Effect Of Molecular Structure Research Articles

Photodegradation of norfloxacin in ice: Role of the fluorine substituent

Ice is an important medium in cold regions, because it regulates the environmental behaviors and the fate of pollutants. The photodegradation of fluoroquinolone (FQ) antibiotics as emerging contaminants of concern in ice remains poorly understood. Here, the photodegradation of fluorine-containing norfloxacin (NOR) as one model of FQs in ice formed from freezing solutions was investigated. Pipemidic acid (PPA) as a structural analogue of NOR was selected to compare the effect of molecular structure on the antibiotic photodegradation in the ice. Results suggested that the photodegradation rate constant of NOR in ice relative to pure water increased by 40.0%. Both the absorbance in the absorption spectra and quantum yields of NOR in ice over water increased by 1.4 times. Direct photodegradation mainly caused the defluorination of NOR, which was more important than cleavage and oxidation of the piperazine ring by self-sensitized photooxidation in ice. The defluorination rate of NOR in the ice relative to water increased by about 12.7%. The fluorine substituent played a more important role in the NOR photodegradation in the ice, resulting in a 1.6-fold increase in the photodegradation rate constant of NOR relative to PPA. This work provides a new insight into the role of fluorine substituents in the photodegradation of fluorinated pharmaceuticals in cold regions.

Fabrication of a highly stretchable cellulose with internally and externally dual-plasticized structure

In this study, we developed a highly stretchable internally- and externally-plasticized (i.e., dually-plasticized) cellulose, which is composed of a polydecalactone (PDL)-grafted cellulose copolymer (CgPD) and a hyperbranched polycaprolactone (PCL) external plasticizer (HPC). To investigate the effect of molecular structure of PCL external plasticizers on the plasticization behavior of dually-plasticized celluloses, a linear PCL (LPC) and a star-shaped PCL (SPC) were prepared as control groups. It is observed that specific molecular interactions existed between CgPD and external plasticizers in the dually-plasticized celluloses (i.e., CgPD_LPC, CgPD_SPC, and CgPD_HPC, respectively). Especially, CgPD_HPC exhibited the lowest apparent activation energy (Ea= ∼128.8 kJ mol−1) required to achieve the plasticizing behavior, which resulted in an enhanced ductility (ε = ∼136%) compared to those of the CgPD (ε = ∼75%), whereas CgPD_LPC and CgPD_SPC displayed severely deteriorated values (ε = ∼25 and ∼59%, respectively). In addition, the dually-plasticized cellulose bearing bulkier HPC exhibited further improved stretchability. These results comprehensively indicate that the highly-branched flexible segments of external plasticizer and structural uniformity induced by effective specific interactions between the plasticizing components play crucial roles in improving plasticization abilities of the dually-plasticized cellulose.

EPR Oximetry with Nitroxides: Effects of Molecular Structure, pH, and Electrolyte Concentration

EPR Oximetry with Nitroxides: Effects of Molecular Structure, pH, and Electrolyte Concentration

Exploitation of a new green inhibitor against mild steel corrosion in HCl: Experimental, DFT and MD simulation approach

Origanum Compactum Benth Aqueous extract (OCAqE) have been analysed and investigated as green corrosion inhibitor for mild steel in acid solution (1 M HCl). The analysis of Origanum Compactum Benth Aqueous extract was performed using HPLC-UV-ELSD-MS. Electrochemical techniques, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP), and mass loss were performed and showed that OCAqE is mixed type inhibitor and acts by adsorption on metal surface. OCAqE showed good inhibition efficiency of 92% at a concentration of 0.4 g/L. The adsorption mode of OCAqE on mild steel surface follow Langmuir isotherm. Surface analysis (SEM) of mild steel specimen has shown the decrease in surface deterioration after addition of OCAqE inhibitor to the HCl solution. Density functional theory (DFT) and Molecular dynamics (MD) have been introduced in order to carry out a more rigorous theoretical treatment of the inhibitive performance. The comparative study based on the low-energy electronic structures shown that the trend of inhibition potentials of the major compound of this extract depend on the effect of molecular structure on the electron donating/accepting ability.

Molecular Structure Effect of a Self-Assembled Monolayer on Thermal Resistance across an Interface.

Understanding heat transfer across an interface is essential to a variety of applications, including thermal energy storage systems. Recent studies have shown that introducing a self-assembled monolayer (SAM) can decrease thermal resistance between solid and fluid. However, the effects of the molecular structure of SAM on interfacial thermal resistance (ITR) are still unclear. Using the gold–SAM/PEG system as a model, we performed nonequilibrium molecular dynamics simulations to calculate the ITR between the PEG and gold. We found that increasing the SAM angle value from 100° to 150° could decrease ITR from 140.85 × 10−9 to 113.79 × 10−9 m2 K/W owing to penetration of PEG into SAM chains, which promoted thermal transport across the interface. Moreover, a strong dependence of ITR on bond strength was also observed. When the SAM bond strength increased from 2 to 640 , ITR first decreased from 106.88 × 10−9 to 102.69 × 10−9 m2 K/W and then increased to 123.02 × 10−9 m2 K/W until reaching a steady state. The minimum ITR was obtained when the bond strength of SAM was close to that of PEG melt. The matching vibrational spectra facilitated the thermal transport between SAM chains and PEG. This work provides helpful information regarding the optimized design of SAM to enhance interfacial thermal transport.

Structure-Based Long-Term Biodegradation of the Azo Dye: Insights from the Bacterial Community Succession and Efficiency Comparison

In this study, microbial community dynamics were explored during biological degradation of azo dyes with different chemical structures. The effect of the different molecular structures of the azo dyes was also assessed against the simultaneous removal of color and the bacterial community. Winogradsky columns were inoculated with dewatered sludge and separately fed with six different azo dyes to conduct the sludge acclimatization process, and nine bacterial decolorizing strains were isolated and identified. The decolorization and biodegradation performances of the acclimated system and isolated strains were also determined. Results showed that the bacterial isolates involved in decolorization and the degradation of the azo dyes were mainly associated with the azo dye structure. After 24 h acclimatization at room temperature without specific illumination, immediate decolorization of methyl red (89%) and methyl orange (78%) was observed, due to their simple structure compared to tartrazine (73%). However, after 8 days of acclimatization, methyl red was easily decolorized up to 99%, and about 87% decolorization was observed for orange G (87%), due to its complex chemical structure. Higher degrees of degradation and decolorization were achieved with Pseudomonas geniculate strain Ka38 (Proteobacteria), Bacillus cereus strain 1FFF (Firmicutes) and Klebsiella variicola strain RVEV3 (Proteobacteria) with continuous shaking at 30 °C. The azo dyes with benzene rings were found to be easier to decolorize and degrade with similar microbial communities. Moreover, it seems that the chemical structures of the azo dyes, in a sense, drove the divergent succession of the bacterial community while reducing the diversity. This study gives a deep insight into the feasible structure-based artificial manipulation of bacterial communities and offers theoretical guidance for decolorizing azo dyes with mixed bacteria cultures.

Dehydrogenation of Cycloalkanes over N-Doped Carbon-Supported Catalysts: The Effects of Active Component and Molecular Structure of the Substrate.

Efficient dehydrogenation of cycloalkanes under mild conditions is the key to large-scale application of cycloalkanes as a hydrogen storage medium. In this paper, a series of active metals loaded on nitrogen-doped carbon (M/CN, M = Pt, Pd, Ir, Rh, Au, Ru, Ag, Ni, Cu) were prepared to learn the role of active metals in cycloalkane dehydrogenation with cyclohexane as the model reactant. Only Pt/CN, Pd/CN, Rh/CN and Ir/CN can catalyze the dehydrogenation of cyclohexane under the set conditions. Among them, Pt/CN exhibited the best catalytic activity with the TOF value of 269.32 h−1 at 180 °C, followed by Pd/CN, Rh/CN and Ir/CN successively. More importantly, the difference of catalytic activity between these active metals diminishes with the increase in temperature. This implies that there is a thermodynamic effect of cyclohexane dehydrogenation with the synthetic catalysts, which was evidenced by the study on the activation energy. In addition, the effects of molecular structure on cycloalkane dehydrogenation catalyzed by Pt/CN were studied. The results reveal that cycloalkane dehydrogenation activity and hydrogen production rate can be enhanced by optimizing the type, quantity and position of alkyl substituents on cyclohexane.

Synthesis, characterisation, and effects of molecular structure on phase behaviour of 4-chloro-1,3-diazobenzene bent-core liquid crystals with high photosensitivity

ABSTRACT A series of new compounds were synthesised by adding azo functional groups and chlorine substituent to the central bent-cores to form a 4-chloro-1,3-dizaophenylene bent-core. The structure, mesogenic properties, and photosensitivity of these compounds were characterised. The results show these synthesised compounds exhibit a broad temperature window up to 63.8°C for nematic phase and the rapid rate of trans – cis photoisomerisation. For instance, at 95°C, compound 4c in nematic phase became an isotropic liquid under UV-irradiation in 3 s and could be restored to nematic under natural visible light in 5 s. Quantum mechanics calculation confirms that using azos instead of esters as the central linkages can effectively reduce the molecular dipole moment, which appears to promote favourable mesogenic and photonic characteristics. Moreover, varying the carbon number in the terminal alkyl chains can alter molecular dipole moment and polarisability anisotropy, which are strongly correlated with the phase transition temperature and temperature range of the nematic phase. These findings suggest that 1) changing azo group position can effectively alter the intermolecular interactions by varying molecular polarity and polarisability; 2) reducing long-range electrostatic interactions can promote favourable mesogenic and possibly photonic properties of azobenzene bent-core liquid crystal.

Influence of Isomerism on Radioluminescence of Purely Organic Phosphorescence Scintillators.

There are few reports about purely organic phosphorescence scintillators, and the relationship between molecular structures and radioluminescence in organic scintillators is still unclear. Here, we presented isomerism strategy to study the effect of molecular structures on radioluminescence. The isomers can achieve phosphorescence efficiency of up to 22.8 % by ultraviolet irradiation. Under X-ray irradiation, both m-BA and p-BA show excellent radioluminescence, while o-BA has almost no radioluminescence. Through experimental and theoretical investigation, we found that radioluminescence was not only affected by non-radiation in emissive process, but also highly depended on the material conductivity caused by the different molecular packing. This study not only allows us to clearly understand the relationship between the molecular structures and radioluminescence, but also provides a guidance to rationally design new organic scintillators.

Influence of Isomerism on Radioluminescence of Purely Organic Phosphorescence Scintillators

AbstractThere are few reports about purely organic phosphorescence scintillators, and the relationship between molecular structures and radioluminescence in organic scintillators is still unclear. Here, we presented isomerism strategy to study the effect of molecular structures on radioluminescence. The isomers can achieve phosphorescence efficiency of up to 22.8 % by ultraviolet irradiation. Under X‐ray irradiation, both m‐BA and p‐BA show excellent radioluminescence, while o‐BA has almost no radioluminescence. Through experimental and theoretical investigation, we found that radioluminescence was not only affected by non‐radiation in emissive process, but also highly depended on the material conductivity caused by the different molecular packing. This study not only allows us to clearly understand the relationship between the molecular structures and radioluminescence, but also provides a guidance to rationally design new organic scintillators.

Effect of molecular structure of maleic anhydride, fumaric acid – Isopentenyl polyoxyethylene ether based polycarboxylate superplasticizer on its properties in cement pastes

Polycarboxylate ether (PCE) superplasticizers with different molecular structure were synthesized by copolymerizing macro-monomer with cis-butenedioic anhydride (MAH) and trans-1,2-ethenedicarboxylic acid (FA). Gel permeation chromatography, specific charge density, Fourier transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance were used to characterize these co-polymers. Their Ca2+ binding capacity, adsorption behaviors, retardation effects and dispersion efficiency were investigated by the calcium-ion selective electrode, total organic carbon, X-ray Photoelectron Spectroscopy, zeta potential, calorimetry measurements, mini-cone and rheological tests. Results indicated that PCE containing more FA possesses the higher density of –COO– groups, due to the higher reactivity of FA than MAH. The high density of –COO– groups in PCEs significantly affects their adsorption behaviors, retardation, and dispersion of cement pastes. Intermolecular chelation between –COO– groups and Ca2+ is dominated for FA-PCE, while the main coordination modes between –COO– in MAH-PCE and Ca2+ are intramolecular chelation owing to more adjacently distributed –COO– groups. FA-PCE exhibits larger adsorption amount and thicker adsorption layer compared with MAH-PCE. Hence, the FA-PCE demonstrated stronger dispersion efficiency, with which the cement pastes showed excellent flowability and rheological properties, correspondingly.

Effect of Molecular Structure on Interfacial Electron Transfer Kinetics in the Framework of Classical Marcus Theory

AbstractThe factors affecting electron transfer at semiconductor electrodes sensitised with molecules and in contact with redox electrolytes have been studied for decades. Here, the influence of molecular structural factors enhancing or slowing down electron transfer rates at dye‐sensitised electrode interfaces are analysed by Marcus theory. Back electron transfer between TiO2 electrons and oxidised redox mediators are slowed down by reducing electronic coupling using alkyl chains or by minimising attractive intermolecular forces. Electron transfer between surface‐bound molecules and the electron donors, while generally also slowed down by alkyl chains, can also be enhanced by alkyl‐alkyl interactions. This review highlights the a priori difficult to predict effect of changing molecular structures on electron transfer. Systematic studies employing electron transfer measurements with fast time resolutions is needed to advance knowledge in this important area.

Communication—Effects of Molecular Structures of Quaternary Ammonium Inhibitors on Cu Electrodeposition in Micro Via

Three quaternary ammonium inhibitors with different head groups and tail groups were used for micro via filling and electrochemical analysis. It is found that the cetyl-tail groups played a key role in controlling the rate of Cu electrodeposition, while the trimethylammonium-head and the pyridine-head showed no significantly different effect on the Cu electrodeposition process. The bottom-up filling of micro via (Φ20 μm × 120 μm) was obtained using a single-additive electrolyte system which contained one of the two quaternary ammonium inhibitors with cetyl-tail groups.

Effect of Molecular Structure on Electrochemical Phase Behavior of Phospholipid Bilayers on Au(111).

Lipid bilayers form the basis of biological cell membranes, selective and responsive barriers vital to the function of the cell. The structure and function of the bilayer are controlled by interactions between the constituent molecules and so vary with the composition of the membrane. These interactions also influence how a membrane behaves in the presence of electric fields they frequently experience in nature. In this study, we characterize the electrochemical phase behavior of dipalmitoylphosphatidylcholine (DPPC), a glycerophospholipid prevalent in nature and often used in model systems and healthcare applications. DPPC bilayers were formed on Au(111) electrodes using Langmuir-Blodgett and Langmuir-Schaefer deposition and studied with electrochemical methods, atomic force microscopy (AFM) and in situ polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). The coverage of the substrate determined with AFM is in accord with that estimated from differential capacitance measurements, and the bilayer thickness is slightly higher than for bilayers of the similar but shorter-chained lipid, dimyristoylphosphatidylcholine (DMPC). DPPC bilayers exhibit similar electrochemical response to DMPC bilayers, but the organization of molecules differs, particularly at negative charge densities. Infrared spectra show that DPPC chains tilt as the charge density on the metal is increased in the negative direction, but, unlike in DMPC, the chains then return to their original tilt angle at the most negative potentials. The onset of the increase in the chain tilt angle coincides with a decrease in solvation around the ester carbonyl groups, and the conformation around the acyl chain linkage differs from that in DMPC. We interpret the differences in behavior between bilayers formed from these structurally similar lipids in terms of stronger dispersion forces between DPPC chains and conclude that relatively subtle changes in molecular structure may have a significant impact on a membrane's response to its environment.

Gas permselectivity of hyperbranched polybenzoxazole – silica hybrid membranes treated at different thermal protocols

Hyperbranched polybenzoxazole (HBPBO) – silica hybrids were treated at different thermal protocols and their gas permselectivity were studied. Inter-chain distance and free volume of pristine HBPBO were enlarged with increasing treated temperature. Gas permeability and diffusivity of the HBPBO were considerably increased with increasing treated temperature, which was resulted from increased fractional free volume due to enlarged inter-chain distance. Gas permeability of the HBPBO was further increased by the hybridization with silica, mainly owing to the increased gas diffusivity. This fact indicated additional free volume holes were formed at the HBPBO matrix – silica interfaces. It was worth noting the HBPBO – silica hybrids had a prominent CO2/CH4 permselectivity which exceeded the upper bound, and the CO2/CH4 permselectivity was enhanced with increasing treated temperature. The notable CO2/CH4 permselectivity of the HBPBO – silica hybrids would be achieved by the synergistic effect of characteristic hyperbranched molecular structure, thermal treatment, and hybridization with silica.

Effect of molecular carbon structures on the evolution of the pores and strength of lignite briquette coal with different heating rates

Briquette coal (BC) is the material produced from coal and gas outburst experiments. Preparing BC via the heating and pressure method can improve its low mechanical strength in physical simulation tests and gas outbursts while increasing experimental reliability. However, the influence of heating rate on the mechanical properties and microstructure of BC and the reasons underlying the evolution of its mechanical strength analyzed in terms of carbon molecular structure still need to be further studied. In this study, we developed an experimental system to prepare BC. The influence of the pore and carbon molecular structure on the BC uniaxial compressive strength was examined via a rock mechanics test system, scanning electron microscopy, nuclear magnetic resonance, specific surface area analysis, X-ray diffraction, and Fourier transform infrared spectroscopy. The results indicated that when the heating rate was increased from 3 to 6 °C/min, the briquette structure changed from looser smooth sheets to rough agglomerates of coal. The pore types observed after four different heating treatments (3, 4, 5, and 6 °C/min) on briquette samples were primarily micropores and mesopores. At 5 ℃/min, the number of micropores in the briquette sample were significantly higher than that observed in other samples. All samples exhibited similar adsorption curves as those of inverted “S”-type coal samples, which can be regarded as a combination of Type IV isotherms. With increasing heating rates, the La and Lc first increased and then decreased, with a decrease in Aar/Aal, whereas Hal/H and CH2/CH3 increased. The strength of coal samples under the increasing heating rates were 5.62, 6.43, 7.07, and 5.99 MPa, respectively. The heating rate of 5 ℃/min was found to be the appropriate heating rate for briquette preparation. These results can provide an excellent alternative raw material required for large-scale physical simulation experiments for the prevention and control of coal and gas outbursts.

Electrochemical and theoretical performance of new synthetized pyrazole derivatives as promising corrosion inhibitors for mild steel in acid environment: Molecular structure effect on efficiency

New bi-Pyrazol-Carbohydrazides, N,N-bis (3-Carbohydrazide-5-methylpyrazol-1-yl) methylene (M2PyAz) and 1,4-bis (3-Carbohydrazide-5-methylpyrazol-1-yl) butane (B2PyAz), were synthesized and their inhibitor effect against mild steel (MS) corrosion in 1 M HCl solution has been evaluated. Comparative study of inhibitory action of M2PyAz and B2PyAz was conducted first using weight loss measurements (WL), potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and theoretical computational methods. The inhibition efficiencies of M2PyAz and B2PyAz can reach 98.6% and 87.8% respectively when the optimal concentration is 10–3 M. This result indicates that M2PyAz behave as excellent corrosion inhibitor towards MS because of its molecular size giving a denticity of electron donor atoms. EIS results indicate that the charge transfer resistance increases with augmentation concentration for both inhibitors and the MS corrosion in this system is controlled by a charge transfer process. PDP curves suggest that the M2PyAz and B2PyAz act as mixed type corrosion inhibitors. Free energy of adsorption obtained from the Langmuir isotherm model for both M2PyAz and B2PyAz implies that both molecules inhibit the acid attack mainly by chemisorption. WL-measurements were carried out in temperature range of 308–348 K, illustrating approximately 98.5% and 89% inhibitory efficiency respectively for M2PyAz and B2PyAz after 6 h immersion at 308 K in 1 M HCl solution. SEM images indicates the protective layer growth on the surface of metal in the presence of both inhibitors. SEM images analysis in the presence of both inhibitors confirmed the electrochemical outcomes. Density functional theory (DFT) method and molecular dynamics simulations (MDs) application suggest that M2PyAz and B2PyAz can show excellent corrosion inhibition character. The trend of reactivity of both molecules M2PyAz and B2PyAz is in agreement with experimental study.

Polymerized small molecular acceptor based all-polymer solar cells with an efficiency of 16.16% via tuning polymer blend morphology by molecular design

All-polymer solar cells (all-PSCs) based on polymerized small molecular acceptors (PSMAs) have made significant progress recently. Here, we synthesize two A-DA’D-A small molecule acceptor based PSMAs of PS-Se with benzo[c][1,2,5]thiadiazole A’-core and PN-Se with benzotriazole A’-core, for the studies of the effect of molecular structure on the photovoltaic performance of the PSMAs. The two PSMAs possess broad absorption with PN-Se showing more red-shifted absorption than PS-Se and suitable electronic energy levels for the application as polymer acceptors in the all-PSCs with PBDB-T as polymer donor. Cryogenic transmission electron microscopy visualizes the aggregation behavior of the PBDB-T donor and the PSMA in their solutions. In addition, a bicontinuous-interpenetrating network in the PBDB-T:PN-Se blend film with aggregation size of 10~20 nm is clearly observed by the photoinduced force microscopy. The desirable morphology of the PBDB-T:PN-Se active layer leads its all-PSC showing higher power conversion efficiency of 16.16%.

New insights into the role of molecular structures on the fate and behavior of antibiotics in an osmotic membrane bioreactor

Osmotic membrane bioreactors (OMBRs) have been applied to enhance removal of antibiotics, however, information on the effects of molecular structures on the behavior of antibiotics is still lacking. Herein, adsorption kinetics, transformation pathways, and membrane rejection mechanisms of OMBRs were investigated by adding two typical antibiotics (i.e., sulfadiazine, SDZ, and tetracycline hydrochloride, TC-HCl). 80.70–91.12% of TC-HCl was removed by adsorption and biodegradation, while 17.50–75.14% of SDZ was removed by membrane rejection; this depended on its concentration due to reduced electrostatic interactions and hydrophobic adsorption. The adsorption capacity of TC-HCl (i.e., 1.34±0.01 mg/g) was significantly higher than that of SDZ (i.e., 0.18±0.03 mg/g) due to enhanced π-π interactions, hydrogen bonding and improved electrostatic interactions. The abundant production of polysaccharide-like substances from TC-HCl biodegradation contributed to microbial metabolism and thus enhanced microbial function during TC-HCl biotransformation. The primary degradation pathways were determined by microbial function analysis, and the primary intermediates from TC-HCl degradation were less toxic than those from SDZ degradation due to the different reactions of amino groups. These results and the corresponding mechanism provide a theoretical foundation for the further development of OMBR technology for highly efficient treatment of antibiotic wastewater.

General models for prediction densities and viscosities of saturated and unsaturated fatty acid esters

Biodiesel is a very promising renewable energy, whose properties are determined by fatty acid esters in it. The work aims to develop prediction models based on their molecular structure to estimate the density and viscosity of saturated and unsaturated fatty acid esters in a wide range of temperature and pressure. Densities and viscosities of ethyl hexanoate and ethyl nonanoate were measured from 313.15 K to 363.15 K and at pressures up to 15 MPa to get more experimental data. The effect of temperature, pressure and molecular structure on density and viscosity based on the experimental data in this work and collected from literature found an interesting phenomenon that densities decrease with the increasing carbon atoms number in the chain of the saturated fatty acid esters at low temperature, but there is an opposite trend at high temperature. Two models derived from the Tait equation were proposed for densities with the average absolute relative deviation of 0.15% for saturated fatty acid methyl esters (FAMEs), 0.13% for saturates fatty acid ethyl esters (FAEEs), 0.17% for unsaturated FAMEs, 0.06% for unsaturated FAEEs, respectively. For viscosity, two models based on the Andrade-Tait model were proposed with the average absolute relative deviation of 1.49% for saturated FAMEs, 0.92% for saturated FAEEs, 4.54% for unsaturated FAMEs and 2.15% for unsaturated FAEEs, respectively.