From pirazoloquinolines to annulated azulene dyes: UV–VIS spectroscopy and quantum chemical study

Paper reports UV–Vis absorption and photoluminescence spectra of 6-R derivatives (R=CH₃, O–CH₃, C(C₆H₅)₃, C₆H₅–N–C₁₀H₇) of 4-(2-chlorophenyl)-1,3-diphenyl-1H-pyrazolo[3,4-b]quinoline, belonging to pyrazoloquinoline (PQ) family, likewise its regioisomeric products 10-R derivatives of 6-phenyl-6H-5,6,7-triazadibenzo[f,h]naphtho[3,2,1-cd]azulene representing cyclized seven-membered annulated azulene (AA) dyes. Cyclization of PQs into AAs is accompanied by a significant red shift of the first optical absorption band. This finding agrees with the results of quantum-chemical calculations performed by means of the semiempirical method PM3. As the solvent polarity rises all the dyes exhibit a blue shift of the first absorption band and a red shift of the fluorescence band. Such opposite trends in solvatochromic behavior have been reproduced within the semiempirical calculations in combination with the Lippert–Mataga dielectric polarization model. Depending on solvent polarity AA dyes emit light in the green, green–yellow or orange range of the visible spectrum what may be of interest for potential luminescent or electroluminescent applications.     

Hyperfine interactions in icosahedral quasicrystals: a Mössbauer study

Icosahedral Al₆₅Cu₂₀Fe₁₅ and Al₄₀Cu_9.9Ge₂₅Mn₂₅ ⁵⁷Fe_0.1 quasicrystals are studied using⁵⁷Fe transmission Mössbauer experiments. The spectra are analyzed by distributions of electric-quadrupole interaction accounting for line asymmetries. Temperature dependences of the hyperfine parameters derived comprising average values ofP() distributions, corresponding standard deviations and center shifts are presented in a whole range from 8 to 300 K.     

Global study of electron–quark unparticle interactions

We perform a global fit on parity-conserving electron–quark interactions via spin-1 unparticle exchange. Besides the peculiar features of unparticle exchange due to non-integral values for the scaling dimension \(d_{\mathcal {U}}\) and a non-trivial phase factor \(\exp (-id_{\mathcal {U}}\pi)\) associated with a time-like unparticle propagator, the energy dependence of the unparticle contributions in the scattering amplitudes are also taken into account. The high energy data sets taken into consideration in our analysis are from (1) deep inelastic scattering at high Q ² from ZEUS and H1, (2) Drell–Yan production at Run II of CDF and DØ, and (3) e ⁺ e ^?→ hadrons at LEPII. The hadronic data at LEPII by itself indicated a 3–4 sigma preference of new physics over the Standard Model. However, when all data sets are combined, no preference for unparticle effects can be given. We thus deduce an improved 95% confidence level limit on the unparticle energy scale \(\varLambda_{\mathcal {U}}\).     

Polarizability of a donor impurity in dielectrically modulated core–shell nanodots

Simultaneous effects of the quantum confinement and electric field on the donor states in ZnS/CdSe core–shell nanodots surrounded by a wide-gap dielectric material are investigated. The results show a pronounced blue-shift of the binding energy due to the dielectric confinement. While in smaller dots the electron is located in the core even for off-center impurities, for increased outer radius it becomes squeezed almost entirely into the shell material. Therefore, the impurity states could be tuned by properly tailoring the heterostructure parameters (size, impurity position) and the dielectric environment, as well as by varying the electric field strength.     

Phonon–phonon interactions due to non-linear effects in a linear ion trap

We examine in detail the theory of the intrinsic non-linearities in the dynamics of trapped ions due to the Coulomb interaction. In particular, the possibility of mode–mode coupling, which can be a source of decoherence in trapped ion quantum computation, or can be exploited for parametric down-conversion of phonons, is discussed and conditions under which such coupling is possible are derived. Received: 8 November 2002 / Published online: 26 March 2003 RID="*" ID="*"Permanent address: MIP, Université Pierre et Marie Curie and Département de Physique, école Normale Supérieure, 75005 Paris, France RID="**" ID="**"Corresponding author. Fax: +1-505/667-1931, E-mail: dfvj@lanl.gov     

Electron–phonon coupling in DNA: a systematic study

The coupling of all twelve possible conformational modes of DNA duplexes and four pair-wise correlations among them to positive charge (hole) motion through these biopolymers has been systematically analysed in regular homogeneous B-DNA trimers and tetramers of adenosine–thymidine (AT) and guanosine–cytidine (GC) Watson–Crick pairs using PM3 semiempirical quantum chemistry. Of these only five modes have been found to be most strongly coupled to the electron motion in DNA, namely stretching of H-bonding both in AT and GC, correlated Buckle–Rise and Stagger–Tilt motions in GC and correlated Shear–Twist motion in AT. The parameters for the corresponding polaronic Hamiltonians have been estimated. The nature of these DNA polarons is discussed taking into account the relevant experimental results currently available.     

Atomic-scale study of dislocation–stacking fault tetrahedron interactions. Part I: mechanisms

Stacking fault tetrahedra (SFTs) are formed under irradiation in fcc metals and alloys. The high number density of SFTs observed suggests that they should contribute to radiation-induced hardening and, therefore, be taken into account when estimating mechanical property changes of irradiated materials. The key issue in this is to describe the interaction between a moving dislocation and an individual SFT, which is distinguished by a small physical size of the order of ～1–10?nm. We have performed atomistic simulations of edge and screw dislocations interacting with SFTs of different sizes at different temperatures and strain rates. Five possible interaction outcomes have been identified, involving either partial absorption, or shearing or restoration of SFTs. The mechanisms that give rise to these processes are described and their dependence on interaction parameters, such as SFT size, dislocation–SFT geometry, temperature and stress/strain rate are determined. Mechanisms that help to explain the formation of defect-free channels cleared by gliding dislocations, as observed experimentally, are also discussed. Hardening due to the various mechanisms and their dependence on loading conditions will be presented in a following paper (Part II).     

Rhyolite–dacite–trachyandesite association: a Mössbauer spectroscopy study

Three volcanic dykes, rhyolite, dacite and trachyandesite cutting a radioactive granite, located between Latitudes 22° 47′ 396″–22° 47′ 884″ N and Longitudes 31° 54′ 883″–31° 54′ 894″ E in the south Western Desert of Egypt were sampled and analyzed by X-ray diffraction, ⁵⁷Fe Mössbauer spectroscopy and chemical method. They are consisted of feldspar and quartz together with some paramagnetic minerals including aegirine plus minor riebeckite in the rhyolite; aegirine plus some riebeckite in the dacite; and riebeckite plus trace aegirine in the trachyandesite, respectively. The bulk content of iron in each dyke has characteristic ferric-quadrupole splitting and oxidation values: 0.29 millimeters per second (mm/s) and 100% for rhyolite; 0.31 mm/s and 82% for dacite; and 0.35 mm/s and 0.69% for trachyandesite. Variations in the quadrupole splitting have been attributed to changes from the local crystal chemistry, while the oxidation variations are source-related.     

Quantum–chemical study of photo–excited states in tetragonal SrTiO3 lattice

The nature of photo-excited states in SrTiO₃ has been a topic of intense debate during the last few decades. Using a quantum-chemical method developed for crystals, we present a theoretical interpretation of the structural and electronic properties of triplet excitons in the tetragonal SrTiO₃ crystal. Our study demonstrates that the defect structure may correspond to the Mott–Wannier-type exciton having a considerable distance, 2.14Å, between the hole and the electron parts of the defect. The geometry optimization leads to an extensive defective region containing up to five atoms. However, the obtained magnitudes of atomic movements do not exceed 0.15Å. It is also observed that the self-trapped exciton polarizes the lattice around it. Using the so-called (ΔSCF method, the luminescence energy due to the exciton is found to be equal to 1.13 eV. As it corresponds to the infrared part of the spectrum, the experimentally detected green luminescence due to photo-excited states should be attributed to the singlet excitons.     

Surface-enhanced resonance Raman study of avidin–dye interactions: A model for chromophore-containing proteins

Resonance Raman (RR) and surface-enhanced resonance Raman (SERR) spectroscopy were used to study the behavior of 2-(4′-hydroxyphenylazo)benzoic acid (HABA) at different pH values (2.7–11.8) in solution and bound to avidin. Major changes in the RR spectrum of the dye are observed near pH 8.0 and 3.0. These pH values are close to the pK_a values for the phenolic and carboxylic acid functional groups of HABA and reflect deprotonation of these groups. In addition, however, tautomeric forms of the dye are possible within each pH range and these can be identified from the characteristic vibrational modes of the azo and hydrazone forms of HABA. Similar changes in the SERR spectrum of HABA were also observed as a function of pH. However, a comparison of the RR and SERR spectra has shown that the tautomeric equilbrium is shifted toward the hydrazone form on the Ag surface compared with the effect in solution. The RR and SERR spectra of the HABA-avidin complex are nearly identical and indicative of the hydrazone form of the dye. Hence the complex is not dissociated on the Ag surface. This finding is encouraging with regard to the application of SERR techniques to the study of native proteins containing chromophores.     

First principles study of interactions of oxygen–carbon–vacancy in bcc Fe

Behaviors of C or O in bcc Fe and interactions of C–O and oxygen–carbon–vacancy(O–C–□) are investigated by first principles calculations. Octahedral interstitial site is the most stable position for an O atom in bcc Fe. The migration energy of an O atom in bcc Fe is 0.46 eV. The strength of O–Fe(1 nn) bond(0.32) is slightly greater than that of Fe–Fe metallic bond(0.26). Repulsive interactions of C–C, O–O, and C–O exist in bcc Fe. When the concentration of FIA(FIA refers to C or O) is relatively high, a vacancy can attract four FIAs and form stable FIAs–□ complex.     

CdSe–Au nanorod networks welded by gold domains: a promising structure for nano-optoelectronic components

LiFePO_4?x F _x /C nanorods were prepared by room-temperature solid-state reaction and microwave heating. The structure and morphology of the as-prepared materials were analyzed by X-ray diffractometry and transmission electron microscopy. The results shows that the LiFePO_4?x F _x /C were well crystallized and consisted of nanoparticles with an average diameter of ten to several tens of nanometers, many round grains constituted solid rod-like structure. The length of the rods can be up to several hundreds of nanometers, and their diameters are around 100?nm. The results of electrochemical testing show that the initial discharge capacity of LiFePO_3.85F_0.15/C is 124.7?mAh?g^?1, with a negligible fading after 50 cycles at a constant current density of 1 C at room temperature. The capacity retention rate is 99.5?%, which is higher than that of LiFePO₄/C prepared by the same method. The doping of F helps improve electrical conductivity and Li⁺ diffusion of LiFePO₄/C. This study may provide new insights and understanding on the effect of F-doping on the electrochemical performance of LiFePO₄/C.     

Two-dimensional PC_3 as a promising anode material for potassium-ion batteries: First–principles calculations

With the diversified development of the battery industry, potassium-ion batteries(PIBs) have aroused widespread interest due to their safety and high potassium reserves on earth. However, the lack of suitable anode materials limits their development and application to a certain extent. Based on first-principles calculations, we investigate the possibility of using PC_3 monolayer as the anode material for PIBs. PC_3 sheet has excellent electrical properties and meets the prerequisite of anode materials. The storage capacity of potassium is as high as 1200 m Ah·g~(-1), which is better than many other reported potassium-ion anode materials. In addition, the outstanding advantages of PC_3 sheet, such as low diffusion barrier and moderate open-circuit voltage, make it a potential anode candidate for PIBs.     

Comparative biological study between quinazolinyl–triazinyl semicarbazide and thiosemicarbazide hybrid derivatives

Molecular Diversity - Practical synthesis and biological activities of quinazolinyl–triazinyl semicarbazides (10a–j) and quinazolinyl–triazinyl thiosemicarbazides (11a–j)...     

Cluster ion–solid interactions from meV to MeV energies

The nature of cluster ion–surface interactions changes dramatically with the kinetic energy and mass of the incoming cluster species. In this article we review some recent work on the nature of cluster–surface interactions spanning an energy range from a few tens of meV/atom to several MeV/cluster and cluster sizes in the range of 1–300000 atoms/cluster. We describe five possible distinct outcomes of a single cluster impact event: (i) deposition into a non-epitaxial configuration, (ii) deposition into an epitaxial configuration, (iii) crater formation by liquid flow, (iv) crater formation by hydrostatic pressure, (v) implantation. PACS 65.80.+n; 82.60.Qr; 61.46.Hk; 02.70.Ns     

Using X-PEEM to study biomaterials: Protein and peptide adsorption to a polystyrene–poly(methyl methacrylate)-b-polyacrylic acid blend

Recent synchrotron-based soft X-ray photoemission electron microscopy (X-PEEM) studies of protein and peptide interaction with phase segregated and patterned polymer surfaces in the context of optimization of candidate biomaterials are reviewed and a study of a new system is reported. X-PEEM and atomic force microscopy (AFM) were used to investigate the morphology of a phase-segregated thin film of a polystyrene/poly(methyl methacrylate)-b-polyacrylic acid (PS/PMMA-PAA) blend, and its interactions with negatively charged human serum albumin (HSA) and positively charged SUB-6 (a cationic antimicrobial peptide, RWWKIWVIRWWR-NH₂) at several pHs. At neutral pH, where the polymer surface is partially negatively charged, HSA and SUB-6 peptide showed contrasting adsorption behavior which is interpreted in terms of differences in their electrostatic interactions with the polymer surface.     

Vacancy–solute interactions during ageing of a cold-worked Mg–RE-based alloy

The vacancy–solute interactions during artificial ageing at 250^○C of cold worked samples of a commercial magnesium alloy WE54 (Mg–RE based) were studied by coincidence Doppler broadening of positron annihilation radiation and positron annihilation lifetime spectroscopy. The results show that, in the as-cold-worked state, the vacancies are associated with dislocations that are generated by the cold work and that, after artificial ageing at 250^○C, the vacancies are associated with solute elements and help the formation of precipitate precursors. This mechanism accelerates the formation of hardening precipitates without any apparent changes in the precipitation sequence and in the products of the decomposition of the supersaturated solid solution. The present study demonstrates that the stronger hardening response achieved in the cold-worked samples originates from the presence of a higher concentration of vacancies that is introduced by the cold work and is retained in the first few minutes of ageing.