A spiro‐linked pyrene–naphtho­quinone

The title mol­ecule, 2′‐pyrenyl­spiro­[2,3‐di­hydro‐1H‐cyclo­penta­[b]­naphthalene‐2,5′‐1′,3′‐dioxane]‐4,9‐dione, C₃₂H₂₂O₄, contains an electron‐donating pyrene group spiro‐linked to an electron‐accepting naphtho­quinone. The mol­ecules are V‐shaped in profile and stack to form columns along b with alternating, approximately coplanar, pyrene and naphtho­quinone fragments. Intermolecular contacts within a column are consistent with some degree of π contact and possible long‐range delocalization. Individual columns form a herringbone pattern when the crystal is viewed along b .     

Neural correlates of semantic and syntactic processes in the comprehension of case marked pronouns: Evidence from German and Dutch

Background  

It is well known that both semantic and syntactic information play a role in pronoun resolution in sentences. However, it is unclear what the relative contribution of these sources of information is for the establishment of a coreferential relationship between the pronoun and the antecedent in combination with a local structural case constraint on the pronoun (i.e. case assignment of a pronoun under preposition governing). In a prepositional phrase in German and Dutch, it is the preposition that assigns case to the pronoun. Furthermore, in these languages different overtly case-marked pronouns are used to refer to male and female persons. Thus, one can manipulate biological/syntactic gender features separately from case marking features.     

Solid-state changes in ligand-to-metal charge-transfer spectra of (NH3)5Ru(III)(2,4-dihydroxybenzoate) and (NH3)5Ru(III)(xanthine) chromophores

Five distorted-octahedral complexes containing (NH3)5Ru(III)L ions, where L = 2,4-dihydroxybenzoate or a xanthine, have been studied using a combination of X-ray crystallography, solution and polarized single-crystal electronic absorption spectroscopy, and first principles electronic structure computational techniques. Both yellow (2) and red (3) forms of the complex (NH3)5Ru(III)L, where L = 2,4-dihydroxybenzoate, as well as three xanthine complexes in which L = hypoxanthine-kappaN(7) (4), 7-methylhypoxanthine-kappaN(9) (5), and 1,3,9-trimethylxanthine-kappaN(7) (6) were examined. In the solid state, some of these complexes exhibit split low-energy ligand-to-metal charge-transfer (LMCT) bands. Traditional solid-state effects, such as ligand pi-pi overlap or hydrogen bonding that might lead to splitting of electronic absorption bands, were probed in an attempt to identify the origins of these unusual observations. For comparison, companion studies were carried out for spectroscopically normal reference complexes of the same ligands. Time-dependent density-functional theory (TD-DFT) calculations, employing modified B3LYP-type functionals with increased contributions of exact exchange, attribute the color change in the crystalline complexes 2 and 3 to pi(ligand) --> Ru[d(pi)] LMCT bands which, in the red form (3), arise from ligand donor pi-orbitals split by strongly overlapping phenyl moieties in centrosymmetric (NH3)5Ru(III)(2,4-dihydroxybenzoate) dimers. Complex 5 does not show split visible absorptions, whereas both the polarizations and energies of the split visible absorptions shown by 4 and 6 also suggest assignment as LMCT. No support is found for relating the split absorptions of 4 and 6 to the details of pi-pi xanthine overlap in the solid state; indeed, complex 4 enjoys considerably less pi-stacking overlap than does 5. We feel compelled to attribute the split absorptions in crystalline 4 and 6 to the emergence of a LMCT transition originating in the carbonyl lone pair, potentially deriving intensity from the significant intramolecular N-H...O hydrogen bonding present in both 4 and 6 (but not in 5). The electronic structure calculations suggest an O(n) --> Ru[d(sigma*)] LMCT transition; however, this novel assignment must be considered tentative.     

Structural, infrared, and density functional theory studies of N,N,N',N'-Tetramethylimidazolidinium dichloride: a model for cation-anion association of headgroups and counterions in the interfacial regions of gemini micelles

N,N,N',N'-Tetramethylimidazolidinium dichloride (1-Im-1 2Cl) has been studied as a model system for cation-anion interactions in the interfacial regions of gemini micelles by X-ray crystallography, density functional theory (DFT) calculations, and infrared spectroscopy. Single crystals of 1-Im-1 2Cl contain 1-Im-1 dications, whose five-membered rings adopt a distorted envelope conformation. Eight chloride anions surround each dication, two of which are cradled above and below the five-membered ring (apical) and six of which are dispersed about the periphery of the ring (equatorial). The cations and anions are linked in the solid state by an extensive network of weak C-H...Cl hydrogen bonds that involve all of the H atoms of the dication. The calculated (DFT at the 6-31+G(d) level) structure of the asymmetric unit, which consists of a dication and two apical chloride ions, closely resembles the equivalent unit in the crystal structure with respect to bond distances and angles, the conformation of the 1-Im-1 ring, and the nature and location of the C-H...Cl hydrogen bonds. The calculated IR spectrum predicts a number of absorptions in the 3000 cm(-1) region, assigned as C-H...Cl stretching modes, which are consistent with the presence of an intense band in the observed IR spectrum of the crystals. Over all, this study supports the notion that apical chloride ions interact more strongly with gemini surfactant headgroups by forming multiple hydrogen bonds in ion pairs of a type that cannot be present in the corresponding ion pairs of quaternary headgroups with counterions of single-chain surfactants.     

Cyclic RGD peptidomimetics containing bifunctional diketopiperazine scaffolds as new potent integrin ligands

The synthesis of eight bifunctional diketopiperazine (DKP) scaffolds is described; these were formally derived from 2,3-diaminopropionic acid and aspartic acid (DKP-1-DKP-7) or glutamic acid (DKP-8) and feature an amine and a carboxylic acid functional group. The scaffolds differ in the configuration at the two stereocenters and the substitution at the diketopiperazinic nitrogen atoms. The bifunctional diketopiperazines were introduced into eight cyclic peptidomimetics containing the Arg-Gly-Asp (RGD) sequence. The resulting RGD peptidomimetics were screened for their ability to inhibit biotinylated vitronectin binding to the purified integrins α(v)β(3) and α(v)β(5), which are involved in tumor angiogenesis. Nanomolar IC(50) values were obtained for the RGD peptidomimetics derived from trans DKP scaffolds (DKP-2-DKP-8). Conformational studies of the cyclic RGD peptidomimetics by (1)H?NMR spectroscopy experiments (VT-NMR and NOESY spectroscopy) in aqueous solution and Monte Carlo/Stochastic Dynamics (MC/SD) simulations revealed that the highest affinity ligands display well-defined preferred conformations featuring intramolecular hydrogen-bonded turn motifs and an extended arrangement of the RGD sequence [Cβ(Arg)-Cβ(Asp) average distance ≥8.8??]. Docking studies were performed, starting from the representative conformations obtained from the MC/SD simulations and taking as a reference model the crystal structure of the extracellular segment of integrin α(v)β(3) complexed with the cyclic pentapeptide, Cilengitide. The highest affinity ligands produced top-ranked poses conserving all the important interactions of the X-ray complex.     

A NMR and computational study of Smac mimics targeting both the BIR2 and BIR3 domains in XIAP protein

In this paper we report an extensive NMR analysis of small ligands (Smac mimics) complexed with different constructs of XIAP. The mimics-binding site of XIAP is known as the BIR3 domain - primary, and the linker BIR2 region - secondary site. Interactions between the BIR3 domain and Smac mimics have been extensively studied by X-ray but, as of today, there are scarce data about the interaction between BIR2, or the whole linker-BIR2-BIR3 construct, and Smac mimics. In order to characterize our Smac mimics, we performed a STD NMR study between our 4-substituted, 1-aza-2-oxobicyclo[5.3.0]decane scaffold-based molecules and three different XIAP fragments: single BIR2 and BIR3 domains, and bifunctional linker-BIR2-BIR3. The results were integrated with docking calculations and molecular dynamics simulations. NMR data, which are consistent with biological tests, indicated that the two BIR subunits interact differently with our Smac mimics and suggest that the ligands enter into more intimate contact with the linker-BIR2-BIR3. In conclusion, we observe that the SMAC mimics showed with the construct linker-BIR2-BIR3 a series of NOE contacts that were not observed in the mono-domain ligand:BIR2 or :BIR3 complexes. So, in agreement with the computational models we believe that the linker moieties of the binding site play a key role in the stability of the protein complex.     

How to measure the optical thickness of scattering particles from the phase delay of scattered waves: application to turbid samples

We present a method based on the optical theorem that yields absolute, calibration free estimates of the optical thickness of scattering particles. The thickness is determined from the phase delay of the zero angle scattered wave. It uses a heterodyne scattering scheme operating in the Raman-Nath approximation. The phase is determined by the position of Talbot-like modulations in the two dimensional power spectrum S(qx, qy) of the transmitted beam intensity distribution. The method is quite insensitive to multiple scattering. It is successfully tested to provide quantitative verification of the optical theorem. Exploratory tests on soft matter samples are reported to suggest its wide applicability to turbid samples.     

Stereoselective aldol reactions using ticl4 as stereochemical template

TiCl₄ mediated aldol condensations establish multiple contiguous chiral centers in an almost complete enantio- and diastereoselective way.     

Catechol boron halides: mild and selective reagents for cleavage of common protecting groups

Catechol boron halides (1,X=Cl, Br) cleave certain ether, ester and carbamate protecting groups under mild conditions. The scope and selectivity of these readily available reagents has been examined.