Tandem diazonium salt electroreduction and click chemistry as a novel, efficient route for grafting macromolecules to gold surface

Bis-alkynylated oligoethyleneglycol (OEG) and a monopropargyl-functionalized perfluorinated ethylene glycol (FEG) were clicked to azide-functionalized gold surface (Au–N₃) at room temperature via the well known 1,3 cycloaddition click chemical reaction. The Au–N₃ substrate was obtained by nucleophilic attack of NaN₃ on gold substrates modified by the electrochemical reduction of the , ⁺N₂–C₆H₄–CH₂Br diazonium salt. This electrochemical process yields aryl layer-modified gold of the type Au–C₆H₄–CH₂Br (hereafter Au–Br). The untreated and modified gold plates were examined by XPS, PMIRRAS and contact angle measurements. XPS brought evidence for electrografting aryl layers by the detection of Br3d; azide functionalization by the increase of the N/Br atomic ratio; and click reaction of OEG with Au–N₃ by the increase of O/N ratio. In addition, the perfluorinated plate (Au-FEG) exhibited F1s and characteristic C1s peaks from -(CF₂)₇- chain and terminal CF₃. Infra red spectroscopy (PMIRRAS) evidenced (i) grafting N₃ to Au–Br; (ii) characteristic stretching bands, from ethylene glycol units, C–O–C (1100–1300 cm⁻¹); CF₂ (1000–1100 cm⁻¹) and CF₃ (1100–1350 cm⁻¹) from FEG grafts; and (iii) suppression of alkynyl bands from OEG and FEG after surface click chemistry. More importantly, PMIRRAS results support an important bridging of the bispropargyl oligoethylene glycol at the gold surface. Water drop contact angles were found to be 48.7° and 83.0° for Au-OEG and Au-FEG, respectively, therefore highlighting the control over the hydrophilic/hydrophobic character of the clicked substrate.This work shows that clicking macromolecules to grafted, diazonium salt-derived aryl layers is a novel, simple and valuable approach for designing robust, functional surface organic coatings.     

Continuation of Time Bounds for a Regularized Boussinesq System

We study the periodic solution of a perturbed regularized Boussinesq system (Bona et al., J. Nonlinear Sci. 12:283–318, 2002, Bona et al., Nonlinearity 17:925–952, 2004), namely the system η _t +u _x +β(−η _xxt +u _xxx )+α((ηu) _x +ηη _x +uu _x )=0,u _t +η _x +β(η _xxx −u _xxt )+α((ηu) _x +ηη _x +uu _x )=0, with 0<α,β≤1. We prove that the solution, starting from an initial datum of size ε, remains smaller than ε for a time scale of order (ε ⁻¹ α ⁻¹ β)², whereas the natural time is of order ε ⁻¹ α ⁻¹ β.     

NMR Spectroscopic Assignment of Backbone and Side‐Chain Protons in Fully Protonated Proteins: Microcrystals,Sedimented Assemblies,and Amyloid Fibrils

We demonstrate sensitive detection of alpha protons of fully protonated proteins by solid‐state NMR spectroscopy with 100–111 kHz magic‐angle spinning (MAS). The excellent resolution in the Cα‐Hα plane is demonstrated for 5 proteins, including microcrystals, a sedimented complex, a capsid and amyloid fibrils. A set of 3D spectra based on a Cα–Hα detection block was developed and applied for the sequence‐specific backbone and aliphatic side‐chain resonance assignment using only 500 μg of sample. These developments accelerate structural studies of biomolecular assemblies available in submilligram quantities without the need of protein deuteration.     

Stopping power and energy loss straggling of thin Formvar foil for 0.3–2.7 MeV protons and alpha particles

Stopping power and energy loss straggling data for protons (¹H⁺) and alpha particles (⁴He⁺) crossing Formvar thin polymeric foils (thickness of ～0.3 μm) have been measured in the energy range (0.3–2.7) MeV by using the indirect transmission technique. The determined stopping power data were compared to SRIM-2010, PSTAR or ASTAR calculation codes and then analyzed in term of the modified Bethe–Bloch theory to extract the target mean excitation and ionization potential 〈I〉. A resulting value of 〈I〉≈(69.2±1.8) eV was deduced from proton stopping data. The measured straggling data were corrected from surface roughness effects due to target thickness inhomogeneity observed by the atomic force microscopy (AFM) technique. The obtained data were then compared to derived straggling values by Bohr's and Bethe–Livingston's classical theories or by Yang's empirical formula. A deviation of ～40%–80% from the Bohr's straggling value has been observed for all reported energies, suggesting that the Bohr theory cannot be correctly applied to describe the electronic energy loss straggling process with the used low thickness of Formvar foil. The inner-shell contribution of target electrons to energy loss process is also advanced to explain the observed deviation from experiment in case of He⁺ ions. Finally, the reliability of Bragg's additivity rule was discussed in case of stopping power and straggling results.     

Aminomethylation of Symmetric Dialkylthioureas with Formaldehyde and Amino Acids

Russian Journal of General Chemistry - Condensation of 1,3-dialkylthiourea, formaldehyde, and terminal amino acids (C2, C3, or C4) taken in the 1 : 2 : 1 molar ratio has afforded the terminally...     

Carleman estimates and unique continuation property for the Kadomtsev–Petviashvili equations

We study the unique continuation property for the generalized Kadomtsev–Petviashvili (KP) equations and its regularized version. We use Carleman estimates to prove that if the solution of the KP equations vanishes in an open subset, then this solution is identically equal to zero in the horizontal component of the open subset.     

Energy loss straggling measurements for helium ions in Mylar and polypropylene polymeric foils

In the present contribution, we report results on energy straggling of He ions penetrating Mylar and polypropylene thin polymeric foils. The measurements were performed in the 900–3000 keV incident particle energy range by using the indirect transmission technique developed previously. The experimental straggling data are corrected to consider the roughness effects due to target thickness inhomogeneity. As expected, the roughness contribution to straggling is more important for helium than for proton ions and decreases as the ion energy increases. At low velocities, (<500 keV/amu), the variation of the experimental energy straggling results differs strongly from predictions based on Bohr’s formalism, and with increasing energies, the experimental results approach gradually the Bohr values.