Acid-base properties of 1,2,5-oxadiazoles. 2. Aminofurazans

The behavior of 3-R-4-aminofurazans (R = NH₂, CH₃, OCH₃, N₃, COOH, and NO₂) in sulfuric acid solutions was studied by electronic and PMR spectroscopy. The constants of protonation (pK _aBH+) at the amino group and in the ring were calculated from the changes in the spectra. Dependences of the position of the absorption maxima corresponding to ^* transitions and the pK _aBH+ values and with the ^o substituent constants were found.See [1] for Communication 1.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 321–324, March, 1981.     

ESR investigation of Ti3+ compounds supported on inorganic gels

CpTiCl₂-M-surface complexes (M=Al, Si, Mg, Cp=cyclopentadienyl) supported on Al₂O₃, SiO₂, MgO gels are reduced by Et₃Al, C₃H₅MgBr and BuLi to Ti³⁺ surface compounds which exhibit ESR signals. The g and g values and asymmetry of these signals depend on the kind of gel and reducing agent.

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CpTiCl₂-M ( M=Al, Si, Mg Cp=), Al₂O₃, SiO₂ MgO, Et₃Al, C₃H₅MgBr, BuLi (Et=–C₂H₅ Bu=–C₄H₉) Ti⁺³, . g g .

     

Tetrazoles. 10. Acid-base properties of 5,5′-ditetrazolyls

The constants of detachment (pK_a 1.41 and 4.25) and addition (pK_BH –5.47 and –10.91) of protons for 5,5-ditetrazolyl and of protonation of 1,1-diphenyl-5,5-ditetrazolyl (pK_BH+ –7.47) in aqueous solutions were determined by spectrophotometric and potentiometric methods. By comparison of the acid-base properties of the two compounds it was established that the latter exists in the trans form.See [1] for Communication 9.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1563–1566, November, 1981.     

Mesophasic properties of low molecular weight analogues of nematogenic polycarbonates

The mesophasic behaviour of the following compounds has been investigated by DSC, X-ray diffraction and optical microscopy methods: CH₃(CH₂)₄-CO-R-A _n -R-CO-(CH₂)₄-CH₃,n=9 14, 16 CH₃(CH₂)₄-CO-R-B _n -R-CO-(CH₂)₄-CH₃,n=2, 3A _n=-CO-O-(CH₂)_n–4-O-CO-,B _n =-CO-(OCH₂CH₂) _n -O-CO-,R=-O-Ø-C(CH₃)=N-N=(CH₃)C-Ø-O-,Ø=-C₆H₄ They have been assumed to be low molecular weight models of homologous nematogenic polymers.All the examined compounds exhibit nematic mesomorphism. On complete analogy with the corresponding polymers, the thermodynamic data relative to the nematic-isotropic phase transition show a very reduced, if any, odd-even fluctuation. These data are compared with those obtained for very similar compounds, both polymeric and non-polymeric, containing ester linkages between the rigid and flexible groups, to provide evidence of the reliability of the dimeric compounds as models of the polymeric homologues.

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Zusammenfassung Das mesophasische Verhalten der folgenden Verbindungen wurde mittels DSC, Röntgendiffraktion und optischer Mikroskopie untersucht: CH₃(CH₂)₄-CO-R-A _n -R-CO-(CH₂)₄-CH₃;n=914, 16 CH₃(CH₂)₄-CO-R-B _n -R-CO-(CH₂)₄-CH₃;n=2, 3A _n =-CO-O-(CH₂)_n-4-O-CO-;B _n =-CO-(OCH₂CH₂)_n-O-CO-;R=-O-C₆H₄-C(CH₃)=N-N=(CH₃)C-C₆H₄-O-. Die Verbindungen wurden als Modelle homologer nematogener Polymere mit niedrigem Molekulargewicht angesehen. Alle untersuchten Verbindungen zeigen einen nematischen Mesomorphismus. Analog zu den entsprechenden Polymeren zeigen die sich auf den nematisch-isotropen Phasenübergang beziehenden thermodynamischen Daten eine, wenn überhaupt, sehr reduzierte ungerade-gerade Fluktuation. Diese Daten werden mit denen verglichen, die für sehr ähnliche, sowohl polymère als auch nicht-polymere Verbindungen mit Esterbindungen zwischen den starren und flexiblen Gruppen erhalten wurden, um Beweise für die Zuverlässigkeit der auf dimeren Verbindungen aufbauenden Modelle für polymère Homologe zu erhalten.

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, : CH₃(CH₂)₄-CO-R-A _n -R-CO-(CH₂)₄-CH₃ n=914,16 CH₃(CH₂)₄-CO-R-B _n -R-CO-(CH₂)₄-CH₃ n=2, 3A _n =-CO-O-(CH₂) _n–4-O-CO-;B _n =-CO-(OCH₂CN₂) _n -O-COR =-O--C(CH₃)=N-N=(CH₃)C--O- =C₆H₄ , . . — , , , - . , , ,

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The financial assistance of the Ministero Pubblica Istruzione is acknowledged.     

Reactions of e aq' − H and OH with picolinic acid studied by pulse radiolysis

Rate constants for the reaction of the primary species of water radiolysis, viz. e _aq' ^– , H and OH, with picolinic acid have been determined at various pHs. The semi-reduced species exhibits _max at 305 and 350 nm. It is a strong reductant and has two pK_a values of 1 and 5.7. The OH adduct of this compound also exhibits two pK_a s at 2.1 and 5.2. H-atom reaction with picolinic acid gives rise to a mixture of species.     

Research on 6- and 7-substituted 2-and 4-thioquinolones. Transmission of the electronic effects of substituents in the benzene ring of thioquinolones to the reaction center

The electronic effect of substituents on the acid-base properties of 6- and 7-substituted 2-thionolepidines and 4-thionoquinaldines were investigated. It is shown that the pK _a (–H⁺) values for 6- and 7-substituted 2- and 4-thioquinolones and the pK _a (+H⁺) values for 7-substituted 2-thionolepidines and 6-substituted 4-methylmercaptoquinaldines correlate with the _M substituent constants of Jaffe and Taft. The effect of a substituent is transmitted primarily via an inductive mechanism, regardless of its position.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 399–402, March, 1974.     

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XXXII.1 Solvent Effects on Activation Parameters of Heterolysis of 1-Chloro-1-methylcyclopentane. Correlation Analysis of Solvation Effects

Kinetics of heterolysis of 1-chloro-1-methylcyclopentane in MeOH, BuOH, cyclohexane, i-PrOH, t-BuOH, tert-C₅H₁₁OH, -butyrolactone, MeCN, PhCN, PhNO₂, acetone, PhCOMe, cyclohexanone, and 1,2-dichloroethane at 25-50°C were studied by the verdazyl method. Correlation analysis of solvent effects on activation parameters of the reaction in 8 protic (additionally, AcOH and CF₃CH₂OH) and 8 aprotic solvents together and separately in either group of solvents was performed. In all the solvents studied, two H -S compensation effects were revealed.     

Mass spectrometry of 8-hydroxyquinoline derivatives

In contrast to the fragmentation of the corresponding alkyl aryl ethers, characteristic [M-H]⁺ and [M-H, -CO]⁺ fragments were observed in the fragmentation of 5-nitro(halo)-substituted 8-alkoxyquinolines. It was found by means of deuterium labeling that a hydrogen atom is split out primarily from the alkoxy group. It was demonstrated that an [M-H, -CO]⁺ fragment was formed from the [M-H]⁺ ion, which has a three-ring structure and a quaternary nitrogen atom. The formation of an [M-CO]⁺ fragment is characteristic for the fragmentation of 5(7)-nitro(halo)-substituted 8-hydroxyquinolines. The interrelationship between the intensities of the [M-H]⁺, [M-H, -CO]⁺, and [M-CO]⁺ ion peaks and the protonation constants (pK_a) of the investigated compounds is discussed.Communication 4 from the series Mass spectrometry of biologically active substances, See [1] for communication 3.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 786–791, June, 1984.     

Comparison of temperature,pressure and isotope effects on the proton jump between the hydroxide and oxonium ion

The limiting molar conductances ° of potassium deuteroxide KOD in D₂O and potassium hydroxide KOH in H₂O were determined at 5 and 45°C as a function of pressure to clarify the difference in the temperature, pressure and isotope effects on the proton jump between an OD^– (OH^–) and a D₃O⁺ (H₃O⁺) ion. The excess conductances of the OD^– ion in D₂O and the OH^– ion in H₂O, _E ⁰ (OD^-) and _E ⁰ (OH^-), increase with increasing temperature and pressure as in the case of the excess deuteron and proton conductances, _E ⁰ (D⁺) and _E ⁰ (H⁺). However, the temperature effect on the excess conductance is larger for the OD^–(OH^–) ion than for the D₃O⁺ (H₃O⁺) ion but the pressure effect is much smaller for the OD^– (OH^–) ion than for the D₃O⁺ (H₃O⁺) ion. These findings are correlated with larger activation energies and less negative activation volumes found for the OD^– (OH^–) ion than for the D₃O⁺ (H₃O⁺) ion. Concerning the isotope effect, the value of _E ⁰ (OH^-)/ _E ⁰ (OD^-) deviates considerably from at each temperature and pressure in contrast with that of _E ⁰ (H⁺)/ _E ⁰ (D⁺), although both of them decrease with increasing temperature and pressure. These results are discussed mainly in terms of the difference in repulsive force between the OD^– (OH^–) or the D₃O⁺ (H₃O⁺) ion and the adjacent water molecule, the difference in strength of hydrogen bonds in D₂O and H₂O, and their variations with temperature, pressure, and isotope.     

Nitrogen Trichloride Decomposition in the Presence of Molecular Hydrogen: I. Promotion of Nitrogen Trichloride Decomposition by Molecular Hydrogen Additives Near the Lower Self-Ignition Limit

The promotion of the branched-chain decomposition of nitrogen trichloride by molecular hydrogen additives at room temperature and 20 torr manifests itself in a decrease in the induction period and the acceleration of reactant consumption with an increase in the hydrogen concentration in the NCl₃+ H₂+ He mixtures. The emission spectrum of the H₂+ NCl₃flame contains the intense bands of NCl (b ¹⁺– X ^3–, = 1 – 0, = 0 – 1, and = 0 – 0, where is the vibrational quantum number) and the bands of a hydrogen-free compound. The latter bands can be assigned to electronically excited NCl ₂radicals formed in the H + NCl₃reaction. The calculations restrict the number of elementary reactions favoring promotion. The promotion effect in the system studied should be due to the side reaction of linear branching. The occurrence of the H + NCl₃reaction via two pathways (NHCl + 2Cl and NCl ₂+ HCl) ensures the qualitative agreement between the experimental data and calculation.     

Calculation of lower electronic states of the GaO and InO molecules by the SCF-Xα scattered wave method

In the overlapping atomic spheres approximation of the SCF-X SW method in different variants (spin-restricted, spin-unrestricted, and quasirelativistic), we have calculated fragments of the potential curves for the electronic ground state (X ₂) and the lower excited states (1 ², 2 ², 2 ², 3 ²) of the GaO and InO molecules. We have calculated the spectroscopic constants (T_e, _e, _ex_e, B_e, _e, R_e, A_e) for the molecules in the indicated states, the matrix elements for electronic transitions from the electronic ground state to the excited states, the Franck-Condon factors for the transitions 3 ², 2 ², 2 ² 1 ², X ² (v, v 10). For the InO molecule, we discuss the effect of relativistic corrections on the calculated molecular constants.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 11–19, January–February, 1986.     

Temperature-programmed reduction (TPR) of Co?Ni/Al2O3 catalysts

Reducibility of Co–Ni/Al₂O₃ catalysts has been studied by the TPR method in the temperature range 293–900 K. Results seem to indicate alloying of cobalt and nickel in the process of reduction of the bimetallic systems.

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Co–Ni/Al₂O₃ 293–900 K. .

     

Correlation of nucleae quadrupole resonance frequencies with some chemical constants in the aliphatic series

Linear relationships are established between the nuclear quadrupole resonance frequencies of alkyl chlorides, RCl, on the one hand, and the pK_a values of RCOOH and RNH₂ as well as the Taft ^* constants, on the other hand. Similar linear correlations were found between the NQR frequencies of the substituted compounds XCH₂Cl and the pK_a of XCH₂COOH, XCH₂NH₂, XCH₂OH, as well as the ^* constants of XCH₂ radicals, where X are electronegative substituents. X substituents with unshared electron pairs (RO, RS, F, Cl, Br) are an exception; nevertheless, the deviation of these points is regular and depends linearly on the resonance parameters _R ⁰ or _R of the X substituents. The relationships can be used for an approximation of the ionization constants of a number of fatty acids, for the calculation of the Taft ^* constants of radicals R and XCH₂ and of the resonance parameters _R ⁰ and _R of X substituents with an accuracy which in many cases is in no way inferior to that of the experimental values, and also for the approximate evaluation of the ionization constants of XCH₂NH₂ amines and XCH₂OH alcohols.     

Chemical transformations and evaluation of the basicities of 4,5-dihydropyrrolo[1,2,3-e,f][1,5]benzodiazepin-6(7h)-ones

The alkaline hydrolysis, amidation, and methylation of 4,5-dihydropyrrolo[1,2,3-e,f][1,5]benzodiazepin-6(7H)-one derivatives under various conditions were investigated. The ionization constants (pK) for 1,2-dimethyl-4,5-dihydro[1,2,3-e,f][1,5]benzodiazepin-6(7H)-one were calculated by the Hammett indicator method, and two values, viz., pK ¹ = –2.37 and pK ² = 5.53, which were ascribed to protonation of the diazepine ring and the indole ring of the molecule, respectively, were obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 983–986, July, 1981.     

The influence of ionic surfactants on the acid-base properties and tautomeric equilibrium of 2-dimethylaminomethylphenol

Shifts in the acid-base and tautomeric equilibria have been observed in aqueous solutions of 2-dimethylaminomethylphenol (DAMP) containing surfactants. Cationic micelles of cetyltrimethylammonium bromide increase the dissociation constants of DAMP (pK₁ 0.3, pK₂ 0.5), and anionic micelles of sodium dodecyl sulfate reduce them (pK₁ 1.5, pK₂ 0.3). The constant of tautomeric equilibrium decreases when ionic surfactants are added. This is connected with the better solubilization of the neutral form by micelles.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1215–1218, July, 1994.     

Molecular constants for the 1Σ+ ground state of the ArH+ ion

From the near equilibrium PNO-CEPA potential and dipole moment curves the following molecular constants for the ¹⁺ ground state of the ArH⁺ ion have been calculated: r _e = 1.286Å, _e = 2723 cm^–1, _{e e} = 56 cm^–1, D ₀ = 3.89 eV and ₀ = 2.384 D. The rotationless radiative lifetimes of the five lowest vibrational states are predicted to be 2.28, 1.2, 0.85, 0.64, 0.46 for ArH⁺ and 9.09, 4.71, 3.27, 2.55 and 2.11 for ArD⁺, respectively (all values are in milliseconds and in ascending order of the vibrational levels).Dedicated to Prof. Hermann Hartmann on the occasion of his 65th birthday.     

Thermodynamics of the weak interaction between samarium cation and xylitol in water: A chemical model

The thermodynamic characterization of the weakly complexed model system Sm³⁺-xylitol has been carried out. The standard Gibbs energy enthalpy, entropy, volume and heat capacity of complexation of Sm³⁺ by xylitol have been determined in water at 25°. The stability constant and the enthalpy change have been simultaneously determined by using a calorimetric method. The thermodynamic properties characterizing solely the specific interaction between the cation and the complexing sequence of hydroxyl groups of the ligand have been isolated. The stability constant and the volume of complexation have also been estimated from a similar treatment of the apparent molar volumes. It was found that the reaction between Sm³⁺ and the complexing site of xylitol in water is characterized by: K = 8.1, _rG^o = –5.2 kJ-mol^–1, _rH^o = –13.7 kJ-mol^–1, T_rS^o = –8.5 kJ-mol^–1, _rV^o = 8.8 cm³-mol^–1 and _rC _p ^o = 51 J-K^–1-mol^–1.     

Ordnungsumwandlungen von basischen Poly-α-Aminosäuren

Zusammenfassung Basische Poly-a-aminosäuren wie Poly-L-lysin (PLL) und Poly-Ornithin (PLO) unterliegen infolge Protonierung der basischen Seitengruppen und der damit verbundenen gegenseitigen elektrostatischen Abstoßung einer pH-induzierten Ordnungsumwandlung. Hierbei handelt es sich — wie die CD-Spektren zeigen-wahrscheinlich nicht um eine Helix-Knäuel-, sondern um eine Helix-Helix-Umwandlung. Diese Umwandlung wird in Abhängigkeit von der Temperatur durch Perchlorat-Ionen, oberhalb einer bestimmten Konzentration unabhängig vom Kation im gesamten pH-Bereich vollständig unterdrückt. Mit steigender Perchloratkonzentration wird einmal die UmwandlungstemperaturT _m zu höheren Werten verschoben, andererseits nimmt die Stufenhöhe A[] der spezifischen Drehung sowie die scheinbare oder van't Hoffsche UmwandlungswärmeH _H ab. Dies ist gleichbedeutend mit einer Abnahme der Kooperativität der Umwandlung.Ganz offensichtlich handelt es sich bei der Stabilisierung der -Helix basischer Poly--aminosäuren um einen elektrostatischen Abschirmeffekt der Perchlorationen gegenüber den positiv geladenen Seitengruppen. Kalottenmodelle zeigen, daß die ClO₄-Ionen sterisch sehr gut zwischen die NH₃ ⁺-Seitengruppen passen und so eine linksgängige Superhelix um die rechtsgängige -Helix aufbauen. Hierauf deutet auch der entgegengesetzte Verlauf der polarimetrisch ermittelten Umwandlungskurven hin.In Sulfatlösungen erhält man in Übereinstimmung mit unseren Vorstellungen infolge einer negativen Überschußladung pro Rest nicht das Spektrum der -Helix, sondern das der anscheinend gestreckten Molekelkonformation. Das nur einwertig negative Na-methylsulfat stabilisiert hingegen in höheren Konzentrationen die a-Helix von PLL und PLO.In wäßrig-alkoholischen Lösungen (Äthanol, Methanol, Propanol) steigtT _m bei konstanter ClO_4-Konzentration linear mit dem Alkoholgehalt. Dabei bleibtH _H konstant. Dies bedeutet, daß die scheinbare UmwandlungsentropieS _H wegenT _m =H _H /S _H mit dem Alkoholgehalt abnimmt.Dies folgt anscheinend aus der mit dem Alkoholgehalt abnehmenden Dielektrizitätskonstante (DK) des Mediums. Mit abnehmender DK nimmt aber bei der auf elektrostatischer Abstoßung beruhendenOrdnungsumwandlung die Zahl der inneren Freiheitsgrade des Makromoleküls und damit die Entropie ab.Entsprechend diesen Überlegungen wird in DioxanWasser-Mischungen derselbe, in Wasser-N-Methylformamid (DK 177)-Mischungen mit steigender DK —wie zu erwarten — der entgegengesetzte Effekt beobachtet.

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Summary Due to the protonation of their basic side-chains basic amino-acids undergo a pH-induced order transition process as a consequence of the electrostatic repulsive forces between the positive charged groups.According to CD-spectra this process seems to be not a helix-coil but a helix-helix-transition. Perchlorate ions suppress this transition process depending on temperature and electrolyte concentration at all pH values completely. Increasing ClO₄-concentration shifts the transition temperatureT _m to higher values. On the other hand [] — the difference of the specific rotation before and after the transition — becomes lower and also the heat of transitionH _H decreases with increasing perchlorate concentration, which means that the cooperativity of the transition process decreases too. Obviously the stabilisation of the -helix of basic poly-a-amino acids by C1O₄ ions is due to an electrostatic screening effect. One can show by molecule models that the perchlorate ions fit exactly between the positively charged ammonium groups. In this way a left-handed super-helix of perchlorate ions is formed around the right-handed -helix. This assumption agrees with the inverse character of the polarimetric transition curves without ClO₄4 atmoderate pH-values in the depronated state of the NH₂-groups and in ClO₄ containing solutions at lower pH-values. Consequently SO₄ ions don't stabilize the -helix of basic poly--amino acids because of one negative excess charge per residue along the chain. However, sodium methylsulfate which carries only one negative charge stabilizes the -helix of poly-L-lysine and poly-L-ornithine.In alcohol water mixtures (methanol, ethanol,n-propanol) at constant ClO₄, concentrationT _m increases linearly with increasing alcohol-content up to 50% alcohol, whereasH _H remains constant. This means thatS _H decreases as a consequence ofT _m =H _H . The decrease inS _H is probably due to the fact, that the dielectric constant of the mixture decreases with increasing alcohol concentration. As a consequence the repulsive forces between neighboured side-chains increase and therefore the degrees of freedom of the macromolecule and concomitantly the entropy decreases.According to this assumption the same effect is observed in Doxan-water mixtures and the opposite inN-methylformamide mixtures (d. c. 177) because of the very high dielectric constant between 100 and 140 in the solvent used.

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Mit 19 Abbildungen     

The deprotonation and protonation equilibria of a hypericin derivative in aqueous solution

Summary A hypericin derivative ,'-appended at the methyl groups with two polyethylene glycol moieties (about 23 units long) and capped with acetyl groups was synthesized starting from emodin. This derivative proved to be soluble in water and was investigated by means of spectrophotometric titrations and electrophoresis experiments. Deprotonation at thebay-region hydroxyl group was observed atpK _a=1.6. This was followed by a second deprotonation step of aperi-hydroxyl group at apK _a value of 9.4. This derivative could be protonated at the carbonyl group characterized by apK _a value of –5.7. FrompK _a determinations in water-ethanol mixtures the correspondingpK _a values of hypericin itself determined in such mixtures were extrapolated to the aqueous phase. This resulted in estimatedpK _a values of 1.8, 9.2, and –6.

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Deprotonierungs- und Protonierungsgleichgewichte eines Hypericinderivates in wäßriger Lösung

Zusammenfassung Ein an den Methylgruppen von Hypericin mit endständig acetylierten Polyethylenglykolketten (ungefähr 23 Einheiten lang) ,'-disubstituiertes Derivat wurde ausgehend von Emodin synthetisiert. Dieses Derivat ist wasserlöslich, und es wurde mit Hilfe von spektrophotometrischen Titrationen und Elektrophorese untersucht. Die Deprotonierung derbay-Hydroxylgruppe erfolgt beipK _a=1.6. Diese wird von einem zweiten Deprotonierungsschritt an einerperi-Hydroxylgruppe bei einempK _a-Wert von 9.4 gefolgt. Dieses Derivat konnte an der Carbonylgruppe protoniert werden, was durch einenpK _a-Wert von –5.7 charakterisiert ist. Ausgehend vonpK _a-Messungen in Wasser-Ethanol-Mischungen wurden die entsprechendenpK _a-Werte auch für das Hypericin selbst in wäßriger Phase extrapoliert. Dies führte zu geschätztenpK _a-Werten von 1.8, 9.2 und –6.

     

Research on naphthyridines. 11. Synthesis and ionization constants of substituted 10H-benzo[b]-1,8-naphthyrid-5-ones

3-Substituted 2-alkyl-10H-benzo[b]-1,8-naphthyrid-5-ones were obtained by cyclization of 2-anilinonicotinic acids or the corresponding nitriles. The pK₂ values of these compounds range from –4.63 to –5.98 and correlate with the substituent constants.See [1] for Communication 10.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 372–375, March, 1984.