Highlights from the Faraday discussion on photoinduced processes in nucleic acids and proteins

Javier Segarra-Martía, Remya Ramakrishnanb, Javier Vinalsc and Ashley J. Hughes*d
aLaboratoire de Chimie UMR 5182, ENS de Lyon, 46 allée d'Italie, 69364, Lyon Cedex 07, France. E-mail: javier.segarra-marti@ens-lyon.fr
bIndian Institute of Science Education and Research Thiruvanathapuram, Vithura Campus, Maruthamala, Thiruvananthapuram, Kerala 695551, India. E-mail: remyaramakrishnan16@iisertvm.ac.in
cDepartment of Biochemistry, University of Oxford, South Parks Road, Oxford, OX13QU, UK. E-mail: javier.vinalscamallonga@st-hughs.ox.ac.uk
dB23, Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, UK. E-mail: ashley.hughes@diamond.ac.uk

Received 8th March 2018 , Accepted 8th March 2018

First published on 12th April 2018

Introduction and opening lecture

The Faraday meeting on photoinduced processes in nucleic acids and proteins was held in The Residency Hotel, Thiruvananthapuram, India in January 2018, continuing the meetings initiated by the Royal Society over 110 years ago, with the first meeting taking place in London in 1907. The discussions, originally held exclusively in the UK, have grown from three a year to incorporate seven meetings annually, and they are now held both domestically and internationally. This meeting brought together over eighty scientists from around the globe to discuss advances in photoinduced processes relating to proteins and nucleic acids.

Faraday Discussions are unique international discussion meetings that focus on rapidly developing areas of chemistry and its interfaces with other scientific disciplines. Each one is opened by an introductory lecturer who sets the stage for the discussion. The Faraday discussions have a unique structure which distinguishes them from other conferences. The main talks are all focused on pre-released manuscripts that have been studied in advance of the meeting by the attendees. This leads to a discussion-focused format, whereby talks are limited to only five minutes and are followed by 15 minutes of discussion by delegates following the presentation. This is then rounded off by a general discussion at the end of each session involving all of that session's speakers for a further twenty minutes. At all stages of these discussions, participation is encouraged from all delegates, from the leaders in the field to the new PhD candidates in attendance, and contributions from all are considered. The format of the conference therefore places a focus on debate and discussion of the work being presented. This enables the attendees to concentrate on the pre-published manuscripts and occasionally challenge each others’ views, leading to an intellectual discussion that encourages many new ideas, questions and hypotheses, expanding the knowledge in their field. The format fosters interest in their peers’ work, which in many instances leads to ideas enabling the presenter to expand their research. These comments not only make people think critically about their work, but also help them to improve their research and envision possibilities that they may not have previously considered.

The discussions could be quite lively and pleasingly involved both senior and junior attendees. There was an interesting mix of questions – some people focused on the ‘big picture’ of the project, taking a step back to clearly see the whole, while others were more interested in the important details and techniques that the presenting authors might have not noticed before. In addition to the 24 speakers spread over the 3 days, there were also 10 invited ‘lightning talks’ and 32 posters presented, giving every member a chance to discuss their work and share their results with a large network of peers. Whilst there were plenty of opportunities for formal, recorded discussions, there were also many opportunities for an informal exchange of views through the many breaks that broke up the day, as well as a well-attended conference dinner. The whole conference was flanked by opening and closing lectures of reputed researchers in the field, where they presented their work and introduced the topic of the conference in depth.

All comments and replies made during these captivating discussion sessions were recorded and will be published alongside the papers in the ‘Photoinduced Processes in Nucleic Acids and Proteins’ themed collection of the journal Faraday Discussions.

Opening lecture

The introductory lecture was given to us by the esteemed Professor of Biophysics Ilme Schlichting of the Max Planck institute in Heidelberg. She was subsequently awarded with the Spiers Memorial Award by the Royal Society of Chemistry (Fig. 1).
image file: c8cc90123f-f1.tif
Fig. 1 Professor Ilme Schlichting receiving the Spiers Memorial Award from the Royal Society of Chemistry. This award is given by Professor John Seddon, Faraday standing committee chair, following on from an immersing opening lecture, in recognition of an individual who has made an outstanding contribution to the field of a Faraday Discussion. Also featured in this photo are the scientific committee chairs Professor Anthony Watts (middle) and Dr Mahesh Hariharan (right).

The Spiers Memorial Award is presented once a year to the introductory lecturers who are likely to provide the most stimulating and wide-ranging introduction to the discussion. The receiver of the award is presented with a medal and a certificate by the RSC for their contributions to the field of a Faraday discussion.

Taking the mantle of introducing the delegates to the conference, Professor Schlichting initially introduced the wide scope of the field, from sensory proteins in plants to skin cancer and DNA photolesions. She then went on to describe the latest techniques by which dynamics can be followed in photoreactive species. The earlier section of the presentation ran the delegates through how UV irradiation leads to DNA photolesions and is then repaired via a group of proteins known as DNA photolyases. These photolyases are monomeric proteins similar to cryptochromes which bind more strongly to DNA than undamaged DNA (105-fold stronger). They use fully reduced FADH cofactor in order to be catalytically active. DNA repair is driven via blue light absorption (photoreactivation), and the photoreduction of FAD/FADH˙ (photoactivation) is driven via visible light absorption in the presence of reducing agents. Professor Schlichting used this as an example to illustrate how photolyases work specifically and how this process is entirely triggered by light, demonstrating a photoinduced process in nucleic acids in depth.

The talk then moved on to cover cutting edge experimental technology for those wishing to study the dynamics of photoswitching in proteins. Time-resolved crystallography can be used to this end to study the dark, intermediate and light states of photoswitchable biomolecules, with a previously unobtainable level of precision using X-ray free electron light (X-FEL) sources. These light sources open up new possibilities owing to their high brilliance and femtosecond (fs) pulse lengths. To exemplify the use of X-FEL sources in this field, the example of the reversibly switchable fluorescent protein rsEGFP2 was used. In this experiment, 1 and 3 picosecond (ps) time delays were used within a pump (400 nm, 230 fs)–probe (9.5 keV) setup capturing the initial isomerisation intermediate state. In addition, she gave different examples of well-known proteins and the experiments performed on them using X-FEL, such as bacteriorhodopsin or myoglobin. Professor Schlichting showed the audience the range of questions that X-FEL can help to answer, specially pointing out the time points at which data can be recorded, something that was limited to Synchrotrons before X-FEL became available. To conclude the talk, some time was given to discuss other ultra-fast techniques to study sub-ps time scale events in myoglobin – specifically, the displacement of the heme group from the 0.5 to 150 ps time scale. This concluded in a proposal of a general allosteric mechanism for the transport of local binding energy to remote sites in proteins. Due to time constraints, there were no questions for Professor Schlichting after the introductory lecture, but the attendees took advantage of the coffee breaks to discuss and ask questions about her research and X-FEL. These discussions lead to an impromptu workshop at the end of the conference for some of the student attendees.

Session one: light-induced charge and energy transport in nucleic acids and proteins

The conference started with a session on light-induced charge and energy transport in nucleic acids and proteins. The session was chaired by Dr Mahesh Hariharan (Indian Institute of Science Education and Research, Thiruvananthapuram), who explained that the sessions would consist of a 5 minute presentation followed by 15 minutes of questions for each presenter. The session was kicked off by Professor Gebhard Schertler (Paul Scherrer Institute, Switzerland) on ‘The role of water molecules in phototransduction of retinal proteins and G protein-coupled receptors’ (Paper: 16404, DOI: 10.1039/c7fd00207f). It was explained how water molecules can have a significant role in the changes that occur after activation, such as stabilising the overall structure of the protein when active or inactive through hydrogen bonding, or providing a hydrophilic environment for polar ligands and amino acids in the protein. He concluded that water molecules were essential in the function of membrane proteins, and emphasised the newly available opportunity to use X-ray free electron lasers to analyse water interactions within a protein in more detail.

Following on from this first presentation, Dr Arijit K. De (Indian Institute of Science Education and Research, Mohali, India) presented his work ‘Probing the excited state dynamics of Venus: origin of dual-emission in fluorescent proteins’ (Paper: 17076, DOI: 10.1039/c7fd00187h). Through the use of picosecond fluorescence measurements and femtosecond pump–probe spectroscopy, he explained and discussed the excited state dynamics of the Venus protein when UV photoexcitation leads to dual fluorescence emission. In order to do this, they drew a comparison between Venus and wt-GFP. Through a combination of steady-state and lifetime measurements, they proposed a general mode for fluorescent proteins. Following this presentation, there was a lively discussion for 15 minutes with various questions on the topic.

To finish the first part of the first session, Professor Stefan Haacke (University of Strasbourg, France) took the stage and presented his work ‘Effect of point mutations on the ultrafast photoisomerization of Anabaena sensory rhodopsin’ (Paper: 17086, DOI: 10.1039/c7fd00200a). The work focused on the effect of point mutations on excited state lifetimes (ESL) in the all-trans, 15-anti (AT) and the 13-cis, 15-syn (13C) isomers of the protonated Schiff base of retinal (PSBR). They reported the first detailed study on point mutation in Anabaena sensory rhodopsin and the vibrational spectra of the primary photoproducts, KAT and K13C.

Once the three speakers had presented their work, they were reunited on stage for half an hour, where a lively discussion took place with several questions asked by the audience and themselves. They highlighted how their work was related and what challenges to look for in the field. Afterwards, there was a break with tea and biscuits where the attendees of the conference mingled, talked to each other and sought opportunities to question the speakers on their work.

After the break, we reunited for the second part of the session, chaired by Professor Richard Cogdell (University of Glasgow, United Kingdom). The session started with a presentation by Dr Ganga Periyasami from Bangalore University on the paper ‘Computational studies on ground and excited state charge transfer properties of peptidomimetics’ (Paper: 16453, DOI: 10.1039/c7fd00183e). She went on to talk about peptidomimetics, specially regarding ureidopeptides. The work focused on various substituents, where the ligands at different positions were modified chemically. By studying in-depth hole migrations after ionization, they concluded that this migration occurs in one direction, from the ureido to the carboxylate end, as in the unsubstitued ureidopeptides.

This was followed by Professor Rajaram Swaminathan from the Indian Institute of Technology Guwahati presenting his work ‘Protein charge transfer absorption spectra: an intrinsic probe to monitor structural and oligomeric transitions in proteins’ (Paper: 16629, DOI: 10.1039/c7fd00194k). Their work highlighted the utility of ProCharTS as a label-free intrinsic probe to monitor changes in protein charge, structure and oligomeric state. Throughout the presentation and paper he elaborated on how the ProCharTS absorption serves as an ideal label-free intrinsic probe to monitor protein aggregation in moderately-charged proteins.

The theme of the presentation on ProCharTS was continued by Dr R. Venkatramani from the Tata Institute of Fundamental Research, who presented his work ‘Optical backbone-sidechain charge transfer transitions in proteins sensitive to secondary structure and modifications’ (Paper: 16612, DOI: 10.1039/c7fd00203c). He presented a detailed computational study comparing the absorption of all amino acids that are charged under physiological conditions: Lys, Glu, Arg, Asp and His. Their results showed a direct bearing on the design of optical probes based on ProChaTS for monitoring the structure, dynamics and function of proteins that are rich in charged amino acids.

The last presentation of the afternoon was brought to us by Dr Igor Schapiro from the Hebrew University of Jerusalem, where he talked about his work ‘A QM/MM study of the initial excited state dynamics of green-absorbing proteorhodopsin’ (Paper: 16403. DOI: 10.1039/c7fd00198c). In the presentation, Dr Schapiro explained to the audience how the intended purpose of the article was to make an initial step towards closing the gap between ultrafast spectroscopic studies and computer simulations. This work was the first computational study on the ultrafast photochemistry in green proteorhodopsin (PR). They found that a key amino acid, Y200, could be key to delaying or accelerating the rate as well as the success rate of the isomerisation.

After the speakers had a chance to present and talk about their research, they gathered on stage again to talk about the session and answer some more questions from the audience. ProCharTS was a recurring topic in this session and it therefore received a fair amount of questions regarding its challenges and what the field might have in store for us in the future. Furthermore, there was some lively discussion with Dr Schapiro on his paper and the comparisons he drew between bacteriorhodopsin and his green proteorhodopsin. After the discussion, the session was closed by the chair and the audience thanked the speakers for their work, presentations and answers to the many questions asked by the attendees.

Session two: photocrosslinking between nucleic acids and proteins

The first half of this session was chaired by Professor Rienk van Grondelle (Vrije Universiteit Amsterdam, Netherlands), starting with a paper by Professor Dimitra Markovitsi (CEA Saclay, France), ‘Adenine radicals generated in alternating AT duplexes by direct absorption of low-energy UV radiation’ (Paper: 16408, DOI: 10.1039/c7fd00179g). The ionisation potential of isolated DNA/RNA nucleobases is rather high (∼8 eV) and low-energy (UV-A/B) radiation is thus not expected to generate cations in a sizeable yield. However, in this work, the authors showed that this counter-intuitive mechanism is indeed accessible through their combined study employing nanosecond time-resolved transient absorption spectroscopy and quantum mechanical calculations based on time-dependent density functional theory (TD-DFT). Reaction intermediates other than radicals, formed on the ms timescale directly from singlet excited states, were also identified at shorter wavelengths and were proposed as potential candidates for a precursor to the most abundant AT photoproduct formed in DNA duplexes.

Dr Roberto Improta (CNR, Italy) was up next, presenting his work ‘Photoactivated proton coupled electron transfer in DNA: insights from quantum mechanical calculations’ (Paper: 16486, DOI: 10.1039/c7fd00195a). The work assessed the two main proton-coupled electron transfer events that can potentially occur in DNA by means of employing fragment model systems of guanine–cytosine (GC) and adenine–thymine (AT) alternated duplexes containing up to four base pairs. Whereas an intra-strand charge transfer process is predicted to trigger inter-strand proton transfer involving the cytosine cation in GC, an analogous mechanism does not hold for AT, which is in agreement with the inference of time-resolved IR experiments. Interestingly, both types of system display inter-strand charge transfer coupled to inter-strand proton transfer that is closely placed to a crossing with the ground state, which could facilitate a relatively fast non-radiative deactivation route that may promote their photostability.

Dr Mahesh Hariharan (Indian Institute of Science Education and Research, Thiruvananthapuram, India) was the last speaker of the session on behalf of Professor Frederick D. Lewis (Northwestern University, USA) who unfortunately could not attend the meeting, and he presented the work on fluorescent excimers/exciplexes based on the purine base derivative 8-phenylethynyl-guanine (EG) in DNA hairpins (Paper: 16409, DOI: 10.1039/c7fd00186j). EG is a promising fluorescent DNA base that weakly perturbs the DNA hairpin upon its addition. The inclusion of EG adjacent to guanine resulted in the formation of short-lived (40–80 ps) exciplexes, and hairpins with two or three adjacent EG moieties displayed exciton-coupled circular dichroism in the ground state while forming long-lived fluorescent excited states upon absorption. The incorporated EG moieties were thus placed adjacent to neighbouring bases or other EG base analogues, which provides the close proximity required for exciplex/excimer formation, and whose properties were measured with three different time-resolved spectroscopic methods.

A short general discussion for 15 minutes was then held involving all three speakers prior to afternoon tea. During this discussion a few points were raised, mainly highlighting the difficulties faced by time-resolved experiments in long-lived (ms) regimes, the diverse monomer-based competing channels also accessible in dimeric and multimeric DNA systems, and the strong effect of neighbouring bases towards their specific ionisation potential, as well as the overall importance of excimer/exciplex formation in the photophysics of DNA.

The second part of the session was chaired by Dr Reji Varghese (Indian Institute of Science Education and Research Thiruvananthapuram, India), starting with a contribution from Dr Javier Segarra-Martí (ENS de Lyon, France) that dealt with the simulation of two-dimensional electronic spectroscopy (2DES) in DNA/RNA aggregates, focusing on solvated adenine–adenine monophosphate (ApA) as a test case (Paper: 16770, DOI: 10.1039/c7fd00201g). 2DES has increased in popularity and availability in recent times, and this study showed the potential benefits of these multidimensional spectroscopic methods over established techniques such as standard pump–probe spectroscopy when treating multimeric systems. A main spectral fingerprint was characterised and used to monitor the different conformations attained in the ApA dimeric system, showcasing the potential capabilities of 2DES to disentangle congested spectral windows and discern particular intermolecular interactions that might be obscured with 1D pump–probe set-ups.

Dr Padmaja P. Mishra (Saha Institute of Nuclear Physics, India) followed with a talk about the direct observation of how external forces mediate the conformational dynamics of an integration host factor (IHF, a DNA binding protein)-bound Holliway junction (Paper: 16276, DOI: 10.1039/c7fd00184c). The study investigated isomerisation dynamics under external forces as measured by single-molecule FRET methods, which highlights the imposed restrictions generated by such external stimuli that translate to an increase in the rigidity of the molecular system. Complex non-linear dynamics analyses were carried out to visualise the complex landscape of interconverting states arising due to the external forces, which increase the chaosity of the system at intermediate force values, demonstrating the applicability of non-linear dynamics analyses in the field of biology.

The last speaker of the session was Professor Bern Kohler (Ohio State University, USA), and his work focused on the time-resolved pump–probe characterisation of the excited state dynamics of mononucleotides and DNA strands in glyceline, a deep eutectic solvent (Paper: 16407, DOI: 10.1039/c7fd00205j). Glyceline, a 1[thin space (1/6-em)]:[thin space (1/6-em)]2 mole ratio mixture of choline chloride and glycerol, was shown to be able to retain to a certain degree the secondary structures of DNA present in aqueous solvent, which enables the determination of the impact of specific properties of the solvent with respect to water. Despite their similar conformations, large differences in the dynamics were observed in the different solvents, with a slower excited state decay and vibrational cooling in glyceline compared to water, while the fraction of the population in long-lived channels was lower. In an AT DNA duplex, water was suggested to favour intra-strand charge separation while glyceline promoted inter-strand deactivation channels involving neutral species, where the slower solvation dynamics of the more viscous glyceline may play a role, thus showing how excited state dynamics in nucleic acids are also highly sensitive to the solvent.

A general discussion followed where a series of common points were mentioned, highlighting solvent effects and their ability to heavily modulate the photophysics of DNA and the potential use of FRET measurements under external stimuli for disentangling conformations in biological systems in a more general manner. Upcoming 2DES experiments were also suggested as a potential tool to validate the points previously mentioned, as well as to separate the diverse tautomeric forms present in DNA/RNA nucleobases in solution which display vastly different excited state lifetimes.

Session three: Light induced damage and repair in nucleic acids and proteins

The first part of the third session was chaired by Professor Anthony Watts (University of Oxford, United Kingdom) and was kicked off by a paper presented by Professor Michael R. Jones (University of Bristol, UK) on the engineering of photoproteins from the bacteria Rhodobacter sphaeroides as effective agents within biohybrid photovoltaic materials (Paper: 16405, DOI: 10.1039/c7fd00190h). In this manuscript, Jones et al. describe a novel engineered reaction centre/light harvesting (RCLH) complex that is deficient in the PufX protein. The removal of this protein from the complex (RCLH1X) resulted in an increase in the overall complex stability when subjected to heat stress. The manuscript goes someway towards addressing the concerns that PufX-deficient RCLH1 complexes may not be suitable as components within biohybrid photoelectrochemical cells. The presented results demonstrate that they are in fact equally as effective in supporting photocurrents by interfacing the RCLH1 complexes with metal electrodes and measuring the photocurrent whilst dark and illuminated. This, in combination with the observed increased stability, thereby indicates a possible role for RCLH1X complexes in technological applications. The discussion after this presentation focused on potential mechanisms and the stacking of complexes, which is possible for up to 300 layers.

This was followed by a talk from Dr Tolga Karsili of Temple University (PA, USA) who led us through their paper on mechanistic insights into the photoinduced damage of DNA and RNA nucleobases (Paper: 16806, DOI: 10.1039/c7fd00188f). The paper focused on DNA/RNA photohydrates, a class of lesion formed from near-to-mid UV light absorption and subsequent free radical formation. The mechanism of this lesion formation was studied computationally using high-level structure theory (CASPT2) by mapping the excited state pathways with the associated water molecules. This was done in the gas phase, avoiding environmental perturbations. Following this, in the second part of the paper, the results were extrapolated to the bulk DNA environment in aqueous solution utilising quantum and classical methods (QM/MM:CASPT2/AMBER). The suggested photoreaction shows the ability of guanine to behave as a sensitiser for the splitting of water. This could have occurred as an initial step in the evolution of photosynthesis on a prebiotic earth. Questions and comments following the presentation discussed the expectations of proton transfer and the potential calculation of the absorption spectra. There were also several suggestions of ways to test the excellent theorertical work described within this manuscript experimentally.

The conference then broke for a 15 minute general discussion involving both speakers, followed by afternoon tea. During the general discussion, more questions were directed at the stability of Dr Jones' photoproteins, especially regarding whether water was likely to be an issue going forward. The afternoon tea break granted the opportunity for more informal discussion regarding the presentations and the general mingling of the delegates over tea, coffee and food.

Upon our return, we were treated to a paper presented to us by Professor Carlos E. Crespo-Hernandez from Case Western Reserve University (OH, USA) on the photochemical relaxation pathways of S6-methylthioinosine and O6-methylguanosine in solution (Paper: 17075, DOI: 10.1039/c7fd00193b). The second half of the session was chaired by Dr Dmitra Markovitsi. This manuscript investigated the by-products of enzymatic reactions in certain prodrugs. It is not known if these by-products are harmful to cells via an altered photochemistry. Here, the two by-products were exposed to UV-B radiation using broadband transient absorption spectroscopy, and mechanisms for the electronic relaxations were proposed which are supported by the steady-state absorption and emission measurements, as well as by singlet and triplet vertical excitation energies performed on a subset of ground-state conformational isomers. It was shown that S6-methylation decreases the population in the lowest energy triplet state whilst blueshifting the ground state spectrum. O6-Methylation also resulted in a <10-fold decrease in the rate of conversion to the ground state in acetonitrile and a 40-fold decrease in aqueous solution, and at the same time the ground state spectrum is red-shifted. Discussion following this presentation was varied, ranging from how lucky it is that DNA is photostable enough to allow the evolution of land-based life forms (there is evidence of selection pressure causing this, rather than luck) to the importance of these lesions in disease, especially in forms of cancer.

Finally, there was a presentation by Dr Angelo Giussani of the University of Bologna, Italy regarding the photoinduced formation mechanism of the thymine–thymine (6–4) adduct in DNA, utilising QM and MM approaches (Paper: 17083, DOI: 10.1039/c7fd00202e). This manuscript aims to add theoretical information to the photomechanism behind the creation of the thymine–thymine (6–4) adduct, which can be created when consecutive thymine nucleobases are exposed to UVB irradiation. The two questions investigated specifically were the intrinsic features of the photoreaction (e.g. the possibility of a reaction path along both the singlet and triplet manifolds) and the role of the non-reactive surroundings of the two thymines (e.g. the flexibility of the whole molecule). This furthers previously published work on reduced model systems of DNA by utilising a DNA hairpin whose quantum yield has been previously determined experimentally. The reaction was characterised with high-level QM/MM. The manuscript investigates a possible reaction pathway along the singlet and triplet states. The discussion following Dr Giussani’s presentation surrounded the triplet state and the possibility of reproducing it experimentally.

The two speakers were then invited back on stage for continued discussion regarding the two manuscripts before wrapping up for the day at 5 pm, leaving some free time before the evening’s conference meal took place at 7 pm.

Session four: Bionanophotonics

The first half of the fourth and final session on bionanophotonics, was chaired by Professor John Seddon (Imperial College London, UK), and commenced with a paper presented by Professor Amitabha Chattopadhyay (CSIR-Centre for Cellular and Molecular Biology, India) highlighting the ability of photobleaching image correlation spectroscopy to monitor the cholesterol-dependent oligomeric state of the G-protein-coupled serotonin1A receptor (Paper: 16401, DOI: 10.1039/c7fd00192d). Professor Chattopadhyay briefly described the photobleaching image correlation spectroscopy technique, wherein measuring the fluctuations in fluorescence intensity in space and the spatial autocorrelation function provides the cluster density. The change in cluster density upon photobleaching is governed by the oligomeric state of the protein. The results indicated that the serotonin1A receptors exist mainly as trimers with low contributions from monomers and dimers in the control cells. However, upon depletion of membrane cholesterol, the population of receptor dimers increased. The dimeric receptor was found to be the most active in terms of ligand binding capability. During the discussion, Professor Chattopadhyay mentioned some of the challenges concerning the analysis and size determination of the clusters. The discussion further moved on to the factors affecting the signalling function, which involves the environment in which the experiment is performed and the organization of the oligomers.

The next paper of the session was presented by Dr Ramapurath S. Jayasree (Sree Chitra Tirunal Institute for Medical Sciences and Technology, India), in which Dr Jayasree described a multifunctional nanosystem based on gold nanorods developed by themselves for cancer imaging and therapeutic applications (Paper: 16402, DOI: 10.1039/c7fd00185a). The surface-enhanced Raman scattering capability displayed by the gold nanorods makes them a suitable candidate for photothermal therapy and Raman imaging. The gold nanorod modified with polyethyleneglycol was conjugated with folic acid to achieve targeted drug delivery. Incorporation of the fluorescent chemotherapeutuic drug mitoxantrone into the nanorods facilitated chemotherapy and fluorescence imaging. The discussion after the presentation focused on the mechanism of drug release. The fluorescent drug attached to the gold nanorods via electrostatic interactions was released upon NIR laser irradiation, causing the switching off of the Raman signals. The Raman peaks were masked by the strong fluorescence from the released drug. Cell death was caused both by heat generation from the strong longitudinal NIR absorption of the gold nanorod and by the chemical activity of the drug mitoxantrone.

The third paper presented by Dr Ankona Datta (Tata Institute of Fundamental Research, India) focused on a Forster resonance energy transfer (FRET)-based assay for monitoring phospholipid-induced peptide coil–helix transitions that are conjectured to be significant in the context of proteins facilitating cytoskeletal rearrangements through membrane binding (Paper: 17078, DOI: 10.1039/c7fd00197e). In this paper, a 20 residue peptide (gel 150–169) from the actin-severing protein gelsolin was labelled with a tryptophan donor and IAEDANS acceptor pair. Donor–acceptor energy transfer studies in the presence of increasing concentrations of phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) phospholipids indicated that the coil–helix transition in gel 150–169 can take place at a low mol% and physiologically relevant concentrations of PI(4,5)P2. The positions of the donor–acceptor pair in the peptide were decided based on the inter-residue distance constraints obtained from molecular dynamics simulations of gel 150–169 performed by Dr Ravindra Vekatramani (Tata Institute of Fundamental Research, India). The discussion following the talk involved the relevance of taking into consideration the effect of spacers and the orientation of the donor–acceptor fluorophores in the computational study. The selectivity, binding capacity and nature of interaction between the phospholipid and the peptide were also topics that came up during the discussion.

A variety of concerns were raised during the general discussion and all three speakers took the central stage. Some of the questions raised were regarding the influence of the acidic nature of cancer cells on the mechanism of release of the drug, the possibility of inter-peptide donor–accepter energy transfer, and the effect of the polarity of the lipid environment during FRET studies conducted in the biological environment in general. The session as a whole enlightened the participants on the wide range of applications and the enormous potential encompassing the field of biophotonics. The young attendees learnt about the challenges involved when performing experiments in biological environments and the cautions that must be taken into account when interpreting the results. After the stimulating discussion session, there was a break for tea.

The second half of the fourth session, chaired by Professor Michael R. Jones (University of Bristol, UK), started off with a paper on the self-assembly of fullerene clusters on calf thymus DNA (CT-DNA) templates (Paper: 16576, DOI: 10.1039/c7fd00196g), presented by Dr Joshy Joseph (CSIR-National Institute for Interdisciplinary Science and Technology, India). In this paper, the diverse nature of the interactions of three monosubstituted fullerene derivatives possessing pyridinium, aniline or phenothiazine end groups (F-Py, F-An and F-PTz, respectively) with calf thymus DNA (CT-DNA) were examined using spectroscopic and imaging techniques. The F-An derivative was found to interact through chiral assemblies on the CT-DNA template leading to the formation of condensed aggregates of CT-DNA. The cationic derivative, F-Py, interacted with CT-DNA via electrostatic and groove binding interactions, leading to the precipitation of DNA, while the phenothiazine derivative, F-PTz, formed larger nanoclusters and failed to interact with CT-DNA. The discussion of the paper focused on the factors governing the size of the fullerene clusters, interaction of the clusters with CT-DNA, and the optical and morphological characteristics emerging from the binding of fullerene clusters on CT-DNA templates.

The final paper of the conference was presented by Professor Richard J. Cogdell (University of Glasgow, UK). Professor Cogdell talked about the two types of LH2 complex that occur when Rhodopsuedomonas acidophila strain 7050 is grown under high light (HL) and low light (LL) conditions (Paper: 16402, DOI: 10.1039/c7fd00191f). When the cells are grown under high light (HL) conditions, the major carotenoid in LH2 is rhodopin glucoside and the LH2 complex has its main Bchl a Qy bands at 800 and 850 nm. Under LL conditions, the LH2 complex contains rhodopinal glucoside as the major carotenoid, which is about 50% more efficient in aiding light harvesting than rhodopin glucoside, and the LH2 complex has its main Bchl a Qy bands at 800 and 820 nm. In this paper, Professor Cogdell et al. attempt to comprehend the changes in the photosynthetic membrane composition under different light conditions and energy transfer reactions occurring in B800–820 and B800–850 LH2 complexes by monitoring the absorption spectra over time. The discussion session was dominated by queries regarding the structures of the LH1 and LH2 complexes, changes in the absorption spectra of the two forms of the LH2 complexes, and the possibility of back electron transfer from LH1 back to LH2.

An extensive discussion (Fig. 3) with both of the speakers on the platform followed. The possibility of incorporating fullerene clusters into highly ordered 2D/3D DNA nanostructures constructed via DNA origami, the electron transfer in fullerene–DNA complexes, etc., were touched upon in relation to the paper presented by Dr Joseph on the assembly of fullerene clusters on DNA templates. In relation to Professor Cogdell's work, several questions were raised concerning the mechanism of light intensity detection, the reason for the effect of the carbon source (in which cells were grown) on the shift in absorption spectra, the apoprotein composition of the LH2 complexes under different light intensities, etc. The lively discussion apprised the audience of the intricate nature of photosynthetic mechanisms in microorganisms and the various features that are yet to be explored to get a complete picture. Professor Cogdell proposed that a detailed understanding of the light harnessing technique prevalent in photosynthetic organisms can provide guidelines for the design and engineering of highly efficient light harvesting and energy storage systems. The discussion expanded to broader areas, such as the outcome of the experiment if it was performed in natural habitats with low light, like deep oceans, and possible reasons for the absence of flexibility in the light harvesting mechanism exhibited by the evolutionarily advanced plant kingdom when compared to those found in photosynthetic bacteria.


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Fig. 2 All of the attendees at the conference posing for the traditional group photo.

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Fig. 3 Dr Joshy Joseph (left) and Professor Richard Cogdell (right) discussing each other's work during the general discussion.

Social + poster section

The end of the first day's sessions was an opportunity for some of the poster presenters to show off their work in short ‘lightning talks’. These talks aimed to highlight the best and most interesting work to be displayed in the following poster session. The talks allowed an additional 10 attendees, selected by the scientific committee, to talk – giving some early career researchers valuable experience in public speaking. Following the lightning talks, the poster session began, accompanied by sandwiches and soft drinks (Fig. 4). The session was well-attended and provided another chance for interesting and more informal discussion regarding work conducted across a variety of fields. The posters presented by student participants were assessed for prizes, and the winners were Ms Beena Kumari (IIT Gandhinagar, India) and Mr Vinayak Bhat (Indian Institute of Science Education and Research Thiruvananthapuram, India), who presented their work ‘Fluorescent naphthyl derivatives as preferential quadruplex DNA binders’ and ‘Secondary electron acceptor to modulate the rate of charge recombination in DNA’, respectively (Fig. 4).
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Fig. 4 (a) The poster session granted the opportunity for more work to be presented and discussed over sandwiches and soft drinks, (b and c) the best poster presentation prizes being awarded to Ms Beena Kumari and Mr Vinayak Bhat, respectively, by Professor John Seddon.

There was, of course, a large social element to the conference, giving the attendees the chance to network sociably with one another (Fig. 2), which is always a key element of these events. This allows for collaborations and contacts to be made that would otherwise be nearly impossible to establish via the more convenient means of email. The conference dinner on the second night was well-attended and featured the traditional ‘loving cup ceremony’, which acted as the ideal ice breaker around the tables (Fig. 5) and kick-started a night of pleasant conversation with our peers.


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Fig. 5 Instructions for the loving cup ceremony that started off the conference meal, a great ice breaker.

Aided by an open bar, the discussions over a delightful five course dinner of international delicacies were wide and varied. Some attendees took this chance to talk more about their research with other people and go into depth on some topics. Others used the opportunity to discuss future career paths, while everyone got to know each other personally and share common interests and hobbies. The evening meal was a time to create new friendships which could often, and indeed have, lead to new collaborations amongst the delegates.

Concluding remarks

Professor Rienk van Grondelle (VU Amsterdam, Netherlands) wrapped up the conference nicely with some very interesting concluding remarks where he used slides provided by the different speakers to connect the diverse topics covered during the discussion with a few common points (Fig. 6). These included, among others, the need to move to more accurate spectroscopic methods such as 2DES and to consider complementary approaches (i.e. more than a single spectroscopic method) in order to obtain a clear understanding of the underlying photoinduced phenomena. A keyword that kept repeating itself throughout the entire meeting and that was highlighted in the concluding remarks was charge transfer. Charge transfer was recognised to be central for understanding most of the photoinduced phenomena in biological systems and plays a key role in facilitating biological functions, as exemplified by the specific cases of the first work on vision mediation using rhodopsin, the intrinsic photostability of DNA/RNA and the photorepair mechanisms triggered upon photodamage by proteins known as DNA photolyases. These are just a few of the many examples showcased, and they nicely brought together the seemingly very different talks during the meeting via a few common trends that they all shared.
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Fig. 6 Professor Rienk van Grondelle delivering the concluding lecture.

The importance of quantum coherence towards understanding photoinduced electron transfer phenomena in biological systems was then highlighted, showcasing the concept with an example from Professor Rienk van Grondelle’s own work on light harvesting complexes, where vibronic coherence was suggested to facilitate the charge transfer mechanisms in such intricate systems (Fig. 6). The potential role played by quantum coherence in other systems, such as those of biological relevance outlined above was also suggested, a possibility which is often ignored and where more traditional mechanisms are usually preferred to explain the underlying electronic excited state phenomena mediating these light-induced biological processes. An improvised discussion session followed, wherein the role of coherence in enhancing the efficiency of charge separation in photosynthetic reaction centres was discussed, enlightening the audience on the several open questions that had arisen over the previous couple of days. Professor van Grondelle emphasized the need to get a complete physical picture of the processes taking place in photosynthetic reaction centres for the design of highly efficient and robust light harvesting systems. The discussion offered an opportunity for the attendees to add their comments and contribute to the culmination of the three day-long conference.

Acknowledgements

Dr A. Hughes would like to acknowledge funding from Diamond Light Source (B23) and also funding received from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska–Curie grant agreement no. 665593 awarded to the Science and Technology Facilities Council. The authors would like to acknowledge the Faraday Division, Royal Society of Chemistry (Chemistry Biology Interface Division) and the Indian Institute of Science Education and Research, Thiruvananthapuram, for organising such an exciting scientific conference and for giving the authors an opportunity to meet so many new people in such an interesting part of the world. The authors would also like to kindly acknowledge Dr Mahesh Hariharan (Indian Institute of Science Education and Research, Thiruvananthapuram, India) for use of his photos taken during the event.

Footnotes

Present address: Department of Chemistry, Imperial College London, London, SW7 2AZ, UK.
These authors contributed equally to this work.

This journal is © The Royal Society of Chemistry 2018