Boron nitride photocatalysts for solar fuel synthesis

Reshaping our global energy portfolio in light of the rising anthropogenic CO2 emissions is paramount. Solar fuel production via photocatalysis constitutes a sustainable energy generation route, allowing one to harness the abundance of sunlight for CO2 transformation. In this thesis, we develop a new materials platform for boron nitride (BN) photocatalysts in solar fuel synthesis. We present a proof-of-concept for a porous boron oxynitride (BNO) photocatalyst facilitating gas phase CO2 capture and photoreduction, without doping or cocatalysts. We then present two routes to enhance light harvesting and photoactivity in BN: boron- and oxygen doping. Boron doping yielded B-BNO, the first water-stable, photoactive BN material, facilitating liquid phase H2 evolution under deep visible irradiation (λ > 550 nm) and gas phase CO2 photoreduction. In parallel, we demonstrate that tuning the oxygen content in BNO can lower and vary light harvesting to the deep visible region. Using a systematic design of experiments process, we tune and predict the chemical, paramagnetic and optoelectronic properties of BNO. We probe the role of free radicals and paramagnetic states on the photochemistry of BNO using a combined experimental, computational and first-principles approach. The family of BN photocatalysts all exhibit unique paramagnetism, shown to arise from free radicals in isolated OB3 sites, which we unequivocally confirm as the governing state for red-shifted light harvesting and photoactivity in BNO. Finally, we explore a new avenue in BN photocatalyst design and present the first example of semiconducting BNO quantum dots for CO2 photoreduction. The evolution rates, quantum efficiencies, and selectivities of all the BN materials surpassed P25 TiO2 and graphitic carbon nitride - benchmark photocatalysts in the field. Overall, this thesis opens the door to a radically new generation of BN-based photocatalysts for solar fuels synthesis.Open Acces

Targeted Detection of G-Quadruplexes in Cellular RNAs.

The G-quadruplex (G4) is a non-canonical nucleic acid structure which regulates important cellular processes. RNA G4s have recently been shown to exist in human cells and be biologically significant. Described herein is a new approach to detect and map RNA G4s in cellular transcripts. This method exploits the specific control of RNA G4-cation and RNA G4-ligand interactions during reverse transcription, by using a selective reverse transcriptase to monitor RNA G4-mediated reverse transcriptase stalling (RTS) events. Importantly, a ligation-amplification strategy is coupled with RTS, and enables detection and mapping of G4s in important, low-abundance cellular RNAs. Strong evidence is provided for G4 formation in full-length cellular human telomerase RNA, offering important insights into its cellular function.This study is supported by a European Research Council Advanced grant to S.B. and supports C.K.K., and the Croucher Foundation for a fellowship to C.K.K. We thank Dr. M. Di Antonio, V. Chambers, and G. Mclnroy for providing comments on the manuscript.This is the final version of the article. It first appeared from Wiley via http://dx.doi.org/10.1002/anie.20150089

Single genome retrieval of context-dependent variability in mutation rates for human germline

Abstract Background Accurate knowledge of the core components of substitution rates is of vital importance to understand genome evolution and dynamics. By performing a single-genome and direct analysis of 39,894 retrotransposon remnants, we reveal sequence context-dependent germline nucleotide substitution rates for the human genome. Results The rates are characterised through rate constants in a time-domain, and are made available through a dedicated program (Trek) and a stand-alone database. Due to the nature of the method design and the imposed stringency criteria, we expect our rate constants to be good estimates for the rates of spontaneous mutations. Benefiting from such data, we study the short-range nucleotide (up to 7-mer) organisation and the germline basal substitution propensity (BSP) profile of the human genome; characterise novel, CpG-independent, substitution prone and resistant motifs; confirm a decreased tendency of moieties with low BSP to undergo somatic mutations in a number of cancer types; and, produce a Trek-based estimate of the overall mutation rate in human. Conclusions The extended set of rate constants we report may enrich our resources and help advance our understanding of genome dynamics and evolution, with possible implications for the role of spontaneous mutations in the emergence of pathological genotypes and neutral evolution of proteomes

Pilot embedding for channel estimation and tracking in OFDM systems

Journal ArticleAbstract-We consider the problem of channel estimation and tracking in OFDM systems and explore the idea of adding pilot symbols to the data symbols as a means to conserve bandwidth. The term pilot embedding (PE) is used to refer to this scheme. Compared to the pilot insertion (PI) scheme, i.e., the conventional pilot symbol assisted modulation (PSAM), PE is more bandwidth efficient since no separate subcarriers/timeslots are allocated to pilots. We formalize this by evaluating the capacity of the two schemes and showing that PE indeed has the potential to transmit at a higher rate. The problem of channel tracking using a decision directed approach is reviewed and found to be unreliable, in the sense that the channel estimator fails to track the channel variations after some iterations because of unavoidable decision errors. We propose an ad hoc channel estimation algorithm that uses the embedded pilots along with the past decisions of data for reliable tracking of the channel

Unusual Activity of a Chlamydomonas TET/JBP Family Enzyme.

The Great Oxygenation Event, which occurred on earth around 2.45 billion years ago, opened up the niche for enzymes that could directly oxidize substrates using molecular oxygen (O2), including the 2-oxoglutarate (2OG) and Fe(II)-dependent dioxygenases. 2OGFe-dioxygenases possess a double-stranded β-helix, with an iron center chelated by two histidines and an aspartate.(1) 2OGFe-dioxygenases catalyze the incorporation of one atom of O2 into 2-oxoglutarate, oxidizing it to succinate, and the second atom into an organic substrate. The AlkB family and related clades catalyze this reaction on alkyl adducts on nitrogens of bases, whereas the TET/JBP family catalyzes the oxidation of methyl groups attached to carbons of bases.(1) As enzymes that generate epigenetic marks by modifying DNA or RNA, members of both the AlkB and TET/JBP families have been repeatedly recruited to different eukaryotic lineages

The structure and function of DNA G-Quadruplexes

Guanine-rich DNA sequences can fold into four-stranded, non-canonical secondary structures called G-quadruplexes (G4s). G4s were initially considered a structural curiosity, but recent evidence suggests their involvement in key genome functions such as transcription, replication, genome stability, and epigenetic regulation, together with numerous connections to cancer biology. Collectively, these advances have stimulated research probing G4 mechanisms and consequent opportunities for therapeutic intervention. Here, we provide a perspective on the structure and function of G4s with an emphasis on key molecules and methodological advances that enable the study of G4 structures in human cells. We also critically examine recent mechanistic insights into G4 biology and protein interaction partners and highlight opportunities for drug discovery.The Balasubramanian laboratory is core-funded by Cancer Research UK ( C14303/A17197 ); Cancer Research UK programme ( C9681/A18618 ); S.B. is a Welcome Trust Senior Investigator ( 099232/Z/12/Z ); J.S. gratefully acknowledges funding from the EU H2020 Framework Programme ( H2020-MSCA-IF-2016 , ID: 747297-QAPs )

Exact Quantum Algorithms for Quantum Phase Recognition: Renormalization Group and Error Correction

We explore the relationship between renormalization group (RG) flow and error correction by constructing quantum algorithms that exactly recognize 1D symmetry-protected topological (SPT) phases protected by finite internal Abelian symmetries. For each SPT phase, our algorithm runs a quantum circuit which emulates RG flow: an arbitrary input ground state wavefunction in the phase is mapped to a unique minimally-entangled reference state, thereby allowing for efficient phase identification. This construction is enabled by viewing a generic input state in the phase as a collection of coherent `errors' applied to the reference state, and engineering a quantum circuit to efficiently detect and correct such errors. Importantly, the error correction threshold is proven to coincide exactly with the phase boundary. We discuss the implications of our results in the context of condensed matter physics, machine learning, and near-term quantum algorithms.Comment: 10 pages + appendices v2: extended discussion on RG convergence; added ref

Structural Analysis using SHALiPE to Reveal RNA G-Quadruplex Formation in Human Precursor MicroRNA

RNA G-quadruplex (rG4) structures are of fundamental importance to biology. A novel approach is introduced to detect and structurally map rG4s at single-nucleotide resolution in RNAs. The approach, denoted SHALiPE, couples selective 2'-hydroxyl acylation with lithium ion-based primer extension, and identifies characteristic structural fingerprints for rG4 mapping. We apply SHALiPE to interrogate the human precursor microRNA 149, and reveal the formation of an rG4 structure in this non-coding RNA. Additional analyses support the SHALiPE results and uncover that this rG4 has a parallel topology, is thermally stable, and is conserved in mammals. An in vitro Dicer assay shows that this rG4 inhibits Dicer processing, supporting the potential role of rG4 structures in microRNA maturation and post-transcriptional regulation of mRNAs.This is the accepted manuscript. The final version is available at http://dx.doi.org/10.1002/anie.201603562