A computational study of [2.2]cyclophanes

A computational study of isomeric [2.2]cyclophanes, namely [2.2]paracyclophane 1, [2.2]metacyclophane 2, and [2.2]metaparacyclophane 3, has been carried out. For 1, geometry optimizations performed by various methods at different basis sets showed that MP2/6-31+G(d,p) and B3PW91/6-31+G(d,p) provide the best results in comparison to the X-ray data. Compound 1 has D(2) symmetry with distorted bridges. A conformational search was performed for [2.2]cyclophanes 2 and 3. Each cyclophane exists in two conformations which have different energies in the case of 3 but are degenerate in the case of 2. Relative energies and strain energies at the bridges follow the same order, indicating that the relief of bridge tension and repulsion between pi clouds are determining factors for the stability of [2.2]cyclophanes. Through a decomposition of strain energy, it can be concluded that both the rings or the bridges can absorb strain, but it depends on the conformer of butane that is considered in the calculation of SE(br). Changes in aromaticity of these compounds were evaluated by NICS and HOMA and were compared with benzene and xylenes dimers as models. Despite distortions from planarity and shortening and lengthening of the C-C bonds relative to the mean, the phenyl rings are aromatic. NICS suggests a concentration of electronic density between the rings as a result of bridging process. Computed MK, NPA, and GAPT charges were compared for the isomeric cyclophanes. The GIAO chemical shifts were calculated and indicate that 1 has a larger diamagnetic anisotropy than the other isomers.     

Adhesive transfer of thin viscoelastic films

Micellar suspensions of acrylic diblock copolymers are excellent model materials for studying the adhesive transfer of viscoelastic solids. The micellar structure is maintained in films with a variety of thicknesses, giving films with a well-defined structure and viscoelastic character. Thin films were cast onto elastomeric silicone substrates from micellar suspensions in butanol, and the adhesive interactions between these coated elastomeric substrates and a rigid indenter were quantified. By controlling the adhesive properties of the film/indenter and film/substrate interfaces we were able to obtain very clean transfer of the film from the substrate to the portion of the glass indenter with which the film was in contact. Adhesive failure at the film/substrate interface occurs when the film/indenter interface is able to support an applied energy release rate that is sufficient to result in cavity nucleation at the film/substrate interface. Cavity formation is rapidly followed by delamination of the entire region under the indenter. The final stage in the transfer process involves the failure of the film that bridges the indenter and the elastomeric substrate. This film is remarkably robust and is extended to three times its original width prior to failure. Failure of this film occurs at the periphery of the indenter, giving a transferred film that conforms to the original contact area between the indenter and the coated substrate.     

Measuring the intra-individual variability of the plasma proteome in the chicken model of spontaneous ovarian adenocarcinoma

The domestic chicken (Gallus domesticus) has emerged as a powerful experimental model for studying the onset and progression of spontaneous epithelial ovarian cancer (EOC) with a disease prevalence that can exceed 35% between 2 and 7 years of age. An experimental strategy for biomarker discovery is reported herein that combines the chicken model of EOC, longitudinal plasma sample collection with matched tissues, advanced mass spectrometry-based proteomics, and concepts derived from the index of individuality (Harris, Clin Chem 20: 1535–1542, 1974). Blood was drawn from 148 age-matched chickens starting at 2.5 years of age every 3 months for 1 year. At the conclusion of the 1 year sample collection period, the 73 birds that remained alive were euthanized, necropsied, and tissues were collected. Pathological assessment of resected tissues from these 73 birds confirmed that five birds (6.8%) developed EOC. A proteomics workflow including in-gel digestion, nanoLC coupled to high-performance mass spectrometry, and label-free (spectral counting) quantification was used to measure the biological intra-individual variability (CV_W) of the chicken plasma proteome. Longitudinal plasma sample sets from two birds within the 73-bird biorepository were selected for this study; one bird was considered “healthy” and the second bird developed late-stage EOC. A total of 116 proteins from un-depleted plasma were identified with 80 proteins shared among all sample sets. Analytical variability (CV_A) of the label-free proteomics workflow was measured using a single plasma sample analyzed five times and was found to be ≥CV_W in both birds for 16 proteins (20%) and in either bird for 25 proteins (31%). Ovomacroglobulin (ovostatin) was found to increase (p < 0.001) over a 6 month period in the late-stage EOC bird providing an initial candidate protein for further investigation.     

Some notes on the reaction between ferric and thiocyanate ions

A spectrophotometric study has been made of the reaction between ferric and thiocyanate ions in sulphuric acid solution. The effects of acidity, thiocyanate concentration, persulphate concentration, temperature, light and added beryllium sulphate upon the stability and colour intensity of the solution are described.For analytical applications in the absence of added sulphate ions the best results are obtained at an acid normality of 1.5 to 2.0, while in the presence of beryllium sulphate at molar concentration it is desirable to increase the acid normality to 3.0. Precise control of thiocyanate concentration and temperature is required. The solutions obey Beer's law and an ultimate sensitivity of 0.035 p.p.m. of Fe is obtained when using a I cm cell.     

Silver and palladium complexes of some aromatic azo and azoxy compounds

The complexing ability of derivatives of azobenzene (I) is well known (I) and responsible for the production of a wide variety of dyestuffs and analytical chemicals. While the azo group generally participates in the coordination, the determination of the degree of its interaction is complicated by other functional groups which are also coordinated with the transition metal. In a previous publication (2), we reported the preparation of the silver and palladium complexes of benzo[c]cinnoline (II) and proposed that these results might be used to explain the electron donor properties of azobenzene. We are now reporting the preparation of some additional complexes with ligands containing the azo group.     

Hydrogen-bonding contributions to the lattice energy of salts for second harmonic generation

The lattice energies of a series of organic dihydrogenphosphate salts capable of second harmonic generation (SHG) have been calculated. These calculations, coupled with empirical data, indicate that a minimum of 20–25% of the lattice energy arises from hydrogen-bond interactions. Hydrogen bonding is shown to be a strong enough force to have a profound effect on the overall packing and crystal geometry of such ionic materials, and is thus an important factor to consider for crystal engineering.     

Several convenient methods for the synthesis of 2-amido substituted furans

Several new methods for the synthesis of differently substituted 2-amidofurans are described. The thermolysis of furan-2-carbonyl azide results in a Curtius rearrangement and the resulting furanyl isocyanate was trapped with various organometallic reagents. A second method consists of a C-N cross-coupling reaction of a bromo-substituted furan with various amides, carbamates, and lactams. The CuI-catalyzed cross-coupling reaction between furanyl bromides and amides furnished 2- and 3-substituted amidofurans in 45-95% yield. The third protocol used involves the reaction of cyclic carbinol amides with triflic anhydride. The reaction proceeds under very mild conditions to provide alpha-(trifluoromethyl)sulfonamido-substituted furans in high yield. The resulting iminium ion derived from the reaction of the hydroxy pyrrolidinone with Tf(2)O undergoes a facile ring opening as a consequence of the adjacent hydroxyl group to produce an imino triflate intermediate. Subsequent cyclization of this highly electrophilic imine with the oxygen atom of the adjacent carbonyl group leads to an imino dihydrofuran that reacts further with another equivalent of Tf(2)O to give the observed product.     

Preparation of perhydroisoquinolines via the intramolecular Diels-Alder reaction of N-3,5-hexadienoyl ethyl acrylimidates: a formal synthesis of (+/-)-reserpine

The intramolecular Diels-Alder reaction of N-3,5-hexadienoyl ethyl acrylimidates provides an efficient method for the synthesis of cis-fused hexahydroisoquinolones. As a demonstration of the stereochemical control offered by this cycloaddition, two approaches to the construction of the DE rings of reserpine are reported. In the second entry, N-((4-(trimethylsilyl)ethoxymethoxy)methyl-6-benzyloxy-3Z,5E-hexadienoyl)-1-aza-2-ethoxy-1,3-butadiene (40) undergoes cycloaddition to produce as the major product (4aS,7R,8aS)-7-benzyloxy-5-((2-trimethylsilyl)ethoxymethoxy)methyl-3,4,4a,7,8,8a-hexahydroisoquinol-3-one (41). Cycloadduct 41 is then stereospecifically elaborated to (4aS,5S,6R,7R,8aR)-6-methoxy-5-methoxycarbonyl-7-(3,4,5-trimethoxy)benzoyldecahydroisoquinoline-2-carboxylic acid methyl ester (3), a key intermediate previously transformed to reserpine.     

A theoretical (DFT, GIAO-NMR, NICS) study of the carbocations and oxidation dications from azulenes, homoazulene, benzazulenes, benzohomoazulenes, and the isomeric azulenoazulenes

Protonation of parent azulene (1), homoazulene (8), representative isomeric benzazulenes (9, 9A, and 9B), and benzohomoazulenes (10, 10A, and 10B) as well as the mono- and diprotonation of isomeric azulenoazulenes (11-16) were studied by DFT at the B3LYP/6-31G(d) level. The most likely carbocations were identified based on relative protonation energies. For comparison, complete experimental 13C NMR data were obtained for parent azulenium ion 1H+ and guaiazulenium ion 2H+ in TFA. The oxidation dications derived from benzazulenes (9, 9A, and 9B), benzohomoazulenes (10, 10A, and 10B) and azulenoazulenes (11, 16) were also investigated. For azulenoazulene dications the singlet and triplet states are both minima, but except for 11(2+) and 13(2+), the triplet states are higher in energy. Structural/geometrical changes in the carbocations were examined. GIAO-NMR, NPA charges (and changes in charges), and NICS (and delta NICS) were employed to compute the NMR chemical shifts (delta delta 13C values) in order to derive charge delocalization maps and to gauge relative aromaticitylantiaromaticity in the energetically most favored carbocations and oxidation dications. The emerging trends are discussed and compared. Creation of tropylium or homotropylium entities in the carbocations (monoprotonated) and carbodications (diprotonated) is identified as an important driving force governing the protonation outcomes. Consideration of the AM1-derived delta delta Hf values (and the DFT-derived delta delta G values) suggests that the two-electron oxidation of azulenoazulenes should be experimentally feasible. Given their antiaromatic (paratropic) character, azulenoazulene dications represent interesting targets for NMR study. GIAO-derived charge delocalization mapping allows the most likely sites for nucleophilic attack on the dications to be identified.     

Application of nanoscale packed capillary liquid chromatography (75 μm id) and capillary zone electrophoresis/electrospray ionization mass spectrometry to the analysis of macrolide antibiotics

Nanoscale separation techniques, nanoscale packed capillary columns (75 μm id), and capillary zone electrophoresis (CZE), on-line with electrospray mass spectrometry (ESI/MS), were applied to the separation of a series of ten macrolide antibiotics. Both techniques use sub-microliter-per-minute flow rates through the analytical column and therefore require an electrospray probe that incorporates coaxial sheath flow. Positive ion electrospray mass spectra of these compounds yielded mainly protonated molecules. Fragmentation to yield structurally significant fragment ions was achieved by collision-induced dissociation (CID) at increased skimmer voltages. Separations were achieved using both techniques, with CZE/ESI/MS showing improved peak shapes and detection limits combined with faster analysis times. Nanoscale packed capillary columns provided better chromatographic resolution and was less susceptible to peak broadening caused by overloading of the analytes.