Asymmetrical Platinum and Rhodium Dinuclear Complex Strongly Bound to Filled d z 2 ${{_{{\rm z}{

Heterometallic extended metal atom chains (EMACs) aligned with three types of metal were rationally synthesized by forming unbridged metal-metal bonds based on the interactions between highest occupied and lowest unoccupied molecular orbitals at the d z 2 ${{_{{\rm z}{^{2}}}}}$ orbital. These chains form pentanuclear structures aligned as Rh-Pt-M-Pt-Rh with relatively large formation constants of 5.0×1013  M-2 for M=Pt and 6.3×1011  M-2 for M=Pd, while retaining their backbones in solution. In the case of M=Cu, the original Cu(+2) atoms were reduced to Cu(+1) during the synthetic process. Cu(+1) has an unprecedented trigonal bipyramidal coordination geometry. The reported synthesis based on asymmetrical dinuclear complexes provides a guideline for the synthesis of hetero-EMACs to allow several analogs through judicious combinations realized by tuning the number of metal nuclei and metal species.

Synthesis and characterization of a uranyl(VI) complex with 2,6-pyridine-bis(methylaminophenolato) and its ligand-centred aerobic oxidation mechanism to a diimino derivative.

A uranyl(VI) complex with 2,6-bis(3,5-di-tert-butyl-o-phenolateaminomethyl)pyridine (UO2(tBu-pdaop), 1) was synthesized and thoroughly characterized by 1H NMR, IR, elemental analysis, and single-crystal XRD. Right after the dissolution of complex 1 in pyridine or DMSO, the solution was pale red, whereas it gradually turned to dark purple under an ambient atmosphere. 1H NMR spectra at the initial and final states suggested that both of the two aminomethyl groups in 1 were converted to azomethine ones through aerobic oxidation. Indeed, a uranyl(VI) complex with 2,6-bis(3,5-di-tert-butyl-o-phenolateiminomethyl)pyridine (UO2(tBu-pdiop), 2) was obtained from the concentrated solution once the reaction was completed, and was characterized by IR, and single-crystal XRD. Kinetic analyses as well as mechanistic studies based on quantum chemical calculations suggested that hydrogen atom transfer from one of the amino groups in complex 1 to nearby O2 initiates the stepwise oxidation processes to finally afford 2. The present findings demonstrate the novel reactivity of a uranyl(VI) complex, and provide new insights to construct thermally-driven molecular conversion systems by a UO22+ complex catalyst.

Preparation of tricationic tris(pyridylpalladium(II)) metallacyclophane as an anion receptor.

A tricationic tris(pyridylpalladium(II)) metallacyclophane was prepared from 3,5-dibromopyridine by a successive treatment with tetrakis(triphenylphosphine)palladium(0), diphosphine, and silver salt. Single-crystal X-ray diffraction analysis revealed that the metallacyclophane incorporated one of three counter anions into its hole-shaped cavity to form multidentate C-H⋯anion interactions. Solution-phase 1H NMR experiments in DMSO-d6 indicated that the metallacyclophane exhibited selective binding behavior toward nitrate, tetrafluoroborate, p-toluenesulfonate, perchlorate, and hydrogen sulfate ions, whereas the hexafluoroantimonate ion exhibited only weak interaction toward the metallacyclophane. This anion recognition behavior was further demonstrated by an extraction experiment of water-soluble sulfonate dyes.

Reactivity of Boronic Acids toward Catechols in Aqueous Solution.

Fundamental information on the reactivities of boronic acids toward catechols in aqueous solution is required in all the fields dealing with boronic acid. However, comprehensive studies on reactivity are often hindered by so-called "proton ambiguity," which makes it impossible for the rate constants of boronic acid and boronate ion to be determined separately. Herein, we set up two reaction systems without proton ambiguity: (1) Alizarin Red S and (2) Tiron with several boronic acids (RB(OH)2) with different pKas and performed kinetic and equilibrium studies on the reaction systems. It was shown that the logarithms of the rate constants of RB(OH)2 and its conjugate boronate ion (RB(OH)3-) decreased and increased linearly, respectively, with increasing pKa of RB(OH)2 for both systems. Consequently, the reactivities of RB(OH)2 and RB(OH)3- were reversed at high RB(OH)2 pKa. It was also shown that the bulky o- substituents of phenylboronic acids retarded the backward reactions, resulting in enhancement of the formation constants of boronic acid-catechol esters.

Methoxy-substituted tetrakisquinoline analogs of EGTA and BAPTA for fluorescence detection of Cd2+ .

EGTA (ethylene glycol bis(2-aminoethyl ether)-N,N,N',N'-tetraacetic acid) and BAPTA (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid) are well-known Ca2+ chelators that have four carboxylates, two nitrogen atoms and two ether oxygen atoms. In the present study, we prepared EGTQ (N,N,N',N'-tetrakis(2-quinolylmethyl)-1,2-bis(2-aminoethoxy)ethane) and BAPTQ (N,N,N',N'-tetrakis(2-quinolylmethyl)-1,2-bis(2-aminophenoxy)ethane) as quinoline alternatives of EGTA and BAPTA, respectively. In methanol-HEPES buffer solution (9 : 1, 50 mM HEPES, 0.1 M KCl, pH = 7.5), EGTQ exhibits fluorescence enhancement induced by Zn2+ and Cd2+ with poor selectivity, but BAPTQ did not exhibit a fluorescence response to either metal ion. Introduction of three methoxy substituents at the 5,6,7-positions of each quinoline moiety in BAPTQ specifically enhanced the fluorescence intensity of the Cd2+ complex, establishing the Cd2+-specific probe TriMeOBAPTQ (N,N,N',N'-tetrakis(5,6,7-trimethoxy-2-quinolylmethyl)-1,2-bis(2-aminophenoxy)ethane). In contrast, TriMeOEGTQ (N,N,N',N'-tetrakis(5,6,7-trimethoxy-2-quinolylmethyl)-1,2-bis(2-aminoethoxy)ethane) maintains a poor Cd2+/Zn2+ selectivity in its fluorescence response. Although the crystal structures of Cd2+/Zn2+ complexes with EGTQ and BAPTQ derivatives reveal the formation of multiple components including mononuclear and dinuclear complexes, the dinuclear Cd2+ and Zn2+ complexes with a linearly extended structure are regarded as possible fluorescent species in the solution. The conformational restriction of BAPTQ due to the orthophenylene moieties in the molecular skeleton is responsible for the formation of the weakly fluorescent, OH-bridged dizinc complex, which is critical to the strict Cd2+-specificity in the fluorescence response of TriMeOBAPTQ.

Coordination structure and extraction behavior of a silver ion with N-substituted-9-aza-3,6,12,15-tetrathiaheptadecanes: significant effect of Ph-C-N framework on the extractability.

N-Substituted-9-aza-3,6,12,15-tetrathiaheptadecanes having Ph-C-N frameworks (N-R-ATH; R = benzyl (N-Bn-ATH), 4-nitrobenzyl (N-NO2Bn-ATH), and diphenylmethyl (N-Ph2CH-ATH)) were synthesized, and their Ag(i) complexes were structurally characterized. X-Ray crystal structure analyses of [Ag(N-R-ATH)](BF4) (R = Bn and Ph2CH) revealed monomeric tetra-S-coordinated complex cation structures without the N-coordination, and a benzene ring of the N-R group covered over the amine nitrogen atom. The precise extraction analyses of a Ag(i) ion with ATH derivatives (L = N-R-ATHs and N-H-ATH) associated with the (1)H NMR analyses of the [Ag(L)](+) complexes in polar and non-polar solvents revealed that the introduction of the N-substituent significantly enhanced the extractability of Ag(+), due to the "hydrophobic cover" effect by the Ph-C-N framework in the [Ag(N-R-ATH)](+) complexes.

Pyridinium-based Task-specific Ionic Liquid with a Monothioether Group for Selective Extraction of Class b Metal Ions.

A pyridinium-based task-specific ionic liquid (TSIL) with a monothioether group, [3-TPPy][NTf2], extracted typical class b metal ions, such as Ag(I), Cu(I), Pd(II), and Pt(II), in high selectivity. It was found that the composition ratio of the extracted Ag(I) and Cu(I) species depended on the TSIL concentration, and that TSIL extracted these metal ions through mono-S-coordinated complex formation at low TSIL concentrations. [3-TPPy][NTf2] can be recycled in the extraction-recovery process, which is of a great advantage for practical use in environmentally benign separation methods.

Universal reaction mechanism of boronic acids with diols in aqueous solution: kinetics and the basic concept of a conditional formation constant.

To establish a detailed reaction mechanism for the condensation between a boronic acid, RB(OH)2, and a diol, H2L, in aqueous solution, the acid dissociation constants (Ka(BL)) of boronic acid diol esters (HBLs) were determined based on the well-established concept of conditional formation constants of metal complexes. The pKa values of HBLs were 2.30, 2.77, and 2.00 for the reaction systems, 2,4-difluorophenylboronic acid and chromotropic acid, 3-nitrophenylboronic acid and alizarin red S, and phenylboronic acid and alizarin red S, respectively. A general and precise reaction mechanism of RB(OH)2 with H2L in aqueous solution, which can serve as a universal reaction mechanism for RB(OH)2 and H2L, was proposed on the basis of (a) the relative kinetic reactivities of the RB(OH)2 and its conjugate base, that is, the boronate ion, toward H2L, and (b) the determined pKa values of HBLs. The use of the conditional formation constant, K', based on the main reaction: RB(OH)2 + H2L (K1)⇌ RB(L)(OH)(-) + H3O(+) instead of the binding constant has been proposed for the general reaction of uncomplexed boronic acid species (B') with uncomplexed diol species (L') to form boronic acid diol complex species (esters, BL') in aqueous solution at pH 5-11: B' + L' (K')⇌ BL'. The proposed reaction mechanism explains perfectly the formation of boronic acid diol ester in aqueous solution.

Bis(2-quinolylmethyl)ethylenediaminediacetic acids (BQENDAs), TQEN-EDTA hybrid molecules as fluorescent zinc sensors.

Molecular hybrids of TQEN (N,N,N',N'-tetrakis(2-quinolylmethyl)ethylenediamine) and EDTA (ethylenediamine-N,N,N',N'-tetraacetic acid) were examined as fluorescent Zn(2+) sensors. Upon the addition of Zn(2+), N,N-BQENDA (N,N-bis(2-quinolylmethyl)ethylenediamine-N',N'-diacetic acid, 1a) exhibits a 30-fold emission enhancement at 456 nm (λex = 315 nm, ϕZn = 0.018) in buffer (HEPES, pH = 7.5, 100 mM KCl). The fluorescence enhancement is Zn(2+)-specific as Cd(2+) induces much smaller increases (ICd/I0 = 5 and ICd/IZn = 16%). These spectroscopic properties, as well as the excellent water-solubility, represent a significant improvement compared to the parent TQEN sensor (ϕZn = 0.007, ICd/IZn = 64%). The isoquinoline analog N,N-1-isoBQENDA (N,N-bis(1-isoquinolylmethyl)ethylenediamine-N',N'-diacetic acid, 1b) possesses a similar Zn(2+) fluorescence response to the parent 1-isoTQEN (N,N,N',N'-tetrakis(1-isoquinolylmethyl)ethylenediamine) sensor, but exhibits diminished fluorescence intensity. Apo 1a and 1b extract more than 50% of the Zn(2+) from an equimolar amount of [Zn(TPEN)](2+) (TPEN = N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine) or [Zn(EDTA)](2-), whereas TPEN and EDTA cannot effectively remove Zn(2+) from [Zn(1a)] and [Zn(1b)]. The reduction of steric crowding in [Zn(TQEN)](2+) resulting from the substitution of two quinolines with carboxylates enhances the interaction between the metal ion and the remaining quinoline nitrogen atoms. The stronger bonding interaction results in enhanced emission intensity, Zn(2+) selectivity and metal ion affinity. This is in contrast to [Zn(1-isoTQEN)](2+) where the isoquinoline-carboxylate replacement does not relieve any coordination distortion, therefore no significant changes in fluorescence or metal binding properties are observed.

Characterization of one-electron oxidized copper(II)-salophen-type complexes; effects of electronic and geometrical structures on reactivities.

One-electron oxidized salophen-type complexes, [Cu(salophen)](+) (H2salophen = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-diaminobenzene), and its methoxy derivatives, [Cu(MeO-salophen)](+) and [Cu(salophen-(MeO)2)](+) (H2MeO-salophen = N,N'-bis(3-tert-butyl-5-methoxysalicylidene)-1,2-diaminobenzene, H2salophen-(MeO)2 = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-diamino-4,5-dimethoxybenzene), have been synthesized and structurally characterized, and their reactivities have been investigated. The solid state structures of the one-electron oxidized forms of these complexes suggested that [Cu(salophen)](+) and [Cu(MeO-salophen)](+) can be assigned to relatively localized Cu(ii)-phenoxyl radical complexes, while [Cu(salophen-(MeO)2)](+) is the diiminobenzene radical complex. On the other hand, [Cu(salophen)](+) in solution showed a different electronic structure from that of the solid sample, the radical electron being delocalized over the whole π-conjugated ligand. The reaction of these oxidized complexes with benzyl alcohol has been investigated in the presence of a large excess of substrate, which revealed the difference in the kinetic behavior between the complexes. The mechanisms of the oxidation have been discussed on the basis of the electronic and geometrical structures and the reaction kinetics.

Quinoline-based fluorescent zinc sensors with enhanced fluorescence intensity, Zn/Cd selectivity and metal binding affinity by conformational restriction.

Two cyclohexanediamine-based tetrakisquinoline derivatives, N,N,N',N'-tetrakis(2-quinolylmethyl)-trans-1,2-cyclohexanediamine (TQDACH) and N,N,N',N'-tetrakis(1-isoquinolylmethyl)-trans-1,2-cyclohexanediamine (1-isoTQDACH), have been prepared and their zinc-induced fluorescent response was investigated. In DMF-H2O (1 : 1) solution, TQDACH exhibits increase of fluorescence at 455 nm in the presence of 1 eq. of zinc ion (λ(ex) = 317 nm, φ = 0.010). Similarly, 1-isoTQDACH exhibited fluorescence enhancement upon binding with zinc (λ(ex) = 325 nm, λ(em) = 352 and 475 nm, φ = 0.032). The fluorescence intensity ratio induced by cadmium relative to zinc (I(Cd)/I(Zn)) for these 1,2-cyclohexanediamine probes is lower than those for the corresponding ethylenediamine derivatives, TQEN and 1-isoTQEN. Crystal structures of the zinc and cadmium complexes of TQDACH and 1-isoTQDACH reveal the superior metal binding ability of the 1,2-cyclohexanediamine and isoquinoline moieties in comparison to ethylenediamine and quinoline. The conformational restriction afforded by the 1,2-cyclohexanediamine skeleton upon zinc binding leads to enhanced fluorescence intensity and strong metal binding affinity.

Relative kinetic reactivity of boronic acid and boronate ion towards Tiron, 2,2'-biphenol, and propylene glycol.

Reaction systems of boronic acid (RB(OH2), R = phenyl or 3-fluorophenyl) with diols and no proton ambiguity were elaborately set up, and kinetic measurements were conducted to elucidate the relative reactivities of RB(OH)2 and RB(OH)3(-). In the reactions of phenylboronic and 3-fluorophenylboronic acids with propylene glycol, the reactivity order was: RB(OH)2 >> RB(OH)3(-), whereas in the reactions of 3-pyridylboronic acid with Tiron and 2,2'-biphenol, the reactivity of RB(OH)2 was comparable to that of RB(OH)3(-). These results are in contrast to those that have been previously reported, and widely accepted for over thirty years, that concluded that the reactivity of RB(OH)3(-) is several orders of magnitude higher than that of RB(OH)2. The reactivity of Tiron with 3-pyridylboronic acid is affected by the protonation of one of its sulfonate groups.

New insights into the electronic structure and reactivity of one-electron oxidized copper(II)-(disalicylidene)diamine complexes.

The neutral and one-electron oxidized Cu(II) six-membered chelate 1,3-Salcn (1,3-Salcn = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,3-cyclohexanediamine) complexes have been investigated and compared with the five-membered chelate 1,2-Salcn (N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-(1R,2R)-diamine) complexes. Cyclic voltammetry of Cu(1,3-Salcn) showed two reversible redox waves at 0.48 and 0.68 V, which are only 0.03 V higher than those of Cu(1,2-Salcn). Reaction of Cu(1,3-Salcn) with 1 equiv of AgSbF6 afforded the oxidized complex which exists as a ligand-based radical species in solution and in the solid state. The X-ray crystal structure of the oxidized complex, [Cu(1,3-Salcn)]SbF6, exhibited an asymmetric metal binding environment with a longer Cu-O bond and quinoid distortion in the phenolate moiety on one side, demonstrating at least partial ligand radical localization in the solid state. The ligand oxidation is also supported by XPS and temperature dependent magnetic susceptibility. The electronic structure of the [Cu(1,3-Salcn)](+) complex was further probed by UV-vis-NIR, resonance Raman, and electron paramagnetic resonance (EPR) measurements, and by theoretical calculations, indicating that the phenoxyl radical electron is relatively localized on one phenolate moiety in the molecule. The reactivity of [Cu(1,3-Salcn)](+) with benzyl alcohol was also studied. Quantitative conversion of benzyl alcohol to benzaldehyde was observed, with a faster reaction rate in comparison with [Cu(1,2-Salcn)](+). The kinetic isotope effect (KIE = k(H)/k(D)) of benzyl alcohol oxidation by [Cu(1,3-Salcn)](+) was estimated to be 13, which is smaller than the value reported for [Cu(1,2-Salcn)](+). The activation energy difference between [Cu(1,2-Salcn)](+) and [Cu(1,3-Salcn)](+) was in good agreement with the energy calculated from KIE. This correlation suggests that the Cu(II)-phenoxyl radical species, characterized for [Cu(1,2-salcn)](+) is more reactive for hydrogen abstraction from benzyl alcohol in comparison to the 1:1 mixture of Cu(III)-phenolate and Cu(II)-phenoxyl radical species, [Cu(1,2-Salcn)](+). Thus, the Cu(II)-phenoxyl radical species accelerates benzyl alcohol oxidation in comparison with the Cu(III)-phenolate ground state complex, in spite of the similar activated intermediate and oxidation pathway.

Quinoline-based, glucose-pendant fluorescent zinc probes.

Quinoline-based tetradentate ligands with glucose pendants, N,N'-bis[2-(ß-d-glucopyranosyloxy)ethyl]-N,N'-bis[(6-methoxyquinolin-2-yl)methyl]ethylenediamine (N,N'-6-MeOBQBGEN) and its N,N-counterpart, N,N-6-MeOBQBGEN, have been prepared, and their fluorescence-spectral changes upon Zn binding were investigated. Upon excitation at 336 nm, N,N'-6-MeOBQBGEN showed weak fluorescence (ϕ ≈ 0.016) in HEPES buffer (HEPES 50 mM, KCl 100 mM, pH 7.5). In the presence of Zn, N,N'-6-MeOBQBGEN exhibited a significant increase in fluorescence (ϕ = 0.096) at 414 nm. The fluorescence enhancement is specific for Zn and Cd (I(Cd) /I(Zn) of 50% at 414 nm). On the other hand, N,N-6-MeOBQBGEN exhibited a smaller fluorescence enhancement upon Zn complexation (ϕ = 0.043, λ(ex) = 334 nm, λ(em) = 407 nm) compared with N,N'-6-MeOBQBGEN. Fluorescence microscopic analysis using PC-12 rat adrenal cells revealed that N,N'-6-MeOBQBGEN exhibits a 1.8-fold higher fluorescence-signal response to Zn ion concentration compared with sugar-depleted compound 2 (N,N'-bis[(6-methoxyquinolin-2-yl)methyl]ethylenediamine), due to its enhanced uptake into cells due to the targeting ability of the attached carbohydrates.

Zinc-specific fluorescent response of tris(isoquinolylmethyl)amines (isoTQAs).

Isoquinoline-based tetradentate ligands with C(3)-symmetry, tris(1- or 3-isoquinolylmethyl)amine (1- or 3-isoTQA), have been prepared and their zinc-induced fluorescence enhancement was investigated. Upon excitation at 324 nm, 1-isoTQA shows very weak fluorescence (ϕ = ∼0.003) in DMF/H(2)O (1/1) solution. In the presence of zinc ion, 1-isoTQA exhibits fluorescence increase (ϕ = 0.041) at 359 and 470 nm. This fluorescence enhancement at 470 nm is specific for zinc. However, 3-isoTQA exhibited a smaller fluorescence enhancement upon zinc complexation (ϕ = 0.017, λ(em) = 360 and 464 nm) compared with 1-isoTQA. Crystal structures of zinc complexes of isoTQAs demonstrate the diminished steric crowding and shorter Zn-N(aromatic) distances compared with isoTQENs (N,N,N',N'-tetrakis(isoquinolylmethyl)ethylenediamines) leads to a higher fluorescent response toward zinc relative to cadmium.

Formation mechanism of 2-methyl-2-buten-1,4-diol and 2-methyl-3-buten-1,2-diol from 2-methyl-1,3-butadiene on a head-to-head pivalamidato-bridged cis-diammineplatinum(III) binuclear complex.

Reactions of a pivalamidato-bridged head-to-head (HH) platinum(III) binuclear complex with 2-methyl-1,3-butadiene (isoprene) and p-styrenesulfonate and of an α-pyrrolidonato-bridged HH platinum(III) binuclear complex with p-styrenesulfonate were studied kinetically using UV-vis spectrophotometry and (1)H NMR spectroscopy, and detailed reaction mechanisms are proposed. Pt(III) binuclear complexes react with p-styrenesulfonate in four successive steps with mechanisms similar to that for an HH α-pyridonato-bridged Pt(III) binuclear complex with p-styrenesulfonate. In the case of isoprene, four steps were observed on the basis of UV-vis spectrophotometry. However, the reaction kinetics for steps 1 and 2 correspond to those for the previous reaction system, and those for steps 3 and 4 do not correspond to those for the previous system or to those observed by using (1)H NMR spectroscopy for the present isoprene system. By using UV-vis spectrophotometry, it was shown that isoprene preferentially π-coordinates to the Pt(N(2)O(2)) atom via the double bond adjacent to the methyl group in step 1. In step 2, a second isoprene molecule π-coordinates to the Pt(N(4)) atom, which is the rate-determining step, followed by nucleophilic attack of a water molecule on the π-coordinated isoprene on the Pt(N(2)O(2)) atom to form two isomeric σ-complexes. In the same step, π-coordinated isoprene on the Pt(N(4)) atom of the σ-complexes is released. This is different from the reaction of the Pt(III) binuclear complexes with other olefins. In step 3, reductive elimination of the σ-complexes occurs to form two diols and the HH pivalamidato-bridged Pt(II) binuclear complex. Finally, acid decomposition of the Pt(II) binuclear complex occurs to form monomers in step 4. From (1)H NMR spectroscopic observations, fast isomerization between σ-complexes and reductive elimination of the σ-complexes occurs in step 3, and isomerization from a 1,4-diol to a 1,2-diol occurs in step 4.

Optimization of conditions for the determination of boron by a ruthenium(II) complex having diol moiety: A mechanistic study.

Two ruthenium(II) complexes, [Ru(bpy)(2)(dhbpy-H(-1))](+) and [Ru(bpy)(2)(dhphen)](2+) (bpy=2,2'-bipyridine, dhbpy=3,3'-dihydroxy-2,2'-bipyridine, dhphen=5,6-dihydroxy-1,10-phenanthroline) were examined for use as a colorimetric reagent for the determination of boron. The reactions of boric acid with these two complexes were thermodynamically and kinetically studied in detail in order to specify the reactive species and to set up optimum condition for the determination of boron. The detailed analysis of the kinetic data for the reaction of the latter water-soluble complex showed that both boric acid and borate ion were reactive in an alkaline solution. The thermodynamically and kinetically optimum pH for the determination of boron was ca. 9 at 25 degrees C. A spectrofluorimetric determination of boron with the latter complex was attempted at 600nm with excitation at 360nm, and at pH 8.9 using CHES (N-cyclohexyl-2-aminoethanesulfonic acid) buffer. It was found that a trace amount of boron as low as ca. 2x10(-5)M ( approximately 1ppm) could be detectable.

Kinetic evidence for high reactivity of 3-nitrophenylboronic acid compared to its conjugate boronate ion in reactions with ethylene and propylene glycols.

The rate constants for a boronate ion were determined for the first time using the reaction systems of 3-nitrophenylboronic acid (3-NO2PhB(OH)2) with ethylene glycol (EG) and propylene glycol (PG) in an alkaline solution: the rate constants (25 degrees C, I = 0.10 M) for the reactions of 3-NO2PhB(OH)3- are 1.2 M(-1) s(-1) (EG) and 1.5 M(-1) s(-1) (PG), which are at least 10(3) times smaller than those for the reactions of 3-NO 2PhB(OH)2 [1.0 x 10(4) M(-1) s(-1) (EG) and 5.8 x 10(3) M(-1) s(-1) (PG)].

Which is reactive in alkaline solution, boronate ion or boronic acid? Kinetic evidence for reactive trigonal boronic acid in an alkaline solution.

That boronic acid is a reactive species toward a diol moiety even in an alkaline solution and that the boronate ion is not very reactive were demonstrated by the estimated upper limit of the rate constants for the reactions of some boronic acids with 2,2'-biphenol and 2,3-dihydroxynaphthalene in a neutral-alkaline solution, which will correct a common misunderstanding in boron chemistry and would renew the idea of effective boronic acid sensor design for carbohydrates.

Isomerization reaction of head-to-head alpha-pyridonato-bridged ethylenediaminepalladium(II) binuclear complex, [Pd2(en)2(C5H4NO)2]2+, in aqueous solution.

Head-to-head bis(alpha-pyridonato)-bridged bis(ethylenediamine)dipalladium(ii), HH-[Pd(2)(en)(2)(alpha-pyridonato)(2)](ClO(4))(2), was synthesized and structurally characterized by X-ray crystallography. The (1)H NMR spectra show that the head-to-head (HH) dimer produces the head-to-tail (HT) dimer and monomers ([Pd(en)(alpha-pyridone)(2)](2+), [Pd(en)(H(2)O)(alpha-pyridone)](2+), [Pd(en)(H(2)O)(2)](2+), etc.) in aqueous solution, and the relative amount of dimers to monomers is dependent on the total concentration of the HH dimer dissolved as well as the acidity of the solution. It was found that the formation of the HH and HT dimers from the monomers is fast, and the HT dimer is produced from the HH dimer only via coexisting monomers, i.e., there is no direct isomerization path between the HH and HT dimers. The kinetic analyses for the HH <==>HT isomerization reaction with time-resolved (1)H NMR measurements revealed that the reaction proceeds via first-order kinetics, which was explained based on a relaxation process. The rate determining step for HH <==>HT isomerization is the reaction step between the mono-alpha-pyridone complex and the bis-alpha-pyridone complex, [Pd(en)(H(2)O)(alpha-pyridone)](2+)+alpha-pyridone <==> [Pd(en)(alpha-pyridone)(2)](2+).