Synthesis, stabilities, and redox behavior of Di(1-azulenyl)(6-azulenyl)methylium hexafluorophosphates. Generation of a donor-acceptor-substituted neutral radical by azulenes

Several di(1-azulenyl)(6-azulenyl)methanes and 1,3-bis[(1-azulenyl)(6-azulenyl)methyl]azulenes were prepared by the condensation reaction of azulenes with diethyl 6-formylazulene-1,3-dicarboxylate under acidic conditions. The products were converted into di(1-azulenyl)(6-azulenyl)methylium hexafluorophosphates and azulene-1,3-diylbis[(1-azulenyl)(6-azulenyl)methylium] bis(hexafluorophosphate)s via hydride abstraction reaction with DDQ following the exchange of counterions. These mono- and dications exhibited high stability with large pK(R)(+) values (5.6-10.1), despite the captodative substitution of azulenes. The electrochemical reduction of the monocations upon cyclic voltammetry (CV) exhibited a reversible two-step, one-electron reduction wave with a small difference between the first reduction potential (E(1)(red)) and the second one (E(2)(red)), which exhibited the generation of highly amphoteric neutral radicals in solution. The electrochemical reduction of dications showed voltammograms, which were characterized by subsequent two single-electron waves and a two-electron transfer upon CV attributable to the formation of a radical cation, a diradical (or twitter ionic structure), and a dianionic species, respectively. Formation of a persistent neutral radical from a monocation was revealed by ESR and UV-vis spectroscopies and theoretical calculations. The ESR spectra of the neutral radical gave two hyperfine coupling constants: a(H) = 0.083 (6H) and 0.166 mT (9H) (g = 2.0024), indicating that an unpaired electron delocalizes over all three of the azulene rings. The stable monoanion, which shows the localization of the charge on the 6-azulenyl substituent, was also successfully generated from the di(1-azulenyl)(6-azulenyl)methane derivative.     

Synthesis, stabilities, and redox behavior of mono-, di-, and tetracations composed of di(1-azulenyl)methylium units connected to a benzene ring by phenyl- and 2-thienylacetylene spacers. A concept of a cyanine-cyanine hybrid as a stabilized electrochromic system

This paper describes the preparation of two tetracations 4a(4+) and 4b(4+) composed of di(1-azulenyl)methylium units based on a new structural principle of a cyanine-cyanine hybrid for the design of electrochromic materials with two color changes. Di- and monocations 5a(2+), 5b(2+) and 6a+, 6b+ composed of di(1-azulenyl)methylium units were also prepared for the purpose of comparison. The pKR+ values of the tetracations are rather high despite their tetracationic structure, although the stability of these cations decreases with the increase of the number of the existing cation units. The cyclic voltammetry (CV) of these cations revealed the presumed multielectron redox properties. However, the tetracations did not exhibit the idealized electrochemical behavior, in which subsequent two-electron reduction was presumed as the cyanine-cyanine hybrid, probably due to the less effective electrochemical interaction among the positive charges. The scope of the creation of the novel polyelectrochromic materials taking the new structural principle is demonstrated by these examples.     

Synthesis, properties, and OFET characteristics of 5,5'-di(2-azulenyl)-2,2'-bithiophene (DAzBT) and 2,5-di(2-azulenyl)-thieno[3,2-b]thiophene (DAzTT)

Two azulene-based π-conjugated systems, 5,5'-di(2-azulenyl)-2,2'-bithiophene and 2,5-di(2-azulenyl)-thieno[3,2-b]thiophene, were constructed via Suzuki-Miyaura cross-coupling reactions. The crystal structures of both revealed an edge-to-face orientation in a well-defined herringbone packing. The molecules stood nearly perpendicular to the substrate in the film form, with features of an organic field-effect transistor at hole mobilities of up to 5.0 × 10(-2) cm(2) V(-1) s(-1).     

Synthesis and redox behavior of azulene-substituted benzene derivatives and (eta(5)-cyclopentadienyl)[tetra- and di(6-azulenyl)cyclobutadiene]cobalt complexes

1,2-Di(6-azulenyl)tetraphenylbenzenes and (6-azulenyl)pentaphenylbenzenes were synthesized by Diels-Alder reactions of di(6-azulenyl)acetylenes and 6-(phenylethynyl)azulenes with tetraphenylcyclopentadienone. Cobalt-mediated cyclooligomerization of mono- and di(6-azulenyl)acetylenes afforded 1,3,5- and 1,2,4-tri(6-azulenyl)benzene derivatives together with (eta(5)-cyclopentadienyl)[tetra- and di(6-azulenyl)cyclobutadiene]cobalt complexes. The redox behavior of these novel (6-azulenyl)benzene derivatives and [tetra- and di(6-azulenyl)cyclobutadiene]cobalt complexes was examined by cyclic voltammetry (CV). Mono(6-azulenyl)benzenes exhibited a reduction wave upon CV. In contrast, 1,2-di(6-azulenyl)benzenes showed a two-step reduction wave at the similar potential region upon CV, which revealed the formation of a dianion stabilized by 6-azulenyl substituents under electrochemical reduction conditions. Three 6-azulenyl substituents on benzene in a 1,2,4 relationship also increased electron-accepting properties because of the formation of a closed-shell dianionic structure, whereas 1,3,5-tri(6-azulenyl)benzenes were reduced stepwise.     

Tuning delocalization in the radical cations of 1,4-bis[4-(diarylamino)styryl]benzenes, 2,5-bis[4-(diarylamino)styryl]thiophenes, and 2,5-bis[4-(diarylamino)styryl]pyrroles through substituent effects

Radical cations have been generated for 10 bis[4-(diarylamino)styryl]arenes and heteroarenes to investigate the effect of the electron-richness of the terminal groups and of the bridging (hetero)arene on delocalization. The intervalence charge-transfer bands of these radical cations vary from weak broad Gaussians, indicative of localized class-II mixed-valence species, to strong relatively narrow asymmetric bands, characteristic of delocalized class-III bis(diarylamino) species, to narrow symmetric bands in cases where the bridge contribution to the singly occupied molecular orbital is largest. Hush analysis of these bands yields estimates of the electronic coupling varying from 480 cm(-1) (electron-poor bridge, most electron-rich terminal aryl groups) to 1000 cm(-1) (electron-rich bridge, least electron-rich termini) if the diabatic electron-transfer distance, R(ab), is equated to the N-N separation. Computational and electron spin resonance (ESR) evidence for displacement of the diabatic states into the bridge (reduced R(ab)) suggests that these values are underestimates and that even more variation is to be expected through the series. Several dications have also been studied. The vis-NIR absorption of the dication of (E,E)-1,4-bis{4-[bis(4-n-butoxyphenyl)amino]styryl}-2,5-dicyanobenzene is seen at an energy similar to that of the strongest band in the spectrum of the corresponding weakly coupled monocation, with approximately twice the absorptivity, and its ESR spectrum suggests essentially noninteracting radical centers. In contrast, the electronic spectra of class-III monocations show no clear relationship to those of the corresponding dications, which ESR reveals to be singlet species.     

Synthesis and intramolecular pericyclization of 1-azulenyl thioketones

Several azulene-substituted thioketones, 1-thiobenzoylazulene (1a) and di(1-azulenyl) thioketone (2a) and their derivatives (1b and 2b-d) with alkyl substituents on each azulene ring, were prepared and their intramolecular pericyclization reaction was examined. The thioketones with a 3-alkyl substituent on each azulene ring exhibited the presumed pericyclization reaction under thermal and acid-catalyzed conditions, although the cases of the 1-azulenyl thioketones without the 3-alkyl substituents afforded a complex mixture under similar conditions. The intramolecular reaction following the intramolecular hydrogen transfer afforded the products 13b, 14b, and 14c. The products 13b and 14b were converted into the corresponding cations 18(+) and 19(+), which have structural similarity with that of the phenalenyl cation. These cations exhibited the expected two-step reduction waves upon CV, although the ESR analysis revealed that the neutral radical state did not have the presumed high stability.     

1-Boraadamantane: reactivity towards di(1-alkynyl)silicon and -tin compounds: first access to 7-metalla-2,5-diboranorbornane derivatives

1-Boraadamantane (1) reacts with di(1-alkynyl)silicon and -tin compounds 2 (Me2M(C...CR)2: M=Si; R=Me (a), tBu (b), SiMe3 (c); M=Sn, R=SiMe3 (e)) in a 1:1 ratio by intermolecular 1,1-alkylboration, followed by intramolecular 1,1-vinylboration, to give siloles 5a-c and the stannole 5e, respectively, in which the tricyclic 1-boraadamantane system is enlarged by two carbon atoms. Owing to the high reactivity of 1, a second fast intermolecular 1,1-alkylboration competes with the intramolecular 1,1-vinylboration as the second major step in the reaction if the substituent R at the C...C bond is small (2a) and/or if the M-C... bond is also highly reactive, as in 2d (M=Sn, R= Me) and 2e (M=Sn, R=SiMe3). This leads finally to the novel octacyclic 7-metalla-2,5-diboranorbornane derivatives 8a, 8d, and 8e, of which 8e was characterized by X-ray analysis in the solid state. 1,1,2,2-Tetramethyldi(1-propynyl)disilane, MeC...C-SiMe2SiMe2-C...CMe (3), reacts with 1 to give mainly a 1,2-dihydro-1,2,5-disilaborepine derivative 9 and the octacyclic compound 11, which is analogous to 8a but with an Me4Si2 bridge. All new products were characterized in solution by 1H, 11B, 13C, 29Si, and 119Sn NMR spectroscopy. For 8 and 11, highly resolved 29Si and 119Sn NMR spectra revealed the first two-bond isotope-induced chemical shifts, 2delta10/11B(29Si) and 2delta10/11B(119Sn) respectively, to be reported.     

Synthesis and properties of hexakis(6-octyl-2-azulenyl)benzene as a multielectron redox system with liquid crystalline behavior

[structure: see text] This paper describes the cyclotrimerization reaction of di(2-azulenyl)acetylenes (2a,b) catalyzed by Co2(CO)8 to produce hexa(2-azulenyl)benzene derivatives (1a,b). The cyclooligomerization of 2a and 2b utilizing CpCo(CO)2 as a catalyst produced (eta5-cyclopentadienyl)[tetra(2-azulenyl)cyclobutadiene]cobalt complexes (3a,b). The redox behavior of hexakis(6-octyl-2-azulenyl)benzene (1b), bis(6-octyl-2-azulenyl)acetylene (2b), and the cobalt complexes 3a and 3b along with 6-octyl-2-phenylazulene (19) was examined by cyclic voltammetry (CV). The reduction of compound 1b exhibited multiple-electron transfers in one step upon CV with a reduction potential similar to that of compound 19. However, the CVs of compounds 2b, 3a, and 3b were characterized by stepwise waves because of the reduction of each azulene ring. The mesomorphic behaviors of 1b, 2b, and 19 were also studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD) techniques. A new series of azulene derivatives, 1b, 2b, and 19, substituted by a long alkyl chain at the 6-position shows mesomorphism with crystalline polymorphs. Compound 1b showed a large temperature range of hexagonal columnar mesophases (Col(ho)) from 115.5 to 199.9 degrees C. Compound 2b has rectangular columnar (Col(ro)), smectic E (S(E)), and nematic (N) mesophases. Compound 19 exhibited an S(E) mesophase.     

Azulene-substituted aromatic amines. synthesis and amphoteric redox behavior of N,N-Di(6-azulenyl)-p-toluidine and N,N,N',N'-tetra(6-azulenyl)-p-phenylenediamine and their derivatives

[reaction: see text] N,N-Di(6-azulenyl)-p-toluidine (1a) and N,N,N',N'-tetra(6-azulenyl)-p-phenylenediamine (2a) and their derivatives with 1,3-bis(ethoxycarbonyl) substituents on each 6-azulenyl group (1b and 2b) were prepared by Pd-catalyzed amine azulenylation and characterized as a study into new aromatic amines for multistage amphoteric redox materials. The redox behavior of each compound was characterized by cyclic voltammetry. These compounds undergo facile reduction to stable anion radicals and dianion diradicals owing to the resonance stabilization between the 6-azulenyl groups and exhibit electrochemical oxidation depending on the amine subunits. The ESR measurement of anion radicals and a dianion diradical generated by the electrochemical reduction of amine 1b and diamine 2b revealed that the unpaired electron of these radicals delocalizes over the entire azulene ring including the central nitrogen atoms. UV-vis spectral analysis of amines 1a,b and diamines 2a,b, taken during the electrochemical reduction, exhibited a gradual decrease of the absorption bands of the neutral species along with an increase of the new absorption maxima at 625, 605, 640, and 610 nm, respectively, with the development of well-defined isosbestic points at 502, 562, 478, and 545 nm, respectively. As indicated by a combined ESR and UV-vis spectral study, the species giving rise to the new absorption maxima are concluded to be the generation of anion radicals and dianion diradicals of aromatic amines and diamines with high thermodynamic stability.     

Synthesis and characterization of novel monocarbollide exo-closo-(pi-arene)biruthenacarboranes [(PPh3)mClRu(eta6-C6H5R)Ru'CB10H11-n(OMe)n] (where R = H, m = 2, n = 1; R = mu-PPh2, m = 1, n = 0, 1)

The monocarbon carborane [Cs][nido-7-CB(10)H(13)] reacts with the 16-electron [RuCl(2)(PPh(3))(3)] in a solution of benzene/methanol in the presence of N,N,N',N'-tetramethylnaphthalene-1,8-diamine as the base to give a series of 12-vertex monocarbon arene-biruthenacarborane complexes of two types: [closo-2-[7,11-exo-RuClPPh(3)(mu,eta(6)-C(6)H(5)PPh(2))]-7,11-(mu-H)(2)-2,1-RuCB(10)H(8)R] (5, R = H; 6, R = 6-MeO; 7, R = 3-MeO) and [closo-2-(eta(6)-C(6)H(6))-10,11,12-[exo-RuCl(PPh(3))(2)]-10,11,12-(mu-H)(3)-2,1-RuCB(10)H(7)R(1)] (8a, R(1) = 6-MeO; 8b, R(1) = 3-MeO, inseparable mixture of isomers) along with trace amounts of 10-vertex mononuclear hypercloso/isocloso-type complexes [2,2-(PPh(3))(2)-2-H-3,9-(MeO)(2)-2,1-RuCB(8)H(7)] (9) and [2,5-(Ph(3)P)-2-Cl-2-H-3,9-(MeO)(2)-2,1-RuCB(8)H(6)] (10). Binuclear ruthenacarborane clusters of both series were characterized by a combination of analytical and multinuclear NMR spectroscopic data and by single-crystal X-ray diffraction studies of three selected complexes, 6-8. In solution, isomers 8a,b have been shown to undergo the isomerization process through the scrambling of the exo-[RuCl(PPh(3))(2)] fragment about two adjacent triangular cage boron faces B(7)B(11)B(12) and B(8)B(9)B(12).     

UV/vis, 1H, and 13C NMR spectroscopic studies to determine mangiferin pKa values

The acid constants of mangiferin (a natural xanthonoid) in aqueous solution were determined through an UV/vis spectroscopic study employing the SQUAD program as a computational tool. A NMR study complements the pK(a) values assignment and evidences a H-bridge presence on 1-C. The chemical model used was consistent with the experimental data obtained. The pK(a) values determined with this procedure were as follows: H(4)(MGF)=H(3)(MGF)(-)+H(+), pKa1 (6-H)=6.52+/-0.06; H(3)(MGF)(-)=H(2)(MGF)(2-)+H(+), pKa2 (3-H)=7.97+/-0.06; H(2)(MGF)(2-)=H(MGF)(3-)+H(+), pKa3 (7-H)=9.44+/-0.04; H(MGF)(3-)=(MGF)(4-)+H(+), pKa4 (1-H)=12.10+/-0.01; where it has been considered mangiferin C(19)H(18)O(11) as H(4)(MGF). Mangiferin UV/vis spectral behavior, stability study in aqueous solution as well as NMR spectroscopy studies: one-dimensional (1)H,(13)C, 2D correlated (1)H/(13)C performed by (g)-HSQC and (g)-HMBC methods; are also presented. pK(a) values determination of H(4)(MGF) in aqueous solution is a necessary contribution to subsequent pharmacokinetic study, and a step towards the understanding of its biological effects.     

Synthesis and conformational analysis of N-aryl-N-(6-azulenyl)acetamides

We synthesized a series of N-(6-azulenyl)-N-arylacetamides, and investigated their conformational preferences in solution and in the crystalline state by means of NMR and X-ray analyses. The results indicated that the conformational preferences of these amides are dependent on both the relative π-electron densities of the N-aromatic parts and the three-dimensional relationship of the carbonyl group to the aryl groups. The N-(6-azulenyl) group has a very different effect from the previously reported N-(2-azulenyl) group on the conformational preferences of aromatic amides.     

Determination of the intrinsic site pK(a) value and cooperativity of the symmetrical hexadentate chelator N,N',N'-tris[2-(3-hydroxy-2-oxo-1,2-dihydropyridin-1-yl)acetamido]ethylamine

The three overlapping pK(a) values of N,N',N'-tris[2-(3-hydroxy-2-oxo-1,2-dihydropyridin-1-yl)acetamido]ethylamine, a tripodal hexadentate chelator formed from three 3-hydroxy-2(1H)-pyridinone moieties amide linked to tris-(2-aminoethyl)amine, were determined by simultaneous spectrophotometric and potentiometric titration. The data was analysed by non-linear regression with constraints to deal with (a) the highly correlated absorptivities and (b) the highly correlated pK(a) values. The three pK(a) values were optimized first from the spectrophotometric data (absorbance vs. pH) by non-linear regression to a model in which the molar absorptivity of the ith species ((i)) was constrained by the correlation equation (i) = epsilon (0) + (epsilon (3) - epsilon (0))i 3 with i = 0, 1, 2, 3, where (3) and (0) represent the molar absorptivities of the most protonated and least protonated species, respectively. The molar absorbitivity of the four species defined by three pK(a) values is, therefore, linearly related to proton stoichiometry. The pK(a) values were then optimized from the potentiometric data (pH vs. titrant volume) by non-linear regression to a model in which the three pK(a) values were constrained by the correlation equation pK(a(i)) = pK(a(int)) + b(i - 1) + (i - 2)log(3) where i = 1, 2 or 3. This expresses the three pK(a) values in terms of only two optimizable parameters, the intrinsic site pK(a) (pK(a(int))) and the interaction energy between sites (b). The fixed term (i - 2)log(3) accounts for the statistical effect on the pK(a) values of three equivalent ionizable sites. The modified analytical derivatives required for optimization of these parameters by the Gauss-Newton-Marquardt algorithm and the merits of optimizing pK(a) values with these two correlation equations are discussed. The optimized pK(a) values were 9.31 +/- 0.01, 8.75 +/- 0.01 and 8.19 +/- 0.01. The separation between pK(a) values is 0.58 comprising 0.477 for the statistical effect and 0.081 for the interaction energy while the intrinsic site pK(a) is 8.672 +/- 0.005. The tertiary amine at the centre of the tripodal backbone has a pK(a) of 5.88 +/- 0.03.     

Synthesis, properties, and redox behavior of mono-, bis-, and tris[1,1,4,4,-tetracyano-2-(1-azulenyl)-3-butadienyl] chromophores binding with benzene and thiophene cores

Mono-, bis-, tris-, and tetrakis(1-azulenylethynyl)benzene and mono- and bis(1-azulenylethynyl)thiophene derivatives 5-10 have been prepared by Pd-catalyzed alkynylation of ethynyl arenes with 1-iodoazulene derivative or the 1-ethynylazulene derivative with tetraiodobenzene and iodothiophenes under Sonogashira-Hagihara conditions. Compounds 5-10 reacted with tetracyanoethylene in a [2+2] cycloaddition reaction to afford the corresponding 1,1,4,4,-tetracyano-2-(5-isopropyl-3-methoxycarbonyl-1-azulenyl)-3-butadienyl chromophores 12-16 in excellent yields, except for the reaction of the tetrakis(1-azulenylethynyl)benzene derivative. 1,1,4,4,-Tetracyano-2,3-bis(1-azulenyl)butadiene (17) was also prepared by the similar reaction of bis(1-azulenyl)acetylene (11) with tetracyanoethylene (TCNE). The redox behavior of novel azulene derivatives 12-17 was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed multistep electrochemical reduction properties. Moreover, a significant color change was observed by visible spectroscopy under electrochemical reduction conditions.     

Regioselective intramolecular ring closure of 2-amino-6-bromo-2,6-dideoxyhexono-1,4-lactones to 5- or 6-membered iminuronic acid analogues: synthesis of 1-deoxymannojirimycin and 2,5-dideoxy-2,5-imino-D-glucitol

1-Deoxymannojirimycin (8c) was synthesised from 2-amino-6-bromo-2,6-dideoxy-D-mannono-1,4-lactone (7) by intramolecular direct displacement of the C-6 bromine employing non-aqueous base treatment followed by reduction of the intermediate methyl ester. Likewise, using aqueous base at pH 12, ring closure took place by 5-exo attack on the 5,6-epoxide leading to 2,5-dideoxy-2,5-imino-L-gulonic acid (9b), which was reduced to 2,5-dideoxy-2,5-imino-D-glucitol (9b). The method was further applied to 2-amino-6-bromo-2,6-dideoxy-D-galacto- as well as D-talo-1,4-lactones (14 and 15). However, only the corresponding six-membered ring 1,5-iminuronic acid mimetics, namely (2R,3R,4S,5R)-3,4,5-trihydroxypipecolic acid (2,6-dideoxy-2,6-imino-D-galactonic acid, 16) and (2S,3R,4S,5R)-3,4,5-trihydroxypipecolic acid (2,6-dideoxy-2,6-imino-D-talonic acid, 17), were obtained. The corresponding enantiomers, L-galacto- as well as L-talo-2-amino-6-bromo-2,6-dideoxy-1,4-lactones ent-14 and ent-15, reacted accordingly to give the D-galacto- and L-altro-1,5-iminuronic acid mimetics, (2S,3S,4R,5S)-3,4,5-trihydroxypipecolic acid (2,6-dideoxy-2,6-imino-L-galactonic acid, ent-16) and (2R,3S,4R,5S)-3,4,5-trihydroxypipecolic acids (2,6-dideoxy-2,6-imino-L-talonic acid, ent-17), respectively.     

Theoretical notions of aromaticity and antiaromaticity: phenalenyl ions versus fluorenyl ions

The dications 6, 7, and 8 and dianions 9, 10, and 11 of the bistricyclic aromatic enes bifluorenylidene (1), 1,1'-biphenalenylidene (2), and 9-(9H-fluoren-9-ylidene)-1H-phenalene (4), as well as monocations 12a and 13a and monoanions 14a and 15a of phenalene (3) and fluorene (5), were subjected to a systematic DFT and ab initio study. B3LYP and MP2 methods were employed to estimate the relative aromaticity/antiaromaticity of these ions, using energetic, magnetic, and structural criteria. The couplings of monoions 12a-15a to give the respective diions 6-11 result in a similar destabilization in both the fluorene and phenalene series. The interactions between the C13H8 units in diions 6-11 are weak and are not expected to result in a significant loss of aromaticity/gain of antiaromaticity, as compared with the respective monoions. The antiaromaticity of bifluorenylidene dication (6), relative to that of two fluorenyl cations (12a), is only slightly enhanced as compared with the aromaticity of biphenalenylidene dication ((E)-7)) relative to that of two phenalenyl cations (13a). In particular, the homodesmotic reaction 6 + 2.13a = (E)-7 + 2.12a is only slightly exothermic, DeltaE(Tot) = -6.0 kJ/mol. The energetic effect of the analogous reaction involving anions 9 + 2.15a = (E)-10 + 2.14a is even smaller, DeltaE(Tot) = -3.4 kJ/mol. Bifluorenylidene dianion (9) and 1,1'-biphenalenylidene dianion ((E)-10) are aromatic, but the employed criteria disagree about their relative aromaticity. The electronic and structural properties of heteromerous dication 8 and dianion 11 lie between those of the homomerous diions. Thus, dications 6-8 and dianions 9-11 form a continuum of aromaticity/antiaromaticity.     

Purification of xylenol orange by preparative paper chromatography, and examination of its zirconium complex

Preparative paper chromatography is proposed as a suitable method for purification of Xylenol Orange (XO). The last three dissociation constants of pure XO have been determined with the aid of the program SPEKTFOT, the values found being pK(9) = 12.34; pK(8) = 10.66; pK(7) = 6.69 (0.1M KNO(3), 20 +/- 0.5 degrees ). The complexation of zirconium with the purified reagent has been studied and the co-existence of ML and M(2) L complexes proved by use of the program DALSFEK. The following conditional stability constants of the complexes and their molar absorptivities were computed: log beta'(ml) 4.58; log beta'(M(2)L) 11.59; (ML) 2.00 x 10(4); (M(2)L) 9.40x 10(4) l.mole(-1).cm(-1) at 550 nm.     

Protonated benzofuran,anthracene, naphthalene,benzene, ethene,and ethyne: measurements and estimates of pK(a) and pK(R)

Aqueous solvolyses of acyl derivatives of hydrates (water adducts) of anthracene and benzofuran yield carbocations which undergo competitive deprotonation to form the aromatic molecules and nucleophilic reaction with water to give the aromatic hydrates. Trapping experiments with azide ions yield rate constants k(p) for the deprotonation and k(H2O) for the nucleophilic reaction based on the "azide clock". Combining these with rate constants for (a) the H(+)-catalyzed reaction of the hydrate to form the carbocation and (b) hydrogen isotope exchange of the aromatic molecule (from the literature) yields pK(R) = -6.0 and -9.4 and pK(a) = -13.5 and -16.3 for the protonated anthracene and protonated benzofuran, respectively. These pK values may be compared with pK(R) = -6.7 for naphthalene hydrate (1-hydroxy-1,2-dihydronaphthalene), extrapolated to water from measurements by Pirinccioglu and Thibblin for acetonitrile-water mixtures, and pK(a) = -20.4 for the 2-protonated naphthalene from combining k(p) with an exchange rate constant. The differences between pK(R) and pK(a) correspond to pK(H2O), the equilibrium constant for hydration of the aromatic molecule (pK(H2O) = pK(R) - pK(a)). For naphthalene and anthracene values of pK(H2O) = +13.7 and +7.5 compare with independent estimates of +14.2 and +7.4. For benzene, pK(a) = -24.3 is derived from an exchange rate constant and an assigned value for the reverse rate constant close to the limit for solvent relaxation. Combining this pK(a) with calculated values of pK(H2O) gives pK(R) = -2.4 and -2.1 for protonated benzenes forming 1,2- and 1,4-hydrates, respectively. Coincidentally, the rate constant for protonation of benzene is similar to those for protonation of ethylene and acetylene (Lucchini, V.; Modena, G. J. Am. Chem Soc. 1990, 112, 6291). Values of pK(a) for the ethyl and vinyl cations (-24.8) may thus be derived in the same way as that for the benzenonium ion. Combining these with appropriate values of pK(H2O) then yields pK(R) = -39.8 and -29.6 for the vinyl and ethyl cations, respectively.     

Amplified potentiometric determination of pK(00), pK(0), pK(l), and pK(2) of hydrogen sulfides with Ag(2)S ISE

The chemical capacitor theory has been applied to accurately determine dissociation constants of H(2)S with the Ag(2)S ion-selective electrode (ISE). The theory's principle is based on the measurement of the change in electrode charge density as a result of protonated or unprotonated sulfide adsorbed on the electrode surface. This charge density is related to the potential. Connection of each individual capacitor in series amplifies the potential according to the equation, E(total)=E(1)+E(2)+E(3)+cdots, three dots, centeredE(n). As the charges of individual capacitors are concentrated to one capacitor area, the charge density rises, and the potential increases. The pK(00), pK(0), pK(1), and pK(2) are reported as 1.8, 2.12, 7.05, and 12.0, respectively. The pK(00) and pK(0) are reported here for the first time. The pK(1) agrees well with the literature values; however, the pK(2) differs from those reported recently under extreme conditions. Reasons for disproving the unreasonably high pK(2)>17-19 values are given based on calculations. Mainly, when pK(2)>17-19, the experimental results do not fit the equilibrium equations, pH=(pK(1)+pK(2))/2, pK(1)=(pK(0)+pK(2))/2, and pH=pK(2)+log(HS(-))/(S(2-)).     

Asymmetric Synthesis and DNA Intercalation of (-)-6-[[(Aminoalkyl)oxy]methyl]-4-demethoxy-6,7- dideoxydaunomycinones(1)(,)

The BF(3).Et(2)O-promoted Diels-Alder addition of 1-acetylvinyl RADO(Et)-ate (RADO(Et)-ate = 3-ethyl-2-oxo-6,8-dioxa-3-azabicyclo[3.2.1]octane-7-exo-carboxylate) to 1-(dimethoxymethyl)-2,3,5,6-tetramethylidene-7-oxabicyclo[2.2.1]heptane led to one major monoadduct that added to 1,2-didehydrobenzene and was converted into (-)-4-demethoxy-7-deoxydaunomycinone and (2R)-12-acetoxy-2-acetyl-5-(bromomethyl)-1,2,3,4-tetrahydronaphthacen-2-yl RADO(Et)-ate. The latter compound was used to construct (8R)-8-acetyl-6,8-dihydroxy-11-[[(3'-[(aminopropyl)oxy]-, -4'-[(aminobutyl)oxy], and -5'-[(aminopentyl)oxy]methyl]-7,8,9,10-tetrahydronaphthacene-5,12-dione hydrochloride (-)-8, (-)-9, (-)-10, respectively, as well as (8R)-8-acetyl-6,8-dihydroxy-11- [[[2'-[(3"-aminopropyl)amino]ethyl]oxy]- ((-)-11) and -[[3'-[(3"-aminopropyl)amino]propyl]oxy]methyl]-7,8,9, 10-tetrahydronaphthacene-5,12-dione hydrochloride ((-)-12). (8R)-8-Acetyl-6,8-dihydroxy-11-[[(alpha-L-daunosaminyl)oxy]methyl]-7,8,9,10-tetrahydronaphthacene-5,12-dione hydrochloride ((-)-13), a mimic of idarubicin, was also prepared. Absorbance and fluorescence titration experiments showed (-)-8, (-)-9, and (-)-10 to intercalate calf thymus DNA whereas (-)-11, (-)-12, and (-)-13 did not. The best intercalator was (-)-9 (K(b) = (1.1 +/- 0.1) x 10(5) M(-)(1)) with the [(4'-aminobutyl)oxy]methyl chain. Inhibition of topoisomerase II-induced DNA strand religation was observed for (-)-8 at a concentration of 50 &mgr;M.