scholarly journals Terahertz Spectral Properties of 5-Substituted Uracils

Sensors ◽  
2021 ◽  
Vol 21 (24) ◽  
pp. 8292
Author(s):  
Kaixuan Li ◽  
Ding Li ◽  
Yan Zhang
Keyword(s):  
Absorption Spectra ◽  
Wide Spectrum ◽  
Molecular Structures ◽  
Absorption Peak ◽  
Molecular Vibration ◽  
Terahertz Time Domain Spectroscopy ◽  
Additional Absorption ◽  
Low Frequencies ◽  
Relative Atomic Mass ◽  
Good Agreement

Applications of terahertz time-domain spectroscopy (THz-TDS) in the fields of chemistry and biomedicine have recently received increased attention. Specifically, THz-TDS is particularly effective for the identification of alkaloid molecules, because it can distinguish the vibration types of base molecules in the THz band and provide a direct characteristic spectrum for the configuration and conformation of biomolecules. However, when THz-TDS technology is used to identify alkaloid molecules, most of them are concentrated in the 0.1–3.0 THz band, limiting the amount of information that can be obtained. In this work, a wide-spectrum THz-TDS system was independently built to explore the absorption spectra of uracil and its 5-substituents in the range of 1.3–6.0 THz. We found that, in the THz band, uracil and its 5-substituents have similar absorption peaks near 4.9 and 3.3 THz, while the 5-substituents have an additional absorption peak in the range of 1.5–2.5 THz. This absorption peak is red-shifted as the relative atomic mass of the 5-substituted atoms increases. Gaussian software was adopted to calculate the absorption spectra of the samples. The simulation conclusions were in good agreement with the experimental results, revealing that the vibration of the base molecule at low frequencies can be attributed to the inter-molecular vibration. This work demonstrates that THz-TDS technology can be used to accurately identify biomolecules with similar molecular structures, reflecting the importance of molecular structure in biological activity.

scholarly journals In Vitro Characterization of the Antibacterial Spectrum of Novel Bacterial Type II Topoisomerase Inhibitors of the Aminobenzimidazole Class

2006 ◽  
Vol 50 (4) ◽  
pp. 1228-1237 ◽  
Author(s):  
Nagraj Mani ◽  
Christian H. Gross ◽  
Jonathan D. Parsons ◽  
Brian Hanzelka ◽  
Ute Müh ◽  
...  
Keyword(s):  
Bacterial Resistance ◽  
Wide Spectrum ◽  
Dna Gyrase ◽  
Antibacterial Activities ◽  
Mechanisms Of Action ◽  
Fluoroquinolone Resistance ◽  
Topoisomerase Iv ◽  
Low Frequencies

ABSTRACT Antibiotics with novel mechanisms of action are becoming increasingly important in the battle against bacterial resistance to all currently used classes of antibiotics. Bacterial DNA gyrase and topoisomerase IV (topoIV) are the familiar targets of fluoroquinolone and coumarin antibiotics. Here we present the characterization of two members of a new class of synthetic bacterial topoII ATPase inhibitors: VRT-125853 and VRT-752586. These aminobenzimidazole compounds were potent inhibitors of both DNA gyrase and topoIV and had excellent antibacterial activities against a wide spectrum of problematic pathogens responsible for both nosocomial and community-acquired infections, including staphylococci, streptococci, enterococci, and mycobacteria. Consistent with the novelty of their structures and mechanisms of action, antibacterial potency was unaffected by commonly encountered resistance phenotypes, including fluoroquinolone resistance. In time-kill assays, VRT-125853 and VRT-752586 were bactericidal against Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus faecalis, and Haemophilus influenzae, causing 3-log reductions in viable cells within 24 h. Finally, similar to the fluoroquinolones, relatively low frequencies of spontaneous resistance to VRT-125853 and VRT-752586 were found, a property consistent with their in vitro dual-targeting activities.

High Amplitude Sound Propagation at Low Frequencies in a Flow Duct Lined With Resonators: A Time Domain Solution

1988 ◽  
Vol 110 (4) ◽  
pp. 545-551 ◽  
Author(s):  
A. Cummings ◽  
I.-J. Chang
Keyword(s):  
Time Domain ◽  
Internal Combustion Engines ◽  
Sound Propagation ◽  
Sound Field ◽  
High Amplitude ◽  
Combustion Engines ◽  
Low Frequencies ◽  
The Time Domain ◽  
Flow Duct ◽  
Good Agreement

A quasi one-dimensional analysis of sound transmission in a flow duct lined with an array of nonlinear resonators is described. The solution to the equations describing the sound field and the hydrodynamic flow in the neighborhood of the resonator orifices is performed numerically in the time domain, with the object of properly accounting for the nonlinear interaction between the acoustic field and the resonators. Experimental data are compared to numerical computations in the time domain and generally very good agreement is noted. The method described here may readily be extended for use in the design of exhaust mufflers for internal combustion engines.

Furan and Thiophene Analogs of Phenanthrene A Theoretical Study of the Absorption Spectra of Benzodifurans, Benzodithiophenes and Thienobenzofurans

1971 ◽  
Vol 26 (12) ◽  
pp. 1235-1240 ◽  
Author(s):  
L. Klasinc ◽  
J. V. Knop
Keyword(s):  
Absorption Spectra ◽  
Theoretical Study ◽  
Oscillator Strengths ◽  
Electron Transitions ◽  
Good Agreement ◽  
Lcao Mo

The LCAO -MO -SCF -CI method was applied to benzo(1,2-b : 4,3-b′) -difuran and -dithiophene, benzo (2,1-b : 3,4-b′) -difuran and -dithiophene, benzo (1,2-b : 3,4-b′) -difuran and -dithiophene, thieno (2,3-e) benzofuran, thieno (3,2-e) benzofuran, thieno (3,2-g) benzofuran, thieno (2,3-g) benzofuran, benzofuran, benzothiophene and phenanthrene. The calculated π-electron transitions and their oscillator strengths are in good agreement with known absorption spectra. The resemblance of these spectra to the absorption spectra of phenanthrene and phenanthrolines is discussed.

ab initio MO Optimization of Molecular Structures of Fluoro- and Chloro-Substituted Dibenzo-p-dioxines and the Effect of Halogen Substitution at the 2,3,7,8-Positions on Metabolic Attack

1997 ◽  
Vol 52 (11) ◽  
pp. 1418-1431 ◽  
Author(s):  
Roland Weber ◽  
Till Kühn ◽  
Hanspaul Hagenmaier ◽  
Günter Häfelinger
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Energy Gap ◽  
Substituent Effects ◽  
Molecular Structures ◽  
X Ray ◽  
Degree Pattern ◽  
Chlorine Substituent ◽  
Homo Lumo ◽  
Good Agreement

Full ab initio optimizations were performed on the molecular structures of 24 fluorinated and chlorinated dibenzodioxines (PFDD/PCDD ) and dibenzofurans (PFDF/PCDF). Reasonable agreement was found by comparing the geometries of four calculated structures with known X-ray data from the literature. For the fluorine substituent, calculated electron densities (Mulliken total charges and π-electron charges) clearly demonstrate the opposite influence of the inductive (I) and mesomeric (M) effect. The changes in π-densities at carbons in ortho-, meta- and para-position are constant for each fluorine substituent (independent of degree, pattern, and position of substitution). It is thus possible to calculate the π-densities of the substituted dioxines by increments starting from dibenzodioxine. π-Charges from quantum mechanical calculations and the increment system show good agreement even for OctaFDD (O8FDD ), where eight substituent effects are acting additively. Compared with fluorine, the chlorine substituent exercises a smaller -I-effect and a clearly weaker +M-effect. The HOMO coefficients of the unsubstituted dibenzodioxine and dibenzofuran, extracted from ab initio calculations, yield a good explanation for the observed regioselective metabolic attack at the 2,3,7,8-positions. The squares of the HOMO-coefficients of the 2,3,7,8-positions in dibenzodioxine (DD ) are about ten times greater than those of the 1,4,6,9-positions. These HOMO coefficients are practically unaffected by halide substitution. But halogen substitution reduces strongly the electron density at the halogen-bound carbon, which, however, is a necessary prerequisite for the electrophilic oxygen transfer during metabolism. One would therefore expect halogen substitution of dibenzodioxine and dibenzofuran (DF) at the 2,3,7,8-position to hinder metabolism, as is indeed found. This provides a plausible explanation for the highly selective tissue retention of 2,3,7,8-substituted PCDDs and PCDFs. Our ab initio calculations of five tetra CDDs (T4CDDs) confirm the postulate of Kobayashi et al. [1 ] who, using semiempirical calculations, found a correlation between the toxicity of a dioxine congener and its absolute molecular hardness. The 2,3,7,8-T4CDD also exhibits the smallest absolute hardness (derived from the HOMO-LUMO energy gap) in our calculations.

Enhancement of acoustic absorption of a rigidly backed poroelastic plate with periodic elliptic inclusions

2019 ◽  
Vol 33 (30) ◽  
pp. 1950367
Author(s):  
Hongbo Zhang ◽  
Bilong Liu
Keyword(s):  
Material Properties ◽  
Composite Plate ◽  
Incidence Angle ◽  
Major Axis ◽  
Acoustic Energy ◽  
Absorption Peak ◽  
Acoustic Absorption ◽  
The Finite Element Method ◽  
Solid Materials ◽  
Low Frequencies

Perfect acoustic absorption is an important issue for a lot of applications. In this paper, a rigidly backed poroelastic plate with periodic elliptic inclusions is proposed to achieve perfect acoustic absorption at low frequencies by using the finite element method (FEM) with the porous material considered as fluid and solid materials. The absorption of the acoustic energy in such a composite plate resulting from viscous and thermal losses is enhanced by the resonances of the inclusions and energy trapping between the upper part of the poroelastic plate and the inclusion at low frequencies. The influence of the geometry, the incidence angle and the material properties on the absorption coefficient are investigated in detail. Our results show that increasing the major axis of the inclusion, the first absorption peak is pushed to lower frequencies and its value is first increased upto one and then it is decreased. The major axis is the most important parameter to tune the absorption peak, when the thickness is not changed. Once the major axis is determined, perfect acoustic absorption persists even if other parameters are changed. The reported results pave the way for the design of absorption devices which could be used to solve the major issue of noise control.

scholarly journals MINDO/3 Study of the Protonation of Phenol and Methylphenols

1982 ◽  
Vol 37 (7) ◽  
pp. 688-696
Author(s):  
M. Eckert-Maksić
Keyword(s):  
Structural Changes ◽  
Molecular Structures ◽  
Good Agreement

Abstract The electronic and molecular structures of phenol and its ortho-meta-, and para-methyl derivates as well as their conjugate acids were studied by the semiempirical MINDO/3 method. The calculations predict substantial structural changes upon protonation. Theoretically predict-ed protonation sites are in very good agreement with experimentally observed modes of protonation under superacidic conditions.

Molecular Structures and Absorption Spectra Assignment of Corrole NH Tautomers

2014 ◽  
Vol 118 (5) ◽  
pp. 862-871 ◽  
Author(s):  
Wichard Beenken ◽  
Martin Presselt ◽  
Thien H. Ngo ◽  
Wim Dehaen ◽  
Wouter Maes ◽  
...  
Keyword(s):  
Absorption Spectra ◽  
Molecular Structures

scholarly journals Terahertz Time-Domain Polarimetry in Reflection for Film Characterization

Sensors ◽  
2020 ◽  
Vol 20 (12) ◽  
pp. 3352
Author(s):  
Sandrine van Frank ◽  
Elisabeth Leiss-Holzinger ◽  
Michael Pfleger ◽  
Christian Rankl
Keyword(s):  
Optical Properties ◽  
Time Domain ◽  
Terahertz Spectroscopy ◽  
Single Layer ◽  
Measured Signal ◽  
Terahertz Time Domain Spectroscopy ◽  
Wide Range ◽  
Reflection Geometry ◽  
Layer Thin Film ◽  
Good Agreement

Terahertz time-domain spectroscopy is a useful technique to characterize layered samples and thin films. It gives access to their optical properties and thickness. Such measurements are done in transmission, which requires access to the sample from opposite sides. In reality this is not always possible. In such cases, reflection measurements are the only option, but they are more difficult to implement. Here we propose a method to characterize films in reflection geometry using a polarimetric approach based on the identification of Brewster angle and modeling of the measured signal to extract the refractive index and thickness of the sample. The technique is demonstrated experimentally on an unsupported single layer thin film sample. The extracted optical properties and thickness were in good agreement with established transmission terahertz spectroscopy measurements. The new method has the potential to cover a wide range of applications, both for research and industrial purposes.

Investigation of aging characteristics in explosive using terahertz time-domain spectroscopy

2019 ◽  
Vol 33 (24) ◽  
pp. 1950272 ◽  
Author(s):  
Wei Shi ◽  
Chengang Dong ◽  
Lei Hou ◽  
Zhiyang Xing ◽  
Qian Sun ◽  
...  
Keyword(s):  
Absorption Spectrum ◽  
Fourier Transform ◽  
Absorption Spectra ◽  
Time Domain ◽  
Detection System ◽  
Coherent Detection ◽  
Terahertz Time Domain Spectroscopy ◽  
Time Domain Spectroscopy ◽  
Terahertz Absorption ◽  
Spectroscopy System

The terahertz absorption spectrum of the five aging explosive samples (PETN, RDX, HMX, LLM-105 and TATB) was measured and calculated by Terahertz time-domain spectroscopy system (THz-TDS) and air-biased coherent detection system (ZAP-ABCD), respectively. In this paper, compared with the unaging explosive, each aging explosive sample’s terahertz time-domain spectra were obtained and the terahertz absorption spectra were calculated by using Fourier transform and Lambert’s law. The results show that there are several terahertz absorption peaks which were called “fingerprint spectra” for different aging explosive samples in the range of 0.3–6.0 THz spectrum. Meanwhile, the results also show that the locations of the characteristic absorption peaks are not the same. Moreover, the unaging and aging explosive samples have obviously different terahertz absorption spectra.

scholarly journals Numerical Prediction of Far-Field Combustion Noise from Aeronautical Engines

Acoustics ◽  
2019 ◽  
Vol 1 (1) ◽  
pp. 174-198 ◽  
Author(s):  
Mélissa Férand ◽  
Thomas Livebardon ◽  
Stéphane Moreau ◽  
Marlène Sanjosé
Keyword(s):  
Temperature Field ◽  
Low Power ◽  
Combustion Chamber ◽  
High Power ◽  
Acoustic Propagation ◽  
Combustion Noise ◽  
Far Field ◽  
Low Frequencies ◽  
Turboshaft Engine ◽  
Good Agreement

A hybrid methodology combining a detailed Large Eddy Simulation of a combustion chamber sector, an analytical propagation model of the extracted acoustic and entropy waves at the combustor exit through the turbine stages, and a far-field acoustic propagation through a variable exhaust temperature field was shown to predict far-field combustion noise from helicopter and aircraft propulsion systems accurately for the first time. For the single-stream turboshaft engine, the validation was achieved from engine core to the turbine exit. Propagation to the far field was then performed through a modeled axisymmetric jet. Its temperature modified the acoustic propagation of combustion noise significantly and a simple analytical model based on the Snell–Descarte law was shown to predict the directivity for axisymmetric single jet exhaust accurately. Good agreement with measured far-field spectra for all turboshaft-engine regimes below 2 kHz stresses that combustion noise is most likely the dominant noise source at low frequencies in such engines. For the more complex dual-stream turbofan engine, two regime computations showed that direct noise is mostly generated by the unsteady flame dynamics and the indirect combustion noise by the temperature stratification induced by the dilution holes in the combustion chamber, as found previously in the turboshaft case. However, in the turboengine, direct noise was found dominant at the combustor exit for the low power case and equivalent contributions of both combustion noise sources for the high power case. The propagation to the far-field was achieved through the temperature field provided by a Reynolds-Averaged Navier–Stokes simulation. Good agreement with measured spectra was also found at low frequencies for the low power turboengine case. At high power, however, turboengine jet noise overcomes combustion noise at low frequencies.

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