Layer-by-layer deposition of rhenium-containing hyperbranched polymers and fabrication of photovoltaic cells

Multilayer thin films were prepared by the layer-by-layer (LBL) deposition method using a rhenium-containing hyperbranched polymer and poly[2-(3-thienyl)ethoxy-4-butylsulfonate] (PTEBS). The radii of gyration of the hyperbranched polymer in solutions with different salt concentrations were measured by laser light scattering. A significant decrease in molecular size was observed when sodium trifluoromethanesulfonate was used as the electrolyte. The conditions of preparing the multilayer thin films by LBL deposition were studied. The growth of the multilayer films was monitored by absorption spectroscopy and spectroscopic ellipsometry, and the surface morphologies of the resulting films were studied by atomic force microscopy. When the pH of a PTEBS solution was kept at 6 and in the presence of salt, polymer films with maximum thickness were obtained. The multilayer films were also fabricated into photovoltaic cells and their photocurrent responses were measured upon irradiation with simulated air mass (AM) 1.5 solar light. The open-circuit voltage, short-circuit current, fill factor, and power conversion efficiency of the devices were 1.2 V, 27.1 mu A cm(-2), 0.19, and 6.1x10(-3) %, respectively. The high open-circuit voltage was attributed to the difference in the HOMO level of the PTEBS donor and the LUMO level of the hyperbranched polymer acceptor. A plot of incident photon-to-electron conversion efficiency versus wavelength also suggests that the PTEBS/hyperbranched polymer junction is involved in the photosensitization process, in which a maximum was observed at approximately 420 nm. The relatively high capacitance, determined from the measured photocurrent rise and decay profiles, can be attributed to the presence of large counter anions in the polymer film.     

"Click" synthesis of small-molecule inhibitors targeting caspases

A panel of 198 P4-diversified aldehyde (reversible) and vinyl sulfone (irreversible) inhibitors is successfully synthesized via an efficient "click chemistry" platform and directly screened against caspase-3 and -7 for inhibition.     

Light and neutron scattering study of PEG-oleate and its use in emulsion polymerization

Steric stabilization of colloids forms a robust mechanism to obtain colloids that are stable in a variety of environments, and that can be used to study the phase behavior of hard or soft spheres. We report the synthesis of sterically stabilized colloids in an aqueous environment using readily dissolvable surfactants, with an unsaturated hydrophobic tail. We synthesized a new surfactant by esterification of a poly(ethylene glycol) (PEG) chain of 4.1 kg/mol with oleic acid, called PEG4OA. The micellization of PEG4OA was characterized by light and neutron scattering, which yielded values for the aggregation number and the overall size that are in excellent agreement with a comparable surfactant with a saturated octadecane chain, Brij 700. We successfully used PEG4OA in the emulsion polymerization of polystyrene colloids. In comparison with the smaller surfactant Tween 80, PEG4OA yielded smaller colloids with radii around 50 nm, and the addition of 1-dodecanethiol reduced the formation of aggregates during the synthesis. A contrast variation study with small angle neutron scattering (SANS) showed that a dense PEG layer was grafted to the colloid surface.     

Instrument and process independent binning and baseline correction methods for liquid chromatography–high resolution-mass spectrometry deconvolution

Setting appropriate bin sizes to aggregate hyphenated high-resolution mass spectrometry data, belonging to similar mass over charge (m/z) channels, is vital to metabolite quantification and further identification. In a high-resolution mass spectrometer when mass accuracy (ppm) varies as a function of molecular mass, which usually is the case while reading m/z from low to high values, it becomes a challenge to determine suitable bin sizes satisfying all m/z ranges. Similarly, the chromatographic process within a hyphenated system, like any other controlled processes, introduces some process driven systematic behavior that ultimately distorts the mass chromatogram signal. This is especially seen in liquid chromatogram–mass spectrometry (LC–MS) measurements where the gradient of the solvent and the washing step cycle—part of the chromatographic process, produce a mass chromatogram with a non-uniform baseline along the retention time axis. Hence prior to any automatic signal decomposition techniques like deconvolution, it is a equally vital to perform the baseline correction step for absolute metabolite quantification. This paper will discuss an instrument and process independent solution to the binning and the baseline correction problem discussed above, seen together, as an effective pre-processing step toward liquid chromatography–high resolution-mass spectrometry (LC–HR-MS) data deconvolution.     

Transport limitations in ion exchange membranes at low salt concentrations

In this work we show that the electrical resistance of ion exchange membranes strongly depends on the solution concentration: especially at low solution concentrations (<0.1 M NaCl) we observe a very strong increase in electrical resistance of the membrane with decreasing concentration. To understand and clarify this behavior we systematically investigate the influence of the solution concentration on ion transport phenomena in two anion exchange membranes (Neosepta AMX and Fumasep FAD) and two cation exchange membranes (Neosepta CMX and Fumasep FKD) in the concentration range from 0.017 M to 0.5 M NaCl and for different hydrodynamic conditions. The results are highly valuable for processes that operate in the low concentration range (<0.5 M) such as reverse electrodialysis, electrodialysis, microbial fuel cells and capacitive deionization, where the standard membrane characterization values as usually determined in 0.5 M NaCl solutions do not represent the practical application.     

Tracy–Widom statistic for the largest eigenvalue of autoscaled real matrices

Eigenanalysis is common practice in biostatistics, and the largest eigenvalue of a data set contains valuable information about the data. However, to make inferences about the size of the largest eigenvalue, its distribution must be known. Johnstone's theorem states that the largest eigenvalues l₁ of real random covariance matrices are distributed according to the Tracy–Widom distribution of order 1 when properly normalized to , where η_np and ξ_np are functions of the data matrix dimensions n and p. Very often, data are expressed in terms of correlations (autoscaling) for which case Johnstone's theorem does not work because the normalizing parameters η_np and ξ_np are not theoretically known. In this paper we propose a semi‐empirical method based on test‐equating theory to numerically approximate the normalization parameters in the case of autoscaled matrices. This opens the way of making inferences regarding the largest eigenvalue of an autoscaled data set. The method is illustrated by means of application to two real‐life data sets. Copyright © 2011 John Wiley & Sons, Ltd.     

Switching positions: Assessing the dynamics of conjugational heterogeneity in antibody–drug conjugates using CE-SDS

Antibody–drug conjugates (ADCs) are a prospective class of new oncology therapeutics with the ability to deliver a cytotoxic drug to a targeted location. The concept appears simple, but ADCs are highly complex due to their intrinsic heterogeneity. Randomly conjugated ADCs, for instance, are composed of conjugated species carrying between 0 and 8 linker-drug molecules, with several positional isomers that vary in drug distribution across the antibody. The drug load, expressed as drug-to-antibody ratio (DAR), is a critical quality attribute and should be well controlled, together with the distribution of drug molecules. Here, the impact of the duration of disulfide bond reduction on the DAR was investigated by quantitating the (isomeric) DAR species in ADCs produced with varying reduction times. Although hydrophobic interaction chromatography showed a constant DAR value as a function of reduction time, data obtained by non-reducing CE-SDS revealed an unexpected dynamic in the positional conjugated isomers. The insights obtained have improved our understanding of the correlation between the disulfide bond reduction, an important step in the manufacturing of a cysteine-conjugated ADC, and the conjugational heterogeneity.