Halide ion determination from luminescence of the diprotonated form of porphyrin

We have studied quenching of the fluorescence of the diprotonated form of 3,7,13,17-tetramethyl-2,8,12,18-tetrabutylporphyrin by iodide ions in solutions. We have established that there is both static quenching of fluorescence when nonfluorescent complexes are formed with the iodide ions, as a result of an internal heavy atom effect, and also dynamic diffusion-controlled quenching. Based on analysis of the dependences of the fluorescence intensity and fluorescence lifetime on the iodide ion concentration in solution, we suggest using the diprotonated form of this porphyrin as the base compound for designing a fluorescent molecular receptor for halide ions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 750–755, November–December, 2007.     

Two-photon absorption of tetraphenylporphin free base

We study two-photon absorption (TPA) spectra for toluene solution of 5,10,15,20-tetraphenyl-21H,23H-porphin (H₂TPP) in B and Q bands regions and find the maximum TPA cross-section values of 25 and 1-6 GM in laser wavelength ranges, 730-790 and 1100-1400 nm, correspondingly. In the 730-790 nm range the spectrum is attributed to parity allowed two-photon transition into g parity state, positioned nearby B state. Much lower TPA cross-section of ∼1 GM is measured for the transition into pure electronic Q state and it is due to the contribution of only those low-symmetry H₂TPP confomers, where mutual orientation of the porphyrin plane and the four phenyl rings lifts the center of inversion. The intermediate values of TPA cross-section of ∼6 GM are observed for the transition into vibronic Q states and are explained by TPA-allowed transition into vibronic states, which can occur even for totally centrosymmetrical molecules. Measurement of two-photon polarization ratio, Ω=σ_circ/σ_lin, shows that for parity allowed g→g transition Ω =1.05±0.05 and for transitions into electronic and vibronic Q-states, Ω=0.62±0.06 and 0.79±0.1 (depending on wavelength), respectively. Quantum-chemical calculations of both u and g parity excited energy levels of H₂TPP molecule are performed by CNDO/S method and the results are in good agreement with the experimental data.     

Nuclear spin relaxation in paramagnetic systems (S>/=1) under fast rotation conditions

A new theoretical model for nuclear spin relaxation in paramagnetic systems in solution has been developed. Fast rotational motion is included in the model, both as a source of modulation of the static zero-field splitting, which provides a mechanism for electron spin relaxation, and as an origin of the stochastic variation of the electron spin-nuclear spin dipole-dipole interaction leading to nuclear spin relaxation. At the limit of low magnetic field, the model is essentially identical to the earlier formulations from our laboratory, but new closed-form expressions are given for the inner- and outer-sphere relaxation at the high-field limit. Numerical comparisons with a general theory are reported for the inner-sphere case. In addition, some nuclear magnetic relaxation dispersion (NMRD) profiles from the literature are considered for systems where experiments have been done with both low-molecular weight paramagnetic complexes and their adducts with proteins. Previously developed theories are used to interpret data for the slowly rotating protein adducts, and good fits of the fast-rotating counterparts are obtained by further adjustment of one or two additional parameters.     

Structure constants of algebras of projective representations of point groups

Structure constants (MIRREPS) of algebras of characters of irreducible projective representations of all three-dimensional point groups are listed. Possible applications of the MIRREPS are indicated.     

Synthesis of an ordered macroporous carbon with 62 nm spherical pores that exhibit unique gas adsorption properties

An ordered macroporous carbon with 62 nm spherical pores was synthesized using colloidal-crystal templating and found to exhibit unique gas adsorption properties that have been so far attributed to adsorption in mesopores (size below 50 nm).     

Nonlinear energy interchange between the natural modes of freely vibrating circular cylindrical shells filled with liquid

Free nonlinear multimode vibrations of thin cylindrical shells filled with partially ideal incompressible liquid are considered. The resonance case is studied where the values of two of the natural frequencies of the shell-liquid system are close. For this case, the first integrals that relate the amplitude and phase parameters for the corresponding modes are obtained. S. P. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev. Translated from Prikladnaya Mekhanika, Vol. 36, No. 1, pp. 115–122, January, 2000.     

The Problem of Forced Nonlinear Vibrations of Cylindrical Shells Completely Filled with Liquid

The forced nonlinear vibrations of a thin cylindrical shell completely filled with a liquid are studied. A refined mathematical model is used. The model takes into account the nonlinear terms up to the fifth power of the generalized displacement of the shell. The Bogolyubov’Mitropolsky averaging method is used to plot amplitude’frequency response curves for steady-state vibrations. The steady-state vibrations at the frequency of principal harmonic resonance are analyzed for stability__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 2, pp. 52–59, February 2005.     

The power of in situ pulsed laser deposition synchrotron characterization for the detection of domain formation during growth of Ba0.5Sr0.5TiO3 on MgO

A highly sophisticated pulsed laser deposition (PLD) chamber has recently been installed at the NANO beamline at the synchrotron facility ANKA (Karlsruhe, Germany), which allows for comprehensive studies on the PLD growth process of dielectric, ferroelectric and ferromagnetic thin films in epitaxial oxide heterostructures or even multilayer systems by combining in situ reflective high‐energy diffraction with the in situ synchrotron high‐resolution X‐ray diffraction and surface diffraction methods. The modularity of the in situ PLD chamber offers the opportunity to explore the microstructure of the grown thin films as a function of the substrate temperature, gas pressure, laser fluence and target–substrate separation distance. Ba_0.5Sr_0.5TiO₃ grown on MgO represents the first system that is grown in this in situ PLD chamber and studied by in situ X‐ray reflectivity, in situ two‐dimensional reciprocal space mapping of symmetric X‐ray diffraction and acquisition of time‐resolved diffraction profiles during the ablation process. In situ PLD synchrotron investigation has revealed the occurrence of structural distortion as well as domain formation and misfit dislocation which all depend strongly on the film thickness. The microstructure transformation has been accurately detected with a time resolution of 1 s. The acquisition of two‐dimensional reciprocal space maps during the PLD growth has the advantage of simultaneously monitoring the changes of the crystalline structure as well as the formation of defects. The stability of the morphology during the PLD growth is demonstrated to be remarkably affected by the film thickness. A critical thickness for the domain formation in Ba_0.5Sr_0.5TiO₃ grown on MgO could be determined from the acquisition of time‐resolved diffraction profiles during the PLD growth. A splitting of the diffraction peak into two distinguishable peaks has revealed a morphology change due to modification of the internal strain during growth.     

Infrared absorption study of hexapentyloxytriphenylene A discotic liquid crystal

Abstract

Fourier transform infrared absorption (FTIR) spectroscopy has been used to study a discotic liquid crystal. IR spectra are reported as a function of temperature for hexapentyloxytriphenylene (H5T). The order parameter S has been determined using unpolarized radiation and by comparing the spectra of the discotic phase with that of the isotropic phase. Variations in frequency for some of the most significant bands are presented as a function of temperature.     

Spectrophotometric study of 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin in the system 1,8-diazabicyclo[5.4.0]undec-7-ene-acetonitrile at 298 K. Deprotonation of the pyrrole rings and complex formation with Zn(OAc)2

Acid-base and complexing properties of 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin in the system 1,8-diazabicyclo[5.4.0]undec-7-ene-acetonitrile were studied at 298 K by spectrophotometric titration. The titration of 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin with 1,8-diazabicyclo[5.4.0]-undec-7-ene was accompanied by successive deprotonation of the pyrrole nitrogen atoms with formation of the corresponding mono- and dianions, and the acid dissociation constants were determined. Complex formation of doubly deprotonated 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin with zinc acetate was studied.