22 research outputs found
Intramolecular charge transfer with the planarized 4-cyanofluorazene and its flexible counterpart 4-cyano-N-phenylpyrrole. Picosecond fluorescence decays and femtosecond excited-state absorption.
No full textThe fluorescence spectrum of the rigidified 4-cyanofluorazene (FPP4C) in n-hexane consists of a dual emission from a locally excited (LE) and an intramolecular charge-transfer (ICT) state, with an ICT/LE fluorescence quantum yield ratio of Phi'(ICT)/Phi(LE) = 3.3 at 25 degrees C. With the flexible 4-cyano-N-phenylpyrrole (PP4C) in n-hexane, such an ICT reaction also takes place, with Phi'(ICT)/Phi(LE) = 1.5, indicating that for this reaction, a perpendicular twist of the pyrrole and benzonitrile moieties is not required. The ICT emission band of FPP4C and PP4C in n-hexane has vibrational structure, but a structureless band is observed in all other solvents more polar than the alkanes. The enthalpy difference Delta H of the LE -> ICT reaction in n-hexane, -11 kJ/mol for FPP4C and -7 kJ/mol for PP4C, is determined by analyzing the temperature dependence of Phi'(ICT)/Phi(LE). Using these data, the energy E(FC,ICT) of the Franck-Condon ground state populated by the ICT emission is calculated, 41 (FPP4C) and 40 kJ/mol (PP4C). These large values for E(FC,ICT) lead to the conclusion that with FPP4C and PP4C, direct ICT excitation, bypassing LE, does not take place. FPP4C has an ICT dipole moment of 15 D, similar to that of PP4C (16 D). Picosecond fluorescence decays allow the determination of the ICT lifetime, from which the radiative rate constant k(f)'(ICT) is derived, with comparable values for FPP4C and PP4C. This shows that an argument for a twisted ICT state of PP4C cannot come from k(f)'(ICT). After correction for the solvent refractive index and the energy of the emission maximum (v) over tilde (max)(ICT), it appears that k(f)'(ICT) is solvent-polarity-independent. Femtosecond transient absorption with FPP4C and PP4C in n-hexane reveals that the ICT state is already nearly fully present at 100 fs after excitation, in rapid equilibrium with LE. In MeCN, the ICT state of FPP4C and PP4C is likewise largely developed at this delay time, and the reaction is limited by dielectric solvent relaxation, which shows that the ICT reaction is ultrafast, at the experimental time limit of 50 fs. PP4C and FPP4C have a similar planar ICT structure, without an appreciable twist of the pyrrole and benzonitrile subgroups. Their crystal structure is compared with calculations for the S-0 ground state.Hungarian Science Foundation [76278
Intramolecular charge transfer with 4-fluorofluorazene and the flexible 4-fluoro-N-phenylpyrrole.
No full textWith 4-fluorofluorazene (FPP4F) and its flexible counterpart 4-fluoro-N-phenylpyrrole (PP4F) an intramolecular charge transfer (ICT) reaction occurs in the singlet excited state in sufficiently polar solvents. The ICT reaction begins to appear in tetrahydrofuran (E = 7.4) for FPP4F and in the more polar 1,2-dichloroethane (epsilon = 10.4) with PP4F, showing its presence by dual fluorescence from a locally excited (LE) and an ICT state. Only LE fluorescence is observed in less polar solvents such as n-hexane. The ICT reaction is more pronounced with FPP4F than for PP4F, due to the smaller energy gal) Delta E(S(1),S(2)) of the former molecule, in accordance with the PICT model. The occurrence of an ICT reaction is confirmed by the ICT dipole moments mu(e)(ICT) of 12 D (FPP4F) and 10 D (PP4F), clearly larger than mu(e)(LE) of similar to 4 D for FPP4F and PP4F. Isoemissive points are found in the fluorescence spectra of FPP4F and PP4F in acetonitrile (MeCN), ethyl cyanide (EtCN), and n-propyl cyanide (PrCN) as a function of temperature, confirming the two-state (LE and ICT) reaction mechanism. From plots of the logarithm of the ICT/LE fluorescence quantum yield ratio versus the reciprocal absolute temperature in these solvents, the ICT reaction enthalpies Delta H are determined, with larger -Delta H values for FPP4F than for PP4F: 19.2 as compared with 14.9 kJ/mol in MeCN, as an example. The picosecond fluorescence decay of PP4F at -45 degrees C becomes slower with decreasing solvent polarity, 5.1 ps (MeCN), 14 ps (EtCN), and 35 ps (PrCN), from which the LE -> ICT reaction rate constant is calculated, decreasing from 19 x 10(10) to 2.1 x 10(10) s(-1) between MeCN and PrCN. The femtosecond LE excited-state absorption spectra of FPP4F and PP4F do not undergo any time development in n-hexane (no ICT reaction), but show a fast ICT reaction in MeCN at 22 degrees C, with decay times of 1.1 ps (FPP4F) and 3.3 ps (PP4F). It is concluded that FPP4F and PP4F have a planar ICT state (PICT model), indicating that a perpendicular twist of the donor and acceptor subgroups in a donor/acceptor molecule is not a requirement for fast and efficient ICT. The molecular structures of FPP4F and PP4F obtained from X-ray crystal analysis reveal that the pyrrole group of PP4F is twisted over an angle theta = 25 degrees relative to the fluorophenyl moiety in the ground state, whereas as expected r-PP4F is practically planar (theta = 2 degrees). The pyrrole-phenyl bond length of FPP4F (140.7 pm) is shorter than that for PP4F (141.8 pm).Hungarian Science Foundation [76278
C coupling constants in alkyl-substituted cyclopropenes: experimental and theoretical studies
No full textMeasurements of one-bond carbon-carbon coupling constants, (1)J(C, C), were performed for two series of compounds, alkyl-substituted cyclopropenes and cyclopropanes. The experimental data were complemented by a set of DFT-calculated J couplings for the parent cyclopropene (1), its methyl and silyl derivatives and, additionally, for 1-methylcyclobutene (3), 1-methylcyclopentene (4) and 1-methylcyclohexene (5) and good agreement was observed between the experimental and the calculated data; all the trends are perfectly maintained, including a dramatic decrease in the couplings across endocyclic single bonds in cyclopropene and its derivatives, and a significant decrease in the corresponding couplings in cyclobutene. Using the data obtained, the s characters of the carbon hybrid orbitals involved in the formation of the cyclopropene were calculated. The results clearly show that the ring closure and the related strain exerted upon the cyclopropene molecule only slightly disturb the electron structure of the double bond. The s character of the corresponding carbon orbital is 0.314 in cyclopropene vs the theoretical value of 0.333 in ethene. This is at variance with the endo- and exocyclic single bonds, where the s characters of the orbitals forming the endocyclic single bonds are much smaller than those of the bonds in the open-chain compounds, i.e. 0.229 (C-1 and/or C-2) and 0.166 (C-3). The s values calculated for the exocyclic CH bonds are 0.334 for C-3 and 0.456 for C-1 and/or C-2. Copyright (C) 2002 John Wiley Sons, Ltd
ortho-Azobenzenophanes: Photochemical and Thermal Reactions of [2,2][2,2′]Azobenzenophane
No full textProblematyka wolności sumienia w świetle współczesnych wyzwań
No full textIn the first section the article presents the three main dimensions of conscience.
There is no doubt that the primary dimension is the dimension of
individual conscience. It is the “guardian of the integrity of” moral person
(E. Fromm). It is so closely associated with the self-consciousness of people
that acting against the judgment of conscience, a man acts against himself.
Conscience is also “a window on what is common” (Joseph Ratzinger), to
moral truth, what is the revelation of the objective dimension of conscience.
Finally, it is important religious dimension. It manifests itself in defining
conscience as the voice of God.
In the second section the author analyzes the key element of the contemporary
dispute about conscience that is his relationship to authority, both
the state and the church. There is no doubt that state law should respect the
freedom of conscience of citizens and, in situations of serious conflicts –
provide the opportunity to invoke the conscience clause. In contrast to the
pluralistic society ecclesial community has the right to have moral convictions
stemming form faith, which are crucial to belong to the individual
religious community. This does not invalidate in any way the importance of
conscience, which remains the final court (although not the highest standard,
which is God) of moral action
Crystal and solution structures of 7-amino-actinomycin D complexes with d(TTAGBrUT), d(TTAGTT) and d(TTTAGTTT)
No full textSynopsis: In the crystal, actinomycin D intercalates between G-T wobble pairs of DNA involving the sequence d(TTAGTT); in solution, the dominant binding is between guanine and actinomycin.
Abstract: The formation of the complex of 7-amino-actinomycin D with potentially single-stranded DNA has been studied by X-ray crystallography in the solid state, by NMR in solution, and by molecular modeling. The crystal structures of the complex with 5'-TTAG[Br5U]T-3' provide interesting examples of MAD phasing, in which the dispersive component of the MAD signal was almost certainly enhanced by radiation damage. The trigonal and orthorhombic crystal modifications both contain antibiotic molecules and DNA strands in the form of a 2:4 complex; in the orthorhombic form there is one such complex in the asymmetric unit, in the trigonal structure there are four. In both structures the phenoxazone ring of the first drug intercalates between a BrU-G (analogous to T-G) wobble pair and a G-T pair where the T is part of symmetry related molecule. The chromophore of the second actinomycin intercalates between BrU-G and G-BrU wobble pairs of the partially paired third and fourth strands. The base stacking also involves (A*T)*T triplets and Watson-Crick A-T pairs and leads to similar complex three-dimensional networks in both structures with looping-out of unpaired bases. Although the available NOE-constraints of a solution containing the antibiotic and d(TTTAGTTT) strands in the ratio 1:1 are insufficient for determining the structure of the complex from the NMR data alone, they are consistent with the intercalation geometry observed in the crystal structure. Molecular dynamics (MD) trajectories starting from the 1:2 complexes observed in the crystal showed that although the thymines flanking the d(AGT) core are rather flexible and the G-T pairing is not permanently preserved, both strands remain bound to the actinomycin by strong interactions between it and the guanines between which it is sandwiched. Similar strong binding (hemi-intercalation) of the actinomycin to a single guanine was observed in the MD trajectories of a 1:1 complex. The dominant interaction is between the antibiotic and guanine, but the complexes are stabilized further by promiscuous base-pairing
Activation of a dienediyne model of neocarzinostatin chromophore through an acid mediated solvolysis. Evidence for a new cyclization mode of enyne[3]cumulenes
No full textProblematyka wolności sumienia w świetle współczesnych wyzwań
No full textIn the first section the article presents the three main dimensions of conscience.There is no doubt that the primary dimension is the dimension ofindividual conscience. It is the “guardian of the integrity of” moral person(E. Fromm). It is so closely associated with the self-consciousness of peoplethat acting against the judgment of conscience, a man acts against himself.Conscience is also “a window on what is common” (Joseph Ratzinger), tomoral truth, what is the revelation of the objective dimension of conscience.Finally, it is important religious dimension. It manifests itself in definingconscience as the voice of God.In the second section the author analyzes the key element of the contemporarydispute about conscience that is his relationship to authority, boththe state and the church. There is no doubt that state law should respect thefreedom of conscience of citizens and, in situations of serious conflicts –provide the opportunity to invoke the conscience clause. In contrast to thepluralistic society ecclesial community has the right to have moral convictionsstemming form faith, which are crucial to belong to the individualreligious community. This does not invalidate in any way the importance ofconscience, which remains the final court (although not the highest standard,which is God) of moral action.In the first section the article presents the three main dimensions of conscience.There is no doubt that the primary dimension is the dimension ofindividual conscience. It is the “guardian of the integrity of” moral person(E. Fromm). It is so closely associated with the self-consciousness of peoplethat acting against the judgment of conscience, a man acts against himself.Conscience is also “a window on what is common” (Joseph Ratzinger), tomoral truth, what is the revelation of the objective dimension of conscience.Finally, it is important religious dimension. It manifests itself in definingconscience as the voice of God.In the second section the author analyzes the key element of the contemporarydispute about conscience that is his relationship to authority, boththe state and the church. There is no doubt that state law should respect thefreedom of conscience of citizens and, in situations of serious conflicts –provide the opportunity to invoke the conscience clause. In contrast to thepluralistic society ecclesial community has the right to have moral convictionsstemming form faith, which are crucial to belong to the individualreligious community. This does not invalidate in any way the importance ofconscience, which remains the final court (although not the highest standard,which is God) of moral action
Przesłanie Humanae vitae z perspektywy pięćdziesiątej rocznicy ogłoszenia encykliki
No full textThe author of this article explores the understanding of the message of the encyclical Humanae vitae based on three crucial points. The first one concerns the concept of human person. Unlike the evolutionary approach wherein the human being is thought under the aspect of its biological facticity, human person is viewed here as a “unitotality”, an indissolubly whole of the body and the soul whereby the human body has not only a function but also reveals a deeper meaning. The second point is the nature of the conjugal act. It exhibits the reciprocal gift of a man and a woman in their totality as persons. Due to this totality the two meanings contained in the conjugal act, namely the meaning of loving personal unity and the meaning of procreativeness should not be consciously separated. The matter is hereby not a bond between two things or biological facts but a bond between meanings. The objection of the naturalistic fallacy is also here unjustified. Finally the third point is the theological dimension which highlights that the double meaning of the conjugal act comes from God the Creator and as innate into the human nature and the nature of human love and as such should be respected. The contemporary controversy concentrates the question either the sexuality-conjugality-procreation nexus concerns every single conjugal act or if it might concern the marital life as a whole whereas the married couple can make some single sexual acts consciously unfruitful.Autor niniejszego artykułu stara się zgłębić przesłanie Humanae vitae w oparciu o trzy kluczowe punkty. Pierwszym z nich jest koncept osoby ludzkiej. W odróżnieniu od podejścia ewolucyjnego, w którym osoba ludzka jest postrzegana w aspekcie jej biologicznej faktyczności, jest ona tutaj widziana jako “unitotality” – nierozdzielna jedność ciała i ducha, przy czym ludzkie ciało pełni nie tylko pewne funkcje, ale niesie w sobie głębokie znaczenie. Drugim punktem jest natura aktu małżeńskiego. Ujawnia on wzajemny dar męża i żony obejmujący całość osoby. Poprzez całkowitość oddania dwa znaczenia zawarte w akcie małżeńskim, mianowicie znaczenie jednoczące miłości oraz znaczenia prokreacyjne, nie powinny być rozdzielane. Chodzi tutaj jednak nie o powiązanie między biologicznymi faktami, ale o powiązanie między znaczeniami. Zarzut błędu naturalistycznego nie jest tu uzasadniony. Wreszcie trzeci punkt dotyczy teologicznego wymiaru, według którego związek obydwu wyżej wymienionych znaczeń pochodzi od Boga Stwórcy i jako wpisany w ludzką naturę oraz naturę miłości, powinien być respektowany. Współczesna kontrowersja skupia się na pytaniu, czy związek między seksualnością, zjednoczeniem małżeńskim a prokreacją dotyczy każdego aktu małżeńskiego lub też czy może równie dobrze dotyczyć całości życia małżeńskiego, podczas gdy para małżeńska może uczynić niektóre akty małżeńskie świadomie niepłodnymi
Dyskusja o nierozerwalności małżeństwa na marginesie adhortacji Amoris laetitia: Pytania otwarte
No full textThe indissolubility of sacramental marriage has been over the centuries the crucial point of the teaching of the Catholic Church about marriage based on the Jesus’ expressions about marriage and divorce. The indissolubility ofmarriage can be understood in a twofold manner. The first dimension is the moral indissolubility which means a serious moral obligation of being faithful towards the husband. Marriage should not be dissolved but in fact it is dissolved in an increasing number of Christian couples. But there is also the second dimension – the ontological indissolubility. Being a creation of God the sacramental marriage cannot be dissolved, even if the relationship breaks apart. Though Pope Francis emphasizes that the Church’s teaching about marriage remains unchanged, some passages of the Papal Letter cannot be interpreted clearly. As a result, the statements of the particular bishop conferences as well as the guidelines launched by some bishops concerning the pastoral care of divorced and remarried couples are ambiguous. The author of the article stands for the integral keeping of the entire teaching of the church about the indissolubility of the sacramental marriage in every new proposal for the pastoral careof people living in “irregular” situations.Nierozerwalność sakramentalnego małżeństwa była przez wieki centralnym punktem nauczania Kościoła katolickiego o małżeństwie, bazującego na wypowiedziach Jezusa na temat małżeństwa i rozwodu. Pojęcie „nierozerwalnośćmałżeństwa” można rozumieć w dwojaki sposób. Pierwszym wymiarem jest nierozerwalność moralna, która oznacza poważne zobowiązanie do wierności wobec prawowitego małżonka. Małżeństwo nie powinno być rozwiązywane, jednak w praktyce rozpada się i ostatecznie rozchodzi się pokaźna liczba chrześcijańskich małżeństw. Jednak jest jeszcze drugi wymiar, jakim jest nierozerwalność ontologiczna. Jako Boże dzieło sakramentalne małżeństwo nie tylko nie powinno, ale nie może zostać rozwiązane nawet wtedy, gdy rozpada się relacja między małżonkami. Mimo deklaracji papieża Franciszka, że nauczanie Kościoła w tym obszarze pozostaje niezmienione, pewne fragmenty adhortacji mogą być różnie interpretowane. W efekcie oświadczenia różnych episkopatów oraz pierwsze instrukcje duszpasterskie wydane przez biskupów, a dotyczące duszpasterstwa rozwiedzionych żyjących w nowych związkach, są bardzo różne. Autor artykułu opowiada się za tym, by we wszystkich nowych propozycjach dotyczących duszpasterstwa osób znajdujących się w sytuacjach nieregularnych zachowana została integralność nauczania Kościoła o nierozerwalności małżeństwa
