Spectral studies on the interaction of yttrium ion with the ligands of phenolic groups: N,N'-Ethylenebis[2-(o-hydroxyphenolic)glycine] and N,N'-di(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid

The interactions of yttrium with N,N'-ethylenebis[2-(o-hydroxyphenolic)glycine] (EHPG) and N,N'-di(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED) are investigated by using UV difference and fluorescence spectra methods in 0.1M N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid (Hepes) at pH 7.4. Yttrium binding produces two UV difference peaks near 240 and 294 nm, respectively, that both are the characteristic of phenolic groups binding to yttrium. The molar extinction coefficient of Y-EHPG and Y-HBED are (15.7 +/- 0.40) x 10(3), (15.8 +/- 0.80) x 10(3)cm(-1)M(-1) at 240 nm, respectively. Using EDTA as a competitor the obtained conditional equilibrium constants of the complexes are logK(Y-EHPG) = 15.07 +/- 0.32 and logK(Y-HBED) = 15.18 +/- 0.26, respectively. However, the effects of yttrium binding on the fluorescence intensity of EHPG and HBED are quite different, the former showing a decrease but the latter an increase.     

Spectral studies on the interaction between lanthanum ion and the ligand: N,N'-ethylenebis-[2-(o-hydroxyphenolic)glycine

The interaction between N,N'-ethylenebis-[2-(o-hydroxyphenolic)glycine] (EHPG) and lanthanum was studied by the difference UV spectra and fluorescence spectra. At pH 7.4, 0.01 M N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid (Hepes), with the addition of 1.0 x 10(-3)M lanthanum, two new peaks were observed at 238 nm and 294 nm by absorptivity spectroscopy compared with blank solution EHPG suggesting the interaction of lanthanum and EHPG. At the same time, the reaction could be measured by fluorescence spectra. The fluorescence intensity of EHPG at 310 nm was significantly decreased in the presence of lanthanum. The 1:1 stoichiometric ratio of EHPG to lanthanum was confirmed by both fluorescence and UV titration curves. In addition, the molar absorptivity of La-EHPG at 238 nm is (1.23+/-0.01)x10(4)cm(-1)M(-1). The conditional binding constant was calculated to be log K(La-EHPG)=12.09+/-0.37 on the basis of the result of UV titration curves.     

Spectral study on the binding of gadolinium ions with apoovotransferrin

The binding of Gd3+ ion to apoovotransferrin (apoOTf) was monitored by means of UV difference spectra in 0.01M Hepes, pH 7.4 at 25 degrees C. Used 2-p-toluidinylnaphthalene-6-sulfonate (TNS) as fluorescence probe the conformational changes of protein were studied while gadolinium ions bound to apoOTf. The results show that Gd3+ binding produces peaks at 244 and 294 nm that is the characteristic of binding at the apoOTf specific metal-binding sites. At 244 nm the molar absorptivity of Gd-apoOTf complex is (1.99+/-0.17)x10(4)cm(-1)M(-1). The apparent binding constants for the complexes of Gd3+ with apoovotransferrin are logK(1)=7.61+/-0.14 and logK(2)=4.96+/-0.26. A very large conformational change of apoovotransferrin appears when Gd3+ is bound to the N-terminal binding site. When Gd3+ is bound to C-terminal binding site there is less conformational change.     

Characterization of melittin binding to Euplotes octocarinatus centrin

In the presence of 1.0mM Ca(2+), the interaction between Euplotes octocarinatus centrin (EoCen) and melittin (ME) was studied by means of fluorescence spectra. In 0.1M N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid (Hepes) and 150mM NaCl at pH 7.4, fluorescence peak of ME was observed at about 353nm indicating that micro-environment of Tryptophan (Trp) residue in ME was hydrophilic. With the addition of 3.2x10(-4)M calcium saturated EoCen (holoEoCen), the peak of ME was blue-shifted to 339nm, which may be resulted from micro-environmental changes of the peptide. At the same time, fluorescence emission of ME was increased significantly suggesting that new complex of ME-holoEoCen was formed under the experimental conditions. Based on the fluorescence titration curves, the 1:1 stoichiometric ratio of holoEoCen to ME was confirmed. In addition, the conditional binding constant of holoEoCen with ME was calculated to be logK(ME-holoEoCen)=6.59+/-0.14.     

Spectroscopic analysis of the interaction between gallium(III) and apoovotransferrin

Ovotransferrin is a main member of transferrin family and has a dual role in both the transport of iron and antibacterial function. Gallium-67 is widely used as an imaging agent for tumors. It has been reported that Ga(3+) can bind to apoovotransferrin at two sites, one in the N-terminal lobe and another in the C-terminal lobe. However, several details of the interaction between Ga(3+) and apoOTf remain unclear. Here, we report detailed investigations into the interactions of Ga(3+) with apoovotransferrin at the molecular level. First, the characteristics of Ga(3+) binding to apoovotransferrin were analyzed using UV difference spectra. The results show that Ga(3+) prefers to bind to the N-terminal site rather than the C-terminal site under the experimental conditions. Effective stability constants of logK(N)=18.88+/-0.24 and logK(C)=17.65+/-0.12 were determined. Second, conformational changes in apoovotransferrin during Ga(3+) binding were studied using 2-p-toluidinylnaphthalene-6-sulfonate (TNS) as a fluorescence probe. Apoovotransferrin undergoes a large conformational change when Ga(3+) binds to the N-terminal site, and a smaller conformational change when the ion binds to the C-terminal site. UV difference spectra were also used to measure the rate at which EDTA removes Ga(3+) from ovotransferrin carrying one Ga(3+) at the N-terminal site. Ga(3+) removal from the N-terminal binding site follows simple saturation kinetics.     

La(Ⅲ)、Eu(Ⅲ)与HBED配合的紫外差光谱研究

在0.01mol·L     

Reaction of HO with glycolaldehyde, HOCH2CHO: rate coefficients (240-362 K) and mechanism

Absolute rate coefficients for the title reaction, HO+HOCH2CHO-->products (R1), were measured over the temperature range 240-362 K using the technique of pulsed laser photolytic generation of the HO radical coupled to detection by pulsed laser induced fluorescence. Within experimental error, the rate coefficient, k1, is independent of temperature over the range covered and is given by k1(240-362 K)=(8.0+/-0.8)x10(-12) cm3 molecule-1 s-1. The effects of the hydroxy substituent and hydrogen bonding on the rate coefficient are discussed based on theoretical calculations. The present results, which extend the database on the title reaction to a range of temperatures, indicate that R1 is the dominant loss process for HOCH2CHO throughout the troposphere. As part of this work, the absorption cross-section of HOCH2CHO at 184.9 nm was determined to be (3.85+/-0.2)x10(-18) cm2 molecule-1, and the quantum yield of HO formation from the photolysis of HOCH2CHO at 248 nm was found to be (7.0+/-1.5)x10(-2).     

ESR and optical study of Cu2+ doped calcium malonate dihydrate

The ESR study of Cu(2+) doped calcium malonate dihydrate has been done at room temperature. Four magnetically in-equivalent sites for Cu(2+) have been observed. The spin-Hamiltonian parameters evaluated with the fitting of spectra to rhombic symmetry crystalline field are for Cu(2+) site (I): g(x)=2.0963+/-0.0002, g(y)=2.1316+/-0.0002, g(z)=2.4137+/-0.0002, A(x)=(32+/-2)x10(-4)cm(-1), A(y)=(34+/-2)x10(-4)cm(-1), A(z)=(49+/-2)x10(-4)cm(-1), for site (II): g(x)=2.0668+/-0.0002, g(y)=2.0800+/-0.0002, g(z)=2.3561+/-0.0002, A(x)=(34+/-2)x10(-4)cm(-1), A(y)=(36+/-2)x10(-4)cm(-1), A(z)=(51+/-2)x10(-4)cm(-1), for site (III): g(x)=2.0438+/-0.0002, g(y)=2.0623+/-0.0002, g(z)=2.2821+/-0.0002, A(x)=(34+/-2)x10(-4)cm(-1), A(y)=(36+/-2)x10(-4)cm(-1), A(z)=(53+/-2)x10(-4)cm(-1), and for site (IV): g(x)=2.0063+/-0.0002, g(y)=2.0241+/-0.0002, g(z)=2.2357+/-0.0002, A(x)=(35+/-2)x10(-4)cm(-1), A(y)=(37+/-2)x10(-4)cm(-1), A(z)=(54+/-2)x10(-4)cm(-1). The ground state wave function of Cu(2+) has also been determined. The g-anisotropy has been estimated and compared with the experimental value. Further with the help of optical study the nature of bonding of metal ion with different ligands in the complex has been discussed.     

Rate coefficients for the reaction of OH with (E)-2-pentenal, (E)-2-hexenal, and (E)-2-heptenal

Rate coefficients for the gas-phase reaction of the OH radical with (E)-2-pentenal (CH(3)CH(2)CH[double bond]CHCHO), (E)-2-hexenal (CH(3)(CH(2))(2)CH[double bond]CHCHO), and (E)-2-heptenal (CH(3)(CH(2))(3)CH[double bond]CHCHO), a series of unsaturated aldehydes, over the temperature range 244-374 K at pressures between 23 and 150 Torr (He, N(2)) are reported. Rate coefficients were measured under pseudo-first-order conditions in OH with OH radicals produced via pulsed laser photolysis of HNO(3) or H(2)O(2) at 248 nm and detected by pulsed laser-induced fluorescence. The rate coefficients were independent of pressure and the room temperature rate coefficients and Arrhenius expressions obtained are (cm(3) molecule(-1) s(-1) units): k(1)(297 K)=(4.3 +/- 0.6)x 10(-11), k(1)(T)=(7.9 +/- 1.2)x 10(-12) exp[(510 +/- 20)/T]; k(2)(297 K)=(4.4 +/- 0.5)x 10(-11), k(2)(T)=(7.5 +/- 1.1)x 10(-12) exp[(520 +/- 30)/T]; and k(3)(297 K)=(4.4 +/- 0.7)x 10(-11), k(3)(T)=(9.7 +/- 1.5)x 10(-12) exp[(450 +/- 20)/T] for (E)-2-pentenal, (E)-2-hexenal and (E)-2-heptenal, respectively. The quoted uncertainties are 2sigma(95% confidence level) and include estimated systematic errors. Rate coefficients are compared with previously published room temperature values and the discrepancies are discussed. The atmospheric degradation of unsaturated aldehydes is also discussed.     

Ultrafast excited-state dynamics of rhenium(I) photosensitizers [Re(Cl)(CO)3(N,N)] and [Re(imidazole)(CO)3(N,N)]+: diimine effects

Femto- to picosecond excited-state dynamics of the complexes [Re(L)(CO)(3)(N,N)](n) (N,N = bpy, phen, 4,7-dimethyl-phen (dmp); L = Cl, n = 0; L = imidazole, n = 1+) were investigated using fluorescence up-conversion, transient absorption in the 650-285 nm range (using broad-band UV probe pulses around 300 nm) and picosecond time-resolved IR (TRIR) spectroscopy in the region of CO stretching vibrations. Optically populated singlet charge-transfer (CT) state(s) undergo femtosecond intersystem crossing to at least two hot triplet states with a rate that is faster in Cl (～100 fs)(-1) than in imidazole (～150 fs)(-1) complexes but essentially independent of the N,N ligand. TRIR spectra indicate the presence of two long-lived triplet states that are populated simultaneously and equilibrate in a few picoseconds. The minor state accounts for less than 20% of the relaxed excited population. UV-vis transient spectra were assigned using open-shell time-dependent density functional theory calculations on the lowest triplet CT state. Visible excited-state absorption originates mostly from mixed L;N,N(?-) → Re(II) ligand-to-metal CT transitions. Excited bpy complexes show the characteristic sharp near-UV band (Cl, 373 nm; imH, 365 nm) due to two predominantly ππ*(bpy(?-)) transitions. For phen and dmp, the UV excited-state absorption occurs at ～305 nm, originating from a series of mixed ππ* and Re → CO;N,N(?-) MLCT transitions. UV-vis transient absorption features exhibit small intensity- and band-shape changes occurring with several lifetimes in the 1-5 ps range, while TRIR bands show small intensity changes (≤5 ps) and shifts (～1 and 6-10 ps) to higher wavenumbers. These spectral changes are attributable to convoluted electronic and vibrational relaxation steps and equilibration between the two lowest triplets. Still slower changes (≥15 ps), manifested mostly by the excited-state UV band, probably involve local-solvent restructuring. Implications of the observed excited-state behavior for the development and use of Re-based sensitizers and probes are discussed.     

Sorption of Pu(VI) onto TiO2

The sorption of Pu(VI) onto TiO(2) was studied as a function of pH (2-10) and Pu concentration (10(-8)-10(-4) M) under an N(2) atmosphere, in 0.016 and 0.1 M NaClO(4). A batch-wise method was used, in which pH was measured in separate experimental containers after removal of a sample to determine the amount of Pu that had been sorbed. As Pu is radioactive, it was used as a tracer and measured by liquid scintillation counting. No ionic strength dependence was discerned, which was taken as an indication of inner sphere complex formation. In the interval of pH 2-7 the system could be described by the formation of two positively charged surface complexes using a 1-pK Stern model. Sorption of the plutonyl ion (PuO(2)(2+)) and the first hydrolysis species (PuO(2)(OH)(+)) was estimated using FITEQL to logK(1)=6.9 and logK(2)=1.4, respectively.     

Energetics of C-Cl, C-Br, and C-I bonds in haloacetic acids: enthalpies of formation of XCH2COOH (X=CI, Br, I) compounds and the carboxymethyl radical

The standard molar enthalpies of formation of chloro-, bromo-, and iodoacetic acids in the crystalline state, at 298.15 K, were determined as deltafH(o)m(C2H3O2Cl, cr alpha)=-(509.74+/- 0.49) kJ x mol(-1), deltafH(o)m(C2H3O2Br, cr I)-(466.98 +/- 1.08) kJ x mol(-1), and deltafH(o)m (C2H3O2I, cr)=-(415.44 +/- 1.53) kJ x mol(-1), respectively, by rotating-bomb combustion calorimetry. Vapor pressure versus temperature measurements by the Knudsen effusion method led to deltasubH(o)m(C2H3O2Cl)=(82.19 +/- 0.92) kJ x mol(-1), deltasubH(o)m(C2H3O2Br)=(83.50 +/- 2.95) kJ x mol(-1), and deltasubH(o)m-(C2H3O2I) = (86.47 +/- 1.02) kJ x mol(-1), at 298.15 K. From the obtained deltafH(o)m(cr) and deltasubH(o)m values it was possible to derive deltafH(o)m(C2H3O2Cl, g)=-(427.55 +/- 1.04) kJ x mol(-1), deltafH(o)m (C2H3O2Br, g)=-(383.48 +/- 3.14) kJ x mol(-1), and deltafH(o)m(C2H3O2I, g)=-(328.97 +/- 1.84) kJ x mol(-1). These data, taken with a published value of the enthalpy of formation of acetic acid, and the enthalpy of formation of the carboxymethyl radical, deltafH(o)m(CH2COOH, g)=-(238 +/- 2) kJ x mol(-1), obtained from density functional theory calculations, led to DHo(H-CH2COOH)=(412.8 +/- 3.2) kJ x mol(-1), DHo(Cl-CH2COOH)=(310.9 +/- 2.2) kJ x mol(-1), DHo(Br-CH2COOH)=(257.4 +/- 3.7) kJ x mol(-1), and DHo(I-CH2COOH)=(197.8 +/- 2.7) kJ x mol(-1). A discussion of the C-X bonding energetics in XCH2COOH, CH3X, C2H5X, C2H3X, and C6H5X (X=H, Cl, Br, I) compounds is presented.     

Synthesis and coordination properties of new macrocyclic ligands: equilibrium studies and crystal structures

The synthesis and characterization of two new macrocyclic ligands, the bis-macrocyclic compound 2,6-bis(1,4,13-triaza-7,10-dioxacyclopentadec-1-ylmethyl)phenol (L) and 38-methoxy-1,4,13,16,19,28-hexaaza-7,10,22,25-tetraoxatricyclo[14.14.7.1(32,36)]octatriconta-32,34,Delta(36,38)-triene (L1) are reported. Equilibrium studies of basicity and coordination properties toward metal ions such as Cu(II), Zn(II), Cd(II) and Pb(II) were performed for ligand by potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, I= 0.15 mol dm(-3)). L behaves as a hexaprotic base (logK(1)= 10.93, logK(2)= 9.70, logK(3)= 8.79, logK(4)= 8.05, logK(5)= 6.83, logK(6)= 2.55). All metal ions form stable mono- and dinuclear complexes: logK(MLH(-1))= 25.61 for Cu(II), 15.37 for Zn(II), 12.58 for Cd(II) and 13.79 for Pb(II); logK(M(2)LH(-1))= 31.61 for Cu(II), 23.38 for Zn(II), 24.49 for Cd(II) and 23.68 for Pb(II). All these dinuclear species show a great tendency to add the OH(-) group: the equilibrium constant for the addition reaction was found to be logK(M(2)LH(-1)OH)= 4.77 for Cu(II), 5.66 for Zn(II), 2.8 for Cd(II) and 3.18 for Pb(II). In the case of Ni(II), kinetic inertness prevents the possibility of solution studies. The dinuclear solid adducts [Ni(2)H(-1)L(N(3))(3)].EtOH and [Cu(2)H(-1)L(N(3))](ClO(4))(2) were characterized by X-ray analysis.     

Synthesis,structure, spectroscopic,and DNA binding properties of Co(III) and Ni(II) complexes with ((E)-2-(amino((pyridin-2-ylmethylene)amino)methylene)maleonitrile)

Two new complexes, [Co(L)₂]Cl·(MeOH)₂ (1) and [Ni(L)₂]₄·EtOH (2) (L?=?(E)-2-(amino((pyridin-2-ylmethylene)amino)methylene)maleonitrile), were synthesized and characterized by X-ray crystallography, IR, UV, and fluorescence spectroscopy. According to X-ray crystallographic studies, each metal was six-coordinate with six nitrogens from two ligands. Both complexes form two-dimensional supramolecular networks via hydrogen bonding and π–π interactions. Ultraviolet and visible spectra showed that absorptions arise from π–π ^?, MLCT, and d–d electron transitions. Fluorescence spectroscopy revealed moderate intercalative binding of these two complexes with EB–DNA, with apparent binding constant (K _app) values of 9.14?×?10⁵ and 3.20?×?10^5?M^?1 for Co(III) and Ni(II) complexes, respectively. UV–visible absorption spectra showed that the absorption of DNA at 260?nm was quenched for 2 but quenched then improved for 1 with addition of complexes, tentatively attributed to the effect of the combined intercalative binding and electrostatic interaction for 1.     

Fluorescence quenching of three molecular weight fractions of a soil fulvic acid by UO(2)(II)

A soil fulvic acid isolated from a Korean forest was divided into three different molecular weight fractions (F1: less than 220 Da; F2: 220-1000 Da; and F3: 1000-4000 Da) by gel filtration chromatography and the fractions were studied by synchronous fluorescence (SyF) spectroscopy. Analysis of the SyF spectra for the fulvic acid fractions showed that the fractions with molecules of larger sizes have a higher content of condensed aromatic compounds. The information about their interaction with UO(2)(II) ions in an aqueous solution (100 mg l(-1) of fulvic acid, in 0.1 M NaClO(4) at pH 3.5) was obtained from the measurement of SyF spectra at increasing concentrations of metal ions. Self-modeling mixture analysis of the quenching spectra gives two distinct peak components having a maximum peak position of 386 (type I) and 498 nm (type II) for all the size-fractionated fulvic acids. From the analysis of the quenching profiles of the peaks, using a non-linear method, the concentration of binding sites (C(L)), and the corresponding stability constants (logK) were calculated. The stability constants of the UO(2)(II)-fulvate complexes ranged from 4.10 to 5.33, and increased with higher molecular weight fractions, which indicates a stronger affinity for UO(2)(II) in the fraction with molecules of larger size.     

Interaction of l-malic acid with alkaline metals and open chain polyammonium cations in aqueous solution

This work reports a potentiometric, calorimetric and spectropolarimetric ultraviolet circular dichroism (UV/CD) study of the interaction of l-malic acid with alkaline metals or (poly)ammonium (methylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, spermine, tetraethylenepentamine and pentaethylenehexamine) cations. Stability data (logK, DeltaG(0)) were obtained potentiometrically for the l-malic acid with (poly)ammonium cations systems; calorimetric measurements (25 degrees C) made it possible to obtain DeltaH(0) and TDeltaS(0) values for the complexes formed in the systems under examination. logK values calculated (for the reaction: H(i)A(i+)+H(j)L((j-z))=ALH(r)((i+j-z)), with r=i+j) range between 0.8 and 4.6, i.e., the interactions are from weak to fairly strong while maximum stability for each system is given by the species with the highest z(anion)xz(cation) (z=charge) value. Enthalpy changes associated with reactions H(n)A(n+)+L(2-)=ALH(n)((n-2)) and H(n)A(n+)+HL(-)=ALH(n+1)((n-1)) are always positive and increase progressively with n. The same is valid for T DeltaS(0) values, which indicate that these species are entropically stabilized, as expected for electrostatic interactions. It was verified that the UV/CD signal depends on both ionic medium and ionic strength value; for comparison, we used the l-malic acid signal recorded in tetramethylammonium chloride as baseline background salt (as in potentiometry). UV/CD spectra were recorded for solutions containing both cationic and anionic species. When the cation was a protonated polyamine, CD spectra calculations were performed for most stable ion pairs: the results show remarkable differences in Deltaepsilon (dm(3) mol(-1) cm(-1)) values at 205 nm (which is the l-malate UV/CD lambda(max)) between the chiral ligand and its complex with a polyamine.     

Spectral study on the interaction of cryptophane-A and neutral molecules CHnCl4-n (n=0, 1, 2)

Cryptophane-A was synthesized from vanillin by a three-step method and its spectroscopic properties in different organic solvents were determined. Two absorption bands at about 240-250 and 280-290 nm were observed for cryptophane-A. A fluorescence emission peak was obtained at 320-330 nm using a solution of approximately 10(-5)M cryptophane-A. The interaction of cryptophane-A with chlorinated compounds CH(n)Cl(4 - n) (n=0, 1, 2) in dioxane and ethyl acetate solvents were studied in detail by fluorescence spectroscopy, respectively. The results show that cryptophane-A is well suited for inclusion of CH(2)Cl(2) to form a stable 1:1 complex and the binding constant was estimated to be 19+/-2M(-1). These results were also confirmed by (1)H NMR and CPK models. Larger similar molecules such as CHCl(3) and CCl(4) are unable to enter the cavity of cryptophane-A because of their bigger sizes. However, the fluorescence emission of cryptophane-A can be efficiently quenched by CHCl(3) and CCl(4), following the Stern-Volmer relationship.     

Fluorescence and DNA-binding properties of neodymium(III) and praseodymium(III) complexes containing 1,10-phenanthroline

The binding of neodymium(III) and praseodymium(III) complexes containing 1,10-phenanthroline, [M(phen)2Cl3·OH2] (M=Nd (1), Pr (2)), to DNA has been investigated by absorption, emission, and viscosity measurements. The complexes show absorption decreasing in charge transfer band, fluorescence decrement when bound to DNA. The binding constant Kb has been determined by absorption measurement for both complexes and found to be (6.76±0.12)×10(4) for 1 and (1.83±0.15)×10(4)M(-1), for 2. The fluorescence of [M(phen)2Cl3·OH2] (M=Nd (1), Pr (2)) has been studied in detail. The results of fluorescence titration reveal that DNA has the strong ability to quenching the intrinsic fluorescence of Nd(III) and Pr(III) complexes through the static quenching procedure. The binding site number n, apparent binding constant Kb and the Stern-Volmer constant kSV are determined. Thermodynamic parameters, enthalpy change (ΔH°) and entropy change (ΔS°), are calculated according to relevant fluorescent data and Van't Hoff equation. The experimental data suggest that the complexes bind to DNA by non-intercalative mode. Major groove binding is the preferred mode of interaction for [M(phen)2Cl3·OH2] (M=Nd (1), Pr (2)) with DNA.     

脱铁伴清蛋白两结合位点不同酪氨酸氢键的特性

The interaction of gallium（Ⅲ） with the ligands containing phenolic group（s）, such as salicylic acid, 8-hydroxyquinoline, N,N＇-bis（2-hydroxybenzyl）ethylenediamine-N,N＇diacetic acid （HBED）, N,N＇-ethylenebis[2-（o- hydroxyphenyl）glycine （EHPG）, and ovotransferrin, was studied, respectively, by means of fluorescence in 0.01 mol/L Hepes at pH 7.4 and room temperature. Fluorescence intensity showed an increase when gallium（Ⅲ） was bound to 8-hydroxyquinoline and HBED. In contrast, it was decreased with the interaction of gallium（Ⅲ） with salicylic acid and EHPG. At pH 7.4, there was N…H-O type intramolecular hydrogen bond in the former, and the latter existed O…H-O type intramolecular hydrogen bond. Fluorescence titration of apoovotransferrin with gallium（Ⅲ） displayed that the fluorescence intensity was decreased at the N-terminal binding site, while enhanced at the C-terminal binding site. It can account for the O…H-O type intramolecular hydrogen bonds for the phenolic groups of Tyr92 and Tyr191 residues at the N-terminal binding site. And there are N…H-O type intramolecular hydrogen bonds for Tyr431 and Tyr524 residues at the C-terminal binding site. In addition, under the same conditions, the conditional binding constant of gallium（Ⅲ） with EHPG or HBED determined by fluorescence method is lg KGa-EHPG=19.18 or lg KGa-HBED= 19.08.     

Relaxation of H2O from its /04>- vibrational state in collisions with H2O, Ar, H2, N2, and O2

We report rate coefficients at 293 K for the collisional relaxation of H2O molecules from the highly excited /04>(+/-) vibrational states in collisions with H2O, Ar, H2, N2, and O2. In our experiments, the mid R:04(-) state is populated by direct absorption of radiation from a pulsed dye laser tuned to approximately 719 nm. Evolution of the population in the (/04>(+/-)) levels is observed using the combination of a frequency-quadrupled Nd:YAG laser, which selectively photolyses H2O(/04>(+/-)), and a frequency-doubled dye laser, which observes the OH(v=0) produced by photodissociation via laser-induced fluorescence. The delay between the pulse from the pump laser and those from the photolysis and probe lasers was systematically varied to generate kinetic decays. The rate coefficients for relaxation of H2O(/04>(+/-)) obtained from these experiments, in units of cm3 molecule(-1) s(-1), are: k(H2O)=(4.1+/-1.2) x 10(-10), k(Ar)=(4.9+/-1.1) x 10(-12), k(H2)=(6.8+/-1.1) x 10(-12), k(N2)=(7.7+/-1.5) x 10(-12), k(O2)=(6.7+/-1.4) x 10(-12). The implications of these results for our previous reports of rate constants for the removal of H2O molecules in selected vibrational states by collisions with H atoms (P. W. Barnes et al., Faraday Discuss. Chem. Soc. 113, 167 (1999) and P. W. Barnes et al., J. Chem. Phys. 115, 4586 (2001).) are fully discussed.