scholarly journals Diazocine-functionalized TATA platforms

2019 ◽  
Vol 15 ◽  
pp. 1485-1490 ◽  
Author(s):  
Roland Löw ◽  
Talina Rusch ◽  
Fynn Röhricht ◽  
Olaf Magnussen ◽  
Rainer Herges
Keyword(s):  
Metal Surface ◽  
Gold Surface ◽  
Electronic Coupling ◽  
Molecular Architecture ◽  
Rate Acceleration ◽  
Spin Switch ◽  
Bulk Gold

Recently, it has been shown that the thermochemical cis→trans isomerization of azobenzenes is accelerated by a factor of more than 1000 by electronic coupling to a gold surface via a conjugated system with 11 bonds and a distance of 14 Å. The corresponding molecular architecture consists of a platform (triazatriangulenium (TATA)) which adsorbs on the gold surface, with an acetylene spacer standing upright, like a post in the middle of the platform and the azobenzene unit mounted on top. The rate acceleration is due to a very peculiar thermal singlet–triplet–singlet mechanism mediated by bulk gold. To investigate this mechanism further and to examine scope and limitation of the “spin-switch catalysis” we now prepared analogous diazocine systems. Diazocines, in contrast to azobenzenes, are stable in the cis-configuration. Upon irradiation with light of 405 nm the cis-configuration isomerizes to the trans-form, which slowly returns back to the stable cis-isomer. To investigate the thermal trans→cis isomerization as a function of the conjugation to the metal surface, we connected the acetylene spacer in meta (weak conjugation) and in para (strong conjugation) position. Both isomers form ordered monolayers on Au(111) surfaces.

scholarly journals Diazocine functionalized TATA Platforms

2019 ◽  
Author(s):  
Roland Löw ◽  
Talina Rusch ◽  
Fynn Röhricht ◽  
Olaf M Magnussen ◽  
Rainer Herges
Keyword(s):  
Metal Surface ◽  
Gold Surface ◽  
Electronic Coupling ◽  
Molecular Architecture ◽  
Rate Acceleration ◽  
Spin Switch ◽  
Bulk Gold

Recently, it has been shown that the thermochemical cis→trans isomerization of azobenzenes is accelerated by a factor of more than 1000 by electronic coupling to a gold surface via a conjugated system with 11 bonds and a distance of 14 Å. The corresponding molecular architecture consists of a platform (triazatriangulenium (TATA)) which adsorbs on the gold surface, with an acetylene spacer standing upright, like a post in the middle of the platform and the azobenzene unit mounted on top. The rate acceleration is due to a very peculiar thermal singlet-triplet-singlet mechanism mediated by bulk gold. To investigate this mechanism further and to examine scope and limitation of the “spin-switch catalysis” we now prepared analogous diazocine systems. Diazocines, in contrast to azobenzenes, are stable in the cis configuration. Upon irradiation with light of 405 nm the cis configuration isomerizes to the trans form, which slowly returns back to the stable cis isomer. To investigate the thermal trans→cis isomerization as a function of the conjugation to the metal surface, we connected the acetylene spacer in meta (weak conjugation) and in para (strong conjugation) position. Both isomers form ordered monolayers on Au(111) surfaces.

scholarly journals Role of intramolecular hydrogen bonds in promoting electron flow through amino acid and oligopeptide conjugates

2021 ◽  
Vol 118 (11) ◽  
pp. e2026462118
Author(s):  
Rafał Orłowski ◽  
John A. Clark ◽  
James B. Derr ◽  
Eli M. Espinoza ◽  
Maximilian F. Mayther ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Hydrogen Bonds ◽  
Electron Flow ◽  
Intramolecular Hydrogen Bonding ◽  
Electronic Coupling ◽  
Molecular Architecture ◽  
Energy Flows ◽  
Donor And Acceptor ◽  
Donor Acceptor ◽  
Intramolecular Hydrogen

Elucidating the factors that control charge transfer rates in relatively flexible conjugates is of importance for understanding energy flows in biology as well as assisting the design and construction of electronic devices. Here, we report ultrafast electron transfer (ET) and hole transfer (HT) between a corrole (Cor) donor linked to a perylene-diimide (PDI) acceptor by a tetrameric alanine (Ala)4. Selective photoexcitation of the donor and acceptor triggers subpicosecond and picosecond ET and HT. Replacement of the (Ala)4 linker with either a single alanine or phenylalanine does not substantially affect the ET and HT kinetics. We infer that electronic coupling in these reactions is not mediated by tetrapeptide backbone nor by direct donor–acceptor interactions. Employing a combination of NMR, circular dichroism, and computational studies, we show that intramolecular hydrogen bonding brings the donor and the acceptor into proximity in a “scorpion-shaped” molecular architecture, thereby accounting for the unusually high ET and HT rates. Photoinduced charge transfer relies on a (Cor)NH…O=C–NH…O=C(PDI) electronic-coupling pathway involving two pivotal hydrogen bonds and a central amide group as a mediator. Our work provides guidelines for construction of effective donor–acceptor assemblies linked by long flexible bridges as well as insights into structural motifs for mediating ET and HT in proteins.

Long‐Distance Rate Acceleration by Bulk Gold

2019 ◽  
Vol 58 (20) ◽  
pp. 6574-6578 ◽  
Author(s):  
Alexander Schlimm ◽  
Roland Löw ◽  
Talina Rusch ◽  
Fynn Röhricht ◽  
Thomas Strunskus ◽  
...  
Keyword(s):  
Long Distance ◽  
Rate Acceleration ◽  
Bulk Gold

scholarly journals The role of adatoms in chloride-activated colloidal silver nanoparticles for surface-enhanced Raman scattering enhancement

2018 ◽  
Vol 9 ◽  
pp. 2236-2247 ◽  
Author(s):  
Nicolae Leopold ◽  
Andrei Stefancu ◽  
Krisztian Herman ◽  
István Sz Tódor ◽  
Stefania D Iancu ◽  
...  
Keyword(s):  
Silver Nanoparticles ◽  
Raman Scattering ◽  
Metal Surface ◽  
Surface Enhanced Raman Scattering ◽  
Electronic Coupling ◽  
Colloidal Silver ◽  
Colloidal Silver Nanoparticles ◽  
Surface Enhanced ◽  
Surface Enhanced Raman ◽  
Enhanced Raman Scattering

Chloride-capped silver nanoparticles (Cl-AgNPs) allow for high-intensity surface-enhanced Raman scattering (SERS) spectra of cationic molecules to be obtained (even at nanomolar concentration) and may also play a key role in understanding some fundamental principles behind SERS. In this study, we describe a fast (<10 min) and simple protocol for obtaining highly SERS-active colloidal silver nanoparticles (AgNPs) with a mean diameter of 36 nm by photoconversion from AgCl precursor microparticles in the absence of any organic reducing or capping agent. The resulting AgNPs are already SERS-activated by the Cl− ions chemisorbed onto the metal surface where the chloride concentration in the colloidal solution is 10−2 M. Consequently, the enhanced SERS spectra of cationic dyes (e.g., crystal violet or 9-aminoacridine) demonstrate the advantages of Cl-AgNPs compared to the as-synthesized AgNPs obtained by standard Ag+ reduction with hydroxylamine (hya-AgNPS) or citrate (cit-AgNPs). The results of SERS experiments on anionic and cationic test molecules comparing Cl-AgNPs, hya-AgNPs and cit-AgNPs colloids activated with different amounts of Cl− and/or cations such as Ag+, Mg2+ or Ca2+ can be explained within the understanding of the adatom model – the chemisorption of cationic analytes onto the metal surface is mediated by the Cl− ions, whereas ions like Ag+, Mg2+ or Ca2+ mediate the electronic coupling of anionic species to the silver metal surface. Moreover, the SERS effect is switched on only after the electronic coupling of the adsorbate to the silver surface at SERS-active sites. The experiments presented in this study highlight the SERS-activating role played by ions such as Cl−, Ag+, Mg2+ or Ca2+, which is a process that seems to prevail over the Raman enhancement due to nanoparticle aggregation.

Long‐Distance Rate Acceleration by Bulk Gold

2019 ◽  
Vol 131 (20) ◽  
pp. 6646-6650 ◽  
Author(s):  
Alexander Schlimm ◽  
Roland Löw ◽  
Talina Rusch ◽  
Fynn Röhricht ◽  
Thomas Strunskus ◽  
...  
Keyword(s):  
Long Distance ◽  
Rate Acceleration ◽  
Bulk Gold

Study of Silicon-metal Interaction in Adsorption Process: An Ab-initio Approach

2011 ◽  
Vol 1305 ◽  
Author(s):  
Sudip Chakraborty ◽  
S. V. Ghaisas ◽  
Chiranjib Majumder
Keyword(s):  
Metal Surface ◽  
Density Functional ◽  
Electrical Contact ◽  
Island Size ◽  
Functional Theory ◽  
The Difference ◽  
Ab Initio Approach ◽  
Bulk Gold ◽  
Cluster Level

Abstract:The formation of metal silicide plays important role in deciding the nature of the contact on silicon.Due to their chemically neautral nature,Au and Ag are used as contact metals in various devices.In particular the role of silicides is known to be crucial in defining the behavior of the electrical contact. The interaction of these metals with silicon at cluster level is still under the study.For naoscale devices, the nature at such interaction carries lot more inportance. Bulk Gold silicide(Cohesive energy ~ 3.81eV/atom) shows higher stability compared to silver silicide(Cohesive enrgy ~ 2.95 eV/atom). In the present work we show computational results based on Density Functional Theory(DFT) of Si cluster adsorption on Ag(111) surface and compare with the results of Si adsorption on Au(111). These results bring out the difference in Si cluster-metal surface interactions at the nanoscale. In particular the Si island-metal surface interaction shows island size dependence. We have presented results for most stable orientations only.

Study of the Molecular Architecture of Keratin Filaments by Electron Microscopy

1982 ◽  
Vol 40 ◽  
pp. 118-119
Author(s):  
U. Aebi ◽  
P. Rew ◽  
T.-T. Sun
Keyword(s):  
Electron Microscopy ◽  
Structural Organization ◽  
Cell Types ◽  
Structural Features ◽  
Molecular Architecture ◽  
The Past ◽  
Keratin Filaments ◽  
Different Types ◽  
10 Nm Filaments ◽  
Different Cell Types

Various types of intermediate-sized (10-nm) filaments have been found and described in many different cell types during the past few years. Despite the differences in the chemical composition among the different types of filaments, they all yield common structural features: they are usually up to several microns long and have a diameter of 7 to 10 nm; there is evidence that they are made of several 2 to 3.5 nm wide protofilaments which are helically wound around each other; the secondary structure of the polypeptides constituting the filaments is rich in ∞-helix. However a detailed description of their structural organization is lacking to date.

Electrochemical nucleation and growth of copper on iron and aluminum: A TEM study of industrial copper cementation

1978 ◽  
Vol 36 (1) ◽  
pp. 454-455
Author(s):  
L.E. Murr ◽  
V. Annamalai
Keyword(s):  
Metal Surface ◽  
Copper Deposit ◽  
Nucleation And Growth ◽  
16Th Century ◽  
Electrochemical Reactions ◽  
Mine Shaft ◽  
De Re ◽  
Copper Precipitation ◽  
Electrochemical Nucleation ◽  
Interesting System

Georgius Agricola in 1556 in his classical book, “De Re Metallica”, mentioned a strange water drawn from a mine shaft near Schmölnitz in Hungary that eroded iron and turned it into copper. This precipitation (or cementation) of copper on iron was employed as a commercial technique for producing copper at the Rio Tinto Mines in Spain in the 16th Century, and it continues today to account for as much as 15 percent of the copper produced by several U.S. copper companies.In addition to the Cu/Fe system, many other similar heterogeneous, electrochemical reactions can occur where ions from solution are reduced to metal on a more electropositive metal surface. In the case of copper precipitation from solution, aluminum is also an interesting system because of economic, environmental (ecological) and energy considerations. In studies of copper cementation on aluminum as an alternative to the historical Cu/Fe system, it was noticed that the two systems (Cu/Fe and Cu/Al) were kinetically very different, and that this difference was due in large part to differences in the structure of the residual, cement-copper deposit.

Exploration of cell wall architecture with the rapid-freeze deep-etch technique

1993 ◽  
Vol 51 ◽  
pp. 128-129
Author(s):  
Béatrice Satiat-Jeunemaitre ◽  
Chris Hawes
Keyword(s):  
Plant Cell ◽  
Cell Walls ◽  
Cell Biology ◽  
Molecular Model ◽  
Three Dimensional ◽  
Secretory Activity ◽  
Wall Structure ◽  
Specimen Preparation ◽  
Molecular Architecture ◽  
Plant Cell Walls

The comprehension of the molecular architecture of plant cell walls is one of the best examples in cell biology which illustrates how developments in microscopy have extended the frontiers of a topic. Indeed from the first electron microscope observation of cell walls it has become apparent that our understanding of wall structure has advanced hand in hand with improvements in the technology of specimen preparation for electron microscopy. Cell walls are sub-cellular compartments outside the peripheral plasma membrane, the construction of which depends on a complex cellular biosynthetic and secretory activity (1). They are composed of interwoven polymers, synthesised independently, which together perform a number of varied functions. Biochemical studies have provided us with much data on the varied molecular composition of plant cell walls. However, the detailed intermolecular relationships and the three dimensional arrangement of the polymers in situ remains a mystery. The difficulty in establishing a general molecular model for plant cell walls is also complicated by the vast diversity in wall composition among plant species.

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