'Off-On' Fluorescent Sensors for Physiological levels of Magnesium Ions based on Photoinduced Electron Transfer (PET) which also behave as OR Logic Gates

The fluorescence of molecules 1-3 is enhanced by factors of up to 67 in the presence of magnesium and calcium ions in neutral water which allows the selective monitoring of magnesium ions under simulated physiological conditions and permits the construction of truth tables with OR logic when these molecules are viewed as ion input-photon output molecuIar devices.

Direct Visual Indication of pH Windows: 'Off-On-Off' Fluorescent PET (Photoinduced Electron Transfer) Sensors/Switches

1–3, which contain a fluorophore and two proton receptors with opposite PET (photoinduced electron transfer) characteristics, only display strong fluorescence within a pH window whose position and width are tunable.

Arenedicarboximide Building Blocks for Fluorescent Photoinduced Electron Transfer pH Sensors Applicable with Different Media and Communication Wavelengths

N-(aminoalkyl)-4-chloronaphthalene-
1,8-dicarboximides 1, N-
(aminoalkyl)-4-acetamidonaphthalene-
1,8-dicarboximides 3 and N,N'-bis(aminoalkyl)-
perylene-3,4:9,10-tetracarboxydiimides
4 show good fluorescent off ±
on switching in aqueous alcoholic solution
with protons as required for fluorescent
PET sensor design. The excitation
wavelengths lie in the ultraviolet
(lmaxˆ345 and 351 nm) for 1 and 3 and
in the blue-green (lmaxˆ528, 492 and
461 nm) for 4; the emission wavelengths
lie in the violet (lmaxˆ408 nm) for 1, in
the blue (lmaxˆ474 nm) for 3 and in the
yellow-orange (lmaxˆ543 and 583 nm)
for 4. Compound 4b shows substantial
fluorescence enhancement with protons
when immobilized in a poly(vinylchloride)
matrix, provided that 2-nitrophenyloctyl
ether plasticizer and potassium
tetrakis(4-chlorophenyl)borate additive
are present to prevent dye crystallization
and to facilitate proton diffusion
into the membrane, respectively.

A small supramolecular system which emulates the unidirectional, path-selective photoinduced electron transfer (PET) of the bacterial photosynthetic reaction centre (PRC)

The singlet excited state of the 4-aminonaphthalimide fluorophore in 1a and 1b directs electron transfer from intramolecular but external amine groups along only one of two available paths.

Measurement of Local Sodium Ion Levels near Micellar Surfaces with Fluorescent PET (Photoinduced Electron Transfer) Sensors

Na+ near membranes controls our nerve signals, besides several other crucial bioprocesses. We demonstrate that fluorescent PET (photoinduced electron transfer) sensor molecules target Na+ in nanospaces near micellar membranes with excellent discrimination against H+. They find that Na+ near anionic micelles is concentrated by factors of upto 160. Sensor molecules which are not held tight to the micelle surface find a Na+ amplification factor of 8 only. These findings are strengthened by the employment of control compounds whose PET processes are permanently ‘on’ or permanently ‘off’.

Contribution of direct electron transfer mechanisms to overall electron transfer in microbial fuel cells utilising Shewanella oneidensis as biocatalyst

Objectives To investigate the contribution of direct electron transfer mechanisms to electricity production in microbial fuel cells by physically retaining Shewanella oneidensis cells close to or away from the anode electrode. Results A maximum power output of 114 ± 6 mWm−2 was obtained when cells were retained close to the anode using a dialysis membrane. This was 3.5 times more than when the cells were separated away from the anode. Without the membrane the maximum power output was 129 ± 6 mWm−2. The direct mechanisms of electron transfer contributed significantly to overall electron transfer from S. oneidensis to electrodes, a result that was corroborated by another experiment where S. oneidensis cells were entrapped in alginate gels. Conclusion S. oneidensis transfers electrons primarily by direct electron transfer as opposed to mediated electron transfer.

The electron transfer complex between nitrous oxide reductase and its electron donors

J Biol Inorg Chem (2011) 16:1241–1254 DOI 10.1007/s00775-011-0812-9

Electron transfer chains in sulfate reducing bacteria

Dissertação para a obtenção de grau de doutor em Bioquímica pelo Instituto de Tecnologia Química e Biológica. Universidade Nova de Lisboa.

Orientation of Non-Native 2-Monosubstituted and 2,3-Disubstituted 1,4-Naphthoquinones in the A1 binding site of PSI and the effect on the rate of electron transfer : an electron paramagnetic resonance spectroscopy study

The proce-ss ofoxygenic photosynthesis is vital to life on Earth. the central event in photosynthesis is light induced electron transfer that converts light into energy for growth. Ofparticular significance is the membrane bound multisubunit protein known as Photosystem I (PSI). PSI is a reaction centre that is responsible for the transfer of electrons across the membrane to reduce NADP+ to NADPH. The recent publication ofa high resolution X-ray structure of PSI has shown new information about the structure, in particular the electron transfer cofactors, which allows us to study it in more detail. In PSI, the secondary acceptor is crucial for forward electron transfer. In this thesis, the effect of removing the native acceptor phylloquinone and replacing it with a series of structurally related quinones was investigated via transient electron paramagnetic resonance (EPR) experiments. The orientation of non native quinones in the binding site and their ability to function in the electron transfer process was determined. It was found that PSI will readily accept alkyl naphthoquinones and anthraquinone. Q band EPR experiments revealed that the non-native quinones are incorporated into the binding site with the same orientation of the headgroup as in the native system. X band EPR spectra and deuteration experiments indicate that monosubstituted naphthoquinones are bound to the Al site with their side group in the position occupied by the methyl group in native PSI (meta to the hydrogen bonded carbonyl oxygen). X band EPR experiments show that 2, 3- disubstituted methyl naphthoquinones are also incorporated into the Al site in the same orientation as phylloquinone, even with the presence of a halogen- or sulfur-containing side chain in the position normally occupied by the phytyl tail ofphylloquinone. The exception to this is 2-bromo-3-methyl --.- _. -. - -- - - 4 _._ _ _ - _ _ naphthoquinone which has a poorly resolved spectrum, making determination of the orientation difficuh. All of the non-native quinones studied act as efficient electron acceptors. However, forward electron transfer past the quinone could only be demonstrated for anthraquinone, which has a more negative midpoint potential than phylloquinone. In the case of anthraquinone, an increased rate of forward electron transfer compared to native PSI was found. From these results we can conclude that the rate ofelectron transfer from Al to Fx in native PSI lies in the normal region ofthe Marcus Curve.

Electron Transfer Involving the Phylloquinone (A1) Cofactor of Photosystem I Examined with Time Resolved Absorbance and Electron Paramagnetic Resonance Spectroscopy

The dependence of the electron transfer (ET) rate on the Photosystem I (PSI) cofactor phylloquinone (A1) is studied by time-resolved absorbance and electron paramagnetic resonance (EPR) spectroscopy. Two active branches (A and B) of electron transfer converge to the FX cofactor from the A1A and A1B quinone. The work described in Chapter 5 investigates the single hydrogen bond from the amino acid residue PsaA-L722 backbone nitrogen to A1A for its effect on the electron transfer rate to FX. Room temperature transient EPR measurements show an increase in the rate for the A1A- to FX for the PsaA-L722T mutant and an increased hyperfine coupling to the 2-methyl group of A1A when compared to wild type. The Arrhenius plot of the A1A- to FX ET in the PsaA-L722T mutant suggests that the increased rate is probably the result of a slight change in the electronic coupling between A1A- and FX. The reasons for the non-Arrhenius behavior are discussed. The work discussed in Chapter 6 investigates the directionality of ET at low temperature by blocking ET to the iron-sulfur clusters FX, FA and FB in the menB deletion mutant strain of Synechocyctis sp. PCC 6803, which is unable to synthesize phylloquinone, by incorporating the high midpoint potential (49 mV vs SHE) 2,3-dichloro-1,4-naphthoquinone (Cl2NQ) into the A1A and A1B binding sites. Various EPR spectroscopic techniques were implemented to differentiate between the spectral features created from A and B- branch electron transfer. The implications of this result for the directionality of electron transfer in PS I are discussed. The work discussed in Chapter 7 was done to study the dependence of the heterogeneous ET at low temperature on A1 midpoint potential. The menB PSI mutant contains plastiquinone-9 in the A1 binding site. The solution midpoint potential of the quinone measures 100 mV more positive then wild-type phylloquinone. The irreversible ET to the terminal acceptors FA and FB at low temperature is not controlled by the forward step from A1 to FX as expected due to the thermodynamic differences of the A1 cofactor in the two active branches A and B. Alternatives for the ET heterogeneity are discussed.