scholarly journals Cyclic Aromaticity within Huckel and Quasi-Correlated Huckel-like Models

2018 ◽  
Keyword(s):  
Tight Binding ◽  
Type Systems ◽  
Polycyclic Aromatic ◽  
Highly Correlated ◽  
Net Charges ◽  
Graphene Structures ◽  
Structural Classes ◽  
Nontrivial Topology ◽  
Dianionic Form ◽  
Local Aromaticity

The paper deals with quantifying aromaticity in π-electron networks by unsophisticated MO techniques. The focus is placed on local aromaticity measures associated with individual benzenoid rings. We revised the ring aromaticity index due to Cioslowski et al (2007) by including explicitly net charges and electron unpairing effects. Our previously introduced quasi-correlated tight-binding (QCTB) approximation serves here as an easily available tool for taking account of π-electron correlations. The latter crucially influence the behavior of large and even small conjugated π-structures with a nontrivial topology. Numerical applications of Hückel and QCTB models to measuring local aromaticity are reported for various structural classes (polycyclic aromatic hydrocarbons (PAHs), graphene nanoflakes, and others). We analytically investigate the aromaticity in conjugated monocycles CNHN (neutral and charged ones). Furthermore, in the same manner several PAH structures (oligocenes, pyrene, perylene, etc.) are considered in their charged states, and the results are compared with those of related quinoid-type systems, such as p-diphenoquinodimethane. It is shown that, unlike usual PAHs, quinodimethane structures tend to increase their aromaticity in dicationic (dianionic) form. In our studies of nanographene aromaticity we find a decrease of the local aromaticity as we move to a center of graphene structures, that is in a sharp contrast to the predictions of NICS (nucleus independent chemical shift), a rather criticized approach. A particular emphasis is being put on measuring local aromaticity in highly correlated π-systems. Typical non-Kekule hydrocarbons (e.g., triangulene radical and polyradicals), are also studied within QCTB by which characteristic difficulties caused by the occurrence of many non-bonding π-MOs, are simply obviated.

scholarly journals Toxic Effects of Heavy Metals and Organic Polycyclic Aromatic Hydrocarbons in Sediment Porewater on the Amphipod Hyalella azteca and Zebrafish Brachydanio rerio Embryos from Different Rivers in Taiwan

2021 ◽  
Vol 11 (17) ◽  
pp. 8021
Author(s):  
Shao-Yang Hu ◽  
Chi-Ying Hsieh ◽  
Hans-Uwe Dahms ◽  
Yu-Hsien Tseng ◽  
Jesse Chen ◽  
...  
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Aromatic Hydrocarbons ◽  
Detection Rate ◽  
Hyalella Azteca ◽  
Toxic Effects ◽  
Brachydanio Rerio ◽  
Aquatic Life ◽  
Polycyclic Aromatic ◽  
Pahs Concentration ◽  
Highly Correlated

The amphipod (Hyalella azteca) and zebrafish (Brachydanio rerio) embryos were used for toxicological sediment porewater testing. Porewaters from 35 sampling stations of eight streams in southern Taiwan were screened for toxic effects and their relationship with 6 metal and 16 polycyclic aromatic hydrocarbons (PAHs). Concentration analysis results showed that the following PAHs, naphththalene, benzo(b)fluoranthene, dibenz(a,h)anthracene, acenaphthalene, and the heavy metal cadmium were not detected in 35 sampling stations. The highest detection rate of 94.1% was caused by the PAHs fluoranthene and pyrene. The highest detection rate of the metal zinc was 88.6% of 35 analyzed samples. The majority of samples (88%) were classified as level tier 1 according to USEPA national sediment inventory. This indicates the probability of adverse effects on aquatic life or human health. The results of a zebrafish embryo test showed that heart rate and survival were significantly reduced with all porewater samples. Therefore, fish exposed to contaminated river conditions may be affected in their cardiovascular functions. Looking at correlations between toxic effects of metals and PAHs, we found that phenanthrene, anthracene, pyrene, benzo(a)anthracene, chrysene, benzo(b)fluoranthene, and benzo(a)pyrene were low, while fluorene was highly correlated with toxic effects of metals.

scholarly journals Fullerene-Tetrabenzofluorene (C60-TBF) in Multivalent Photosensitisation for Enhanced ZnO-based Photo-catalysts: Mono vs. Hexakis Adduct

2022 ◽  
Author(s):  
Munusamy Krishnamurthy ◽  
Philip Hope ◽  
P Ramar ◽  
A. A. Boopathi ◽  
Srinivasan Sampath ◽  
...  
Keyword(s):  
Self Assembly ◽  
Hydrogen Generation ◽  
Active Material ◽  
Type Systems ◽  
Clear Understanding ◽  
Catalytic Method ◽  
Design Synthesis ◽  
Polycyclic Aromatic ◽  
Assembly Behavior ◽  
Comparative Results

Photo-catalysts offer a simple catalytic method with widespread applications like degradation of polluting dyes, hydrogen generation from water, etc., in the presence of a photon source like sunlight. The development of a second-generation photo-catalyst in the form of a nanocomposite is an integral part of research to improve the practical usefulness and efficiency of the process. A systematic study using the active material with controlled functional groups is required to understand the process in detail as well as to develop efficient photocatalytic systems. In this paper, we report the design, synthesis, detailed physicochemical studies, and self-assembly of interesting materials where fullerenes have been functionalized with polycyclic, aromatic, conjugated, butterfly-shaped molecules like Tetrabenzofluorene (TBF) using a well-known click chemistry approach. Detailed analyses using spectroscopic, electrochemical, and microscopic or X-ray diffraction (single crystal) techniques were undertaken for a clear understanding of their photophysical or self-assembly behavior. The functionalized fullerene material was mainly used so that comparative results could be presented where two units (mono adduct) or twelve units (hexakis adduct) of TBF molecules were attached separately. These comparative studies were beneficial for unambiguous interpretation of results and drawing definitive conclusions regarding the energy transfer with cascade-type systems. Finally, those results were useful for the logical understanding of photo-catalytic experiments using those designer fullerene materials.

scholarly journals Polycyclic aromatic hydrocarbons in the snow cover of the northern city agglomeration

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
A. Yu. Kozhevnikov ◽  
D. I. Falev ◽  
S. A. Sypalov ◽  
I. S. Kozhevnikova ◽  
D. S. Kosyakov
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Aromatic Hydrocarbons ◽  
High Performance ◽  
Molecular Weights ◽  
Average Maximum ◽  
Solid Fuel Combustion ◽  
Polycyclic Aromatic ◽  
Highly Correlated ◽  
Northern City ◽  
Snow Samples

AbstractSixteen priority polycyclic aromatic hydrocarbons (PAHs) were qualitatively and quantitatively assessed by high-performance liquid chromatography with fluorescence detection in snow samples collected at 46 sites of Arkhangelsk as a world’s largest city above 64 degrees north latitude. The average, maximum and minimum PAH concentrations in snow were 168, 665, and 16 ng/kg, respectively. The average toxic equivalent value in benzo(a)pyrene units was 3.6 ng/kg, which is three-fold lower than the established maximum permissible concentration and considered an evidence of a low/moderate level of snow pollution with PAHs. The pollution origin was assessed using specific markers based on PAHs ratios in the studied samples. The pyrogenic sources of PAH emission were predominate, whereas the significant contributions from both transport and solid fuel combustion were observed. Benzo(a)pyrene concentrations are highly correlated with the levels of other PAHs with higher molecular weights.

scholarly journals Dissociation of polycyclic aromatic hydrocarbons: molecular dynamics studies

2017 ◽  
Vol 375 (2092) ◽  
pp. 20160195 ◽  
Author(s):  
A. Simon ◽  
M. Rapacioli ◽  
G. Rouaut ◽  
G. Trinquier ◽  
F. X. Gadéa
Keyword(s):  
Molecular Dynamics ◽  
Internal Energy ◽  
Density Functional ◽  
Tight Binding ◽  
Radical Cations ◽  
Branching Ratios ◽  
Point Of View ◽  
Statistical Dynamics ◽  
Polycyclic Aromatic ◽  
Dynamics Simulations

We present dynamical studies of the dissociation of polycyclic aromatic hydrocarbon (PAH) radical cations in their ground electronic states with significant internal energy. Molecular dynamics simulations are performed, the electronic structure being described on-the-fly at the self-consistent-charge density functional-based tight binding (SCC–DFTB) level of theory. The SCC–DFTB approach is first benchmarked against DFT results. Extensive simulations are achieved for naphthalene , pyrene and coronene at several energies. Such studies enable one to derive significant trends on branching ratios, kinetics, structures and hints on the formation mechanism of the ejected neutral fragments. In particular, dependence of branching ratios on PAH size and energy were retrieved. The losses of H and C 2 H 2 (recognized as the ethyne molecule) were identified as major dissociation channels. The H/C 2 H 2 ratio was found to increase with PAH size and to decrease with energy. For , which is the most interesting PAH from the astrophysical point of view, the loss of H was found as the quasi-only channel for an internal energy of 30 eV. Overall, in line with experimental trends, decreasing the internal energy or increasing the PAH size will favour the hydrogen loss channels with respect to carbonaceous fragments. This article is part of the themed issue ‘Theoretical and computational studies of non-equilibrium and non-statistical dynamics in the gas phase, in the condensed phase and at interfaces’.

Photochemical Evolution of Interstellar/Precometary Organic Material

1997 ◽  
Vol 161 ◽  
pp. 23-47 ◽  
Author(s):  
Louis J. Allamandola ◽  
Max P. Bernstein ◽  
Scott A. Sandford
Keyword(s):  
Origin Of Life ◽  
Building Blocks ◽  
Complex Species ◽  
Infrared Observations ◽  
Interstellar Ice ◽  
Polycyclic Aromatic ◽  
Ultraviolet Photolysis ◽  
The Origin Of Life ◽  
Simple Molecules ◽  
Complex Organic

AbstractInfrared observations, combined with realistic laboratory simulations, have revolutionized our understanding of interstellar ice and dust, the building blocks of comets. Since comets are thought to be a major source of the volatiles on the primative earth, their organic inventory is of central importance to questions concerning the origin of life. Ices in molecular clouds contain the very simple molecules H2O, CH3OH, CO, CO2, CH4, H2, and probably some NH3and H2CO, as well as more complex species including nitriles, ketones, and esters. The evidence for these, as well as carbonrich materials such as polycyclic aromatic hydrocarbons (PAHs), microdiamonds, and amorphous carbon is briefly reviewed. This is followed by a detailed summary of interstellar/precometary ice photochemical evolution based on laboratory studies of realistic polar ice analogs. Ultraviolet photolysis of these ices produces H2, H2CO, CO2, CO, CH4, HCO, and the moderately complex organic molecules: CH3CH2OH (ethanol), HC(= O)NH2(formamide), CH3C(= O)NH2(acetamide), R-CN (nitriles), and hexamethylenetetramine (HMT, C6H12N4), as well as more complex species including polyoxymethylene and related species (POMs), amides, and ketones. The ready formation of these organic species from simple starting mixtures, the ice chemistry that ensues when these ices are mildly warmed, plus the observation that the more complex refractory photoproducts show lipid-like behavior and readily self organize into droplets upon exposure to liquid water suggest that comets may have played an important role in the origin of life.

Transmission Electron Microscopy of Evaporated Perylene Thin Films

1990 ◽  
Vol 48 (2) ◽  
pp. 336-337
Author(s):  
C. Ewins ◽  
J.R. Fryer
Keyword(s):  
Electron Microscopy ◽  
Thin Films ◽  
Transmission Electron Microscopy ◽  
Molecular Electronics ◽  
High Vacuum ◽  
Amorphous Layer ◽  
Electric Heater ◽  
Transmission Electron ◽  
Polycyclic Aromatic

The preparation of thin films of organic molecules is currently receiving much attention because of the need to produce good quality thin films for molecular electronics. We have produced thin films of the polycyclic aromatic, perylene C10H12 by evaporation under high vacuum onto a potassium chloride (KCl) substrate. The role of substrate temperature in determining the morphology and crystallography of the films was then investigated by transmission electron microscopy (TEM).The substrate studied was the (001) face of a freshly cleaved crystal of KCl. The temperature of the KCl was controlled by an electric heater or a cold finger. The KCl was heated to 200°C under a vacuum of 10-6 torr and allowed to cool to the desired temperature. The perylene was then evaporated over a period of one minute from a molybdenum boat at a distance of 10cm from the KCl. The perylene thin film was then backed with an amorphous layer of carbon and floated onto copper microscope grids.

Cannabis use in Switzerland: The role of attribution of drug use to friends, urbanization and repression 1The study was supported by the Swiss Federal Office of Public Health (Bundesamt für Gesundheit BAG) Grant 316.96.5980.

2001 ◽  
Vol 60 (2) ◽  
pp. 99-107 ◽  
Author(s):  
Holger Schmid
Keyword(s):  
Drug Use ◽  
Urban Areas ◽  
Hierarchical Linear Model ◽  
Cannabis Use ◽  
School Aged Children ◽  
Structural Variables ◽  
Hbsc Study ◽  
Nationally Representative ◽  
Highly Correlated ◽  
Individual Use

Cannabis use does not show homogeneous patterns in a country. In particular, urbanization appears to influence prevalence rates, with higher rates in urban areas. A hierarchical linear model (HLM) was employed to analyze these structural influences on individuals in Switzerland. Data for this analysis were taken from the Switzerland survey of Health Behavior in School-Aged Children (HBSC) Study, the most recent survey to assess drug use in a nationally representative sample of 3473 15-year-olds. A total of 1487 male and 1620 female students indicated their cannabis use and their attributions of drug use to friends. As second level variables we included address density in the 26 Swiss Cantons as an indicator of urbanization and officially recorded offences of cannabis use in the Cantons as an indicator of repressive policy. Attribution of drug use to friends is highly correlated with cannabis use. The correlation is even more pronounced in urban Cantons. However, no association between recorded offences and cannabis use was found. The results suggest that structural variables influence individuals. Living in an urban area effects the attribution of drug use to friends. On the other hand repressive policy does not affect individual use.

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