = PF(6)-, ClO(4)-, SbF(6)-, and 0.115 > x > 0.001) at approximately 300 K were measured by means of time-correlated single-photon counting. Rates of excitation hopping calculated on the basis of an interaction between transition dipoles of a donor cation and an acceptor cation are insufficient to simulate the single-exponential decays (x = 0.0099) and the multiexponential decays (x = 0.060 and 0.115) of the PF(6)- salt crystals. A limiting rate of excitation hopping to an imaginary cation at the van der Waals distance via a super-exchange interaction between d orbitals through the bpy ligands was determined to be 0.83 x 10(10) s(-1) on average by means of a step-by-step Monte Carlo simulation, assuming an distance-attenuation factor, beta, of the exchange interaction of 10 nm-1. The total rate of excitation hopping via both a dipole-dipole mechanism and a super-exchange mechanism to the neighboring sites of the cation was calculated to be 5.4 x 10(9) s(-1) for the PF(6)- crystal. Anisotropic diffusion constants estimated from the hopping rates and lengths in the PF(6)- crystal are 9.3 x 10(-6), 9.1 x 10(-6), and 1.4 x 10(-6) cm(2)s(-1) along the a axis, the b axis, and the c axis, respectively, which are compared with an isotropic diffusion constant, 1.3 x 10(-6) cm(2) s(-1), estimated from the pseudo-bimolecular rate constant of excitation transfer to [Os(bpy)(3)](2+), using an isotropic Smoluchowski equation. A multiexponential emission decay of [Ru(0.885)Os(0.115)(bpy)(3)](PF(6))(2) was also simulated to determined the limiting rate of excitation transfer to [Os(bpy)(3)](2+) at the van der Waals distance (2.6 x 10(11) s(-1)). The magnitude of beta determined is 6.5 and 11.5 nm(-1) for the ClO(4)- and the SbF(6)- salt crystals, respectively, on reference to that of beta (10 nm(-1)) for the PF(6)- salt crystal.     

Mechanistic studies of nitric oxide reactions with water soluble iron(II), cobalt(II), and iron(III) porphyrin complexes in aqueous solutions: implications for biological activity.

The reactions of nitric oxide and carbon monoxide with water soluble iron and cobalt porphyrin complexes were investigated over the temperature range 298-318 K and the hydrostatic pressure range 0.1-250 MPa [porphyrin ligands: TPPS = tetra-meso-(4-sulfonatophenyl)porphinate and TMPS = tetra-meso-(sulfonatomesityl)porphinate]. Large and positive DeltaS(double dagger) and DeltaV(double dagger) values were observed for NO binding to and release from iron(III) complexes Fe(III)(TPPS) and Fe(III)(TMPS) consistent with a dissociative ligand exchange mechanism where the lability of coordinated water dominates the reactivity with NO. Small positive values for Delta and Delta for the fast reactions of NO with the iron(II) and cobalt(II) analogues (k(on) = 1.5 x 10(9) and 1.9 x 10(9) M(-1) s(-1) for Fe(II)(TPPS) and Co(II)(TPPS), respectively) indicate a mechanism dominated by diffusion processes in these cases. However, reaction of CO with the Fe(II) complexes (k(on) = 3.6 x 10(7) M(-1) s(-1) for Fe(II)(TPPS)) displays negative Delta and Delta values, consistent with a mechanism dominated by activation rather than diffusion terms. Measurements of NO dissociation rates from Fe(II)(TPPS)(NO) and Co(II)(TPPS)(NO) by trapping free NO gave k(off) values of 6.3 x 10(-4) s(-1) and 1.5 x 10(-4) s(-1). The respective M(II)(TPPS)(NO) formation constants calculated from k(on)/k(off) ratios were 2.4 x 10(12) and 1.3 x 10(13) M(-1), many orders of magnitude larger than that (1.1 x 10(3) M(-1)) for the reaction of Fe(III)(TPPS) with NO.     

Generation of a peroxynitrato metal complex from nitrogen dioxide and coordinated superoxide

The reaction between photogenerated NO(2) radicals and a superoxochromium(III) complex, Cr(aq)OO(2+), occurs with rate constants k(Cr)(20) = (2.8 +/- 0.2) x 10(8) M(-)(1) s(-)(1) (20 vol % acetonitrile in water) and k(Cr)(40) = (2.6 +/- 0.5) x 10(8) M(-)(1) s(-)(1) (40 vol % acetonitrile) in aerated acidic solutions and ambient temperature. The product was deduced to be a peroxynitrato complex, Cr(aq)OONO(2)(2+), which undergoes homolytic cleavage of an N-O bond to return to the starting materials, the rate constants in the two solvent mixtures being k(H)(20) = 172 +/- 4 s(-)(1) and k(H)(40) = 197 +/- 7 s(-)(1). NO(2) reacts rapidly with 10-methyl-9,10-dihydroacridine, k(A)(20) = 2.2 x 10(7) M(-)(1) s(-)(1), k(A)(40) = (9.4 +/- 0.2) x 10(6) M(-)(1) s(-)(1), and with N,N,N',N'-tetramethylphenylenediamine, k(T)(40) = (1.84 +/- 0.03) x 10(8) M(-)(1) s(-)(1).     

Gas-phase rate coefficients for the reactions of nitrate radicals with (Z)-pent-2-ene, (E)-pent-2-ene, (Z)-hex-2-ene, (E)-hex-2-ene, (Z)-hex-3-ene, (E)-hex-3-ene and (E)-3-methylpent-2-ene at room temperature

Rate coefficients for reactions of nitrate radicals (NO3) with (Z)-pent-2-ene, (E)-pent-2-ene, (Z)-hex-2-ene, (E)-hex-2-ene, (Z)-hex-3-ene, (E)-hex-3-ene and (E)-3-methylpent-2-ene were determined to be (6.55 +/- 0.78)x 10(-13) cm3 molecule(-1) s(-1), (3.78 +/- 0.45)x 10(-13) cm3 molecule(-1) s(-1), (5.30 +/- 0.73)x 10(-13) cm(3) molecule(-1) s(-1), (3.83 +/- 0.47)x 10(-13) cm(3) molecule(-1) s(-1), (4.37 +/- 0.49)x 10(-13) cm(3) molecule(-1) s(-1), (3.61 +/- 0.40)x 10(-13) cm3 molecule(-1) s(-1) and (8.9 +/- 1.5)x 10(-12) cm3 molecule(-1) s(-1), respectively. We performed kinetic experiments at room temperature and atmospheric pressure using a relative-rate technique with GC-FID analysis. The experimental results demonstrate a surprisingly large cis-trans(Z-E) effect, particularly in the case of the pent-2-enes, where the ratio of rate coefficients is ca. 1.7. Rate coefficients are discussed in terms of electronic and steric influences, and our results give some insight into the effects of chain length and position of the double bond on the reaction of NO3 with unsaturated hydrocarbons. Atmospheric lifetimes were calculated with respect to important oxidants in the troposphere for the alkenes studied, and NO3-initiated oxidation is found to be the dominant degradation route for (Z)-pent-2-ene, (Z)-hex-3-ene and (E)-3-methylpent-2-ene.     

Mass analyzed threshold ionization spectra of phenol...Ar2: ionization energy and cation intermolecular vibrational frequencies

The phenol(+)...Ar(2) complex has been characterized in a supersonic jet by mass analyzed threshold ionization (MATI) spectroscopy via different intermediate intermolecular vibrational states of the first electronically excited state (S(1)). From the spectra recorded via the S(1)0(0) origin and the S(1)β(x) intermolecular vibrational state, the ionization energy (IE) has been determined as 68,288 ± 5 cm(-1), displaying a red shift of 340 cm(-1) from the IE of the phenol(+) monomer. Well-resolved, nearly harmonic vibrational progressions with a fundamental frequency of 10 cm(-1) have been observed in the ion ground state (D(0)) and assigned to the symmetric van der Waals (vdW) bending mode, β(x), along the x axis containing the C-O bond. MATI spectra recorded via the S(1) state involving other higher-lying intermolecular vibrational states (σ(s)(1), β(x)(3), σ(s)(1)β(x)(1), σ(s)(1)β(x)(2)) are characterized by unresolved broad structures.     

Photophysics of the fluorescent pH indicator BCECF

The photophysical behavior of BCECF [2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein]--currently the most widely used fluorescent pH indicator for near-neutral intracellular pH measurements--has been explored by using absorption and steady-state and time-resolved fluorescence measurements. The influence of ionic strength as well as total buffer concentration on the absorbance and steady-state fluorescence has been investigated. The apparent acidity constant of the pH indicator determined by absorbance and fluorescence titration is dependent on the added buffer and salt concentrations. A semiempirical model is proposed to rationalize the variations in the apparent pKa values. The excited-state proton exchange of BCECF at physiological pH becomes reversible upon addition of phosphate buffer, inducing a pH-dependent change of the fluorescence decay times. Fluorescence decay traces collected as a function of total buffer concentration and pH were analyzed by global compartmental analysis yielding the following values of the rate constants describing excited-state dynamics of BCECF: k01 = 3.4 x 10(8) s(-1), k02 = 2.6 x 10(8) s(-1), k21 approximately 1 x 10(6) M(-1) s(-1), k12(B) = 1.4 x 10(8) M(-1) s(-1), and k21(B) = 4.3 x 10(7) M(-1) s(-1).