Excess Electron Transfer Research Articles

Mn-doping induced ferromagnetism and enhanced superconductivity inBi4−xMnxO4S3(0.075≤x≤0.15)

We demonstrate that Mn-doping in the layered sulfides Bi_4O_4S_3 leads to stable Bi_4-x Mn_x O_4 S_3 compounds that exhibit both long-range ferromagnetism and enhanced superconductivity for 0.075 < = x < = 0.15, with a possible record superconducting transition temperature (T_c) = 15 K among all BiS_2-based superconductors. We conjecture that the coexistence of superconductivity and ferromagnetism may be attributed to Mn-doping in the spacer Bi2O2 layers away from the superconducting BiS_2 layers, whereas the enhancement of T_c may be due to excess electron transfer to BiS_2 from the Mn4+/Mn3+-substitutions in Bi_2O_2. This notion is empirically corroborated by the increased electron-carrier densities upon Mn doping, and by further studies of the Bi_4-x A_x O_4 S_3 compounds (A = Co, Ni; x = 0.1, 0.125), where the T_c values remain comparable to that of the undoped Bi_4O_4S_3 system (= 4.5 K) due to lack of 4+ valences in either Co or Ni ions for excess electron transfer to the BiS_2 layers. These findings therefore shed new light on feasible pathways to enhance the T_c values of BiS_2-based superconductors.

An External Electric Field Manipulated Second-Order Nonlinear Optical Switch of an Electride Molecule: A Long-Range Electron Transfer Forms a Lone Excess Electron Pair and Quenches Singlet Diradical

An electride molecule e–···K(1)+···calix[4]pyrrole···K(2)+···e– as an external electric field (F) manipulated nonlinear optical (NLO) switch is designed theoretically for the first time. As this molecule is an unusual singlet diradical electride molecule with two easily driven excess electrons (by electric field) at two opposite ends of the molecule, a novel switching mechanism of electronic structure isomerization emerges as a distinctive nonbonding evolution in the electride molecule. A small electric field driving leads to a long-range excess electron transfer from one side K(1) through the middle calix[4]pyrrole to the other side K(2), forms a lone excess electron pair of s-type rather than a single bond, and quenches the singlet diradical. Meanwhile, the molecular electronic structure becomes K(1)+···calix[4]pyrrole···K(2)+···2e–. Therefore, the small electric field driving brings a very high static first hyperpolarizability (β0) contrast from 0 (F = 0, Off form) to 4.060 × 105 au (F = a small nonzer...

Sequence-Dependent Photocurrent Generation through Long-Distance Excess-Electron Transfer in DNA.

Given its well-ordered continuous π stacking of nucleobases, DNA has been considered as a biomaterial for charge transfer in biosensors. For cathodic photocurrent generation resulting from hole transfer in DNA, sensitivity to DNA structure and base-pair stacking has been confirmed. However, such information has not been provided for anodic photocurrent generation resulting from excess-electron transfer in DNA. In the present study, we measured the anodic photocurrent of a DNA-modified Au electrode. Our results demonstrate long-distance excess-electron transfer in DNA, which is dominated by a hopping mechanism, and the photocurrent generation is sequence dependent.

Examining cooperative binding of Sox2 on DC5 regulatory element upon complex formation with Pax6 through excess electron transfer assay.

Functional cooperativity among transcription factors on regulatory genetic elements is pivotal for milestone decision-making in various cellular processes including mammalian development. However, their molecular interaction during the cooperative binding cannot be precisely understood due to lack of efficient tools for the analyses of protein–DNA interaction in the transcription complex. Here, we demonstrate that photoinduced excess electron transfer assay can be used for analysing cooperativity of proteins in transcription complex using cooperative binding of Pax6 to Sox2 on the regulatory DNA element (DC5 enhancer) as an example. In this assay, BrU-labelled DC5 was introduced for the efficient detection of transferred electrons from Sox2 and Pax6 to the DNA, and guanine base in the complementary strand was replaced with hypoxanthine (I) to block intra-strand electron transfer at the Sox2-binding site. By examining DNA cleavage occurred as a result of the electron transfer process, from tryptophan residues of Sox2 and Pax6 to DNA after irradiation at 280 nm, we not only confirmed their binding to DNA but also observed their increased occupancy on DC5 with respect to that of Sox2 and Pax6 alone as a result of their cooperative interaction.

Computational Study of Excess Electron Mobility in High-Pressure Liquid Benzene

In recent years, excess electron transfer in organic liquids has attracted increasing interest owing to the emerging class of liquid organic semiconductors. In this study, to achieve a comprehensive understanding of electron conduction in liquids, we investigate hopping electron conduction in liquids from an atomistic viewpoint. High-pressure liquid benzene is chosen as a simple model system. Hopping electron mobility is computed using a combination of molecular dynamics simulations, quantum chemical calculations, and kinetic Monte Carlo methods. The computed electron mobility is in good agreement with the experimental values. Because the amplitude of the intermolecular vibration observed in liquids is larger compared to that in solids, the effect of dynamic disorder on electron mobility is investigated. The time scale of the change in electronic couplings due to the rotation of molecules is comparable to that of the electron residence time at each benzene molecule at the absence of change in the arrangement of a benzene dimer. Thus, the effect of dynamic disorder is evaluated by a Monte Carlo-based analysis. It is shown that the effect of dynamic disorder on electron mobility is small even though electronic couplings between molecules fluctuate by more than an order of magnitude.

Excess-Electron Transfer in DNA by a Fluctuation-Assisted Hopping Mechanism.

The dynamics of excess-electron transfer in DNA has attracted the attention of scientists from all kinds of research fields because of its importance in biological processes. To date, several studies on excess-electron transfer in consecutive adenine (A):thymine (T) sequences in donor-DNA-acceptor systems have been published. However, the reported excess-electron transfer rate constants for consecutive T's are in the range of 10(10)-10(11) s(-1) depending on the photosensitizing electron donor, which provides various driving forces for excess-electron injection into DNA. In this study, we employed a strongly electron-donating photosensitizer, a dimer of 3,4-ethylenedioxythiophene (2E), and an electron acceptor, diphenylacetylene (DPA), to synthesize a series of modified DNA oligomers (2-Tn, n = 3-6) in order to investigate the excess-electron transfer dynamics in these donor-DNA-acceptor systems using femtosecond laser flash photolysis. The relation between the free energy change for charge injection and the excess-electron transfer rate among consecutive T's provided an intrinsic excess-electron hopping rate constant of (3.8 ± 1.5) × 10(10) s(-1) in the DNA, which is consistent with the fluctuation frequency of the DNA sugar backbone and bases (3.3 × 10(10) s(-1)). Thus, we discuss the effect of structural fluctuations on the excess-electron hopping in DNA.

Introducing a New Concept of De-Radioactivity

De-radioactivity is characteristically opposed to the concept of radioactivity. The possible mechanism behind the concept of de-radioactivity involves the intra-trapping, intra-embedding and intra-fixing of the metallic radioisotope or stable isotope within the framework of the novel molecules loaded with the potential transfer of excess electrons to the metal nucleus to suppress the decay of the instable neutron to the proton and electron with the release of energy, stabilising the stable isotopes or metal radioisotopes so strongly as to result in zero dissociation of metal (stable isotope or metal radioisotope) and thus depriving metal radioisotope of its free status - an essential condition of metal radioisotope to decay. The whole study has been based on metal stable isotopes extendable to metal radioisotopes. The novel molecules (SSS-101, SSS-102, SSS-103 and SSS-104) which bring about intra-trapping and intra-fixing of the metal radioisotopes are called Radiostabilisers. Humanity may find a silver lining in this new concept for future safety with its possible wide spectrum practical applications. Radiostabilisers may help in the purification and reclaiming of metal radioisotope(s) contaminated sea-water or water, atmospherics and the nuclear liquid waste materials. The radiostabilisers fail to intra-trap the stable or radioisotopes of hydrogen, helium, carbon, boron, phosphorus, iodine, neon, argon, krypton, xenon, oxygen, fluorine, sulphur and chlorine.

Dynamics of Excess-Electron Transfer through Alternating Adenine:Thymine Sequences in DNA.

This paper presents the results of an investigation into the sequence-dependent excess-electron transfer (EET) dynamics in DNA, which plays an important role in DNA damage/repair. There are many published studies on EET in consecutive adenine:thymine (A:T) sequences (Tn), but those in alternating A:T sequences (ATn) remain limited. Here, two series of functionalized DNA oligomers, Tn and ATn, were synthesized with a strongly electron-donating photosensitizer, a trimer of ethylenedioxythiophene (3 E), and an electron acceptor, diphenylacetylene (DPA). Laser flash photolysis experiments showed that the EET rate constant of AT3 is two times lower than that of T3 due to the lack of π-stacking of Ts in AT3. Thus, it was indicated that excess-electron hopping is affected by the interaction between LUMOs of nucleotides.

How Does Guanine-Cytosine Base Pair Affect Excess-Electron Transfer in DNA?

Charge transfer and proton transfer in DNA have attracted wide attention due to their relevance in biological processes and so on. Especially, excess-electron transfer (EET) in DNA has strong relation to DNA repair. However, our understanding on EET in DNA still remains limited. Herein, by using a strongly electron-donating photosensitizer, trimer of 3,4-ethylenedioxythiophene (3E), and an electron acceptor, diphenylacetylene (DPA), two series of functionalized DNA oligomers were synthesized for investigation of EET dynamics in DNA. The transient absorption measurements during femtosecond laser flash photolysis showed that guanine:cytosine (G:C) base pair affects EET dynamics in DNA by two possible mechanisms: the excess-electron quenching by proton transfer with the complementary G after formation of C(•-) and the EET hindrance by inserting a G:C base pair as a potential barrier in consecutive thymines (T's). In the present paper, we provided useful information based on the direct kinetic measurements, which allowed us to discuss EET through oligonucleotides for the investigation of DNA damage/repair.

Driving Force Dependence of Charge Separation and Recombination Processes in Dyads of Nucleotides and Strongly Electron-Donating Oligothiophenes

Charge transfer in DNA has attracted great attention of scientists because of its importance in biological processes. However, our knowledge on excess-electron transfer in DNA still remains limited in comparison to numerous studies of hole transfer in DNA. To clarify the dynamics of excess-electron transfer in DNA by photochemical techniques, new electron-donating photosensitizers should be developed. Herein, a terthiophene and two 3,4-ethylenedioxythiophene oligomers were used as photosensitizers in dyads including natural nucleobases as electron acceptors. The charge separation and recombination processes in the dyads were investigated by femtosecond laser flash photolysis, and the driving force dependence of these rate constants was discussed on the basis of the Marcus theory. From this study, the conformation effect on charge recombination process was found. We expect that 3,4-ethylenedioxythiophene oligomers are useful in investigation of excess-electron-transfer dynamics in DNA.

Marcus理論に基づいたDNAの過剰電子輸送に関する理論的研究

DNAは電荷輸送特性を有し，生理的な機能のみならず電荷輸送デバイスとしての応用が期待されている．電荷輸送特性のうち，ホール移動に関して，実験的・理論的研究から多くの知見が得られてきた．しかしながら，過剰電子移動(EET)に対する知見は限定的である．本研究ではMarcus理論に基づいて，密度汎関数理論(DFT)レベルの量子化学計算によるDNA内EET速度の算出を試みた．隣接チミン間のEET速度の計算値(2.31 − 3.49 × 1010 s−1)は，実験値(4.4 ± 0.3 × 1010 s−1)を良く再現した．また，ミスマッチ(MM)塩基対を含む系に本手法を適用し，MM塩基対の挿入によるEET速度低下のメカニズムを明らかにした．

Enhancement of Excess Electron Transfer Efficiency in DNA Containing a Phenothiazine Donor and Multiple Stable Phenanthrenyl Base Pairs

EET grown ohm: Excess electron transfer (EET) was observed within a DNA duplex containing π-stacked phenothiazine as an electron donor, phenanthrenes as electron carriers and 5-bromouracil as an electron trap. Increasing the number of phenanthrenyl base pairs increased EET efficiency.

Charge transfer in DNA

In the past few decades, charge transfer in DNA has attracted considerable attention from researchers in a wide variety of fields ranging from bioscience and physical chemistry to nanotechnology. Charge transfer in DNA has been investigated using various techniques. Among them, time-resolved spectroscopic methods have provided information on charge-transfer dynamics in DNA, an important basis for therapy applications, nanomaterials, and so on. In charge transfer in DNA, holes and excess electrons act as positive and negative charge carriers, respectively. Hole-transfer (HT) dynamics have been investigated in detail, while the dynamics of excess electron transfer (EET) have only become clear rather recently. In the present paper, we summarize studies on the dynamics of HT and EET by several groups including ourselves.

97 Study on electron transfer through RNA/DNA duplex using pyrene and 5-bromouracil as an electron donor and acceptor pair

Because of potential applications in nanoscale devices, DNA-mediated charge transfer (CT) has attracted much interest. Through spectroscopic and chemical studies, it has been shown that both positive and negative charges injected into DNA bases can move through DNA over significant distances. The factors affecting to DNA-mediated CT are the nature of the charge donor and acceptor, the structural dynamics of DNA, and the intervening base sequences or the integrity of the base stacks. The last factor led to the electrochemical devices to detect the perturbations of DNA stacks such as a mismatch base pair. The photo-induced charge migration in DNA possessing a donor–acceptor pair has resulted in the long-lived charge separated state. This charge separation offers important insights for the development of photo-energy conversion devices such as solar cells. In contrast to the DNA-mediated CT, little attention has been paid for CT in a RNA duplex. Since RNA duplexes have the base stacking overlaps and dynamics that are significantly different from those of DNA–DNA as well as of DNA–RNA duplexes, they are another choice of attractive medium for CT. We have conducted the research on CT in RNA duplexes consisting of a pendant donor (pyrene) and acceptor (5-bromouracil or nitrobenzene) pair. We have found that long-range excess electron transfer occurs through RNA π-stacks with double exponential distance dependence. This finding should contribute to uncover the mechanism of RNA-mediated electron transfer and open a way for development of RNA-based devices that control electron migrations. By contrast, the pyrene-donor and 5-bromouracil-acceptor system indicates that DNA may not act as an efficient medium for the excess electron transfer.

Excess Electron Trapping in Duplex DNA: Long Range Transfer via Stacked Adenines

An understanding of charge transfer (CT) in DNA lies at the root of assessing the risks and benefits of exposure to ionizing radiation. Energy deposition by high-energy photons and fast-charged particles creates holes and excess electrons (EEs) in DNA, and the subsequent reactions determine the complexity of DNA damage and ultimately the risk of disease. Further interest in CT comes from the possibility that hole transfer, excess electron transfer (EET), or both in DNA might be used to develop nanoscale circuits. To study EET in DNA, EPR spectroscopy was used to determine the distribution of EE trapping by oligodeoxynucleotides irradiated and observed at 4 K. Our results indicate that stretches of consecutive adenine bases on the same strand serve as an ideal conduit for intrastrand EET in duplex DNA at 4 K. Specifically, we show that A is an efficient trap for EE at 4 K if, and only if, the A strand of the duplex does not contain one of the other three bases. If there is a T, C, or G on the A strand, then trapping occurs at T or C instead of A. This holds true for stretches up to 32 A's. Whereas T competes effectively against A for the EE, it does not compete effectively against C. Long stretches of T pass the majority of EE to C. Our results show that AT stretches channel EE to cytosine, an end point with significance to both radiation damage and the photochemical repair of pyrimidine dimers.

Distance Dependence of Triplet Energy Transfer in Water and Organic Solvents: A QM/MD Study

The possibility to optimize optoelectronic devices, such as organic light-emitting diodes or solar cells, by exploiting the special characteristics of triplet electronic states and their migration ability is attracting increased attention. In this study, we analyze how an intervening solvent modifies the distance dependence of triplet electronic energy transfer (TEET) processes by combining molecular dynamics simulations with quantum chemical calculations of the transfer matrix elements using the Fragment Excitation Difference (FED) method. We determine the β parameter characterizing the exponential distance decay of TEET rates in a stacked perylene dimer in water, chloroform, and benzene solutions. Our results indicate that the solvent dependence of β (βvacuum = 5.14 Å–1 > βwater = 3.77 Å–1 > βchloroform = 3.61 Å–1 > βbenzene = 3.44 Å–1) can be rationalized adopting the McConnell model of superexchange, where smaller triplet energy differences between the donor and the solvent lead to smaller β constants. We also estimate the decay of hole transfer (HT) and excess electron transfer (EET) processes in the system using the Fragment Charge Difference (FCD) method and find that βTEET can be reasonably well approximated by the sum of βEET and βHT constants.

Excess-Electron Injection and Transfer in Terthiophene-Modified DNA: Terthiophene as a Photosensitizing Electron Donor for Thymine, Cytosine, and Adenine

Excess-electron transfer (EET) in DNA has attracted wide attention owing to its close relation to DNA repair and nanowires. To clarify the dynamics of EET in DNA, a photosensitizing electron donor that can donate an excess electron to a variety of DNA sequences has to be developed. Herein, a terthiophene (3T) derivative was used as the photosensitizing electron donor. From the dyad systems in which 3T was connected to a single nucleobase, it was revealed that (1) 3T* donates an excess electron efficiently to thymine, cytosine, and adenine, despite adenine being a well-known hole conductor. The free-energy dependence of the electron-transfer rate was explained on the basis of the Marcus theory. From the DNA hairpins, it became clear that (1) 3T* can donate an excess electron not only to the adjacent nucleobase but also to the neighbor one nucleobase further along and so on. From the charge-injection rate, the possibilities of smaller β value and/or charge delocalization were discussed. In addition, EET through consecutive cytosine nucleobases was suggested.

Hole and excess electron transfer dynamics in DNA

Charge transfer in DNA attracts substantial attention from researchers in a wide group of fields such as bioscience, nanotechnology and physical chemistry. It is well known that both positive and negative charges, which are holes and excess electrons, respectively, contribute to the charge transfer in DNA. In the case of hole transfer in DNA, detailed mechanisms and dynamical parameters have been estimated by means of time-resolved spectroscopic methods and product analysis. On the other hand, detailed dynamics of excess electron transfer have not been established yet, although several aspects have been revealed by the continuous efforts of various research groups. In the present Perspective, studies on the charge transfer dynamics in DNA are summarized.

Drastic enhancement of excess electron-transfer efficiency through DNA by inserting consecutive 5-phenylethynyl-2′-deoxyuridines as a modulator

5-(Phenylethynyl)-2'-deoxyuridine ((Ph)U) was consecutively incorporated into oligodeoxynucleotides as an electron transport modulator for regulating DNA-mediated excess electron transfer (EET). Upon photoexcitation of the ethynylpyrene chromophore, extremely high EET efficiencies through DNA containing consecutive (Ph)Us were observed using 5-bromouracil as a distal electron trap.

Excess electron transfer dynamics in DNA hairpins conjugated with N,N-dimethylaminopyrene as a photosensitizing electron donor

Excess electron transfer dynamics in DNA hairpins was investigated by femtosecond laser flash photolysis of a donor-DNA-acceptor system using N,N-dimethylaminopyrene and diphenylacetylene as an electron donor and acceptor, respectively. It was revealed that the excess electron hopping rate between T's is faster than that of the hole.