Efficiency of electron transport processes

In order to study the interfacial electron transfer, selfassembled monolayers (SAMs) on electrode surface have been attractive as a model system because they provide a stable and structurally well-defined monolayer with an adjustable thickness and desirable function. This characteristic of SAMs affords an opportunity to study fundamental issues such as the effects of distance and interfacial structure on the long-range electron transfer kinetics between a redox active species and an electrode. Weaver and Li obtained the first evidence of the distance-dependence of heterogeneous electron transfer rate constant for reduction of pentaaminecobalt(III) complexes anchored to gold and mercury surface. After Chidsey and co-workers reported heterogeneous electron transfer rate and electron tunneling constant (β) for the ferrocene-terminated alkanethiol monolayers with different alkyl chain length, a number of groups have reported β values for SAMs containing redox couples such as pentaamine (pyridine) Ru(II) complex, Os(II) bipyridyl complex, viologen, naphtoquinone, azobenzene, and hydroquinone. All of these reports demonstrated that the logarithmic heterogeneous apparent rate constant (kapp) linearly decreases as the distance between the electroactive center and the electrode surface increases as expected by Marcus theory. Those investigations on the distance dependence of electron transfer gave β values which are roughly ranging from 0.7 to 1.3 per methylene unit in the alkyl chain spacer. It is interesting to note that these β values are quite similar each other in their magnitude even though the electroactive SAMs contain different redox molecules and they follow significantly different electron transfer mechanism each other. For example, the electron transfer of ruthenium complex containing pentaamine and pyridine tether is highly reversible due to one-electron outer-sphere redox couple. However, redox center such as azobenzene undergoes substantially slow heterogeneous electron transfer because of its protonation reaction and structural change during its 2e−, 2H redox process. Among these redox centers studied, the electron transfer kinetics of a hydroquinone (H2Q) is also quite complicated due to its 2e −, 2H transfer reaction though Laviron presented a theoretical treatment of proton-coupled electron transfer reaction based on the nine-member square scheme. The electrochemical properties of hydroquinone/benzoquinone derivatives have been extensively studied in solutions because of their important biological activities. Especially, Hubbard and Soriaga have studied on the orientation of various quinones and mercaptohydroquinone derivatives adsorbed on metal surfaces using thin-layer electrochemistry. And Uosaki and coworkers have investigated the pH dependent redox behaviors of mercaptohydroquinone adsorbed on gold surface. We have reported the distance dependence of heterogeneous proton-coupled electron transfer rate constant of H2Q redox center in ω-mercaptoalkylhydroquinone SAMs on gold in 0.1 M HClO4 solution a few years ago. The β value reported for the H2Q-SAMs was 1.04 ± 0.06 and it was in good agreement with the values for the electroactive SAM systems reported up to now. However, the electron transfer kinetics of the H2Q-SAMs on gold shows remarkably different kinetic behavior in 0.1 M NaOH solution. In this note, we report an unusual observation for long range electron transfer in the ω-mercaptoalkylhydroquinone SAMs on gold electrode in a strong basic media. At this moment, the distance dependence of electron transfer of H2Q group is not observed in basic solution unlike that in acidic condition. Almost zero value of β determined from this phenomenon, to the best of our knowledge, is the first one in investigation of electron tunneling constant for long range electron transfer in the electroactive SAMs so far. The present work provides some understandings on the controlling factors related to proton-coupled electron transfer reaction nature.

Qualitative and quantitative criteria of irreversibility of electron transfer in cyclic voltammetry (CV) of tricarbonyl(N,N‐diphenylcyclohexadienecarboxamide)iron complexes were investigated. The measurement of the heterogeneous rate constants for electron transfer according to CV data over an extended range of free energy change ( ΔG) for these complexes are described. Kinetic analyses of the electrochemical technique demonstrates that when the applied potential exceeds the standard potential E°, the experimental rate constant ke represents an accurate measurement of the intrinsic rate constant k1 for electron transfer. However, as the applied potential is less than E°, the reversibility of the electron‐transfer process becomes increasingly more important, and the rate constants for reverse electron transfer k‐t and decomposition k2 of the electrogenerated intermediate have to be taken into account.

We have investigated the ionic strength (0.1-0.5 M NaCl) and pH dependence (4.0-7.5) of the electron transfer (ET) rate constants for oxidation and reduction of the bacterial di-heme protein cytochrome c4 (cyt c4; Pseudomonas stutzeri, ATCC No. 11607) by [Co(bipy)3]3+/2+ (bipy = 2,2'-bipyridine). The kinetics is bi- or tri-phasic, and a mechanism based on cooperative ET at both hemes, slow intramolecular ET and electrostatically dominated inter-heme interaction is presently best in line with all the available data. The ionic strength and pH dependence of the rate constants and reduction potentials is weak. The rate constants mostly decrease by 0-50% in the ionic strength range 0.1-0.5 M. The macroscopic potentials decrease by < 10 mV. Three of the microscopic potentials increase by 10-25 mV, while the fourth one decreases by 50 mV, but the accuracy of the microscopic reduction potential values is low. There is no pH dependence of the rate constants in the range 6.0-7.5, but most rate constants drop to half the 6.0-7.5 value in the range 4.0-6.0, leaving the reduction potentials almost unaffected. The small effects are unexpected in view of the highly charged and strongly dipolar character, and the many hydrogen bond contacts of cyt c4. These small effects must be related to the detailed rather the overall charge distribution of cyt c4.

Purpose – This paper aims to describe the creation of innovative and intelligent systems to optimise energy efficiency in manufacturing. The systems monitor energy consumption using ambient intelligence (AmI) and knowledge management (KM) technologies. Together they create a decision support system as an innovative add-on to currently used energy management systems. Design/methodology/approach – Energy consumption data (ECD) are processed within a service-oriented architecture-based platform. The platform provides condition-based energy consumption warning, online diagnostics of energy-related problems, support to manufacturing process lines installation and ramp-up phase and continuous improvement/optimisation of energy efficiency. The systems monitor energy consumption using AmI and KM technologies. Together they create a decision support system as an innovative add-on to currently used energy management systems. Findings – The systems produce an improvement in energy efficiency in manufacturing small- and medium-sized enterprises (SMEs). The systems provide more comprehensive information about energy use and some knowledge-based support. Research limitations/implications – Prototype systems were trialled in a manufacturing company that produces mooring chains for the offshore oil and gas industry, an energy intensive manufacturing operation. The paper describes a case study involving energy-intensive processes that addressed different manufacturing concepts and involved the manufacture of mooring chains for offshore platforms. The system was developed to support online detection of energy efficiency problems. Practical implications – Energy efficiency can be optimised in assembly and manufacturing processes. The systems produce an improvement in energy efficiency in manufacturing SMEs. The systems provide more comprehensive information about energy use and some knowledge-based support. Social implications – This research addresses two of the most critical problems in energy management in industrial production technologies: how to efficiently and promptly acquire and provide information online for optimising energy consumption and how to effectively use such knowledge to support decision making. Originality/value – This research was inspired by the need for industry to have effective tools for energy efficiency, and that opportunities for industry to take up energy efficiency measures are mostly not carried out. The research combined AmI and KM technologies and involved new uses of sensors, including wireless intelligent sensor networks, to measure environment parameters and conditions as well as to process performance and behaviour aspects, such as material flow using smart tags in highly flexible manufacturing or temperature distribution over machines. The information obtained could be correlated with standard ECD to monitor energy efficiency and identify problems. The new approach can provide effective ways to collect more information to give a new insight into energy consumption within a manufacturing system.

Photoinduced electron transfer processes between C 60/ C 70 and phthalocyanines such as tetra-tert-butylphthalocyanine ( H 2 TBPc ) and its zinc derivative ( ZnTBPc ) in polar solvents have been studied by observing the transient absorption spectra in the visible and near-IR regions. Upon predominant excitation of TBPcs with a 670 nm laser pulse in polar solvents, growth of the transient absorption bands of [Formula: see text] and [Formula: see text] was observed, accompanied by a concurrent decay of the triplet states of TBPcs (3 TBPc *). Thus it is confirmed that electron transfer occurs via 3 TBPc * in polar solvents. The electron transfer rate constants and efficiencies of electron transfer via 3 ZnTBPc * are greater than those via 3 H 2 TBPc * owing to the electron ejection ability of 3 ZnTBPc *. Solvent effects on the forward and backward electron transfer processes have been evaluated.

Currently, the traditional magnesium oxide production process is facing exceptional challenges arising from carbon emission restrictions and environmental protection. Waste bischofite pyrolysis has attracted much attention as a promising technology to address these challenges. Nonetheless, this process has primarily been demonstrated on a laboratory scale, with limited studies on an industrial scale. A comprehensive exergy analysis was conducted for the entire process and individual subunits within the pyrolysis process to identify potential areas for process enhancement. A FORTRAN subroutine based on empirical correlations of pyrolysis product yields was developed considering the impact of decomposition reactions on the simulation. Furthermore, the optimization of energy and exergy efficiency of the system was discussed in terms of the carbon dioxide emission factor, equivalence ratio, and pyrolysis temperature. The results show that the primary energy bottleneck lies in the combustion phase. In addition, the optimal energy and exergy efficiency conditions are a carbon dioxide emission factor of 5.3, an equivalent ratio of 1.15, and a pyrolysis temperature of 1100 °C. In comparison to the pilot-scale conditions, the energy efficiency and exergy efficiency increase by 2.55 and 3.61%, respectively. At this time, the MgO yield is 100%, and the HCl concentration is above 9.33%.

Complexes of CdS nanorods and [FeFe] hydrogenase I from Clostridium acetobutylicum have been shown to photochemically produce H2. This study examines the role of the ligands that passivate the nanocrystal surfaces in the electron transfer from photoexcited CdS to hydrogenase and the H2 generation that follows. We functionalized CdS nanorods with a series of mercaptocarboxylate surface-capping ligands of varying lengths and measured their photoexcited electron relaxation by transient absorption (TA) spectroscopy before and after hydrogenase adsorption. Rate constants for electron transfer from the nanocrystals to the enzyme, extracted by modeling of TA kinetics, decrease exponentially with ligand length, suggesting that the ligand layer acts as a barrier to charge transfer and controls the degree of electronic coupling. Relative light-driven H2 production efficiencies follow the relative quantum efficiencies of electron transfer, revealing the critical role of surface-capping ligands in determining the photochemical activity of these nanocrystal–enzyme complexes. Our results suggest that the H2 production in this system could be maximized with a choice of a surface-capping ligand that decreases the distance between the nanocrystal surface and the electron injection site of the enzyme.

Kinetic Monte Carlo simulation was applied to investigation of kinetics and photodecomposition mechanism of methylene blue over P25, P25-graphene, and P25-CNT nanocomposite catalyst under UV and visible irradiations. The reaction kinetic mechanisms of each abovementioned catalytic systems has been attained. The rate constants values for the each step of the reaction mechanisms (including recombination and charge transfer) were obtained as adjustable parameters by kinetic Monte Carlo simulation. The high value of the rate constant for electron transfer to graphene and CNT exhibits this transmission is occurred fast. The photoinduced electrons and holes can recombine with rate constant value about 0.001 min–1, but the rate constant of electron transfer is much higher than recombination. It was shown the rate constant of electron transfer to graphene is equal to CNT. There is a small difference between photocatalytic activity of P25-Gr and P25-CNT. The kinetic Monte Carlo simulation results of this research have satisfactorily agreement with the available experimental data for the methylene blue photodegradation.

The substantial electronic distinctions between bacteriochlorophyll (BChl) and its Mg-free analogue bacteriopheophytin (BPh) are exploited in two sets of Rhodobacter capsulatus reaction center (RC) mutants that contain a heterodimeric BChl-BPh primary electron donor (D). The BPh component of the M-heterodimer (Mhd) or L-heterodimer (Lhd) obtains from substituting a Leu for His M200 or for His L173, respectively. Lhd-β and Mhd-β RCs serve as the initial templates in the two mutant sets, where β denotes that the L-side BPh acceptor (HL) has been replaced by a BChl (due to substituting His for Leu M212). Three variants each of Lhd-β and Mhd-β mutants were constructed: (1) a swap (denoted YF) of the native Phe (L181) and Tyr (M208) residues, which flank D and the nearby M- and L-side monomeric BChl cofactors, respectively, giving Tyr (L181) and Phe (M208); (2) addition of a hydrogen bond (denoted L131LH) to the ring V keto group of the L-macrocycle of D, via replacing the native Leu at L131 with His; (3) the combination of 1 and 2. A low yield of electron transfer (ET) to the M-side BPh (HM) is observed in all four Lhd-containing RCs. Comparison with the yield of ET to β on the L-side shows that electron density on the L-macrocycle of D* favors ET to the M-side cofactors and vice versa. Increasing or decreasing the electronic asymmetry of D* via the YF, L131LH mutations or the combination results in consistent trends in the characteristics of the long-wavelength ground state absorption band of D, the rate constant of internal conversion of D* to the ground state, and the rate constants for ET to both the L- and M-side cofactors. A surprising correlation is that an increase in the charge asymmetry in D* not only increases the D* internal-conversion rate constant, but also the rate constants for ET to both the L- and M-side cofactors, spanning time scales of tens of picoseconds to several nanoseconds. The YF swap has a previously unrecognized effect on the electronic asymmetry of D*, resulting in increased charge asymmetry for the Mhd and decreased charge asymmetry for the Lhd. This result indicates that the native Tyr (M208) and Phe (L181) in the wild-type RC promote an electron distribution in P* that is the reverse of that favorable for ET to the photoactive L-branch. This conclusion reinforces the view that the native configuration of these residues promotes ET to the L branch primarily by poising the free energies of the charge-separated states. Overall, this work addresses the extent to which electronic couplings complement energetics in underpinning the directionality of ET in the bacterial RC.

We report the use of evanescent wave cavity ring-down spectroscopy (EW-CRDS) to monitor the reduction by ethylenediaminetetraacetic acid iron(II) complex, [FeEDTA](2-), of an adsorbed layer of oxidized cytochrome c immobilized on fused silica. The adsorption of cytochrome c at the silica-water interface was also probed using EW-CRDS and found to be in qualitative agreement with previous studies. The reduction of the adsorbed cytochrome c was achieved by using a strategically positioned electrode to electrogenerate FeEDTA(2-), which diffused to the silica surface and reduced the cytochrome c. The difference in the absorption spectra of the reduced and oxidized forms of cytochrome c at 400 nm allowed the direct monitoring of the electron transfer in real time. Using finite-element modelling, the rate constant of electron transfer (ET) between FeEDTA(2-) and cytochrome c was found to be 4.3(± 0.6) × 10(-9) cm s(-1) equivalent to 2.7(± 0.4) M(-1) s(-1). The latter value is considerably lower than previously reported ET rate constants between cytochrome c and FeEDTA(2-) in solution, which can be attributed to the confinement of the immobilized cytochrome c on the surface and possible effects from molecular crowding. This study highlights the importance of new methods which can be used to study ET at interfaces and opens up the possibility of studying ET to proteins in biologically relevant environments using EW-CRDS.

The synthesis of a series of donor–acceptor podands is described. The dependence of the rate constants of intramolecular photoinduced electron transfer on the exothermicity of the reaction was studied by stationary and time-resolved fluorescence spectroscopy. 1H NMR and computational studies suggest that the conformational change of the podands is restricted by K+ binding. As a result, the occurrence of highly exothermic photoinduced electron transfer reaction within the Marcus inverted region was observed.

Cell discontinuous transmission (DTX) has been proposed as a solution to reduce the energy consumption of cellular networks. This paper investigates the impact of network traffic load on the spectral and energy efficiency of cellular networks with DTX. The signal-to-interference-plus-noise ratio (SINR) distribution as a function of traffic load is derived first. Then, the sufficient condition for ignoring thermal noise and simplifying the SINR distribution is investigated. Based on the simplified SINR distribution, the network spectral and energy efficiency as functions of network traffic load are derived. It is shown that the network spectral efficiency increases monotonically in traffic load, while the optimal network energy efficiency depends on the ratio of the sleep-mode power consumption to the active-mode power consumption of base stations. If the ratio is larger than a certain threshold, the network energy efficiency increases monotonically with network traffic load and is maximized when the network is fully loaded. Otherwise, the network energy efficiency first increases and then decreases in network traffic load. The optimal load can be identified with a binary search algorithm. The power ratio threshold depends solely on the path loss exponent α, e.g., 56% for α = 4. All these analytic results are further validated by the numerical simulations.

Six-electron oxidation of anthracene to anthraquinone by a nonheme MnIV -oxo complex, [(Bn-TPEN)MnIV (O)]2+ , proceeds through a rate-determining electron transfer from anthracene to [(Bn-TPEN)MnIV (O)]2+ , followed by subsequent fast oxidation reactions to give anthraquinone. The reduced MnII complex ([(Bn-TPEN)MnII ]2+ ) is oxidized by [(Bn-TPEN)MnIV (O)]2+ rapidly to produce the μ-oxo dimer ([(Bn-TPEN)MnIII -O-MnIII (Bn-TPEN)]4+ ). The oxygen atoms of the anthraquinone product were found to derive from the manganese-oxo species by the 18 O-labelling experiments. In the presence of Sc3+ ion, formation of an anthracene radical cation was directly detected in the electron transfer from anthracene to a Sc3+ ion-bound MnIV (O) complex, [(Bn-TPEN)MnIV (O)-(Sc(OTf)3 )2 ]2+ , followed by subsequent further oxidation to yield anthraquinone. When anthracene was replaced by 9,10-dimethylanthracene, electron transfer from 9,10-dimethylanthracene to [(Bn-TPEN)MnIV (O)-(Sc(OTf)3 )2 ]2+ occurred rapidly to produce stable 9,10-dimethylanthracene radical cation. The driving force dependence of the rate constants of electron transfer from the anthracene derivatives to [(Bn-TPEN)MnIV (O)]2+ and [(Bn-TPEN)MnIV (O)-(Sc(OTf)3 )2 ]2+ was well-evaluated in light of the Marcus theory of electron transfer.

Energy efficiency evaluation of industrial park customers is carried out to help customers develop optimization strategies and improve the energy efficiency level. The evaluation indexes are proposed based on pressure-state-response (PSR) model and the redundant indexes are selected by combining principal component analysis (PCA) and correlation analysis. Thus the dynamic energy efficiency index system is constructed. The weight of indexes is calculated by the entropy weight method (EWM). An energy efficiency evaluation model based on improved Grey-technique for order preference by similarity to ideal solution (TOPSIS) is proposed, which replaces the Euclidean distance by weighted grey correlation degree and can accurately evaluate customers’ energy efficiency level. An energy efficiency optimization model is proposed, which can maximize optimization benefits while improving energy efficiency. The validity of the evaluation and optimization models is verified by the case study of an industrial park.

Diffusion-controlled rate constant of electron transfer at the oil|water interface