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1.
Phys Chem Chem Phys ; 21(38): 21329-21340, 2019 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-31531442

RESUMO

The interaction of a water molecule with ferric heme-iron protoporphyrin ([PP FeIII]+) has been investigated in the gas phase in an ion trap and studied theoretically by density functional theory. It is found that the interaction of water with ferric heme leads to a stable [PP-FeIII-H2O]+ complex in the intermediate spin state (S = 3/2), in the same state as its unligated [PP-FeIII]+ homologue, without spin crossing during water attachment. Using the Van't Hoff equation, the reaction enthalpy for the formation of a Fe-OH2 bond has been determined for [PP-FeIII-H2O]+ and [PP-FeIII-(H2O)2]+. The corrected binding energy for a single Fe-H2O bond is -12.2 ± 0.6 kcal mol-1, while DFT calculations at the OPBE level yield -11.7 kcal mol-1. The binding energy of the second ligation yielding a six coordinated FeIII atom is decreased with a bond energy of -9 ± 0.9 kcal mol-1, well reproduced by calculations as -7.1 kcal mol-1. However, calculations reveal features of a weaker bond type, such as a rather long Fe-O bond with 2.28 Å for the [PP-FeIII-H2O]+ complex and the absence of a spin change by complexation. Thus despite a strong bond with H2O, the FeIII atom does not show, through theoretical modelling, a strong acceptor character in its half filled 3dz2 orbital. It is also observed that the binding properties of H2O to hemes seem strikingly specific to ferric heme and we have shown, experimentally and theoretically, that the affinity of H2O for protonated heme [H PP-Fe]+, an intermediate between FeIII and FeII, is strongly reduced compared to that for ferric heme.

2.
Phys Chem Chem Phys ; 21(26): 14453-14464, 2019 Jul 14.
Artigo em Inglês | MEDLINE | ID: mdl-31210192

RESUMO

Single photon ionization and subsequent unimolecular ion decomposition were studied on jet-cooled benzophenone and fluorenone separately, using VUV synchrotron radiation in a photoion/photoelectron coincidence setup. Slow PhotoElectron Spectra (SPES) were recorded in coincidence with either the parent or the fragment ions for hν < 12.5 eV. Dissociative ionization is observed for benzophenone only. The full interpretation of the measurements, including the identification of the neutral and ionic species when dissociative ionization is at play, benefits from high level ab initio computations for determining the equilibrium structures and the energetics of the neutral and ionized molecules and of their fragments. Electronically excited states of the parent molecular ions were calculated also. From this analysis, an accurate experimental determination of the energetics of the benzophenone and fluorenone ions and of their fragmentation channels is available: adiabatic ionization energies of benzophenone at 8.923 ± 0.005 eV and of fluorenone at 8.356 ± 0.007 eV; and appearance energies of benzophenone fragment ions at 11.04 ± 0.02 eV (loss of C6H5), 11.28 ± 0.02 eV (loss of H) and 11.45 ± 0.02 eV (loss of CO). The corresponding fragmentation mechanisms are explored, showing likely concerted bonds rearrangement. Possible pre-ionizing fragmentation is discussed in light of the spectra presented. The structural rigidity of fluorenone diarylketone seems to be the origin of the inhibition of the fragmentation of its cation.

3.
Phys Chem Chem Phys ; 21(4): 1750-1760, 2019 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-30623949

RESUMO

The binding energy of CO, O2 and NO to isolated ferric heme, [FeIIIP]+, was studied in the presence and absence of a σ donor (N-methylimidazole and histidine) as the trans axial ligand. This study combines the experimental determination of binding enthalpies by equilibrium measurements in a low temperature ion trap using the van't Hoff equation and high level DFT calculations. It was found that the presence of N-methylimidazole as the axial ligand on the [FeIIIP]+ porphyrin dramatically weakens the [FeIIIP-ligand]+ bond with an up to sevenfold decrease in binding energy owing to the σ donation by N-methylimidazole to the FeIII(3d) orbitals. This trans σ donor effect is characteristic of ligation to iron in hemes in both ferrous and ferric redox forms; however, to date, this has not been observed for ferric heme.


Assuntos
Hemina , Imidazóis , Sítios de Ligação , Hemina/química , Hemina/metabolismo , Imidazóis/química , Imidazóis/metabolismo , Ferro/química , Ferro/metabolismo , Ligantes , Termodinâmica
4.
Phys Chem Chem Phys ; 21(3): 1038-1045, 2019 Jan 17.
Artigo em Inglês | MEDLINE | ID: mdl-30289418

RESUMO

Near-infrared spectroscopy of the C2H2-Ar, Kr complexes was performed in the spectral region overlapping the ν3/ν2 + ν4 + ν5 Fermi-type resonance of C2H2. The experiment was conducted along the HElium NanoDroplet Isolation (HENDI) technique in order to study the coupling dynamics between a floppy molecular system (C2H2-Ar and C2H2-Kr) and a mesoscopic quantum liquid (the droplet). Calculations were performed using a spectral element based close-coupling program and state-of-the-art 2-dimensional potential energy surfaces to determine the bound states of the C2H2-Ar and C2H2-Kr complexes and simulate the observed spectra. This furnished a quantitative basis to unravel how the superfluid and non-superfluid components of the droplet affect the rotation and the deformation dynamics of the hosted complex.

5.
Phys Chem Chem Phys ; 20(17): 11730-11739, 2018 May 03.
Artigo em Inglês | MEDLINE | ID: mdl-29687125

RESUMO

A combined theoretical and experimental approach has been used to investigate the binding energy of a ruthenium metalloporphyrin ligated with CO, ruthenium tetraphenylporphyrin [RuII TPP], in the RuII oxidation degree. Measurements performed with VUV ionization using the DESIRS beamline at Synchrotron SOLEIL led to adiabatic ionization energies of [RuII TPP] and its complex with CO, [RuII TPP-CO], of 6.48 ± 0.03 eV and 6.60 ± 0.03 eV, respectively, while the ion dissociation threshold of [RuII TPP-CO]+ is measured to be 8.36 ± 0.03 eV using the ground-state neutral complex. These experimental data are used to derive the binding energies of the CO ligand in neutral and cationic complexes (1.88 ± 0.06 eV and 1.76 ± 0.06 eV, respectively) using a Born-Haber cycle. Density functional theory calculations, in very satisfactory agreement with the experimental results, help to get insights into the metal-ligand bond. Notably, the high ligation energies can be rationalized in terms of the ruthenium orbital structure, which is singular compared to that of the iron atom. Thus, beyond indications of a strengthening of the Ru-CO bond due to the decrease in the CO vibrational frequency in the complex as compared to the Fe-CO bond, high-level calculations are essential to accurately describe the metal ligand (CO) bond and show that the Ru-CO bond energy is strongly affected by the splitting of triplet and singlet spin states in uncomplexed [Ru TPP].

6.
Phys Chem Chem Phys ; 20(16): 11206-11214, 2018 Apr 25.
Artigo em Inglês | MEDLINE | ID: mdl-29632903

RESUMO

The present work combines time-resolved photoelectron spectroscopy on isolated species with high-level data processing to address an issue which usually pertains to materials science: the electronic relaxation dynamics towards the formation of a self-trapped exciton (STE). Such excitons are common excited states in ionic crystals, silica and rare gas matrices. They are associated with a strong local deformation of the matrix. Argon clusters were taken as a model. They are excited initially to a Wannier exciton at 14 eV and their evolution towards the formation of an STE has showed an unusual type of vibronic relaxation where the electronic excitation of the cluster decreases linearly as a function of time with a 0.59 ± 0.06 eV ps-1 rate. The decay was followed for 3.0 ps, and the STE formation occurred in ∼5.1 ± 0.7 ps.

7.
Chemistry ; 23(54): 13493-13500, 2017 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-28744916

RESUMO

With a view to characterizing the influence of the electronic structure of the Fe atom on the nature of its bond with dioxygen (O2 ) in heme compounds, a study of the UV/Vis action spectra and binding energies of heme-O2 molecules has been undertaken in the gas phase. The binding reaction of protonated ferrous heme [FeII -hemeH]+ with O2 has been studied in the gas phase by determining the equilibrium of complexed [FeII -hemeH(O2 )]+ with uncomplexed protonated heme in an ion trap at controlled temperatures. The binding energy of O2 to the Fe atom of protonated ferrous heme was obtained from a van't Hoff plot. Surprisingly, this energy (1540±170 cm-1 , 18.4±2 kJ mol-1 ) is intermediate between those of ferric heme and ferrous heme. This result is interpreted in terms of a delocalization of the positive charge over the porphyrin cycle, such that the Fe atom bears a fractional positive charge. The resulting electron distribution on the Fe atom differs notably from that of a purely low-spin ferrous heme [FeII -heme(O2 )] complex, as deduced from its absorption spectrum. It also differs from that of ferric heme [FeIII -heme(O2 )]+ , as evidenced by the absorption spectra. Protonated heme creates a specific bond that cannot accommodate strong σ donation.


Assuntos
Compostos Férricos/química , Compostos Ferrosos/química , Gases/química , Heme/química , Oxigênio/química , Cinética , Prótons , Espectrofotometria , Temperatura Ambiente , Termodinâmica
8.
Phys Chem Chem Phys ; 18(33): 22914-20, 2016 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-27485671

RESUMO

Direct measurements of Single vibronic Level InterSystem Crossing (SLISC) have been performed on the fluorenone molecule in the gas phase, by time resolved photoelectron and photoion spectroscopy. Vibronic transitions above the S1 nπ* origin were excited in the 432-420 nm region and the decay of S1 and growth of T1(3)ππ* could be observed within a 10 ns time domain. The ionization potential is measured as 8.33 ± 0.04 eV. The energy of the first excited triplet state of fluorenone, T1 has been characterized directly at 18 640 ± 250 cm(-1). The internal conversion of S1 to S0 is found to amount to ∼15% of the population decay, thus ISC is the dominant electronic relaxation process. ISC, although favored by the S1(1)nπ*-T1(3)ππ* coupling scheme, is 3 orders of magnitude less efficient than in the similar molecule benzophenone. Thus, the planarity of the fluorenone molecule disfavors the exploration of the configuration space where surface crossings would create high ISC probability, which occurs in benzophenone through surface crossings. The time evolution of S1 fluorenone is well accounted for by the statistical decay of individual levels into a quasi-continuum of T1 vibronic levels.

9.
Phys Chem Chem Phys ; 18(25): 16700-8, 2016 Jun 22.
Artigo em Inglês | MEDLINE | ID: mdl-27270590

RESUMO

In this article we present a joint study by time-of-flight mass spectroscopy and density functional theory of cobalt protoporphyrin dimer complexes. The main novelty of the experimental part is to reveal the formation of porphyrin dimers that eventually include a chlorine atom. Density functional theory calculations have been performed to shed light on the structural and electronic properties of monomers and dimers that may be formed experimentally. Various geometries of the monomers are analyzed in the two lowest spin states. The electronic structures are examined by means of population analysis relying on the iterative Hirshfeld scheme and the topological analyses of the electron localization function. It is shown that the cobalt ligand bond is purely ionic in the triplet states but shows a noticeable covalent character in the singlet state. Ionization potential of Co-protoporphyrin and binding energies of the chlorine ligand are also reported. Concerning the dimers, several association patterns are investigated for the chlorinated and non-chlorinated complexes. It is found that the structures of the most stable complexes involve four hydrogen bonds between the carboxylic acid moieties of the protoporphyrins. However other association modes are likely to be possible in the experiments.

10.
J Phys Chem A ; 119(23): 5901-2, 2015 Jun 11.
Artigo em Inglês | MEDLINE | ID: mdl-26062882
11.
Phys Chem Chem Phys ; 17(39): 25693-9, 2015 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-26059068

RESUMO

While ferrous heme (Fe(II)) within hemoproteins binds dioxygen efficiently, it has not yet been possible to observe the analog complex with ferric heme (Fe(III)). We present the first observation and characterization of the latter complex in a cooled ion trap. The bond formation enthalpy of ferric heme-O2 has been derived from the Van't Hoff equation by means of temperature dependent measurements. The binding energy of the [heme Fe(III)-O2](+) ionic complex is rather strong as compared to that of [heme Fe(III)-N2](+), showing the formation of an incipient Fe-O bond, which is confirmed by the electronic absorption spectra of the two complexes. This first observation of the [heme Fe(III)-O2](+) complex lays the basis for the precise description of its electronic states.


Assuntos
Compostos Férricos/química , Heme/química , Ferro/química , Oxigênio/química , Sítios de Ligação , Hemeproteínas/química , Modelos Moleculares , Termodinâmica
12.
J Phys Chem A ; 119(23): 6148-54, 2015 Jun 11.
Artigo em Inglês | MEDLINE | ID: mdl-25866992

RESUMO

We report on the single photoionization of jet-cooled benzophenone using a tunable source of VUV synchrotron radiation coupled with a photoion/photoelectron coincidence acquisition device. The assignment and the interpretation of the spectra are based on a characterization by ab initio and density functional theory calculations of the geometry and of the electronic states of the cation. The absence of structures in the slow photoelectron spectrum is explained by a congestion of the spectrum due to the dense vibrational progressions of the very low frequency torsional mode in the cation either in pure form or in combination bands. Also a high density of electronic states has been found in the cation. Presently, we estimate the experimental adiabatic and vertical ionization energy of benzophenone at 8.80 ± 0.01 and 8.878 ± 0.005 eV, respectively. The ionization energy as well as the energies of the excited states are compared to the calculated ones.

13.
J Chem Phys ; 141(17): 174310, 2014 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-25381517

RESUMO

Hemoprotein mimics, cobalt picket fence porphyrins have been prepared in the gas phase as neutral molecules for the first time. Their ligation properties have been studied with 1-methylimidazole and compared with those of other cobalt porphyrins, tetraphenyl porphyrin, and cobalt protoporphyrin IX chloride, in view of studying the sterical properties of the ligation. It is shown that the cobalt picket fence porphyrin can only accept one 1-methylimidazole ligand in contrast to less sterically crowded porphyrins like cobalt tetraphenylporphyrin that present two accessible ligation sites. The femtosecond dynamics of these ligated systems have been studied after excitation at 400 nm, in comparison with the unligated ones. The observed transients are formed in much shorter times, 30 fs for the ligated species, as compared to free species (100 fs), supporting the porphyrin to metal charge transfer nature of these transients. The similar decays of the ligated transients <1 ps reveal the absence of photodissociation of the cobalt-1-methylimidazole bond at this step of evolution.


Assuntos
Gases/química , Hemeproteínas/química , Imidazóis/química , Protoporfirinas/química , Estrutura Molecular
14.
Phys Chem Chem Phys ; 16(40): 22262-72, 2014 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-25219416

RESUMO

State-of-the-art experimental and theoretical tools were used to investigate the gas-phase relaxation dynamics of various photoexcited photochromic dithienylethene molecules in situations where several relaxation channels are simultaneously at play. Unconstrained and constrained dynamics were addressed by considering unbridged and bridged molecules with a polyether bridge of various sizes (from 2 to 4 units). Time-resolved ultrafast ionization spectroscopy techniques were used to probe the dynamics. This revealed the existence of several relaxation pathways from the first excited state to the ground-state. Characteristic times were determined for each process. These channels compete at an early stage of the dynamics only when the initial wavepacket splits into two parts. A striking excited state wavepacket oscillation is observed in bridged molecules. A general reaction mechanism is proposed which rationalizes the carbon-carbon distance rule which is widely used as an empirical tool to predict the photoactivity of photochromic molecules in crystals.

15.
Phys Chem Chem Phys ; 16(20): 9610-8, 2014 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-24728443

RESUMO

Benzophenone is a prototype molecule for photochemistry in the triplet state through its high triplet yield and reactivity. We have investigated its dynamics of triplet formation under the isolated gas phase conditions via femtosecond and nanosecond time resolved photoelectron spectroscopy. This represents the complete evolution from the excitation in S2 to the final decay of T1 to the ground state S0. We have found that the triplet formation can be described almost as a direct process in preparing T1, the lowest reacting triplet state, from the S1 state after S2 → S1 internal conversion. The molecule was also deposited by a pick-up technique on cold argon clusters providing a soft relaxation medium without evaporation of the molecule and the mechanism was identical. This cluster technique is a model for medium influenced electronic relaxation and provides a continuous transition from the isolated gas phase to the relaxation dynamics in solution.

16.
Phys Chem Chem Phys ; 16(2): 516-26, 2014 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-24121442

RESUMO

This paper is a joint experimental and theoretical approach concerning a molecule deposited on a large argon cluster. The spectroscopy and the dynamics of the deposited molecule are measured using the photoelectron spectroscopy. The absorption spectrum of the deposited molecule shows two solvation sites populated in the ground state. The combined dynamics reveals that the population ratio of the two sites is reversed when the molecule is electronically excited. This work provides the timescale of the corresponding solvation dynamics. Theoretical calculation supports the interpretation. More generally, close examination of the short time dynamics (0-6 ps) of DABCO···Ar(n) gives insights into the ultrafast relaxation dynamics of molecules deposited at interfaces and provides hence the time scale for deposited molecules to adapt to their neighborhoods.

17.
Phys Chem Chem Phys ; 16(2): 581-7, 2014 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-24196979

RESUMO

How much time does it take for a wavepacket to roam on a multidimensional potential energy surface? This combined theoretical and pump-probe femtosecond time experiment on 2-hydroxypyridine proposes an answer. Bypassing the well-established transition state and conical intersection relaxation pathways, this molecular system undergoes relaxation into the S1 excited state: the central ring is destabilized by the electronic excitation, within ~100 fs after absorption of the pump photon, then the H-atom bound to oxygen undergoes a roaming behavior when it couples to other degrees of freedom of the molecule. The timescale of the latter process is measured to be ~1.3 ps. Further evolution of the wavepacket is either an oscillation onto the S1 potential or a conversion into the triplet state for timescale larger than ~110 ps. Our work introduces a new tool for the understanding of time-resolved relaxation dynamics applied to large molecules through the roaming dynamics characterized by its strongly delocalized wavepacket on flat molecular potential energy surfaces.

18.
J Phys Chem A ; 117(34): 8111-8, 2013 Aug 29.
Artigo em Inglês | MEDLINE | ID: mdl-23675770

RESUMO

The ultrafast dynamics of copper tetraphenylporphyrin (CuTPP), copper octaethylporphyrin (CuOEP), and of the free base tetraphenylporphyrin (H2TPP), excited in the S2 state have been investigated in the gas phase by femtosecond pump/probe experiments. The porphyrins were excited in the Soret band at 400 nm. Strikingly, the S2-S1 internal conversion in H2TPP is very rapid (110 fs), as compared to that of ZnTPP (600 fs), previously observed. In turn, CuTPP and CuOEP, excited in S2, follow an efficient and different relaxation pathway from that of other open-shell metalloporphyrins. These two molecules exhibit a sequential four-step decay ending on a slow evolution in the nanosecond range (2)S2 → (2)CT → (2)T → (2)Ground State. This latter evolution is linked to the formation of the (2)T, tripdoublet state in CuTPP, observed in the condensed phase. It is shown that an intermediate charge transfer state plays a crucial role in linking the porphyrin centered (1)ππ* and (3)ππ* configurations. A simple model is presented that allows a rapid evolution between these two configurations, via coupling of the porphyrin π system with the free d electron on the copper. The mechanism obviates the need for the spin orbit coupling within the porphyrin. The result is that these copper porphyrins can exhibit an ultrafast apparent intersystem crossing, unprecedented for organic molecules.


Assuntos
Complexos de Coordenação/química , Cobre/química , Elétrons , Metaloporfirinas/química , Porfirinas/química , Gases/química , Modelos Químicos , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz , Termodinâmica , Fatores de Tempo
19.
Phys Rev Lett ; 109(19): 193401, 2012 Nov 09.
Artigo em Inglês | MEDLINE | ID: mdl-23215381

RESUMO

This experimental work focuses on the complex autoionization dynamics of Ar(2) clusters below the first ionization energy of the argon atom. Ar(2) is submitted to vacuum ultraviolet radiation, and the photoelectron spectra are collected in coincidence with the cluster ions. The ionization dynamics is revealed by the dependence on the photon energy. We applied a new experimental method which we developed to analyze the photoelectron signal. Thus, we were able (i) to get the complete vibrational progression of Ar(2)(+) that was never observed up to now, especially identifying the 0-0 transition overcoming the usual Franck-Condon limitations during single photoionization, and (ii) to obtain the projections of the vibrational wave functions of the autoionizing states over the Ar(2)(+) functions. This method provides a powerful tool to test the potential energy curves computed by high level theoretical calculations on Rydberg states.

20.
J Phys Chem A ; 115(34): 9620-32, 2011 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-21770416

RESUMO

The spectroscopy of the ZrF radical, produced by a laser ablation-molecular beam experimental setup, has been investigated for the first time using a two-color two-photon (1 + 1') REMPI scheme and time-of-flight (TOF) mass spectrometry detection. The region of intense bands 400-470 nm has been studied, based upon the first spectroscopic observations of the isovalent ZrCl radical by Carroll and Daly. The overall spectrum observed is complex. However, simultaneous and individual ion detection of the five naturally occurring isotopologues of ZrF has provided a crucial means of identifying band origins and characterization via the isotopic shift, δ(iso), of the numerous vibronic transitions recorded. Hence, five (0-0) transitions, of which only two were free of overlap with other transitions, have been identified. The most intense (0-0) transition at 23113 cm(-1) presented an unambiguously characteristic RQP rotational structure. From rotational contour simulations of the observed spectra, the nature of the ground electronic state is found to be unambiguously of (2)Δ symmetry, leading to the assignment of this band as (0-0) (2)Δ â† X(2)Δ at 23113 cm(-1). A set of transitions (1-0) (2)Δ â† X(2)Δ at 22105 cm(-1) and (2-0) (2)Φ â† X(2)Δ at 22944 cm(-1) involving the X(2)Δ state has also been identified and analyzed. Furthermore, a second series of transitions with lesser intensity has also been related to the long-lived metastable (4)Σ(-) state: (3-0) (4)Π(-1/2) ← (4)Σ(-) at 21801 cm(-1), (2-0) (4)Π(-1/2) ← (4)Σ(-) at 21285 cm(-1) and (2-0) (4)Σ(-) ← (4)Σ(-) at 23568 cm(-1). These spectroscopic assignments are supported by MRCI ab initio calculations, performed using the MOLPRO quantum chemistry package, and show that the low-lying excited states of the ZrF radical are the (4)Σ(-) and (4)Φ states lying at 2383 and 4179 cm(-1) respectively above the ground X(2)Δ state. The difference in the nature of ground state and ordering of the first electronic states with TiF (X(4)Φ)(2-4) and ZrCl,(5) respectively, is examined in terms of the ligand field theory (LFT)(7) applied to diatomic molecules. These results give a precise description of the electronic structure of the low lying electronic states of the ZrF transition metal radical.


Assuntos
Química Física , Halogênios/química , Elementos de Transição/química , Elétrons , Lasers , Ligantes , Estrutura Molecular , Fótons , Teoria Quântica , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz , Termodinâmica , Vibração
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