Analysis of the pulsed-laser-induced fluorescence spectrum of the chlorophyll a dimer in solution

Wilton, A. C. De; Haley, L. V.; Koningstein, J. A.

doi:10.1021/j150650a009

Cited by 11 publications

(5 citation statements)

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“…Energetics [kcal ·mol À1 ] for the HydrationProcesses of Chla Monomers in the Gas Phase a ) b ) and in Cyclohexane Solution zation.Aspredicted above,the formation of the dihydrated monomer with af ive coordinated Mg structurew as the most favorable hydration process.T he hydrationo ft he dimer was weakly exergonic compared with the hydration of Chla monomeric species.T he predicted structure of the tetrahydrated dimerc omplex was more stable than the dihydrated dimerb ecause of cooperatively between the MgÀH 2 Oi nteraction and H 2 OÀH 2 Oa nd H 2 OÀCO Hbonds.A ccording to these results,i nn on polar solvent, Chla will readly formm onomeric and dimeric hydrated complexes in the presence of H 2 O, even in the form of traces.T he dihydrate/tetrahydrate equilibrium will be slightlys hifted toward the formation of the tetrahydrated dimers.These results agreed with the experimentalfindings that, in the presence of small amounts of H 2 O, there is formation of mono and dihydrated Chla species,aswell as their corresponding dimers[19][28]. They corroboratethe experiments facts that upon further addition of H 2 Ot oa solution inducingCha aggregation, the equilibrium mixture is greatly shifted in favour of the dihydrated polymeric Chla form (Chla-2 H 2 O) n[19][27][72]. It has to be noted that the structure of this aggregate has been the subject of extensive debate in the literature[31] [37][73].E vidence for the presence of neutral structural H 2 Om olecules forming aH -bonded network in an arrangement similar to that of crystals of ethyl chlorophyllide(a) dihydrate[23] has been reported[36][37][73].…”

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Theoretical Study of the Dimerization of Chlorophyll (a) and Its Hydrates: Implication for Chlorophyll (a) Aggregation

Fredj

2016

Helvetica Chimica Acta

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Dimeric structures chlorophyll (a) (Chla) and their mono‐ and dihydrated have been suggested to play an important role in the mechanism of photoreaction center chlorophyll special pairs PSI and PSII. Despite their functional importance, the molecular basis structures for interacting two Chla molecules and the structural stabilization role of H2O in the formation of hydrated Chla dimer complexes is poorly understood. In this article, the different coordination modes between two interacting Chla molecules and the configurational (orientation and distance) features between the dimer and bound H2O molecules are characterized by means of super molecule approach the density functional theory DFT. An estimation of the thermodynamic quantities is made for Chla dimerization and hydration processes. The results indicate that structure including ester linkages via H2O hydrogen bonding is the most favorable conformation for the dihydrated chlorophyll (a) dimer at B3LYP/6‐31G*‐DCP level of calculation. The dispersion interaction is shown to be of great significance for the Chla dimer stabilization. In aqueous nonpolar solvent, the thermodynamics show that Chla has a slightly stronger driving force for full hydration than for dimerization and that hydration of the dimers is rather weakly exergonic. The tetrahydrated dimers having a similar arrangement to that in crystals of ethyl chlorophyllide (a) dihydrate are found to be more stable than the Chla dihydrated dimer. The data underscore the key role of H‐bonding in the stability of Chla‐H2O adducts and, in particular, the great importance of the Chla monomeric dihydrated species in the hydration and dimerization of Chla in aqueous media. Clearly, the Chla dihydrates (Chla‐2 H2O) are found more stable than the monohydrates (Chla‐H2O) and the Chla dimers (Chla2), owing to a particular structure in which cooperative interactions occur between the H2O molecules and Chla. Calculations also indicate that the most thermodynamically preferred pathway for the formation of Chla dimer hydrates can be represented by two steps: the first corresponds to the formation of Chla monomeric dihydrates and the second is the dimerization of the dihydrates on to tetrahydrated Chla dimers. These results allow to obtain a new possible pathway for Chla dimer formation processes and could provide new insights to the aggregation of chlorophyll (a) in solution.

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confidence: 86%

Theoretical Study of the Dimerization of Chlorophyll (a) and Its Hydrates: Implication for Chlorophyll (a) Aggregation

Fredj

2016

Helvetica Chimica Acta

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“…0 values were taken in the absence of added "ZnS". Emission intensities may somewhat vary from day to day; therefore, the / 0 values reported include and 0 values, measured within less than 1 h. 4 In terms of the ZnS molecules (which is only half of the concentration of "ZnS"). The rate constants were calculated as kq = 7-_1[ZnS]_1(l -/ 0)/( / 0 -"/ ), where r is the lifetime of the secondary electron-hole pair in the absence of ZnS (14 ns).…”

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confidence: 99%

Sandwich colloids of zinc oxide and zinc sulfide in aqueous solutions

Rabani¹

1989

J. Phys. Chem.

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Another difference is that little if any evidence for NH4C1+ or H+(NH4C1) exists in the mass spectra. This region of the mass spectrum is also shown in Figure 5. Oddly, Cheung et al.21 report observing NH4C1+. Goldfinger and Verhagen16 also failed to observe the molecular ion in a Knudsen cell experiment in which they vaporized solid ND4C1. They inferred the presence of the gas-phase ND4C1 from the appearance of ND4+. They suggest that a stable molecular ion would be observed only if the electron was removed from the ammonium rather than the chloride. In calculations by Clementi,18,35 the highest occupied orbitals are largely centered on the chlorine atom. Thus, ionization should be expected to result in fragmentation. The observation of NH4I+ ion and not the NH4C1+ ion may well be related to the higher polarizability of atomic I (4.3 Á3) compared to atomic chlorine (2.1 Á3) which could facilitate the retention of I compared to Cl in the cluster after ionization. ConclusionsThe experimental findings of the present study show that hydrogen halides easily become incorporated in ammonia clusters.

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“…Valuable additional information in particular concerning the optical properties can be gained from luminescence spectroscopy. This, however, is challenging due to the low fluorescence quantum yield in dilute solution [14], which is expected to be further reduced down to 10 À5 in thin films due to strong intermolecular coupling [15]. The luminescence studies of solid metal-free porphyrazines have been limited to unsubstituted metal-free phthalocyanine PcH 2 in the form of thin films [16][17][18][19][20], crystals [21], liquid crystals [22,23], as well as to some of their metal complexes [16,21] using laser excitation.…”

Section: Introductionmentioning

confidence: 99%

Absorption, luminescence, and Raman spectroscopic properties of thin films of benzo-annelated metal-free porphyrazines

Freyer

Neacsu

Raschke

2008

Journal of Luminescence

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Analysis of the pulsed-laser-induced fluorescence spectrum of the chlorophyll a dimer in solution

Cited by 11 publications

References 7 publications

Theoretical Study of the Dimerization of Chlorophyll (a) and Its Hydrates: Implication for Chlorophyll (a) Aggregation

Theoretical Study of the Dimerization of Chlorophyll (a) and Its Hydrates: Implication for Chlorophyll (a) Aggregation

Sandwich colloids of zinc oxide and zinc sulfide in aqueous solutions

Absorption, luminescence, and Raman spectroscopic properties of thin films of benzo-annelated metal-free porphyrazines

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