Formation and optical properties of self-organized pentameric porphyrin arrays

Principles of formation, electronic absorption and fluorescence spectra are reported for self-organized pentameric arrays of tetrapyrrolic macrocycles. In these arrays two molecules of Zn-porphyrin dimers, Zn(II)l,4-bis[5-(10,15,20-tri-p-hexylphenylporphyrinyl)]-benzene ((ZnHTPP)₂) are bound via one molecule of a tetrapyridyl-substituted free base of porphyrin or tetrahydroporphyrin. The process of self-assembly is based on the twofold coordination of the central Zn ions !n the dimer with the nitrogen atoms of the pyridyl rings in the free base which is strong enough to make the complexes stable at room temperature. The formation of the complexes can be followed by changes in the absorption bands of (ZnHTPP)₂ characteristic of an axial extra-ligation of Zn-porphyrins with pyridine or pyridyl-substituted compounds. The spectral behavior of the free bases in the pentads is determined by a non-planar distortion of their macrocycle caused by the two-point binding with the dimers. The fluorescence intensity of the Zn-porphyrin dimer decreases essentially upon complexation with the tetrapyridyl-substituted free bases. This quenching effect is assigned to a singlet-silaglet energy transfer from the complexed Zn-porphyrin dimers to the free base subunit in the pentad

Satellite traceology: experience of using in the interests of mammalogy for protection of ice-associated marine mammals

Advanced technology of satellite traceology is presented on the base of using the synthetic aperture radar (SAR) with high space and deep resolution installed for the first time onboard Soviet space station Almaz and now functioning successfully onboard the satellites Envisat and RADARSAT. The SAR traceology is the central issue of the satellite eco-criminology and concerns to theory of the traces formation, variability, and preservation in undamaged state. Ships coordinates, their traces and complexity of ice routing are fixed by the method of satellite charting, and their possible influence on ice-associated marine mammals is assessed. Numerous examples of SAR satellite control on navigation in stormy weather and ships’ presence in ice with different compactness, origin and age are overviewed, as well as impact of travel facilities on ice-associated animals welfare. Some incidents potentially dangerous for marine mammals are considered for the Gulf of Finland (Baltic Sea). Parameters of the ice cover, as openings, large fractures, and polynyas made by icebreakers in this area were determined on the base of the satellite SAR data, comprehensive digital ice maps with scheme of real ships’ routes in the ice were prepared, and the routes correspondence with ESIMO demands was assessed. The satellite SAR survey in the Kandalaksha Bay (White Sea) allowed to fix that winter navigation in the White Sea provoked formation of fractures and polynyas and reduced the sea ice area suitable for reproduction of greenland seals. For validation of this situation, airborne control was organized aboard the aircraft L-410 «Nord» that provided panoramic and IR images of ship channel through the rookeries of the seals in time of their reproduction. Besides, the aircraft made observations of pacific walruses behavior in the Bering Sea which were superposed with the satellite SAR and passive microwave survey in frame of the project «Pacific Walrus». Traceological control of the sea ice in the Anadyr Bay (Bering Sea) allowed to determine the size of openings in the ice and to assess the influence of tide and wind on welfare of ice-associated marine mammals. Some cases of infringement the regulation of navigation were revealed by means of the satellite SAR traceology

Complexation and interchromophoric interactions in self-organized porphyrin and chlorin triads

Spectral properties and equilibrium constants of multimolecular complexes (triads) formed by 2-fold coordination of dipyridyl-substituted free bases of porphyrin, chlorin, or tetrahydroporphyrin with Zn-porphyrin and Zn-chlorin dimers bridged by either of two different spacers between the monomeric entities have been studied in methylcyclohexane at room temperature. The ability of the dimers bridged by a -CH2-CH2- spacer to form complexes with the free bases is found to be much lower than that for the dimers with a phenyl spacer having complexation constants up to Kc = 5 × 10⁷ M⁻¹. The complexation equilibrium is also affected strongly by the chemical nature of the free base and the position of the pyridyl substituents. Spectral effects occurring upon complexation in absorption spectra of the dimers are mainly due to ligation effects. Strong quenching of the dimer fluorescence in the complexes is attributed to effective singlet-singlet energy transfer (ET) to the ligands

Spectroscopy of interchromophoric interactions in self-organized porphyrin and chlorin complexes

Spectral-luminescent properties of multimolecular complexes (triads and pentads, complexation constants range from 5∙10⁶ to 5∙10⁷ M⁻¹) formed by two-fold coordination of dipyridyl and tetra-pyridyl substituted porphyrin or related molecules with Zn-porphyrin and Zn-chlorin dimers having various spacers between macrocycles (-CH₂-CH₂- or phenyl ring) have been studied in methylcyclohexane solutions in a temperature range from 140 to 360 K. The red shift of Zn-dimer electronic Q- and B-bands (∆ν≤550 cm⁻¹) upon complexation with pyridyl containing ligands is explained in terms of extra-ligation which influences the relative position for HOMO’s a₁ᵤ, and a₂ᵤ according to the four-orbital model. The splitting of Zn-dimer B-bands (∆E≥600 cm⁻¹) as well as the significant transformation of these bands in trimeric and pentameric complexes (redistribution of the absorption band intensities in Soret region and appearance of complicated splitted spectral manifolds ∆ν≤1900 cm⁻¹) is connected with excitonic interactions of strong B-transitions of π-conjugated macrocycles included in the complex. Observed experimental splittings are compared with theoretical values calculated using the point dipole approximation and a computer-simulated geometry of the complexes under investigation. It has been observed that mutual influence of π-electronic macrocycles in the complexes leads to the red shift of porphyrin extra-ligand free base Q-bands (∆ν≈120 cm⁻¹) and is accompanied by quenching a fluorescence of certain components

Phenotypic effects of the dwarfing gene Rht-17 in spring durum wheat under two climatic conditions

Alleles of the genes, conferring a dwarfing phenotype, play a crucial role in wheat breeding, as they not only reduce plant height, ensuring their resistance to lodging, but also have a number of positive and negative pleiotropic effects on plant productivity. Durum wheat carries only two subgenomes (A and B), which limits the use of the D-subgenome genes and requires the expansion of the arsenal of dwarfing alleles and the study of their effects on height and agronomically important traits. We studied the effect of the gibberellin-insensitive allele Rht-B1p in the B2F2:3 families, developed by crossing Chris Mutant /#517//LD222 in a field experiment in Moscow and Krasnodar. In our experiments, plants homozygous for Rht-B1p were shorter than those homozygous for the wild-type allele Rht-B1a by 36.3 cm (40 %) in Moscow and 49.5 cm (48 %) in Krasnodar. In the field experiment in Krasnodar, each plant with Rht-B1p had one less internode than any plant with Rht-B1a, which additionally contributed to the decrease in plant height. Grain weight per main spike was lower in plants with Rht-B1p than in plants with Rht-B1a by 12 % in Moscow and by 23 % in Krasnodar due to a decrease in 1000 grain weight in both regions of the field experiment. The number of grains per main spike in plants with Rht-B1p was higher in comparison to that with Rht-B1a by 6.5 % in Moscow due to an increase in spikelet number per main spike and by 11 % in Krasnodar due to an increase in grain number per spikelet. The onset of heading in plants with Rht-B1p in comparison with the plants with the wild-type allele Rht-B1a was 7 days later in Krasnodar. The possibility and prospects for the use of Rht-B1p in the breeding of durum wheat are discussed

The Effects of Climate Change on Harp Seals (Pagophilus groenlandicus)

Harp seals (Pagophilus groenlandicus) have evolved life history strategies to exploit seasonal sea ice as a breeding platform. As such, individuals are prepared to deal with fluctuations in the quantity and quality of ice in their breeding areas. It remains unclear, however, how shifts in climate may affect seal populations. The present study assesses the effects of climate change on harp seals through three linked analyses. First, we tested the effects of short-term climate variability on young-of-the year harp seal mortality using a linear regression of sea ice cover in the Gulf of St. Lawrence against stranding rates of dead harp seals in the region during 1992 to 2010. A similar regression of stranding rates and North Atlantic Oscillation (NAO) index values was also conducted. These analyses revealed negative correlations between both ice cover and NAO conditions and seal mortality, indicating that lighter ice cover and lower NAO values result in higher mortality. A retrospective cross-correlation analysis of NAO conditions and sea ice cover from 1978 to 2011 revealed that NAO-related changes in sea ice may have contributed to the depletion of seals on the east coast of Canada during 1950 to 1972, and to their recovery during 1973 to 2000. This historical retrospective also reveals opposite links between neonatal mortality in harp seals in the Northeast Atlantic and NAO phase. Finally, an assessment of the long-term trends in sea ice cover in the breeding regions of harp seals across the entire North Atlantic during 1979 through 2011 using multiple linear regression models and mixed effects linear regression models revealed that sea ice cover in all harp seal breeding regions has been declining by as much as 6 percent per decade over the time series of available satellite data

Spectral Рeculiarities of NH-Tautomerism in Isocycle-Containing Porphyrins and their Covalently Linked Dimers

It has been found experimentally that a whole class of isocycle-containing porphyrins, including synthetic and natural objects and their covalently linked dimers, shows NH-tautomerism which manifests itself in isotropic solutions in normal electronic spectra both at 77 K and higher temperatures (up to 500 K)

NH-tautomerism and visible absorption spectra of porphyrins with nonsymmetrical substitution: oscillator model and mo calculations

On the basis or experiments Ihe oscillator model has been established for individual NH tautomers or porphyrins with asymmetrical substitution. CNDO/2 calculations explain the inversion of Q ₓ (O.O) and Q y (O.O) electronic transition intensities in NH tautomers as a consequence of the inversion of LUMO coefficients c₁ and c₂ for fixed x and y molecular oscillators