Academic literature on the topic 'Double electron transfer (DET)'

Using Localized Surface Plasmon Resonance Effect for Enhancing Electrochemical reactions has been reported earlier both in terms of direct electron injection/transfer (DET) in outer-sphere reductive processes as well as charge injection into semiconductors via plasmon-induced resonant electron transfer processes (PIRE). While the former (DET) is mostly influenced by the lifetimes of the ejected hot electrons and their rapid cooling at the interface. For inner sphere reductive processes via the LSPR phenomenon, direct charge injection into the LUMO states of the adsorbed species is required. In this regard, it is imperative to distinguish between the inter-band charge transfer of the adsorbed species because of exposure to photons. In contrast to these charge injection into semiconductors via plasmon-induced resonant electron transfer processes (PIRE) is less understood and more complex. In this presentation, we will use the well-known endothermic anodic oxygen evolution reaction (OER) in alkaline pH to showcase fundamental aspects of charge injection and its effect on the hole-driven OER mechanism. For this well know OER catalyst, layered double hydroxides of Ni with Fe and Co dopants will be used. Electrochemical enhancement of OER will be explained based on detailed structural motifs of the semiconductors its band structure and the resonance effect of Au induced by the LSPR effect. The presence of direct and Indirect bandgaps will be discussed in the context of three possible mechanisms: (i) Charge carriers are directly injected via LSPR into the semiconductor. The conduction band of the semiconductor is usually (-0.1 to 0.0 eV vs. NHE) and the valence band is between (2.00 and 3.5 eV) which corresponds to electron energy between -2.00 to 3.5 eV vs NHE. For LSPR nanoparticles SPR energy is between 1.0 and 4.0 eV. Also, the Fermi energy of LSPR is usually 0.0 vs. NHE. Hence LSPR only enables energetic electrons to be transferred from metals to semiconductors. It is the interface between LSPR and the semiconductor which is important. Charge injection is more prevalent when metal LSPR is of lower energy than the semiconductor. Direct electron transfer (DET). (ii) Transfer not involving direct electron injection but via (a) near field electromagnetic and (b) resonant photon scattering mechanism. This has been shown to work by adding a thin dielectric material between the LSPR and semiconductor. This would be most likely in the case of OER where surface localized plasmons will be the most important determinant as opposed to recombination events in the bulk of the semiconductor. This is most important for OER as it depends on the surface hole concentration. It should be noted that larger nanoparticles (>50 nm) have increased resonant photon scattering. Such a mechanism is more prevalent when we have an overlap between metal LSPR and semiconductor bands leading to plasmon induced resonant electron transfer (PIRET). (iii) When metal LSPR is in direct contact with the semiconductor all three phenomenon could be active.

NiFe-layered double hydroxides (NiFe-LDH) have been reported to possess exceptional oxygen evolution reaction (OER) activity. However, maintaining the stability of high activity over a long time remains a critical challenge that needs to be addressed for their practical application. Here, we report a custom-sized deep recombination of 2D graphene oxide with NiFe-LDH (NiFe-LDH/GO/NF) through a simple electrodeposition method that improves OER activity and achieves excellent stability. The excellent performance of the catalyst mainly comes from the three-phase interface and electron transport channel dredged by the three-dimensional structure constructed by the deep composite, which can not only significantly reduce its charge and electron transfer resistance, improving the material conductivity, but it also effectively increases the specific surface area, inhibits aggregation, and exposes rich active sites. In addition, GO with good conductivity not only supports NiFe-LDH well but also increases the heterogeneous interface, putting the NiFe-LDH/GO composites in close contact with Ni foam and increasing the electrocatalytic stability of the NiFe-LDH/GO/NF. The experimental results show that the overpotential of NiFe-LDH/20,000GO/NF is only 295 mV at a current density of 100 mA cm−2; the Tafel slope is 52 mV dec−1, and the charge transfer resistance (Rct) is only 0.601 Ω in 1 M KOH. This indicates that GO has excellent potential to assist in constructing geometric and electronic structures of NiFe-LDH in long-term applications.

The major challenge in the fabrication of fluorescent silica nanoparticles (FSNs) based on dye-doped silica nanoparticles (DDSNs) is aggregation-caused fluorescence quenching. Here, we constructed an FSN based on a double emission enhancement (DEE) platform. A thio-reactive fluorescence turn-on molecule, N-butyl-4-(4-maleimidostyryl)-1,8-naphthalimide (CS), was bound to a silane coupling agent, (3-mercaptopropyl)-trimethoxysilane (MPTMS), and the product N-butyl-4-(3-(trimethoxysilyl-propylthio)styryl)-1,8-naphthalimide (CSP) was further used to fabricate a core–shell nanoparticle through the Stöber method. We concluded that the turn-on emission by CSP originated from the photoinduced electron transfer (PET) between the maleimide moiety and the CSP core scaffold, and the second emission enhancement was attributed to the aggregation-induced emission enhancement (AIEE) in CSP when encapsulated inside a core–shell nanoparticle. Thus, FSNs could be obtained through DEE based on a combination of PET and AIEE effects. Systematic investigations verified that the resulting FSNs showed the traditional solvent-independent and photostable optical properties. The results implied that the novel FSNs are suitable as biomarkers in living cells and function as fluorescent visualizing agents for intracellular imaging and drug carriers.

Currently, precious metal group materials are known as the efficient and widely used oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysts. The exorbitant prices and scarcity of the precious metals have stimulated scale exploration of alternative non-precious metal catalysts with low-cost and high performance. Layered double hydroxides (LDHs) are a promising precursor to prepare cost-effective and high-performance catalysts because they possess abundant micropores and nitrogen self-doping after pyrolysis, which can accelerate the electron transfer and serve as active sites for efficient OER. Herein, we developed a new highly active NiFeMn-layered double hydroxide (NFM LDH) based electrocatalyst for OER. Through building NFM hydroxide/oxyhydroxide heterojunction and incorporation of conductive graphene, the prepared NFM LDH-based electrocatalyst delivers a low overpotential of 338 mV at current density of 10 mA cm−2 with a small Tafel slope of 67 mV dec−1, which are superior to those of commercial RuO2 catalyst for OER. The LDH/OOH heterojunction involves strong interfacial coupling, which modulates the local electronic environment and boosts the kinetics of charge transfer. In addition, the high valence Fe3+ and Mn3+ species formed after NaOH treatment provide more active sites and promote the Ni2+ to higher oxidation states during the O2 evolution. Moreover, graphene contributes a lot to the reduction of charge transfer resistance. The combining effects have greatly enhanced the catalytic ability for OER, demonstrating that the synthesized NFM LDH/OOH heterojunction with graphene linkage can be practically applied as a high-performance electrocatalyst for oxygen production via water splitting.

The oxygen evolution reaction (OER) is a key half-reaction in electrocatalytic water splitting. Large-scale water electrolysis is hampered by commercial noble-metal-based OER electrocatalysts owing to their high cost. To address these issues, we present a facile, one-pot, room-temperature co-precipitation approach to quickly synthesize carbon-nanotube-interconnected amorphous NiFe-layered double hydroxides (NiFe-LDH@CNT) as cost-effective, efficient, and stable OER electrocatalysts. The hybrid catalyst NiFe-LDH@CNT delivered outstanding OER activity with a low onset overpotential of 255 mV and a small Tafel slope of 51.36 mV dec−1, as well as outstanding long-term stability. The high catalytic capability of NiFe-LDH@CNT is associated with the synergistic effects of its room-temperature synthesized amorphous structure, bi-metallic modulation, and conductive CNT skeleton. The room-temperature synthesis can not only offer economic feasibility, but can also allow amorphous NiFe-LDH to be obtained without crystalline boundaries, facilitating long-term stability during the OER process. The bi-metallic nature of NiFe-LDH guarantees a modified electronic structure, providing additional catalytic sites. Simultaneously, the highly conductive CNT network fosters a nanoporous structure, facilitating electron transfer and O2 release and enriching catalytic sites. This study introduces an innovative approach to purposefully design nanoarchitecture and easily synthesize amorphous transition-metal-based OER catalysts, ensuring their cost effectiveness, production efficiency, and long-term stability.

The oxygen evolution reaction (OER) is a slow step in electrocatalytic water splitting. NiFe layered double hydroxides (LDH) have shown promise as affordable OER electrocatalysts, but their performance is hindered by poor charge transfer and sluggish kinetics. To address this, we doped NiFe LDH with sulfur (S) using an in situ electrodeposition method. By growing S-doped NiFe LDH on Cu nanoarrays, we created core–shell structures that improved both the thermodynamics and kinetics of OER. The resulting S-NiFe LDH@Cu core–shell nanoarrays exhibited enhanced activity in water oxidation, with a low potential of 236 mV (at 50 mA cm−2) and a small Tafel slope of 50.64 mV dec−1. Moreover, our alkaline electrolyzer, based on these materials, demonstrated remarkable activity, with a low voltage of 1.56 V at 100 mA cm−2 and excellent durability. The core–shell nanoarray structures provided a larger electroactive surface area, facilitated fast electron transport, and allowed for effective gas release. These findings highlight the potential of S-NiFe LDH@Cu core–shell nanoarrays as efficient OER electrocatalysts.

The anisotropic growth of plant cells depends on cell walls having anisotropic mechanical properties, which are hypothesized to arise from aligned cellulose microfibrils. To test this hypothesis and to identify genes involved in controlling plant shape, we isolated mutants in Arabidopsis thaliana in which the degree of anisotropic expansion of the root is reduced. We report here the characterization of mutants at two new loci, RADIALLY SWOLLEN 4 (RSW4) and RSW7. The radial swelling phenotype is temperature sensitive, being moderate (rsw7) or negligible (rsw4) at the permissive temperature, 19°C, and pronounced at the restrictive temperature, 30°C. After transfer to 30°C, the primary root’s elongation rate decreases and diameter increases, with all tissues swelling radially. Swelling is accompanied by ectopic cell production but swelling is not reduced when the extra cell production is eliminated chemically. A double mutant was generated, whose roots swell constitutively and more than either parent. Based on analytical determination of acid-insoluble glucose, the amount of cellulose was normal in rsw4 and slightly elevated in rsw7. The orientation of cortical microtubules was examined with immunofluorescence in whole mounts and in semi-thin plastic sections, and the orientation of microfibrils was examined with field-emission scanning electron microscopy and quantitative polarized-light microscopy. In the swollen regions of both mutants, cortical microtubules and cellulose microfibrils are neither depleted nor disoriented. Thus, oriented microtubules and microfibrils themselves are insufficient to limit radial expansion; to build a wall with high mechanical anisotropy, additional factors are required, supplied in part by RSW4 and RSW7.

For large-scale energy applications, conceiving low-cost and simple earth-abundant electrocatalysts are more difficult. By using an aqueous chemical technique, MnO2 was added into Co3O4 with varying concentrations to prepare MnO2@Co3O4 nanocomposite (CM). In an aqueous solution of 1 M KOH, the electrocatalyst with a greater concentration of MnO2 outperforms in terms of OER. To confirm the composition, crystalline structure, and morphology of the electrocatalyst, analytical methods such as X-ray diffraction (XRD) techniques, Fourier transformed infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used. At 20 mA/cm2 current density, the electrocatalyst had a lowest overpotential of 310 mV verses Reversible hydrogen electrode (RHE). The CM-0.4 electrocatalyst has a small Tafel slope value and charge transfer resistance of approximately 72 mV/dec and 74 Ω which confirm its high catalytic activity. The electrocatalyst reveals a double layer capacitance (Rct) of 18 µF/cm2 and an electrochemical active surface area (ECSA) of 450 cm2, demonstrating that addition of MnO2 impurities into Co3O4 enhances the active catalyst sites. These findings contribute to the knowledge of these kind of catalysts, that will assist in the development of novel electrocatalysts which are feasible for prospective energy generation technologies.

Direct electron transfer (DET)-type bioelectrocatalysis, which couples the electrode reactions and catalytic functions of redox enzymes without any redox mediator, is one of the most intriguing subjects that has been studied over the past few decades in the field of bioelectrochemistry. In order to realize the DET-type bioelectrocatalysis and improve the performance, nanostructures of the electrode surface have to be carefully tuned for each enzyme. In addition, enzymes can also be tuned by the protein engineering approach for the DET-type reaction. This review summarizes the recent progresses in this field of the research while considering the importance of nanostructure of electrodes as well as redox enzymes. This review also describes the basic concepts and theoretical aspects of DET-type bioelectrocatalysis, the significance of nanostructures as scaffolds for DET-type reactions, protein engineering approaches for DET-type reactions, and concepts and facts of bidirectional DET-type reactions from a cross-disciplinary viewpoint.

The accurate determination of analyte concentrations with selective, fast, and robust methods is the key for process control, product analysis, environmental compliance, and medical applications. Enzyme-based biosensors meet these requirements to a high degree and can be operated with simple, cost efficient, and easy to use devices. This review focuses on enzymes capable of direct electron transfer (DET) to electrodes and also the electrode materials which can enable or enhance the DET type bioelectrocatalysis. It presents amperometric biosensors for the quantification of important medical, technical, and environmental analytes and it carves out the requirements for enzymes and electrode materials in DET-based third generation biosensors. This review critically surveys enzymes and biosensors for which DET has been reported. Single- or multi-cofactor enzymes featuring copper centers, hemes, FAD, FMN, or PQQ as prosthetic groups as well as fusion enzymes are presented. Nanomaterials, nanostructured electrodes, chemical surface modifications, and protein immobilization strategies are reviewed for their ability to support direct electrochemistry of enzymes. The combination of both biosensor elements—enzymes and electrodes—is evaluated by comparison of substrate specificity, current density, sensitivity, and the range of detection.

Durant ces dernières décennies, la réactivité des donneurs d’électrons organiques de type énamine (DEO) a été largement exploitée dans des réactions de réduction par transfert électronique. De part leurs forts pouvoir réducteur avec des potentiels redox exceptionellement négatifs, les DEOs sont capables de transférer spontanément un ou deux électrons à des substrats organiques, formant ainsi des intermédiaires radicalaires ou anioniques. Cependant, ces DEOs sont toujours utilisés en quantité stœchiométrique, ce qui limite leur compétivité face aux catalyseurs organométalliques et organiques.Les travaux de cette thèse consistent à répondre à cette problématique en développant un nouveau système catalytique avec ces DEOs. Pour cela, plusieurs stratégies ont été envisagées. Dans une première méthode, une quantité catalytique du DEO serait utilisée pour amorcer le transfert d’électron pour la réduction du substrat. L’oxydation d’intermédiaires radicalaires générés, permettrait alors de régénérer le DEO. Cette stratégie n’a malheureusement pas donné de résultat. Une seconde méthode consisterait à régénérer le DEO à partir de la forme oxydée DEO2+, stable à l’air et d’un donneur d’électron sacrificiel (amine tertiaire, dithionite de sodium ou Rongalite®) sous photoactivation. Plusieurs étapes d’optimisation ont permis d’aboutir à un système catalytique photoredox efficace avec la forme oxydée comme photocatalyseur et la Rongalite® en tant que donneur sacrificiel. Ce nouveau système catalytique photoredox a été appliqué à la réduction de divers groupements fonctionnels (sulfone, halogénure d’aryle, triflate) par transfert mono et biélectronique
During this last decade, the reactivity of enamine-based organic electron donor (OED) has been widely explored in electron transfer processes. With exceptionally negative redox potentials, OEDs spontaneously promote single (SET) or double electron transfer (DET) to an organic substrate, to form radical or anionic intermediates. However, the use of stoichiometric amount of OEDs limits their competitivity compared to their organometallic and organic catalysts. This thesis project consisted in developing a new catalytic system with OEDs. Different strategies were envisaged. In a first method a catalytic amount of OED would initiate the electron transfer to reduce the substrate. The oxidation of the generated radical intermediate would allow the regeneration of OED. Unfortunately, this strategy was unsuccessful. The second strategy would consist in regenerating the OED from its air-stable oxidized form OED2+ and a sacrificial electron donor (tertiary amine, sodium dithionite or Rongalite®) under photoactivation. Several optimizing steps allowed the development of a new efficient catalytic photoredox system with the oxidized form as photocatalyst and Rongalite® as sacrificial electron donor. This new photoredox catalytic system was applied to the reduction of various functionals groups (sulfone, aryl halide and triflate) by single electron transfer (SET) and double electron transfer (DET). The reactivity of the photocatalytic system was also explored in radical addition reactions

In this research the environmental effects related to the position of a redox moiety with the electrochemical double layer were studied. This project was made possible with the synthesis of a series of lengths of ferrocene derived alkanethiols, a series of lengths of ferrocene derived norbornylogous bridges and a series of lengths of anthraquinone derived norbornylogous bridges. The series of ferrocene derived alkanethiols were used to study the effect of gradually varying the polarity of the self-assembled monolayers (SAMs) surface on the standard electron transfer rate constant and formal potential. This was achieved by varying the portion of hydroxyl to methyl terminated alkanethiol diluent in the SAM preparation step. It was found that the formal potential increased with a decreasing proportion of hydroxyl terminated diluent and increasing length of the diluent. For pure hydroxyl terminated diluent the formal potential was relatively independent of length. It was found that the rate constant increased for short alkane chain lengths with decreasing proportion of hydroxyl terminated diluent. However, it decreased in magnitude with long alkane chain lengths for low proportions of hydroxyl terminated diluent. The norbornylogous bridges were shown to stand proud above the diluent with a similar tilt angle as the alkanethiol diluent. The ferrocene derived norbornylogous bridges showed hydroxyl terminated monolayers had a slower rate constant then methyl terminated diluents independent of length and that it is highly probable that an alkane bridged redox moiety is located very close to the surface of the monolayer. SAMs were created with the ferrocene of the ferrocene derived norbornylogous bridges located at various heights above the monolayers surface. This was done by using various lengths of hydroxyl terminated diluent. It was found that the rate constant and the formal potential decreased with height above the surface. Interfacial potential distribution was used to account for this and to estimate a ??true?? formal potential. The anthraquinone derived norbornylogous bridges were tested at various pH values and heights above the surface. It was found that an accurate estimate for the electron transfer mechanism can not be made for surface bound species due to the effects of interfacial potential distribution. They demonstrated a novel technique for estimating the point of zero charge of the electrode.

The ICRP recommends a radiation weighting factor of one for all low-LET radiation. However, many experimental studies find inconsistencies between low-LET RBE and the ICRP's current radiation weighting factor. Generally, there is evidence that dependence exists between radiation energy and radiation RBE where lower energy radiations tend to have a greater biological effect than higher energy radiation. Specifically, the radiations of tritium and carbon K-shell x-rays have been studied in numerous experiments and the biological effects of both of these radiations are consistently greater than that of Co-60. In this work, the relationship between radiation energy and radiation effect has been investigated with the use of a newly developed double strand break (DSB) yield estimation algorithm. This algorithm makes use of a detailed solenoidal 30 nm DNA chromatin model to describe the radiation-sensitive biological target. In addition to the DNA model, NOREC, an event by event Monte Carlo code, was used in this algorithm to characterize the electron track. As an alternative to the conventional approach of computationally simulating DNA damage by spatial overlay of an electron track on DNA, this algorithm instead focuses on quantifying the distance between ionizations in an electron track and next determining the likelihood that any given ionization pair forms a DSB. The first step of the algorithm involves electron characterization while the second step relies on DNA molecule characterization. By assuming a DSB biological endpoint and determining the DSB yield as a function of electron energy, energy dependent RBE values were estimated for monoenergetic electrons from 10 eV to 1 MeV. Photon RBE values, x-ray RBE values and radionuclide RBE values were also calculated and reported in this work in addition to electron RBE values. Photon RBE values were estimated based upon the electron RBE calculation. Photon RBE values were reported from 1 eV to 10 MeV. In turn, x-ray RBE values were calculated based upon photon values for several tube voltage and filter combinations. Finally, RBE values for over 1000 radionuclides were estimated and reported.

Uvod: Višeplodne trudnoće se javljaju u 1,5% svih trudnoća nakon spontane koncepcije, dok nakon postupaka vantelesne oplodnje ovaj postotak u Evropi iznosi preko 20% uz velike varijacije među zemljama. U našoj sredini, stopa višeplodnih trudnoća nakon postupaka vantelesne oplodnje iznosi daleko iznad 30%. Pojava hipertenzivnog sindroma u trudnoći, gestacijskog dijabetesa, operativnog završavanja trudnoće, prevremenog porođaja, male porođajne telesne mase, neuroloških sekvela kod rođene dece i gotovo svih drugih komplikacija po majku i plod, kao i celokupno opterećenje zdravstvenog sistema višestruko su veći kod višeplodnih u odnosu na jednoplodne trudnoće i udeo navednih komplikacija raste sa brojem plodova. Sa druge strane deca iz postupaka vantelesne oplodnje čine i do 4,5% sve živorođene dece u pojedinim zemljama, što uz činjenicu da infertilitet pogađa 16-18% parova u našoj sredini daje ovoj pojavi posebnu dimenziju i činije i društvenim problemom. Perinatalni ishodi trudnoća iz postupaka vantelesne oplodnje su u velikoj meri kompromitovani visokom stopom multiplih trudnoća, koje se danas smatraju komplikacijom, a ne uspehom postupaka vantelesne oplodnje. Jednoplodne trudnoće iz postupaka vantelesne oplodnje u većim studijama pokazuju diskretno slabije perinatalne ishode u odnosu na one spontano začete, dok kod višeplodnih trudnoća ova korelacija nije jasno izražena i dokumentovana, uz prisutnu dilemu da li je višeplodnost sama po sebi ili način koncepcije glavni problem u zapaženoj pojavi. Cilj rada: Uporediti perinatalne ishode višeplodnih trudnoća nastalih postupcima vantelesne oplodnje i spontano začetih kao i perinatalne ishode jednoplodnih i višeplodnih trudnoća iz postupaka vantelesne oplodnje. Pored navdenog cilj rada je i ukazati sveobuhvatnost navedenog problema i na moguća rešenja za smanjenje njihove učestalosti. Materijal i metode: Kombinacijom retrospektivne opservacione studije i prospektivne longitudinalne kohortne studije u periodu analizom perinatalnih ishoda pacijentkinja porođenih na Klinici za ginekologiju i akušerstvo Kliničkog centra Vojvodine u periodu od od 01.01.2008. do 31.12.2010. godine, studija je analizirala i poredila perinatalne ishode kod 174 spontano začete višeplodne trudnoće, 163 višeplodne trudnoće nastale postupkom vantelesne oplodnje, kao i 155 jednoplodnih trudnoća začete postupkom vantelesne oplodnje. Analizirani parametric bili su telesna masa novorođenčeta, dostignuta gestacijska starost, vrednosti Apgar skora, učestalost hipertenzivnog sindroma kod majke i brojni drugi parametri perinatalnog ishoda. Uzeti od strane obučenih kliničara i unošeni u posebno dizajniranu bazu podataka, rezultati su statistički analizirani u program JMP ver 9.0 (SAS publisher) uz korišćenje ANOVA analize za testiranje statističke značajnosti između srednjih vrednosti kontinuiranih varijabli, dok je statistička značajnost razlike učestalosti kategorijskih varijabli je određivana Pearsonovim χ2 testom. Rezultati: Jednoplodne ART trudnoće uz prosečnu starost od 33,5 godine, prosečnu gestacijsku starost na porođaju od 38,26 gn, udeo prevremenih porođaja od 12,9%, prosečnu telesnu masu od 3258 g, AS u prvom minutu od 8,35 i u petom minutu od 9,2, stopu carskog reza od 65,81%, udeo GDM-a od 7,1%, anemije od 41,94% i preeklampsije od 4,52%, ima sve relevantne parametre perinatalnog ishoda statistički značajno (p<0.0001) superiornije od kako ART tako i non ART blizanačkih trudnoća. ART blizanačke trudnoće pokazale su prosečnu starost majke od 32,9 godina, prosečnu gestacijsku starost na porođaju od 35,6 gn, udeo prevremenih porođaja od 58,27%, prosečnu telesnu masu od 2374 g, AS u prvom minutu od 7,45 i u petom minutu od 8,65, stopu carskog reza od 83,7%, udeo GDM-a od 15,11%, anemije od 78,42% i preeklampsije od 12,23%, dok su non ART blizanačke trudnoće pokazale prosečnu starost majke od 28,8 godina, prosečnu gestacijsku starost na porođaju od 36,08 gn, udeo prevremenih porođaja od 49,71%, prosečnu telesnu masu od 2433 g, AS u prvom minutu od 7,75 i u petom minutu od 8,75, stopu carskog reza od 58,33%, udeo GDM-a od 7,02%, anemije od 67,84% i preeklampsije od 11,11%. Pored godina majke i udela carskog reza koji su bili viši u ART blizanačkim trudnoćama (<0.0001), kao i blago veće pojavi poremećaja količine plodove vode (p=0,033), gotovo svi ostali pokazatelji toka i ishoda trudnoće bili su komparabilni u navedenim grupama. Diskusija i zaključak: Studija je pokazala da su tok i ishod višeplodnih trudnoća nastalih spontano i postupcima vantelesne oplodnje ekvivalentni u gotovo svim pokazateljima uz sličnu prosečnu telesnu masu i gestacijsku starost novorođenčadi, kao i da su svi navedeni parametri ovih višeplodnih trudnoća bez obzira na način koncepcije upadljivo i podjednako lošiji u poređenju sa jednoplodnim trudnoćama iz postupka vantelesne oplodnje. Izuzimajući višeplodnost kao factor rizika deca iz postupaka vantelesne oplodnje su generalno zdrava. Sama višeplodnost, a ne način koncepcije predstavljaju problem, koje se sa pravom smatra najvećom komplikacijom vantelesne oplodnje. Dodatna analiza iskustava drugih zdravstvenih sistema ukazuje da jedino široka i sveobuhvatna implementacija strategije vraćanja samo jednog embriona (Single embryo transfer – SET) može da dovede do smanjivanje stope multiplih trudnoća nakon postupaka vantelesne oplodnje, i sledstvenih komplikacija, a bez ugrožavanja samog uspeha vantelesne oplodnje. Iskustva drugih zdravstvenih sistema ukazuju da je uspešna implementacija SET-a jedino moguća uz angažovanje celog društva, zajedno sa brojnim legislativnim merama iz domena nadzora, kontrole i finansiranja postupaka vantelesne oplodnje. Obim i način finansiranja postupaka vantelesne oplodnje od strane države (uz više besplatnih pokušaja za infertilne parove) uz obaveznu upotrebu SET-a, i sistema krioprezervacije na osnovu primera iz prakse predstavlja ključ u borbi za smanjenje problema višeplodnih trudnoća nakon postupaka vantelesne oplodnje.
Introduction: Multiple pregnancies occur in 1.5% of all pregnancies after spontaneous conception and in more than 20 % of all pregnancies concieved after assisted reproductive technologies in Europe, with large variations between countries. In our setting, the rate of multiple pregnancies after the ART is well above 30%. The occurrence of hypertensive syndrome in pregnancy, gestational diabetes, operative delivery, premature birth, low birth weight, neurological and developmental impairment in children, and almost all the other complications for the mother and fetus, as well as the entire burden of the health system are several times higher in multiple pregnancies compared with singleton pregnancies. Incidence of  forementioned complications rises with number of fetuses. On the other hand, children from in vitro fertilization procedures make up 4.5% of all live births in some countries, which together with the fact that infertility affects aproximately 16-18% of couples in our country gives an extra dimension to this phenomenon and makes it not just medical but wider social problem. Perinatal outcomes of pregnancies after assisted reproductive technologies (ART) are greatly compromised by the high rate of multiple pregnancies, which are now considered to be a complication rather than success of ART procedures. ART Singleton pregnancies have, in larger studies, show discretely lower perinatal outcomes compared with those conceived spontaneously, while for the multiple pregnancies, this correlation is not clearly expressed and documented. There remains dilemma whether multiplicity itself or the way of conception (ART vs. non ART) constitutes a major problem in the observed differences regarding perinatal outcome of ART pregnancies. Objective: To compare the perinatal outcomes of multiple pregnancies conceived by In vitro fertilization (IVF) and spontaneously and perinatal outcomes of IVF conceived singleton and multiple pregnancies. Additional aim of this thesis is to point out the complexity of this problem and offer possible solutions. Materials and Methods: Design of a study was a combination of retrospective and prospective observational longitudinal cohort study. Analysis included pregnancies which had delivery at the Department of Gynecology and Obstetrics, Clinical Center of Vojvodina in the period from 1.01.2008. to 31.12.2010. The study analyzed and compared the perinatal outcomes in 174 spontaneous conceived multiple pregnancies, 163 multiple pregnancies resulting from IVF procedures, and 155 singleton pregnancies conceived by IVF procedure. Analyzed parameters were newborns birth weight, gestational age at delivery, the value of the Apgar score, occurrence of hypertensive syndrome in pregnancy, gestational diabetes, as well as numerous parameters of perinatal outcome. Taken by trained clinicians and were entered into a specially designed database, the results were statistically analyzed in JMP ver 9.0 software (SAS publisher) using ANOVA analysis to test the statistical significance between the mean values of continuous variables, while the statistical significance of the difference in frequency of categorical variables was assessed by Pearsons χ2 test. Results: ART singleton pregnancies had an average mothers age of 33.5 years, the average gestational age at birth of 38.26 gestational weeks (gw), preterm delivery rate of 12.9%, average birth weight 3258 g, Apgar score (AS) in the first minute 8.35, and in the fifth minute 9.2, cesarean section rate 65.81%, Gestational diabetes (GDM) in 7.1% pregnancies, anemia occurred in 41.94% of pregnancies, while preeclampsia was observed in 4.52% of all pregnancies. All relevant parameters of perinatal outcome were significantly (p<0.0001) superior to both ART and non-ART twin pregnancies. ART twin pregnancy showed the average mothers age of 32.9 years, the average gestational age at birth of 35.6 gw, the preterm delivery rate 58.27%, the average body weight newborns 2374 g, AS in the first minute of 7.45, and in the fifth minute of 8.65, the cesarean section rate of 83.7%, GDM in 15.11% of all pregnancies, anemia occurred in 78.42% and preeclampsia in 12.23% of pregnancies, while the non-ART twin pregnancy showed an average mothers age of 28.8 years, the average gestational age at birth of 36.08 gw, the preterm delivery rate of 49.71%, the average body weight of 2433 g, AS in the first minute of 7.75 in the fifth minute 8.75, the caesarian section rate of 58.33%, GDM-a occurred in 7.02%, anemia in 67.84% and preeclampsia in 11.11% of pregnancies. Except for maternal age and the caesarean section rate, which were significantly higher in ART twin pregnancies (p<0.0001), as well as small increase in proportion of amniotic fluid volume disorders (p = 0.033), almost all other parameters of perinatal outcome of were comparable in these groups. Discussion and Conclusion: The study showed that the course and outcome of multiple pregnancies conceived spontaneous and after IVF procedures are equivalent in almost all parameters with similar average body weight and gestational age at birth, and that all these parameters of multiple pregnancies regardless of the conception mode are equally worse compared with singleton pregnancies from IVF procedures. With the exception of multiplicity as a risk factor children from in vitro fertilization procedures are generally healthy. Multiplicity itself and not the mode of conception presented a problem, which is rightly considered the major complication of IVF today. Additional analysis of the experiences of other health system indicates that only a broad and comprehensive implementation of strategy to return only one embryo (SET–single embryo transfer) can lead to a reduction of the rate of multiple pregnancies after IVF procedures, and the accompanying complications, without compromising IVF success. The experience of other health systems indicate that a successful implementation of SET is only possible with the involvement of the whole society, along with a number of legislative measures in the field of monitoring, control and reimbursement of assisted reproduction procedures. The scope and funding of an IVF procedures (with more free attempts for infertile couples, reimbursed by public health) with mandatory use of SET, and good cryopreservation programs are, based on examples in other countries who had successfully dealt with his problem, is the key in reducing the problem of multiple pregnancies after IVF procedures.

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The DNA helix, containing a stacked array of aromatic base pairs, presents a novel medium in which electron transfer mediated by a molecular [pi]-stack can be investigated. To probe electron transfer through DNA, we have constructed duplex assemblies modified with photo- and redox-active probes and applied spectroscopic and electrochemical approaches to the study of DNA-mediated charge transport. Photoinduced electron transfer between intercalators was examined as a function of distance in a series of small DNA duplexes covalently modified with ethidium (Et) and [...]. At distances up to 35 [...], electron transfer occurs on the subnanosecond time scale ([...]). In duplexes containing disruptive base mismatches, large decreases in electron-transfer yields are observed, confirming that the electron transfer pathway proceeds through the stacked base pairs. Hence, it was demonstrated for the first time that DNA-mediated electron transfer between intercalators is exceptionally efficient, only weakly dependent on distance, but highly sensitive to perturbations in base stacking. To investigate a DNA base within the [pi]-stack as a reactant, ethidium-modified duplexes containing the base analogue deazaguanine were synthesized. The photooxidation of deazaguanine by ethidium also proceeds on a subnanosecond time scale ([...]) and exhibits a shallow distance dependence. The efficiency and overall distance dependence is sensitive to the stacking of deazaguanine as determined by flanking sequence. These studies again showed that the DNA base stack can mediate extremely fast, long-range charge transport, and further elucidated that stacking interactions are critical in modulating the efficiency of this phenomenon. Using base-base photochemistry, electron transfer through DNA was probed directly without external donors and acceptors. Using fluorescent analogues of adenine that selectively oxidize guanine, electron transfer through the DNA [pi]-stack was investigated as a function of reactant stacking and energetics. Small variations in each of these factors lead to remarkable changes in the kinetics of DNA-mediated electron transfer and values of [beta], a parameter reflecting the exponential dependence of electron transfer on distance, were measured ranging from [...] to [...]. The DNA base stack was shown to exhibit insulator to "wire"-like properties, depending on the structure and energetics of reactants employed to probe this medium. To investigate DNA-mediated electron transfer using electrochemical methods, we assembled DNA films and incorporated intercalating redox-active molecules into the monolayers. Surface characterization techniques were employed to determine the orientation of the DNA helices within the films. With the intercalator daunomycin crosslinked to DNA duplexes immobilized on gold, efficient electron transfer over distances greater than 30 [...] was observed. Base mismatches also attenuate this long-range reaction, providing a new method for the electrochemical detection of genomic mutations. These studies have provided essential measurements of electron transfer in DNA over known, fixed distances. It is now apparent that stacking interactions modulate the efficiency of this phenomenon, an observation that may explain the range of conflicting results reported within this field. Moreover, as experimental evidence increasingly supports the notion that ultrafast charge transport can occur through the DNA helix over long distances, the implications for biological systems can now be considered. Our findings point to the DNA [pi]-stack as not only a carrier of genetic information, but also a pathway which is conducive to charge transport.

博士
國立中正大學
化學研究所
90
Abstract Unlike 7-azaindole consisting of the tetrameric configuration, 3-methyl-7-azaindole (3MAI) exists solely as intact double hydrogen-bonded dimeric forms in a single crystal. Both steady state and time-resolved measurements down to 8.0 K reveal remarkable deuterium isotope effects on the rate of excited-state double proton transfer (ESDPT) in the N(1)-deuterated 3MAI (3MAI-d) single crystal. The rates of ESDPT for the 3MAI-d dimer resolved at < 150 K are mainly governed by the proton tunneling mechanism. At < 12 K, the nearly temperature-independent ESDPT dynamics lead us to qualitatively deduce a barrier height of ~ 1.73 kcal/mol for the 3MAI-d dimer. The results provide an ideal model to investigate the intrinsic ESDPT dynamics for 7-azaindole analogues in which the structural information is well documented. The mechanism of excited-state double proton transfer (ESDPT) reaction of 7-azaindoles in pure water has been solved through design and syntheses of 3-Cyano-7-azaindole (3CAI) and its derivatives. Dual emission consisting of normal (lmax = 350 nm) and tautomer band (lmax = 475 nm) was resolved for 3CAI in pure water. Dynamical studies clearly revealed that the entire rise time of the tautomer emission of 850 ps is identical with the decay time (tf = 855 ps) of the normal emission. Remarkable deuterium isotope effect was observed in D2O where the rise time of 3.50 ns of the tautomer emission correlates well with the lifetime (3.45 ns) of the normal emission. The results lead us to conclude that dynamics of ESDPT with a rate of 850 ps-1 in water (or 3.50 ns-1 in D2O) originate from the entire ground-state solvated species, resolving a long-standing controversy regarding the mechanism of water catalyzed ESDPT in 7-azaindoles. We have demonstrated a new class of donor-{saturated hydrocarbon bridge}-acceptor (D-B-A) dyads based on a systematic approach to evaluate the corresponding photoinduced electron transfer process. Among these dyads heptacyclo[6.6.0.02,6.03,13.04,11.05,9.010,14]tetradecane (HCTD) was used as a unique spacer, which possesses a geometry of high symmetry (D2d), rigidity and linearity so that electron transfer processes can be examined between donor and acceptor substituents aligned along a straight line across the s-framework. In certain cases, via synthetic routes, the relative orientation of p-orbitals between donor and acceptor was adjusted to either a coplanar (0º) or perpendicular (90º) dihedral angle with respect to each other so that a comparative study could be made by tuning their relative electron coupling properties. The results in combination with theoretical approaches render valuable information on the spectroscopy and dynamics of excited-state electron transfer as functions of donor/acceptor electronic states, orientation as well as solvent properties.

博士
國立中央大學
化學研究所
96
This thesis is aimed to study the relationship between the photoinduced intramolecular electron transfer processes and the excited-state C-N bond cleavage reaction as well as intramolecular exciplex formation of a series of amine-bridge-stilbene derivatives. The fluorescence spectra of DPhI, MPhI and DEtI show dual fluorescence in polar solvents, but DCEtI and DPyI display only the locally-excited (LE) fluorescence in both nonpolar and polar solvents. Compounds DPhI and MPhI in nonpolar and polar solvents and DPyI and DPyCI in CH3CN undergo the C-N bond cleavage, leading to the formation of HI and CI of higher fluorescence quantum yields (Φf). However, such a C-N bond fragmentation reaction was not observed for DEtI in either nonpolar or polar solvents. The Φf and the quantum yields of the C-N bond cleavage reaction (Φfra) for DPyI and DPyCI increase as increasing the solvent polarity. In contrast, an opposite solvent dependence of Φfra was observed for DPhI and MPhI because the intramolecular electron transfer and back electron transfer processes locate in the Marcus normal and inverted region, respectively, and the value of ΦBET increases more than that of ΦICT with increasing the solvent polarity. Compounds DPyI2 and DPyI3 display only the LE fluorescence in both nonpolar and polar solvents, but the fluorescence quantum yields decrease and the fluorescence life times increase with increasing the solvent polarity. This indicates the presence of electron donor and acceptor interactions. Compounds DPhI2 and DPhI3 show dual fluorescence in moderate and highly polar solvents, and the long-wavelength emission band results from intramolecular exciplexes. When compared with the one-mothylene-bridged compounds, compounds DPyI2, DPyI3, DPhI2 and DPhI3 do not undergo the cleavage of C-N bond in both nonpolar and polar solvents.

London or dispersion interactions are weak van der Waals (vdW) interactions. They are important in determining the structure and properties of many chemical and biochemical systems. In this thesis, an optimizer using the nonempirical generalized gradient approximation (GGA) functional PW86+PBE+XDM, to capture van der Waals interactions, is presented. The work in this thesis covers the assessment of a variety of basis sets for their ability to reproduce accurate GGA repulsive and binding energies. Selected basis sets were then used to compute binding energies of 65 vdW complexes at equilibrium. This functional was also tested for binding energies of two sets of vdW complexes at distorted geometries. The last part deals with forces to investigate their accuracy using PW86+PBE+XDM in order to build an optimizer for vdW complexes using a nonempirical DFT method. Eventually, after confirming a high reproducibility of the optimizer on the geometries and binding energies, it was used in two biologically relevant applications. This optimizer is a unique tool to compute deformation energies with a nonempirical DFT method. The second part of this thesis covers a biologically relevant application where a conventional DFT is used. This application is related to the carrier of the genetic codes in living cells, DNA. DNA undergoes harmful mutations under external perturbations such as applied external electric fields. In this study, DNA base pairs were first mimicked by a simpler model, namely, the formic acid dimer. The effect of applied external electric fields on the geometries of the formic acid dimer is studied. The effect of these applied fields on the potential energy surface, the barrier height and the frequency of the double proton transfer in the formic acid dimer are also investigated. The study was then repeated on DNA base pairs to study the effect of an external applied electric field on the tunneling corrected rate constants of the double proton transfer reactions in AT and GC.

The three basic parameters controlling electron transfer are presented: electronic interaction, structural change and interelectronic repulsion. Then electron transfer in discrete molecular systems is considered, with cases of inter- and intramolecular transfers. The semi-classical (Marcus—Hush) and quantum models are developed, and the properties of mixed valence systems are described. Double exchange in magnetic mixed valence entities is introduced. Biological electron transfer in proteins is briefly presented. The conductivity in extended molecular solids (in particular organic conductors) is tackled starting from band theory, with examples such as KCP, polyacetylene and TTF-TCNQ. It is shown that electron–phonon interaction can change the geometrical structure and alter conductivity through Peierls distortion. Another important effect occurs in narrow-band systems where the interelectronic repulsion plays a leading role, for instance in Mott insulators.

This article examines disorder-induced electron localization in molecular-based materials, using DNA and pentacene molecular crystals as examples. In DNA, the disorder is intrinsic and strong, resulting in very short localization lengths. The pentacene crystal, on the other hand, is intrinsically homogeneous and the disorder is extrinsic and weak, which makes a metal–insulator transition (MIT) possible. After providing an overview of carbon-based materials for electronic applications, the article explains the methodology for calculating the localization properties of a DNA double strand and a pentacene molecular crystal, namely Hamiltonian, transfer matrix, and finite-size scaling. It also discusses the results, which show a substantial increase in the localization length of the electronic state with correlated disorder as compared to the case of uncorrelated disorder.

Double ionisation of most of the experimentally accessible diatomic molecules has been studied previously by several techniques, including Auger spectroscopy, double electron transfer, kinetic energy release, and high-level theory. New double photoionisation spectra of HBr, HI, N2, CO, NO, O2, Br2, ICl, and I2 are presented here with analysis to identify the electronic states of the doubly charged ions. A simple empirical model is introduced to estimate double ionisation energies on the basis of orbital energies. For CO, NO, and O2, an indirect double ionisation mechanism is found, involving dissociation of a singly charged molecular ion followed by atomic autoionisation of one fragment. Energies of the dication states are listed with distinction between adiabatic and vertical values.

This article describes the new phenomena of chemical substances encapsulated in the hollow spaces of carbon nanotubes, with particular emphasis on the nanospace of single-wall carbon nanotubes (SWNTs) that have nanospaces of about 1 nm in diameter. It begins with a brief introduction to the filling methods and the filling of multiwalled carbon nanotubes, followed by a discussion of the structures, phase transitions and chemical reactions of some typical fullerenes, endohedral metallofullerenes, fullerene derivatives, and inorganic and organic compounds, in the nanospace of SWNTs. The electron transfer between dopants and SWNTs is also examined. The article also considers the filling of double-walled carbon nanotubes.

This chapter highlights common six-electron group transfer reactions, such as the broken π-bonds that allow the existing and new σ-bonds to complete a ring in the product. It emphasizes that the ene reaction is similar to the diene reaction but with only one double bond, while the metalla-ene reaction occurs when the atom transferred is a metal atom. It also describes the purely thermal aldol reaction of an enol and a ketone, which is identified as a hetero group transfer reaction. The chapter mentions how the ene reaction was proven to be particularly powerful in synthesis when carried out intramolecularly. It discusses the usual increase in rate for an intramolecular reaction that allows even unreactive partners like hydrocarbons to combine.

When training models to learn the relationship between two or more variables, we expect to see previously demonstrated knowledge about that relationship reflected in the resulting estimators. For some domains, such as healthcare, it is imperative for actual implementation of those models that their predictions respect this knowledge. In this study we focus on Assisted Reproduction Technology (ART), the subspecialty of gynecology occupied with treating human infertility, and where the goal of any treatment is the delivery of a healthy newborn. A common ART treatment is In vitro Fertilization (IVF), where embryos are generated in vitro from collected sperm and oocytes, and transferred to the uterus of the patient after selecting those most likely to give rise to a healthy pregnancy. IVF has an approximate 30% successes rate per cycle; to palliate for this low success rate, a common practice so far has been to transfer two embryos simultaneously, aiming to increase the chances of a favorable outcome. While increasing overall live birth rates, this method has also led to an alarmingly high rate of twin and triplet births, associated with four times higher risk of perinatal mortality and increased obstetric complications. Our objective is to predict the chances of both pregnancy (P) and multiple pregnancy (MP) following either single embryo transfer (SET) or double embryo transfer (DET), and in so facilitating an informed decision on how many embryos to transfer. From existing literature, it is known that: (1) it is not possible for the chances of both P and MP to be decreased by increasing the number of embryos; (2) MP chances cannot be higher than P; and (3) chances of pregnancy are highly correlated with age, embryo stage, and quality. With a dataset generated from an existing observational study, we trained several state-of-the-art classifiers to predict P and MP given SET and DET. Analyzing the results, all classifiers achieved promising AUC scores. However, Random Forest and Gradient Boosting predicted negative chance differences in many instances when increasing the number of embryos infringing the first constraint. Logistic Regression predicted always positive differences, but in some instances it infringes the second constraint, predicting higher chances of MP than of P. Moreover, it showed little to no variation across ages or embryo stages violating third constraint. Conventional Machine Learning models struggle to reflect the real-world outcomes when using DET versus SET in specific patients. More informative variables could help, but it is already worrisome that variables as important as age and embryo stage do not result already in any variation, and that when models do show variation, in many cases they predicted decreasing chances of success with more embryos. We conclude that new and different approaches are needed to correctly model this scenario and, likely, many others resembling this one.

When training models to learn the relationship between two or more variables, we expect to see previously demonstrated knowledge about that relationship reflected in the resulting estimators. For some domains, such as healthcare, it is imperative for actual implementation of those models that their predictions respect this knowledge. In this study we focus on Assisted Reproduction Technology (ART), the subspecialty of gynecology occupied with treating human infertility, and where the goal of any treatment is the delivery of a healthy newborn. A common ART treatment is In vitro Fertilization (IVF), where embryos are generated in vitro from collected sperm and oocytes, and transferred to the uterus of the patient after selecting those most likely to give rise to a healthy pregnancy. IVF has an approximate 30% successes rate per cycle; to palliate for this low success rate, a common practice so far has been to transfer two embryos simultaneously, aiming to increase the chances of a favorable outcome. While increasing overall live birth rates, this method has also led to an alarmingly high rate of twin and triplet births, associated with four times higher risk of perinatal mortality and increased obstetric complications. Our objective is to predict the chances of both pregnancy (P) and multiple pregnancy (MP) following either single embryo transfer (SET) or double embryo transfer (DET), and in so facilitating an informed decision on how many embryos to transfer. From existing literature, it is known that: (1) it is not possible for the chances of both P and MP to be decreased by increasing the number of embryos; (2) MP chances cannot be higher than P; and (3) chances of pregnancy are highly correlated with age, embryo stage, and quality. With a dataset generated from an existing observational study, we trained several state-of-the-art classifiers to predict P and MP given SET and DET. Analyzing the results, all classifiers achieved promising AUC scores. However, Random Forest and Gradient Boosting predicted negative chance differences in many instances when increasing the number of embryos infringing the first constraint. Logistic Regression predicted always positive differences, but in some instances it infringes the second constraint, predicting higher chances of MP than of P. Moreover, it showed little to no variation across ages or embryo stages violating third constraint. Conventional Machine Learning models struggle to reflect the real-world outcomes when using DET versus SET in specific patients. More informative variables could help, but it is already worrisome that variables as important as age and embryo stage do not result already in any variation, and that when models do show variation, in many cases they predicted decreasing chances of success with more embryos. We conclude that new and different approaches are needed to correctly model this scenario and, likely, many others resembling this one.

This paper reports the first ultrafast studies on the rates of DNA-mediated forward and reverse electron transfer between photoexcited [M(phen)2dppz]2+ (M=Ru or Os, phen =1,10-phenanthroline, dppz = dipyrido[3,2:a-2′,3′:c]-phenazine) and various electron acceptors in order to ultimately determine the distance dependence of electron transfer kinetics with DNA as an environment.1,2 Previously Barton, Turro, and coworkers have presented evidence that electron transfer in DNA can occur rapidly over an extraordinarily large distance3 with a more shallow distance dependence than that for other media, such as liquids and proteins.4,5 Some theoretical work supports the shallow distance dependence which is attributed to a long range, thermally activated coherent mechanism involving virtual excitation of the DNA "bridge".6 Utilizing time-correlated single photon counting (TCSPC), we observe a substantial fraction of photoexcited [M(phen)2dppz]2+ (M=Ru, Os) exhibits fast oxidative quenching (kq > 3 x 1010 s−1) in the presence of intercalating Rh(III) acceptors while the remaining excited-state species exhibit a range of quenching constants less than 108 s_1. Transient-absorption experiments on the picosecond timescale indicate that, for a series of donors bound to mixed sequence DNA, the majority of back electron transfer is also very fast (ca. 1010 s−1). Importantly, the rate constant for the fast ground-state recovery is independent of loading of Rh(III) intercalators on DNA. As shown in Figure 1, regardless of whether the average loading of metal complexes is 1 in 33 basepairs or 1 in 10 basepairs, the fast bleach recovery exhibited by [Ru(phen)2dppz]2+ is well fit under all conditions by an exponential decay of 9 x 109s−1. Separate ultrafast data suggests that, like the recombination reaction, the fast quenching *M2+ is simple first-order at early time. If the early time electron transfer kinetics were not simple first order, and the electron transfer rate decayed with an exponential distance dependence (i.e. ≅ a factor of 30 per base step [3.4 Å]), our TCSPC apparatus should be able to observe some evidence of the slower components with rate constants in the range of 1010 - 108 s−1. The absence of rates in this range is evidence that the electron transfer is simple first order at time < 10 ns. This result has implications with regards to the donor-acceptor separations on DNA. Throughout most of the titration, intercalators are dilute on the double helix and statistics show that the amount of fast quenching and ground-state recovery observed is too great to be accounted for by random loading of nearest-neighbor pairs. Thus, either the electron transfer reaction must involve clustering of the donor and acceptor on the helix or the DNA-mediated interaction must occur over long distance.

Time-resolved techniques have lately been applied to the study of the dynamics of tunneling in semiconductor quantum well (QW) structures.1,2 The physics of tunneling in coupled QW structures has also been a topic of much recent interest.2,3 We have applied the technique of time-resolved photoluminescence (PL) spectroscopy to investigate tunneling in a novel asymmetric GaAs/AlGaAs double QW structure. We report in this paper the direct observation of PL from a charge-transfer" (CT) state, which is built up by electron and hole tunneling in opposite directions between the QW's.

Agrobacteriumtumefaciensmediates genetic transformation of plants. The possibility of exchanging the natural genes for other DNA has led to Agrobacterium’s emergence as the primary vector for genetic modification of plants. The similarity among eukaryotic mechanisms of nuclear import also suggests use of its active elements as media for non-viral genetic therapy in animals. These considerations motivate the present study of the process that carries DNA of bacterial origin into the host nucleus. The infective pathway of Agrobacterium involves excision of a single-stranded DNA molecule (T-strand) from the bacterial tumor-inducing plasmid. This transferred DNA (T-DNA) travels to the host cell cytoplasm along with two virulence proteins, VirD2 and VirE2, through a specific bacteriumplant channel(s). Little is known about the precise structure and composition of the resulting complex within the host cell and even less is known about the mechanism of its nuclear import and integration into the host cell genome. In the present proposal we combined the expertise of the US and Israeli labs and revealed many of the biophysical and biological properties of the genetic transformation process, thus enhancing our understanding of the processes leading to nuclear import and integration of the Agrobacterium T-DNA. Specifically, we sought to: I. Elucidate the interaction of the T-strand with its chaperones. II. Analyzing the three-dimensional structure of the T-complex and its chaperones in vitro. III. Analyze kinetics of T-complex formation and T-complex nuclear import. During the past three years we accomplished our goals and made the following major discoveries: (1) Resolved the VirE2-ssDNA three-dimensional structure. (2) Characterized VirE2-ssDNA assembly and aggregation, along with regulation by VirE1. (3) Studied VirE2-ssDNA nuclear import by electron tomography. (4) Showed that T-DNA integrates via double-stranded (ds) intermediates. (5) Identified that Arabidopsis Ku80 interacts with dsT-DNA intermediates and is essential for T-DNA integration. (6) Found a role of targeted proteolysis in T-DNA uncoating. Our research provide significant physical, molecular, and structural insights into the Tcomplex structure and composition, the effect of host receptors on its nuclear import, the mechanism of T-DNA nuclear import, proteolysis and integration in host cells. Understanding the mechanical and molecular basis for T-DNA nuclear import and integration is an essential key for the development of new strategies for genetic transformation of recalcitrant plant species. Thus, the knowledge gained in this study can potentially be applied to enhance the transformation process by interfering with key steps of the transformation process (i.e. nuclear import, proteolysis and integration). Finally, in addition to the study of Agrobacterium-host interaction, our research also revealed some fundamental insights into basic cellular mechanisms of nuclear import, targeted proteolysis, protein-DNA interactions and DNA repair.