3,4‐Di­hydro‐6‐methyl‐3‐β‐d‐ribo­furan­osyl‐4,5′‐cyclo‐9H‐imidazo[1,2‐a]­purin‐9‐one hydrate

In the title compound, C₁₃H₁₃N₅O₄·H₂O (4,5′‐cyclo­wyosine·H₂O), the cyclization forces a syn arrangement of the aglycon with respect to the sugar moiety. The ribo­furan­ose part of the mol­ecule displays a β‐d configuration with an envelope C1′‐endo pucker. The mol­ecules are arranged in columns along the short a axis and are linked to water mol­ecules through O—H?O and O—H?N hydrogen bonds.     

Anionic carbonyl complexes of the group VI transition metals with sulfur containing ligands

Anionic complexes of the type [M(CO)₄(dpet)]^? (where M is Cr, Mo or W and dpet is the anion of 2-(diphenylphosphino)ethanthiol) are readily prepared by the reaction of the Tl(dpet) and [M(CO)₅X]^? anions (X = halogen). These complex anions appear to have the normal octahedral geometry with the dpet ligand coordinated through both the P and S atoms. When treated with methyl or allyl halides, neutral complexes of the type M(CO)₄(dpet—R) are formed (where R is an allyl or methyl group now bound to the sulfur atom). By treating Tl^I salts of o-aminothiophenol (atp), o-methylmercaptophenol (nmp) and methylxanthic acid (mxt), with [M(CO)₅]^? anions, the respective complexes [M(CO)₄(atp)]^?, [M(CO)₄(mmp)]^? and [M(CO)₅(mxt)]^? are formed.     

Strong coupling expansion for classical statistical dynamics

We discuss the simple, randomly driven systemdx/dt = –x –x³ +f(t), wheref(t) is a Gaussian random function or stirring force with f(t)f(t) = (t – t). We show how to obtain approximately the coefficients of the expansion of the equal-time Green's functions as power series in (1/R)ⁿ, whereR is the internal Reynolds number ()^1/2/, by using a new expansion for the path integral representation of the generating functional for the correlation functions. Exploiting the fact that the action for the randomly driven system is related to that of a quantum mechanical anharmonic oscillator with Hamiltonianp ²/2 +m ² x ²/2 +vx ⁴ +x ⁶/2, we evaluate the path integral on a lattice by assuming that thex ⁶ term dominates the action. This gives an expansion of the lattice theory Green's functions as power series in 1/(a)^1/3, wherea is the lattice spacing. Using Padé approximants to extrapolate toa = 0, we obtain the desired large-Reynolds-number expansion of the two-point function.Supported financially by the National Science Foundation and the U.S. Department of Energy.     

Bis(tetramethylammonium) hexaaquadodeca‐μ‐bromo‐octahedro‐hexatantalum tetrabromide dihydrate

The novel title compound, [(CH₃)₄N]₂[Ta₆Br₁₂(H₂O)₆]Br₄·2H₂O, with a [Ta₆Br₁₂]²⁺ cluster unit, has been prepared and structurally characterized. The compound crystallizes in space group C2/c, with a twofold axis passing through the cluster and the centre of symmetry located between the clusters. The nearest neighbouring cluster units are aligned along the crystallographic c axis, forming a one‐dimensional chain pattern.     

Complete ozonolysis of alkyl substituted ethenes at -60 degrees C: distributions of ozonide and oligomeric products

The distribution of ozonide and oligomeric structures formed on complete ozonolysis of alkenes in a non-participating solvent at -60 degrees C is governed by the alkyl substitution around the carbon-carbon double bond. The ozonolysis of a 1,1-alkyl substituted ethene generally favours the formation of an ozonide (a 1,2,4-trioxolane). Whereas the ozonolysis of a 1,1,2-alkyl substituted ethene also produces ozonide, a considerable amount of the ozonised products are oligomeric in nature. For example, the ozonolysis of 3-methylpent-2-ene in solution to high conversion in pentane yields oligomers with structural units derived from the fragmentation products of the primary ozonide (a 1,2,3-trioxolane) which are namely butanone carbonyl oxide and acetaldehyde; these can be characterised by electrospray ionisation mass spectroscopy (ESI-MS) under soft ionisation conditions. The predominant oligomers formed are rich in carbonyl oxide units (80 + mol%) and are cyclic in nature. A small proportion of the oligomers formed are open chain compounds with end groups that suggest that chain termination is brought about either by water or by hydrogen peroxide. Residual water in the solvent will react with the carbonyl oxides to produce 2-methoxybut-2-yl hydroperoxide, which we propose readily decomposes generating hydrogen peroxide. A significant yield of oligomers also is obtained from the ozonolysis of a 1,2-alkyl substituted ethene. The ozonolysis of trans-hex-2-ene in pentane yields oligomers containing up to four structural units and are predicted to be mainly cyclic.     

Crystal structure of synthetic Cu3SeO4(OH)4

Summary The crystal structure of synthetic Cu₃SeO₄(OH)₄ was determined by single crystal X-ray methods:a=8.382 (2) Å,b=6.087 (1) Å,c=12.285 (2) Å,V=626.8 ų,Z=4, space group Pnma,R=0.026,R _w =0.021 for 1255 independent reflections (sin / 0.8 Å^–1). The crystal structure is isotypic to that of the mineral antlerite, Cu₃SO₄(OH)₄. The copper atoms are Jahn-Teller distorted with Cu^[4+2]O₆ polyhedra forming triple chains along [010]. These chains are linked via SeO₄ tetrahedra and weak hydrogen bonds to a framework structure.

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Die Kristallstruktur von synthetischem Cu₃SeO₄(OH)₄

Zusammenfassung Die Kristallstruktur von synthetischem Cu₃SeO₄(OH)₄ wurde mittels Einkristall-Röntgenmethoden ermittelt:a=8.382 (2) Å,b=6.087 (1) Å,c=12.285 (2) Å,V=626.8 ų,Z=4, Raumgruppe Pnma,R=0.026,R _w =0.021 für 1255 unabhängige Reflexe (sin / 0.8 Å^–1). Die Kristallstruktur ist isotyp mit der des Minerals Antlerit, Cu₃SO₄(OH)₄. Die Kupferatome sind Jahn-Teller-verzerrt, die Cu^[4+2]O₆ Polyeder bilden Dreierketten entlang [010]. Diese Ketten sind über SeO₄-Tetraeder und schwache Wasserstoffbrücken zu einer Gerüststruktur verbunden.

     

RNA-catalyzed RNA ligation on an external RNA template

Variants of the hc ligase ribozyme, which catalyzes ligation of the 3' end of an RNA substrate to the 5' end of the ribozyme, were utilized to evolve a ribozyme that catalyzes ligation reactions on an external RNA template. The evolved ribozyme catalyzes the joining of an oligonucleotide 3'-hydroxyl to the 5'-triphosphate of an RNA hairpin molecule. The ribozyme can also utilize various substrate sequences, demonstrating a largely sequence-independent mechanism for substrate recognition. The ribozyme also carries out the ligation of two oligonucleotides that are bound at adjacent positions on a complementary template. Finally, it catalyzes addition of mononucleoside 5'-triphosphates onto the 3' end of an oligonucleotide primer in a template-dependent manner. The development of ribozymes that catalyze polymerase-type reactions contributes to the notion that an RNA world could have existed during the early history of life on Earth.     

A total synthesis of phomactin A

A total synthesis of phomactin A (1) based on a Cr(II)/Ni(II) macrocyclisation from the aldehyde vinyl iodide 11, leading to 12, followed by elaboration of the epoxyketone 16, which then undergoes spontaneous pyran-hemiacetal formation on deprotection, is described.     

Fourier transform infrared studies of alternate acid-amine Langmuir-Blodgett films with pyroelectric properties

FTIR-RAIRS and ATR techniques are shown to provide a powerful means of investigating the molecular behaviour responsible for the pyroelectric properties of organic monolayer assemblies on silicon and aluminised glass. Spectral changes, associated with either proton transfer or head group rearrangement, are well correlated with the level of pyroelectric response for two different devices. The technique promises to be extremely important for the elucidation of the microscopic properties of molecular electronic devices.     

Isotope effects in electron-donor-acceptor complexes involving aromatic hydrocarbons and fluoranil from NMR shift measurements

Equilibrium constants and NMR shift parameters have been determined for complexes of benzene, toluene and p-xylene and their perdeutero-analogues with fluoranil in cyclohexane solution from NMR shift measurements. Isotope effects are observed in the 1:1 equilibrium constants for the complexes of p-xylene $\text{(}\text{K}{}_1\text{(D)}\text{K}{}_1\text{(H)}$= 1.1₀) and toluene $\text{(}\text{K}{}_1\text{(D)}\text{K}{}_1\text{(H)}$ = 1.0₉). A much smaller effect was observed for the benzene complex which could not be quantified. These results may be interpreted through either the larger electronegativity of H over D, or the greater steric requirements of H over D.