XPS study of the effect of the conditions of peptide chemisorption to gold and silver coated polymer surfaces

Chemisorption of peptides and active moieties onto gold and silver coated surfaces is an attractive method for studying the effect of fundamental surface properties on biological interactions. In theory, the monolayers formed have a high density of the active group of interest, and the relatively mild conditions associated with chemisorption should allow biological activity to be maintained. While the conditions for chemisorption are widely reported in the literature, significant differences exist between research groups and the effects of changing these conditions on the resultant surface have not been fully examined. Furthermore, comparisons have not been made between gold and silver as potential substrates in these applications. In the current work, glutathione and cysteine were chemisorbed onto gold- and silver-coated polymers. The effect of varying the chemisorption conditions was evaluated by XPS analysis of the resultant surfaces. Factors identified as having potentially significant effects on chemisorption procedure included chemisorption time, peptide concentration, peptide, pH of the chemisorption solution, mixing and material of the incubation container. Factor significance was evaluated using a two level fractional factorial design of experiments (DOE), with sulfur content determined by XPS used as a measure of chemisorption effectiveness. Significant differences were noted between the silver and gold-coated surfaces, with a higher amount of sulfur and hence, by inference, peptide found in general on silver surfaces reacted under identical conditions. On the gold surfaces, peptide concentration, peptide type, and chemisorption time were found to have a significant effect on the composition of the resulting surface. On the silver surfaces, factor specific differences were not as significant but there were a number of two factor interactions. The results provide further evidence of the differences in interactions with thiol between silver and gold and suggest that changes in the chemisorption conditions can dramatically affect the resultant surface composition.     

Impact of ligand exchange in hydrogen production from cobaloxime-containing photocatalytic systems

Ligand exchange on the Co(dmgH)(2)(py)Cl water reduction catalyst was explored under photocatalytic conditions. The photosensitizer fluorescein was connected to the catalyst through the axially coordinated pyridine. While this two-component complex produces H(2) from water under visible light irradiation in the presence of triethanolamine (TEOA), it is less active than a system containing separate fluorescein and [Co(III)(dmgH)(2)(py)Cl] components. NMR and photolysis experiments show that the Co catalyst undergoes pyridine exchange. Interestingly, glyoximate ligand exchange was also observed photocatalytically and by NMR spectroscopy, thereby showing that integrated systems in which the photosensitizer is linked directly to the Co(dmgH)(2)(py)Cl catalyst may not remain intact during H(2) photogeneration. These studies have also given rise to insights into the catalyst decomposition mechanism.     

Absolute backscatter coefficient estimates of tissue-mimicking phantoms in the 5-50 MHz frequency range

Absolute backscatter coefficients in tissue-mimicking phantoms were experimentally determined in the 5-50 MHz frequency range using a broadband technique. A focused broadband transducer from a commercial research system, the VisualSonics Vevo 770, was used with two tissue-mimicking phantoms. The phantoms differed regarding the thin layers covering their surfaces to prevent desiccation and regarding glass bead concentrations and diameter distributions. Ultrasound scanning of these phantoms was performed through the thin layer. To avoid signal saturation, the power spectra obtained from the backscattered radio frequency signals were calibrated by using the signal from a liquid planar reflector, a water-brominated hydrocarbon interface with acoustic impedance close to that of water. Experimental values of absolute backscatter coefficients were compared with those predicted by the Faran scattering model over the frequency range 5-50 MHz. The mean percent difference and standard deviation was 54%?±?45% for the phantom with a mean glass bead diameter of 5.40 μm and was 47%?±?28% for the phantom with 5.16 μm mean diameter beads.     

Probing the high momentum component of the deuteron at high Q2

The (2)H(e,e'p)n cross section at a momentum transfer of 3.5 (GeV/c)(2) was measured over a kinematical range that made it possible to study this reaction for a set of fixed missing momenta as a function of the neutron recoil angle θ(nq) and to extract missing momentum distributions for fixed values of θ(nq) up to 0.55 GeV/c. In the region of 35°≤θ(nq)≤45° recent calculations, which predict that final-state interactions are small, agree reasonably well with the experimental data. Therefore, these experimental reduced cross sections provide direct access to the high momentum component of the deuteron momentum distribution in exclusive deuteron electrodisintegration.     

Two Cu21 clusters with pseudo-D3 symmetry derived from the D-saccharate pentaanion, C6H5O8(5-)

The combination of Cu(NO₃)₂, potassium hydrogen saccharate (KC₆H₉O₈) and 1,10‐phenanthroline (phen) yields a pair of chiral cluster compounds, each with composition Cu₂₁(C₆H₅O₈)₆(phen)₁₂(NO₃)₁₂?solvate. One of the compounds forms as orthorhombic crystals, while the other forms cubic crystals. Each of the clusters has D₃ or approximate D₃ symmetry, but the arrangement of the saccharate ion in the clusters is quite different in the two cases. The clusters in the cubic form interact with neighbouring clusters through face‐to‐face π interactions involving the phen ligands, an association that leads to the generation of very large solvent‐filled spaces in the crystal structure. In contrast the clusters in the orthorhombic form are much more densely packed. At the centre of each cluster that crystallises in the orthorhombic form is a nitrate anion that binds to six Cu^II centres. ESI mass spectral studies indicate that the Cu₂₁ clusters exist in solution. Solid‐state magnetic studies of the cubic form of Cu₂₁ show that antiferromagnetic coupling occurs to leave a non‐zero‐spin ground state, and comparisons are made to the magnetic data for other large Cu^II clusters.     

Generalised Gagliardo–Nirenberg Inequalities Using Weak Lebesgue Spaces and BMO

Using elementary arguments based on the Fourier transform we prove that for ${1 \leq q < p < \infty}$ and ${s \geq 0}$ with s > n(1/2 ? 1/p), if ${f \in L^{q,\infty} (\mathbb{R}^n) \cap \dot{H}^s (\mathbb{R}^n)}$ , then ${f \in L^p(\mathbb{R}^n)}$ and there exists a constant c _p,q,s such that $$\| f \|_{L^{p}} \leq c_{p,q,s} \| f \|^\theta _{L^{q,\infty}} \| f \|^{1-\theta}_{\dot{H}^s},$$ where 1/p = θ/q + (1?θ)(1/2?s/n). In particular, in ${\mathbb{R}^2}$ we obtain the generalised Ladyzhenskaya inequality ${\| f \| _{L^4} \leq c \| f \|^{1/2}_{L^{2,\infty}} \| f \|^{1/2}_{\dot{H}^1}}$ .We also show that for s = n/2 and q > 1 the norm in ${\| f \|_{\dot{H}^{n/2}}}$ can be replaced by the norm in BMO. As well as giving relatively simple proofs of these inequalities, this paper provides a brief primer of some basic concepts in harmonic analysis, including weak spaces, the Fourier transform, the Lebesgue Differentiation Theorem, and Calderon–Zygmund decompositions.     

Existence and Uniqueness for a Coupled Parabolic-Elliptic Model with Applications to Magnetic Relaxation

We prove the existence, uniqueness and regularity of weak solutions of a coupled parabolic-elliptic model in 2D, and the existence of weak solutions in 3D; we consider the standard equations of magnetohydrodynamics with the advective terms removed from the velocity equation. Despite the apparent simplicity of the model, the proof in 2D requires results that are at the limit of what is available, including elliptic regularity in L ¹ and a strengthened form of the Ladyzhenskaya inequality $$\| f \|_{L^{4}} \leqq c \| f \|_{L^{2,\infty}}^{1/2} \|\nabla f\|_{L^{2}}^{1/2},$$ which we derive using the theory of interpolation. The model potentially has applications to the method of magnetic relaxation introduced by Moffatt (J Fluid Mech 159:359–378, 1985) to construct stationary Euler flows with non-trivial topology.     

Matroid optimisation problems with nested non-linear monomials in the objective function

We derive a new approximate version of the alternating direction method of multipliers (ADMM) which uses a relative error criterion. The new version is somewhat restrictive and allows only one of the two subproblems to be minimized approximately, but nevertheless covers commonly encountered special cases. The derivation exploits the long-established relationship between the ADMM and both the proximal point algorithm (PPA) and Douglas–Rachford (DR) splitting for maximal monotone operators, along with a relative-error of the PPA due to Solodov and Svaiter. In the course of analysis, we also derive a version of DR splitting in which one operator may be evaluated approximately using a relative error criterion. We computationally evaluate our method on several classes of test problems and find that it significantly outperforms several alternatives on one problem class.     

Transparent aluminosilicate gels from single alkoxides: Current directions

This article presents a short review of current and future trends in the synthesis of non-stoichiometric, transparent aluminosilicate gels. An overview of currently accessible compositions is also provided.     

Methods for estimating the similarity parameter of clouds from internal measurements of the scattered radiation field

The similarity parameter is a combination of the single scattering albedo and the scattering asymmetry factor and can be used in conjunction with particle-size information to estimate the fractional absorption of a cloud layer. Methods are presented for estimating the parameter without estimating the optical thickness of the cloud or the ground albedo, but radiance measurements must be made at two elevations deep within the cloud layer. If the radiance data is for a sufficient number of directions, then one method can be used to give the parameter without using any correlation of the parameter with properties of the cloud. With the appropriate correlations, the parameter can be obtained using either the mean radiance and net flux or the radiance in only the zenith and nadir directions. The methods are based on an asymptotic transport theory and are shown to be a special case of more general transport results.