bluuebunny/crossref_metadata_2025_split huggingface dataset:
From Breathing Pores to Three-Dimensional Ionic Self-Assembly Under Electrochemical Control
Authors: Mertens Stijn F. L. , Cui Kang , Ivasenko Oleksandr , Mali Kunal , Walter Michael , Feng Xinliang , Müllen Klaus , De Feyter Steven 
Published: February 2020

Molecular self-assembly at the solid–liquid interface is highly developed, yet still faces several challenges, in particular related to reaching into the third dimension. Here, we demonstrate the spontaneous and reversible transition between two- and three-dimensional self-assembly of a charged polyaromatic molecule at the solid–liquid interface under electrochemical conditions, using in situ scanning tunnelling microscopy. By tuning the interfacial potential, we can selectively organise our target molecules in an open porous pattern, stretch these pores to accommodate another molecule and form an auto-host–guest structure, or stack the building blocks in a stratified bilayer. Using a simple electrostatic model, we rationalise which charge density is required to enable bilayer formation, and conversely, which molecular size/charge ratio is necessary in the design of new building blocks. Our findings could form the basis of electrochemically controlled dynamic host–guest systems and 3D structures such as artificial receptors.
References
[1] K. Cui, K.S. Mali, O. Ivasenko, D. Wu, X. Feng, M. Walter, K. Müllen, S. De Feyter, S.F.L. Mertens, Angew. Chem., Int. Ed. 53, 12951 (2014).
[2] K. Cui, O. Ivasenko, K. S. Mali, D. Wu, X. Feng, K. Müllen, S. De Feyter, S. F. L. Mertens, Chem. Commun. 50, 10376 (2014).

Figure 1
Silicon Nanocrystals Coated By Porphyrins As Light-Harvesting Antennae
Authors: Ceroni Paola , Locritani Mirko , Fermi Andrea , Bergamini Giacomo , Yu Yixuan , Korgel Brian A. 
Published: February 2020

Silicon (Si) is a widely used semiconductor, in part because it is abundant, widely available and essentially non-toxic. From the photophysical point of view, it exhibits weak light absorption and emission because it has an indirect bandgap. Conversely, Si nanocrystals (SiNCs) in the quantum size range (2-12 nm) can be made as viable light emitters with emission wavelength that can be tuned from the near-infrared (NIR) into the visible by decreasing their size [1-3]. Covalent Si-to-carbon bonding also offers the possibility of integrating inorganic and organic components into robust structures. Most optical studies of SiNCs have focused on alkyl-passivated nanocrystals, while little is known about the interaction between such nanocrystals and chromophoric units attached to the core. Therefore we have studied the interaction of an inorganic silicon nanoparticle core with appended organic chromophores for the development of novel luminescent materials.
The synthesis of luminescent colloidal nanocrystals of silicon is still a difficult task in terms of reliability and reproducibility. We report the thermal decomposition of hydrogen silsequioxane, followed by etching and hydrosilylation [4]. This method isolated SiNCs with good yields, high surface coverage and exceptional control over the dimensions and optical properties of the materials.
In the present work, the H-terminated nanocrystals were used as a platform for co-passivation with dodecene and different organic chromophores [5] by thermal hydrosilylation. For example, we functionalised two families of SiNC of average diameter of 2.5 and 5 nm with porphyrin chromophores: porphyrin excitation results in an efficient energy transfer to the nanocrystal core. To the best of our knowledge this is the first time in which highly efficient light harvesting from photoactive units to the silicon core have been demonstrated. This approach enabled us to circumvent the drawback of the low molar absorption coefficient of SiNCs. The investigated hybrid material exhibits high quantum yield also in the NIR spectral region with lifetime in the µs range.
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1995, 117, 2915-2922.
[2] Mastronardi, M. L.; Henderson, E. J.; Puzzo,D. P.; Ozin, G. A. Adv. Mater.
2012, 24, 5890-5898.
[3] Kelly, J. A.; Hendersonw, E. J.; Veinot, J. G. C. Chem. Commun. 2010, 46, 8704–8718
[4] Hessel, C. M.; Reid,D.; Panthani, M. G.; Rasch, M. R.;Goodfellow, B. W.; Wei, J.; Fujii, H.; Akhavan,V.; Korgel, B. A. Chem.
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2012, 24, 393−401.
[5] Locritani, M.; Yu, Y.; Bergamini, G.; Molloy, J. K.; Baroncini, M.; Korgel, B. A.; Ceroni, P. J. Phys. Chem. Lett.
2014, 5, 3325-3329.

Figure 1
Role of the Heme Axial Ligand on the Reactivity of High-Valent Oxo-Iron Porphyrin Intermediate
Authors: Fujii Hiroshi 
Published: February 2020

High-valent iron oxo species have been known as the key reaction intermediates in the catalytic cycles of oxygen activating iron enzymes. In heme enzymes, oxoiron(IV) porphyrin π-cation radical species named compound I were characterized in the catalytic cycles of peroxidases, catalases, and cytochrome P450. These heme enzymes have the same heme (iron protoporphyrin IX), but different heme proximal (axial) ligands; histidine in peroxidase, tyrosine in catalase, and cysteine in cytochrome P450, which are highly conserved in these heme enzymes. Therefore, the axial ligand has been believed to tune the reactivity of compound I. To reveal functional role of the axial ligand, the axial ligand effect on the reactivity of high-valent iron oxo species has been studied systematically with synthetic enzyme model complexes. In this presentation, we present how the heme axial ligand modulate the reactivity of compound I. Compound I model complexes, (TMP+
·)FeIVO(L), changed its reactivity by identity of the axial ligand, but the reactivity did not correlate with any spectroscopic data of (TMP+
·)FeIVO(L), such as the redox potential and Fe=O bond strength. Surprisingly, a clear correlation was found between the reactivity of (TMP+
·)FeIVO(L) and FeII/FeIII redox potential of (TMP)FeIIIL, the final reaction product. Axail ligand-exchange experiments and theoretical calculations showed linear free-energy relationship, in which the axial ligand modulates the reaction free energy by changing the stability of (TMP)FeIII(L) more significantly than (TMP+
·)FeIVO(L). All results indicate that the reactivity of compound I is controlled by thermodynamic stability of the ground state of the final reaction product, not but compound I itself. Therefore, the heme axial ligand activates compound I by stabilizing the resting state, not by activating compound I. The proposed mechanism can be explained by the trans-ligand effect of the oxo-ligand, which migrates from compound I to substrate in the reaction.
Developments of Porphyrin Derivatives As Photosensitizers for Photodynamic Therapy
Authors: Horiuchi Hiroaki 
Published: February 2020

Photodynamic therapy (PDT) is accepted as one of the promising treatments for cancers. In PDT, three individually nontoxic components (photosensitizer, light, and molecular oxygen) are combined only in tumor tissue to produce reactive oxygen species (ROS), particularly singlet oxygen. Thus the patient can improve the quality of life by PDT different from conventional therapies, such as radiotherapy, surgery or chemotherapy. To develop PDT, improvements of the photosensitizing drug are required. Mainly, there are two methods to improve photosensitizers. The first is improvement of photodynamic activity. The second method is to reduce side effects. Tetraphenylporphyrin (TPP) is one of the most fundamental photosensitizers for PDT and thus we have tried to improve its activity and also tried to suppress its side effects.
First, we have tried to improve the activity. Factors controlling the activity involve accumulation efficiency to tumors, cellular uptake efficiency, light absorption efficiency in the red to near-IR region, and quantum yield of singlet oxygen sensitization. We substituted silyl groups to water-soluble TPP derivatives, because silicon is considered to have potential for improving pharmacological and/or photochemical efficiencies. Quantum yield of singlet oxygen sensitization has evaluated by monitoring near-IR phosphorescence from singlet oxygen sensitized, and found that silylation improve the quantum yield. Cell-culture studies have been carried out to evaluate pharmacological properties. We found that silylation also improve cellular uptake efficiency. We carried out in vivo study by using tumor-bearing mice. Silylation also improve selective accumulation efficiency. As a results of these improvements, in vivo PDT activity was found to be enhanced by silylation significantly [1].
Second, we have tried to suppress the side effects. Although the photosensitizer used for PDT possesses tumor selectivity, its concentration is not negligibly small in normal tissue such as skin. Photosensitizers themselves show no side effects in the dark, but under the sun or room light, the side effect will be induced. Thus patients have to remain in a dark room until almost all the photosensitizers injected are eliminated. These long periods are one of the reasons for hesitation in selecting PDT as a cancer treatment. To suppress the side effects, we introduced ON/OFF switching mechanism to photosensitizers. We selected very simple modification i.e. just introduction of amino group(s) to phenyl moiety of TPP derivative to switch photosensitization efficiency by acidity. In the neutral condition, the photosensitization efficiency was low (OFF state) because of photo-induced electron transfer quenching from the aromatic amine moiety to porphyrin moiety. In the acidic condition, the photosensitization efficiency recovered (ON state) by the protonation of amino group. This system is expected to be as a pH-activatable photosensitizer.
[1] H. Horiuchi et al., Chem. Eur. J., (2014), 20, 6054.
Engineering Self-Assembled Materials through Serendipity
Authors: Bonifazi Davide 
Published: February 2020

Organic architectures are considered amongst the most promising candidates for engineering molecular-based devices. It is however necessary to develop systems that can form at interfaces organized molecular assemblies featuring addressable and controllable arrangements. In this respect, the hierarchical self-assembly of organic molecules featuring complementary non-covalent recognition sites allowing the simultaneous assembly of several units and long-range order is one of the most promising approaches.
In this talk, I will describe our approaches to engineer multidimensional structures through the exploitation of weak interactions established by programmed molecules. Quoting a letter (dated 28 January 1754) from Horace Walpole to Horace Mann, he said he formed it from the Persian fairy tale “The Three Princes of Serendip”, whose heroes "were always making discoveries, by accidents and sagacity, of things they were not in quest of". Therefore, specific serendipitous examples will be discussed with the attempt to answer to the question of whether and how the supramolecular approach can bridge organic chemistry with molecular organization and to which extend we can achieve macroscopic functions solely through molecular engineering.
Electroreduction of Oxygen with Brominated Metallo-Corroles
Authors: Elbaz Lior , Levi Naomi , Gross Zeev , Mahammed Atif 
Published: February 2020

Fuel cell technology raised new interest over the past two decades due to the increasing oil prices, non-sustainability of fossil fuel and the consequences of combustion on air pollution and climate changes. Two aspects limit the practicality and energy conversion efficiency in polymer electrolyte membrane fuel cells: the rate-limiting oxygen reduction reaction at the cathode and the low abundance and high cost of platinum, which still remains the most efficient catalyst.
Significant effort has been made to develop alternative non-precious metal catalysts (NPMCs) for oxygen reduction. Many of those catalysts have been inspired by biological processes in that their active centers consist of transition metal complexes such as metallo-porphyrins. So far, studies conducted with such catalysts show that their activity and stability is lower than that of the state-of-the-art platinum based catalysts. In most recent years a new class of NPMCs has shown great promise; the metallo-corroles.
A series of first row transition metal β-pyrrole-brominated 5,10,15-tris(penta-fluorophenyl)- Corroles [M(tpfc)Br8, M=Mn, Fe, Co, Ni and Cu] were synthe-sized and tested as catalysts for oxygen reduction in acidic aqueous solutions. Both the reduced form and the oxidized forms of these corroles were chara-cterizes by means of NMR, EPR and UV-vis measurements. Rotating Ring-Disk electrode (RRDE) was used to test the kinetic performance of these corroles in the catalytic reaction of oxygen reduction (ORR). The corroles were adsorbed on a high surface area carbon powder (BP2000) prior to electro-chemical measurements, to create a unique composite material. The comparison between the corroles with different metal centers showed a favorable catalytic performance of the ORR in the case of the Co-Corrole, which showed an onset potential of only 0.8V vs. RHE (Figure 1).

Figure 1
Reactivity and Spectroscopic Studies of Oxygen Reduction Reaction of Bio-Inspired Molecular Catalysts
Authors: Ohta Takehiro , Nagaraju Perumandla , Naruta Yoshinori 
Published: February 2020

Studies of oxygen reduction reaction (ORR) catalyzed by bio-inspired porphyrin catalysts is important for developing non-precious metal catalysts of fuel cell and for fundamental understanding of the reaction mechanism. Molecular catalysts have advantage in study of ORR with more facile access to the reaction mechanism experimentally compared to biological and inhomogeneous systems. We have previously shown that an axial ligand tethered iron porphyrin complex shows a crucial role in dioxygen activation [1]. As a next generation model a hanging hydrogen bond donor was incorporated at the distal site of heme that could stabilize heme bound intermediates and may induce proton-coupled electron transfer mechanism. In ORR desorption of an OH ligand and formation of OOH intermediate are most energy demanding steps [2]. Our new model showed that the hydrogen bonding interaction can alter the thermodynamic properties of ORR facilitating efficient electron transfer to heme bound O2. Resonance Raman studies of reaction intermediates provide direct evidence of reaction mechanisms as well as probe of metal-ligand and ligand internal covalency: As expected the incorporated hydrogen bond donor was found to interact with heme bound oxygen ligand. The thermochemical properties of ORR were examined with density functional theory calculations, demonstrating H-bonding and axial ligation of heme are crucial structural mechanism in activation of O2. The Sabatier principle states metal-ligand interaction is a descriptor of catalysts [2]. However in inhomogeneous system the reaction mechanism is not understood well due to difficulty of vibrational spectroscopic studies of the in situ reaction. Thus our approach to study ORR provides deep insights into the molecular mechanism of electrocatalysts. The structure/reactivity correlation gained by our reactivity and spectroscopic studies of bio-inspired molecular catalysts will be discussed.
[1] (a) J.-G. Liu, T. Ohta, S. Yamaguchi, T. Ogura, S. Sakamoto, Y. Maeda, Y. Naruta, Angew. Chem. Int. Ed., 48, 9262-9267 (2009). (b) T. Ohta, J.-G. Liu, Y. Naruta, Coord. Chem. Rev., 257, 407-413 (2013).
[2] J. K. Nørskov et al., J. Phys. Chem. B, 108, 17886-17892 (2004)
Localized Corrosion of Carbon Steel in Simulated Concrete Pore Solution: Influence of Chloride Ion and Temperature
Authors: Sharifi-Asl Samin , Kursten Bruno , Macdonald Digby D 
Published: February 2020

Passivity breakdown on carbon steel, which is the reference candidate material for fabricating high-level nuclear waste containers in Belgium, has been studied and the data are interpreted in terms of the point defect model (PDM). The near normal distribution in breakdown potential, measured in deaerated simulated concrete pore water solution (pH 12.5) at different chloride concentrations and temperatures are in satisfactory agreement with prediction of the PDM. An increase in temperature from 25°C to 85°C results in a decrease in localized corrosion resistance according to a linear relationship between the critical breakdown voltage, Eb
, and log(chloride activity) for all chloride concentrations. The linear dependence of the passivity breakdown potential on the square root of potential scan rate (ν1/2), as predicted by the PDM, yields an estimate of the critical areal concentration of condensed cation vacancies at the metal/film interface (ξ<=5.45×1014cm-2 at 85oC and <=1.07×1014cm-2 at 55oC ) that leads to the passivity breakdown. The experimental distributions in the breakdown potential for carbon steel at 55oC and 85oC are in satisfactory agreement with the relevant calculated distributions.

Acknowledgment: The authors gratefully acknowledge the support of this work by ONDRAF-NIRAS of Belgium.
Microscopic Surface Studies of Modified Nickel-Based Superalloy 718 after Corrosion Fatigue in Simulated Sour Environment
Authors: Ziomek-Moroz Margaret , Hawk Jeffrey A. , Collins Keith , Rozman Kyle , Thodla Ramgopal , Gui Feng 
Published: February 2020

The Unites States predicted 60% growth in energy demand by 2030 makes oil and natural gas primary target fuels for energy generation. The fact that the peak of oil production from shallow wells (< 5000 m) is about to be reached, thereby pushing the oil and natural gas industry into deeper wells. However, drilling to depths greater than 5000 m requires materials with high strength-to weight ratio, excellent corrosion resistance in H2S-contating sour environments, and high toughness.
Ni-based superalloy, also called Alloy 718, has been considered for use as a bottom-hole component during offshore drilling due to its good general corrosion resistance and lack of magnetism. However, its susceptibility to environmentally assisted cracking (EAC) has not been studied for microstructures with increased high strength. To fill this technology gap, the National Energy Technology Laboratory in collaboration with DNV is currently studying mechanisms of fatigue crack growth rate (FCGR) for Alloy718, oil grade version, in simulated sour well environments.
The FCGR behavior of oil grade Alloy 718, was investigated by monitoring crack growth rate in deaerated 0.2% and 20 % NaCl solutions, respectively, in contact with H2S and CO2 as a function of frequency. The partial pressures for H2S (pH2S) was 692 kPa and for CO2 (pCO2) was 3458 kPa in each solution. Each fatigue experiment was performed at 177°C at ΔK=1392 Nmm-3/2 and R=0.2 in the frequency sequence 1Hz/ 0.3Hz/ 0.1Hz/ 0.03Hz/ 0.01Hz/ 0.003Hz followed by ΔK=522 Nmm-3/2 and R=0.7 in the sequence 1Hz/ 0.3Hz/ 0.1Hz/ 0.03Hz/ 0.01Hz in an autoclave. Surface investigations were augmented by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). In this study, research focused on surface analyses supported by the fatigue crack growth rate measurements.
SEM backscatter electron (BSE) micrograph of the fracture surface after the fatigue experiment carried in 0.2% NaCl containing CO2 and H2S revealed no accumulation of the corrosion products The EDS chemical analysis near the crack tip found mostly nickel. In general, only transgranular crack growth was observed over the investigated ΔK and frequency scans.

SEM investigations of the fracture surface of the sample after the fatigue test in the 20% NaCl containing CO2 and H2S. sour environment at 177°C revealed the presence of secondary cracks, bright inclusions, and beach marks. The EDS chemical analysis of the bright inclusion, showed a (Nb, C)-rich phase. Also, corrosion products were not detected near the crack tip.
It appears that the passive layer is disturbed by the cyclic stress in each solution. The presence of secondary cracks at the crack tip of Alloy 718 in 20% NaCl/pH2S = 692 kPa/ pCO2=3458kPa indicates that this environment is more aggressive than 0.2% NaCl/ pH2S = 692 kPa/ pCO2=3458kPa.
Effect of Zinc Diffusion Distribution on Corrosion Behavior of Brazed Tube/Fin Assemblies of Aluminum Automotive Condensers
Authors: Guia-Tello Juan C. , Pech-Canul Maximo A. , Pech-Canul Martin I. , Gorocica-Diaz Jorge A. , Arana-Guillén René , Puch-Bleis José 
Published: February 2020

The aim of this research is the evaluation of corrosion behavior in Sea Water Acidified Accelerated Test (SWAAT) solution of tube/fin assemblies from two aluminum condenser prototypes with micro-channel tubes having similar compositions but different amount of sprayed zinc per unit area (5.5 and 4.2 g/m2, respectively). Such assemblies (Fig. 1) were brazed in a laboratory furnace under a pure nitrogen atmosphere. In order to simulate conditions for different diffusion rate and penetration depth, two sets of brazing parameters were selected: set A (610°C, 4min) and set B (600°C, 2min). The results of potentiodynamic polarization and electrochemical impedance measurements showed for both prototypes that the sample brazed under set B parameters exhibited lower corrosion rate compared to that brazed under set A parameters. The sample with lowest corrosion rate was the one with microchannel tubes containing 5.5 g/m2 of zinc before brazing. The observed corrosion behavior was correlated to zinc diffusion profiles obtained from SEM-EDS analysis. Galvanic current measurements showed that for short immersion times (1h) the tube is anodic to the fins, but the current is not stable and there is an evolution to lower values, suggesting that for long immersion periods there might be a inversion in the galvanic coupling.

Figure 1