Strong Basicity Research Articles

Amino acids in chitin — glucan complex ofAspergillus niger

DeproteinatedA. niger biomass contains several covalently bound amino acids. The most abundant are arginine, serine, and proline in molar ratio of 3:2:2. One order of magnitude less is the amount of valine, phenylalanine, leucine and glycine. On deacetylation and separation of chitosan from glucan, the main three amino acids remain bound predominantly to chitosan, whereas the hydrophobic amino acids accompany mainly glucan. The presence of arginine could be the cause of stronger basicity of fungal chitosan compared to polyglucosamine.

Reactions of methylbutynol on alkali-exchanged zeolites. A Lewis acid-base selectivity study

Alkali-exchanged zeolites have both Lewis acid and Lewis base centres. They provide an easy way to tune up the relative strengths of these two sites by controlling Si/Al ratio and electropositivity of the counter cation. These effects can be monitored both byFTIR and N1s XPS of chemisorbed pyrrole. A systematic study of the relationship between acid-base properties and the reactions of methylbutynol (MBOH) was performed over these alkali-exchanged zeolites. The results show that the Lewis base centres catalyze the cleavage reaction ofMBOH, which produces acetone and acetylene, while the strong Lewis acid centres catalyze the dehydration ofMBOH to 3-methyl-3-buten-1-yne (MBYNE). The strong basicity of alkaliexchangedX zeolites produces almost 100% selectivity to acetone and acetylene, whereas the strong Lewis acidity of alkali-exchangedZSM-5 zeolites results in a high selectivity toMBYNE. Compared with the catalytic results overH-ZSM-5 zeolites, it is further concluded that the catalytic conversion ofMBOH to 3-methyl-3-butene-2-one (MIPK) requires the presence of not Lewis acid but strong Bronsted acid sites. The reactions ofMBOH over acid-base catalysts are considered as standard reactions for the characterization of acid and base centres. A correlation between these reactions and theFTIR, andXPS of pyrrole data will be discussed. The deactivation mechanism duringMBOH conversion over alkali-exchanged zeolites is further discussed.

Cooxidation of enones during reaction of superoxide with acidic aromatic amines.

Enones can be epoxidized by O2-· in the presence of various compounds having an acidic >NH group. Cyclic voltammetry and ESR study show that O2-· was disproportionated into H2O2 and O2 by these compounds. Furthermore, H2O2 was deprotonated by unreacted O2-· and HOO- was formed, which is widely known to be the effective oxidant in the epoxidation of enones. This confirms the strong basicity of O2-· in aprotic media, and we propose an alternative scheme for the Haber-Weiss reaction in the absence of metal ions.

Hydrogenation Pathway of Quinolines over Raney Nickel and Ru/C

Abstract Quinoline, 2-methylquinoline, and 8-methylquinoline were hydrogenated over Raney nickel (R-Ni) under 10 atm hydrogen pressure at about 200°C and over ruthenium on carbon (Ru/C) under 100 atm hydrogen pressure at 150°C. All the substrates were commonly hydrogenated into the initial products, 1,2,3,4-tetrahydroquinolines. The initial products were competitively converted over R-Ni to the final products, decahydroquinolines, directly or via 5,6,7,8-tetrahydroquinolines which were mainly formed from the initial products by isomerization. Ru/C promoted exclusively the direct hydrogenation of 1,2,3,4-tetrahydro derivatives to the final products. The hydrogenation and isomerization of 1,2,3,4-tetrahydroquinoline was completely inhibited in the competitive hydrogenation of quinoline and isoquinoline over R-Ni. Such features of these substrates are explained by the strong basicity of 1,2,3,4-tetrahydroisoquinoline. Roles of 1,2,3,4-tetrahydroisoquinoline are much moderate on Ru/C, where the π-coordination may be important. The effects of methyl substituent and different reactivities of quinoline and isoquinoline are discussed in terms of the steric hindrance on adsorption, heats of hydrogenation, basicities, and electronic properties of the related compound, which are calculated according to the MNDO-PM3 method.

Synthesis of 1‐acyl‐5‐pyrazolones and pyrrolidino[2,3‐c]pyrazol‐3‐ones

AbstractThe reactivity of acetamidrazones I in strong basicity conditions was examined. When compounds I are reacted with equivalent quantities of α‐haloketones in sodium alcoholate, the pyrrolidino[2,3‐c]pyrazol‐3‐ones IV were obtained by intermediate formation of 1‐acyl‐3‐amino‐5‐pyrazolones III.

Alkylation of ketones by use of solid KOH in dimethyl sulfoxide

A mixture of solid KOH in dimethyl sulfoxide has a strong basicity, but only a low nucleophilicity and is used for methylation of ketones. With this simple and inexpensive reagent complete methylation with yields up to 90% can be achieved.

Fourier transform IR spectroscopy of collagen and gelatin solutions: deconvolution of the amide I band for conformational studies.

AbstractThe ir spectra of lathyritic rat skin collagen and calf skin gelatin solutions at a variety of temperatures were obtained using Fourier transform ir spectroscopy and a 9‐reflection, 2‐pass ZnSe prism sample cell. The spectra were then deconvolved (based on Kauppinnen's method) and the behavior of the amide I band at ∼ 1650 cm−1 observed in detail. Throughout the temperature range studied (4–50°C), three component absorption peaks within the amide I band (at 1633, 1643, and 1660 cm−1) are common to the spectra irrespective of the degree of triple helix content of the sample. Changes in the relative intensities of these component peaks are, however, conformationally dependent. During denaturation of the triple helix, the dominant 1660‐cm−1 component in the native collagen spectrum diminishes and the 1633‐cm−1 peak becomes relatively intensified. The inherently strong basicity of the carbonyl group of the proline residues together with the frequent occurrence of this imino acid in the X position of the Gly‐X‐Y triplet of collagen largely accounts for the −30‐cm−1 shift of the amide I band during denaturation. Temperature and conformationally dependent changes in the fine structure of the amide I band from dilute solutions of collagen can be monitored in a reproducible and quantitative fashion.

ChemInform Abstract: Reactivity of Ruthenium Carbonyls on Metal Oxide Surfaces. Effects of the Surface Acid‐Base Chemistry.

AbstractBy means of IR and electronic spectroscopy as well as electron microscopy the reactivity of H4Ru4(CO)12 clusters supported on the metal oxides SiO2, TiO2, γ‐Al2O3 and MgO is investigated.

Reactivity of ruthenium carbonyls on metal oxide surfaces: effects of the surface acid-base chemistry

The reactivity of tetraruthenium carbonyl clusters supported on metal oxides (SiO 2, TiO 2, γ-Al 2O 3, and MgO) under various atmospheres has been investigated by infrared and ultraviolet-visible spectroscopies and electron microscopy. [H 4Ru 4(CO) 12] physisorbed on SiO 2 easily decomposes and aggregates to form metal particles. The tetraruthenium clusters supported on TiO 2 are oxidized by surface hydroxyl groups, giving mononuclear complexes; virtually the same chemistry occurs, but less readily, on γ-Al 2O 3. The tetramthenium clusters supported on MgO, in contrast, are highly resistant to oxidation. The strong basicity of this support leads to an increased stability of small polynuclear complexes, hindering the formation of oxidized complexes and aggregated metallic structures. The unique character of the basic support appears to be related to the tendency of the support to form and stabilize cluster anions.

Nature of the strong basicity of superbases, unsolvated hydroxide ions?

The basicity of so-called superbases is ascribed to the presence of free, i.e., naked, hydroxide ions. Infrared spectroscopic studies of various KOH (and KOCH 3) crown ether dicyclohexyl-18-crown-6 and dibenzo-18-crown-6) and Sr(OH) 2 cryptand(222) solutions in polar (methanol, chloroform) and non-polar solvents (toluene, n-heptane) revealed that unsolvated OH − ions are not present in such strong basic solutions. Formation of potassium crown ether complexes shown by the i.r. bands at 1095–1102 and 990–995 cm −1 (dicyclohexyl-18-crown-6) is always accompanied (and only possible if) by that of methoxide ions (i.r. band at 1050–1060 cm −1). The presence of solvated OH − ions cannot be excluded.

Purification and characterization of a low molecular weight basic protein from marine turtle egg white

The egg white of marine turtle ( Caretta caretta Linn.) and one species of tortoise ( Geomyda trijuga trijuga Schariggar) contain a low molecular weight basic protein. It has been purified to homogeneity from the egg white of marine turtle and characterized in terms of its major physicochemical and chemical properties. The molecular weight of this protein calculated from gel filtration, sodium dodecyl sulfate-gel electrophoresis in the presence of urea, sedimentation-diffusion data, and amino acid composition is 4300. Its isoelectric point is at pH 11.1 and intrinsic viscosity is 0.038 dl g −1 in 0.2 m NaCl. It has a Stokes radius of 12.6 Å and a diffusion coefficient of 16.50 × 10 −7 cm 2 s −1. Analysis of the far-ultraviolet circular dichroic spectrum has shown that the basic protein contains 27% β-pleated sheet and little or no α-helix. It possesses a single polypeptide chain of 40 amino acid residues with three disulfide bonds. It lacks serine, methionine, phenylalanine, and carbohydrate moiety. It binds to DNA and stimulates ATPase activity due to its strong basicity. The complex of DNA-basic protein is partially resistant to the action of DNase.

Phosphatranes as unusual stabilizing structures for hypervalent phosphorus: 10-P-5 mono- and divalent cations

'H, I3C, and 'IP NMR evidence are presented for the formation of the hypervalent hosphorus mono- and divalent cations [HYP(OCH2CH2)3N]+,[ H2YP(OCH2CH2)3N]2+a,n d [R2YP(OCH2CH2)3N]2+(Y = 0, S; R = Me, Et). These new IO-P-5 cations are apparently stabilized by the presence of three five-membered rings chelating the phosphorus and also by the strong basicity of the apical chalcogen arising from its participation in the three-center, four-electron bonding system along the axis of the trigonal-bipyramidal structure.

Quantitative structure‐activity relationships: Molecular structures and different modes of exposure affecting transport and toxicities of chemicals: QSAR analysis

AbstractAlthough relatively few systematic studies have been reported on the disposition of various toxicants or pollutants, considerable effort has been devoted to disposition studies on various drugs and simple organic molecules. Our group and others have in the last few years reported the quantitative structure‐activity relationships (QSAR) on the absorption, distribution and metabolism of several series of organic compounds. The mathematical model embodies the concept of the pH partition hypothesis and the Sutherland‐Einstein diffusion equation, as well as Hansch's parabolic model. For most exogenous molecules of intermediate mol wt (102 to 104), passive diffusion through the lipoprotein barrier appears to be the most important route among the known mechanisms of absorption, with an ideal lipophilic character (log P0) around 0.5 to 3. For polar and/or high mol wt compounds (>104) passage through interstitial space becomes mainly a negative function of log mol wt. High mol wt compounds and strong acids and bases (highly ionized) should not be absorbed readily based on the generalizations obtained. However, this does not eliminate the adsorption or binding of these compounds onto the membrane, or direct tissue damage caused by the strong acidity or basicity. Other mechanisms of absorption such as pinocytosis of liquid droplets and phagocytosis of solids are possible, but no quantitative data are available for analysis. Evidence is also presented to show that strong acids or bases can be absorbed as ion pairs with appropriate counter ions.Specific examples of QSAR using the following general equation and its simplified forms are presentedlog A = ‐a · (log P)2 + b · log P + c · log (U/D) + d · log mol wt + e · χ + f.The types of compounds discussed include nonelectrolytes, weak acids and bases, cationic molecules, strong acids, surfactants and some high mol wt substances. Relationships of the absorption via different routes (e.g., gastric, intestinal, percutaneous and corneal) are compared.

Quantum-chemical studies of alumina. Part 1.—Brønsted acidity and basicity

This work is part of a series intended to clarify the relationship between the microscopic surface structure and the acid-base nature of the Al2O3 system using ab initio molecular-orbital calculations for many cluster models. This paper deals with Bronsted acidity and basicity. The strong acidity of an OH group is caused by the high coordination of Al atoms (maximum 3) to the O atom in the OH group and the low coordination of O atoms to these Al atoms, while strong basicity is obtained by the opposite conditions to the number of atoms around the central O atom of the active site. Terminal OH groups or lattice O atoms in the dehydrated surface of alumina usually have no strong acidity or basicity, respectively, while O atoms in some terminal OH groups have fairly strong basicity.

Infrared spectroscopic study of the adsorption of hydrogen and carbon monoxide on highly dehydroxylated thoria

Hydrogen adsorption on thoria activated at 973 K (ThO2-973) leads to weak bands at 1115 and 860 cm–1 and a shoulder at 910 cm–1 due to partially reversibly adsorbed bridged species Th—H—Th. The uptake is very small. The adsorption of CO on ThO2-973 turns the disc orange-yellow and gives rise to a large number of species, some of which are reversibly adsorbed. These species are characterized by a band at 2171 cm–1 and are coordinated to Lewis-acid sites. In addition to the carbonate and formate species, at least four types of irreversibly adsorbed species are formed. Three of them are characterized by bands in the 1200–1000 cm–1 frequency range and can be assigned to v(CO) vibrations of –O—CC—O– species; another possibility is the formation of CO2–2 species because of the strong basicity of thoria. The irreversibly adsorbed species are very sensitive to O2 and H2O but are not reduced by H2. Irreversibly adsorbed hydrogen species react with reversibly adsorbed CO species or CO gas, leading to species similar to those formed on adsorption of HCHO.

ChemInform Abstract: THEORETICAL APPROACH TO THE BASICITY OF ALKALINE EARTH METAL OXIDE CATALYSTS. RELATIONSHIP BETWEEN BASICITY AND SURFACE STRUCTURE OF MAGNESIUM OXIDE

Molecular-orbital calculations of cluster models for various structures of the MgO surface have been performed in order to clarify the relationship between basicity and microscopic structure. The surface is regarded as being constructed of many long —MgO— chains interwoven or entangled in a complex manner. Ways in which interactions between the chains affect the basicity of an oxygen site are discussed. The main factors generating stronger basicity are concluded to be (i) fewer Mg atoms coordinated to the central oxygen atom in the basic site and (ii) more O atoms coordinated to the Mg atoms adjacent to the central oxygen atom. This result agrees well with the experimental fact that magnesium hydroxide is dehydrated to a basic catalyst with the maximum number of basic sites by calcination at an appropriately moderate temperature.

Synthesis and characterization of dinuclear niobium(IV), niobium(III) and tantalum(III) chloride complexes with strongly basic phosphanes: PCy3 and P(Bu-t)3

The reactions between niobium and tantalum pentachlorides and tri-t-butylphosphane and tricyclohexylphosphane under various reducing conditions (magnesium turnings, amalgamated magnesium or sodium naphthalenide) were investigated. The products are highly dependent on the experimental conditions. Niobium(IV) adducts: Nb2Cl8[P(Bu-t)3]2 and Nb2Cl8(PCy3)4 were obtained with magnesium turnings, while reduction to Ta2Cl6(PCy3)3 occurred under similar conditions with tantalum. Ligand exchanges from NbCl4(THF)2 also yielded niobium(IV) adducts Nb2Cl8(PR3)3. The formation of the first soluble diamagnetic niobium(IV) adducts appears to be favored by the strong basicity of PCy3 and P(Bu-t)3. However, these crowded niobium(IV) complexes are unstable both in the solid and in solution with respect to niobium(III). Derivatives in oxidation state 3: M2Cl6(PCy3)3 (M=Nb or Ta), Ta2Cl6[P(Bu-t)3]3 and Nb2Cl6[P(Bu-t)3]2 were formed more efficiently with amalgamated magnesium or with sodium naphthalenide. Activation of dinitrogen under mild conditions (normal pressure, room temperature) was observed during the reduction process with magnesium, for both tantalum and niobium; an unstable adduct, Nb2Cl6[P(Bu-t)3]3N2, could be isolated. All products were characterized by elemental analysis, magnetic susceptibility measurements and i.r. spectroscopy; their molecular structure is discussed in terms of the1H and31P n.m.r. data.

Dihydropyrimidines and related structures. I. N2‐substituted 2‐pyrimidinamines and dihydro‐2‐pyrimidinamines by reaction of phenylbutenones and monosubstituted guanidines

AbstractThe reactions of monosubstituted guanidines 2 with phenylbutenones 7 and 10 exclusively yield N2‐substituted 2‐pyrimidinamines 8 and 9. The structure of the reaction products is proved and their differing stability is discussed. Action of methyl‐ and benzylguanidine respectively (2b, c) on 4‐phenyl‐3‐buten‐2‐one (7) and of 2c on l‐phenyl‐2‐buten‐1‐one (10) under atmospheric oxygen affords aromatic N2‐substituted 2‐pyrimidinamines 9b and c. The dihydropyrimidines 8b and c, probable intermediates of the reactions, could not be isolated. In contrast, heating of arylguanidines 2d, e with 7 leads to stable dihydropyrimidinarnines 8d and e, which can be isolated as bases. Addition of methanol to 8d yields 6‐methoxy‐2‐pyrimidinamine 11d, boiling of 8d in DMF affords 9d. Under nitrogen, guanidine adds to 7 to yield aminopyrimidinol 13a, which is transformed by heating in benzene into pyrimidine 9a. The low stability of 8a‐c is attributed to their strong basicity, the greater stability of 8d and e to their lower basicity. The structural formulae of 8d, e and 9b‐d and their salts respectively were established partly (8e) by nmr and partly (9b‐d) by comparison of the corresponding picrates with authentic samples [17].

Half-wave potentials of electroactive substances in hexamethylphosphoric triamide

Abstract

Properties of Magnesium Oxides Prepared from Various Salts and Their Catalytic Activity in 1-Butene Isomerization

Abstract The basicity, one-electron donor property, and surface area were examined on the magnesium oxide catalysts prepared from six different kinds of magnesium salts. Magnesium oxide prepared from magnesium nitrate, oxalate, and acetate exhibited strong basicity and relatively large surface area and, on the other hand, MgO prepared from magnesium chloride, carbonate and sulfate had relatively weak basicity and small surface area. Number of one-electron donor centers hardly changed in the variety of magnesium oxides, except the one prepared from magnesium chloride. Magnesium oxide prepared from chloride showed both the lowest basicity with less strength than H−=15.0 and surface area in the six kinds of catalysts. In order to examine the influence of remaining anions in MgO a variety of catalysts were prepared by the addition of ammonium chloride, sulfate, and carbonate, respectively in MgO prepared from the nitrate. Ammonium chloride brought the greatest influence on the basicity, one-electron donor property, and surface area. Thus the remaining chloride ion greatly affected such properties as cited above. Sodium nitrite which decomposes at higher temperature than 320 °C was added to the magnesium oxides for the examination of the effect of the sodium cation. The amount of the basicity with a moderate strength (H−=15.0–22.3) increased by the addition of NaNO2. This was ascribed to the formation of the moderate strength of basicity by the interaction of Na2O, one of the decomposed products of NaNO2 and MgO. Isomerization of 1-butene was carried out on the six kinds of catalysts at 30 °C. The magnesium oxides prepared from nitrate, oxalate, and acetate salts (group A) exhibited isomerization activity and the ones from chloride, sulfate, and carbonate (group B) did not entirely. The isomerization activity could be correlated with the stronger basicity than H−=22.3. Temperature pregrammed desorption curves of acetic acid adsorbed on the catalysts indicated two peaks at around 350 and 420 °C in group A catalysts and only one at 350 °C in group B. The desorbed peak at around 420 °C was assigned to the adsorbed acetic acid on the stronger basic sites than H−=22.3.