The mechanisms of nonradiative deactivation of a phenylalanine residue after near-UV photoexcitation have been investigated in an isolated peptide chain model (N-acetylphenylalaninylamide, NAPA) both ...experimentally and theoretically. Lifetime measurements at the origin of the first ππ* state of jet-cooled NAPA molecules have shown that (i) among the three most stable conformers of the molecule, the folded conformer NAPA B is ∼50-times shorter lived than the extended major conformer NAPA A and (ii) this lifetime is virtually insensitive to deuteration at the NH(2) and NH sites. Concurrent time-dependent density functional theory (TDDFT) based nonadiabatic dynamics simulations in the full dimensionality, carried out for the NAPA B conformer, provided direct insights on novel classes of ultrafast deactivation mechanisms, proceeding through several conical intersections and leading in fine to the ground state. These mechanisms are found to be triggered either (i) by a stretch of the N(Phe)H bond, which leads to an H-transfer to the ring, or (ii) by specific backbone amide distortions. The potential energy surfaces of the NAPA conformers along these critical pathways have been characterized more accurately using the coupled cluster doubles (CC2) method and shown to exhibit barriers that can be overcome with moderate excess energies. These results analyzed in the light of the experimental findings enabled us to assign the short lifetime of NAPA B conformer to a number of easily accessible exit channels from the initial ππ* surface, most importantly the one involving a transfer of electronic excitation to an nπ* surface, induced by distortions of the backbone peptide bond.
A conformation-selective photophysics study in phenylalanine model peptides, combining pump-probe gas phase experiments and excited state calculations, highlights for the first time the quenching ...properties of a primary amide group (through its nπ* excited state) along with the effect of vibrational energy that facilitates access to the conical intersection area.
A combination of multireference CASSCF/CASPT2 and time-dependent DFT (TD-B3P86) theoretical treatments was employed to test their predictions against recently proposed assignments of the vacuum-UV ...spectra of fluorene and its three heteroanalogues-dibenzofuran, carbazole, and dibenzothiophene-up to the ionization threshold. For the low-lying transitions, the theoretically based assignments are generally not problematic because of the well-resolved bands, although, even in this region, the two methods yield some opposing predictions. Further on toward the vacuum region, the assignments prove increasingly challenging because of predicted crowding of transitions, many of which exhibit significant intensity. Some of the transitions in this region and beyond-toward the ionization thresholds-are thus necessarily assigned only tentatively. Overall, the two methods are frequently found to complement each other well, and equivalent transitions usually appear as bracketed from the high- (CASPT2) and low- (TD-B3P86) energy sides.
Two BODIPY phenolic esters 1 and 2 were synthesized and their acid-catalyzed hydrolytic and esterase enzymatic stability was demonstrated. Their photophysical properties were investigated in solvents ...of different polarity. Their spectral properties are the typical of BODIPY dyes with narrow absorption and emission spectra in the visible spectral region and large molar absorption coefficients (≈500 nm, ε = 40000-50000 M−1cm−1). The derivative with methyl substituted BODIPY core 2 shows quantum yields of fluorescence one magnitude higher (Φf = 0.30–0.55) compared to the BODIPY without methyl groups. Solvents affect very weakly spectral properties, with more pronounced effect of the solvent polarizability than the solvent polarity. Both BODIPY dyes show pH responsive fluorescence in aqueous solution (pKa = 2.72 ± 0.08 and 4.18 ± 0.05), with quenching of fluorescence by protonation due to PET from the BODIPY to phenol, rendering them applicable for intracellular pH measurements. The feasibility of the PET in the protonated form of 1 was corroborated by electrochemical measurements and calculation of ΔETGo for PET, and (time-dependent) density functional theory computations. This less frequently encountered quenching mechanism where the BODIPY is an electron donor provides new opportunities in the rational design of new generations of fluorescent sensors. The applicability for intracellular measurements was demonstrated by confocal fluorescence microscopy on H460 human cancer cell line.
Display omitted
•Two BODIPY phenolic esters 1 and 2 were synthesized and their photophysical properties were investigated.•The BODIPY with methyl substituents 1 shows quantum yields of fluorescence one magnitude higher (Φf = 0.30–0.55) compared to 2.•Both BODIPY dyes show pH responsive fluorescence in aqueous solution (pKa = 2.72 ± 0.08 and 4.18 ± 0.05).•In acidic media, quenching of fluorescence takes place due to PET from the BODIPY to phenol.•The applicability was demonstrated by confocal fluorescence microscopy on H460 human cancer cell line.
The photoionization of three stable nitroxyl radicals has been studied in the valence and core regions using synchrotron radiation. We observed different variations of the relative band intensities ...with the photon energy for two pyrrolidine nitroxyls (nitroxyl8 and nitroxyl9) in the valence ionization region. This is due to strong intramolecular interactions between the amide substituent and the ring π-orbital when present. In the core ionization region we observed chemical shifts which were consistent with the relative electron affinities of different atoms. We also observed the multiplet splitting of core level binding energies in the final ionic states. The core electron binding energies calculated via the restricted open shell Hartree-Fock based ΔSCF method exhibit good agreement with the experimental core ionization bands and with the assignment of the spectra by empirical analysis.
Nonadiabatic dynamics in the framework of time-dependent density functional theory was used to simulate gas-phase relaxation dynamics of pairs of conformations of formic acid monomers (cis and trans ...FAM) and dimers (acyclic aFAD and cyclic cFAD). In the early phase of the excited state dynamics, elongation of the C═O bond and pyramidalization of the carbon atom is observed in both FAM and FAD. Subsequently, the photodynamics of FAM is shown to be dominated by fragmentation processes occurring mostly in the excited state and resulting in HCO and OH radicals. In only a few cases does the dissociation take place from the vibrationally excited ground electronic state, whereby CO and H(2)O are the major reaction products. In the dimers, single proton transfer triggers ultrafast relaxation to the ground electronic state. In the single hydrogen bonded dimer about half of the trajectories dissociate into electronically excited monomers, whereas this potentially destructive dissociation is effectively suppressed in the double hydrogen bonded dimer. Upon relaxation to the ground electronic state, separation of FAD into monomers takes place, but without their further fragmentation on the time scale of the simulation. We conclude that the crucial difference between the FAM and FAD photodynamics is that the latter is dominated by nondestructive radiationless deactivation pathways during which a key protective role is assumed by the single (aFAD) or double (cFAD) intermonomer hydrogen bonds.
The paper studies the morphological variability of the service tree populations in the continental and Mediterranean regions of Croatia. The inter- and intra-population variability, as well as ...eco-geographic population differentiation, was established on the basis of eight measured morphological characteristics of two types of leaflets (lateral and terminal) and two derived ratios, using descriptive and multivariate statistical methods. The conducted research established a high variability of morphological characteristics. In comparison with lateral leaflets, terminal leaflets showed a higher degree of variability for the majority of the studied variables. The differences between the trees within populations, as well as the differences between populations, were confirmed for all studied characteristics. The study also confirmed a trend of population variations according to the eco-geographic principle. Populations from climatically different and geographically distant habitats, in other words from the Mediterranean and the continental region, differed in the majority of studied characteristics. In addition to the established pattern of ecotypical variability between the continental and the Mediterranean regions, the clinal variability with regard to altitude and mean annual temperature was also confirmed. Small, although statistically significant clinal variability with regard to the longitude was recorded for two measured characteristics. The conducted study provided insights into the variability of the service tree populations in Croatia, which is a basis for further research that should be implemented in order to produce guidelines for the breeding and conservation of genetic resources of this rare and endangered noble hardwood species.
Prirodni fenomen, Kočje, 1962. godine proglašen je posebnim rezervatom šumske vegetacije, dok je njegov glavni fenomen šuma stogodišnjih stabala hrasta crnike (
Quercus ilex
L.). Rezervat je ...sjemenskog postanka s ponekom panjačom. Osim s vegetacijskog gledišta, Kočje je specifično i zbog niza geomorfoloških oblika. Šumu ovog rezervata se može svrstati u šumu hrasta crnike i crnog jasena. U radu su dani rezultati opsežnih istraživanja koja su provedena u prvoj polovici 2015. godine, a uključivala su strukturna, vegetacijska i mikroklimatska mjerenja. Strukturna izmjera stabala provedena je na području cijelog rezervata, a vegetacijska i mikroklimatološka istraživanja su obuhvatila 7 pokusnih ploha.Rezultati su pokazali da inventarizirana stabala hrasta crnike (140) pokazuju konstantno opadanje vitaliteta, što je sasvim razumljivo i vezano na njihovu stoljetnu dob. Ustanovljeno je i da su najbrojnije vrste u fazi ponika i pomladka:
Laurus nobilis
L. i
Viburnum tinus
L., dok hrast crnika prevladava u nadstojnoj etaži. S obzirom na strukturne tablice sastojina na pokusnim plohama 1.-7. kao i na ukupne iznose drvne zalihe, došlo se do spoznaje da se sklopljeni dio šume rezervata i dalje nalazi u stadiju visoke crnikove šume.Iz fitocenoloških snimki (tablica 12) također uočavamo tu heterogenost staničnih uvjeta budući osim tipičnih vrsta asocijacije
Fraxino orni–Quercetum ilicis
Horvatić (1956.) 1958.
(Šuma hrasta crnike i crnog jasena) ovisno o geološko-morfološkim, hidrološkim, pedološkim i mikroklimatskim prilikama pridolaze vrste koje nisu tipične za šumsku vegetaciju. Ponajprije paprati, vegetacija stijena, mahovina i sl. Pokrovnost vegetacije u rezervatu Kočje nije jednolična. Središnji dio gdje prevladavaju stara stabla crnike pokrovnost sloja drveća je 90-95 % (100 %), grmlje pokriva 30-100 %. Pokrovnost sloja prizemnog rašća je također različita i ovisi o pokrovnosti sloja grmlja i drveća, tako da je od 5-80 %. Isto tako u rezervatu nalazimo gusti sloj nerazgrađenog listinca najčešće od 2 do 5 cm, a u „džepovima“, škrapama između stijena 10 do 15 cm. Tu ga najviše nanosi voda za jakih kiša.Mikroklimatskim istraživanjima je potvrđeno da kolebanja mikroklimatskih elemenata (temperatura i količina svjetla) ovise o stupnju sklopljenosti sastojine u sloju drveća i grmlja te geomorfološkim situacijama na plohama.
The natural phenomenon of Kočje, was declared as a special reserve of forest vegetation in 1962, while its main phenomenon is a forest of hundred-year-old holm oak trees (
Quercus ilex
L.). It is a reserve of seed production with some sedges. Apart from it´s vegetation , Kočje has number of geomorphological forms. The forest of this reserve is classified as a forest of holm oak and black ash. The paper presents the results of extensive research conducted in the first half of 2015, which included structural, vegetation and microclimate measurements. The structural survey of the trees was carried out in the entire area of the reserve, and the vegetation and microclimatological research included 7 test plots.The results showed that the inventoried holm oak trees (140) show a constant decline in vitality, which is quite understandable and related to their age and most of numerous species are in the stage of ponics and saplings:
Laurus nobilis
and
Viburnum tinus
, while holm oak predominates in the upper layer. With regard to the structural tables of the stands on experimental plots 1.-7. (tables 2-8), as well as the total amount of wood stock, it is conformed that the closed part of the reserve’s forest is still in the stage of high holm oak forest.Phytocenological recordings (table 12) are showing that there is an heterogeneity of cellular conditions, since, in addition to the typical species of the association Fraxino orni–Quercetum ilicis Horvatić (1956) 1958 (Black oak and black ash forest), depending on geological-morphological, hydrological, pedological and microclimatic conditions, additional species which are not typical for forest vegetation. Primarily ferns, rock vegetation, mosses, etc. The vegetation cover in Kočje reserve is anuniform. In the central part where old holm oak trees predominate, the tree layer coverage is 90-95 % (100 %), bushes cover 30-100 %. The coverage of the layer of ground growth is also different and depends on the coverage of the layer of bushes and trees, so it is from 5-80 %. In the reserve, we find a thick layer of undecomposed leaf (2-5 cm), and in “pockets”, scraps between rocks, (10-15 cm). It is mostly applied by water during heavy rains. The microclimatic research has confirmed that the fluctuations of microclimatic elements (temperature and amount of light) depend on the degree of assembly of the stand in the layer of trees and bushes and the geomorphological conditions on the surfaces (stone corridors, arched and narrow passages, boulders, obstacles, etc.).
PDF
