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Introduction
Published in Armen S. Casparian, Gergely Sirokman, Ann O. Omollo, Rapid Review of Chemistry for the Life Sciences and Engineering, 2021
Armen S. Casparian, Gergely Sirokman, Ann O. Omollo
Electronegativity: Electronegativity is the ability of an atom in covalently bonded molecule to attract electrons to itself. It is the atom’s pulling power to attract electrons to itself. The difference in pulling power or attracting electrons between the two atoms in a molecule is what determines its charge distribution and polarity. The scale of electronegativities runs from 0.0 to 4.0. Cesium and francium are alkali metals and have the lowest electronegativity values (often <1), while fluorine has the highest (3.98) followed by oxygen (3.44) and chlorine (3.16). The greater the difference in electronegativity values between two atoms bonded in a molecule, the greater the degree of polarity. All three of these quantities play a role in determining bond length, bond energy, and many other chemical and physical properties, and ultimately chemical reactivity.
Materials for Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
What are the roles of caps or ligands on QD surfaces? The caps or ligands serve three-fold purposes: (i) partial passivation of dangling bonds on the surfaces of QDs; (ii) prevention of agglomeration of QDs through steric hinderance (the prevention or retardation of inter- or intramolecular interactions by the blockage of access to a reactive site by nearby groups, which arises from the crowding resulting from spatial structure of a molecule); and (iii) conferring solubility to the QDs. Solubility of the QD is not necessarily the same as that of the ligand. The ligands generally have two functional groups, one group binding with the QD and the other group interacting with the environment. A QD coated with molecules of a surfactant (compounds which lower the surface tension of a liquid) presents hydrocarbon chains to the environment, whereas the polar head groups of the surfactant associate with the QD surface. Consequently, a surfactant-coated QD is water insoluble but is easily dispersed in nonpolar organic solvents, such as toluene (C7H8 or C6H5CH3) or hexane (C6H14). Polarity refers to a separation of electric charge, leading to a molecule or its chemical groups having an electric dipole or multipole moment.
Filtrative Particle Removal
Published in Maik W. Jornitz, Filtration and Purification in the Biopharmaceutical Industry, 2019
The terms “hydrophilic” and “hydrophobic,” respectively, from the Greek, denote a fondness or love of water, and an antipathy to water. Molecules exhibit these qualities according to the polarity or nonpolarity of their constituting atomic arrangements. Generally, polarity derives from oxygen atoms such as are present in ethers, esters, alcohols, carboxylic acids, etc. The oxygen atom is strongly electronegative. In its participation in covalent bonding, it retains more than its share of the bonding electrons. The polar areas result from the partial charges caused by such unequal sharing of bonding electrons. The partial electrical charges (to be detailed below) result in hydrations, in aqueous solubility, and in other manifestations of hydrogen bonding. The nonpolar molecules, lacking obvious electrical charges, have no affinity for H- bonding, or, presumably, for the mutual interactions of opposite electrical charges. However, complex structures such as proteins, polymers, and the organism and filter surfaces composed of them may have multiple sites of polar and nonpolar character.
Response surface methodology to optimize ultrasonic-assisted extraction of crude oil from oily sludge
Published in Petroleum Science and Technology, 2022
Yongjun You, Chong Liu, Qi Xu, Xuefei Hu, Simin Zhang, Changhan Wang, Huanliang Guo, Chao Tang
The PE, XY, EAC, MC, and EA oil recovery rates reached 14.6% ± 1.2%, 42.5% ± 1.6%, 33.4% ± 0.8%, 23.3% ± 0.9%, and 13.6% ± 0.5%, respectively (Figure 2). While non-polar solutes are soluble in non-polar solvents, there is a positive correlation between increasing non-polarity of the solute and increased solubility in non-polar solvents (Cao and Heeger 1992). Our results demonstrate that oil recovery is significantly impacted when solvent polarity is too high or too low. Some scholars reported that organic compounds are generally non-polar or weakly polar (Cao and Heeger 1992). Consequently, they are difficult to dissolve in highly polar solvents, but dissolve easily in non-polar or weakly polar organic solvents (Cao and Heeger 1992). Here, polar solvent XY (medium polarity of ∼1.4) exhibited the best extraction. Considering the high volatility and elevated cost of solvents, follow-up experiments should keep solvents in tightly closed vessels to prevent the evaporation of volatile compounds. Recovered solvent can then enter the refinery for gasoline or diesel production.
Separation of low polarity petroleum sulfonate: Eluant selection, characterization, and theoretical calculation
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2019
Xintong Liu, Yanan Xue, Youyi Zhu, Jian Fan, Shixiang Liu, Hongda Li, Yanjun Zhao, Wenjun Li
In this study, the petroleum sulfonate samples were separated via polarity separation method. We conducted a large number of experimental tests on the basis of the polarity separation method, and four suitable eluting agents were selected to separate the low polarity components. The structure of petroleum sulfonate, such as the types of functional groups, aromaticity, mass distribution, and so on are fully characterized and represented in detail. Through the combination of theoretical calculation and experimental data, structure information of the petroleum sulfonate was reasonable deduced. Therefore, this study revealed the reasons for discrepant polarities, and it will provide a foundation for the petroleum sulfonate evaluation.
Energy-transfer versus electron-transfer reactions for the light-harvesting phthalocyanine/ dithiolato-bisimino zinc system
Published in Journal of Coordination Chemistry, 2020
Eman Soliman, Mohamed EL-Khouly, Abd El-Motaleb M. Ramadan, Ibrahim EL-Mehasseb, Shaban Y. Shaban
In quest of light harvesting systems, the interaction of a dithiolato-bisimino zinc complex, {2,6-bis(2-mercapto-3,5-ditert-butylphenylaminomethyl)pyridine zinc(II)} (DBZ) and phthalocyanine (Pc) is investigated in THF and toluene. In toluene, static fluorescence quenching is observed, indicating that a ground state complex is formed between the donor DBZ and the acceptor Pc. The donor–acceptor distance, r, of 4.28 nm indicates a non-radiative transfer process with high probability. Based on the lifetime values of DBZ in the absence and presence of phthalocyanine, the rate constant (kET) and the quantum yield (ΦET) of the energy transfer were found to be 2.63 × 108 and 0.47, respectively. Binding constants and the number of binding sites were determined in both cases. The observed thermodynamic parameters suggest spontaneity of the binding for DBZ to Pc and the key interacting forces involved hydrogen bonds, van der Waals forces or π-π stacking. In THF, electron transfer from the electron donating Pc to the electron accepting DBZ complex occurred via the singlet Pc and the process is thermodynamically feasible. The difference in behavior in the two solvents can therefore be understood in terms of the following: i) The coordination ability of these two solvents since the toluene coordinates much less than THF according to the coordinating ability index aTM values [41] and the presence of lone pairs and electron-rich donors on THF can make it a stronger nucleophile. pytBuN2H2S22 structure enforces the zinc center to have distorted square pyramidal geometry and the zinc center is not within the plane [11]. After coordination of THF from the opposite sides to the pyridine moiety, both THF and pytBuN2H2S22 structurally neutralize each other and the zinc ion may reside within the plane, which leads to different behavior [42]; ii) The polarity of the solvent can also have an impact on the reaction pathway since polar solvents usually favor reactions involving charged species such as electron transfer [43]. Thus, in our case we ascribe the observed effects to the difference in polarity and the nucleophilic character of the solvent, i.e. the donor strength of the coordinated solvent.