bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conformational Preference of 2‐(Halomethyl)‐ and 2‐(Oxymethyl)Pyridines: Microwave Spectrum, Ab Initio, and MM3 Studies of 2‐(Fluoromethyl)Pyridine
Authors: Moberg Christina , Adolfsson Hans , Wärnmark Kenneth , Norrby Per‐Ola , Marstokk Karl‐Magnus , Møllendal Harald 
Published: July 2007

AbstractOne single conformer was assigned from the microwave spectrum of 2‐(fluoromethyl)pyridine, investigated in the gas phase in the 26.0–39.0 GHz spectral region at about –10°C. Its Cα–F bond was found to be coplanar with the ring and anti to the N–C2 bond (syn to the C2–C3 bond). There was no indication in the microwave spectrum of the presence of other rotameric forms of the molecule.The results of the spectroscopic study were backed up by ab initio calculations at the MP2/6‐31 G** (frozen core) level. These calculations predict that the assigned conformer is the only stable form of the molecule. The transition state was calculated to have the CH2F group 180° from the stable anti conformation. The energy of the transition state was computed to be 20.2 kJ mol‐1 higher than the energy of the anti rotamer.The results are interpreted in terms of a stereoelectronic effect, and the orbital overlaps responsible for the observed effect are discussed. It is shown that 2‐(fluoromethyl)pyridine serves as a good model for 2‐(alkoxymethyl)pyridines, previously found to show the same conformational preference.
Emission from Zeolite‐Occluded Manganese–Diimine Complexes
Authors: Knops‐Gerrits Peter‐Paul H. J. M. , De Schryver Frans C. , Auweraer Mark Van Der , Mingroot Hans Van , Li Xiao‐Yuan , Jacobs Pierre A. 
Published: July 2007

AbstractManganese complexes of 2,2′‐bipyridine (bpy) and 1,10‐phenantroline (phen) have been synthesised in the supercages of cubic NaX and NaY and in the hypercages of the hexagonal NaEMT faujasites. The coordination and redox chemistry were studied with ESCA, CA, FT‐IR, FT‐Raman, diffuse reflectance and emission techniques. FT‐IR/FT‐Raman shows cis coordination for all complexes and a high Mn–N stretching frequency in the phen complexes as a result of steric constraints imposed by the ligand. [Mn(bpy)2]2+ in the different zeolites shows metal‐to‐ligand charge transfer (MLCT; at 495 nm); for [Mn(phen)2]2+‐NaY the MLCt is broadened owing to complex distortion. On MLCT excitation [Mn(bpy)2]2+ complexes show an ipsochromic shift in the emission and an increase in quantum yield with increasing steric restrictions imposed by the zeolite. The ipsochromic shift of the emission band of [Mn(phen)2]2+ in NaY results from the combined effect of the ligand field (this suggests emission from a CT state) and of coordinative distortion. The key factor influencing the emission properties is found to be the overall matrix‐induced complex distortion. Cation stabilisation of the ligand anion affects emission indirectly. The decay times for [Mn‐(bpy)2]2+‐NaY are in the millisecond range (7.5–11.5 ms). A proposed model for excitation and emission properties of zeolite‐occluded MnII complexes involves excitation of a quartet CT state, intersystem crossing and subsequent emission. The enhanced stability of the coordination sphere in the zeolite allows complexes to luminesce from a CT state, which is not detected in solution. The zeolite behaves as a supramolecular cryptating agent, protecting complexes from photodissociation.
O‐Atom Transfer to Fe+n Clusters (n = 2–10) from O2, N2O and CO2: “Microoxides of Iron”
Authors: Gehret Oliver , Irion Manfred P. 
Published: July 2007

AbstractWe report on the gas phase reactions of small Fe+n clusters (n = 2–10) with O2, N2O and CO2 in an FT‐ICR mass spectrometer. Under our experimental conditions, clusters of all sizes reacted readily with O2 and all but the dimer reacted with N2O. Only the smallest Fe+n clusters (n = 2–4) appeared to activate CO2. For all X–O molecules (X = O, N2, CO), reaction pathways were observed that include the transfer of O atoms. In addition, the reactions with O2 and N2O were accompanied by the loss of one or two Fe atoms. Thermochemical considerations based upon the well‐known X–O bond energies were used to calculate Fen‐O+ bond dissociation energies (BDEs) for sizes n = 2–6; these amount to roughly 550 kJ mol‐1 and thus are considerably higher than the BDE of the Fe‐O+ ion. All oxidation reactions of the Fe+n clusters (n = 2–6) studied in more detail were terminated by products of FexOx+ stoichiometry (x = 1–4). These “microoxides of iron” are not able to activate any further X–O bonds. Secondary reactions of FexOx+ clusters with C6H6, C2H4 and NH3 were investigated for two selected sizes (x = 2, 3) and compared with reactions of the naked Fe+n clusters.
Fluorescence Redox Switching Systems Operating through Metal Centres: the NiIII/NiII Couple
Authors: Fabbrizzi Luigi , Licchelli Maurizio , De Santis Giancarlo , Sardone Nicola , Velders Aldo Hendrikus 
Published: July 2007

AbstractThe covalently linked two‐component systems 3 and 4 display fluorescence redox switching activity: the NiIII form quenches the fluorescence of the proximate aromatic fluorophore, whereas the NiII form does not. Thus, fluorescence can be switched on and off at will through the reversible NiII/NiIII redox reaction, which is carried out both electrochemically (in MeCN) and chemically (in EtOH). Quenching of the excited fluorophore F* is ascribed to a thermodynamically favoured F*‐to‐NiIII electron transfer mechanism. The more flexible system 5 does not work as a switch, since the fluorescence of the anthracene subunit is quenched in both NilII and NiIII forms (an OFF/OFF situation), through an energy transfer mechanism. The crystal and molecular structure of 4 in its protonated form is also described.
A Theoretical Study of the Additivity of Proton Affinities in Aromatics: Polysubstituted Benzenes
Authors: Eckert‐Maksik Mirjana , Klessinger Martin , Maksii Zvonimir B. 
Published: July 2007

AbstractAn additivity rule for proton affinities (PAS) in polysubstituted benzenes is derived from the MP2(fc)/6‐31 G**//HF/6‐31 G* + ZPE(HF/6‐31 G*) theoretical model by use of the concepts of homodesmic reactions and independent substituents. The performance of the additivity rule of thumb is very good; this is evidenced by the excellent agreement of the estimated PAS with the latest experimental data. We believe that the additivity should work for larger aromatic compounds too. The PA increments, which characterize the influence of each substituent on a particular site of the benzene ring undergoing electrophilic substitution, proved useful in discussing various chemical properties of this family of compounds.
Alkali‐Metal Cation Binding by Self‐Assembled Cryptand‐Type Supermolecules
Authors: Albrecht Markus , Röttele Herbert , Burger Peter 
Published: July 2007

AbstractReaction of three equivalents of alkyl‐bridged biscatechol ligands (1‐3)‐H4 with two equivalents of [(acac)2TiO] in the presence of two equivalents of alkalimetal carbonate (M = Na, K) affords helicate‐ or meso‐helicate‐type supramolecular coordination compounds by spontaneous self‐assembly processes. The cryptand‐type structure of the binuclear tetraanions [(1)3Ti2]4‐ or [(2)3Ti2]4‐ permits inclusion of sodium cations; this was observed by 23Na NMR spectroscopy in solution. Competition experiments with potassium or lithium cations revealed that potassium but not lithium easily displaces the sodium ions from the cavity. Titration experiments indicated that the binding constant for potassium is significantly higher than for sodium. On the other hand, for the large tetraanion [(3)3Ti2]4‐ with hexamethylene spacers, no binding of alkali‐metal ions could be observed by NMR spectroscopy in solution. In the solid state, however, two potassium ions could be incorporated in the interior of the cryptand‐type helicate.
Synthesis and Structure of a Bis(Double Helicate) and its Cryptatoclathrate
Authors: Saalfrank Rolf W. , Harbig Roland , Nachtrab Jochen , Bauer Walter , Zeller Klaus‐Peter , Stalke Dietmar , Teichert Markus 
Published: July 2007

AbstractThe structures of the hitherto unknown bis(double helicate) 10 and its cryptatoclathrate (10)2·2THF were unequivocally determined by X‐ray diffraction. Bis(double helicate) 10 is formed in a one‐pot synthesis starting from CH‐acidic bis (tetrazolylmethyl ketone) 9 and Zn(OAc)2. The formation of racemic, homochiral 10 from [Zn2L32] fragments, which are formed in a self‐assembly process, is governed by chiral self‐recognition. According to NMR studies only 10 is present in solution. 13C CP/MAS NMR spectroscopy and X‐ray analysis confirm aggregation of 10 with two molecules of THF to yield the inclusion compound (10)2·2 THF in the solid state.
Phosphorus‐Containing Dendrimers: Synthesis of Macromolecules with Multiple Tri‐ and Tetrafunctionalization
Authors: Lartigue Marie‐Laure , Slany Michael , Caminade Anne‐Marie , Majoral Jean‐Pierre 
Published: July 2007

AbstractA variety of dendrimers up to generation 7 possessing terminal P(S)Cl2, (3‐[G1]‐3‐[G7]) or P(O)Cl2, (7‐[G1]‐7‐[G3], 7‐[G3, 7‐[G7) have been tri‐ and tetrafunctionalized. Selective monosubstitution of P(X)Cl2 (X = S, 0) termini with allylamine or propargylamine gave the trifunctionalized dendrimers 5‐[G1], 5‐[G7], 8‐[G1], 8‐[G3], 10[G1], 11‐[G4], ll‐[G4], 12‐[G1]‐12‐[G3], 12‐[G5], and 12‐[G7]. Reaction of dendrimers 4‐[G1] and 4‐[G4], possessing terminal P(S)[N‐allyl) fragments, with propargylamine afforded trifunctionalized dendrimers l4‐[G1 and l4‐[G4]. Multiply trifunctionalized macromolecules 13‐[G2] and 13‐[G3] with P(S)(NH‐allyl)(NH‐propargyl) moieties at the surface were prepared by treatment of 8‐[G2] and 8‐[G3] with propargylamine. Dendrimers 15‐[G1]‐l5‐[G3] and l6‐[G1]‐l6‐[G3] with P(O)(NH‐allyl)(OC6H4CHO) and P(O)(NH‐propargyl)(OC6H4CHO) termini were also synthesized. Reaction of hydrazine or cyanomethylenetriphenylphosphorane (17) with compounds 15‐[G1], 15‐[G3], and 16‐[G1]‐16‐[G3] led to the multiply tetrafunctionalized dendrimers 18‐[G1], 18‐[G3], 19‐[G1], 20‐[G1]‐20‐[G3], 21‐[G1], and 21‐[G2].
The [Fe(etz)6](BF4)2 Spin‐Crossover System—Part One: High‐Spin ⇌ Low‐Spin Transition in Two Lattice Sites
Authors: Hauser Andreas , Gütlich Philipp , Hinek Roland , Spiering Hartmut , Schollmeyer Dieter 
Published: July 2007

AbstractThe [Fe(etz),](BF,), spin‐cross‐over system (etz = 1‐ethyl‐1 H‐tetrazole) crystallizes in space group P1, with the following lattice constants at 298 K: a 10.419(3), b=15.709(1), c = 18.890(2) Å = α = 71.223(9), β =77.986(10), and γ = 84.62(1)° V = 2862.0(9) Å3 and Z = 3. Two nonequivalent lattice sites, one without (site A) and one with (site B) inversion symmetry, are observed. The population of the two sites nA:nB is 2:l. Iron(II) on site A undergoes a thermal low‐spin (LS) → high‐spin (HS) transition with T1/2I, = 105 K. whereas that on site B remains in the high‐spin state down to cryogenic temperatures. Application of external pressure of up to 1200 bar between 200 and 60 K does not cause formation of the low‐spin state on site B. On site A the high‐spin state can be populated as a metastable state at 20 K by irradiating the sample with λ = 514.5 nm; on site B a light‐induced population of the low‐spin state can be achieved with λ = 820 nm.
First Observation of a [1,7] Boron Shift—Three Independent Fluxional Processes in the Tricarbonyliron Complex of Cycloheptatrienyl(dipropyl)borane
Authors: Gridnev Ilya D. , Tok Oleg L. , Bubnov Yuri N. , Gurskii Mikhail E. 
Published: July 2007

AbstractThe fluxional behavior of [1–4‐η4 ‐ exo ‐ 7 ‐ dipropylborylcyclohepta ‐ 1,3,5‐triene]tricarbonyliron (14) has been studied by dynamic NMR. The 2 D 1H and 13C EXSY NMR experiments carried out at various temperatures revealed that three independent fluxional processes occur in 14. The fastest rearrangement is a [1,7] B sigmatropic shift accompanied by [1,2] Fe migration (EA = 71.2±2.3 kJ mol‐1, ln A = 32±1). Two other rearrangements also take place: [1,3] B sigmatropic and [1,3] Fe haptotropic migrations. The analysis of the observed selectivity towards [1,j] B sigmatropic shifts ([1,3] and [1,7] B shifts are observed, but [1,5] B shifts are not) in terms of theoretical predictions gives reason to assume that the [1,j] boron migrations occur with inversion of configuration at the migrating atom.
Efficient Stereoselective Synthesis of Plasmenylcholines
Authors: Rui Yuanjin , Thompson David H. 
Published: July 2007

AbstractThe first practical total chemical synthesis of a plasmenylcholine (1–O‐1'‐(Z)‐hexadecenyl‐2‐hexadecanoyl‐sn‐glycero‐3‐phosphocholine) with pure (Z) olefin stereochemistry is reported. Monopalmitin was doubly protected as the 3‐TBDPS‐2‐TBDMS ethers (tert‐butyldiphenylsilyl‐, tert‐butyldimethylsilyl‐) and converted to the corresponding 1‐O‐1′‐(Z)‐hexadecenyl‐2‐TBDMS‐3‐TBDPS‐glyceryl ether (by the method of ref. [43]). Clean deprotection with tetra‐butylammonium fluoride in the presence of imidazole gave 1‐O‐1′‐(Z)‐hexadecenylglycerol in >90% yield. Resilylation with TBDPSCl followed by acylation of the sn‐2 alcohol with palmitoyl chloride and deprotection of the resulting 3‐TBDPS‐2‐hexadecanoyl‐1–O‐1′‐(Z)‐hexadecenylglycerol at –20°C with Bu4NF gave 2‐hexadecanoyl‐1–O‐1′‐(Z)‐hexadecenylglycerol in 86% yield. The 3‐phosphocholine group was attached by phosphorylating the free hydroxyl with 2‐chloro‐2‐oxo‐1,3,2‐dioxaphospholane in the presence of pyridine, instead of Et3N, as base to avoid acyl migration; the dioxaphospholane triester intermediate was subsequently cleaved with Me3N to give 1‐O‐1′‐(Z)‐hexadecenyl‐2‐hexadecanoyl‐sn‐glycero‐3‐phosphocholine in 18% overall yield from monopalmitin. The efficiency and flexibility of this route makes it well‐suited to the preparation of a wide variety of 1‐, 2‐, and 3‐substituted as well as isotopically labeled plasmenylcholines for biophysical and biochemical studies.
Thermochemistry of Metal Nitrides in the Ca/Zn/N System
Authors: McHale James M. , Navrotsky Alexandra , Kowach Glen R. , Disalvo Francis J. 
Published: July 2007

AbstractThe energetics of ternary oxide formation is reasonably well understood, but little is known of the energetics of ternary nitride formation. We have developed new procedures for high‐temperature oxide melt solution calorimetry on metal nitrides and employed them to study compounds in the Ca/Zn/N system. The calorimetry utilized the easy reduction of MoO3 in the solvent to supply a pathway for rapid oxidation of “N3–” to N2 gas. These experiments represent the first high‐temperature solution calorimetry of ternary metal nitrides. The results indicate that Ca3N2 acts as a basic nitride analogous to CaO in oxide systems, while Zn3N2 acts as an acidic nitride (“N3–” acceptor) in this ternary nitride system.
Organometallic Half‐Sandwich Complexes Promote the Formation of Linear Oligopeptides from Amino Acid Esters
Authors: Robl Christian , Maurus Michael , Sünkel Karlheinz , Beck Wolfgang , Krämer Roland , Polborn K. 
Published: July 2007

AbstractOrganometallic dipeptide ester complexes of the general formula [(L)M(Cl)(K2‐NH2CH2CONCH2CO2R)] (1: LCp*, MRh, 2: LCp*, MIr, 3: Lη6‐C6Me6, MRu) react smoothly with various α‐L‐amino acid esters in the presence of NEt3 to yield the tripeptide ester complexes [(L)M(Cl)(K2‐NH2CHR'CONCH2CONHCH2CO2R)] (5–7). In the same fashion chloro K2‐tetrapeptide ester complexes 10 and 11 are obtained either from tripeptide ester complexes or by subsequent addition of two equivalents of amino acid ester to a dipeptide ester complex. When the strong base NaOMe is used in the reaction of the diglycine ester compounds with amino acid esters. K3‐tripeptide ester complexes 12 and 13 are produced, in which one of the two coordinated peptide nitrogen atoms is pyramidal. The hexamethylbenzene ruthenium complexes 13 with tripeptide ligands are formed with very high diastereoselectivity. A plausible reaction mechanism for the metal‐promoted peptide synthesis is presented. Synthesis and isolation of the peptide esters proceeds without racemization.
Acid‐Base Properties of Adenosine 5′‐O‐Thiomonophosphate in Aqueous Solution
Authors: Song Bin , Sigel Roland K. O. , Sigel Helmut 
Published: July 2007

AbstractThe acidity constants of H2‐(AMPS)± were determined by potentiometric pH titrations in aqueous solution at 25°C and I=0.1M (NaNO3). Titrations with a combined single‐junction glass electrode were hampered in the presence of AMPS by a “poisoning” effect; the problem could be avoided by use of two separated electrodes. The values of the acidity constants PKHH2(AMPS) = 3.72 ± 0.03 and pKHH2(AMPS) = 4.83 ± 0.02 are relatively close to each other; the buffer regions of the two equilibria overlap, and therefore a micro acidity constant scheme was developed and the constants for the various sites calculated. It is concluded that the thiophosphateprotonated species (AMPS⋅H)− dominates at about 75% occurrence, while the form (H⋅AMPS)−, with the proton at the N1 site of the adenine residue, occurs at about 25%. Semiempirical AM1 and PM3 calculations including water as a solvent locate the proton in (AMPS⋅H)− mainly on the terminal oxygen atoms rather than the sulfur. The acid‐base properties of H2(AMPS)± are considerably more complicated than those of the parent nucleotide, H2(AMP)±; for the latter the two (intrinsic) acidity constants are well separated and consequently practically all protons have left the N1 site before deprotonation at the monoprotonated phosphate group occurs. Finally, an estimate for the acidity constants of H2(ATPγS)2‐ is given.
Synthesis and Reactivity of [(η6‐Biphenylene)Mn(CO)3]+
Authors: Dullaghan Conor A. , Carpenter Gene B. , Sweigart D. A. 
Published: July 2007

AbstractBiphenylene readily coordinates through one of the phenyl rings to form [(η6‐biphenylene)Mn(CO)3]+ (2+), the X‐ray structure of which is reported. The nucleophiles H−, Me−, Me3CC(O)CH−2 and P(OEt)3 add to 2+ at a bridgehead carbon to afford high yields of cyclohexadienyl complexes (3); the X‐ray structure of the product of hydride addition is reported. P(OMe)3 adds to 2+ to give 3, which then undergoes a spontaneous Arbuzov elimination to the dimethyl phosphonate adduct. Nucleophilic additions to 2+ are unusual in that they occur at a substituted (bridgehead) carbon. A kinetic and thermodynamic study of the reaction with P(OEt)3 shows that the bridgehead carbons in 2+ are orders of magnitude more electrophilic than are the arene carbons in unstrained [(arene)Mn(CO)3]+ systems.
Theoretical Investigation of the Mechanism of the Baeyer‐Villiger Reaction in Nonpolar Solvents
Authors: Okuno Yoshishige 
Published: July 2007

AbstractThe Baeyer‐Villiger reaction of p‐anisaldehyde with peroxyacetic acid in nonpolar solvents to give p‐anisylformate was examined on the basis of ab initio molecular orbital calculations. To explain the experimental observations, the free‐energy change was evaluated for each case in the absence and in the presence of an acid catalyst. It was found that, without catalysts, the rate‐determining step corresponds to the carbonyl addition of peroxyacetic acid to p‐anisaldehyde and the reaction hardly occurs. Acetic acid was found to catalyze the carbonyl addition and change the rate‐determining step from the carbonyl addition to the migration of the carbonyl‐adduct intermediate. Trifluoroacetic acid was observed to catalyze both the carbonyl addition and migration, and the carbonyl addition was demonstrated to be a rate‐determining step. The results provided a convincing explanation of the complex kinetics seen experimentally. Further calculations were performed for the reaction of benzaldehyde with peroxyacetic acid to give phenylformate. Migratory aptitude was found to depend on the catalyst. Isotope effects were also investigated, and the exceptional isotope effect observed experimentally was shown to be due to the rate‐determining carbonyl addition caused by autocatalysis. It is concluded that the mechanism of the reaction varies with catalysis or substituent effects.
Syntheses, Crystal Structures, and Properties of Novel Heterooctametallic Clusters Na2M'2[M3O4(O2CEt)8]2 (M' = Fe, Cr, Mo; M3 = Mo3, MoW2, W3)
Authors: Xu Li , Li Zhaohui , Liu Huang , Huang Jinshun , Zhang Qianer 
Published: July 2007

AbstractA mixture of Na2MO4, M(CO)6, FeCl3·6H2O, and (EtCO)2O was heated at 120°C to produce the heterooctanuclear clusters Na2Fe2[M3O4‐(O2CEt)8]2 (M = Mo, 1; W, 2). The bioxo‐capped clusters Na[M3O2(O2CEt)9] (M3 = MoW2, W3) were treated with Fe‐(CO)5, Cr(CO)6, and Mo(CO)6 in (EtCO)2O at 120°C to afford Na2M'2‐[MoW2O4(O2CEt)8]2 (M' = Fe, 3; Cr, 4; Mo, 5) and Na2Mo2[W3O4(O2CEt)8]2 (6), respectively. The isomorphous clusters 1, 2, 5, and 6 were characterized by X‐ray crystallography. The structures, similar to those of the analogues Na2Cr2[M3O4‐(O2CEt)8] (M = Mo, 7; W, 8) and Na2V2[M3O4(O2CEt)8]2 (M = Mo, 9; W, 10), consist of two incomplete cubane‐type [M3O4(O2Et)8]4‐ units centrosymmetrically bridged by two M'(III) metal ions through μ‐oxo and propionate groups; the resulting cluster dianions are linked by Na+ ions into infinite chains. Clusters 1–10 do not dissolve in water and common organic solvents at room temperature. Unlike the chromium(III) clusters 7 and 8, the iron(III) and vanadium(III) clusters 1 and 9 are soluble in aqueous acid solution, as a result of their decomposition into isolated [Mo3O4]4+ cluster units. Temperature‐dependent magnetic susceptibilities of 1, 2, and 7–10 were measured over the range 2–200 K and modeled by means of the spin‐Hamiltonian H = – 2JS1S2 to give spin exchange coupling constants J/k of –0.60, –0.72, –1.76, –1.31, –4.80, and –1.46 K, respectively. These figures show that antiferromagnetic spin exchange coupling interactions between the magnetic, bridging M'(III) ions are very weak. These species show characteristic bands in the IR spectra at 740–820 cm−1, which can probably be assigned to ṽ(M‐μ‐O).
Screening of Various Catalysts for the Asymmetric Cyclopropanation of Structurally Typical Silyl Enol Ethers—Scope and Limitations of Evans's Bisoxazoline Copper Catalyst
Authors: Schumacher Ralf , Reißig Hans‐Ulrich , Dammast Franziska 
Published: July 2007

AbstractThe scope and limitations of asymmetric syntheses of 2‐siloxycyclopropanecarboxylates 3 were examined by combination of structurally typical silyl enol ethers and methyl diazoacetate with various chiral catalysts. It was found that the Schiff base complex 5ṁCu(OAc)2 and the bisoxazoline complex 6ṁCuOTf gave the highest stereoselectivities (e.g., 72% ee for cis‐3d with 5ṁCu(OAc)2 as catalyst or 76% and 73% ee for cis‐ and trans‐3a, respectively, with 6‐CuOTf as catalyst). High enantioselectivities or diastereoselectivities were obtained. Other catalysts based on copper, rhodium or ruthenium complexes afforded significantly lower values. In further investigations, Evans's bisoxazoline complex 6‐CuOTf proved to be limited to 1,1‐disubstituted silyl enol ethers (e.g. 1a and 1e) for high enantiomeric excesses (up to > 95%, poor diastereoselectivities) and to 1,2‐substituted enol ethers (e.g. 1e) for high diastereoselectivities (cis:trans < 3:97, eetrans = 49%).
Functionalized Lipid Tubules as Tools for Helical Crystallization of Proteins
Authors: Ringler Philippe , Müller Wolfgang , Ringsdorf Helmut , Brisson Alain 
Published: July 2007

AbstractThe development of functional supramolecular devices built by self‐assembly of elementary molecules and with bioactive properties arouses considerable interest in the field of nanotechnology and new materials. We report here the formation of a new class of lipid tubules exhibiting both properties of molecular recognition and crystal formation for the protein streptavidin. These lipid tubules, made of biotin‐containing dioctadecylamine molecules, are straight hollow cylinders with a constant diameter of 27 nm and variable length up to several micrometers. They are unilamellar with an inner diameter of about 16 nm, as shown by cryoelectron microscopy. Streptavidin binds to the biotinylated tubules and assembles spontaneously into ordered helical arrays at the tube surface. These crystals exhibit regular order up to about 1.5 nm resolution. In addition, the helical streptavidin arrays act as functionalized supramolecular devices that bind a wide variety of biotinylated objects, as demonstrated here with proteins and liposomes.