Contribution to the Protonation of a Calix[4]arene: DFT Calculated Structure of Protonated <Emphasis Type="Italic">p-tert</Emphasis>-Butylcalix[4]arenetetrakis(<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diethylacetamide)

Summary. By using DFT calculations, the most probable structure of the p-tert-butylcalix[4]arenetetrakis(N,N-diethylacetamide) · H₃O⁺ complex species was derived. In this complex, the hydroxonium ion H₃O⁺ is predominantly bound by strong hydrogen bonds to three phenoxy oxygens of the ligand and partly to the remaining phenoxy oxygen atom by two somewhat weaker hydrogen bonds. Besides, the H₃O⁺ cation is also bound to two carbonyl oxygens of the mentioned ligand by further two weaker hydrogen bonds.     

<Emphasis Type="Italic">Raman</Emphasis> Spectroscopy and <Emphasis Type="Italic">Ab-Initio</Emphasis> Model Calculations on Ionic Liquids

Summary. A review of the recent developments in the study and understanding of room temperature ionic liquids are given. An intimate picture of how and why these liquids are not crystals at ambient conditions is attempted, based on evidence from crystallographical results combined with vibrational spectroscopy and ab-initio molecular orbital calculations. A discussion is given, based mainly on some recent FT-Raman spectroscopic results on the model ionic liquid system of 1-butyl-3-methylimidazolium ([C₄ mim][X]) salts. The rotational isomerism of the [C₄ mim]⁺ cation is described: the presence of anti and gauche conformers that has been elucidated in remarkable papers by Hamaguchi et al. Such presence of a conformational equilibrium seems to be a general feature of the room temperature liquids. Then the “localized structure features” that apparently exist in ionic liquids are described. It is hoped that the structural resolving power of Raman spectroscopy will be appreciated by the reader. It is of remarkable use on crystals of known different conformations and on the corresponding liquids, especially in combination with modern quantum mechanics calculations. It is hoped that these interdisciplinary methods will be applied to many more systems in the future. A few examples will be discussed.     

Chromium tricarbonyl complexes of 1,2-and 1,4-dihydronaphthalene. Synthesis and metal-induced thermal isomerizations involving <Emphasis Type="Italic">endo</Emphasis>-hydrogen atoms

Reactions of 1,4-dihydronaphthalene with (NH₃)₃Cr(CO)₃ or Py₃Cr(CO)₃ in the presence of BF₃·Et₂O afford a mixture of isomeric η⁶-chromium tricarbonyl complexes of 1,4-and 1,2-dihydronaphthalene in the ratio 63: 37 and 55: 45, respectively. The complexes were separated by chromatography. At 130 °C in different solvents these complexes undergo thermally induced reversible rearrangement studied by the ²H NMR method for the deuterated derivatives. Analysis of the ²H NMR spectra showed that the isomerization occurs due to metal-induced 1,5-shifts of the endo-hydrogen atoms. The isomerization mechanism was studied by quantum chemical DFT calculations. The calculations showed that the process occurs with the maximum activation barrier (33.2 kcal mol⁻¹) through a series of agostic and hydride intermediates and transition states in which the chromium atom stereospecifically activates the endo-hydrogen atoms only. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 235–246, February, 2007.     

Study on Inclusion Complex Formation of <Emphasis Type="Italic">m</Emphasis>-Aminobenzoic Acid with Native and Substituted <Emphasis Type="Italic">β</Emphasis>-Cyclodextrins

The complex formation of native and substituted β-cyclodextrins with m-aminobenzoic acid in water was characterized by calorimetry, ¹H NMR and UV spectroscopic studies. These studies showed that β-, hydroxypropyl-β- and methyl-β-cyclodextrins form 1:1 inclusion complexes with m-aminobenzoic acid. The thermodynamic properties of complex formation (K,Δ_c G ^o,Δ_c H ^o,Δ_c S ^o) were calculated. It was found that the processes of complexation are mainly favorable entropically. Introduction of hydroxypropyl- and methyl-substituents into the β-CD molecule results in negligible enhancement of stability of the complexes formed. The structure of these substituents has no influence on the stability constant values. The insertion of the carboxylic group of m-aminobenzoic acid into the cyclodextrin cavity was confirmed by ¹H NMR data.     

Microstructure of 1,2-<Emphasis Type="Italic">trans</Emphasis>-and 1,4-<Emphasis Type="Italic">trans</Emphasis>-poly(penta-1,3-dienes)

Microstructures of 1,2-trans-and 1,4-trans-poly(penta-1,3-dienes) synthesized using different catalysts were determined by high resolution ¹³C NMR spectroscopy. The content of dyad combinations of the 1,4-and 1,2-structures was quantitatively determined in hydrogenated poly(penta-1,3-dienes) from the ratio of intensities of the characteristic signals of the carbon atoms of the methylene groups in the ¹³C NMR spectra. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1113–1118, June, 2007.     

Reactions of <Emphasis Type="Italic">N</Emphasis>-alkyl- and <Emphasis Type="Italic">N</Emphasis>-aryltrihalogenoacetamides with phosphorus pentachloride

In the study of reactions of N-alkyl- and N-aryltrihalogenoacetamides with PCl₅, it was demonstrated for the first time that 3-alkyl(aryl)-2,2,2,4 tetrachloro-4-trihalomethyl-1,3,2-λ⁵-oxazaphosphetanes are intermediates in the synthesis of trihaloacetimidoyl chlorides. According to quantum-chemical calculations, acyclic N-tetrachlorophosphoranes, which are the primary products in the reactions of trihaloacetamides with PCl⁵, undergo rapid cyclization into the corresponding phosphorates and subsequent 1,3-chlorotropic migration gives rise to oxazaphosphetanes with the five-coordinate P atom.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 739-744, March, 2005.     

Synthesis of 2,3-<Emphasis Type="Italic">cis</Emphasis> Stereomeric Emetamines <Emphasis Type="Italic">via Reissert</Emphasis> Compounds

Summary. Alkylation of Reissert compounds with certain benzoquinolizinone derivatives followed by hydrolytic cleavage afforded the core of the title compounds in a two step sequence. Finally, the lactam intermediates were reduced with DIBAH giving the target compounds, the structural and stereochemical assignments of which were achieved by ¹³C NMR spectroscopy. Part of PhD thesis, LMU München, D     

Norditerpene Alkaloids from <Emphasis Type="Italic">Delphinium cuneatum</Emphasis>

A mixture of two new norditerpene alkaloids consisting of two regioisomers was isolated from the total alkaloids of Delphinium cuneatum roots. Their structures were proposed as 16-demethoxydelavaine (2a and b) on the basis of PMR, ¹³C NMR, IR, and mass spectra. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 467–468, September–October, 2005.     

Hydrolyzed Tannin from <Emphasis Type="Italic">Euphorbia glareosa</Emphasis> Leaves

Hydrolyzed tannin (I), the structure of which was established using chemical investigations and UV, IR, PMR and ¹³C NMR spectra, was isolated from Euphorbia glareosa leaves.__________Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 250–251, May–June, 2005.     

Proton affinities of fluoro derivatives of benzene,toluene, and<Emphasis Type="Italic">m</Emphasis>-xylene from<Emphasis Type="Italic">ab initio</Emphasis> MP2 calculations

The proton affinity (PA) energies of fluoro derivatives of benzene, toluene, andm-xylene were obtained fromab initio MP2-FC/6-31G^* calculations and compared with experimental results. Protonated forms of the molecules, resulting from different ways of proton addition, were studied. Relative concentrations of isomeric arenonium ions were calculated and compared with the results of NMR studies on arenonium ions in solutions. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1847–1849, November, 2000.     

Order-<Emphasis Type="Italic">N</Emphasis> and embedded-cluster first-principles DFT calculations using SIESTA/Mosaico

Order-N and embedded-cluster first-principles DFT calculations have been performed with the Mosaico method for energy optimization (Seijo and Barandiarán in J Chem Phys 121:6698, 2004) for the first time. The Hamiltonian matrix elements have been computed with the SIESTA code. The order-N behavior of the method in DFT calculations was shown in total energy calculations performed on bulk silicon using supercells up to Si₈₀₀₀. The sizes of the orbital-specific-basis-sets needed for precise calculations have been explored in demanding (bulk silicon) and favorable (water clusters) cases for a method based on the calculation of localized molecular orbitals. Embedded-cluster calculations, which are much faster than full-system calculations, have been performed on an Si-vacancy of bulk silicon and on a water cluster with a displacing water molecule. The feasiability of calculations of this type with Mosaico has been demonstrated. The sizes of the variationally free, active clusters which are needed for an agreement with full-system calculations have been explored and result to be reasonably small. Contribution to the Serafin Fraga Memorial Issue.     

Facile synthesis and biological evaluation of novel fluorine-containing <Emphasis Type="Italic">N</Emphasis>-nitro-<Emphasis Type="Italic">N</Emphasis>′-substituted phenylurea

Twenty-two novel N-nitro-N′-substituted phenyl-N-(2,6-dibromo-4-fluorophenyl)urea derivatives were designed and synthesized via a simple and convenient BTC ‘one-pot’ procedure using DMAP as the catalyst. The structures of all newly synthesized compounds were confirmed by IR, ¹H NMR, and elemental analysis, and a part has been identified by ¹³C NMR. The preliminary bioassay indicates that the target compounds possesses moderate herbicidal activity against Sorghum sudanense. However, some of the title compounds presented high plant growth regulating activity against rape.     

DFT-calculated structure of protonated tetraphenyl <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">tert</Emphasis>-butylcalix[4]arene tetraketone

Using DFT calculations, two of the most probable structures (A, B) of the tetraphenyl p-tert-butylcalix[4]arene tetraketone·H₃O⁺ cationic complex species were derived. The hydroxonium ion H₃O⁺, placed in the coordination cavity formed by the calix[4]arene lower-rim groups, is bound by strong hydrogen bonds to the phenoxy oxygen atoms of the calix[4]arene ligand (structures A, B) and also to one carbonyl oxygen (structure B). Correspondence: Emanuel Makrlík, Faculty of Applied Sciences, University of West Bohemia, Pilsen, Czech Republic.     

Diterpenoid acids from <Emphasis Type="Italic">Pinus koraiensis</Emphasis>

Two new diterpenoid acids, pinusenocarp (1) and pinusenoid (2), were isolated from the pine cone of Pinus koraiensis. All the compounds were characterized on the basis of spectral analysis, viz. ¹H NMR, ¹³C NMR, IR, UV, ESI-MS, and elemental analysis.     

Structure of cyclochivinoside C from <Emphasis Type="Italic">Astragalus chivensis</Emphasis>

The new cycloartane glycoside cyclochivinoside C, 24S-cycloartan-3β,6α,16β,24,25-pentaol 3,16-di-O-β-D-glucopyranoside, was isolated from the aerial part of Astragalus chivensis. The structures of the isolated compounds were established by chemical transformations and PMR and ¹³C NMR spectra. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 460–462, September–October, 2007.     

A new method for modification of <Emphasis Type="Italic">CN</Emphasis>-palladacycles

The reaction of benzylaminate CN-palladacycle with chlorine dioxide was found to produce the 3-chlorine-substituted analog through the formal insertion of chlorine into the Pd-C bond followed by repeated ortho-palladation of the modified ligand. The structure of the resulting dimeric complex was confirmed by X-ray diffraction study of its triphenylphosphine derivative. A comparison of the ¹H NMR spectra of the phosphine adducts of the starting and chlorinated complexes shows high conformational stability of the new palladacycle. Advantages of the new route to conformational stabilization of labile palladacycles are discussed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2010–2019, September, 2005. Dedicated to Academician N. S. Zefirov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2010–2019, September, 2005.     

UV/Vis Spectroscopic Properties of <Emphasis Type="Italic">N</Emphasis>-(2′-Hydroxy-4′-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethyl-aminobenzylidene)-4-nitroaniline in Various Solvents and Solid Environments

Summary.  N-(2′-Hydroxy-4′-N,N-dimethylaminobenzylidene)-4-nitroaniline [HDBN] has been used as a model for investigating intra- and intermolecular D–A (donor–acceptor) interactions in various environments by means of UV/Vis spectroscopy. UV/Vis spectra of HDBN have been measured in various solvents, ethanolic solutions of different pH, adsorbed on silica, and in the solid state. A bathochromic shift of ν_max is observed with increasing the dipolarity/polarizability and HBD (hydrogen bond donor) capacity of the solvent, which is described by means of a multiple LSE (linear solvation energy) relationship in terms of the empirical Kamlet-Taft solvent polarity parameters. The adsorption of HDBN on Aerosil^? 300-silica particles in non-HBA (hydrogen bond acceptor) solvents is explained in the same sense. Mobile protons and sol–gel entrapping cause a hypsochromic shift due to protonation of the lone electron pair of the 4′-N,N-dimethylamino group. Hydroxide ions attack the 2′-hydroxy group which causes a bathochromic shift. A strong intramolecular hydrogen bond between the 2′-hydroxyl hydrogen and the imine nitrogen atom is present in the solid-state structure causing an unprecedented bathochromic shift. Corresponding author. E-mail: stefan.spange@chemie.tu-chemnitz.de Received July 8, 2002; accepted (revised) September 30, 2002     

Electrochemical thiocyanation of dodecahydro-7,8-dicarba-<Emphasis Type="Italic">nido</Emphasis>-undecaborate and 7,8-dimethyldecahydro-7,8-dicarba-<Emphasis Type="Italic">nido</Emphasis>-undecaborate monoanions

Electrochemical thiocyanation of the dodecahydro-7,8-dicarba-nido-undecaborate and 7,8-dimethyldecahydro-7,8-dicarba-nido-undecaborate monoanions afforded thiocyanate derivatives of these compounds, which were isolated as alkylammonium salts. The structures of the synthesized compounds were determined by the data from IR, ¹H and ¹¹B NMR, and ¹¹B-¹¹B NMR COSY spectroscopy. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1553–1556, July, 2005.     

Synthesis and characterization of novel (<Emphasis Type="Italic">E</Emphasis>,<Emphasis Type="Italic">E</Emphasis>)-dioxime and its mono- and polynuclear metal complexes containing azacrown moieties

The novel (E,E)-dioxime,7,8-bis(hydroxyimino)-1,14-bis(monoaza[8]crown-6)-benzo[f]-4,11-dioxa-1,14-diazadecane[7,8-g]quinoxaline (H₂L), has been synthesized by the reaction of 6,7-diamino-1,12-bis(monoaza[18]crown-6)benzo[f]-4,9-dioxa-1,12-diazadecane (4) which has been prepared by the reduction of 6,7-dinitro-1,12-bis(mono-aza[18]crown-6)benzo[f]-4,9-dioxa-1,12-diazdecane (3) and cyanogendi-N-oxide. Mononuclear Ni^II and Cu^II complexes of H₂L have a metal:ligand ratio of 1:2 and the ligand coordinates through two hydroxyimino nitrogen atoms, as do most of the (E,E)-dioximes. The hydrogen-bridged Ni^II complex was converted into its BF ₂ ⁺ capped anologue by the reaction with BF₃ · Et₂O. The reaction of the Cu^II complex with 2,2′-dipyridyl as an end-cap ligand gave the homotrinuclear complex. Structures for the ligand and its complexes are proposed in accordance with elemental analysis, magnetic susceptibility measurements, ¹H, ¹³C-n.m.r, IR and MS spectral data.     

Mechanism of OH radical-induced oxidation of <Emphasis Type="Italic">p</Emphasis>-cresol to <Emphasis Type="Italic">p</Emphasis>-methylphenoxyl radical

The OH radical-induced oxidation of p-cresol to p-methylphenoxyl radical was studied in aqueous solution in a wide pH range by means of pulse radiolysis combined with optical spectroscopy. OH-adduct cyclohexadienyl type radicals were identified as intermediates of the reaction. In the acidic pH range the first-order rate coefficient of phenoxyl radical formation was found linearly dependent on the H₃O⁺ concentration yielding a bimolecular rate coefficient of 1.8 × 10⁸ mol^–1 dm³ s^–1. In the alkaline range a linear dependence was found on the OH^– concentration with rate coefficient of 4.9 × 10¹⁰ mol^–1 dm³ s^–1. These findings were interpreted in terms of acid-base catalysis of the H₂O elimination from the OH-adduct. With the time resolution applied, 30 ns, the radical cation p-CH₃C₆H₄OH^+. was not observed as intermediate.