Cyclophanes—13: Crystal and molecular structure of [2.2][2,5]furano(1,4)naphthalenophane

The crystal and molecular structure of [2.2](2,5)furano(1,4)naphthalenophane (1) was determined by X-ray crystallography. The molecule exists in the anti-conformation and the study represents the first instance in which the structural features of a naphthalenoid ring within a cyclophane were determined. Crystals of cyclophane 1 are orthorhombic, space group Pbca, with a = 7.859(2). b = 11.482(3) and c = 28.818(8) Å. While the nonbridged portion of the naphthalenoid ring is planar, the portion which is bridged to the furanoid ring through its 1 and 4 C atoms is puckered and boat-shaped. These C atoms are positioned 14° out of the plane of the other four C atoms of this ring. The furanoid ring is essentially planar but is not parallel to the naphthalenoid ring. It is inclined 22° to the least squares plane of the bridged portion of the naphthalenoid ring. This angle of inclination staggers the atoms of the furanoid and bridged naphthalenoid ring and positions the 3 and 4 C atoms, the 2 and 5 C atoms and the 0 atom of the furanoid ring 3.4. 2.9 and 2.6 Å. respectively, from the least squares plane of the bridged portion of the naphthalenoid ring. While the internal angles around the bridging C atoms α- to the naphthalenoid ring are 109°, those α- to the furanoid ring are 113°. In addition unusually large bond angles ($\text{\$}\text{?}$137°) at the 2 and 5 C atoms of the furanoid ring, external to the ring, are also observed. The distortions are considered with respect to the strain within the cyclophane macrocycle and are compared with other similar systems.     

PROPERTIES OF THE ULTRAVIOLET-LIGHT-MEDIATED BINDING OF BOVINE SERUM ALBUMIN TO DNA*

Abstract— The binding of DNA to protein mediated by U V (254 nm) radiation has been investigated using binding of the complex to Millipore membrane filters as an assay technique. The reaction proceeds through an activated protein intermediate which then reacts with the DNA. The activated protein has a half-life of about 75 min at 0°C and about 18 min at 37°C. Short wavelengths are more efficient in forming the complex than wavelengths in the 250–280 nm range. N-ethyl maleimide treatment of protein before irradiation markedly inhibits the reaction.     

Factors controlling the efficiencies of photoinduced electron-transfer reactions

The overall efficiencies of photoinduced electron transfer reactions in polar solvents are usually determined by the efficiency with which separated radical ions are formed from the initially formed geminate radical-ion pairs. These separation efficiencies are determined by the competition between retum electron transfer and separation within the geminate pairs. A method is described for determining whether variations in the quantum yields for formation of separated radical ions are due to changes in the reorganization parameters for the return electron transfer reactions, or to other factors. The use of the method is illustrated in studies of the effects of varying steric bulk and molecular size of the donors, and also in studies of the effect of using a charged sensitizer.     

Quantum chemical modeling for 157 nm photolithography

In its continuing quest for smaller length scales, the electronics industry plans to introduce 157 nm as the next lithographic wavelength. Accordingly, there is a pressing need to develop photoresists that are more transparent, and pellicles that are both more transparent and more durable. With the advent and popularization of time-dependent density functional theory (TD-DFT), we now have a practical quantum chemical method for calculating excitation energies and transition moments in the vacuum ultraviolet (VUV) which can greatly assist in the scouting of highly transparent materials. We have performed TD-DFT calculations for a broad variety of fluorinated molecules and we will report calculated VUV photoabsorption spectra for a large family of model fluorohexanes. These calculations, which span a range from 1-fluorohexane to CH₃CF₂CF₂CF₂CF₂CH₃, illustrate some of the principles one may use to design low absorption polymeric materials.     

Non-chair six-membered-ring conformations. Preference for a twist-boat (or skew) structure in α- -sorbopyranose derivatives

The conformational preferences for 2,3-O-isopropylidene-α- -sorbopyranose derivatives 3–6 were determined by using ¹H NMR data and empirical force field calculations. Proton NMR studies of 3–6 indicate that a twist-boat (or skew) conformation (³S₀) prevails over possible chair forms for each compound. Force-field calculations (MM2, MNDO, AM1) on a model 2,3-O-isopropylidene-α- -sorbopyranose system (18) indicate that the ³S₀ conformation is among the low-energy structures. X-Ray crystallographic analysis of α- -sorbopyranose sulfamate 3, a compound with potent anticonvulsant activity, demonstrates that the ³S₀ skew conformation is manifested in the solid state, as well.     

Fluorinated tropylium ions in the mass spectra of some polyfluoroaromatic compounds

The most prominent ion in the mass spectra of C₆F₅CH₂X (X ? H, Br, CH:CH₂, COCl, and CH₂C₆F₅) is C₇F₅H₂⁺, formulated as the pentafluorotropylium cation. This ion is also found, in an amount comparable to the parent ion, in the spectrum of (C₆F₅)₂CH₂. The heptafluorotropylium cation is found similarly in the spectrum of C₆F₅CF₃. The mass spectra of (C₆F₅)₂CHBr and [(C₆H₅)₂CH]₂ exhibit an ion C₁₃F₁₀H⁺ as the base peak, which is probably a pentafluorophenylpentafluorotropylium cation. The alcohol (C₆F₅)₂CHOH shows loss of C₆F₅, followed by 2H, as a major breakdown pathway. The mode of formation, and the subsequent fragmentation, of the major ions in these spectra, are discussed.     

Synthesis of 2S-carboxy-3R,4R,5S-trihydroxypiperidine; a naturally occurring inhibitor of β-D-glucuronidase

The glucuronic acid analog 5 of 1-deoxynojirimycin has been synthesized in good overall yield from D-glucose.     

Synthesis of optically active leukotriene (SRS-A) intermediates

In an approach to SRS-A and analogues thereof, the key (5$\text{S}$, 6$\text{S}$)-epoxy alcohol $\text{9}$ and its 6-epimer $\text{18}$ were prepared starting from $\text{D}$-araboascorbic acid and $\text{L}$-diethyl tartrate, respectively.     

The oxidation of water by cerium(IV) catalysed by nanoparticulate RuO2 on mesoporous silica

Mesoporous silicates are prepared by templating on the hexagonal (H1) mesophase of surfactant bipyridine complexes of ruthenium(II) using a true liquid-crystal templating approach. On calcination, the surfactant template is removed except for the central metal ion that is oxidised, forming nanoparticles of RuO2 that deposit within the pores. RuO2 is a known oxidation catalyst and, despite its anhydrous nature in these silicates, is found to be very active in catalyzing the oxidation of water by acidic CeIV.     

Reduction of Secondary Carboxamides to Imines

This article reports in detail on the discovery that zirconium(IV) salts of secondary amides and lactams are transformed by Cp(2)ZrHCl to N-substituted imines in one step. The method represents the first controlled reduction of amides and lactams to the corresponding imines, a transformation that is otherwise very difficult to achieve because imines are reduced more rapidly than carboxamides by most metal hydride reagents. No products of reductive cleavage of the carboxamides are observed. Efforts to replace 2 mol equiv of Cp(2)ZrHCl with simpler, less costly alternatives led to the finding that a diisobutylaluminum enolate can be substituted for the initial zirconium enolate. Such aluminum amides are smoothly reduced to the corresponding imine using Cp(2)ZrHCl in good yield. Moreover, aluminum amides are also reduced to imines using either low-valent titanium species or triethylsilane. In these alternative procedures, use of Cp(2)ZrHCl is eliminated altogether in the title transformation.