Synthesis and characterization of new flavin systems with biomimetic and photovoltaic applications

This thesis describes the incorporation of a flavin unit into a range of systems spanning photovoltaics and biomimetic self-assembly. The flavin unit is better known as a cofactor in a range of enzymes. However, the unique physical and self-assembly properties were exploited in this research programme to develop new systems with photovoltaic and biomimetic self-assembly applications. In Chapter 1 a general introduction relating to flavins and photovoltaics is provided. In Chapter 2, the aim was to explore the effect of the addition of fullerene to a range of acceptors in the expectation of forming new acceptor materials with a wide range of LUMO energies. In Chapter 3, the aim was to investigate the effect of coupling a flavin unit to a naphthalenediimides (NDI) unit in the expectation of forming hybrid materials for solar energy conversion. Chapter 4 describes the formation of conjugated polymers featuring a flavin moiety, in the expectation that these materials will have photovoltaic properties. Chapter 5 describes the synthesis of push-pull flavin systems with pH dependent visisble light absorption characteristics. Finally Chapter 6 describes the synthesis of water soluble ammonium salts to furnish new micelle based systems with hydrogen bonding recognition properties

Synthesis and Characterization of Naphthalenediimide-Functionalized Flavin Derivatives

Two acceptor–acceptor dyads have been synthesized featuring a flavin moiety and a naphthalenediimide (NDI) unit. The NDI unit is linked to the flavin through a short spacer group via either the N(3) or N(10) positions of the flavin. We have investigated the UV-Vis and redox properties of these multi-electron accepting systems which indicate that these materials display the collective properties of their component systems. Fluorescence spectroscopy measurements have revealed that their emission properties are dominated by the flavin unit

Correction: Zainalabdeen, N., et al., Synthesis and Characterization of Naphthalenediimide-Functionalized Flavin Derivatives. Int. J. Mol. Sci. 2013, 14, 7468–7479.

Note: In lieu of an abstract, this is an excerpt from the first page. In the original version of the manuscript [1] some of the analytical data for compounds 1 and 2 were incorrect. The correct NMR data are presented below. The authors apologize for any inconvenience this may have caused to the readers of this journal. Compound 1: 1H NMR (500 MHz, DMSO-d6) δ 11.64 (s, 1H), 8.73 (s, 4H), 8.57 (d, J = 1.4 Hz, 1H), 8.16 (dd, J = 8.9, 1.4 Hz, 1H), 7.81 (d, J = 8.5 Hz, 2H), 7.64 (d, J = 8.5 Hz, 2H), 6.99 (d, J = 8.9 Hz, 1H), 4.08 (t, J = 7.0 Hz, 2H), 3.28 (m, 2H), 1.69 (quin, J = 7.0 Hz, 2H), 1.33 (m, 8H), 0.86 (t, J = 6.8 Hz, 3H). 13C NMR (125 MHz, DMSO-d6) δ 162.6 (2xC = 0), 162.3 (2xC = 0), 158.9, 155.1, 151.9, 140.8, 136.6, 136.1, 135.2, 133.7, 131.1 (2xC), 130.5 (4xC), 130.3 (q, J = 4 Hz), 128.6 (q, J = 4 Hz), 128.4 (2xC), 126.6, 126.5 (2xC), 126.4 (q, J = 31 Hz), 126.3 (2xC), 126.2, 123.2 (q, J = 271 Hz), 117.8, 39.9, 30.9, 28.5, 28.3, 27.1, 26.3, 21.9, 13.7. Compound 2: 1H NMR (500 MHz, CDCl3) δ 8.77 (s, 4H), 8.58 (d, J = 1.4 Hz, 1H), 8.03 (dd, J = 9.1, 1.4 Hz, 1H), 7.87 (d, J = 8.4 Hz, 2H), 7.76 (d, J = 9.1 Hz, 1H), 7.27 (d, J = 8.4 Hz, 2H), 5.37 (s, 2H), 4.61 (br s, 2H), 4.19 (t, 2H), 2.47 (sept, J = 6.7 Hz, 1H), 1.74 (m, 2H), 1.47–1.23 (m, 10H), 1.07 (d, J = 6.7 Hz, 6H), 0.87 (t, J = 6.9 Hz, 3H). 13C NMR (125 MHz, CDCl3) δ 163.1 (2xC = O), 162.9 (2xC = O), 159.0, 155.0, 149.9, 138.9, 137.5, 135.2, 134.9, 134.3, 131.7 (2xC), 131.5 (2xC), 131.2 (q, J = 4 Hz), 131.1 (4xC), 130.9 (q, J = 4 Hz), 128.6 (2xC), 127.1 (2xC), 127.0 (q, J = 28 Hz), 126.8 (2xC), 123.1 (q, J = 270 Hz), 116.9, 51.5, 44.9, 41.2, 31.9, 29.4, 29.3, 28.2, 27.6, 27.2, 22.8, 20.2 (2xC), 14.2

Acceptability and feasibility of strategies to shield the vulnerable during the COVID-19 outbreak: a qualitative study in six Sudanese communities.

BACKGROUND: Shielding of high-risk groups from coronavirus disease (COVID-19) has been suggested as a realistic alternative to severe movement restrictions during the COVID-19 epidemic in low-income countries. The intervention entails the establishment of 'green zones' for high-risk persons to live in, either within their homes or in communal structures, in a safe and dignified manner, for extended periods of time during the epidemic. To our knowledge, this concept has not been tested or evaluated in resource-poor settings. This study aimed to explore the acceptability and feasibility of strategies to shield persons at higher risk of severe COVID-19 outcomes, during the COVID-19 epidemic in six communities in Sudan. METHODS: We purposively sampled participants from six communities, illustrative of urban, rural and forcibly-displaced settings. In-depth telephone interviews were held with 59 members of households with one or more members at higher risk of severe COVID-19 outcomes. Follow-up interviews were held with 30 community members after movement restrictions were eased across the country. All interviews were audio-recorded, transcribed verbatim, and analysed using a two-stage deductive and inductive thematic analysis. RESULTS: Most participants were aware that some people are at higher risk of severe COVID-19 outcomes but were unaware of the concept of shielding. Most participants found shielding acceptable and consistent with cultural inclinations to respect elders and protect the vulnerable. However, extra-household shielding arrangements were mostly seen as socially unacceptable. Participants reported feasibility concerns related to the reduced socialisation of shielded persons and loss of income for shielding families. The acceptability and feasibility of shielding strategies were reduced after movement restrictions were eased, as participants reported lower perception of risk in their communities and increased pressure to comply with social commitments outside the house. CONCLUSION: Shielding is generally acceptable in the study communities. Acceptability is influenced by feasibility, and by contextual changes in the epidemic and associated policy response. The promotion of shielding should capitalise on the cultural and moral sense of duty towards elders and vulnerable groups. Communities and households should be provided with practical guidance to implement feasible shielding options. Households must be socially, psychologically and financially supported to adopt and sustain shielding effectively

Synthesis and Characterization of Naphthalenediimide-Functionalized Flavin Derivatives

Two acceptor–acceptor dyads have been synthesized featuring a flavin moiety and a naphthalenediimide (NDI) unit. The NDI unit is linked to the flavin through a short spacer group via either the N(3) or N(10) positions of the flavin. We have investigated the UV-Vis and redox properties of these multi-electron accepting systems which indicate that these materials display the collective properties of their component systems. Fluorescence spectroscopy measurements have revealed that their emission properties are dominated by the flavin unit

Excited state charge redistribution and dynamics in the donor-π-acceptor flavin derivative ABFL

Chromophores containing a donor-π-acceptor (D-π-A) motif have been shown to exhibit many interesting photophysical properties. The lowest electronic transition of a flavin derivative containing this motif, azobenzylflavin (ABFL), has previously been shown to be highly sensitive to solvent environment and hydrogen bonding ligands. To better understand this sensitivity, we have investigated the excited state charge redistribution and dynamics of ABFL in a low-dielectric, non-hydrogen bonding solvent by steady-state Stark and femtosecond optical transient absorption spectroscopies. The Stark measurements reveal the difference dipole moment, Δμ01, between the ground and first excited states to be 22.3 ± 0.9 D. The direction of Δμ01 in the molecular frame was assigned with the aid of TD-DFT and finite field calculations, verifying the hypothesis that electron density moves from the diethylaniline donor to the flavin acceptor in the excited state. The magnitude of the difference dipole moment was used to estimate the hyperpolarizability of ABFL, β0 = 720 × 10–30 esu. Subsequent excited state decay via charge recombination was shown to take place in a few picoseconds. The data was best fit to a kinetic model composed of a sub-picosecond internal conversion step from S2→S1, followed by a 5 ps decay to the ground state. A competing process involving formation of an additional long-lived state from S1 was also observed. Cyclic voltammetry shows one oxidation and two reduction waves and is completely reversible. This analysis lays the groundwork for developing new flavin dyads with the desired excited electronic state properties for applications such as nonlinear optical devices, molecular electronics applications, or dye-sensitized solar cells