bluuebunny/crossref_metadata_2025 huggingface dataset:
Double Subroutine Self‐Assembly; Spontaneous Generation of a Nanocyclic Dodecanuclear Cu1 Inorganic Architecture
Authors: Funeriu Daniel P. , Lehn Jean‐Marie , Baum Gerhard , Fenske Dieter
Published: July 2007

The newly synthesised ligand 2 combines binding components known to undergo specific and distinct self‐assembly processes with Cu1 ions. It complexes Cu1 to form, in almost quantitative yield, a large inorganic architecture 1 made up from four ligand molecules and twelve metal ions. The structure of 1 was ascertained by X‐ray radiocrystallography as well as by NMR spectroscopy and electrospray mass spectrometry. It consists of a macrocycle of nanometric dimension with an external diameter of 28 Å; the central cavity has a diameter of 11 Å, which contains four PF−6 anions as well as solvent molecules. The spontaneous formation of 1 results from a self‐assembly process based on a “program” combining two assembly subroutines, each specific to one of the ligand subunits. Self‐assembly through double or, more generally, multiple subroutines can be used to generate a wide variety of highly complex inorganic supramolecular architectures by combination of two or more assembly processes.
Enantioselective Construction of Highly Functionalized Indoloquinolizines—congeners to Polycyclic Indole Alkaloids
Authors: Lock Ralf , Waldmann Herbert
Published: July 2007

Indolo[2,3‐a]quinolizines have been prepared in enantiomerically pure form by a very short and efficient synthetic sequence consisting of a) formation of imines of tryptophan esters, b) their enantioselective reaction with substituted silyloxydienes mediated by a chiral or an achiral boron Lewis acid, and c) subsequent ring closure initiated by conversion of the generated vinylogous amides into vinylogous imidoyl chlorides. With this strategy various substituents can be incorporated directly into the 1‐position of the heterocyclic framework of complex indole alkaloids by the choice of an appropriate silyloxydiene, so that subsequent derivatization of the alkaloid precursor at this position is rendered unnecessary.
Quantum‐Chemical Investigations of Stabilizing Interactions in μ‐Diborylcarbene Dicobalt Complexes with a Planar Tetracoordinate Carbon Atom
Authors: Hyla‐Kryspin Isabella , Gleiter Rolf , Rohmer Marie‐Madelaine , Devemy Jérôme , Gunale Anuradha , Pritzkow Hans , Siebert Walter
Published: July 2007

Quantum‐chemical methods have been employed to study the nature of stabilization in dinuclear cobalt complexes of the general formula [{(C5H5)Co}2(μ‐CR12BCBR2R3)] (6) as well as the “antivan't Hoff–Le Bel” configuration of the planar tetracoordinate carbon (ptC) atom of the bridging diborylcarbene ligand 9. Extended Hückel and ab initio Hartree‐Fock calculations have been carried out for the model compounds 6b (R1 = R2 = R3 = H) and 6c (R1 = R2 = H; R3 = C6H5). Ab initio electron deformation density maps and natural population analysis calculations show that complexes 6 are stabilized through push–pull effects by which the ptC experiences π electron density delocalization and σ electron density accumulation. The calculated electronic configuration of the ptC in the free ligand 9b is σ2.978π1.501, and in 6b σ3.944π1.356. Electron density donation from one cobalt atom to an aryl group on the bridging ligand further contributes to the stabilization of the complexes 6.
Adsorption of Ionophores and of Their Cation Complexes at the Water/Chloroform Interface: A Molecular Dynamics Study of a [2.2.2]Cryptand and of Phosphoryl‐Containing Podands
Authors: Varnek A. , Troxler L. , Wipff G.
Published: July 2007

We report molecular dynamics simulations on ionophores of different topologies and on their complexes with alkali and alkaline‐earth cations, with or without counterion, at the water/chloroform interface. As ionophores we consider two phosphoryl‐containing podands (the “chainlike” monopodand MP and the “octopuslike” tripodand TP) and the bicyclic cryptand 222. We find that all the solutes behave as surfactants: they remain adsorbed at the interface, without migrating to bulk phases. Their precise location and solvation depend on the nature and conformation of the ionophore, of the cation and of the counterion. Schematically, two types of solutes can be distinguished, depending on their hydrophilic/hydrophobic character. The first type (cryptand 222 and its complexes, or the [MP⋅K+] complex), which have a hydrophobic exterior, stay on the chloroform side of the interface and are partially hydrated by “water fingers”. The second type (free MP and TP, [MP⋅K+]Pic‐ and [MP⋅Sr2+](Pic‐)2 complexes), which are more hydrophilic, are partitioned to a greater extent between the two liquid phases. The status of the ion pairs at the interface depends on the interplay between cation … anion and anion … solvent interactions. When cation‐anion interactions are strong enough (as in [MP⋅Sr2+](Pic‐)2), the ion pairs remain intimate. Otherwise they dissociate, leading to solvent‐separated ion pairs adsorbed at the interface (in the [222⋅K+] Pic‐ complex) or to the migration of the anion to the water phase (in the [222⋅K+] Cl‐ complex).
Electron Transfer in Dinuclear Cobalt Complexes with “Non‐innocent” Bridging Ligands
Authors: Heinze Katja , Huttner Gottfried , Zsolnai Laszlo , Jacobi Albrecht , Schober Peter
Published: July 2007

Reaction of tripod cobalt(II) templates [{CH3C(CH2PAr2)3}CoII] with potentially bridging ligands L generates the dinuclear compounds [(tripod)‐Co‐L‐Co(tripod)]2+. With L = oxalate (C2O2‐4) a biscobalt(II) complex (1) is formed, while with L = C6H2O2‐4, the dianion derived from 2,5‐dihydroxy‐1,4=benzoquinone (anilic acid), two‐electron transfer within the dimetallic unit occurs and a biscobalt(III) charge distribution results (2a), as shown by X‐ray structural analyses of 1 and 2a, NMR spectroscopy, and theoretical investigations by the INDO method. Complex 2a exhibits an unusually intense, low‐energy absorption in its electronic spectrum; this is explained with a simple MO model. One‐electron reduction of 2a generates the corresponding mixed‐valence complex, which is highly stabilised through extensive electron delocalisation. Substituents at the 3,6 positions of the bridging ligand (Cl, Br, I, NO2, Me, iPr, Ph; 2b‐h) as well as alkyl substitution at the aromatic rings of the tripod ligands (3, 4) influence the optical and electrochemical properties consistent with the proposed model of charge distribution. Formal replacement of one [(tripod)CoIII]3+ moiety by [CH2]2+ leads to the mononuclear complex 6, which is shown to be a typical [(tripod)CoIII=(catecholato)]+ complex. Therefore the substantially different optical and electrochemical properties of the dinuclear complexes with respect to those of 6 result from strong metal‐metal interactions mediated by the bridging ligand.
Macrocyclic Ethers and Their Inclusion Complexes
Authors: Ratilainen Jari , Airola Karri , Nieger Martin , Böhme Marc , Huuskonen Juhani , Rissanen Kari , Nieger D. R. M.
Published: July 2007

The synthesis and characterisation of eleven new macrocyclic ethers (up to 96‐membered [6+6] gigantocycle) with well‐defined cavities are described. Syntheses of the macrocycles M1–M7 were performed under high‐dilution conditions. A “supramolecular” purification method was used for the small [2+2] macrocycles M3–M7, which separated selectively from the reaction mixture on recrystallisation from a dichloromethane/diethyl ether solution mixture. This proved to be an excellent method for purifying [2+2] macrocyclic ethers containing 1,1‐diphenylmethane moieties, and the separation was nearly quantitative. Molecular inclusion of dichloromethane in the cavities of noncovalently bonded macrocyclic ethers M2–M5 was studied by X‐ray diffraction in the solid state. Additionally, clathrate formation was found for macrocycles M1 (including diethyl ether), M2 (including water), M6 (including benzene) and M7 (including benzene).
Alkyne–Carbene Chelate Complexes of Chromium: Arrested Intermediates in the Benzannulation Reaction and Precursors of Densely Functionalized Centrosymmetric Chrysenes
Authors: Hohmann Frank , Siemoneit Sabine , Kotila Sirpa , Heinz Dötz Karl , Nieger Martin
Published: July 2007

Tetracarbonyl‐π2‐alkyne–carbene chromium(0) complexes 3a–c stabilized by a rigid C2‐arene unit bridging the alkyne and the carbene ligands were synthesized from their pentacarbonyl precursors 2a–c by low‐temperature photodecarbonylation. The chelates 3a–c are the first stable alkyne–carbene complexes containing a Group VIB metal carbonyl unit, and can be regarded as arrested intermediates in the chromium‐mediated benzannulation reaction. Comparative X‐ray and 13C NMR studies indicate only weak coordination of the alkyne, both in the solid state and in solution. Decomposition of chelates 3a–c as well as the thermal decarbonylation of their pentacarbonyl precursors 2a–c results in dimerization of the alkynylcarbene ligands to give densely substituted oxygenated chrysene derivatives. A modification of the substitution pattern in the central chrysene rings results in a gradual distortion of the arene system across the central CC arene bond.
Crystalline Mono‐ and Multilayer Self‐Assemblies of Oligothiophenes at the Air–Water Interface
Authors: Isz Sandrine , Weissbuch Isabelle , Kjaer Kristian , Bouwman Wim G. , Als‐Nielsen Jens , Palacin Serge , Ruaudel‐Teixier Annie , Leiserowitz Leslie , Lahav Meir
Published: July 2007

The formation of Langmuir monolayers at the air–water interface has long been believed to be limited to amphiphilic molecules containing a hydrophobic chain and a hydrophilic headgroup. Here we report the formation of crystalline mono‐ and multilayer self‐assemblies of oligothiophenes, a class of aromatic nonamphiphilic molecules, self‐aggregated at the air–water interface. As model systems we have examined the deposition of quaterthiophene (S4), quin‐quethiophene (S5), and sexithiophene (S6) from chloroform solutions on the water surface. The structures of the films were determined by surface pressure–area isotherms, by scanning force microscopy (SFM) after transfer of the films onto atomically smooth mica, by cryo‐transmission electron microscopy (Cryo‐TEM) on vitreous ice, and by grazing incidence synchrotron X‐ray diffraction (GID) directly on the water surface. S4forms two polymorphic crystalline multilayers. In polymorph α, of structure very similar to that of the three‐dimensional solid, the molecules are aligned with their long molecular axis tilted by about 23° from the normal to the water surface. In polymorph β the long molecular axis is perpendicular to the water surface. S5self‐aggregates at the water surface to form mixtures of monolayers and bilayers of the β polymorph; S6forms primarily crystalline monolayers of both α and β forms. The crystalline assemblies preserve their integrity during transfer from the water surface onto solid supports. The relevance of the present results for the understanding of the early stages of crystal nucleation is presented.
Localization Patterns in Interstitial Space: A Special Property of the Electron Localization Function (ELF)
Authors: Nesper Reinhard , Wengert Steffen
Published: July 2007

The electron localization function (ELF) is a new descriptor of chemical bonding in real space which has turned out to be enormously powerful. We show here that the ELF also has predictive power. By analysis of the interstitial space, undetected atoms can be recognized by localization patterns in such regions. The importance of this approach is that the correct number of valence electrons is unknown before the calculations. The method was tested for the compounds Ca4Sb2O, Ba3Ge4X, Ba10Ge7O3, and for the so‐called second SrSi modification, which, according to our analysis, very probably has the composition Sr10Si10X. In these cases the positions of the heteroatoms O and X were located and, in the case of X, proposals for a preferred atom type or group are made. Even in cases where the missing atoms are the majority component the approach was quite successful. As an example, the structure of CaH2 was generated from the known Ca positions by a two‐step iterative procedure.
The Cation‐Dinitrogen Interaction in the “Benzyldiazonium ion”: Preferential Electrostatic Complex Formation and Dinitrogen Catalysis of Benzyl Cation Rotational Automerization
Authors: Glaser Rainer , Farmer David
Published: July 2007

Diazonium ions are reactive intermediates in deamination reactions pertinent to chemical carcinogenesis. While methyldiazonium ion has been shown to exist as a short‐lived intermediate in the gas phase and in solution, benzyldiazonium ions have never been observed, and the reaction intermediates in deaminations of benzyl systems remain a matter of debate. We therefore studied the benzylcation‐dinitrogen interaction by ab initio methods; several important conclusions resulted. Analysis of the potential energy surface at the level MP4(sdtq)/6‐31 G*/ MP 2(full)/6‐31 G* + ΔVZPE(MP 2(full)/6‐31 G*) revealed that a classical “benzyldiazonium ion” does not exist. The interaction of N2with benzyl cationM‐1results in an electrostatically bound complex2Cwith a long CN distance (2.935 Å) as the most stable structure. A covalently bound planar benzyldiazonium ion2Awith a “normal” CN bond length (1.514 Å) is the transition‐state structure for automerization of the electrostatic complex with concomitant rotation about the exocyclic CC bond. The potential energy surface characteristics result from the highly efficient π‐dative Ph → CH2bonding inM‐1; this is clearly demonstrated in its structure and that of its transition state for rotational automerizationTS‐1by the very high activation barrier for rotation (47.6 kcalmol−1!) and by the gradient vector fields of the total electron densities of conformers of1and2. The rotational barrier for1is reduced to 27.9 kcalmol−1in the N2complex2, and the potential energy surface characteristics of benzyldiazonium ion essentially facilitate the N2‐catalyzed rotational isomerization of benzyl cation. The benzyldiazonium ion system shows for the first time that the interaction of a donor molecule with a carbenium ion with a valence LUMO can lead to the formation of an electrostatic complex as opposed to dative bond formation. Dative σ‐bond formation between N2and the CH2carbon of1is energetically not competitive with dative Ph → CH2π;‐bond formation.
Metal‐Template Electrophilic Substitution on Phenols: Synthesis and Crystal Structure of Bromomagnesium Phenolate and Its Reactive Complex with para‐Isopropylbenzaldehyde
Authors: Bocelli Gabriele , Cantoni Andrea , Sartori Giovanni , Maggi Raimondo , Bigi Franca
Published: July 2007

The crystal structures of the bromomagnesium phenolate 5 and its complex 7 with para‐isopropylbenzaldehyde are reported; for the first time it has been possible to demonstrate that the reactive complex 7, responsible for the complete ortho‐regioselective control in the alkylation of phenoxymagnesium bromides with aldehydes, is not obtained by simple replacement of the ethereal ligand but by expansion of the metal coordination sphere from 4 (usual tetrahedral configuration) to 5. We infer from 1H NMR studies that the magnesium coordination of complex 7 in solution is analogous to that shown in the solid state, with a complexed ethereal molecule.
Zirconium‐Mediated Intramolecular Coupling of Terminal Alkynes and Their Subsequent Carbonylation: Novel Synthesis of Seven‐ and Eight‐Membered Heterocycles
Authors: Barluenga José , Sanz Roberto , Fañanás Francisco J.
Published: July 2007

The development of a new method for the intramolecular coupling of terminal alkynes and for the synthesis of seven‐ and eight‐membered benzoheterocycles is reported. The key steps involve the generation of zirconocene‐alkyne complexes from 2‐bromoalkenes and the subsequent intramolecular carbometalation of olefins or acetylides. The 8‐unsubstituted zirconabicyclopentenes were carbonylated to afford unexpected products and allow access to polyfunctionalized molecules from simple starting materials.
The First Peralkylated Phosphino(stibino)methanes and Their Organometallic Rhodium Complexes
Authors: Manger Matthias , Wolf Justin , Laubender Matthias , Teichert Markus , Stalke Dietmar , Werner Helmut
Published: July 2007

The first representatives of phosphino(stibino)methanes R2PCH2Sb‐R′2 (3–5) with bulky alkyl or cycloalkyl groups R and R′ were prepared in two steps from Ph3SnCH2I via the isolated stannylated phosphanes Ph3SnCH2PR2 (1, 2) as intermediates. X‐ray structural analysis of 5 (R = C6H11, R′ = tBu) reveals that the lone pairs and the substituents R and R′ at phosphorus and antimony and the hydrogen atoms of the CH2 bridge adopt staggered conformations. Treatment of [{C8H12RhCl}2] with 3–5 affords the neutral compounds [Rh‐Cl(η4‐C8H12)(κ‐P‐R2PCH2SbR′2)] (6–8), of which 7 and 8 react with CH3MgI to give the corresponding methylrhodium derivatives [RhCH3(η4‐C8H12)(κ‐P‐R2‐PCH2SbR′2)] (9, 10). Cationic complexes [Rh(η4‐C8H12)(η2‐P,Sb‐R2PCH2SbR′2)]‐X (X = PF6: 11a, 12a, 13; X = BPh4: 11b, 12b) containing the phosphino(stibino)methanes as chelating ligands were obtained either from [{C8H12RhCl}2], R2PCH2SbR′2 and MX, or (for 13) from 8 and AgPF6. Compound 12a (R = iPr, R′ = tBu) was characterized by X‐ray crystallography. The PF6 salts 11a, 12a, and 13 react with CH2N2 by insertion of CH2 into the Rh–Sb bond to yield the complexes 14–16, the first examples of transition‐metal compounds with Sb ylides as ligands. Treatment of BPh4 salts 11b and 12b with H2 gives the half‐sand‐wich‐type complexes [(η6‐C6H5BPh3)Rh(κ2‐P,Sb‐R2PCH2SbR′2)] (17, 18), in which the tetraphenylborate is coordinated like a substituted arene to the metal center.
Chiral Lewis Acid Controlled Synthesis (CLAC Synthesis): Chiral Lewis Acids Influence the Reaction Course in Asymmetric Aldol Reactions for the Synthesis of Enantiomeric Dihydroxythioester Derivatives in the Presence of Chiral Diamines Derived from L‐Proline
Authors: Kobayashi Shū , Horibe Mineko
Published: July 2007

Both enantiomers of 2,3‐dihy‐droxythioester derivatives were prepared with almost perfect stereochemical control by chiral Lewis acid controlled synthesis (CLAC synthesis). CLAC synthesis means synthesis of all individual diastereomers or enantiomers from the same starting materials by designing chiral Lewis acids. For example, (Z)‐1‐ethyl‐thio‐1‐(trimethylsiloxy)‐2‐(tert‐butyldi‐methylsiloxy)ethene (1) reacted with aldehydes in the presence of chiral tin(II) Lewis acids using (S)‐1‐methyl‐2‐[(isoin‐dolinyl)methyl]pyrrolidine (4) and (S)‐1‐methyl‐2‐[(indolinyl)methyl]pyrrolidine (5) to afford enantiomeric dihydroxy‐thioester derivatives. Chiral diamines 4 and 5, which were readily prepared from L‐proline, differ only in the fusion point of the benzene ring connected to the pyrrolidine moiety. The unique selectivities were ascribed to the conformational difference between the chiral tin(II) Lewis acids of chiral diamines 4 and 5, and the function of chiral sources for obtaining high selectivities has also been clarified.
Cope Rearrangements versus Retro Diels‐Alder Reactions
Authors: Beck Karin , Hoffman Petra , Hünig Siegfried
Published: July 2007

The two isomeric [4+2] cyclo‐adducts from two different 1,3‐dienes may result from direct cycloadditions as well as from Cope rearrangements (Scheme 1). This general question is tackled by employing two energetically different types of dienes, protonated pyrazolines (1H+, 2H+) or dihydropyridazines (3H+), prepared in situ from their trimers and alicyclic (4–6) or aliphatic (7–9) 1,3‐dienes. Depending on structural features and conditions (amount of acid, reaction time), various ratios of the two isomeric [4+2] cycloadducts A and B are obtained; A and B are azo compounds 10, 14, 16, 20, 22, 24, 27, 32, 34, 36–39, 41, 42, pyrazolines endo‐11, endo‐13, endo‐15, endo‐endo‐17, endo‐18, endo‐19, 21, 23, 25, 26, 28, and hydropyridazines 31, endo‐33, endo‐35, 40 and 43 (Schemes 3, 4). These results were backed by others from acid‐catalyzed isomerizations, trapping experiments, and calculations of the equilibria (ΔΔH) between the isomers (by analogy with the corresponding olefins). A critical discussion reveals: a) Azo compounds 20, 22, 24, 27, 34, 38, and 42 must result from a [4++2] cycloaddition with inverse electron demand, whereas hydropyridazines endo‐33, endo‐35, 40, and 43 originate from a [4+2+] cycloaddition with normal electron demand. b) All isomerizations occur by a [3,3] sigmatropic rearrangement; [4+2] cycloreversion is energetically disfavored. c) A clear‐cut distinction between the [4++2] or [4+2+] cycloaddition reaction routes to the energetically well‐balanced systems 10→endo‐11 and 12→endo‐13 is not possible. d) The two cycloadditions may well favor a nonconcerted reaction through an allylic cationic intermediate which also governs the [3,3] rearrangements (Scheme 8).
Type B Semiconductor Photocatalysis: The Synthesis of Homoallyl Amines by Cadmium Sulfide‐Catalyzed Linear Photoaddition of Olefins and Enol/allyl Ethers to N‐Phenylbenzophenone Imine
Authors: Keck Helmut , Schindler Wolfram , Knoch Falk , Kisch Horst
Published: July 2007

Homoallyl amines were synthesized by visible‐light irradiation of CdS powder in the presence of N‐phenylbenzophenone imine and cyclohexene, 2,3‐dihydrofuran, 2,5‐dihydrofuran, 3,4‐dihydropyran, 2‐pentene, cyclopentene, 1‐methylcyclohexene, or α‐pinene. The structures of the products from the last three olefins were determined by single‐crystal X‐ray analysis to prove that C‐alkylation of the imine had occurred. Thus, the reaction is formally an insertion of the imine into an allylic C‐H bond of the olefin. It is proposed that a photogenerated electron–hole pair reduces the imine to an α‐aminodiphenylmethyl radical and oxidizes the olefin with concomitant deprotonation to the corresponding allyl radical. Heterocoupling of these intermediates affords the final addition product. The overall reaction is therefore classified as type B semiconductor photocatalysis. The presence of acetic acid accelerates the reaction by rendering the reduction potential of the imine more positive. In the series 2,5‐dihydrofuran/cyclopentene/3,4‐dihydropyran, the decrease in apparent quantum yield with increasing driving force of olefin oxidation points to a significant contribution of secondary back electron transfer.
In Search for Mononuclear Helical Lanthanide Building Blocks with Predetermined Properties: Lanthanide Complexes with Diethyl Pyridine‐2, 6‐Dicarboxylate
Authors: Renaud Fabien , Piguet Claude , Bernardinelli Gérald , Bünzli Jean‐Claude G. , Hopfgartner Gérard
Published: July 2007

The ligand diethyl pyridine‐2, 6‐dicarboxylate (L5) reacts with LnIII in acetonitrile to successively give the complexes [Ln(L5)i]3+ (Ln = La to Lu, i = 1‐3). Spectroscopic investigations (ES‐MS, UV/Vis, NMR) show that the 1:3 complexes [Ln(L5)3]3+ have poor stability in solution and exist as a mixture of rapidly interconverting conformers. Variable‐temperature NMR data show that the helical P→M interconversion and dynamic on‐off equilibria of the ester side arms both control the observed average structure in solution. Contrary to similar lanthanide building blocks possessing benzimidazole or carboxamide side arms, [Eu(L5)3]3+ has a sizable quantum yield in anhydrous acetonitrile; this has been attributed to an improved ligand → EuIII energy transfer resulting from a good energetic match between the ligand‐ and metal‐centered excited states. Pure 1:3 complexes cannot be isolated in the solid state, but crystalline 1:2 complexes [Ln(L5)2](TfO)3.nH2O have been prepared. The X‐ray crystal structure of [Eu(L5)2(TfO)2(OH2)]TfO (1) reveals two meridionally tricoordinated ligands L5, but the long Eu‐O(ester) bonds imply only weak interactions between the carbonyl groups of the ester side arms and EuIII, providing a limited protection of the metallic site. The photophysical studies show that nonacoordinate EuIII in 1 binds an additional water molecule to give a decacoordinate complex in the solid state, thus confirming the accessibility of the metallic site for further complexation.
Synthesis of Pyrazinoporphyrazine Derivatives Functionalised with Tetrathiafulvalene (TTF) Units: X‐Ray Crystal Structures of Two Related ttf Cyclophanes and Two Bis(1,3‐Dithiole‐2‐Thione) Intermediates
Authors: Wang C. S. , Bryce M. R. , Batsanov A. S. , Howard J. A. K.
Published: July 2007

The pyrazinoporphyrazine system 13 (metal‐free, zinc and copper derivatives) has been synthesised by tetramerisation of 2,3‐dicyanopyrazine monomer unit 10. The structure of 13a‐c has been established by 1H NMR spectroscopy, UV/Vis spectrophotometry, MALDI‐TOF mass spectrometry, cyclic voltammetry and differential pulse voltammetry. The electrochemical redox behaviour of 13a‐c is strongly solvent dependent. The expected two‐stage oxidation of the tetrathiafulvalene (TTF) units of 13a‐c was observed in a range of solvents; in addition, oxidation and reduction of the pyrazinoporphyrazine core of the metal‐free derivative 13a was detected in benzonitrile. On excitation of 13 in the Q‐band region no fluorescence was observed, which is presumably the consequence of intramolecular charge transfer between the TTF moieties and the excited state of the central porphyrazine. Molecular modelling studies on 13a and 13c are reported. During the course of this work, the novel TTF macrocycles 11 and 20 were synthesised; their X‐ray crystal structures reveal severely bent TTF units, the conformations of which are discussed in detail. The X‐ray crystal structures of the bis(1,3‐dithiole) systems 15 and 18 have also been determined.
N‐Alkyloxycarbonyl‐3‐aryloxaziridines: Their Preparation, Structure, and Utilization As Electrophilic Amination Reagents
Authors: Vidal Joëlle , Damestoy Stéphanie , Guy Laure , Hannachi Jean‐Christophe , Aubry André , Collet Andreé , Aubry André
Published: July 2007

This paper reports the synthesis of a series of N‐protected oxaziridines (N‐Moc, Boc, Z or Fmoc) and discusses their ability to deliver their N‐alkoxycar‐bonyl fragment to amines, enolates, sulfur, and phosphorus nucleophiles (electrophilic amination). These oxaziridines are prepared by oxidation of the corresponding imines with oxone or anhydrous MCPBA lithium salt as the source of oxygen. They transfer their N‐protected fragment to primary and secondary amines to give protected hydrazines in fair to excellent yield. The nitrogen transfer to free amino acids (in form of their R4N+ salts) is particularly fast, even at low temperature, providing L (or D) N‐protected α‐hydrazino acids. Enolates are C‐aminated to give N‐protected α‐amino ketones, esters, or amides in modest yield, due to a side aldol reaction of the unreacted enolate with the released benzaldehyde. With tertiary amines (Et3N), sulfides (PhSMe), and phosphines (Ph3P), amination and oxidation proceed in a parallel way; the amount of amination product increases when the temperature is lowered (kinetic control). Some of the factors that can orient the oxaziridine reactivity towards amination or oxidation of nucleophiles are considered.
Synthesis and Properties ofO‐Glycosyl Calix[4]Arenes (Calixsugars)
Authors: Dondoni Alessandro , Marra Alberto , Scherrmann Marie‐Christine , Casnati Alessandro , Sansone Francesco , Ungaro Rocco
Published: July 2007

ModelO‐glycosylation reactions at either rim of calix[4]arenes are described with the aim of providing access to a new family of carbohydrate‐containing calixarene derivatives named calixsugars. One or two sugar moieties (D‐mannofuranose and D‐glucopyranose) were introduced at the lower rim of the parent calix[4]arene by glycosylation of the phenolic hydroxyl groups by means of a Mitsunobu reaction. Tetrapropoxy calix[4]arenes bearing two or four hydroxymethyl groups at the upper rim were coupled with perbenzoylated thioethyl D‐galactoside and D‐lactoside in the presence of the thiophilic promoter copper(III) triflate. In this way β‐linked bis‐ and tetrakis‐O‐galactosyl calix[4]arenes were obtained in good yield, the latter showing some solubility in water. For theO‐lactosyl derivatives only the bis‐substituted compound could be obtained because of the competing formation of an intramolecular ether linkage between 1,3‐hydroxymethyl groups. Preliminary binding studies showed some affinity of the galactose‐containing calixsugars toward charged carbohydrates and dihydrogen phosphate anion.
Gas‐Phase Reactions at Low Temperatures: Towards Absolute Zero
Authors: Smith Ian W. M. , Sims Ian R. , Rowe Bertrand R. , Rowe B. R.
Published: July 2007

Very recently, methods have been developed for studying the rates of chemical reactions between electrically neutral species in the gas phase at temperatures as low as 13 K. Here we review this exciting development in gasphase chemical kinetics. Emphasis is placed on the importance of the information which the experiments have provided, both from the viewpoint of posing new questions about the factors which control chemical reactivity and because of their relevance to the modelling of molecular synthesis in interstellar clouds.
Molecules in Space
Authors: Williams David A.
Published: July 2007

The distribution and nature of interstellar matter in the Galaxy is described. The chemical processes by which the rich variety of molecular species arise are briefly sketched. The importance of interstellar molecules in influencing the evolution of the Galaxy is emphasized.
Electrochemically Induced Molecular Motions in Pseudorotaxanes: A Case of Dual‐Mode (Oxidative and Reductive) Dethreading
Authors: Asakawa Masumi , Ashton Peter R. , Balzani Vincenzo , Credi Alberto , Mattersteig Gunter , Matthews Owen A. , Montalti Marco , Spencer Neil , Stoddart J. Fraser , Venturi Margherita
Published: July 2007

The electrochemical and spectroscopic properties of a pseudorotaxane formed in acetonitrile solution by self‐assembly of a wire‐type electron donor based on the tetrathiafulvalene unit and the cyclobis(paraquat‐p‐phenylene) tetracationic electron acceptor have been investigated. We show that a) reversible dethreading/rethreading cycles of the pseudorotaxane can be performed by either oxidation and successive reduction of the electron‐donor wire or reduction and successive oxidation of the electron‐accepting tetracationic cyclophane, and b) because of this special behavior, the input (electrochemical)/output (absorption spectrum) characteristics of this molecular‐level system correspond to those of an XNOR logic gate.
Oligonucleotide Analogues with 4‐Hydroxy‐N‐Acetylprolinol as Sugar Substitute
Authors: Ceulemans Griet , Van Aerschot Arthur , Wroblowski Berthold , Rozenski Jef , Hendrix Chris , Herdewijn Piet
Published: July 2007

Modified oligonucleotides incorporating trans‐4‐hydroxy‐N‐acetyl‐L‐prolinol (trans‐4‐HO‐L‐NAP) or its D‐analogue as sugar substitute were synthesised with adenine and thymine as nucleobases. All‐adenine oligonucleotides built from (2S,4S) or (2R,4R)‐cis‐4‐hydroxy‐N‐acetylprolinol were likewise prepared. Hybridisation studies revealed that heterocomplexes formed between polyU and homochiral trans‐4‐hydroxy‐N‐acetylprolinol‐based oligomers of the same as well as of opposite chirality (polyU/trans‐DA*13 and polyU/trans‐LA*13). The former, however, were triple‐stranded. Other complexes with ribonucleic acids were polyA/trans‐LT*13 and polyU/cis‐LA*13. Heteroduplexes with deoxynucleic acids were formed between trans‐LA*13 and oligothymidylate. Interaction was also observed for cis‐LA*13 and oligothymidylate, but not with the D‐hydroxyprolinol analogues. Microcalorimetry proved this interaction to be the formation of a triple‐stranded complex. Two heteroduplexes, trans‐LA*13/dT13 and trans‐LA*13/polyU, had similar or slightly increased stability when compared to the natural dA13/dT13 or dA13/polyU systems. Microcalorimetry clearly indicated the formation of a duplex, in contrast to interactions with N‐acetylprolinol oligonucleotides of different stereochemistry. Moreover, the enthalpy change was of the same magnitude but the association constant was slightly lower. Natural nucleic acids thus clearly prefer hybridisation with L‐hydroxyprolinol oligomers over D‐hydroxyprolinol oligomers. For the series investigated, the L‐trans oligomers (Figure 1) seem best to mimic natural oligonucleotides. These modified oligonucleotides formed homocomplexes if both strands were of the same chirality, that is, homocomplexes formed between trans‐LA* and trans‐LT* and between trans‐DA* and trans‐DT*, reflecting the isochiral pu‐py pairing found in natural nucleic acids. Once more, however, calorimetry proved these to be triplex interactions. Heterochiral pairing was not observed between modified oligonucleotides, but only between modified oligonucleotides and natural polyU. The thermal stabilities of these heterochiral complexes differed clearly.
Mechanisms and Stereochemistry of Acid‐Induced Ring Opening of Optically Active 1,2‐Propene Oxides in the Gas Phase
Authors: Troiani Anna , Filippi Antonello , Speranza Maurizio
Published: July 2007

The acid‐induced ring opening of (S)‐(—)‐1,2‐propene oxide (1S) and (R)‐(+)‐1,2‐propene oxide (1R) has been investigated in gaseous CH4 and CH3F at 720 torr and in the presence of a nucleophile, NuOH (Nu = H or CH3). The mechanism of the ring‐opening reaction has been assessed by modulating the composition of the gaseous mixture. Two reaction pathways are operative in the gas phase, both proceeding through complete inversion of configuration of the reaction center. A first process is detectable only in the CH3F/H2O systems and takes place within a persistent proton‐bound complex generated by interaction of the epoxide with the CH3OH+2 ion, formed by methylation of H2O with (CH3)2F+. Such an intracomplex ring‐opening pathway proceeds through proton transfer from the CH3OH+2 ion to the epoxide followed by motion of the neutral CH3OH moiety around the 1‐H‐oxonia‐2‐methyl‐cyclo‐propane structure (H‐1R or H‐1S) (k<108 s‐1) before attacking the ring carbons from the rear. In all the other systems with added CH3OH, this intracomplex pathway is preceded by a faster “extracomplex” pathway involving the attack of an external CH3OH molecule on the proton‐bound adduct. The regioselectivity of the intracomplex process is similar to that of the extracomplex pathway. Both are characterized by a slight preference for the Cβ center of H‐1 R (or H‐1S) (extra‐complex path regioselectivity: α/β = 0.72±0.05; intracomplex path regioselectivity: α/β = 0.71±0.05). The regioselectivity of H‐1 R (or H‐1S) is substantially different from that of the 1‐Me‐oxonia‐2‐methyl‐cyclopropanes (Me‐1 R or Me‐1 S) toward the same nucleophile NuOH (α/β = 4.1±0.35 (Nu = H); 2.28±0.16 (Nu = CH3)). This difference is attributed to a transition structure wherein the Cα–O bond rupture increases from H‐1 R (or H‐1 S) to Me‐1 R (or Me‐1 S) and in passing from CH3OH to H2O. The regioand stereoselectivity of the gas‐phase acid‐induced ring opening of 1 S and 1 R are compared with those of related reactions carried out in solution.
Heterolytic Activation of Dihydrogen at Transition‐Metal Sulfur Sites in Coordinatively Unsaturated [rh(L)(“buS4”)]BF4 Complexes, Involving Neutral Hydrides, Thiol Hydrides, and Thiol–Hydride Proton Scrambling (L = CO, PCy3; “buS4”2‐ = 1,2‐Bis[(2‐mercapto‐3,5‐di‐tert‐butylphenylthio]ethane2‐)
Authors: Sellmann Dieter , Rackelmann Gabriele H. , Heinemann Frank W.
Published: July 2007

[Rh(H)(L)(“buS4”)] complexes (L = CO (1), PCy3 (2); “buS4”2‐ = 1,2‐bis[(2‐mercapto‐3,5‐di‐tert‐butylphenylthio)ethane2‐]) catalyze the D2/H+ exchange between D2 and EtOH protons in the presence of catalytic amounts of Brønsted acids. A mechanism and complete cycle for the heterolytic D2 cleavage are proposed that are based on characterization of key intermediates and monitoring of key reactions. The key intermediates are the thiol hydride complexes [Rh(H)(L)(“buS4”‐H)]BF4, L = CO (3), PCy3 (4), the coordinatively unsaturated complexes [Rh(L)(“buS4”)]BF4, L = CO (5), PCy3 (6), which are the actual catalysts, and the deuterium‐labeled derivatives of 1–4. Complexes 3 and 4 form from 1 and 2 by protonation with HBF4, and they release H2 to give 5 and 6. Complex 5 dimerizes in the solid state and was characterized by X‐ray structure determination of 5·8CH2Cl2 (triclinic space group P\documentclass{article}\pagestyle{empty}\begin{document}$ \bar 1 $\end{document}, a = 1048.2(4) pm, b = 1430.0(5) pm, c = 1785.7(7) pm, α = 100.49(3)°, β = 102.92(3)°; γ = 103.68(3)°, Z = 1). Complex 6 is mononuclear and adds H2O or THF reversibly to give the highly labile [Rh(L)(PCy3)(“buS4”)]BF4, L = H2O (7), THF (8). CO is irreversibly added to give the stable [Rh(CO)‐(PCy3)(“buS4”)]BF4 (9), whose high‐frequency ν(CO) (2081 cm‐1) indicates a relatively low electron density at the Rh center. Complex 6 also adds to H2 to give 4, which can be deprotonated by solid Na2CO3 or H2O to yield neutral 2. 1H NMR and 2H NMR spectroscopy revealed the scrambling of thiol protons and hydride ligands in 3 and 4 and its deuterium‐labeled derivatives. This exchange of thiol protons for hydride ligands is explained by a transient [Rh(η2‐H2)] species. Low‐temperature 1H/2H NMR spectroscopy showed that protonation of 2 yields four diastereomers of 4 resulting from protonation of the four stereochemically nonequivalent lone pairs at the thiolate donors of 2. The relevance of these findings to H2 activation at transitionmetal sulfur sites in hydrogenases or hydrotreatment catalysts, and differences from the H2 cleavage achieved with other complexes not containing “built‐in” Brønsted‐basic centers, are discussed.
Commentary on ‘Modification of the home environment for the reduction of injuries’, with response from review author
Authors: King W. James
Published: July 2007

This is a commentary on a Cochrane review, published in this issue of EBCH, first published as: Lyons RA, John A, Brophy S, Jones SJ, Johansen A, Kemp A, Lannon S, Patterson J, Rolfe B, Sander LV, Weightman A. Modification of the home environment for the reduction of injuries. Cochrane Database of Systematic Reviews 2006, Issue 4. Art. No.: CD003600. DOI: 10.1002/14 651 858.CD003600.pub2.

Further information for this Cochrane review is available in this issue of EBCH in the accompanying EBCH Summary and Characteristics and Key Findings Tables articles. Copyright © 2007 John Wiley & Sons, Ltd.
Written action plans (WAP) for children with asthma: Shoo be do wah or should we do WAP?
Authors: Fitzgerald Dominic A.
Published: July 2007

This is a commentary on a Cochrane review, published in this issue of EBCH, first published as: Bhogal S, Zemek R, Ducharme FM. Written action plans for asthma in children. Cochrane Database of Systematic Reviews 2006, Issue 3. Art. No.: CD005306. DOI: 10.1002/14 651 858.CD005306.pub2.

Further information for this Cochrane review is available in this issue of EBCH in the accompanying EBCH Summary and Characteristics and Key Findings Tables articles. Copyright © 2007 John Wiley & Sons, Ltd.
Characteristics and key findings for ‘Modification of the home environment for the reduction of injuries’
Authors: van Dalen Elvira , Offringa Martin , Kremer Leontien
Published: July 2007

These are the characteristics and key findings for a Cochrane review, published in this issue of EBCH, first published as: Lyons RA, John A, Brophy S, Jones SJ, Johansen A, Kemp A, Lannon S, Patterson J, Rolfe B, Sander LV, Weightman A. Modification of the home environment for the reduction of injuries. Cochrane Database of Systematic Reviews 2006, Issue 4. Art. No.: CD003600. DOI: 10.1002/14 651 858.CD003600.pub2.

Further information for this Cochrane review is available in this issue of EBCH in the accompanying EBCH Summary and Commentary articles. Copyright © 2007 John Wiley & Sons, Ltd.
The Cochrane Library and dietary prevention of allergic disease and food hypersensitivity in children: an umbrella review
Authors: Osborn David A. , Sinn John K.
Published: July 2007

Background

Dietary interventions, including avoiding allergy‐inducing foods in pregnant or lactating women and their infants, and the use dietary modifications such as prebiotics and probiotics, may prevent sensitization and subsequent allergic disease and food hypersensitivity in infants.

Objectives

To determine the evidence from Cochrane Systematic Reviews for dietary interventions for the primary prevention of clinical allergic disease or food hypersensitivity.

Methods

The Cochrane Database of Systematic Reviews was searched for systematic reviews examining prevention of allergic disease and/or food hypersensitivity. Two reviewers independently assessed review quality, reviewed assessments of study quality and extracted reported data.

Main results

Six reviews were eligible. All reviews had concerns regarding the methodological quality of included studies and several had insufficient numbers of enrolled infants to provide precise estimates of effect. There is insufficient evidence to support the use and safety of maternal dietary allergen restriction during pregnancy and/or lactation for prevention of allergic disease in high‐risk infants. In high‐risk infants unable to be exclusively breast‐fed, there is some evidence for use of a hydrolysed infant formula for prevention of allergic disease, although the evidence is not conclusive. Evidence suggests that soy‐based infant formula should not be recommended. One trial of prebiotic supplemented formula reported a significant reduction in eczema up to 6 months of age. Meta‐analysis of 5 trials of probiotic supplements found a significant reduction in infant eczema, although trial results were heterogeneous.

Authors' conclusions

In high‐risk infants, there is no evidence to support the use of dietary interventions in pregnant or lactating women, or the use of soy‐based formula in infants for prevention of allergic disease. There is insufficient evidence to recommend the use of prebiotics or probiotics. Further trials of hydrolysed infant formula, prebiotics and probiotics are warranted. Copyright © 2007 John Wiley & Sons, Ltd.
Hypoglycemia, brain energetics, and hypoglycemic neuronal death
Authors: Suh Sang Won , Hamby Aaron M. , Swanson Raymond A.
Published: July 2007

Hypoglycemia is a common and serious problem among diabetic patients receiving treatment with insulin or other glucose‐lowering drugs. Moderate hypoglycemia impairs neurological function, and severe hypoglycemia leads to death of selectively vulnerable neurons. Recent advances have shed new light on the underlying processes that cause neuronal death in hypoglycemia and the factors that may render specific neuronal populations especially vulnerable to hypoglycemia. In addition to its clinical importance, the pathophysiology of hypoglycemia is an indicator of the unique bioenergetic properties of the central nervous system, in particular the metabolic coupling of neuronal and astrocyte metabolism. This review will focus on relationships between bioenergetics and brain dysfunction in hypoglycemia, the neuronal cell death program triggered by hypoglycemia, and the role of astrocytes in these processes. © 2007 Wiley‐Liss, Inc.
Astrocyte control of the cerebrovasculature
Authors: Gordon Grant R. J. , Mulligan Sean J. , MacVicar Brian A.
Published: July 2007

The control of cerebral vessel diameter is of fundamental importance in maintaining healthy brain function because it is critical to match cerebral blood flow (CBF) to the metabolic demand of active neurons. Recent studies have shown that astrocytes are critical players in the regulation of cerebral blood vessel diameter and that there are several molecular pathways through which astrocytes can elicit these changes. Increased intracellular Ca2+ in astrocytes has demonstrated a dichotomy in vasomotor responses by causing the constriction as well as the dilation of neighboring blood vessels. The production of arachidonic acid (AA) in astrocytes by Ca2+ sensitive phospholipase A2 (PLA2) has been shown to be common to both constriction and dilation mechanisms. Constriction results from the conversion of AA to 20‐hydroxyeicosatetraenoic acid (20‐HETE) and dilation from the production of prostaglandin E2 (PGE2) or epoxyeicosatrienoic acid (EET) and the level of nitric oxide (NO) appears to dictate which of these two pathways is recruited. In addition the activation of Ca2+ activated K+ channels in astrocyte endfeet and the efflux of K+ has also been suggested to modify vascular tone by hyperpolarization and relaxation of smooth muscle cells (SMCs). The wide range of putative pathways indicates that more work is needed to clarify the contributions of astrocytes to vascular dynamics under different cellular conditions. Nonetheless it is clear that astrocytes are important albeit complicated regulators of CBF. © 2007 Wiley‐Liss, Inc.
Increase in nuclease resistance and incorporation of NF‐κB decoy oligodeoxynucleotides by modification of the 3′‐terminus
Authors: Osako Mariana Kiomy , Tomita Naruya , Nakagami Hironori , Kunugiza Yasuo , Yoshino Masafumi , Yuyama Kazuhiko , Tomita Tetsuya , Yoshikawa Hideki , Ogihara Toshio , Morishita Ryuichi
Published: July 2007

Background

For the development of molecular therapy based on oligodeoxynucleotides (ODN), ODN have to be stable against nucleases and be specific to the target transcription factor. To decrease non‐specific binding and degradation from the 3′‐terminus of ODN, we designed partially annealed ODN by binding the extremities of two single strands, resulting in a ribbon‐shaped ODN, so called ribbon‐type decoy ODN (R‐ODN).

Methods

We evaluated the efficiency in the process of enzymatic ligation of R‐ODN, the binding activity to nuclear factor‐κB (NF‐κB), and the stability against Exonuclease III and nucleases present in serum. The functional activity of R‐ODN to inhibit NF‐κBin vitrowas evaluated in human aortic smooth muscle cells (VSMC): TNF‐α‐induced proliferation rate and MMP‐9 expression were assessed after R‐ODN transfection.

Results and conclusions

Although R‐ODN have a phosphodiester backbone, their physical conformation was designed to provide nuclease resistance without interfering with their binding activity. As expected, R‐ODN showed more resistance to exonucleases and stability in 100% serum than non‐modified decoy ODN (N‐ODN). Importantly, the R‐ODN construction did not interfere with its binding activity to NF‐κB, similar to N‐ODN. Transfection of R‐ODN significantly inhibited the expression of MMP‐9 induced by TNF‐α in VSMC as assessed by real‐time polymerase chain reaction (PCR), and R‐ODN also inhibited the proliferation of VSMC induced by TNF‐α (10 ng/ml), similar to phosphorothioate decoy ODN. Overall, the development of ribbon NF‐κB decoy ODN could provide a useful tool for basic and clinical research. Copyright © 2007 John Wiley & Sons, Ltd.
Pseudosugars, 34. Synthesis of 5a‐carba‐β‐D‐glycosylceramide analogs linked by imino, ether and sulfide bridges
Authors: Tsunoda Hidetoshi , Ogawa Seiichiro
Published: July 2007

Carbocyclic analogs of glycoceramides, (2S,3R,4E)‐1‐(5a‐carba‐β‐D‐glycopyranosyl)‐2‐(hexadecanoylamino)‐4‐octa‐decen‐3‐ols E‐3‐E‐6, linked by imino, ether and sulfide bridges, were synthesized by coupling of aziridines, as the sphingosine precursors, with protected 1‐amino, 1‐hydroxy and 1‐mercapto derivatives of 5a‐carba sugars and subsequent deprotection and N‐acylation. Biological assay of 5a‐carbaglycosylceramides showed that both imino‐linked E‐3 and E‐4 having gluco and galacto configurations are mild immunomodulators and possess a mild inhibitory activity against gluco‐ and galactocerebrosidases. These findings prompted us to prepare the corresponding Z‐isomers Z‐3 and Z‐4, which interestingly show a similar enzyme‐inhibitory activity.