bluuebunny/crossref_metadata_2025 huggingface dataset:
NMR spectroscopy and molecular‐mechanics calculations in supramolecular chemistry
Authors: Schneider Hans‐Jörg
Published: September 2010

The role of NMR spectroscopy techniques, with emphasis on shielding variations and nuclear Overhauser effects for structural elucidation of host‐guest compounds in solution, is discussed on the basis of selected cyclophane and cyclodextrin associations. Force‐field calculations are shown to be an important prerequisite for such studies, and for evaluation of possible binding modes and mechanisms between host and guest. Present limitations of both computational and NMR spectroscopic methods are pointed out with respect to accurate conformational analyses and to the prediction of association constants.
Dicopper (I) trefoil knots: Demetallation kinetic studies and molecular structures
Authors: Albrecht‐Gary A. M. , Meyer M. , Dietrich‐Buchecker C. O. , Sauvage J. P. , Guilhem J. , Pascard C.
Published: September 2010

X‐ray structures of knotted dicopper(I) complexes and demetallation kinetic studies of trefoil knots and related face‐to‐face complexes are presented and discussed.
A new approach to controlling catenated structures
Authors: Amabilino David B. , Stoddart J. Fraser
Published: September 2010

A [2]catenane comprised of a macrocyclic polyether, analagous to bisparaphenylene 34‐crown‐10 ‐ but incorporating catechol units in its tetraethyleneglycol chains – and the cyclobis(paraquat‐p‐phenylene) tetracation, has been self‐assembled and shown to exist in solution as a non‐equimolar mixture of translational isomers.
Use of (chloromethyl) dimethylphenylsilane in sugar chemistry. Stereo‐controlled approach to destomic acid and 1‐deoxy‐nojirimycin
Authors: Smid P. , Schipper F. J. M. , Broxterman H. J. G. , Boons G. J. P. H. , van der Marel G. A. , van Boom J. H.
Published: September 2010

Addition of [(phenyldimethylsilyl)methyl]magnesium chloride (1d) to 1,2:3,4‐di‐O‐iso‐propylidene‐α‐D‐galacto‐hexodialdo‐1,5‐pyranose, and further processing of the resulting anti‐α‐hydroxy‐silane adduct by a well‐established sequence of reactions, gives a precursor to destomic acid 2. Similarly, addition of the Grignard reagent 1d to 3‐O‐benzyl‐1,2‐O‐isopropylidene‐α‐D‐xylo‐pentodialdo‐1,4‐furanose proceeds with a high degree of stereoselectivity to give, after further elaboration of the syn‐α‐hydroxy‐silane adduct, the antibiotic 1‐deoxynojirimycin.
Mechanistic study of decomposition of cyclohexyl hydroperoxide catalysed by manganese(III) tetraarylporphyrins
Authors: Hansen Carola B. , Mul Guido , Tabor Roland B. J. , Drenth Wiendelt
Published: September 2010

The reaction between manganese(III) tetraarylporphyrins and cyclohexyl hydroperoxide has been investigated. Since pyridine increases the decomposition rate of cyclohexyl hydroperoxide, all experiments were performed in the presence of pyridine. Experiments with 2,6‐di‐tert‐butylpyridine showed that pyridine increases the reaction rate by ligation to the manganese porphyrin as well as by acting as a base. Cyclohexyl hydroperoxide is decomposed into cyclohexanol and cyclohexanone. Since neither 3,3,5,5‐tetramethylcyclohexanol nor cyclohexanol‐d12 are oxidized under these reaction conditions, cyclohexanone is formed directly from the peroxide and not by oxidation of the alcohol. During the reaction, a manganese(V)oxo porphyrin complex is formed. This complex may react with (i) the peroxide under formation of cyclohexanol and molecular oxygen, (ii) the solvent cyclohexane, or (iii) manganese(III) porphyrin. The latter reaction leads to destruction of the catalyst. This destruction is prevented by introduction of bulky groups on the ortho positions of the phenyl. The scission of the hydroperoxide is suggested to be heterolytic. It is also base‐catalysed. The rate‐determining step in the decomposition of cyclohexyl hydroperoxide is scission of the oxygenoxygen bond of the manganese peroxyl porphyrin complex. A mechanism in line with the kinetic data is proposed.
Hydrolysis of 4‐nitrophenyl esters of picolinic acid and N‐protected amino acids by metalloenzyme models in vesicular assemblies
Authors: Weijnen John G. J. , Koudijs Arie , Tap Paul G. J. A. , Engbersen Johan F. J.
Published: September 2010

Mixed vesicles of N‐dodecyl‐N,N‐dimethyl‐1‐octadecanaminium bromide (C18C12) and functionalised 1,10‐phenanthroline ligands having two long alkyl chains and a nucleophilic hydroxymethyl (1), (S)‐2‐(hydroxymethyl)pyrrolidine (2) or ephedrine group (3, 4) at the α position, were investigated for their catalytic activities and enantioselectivities in the hydrolysis of 4‐nitrophenyl esters of picolinic acid (PNPP) and N‐protected leucine [D(L)‐Z‐Leu‐PNP and D(L)‐C12‐Lcu‐PNP] in the presence of metal ions. The ZnII complex of the chiral ligand 2 in C18C12 vesicles exhibits the highest activity toward PNPP. The highest enantioselectivity in the stereoselective hydrolysis of D(L)‐C12‐Lcu‐PNP (kLa,obs/kDa,obs = 3.6) was attained with the metallocatalyst 2‐ZnII, whereas with 2‐CuII an inversion of stereoselectivity was observed (kLa,obs/kDa,obs = 0.68). The composition of the matrix in which catalyst and substrate are concentrated, affects the rate of hydrolysis but not the enantioselectivity. The rate of hydrolysis and the stereoselectivity are discussed in terms of the structure of the ligand, coordination geometry of the metal ion and the position of the metalloamphiphile in the surfactant aggregate.
Reactions of thebaine and 6‐demethoxythebaine anions with carbonyl compounds; novel Diels‐Alder adducts from 5β‐substituted thebaines (chemistry of opium alkaloids, Part XXXIX)
Authors: Woudenberg R. H. , Lie T. S. , Maat L.
Published: September 2010

Reaction of the anions of thebaine and 6‐demethoxythebaine with 2‐propanone gave the 5β‐(dimethylmethanol)‐substituted analogues 3 and 5 and the isomeric C‐7‐substituted morphinan‐5,8‐dienes 4, 6 and 7, respectively. No reaction took place with methanal. Therefore, thebaine‐5β‐methanol (10) was prepared by reacting the anion with alkyl chloroformate followed by lithium aluminium hydride reduction. Diels‐Alder reaction of diene 10 with ethyl acrylate gave the 6α,14α‐ethenoisomorphinan 11. Of the morphinan‐6,8‐dienes 3 and 5, only diene 5 showed a reaction, namely rearrangement followed by cycloaddition with ethyl acrylate, yielding three adducts. The structure of the major adduct 13 was elucidated using 1D‐ and 2D‐NMR techniques and revealed an aporphine‐like structure. Furthermore, the conversion of 11 into a new etorphine analogue 16 was accomplished by treatment with methylmagnesium bromide followed by 3‐O‐demethylation.
Synthesis of neopine and its 5β‐ and 7‐substituted derivatives (chemistry of opium alkaloids, part XL≠)
Authors: Meuzelaar G. J. , Woudenberg R. H. , Sinnema A. , Maat L.
Published: September 2010

Heating 14β‐bromocodeine (3) with methanol and triethylamine yielded 6α, 7α‐epoxy‐6‐deoxyneopine (5). The epoxide 5 was reduced to neopine (7) with lithium aluminium hydride, whereas reaction of 5 with sodium methoxide gave 7β‐methoxyneopine (9). Similar reactions were performed with 14β‐bromo‐5β‐methylcodeine (4), yielding the corresponding 5β‐methyl derivatives 6, 8 and 10. Acetylation of 3 and 4 gave 6α‐O‐acetyl‐14β‐bromocodeine (11) and its 5β‐methyl analogue 12, respectively, from which the ortho esters 13 and 14 were obtained after treatment with methanol. Acid hydrolysis of 13 or, better, solvolysis of 11 in water yielded a mixture of 6α‐O‐acetyl‐7α‐hydroxyneopine (15) and 7α‐acetoxyneopine (17). Under the same conditions 12 and 14 gave the 5β‐methyl analogues 16 and 18.
Regioselective introduction of functional groups in α‐diimines by means of dialkylzinc compounds. Synthesis of functionalized 2‐ and 3‐pyrrolidinone derivatives
Authors: Wissing Elmo , Kleijn Henk , Boersma Jaap , van Koten Gerard
Published: September 2010

Alkylation of the 1,4‐diaza‐1,3‐butadiene t‐BuN=CH‐CH=N t‐Bu (t‐BuDAB) by functionally substituted diorganozinc compounds Zn[(CHR1XCH2)nXR2]2 (n = 1–3, R1 = H, Me, XR2 = OMe, OBn, SEt, NMe2, COOEt) occurs regioselectively. Alkylation occurs at the nitrogen atom of the N=C‐C=N skeleton of t‐BuDAB when primary diorganozinc compounds are used (R1 = H), but at the carbon atom when secondary and benzylic diorganozinc compounds are employed. The functional groups in the diorganozinc reagents proved to be important for the alkylation reaction only in the case of Zn[(CH2)3NMe2]2 (7) and Zn(C6H4CH2NMe2−2)2 (16), in which the strongly coordinating NMe2 groups give either a decrease of the alkylation rate (7), or no reactivity at all (16). When t‐BuDAB is reacted with Zn[(CH2)2COOEt]2 (10) alone, a 3‐pyrrolidinone (10c) is formed, whereas the same reaction with a mixture of 10 and ClZn(CH2)2COOEt affords a 2‐pyrrolidinone (10b). The reactions involve a two‐step process involving prior regioselective introduction of the alkyl group either at the N or C atom of an imine unit followed by an intramolecular nucleophilic substitution leading to 10b or 10c, respectively. The molecular structure of 10c shows the functionalized heterocycle to be part of a conjugated enamine system.
Synthesis of carba‐strigol analogues
Authors: Kishimba M. A. , Zwanenburg B.
Published: September 2010

Carba analogues 1, 14, 15 and 16 of Strigol were synthesised in which the vinyl ether oxygen is replaced by methylene. Compound 1 was prepared by the Wittig reaction of ylid 2 with aldehyde 3. Compounds 14, 15 and 16, for which this approach failed, were prepared by reaction of aldehyde 20 with lactones 17, 18 and 19, respectively, using the method of Tanaka et al.35,36, or with phosphonates 32 and 33, in a Wittig‐Horner reaction. Subsequent oxidative elimination of the thioether moiety gave the desired products.
Peptides from chiral Cα,α‐disubstituted glycines. Synthesis and conformational analysis of homochiral (αMe) Leu / Ala model peptides
Authors: Kamphuis J. , Boesten W. H. J. , Schoemaker H. E. , Aubry A. , Bayeul D. , Dautant A. , Pantano M. , Formaggio F. , Crisma M. , Bonora G. M. , Toniolo C.
Published: September 2010

Homochiral (αMe)Leu/Ala and Leu/Ala model peptides were synthesized by solution methods and fully characterized. A solution conformational analysis of the tripeptides was carried out using FT‐IR absorption and 1H NMR. The crystal‐state structure of Z‐D‐(αMe)Leu‐(D‐Ala)2‐OMe monohydrate was resolved by X‐ray diffraction. The results obtained support the conclusion that the tendency of the non‐coded (αMe)Leu residue to fold into β‐bends and helical structures is markedly higher than that of its unmethylated protein counterpart (Leu).
An expeditious route to methylphosphonate analogues of DNA
Authors: Kuyl‐Yeheskiely E. , Meeuwenoord N. J. , van der Marel G. A. , van Boom J. H.
Published: September 2010

Protection of the exocyclic amino groups of both nucleobases adenine and guanine with the N,N‐dimethylformamidine and cytosine with the isobutyryl group presents a convenient and economical N‐protective‐group‐strategy for the solid‐phase synthesis of DNA fragments containing methylphosphonate linkages at predetermined locations. Thus, the post‐synthesis removal of the N‐protective groups with hydrazine hydrate (16 h at 20°C) afforded immobilized fragments, which were then cleaved from the solid support and deprotected at the phosphorus by treatment with ammonia in methanol (2 h at 20°C) to yield high‐quality products.
Synthesis of six novel retinals and their interaction with bacterioopsin
Authors: Groesbeek M. , Kirillova Y. G. , Boeff R. , Lugtenburg J.
Published: September 2010

The synthesis and spectroscopic characterization of six novel chemically modified retinals, is described, prepared by a single strategy: all‐E‐10,12‐ethanoretinal (1), all‐E‐10,12‐propanoretinal (2), all‐E‐10,12‐ethano‐20‐norretinal (3), all‐E‐20‐nor‐10,12‐propanoretinal (4), all‐E‐12,14‐ethano‐20‐norretinal (5), and all‐E‐20‐nor‐12,14‐propanoretinal (6). For this strategy we developed two novel synthons, 2‐(diethoxyphosphinyl) hexanedinitrile and 2‐(diethoxyphosphinyl) heptanedinitrile which were prepared in their deprotonated form from hexanedinitrile and heptanedinitrile. Bacterioopsin was incubated with each of 1 to 6. Only 1 and 3 form bacteriorhodopsin analogues (bR‐1 and bR‐3). bR‐1 shows light‐dark adaptation and an approx. 50% light‐driven proton‐pump action. bR‐3 does not show light‐dark adaptation or proton‐pump action. It is also shown that the protein can efficiently accommodate retinal with the 10,12‐ethano group whereas the corresponding retinal with the 10,12‐propano group does not fit in the binding site.
Solution structures of hydrido‐rhodium diphosphite hydroformylation catalysts
Authors: van Leeuwen Piet W. N. M. , Buisman Godfried J. H. , van Rooy Annemiek , Kamer Paul C. J.
Published: September 2010

The NMR spectroscopy data for five hydroformylation catalysts RhH(CO)2(P‐P) (P‐P = diphosphite bidentate ligand) are reported and interpreted in terms of equatorial and axial coordination of the phosphorus and carbon monoxide ligands in a trigonal bipyramidal structure.
Conformational analysis of all‐E‐retinal, all‐E‐8,16‐methanoretinal, (1S)‐all‐E‐8,16‐methano‐18‐norretinal, and all‐E‐17,18‐dinor‐8,16‐methanoretinal by means of NMR spectroscopy and molecular dynamics
Authors: Ippel J.H. , Spijker‐Assink M.B. , Groesbeek M. , van der Steen R. , Altona C. , Lugtenburg J.
Published: September 2010

The conformations of all‐E‐retinal (1), (1S)‐all‐E‐8,16‐methano‐18‐norretinal [(1S)‐2], all‐E‐8,16‐methanoretinal (3) and all‐E‐17,18‐dinor‐8,16‐methanoretinal (4) in solution were studied by 1H‐NMR spectroscopy and molecular‐mechanics and molecular‐dynamics simulations. The 1H‐NMR spectrum of 1 is characterized by fast inversion of two half‐chair rings and by a skewed 6‐s‐cis geometry of the polyene chain. Molecular‐dynamics simulations at 1000K on 1 show the existence of two, dynamically stable, skewed 6‐s‐cis conformers (torsion angle C5‐C6‐C7‐C8: 84° and —83°), separated by a 6‐s‐trans transition state. The conformationally locked structures of 2, 3 and 4 have similar conformations and are, in a geometrical sense, ideal model compounds to study rhodopsins with a well‐defined 6‐s‐trans orientation of the chromophore.
Acid‐induced decomposition of coenzyme B12 and variants
Authors: Gerards L.E.H. , Balt S.
Published: September 2010

The acid‐catalyzed heterolytic cleavage of the Co‐C bond in coenzyme B12 (1) and adocobinamide hydroxide (2) was studied using the excess‐acidity functions of Cox and Yates. The results are compared to the acid‐induced decomposition of methyl(5′‐deoxyribofuranosyl)cobalamin (3) and (2‐ethoxyethyl)cobalamin (4). Evidence is presented to view the bond cleavage in the compounds 1, 2 and 3 as an A2 mechanism or as an Ia substitution at Co3+, with water as the nucleophile, and in 4 as an A1 mechanism. For 1, the temperature dependence (289‐320 K) gives ΔS‡ = − 96 J/(K· mol), in agreement with the Ia (A2) mechanism. For the A2 reactions the volumes of activation [ΔV‡ = −11.4 (1), −8.2 (2) and −11.5 (3) cm3/mol in 2‐4M acid at 298K] are consistent with the proposed mechanism, but ΔV‡ for the A1 mechanism of 4 is exceptionally negative (‐7.2 cm3 /mol), probably due to intramolecular coordination in the transition state. A comparison with the much slower acid‐induced decomposition of 5′‐deoxyadenosine brings out the labilization of the furanosyl oxygen bridge by coordination of the 5′‐deoxyadenosyl or 5′‐deoxyribofuranosyl group at the β‐position to cobalt. For 5′‐deoxyadenosine the excess‐acidity treatment and the activation volume (ΔV‡ = 1.7 cm3/mol in 2 M acid) indicate a clear A1 mechanism.
Synthesis of bicyclic 3‐pyrazolidinones via π‐cyclization reactions of exocyclic N‐acylhydrazonium ions
Authors: Rutjes Floris P. J. T. , Udding Jan H. , Hiemstra Henk , Speckamp W. Nico
Published: September 2010

The preparation of several a‐fused 3‐pyrazolidinones is described starting from 5,5‐di‐methyl‐3‐pyrazolidinone and using an acid‐induced cyclization of a π‐nucleophile tethered to N‐1 onto a cationic carbon bonded to N‐2 (an exocyclic N‐acylhydrazonium intermediate). The cyclization reactions proceed best with activated π‐nucleophiles such as allyl‐ and propargylsilanes. In the case of an ester substituent at the cationic carbon, structural analogues of antibacterial bicyclic pyrazolidinones are obtained. The stereochemistry of one product is established by X‐ray crystallographic analysis. Two cyclization products showed NMR spectra with very broad signals due to relatively high nitrogen‐inversion barriers (ca. 13 kcal/mole).
Synthesis and spectroscopic characterisation of 13C‐labelled ubiquinone‐0 and ubiquinone‐10
Authors: van Liemt W.B.S. , Steggerda W.F. , Esmeijer R. , Lugtenburg J.
Published: September 2010

(1‐13C)‐, (2‐13C)‐, (3‐13C)‐, (3‐13CH3)‐, (4‐13C), and (13CH3O)2‐ ubiquinone‐10 and the corresponding (1‐13C)‐, (6‐13C)‐, (5‐13C)‐, (5‐13CH3)‐, (4‐13C)‐, and (13CH3O)2‐ubiquinone‐0 have been synthesised from simple labelled starting materials via a single reaction scheme. The ubiquinones have been characterised using mass spectrometry, 1H NMR and 13C NMR. The spectroscopic results indicate that, within experimental error, the syntheses have been accomplished without scrambling or dilution of label. All labelled ubiquinones have been synthesised on a decigram scale.
Aggregation behaviour of a phospholipid based on D‐(‐)‐threitol
Authors: Feiters M.C. , Nolte R.J.M. , Zwanenburg B.
Published: September 2010

The aggregation behaviour of a synthetic C4 phospholipid, containing two phosphate groups and two stearoyl groups, has been studied. The surfactant formed different types of aggregates in water depending on the concentration, the temperature and the treatment of the samples. Tilted bilayers were found at high surfactant concentrations, whereas at low surfactant concentrations intercalated bilayers could be identified. The intercalated structures could be converted into very small vesicles upon sonication. Tube‐like aggregates were formed after storage at low temperature, which coagulated into thread‐like superstructures.
The effects of salts and surfactants on the physical stability of lamellar liquid‐crystalline systems
Authors: van de Pas J.C. , Buytenhek C.J. , Brouwn L.F.
Published: September 2010

The effects of the salting‐out effectiveness of electrolytes and of the salting‐out resistance of surfactants on the physical stability of lamellar phase systems, consisting of sodium dodecylbenzenesulphonate, a co‐surfactant, an electrolyte and water, have been investigated. A correlation was found between (i) the electrolyte concentration necessary to induce salting‐out/phase separation of a micellar solution of the co‐surfactant and (ii) the maximum electrolyte concentration which can be incorporated into a lamellar phase system formed from the co‐surfactant before physical instability is observed. High concentrations of salting‐out electrolyte can be added to lamellar phase systems before instability is observed, when the co‐surfactant has a high resistance against salting‐out effects.
Synthesis and polymorphism of deuterium labeled unsaturated monogalactosyl diglyceride as studied by 2H NMR
Authors: Chupin Vladimir , Smirnova Svetlana , de Kruijff Ben
Published: September 2010

The synthesis and polymorphism of deuterium‐labeled 1,2‐di‐O‐[11‐2H2)‐oleoyl]‐3‐O‐β‐D‐galactopyranosyl)‐rac‐glycerol is described. 2H‐NMR studies show that this lipid in its hydrated state adopts a lamellar phase below ‐ 5°C and an inverted hexagonal phase above ‐ 5°C.
Methacrylate resin membranes by Gel‐Template‐Leaching: Concept and scope
Authors: Gankema Harold , Hempenius Mark A. , Möller Martin
Published: September 2010

A method of preparation of microporous membranes is described, based on the removal of a crystalline (perfluoroalkyl)alkane [F(CF2)m‐(CH2)nH] network from a cross‐linked methacrylate matrix. (Perfluoroalkyl)alkanes with a particular (CF2)m/(CH2)n balance form gels of interconnected long‐needle crystals upon crystallization from dilute solution. A template of this gel structure was prepared employing a mixture of suitable methacrylate monomers as a solvent. The solvent was first cured by low‐temperature UV‐initiated copolymerization/cross‐linking and subsequently the crystalline network was removed by extraction or sublimation. The resulting microporous morphologies were monitored by optical microscopy, scanning electron microscopy and scanning force microscopy. The cylindrical pore sizes could be varied deliberately by changing the (perfluoroalkyl)alkane, its concentration, and the degree of undercooling upon gelation. Maximum pore diameters varied between 12 nm and 145 nm. Flux measurements showed a decrease in pore size upon increasing the operation temperature of the membrane. A change in the temperature coefficient has been correlated with the glass transition temperature of the membrane. After saponification of the pore surfaces, the pores became smaller, which is probably due to swelling of the top layer of the surfaces. Introduction of sodium‐sulfonate groups on the inner pore surfaces resulted in a certain cation selectivity.
Second‐harmonic generation from thin films of mixtures of an aggregated chiral 4‐nitroazobenzene dye and amylose acetate
Authors: Schoondorp Monique A. , Schouten Arend Jan , Hulshof Jos B. E. , Schudde Ebe P. , Feringa Ben L.
Published: September 2010

Second‐harmonic generation (SHG) from both Langmuir‐Blodgett (LB) films and solvent‐cast films of mixtures of a chiral nonlinear optical (NLO) dye, an ester of palmitic acid and 4‐nitro‐4′‐[(3R)‐hydroxypyrrolidinyl]azobenzene (KMES16) and amylose acetate is investigated. Results are discussed concerning the structure of the films. The NLO‐active molecules form crystalline domains in which the molecules are aligned anti‐parallel without a centre of symmetry (crystal point group P21). The dye domains behave like H aggregates. LB multilayer films show no significant SHG when measured “as deposited”. After heating and cooling down unexpectedly large SHG is measured. Cast films of the same mixtures also show SHG. The effect is attributed partly to a crystal‐size effect and an enhancement of the SHG by H aggregates is suggested. In this paper, we describe SHG of thin layers without the execution of extended procedures to orient the molecules.
The relationship between the molecular structure of polyhydroxy amphiphiles and their aggregation behaviour in water. I. The contact preparation method as a tool for empirical studies
Authors: van Doren Henk A. , Wingert Lavinia M.
Published: September 2010

The lyotropic liquid‐crystalline behaviour of several dozens of (nonionic) polyhydroxy amphiphiles was studied by observing the penetration of water into the bulk of a sample of amphiphile on a microscope slide and identifying the mesophases observed at the interface with the aqueous solution. The compounds were plotted as a function of the total number of hydroxyl and carbonyl groups vs. the total number of carbon atoms in the (hydrophobic) alkyl chain(s). The symbol used for each compound was chosen to indicate the mesophase observed. In this manner, a clear picture emerged of the relationship between overall molecular structure and type of lyotropic phase(s) formed. Based on this plot it becomes possible to predict the type of lyotropic phase that will be formed at the amphiphile‐water interface. Lyotropic mesophases are generally considered to be built up from the aggregates found in dilute aqueous solution. Therefore, a contact preparation also constitutes a simple test for the prediction of the type of aggregate an amphiphile will form in dilute aqueous solution. A useful tool for the design of new surfactants is thus provided.
Synthesis of 4‐imidazolin‐2‐ones from α‐bromo ketimines
Authors: De Kimpe Norbert , De Smaele Dirk , Stanoeva Elena , Tinant Bernard , Declercq Jean‐Paul
Published: September 2010

A novel synthesis of 1,4‐dialkyl‐5‐aryl‐4‐imidazolin‐2‐ones 3 has been achieved by reaction of α‐bromo ketimines 2 with potassium cyanate in dimethylformamide. The structural assignment of these heterocycles was performed by spectrometric methods, comparison with a known compound and X‐ray crystallographic analysis of the acetyl derivative 8.
Synthesis of 5‐(β‐D‐glucopyranosyloxymethyl)‐2′‐deoxyuridine and derivatives thereof. A modified d‐nucleoside from the DNA of Trypanosoma brucei
Authors: Wijsman E. R. , van den Berg O. , Kuyl‐Yeheskiely E. , van der Marel G. A. , van Boom J. H.
Published: September 2010

An appropriately protected 3′‐phosphoramidite and 5′‐phosphate derivative of the modified 2′‐deoxyuridine were obtained by β‐glycosylation of a properly protected 5‐hydroxymethyl‐2′‐deoxyuridine, and subsequent elaboration of the resulting intermediates using standard protocols devised in nucleic acids chemistry.
Conformations and rotational barriers of di‐ and tetraarylporphyrins; a computational and experimental study
Authors: Schrijvers Robert , van Dijk Marinus , Sanders Georgine M. , Sudhölter Ernst J. R.
Published: September 2010

The usefulness of molecular‐mechanics calculations in the study of the conformational properties of several tetraarylporphyrins and diarylporphyrins is demonstrated. Energy‐minimized conformations and rotational barriers of several substituted and unsubstituted arylporphyrins correspond very well with experimental results.
Vanadium in cationic and anionic positions as a promoter of 12‐molybdophosphoric‐acid‐based catalysts
Authors: Bergier T. , Brückman K. , Haber J.
Published: September 2010

Derivatives of 12‐molybdophosphoric acid (H3PMo12O40), containing vanadium in the form of a vanadyl cation or substituted as addenda in Keggin anions, have been synthesized and characterized by IR, LRS, XPS, NMR, and DTA/DTG. Their catalytic behavior in the oxidation of methanol, butane and pentane has been determined. Both catalysts exhibit strong acidity, due to hydrolysis of the secondary structure in the case of the salt. The vanadium atom performs its role as the active site for the activation of hydrocarbon molecules irrespective of whether it is present as a cation or incorporated in Keggin anions.
On the positional reactivity order in the sulfonation of phenyl‐and naphthyl‐substituted naphthalenes with SO3
Authors: Cerfontain Hans , Zou Yousi , Bakker Bert H.
Published: September 2010

The sulfonation of 1‐ and 2‐phenylnaphthalene, 1,1′‐ and 2,2′‐binaphthyl, and that of the 2,2′‐dihydroxy, 2,2′‐dimethoxy and 2,2′‐dimesyloxy derivatives of 1,1′‐binaphthyl with SO3 in dichloromethane as solvent was studied at 22 ± 2°C. Sulfonation of 1‐phenylnaphthalene and 1,1′‐binaphthyl leads to substitution at (each of) the α‐naphthyl moieties, initially at the 4‐position and subsequently at the 6‐ and 7‐position, in a ratio of approximately 8:92 and 14:86, respectively. Upon sulfonation the more planar 2‐phenylnaphthalene and 2,2′‐binaphthyl both give initially the 8‐sulfonic acid derivative (8‐S) and subsequently a mixture of 8,4′‐S2 and 8,8′‐S2, respectively; their further sulfonation affords mixtures of the 4,8,4′‐S3 + 6,8,4′‐S3 and of the 4,8,8′‐S3 + 6,8,8′‐S3, respectively, both in an isomer ratio of approximately 19:81.

Sulfonation of 2,2′‐dimethoxy‐1,1′‐binaphthyl gives initially the 3‐S and 6‐S derivatives in an isomer ratio of approximately 13:87 subsequently the 3,6′‐S2 and 6,6′‐S2 derivatives and eventually the 3,6,4′,6′‐S4 and 4,6,4′,6′‐S4 derivatives. Monosulfonation of 2,2′‐dimesyloxy‐1,1′‐binaphthyl gives the 5‐S and 6‐S in a ratio of 58:42. With a large excess of SO3, 4,6,4′,6′‐S4, 4,6,5′,7′‐S4 and 5,7,5′,7′‐S4 are eventually formed. Sulfonation of 2,2′‐dihydroxy‐1,1′‐binaphthyl gives initially the 5‐S and 6‐S, the ratio of which increases upon increasing the amount of SO3 employed from approximately 35:65 on using ≤ 1.0 mol‐equiv. of SO3 to approximately 62:38 on using > 6.0 mol‐equiv. of SO3. Under the latter conditions the substrate species undergoing sulfonation is proposed to be the di‐sulfated species 3.
Odd‐even effects in the optical properties of chiral twin liquid‐crystalline cholesteryl ω‐(cyanobiphenylyloxy) alkanoates
Authors: Marcelis Antonius T. M. , Koudijs Arie , Sudhölter Ernst J. R.
Published: September 2010

A series of novel cholesteryl w‐(cyanobiphenylyloxy)alkanoate esters with a varying number (2–7 and 10) of methylene units in the alkanoate spacer was synthesized and their mesogenic properties were investigated by polarization microscopy and differential scanning calorimetry. All compounds show a broad range of enantiotropic liquid‐crystalline behavior. Both the cholesteric‐isotropic and the smectic‐cholesteric transition temperatures show a pronounced odd‐even effect as a function of spacer length. The selective reflection wavelength of the cholesteric phases has been determined as a function of spacer length and temperature. For the first time, we have shown that the reflection wavelength also shows a pronounced odd‐even effect. The compounds with an even number of methylene units reflect at much lower wavelengths than the compounds with an odd number of methylene units. The reflection wavelength of the latter compounds decreases strongly with temperature, whereas the reflection wavelength of the compounds with the even spacers is almost independent of the temperature. The odd‐even effect in the optical properties attenuates with increasing spacer length.
Synthesis of thiophene‐2‐phosphonates via α,β‐unsaturated sulfines as intermediates
Authors: van der Linden Johannes B. , Lucassen André C. B. , Zwanenburg Binne
Published: September 2010

Heteroconjugate addition of various alkyllithium reagents to α‐silylallenephosphonates 3b,c has been accomplished in high yields. The formation of thiophene‐2‐phosphonates 5, by heteroconjugate addition of organolithium to 3bc, followed by treatment with sulfur dioxide, proceeds in reasonable yields via the intermediate formation of α,β‐unsaturated sulfines 4. An alternative synthesis of the heteroconjugate addition product diethyl 1‐(trimethylsily)‐2,3‐dimethylbut‐2‐ene‐1‐phosphonate 6a from 2,3‐dimethylbut‐2‐enyl bromide has also been described.
The synthesis of 3‐alkyl‐ and 3‐aryl‐β‐lactams from zinc enolates and imines
Authors: van Maanen Hendrik L. , Kleijn Henk , Jastrzebski Johann T. B. H. , van Koten Gerard
Published: September 2010

Chlorozinc enolates of (hetero)aryl‐, alkyl‐ and silyl‐substituted acetates were reacted with imines and α‐diimines. The zinc‐mediated reaction of (hetero)aryl‐substituted acetates with imines afforded trans‐β‐lactams in good yields and with excellent selectivity. Zinc enolates of non‐functionalized alkanoates yielded the corresponding 3‐alkyl‐β‐lactams (predominantly trans) in moderate yields. Bulky substituents increase the rate and enhance the cis‐trans selectivity of the reaction. Methyl 2‐(trimethylsilyl)acetate does not afford 3‐(trimethylsilyl)‐β‐lactams via the zinc‐mediated reaction with imines, but N‐(trimethylsilyl)‐β‐amino esters, which are formed via an intramolecular silyl shift. The desilylated β‐amino esters were obtained from the zinc enolate of methyl acetate, albeit in moderate conversion, and careful control of the reaction conditions was necessary to avoid side‐reactions. The substituent effects are discussed in terms of pre‐equilibria involving the enolate and six‐membered cyclic transition states.
Amination of dinitrobenzenes with liquid methylamine/potassium‐permanganate
Authors: Woźniak Marian , Grzegożek Maria , Roszkiewicz Witold , Szpakiewicz Barbara
Published: September 2010

1,3‐Dinitrobenzene (1a) and some simple monosubstituted derivatives (1b–g) were aminated with a liquid methylamine solution of potassium permanganate (LMA/PP) to give the corresponding mono‐ and bis(methylamino)‐substituted compounds (3a‐e and 4a). 1,2‐Dinitrobenzene (1i) was aminated with LMA/PP to give 2‐(methylamino)‐1‐nitrobenzene (3f) in high yield. The intermediacy of 4‐(methylamino) σ‐adducts of 1,3‐dinitrobenzene (2a), 2‐chloro‐ (2b) and 2‐amino‐1,3‐dinitrobenzene (2c) was established by 1H‐NMR spectroscopy. Quantum‐chemical calculations for the dinitrobenzenes suggest that, in general, the experimentally observed regioselectivity of the methylamination is satisfactorily described by frontier molecular orbital (FMO) interaction of the reagents.
Metallation and functionalization of N‐vinylpyrrole
Authors: Mal'Kina A. G. , Tarasova O. A. , Trofimov B. A. , Verkruijsse H. D. , van der Kerk A. C. H. T. M. , Brandsma L.
Published: September 2010

Metallation of N‐vinylpyrrole under presumed kinetic conditions, using n‐butyllithium in THF/hexane mixtures, n‐butyllithium/N,N,N′,N′‐tetramethylethanediamine in hexane, or n‐butyllithium/potassium tert‐butoxide (1:1 molar ratio) in THF/hexane mixtures gives almost equal amounts of derivatives metallated at the α‐vinyl or 2‐pyrrole position. In the presence of 7–10 mol% diisopropylamine the α‐vinyl‐lithiated compound is transformed relatively slowly into the pyrrole‐lithiated derivative at ∼ +30°c. The combined use of catalytic amounts of diisopropylamine and equivalent amounts of n‐butyllithium and potassium tert‐butoxide gives rise to a fast and almost complete conversion into the pyrrole‐metallated derivative at temperatures in the range ‐60 to –80°c. A number of 2‐substituted N‐vinylpyrroles have been obtained in good yields by reaction with various electrophilic reagents, in most cases preceded by the addition of anhydrous lithium bromide. N‐Deprotection is successful only in the case of N‐vinyl‐2‐pyrrole‐carboxaldehyde.
Redox behavior of trimanganese tetraoxide catalysts
Authors: Weimin Wang , Yongnian Yang , Jiayu Zhang
Published: September 2010

New methods were used to prepare a nearly stoichiometric Mn3O4 catalyst. The redox behavior of two kinds of Mn3O4 (i.e. the non‐ and nearly stoichiometric Mn3O4) were compared. The relations between the IR parameters, Mn/O stoichiometry and redox properties of Mn3O4 were established. It was found that the Mn/O stoichiometry but not IR parameters was closely related to the redox behavior of the compounds.
Transformations of the tetracyclic skeleton of eudistomins by neighboring‐group participation in the Mitsunobu reaction
Authors: van Maarseveen Jan H. , Oberyé Elna H. H. , Bolster Marjon B. , Scheeren Hans W. , Kruse Chris G.
Published: September 2010

Mitsunobu reaction mediated introduction of nitrogen nucleophiles into trans 1‐hydroxy eudistomins afforded in high yields rearranged products instead of the anticipated cis eudistomins due to neighboring group participations. Transannular interaction in the 6,5,6,7‐membered tetracyclic ring system of the sulfur atom in the 1,6,2‐oxathiazepine ring, to give a thiiranium ion containing intermediate, was followed by intermolecular attack of the present nucleophiles to give a 6,5,6,6‐membered tetracyclic ring system, now with a 1,5,2‐oxathiazine ring. Substitution of the hydroxyl group in a trans 1‐hydroxy dethia carba eudistomin derivative (i.e. with a 1,2‐oxazepine ring) also gave rearranged products due to transannular interaction from the bridgehead nitrogen atom, to give via an aziridinium ion intermediate, products with a 6,5,7,6‐membered tetracyclic ring system containing an 1,2‐oxazine ring.
Chiral basket‐shaped host compounds derived from diphenylglycoluril
Authors: Coolen H. K. A. C. , Engelkamp H. , Reek J. N. H. , Priem A. H. , Nolte R. J. M. , van Leeuwen P. W. N. M.
Published: September 2010

The design and synthesis of two novel chiral receptors derived from diphenylglycoluril are described. The chirality in these molecules is due to the unsymmetrical positioning of amino functions in the crown ether rings with respect to the diphenylglycoluril subunit.
Chemical properties of butadienyl anions in the gas‐phase
Authors: de Visser Sam P. , de Koning Leo J. , van der Hart Wim J. , Nibbering Nico M. M.
Published: September 2010

Proton abstraction from 1,3‐butadiene by strong anionic bases in a Fourier‐transform ion‐cyclotron resonance mass spectrometer at relatively low pressure, yields an isomeric mixture of 1‐ and 2‐butadienyl anions. The gas‐phase acidity, ΔG°acid, of 1,3‐butadiene, associated with proton abstraction from the 2‐position, leading to 2‐butadienyl anions, is determined as 1627 ± 2 kJ/mol. 1‐Butadienyl anions, formed by proton abstraction from the 1‐position in 1,3‐butadiene, are found to be about 10 kJ/mol less stable than 2‐butadienyl anions. This stability difference is confirmed by high‐level ab‐initio calculations, which predict a planar, charge‐localized structure for the 1‐butadienyl anions, in which the butadiene π‐system is still intact. Additional stabilization of the 2‐butadienyl anion is realized by a 100° rotation of the central CC bond, which breaks up the butadiene π‐system in order to achieve allylic charge delocalization leading to a structure with two nearly orthogonal π‐systems. The isomeric 1‐ and 2‐butadienyl anions can be distinguished and identified conveniently and unambiguously by a probe reaction with nitrous oxide, which clearly reveals the distinct chemical nature of the two isomeric butadienyl anions.
Intramolecular hydrogen bonding in acylated 2,2′‐bipyridine‐3,3′‐diamines
Authors: Palmans A. R. A. , Vekemans J. A. J. M. , Meijer E. W.
Published: September 2010

Various di‐ and monoacylated 2,2′‐bipyridine‐3,3′‐diamines (amides 1a‐f, 8, 9, ureas 1g‐h, 8b and acylureas 1i‐j) have been synthesized and characterized. All molecules show strong intramolecular hydrogen bonding between the acyl NH of one ring and the pyridine N‐1 of the other (and vice versa), as is deduced from the low field 1H NMR resonances of the acyl NH protons, which range from δ 12.6 to 15.0 ppm in CDCl3. The nature of the secondary structure of the (di)acylated 2,2′‐bipyridine‐3,3′‐diamines has been investigated using a variety of techniques including variable‐temperature 1H NMR and CD spectroscopy.
Peptides from chiral Cαα‐disubstituted glycines. On the helical screw sense of isovaline peptides
Authors: Crisma M. , Valle G. , Pantano M. , Formaggio F. , Bonora G. M. , Toniolo C. , Kamphuis J.
Published: September 2010

The preferred conformation of three Nα‐acetylated Aib/Iva host/guest pentapeptide esters and their Nα‐benzyloxycarbonylated synthetic precursors, prepared by solution methods and fully characterized, were examined in chloroform solution using FT‐IR absorption and 1H‐NMR and in the crystal state by X‐ray diffraction. All these peptides are folded in a 310‐helix structure, irrespective of the experimental conditions used in the conformational analysis. In the crystal state the screw sense preference of the helical structure that is formed seems to be governed by the position of the single Iva residue in the peptide main chain, the ethyl side‐chain disposition, and the nature of the Nα‐blocking group.
Gilvocarcins
Authors: Hua Duy H. , Saha Shankar
Published: September 2010

Syntheses of the aglycones of gilvocarcins, gilvocarcin‐related C‐glycosides, and (+)‐gilvocarcin M are described. Variety of methodologies have been reported for the construction of the aglycones of gilvocarcins including Meerwein and Diels‐Alder reactions, nucleophilic aromatic substitution, palladium‐catalyzed coupling, Suzuki biaryl coupling, Dotz carbene chromium benzannulation, conjugate addition to naphthoquinone ketals, and Pechmann condensation. In the syntheses of gilvocarcin‐related C‐glycosides, only those reactions involving palladium‐mediated coupling, Lewis‐acid‐mediated condensation, cuprate reagents, and reductive aromatization of quinol ketals were surveyed.
The analysis of very small samples of repeated measurements I: An adjusted sandwich estimator
Authors: Skene Simon S. , Kenward Michael G.
Published: September 2010

The statistical analysis of repeated measures or longitudinal data always requires the accommodation of the covariance structure of the repeated measurements at some stage in the analysis. The general linear mixed model is often used for such analyses, and allows for the specification of both a mean model and a covariance structure. Often the covariance structure itself is not of direct interest, but only a means to producing valid inferences about the response. Existing methods of analysis are often inadequate where the sample size is small. More precisely, statistical measures of goodness of fit are not necessarily the right measure of the appropriateness of a covariance structure and inferences based on conventional Wald‐type procedures do not approximate sufficiently well their nominal properties when data are unbalanced or incomplete. This is shown to be the case when adopting the Kenward–Roger adjustment where the sample size is very small. A generalization of an approach to Wald tests using a bias‐adjusted empirical sandwich estimator for the covariance matrix of the fixed effects parameters from generalized estimating equations is developed for Gaussian repeated measurements. This is shown to attain the correct test size but has very low power. Copyright © 2010 John Wiley & Sons, Ltd.
Seiltausch unter Verkehr an der Rheinbrücke Flehe
Authors: Gurtmann Stefan , Hamme Markus , Marzahn Gero , Sieberth Sven
Published: September 2010

Es wird über den Seiltausch an der Rheinbrücke Flehe berichtet. Auf Grund umfangreicher Schäden an der Seilabspannung mussten neun Tragseile der Rheinbrücke Flehe im Zuge der Bundesautobahn A46 getauscht werden. Wegen der sehr hohen täglichen Verkehrsbelastung waren Eingriffe in den laufenden Verkehr weitgehend zu verhindern, so dass der Seiltausch bei laufendem Verkehr durchgeführt wurde. Diese komplexe Aufgabe stellte höchste Anforderungen an alle Beteiligten, wurde aber letztlich mit einem erfolgreichen Abschluss der Maßnahme belohnt.

Replacing stay‐cables of the Rhine River crossing Rheinbrücke Flehe, Germany. The paper reports on the replacement works of nine stay cables of the Rhine River Bridge Flehe, a cable‐stayed bridge south of Düsseldorf, Germany. Due to a long service life the stay cables showed some signs of damage and needed to be repaired. Because of foremost damages of nine cables especially open fractures of single wires, they had to be replaced instead. The replacement not only required enormous structural and technical skills, but also engagement of all involved in. This was mainly due to the necessity of keeping the traffic uninterrupted and to prevent any closures of lanes. This administrational demand was successfully mastered. Besides slightly narrowed lanes widths, the bridge's traffic area remained unaffected by this replacement work with traffic able to continue flowing throughout the project.
Minitab
Authors: Alin Aylin
Published: September 2010

Statistical software is an inevitable part of statistical analyses. Minitab is a well‐known statistical software, which was developed in 1972 by three university instructors as a teaching tool for introductory statistics courses. But, today it has strengthened its position not only in introductory statistics courses but also in advance statistical courses at universities, and even in government, business, and industry. In this article, some properties of the software and some of the improvements made by its latest version are presented and its importance as a teaching tool has been emphasized. WIREs Comp Stat 2010 2 723–727 DOI: 10.1002/wics.113

This article is categorized under:

Software for Computational Statistics > Software/Statistical Software
A Heterotetranuclear Metal Complex {Ni2Na2} with Azido Bridges
Authors: Ge Cheng‐Min , Zhang Shu‐Hua , Feng Chao , Wang Yin‐Guang , Li Wei
Published: September 2010

The reaction of Ni(ClO4)2·6H2O with 3‐ethoxy‐2‐hydroxybenzaldehyde (Hemp), methylamine, and NaN3 in DMF solution, under solvothermal conditions, leads to the formation of the heterotetrametallic cluster [Ni2Na2(μ1,1,1‐N3)2(emimp)4(DMF)2] (I) (emimp = 2‐ethoxy‐6‐formyl‐phenolate anion, DMF = N,N‐dimethyl‐formamide). Compound I displays dominant ferromagnetic interactions through μ1,1,1‐N3 bridging mode.
Syntheses, Structures, and Luminescent Properties of Two Novel Coordination Polymers with Dipicolinate and Diimidazole Ligands
Authors: Liu Tong‐Fei , Wu Wan‐Fei , Zhang Wei‐Guo , Cui Guang‐Hua
Published: September 2010

Two novel coordination polymers, [Zn(dpc)(bmix)0.5]n (1), [Pb(dpc)(bmix)0.5]n (2), [dpc = dipicolinate, bmix = 1,4‐bis(2‐methylimidazole‐1‐ylmethyl)benzene], were hydrothermally synthesized and characterized by elemental analyses, IR spectroscopy, TGA, and X‐ray single crystal diffraction. In both complexes, the dipicolinate and bmix ligands act as spacers to link metal ions to give a 2D corrugated (6,3) network of 1 and a 3D microporous framework of 2, respectively. The difference in the architectures is due to a diverging coordination mode of the carboxylate function. Furthermore, solid state fluorescence properties of the two complexes were investigated at room temperature.
Thermistoren als Temperaturmeßelemente
Authors: Wagner Wolfgang
Published: September 2010

Es wird eine Übersicht über die Eigenschaften und die Anwendungsmöglichkeiten temperaturabhängiger Halbleiterwiderstände, besonders hinsichtlich ihrer Verwendung ale Temperaturmeßorgane bei physikalisch‐chemischen Untersuchungen, gegeben.
PERIODIC SOLUTIONS OF SINGULAR DIFFERENTIAL EQUATIONS WITH SIGN-CHANGING POTENTIAL
Authors: CHU JIFENG , ZHANG ZIHENG
Published: September 2010

In this paper we study the existence of positive periodic solutions to second-order singular differential equations with the sign-changing potential. Both the repulsive case and the attractive case are studied. The proof is based on Schauder’s fixed point theorem. Recent results in the literature are generalized and significantly improved.
PRONORMALITY IN GENERALIZEDFC-GROUPS
Authors: ROMANO E. , VINCENZI G.
Published: September 2010

We extend some results known forFC-groups to the classFC*of generalizedFC-groups introduced in de Giovanniet al.[‘Groups with restricted conjugacy classes’,Serdica Math. J.28(3) (2002), 241–254]. The main theorems pertain to the join of pronormal subgroups. The relevant role that the Wielandt subgroup plays in anFC*-group is pointed out.
Effects of bite size and duration of oral processing on retro-nasal aroma release – features contributing to meal termination
Authors: Ruijschop Rianne M. A. J. , Zijlstra Nicolien , Boelrijk Alexandra E. M. , Dijkstra Annereinou , Burgering Maurits J. M. , Graaf Cees de , Westerterp-Plantenga Margriet S.
Published: September 2010

The brain response to a retro-nasally sensed food odour signals the perception of food and it is suggested to be related to satiation. It is hypothesised that consuming food either in multiple small bite sizes or with a longer durations of oral processing may evoke substantial oral processing per gram consumed and an increase in transit time in the oral cavity. This is expected to result in a higher cumulative retro-nasal aroma stimulation, which in turn may lead to increased feelings of satiation and decreased food intake. Using real-time atmospheric pressure chemical ionisation-MS, in vivo retro-nasal aroma release was assessed for twenty-one young, healthy and normal-weight subjects consuming dark chocolate-flavoured custard. Subjects were exposed to both free or fixed bite size (5 and 15 g) and durations of oral processing before swallowing (3 and 9 s) in a cross-over design. For a fixed amount of dark chocolate-flavoured custard, consumption in multiple small bite sizes resulted in a significantly higher cumulative extent of retro-nasal aroma release per gram consumed compared with a smaller amount of large bite sizes. In addition, a longer duration of oral processing tended to result in a higher cumulative extent of retro-nasal aroma release per gram consumed compared with a short duration of oral processing. An interaction effect of bite size and duration of oral processing was not observed. In conclusion, decreasing bite size or increasing duration of oral processing led to a higher cumulative retro-nasal aroma stimulation per gram consumed. Hence, adapting bite size or duration of oral processing indicates that meal termination can be accelerated by increasing the extent of retro-nasal aroma release and, subsequently, the satiation.