通过调控晶体结构提高氧气还原反应电催化活性:MPt金属间相纳米晶（英文）

燃料电池的正极主要发生氧还原反应(ORR),但是该反应的动力学速率较慢,需要催化剂来降低反应的过电势.目前商用的催化剂是碳载铂纳米粒子催化剂,但是铂高昂的价格严重阻碍了燃料电池的大规模商业化.近年来的理论和实验研究表明,过渡金属(M)与铂(Pt)形成的纳米晶合金(MPt)能够作为有效的ORR催化剂,同时由于引入价格低廉的过渡金属,催化剂成本有所降低.然而,即使合金化的催化剂具有良好的初始催化性能,但是在燃料电池的实际操作环境,即高电压、高温和酸性条件,长时间运行之后,过渡金属很容易被腐蚀流失,从而留下表面配位数较低的铂原子,而这些铂原子对ORR反应几乎没有催化作用,导致催化剂逐渐失活,燃料电池的输出功率逐渐降低.最近一些研究表明,铂基催化剂在一定条件下,例如加热,能够发生固态相变,形成结构有序的即金属间纳米晶(iNCs).与无序排列的合金相比,这种有序的MPt能够调控表面铂原子与含氧中间体的结合能,可以进一步提高ORR活性;同时,由于在金属间纳米晶中铂原子与过渡金属原子具有很强的相互作用,过渡金属在酸性溶液中也不容易被腐蚀,从而大大提高了催化剂的稳定性.本综述以FePt,CoPt和PbPt为例,总结了它们的相变规律和条件,同时关注它们的合成-结构-性能的构效关系,突出金属间结构在提高活性和稳定性方面的优势.最后,为了进一步提高MPt金属间纳米晶的活性,我们提出一些可能的方向和观点,包括:(1)在实现无序-相变的同时实现形貌调控来提高催化剂活性;(2)关注尺寸效应,尽可能减小MPt金属间纳米晶的尺寸,提高铂的利用率,从而提高催化剂活性;(3)关注材料的有序程度,尽可能提高材料的有序度,充分发挥金属间纳米晶对于氧还原反应的优势     

高氮化合物及其含能材料

高氮含能化合物及其含能材料是新型含能材料领域的研究热点之一。相比于传统的含能材料,高氮含能材料具有很多优异或独特的理化性能和爆轰性能。本文综述了新型高氮化合物及其含能材料的研究进展,介绍了国内外近十年来众多研究小组的相关工作,重点阐述了四嗪、四唑和呋咱3大类高氮含能化合物的合成、性能及应用研究进展。结合作者的研究工作,进一步探讨了高氮含能化合物在钝感高能炸药、推进剂和新型气体发生剂等含能材料领域中的应用前景。     

Isolation and identification of the anti-isohumulones and the anti-acetylhumulinic acids

The anti-isohumulones [5-(3-methylbutanoyl)-2-(3-methylbut-2-enyl)-4-hydroxy-4-(4-methylpent-3-enoyl)-cyclopentane-1,3-diones] and the anti-acetylhumulinic acids [5-(3-methylbutanoyl)-2-(3-methylbut-2-enyl)-4-ethanoyl-4-hydroxy-cyclopentane 1,3-diones] have been isolated from an isomerisation reaction mixture of humulone [2-(3-methylbutanoyl)-4,6-di(3-methylbut-2-enyl)-6-hydroxy-cyclohexane-l,3,5-trione] by counter-current distribution and identified by spectroscopic techniques. The formation mechanism is presented and the stereochemical consequences are discussed. The anti-isohumulones are the most bitter hop compounds presently known.     

Experimental and modeling studies of the pressure and temperature dependences of the kinetics and the OH yields in the acetyl + O2 reaction

The acetyl + O(2) reaction has been studied by observing the time dependence of OH by laser-induced fluorescence (LIF) and by electronic structure/master equation analysis. The experimental OH time profiles were analyzed to obtain the kinetics of the acetyl + O(2) reaction and the relative OH yields over the temperature range of 213-500 K in helium at pressures in the range of 5-600 Torr. More limited measurements were made in N(2) and for CD(3)CO + O(2). The relative OH yields were converted into absolute yields by assuming that the OH yield at zero pressure is unity. Electronic structure calculations of the stationary points of the potential energy surface were used with a master equation analysis to fit the experimental data in He using the high-pressure limiting rate coefficient for the reaction, k(∞)(T), and the energy transfer parameter, (ΔE(d)), as variable parameters. The best-fit parameters obtained are k(∞) = 6.2 × 10(-12) cm(-3) molecule(-1) s(-1), independent of temperature over the experimental range, and (ΔE(d))(He) = 160(T/298?K) cm(-1). The fits in N(2), using the same k(∞)(T), gave (ΔE(d))(N(2)) = 270(T/298?K) cm(-1). The rate coefficients for formation of OH and CH(3)C(O)O(2) are provided in parametrized form, based on modified Troe expressions, from the best-fit master equation calculations, over the pressure and temperature ranges of 1 ≤ p/Torr ≤ 1.5 × 10(5) and 200 ≤ T/K ≤ 1000 for He and N(2) as the bath gas. The minor channels, leading to HO(2) + CH(2)CO and CH(2)C(O)OOH, generally have yields <1% over this range.     

Synthesis and pharmacological effects of the enantiomers of the N-phenethyl analogues of the ortho and para e- and f-oxide-bridged phenylmorphans

The N-phenethyl analogues of (1R*,4aR*,9aS*)-2-phenethyl-1,3,4,9a-tetrahydro-2H-1,4a-propanobenzofuro[2,3-c]pyridin-6-ol and 8-ol and (1R*,4aR*,9aR*)-2-phenethyl-1,3,4,9a-tetrahydro-2H-1,4a-propanobenzofuro[2.3-c]pyridin-6-ol and 8-ol, the ortho- (43) and para-hydroxy e- (20), and f-oxide-bridged 5-phenylmorphans (53 and 26) were prepared in racemic and enantiomerically pure forms from a common precursor, the quaternary salt 12. Optical resolutions were accomplished by salt formation with suitable enantiomerically pure chiral acids or by preparative HPLC on a chiral support. The N-phenethyl (-)- para-e enantiomer (1S,4aS,9aR-(-)-20) was found to be a mu-opioid agonist with morphine-like antinociceptive activity in a mouse assay. In contrast, the N-phenethyl (-)-ortho-f enantiomer (1R,4aR,9aR-(-)-53) had good affinity for the mu-opioid receptor (K(i) = 7 nM) and was found to be a mu-antagonist both in the [(35)S]GTP-gamma-S assay and in vivo. The molecular structures of these rigid enantiomers were energy minimized with density functional theory at the level B3LYP/6-31G* level, and then overlaid on a known potent mu-agonist. This superposition study suggests that the agonist activity of the oxide-bridged 5-phenylmorphans can be attributed to formation of a seven membered ring that is hypothesized to facilitate a proton transfer from the protonated nitrogen to a proton acceptor in the mu-opioid receptor.     

New study of the stability and of the spectroscopy of the molecular anions NCO- and CNO-

Using highly correlated wave functions, the ground and the low lying excited states of the molecular NCO(-) and CNO(-) anions have been reinvestigated. The stability of the electronic ground state of the two isomers with respect to dissociation and to electron detachment has been checked along the isomerization pathway. The regions of stability of the excited electronic states have been analyzed and identified and it is shown that only the ground state is stable and the corresponding potential energy surface presents three equilibrium positions. The rovibronic spectroscopy of the X (1)Σ(+) state of both NCO(-) and CNO(-) isomers has been determined by a variational approach leading to remarkable agreement with experimental data.     

Contribution of the intramolecular hydrogen bond to the shift of the pKa value and the oxidation potential of phenols and phenolate anions

Intramolecularly OHO[double bond, length as m-dash]C hydrogen bonded phenols, 2-HO-C6H2-3,5-(t-Bu)2-CONH-t-Bu (1-OH), 2-HO-C6H2-5-t-Bu-1,3-(CONH-t-Bu)2 (2-OH) and 2-HO-C6H2-3,5-(t-Bu)2-NHCO-t-Bu (4-OH), were synthesized and their phenolate anions were prepared as tetraethylammonium salts (-1O-(NEt4+), 2-O-(NEt4+) and 4-O-(NEt4+)) with intramolecular NHO(oxyanion) hydrogen bonds. 4-HO-C(6)H(2)-3,5-t-Bu(2)-CONH-t-Bu (3-OH) and its phenolate anion, 3-O-(NEt4+), were synthesized as non-hydrogen bonded references. The presence of intramolecular hydrogen bonds was established through the crystallographic analysis and/or (1)H NMR spectroscopic results. Intramolecular NHO(phenol) hydrogen bonds shift the pK(a) of the phenol to a more acidic value. The results of cyclic voltammetry show that the intramolecular OH...O=C hydrogen bond negatively shifts the oxidation potential of the phenol. In contrast, the intramolecular NHO(oxyanion) hydrogen bond positively shifts the oxidation potential of the phenolate anion, preventing oxidation. These contributions of the hydrogen bond to the pKa value and the oxidation potentials probably play an important role in the formation of a tyrosyl radical in photosystem II.     

Effects of fluorine on the structures and energetics of the propynyl and propargyl radicals and their anions

[reaction: see text] The adiabatic electron affinity (EA(ad)) of the CH(3)-C[triple bond]C(*) radical [experiment = 2.718 +/- 0.008 eV] and the gas-phase basicity of the CH(3)-C[triple bond]C:(-) anion [experiment = 373.4 +/- 2 kcal/mol] have been compared with those of their fluorine derivatives. The latter are studied using theoretical methods. It is found that there are large effects on the electron affinities and gas-phase basicities as the H atoms of the alpha-CH(3) group in the propynyl system are substituted by F atoms. The predicted electron affinities are 3.31 eV (FCH(2)-C[triple bond]C(*)), 3.86 eV (F(2)CH-C[triple bond]C(*)), and 4.24 eV (F(3)C-C[triple bond]C(*)), and the predicted gas-phase basicities of the fluorocarbanion derivatives are 366.4 kcal/mol (FCH(2)-C[triple bond]C:(-)), 356.6 kcal/mol (F(2)CH-C[triple bond]C:(-)), and 349.8 kcal/mol (F(3)C-C[triple bond]C:(-)). It is concluded that the electron affinities of fluoropropynyl radicals increase and the gas-phase basicities decrease as F atoms sequentially replace H atoms of the alpha-CH(3) in the propynyl system. The propargyl radicals, lower in energy than the isomeric propynyl radicals, are also examined and their electron affinities are predicted to be 0.98 eV ((*)CH(2)-C[triple bond]CH), 1.18 eV ((*)CFH-C[triple bond]CH), 1.32 eV ((*)CF(2)-C[triple bond] CH), 1.71 eV ((*)CH(2)-C[triple bond]CF), 2.05 eV ((*)CFH-C[triple bond]CF), and 2.23 eV ((*)CF(2)-C[triple bond]CF).     

Photoisomerization of the green fluorescence protein chromophore and the meta- and para-amino analogues

The Z --> E photoisomerization and fluorescence quantum yields for the wild-type green fluorescence protein (GFP) chromophore (p-HBDI) and its meta- and para-amino analogues (m-ABDI and p-ABDI) in aprotic solvents (hexane, THF, and acetonitrile) and protic solvents (methanol and 10-20% H(2)O in THF) are reported. The dramatic decrease in the quantum yields on going from aprotic to protic solvents indicates the important role of solvent-solute hydrogen bonding in the nonradiative decay pathways. The enhanced fluorescence of m-ABDI is also discussed.     

Entropy change on the cooling and heating paths between liquid and glass and the residual entropy

We analyze the C(p)-T data for the glassy state of eight materials of varied molecular interactions and structures to investigate how the use of the C(p)d ln T integral in the time-dependent (nonreversible) thermodynamic path between a liquid and glass affects our estimates of the entropy. Since the change in entropy on such a path cannot be determined, we estimate the upper and lower values of the change, Δσ, from the C(p)d ln T integral. For the same rates of cooling and heating and without annealing, Δσ on the cooling path is negligibly different from that on the heating path. The difference is ～1∕60th-1∕25th of the lowest known value of the residual entropy and even less than the configurational entropy of the supercooled liquid at its kinetic freezing temperature. Thus use of the C(p)d ln T integral in the nonreversible path does not introduce significant errors in estimating the residual entropy. Dynamic C(p) data cannot be used to infer that configurational entropy decreases on glass formation. Time dependence of the C(p)-T path has little consequence for reality of the residual entropy.     

Comparison of the structure and the transport properties of low-set and high-set curdlan hydrogels

Curdlan, a bacterial polysaccharide, can form different types of thermogels, having the very same chemical composition, but whose structures depend on the incubation temperature. Structural characterization of 10% (w/v) low-set and high-set curdlan gels was carried out by Fourier transformed infrared (FT-IR) imaging and environmental scanning electron microscopy (eSEM) in the hydrated state. Considerable differences were observed between the two gels, the high-set one being overall more homogeneous. The self-diffusion coefficients of a series of analytes of different sizes (water, phosphate, glucose-6-phosphate, polyphosphate, polyethylene glycol, and dextran labelled with rhodamine B) were measured in aqueous solution (D(s)(sln)) and in both types of curdlan gels (D(s)(gel)) using (1)H and (31)P pulsed field gradient nuclear magnetic resonance (PFG NMR) spectroscopy. The mutual-diffusion coefficients (D(m)(gel)) of dextran in the curdlan gels were determined from release experiments based on fluorescence spectroscopy. The dependence of the relative diffusion coefficient (D(s)(gel)D(s)(sln)) on the size of the analyte, expressed by its hydrodynamic radius (R(h)), could be expressed by D(s)(gel)D(s)(sln) ∝ exp(-R(h)(0.46)), valid for both types of gels. The self-diffusion measurements for the largest investigated analytes were not compatible with a single diffusion coefficient and, therefore, were analysed using an approach based on a normal distribution of self-diffusion coefficients. In the hydrogels, broadening of the self-diffusion coefficient distribution increased as a function of the analyte size. This phenomenon was associated with the limited distance travelled by the analytes during the measurements, and it is inferred that the distribution of diffusion coefficients is representative of the distribution of local environments of the individual analyte. It was found that the structural differences observed between both types of curdlan gels are not correlated with the gel transport properties, highlighting the complexity of the relationship between structural details and transport properties in gels.     

Solution self-assembly and adsorption at the air-water interface of the monorhamnose and dirhamnose rhamnolipids and their mixtures

The self-assembly in solution and adsorption at the air-water interface, measured by small-angle neutron scattering, SANS, and neutron reflectivity, NR, of the monorhamnose and dirhamnose rhamnolipids (R1, R2) and their mixtures, are discussed. The production of the deuterium-labeled rhamnolipids (required for the NR studies) from a Pseudomonas aeruginosa culture and their separation into the pure R1 and R2 components is described. At the air-water interface, R1 and R2 exhibit Langmuir-like adsorption isotherms, with saturated area/molecule values of about 60 and 75 ?(2), respectively. In R1/R2 mixtures, there is a strong partitioning of R1 to the surface and R2 competes less favorably because of the steric or packing constraints of the larger R2 dirhamnose headgroup. In dilute solution (<20 mM), R1 and R2 form small globular micelles, L(1), with aggregation numbers of about 50 and 30, respectively. At higher solution concentrations, R1 has a predominantly planar structure, L(α) (unilamellar, ULV, or bilamellar, BLV, vesicles) whereas R2 remains globular, with an aggregation number that increases with increasing surfactant concentration. For R1/R2 mixtures, solutions rich in R2 are predominantly micellar whereas solutions rich in R1 have a more planar structure. At an intermediate composition (60 to 80 mol % R1), there are mixed L(α)/L(1) and L(1)/L(α) regions. However, the higher preferred curvature associated with R2 tends to dominate the mixed R1/R2 microstructure and its associated phase behavior.     

Quasiclassical trajectory calculations comparing the reactivity and dynamics of symmetric and asymmetric stretch and the role of the bending mode excitations of methane in the Cl + CH4 reaction

To analyze the effects of the symmetric (nu(1)) and asymmetric (nu(3)) stretch mode excitations and the role played by the "umbrella" bending (nu(4)) mode excitation in the reactivity and the dynamics of the gas-phase Cl+CH(4) reaction, an exhaustive dynamics study was performed. Quasiclassical trajectory (QCT) calculations, including corrections to avoid zero-point energy leakage along the trajectories, were used in this work on an analytical potential energy surface previously developed by Espinosa-Garcia et al. [J. Chem. Phys. (to be published)]. First, with respect to the reactivity, we found that the nu(1) mode excitation is more reactive than the nu(3) mode by a factor of 1.20, in agreement with the experimental tendency between these modes. The inclusion of the nu(4) bending mode practically does not affect this relative reactivity, (nu(1+)nu(4))(nu(3+)nu(4)) = 1.16. Second, with respect to the dynamics (rotovibrational and angular distributions of the products), the two stretch modes, nu(1) and nu(3), give very similar pictures, reproducing the experimental behavior, and the nu(4) "umbrella" mode does not affect the dynamics. The satisfactory reproduction (always qualitatively acceptable and sometimes even quantitatively) of a great variety of experimental data by the QCT study presented here lends confidence to the potential energy surface constructed by Espinosa-Garcia et al. [J. Chem. Phys. (to be published)].     

Composition and enantiomeric analysis of the essential oil of the fruits and the leaves of Pistacia vera from Greece

The essential oils of the fruits and the leaves of pistachio (Pistacia vera L.) were analyzed by GC and GC/MS. Fresh unripe pistachio fruits were richer in essential oil (0.5%, w/w) than the leaves (0.1%, w/w). Twenty one compounds were identified in the essential oil of the fruits and the major components were (+)-alpha-pinene (54.6%) and terpinolene (31.2%). The enantiomeric ratio of the major constituents of the essential oil of the fruits was determined using chiral GC/MS and it was found that the (+)/(-)-alpha-pinene ratio was 99.5:0.5, (+)/(-)-limonene 80:20, (+)/(-)-beta-pinene 96:4, and (+)/(-)-alpha-terpineol 0:100. Thirty three compounds were identified in the essential oil of the leaves and the major components were found to be alpha-pinene (30.0%), terpinolene (17.6%) and bornyl acetate (11.3%).     

A theoretical study of the fine and hyperfine interactions in the NCO and CNO radicals

The geometries, the harmonic vibrational frequencies, and the Renner-Teller parameter have been reported for the NCO(+)(X (3)Sigma(-)), NCO(X (2)Pi,A (2)Sigma(+),B (2)Pi,2 (2)Sigma(+)), NCO(-)(X (1)Sigma(+)), CNO(+)(X), CNO(X (2)Pi,A (2)Sigma(+),B (2)Pi,2 (2)Sigma(+)), and CNO(-)(X (1)Sigma(+)) systems at the full valence-complete active space self-consistent-field (fv-CASSCF) level of theory. The (2)Pi electronic states of the NCO and CNO radicals have two distinct real vibrational frequencies for the bending modes and these states are subject to the type A Renner-Teller effect. The total energy of CNO(+) without zero point energy correction of the linear geometry is approximately 31 cm(-1) higher than the bent geometry at the fv-CASSCF level and the inversion barrier vanishes after the zero point energy correction; therefore, the ground state of the CNO(+) may possess a quasilinear geometry. The spin-orbit coupling constants estimated using atomic mean field Hamiltonian at the fv-CASSCF level of theory are in better agreement with the experimental values. The excitation energies, the electron affinity, and the ionization potential have been computed at the complete active space second order perturbation theory (CASPT2) and the multireference singles and doubles configuration (MRSD-CI) levels of theory. The computed values of the electric hyperfine coupling constants for the (14)N atom in the ground state of the NCO radical agree well with the experimental data. The magnetic hyperfine coupling constants (HFCC's) have been estimated employing the configuration selected MRSD-CI and the multireference singles configuration interaction (MRS-CI) methods using iterative natural orbitals (ino) as one particle basis. Sufficiently accurate value of the isotropic contribution to the HFCC's can be obtained using an MRS-CI-ino procedure.     

Scaling and the Smoluchowski equations

The Smoluchowski equations, which describe coalescence growth, take into account combination reactions between a j-mer and a k-mer to form a (j+k)-mer, but not breakup of larger clusters to smaller ones. All combination reactions are assumed to be second order, with rate constants K(jk). The K(jk) are said to scale if K(lambda j,gamma k) = lambda(mu)gamma(nu)K(jk) for j < or = k. It can then be shown that, for large k, the number density or population of k-mers is given by Ak(a)e(-bk), where A is a normalization constant (a function of a, b, and time), a = -(mu+nu), and b(mu+nu-1) depends linearly on time. We prove this in a simple, transparent manner. We also discuss the origin of odd-even population oscillations for small k. A common scaling arises from the ballistic model, which assumes that the velocity of a k-mer is proportional to 1/square root of m(k) (Maxwell distribution), i.e., thermal equilibrium. This does not hold for the nascent distribution of clusters produced from monomers by reactive collisions. By direct calculation, invoking conservation of momentum in collisions, we show that, for this distribution, velocities are proportional to m(k)(-0.577). This leads to mu+nu = 0.090, intermediate between the ballistic (0.167) and diffusive (0.000) results. These results are discussed in light of the existence of systems in the experimental literature which apparently correspond to very negative values of mu+nu.     

High-pressure synthesis and study of the crystal and magnetic structure of the distorted SeNiO3 and SeMnO3 perovskites

We describe the preparation of SeMO(3) (M = Ni, Mn) under high pressure conditions (3.5 GPa), starting from reactive H(2)SeO(3) and MO mixtures, contained in sealed gold capsules under the reaction conditions 850 degrees C for 1 h. The polycrystalline samples have been studied by neutron powder diffraction (NPD) data and magnetization measurements. SeMO(3) (M = Ni, Mn) are orthorhombically distorted perovskites (space group Pnma). Below T(N) approximately 104 K (M = Ni) and T(N) approximately 53.5 K (M = Mn) these oxides experience an antiferromagnetic ordering, as demonstrated by susceptibility and NPD measurements. The magnetic reflections observed in the neutron patterns can be indexed with a propagation vector k = 0. Both compounds present the same magnetic structure, which is given by the basis vector (0, 0, A(z)). It can be described as antiferromagnetic (010) layers of magnetic moments lying along the c direction, which are antiferromagnetically coupled along the b direction. For the Ni(2+) ions, the ordered magnetic moment at T = 2.3 K is 2.11(3) micro(B), whereas for Mn(2+) at T = 2.6 K, |m| = 4.64(2) micro(B), consistent with the electronic configurations te (Ni(2+)) and te (Mn(2+)).     

Cobalamins and the spectrochemical series

UV-visible-NIR spectra of a variety of cobalamins were run in water and methanol. A broad absorption band (band A) with extinction coefficients of about an order of magnitude less than those of the alphabeta bands was found in the red and NIR regions for Cl-cobalamin (Cl-cbl), Br-cbl, I-cbl, SC(NH(2))(2)-cbl(+) and SeCN-cbl. OCrO(3)-cbl(-), which also has a broad absorption band in the NIR was prepared for the first time. After deconvolution, similar broad bands were seen in the visible region for many other cobalamins. The wavelengths for band A placed the cobalamins in an order similar to the spectrochemical series but different from that of the alphabeta and gamma bands (pi-pi* transitions), which follow the nephelauxetic series. Band A was ascribed to a ligand-to-metal charge transfer (LMCT) transition from a pi orbital in the corrin ring to Co(iii). This is the first systematic study of LMCT bands in cobalamins.     

Competition between transferrin and the serum ligands citrate and phosphate for the binding of aluminum

A key issue regarding the speciation of Al(3+) in serum is how well the ligands citric acid and phosphate can compete with the iron transport protein serum transferrin for the aluminum. Previous studies have attempted to measure binding constants for each ligand separately, but experimental problems make it very difficult to obtain stability constants with the accuracy required to make a meaningful comparison between these ligands. In this study, effective binding constants for Al-citrate and Al-phosphate at pH 7.4 have been determined using difference UV spectroscopy to monitor the direct competition between these ligands and transferrin. The analysis of this competition equilibrium also includes the binding of citrate and phosphate as anions to apotransferrin. The effective binding constants are 10(11.59) for the 1:1 Al-citrate complexes and 10(14.90) for the 1:2 Al-citrate complexes. The effective binding constant for the 1:2 Al-phosphate complex is 10(12.02). No 1:1 Al-phosphate complex was detected. Speciation calculations based on these effective binding constants indicate that, at serum concentrations of citrate and phosphate, citrate will be the primary low-molecular-mass ligand for aluminum. Formal stability constants for the Al-citrate system have also been determined by potentiometric methods. This equilibrium system is quite complex, and information from both electrospray mass spectrometry and difference UV experiments has been used to select the best model for fitting the potentiometric data. The mass spectra contain peaks that have been assigned to complexes having aluminum:citrate stoichiometries of 1:1, 1:2, 2:2, 2:3, and 3:3. The difference UV results were used to determine the stability constant for Al(H(-1)cta)-, which was then used in the least-squares fitting of the potentiometric data to determine stability constants for Al(Hcta)+, Al(cta), Al(cta)2(3-), Al(H(-1)cta)(cta)(4-), Al2(H(-1)cta)2(2-), and Al3(H(-1)cta)3(OH)(4-).