Structure and magnetic properties of 2,4,6,8-tetra(<Emphasis Type="Italic">tert</Emphasis>-butyl)phenoxazin-1-one adducts with cobalt(II) salts

Complex formation reaction of redox-active 2,4,6,8-tetra(tert-butyl)phenoxazin-1-one with cobalt(II) chloride leading to the dimeric adduct has been studied. UV spectroscopy studies have revealed the equilibrium of the formed adduct with dissociated form of the complex in the acetonitrile solution. In the presence of ethylene glycol, the complex formation with cobalt(II) perchlorate has afforded the high-spin trimolecular adduct. Crystal structure of the obtained adducts has been studied by means of X-ray diffraction analysis.     

A novel diamine adduct of zinc bis(2-thenoyl-trifluoroacetonate) as a promising precursor for MOCVD of zinc oxide films

A novel diamine (N,N,N',N'-tetramethyletilendiamine) adduct of zinc bis(2-thenoyl-trifluoroacetonate) has been synthesized in a single-step reaction. Single-crystal X-ray diffraction studies of Zn(tta)(2).tmeda provide evidence of a mononuclear structure with a six-coordinated zinc ion. The thermal behavior of this adduct points to mass-transport properties suitable for its application to MOCVD processes. This novel compound has been successfully applied as a precursor for the deposition of ZnO films on (100) Si and quartz substrates. The good quality of the deposited films indicates that the adduct is a very attractive precursor for MOCVD applications.     

The chemistry of bent bonds : XLIV. Chemical evidence for the structure of the adduct obtained from quadricyclane and di-μ-chlorotetracarbonyldirhodium(I)

The structure of the adduct obtained from the reaction of tetracyclo [3.2.0.0^2,70^4,6] heptane (quadrdicyclane with di-gm-chlorotetracarbonyldirhodium(I) has been established on the basis of chemical evidence. The structure proposed by Cassar and Halpern was confirmed on the basis of the tricyclic alcohol isolated from the lithium aluminum deuteride reduction of the initially formed rhodium containing adduct.     

Identification of an "end-on" nickel-superoxo adduct, [Ni(tmc)(O2)]+

An "end-on" Ni2+-superoxo adduct has been prepared via two independent synthetic routes and its structure ascertained by spectroscopic and computational methods. The new structure type in nickel coordination chemistry is supported by resonance Raman and EPR spectroscopic features, the former displaying a high frequency nu (O-O) mode (1131 cm-1) consistent with significant superoxo character. The Ni2+-superoxo adduct oxidizes PPh3 to OPPh3 in quantitative yield.     

Determination of the structure of the adduct from guanosine and glycidaldehyde

The complete structure of the 1:1 adduct between guanosine and glycidaldehyde has been unequivocally determined by high-field NMR data and by synthesis of related model compounds.     

The first chemical synthesis of the core structure of the benzoylhydrazine-NAD adduct, a competitive inhibitor of the Mycobacterium tuberculosis enoyl reductase

[reaction: see text] An isoniazid-NAD adduct has been recently proposed as the ultimate metabolite responsible for the antituberculous activity of isoniazid (INH). Its structure results from binding of the isonicotinoyl radical at C4 position of the nicotinamide ring of NAD with further possible and debated cyclization to form a cyclic hemiamidal derivative. Replacing the pyridine cycle of INH in INH-NAD adduct by a phenyl cycle (BH-NAD adduct) was shown previously to still retain the activity. On these bases, the core structure (4-benzoyl-1,4-dihydronicotinamide ribonucleoside) of the BH-NAD adduct and a series of analogues have been synthesized by using 3,4-pyridinedicarboximide as starting material. Depending on the nature of the substituent (pyridine or aryl) and on the oxidized or the reduced state of the nicotinamide nucleus, they were found either in a cyclized hemiamidal or an opened form or were shown to exist in equilibrium under cyclized or opened forms. Although none of these compounds could significantly inhibit activity of the InhA or MabA reductases (two possible targets of isoniazid), they represent attractive targets to develop potential second-generation inhibitors, including the total chemical synthesis of the bioactive BH-NAD adduct.     

Synthesis and characterization of a bisadduct of La@C82

A bisadduct of La@C82 has been synthesized in a good yield by a Bingel-Hirsch reaction. Its structure has been well-defined by X-ray crystallographic analysis. A pair of enantiomers of the adduct form a dimer in the single crystal.     

Synthesis and chemical structure of natural rubber adduct with SO2 and study of the thermal stability

Natural rubber (NR, cis-1,4-polyisoprene) was reacted in solution with SO₂ at room temperature in different solvents (tetrahydrofuran, CHCl₃, CH₂Cl₂ and tetralin). The reaction product consisted of an adduct between NR and SO₂. The chemical structure of the adduct was studied by FT-IR spectroscopy, by thermogravimetry coupled with FT-IR (TGA-FT-IR), by differential thermal analysis (DTA) and by derivative thermogravimetry (DTG). The maximum SO₂ uptake from NR was 21% as determined by TGA. The TGA of the NR-SO₂ shows that the adduct decomposes in two steps initially releasing SO₂ at lower temperature and then decomposing at higher temperature like common NR. It is proposed that the chemical structure of the NR-SO₂ adduct consists of SO₂ molecules added to the double bonds of the isoprene units forming a sulfone derivative with three-membered rings known as thiirane-1,1-dioxide. On heating the thiirane ring decomposes releasing SO₂ in an extrusion reaction giving back the NR macromolecule.The possible potential applications of the NR-SO₂ adduct which is cheap and easy to prepare are outlined.     

Experimental and theoretical study of the atmospherically important O2-H2O complex

The theoretically predicted water-oxygen van der Waals adduct has been experimentally confirmed by vibrational characterization using matrix isolation spectroscopic studies at 10 K. Vibrational bands for asymmetric and symmetric OH-stretching for this adduct have been found at 3728 cm(-1) and 3639 cm(-1), respectively. Theoretical calculations performed with Gaussian 98 software at the MP2/6-311++G(2d,2p) level of theory support the alternative structure of the hydrated complex proposed by this study.     

Formation and structure of a novel enediyne-RNA base covalent adduct

The structure of an unusual covalent adduct formed by thiol-activated neocarzinostatin chromophore (NCS-chrom) and a RNA-DNA hybrid having an overhang of four unpaired residues at the 3'-end of the RNA strand has been elucidated by MS and NMR spectroscopic analyses. Unlike previously characterized adducts formed by NCS-chrom on the sugar residue of the DNA target, this adduct has been found to be on one of the uracil bases in the RNA overhang. Covalent linkage is between C-6 of the post-activated NCS-chrom and C-5 of the uracil. A novel mechanism involving adduction of the NCS-chrom C-6 radical, generated by 2-mercaptoethanol activation, to C-5 of the uracil at the U9 position of the RNA 11-mer, oxidation by dioxygen, reduction by the thiol, and subsequent dehydration is proposed for adduct formation.     

Fullerene-acene chemistry: diastereoselective synthesis of a cis,cis-tris[60]fullerene adduct of 6,8,15,17-tetraphenylheptacene

[structure: see text]. A one-pot, diastereoselective synthesis of a cis,cis-tris[60]fullerene adduct of 6,8,15,17-tetraphenylheptacene has been demonstrated starting from [60]fullerene and 5,7,9,14,16,18-hexahydro-6,8,15,17-tetraphenylheptacene.     

Structural characterization of N-acetyl-2-aminofluorene (AAF) adducts to guanine and deoxyguanosine via a molecular mechanics, semi-empirical, and density functional theory cascade

After hepatic activation, the carcinogen N-acetyl-2-aminofluorene (AAF) may form a major or a minor adduct with DNA, both in vivo and in vitro. The structure of the minor adduct has not been experimentally determined but is believed to be of importance due to its persistence in vivo. In the present study, four varieties of modified AAF have been studied computationally; AAF bonded to C8 of guanine or deoxyguanosine (major adduct), and AAF bonded to N² of guanine or deoxyguanosine (minor adduct). A computational cascade was employed to search for low-energy conformers of each molecule. Each adduct was subjected to a series of systematic searches of thousands of structures using molecular mechanics. After convergence with respect to the search parameters was obtained, the resulting conformers were then geometry optimized via the semi-empirical AM1 method. Subsets were then submitted to non-local Becke–Perdew density functional theory geometry optimization. The structures thus predicted of the guanine major adduct compare favorably with NMR and X-ray crystallographic data. The major adducts reveal an energetic preference for adoption of one of two orientations, with guanine or deoxyguanosine oriented either perpendicular to the fluorenyl ring moiety or approximately 45° with respect to the fluorenyl structure. Repulsion between the ribose sugar and acetyl group in deoxyguanosine disrupts the ‘ideal’ dihedral angles observed in the guanine adduct. Results for the N² structures similarly point toward two general conformer classes, one of which is characterized by hydrogen bonding between the acetyl O and the H bonded to N² of guanine, and the other by minimization of repulsion between the guanine structure and the acetyl group. In the case of deoxyguanosine, results differ somewhat from guanine due to an attractive interaction between the acetyl group and the ribose O5′. These results provide substantial motivation for further experimental work on AAF adduct complexes.     

Synthesis and spin-trapping behavior of 5-ChEPMPO, a cholesteryl ester analogue of the spin trap DEPMPO

[structure: see text] 5-(Cholesteryloxyethoxyphosphoryl)-5-methylpyrroline N-oxide (5-ChEPMPO), a DEPMPO analogue bearing a cholesterol group on the phosphorus atom, has been prepared and used to trap peroxyl-, alkoxyl-, thiyl-, and carbon-centered radicals in organic solvent. The important steric hindrance in 5-ChEPMPO does not affect the properties of 5-ChEPMPO in comparison to DEPMPO for the spin trapping of an enantiopure linoleic acid hydroperoxide. The 5-ChEPMPO-OOL spin adduct was observed by ESR and confirmed by ESI-MS/MS experiments. The relaxation terms of the 5-ChEPMPO-lipid peroxyl spin adduct were compared with those of other peroxyl spin adducts, and it was shown that the cholesteryl group has only a weak influence on the exchange rate between adduct conformers.     

A new approach toward the synthesis of C,D-cis coupled steroid and C,D-cis coupled d-homosteroid skeletons

A short and efficient procedure has been developed for the synthesis of C,D-cis coupled steroid and d-homo steroid skeletons. A Mukaiyama reaction with transfer of the silyl group of the starting silyl enol ether to the enol of the adduct followed by addition of vinyl magnesium bromide to the unprotected carbonyl group leads to adducts which can be cyclized with ZnBr₂. The synthesis of functionalized steroid skeletons in overall yields of about 50% in four steps can be achieved in this way.     

AN IMPROVED SYNTHETIC METHOD FOR DIPHENYL-1-PYRENYLPHOSPHINE AND THE PROPERTIES AND STRUCTURE OF ITS BORANE ADDUCT

An efficient synthetic method for diphenyl-1-pyrenylphosphine, DPPP, has been developed involving a low temperature Li-Br exchange reaction using the commercially available 1-bromopyrene. An estimate of the donor ability of this phosphine has been obtained by measuring the A₁υ (CO) band of the Ni(CO)₃L complex which was found to be 0.4 wave numbers lower than that from the PPh₃ complex indicating that DPPP is a slightly better donor than PPh₃. The BH₃ adduct of DPPP has been prepared and, as the situation for the oxide of DPPP, this adduct is fluorescent. It is estimated that the fluorescence intensity is about half that of DPPPO. An x-ray structure of this adduct has been obtained, and the bond lengths and angles appear to be in expected ranges.     

MgCl(2)·4((CH(3))(2)CHCH(2)OH): A new molecular adduct for the preparation of TiCl(x)/MgCl(2) catalyst for olefin polymerization

A new molecular adduct of MgCl(2) with isobutanol, namely MgCl(2)·4((CH(3))(2)CHCH(2)OH) (MgiBOH), has been prepared as a precursor to the supporting material for an olefin polymerization catalyst. The MgiBOH adduct and final titanated Ziegler-Natta catalysts have been thoroughly characterized by powder XRD, thermal analysis, Raman spectroscopy and solid-state NMR for structural and spectroscopy aspects. A peak observed at 712 cm(-1) in the Raman spectra of MgiBOH indicates the characteristic Mg-O(6) breathing mode and the formation of the adduct. The diffraction feature at 2θ = 7.8° (d = 11.223 ?) in the XRD confirms the adduct formation and the layered structure. The aim of the present article is to study how the insertion of a bulky isobutanol moiety affects the structural and electronic properties of the MgCl(2)·isobutanol molecular adduct. Indeed, the focus of the present study is to explore how the presence of isobutanol, in the initial molecular adduct, influences the final Z-N catalyst properties and its activity.     

Reaction of a stable aminoarylcarbene with 2-chloroacrylonitrile: dearomatizing cyclization rather than cyclopropanation

The reaction of a stable aminoarylcarbene with 2-chloroacrylonitrile is reported. The resulting 1/1 adduct has been spectroscopically and structurally characterized. The initial Michael addition is not followed by cyclopropane formation but by a dearomatizing cyclization affording an original bicyclic structure.     

Novel porphyrin-quinazoline conjugates via the Diels-Alder reaction

Novel derivatives of meso-tetraphenylporphyrin with appended quinazoline moieties were synthesized, via the Diels-Alder reaction, between a 4-(porphyrinyl)pyrimidine ortho-quinodimethane and 1,4-benzoquinone, 1,4-naphthoquinone and N-(p-nitrophenyl)maleimide. The structure of one bis adduct was established by X-ray crystallography and mass spectrometry. We have unequivocally confirmed that the 2:1 adducts obtained from the reaction of pyrimidine-fused 3-sulfolenes with N-arylmaleimides have an open-chain structure and not a cyclooctapyrimidine structure, as previously published.     

Sodium adduct formation efficiency in ESI source

Formation of sodium adducts in electrospray (ESI) has been known for long time, but has not been used extensively in practice, and several important aspects of Na⁺ adduct formation in ESI source have been almost unexplored: the ionization efficiency of different molecules via Na⁺ adduct formation, its dependence on molecular structure and Na⁺ ion concentration in solution, fragmentation behaviour of the adducts as well as the ruggedness (a prerequisite for wider practical use) of ionization via Na⁺ adduct formation. In this work, we have developed a parameter describing sodium adducts formation efficiency (SAFE) of neutral molecules and have built a SAFE scale that ranges for over four orders of magnitude and contains 19 compounds. In general, oxygen bases have higher efficiency of Na⁺ adducts formation than nitrogen bases because of the higher partial negative charge on oxygen atoms and competition from protonation in the case of nitrogen bases. Chelating ability strongly increases the Na⁺ adduct formation efficiency. We show that not only protonation but also Na⁺ adduct formation is a quantitative and reproducible process if relative measurements are performed. Copyright © 2013 John Wiley & Sons, Ltd.