Electrochemical Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy of Imidazole Ring Functionalized Monolayer on Smooth Gold Electrode

The imidazole ring (Im) of histidine side chains plays a unique role in the function of proteins through covalent bonding with metal ions and hydrogen bonding interactions with adjusted biomolecules and water. At biological interfaces, these interactions are modified because of the presence of an electric field. Self-assembled monolayers (SAMs) with the functional Im group mimic the histidine side chain at electrified interfaces. In this study, we applied in-situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) to probe the structure and hydrogen bonding of Im-functionalized SAM on smooth Au at the electrochemical interface. The self-assembly of molecules on the Au induced the proton shift from N1 atom (Tautomer-I), which is the dominant form of Im in the bulk sample, to N3 atom (Tautomer-II). The impact of electrode potential on the hydrogen bonding interaction strength of the Im ring was identified by SHINERS. Temperature-Raman measurements and density functional theory (DFT) analysis revealed the spectral marker for Im ring packing (mode near 1496–1480 cm⁻¹) that allowed us to associate the confined and strongly hydrogen bonded interfacial Im groups with electrode polarization at −0.8 V. Reflection adsorption IR (RAIR) spectra of SAMs with and without Im revealed that the bulky ring prevented the formation of a strongly hydrogen bonded amide group network.     

Raman spectroelectrochemical study of electrode reactions of hydroquinone at electrodes modified with Nile blue and other azine type redox mediators

Journal of Solid State Electrochemistry - Electrooxidation of hydroquinone (HQ) to benzoquinone (BQ) has been studied by Raman spectroelectrochemistry at a gold electrode modified with adsorbed or...     

A Red-Light-Driven CO-Releasing Complex: Photoreactivities and Excited-State Dynamics of Highly Distorted Tricarbonyl Rhenium Phthalocyanines

A complex comprising one [Re(CO)₃]⁺ unit and a phthalocyanine (Pc) ligand ( Re₁Pc ) is shown to function as a photo-induced CO-releasing molecule (photoCORM) in the presence of O₂ and a coordinative solvent under irradiation with red light, which can deeply penetrate living tissues. Transient absorption spectroscopic measurements indicate very short excited-state lifetimes and ultrafast intersystem crossing for Re₁Pc and Re₂Pc , which contains two [Re(CO)₃]⁺ units. The excited-state properties are ascribed to efficient spin–orbit coupling and large Franck–Condon factors originating from the complexes’ distorted structures, that is, unsymmetric coordination of [Re(CO)₃]⁺ unit(s), one of which was confirmed by single-crystal X-ray analysis of a symmetrically substituted Pc with two [Re(CO)₃]⁺ units. Re₁Pc represents a promising red-light-driven photoCORM that can be applied in biological environments or therapeutic applications.     

Metal Ion Modulated Torsion Angle in a Ditopic Oligothiophene Ligand: Toward Supramolecular Control of π Conjugation

A π‐conjugated oligomer bearing two 15‐crown‐5‐containing styryl moieties connected at the inner β positions of the terminal thiophene nuclei can adopt either a U or a Z shape depending on the structures of its complexes with magnesium and barium ions. We show that barium cations lead to the formation of a mononuclear complex in solution, which causes the system to fold into the U shape. Magnesium ions lead to the same effect at low concentration, but force the ligand to adopt the Z‐shaped geometry at high concentrations favoring formation of a binuclear complex. These geometrical reorganizations in solution are accompanied by profound changes in spectroscopic properties, which can be rationalized in terms of variations in the extent of electron delocalization along the oligothiophene backbone. The effects are analyzed by mass spectrometry and ¹H NMR, UV/Vis absorption, and fluorescence spectroscopy in the steady‐state and time‐resolved regimes. The experimental results are compared to data calculated by using MOPAC2007 with the PM6 Hamiltonian including the COSMO solvation model.     

Role of Phe‐D5 isotopically labeled analogues of bradykinin on elucidation of its adsorption mode on Ag,Au, and Cu electrodes. Surface‐enhanced Raman spectroscopy studies

Raman (RS), surface‐enhanced Raman scattering (SERS), electrochemistry, and isotopic effect methods were used to characterize selective adsorption of two isotopically labeled bradykinin analogues, [(Phe‐D₅)⁵]BK and [(Phe‐D₅)⁸]BK, a hormone which is known to be involved in small‐cell and non‐small‐cell lung carcinoma and prostate cancer. The investigated analogues contain Phe residue, at position 5 or 8 in the amino acid sequence, substituted by Phe‐D₅ (five protons of L‐phenylalanine ring substituted by deuterium). [(Phe‐D₅)⁵]BK and [(Phe‐D₅)⁸]BK were immobilized onto electrochemically roughened Ag, Au, and Cu electrode surfaces under different applied electrode potentials (−1.000 V to 0.200 V) in an aqueous solution containing 0.01 M phosphate buffer (pH = 7.0) and 0.1 M Na₂SO₄. Based on the analyses of the spectral profiles in the 920 – 1050 cm⁻¹ spectral range, specific conclusions were drawn with respect to the Phe⋅⋅⋅metal interactions and changes in the interaction that occurred when the adsorption conditions were varied. Copyright © 2013 John Wiley & Sons, Ltd.     

Large scale multi-configuration Hartree-Fock calculation of the hyperfine structure of the ground state of vanadium

The hyperfine structure of the ground state of vanadium, ⁵¹VI, is calculated in the nonrelativistic framework of the multi-configuration Hartree-Fock approximation. A configuration state function limiting algorithm is used to make the calculations feasible and to study the influence of core, valence and core-valence correlations in detail. The obtained configuration state function space captures the most important orbital correlations within 2%. Further correlations are included through configuration interaction calculation. The atomic state functions are used to evaluate the magnetic dipole hyperfine factor A and the electric quadrupole factor B. It turns out that the ab initio calculation can not capture the core polarization of the 2s shell. It introduces an error that is higher than the Hartree-Fock approximation. However, the detailed correlations being observed suggest the introduction of a wrong correlation orbital due to the algorithm being used. Neglecting this orbital leads to good agreement with 2% deviation from the experimental values for the A factors.     

Quantum dot materials for terahertz generation applications

Compact and tunable semiconductor terahertz sources providing direct electrical control, efficient operation at room temperatures and device integration opportunities are of great interest at the present time. One of the most well‐established techniques for terahertz generation utilises photoconductive antennas driven by ultrafast pulsed or dual‐wavelength continuous wave laser systems, though some limitations, such as confined optical wavelength pumping range and thermal breakdown, still exist. The use of quantum dot‐based semiconductor materials, having unique carrier dynamics and material properties, can help to overcome limitations and enable efficient optical‐to‐terahertz signal conversion at room temperatures. Here we discuss the construction of novel and versatile terahertz transceiver systems based on quantum dot semiconductor devices. Configurable, energy‐dependent optical and electronic characteristics of quantum‐dot‐based semiconductors are described, and the resonant response to optical pump wavelength is revealed. Terahertz signal generation and detection at energies that resonantly excite only the implanted quantum dots opens the potential for using compact quantum dot‐based semiconductor lasers as pump sources. Proof‐of‐concept experiments are demonstrated here that show quantum dot‐based samples to have higher optical pump damage thresholds and reduced carrier lifetime with increasing pump power.

     

Adsorption of l-histidine on copper surface as evidenced by surface-enhanced Raman scattering spectroscopy

The adsorption of l-histidine on a copper electrode from H₂O- and D₂O-based solutions is studied by means of surface-enhanced Raman scattering (SERS) spectroscopy. Different adsorption states of histidine are observed depending upon pH, potential, and the presence of the SO²⁻₄ and Cl⁻ ions. In acidic solutions of pH 1.2 the imidazole ring of the adsorbed histidine remains protonated and is not involved in the chemical coordination with the surface. The SO²⁻₄ and Cl⁻ ions compete with histidine for the adsorption sites. In solutions of pH 3.1 three different adsorption states of histidine are observed depending on the potential. Histidine adsorbs with the protonated imidazole ring oriented mainly perpendicularly to the surface at potentials more positive than −0.2 V. Transformation of that adsorption state occurs at more negative potentials. As this takes place, histidine adsorbs through the α-NH₂ group and the neutral imidazole ring. The Cl⁻ ions cause the protonation and detachment of the α-NH₂ group from the surface and the formation of the ion pair NH⁺₃ … Cl⁻ can be observed. In the neutral solution of pH 7.0 histidine adsorbs through the deprotonated nitrogen atom of the imidazole ring and the α-COO⁻ group at E ≥ −0.2 V. However, this adsorption state is transformed into the adsorption state in which the α-NH₂ group and/or neutral imidazole ring participate in the anchoring of histidine to the surface, once the potential becomes more negative. In alkaline solutions of pH 11.9 histidine is adsorbed on the copper surface through the neutral imidazole ring.     

Poisson Distribution for a Sum of Additive Functions

We consider the limit distribution of values of a sum of additive arithmetic functions with shifted argument. The case of the Poisson limit distribution is studied. The functions considered take at most two values on the set of primes, 0 and 1, and satisfy some additional conditions. Some examples are given.