Aromatic Nitrogen Bases Research Articles

The effects of intramolecular hydrogen bonding on the reactivity of phenoxyl radicals in model systems

The effects of hydrogen bonding and spin density at the oxygen atom on the gas-phase reactivity of phenoxyl radicals were investigated experimentally and theoretically in model systems and the dipeptide LysTyr. Gas-phase ion-molecule reactions were carried out between radical cations of several aromatic nitrogen bases with the neutrals nitric oxide and n-propyl thiol. Reactivity of radical cations 4–6 correlated with the spin density. The possibility of hydrogen bonding was explored in compounds which allowed four-, five-, and six-membered rings to be formed between the protonated nitrogen and the phenoxyl oxygen, while possessing similar spin density at the oxygen atom. The N+-H⋯O bond length was calculated to decrease in the series (1–3), consistent with the theoretical calculations finding weak hydrogen bonding in 2 and strong hydrogen bonding in 3. This coincided with the decrease in reaction rates of 1–3 with both nitric oxide and n-propyl thiol. DFT calculations found that the lowest energy structure of the distonic radical cation of the dipeptide [LysTyr(O)]+ has a short hydrogen bond between the protonated Lys side chain and the phenoxyl oxygen, 1.70Å, which is consistent with its low reactivity.

Synthesis, Characterization, Spectroscopic and Photophysical Properties of New [Cu(NCS){(L‐N)2 or (L′‐NN)}(PPh3)] Complexes (L‐N, L′‐NN = Aromatic Nitrogen Base)

AbstractThe syntheses, spectroscopic characterization (IR, 1H and 31P NMR, ESI‐MS) and conductivity studies of the mixed N,P‐donor complexes of copper(I) thiocyanate: [Cu(NCS)(py)2(PPh3)], (2), [Cu(NCS)(Mepy)(PPh3)]2, (3), [Cu(NCS)(phen)(PPh3)], (4), [Cu(NCS)(bpy)(PPh3)], (5), [Cu(NCS)(bpy)(PPh2py)], (6), [Cu(NCS)(py)(PPh2py)], (7), (py = pyridine; Mepy = 2‐methylpyridine; phen = 1,10‐phenanthroline, bpy = 2,2′‐bipyridyl), together with single‐crystal X‐ray structural characterizations of 2, 3, 4 (new polymorph), 5 and 6 are reported, which provides an opportunity to study the effect of the introduction of a pair of nitrogen donors, both unidentate and chelate, on the bonding parameters of the Cu/NCS/P system. Cu–P and Cu–N2(ar) are found to be similar [2.1974(5) and 2.091(2), 2.070(1) Å for py2 adduct 2, cf. 2.1748(9)–2.200(1) and 2.071(2)–2.106(4) Å for the counterpart values for bidentate adducts 4–6]. However, Cu–N(CS) and Cu–N–C are 2.013(2) Å and 157.4(2)° for py2 adduct 2 and 1.946(2)–1.981(8) Å and 166.7(2)–176.58(2)° for bidentate counterparts 4–6. The change is attributed primarily to the closure in the N–Cu–N angle [99.58(8)° for py2 2; 77.7(6)–80.5(3)° for N∧N‐bidentate donors 4–6]. In consequence of the increased steric profile of the Mepy ligand, we find the stoichiometry diminished to 1:1:1, which resulted in theformation of [(Ph3P)MepyCu(SCNNCS)Cu(Mepy)(PPh3)] dimers.TDDFT/CPCM calculations were used to clarify the type of transitions involved in the UV/Vis absorption spectra, and the corresponding experimental photoemission data wereacquired. The 31P CPMAS spectra of the copper derivatives exhibit distorted quartets that afford values for 1JCu,P. Furthermore, the quadrupole‐induced distortion factors were calculated, and in the cases of 2, 4 and 5, the quadrupole coupling constants were obtained, on the basis of the X‐ray structures.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Influence of Stacking on Hydrogen Bonding: Quantum Chemical Study on Pyridine−Benzene Model Complexes

The present work focuses on the influence of aromatic stacking on the ability of an aromatic nitrogen base to accept a hydrogen bond. Substituent effects were studied at the MP2 level for 10 complexes of a substituted benzene stacked with pyridine in a parallel offset conformation. The interaction energies between each substituted benzene and pyridine were analyzed in terms of Hartree−Fock, correlation, and electrostatic contributions. It appears that the basicity of pyridine is directly related to the electrostatic interaction between the cycles. It increases with increasing electron donating character of the benzene substituents. Also, density functional theory based descriptors such as global and local hardnesses and the benzene ring polarizability are found to adequately predict the interaction energy. These findings may be important in the study of DNA/RNA chains.

Manganeseporphyrin-catalysed heterogeneous and unusually chemioselective oxidations of sulfides by monopersulfate in supercritical CO 2

The oxidation of sulfides by Oxone ® in the presence of catalytic amount of various manganese porphyrins in supercritical CO 2 (scCO 2) has been studied. The reactions have been carried out in an anhydrous two phase-system (solid Oxone ®, solid catalyst/scCO 2). In the experimental conditions employed (40°C, 20 MPa), only the new synthesised 5,10,15,20-tetrakis(heptafluoropropyl)porphyrinate manganese(III) chloride showed a slight solubility in scCO 2. In the absence of manganese porphyrin and/or of an aromatic nitrogen base a slow stoichiometric sulfide oxidation leading mainly to sulfoxide is observed in spite of the extremely low solubility of Oxone ® in scCO 2. Conversely, in the presence of 4- tert-butylpyridine and catalytic amount of manganese porphyrins (0.6% with respect to sulfide) enhanced reaction rates are observed. Furthermore, the selectivity of sulfide oxidation reverses and sulfone is formed in larger or comparable amount than sulfoxide even when an excess of sulfide over oxidant is employed. The results collected suggest that the local concentration of the intermediate sulfoxide around the catalyst is higher than that of the bulk supercritical phase thus determining unusual high reaction rates for sulfone formation.

The addition-reaction product of 1,1,1,4,4,4-hexachloro-1,4-disilabutane withN-methylimidazole

The product of the addition reaction of 1,1,1,4,4,4-hexachloro-1, 4-disilabutane with N-methylimidazole is &mgr;-ethylene-C(1):C(2)-bis[dichlorotris(1-methylimidazole-N(3))sili con(IV)] dichloride, C(26)H(40)Cl(4)N(12)Si(2)(2+).2Cl(-). Two of the six Cl atoms are replaced by aromatic nitrogen bases and the coordination sphere of silicon is extended from four to six. The molecule is located on a crystallographic centre of inversion. The environment around the Si atom can be described as a slightly distorted octahedron with the Cl atoms occupying axial positions and the three N-methylimidazole ligands and the ethylene bridge in the equatorial plane.

Trans-Tetrabromobis(3,5-dimethylpyridine)germanium(IV), a non-merohedral twin

The structure of the title compound, [GeBr 4 (C 7 H 9 N) 2 ], is the first example of an addition compound of GeBr 4 with two aromatic nitrogen bases. The molecule, with D 2h symmetry, has crystallographic C 2h site symmetry. The environment around the Ge atom can be described as a slightly distorted octahedron with the dimethylpyridine ligands occupying axial positions and the four bromo ligands in the equatorial plane. The crystal structure is a non-merohedral twin composed of two overlapping monoclinic domains, simulating an orthorhombic symmetry.

Addition compounds of titanium tetrachloride with aromatic nitrogen bases

Three reaction products of an addition reaction of titanium tetrachloride with aromatic nitrogen bases are presented. trans-Tetrachlorobis(3,4-dimethylpyridine)titanium, [TiCl 4 (C 7 H 9 N) 2 ], (I), and trans-tetrachlorobis(4-methylpyridine)titanium, [TiCl 4 (C 6 H 7 N) 2 ], (II), are both neutral complexes in which the central Ti atom is bonded to four Cl and two N atoms of two 3,4-dimethylpyridine and 4-methylpyridine ligands, respectively, resulting in a slightly distorted octahedral environment around the Ti atom. The methylpyridine ligands occupy axial positions, with the four chloro ligands in the equatorial plane. The ionic structure of bis(1-methylimidazolium) hexachlorotitanate(IV) pentachloro(N-methylimidazole-N 3 )titanate(IV), (C 4 H 7 N 2 ) 2 [TiCl 5 (C 4 H 6 N 2 )][TiCl 6 ] 0.5 , (III), consists of a pentachloro(N-methylimidazole-N 3 )titanate anion and half a [TiCl 6 ] 2- complex anion, in both of which the Ti atom appears in a nearly perfect octahedral coordination sphere with two N-methylimidazolium cations as counter-ions.

Catalytic olefin epoxidations with KHSO 5: the first report on manganese hemiporphyrazines as catalysts in oxygenation reactions

The oxidation of cyclooctene to cyclooctene epoxide by Oxone® (2KHSO 5·KHSO 4·K 2SO 4) as probe for evaluating the catalytic activity of a few manganese hemiporphyrazines has been studied. The oxidations have been carried out in an anhydrous two-phase system (solid Oxone®/solid catalyst/1,2-dichloroethane solution). In the absence of manganese hemiporphyrazine and/or of an aromatic nitrogen base only the slow stoichiometric epoxidation by KHSO 5 is observed. On the contrary, in the presence of pyridine and catalytic amount of manganese hemiporphyrazine (0.13–1% with respect to the organic substrate) either suspended in the reaction medium or adsorbed on a suitable polymer (silica gel or poly(vinylpyridine)) enhanced reaction rates are observed. The presence of an axial ligand in the coordination sphere of the catalyst appears to be essential for promoting the catalytic activity of the manganese complex. Moreover, the manganese hemiporphyrazine was subject to a colour change upon addition of the oxidant, thus suggesting the formation of a high valency oxo intermediate that oxidizes the olefin in a successive step. Under the experimental conditions adopted, epoxide yields up to 86% are obtained.

Intraionic, interligand proton transfer in collision-activated macrocyclic complex ions of nickel and copper

Intraionic, interligand proton transfer in collision-activated macrocyclic complex ions of nickel and copper has been observed. The macrocyclic ligand 1,4,8,11-tetraazacyclotetradecane (cyclam) or tris(2-aminoethyl)amine (tren) can transfer, after collision activation, one of its amino protons to an anion, but not to a solvent molecule, adducted to the complex; the neutral, protonated anion then leaves the complex. Proton transfer from the macrocycle to an adducted neutral, aromatic nitrogen base is also possible provided that the proton affinity of the base is sufficiently high. © 1998 John Wiley & Sons, Ltd.

Biomimetic Extradiol Cleavage of Catechols: Insights into the Enzyme Mechanism

Quantitative extradiol cleavage of a catechol derivative is achieved by exposure of complex 1 to O2 in the presence of AgBF4 and an aromatic nitrogen base. These results provide insight into how the regiochemistry of oxidative cleavage may be controlled by the metal centers of the catechol dioxygenases.

Sorption behavior of anthropogenic humic matter

Humic organic matter is a catchall term for persistent biopolymers occurring in soil, sediments, and water. It is known to influence the transport, the bioavailability, and the toxicity of organic and inorganic pollutants profoundly. In addition to natural pathways, humic organic matter may also be formed on the basis of organic compounds arising from human activities. Typical examples include dumps and dump-site leaching water. Our interest is focused on a pond for wastewater from a carbonization plant in the German state of Saxony-Anhalt [1]. The coal wastewaters were originally pink, and turned dark brown as a result of autooxidation processes of organic pollutants including phenols, aromatic nitrogen bases, and PAHs. We designated these dark polymers as anthropogenic humic matter. The anthropogenic humic and fulvic acids are deposited in the sediments at the bottom of the pond and are dissolved colloidally in the water. In contrast to the knowledge about natural organic matter, which was frequently been the subject of interest (see [2, 3] and literature cited therein), the knowledge relating to both the structure and the complexing behavior of anthropogenic humic matter is rather poor. Beyond basic scientific interest, the investigation of the complexing behavior of such anthropogenic humic matter with regard to pollutants may be helpful in developing remediation strategies for contaminated sites. Therefore, our investigations aim to characterize the structure of the humic matter by combining several chromatographic (HPLC, GPC, pyrolysis-GC/MS) and spectroscopic (FTIR, 1H-NMR, ICPMS, thermogravimetry-MS) methods. Furthermore, we ~ire interested in their sorption behavior towards selected organic pollutants in water [4]. Surprisingly, anthropogenic and natural humic materials do not differ significantly in their sorption behavior towards nonpolar hydrocarbons (cf. Fig. 1). Until now, the description of sorption phenomena by physicochemical parameters has been considered impractical. However, by modifying the Flory-Huggins theory we succeeded in obtaining a mathematical expression describing the connection between the lipophilicity of a solute i, expressed by its octanol/water partition coefficient Kow, and its sorption coefficient on organic matter KoM:

Lanthanide Chelates as a Tool in Nucleic Acid Chemistry

The potentiality of lanthanide chelates as photoluminescent markers and cleaving agents of nucleic acids is discussed, the main emphasis being on the chelates derived from aromatic nitrogen bases.

ChemInform Abstract: New “Proton Sponge” Compounds. Part 5. “Proton Sponges” and the Geometry of Hydrogen Bonds: Aromatic Nitrogen Bases with Exceptional Basicities

ChemInformVolume 19, Issue 42 Reviews ChemInform Abstract: New “Proton Sponge” Compounds. Part 5. “Proton Sponges” and the Geometry of Hydrogen Bonds: Aromatic Nitrogen Bases with Exceptional Basicities H. A. STAAB, H. A. STAAB Abt. Org. Chem., MPI med. Forsch., D-6900 HeidelbergSearch for more papers by this authorT. SAUPE, T. SAUPE Abt. Org. Chem., MPI med. Forsch., D-6900 HeidelbergSearch for more papers by this author H. A. STAAB, H. A. STAAB Abt. Org. Chem., MPI med. Forsch., D-6900 HeidelbergSearch for more papers by this authorT. SAUPE, T. SAUPE Abt. Org. Chem., MPI med. Forsch., D-6900 HeidelbergSearch for more papers by this author First published: October 18, 1988 https://doi.org/10.1002/chin.198842380Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume19, Issue42October 18, 1988 RelatedInformation

“Proton Sponges” and the Geometry of Hydrogen Bonds: Aromatic Nitrogen Bases with Exceptional Basicities

AbstractCertain aromatic diamines (the “proton sponges”) are found to have exceptionally high basicity constants: this is due to spatial interaction of the basic centers, which are in close proximity. The two factors which are most important in causing this effect are, on the one hand, the extreme steric strain in these systems and the destabilizing effect of the overlap of the nitrogen lone pairs of the neutral diamines and, on the other, the strong NċHċN hydrogen bonds which are formed on monoprotonation and which lead to a considerable relaxation of the steric strain. By the systematic variation of the structures of such aromatic diamines we have been able to study these effects as a function of steric factors, in particular of the geometry and the bond length of the NċHċN hydrogen bonds, by means of X‐ray structural analysis. The hydrophobic shielding of the basic centers and the NċHċN hydrogen bonds, which was characteristic of the “proton sponge” compounds studied previously, is indeed responsible for the extremely low rate of protonation and deprotonation of these compounds; however, it apparently has no influence on their high thermodynamic basicity. The recent synthesis and basicity determination of a new type of “proton sponge” with no hydrophobic shielding whatever show that not only very strong but also kinetically active bases are accessible using the “proton sponge” concept. Their unusual properties, which are discussed here as the result of steric interactions between two basic centers, provide examples of the fact that cooperative steric interactions of reactive structural elements can lead to properties which cannot be derived from an isolated consideration of the various functional groups. Such “proximity effects” are certainly of general importance in chemistry and biochemistry; the study of their structure‐function relationships is worthy of closer consideration.

Ionisation of methyl glycofuranosides in aqueous alkali metal hydroxides

Equilibrium constants for the ionisation of several methyl glycofuranosides have been determined spectrophotometrically in aqueous alkali metal hydroxides, using aromatic nitrogen bases as indicators for the equilibrium concentration of the hydroxide ion. The results obtained have been compared to the retention of the same compounds on a strong anion-exchange resin. The effects of the glycon configuration on the acidity of methyl glycofuranosides are discussed.

Addition compounds of phosphorus(V)chloride and aromatic nitrogen bases. Crystal structure and proton NMR and Raman spectra of pyrazine-phosphorus(V) chloride

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAddition compounds of phosphorus(V)chloride and aromatic nitrogen bases. Crystal structure and proton NMR and Raman spectra of pyrazine-phosphorus(V) chlorideB. N. Meyer, J. N. Ishley, A. V. Fratini, and H. C. KnachelCite this: Inorg. Chem. 1980, 19, 8, 2324–2327Publication Date (Print):August 1, 1980Publication History Published online1 May 2002Published inissue 1 August 1980https://doi.org/10.1021/ic50210a028RIGHTS & PERMISSIONSArticle Views57Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (497 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Specific ion-molecule interactions of imidazole and 1-methylimidazole in nitrobenzene

We have studied, by conductivity measurements, the formation of hydrogenbonded complexes between imidazoles and ions in the three systems triethylammonium picrate (Et3NHPic)+imidazole (Im), triethylammonium bromide (Et3NHBr)+Im, and Et3NHPic+1-methylimidazole (1-MeIm) in nitrobenzene in order to specify the importance of the two functions of the imidazole molecule, the tertiary nitrogen N3, and the imino group N1-H. While 1-MelIm forms only a single complex with the cationic species Et3NH+, imidazole enters into specific interactions as well with the cations through its basic site N3 and with the anions through its imino group. The complexing of the anions by imidazole, always weaker than the complexing of the cations, is more effective for Br− than for Pic−. Moreover, if imidazole is used as ligand, a 1:2 complex is formed between the cation and the imidazole, in which the second molecule of imidazole is bonded to the N-H group of the first by a hydrogen bond at the tertiary N atom. We did not observe a correlation between the equilibrium constants K 1 + for the complexing of the cation Et3NH+ by imidazole and pyridines (k 1 + for pyridine, 3–4 dimethylpyridine, and imidazole are 8, 24, and 165, respectively) and the pK a values of these ligands due to the fundamental difference in the structure of the imidazole and pyridine molecules, although both are considered as aromatic nitrogen bases.

Basenstabilisierte germylene

The reaction of benzothiazol-2-yltrimethylsilane with trichlorogermane yields 2-trimethylsilylbenzothiazoliumtrichlorogermanate (VI), from which the monomeric benzothiazoledichlorogermylene (IX) is obtained under elimination of trimethylchlorosilane. The constituttion of IX is confirmed by ′H NMR, IR and Mass spectra. The germaniumnitrogen bond in IX is shown to be very reactive: it is easily cleaved by boron trichloride and hydrogen chloride; exchange reactiion take place with aromatic nitrogen bases. A carbene analogous insertion into the carbonhalogen bond occurs with benzyl chloride. Die Umsetzung von Benzothiazol-2-yl-trimethylsilan mit Trichlorgerman führt zum 2-Trimethylsilylbenzothiazoliumtrichlorgermanat (VI), aus welchem unter Trimethylchlorisilan-Abspaltung das monomere Benzothiazoldichlorgermylen (IX) erhalten wird. Die Konstitution von IX wird durch ′H-NMR-, IR- und Massenspektren gesichert. Die GermaniumStickstoff-Bindung in IX erweist sich als sehr reaktiv: sie wird leicht durch Bortrichlorid bzw. Chlorwasserstoff gespalten; mit aromatischen Stickstoffbasen treten Austauschreaktionen ein. Eine carbenanaloge Einschiebung in die KohlenstoffHalogen-Bindung erfolgt bei Umsetzung mit Benzylchlorid.

Complex compounds of titanium(IV) oxide dichloride with some aromatic nitrogenous bases

Complex compounds of titanium(IV) oxide dichloride with some aromatic nitrogenous bases

Reaction between bromophenol blue and aromatic nitrogen bases in chlorobenzene studied with a laser temperature-jump apparatus. Part 2

Reaction between bromophenol blue and aromatic nitrogen bases in chlorobenzene studied with a laser temperature-jump apparatus. Part 2