Regarding the structure of [2.2](2,6,2',7')-naphthalenophane-1,11-diene and its conformational mobility

The synthesis of [2.2](2,6,2',7')naphthalenophane -1,11 - diene 4 has been effected by pyrolysis of the bis-sulphoxide 10, in turn prepared by a ring-contraction procedure of the [3.3]dithiacyclophane 7. The diene 4 has been fully characterized by spectroscopic and chemical methods. The variable-temperature ¹H NMR spectra of the diene 4 indicated that the compound undergoes conformational flipping in solution and has a conformational energy barrier ΔG^≠_25°. 14.9 kcal mol^-1 and a coalescence temperature T_c 38° for the internal protons H_c and H_c' (at 100 MHz). These results differ from those previously recorded. A complete assignment of the pmr spectrum of the cyclophane diene 4 at 270 MHz is presented together with the spectrum of the corresponding saturated [2.2]cyclophane 3.     

On the optical activity of paraffinic hydrocarbons

An expression for potential energy as a function of torsion angle about a saturated CC bond is developed analytically. This equation is used in the development of two methods for the conformational analysis of paraffins-one based on consideration only of exactly staggered conformers and one giving consideration to energy at 1° intervals of torsion angle. Two methods of assigning molecular rotations to hydrocarbon conformers are considered. Various combinations of results so obtained are compared as ways to calculate rotations for paraffins.     

Three-dimensional nonlinear optical chromophores based on metal-to-ligand charge-transfer from ruthenium(II) or iron(II) centers

In this article, we describe a series of new complex salts in which electron-rich transition-metal centers are coordinated to three electron-accepting N-methyl/aryl-2,2':4,4' ':4',4' '-quaterpyridinium ligands. These complexes contain either Ru(II) or Fe(II) ions and have been characterized by using various techniques, including electronic absorption spectroscopy and cyclic voltammetry. Molecular quadratic nonlinear optical (NLO) responses beta have been determined by using hyper-Rayleigh scattering at 800 nm and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d --> pi* metal-to-ligand charge-transfer bands. The latter experiments reveal that these putatively octupolar D(3) chromophores exhibit two substantial components of the beta tensor which are associated with transitions to dipolar excited states. Computations involving time-dependent density-functional theory and the finite field method serve to further illuminate the electronic structures and associated linear and NLO properties of the new chromophoric salts.     

Engineering crystals by the strategy of molecular tectonics

Detailed structures of molecular crystals cannot yet be predicted with consistent accuracy, but the strategy of molecular tectonics offers crystal engineers a powerful tool for designing molecules that are predisposed to form crystals with particular structural features and properties.     

Proton ionizable crown compounds. 18. Comparison of alkali metal transport in a H2O-CH2Cl2-H2O liquid membrane system by four proton-ionizable macrocycles containing the dialkylhydrogenphosphate moiety

The macrocycle-mediated fluxes of alkali, alkaline earth, and several transition metal cations have been determined and compared in a H₂O-CH₂Cl₂-H₂O liquid membrane system using four water-insoluble macrocycles containing a dialkylhydrogenphosphate moiety. Transport of alkali metal cations by these ligands was greatest from a source phase pH = 12 or above into an acid receiving phase (pH = 1.5). Very low fluxes were observed for the transport of the alkaline earth cations and all transition metal ions studied except Ag⁺ and Pb²⁺ which were transported reasonably well by these new macrocycles.Deceased: September 5, 1987.     

Reaction products of W(CO)(6) with formamidines; electronic structure of a W(2)(mu-CO)(2) core with unsymmetric bridging carbonyls

Reactions of W(CO)(6) with formamidines contrast with those of Mo(CO)(6) and Cr(CO)(6) in that the former do not yield quadruply bonded dimetal species. From the reaction of W(CO)(6) with HDAniF (HDAniF = N,N'-di-p-anisylformamidine), several new ditungsten carbonyl compounds (W(2)(mu-CO)(2)(mu-DAniF)(2)(eta(2)-DAniF)(2) (1), W(2)(mu-CO)(2)(mu-DAniF)(2)(eta(2)-DAniF)(eta(2)-CH(2)DAniF) (2), and W(2)(mu-CO)(mu-CNC(6)H(4)OCH(3))(mu-DAniF)(2)(eta(2)-DAniF)(2) (3)) have been isolated and fully characterized. In 2, CH(2)DAniF represents a DAniF ligand in which a methylene group has been added to one of the nitrogen atoms. This ligand binds to the tungsten atom using a nitrogen and a carbon atom. Compound 1 has a tungsten-tungsten bond distance of 2.476(1) A and a planar W(2)(mu-CO)(2) core structure which has C(2)(h)() symmetry with short and long W-C bond distances (1.99(1) and 2.28(1) A, respectively). DFT calculations on a model of 1 indicate that (a) the C(2)(h)() instead of D(2)(h)() symmetry of the ditungsten core may be attributed to W --> CO pi back-bonding interactions and (b) the bond between the tungsten atoms may be formulated as a double bond. The new tetragonal paddlewheel compound W(2)(DAniF)(4) (4) and the edge-sharing bioctahedron W(2)(mu-O)(mu-NC(6)H(3)Cl(2))(mu-D(Cl)PhF)(2)(eta(2)-D(Cl)PhF)(2) (5) (D(Cl)PhF = N,N'-di-(3,5-dichlorophenyl)formamidinate) have also been prepared.     

Asymmetric alkylation of diarylmethane derivatives. Improved results using methoxyethoxy substituent

Alkylation of 2-methoxyethoxyphenyl phenyl methane using sec-BuLi and (−)-sparteine has been carried out in excellent yields and up to 94% ee. The best results were obtained in allylation reactions but methylation, ethylation, benzylation and trimethylsilylation have all been carried out with acceptable ee.     

PHYTOCHROME IN GREEN-TISSUE: PARTIAL PURIFICATION and CHARACTERIZATION OF THE 118-KILODALTON PHYTOCHROME SPECIES FROM LIGHT-GROWN Avena sativa L.*

The predominant, immunochemically-detectable phytochrome polypeptide rapidly extracted directly into boiling sodium dodecyl sulfate-containing buffer from fresh or freeze-dried green Avena tissue has an apparent molecular mass of 118 kilodaltons (kDa). This result indicates that the 118-kDa phytochrome species obtained from green Avena by extraction and rapid processing under non-denaturing conditions in previous studies was not derived by partial proteolysis of a larger polypeptide present in the cell. Additional data do, however, demonstrate the presence in green tissue homogenates of proteolytic activity that can cause a = 6-kDa reduction in apparent molecular mass and a blue-shift in the P_fr absorbance maximum of phytochrome during handling. This proteolytic activity contrasts with that previously encountered in etiolated tissue in that it is not inhibited by phenylmethylsulfonyl fluoride, but is inhibited by iodoacetamide and leupeptin. This result indicates that the activity is associated with a thiol-like protease. A partial purification procedure that incorporates the use of iodacetamide and a novel chromatographic step is described for green-tissue phytochrome. This procedure provides 50% recovery with a 90-fold enrichment of phytochrome relative to the initial extract in which the chromoprotein is 0.003% of the total soluble protein. The final fraction is apparently free of proteolytic activity. Immunoblot analysis of this fraction demonstrates that the predominant immunoreactive band has a monomeric molecular mass of 118 kDa. Comigration of this band with a band exhibiting zinc-induced fluorescence on blots of the partially purified preparations verifies that the 118-kDa species is the principal tetrapyrrole-bearing polypeptide present. Spectral properties of the final fraction are identical to those published for crude green-tissue extracts, indicating the stability of the molecule's spectral properties throughout the procedure. Size exclusion chromatography under nondenaturing conditions shows that the 118-kDa phytochrome species from green tissue comigrates with the dimeric, etiolated-tissue molecule, and is therefore suggestive of similar quaternary structure. Together these data reinforce previous conclusions that the predominant phytochrome molecule present in the living cells of green tissue is resolvable as a 118-kDa species, distinct from the well-characterized 124-kDa molecule from etiolated tissue (Tokuhisa et al., 1985, Planta 164, 321–332), and indicate that the partial purification protocol described here sustains the green-tissue phytochrome in its native state throughout the procedure.     

Rapid assay for hard tissue collagen cross-links using isocratic ion-pair reversed-phase liquid chromatography

Following a detailed study, a rapid and sensitive assay for the naturally fluorescent collagen cross-links pyridinoline and deoxypyridinoline has been developed using ion-pair reversed-phase high-performance liquid chromatography in the presence of 1-octanesulphonic acid (OSA). Pyridinoline and deoxypyridinoline were separated on an Exsil 100 ODS, 5-microns column (100 mm X 4.6 mm I.D.) using 25 mM sodium formate, 5 mM OSA and 1 mM ethylenediaminetetraacetic acid adjusted to pH 3.25, containing 20% (v/v) methanol. The mobile phase flow-rate was 1.5 ml/min. Compounds were detected by their natural fluorescence (xenon lamp; excitation wavelength 290 nm, emission wavelength 400 nm). Peak areas were linear to 25 pmol injected for pyridinoline and 20 pmol injected for deoxypyridinoline (r = 0.99). Intra-assay coefficients of variation for urinary extracts were 7.65 and 9.07% (n = 10), respectively. Limit of detection (signal-to-noise ratio = 5) was 200 fmol injected. Quantification of the cross-links in acid hydrolysates and human urine samples was possible in under 15 min.     

Outer-sphere effects on ligand-field excited-state dynamics: solvent dependence of high-spin to low-spin conversion in [Fe(bpy)3]2+

In condensed phase chemistry, the solvent can have a significant impact on everything from yield to product distribution to mechanism. With regard to photo-induced processes, solvent effects have been well-documented for charge-transfer states wherein the redistribution of charge subsequent to light absorption couples intramolecular dynamics to the local environment of the chromophore. Ligand-field excited states are expected to be largely insensitive to such perturbations given that their electronic rearrangements are localized on the metal center and are therefore insulated from so-called outer-sphere effects by the ligands themselves. In contrast to this expectation, we document herein a nearly two-fold variation in the time constant associated with the ⁵T₂ → ¹A₁ high-spin to low-spin relaxation process of tris(2,2′-bipyridine)iron(ii) ([Fe(bpy)₃]²⁺) across a range of different solvents. Likely origins for this solvent dependence, including relevant solvent properties, ion pairing, and changes in solvation energy, were considered and assessed by studying [Fe(bpy)₃]²⁺ and related derivatives via ultrafast time-resolved absorption spectroscopy and computational analyses. It was concluded that the effect is most likely associated with the volume change of the chromophore arising from the interconfigurational nature of the ⁵T₂ → ¹A₁ relaxation process, resulting in changes to the solvent–solvent and/or solvent–solute interactions of the primary solvation shell sufficient to alter the overall reorganization energy of the system and influencing the kinetics of ground-state recovery.

Time-resolved spectroscopic measurements of ground-state recovery for [Fe(bpy)₃]²⁺ reveal that the solvent can induce an outer-sphere reorganization energy effect on excited-state dynamics involving metal-centered ligand-field electronic states.