Unravelling photoprotection in microbial natural products

Mycosporine-like amino acids have long been known as a natural form of photoprotection for fungi and cyanobacteria. This review will highlight the key time-resolved experimental and theoretical techniques unravelling their photochemistry and photophysics, and directly link this to their use in commercial skin-care products, namely as sunscreen filters. Three case studies have been selected, each having aided advancement in this burgeoning field of research. We discuss these studies in the context of photoprotection and conclude by evaluating the necessary future steps towards translating the photochemistry and photophysics insight of these nature derived sunscreen filters to commercial application

Ultrafast spectroscopy of natural sunscreen filters

Ultraviolet radiation (UVR) has both positive and negative effects on biological systems. In humans, for example, UVR is responsible for producing vitamin D, while excessive exposure to UVR increases the risk of skin cancer. To avoid photodamage, both plants and humans have developed molecular species to deal with any excessive UVR. Two such classes of molecular species in plants are mycosporine-like amino acids and sinapates. Both these species have previously been investigated for their ability to provide protection from UVR and they have been proposed to be the next generation of UV filters to be utilised in commercial sunscreen formulations. The work presented in this thesis builds on the current literature on both mycosporine-like amino acids and cinnamates, a family of molecules structurally similar to sinapates, and currently employed in commercial formulations. The work presented in Chapter 3 discusses the photodynamics of mycosporine-like amino acids motifs, the results of which are used to aid the discussion in Chapter 5 on the photodynamics of natural mycosporine-like amino acids themselves. Chapter 4 published work exploring the structure-dynamics-function relationship for a symmetrically functionalised methyl cinnamate. Again these results are utilised to further explore this relationship in Chapter 5 through additional functionalisation of the methyl cinnamate moiety. All of these experiments were performed on an ultrafast transient electronic absorption setup, the details of which are described in Chapter 2. By conducting studies aiming to understand the intrinsic molecular motions involved in photoprotection like those discussed in this thesis, it is hoped that we can then begin to utilise such structure-dynamics-function approaches to design next generation UV filters that are nature inspired

Unravelling the photoprotection properties of mycosporine amino acid motifs

Photoprotection from harmful ultraviolet (UV) radiation exposure is a key problem in modern society. Mycosporine like amino acids found in fungi, cyanobacteria, macroalgae, phytoplankton and humans, are already presenting a promising form of natural photoprotection in sunscreen formulations. Using time-resolved transient electronic absorption spectroscopy and guided by complementary ab initio calculations, we help to unravel how the core structures of these molecules perform under UV irradiation. Through such detailed insight into the relaxation mechanisms of these ubiquitous molecules, we hope to inspire new thinking in developing next generation sun protecting molecules

Experimental and computational analysis of para-hydroxy methylcinnamate following photoexcitation

Para-hydroxy methylcinnamate is part of the cinnamate family of molecules. Experimental and computational studies have suggested conflicting non-radiative decay routes after photoexcitation to its S1(ππ*) state. One non-radiative decay route involves intersystem crossing mediated by an optically dark singlet state, whilst the other involves direct intersystem crossing to a triplet state. Furthermore, irrespective of the decay mechanism, the lifetime of the initially populated S1(ππ*) state is yet to be accurately measured. In this study, we use time-resolved ion-yield and photoelectron spectroscopies to precisely determine the S1(ππ*) lifetime for the s-cis conformer of para-hydroxy methylcinnamate, combined with time-dependent density functional theory to determine the major non-radiative decay route. We find the S1(ππ*) state lifetime of s-cis para-hydroxy methylcinnamate to be ∼2.5 picoseconds, and the major non-radiative decay route to follow the [1ππ*→1nπ*→3ππ*→S0] pathway. These results also concur with previous photodynamical studies on structurally similar molecules, such as para-coumaric acid and methylcinnamate

Annual performance indicators of enforced driver behaviours in South Australia, 2003

The Centre for Automotive Safety Research at the University of Adelaide was commissioned by the Department for Transport, Energy and Infrastructure to produce a report quantifying performance indicators for selected enforced driver behaviours (drink driving, speeding, restraint use) in South Australia for the calendar year 2003. The total number of breath tests conducted in South Australia in 2003 was 11 percent lower than the level in 2002. However, mobile RBT was introduced for the first time, late in the year, and was found to be a better means of detecting drink drivers than static RBT. Also, spending on anti-drink driving publicity increased markedly in 2003. The year 2003 was significant for the reductions in speed limits introduced in South Australia. Total hours of speed detection decreased by 11 percent, however, due to a marked decrease in the hours of operation of speed cameras in the metropolitan area. The reduction in the use of highly efficient speed cameras was the likely explanation for a 27 percent reduction in the number of drivers charged with speeding offences in 2003. An evaluation of the effect of the reduction in the default urban speed limit revealed that speeds decreased on all roads affected by the change but also, by a smaller magnitude, on arterial roads on which the 60 km/h limit was maintained. Restraint offences increased slightly in 2003 but there were no observational surveys conducted to provide an indication of restraint wearing rates, and so the slight increase in offences could have been due to differences in enforcement. Males were again over-represented in restraint offences and in non-restrained vehicle occupants injured in crashes. The amount of money spent on publicity for restraint use in 2003 was significantly greater than previous years

Investigating the ultrafast dynamics and long-term photostability of an isomer pair, Usujirene and Palythene, from the Mycosporine-like amino acid family

Mycosporine-like amino acids are a prevalent form of photoprotection in micro- and macro-organisms. Using a combination of natural product extraction/purification and femtosecond transient absorption spectroscopy, we studied the relaxation pathway for a common mycosporine-like amino acid pair, usujirene and its geometric isomer palythene, in the first few nanoseconds following photoexcitation. Our studies show that the electronic excited state lifetimes of these molecules persist for only a few hundred femtoseconds before the excited state population is funneled through an energetically accessible conical intersection with subsequent vibrational energy transfer to the solvent. We found that a minor portion of the isomer pair did not recover to their original state within 3 ns after photoexcitation. We investigated the long-term photostability using continuous irradiation at a single wavelength and with a solar simulator to mimic a more real-life environment; high levels of photostability were observed in both experiments. Finally, we employed computational methods to elucidate the photochemical and photophysical properties of usujirene and palythene as well as to reconcile the photoprotective mechanism

Unravelling the photoprotection properties of garden cress sprout extract

Plants, as with humans, require photoprotection against the potentially damaging effects of overexposure to ultraviolet (UV) radiation. Previously, sinapoyl malate (SM) was identified as the photoprotective agent in thale cress. Here, we seek to identify the photoprotective agent in a similar plant, garden cress, which is currently used in the skincare product Detoxophane nc. To achieve this, we explore the photodynamics of both the garden cress sprout extract and Detoxophane nc with femtosecond transient electronic absorption spectroscopy. With the assistance of liquid chromatography-mass spectrometry, we determine that the main UV-absorbing compound in garden cress sprout extract is SM. Importantly, our studies reveal that the photoprotection properties of the SM in the garden cress sprout extract present in Detoxophane nc are not compromised by the formulation environment. The result suggests that Detoxophane nc containing the garden cress sprout extract may offer additional photoprotection to the end user in the form of a UV filter booster

Synergic photoprotection of phenolic compounds present in tomato fruit cuticle : a spectroscopic investigation in solution

Coumaric acids and flavonoids play pivotal roles in protecting plants against ultraviolet radiation (UVR) exposure. In this work, we focus our photoprotection studies on p-coumaric acid and the flavonoid naringenin chalcone. Photoprotection is well-understood in p-coumaric acid; in contrast, information surrounding photoprotection in naringenin chalcone is lacking. Additionally, and vitally, how these two species work in unison to provide photoprotection across the UV-B and UV-A is unknown. Herein, we employ transient absorption spectroscopy together with steady-state irradiation studies to unravel the photoprotection mechanism of a solution of p-coumaric acid and naringenin chalcone. We find that the excited state dynamics of p-coumaric acid are significantly altered in the presence of naringenin chalcone. This finding concurs with quenching of the p-coumaric acid fluorescence with increasing concentration of naringenin chalcone. We propose a Förster energy transfer mechanism is operative via the formation of dipole–dipole interactions between p-coumaric acid and naringenin chalcone. To our knowledge, this is the first demonstration in plants of a synergic effect between two classes of phenolics to bypass the potentially damaging effects of UVR

Exploring the blueprint of photoprotection in Mycosporine-like Amino Acids

Microorganisms require protection against the potentially damaging effects of ultraviolet radiation exposure. Photoprotection is, in part, provided by mycosporine-like amino acids (MAAs). Previous reports have proposed that nonradiative decay mediates the impressive photoprotection abilities of MAAs. In this letter, we present the first ultrafast dynamics study of two MAAs, shinorine and porphyra-334. We demonstrate that, in aqueous solution, these MAAs relax along their S1 coordinates toward the S1/S0 conical intersection within a few hundred femtoseconds after photoexcitation and then traverse the conical intersection and vibrationally cool in approximately 1 ps through heat transfer to the solvent. This new insight allows a quintessential component of microbial life to be unraveled and informs the development of molecular photon-to-heat converters for a myriad of applications

Ultrafast Spectroelectrochemistry of the Catechol/o‐Quinone Redox Couple in Aqueous Buffer Solution

Eumelanin is a natural pigment found in many organisms that provides photoprotection from harmful UV radiation. As a redox‐active biopolymer, the structure of eumelanin is thought to contain different redox states of quinone, including catechol subunits. To further explore the excited state properties of eumelanin, we have investigated the catechol/o‐quinone redox couple by spectroelectrochemical means, in a pH 7.4 aqueous buffered solution, and using a boron doped diamond mesh electrode. At pH 7.4, the two proton, two electron oxidation of catechol is promoted, which facilitates continuous formation of the unstable o‐quinone product in solution. Ultrafast transient absorption (femtosecond to nanosecond) measurements of o‐quinone species involve initial formation of an excited singlet state followed by triplet state formation within 24 ps. In contrast, catechol in aqueous buffer leads to formation of the semiquinone radical Δt>500 ps. Our results demonstrate the rich photochemistry of the catechol/o‐quinone redox couple and provides further insight into the excited state processes of these key building blocks of eumelanin