bluuebunny/crossref_metadata_2025_split huggingface dataset:
Racemic Structure and Optical Resolution by Preferential Crystallization of (±)-Organic Ammonium Hydrogen Malates
Authors: Shiraiwa Tadashi , Sado Yujin , Inoue Mitsuo , Sakamoto Keiji , Miyazaki Hideya , Kurokawa Hidemoto 
Published: July 2006

Abstract
Gibbs energies of formation of racemate, binary melting point diagrams, and ternary solubility diagrams indicate that (±)-propylammonium ((±)-PA salt) and (±)-1,1,3,3-tetramethylbutylammonium ((±)-TMB salt) hydrogen malates are conglomerates at room temperature, whereas (±)-TMB salt forms a racemic compound at its melting point. Free energies of critical nucleation in supersaturated solutions were examined to resolve (±)-PA and -TMB salts efficiently by preferential crystallization. Successive preferential crystallization of (±)-PA salt in methanol at 10 °C and that of (±)-TMB salt in water give (+)- and (−)-PA and -TMB salts with about 90% optical purity. Optically pure (+)- and (−)-malic acids are obtained from purified (−)- and (+)-salts.
Nitrene-Transfer Reaction between Azide and Unsaturated Ether in the Presence of Pd(II) Catalyst
Authors: Migita Toshihiko , Hongoh Kazuya , Naka Hiroyuki , Nakaido Setsuko , Kosugi Masanori 
Published: July 2006

Abstract
Azidoformate reacted with allylic ethers to give 1-alkoxy-1-(alkoxycarbonylimino)alkane under catalysis by PdCl2(PhCN)2. The same imines were formed almost quantitatively by noncatalyzed reaction of the azide with the corresponding vinylic ethers. The rate of the catalyzed reaction was found to be first order each in the allylic ether and in the azide. Easiness of the imine formation from the allylic ethers depended on the nature of azide, decreasing in the order of N3SO2Me&gt;N3CO2Me&gt;N3Ph. Based on these results the most probable mechanism for the catalyzed reaction is proposed.
Crystal and Molecular Structure of (E)-1,1′-Bitetralinylidene
Authors: Ogawa Keiichiro , Suzuki Hiroshi , Futakami Motoko , Yoshimura Shin , Sakurai Tosio , Kobayashi Kimiko , Kira Akira 
Published: July 2006

Abstract
The crystal structure of the title compound was determined by X-ray diffraction. The crystals have monoclinic symmetry with a=13.481(5), b=8.285(5), c=l3.092(3) Å. β=96.24(3)°, and space group P21⁄n with Z=4. The final R-factor was 0.065 for 2191 independent reflections. The torsion angles of the C–Ph bonds are 47.4(4) and 44.4(4)°. The cyclohexene rings have approximate twist-boat conformations. The molecular structure in the crystal is compared with that in the solution phase, that of (E)-stilbenes, and the results of the molecular mechanics calculations. It is also discussed in relation to the molecular packing.
Syntheses and Properties of 2,2′-Binaphtho[1,8-de]-1,3-dithiinylidene and Its Selenium Analog, 2-(1,3-Dithiol-2-ylidene)naphtho[1,8-de]-1,3-dithiin, and 2-(4H-Thiopyran-4-ylidene)naphtho[1,8-de]-1,3-dithiin
Authors: Yui Koji , Aso Yoshio , Otsubo Tetsuo , Ogura Fumio 
Published: July 2006

Abstract
In order to discover new electron donors for conducting charge-transfer complexes, the four title compouds 1–4 composed of two heterocycles have been prepared via 1,8-dichalcogen-bridged naphthalene. The cyclic voltammetery indicates that symmetrical 1 and 2 are poor donors, but unsymmetrical 3 and 4 possess considerable donor abilities. The latter compounds are thus capable of forming some crystalline charge-transfer complexes with strong acceptors such as TCNQ, TCNQF4, and DDQ, which are, however, semi-conducting.
Synthesis, Reactions, Spectral (IR and Visible) and Magnetic Studies of Bimetallic Alkoxides Containing Co(μ-OR)3M(M=Nb or Ta) Bridging Units
Authors: Dubey Raj Kumar , Singh Anirudh , Mehrotra Ram Charan 
Published: July 2006

Abstract
Interactions of CoCl2 with K{M(OPri)6} in 1:2 molar ratio in PriOH and C6H6 result in products with the composition [Co{M(OPri)6}b42] (M=Nb or Ta) in quantitative yields. Interchange reactions of these isopropoxide derivatives with alcohols of varying steric bulk (e.g., MeOH, EtOH, PrnOH, BunOH, and ButOH, or AmtOH) yield derivatives of composition, [Co{M(OR)6}2] (R=Me, Et, Prn, and Bus); [Co{M(OPri)3(OBus)3}2]; [Co{M(OPri)5(OBut)}2] and [Co{M(OPri)2(OR)4}2] (R=But or Amt). All these novel compounds have been characterized by elemental analyses and molecular weight determinations as well as by infrared, visible spectral and magnetic studies.
An Improved Synthesis of Methyl 7-(2-Hydroxy-5-oxo-1-cyclopentenyl)heptanoate
Authors: Naora Hirokazu , Ohnuki Takashi , Nakamura Asao 
Published: July 2006

Abstract
Methyl 7-(2-hydroxy-5-oxo-1-cyclopentenyl)heptanoate, which is a valuable synthon for prostanoids, was prepared in a good yield from dibenzyl malonate via three steps.
Rotational Isomerism in Fluorene Derivatives. XV. Conformational Equilibria of 2-Substituted and 2,7-Disubstituted 9-(2′-Dimethylaminophenyl)fluorene Derivatives and the Effects of Acid on Them
Authors: Nishida Akiko , Takeshita Makoto , Kawano Nobuaki , Fujisaki Shizuo , Kajigaeshi Shoji 
Published: July 2006

Abstract
Several 9-(2′-dimethylaminophenyl)-9-fluorenols (2) and 9-(2′-dimethylaminophenyl)fluorenes (3), which had electron-attracting or electron-releasing groups at 2- or 2,7-positions of the fluorene ring, were synthesized. The conformational equilibria (anti\ightleftarrowssyn) of 2 and 3 in CDCl3 lay near to their syn sides. However, the equilibria of 2 in DMSO-d6 inclined to the anti side. By the addition of trifluoroacetic acid to the solution of 3 in CDCl3, anti-3 salts were formed and stabilized by the N–H···π interaction between the dimethylammonio group and the fluorene ring. In this case, the intensities of the N–H···π interaction were affected by the magnitudes of the π-electron density of the fluorene ring.
Molecular and Electronic Structures of Thieno[3,4-b]thiophene-2-carboxylic Acid and Acetic Thieno[3,4-b]thiophene-2-carboxylic Anhydride. An AM1, MNDO, and CNDO/S Study
Authors: Buemi Giuseppe 
Published: July 2006

Abstract
AM1 and MNDO methods have been used for optimizing the molecular geometry of all the possible conformations of thieno[3,4-b]thiophene-2-carboxylic acid (1), of its methyl ester (2) and of acetic thieno[3,4-b]thiophene-2-carboxylic anhydride (3). Both methods give comparable results for the thieno[3,4-b]thiophene framework but rather different bond angles for the substituent group of 3. In any case, an equilibrium between two (1,2) or more (3) conformations is conceivable. Although the most stable conformations are predicted to be planar, the rotation of the substituent group implies only low energy increase (rotation barriers are calculated to be about 2 kcal mol−1) which allows wide oscillations. The π→π* electronic transitions do not differ appreciably from those of the parent thieno[3,4-b]thiophene molecule and are better accounted for by the conformations having remarkable rotation around the C7–C9 bond.
Photocycloadditions of Cyclodienes to Hexafluorobenzene
Authors: Šket Boris , Zupancic Nataša , Zupan Marko 
Published: July 2006

Abstract
The stereochemistry of photocycloaddition reactions of various cyclodienes to hexafluorobenzene in cyclohexane solution depends on the structure of the cyclodiene and [2+2]cycloadducts are mainly observed. Photoreaction of 1,5-cyclooctadiene with hexafluorobenzene gives nearly equal amounts of syn and anti[2+2]adducts, which are further transformed to tetracyclic systems, contrary to this, the stereochemistry observed by reactions with 1,4-cyclohexadiene depends on the molar ratio of cyclodiene–hexafluorobenzene and 30–54% of syn addition is observed, the syn adduct, however, being further transformed to 2,3,4,5,6,7-hexafluoropentacyclo[6.4.0.02,7.03,11.06,10]dodec-4-ene. Syn selectivity of [2+2]cycloaddition was enhanced when bicyclic dienes were used and it is interesting that in the case of norbornadiene and benzonorbornadiene only exo attack was observed, and no anti attack occurred in the case of benzonorbornene. The quantum yields of [2+2]photocycloaddition reactions depend on the structure of the cyclodiene and the concentrations of hexafluorobenzene and cyclodiene. The quantum yields for norbornadiene and 1,4-cyclohexadiene are nearly the same, while it is two times higher in a photoreaction with 1,5-cyclooctadiene, when equal amounts of hexafluorobenzene and 1,5-cyclooctadiene were irradiated in cyclohexane at λ=253.7 nm.
An Investigation into the Mechanism of Acid-Catalyzed Hydrolysis of N-Benzylbenzohydroxamic Acid
Authors: Ghosh Kallol K , Tandon Shiv G 
Published: July 2006

Abstract
The catalytic effects of hydrochloric, perchloric, and sulfuric acids on the hydrolysis of N-benzylbenzohydroxamic acid (BBHA) have been examined in 10% (v/v) dioxane–water at 55 °C. Plots of the pseudo-first-order rate constants kψ against [H+] show maxima which arise from extensive protonation of the substrate. Analyses of the kinetic data by Bunnett and Bunnett–Olsen criteria, solvent deuterium isotope effects, salt effects and entropies of activation are consistent with a bimolecular mechanism.
A Synthesis of (+)-Cyclaradine, Carbocyclic Analogue of 9-β-d-Arabinofuranosyladenine
Authors: Tadano Kin-ichi , Kimura Hiroshi , Ogawa Seiichiro 
Published: July 2006

Abstract
The title compound, a promising antiviral carbocyclic nucleoside analogue, was synthesized enantiospecifically. The present synthesis involves a coupling reaction of 5-amino-4,6-dichloropyrimidine and (1R,2R,3R,4R)-2,3-dihydroxy-4-(hydroxymethyl)cyclopentanamine which was in turn prepared from d-xylose.
Effects of Some Variables on the Point of Zero Charge of TiO2–ZrO2 Double Oxides
Authors: Karmakar Basudeb , Ganguli Dibyendu 
Published: July 2006

Abstract
Effects of variables such as acid/base reaction temperature, presence of impurities, method of oxide powder preparation, and calcination temperature on the point of zero charge (p.z.c) were investigated for TiO2–ZrO2 (79.41–20.59, wt.%) mixed oxides. The visually determined p.z.c. values were also compared with those arrived at by a computational method to obtain an estimate of the error of determination.
Fe(III)-Catalyzed Aromatic Hydroxylation with H2O2 in the Presence of a Variety of Electron-Transfer Agents
Authors: Tamagaki Seizo , Sasaki Masaaki , Tagaki Waichiro 
Published: July 2006

Abstract
Electron-transfer agents such as N,N,N′,N′-tetramethylphenylenediamine (TMPD), ferrocenes, and phenothiazines have been found to mediate the hydroxylation of benzene with H2O2 in the presence of Fe3+. Of these, TMPD catalyst is the most effective to provide phenol in 80% or better yield based on added H2O2 under the optimized conditions. A general mechanism, involving the rate-determining reduction of Fe3+ to Fe2+ with such mediators, is suggested.
Novel Effects of K-Addition to Ru/SiO2 on Conversion of Cyclohexane
Authors: Lin Zheng-Zhong , Enomoto Toshiyuki , Okuhara Toshio , Misono Makoto 
Published: July 2006

Abstract
The effects of the addition of alkalis to a Ru/SiO2 catalyst upon the conversion (hydrogenolysis and dehydrogenation) of cyclohexane, hydrogenolysis of butane, and hydrogenations of benzene and CO were studied. The addition of K or Cs slightly enhanced the catalytic activity for the hydrogenolysis of cyclohexane, whereas dehydrogenation to benzene was markedly suppressed. This result is contrary to the effect of the addition of Cu or Au to group-VIII metals, as reported in the literature. Changes in the activities became less significant as the atomic number of the added alkali decreased. From a systematic examination by varying the alkali content, it was revealed that dehydrogenation and CO hydrogenation were very sensitively suppressed by an electronic effect imposed by the alkalis, whereas changes in the activities of hydrogenolysis and benzene hydrogenation were not great.
Solvent Extraction of Indium with 3-Hydroxy-2-methyl-1-phenyl-4-pyridone
Authors: Ishii Hajime , Numao Shinji , Odashima Tsugikatsu 
Published: July 2006

Abstract
Extraction behavior of indium has been investigated with 3-hydroxy-2-methyl-1-phenyl-4-pyridone (HMPP) at 25±0.1 °C and an ionic strength of 0.2. The values of the proton-dissociation constants, pKa1 and pKa2, of HMPP were determined spectrophotometrically to be 3.02 and 9.56. The value of the partition coefficient, logKD, of HMPP between 1,2-dichloroethane and water was determined to be 1.35. Indium(III) was extracted into 1,2-dichloroethane by forming a 1 : 3 (metal : ligand) complex with HMPP. The extraction constant, Kex, the overall formation constant, β3, and the distribution constant, KDC, of the indium(III)–HMPP complex were determined, their values being as follows: logKex=2.16, logβ3=32.63, and logKDC=2.26.
Nonstabilized Azomethine Ylides Generated by Decarboxylative Condensation of α-Amino Acids. Structural Variation, Reactivity, and Stereoselectivity
Authors: Kanemasa Shuji , Sakamoto Kazushige , Tsuge Otohiko 
Published: July 2006

Abstract
A variety of aldehydes, containing enolizable aldehydes other than acetaldehyde can be used in the generation method of nonstabilized azomethine ylides by decarboxylative condensation of α-amino acids. Reactivity of the nonstabilized ylides was examined in intermolecular and intramolecular cycloadditions with olefins; stereoselectivity of the intramolecular cycloaddition using nonstabilized ylides was compared with that of ester-stabilized ylides.
Photolysis of Alcohols and Alkanones in Acetone Solutions. Photochemical [2+2]Cycloaddition Reaction between Acetone and Aliphatic Enols
Authors: Shimizu Nobujiro , Miyahara Toru , Mishima Masaaki , Tsuno Yuho 
Published: July 2006

Abstract
Transient enols including those of acetaldehyde, acetone, cyclopentanone, 3-pentanone, 2,4-dimethyl-3-pentanone, 2-butanone, and 2-methyl-3-pentanone were trapped photochemically with acetone via a [2+2]cycloaddition and isolated as corresponding 3-oxetanols in reasonable yields in the photolysis of six different secondary alcohols and two alkanones, 3-octanone and hexanal, in acetone solutions. The trapping experiments indicated the photodehydrogenation of unsymmetrical alcohols, 2-butanol and 2-methyl-3-pentanol, in acetone to be highly regioselective in preference for the formation of the less alkylated enol.
One-Pot Synthesis of Tetrahydrofuran Derivatives from Allylic Alcohols and Vinyl Ethers by Means of Palladium(II) Acetate
Authors: Fugami Keigo , Oshima Koichiro , Utimoto Kiitiro 
Published: July 2006

Abstract
Reaction of allylic alcohol with vinyl ether in the presence of Pd(OAc)2 afforded furan derivatives in good yield. Pd(OAc)2 was essential for the reaction. PdCl2 complex did not afford cyclized product but gave acetal exclusively. Three components were combined at once to produce 4-(3-butenyl)-2-butoxy-4-methyltetrahydrofuran upon treatment of a mixture of 2-methyl-2-propen-1-ol, butyl vinyl ether, and allyl bromide. The reaction could successfully be extended to the synthesis of nitrogen containing heterocycles by use of N-tosyl allylic amines in place of allylic alcohols.
Synthesis of Hydroxy Ketones by Chemoselective Alkylation of Keto Aldehydes with Dialkylzincs Catalyzed by Amino Alcohol, Diamine, or Dilithium Salt of Piperazine
Authors: Soai Kenso , Watanabe Masami , Koyano Masashi 
Published: July 2006

Abstract
Hydroxy ketones were obtained in high yields by the chemoselective alkylation of formyl group of keto aldehydes with dialkylzincs in the presence of such catalysts as 2-dimethylaminoethanol, N,N,N′,N′-tetramethylethylenediamine, or dilithium salt of piperazine.
Electronic Control of Stereoselectivity in the Metal Hydride Reductions of a Series of Substituted 3,4-Dihydro-1,4-ethanonaphthalen-2(1H)-ones
Authors: Okada Keiji , Tomita Seiji , Oda Masaji 
Published: July 2006

Abstract
The anti/syn stereoselectivity in the metal hydride reductions of a series of substituted 3,4-dihydro-1,4-ethanonaphthalen-2(1H)-ones was studied. The observed steroselectivity sequence was found to be parallel with the homoconjugation sequence except for the case of 5,8-dimethoxy-substituted derivative: the portion of anti attack increases as the benzene ring becomes electron-rich. The results were rationalized by Cieplak’s transition state model or by the nonclassical carboncation model. A special coordinated transition state was considered to explain the results for 5,8-dimethoxy-substituted compound.
ESR Studies on Chain Transfer Reactions: Rate Constants for the Reactions of Model Radicals of Polystyrene Growing Chain Ends with Tetrahalomethanes and Thiophenols
Authors: Kuwae Yoko , Kamachi Mikiharu 
Published: July 2006

Abstract
The absolute rate constants for reactions of the model radicals of the growing chain ends of styrene and methacrylonitrile with tetrahalomethanes and thiophenols were determined by spin-trapping methods using ESR spectroscopy. The model radicals were produced by the photodecomposition of 1,1′-diphenylazoethane and 2,2′-azobisisobutyronitrile. In the case of the styrene model radical, the rate constants for the halogen abstraction reaction from CBr4, CBrCl3, and CCl4 were 1.1×107, 2.0×106, and 1.1×105 M−1s−1, respectively, and increased with increasing electron affinity of tetrahalomethanes. The rate constants for the hydrogen abstraction reaction from thiophenols were of the order 106 M−1s−1, independent of the electron-donating and -accepting properties of the para substituents. In the case of the methacrylonitrile model radical, the rate constants for the halogen abstraction reaction from CBr4 and CBrCl3 were 1.1×105 and 4.5×103 M−1s−1, respectively. The rate constants for the hydrogen abstraction reaction from thiophenols with –CH3, –H, and –Cl substituent in the para position were 4.5×104, 2.7×104, and 1.7×104 M−1s−1, respectively. The rate constants decreased with increasing the electron-withdrawing power of the substituent.
Gel Filtration Chromatographic Study of Micellar Growth of Polyethylene Glycol Dodecyl Ethers
Authors: Funasaki Noriaki , Hada Sakae , Neya Saburo 
Published: July 2006

Abstract
The aggregation properties of polyethylene glycol dodecyl ethers (C12En; n=4, 5, and 8) are investigated with frontal gel (Sephadex G-200 and Sephacryl S-500) filtration chromatography (GFC) at 25 °C. At the trailing boundary of derivative GFC patterns for C12E5, unusual two peaks of micelles appear together with a peak of monomer. These micellar peaks are assigned to two types of micelle, viz., large (Rh=30 nm) and small (Rh=5 nm) micelles. As the C12E5 concentration is increased, the peak height for the large micelle increases more rapidly than that for the small micelle. Analysis of the centroid elution volume data by asymptotic theory reveals that the large micelle is the hexamer of the small micelle. This conclusion is supported by computer simulations of the GFC patterns, based on plate theory. In the derivative pattern of the trailing boundary for C12E8, the micellar peak becomes sharper and shifts to larger elution volume side, with increasing concentration. This pattern is well simulated with the assumption of linear concentration dependence of the micellar elution volume. Micelle size of C12E8 appears to remain constant. For C12E4, which is hydrophobically adsorbed on the gels, huge micelles coexist with a small amount of large micelles (Rh=33 nm).
Adsolubilization Behavior of Dyes Caused by Mixed Surfactant Bilayers Formed on Alumina
Authors: Esumi Kunio , Sakamoto Yuichi , Nagahama Tetsuya , Meguro Kenjiro 
Published: July 2006

Abstract
The adsolubilization of dyes (yellow OB and azobenzene) was performed on mixed bilayers consisting of anionic and nonionic surfactants formed on α-alumina. The adsolubilization capacity of the two dyes increased with the increase in the concentration of the dyes solubilized in the supernatant. The mixed bilayer consisting of anionic hydrocarbon (lithium dodecyl sulfate) and nonionic hydrocarbon surfactants (polyoxyethylene nonylphenyl ether) showed a greater adsolubilization capacity than that consisting of anionic fluorocarbon (lithium perfluorooctanesulfonate) and nonionic hydrocarbon surfactants. Further, the adsolubilization capacity of the dyes was affected by the oxyethylene chain length of the nonionic hydrocarbon surfactant in the mixed bilayer.
Studies on the Electrochemical Behavior of Thiadiazole Derivatives. Electroreduction of 2-Benzoylamino-5-[cyanoarylhydrazonomethyl]-1,3,4-thiadiazoles
Authors: Fahmy H M , Abdel Azzem M , Abdul Wahab M , Abdel Fattah N , Aboutabl M A 
Published: July 2006

Abstract
The electrochemical behavior of some 1,3,4-thiadiazole derivatives substituted at C5 (carbon number five in thiadiazole ring) with a hydrazono group has been studied at a dropping mercury electrode (DME) in different pH values. Controlled potential electrolysis (CPE) in alkaline medium, cyclic voltammetry (CV), ultraviolet spectra (UV) and pKa studies confirmed the proposed mechanism.
Transition Sequences of Oscillatory States of a Model Chemical System Showing Chaotic Oscillations
Authors: Morita Makoto , Iwamoto Kazutoshi , Sen\={o} Manabu 
Published: July 2006

Abstract
The transition sequence from a complex oscillation or a combined complex oscillation to a chaotic oscillation of a three-variable model system of chemical reactions were studied through analyses of the bifurcation diagrams. Period-doubling sequences, discontinuous transitions between two different oscillation states, and intermittency-type pseudo-periodic oscillations were observed. A pseudo-periodic oscillation appears when a combined complex oscillation changes to a new oscillatory state under some transition conditions. By changing the conditions, the discontinuous transition becomes to occur, leading the hysteresis behavior of transition.
A Highly Sensitive Fiber-Optic Immunosensor Using a Metal-Complex Compound as a Chemiluminescent Catalyst
Authors: Hara Tadashi , Tsukagoshi Kazuhiko , Arai Akihiro , Imashiro Yuji 
Published: July 2006

Abstract
A highly sensitive fiber-optic immunosensor using an antibody-immobilized optical fiber was developed and introduced into a chemiluminescence complex catalyst immunoassay (CLCCIA) which had been reported by the authors in a previous paper. After optimization of the experimental conditions, human serum albumin as model protein was determined by both competitive immunoassay and sandwich immunoassay, using the fiber-optic immunosensor. Human serum albumin could be determined in the concentration range 1×10−4–1×10−1 g dm−3 with a lower limit of 400 pg by competitive immunoassay while in the concentration range 1×10−5–1×10−1 g dm−3 with a lower limit of 40 pg by sandwich immunoassay. The new fiber-optic immunosensor developed by the authors can be characterized as follows: 1) Highly sensitive for the determination of a small amount of protein, 2) applicable to a wide concentration range of protein sample, 3) feasible with a microvolume of sample, 4) suitable for automated operation, and 5) excellent regarding safety, cost, and treatment.
Spectral Studies on the Cooperative Binding Mechanism of Evans Blue to Poly(N-vinyl-2-pyrrolidone)
Authors: Maruthamuthu Meenakshi , Subramanian E 
Published: July 2006

Abstract
The binding of Evans Blue (EB) to poly(N-vinyl-2-pyrrolidone) (PVP) was studied at two pH’s 7.2 and 11.2 spectrophotometrically by absorbance change method. At pH 7.2, the absorption spectrum of EB changed unusually on adding PVP and this indicated the formation of two types of spectroscopically distinguishable PVP–EB complexes. At very low [PVP], a weak complex was formed which got converted into a strong complex at high [PVP]. Positive cooperativity was found to be operative in this conversion and in the strong complex at higher [PVP]. Scatchard, Hill, and Schwarz methods were employed to analyze this cooperativity and to determine the binding parameters. The analysis revealed: (i) the binding constants for the weak and strong complexes were of the order of 104 and 105 dm3 mol−1 respectively; (ii) positive cooperativity at higher [PVP] was due to the interaction of neighboring binding sites on different polymer chains. At pH 11.2, only one type of complex was formed with higher affinity. But the binding behavior remained the same as at pH 7.2.