bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Mechanisms of Branching Reactions in Melanin Formation - Ab Initio Quantum Chemistry Approach
Authors: Kishida Ryo , Kasai Hideaki 
Published: February 2020

Melanin, a pigment commonly found in animals, consists of two types of oligomeric unit: eumelanin (black to brown) and pheomelanin (yellow to reddish brown). The color of the skin, the hair, and the eyes is mainly determined by the ratio of eumelanin/pheomelanin production. The biosynthesis of melanin has been extensively investigated over the past 100 years. Among all reaction steps in the biosynthesis, reactions of dopachrome and dopaquinone, precursor molecules of melanin, directly affect the composition of melanin.
Dopachrome is spontaneously converted into the monomer of eumelanin via or not via desorption of carboxyl group (decarboxylation). The former (decarboxylative) path is usually preferred whereas the latter (non-decarboxylative) reaction is catalyzed by metal ions such as Cu(II). Depending on the kinetic preference of the two pathways, the carboxyl moiety of eumelanin diversely changes, affecting its properties and functions.
Dopaquinone can immediately undergo intramolecular cyclization, which is a reaction to form a cyclic structure, resulting in eumelanin synthesis. In a competitive manner, another reaction, thiol binding, which is a reaction to form a covalent bond with a sulfhydryl group, can prevail above a certain concentration of thiol compounds in the solution, resulting in pheomelanin synthesis. Thus, the fate of dopaquinone is directly related to the ratio of eumelanin/pheomelanin production.
Mechanistic understanding of the above-mentioned reactions is a key to predict or design the properties and functions of melanin. Therefore, we make use a theoretical approach in which quantum mechanics is applied to molecular systems. Thus, we employ first principles calculation based on density functional theory.
Our results show that the rate-limiting step of dopachrome conversion is deprotonation from β-carbon (β-deprotonation) at the first step. Furthermore, the subsequent steps were found to be regulated by the protonation state of the quinonoid oxygens, which are zwitterionic oxygens bound with benzene ring. Our calculations reveal that the quinonoid protonation facilitates decarboxylation. Cu(II) coordinated by quinonoid oxygens was found to protect the oxygens against protonation, leading to suppression of decarboxylation.
For dopaquinone, we investigate the first step of the cyclization and the thiol binding. To evaluate the effects of substituent bound with the benzene ring, we calculate some dopaquinone-like systems. Our results show that quinones presenting their highest occupied molecular orbital (HOMO) localized at the substituent are reactive for cyclization, and that an anti-bonding shape of lowest unoccupied molecular orbital (LUMO) in the benzene-substituent region is a signature for low reactivity toward thiol compounds.
This view obtained here is consistent with experiments and would provide a physico-chemical basis of melanin synthesis. Our results will be clues for designing new materials using melanin.
Towards Electron Transfer Compounds with Rigid Resistor Units
Authors: Locke Gemma M. , Senge Mathias O. 
Published: February 2020

In nature, the antenna chlorophylls in photosynthetic bacteria are arranged as non-covalent macrorings in a spatially defined manner to absorb and transfer solar energy efficiently to the reaction centers. To mimic this, porphyrin assemblies with rigid, well defined geometries are of interest. In the field of biomimetic porphyrins, the strategy for synthetic chemists has become one of designing novel porphyrin scaffolds that exhibit similar arrangements as those found in nature, for use as model compounds in electron transfer studies. For photochemical systems such as these the correct geometry and spatial arrangement of the molecular building block is mandatory, yet this aspect is often neglected in modern tetrapyrrole chemistry. Here we report on the synthesis of tailored multiporphyrin arrays with defined structures and regiochemical arrangement for use in electron transfer studies. This requires the availability of appropriate scaffold molecules and linker units. While many of these are available, there is a notable absence of rigid, non-conjugating units with defined geometry and we have undertaken to develop synthetic chemistry for the use of cubane and triptycene units in this context.
The lack of research into aliphatically linked, multiporphyrin systems can be explained by the inherent flexibility of standard sp3 linker units. Cubane, with a virtually inflexible carbon skeleton, overcomes this problem, theoretically allowing it to be used as an isolator in bridged porphyrin systems for electron transfer studies. Furthermore, unlike most linker systems used in organic chemistry, cubane is a saturated hydrocarbon, and thus will also serve as an electronic isolator, preventing through bond communication between substituents, a key goal necessary for electron transfer studies to investigate through space versus through bond ET processes. In addition, the rigid three-dimensional framework of triptycene together with its symmetry, shape persistency and ability to project up to six functional groups in a spatially defined 120° orientation makes it an especially attractive scaffold in modern synthesis. The key goal here is the synthesis of a multichromophoric arrays based on the triptycene scaffold to serve as a key model compound both in light harvesting and energy transfer studies, as well as antenna cores for optical drug delivery systems.
(Invited) Construction of Hemoprotein Assembly Via Heme-Heme Pocket Interaction and Its Photochemical Property
Authors: Hayashi Takashi , Mashima Tsuyoshi , Hirayama Shota , Oohora Koji 
Published: February 2020

Hemoproteins are metalloproteins which possess iron porphyrin as a prosthetic group (cofactor). These proteins have received much attention not only as biocatalysts but also as promising building blocks for development of new types of biomaterials. Particularly, the heme cofactor in several hemoproteins such as myoglobin, horseradish peroxidase, cytochrome P450, and cytochrome b
562 are replaceable with an artificial heme analog. To functionalize the hemoproteins, our group has focused on the cofactor-substitution with several porphyrinoid metal complexes.1) Furthermore, we have recently introduced a heme moiety onto the myoglobin surface via covalent linkage to obtain a supramolecular protein polymer via interprotein heme–heme pocket interaction.2) In this presentation, we report the recent results of the hemoprotein assembly which is a model of a light-harvesting system.3)

A hexameric tyrosine-coordinated heme protein (HTHP) containing photosensitizer molecules was prepared in an effort to construct a biomolecule with engineered photochemical properties. Zn protoporphyrin IX (ZnPP) and Zn chlorin e6 (ZnCe6) are inserted into the apoprotein of HTHP to yield reconstituted proteins which maintain the original hexameric structure of HTHP. Femtosecond transient absorption measurements indicate the occurrence of rapid singlet–singlet annihilation within a few picoseconds for each protein completely reconstituted with the six photosensitizer molecules. This finding supports the fact that the photo-induced energy migration occurs whtin the protein with the zinc complex. The fluorescence quenching efficiencies provided by methyl viologen as an electron acceptor for the completely reconstituted proteins with ZnPP and ZnCe6 are 2.3 and 2.6 fold-higher than that of the corresponding partially photosensitizer-inserted proteins, respectively. This indicates that energy migration occurs among the photosensitizers bound within the protein matrices. These findings are expected to lead to development of new protein-based artificial light harvesting systems.
1) Hayashi, T. In Coordination Chemistry in Protein Cages; Ueno, T.; Watanabe, Y., Eds.; Wiley: Hoboken, US, 2013; Chapter 4, pp 87–110.
2) Oohora, K.; Onoda, A.; Hayashi, T. Chem. Commun. 2012, 48, 11714–11726.
3) Oohora, K.; Mashima, T.; Ohkubo, K.; Fukuzumi, S.; Hayashi, T. Chem. Commun. 2015, 51, 11138–11140.
(Invited) Thermodynamics and Kinetics at the Solid-Solution Interface: Who Wins When?
Authors: Hipps K W , Mazur Ursula 
Published: February 2020

The formation of self-assembled two dimensional structures at the solid-solution interface has long been treated as an equilibrium process. In the case of porphyrin adsorption this is seldom true with kinetics often determining the structures observed at temperatures below about 50°C. Using scanning tunneling microscopy (STM) we will demonstrate that molecular scale time evolution studies coupled with concentration variations are essential for determining the extent to which thermodynamics or kinetics control the observed surface structure. Examples will be given of system in thermodynamic equilibrium and of those where kinetics is controlling. We also will demonstrate how coadsorption of two species with very different desorption rates can produce new 2D structures. An interesting example of cooperative adsorption will also be presented.
(Invited) Colour Bricks: Molecule-By-Molecule Supramolecular Arrays of Peryleneimides and Phthalocyanines on Solid Substrates
Authors: Efimov Alexander , Efimova Elena , Sariola-Leikas Essi , Hiltunen Arto , Hakola Hanna , Vivo Paola 
Published: February 2020

Highly ordered thin molecular ﬁlms, from monolayer to multilayer assemblies, promise considerable development for micro- and nanotechnology. In particular, the application of supramolecular chemistry to the direct assembling of functional layers at surfaces added a new and highly diverse class of materials to modern material science. Multicomponent arrays are attractive materials for applications such as nonlinear optical materials, enzyme sensors, solar energy storage devices, and molecular rectiﬁers in several ﬁelds as optics, biotechnology, photo- and electrochemistry.
The talk will describe a recently developed set of perylene and phthalocyanine derivatives from which one can build highly organized multilayered structures on metal oxide surfaces. The essential finding is the use of terpyridyl-crowned perylenemonoimides monoanhydrides as the anchoring substances. Another key point is a proper choice of bis(terpyridyl)perylenediimide or terpyridyl-phthalocyanine linkers. Combination of these two factors allows to assemble highly colored and stable multilayered molecular films by a simple and reproducible procedure. As a proof of concept it has been demonstrated that molecular arrays can be successfully used in solid state DSSC even at ambient conditions.
One can expect many other potential uses of the proposed multilayers. The tpy-perylene spacers of a fixed length make possible a localization of specific ions or chromophores at a controlled depth inside the layer. This would allow to create a gradient of redox potentials across the film and to achieve, e.g. upon photoexcitation, a charge shift into a certain distance and direction. High absorbance of the multilayered films might eliminate the need of using porous structures, while the possibility to cover easily large surfaces is a great advantage in practical applications.

Figure 1
(Keynote) 2D+1D and 2D+0D Hybrid Nanostructures and Their Applications in Electrochemical Energy Storage
Authors: Zhao Mengqiang , Alhabeb Mohamed , Gogotsi Yury 
Published: February 2020

Flexible and binder-free hybrid materials can be prepared by combining nanosheets of graphene, graphene oxide, MXenes (two-dimensional transition metal carbides) and other 2D materials with carbon onions, carbon black, porous carbide-derived carbon nanoparticles, and nanotubes. This helps to overcome the tendency of 2D sheets to restack, which minimizes their surface area accessible to the electrolyte and hinders their overall performance in electrochemical applications. Nanospacers such as carbon nanotubes (CNTs) are often introduced between reduced graphene oxide (rGO) sheets to enhance the electrolyte accessibility and electronic conductivity of the film. However, there are opportunities to use other 2D nanosheet-nanoparticle combinations that provide the desired set of properties due to synergistic effects of the nanoparticles. A brief overview of the carbon-carbon and carbon-carbide hybrids will be provided in this talk.
We have demonstrated fabrication of flexible, sandwich-like Ti3C2 MXene/CNT composite paper electrodes through alternating filtration of MXene and CNT dispersions. Spraying and other manufacturing methods can be used as well. Films containing onion- like carbon (OLC) and reduced graphene oxide (rGO) were also fabricated and compared with those with CNTs. The sandwich-like electrodes exhibited significantly improved electrochemical performance compared to those of pure MXene and randomly mixed MXene/CNT papers. Examples of Li-ion battery and electrochemical capacitor electrodes will be provided.
We also used highly porous carbide derived carbon (CDC) nanoparticles as spacers between graphene sheets and prepared rGO-CDC hybrid electrodes. The electrodes were made by thermal reduction of GO-CDC paper produced by vacuum-assisted filtration of aqueous solutions of GO-CDC composite containing 10-20 wt.% of CDC. Taking advantage of the high surface area and conductivity of rGO and the accessible pores of the CDC, the hybrid electrodes showed specific capacitances as high as 200-210 F/g at a scan rate of 100 mV/s. The addition of CDC between the rGO layers enhances the accessibility of electrodes to the electrolyte ions and good performance of the electrodes with the thickness to 40-50 μm was observed.
A New Approach for Selective Surface Functionalization of Carbon Electrodes in Biosensing by Plasma Direct-Writing
Authors: Thiha Aung , Ibrahim Fatimah , Abd Hamid Sharifah Bee , Madou Marc J 
Published: February 2020

We have found that carbon electrodes fabricated by the C-MEMS process to be chemically very inert. Hence, surface modification is necessary for their use as biosensors and electrochemical electrodes. Functionalization of carbon electrodes in an oxygen plasma or by acid treatment has been reported previously. However, there is often a need for selective functionalization only at specific locations on the electrodes, so that they can function as sensor element and also retain pristine surface chemistry in other areas. In this paper, we introduce a novel plasma direct-writing technique for selective functionalization of carbon electrodes with carboxylic groups at room temperature and atmospheric pressure. We demonstrate the plasma direct-writing on two test platforms. On platform one, we draw patterns of carboxylic functional groups on flat glassy carbon electrodes derived from photolithographically patterned photoresist. The second platform is carbon hybrid structure composed of glassy carbon walls and graphitic carbon nanowires suspended in between them by electromechanical spinning. Functionalization was performed only on nanowires by plasma direct-writing technique. The resulting surface chemistry and wettability of the electrodes are investigated by means of water contact angle measurement, Fourier transform infrared spectroscopy and Raman spectroscopy. Carboxylic group functionalization is a first step towards immobilization of DNA or immunoglobulin for carbon based biosensors. Selective surface functionalization is important for better accuracy in biosensing by preventing unwanted immobilization and their interference. The plasma direct-writing technique not only enables controlled writing of functional groups but also enables control of the degree of functionalization in a simple one step procedure.

Acknowledgement

The authors would like to acknowledge Ministry of Science Technology and Innovation (MOSTI) Science Fund (SF-020-2014), Transdisciplinary Research Grant Scheme (TR002A-2014B), and University of Malaya Flagship Grant (FL001-14AET).
Development of Micro-Supercapacitor Electrodes Based on Hybrid Transition Metal Oxide, Carbonized Silicon Nanowire Array
Authors: Ortaboy Sinem , Alper John , Carraro Carlo , Maboudian Roya 
Published: February 2020

Recently, silicon based supercapacitors have received considerable attention for application in mobile and remote sensing platforms due to their unique properties such as high surface area, low cost, long lifetimes, and excellent charge–discharge capability. These promising energy storage devices store more energy than conventional dielectric capacitors and deliver higher power with longer cycle life than available battery technologies. [1-4]. Recent studies in the field of supercapacitors have focused on the realization of hybrid materials to further improve the energy density of supercapacitors via the introduction of transition metal oxides and conductive polymers, which have pseudocapacitive properties.
Herein, we report the synthesis and the characterization of transition metal-oxide decorated carbonized silicon nanowires (TMO/C/PSiNWs) for high performance supercapacitor electrode materials. Porous silicon nanowires were synthesized using a metal assisted low-temperature wet etching procedure and encapsulated in an ultrathin graphitic carbon sheath by using chemical vapor deposition (CVD) technique. Growth of ultrathin TMO layer on C/SiNWs was carried out by a chemical bath deposition (CBD) method. Scanning electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy studies were performed to characterize of the hybrid electrodes. The energy and power density characteristics of the TMO/C/PSiNW electrodes were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge techniques. All the electrochemical performances were characterized in an 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) ionic liquid electrolyte in a potential range of −0.4−1.6 V vs Ag. Electrochemical measurements revealed that TMO/C/PSiNW showed the significant improvements over the previously reported C/PSiNW in terms of energy density and cycling performance. The enhanced capacitance was attributed to the excellent pseudocapacitive behavior of the TMO..

References:

[1] J.P. Alper, M.S. Kim, M. Vincent, B. Hsia, V. Radmilovic, C. Carraro, R. Maboudian Journal of Power Sources 230 (2013) 298-302.
[2] M.R. Zamfir, H.T. Nguyen, E. Moyen, Y.H. Lee, D. Pribat, J. Mater. Chem. A 1 (2013) 9566–9586.
[3] J.P. Alper, S. Wang, F. Rossi, G. Salviati, N.Yiu, C. Carraro,R. Maboudian, Nano Lett. 2014, 14, 1843−1847.
[4] P. Huang, M. Heon, D. Pech, M. Brunet, P.L. Taberna, Y. Gogotsi, S. Lofland, J.D. Hettinger, P. Simon, Journal of Power Sources, 225 (2013) 240-244.

Acknowledgements

This study was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) 2219- International Postdoctoral Research Fellowship Program (App. No:1059B191401401), and the National Science Foundation of the United States.
Modeling and Characterization of Tissue/Electrode Interface in Capacitive µECoG Glassy Carbon Electrodes
Authors: Goshi Noah , Vomero Maria , Dryg Ian , Seidman Scott , Kassegne Sam 
Published: February 2020

Understanding the chronic immune response to implanted neural electrodes is important from both a patient safety and long-term device functionality standpoint. In this investigation, we focused on examining the effects of the chronic immune response on the long-term functionality of µECoG surface electrodes implanted under the dura matter of in vivo rat models over a period of six weeks. We characterized the abio-bio interface of the explanted devices, and compared the biological layer adhered to capacitive (glassy carbon) electrodes to that of faradaic (Pt) electrodes. In addition, in vitro electrical conductivity tests of the explanted devices were performed, and the results were compared to both previously recorded pre-implant and in vivo conductivity data. Subsequently, the overall corrosion of the capacitive and faradaic electrodes were compared. Because both electrode types were coated in the same insulating material (polyimide) formed in the same geometry, the differences in the chronic immune response to the implanted devices can be attributed to the presence of either capacitive or faradaic electrodes. Further, we support the experimental observation with finite element modeling of the electrode/tissue interface where electric field, Nernst-Planck diffusion of charges, double layer capacitance, and pH distribution are evaluated qualitatively and quantitatively and correlated with experimental results.
Biosensing and Photoinactivation of S.Typhi in Water with ZnO-Rgo Hybridphotocatalysts
Authors: Abd Hamid Sharifah Bee , Lee pui Kee , Teh swee Jyan , Thong kwai Lin 
Published: February 2020

Nanostructured metal oxides, especially zinc oxide, ZnO had attracted great attention for the construction of biosensor due to its high isoelectric point (IEC). This high IEP of ZnO made it a good material for immobilisation of DNA through electrostatic interaction. On the other hand, the good conductivity, large surface area and biocompatibility have made carbon based materials such as reduced graphene oxide, rGO suitable candidate for electrochemical biosensor. In addition, rGO is an unique materials which has the ability to accept the electrons from the photocatalyst, ZnO and to slow down the recombination rate of electron-hole of ZnO. The limitation of ZnO as photocatalyts can be overcomed by forming hybrid with rGO. Thus, we used the rGO-ZnO thin film for biosensing and as photocatalyst for photoinactivation for bacteria in water. In this paper, reduced graphene oxide (rGO) was utilised to form hybrid with zinc oxide (ZnO) by electrodeposition. This rGO-ZnO thin film electrode acted as a hybrid-platform both for electrochemical and photoelectrochemical biosensor for the detection of S.Typhi in water. After biosensing, the same rGO-ZnO thin film, as photocatalyts too, was used to accelerate the sunlight-mediated inactivation of S.Typhi in the water sample.
Acknowledgement
This research is supported by University Malaya Flagship Grant project FL001A-14AET, and Transdisciplinary Research Grant Scheme (TRGS TR002A-2014) from Malaysian Ministry of Higher Education.