Insertion of CO2, CS2, and COS into iron(II)-hydride bonds

The reactions between cis-Fe(dmpe)2H2 (dmpe = Me2PCH2CH2PMe2) (1) or cis-Fe(PP3)H2 (PP3 = P(CH2CH2PMe2)3) (2) and carbon dioxide (CO2), carbon disulfide (CS2), and carbonyl sulfide (COS) are investigated. At 300 K, additions of CO2 (1 atm), CS2 (2 equiv), and COS (1 atm) to 1 result in the formation of a stable transformato hydride, trans-Fe(dmpe)2(OCHO)H (3a), a trans-dithioformato hydride, trans-Fe(dmpe)2(SCHS)H (4a), and a trans-thioformato hydride, trans-Fe(dmpe)2(SCHO)H (5a), respectively. When CS2 and COS are added to cis-Fe(dmpe)2H2 at 195 K, a cis-dithioformato hydride, 4b, and a cis-thioformato hydride, 5b, respectively, are observed as the initially formed products, but there is no evidence of the corresponding cis-formato hydride upon addition of CO2 to cis-Fe(dmpe)2H2. Additions of excess CO2, CS2, and COS to 1 at lower temperatures (195-240 K) result in the formation of a trans-bis(formate), trans-Fe(dmpe)2(OCHO)2 (3b), a trans-bis(dithioformate), trans-Fe(dmpe)2(SCHS)2 (4c), and a cis-bis(thioformate), cis-Fe(dmpe)2(SCHO)2 (5c), respectively. trans-Fe(dmpe)2(SCHO)2 (5d) is prepared by the addition of excess COS at 300 K. Additions of CO2 (1 atm), CS2 (0.75 equiv), and COS (1 atm) to 2 at 300 K result in the formation of a thermally stable, geometrically constrained cis-formato hydride, cis-Fe(PP3)(OCHO)H (6a), a cis-dithioformato hydride, cis-Fe(PP3)(SCHS)H (7a), and a cis-thioformato hydride, cis-Fe(PP3)(SCHO)H (8a), respectively. Additions of excess CO2 and COS to 2 yield a cis-bis(formate), cis-Fe(PP3)(OCHO)2 (6b), and a thermally stable cis-bis(thioformate), cis-Fe(PP3)(SCHO)2 (8b), respectively. All complexes are characterized by multinuclear NMR spectroscopy, with IR spectroscopy and elemental analyses confirming structures of thermally stable complexes where possible. Complexes 3b and 5a are also characterized by X-ray crystallography.     

Submicron streptavidin patterns for protein assembly

Micron and submicron-scale features of aldehyde functionality were fabricated in polymer films by photolithography to develop a platform for protein immobilization and assembly at a biologically relevant scale. Films containing the pH-reactive polymer poly(3,3'-diethoxypropyl methacrylate) and a photoacid generator (PAG) were patterned from 500 nm to 40 mum by exposure to 365 nm (i-line) light. Upon PAG activation and hydrolysis of acetals, aldehyde groups formed. After the films were incubated with a biotinylated aldehyde reactive probe, the X-ray photoelectron spectroscopy results were consistent with biotin being attached to the surface. The background was subsequently passivated by flood exposure and incubation with an aminooxy-terminated poly(ethylene glycol), resulting in a 98% reduction in nonspecific protein adsorption. Protein patterning and assembly was demonstrated using streptavidin, biotinylated anthrax toxin receptor-1, and the protective antigen moiety of anthrax toxin and confirmed by fluorescence microscopy and atomic force microscopy (AFM). AFM demonstrated that 500 nm protein features were achieved. Because of the abundance of biotinylated proteins, this methodology provides a platform for protein immobilization and assembly for various applications in biotechnology.     

Solid phase approaches to N-heterocycles using a sulfur linker cleaved by SmI2

A sulfur HASC (alpha-hetero-atom substituted carbonyl) linker has been utilized in solid-phase approaches to oxindoles and tetrahydroquinolones. The route to oxindoles employs the first Pummerer cyclizations on solid phase, whereas the route to tetrahydroquinolones involves a microwave-assisted Heck reaction followed by a Michael cyclization. In both cases, the linker is cleaved in a traceless fashion by electron transfer from samarium(II) iodide. The routes illustrate the compatibility of the linker system with a number of reaction types and its utility for library synthesis.     

Isolation of tumor cells using size and deformation

The isolation and analysis of circulating tumor cells (CTCs) from blood are the subject of intense research. Although tests to detect metastasis on a molecular level are available, progress has been hampered by a lack of tumor-specific markers and predictable DNA abnormalities. The main challenge in this endeavor is the small number of available cells of interest, 1–2 per mL in whole blood. We have designed a micromachined device to fractionate whole blood using physical means to enrich for and/or isolate rare cells from peripheral circulation. It has arrays of four successively narrower channels, each consisting of a two-dimensional array of columns. Current devices have channels ranging in width from 20 to 5 μm, and in depth from 20 to 5 μm. Several optimizations resulting in the fabrication of a total of 10 derivative devices have been carried out; only two types are used in this study. Both have increasingly narrower gap widths between the columns along the flow axis with 20, 15, 10, and 5 μm spacing all on one device. The first 20 μm wide segment disperses the cell suspension and creates an evenly distributed flow over the entire device, whereas the others were designed to retain increasingly smaller cells. The channel depth is constant across the entire device, the first type was 10 μm deep and the second type is 20 μm deep. When cells from each of eight tumor cell lines were loaded into the device, all cancerous cells were isolated. In mixing experiments using human whole blood, we were able to fractionate cancer cells without interference from the blood cells. Additionally, either intact cells, or DNA, could be extracted for molecular analysis. The ultimate goal of this work is to characterize the cells on the molecular level to provide non-invasive methods to monitor patients, stage disease, and assess treatment efficacy. Furthermore, this work will use gene expression profiles to gain insights into metastasis.     

Towards the development of multisensor for drugs of abuse based on molecular imprinted polymers

The synthetic receptors for cocaine, deoxyephedrine, methadone and morphine were computationally designed and produced using molecular imprinting. The structure and energy of the molecular complexes were analysed by computational techniques. The possible structures of the binding sites in the synthetic receptors have been compared with those of corresponding natural receptors. The composition of imprinted polymers was optimised to allow adequate performance under the same experimental conditions. All selected molecular imprinting polymers (MIPs) demonstrated stronger affinity in comparison with corresponding blank polymers resulting in imprinted factors (I) equal to 1.2 (cocaine), 2.5 (deoxyephedrine), 3.5 (methadone) and 3 (morphine) which suggested that the specific binding site for each molecule was successfully created. The polymers studied possessed good selectivity and affinity towards their templates and could be recommended for the integration with sensor devices. From a practical point of view, especially for multisensor requirements, the synthetic receptors based on imprinted polymers could be superior to natural receptors due to their stability, robustness and compatibility with automation processes required for sensor fabrication.     

Enantiomerically enriched atropisomeric N,N′-diaryl ureas by oxidative kinetic resolution of their 2-sulfanyl derivatives

Atropisomeric N-methyl-N,N′-diaryl ureas may be obtained in enantiomerically enriched form by oxidative kinetic resolution of their sulfide derivatives. The atropisomeric sulfides may be obtained in up to 97:3 er and display high stability to racemisation (half-lives at 25 °C of up to 500 years). Unlike related fully alkylated ureas, the product sulfoxides exhibit relatively weak thermodynamic conformational selectivity.     

Stereoselective synthesis of N-aryl proline amides by biotransformation-Ugi-Smiles sequence

An efficient combination of MAO-N-catalyzed desymmetrization of cyclic meso-amines with Ugi-Smiles multicomponent chemistry produced optically pure N-aryl proline amides. This method represents the first report of a fully asymmetric Ugi-Smiles process.     

Superstructures of donor packing arrangements in a series of molecular charge transfer salts

Three conducting BEDT-TTF charge-transfer salts with tris(oxalato)metallate anions have unit cells containing both[small alpha] and [small beta][double prime] donor packing motifs.     

Rapid liquid chromatography for paralytic shellfish toxin analysis using superficially porous chromatography with AOAC Official Method 2005.06

The bioaccumulation of paralytic shellfish toxins in mussels, oysters, cockles, hard clams, razors, and king scallops is monitored in England, Scotland, and Wales by AOAC Official Method 2005.06 LC-with fluorescence detection (FLD). One of the commonly perceived disadvantages of using this method is the long turnaround time and low throughput in a busy laboratory environment. The chromatographic analysis of each sample typically utilizes a 15 min cycle time to achieve toxin oxidation product separation and column equilibration prior to subsequent analysis. A standard RP C18 analytical column, used successfully in recent years, achieves good separation with a long column lifetime. The analysis of a 40 sample qualitative screening batch takes approximately 18 h, including blanks, standards, and other QC samples. The availability of superficially porous column technology has offered the potential to reduce analysis time while retaining column performance on existing hardware. In this study, AOAC Official Method 2005.06 with LC-FLD was transferred to two different commercially available superficially porous columns, and the method performance characteristics were evaluated. Both columns separated all toxins adequately with cycle times less than half that of the existing method. Linearity for each toxin was acceptable up to two times the European maximum permitted limit of 800 microg di-HCl saxitoxin equivalent/kg flesh. LOD and LOQ values were substantially improved for the majority of toxins, with gonyautoxin 1&4 and neosaxitoxin showing up to a two- and fourfold improvement, respectively, depending on the column used. Quantification results obtained from parallel analysis of contaminated samples were acceptable on both columns. Comparative screen results gave a slight increase in the occurrence of contaminated samples, which was attributed to the improved detection limit for most toxins. Issues with rapidly increasing back pressure, however, were identified with both columns, with a limit of around 500 injections. This compares to the >3000 cycles routinely obtained with the standard RP-C18 HPLC columns currently in use. Overall, the gain achieved with these columns through shorter analysis time and improved analytical sensitivity is potentially of benefit in a high-throughput environment. For the routine high-throughput screening of shellfish samples, however, an improved column lifetime is desirable.     

Understanding the role of base stacking in nucleic acids. MD and QM analysis of tandem GA base pairs in RNA duplexes

Preceding NMR experiments show that the conformation of tandem GA base pairs, an important recurrent non-canonical building block in RNA duplexes, is context dependent. The GA base pairs adopt "sheared" N3(G)-N6(A), N2(G)-N7(A) geometry in the r(CGAG)(2) and r(iGGAiC)(2) contexts while switching to "imino" N1(G)-N1(A), O6(G)-N6(A) geometry in the r(GGAC)(2) and r(iCGAiG)(2) contexts (iC and iG stand for isocytosine and isoguanine, respectively). As base stacking is likely to be one of the key sources of the context dependence of the conformation of GA base pairs, we calculated base stacking energies in duplexes containing such base pairs, to see if this dependence can be predicted by stacking energy calculations. When investigating the context dependence of the GA geometry two different conformations of the same duplex were compared (imino vs. sheared). The geometries were generated via explicit solvent MD simulations of the respective RNA duplexes, while the subsequent QM energy calculations focused on base stacking interactions of the four internal base pairs. Geometrical relaxation of nucleobase atoms prior to the stacking energy computations has a non-negligible effect on the results. The stacking energies were derived at the DFT-D/6-311++G(3df,3pd) level. We show a rather good correspondence between the intrinsic gas-phase stacking energies and the NMR-determined GA geometries. The conformation with more favorable gas-phase stacking is in most cases the one observed in experiments. This correlation is not improved when including solvent effects via the COSMO method. On the other side, the stacking calculations do not predict the relative thermodynamic stability of duplex formation for different sequences.