Alkaloids ofNuphar luteum

Summary 1. The dry rhizomes ofNuphar luteum L. have yielded three sulfur-containing alkaloids: two — thiobinupharidine and neothiobinupharidine — were known substances, the third with composition C₃₀H₄₂O₄N₂S being new and having been given the name of nuphleine.2. A possible structure has been proposed for nuphleine.Khimiya Prirodnykh Soedinenii, Vol. 3, No. 2, pp. 178–182, 1967     

Evaluation of the acidic properties of hydroxycoumarins and choice of solvents for performing potentiometric analysis

The relative acidity constants (pK_a) for 17 hydroxycoumarins in water, methanol, acetone (Ac), dimethylformide (DMFA), and dimethyl sulfoxide (DMSO) have been determined by Henderson's method. The existence of a linear relationship between pK_a in water and pK_a in acetone, dimethylformamide, and dimethyl sulfoxide has been established. From the pK_a values the sequence of neutralization of the hydroxy groups has been determined: their acidic properties decrease in the sequence 4-OH > 7-OH > 6-OH > 8-OH. A quantitative evaluation of the conditions of titration in five solvents on the basis of the titration constants (pK_t) and of the values of the potential jumps and the shape of the potentiometric titration curves has permitted acetone to be proposed as the optimum solvent for the performance of potentiometric analysis.All-Union Scientific-Research Institute of Drug Chemistry and Technology, Khar'kov. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 770–773, November–December, 1985.     

The connection between the ionization constants of alkaloids and their basicities

Summary 1. The pK_a values of a number of indole alkaloids ofVinca erecta in aqueous ethanolic solution and in chloroform have been determined.2. It has been shown that the pK_a value of an alkaloid in water or in chloroform is not connected with the pH of the transition from chloroform into a buffer solution.3. It is impossible to estimate the basicity of an alkaloid from its pK_a value.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 57–59, January–February, 1973.     

Determination of Acid Dissociation Constants of Neamine by Potentiometric and Electrospray Mass Spectral Techniques

The acid dissociation constants of neamine have been measured using potentiometric titrations. The pK_a1, pK_a2, and pK_a3 values of neamine are 6.35 ± 0.2, 7.73 ± 0.15, and 8.62 ± 0.08, respectively. Neamine is readily characterized using positive-ion electrospray ionization–mass spectrometry (ESI–MS). Various protonated species and their solvated ions are mainly observed. Nevertheless, the abundances of the observed speciation over the pH range 5.0–9.8 do not reflect the variation in the bulk solution. Hence, reaction quotients determined from the ESI–MS investigations vary significantly from the pK_a's determined from potentiometric titrations, thereby illustrating that care must be taken in determining thermodynamic properties using the former technique.     

Functional Transformations on the Surface of Poly(ethylene terephthalate) Films under Exposure to Accelerated Electrons

The effect of the electron-beam treatment of poly(ethylene terephthalate) (PETP) films in an air atmosphere on the functional chemical composition of their surface and on the optical properties in the UV region was studied. The mutual functional transformations of surface sites (carbonyl, methyl, and hydroxyl groups) by the action of fast electrons were analyzed as functions of the absorbed dose over the range 25–500 kGy using the adsorption of acid–base indicators with the pK_a values ranging from –5 to 15. Correlation between the absorbed dose, the concentration of certain functional groups (centers with pK_a 5.0 (–CH₃) and 0.8 (–CH₂OH)), the hydrophilicity of films, and the transparency in the UV region of the spectrum was established. The transparency was found to exhibit a pronounced minimum at an absorbed dose of 150–200 kGy. A comparative analysis of PETP surfaces differing by the absence or presence of kaolin (0.1%) as an oxide material additive was performed. Differences in the pK_a distribution of adsorption sites were found, and their dependence on the absorbed dose was studied.     

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.

     

Spectral-luminescence properties and acid-base properties of luminophores obtained from 3-iodo-7-dialkylaminocoumarins

The absorption and fluorescence spectra of the conjugate acids of 7-dialkylaminocoumarins were studied, and their pK_a ^I, pK_a ^II, and pK_a ^* values were determined. It was established with the aid of PMR data that the primary protonation generally involves the nitrogen-containing substituent in the 3 or 4 position, while the secondary protonation involves the nitrogen atom in the 7 position.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1170–1175, September, 1991.     

Quantitative Correlations for the Estimation of Thermodynamic and Molecular Properties of Pyridines and 2,2′-Bipyridyines

Standard heats of formation, entropies, ionization potentials, and molecular dipole moments of a series of pyridines have been calculated by MNDO, AM1 and PM3 methods. Linear relationship have been established which permit a priori estimation of thermodynamic and molecular characteristics of pyridines. Correlation have been found between the values of pK_a for 2,2′-bipyridines for aqueous solutions and their gas phase proton affinities.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, 391–402, March, 2005.     

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.     

A study of naphthyridines

4,4-Diaryl-1,4-dihydro-2,3-benzo-1,8-naphthyridines have been synthesized by the cyclization of diaryl 2-arylaminopyridin-3-yl carbinols. The latter were obtained by the reaction of methyl 2-arylaminonicotinates with arylmagnesium halides. With acid chlorides, the 4,4-diaryl-1, 4-dihydro-2,3-benzo-1,8-naphthyridines form 1-acyl derivatives. The pK_a values of the 4,4-diaryl-1,4-dihydro-2,3-benzo-1,8-naphthyridines in nitrobenzene have been determined, and a correlation has been found of the pK _a values with the ^* constants of the substituents (r=0.955, ^*= –1.53, pK _a ^° calc=2.51, s=0.01).For Communication II, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 119–121, January, 1974.     

2,2-Dimethyl-5-(5-r-2-furfurylidene)-1,3-dioxan-4,6-diones. 1. Synthesis,properties, and structure

5-R-Furanaldehydes react with Meldrum's acid under Knoevenagel reaction conditions. The reaction products have s-cis conformation. The pK _a values of the electroneutral Lewis acids synthesized were determined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1325–1329, October, 1986.     

Spectrophotometric and potentiometric determination of acidic constants of oxo-phenyl pyridinium monoxime and dioxime

The UV absorption spectra of 1-(1-hydroxyimino-2-oxo-2-phenyl) pyridinium chloride (compound I) and 1-(1-hydroxyimino-2-oxo-2-phenyl)-4-hydroxyiminomethyl pyridinium chloride (compound II) in water solution at differentpH values have been measured. The spectral changes, with changingpH, in aqueous solutions are attributed to the dissociation of individual functional groups of the compounds. The mixed acidic constants (pKa) of the investigated monoxime and dioxime, have been determined spectrophotometrically in the series ofBritton-Robinson's buffer solutions in thepH range 3.0–5.19 and 7.70–9.90 (t=25±0.5°C,I=0.2). The followingpKa values have been obtained for monoximepKa ₁=4.30 and for dioximepKa ₁=4.28,pKa ₂=8.36.Thermodynamic acidic constants (pKa) have been determined on the basis of potentiometric titrations and they have been found to bepKa ₁=4.32 for compound I andpKa ₁=4.27,pKa ₂=8.51 for compound II. The values obtained by transferringpKa intopKa are in good agreement with the values obtained potentiometrically.

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Spektrophotometrische und potentiometrische Bestimmung der Aciditätskonstanten von Oxo-Phenyl-Pyridinium-Monooxim und -Dioxim

Zusammenfassung Die UV-Absorptionsspektren von 1-(1-Hydroxyimino-2-oxo-2-phenyl)-pyridiniumchlorid (Verbindung I) und 1-(1-Hydroxyimino-2-oxo-2-phenyl)-4-hydroxyiminomethylpyridiniumchlorid (Verbindung II) wurden in wäßrigen Lösungen bei verschiedenenpH-Werten aufgenommen. Die Änderungen in den Spektren, die in wäßrigen Lösungen mit derpH-Änderung entstehen, können der Dissoziation der einzelnen funktionellen Gruppen der untersuchten Verbindungen zugeschrieben werden. Die Mischaciditätskonstanten (pKa) des untersuchten Monooxims und Dioxims wurden spektrophotometrisch in einer Reihe vonBritton-Robinson-Pufferlösungen inpH-Intervallen 3.0–5.19 und 7.70–9.90 (t=25±0.5°C;I=0.2) bestimmt: für das MonooximpKa ₁=4.30 und für DioximpKa ₁=4.28 undpKa ₂=8.36. Die thermodynamischen Aciditätskonstanten (pKa) wurden aufgrund der potentiometrischen Titration berechnet:pKa ₁=4.32 für die Verbindung I undpKa ₁=4.27 undpKa ₂=8.51 für die Verbindung II. Die durch ÜbertragungpKa inpKa erhaltenen Werte sind mit den über die potentiometrische Methode erhaltenen Werten in guter Übereinstimmung.

     

Palladium catalyzed allylic C-alkylation of highly acidic and enolic heterocyclic substrates: tetronic acid and triacetic acid lactone

Tetronic acid (pK_a 3.76) and triacetic acid lactone (pK_a 4.94) have been alkylated at their active carbon atoms by means of thermodinamically controlled palladium catalyzed allylic alkylations.     

Calculations of pKa values of carboxylic acids in aqueous solution using Möller-Plesset perturbation theory

The acidity constants of some carboxylic acids in aqueous solution have been calculated. The calculations were carried out using Möller-Plesset (MP) perturbation theory. The Polarizable Continuum Model (PCM) is used to describe the solvent. This model furnishes pK_a values that agree more closely with experimental data than those obtained at the level of Hartree-Fock (HF) and Density Functional Theory (DFT-B3LYP). The root-mean-square of errors of the calculated pK_a values are less than 1.0 for the studied acids. The molecules analyzed consist of acids with pK_a values in the range of 1.30 to 5.05, and have been partitioned into three classes. Class I includes acids with pK_a values higher than 4.00. Class II includes strong acids with pK_a values between 3.00 to 4.00. Class III includes very strong acids with pK_a values less than 3.00. The calculated pK_a values for the acids in Class I and Class II agree more closely with experimental values. The root-mean-square of errors for the Class I and Class II compounds are 0.70 and 0.78 pK_a units, respectively.     

General concepts concerning electrooxidation of polynitrocarbanions

Conclusions With polynitrocarbanions of the general formula RC(NO₂)₂ ^– that differ drastically in ease of oxidation and pK_a values of the respective CH acids as examples, it has been established that electrooxidation of polynitrocarbanions has a general character; the individuality of their chemical behavior is determined by the kinetics of the fragmentations involved in the electrode process and the reactions of the intermediate polynitroalkyl radicals with the medium.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 603–608, March, 1987.     

Protolytic equilibrium of certain annelated azoloazines

The first and second protonations of annelated azoloazines have been investigated quantitatively in aqueous solution. Compounds investigated were pyrazolo[1,5-a]pyrimidine (pK_BH ^– 0.03±0.02, pK_BH ²⁺ –7.87±0.30), 1,2,4-triazolo[4,3-b]-1,2,4-triazine (pK_BH ⁺ –0.04±0.02, pK_BH ²⁺ –8.00±0.10), 1,2,4-triazolo[1,5-a]pyrimidine (pK_BH ⁺ 0.21±0.03, pK_BH ²⁺ –9.00±0.09) and its 6R derivatives (R=NO₂, Br, Cl). The annelated azoloazines studied are weaker bases than their unannelated analogs. According to quantum chemical calculations (AM1), protonation of these heterocycles may occur both at the azole and the azine fragments of the molecule.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 816–824, June, 2000.     

Hydrolysis of bis(chloromethyl)phosphonic acid p-nitroanilide in aqueous micellar surfactant solutions

The hydrolysis of bis(chloromethyl)phosphonic acid p-nitroanilide has been studied in the pH range 6.86–13.0 and the effects of ionic surfactant micelles on this process have also been examined. The nature of the micellar effects of cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) on this reaction lead us to conclude that both the neutral and anionic forms of the substrate are reactive, and that in the range of pH > pK_a hydrolysis of the ionic form of the anilide predominates, while at pH < pK_a the reaction of the neutral form is predominant. The binding constants for both the neutral and anionic forms of bis(chloromethyl)phosphonic acid p-nitroanilide in micellar CTAB and SDS solutions have been determined using a kinetic method, as well as by measuring the changes in the acid-base properties of the substrate resulting from the influence of micelles.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1718–1722, August, 1990.     

Dibenzophenoxazon-(5)-derivate als Neutralisationsindicatoren in wasserfreier Essigs?ure

Zusammenfassung Die relativen Basizitätskonstanten von 5H-Dibenzo(a,h)phenoxazon-(5) (I) (K=3,2 · 10^–2), 5H-Dibenzo(a,j)phenoxazon-(5) (II) (K=6,5 · 10^–2), 9-(N-1-Naphthylamino)-5H-dibenzo(a,j)phenoxazon-(5) (III) (K=1,12), 9-(N-2-Naphthylamino)-5H-dibenzo(a, j)phenoxazon-(S) (IV) (K=1,22), 9-Anilino-5H-dibenzo(a,j) phenoxazon-(5) (V) (K=1,28) und 9-(p-Tolylamino)-5H-dibenzo(a,j)phenoxazon-(5) (VI) (K=1,45) wurden für das Puffersystem Acetat-Antipyrinperchlorat in wasserfreier Essigsäure bestimmt. Die Verbindungen II, V und VI wurden zur visuellen Indikation von Titrationen schwacher Basen mit Perchlorsäure in wasserfreier Essigsäure benutzt. Mit Indicator II können Basen mit pK_a(H₂O)-Werten von 2–4 und mit den Indicatoren V und VI stärkere Basen mit pK_a(H₂O)-Werten von 4–7 bestimmt werden.

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Dibenzophenoxazone-(5)-derivatives as neutralisation indicators in non-aqueous acetic acid

The relative basicity constants of 5H-dibenzo(a,h)phenoxazone-(5) (I) (K=3.2×10^–2), 5H-dibenzo(a,j)phenoxazone-(5) (II) (K=6.5×10^–2), 9-(N-1-naphthylamino)-5H-dibenzo(a,j)phenoxazone-(5) (III) (K=1.12), 9-(N-2-naphthylamino)-5H-dibenzo(a,j)phenoxazone-(5) (IV) (K=1.22), 9-anilino-5H-dibenzo(a,j)phenoxazone-(5) (V) (K=1.28) and 9-(p-tolylamino)-5H-dibenzo(a,j)phenoxazone-(5) (VI) (K=1.45) have been determined with respect to the buffer system antipyrine acetate-antipyrine perchlorate in non-aqueous acetic acid. The compounds II, V and VI were employed for visual indication of titrations of weak bases with perchloric acid in non-aqueous acetic acid. Indicator II is convenient for the titration of bases with pK _a (H₂O) values 2–4 and indicators V and VI for bases with pK_a(H₂O) values 4–7.

     

Equilibrium acidity of potassium (3)−1,2-dicarbadodecahyronidoundecaborate (−1)

Conclusion The equilibrium acidity of potassium dicarbadodecahydronidoundecaborate(–1) when metalated with fluorenylpotassium and indenylpotassium in 1,2-dimethoxyethane was determined, and was found to have a pK _a value of 21.1–21.5 on the Streitwieser scale.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 471–472, February, 1972.