Evolution of surface morphologies in multivariant assemblies of surface-tethered diblock copolymers after selective solvent treatment

We study systematically the topography behavior of PHEMA-b-PMMA block as a function of the PHEMA and PMMA block lengths after selectively collapsing the top (PMMA) block by using surface-anchored assemblies of poly(2-hydroxyethyl methacrylate-b-methyl methacrylate), PHEMA-b-PMMA, block copolymer with orthogonally varying lengths of each block. Our experimental results are in excellent qualitative agreement with topology diagrams predicted by self-consistent field calculations of Zhulina and co-workers.     

Quasiparticle lifetimes in pure Al and Pb

We present results of theoretical calculations of the quasiparticle lifetimes in pure Al and Pb which are due to the electron-phonon interaction. A four-plane-wave model is used to describe the electronic structure and the coupling with the phonons. The lattice dynamics is taken from inelastic neutron scattering data. At a given temperature (T) the lifetimes (τ) display considerable variation with position on the Fermi surface (FS). At several points on the FS we obtain through a least-squares fit to our numerical output on the low temperature variation of τ, the best power law of the form AT^α with A and α constants. The exponent α is found to vary significantly from point to point.     

The Personality of O.R. Workers—Are They Different?

This paper is a preliminary attempt to compare the personality of O.R. workers with research scientists and other professionals in the management area. It is based on 16PF personality tests carried out on 56 U.K. operational research workers. The results indicate that this group has a personality profile which is significantly different from the published profiles of the professional groupings. It is believed that the results are highly indicative and justify further research.     

Foreword

Journal of the Operational Research Society -     

Site‐Specific Labeling of Affimers for DNA‐PAINT Microscopy

Optical super‐resolution techniques allow fluorescence imaging below the classical diffraction limit of light. From a technology standpoint, recent methods are approaching molecular‐scale spatial resolution. However, this remarkable achievement is not easily translated to imaging of cellular components, since current labeling approaches are limited by either large label sizes (antibodies) or the sparse availability of small and efficient binders (nanobodies, aptamers, genetically‐encoded tags). In this work, we combined recently developed Affimer reagents with site‐specific DNA modification for high‐efficiency labeling and imaging using DNA‐PAINT. We assayed our approach using an actin Affimer. The small DNA‐conjugated affinity binders could provide a solution for efficient multitarget super‐resolution imaging in the future.     

Identifying sites of protein modification by using matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry and on-line membrane preconcentration-capillary electrophoresis-tandem mass spectrometry

A strategy for rapidly identifying the number and sites of chemical or posttranslational modification of proteins is described. The use of matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry to determine the molecular weight of the adducted protein as well as map the proteolytic digest of peptides offers a rapid method to screen for the possible site of adduction. To unequivocally determine the amino acid sequence of the peptide bearing the adduct as well as structurally characteize the covalent modification, the peptide mixture is subjected to membrane preconcentration-capillary electrophoresis-mass spectrometry and tandem mass spectrometry (mPC-CE-MS/MS). The high resolving separation capability of capillary electrophoresis (CE) afford a chromatograhic step that lends itself to separation of complex mixtures of peptides with minimal sample loss. The membrane preconcentration-CE cartridge allows sample loading volumes 10,000-fold greater than conventional CE. In this work the binding site of the fluorescent label acrylodan to the intestinal fatty binding protein is characterized and shown to be covalently bound at lysine-27, by using mPC-CE-MS/MS.     

Zinc-induced conformational changes in the DNA-binding domain of the vitamin D receptor determined by electrospray ionization mass spectrometry

Electrospray ionization mass Spectrometry (ESI-MS) was used to measure conformational changes within the DNA-binding domain of the vitamin D receptor (VDR DBD) upon binding zinc (Zn²⁺). As increasing concentrations of Zn²⁺ were added to the VDR DBD, a gradual shift in the mass envelope to lower charge states was observed in the multiply charged spectrum. The shift in the charge states was correlated to changes observed in the far-ultraviolet circular dichroic (far-UV CD) spectrum of the protein as it was titrated with Zn²⁺. Both the multiply charged ESI and far-UV CD spectra of the Zn²⁺-titrated protein show that the binding of the first Zn²⁺ ion to the protein results in very little conformational change in the protein. The binding of a second Zn²⁺ ion resulted in a significant alteration in the structure of the protein as indicated by changes in both the multiply charged ESI and far-UV CD spectra. Much smaller changes were seen within the multiply charged ESI or far-UV CD spectra upon increasing the Zn²⁺ concentration beyond 2 mol/mol of protein. The results presented indicate that ESI-MS in combination with CD is a powerful method to measure gross conformational changes induced by the binding of metals to metalloproteins.     

Low temperature aqueous electrospray ionization mass spectrometry of noncovalent complexes

In the present study we describe conditions that permit the characterization of noncovalent protein–substrate complexes in aqueous solution by microspray electrospray ionization-mass spectrometry (ESI-MS), using a heated transfer capillary at low temperature (45 °C). Specifically, we examined the binding of calmodulin to two polypeptides; the calmodulin-binding domain of calmodulin-dependent protein kinase II (CamK-II) and melittin. Calmodulin, a well known calcium-binding protein, binds to a number of small amphipathic peptides in a calcium-dependent manner. Our results directly show that both peptides form equimolar complexes with calmodulin only in the presence of calcium. The stoichiometry necessary for the formation of each complex was 1:1:4 for calmodulin:peptide (melittin or CamK-II):Ca²⁺, respectively. Furthermore, it is demonstrated that the detection of the complex in ESI-MS is source temperature dependent.     

Annealing Effects on Photoconductivity Spectra of CuInSe2 Single Crystals

Photoconductivity spectra of as-grown n-type and p-type CuInSe₂ single crystals and of crystals annealed under maximum and minimum selenium pressure are measured in the photon energy range hv = 0.75 – 3.0 eV and as a function of temperature in the range T = 80 – 320 K. A model with trapping of minority carriers is used to explain the temperature dependence of the photoconductivity. The trap energies present in the samples depend on their preparation conditions.