Experimental and Theoretical Study of Spectroscopy of Binuclear Difluoroborate Dipyrromethene Complexes

Russian Physics Journal - The spectroscopic characteristics of mono and binuclear difluoroborate complexes of dipyrromethenes in various solvents and solid-state polymer media (films) are...     

Association of hydrophilic derivatives of chlorophyll <Emphasis Type="Italic">a</Emphasis> in ethanol–water and ethanol–water–solubilizer systems

Electronic absorption spectroscopy and fluorescence spectroscopy were used to study conditions for the formation of associates of amphiphilic phorbins and chlorins in an ethanol–water system. The conditions and degree of disaggregation in the presence of solubilizing additives of nonionic surfactants (Tween 80) and biocompatible polymers (polyethylene glycol and polyvinylpyrrolidone) were also investigated. The propensity of the macroheterocycles based on chlorophyll a to association in water-alcoholic solutions decreases on going from covalently bound dimeric structures to monomeric ones, on going from phorbins to chlorins and on accumulating hydrophilic glycol or positively charged alkylammonium fragments in the molecule. Among the considered solubilizers, the nonionic surfactant Tween 80 emerged as the most efficient means for destroying chlorin associates in water–alcohol solutions with a high content of water.     

Effect of the Medium on Fluorescence Parameters and Photostability of Porphyrins of Different Structure

Fluorescence and photostability against the action of UV irradiation of different porphyrins in benzene, DMF, and acetic acid media have been studied. The effect of the macroheterocycle structure on the conditions of its thermal decomposition under inert atmosphere has been investigated.     

Effect of Alkyl,Aryl, and <Emphasis Type="Italic">meso</Emphasis>-Aza Substitution on the Thermal Stability of BODIPY

The effect of peripheral alkyl, aryl, and meso-aza substitution on the thermal stability of BODIPYs in an argon or oxygen atmosphere has been analyzed using thermogravimetric study results. It has been shown that an increase in the length of 2,6-alkyl substituents to seven carbon atoms is accompanied by the growth of BODIPY thermal stability by 80°C. The greatest increase in the destruction temperature of BODIPY (by 100°C) is attained via the introduction of phenyl groups in the 1,3,5,7-positions of its dipyrromethenmethene framework. meso-Aza substitution does not almost produce any effect on the thermal stability of BODIPY dyes. The BODIPY destruction beginning temperature decreases by 60–90°C in the presence of air oxygen. The thermal stability of BODIPY tends to decrease with reducing degree and symmetry of alkyl substitution in the dipyrromethene framework. A lower thermal stability of BODIPY in comparison with zinc(II) dipyrromethenates is due to the participation of fluorine atoms in intramolecular redox processes.     

Crystal solvates of tetrakis(3,5-di-t-butylphenyl)-porphyrinates Mn(III), Ni(II) and Zn(II) with pyridine

The crystal solvates of complexes MP (P is the dianion of tetrakis(3,5-di-t-butylphenyl)porphin, M=Ni(II), Zn(II)) and (Ac)MnP with pyridine have been obtained by isothermal evaporation of corresponding solutions at 35°C. The formation and the decomposition temperatures of crystal solvates and enthalpies of evaporation pyridine molecules from those crystal solvates were received using thermogravimetric method. In addition to that, an influence of the type of metal on the compositions, the energetic and thermal stabilities of the received complexes were analyzed.     

Thermal stability of <Emphasis Type="Italic">meso</Emphasis>-substituted metal corroles in inert and oxidative media

The thermal stability of 5,10,15-triphenylcorrole as the simplest representative of meso-substituted corroles and its complexes with d-metals (Cu³⁺, Mn³⁺, Mn⁴⁺, Co³⁺, Co⁴⁺, and Zn²⁺) is studied for the first time via thermogravimetry in oxidizing and inert atmospheres. It is shown that corroles, both as free ligands and in the form of metal complexes, are less thermally stable than porphyrins with a similar structure. It is found that if the free ligands of porphyrins are thermally more stable with respect to thermal oxidation than d-metal complexes, the thermal stability of metal corroles can be both lower and higher than those of free ligands. It is concluded that the order of thermal stability of compounds MnCor < CoCor < H₃Cor < ZnCorH < CuCor is reversed upon moving from an oxidizing to an inert medium. It is shown that corroles complexes with many d-metals (Co, Mn, and others) readily participate in extracoordination reactions with electron-donating solvents, e.g., DMF, as is indicated by spectrophotometry and thermogravimetry.     

Remote helicopter-borne detector for searching of methane leaks

Measurements of the content of various molecular impurities in the ambient air using helicopter- and aircraft-borne systems represent an extremely urgent challenge. In this respect, of special interest are the devices that that provide leakage monitoring in gas lines in order to prevent emergencies. In the paper results of the tunable diode laser-based instrument development and testing are presented.     

Gas phase activation energy for unimolecular dissociation of biomolecular ions determined by focused RAdiation for gaseous multiphoton ENergy transfer (FRAGMENT)

We present a novel approach for the determination of activation energy for the unimolecular dissociation of a large (>50 atoms) ion, based on measurement of the unimolecular dissociation rate constant as a function of continuous-wave CO(2) laser intensity. Following a short ( approximately 1 s) induction period, CO(2) laser irradiation produces an essentially blackbody internal energy distribution, whose 'temperature' varies inversely with laser intensity. The only currently available method for measuring such activation energies is blackbody infrared radiative dissociation (BIRD). Compared with BIRD, FRAGMENT: (a) eliminates the need to heat the surrounding ion trap and vacuum chamber to each of several temperatures (each requiring hours for temperature equilibration); (b) offers a three-fold wider range of effective blackbody temperature; and (c) extends the range of applications to include initially cold ions (e.g., gas-phase H/D exchange). Our FRAGMENT-determined activation energy for dissociation of protonated bradykinin, 1.2 +/- 0.1 eV, agrees within experimental error to the value, 1.3 +/- 0.1 eV, previously reported by Williams et al. from BIRD experiments. Copyright 1999 John Wiley & Sons, Ltd.     

Structure and energetics of β-diketonates. XVI. Molecular structure and vibrational spectrum of zinc acetylacetonate according to gas-phase electron diffraction and quantum-chemical calculations

The molecular structure of zinc acetylacetonate was studied in a simultaneous electron diffraction and mass spectrometric experiment at 376(7) K and by quantum-chemical calculations. The Zn(acac)₂ molecule has a structure of D _2d symmetry with the chelate rings lying in mutually perpendicular planes. The main geometrical parameters of the molecule are r _h1(Zn-O) = 1.942(4) Å, r _h1(C-O) = 1.279(3) Å, r _h1(C-C_r) = 1.398(3) Å, r _h1(C-C _m ) = 1.504(5) Å, ∠(O-Zn-O) = 93.2(7)°, ∠(Zn-O-C) = 125.9(7)°, ∠(C-C_r-C) = 125.8(14)°, ∠(O-C-C _m ) = 115.2(9)°. The effective rotation angle of methyl groups is close to 30°, which is indicative of the free rotation of these groups. The vibration frequencies were obtained by quantumchemical calculations, and the IR spectrum of the Zn(acac)₂ molecule was interpreted.