How seaweeds release the excess energy from sunlight to surrounding sea water

Abstract

We report an atomistic insight into the mechanism regulating the energy released by a porphyra-334 molecule, the ubiquitous photosensitive component of marine algae, in a liquid water environment upon an electron excitation. To quantify this rapidly occurring process, we resort to the Fourier analysis of the mass-weighted auto-correlation function, providing evidence for a remarkable dynamic change in the number of hydrogen bonds among water molecules and between the porphyra-334 and its surrounding hydrating water. Hydrogen bonds between the porphyra-334 and close by water molecules can act directly and rather easily to promote an efficient transfer of the excess kinetic energies of the porphyra-334 to the surrounding solvating water molecules via an activation of the collective modes identified as hydrogen-bond stretching modes in liquid water which eventually results in a disruption of the hydrogen bond network. Since porphyra-334 is present in seaweeds, aquatic cyanobacteria (blue-green algae) and red algae, our findings allow addressing the question how algae in oceans or lakes, upon sunlight absorption, can release large amounts of energy into surrounding water without destabilizing neither their own nor the HO molecular structure.

Unravelling the Photoprotective Mechanisms of Nature-Inspired Ultraviolet Filters Using Ultrafast Spectroscopy

“…Porphyra-334 has also been studied experimentally by Conde et al [ 75 ], who determined the fluorescence quantum yield to be 0.0016, the triplet formation quantum yield to be <0.05 and the photodecomposition quantum yield to be 2–4 × 10 −4 . These very low quantum yields lead to Conde et al [ 75 ] concluding that porphyra-334 undergoes a rapid internal conversion from its electronic excited state to its electronic ground state, which is corroborated by the theoretical work [ 88 , 90 ]. Later work using photoacoustic calorimetry by Conde et al [ 76 ] quantitatively determined that between 96 and 98% of the absorbed energy upon photoexcitation is rapidly released to the surroundings as heat for porphyra-334.…”

“…Within the literature, there have been computational studies on the natural MAAs palythine [ 86 ] and porphyra-334 [ 88 , 90 ]; see Figure 14 for their respective structures. The MEPs of these MAAs are not reproduced here due to the similarity between those that have been presented throughout Section 2.2 of this review.…”

“…Two complementary computational studies have been conducted on porphyra-334 to unravel its photoprotective mechanism [ 88 , 90 ]. The work by Koizumi et al [ 88 ] used first-principles molecular dynamics [ 133 ] on hydrated porphyra-334 to investigate the mechanism that photoexcited porphyra-334 undergoes to dissipate excess energy to surrounding water. The findings were that energy transfer occurred mainly through the activation of hydrogen-bond stretching modes among water molecules.…”

“…Only the hydrogen-bond network of the solvent was disrupted during the simulation, and the first hydration shell of porphyra-334 remained unchanged throughout. The tightness of the first hydration shell hydrogen bonds to porphyra-334 indicates how efficient energy transfer can occur without disruption to chemical bonds in both the solute and the solvent [ 88 ].…”

“…However, Losantos et al [ 84 ] and Woolley et al [ 85 ] have conducted such experiments on MAA motifs. In addition to these studies, complementary theoretical work has modelled the minimum energy relaxation pathways of MAAs and molecules alike, giving insight into their photoprotective mechanisms [ 84 , 86 , 87 , 88 , 89 , 90 ]. Section 2.2 of this review will primarily cover ultrafast spectroscopy and theoretical work conducted to the present date on MAAs and MAA motifs.…”