Binding of carboxylic acids by fluorescent pyridyl ureas

Fluorescent pyrid-2-yl ureas were prepared by treating halogenated 2-aminopyridines with hexyl isocyanate, followed by Sonogashira coupling with arylacetylenes. The sensors emit light of ～360 nm with quantum yields of 0.05-0.1 in acetonitrile solution. Addition of strong organic acids (pK(a) < 13 in CH(3)CN) shifts the fluorescence band to lower energy, and clean isoemissive behavior is observed. Fluorescence response curves (i.e., F/F(0) vs [acid](total)) are hyperbolic in shape for CCl(3)COOH and CF(3)COOH, with association constants on the order of 10(3) M(-1) for both acids. (1)H NMR titrations and DFT analyses indicate that trihaloacetic acids bind in ionized form to the receptors. Pyridine protonation disrupts an intramolecular H-bond, thereby unfolding an array of ureido NH donors for recognition of the corresponding carboxylates. Methanesulfonic acid protonates the sensors, but no evidence for conjugate base binding at the urea moiety is found by NMR. An isosteric control compound that lacks an integrated pyridine does not undergo significant fluorescence changes upon acidification.     

Acid- and base-catalysis in the mononuclear rearrangement of some (Z)-arylhydrazones of 5-amino-3-benzoyl-1,2,4-oxadiazole in toluene: effect of substituents on the course of reaction

The reaction rates for the rearrangement of eleven (Z)-arylhydrazones of 5-amino-3-benzoyl-1,2,4-oxadiazole 3a-k into the relevant (2-aryl-5-phenyl-2H-1,2,3-triazol-4-yl)ureas 4a-k in the presence of trichloroacetic acid or of piperidine have been determined in toluene at 313.1 K. The results have been related to the effect of the aryl substituent by using Hammett and/or Ingold-Yukawa-Tsuno correlations and have been compared with those previously collected in a protic polar solvent (dioxane/water) as well as with those on the analogous rearrangement of the corresponding (Z)-arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole 1a-k in benzene. Some light can thus be shed on the general differences of chemical reactivity between protic polar (or dipolar aprotic) and apolar solvents.     

Cyclodextrin complexation of a stilbene and the self-assembly of a simple molecular device

(E)-4-tert-Butyl-4'-oxystilbene, 1(-), is thermally stable as the (E)-1(-) isomer but may be photoisomerized to the (Z)-1(-) isomer as shown by UV-vis and (1)H NMR studies in aqueous solution. When (E)-1(-) is complexed by alphaCD two inclusion isomers (includomers) form in which alphaCD assumes either of the two possible orientations about the axis of (E)-1(-) in alphaCD.(E)-1(-) for which (1)H NMR studies yield the parameters: k(1)(298 K)= 12.3 +/- 0.6 s(-1), DeltaH(1)(++)= 94.3 +/- 4.7 kJ mol(-1), DeltaS1(++)= 92.0 +/- 5.0 J K(-1) mol(-1), and k(2)(298 K)= 10.7 +/- 0.5 s(-1), DeltaH(2)(++)= 93.1 +/- 4.7 kJ mol(-1), DeltaS2(++)= 87.3 +/- 5.0 J K(-1) mol(-1) for the minor and major includomers, respectively. The betaCD.(E)-1(-) complex either forms a single includomer or its includomers interchange at the fast exchange limit of the (1)H NMR timescale. Complexation of 1(-) by N-(6(A)-deoxy- alpha-cyclodextrin-6(A)-yl)-N'-(6(A)-deoxy- beta-cyclodextrin-6(A)-yl)urea, results in the binary complexes 2.(E)-1(-) in which both CD component annuli are occupied by (E)-1(-) and which exists exclusively in darkness and 2.(Z)-1(-) in which only one CD component is occupied by (Z)-1(-) and exists exclusively in daylight at lambda > or = 300 nm. Irradiation of solutions of the binary complexes at 300 and 355 nm results in photostationary states dominated by 2.(E)-1(-) and 2.(Z)-1(-), respectively. In the presence of 4-methylbenzoate, 4(-), 2.(Z)-1(-) forms the ternary complex 2.(Z)-1(-).4(-) where 4(-) occupies the second CD annulus. Interconversion occurs between 2.(Z)-1(-).4(-) and 2.(E)-1(-)+4(-) under the same conditions as for the binary complexes alone. Similar interactions occur in the presence of 4-methylphenolate and 4-methylphenylsulfonate. The two isomers of each of these systems represent different states of a molecular device, as do the analogous binary complexes of N,N-bis(6(A)-deoxy- beta-cyclodextrin-6(A)-yl)urea, 3, [3.(E)-1(-) and 3.(Z)-1(-), where the latter also forms a ternary complex with 4(-).     

Solubility of Tetra(pyrid-3- and 4-yl)porphines and Their Complexes with <Emphasis Type="Italic">d</Emphasis>-Metals in Chloroform and Ethanol

The solubility of 5,10,15,20-tetra(pyrid-3- and 4-yl)porphine isomers and their coordination compounds with d-metals in the temperature range of 298–318 K is studied. Patterns of the dissolving of porphyrin ligands and the metal complexes they form with Co(II), Cu(II), and Zn(II) in chloroform and ethanol depending on the nature of the metal and the position of the nitrogen atom in the pyridyl substituent of the porphyrin molecule are discussed. The thermodynamic parameters of dissolution are calculated for the investigated compounds.     

Extraordinary behavior of 5-(3,4-dihydroxyphenyl)-10,15,20-tris(N-methylpyridinium-3-yl)porphyrin triiodide in titration with bases and in albumin oxidation

The observed rate constants of the photoinduced oxidation of albumin increased by a factor of 1.5–2 upon deprotonation of the peripheral hydroxyl groups of 5-(3,4-dihydroxyphenyl)-10,15,20-tris(N-methylpyridinium-3-yl)porphyrin triiodide compared to its phenolic form.     

The equilibrium constants of cadmium(II)-, lead(II)-, magnesium(II)-, and zinc(II)-alpha,beta,gamma,delta-tetrakis(1-methylpyridinium-4-yl)porphine complexes

The equilibrium constants of alpha,beta,gamma,delta-tetrakis(1-methylpyridinium-4-yl)porphine (TMPyP) complexes of cadmium(II), lead(II), magnesium(II), and zinc(II) were spectrophotometrically determined using the absorption spectra at the Soret band and the fluorescence spectra. The values of the following constants at 25 degrees C and ionic strength 0.1M were evaluated: K(PbP) = 10(-8.07 +/- 0.09), K(CdP) = 10(-7.68 +/- 0.03), K(ZnP) = 10(1.72 +/- 0.08), and K(MgP) = 10(-7.40 +/- 0.08) by the acid hydrolysis reaction of the TMPyP-metal complex at various pHs; K(PbP) = 10(-7.80 +/- 0.04) and K(CdP) = 10(-7.38 +/- 0.04) were determined by the ligand exchange reaction between TMPyP and nitrilotriacetic acid.     

Synthesis and in vitro anti-human cytomegalovirus (hcmv) activity of certain alkenyl substituted cytosines and 5-halocytosines

The 1-[(Z)-2-penten-1-yl] and 1-(3-methyl-2-buten-1-yl) derivatives of cytosine, 5-bromocytosine, 5-fluorocytosine, and 5-iodocytosine were prepared by a reaction of the sodium salt of the requisite cytosine with (Z)-1-bromo-2-pentene and 4-bromo-2-methyl-2-butene, respectively. The eight alkenylcytosines 5a-5h were evaluated in cell culture for their anti-HCMV activity. Only the derivatives of 5-bromocytosine, 5c and 5d , showed slight activity in this assay.     

Cyclization reactions of nitriles. 50. Regioselectivity in the reactions of quaternized pyridin-3-ylidene malonitrile and cyanoacetate ester derivatives with 1,3-dicarbonyl compounds. Crystal structure of 2-amino-3,5-dicarboethoxy-6-methyl-4-(1-methylpyridinium-3-yl)-4H-pyran iodide

The reaction of quaternized pyridin-3-ylidene malonitrile and cyanoacetate ester derivatives with 1,3-dicarbonyl compounds proceeds highly regioselectively to give substituted 2-amino-4-(1-methylpyridinium-3-yl)-4H-pyran iodides. The structure of 2-amino-3,5-dicarboethoxy-6-methyl-4-(1-methylpyridinium-3-yl)-4H-pyran iodide has been investigated by x-ray structural analysis.See [1] for communication No. 49.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 205–211, February, 1991.     

Photoresponsive change of oxygen-binding affinity of a cobalt schiff-base complex with an axially coordinating stilbazole residue of a copolymer

The reversible binding reaction of oxygen to N,N'-ethylene bis(salicylideneiminato) cobalt(II) (CoS), to which a photoisomerizable stilbazole residue of copolymer 1 coordinated, was investigated. The E form of the stilbazole residues coordinating to CoS, (E)-1-CoS, showed photoisomerization into the Z form, (Z)-1-CoS, on direct ultraviolet irradiation and negligible reverse isomerization. The oxygen-binding equilibrium constant (K) values for (E)-1-CoS and (Z)-1-CoS in toluene were 3.3 x 10(-2) mmHg-1 and 4.8 x 10(-3) mmHg(-1), respectively, at 10 degrees C. Although the pK(a) values of the E and Z forms of the stilbazole residue were similar, the oxygen-binding affinity of (Z)-1-CoS was small in terms of the linear correlation of the logarithm of K (ln K) versus the pK(a). Steric hindrance of the polymer chain of 1 on the coordination of the stilbazole residue of (Z)-1 to CoS was thought to cause the small K. A photoresponsive change of apparent oxygen-binding affinity of 1-CoS along with the E/Z isomerization of the stilbazole residues was observed. The ratio of (Z)-1-CoS converted from (E)-1-CoS by the ultraviolet irradiation could be estimated from analysis of absorption spectra for the oxygen binding of a resulting mixture of (E)-1-CoS and (Z)-1-CoS.     

N-(6-色酮-3-基-亚甲氨基)-S-{[4-芳基-5-(吡啶-4-基)]-1,2,4-三唑-2-基}巯乙酰胺类化合物的合成

N-芳基-2-[(吡啶-4-基)羰基]氨基硫脲1a～1e用NaOH溶液环合, 得到3-巯基-4-芳基-5-(吡啶-4-基)-1,2,4-三唑(2a～2e), 经酯化, 肼解, 得S-{[4-芳基-5-(吡啶-4-基)]-1,2,4-三唑-3-基}巯乙酰肼(3a～3e), 再与3-甲酰基色酮(4a～4d)反应, 合成得到了一系列新化合物5a～5e, 6a～6e, 7a～7e, 8a～8e. 化合物的结构经元素分析, IR, ¹H NMR和MS谱确证.     

Supramolecular assemblies between macrocyclic porphyrin hexamers and star-shaped porphyrin arrays.

The syntheses of eight new star-shaped D(3)-symmetric arrays in which three 15-(pyrid-4-yl)porphyrin subunits are attached to the 1, 3, and 5 positions of a benzene core through linkers consisting of collinear repetitive phenylethynyl units have been carried out using Pd(0)-catalyzed coupling reactions. By the same procedure, an analogous 10-(4-pyridin-yl)porphyrin hexamer in which all positions of the benzene core are substituted has been obtained. Likewise, the preparation of suitably sized cyclic porphyrin hexamers, in which all six or at least three alternate porphyrin rings are complexed with Zn(II) ions, is described in detail. In solution, such cyclic porphyrin hexamers form supramolecular assemblies with the star-shaped polyporphyrins in which the latter are held in the interior of the macrocycle through coordination of the apical pyridine rings with the Zn(II) ions. The suggested structures are supported by (1)H NMR spectroscopic and MALDI-TOF mass spectrometric measurements. They agree with the high values of the binding constants of the corresponding supramolecules, which range between K = 1.1 x 10(10) and 1.4 x10(9) M(-1).     

Application of 2-pyridyl-substituted hemithioindigo as a molecular switch in hydrogen-bonded porphyrins

When the photochromism of 2-(3'-pyridylmethylene)-7-ethylbenzo[b]thiophen-3(2H)-ones (4) was investigated, high thermal stability of the E isomer of 4, 4(E) and good repeatability of the photoinduced E,Z-isomerization were found. Association constants of the 1:1 complexations of 4(Z) and 4(E) with the ureidoporphyrin 1 and with the pentafluorobenzamidoporphyrin 2 were evaluated. We found that 1 captures 4(E) preferentially to 4(Z) and, reversely, 2 prefers 4(Z) to 4(E). On the basis of these differences in the binding ability, we concluded that the repeatable movement of the hemithioindigo, so-called the hemithioindigo shuttle, between two kinds of porphyrins was controlled by the photoirradiation. These movements were applied to create a molecular switch for changes in the quinone distribution between two kinds of porphyrins.     

Kinetic results implicating a polar radical reaction pathway in the rearrangement catalyzed by alpha-methyleneglutarate mutase

alpha-Methyleneglutarate mutase (MGM) catalyzes the rearrangement of 2-methyleneglutarate to 3-methylitaconate (2-methylene-3-methylsuccinate). A putative mechanism for the MGM-catalyzed reaction involves 3-exo cyclization of the 2-methyleneglutaric acid-4-yl radical to a cyclopropylcarbinyl radical intermediate that ring opens to the 3-hydroxycarbonyl-2-methylenebutanoic acid-4-yl radical (3-methylitaconic acid radical). Model reactions for this mechanism were studied by laser flash photolysis kinetic methods. alpha-Ester radicals were produced by 266 nm photolysis of alpha-phenylselenyl ester derivatives. Rate constants for cyclizations of the (Z)-1-ethoxycarbonyl-4-(2,2-diphenylcyclopropyl)-3-buten-1-yl radical ((Z)-8a) and (E)- and (Z)-1,3-di(ethoxycarbonyl)-4-(2,2-diphenylcyclopropyl)-3-buten-1-yl radicals ((E)- and (Z)-8b) were determined. The ester group in (Z)-8a accelerates the 3-exo cyclization in comparison to the parent radical lacking an ester group by a factor of 3, an effect ascribed to a polarized transition state. The ester groups at C3 in radicals 8b slow the 3-exo cyclization reaction by a factor of 50. The rate constant for cyclization of the 2-methyleneglutaric acid-4-yl radical is estimated to be k approximately 2000 s(-1) at ambient temperature. When coupled with the estimated partitioning of the intermediate cyclopropylcarbinyl radical, the overall rate constant for the conversion is estimated to be k approximately equal to 1 x 10(-3) s(-1), which is much too small for any radical reaction and several orders of magnitude too small for kinetic competence for the MGM-catalyzed process. The possibility that the radical reaction in nature involves an unusual mechanism in which polar effects are important is discussed.     

Strategies for electrooptic film fabrication. Influence of pyrrole-pyridine-based dibranched chromophore architecture on covalent self-assembly, thin-film microstructure, and nonlinear optical response

The new dibranched, heterocyclic "push-pull" chromophores bis{1-(pyridin-4-yl)-2-[2-(N-methylpyrrol-5-yl)]ethane}methane (1), 1-(pyrid-4-yl)-2-(N-methyl-5-formylpyrrol-2-yl)ethylene (2), {1-(N-methylpyridinium-4-yl)-2-[2-(N-methylpyrrol-5-yl)]ethane}{(1-(pyridin-4-yl)-2-[2-(N-methylpyrrol-5-yl)]ethane}methane (3), N-methyl-2-[1-(N-methylpyrid-4-yl)ethen-2-yl]-5-[pyrid-4-yl]ethen-2-yl]pyrrole iodide (4), bis{1-(N-methyl-4-pyridinio)-2-[2-(N-methylpyrrol-5-yl)]ethane}methane iodide (5), and N-methyl-2,5-[1-(N-methylpyrid-4-yl)ethen-2-yl]pyrrole iodide (6) have been synthesized and characterized. The neutral (1 and 2) and monomethyl salts (3 and 4) undergo chemisorptive reaction with iodobenzyl-functionalized surfaces to afford chromophore monolayers SA-1/SA-2 and SA-3/SA-4, respectively. Molecular structures and other physicochemical properties have been defined by (1)H NMR, optical spectroscopy, and XRD. Thin-film characterization by a variety of techniques (optical spectroscopy, specular X-ray reflectivity, atomic force microscopy, X-ray photoelectron spectroscopy, and angle-dependent polarized second harmonic generation) underscore the importance of the chromophore molecular architecture as well as film growth method on film microstructure and optical/electrooptic response.     

Isomerization of DNA-bound distilbazolium ligand induced by electron transfer from photoexcited tris(1,10-phenanthroline)Ru(II)

The ability of the DNA duplex to behave as an efficient organized medium for cis-trans isomerization induced by electron transfer (ET) has been explored. Isomerization studies, luminescence quenching and DNA photocleavage assays show that photoexcited Ru(1,10-phenanthroline [phen])3(2+) transfers an electron to E,Z1,4-bis[2-(1-methylpyridinium-4-yl)vinyl]benzene (E,Z pMPVB), which subsequently undergoes one-way isomerization to E,E pMPVB. The unusual feature of the system is manifested by the lack of friction that is usually imposed on the photoisomerizable ligand by highly organized media. The apparent rate of ET in DNA increases when compared with the homogeneous solution. However, after correction for the local concentration of the reagents onto the biopolymer, the rate constant becomes independent of the DNA concentration and is at least 4 x 10(2) times smaller than that in the homogeneous aqueous solution. Using the photoinduced isomerization system, a large enhancement in the efficiency of single-strand break formation was found in plasmid DNA over that for Ru(phen)3(+2) alone using irradiation at lambda > 480 nm.     

Synthesis, Crystal Structure and Bioactivities of 1-（4-Chlorophenyl）-3- [ 5-（pyrid-4-yl）- 1,3,4-thiadiazol-2-yl] urea

The title compound 1-(4-chlorophenyl)-3-[5-(pyrid-4-yl)-1,3,4-thiadiazol-2-yl]urea (C14H10ClN5OS, Mr = 331.79) has been synthesized by the reaction of 2-amino-5-(pyrid-4-yl)- 1,3,4-thiadiazole with 4-chlorobenzoyl azide, and its crystal structure was determined by single-crystal X-ray diffraction. The crystal belongs to triclinic system, space group P with a = 5.8550(8), b = 7.5668(10), c = 16.416(2) , α = 78.364(2), β = 81.204(2), γ = 84.749(2)°, V = 702.58(16) 3, Z = 2, Dc = 1.568 g/cm3, μ = 0.429 mm-1, F(000) = 340, the final R = 0.0442 and wR = 0.1092 for 2001 observed reflections (I > 2σ(I)). X-ray diffraction analysis reveals that the title molecule is nearly planar. In the crystal structure, the molecules are linked by strong intermolecular N-H…N hydrogen bonds together with weak nonclassical intermolecular (C-H…Y, Y = N, O and Cl) hydrogen bonds and stacked through π-π interactions. The preliminary bioassay shows that the title compound exhibits good fungicidal activities against Rhizoctonia solani, Botrytis cinerea and Dothiorella gregaria.     

Enantiodifferentiating photoisomerization of cyclooctene included and sensitized by aroyl-beta-cyclodextrins: a critical enantioselectivity control by substituents

A series of 6-O-benzoyl-beta-cyclodextrins (CDs) with methyl, methoxy, methoxycarbonyl, and bromo substituent(s) at the ortho-, meta-, and/or para-position(s) were synthesized as chiral sensitizing hosts for the use in supramolecular enantiodifferentiating photoisomerization of (Z)-cyclooctene (1Z) to its chiral (E)-isomer (1E). The complex stability constants (K(S)) of the modified beta-CDs with 1Z in aqueous methanol solutions were highly sensitive to the substituent(s) introduced to the benzoate moiety, and the log K(S) values decreased linearly with slightly different slopes with increasing methanol content. The enantiomeric excess (ee) of 1E obtained upon photosensitization with these hosts was a critical function of the size and position of the substituent, varying from almost zero to 46% ee. This indicates that even an apparently small structural difference between methyl and methoxy can critically affect the enantiodifferentiating photoisomerization of a guest included in the chiral cavity, probably through manipulation of both the orientation of ground-state 1Z and the subsequent rotational relaxation of excited 1Z inside the chiral cavity.     

Enols and thioenols of substituted cyanomonothiocarbonylmalonamides: structures, enolization vs. thioenolization, equilibria and conformations

Condensation of organic isothiocyanates with cyanoacetamides gave 24 N- and N'-substituted cyanomonothiocarbonylmalonamides in different tautomeric ratios i.e., amide-thioamides (TMA)R3NHCSCH(CN)CONR1R2 (12), thioamide-enols of amides (E) R3NHCSC(CN)=C(OH)NR1R2 (11)or amide-thioenols (TE) R3NHC(SH)=C(CN)CONR1R2 (13). The equilibrium constants (K(thioenol) =[TE]/[TMA] and K(enol) = [E]/[TMA]) in solution depend on R1, R2, R3 and the solvent. The %(E + TE)for NR1R2 increases in the order NMe2 < NHMe < NH2. The (K(thioenol) + K(enol)) in various solvents follows the order CCl4 > CDCl3 > C6D6 > THF-d8 > (CD3)2CO > CD3CN > DMF-d7 > DMSO-d6. The delta(OH) values are 16.46-17.43 and the delta(SH) values are 3.87-5.26 ppm in non polar solvents, e.g.,CDCl3 and 6.34-6.97 ppm in THF-d8 and CD3CN. An intramolecular O-H...O hydrogen bond leads to the preferred Z-configuration of the enols, and an N-H...O bond stabilizes the thioenols' preferred E-configuration with a non-bonded SH in solution. X-Ray crystallography revealed that systems with high %(E + TE) in solution mostly display the enols 11 in the solid state and systems with lower %(E +TE) in solution display structure 12. The differences in delta(OH), delta(NH), K(enol) and crystallographic data for analogous enol and thioenol systems are compared.     

First study on the thermo-solvatochromism in aqueous 1-(1-Butyl)-3-methylimidazolium tetrafluoroborate: a comparison between the solvation by an ionic liquid and by aqueous alcohols

The thermo-solvatochromic behaviors of 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1-yl) phenolate, RB; 2,6-dichloro-4-(2,4,6-triphenylpyridinium-1-yl) phenolate, WB; 2,6-dibromo-4-[( E)-2-(1-methylpyridinium-4-yl)ethenyl] phenolate, MePMBr 2; 2,6-dibromo-4-[( E)-2-(1-n-octylpyridinium-4-yl)ethenyl] phenolate, OcPMBr 2, have been investigated in binary mixtures of the ionic liquid, IL, 1-(1-butyl)-3-methylimidazolium tetrafluorborate, [BuMeIm][BF 4], and water (W), in the temperature range from 10 to 60 degrees C. Plots of the empirical solvent polarities, E T (probe) in kcal mol (-1), versus the mole fraction of water in the binary mixture, chi w, showed nonlinear, i.e., nonideal behavior. Solvation by these IL-W mixtures shows the following similarities to that by aqueous aliphatic alcohols: The same solvation model can be conveniently employed to treat the data obtained; it is based on the presence in the system-bulk medium and probe solvation shell of IL, W, and the "complex" solvent 1:1 IL-W. The origin of the nonideal solvation behavior appears to be the same, preferential solvation of the probe, in particular by the complex solvent. The strength of association of the IL-W complex, and the polarity of the IL are situated between the corresponding values of aqueous methanol and aqueous ethanol. Temperature increase causes a gradual desolvation of all probes employed. A difference between solvation by IL-W and aqueous alcohols is that probe-solvent hydrophobic interactions appear to play a minor role in case of the former mixture, probably because solvation is dominated by hydrogen-bonding and Coulombic interactions between the ions of the IL and the zwitterionic probes.     

Synthesis and some transformations of 5-benzotriazolyl-3,4-dihydropyrid-2-ones

5-(Benzotriazolyl)-substituted 3,4-dihydropyrid-2-ones were obtained by condensation of 4-benzo-triazolyl-5-phenyl(methyl)-5-oxopentanoic acids with benzyl or aryl amines. Dehydrogenation of 3,4-dihydropyrid-2-ones resulted in 5-benzotriazolyl-substituted pyrid-2-ones and/or 5-(phenylamino)pyrid-2-ones, products of nitrogen elimination from the benzotriazolyl substituent. In turn, 5-benzotriazol-1-yl-substituted pyrid-2-ones eliminated nitrogen under Graebe-Ullmann conditions to give indolopyridones.