The Variable Electronegativity Method. V. Pyridine, the Pyridinium Cation, and the Evaluation of Core-Attraction Integrals

1959 ◽  
Vol 12 (4) ◽  
pp. 554 ◽  
Author(s):  
RD Brown ◽  
ML Heffernan
Keyword(s):  
Dipole Moment ◽  
Electron Distribution ◽  
Chemical Properties ◽  
Theoretical Treatment ◽  
Matrix Elements ◽  
Molecular Dipole ◽  
Theoretical Methods ◽  
Pyridinium Cation ◽  
Electron Repulsion Integrals ◽  
Better Than

A study of pyridine and the pyridinium cation by the VESCF method is reported. Several different methods of evaluating core attractions and electron repulsion integrals have been tried to determine their effect on the resultant energies and orbitals. Satisfactory results for the π-electron distribution and molecular dipole moment of pyridine are obtained. Values of ionization potentials are little better than those given by other theoretical methods and the variable electronegativity technique does not appear to improve the theoretical treatment of ultraviolet spectra. H�ckel MO parameters, evaluated from the VESCF matrix elements, accord with values found in similar studies of other heterocycles and also with values of parameters found necessary to account for the chemical properties of quinoline.

The Variable Electronegativity Method. VII. Pyrazole, Its Anion and Cation

1960 ◽  
Vol 13 (1) ◽  
pp. 49 ◽  
Author(s):  
RD Brown ◽  
ML Heffernan
Keyword(s):  
Dipole Moment ◽  
Electron Distribution ◽  
Nitrogen Heterocycles ◽  
Chemical Properties ◽  
Membered Ring ◽  
Matrix Elements ◽  
Electron Densities ◽  
Ring Nitrogen ◽  
Made In ◽  
Tertiary Nitrogen

Results of a VESCF treatment of pyrazole, its anion, and cation are reported. A comparison is made of the chemical properties of pyrazole and those predicted from the calculated π-electron densities. An ambiguity in the comparison owing to the rapid tautomerization of pyrazole is emphasized. The calculated π-electron distribution in the anion supports the suggestion made in previous papers that the relative electronegativities of carbon and tertiary nitrogen reverse when their π-electron densities exceed 1.2. The dipole moment is predicted to be about 2.5 D for pyrazole, in agreement with observations in solution. Theoretical values of ionization potentials are also presented. An analysis is made of VESCF matrix elements and some empirical guides as to suitable values of coulomb and resonance parameters for five-membered ring nitrogen heterocycles are suggested.

The Variable Electronegativity Method. IV. Glyoxaline, Its Cation and Anion

1959 ◽  
Vol 12 (4) ◽  
pp. 543 ◽  
Author(s):  
RD Brown ◽  
ML Heffernan
Keyword(s):  
Dipole Moment ◽  
Electrophilic Substitution ◽  
Electron Distribution ◽  
Chemical Properties ◽  
Ionization Potentials ◽  
Substitution Reactions ◽  
Resonance Parameters ◽  
Electron Distributions ◽  
Electrophilic Substitution Reactions ◽  
Set Up

Results of VESCF calculations of the π-electron distribution and ionization potentials in glyoxaline and its cation and anion are reported. The electron distributions in these systems are in accordance with the electrophilic substitution reactions observed for glyoxaline and bear out the concept of electronegativity reversal in the anion previously suggested to account for chemical properties of glyoxaline. The dipole moment of glyoxaline, evaluated from the calculated π-electron distribution, agrees with the observed moment, providing further vindication for the VESCF method and support for the suggestion that σ-bond polarizations in heterocycles are slight. Values of the Huckel coulomb and resonance parameters required to make the H�ckel method reproduce the VESCF results for these heterocycles are considered in some detail and it seems feasible to set up empirical rules for selecting appropriate values for the coulomb parameters.

scholarly journals Insights in Behavior of Variably Formulated Alginate-Based Microcapsules for Cell Transplantation

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
Pia Montanucci ◽  
Silvia Terenzi ◽  
Claudio Santi ◽  
Ilaria Pennoni ◽  
Vittorio Bini ◽  
...  
Keyword(s):  
Divalent Cations ◽  
Chemical Properties ◽  
Live Cells ◽  
High Performing ◽  
Physical Chemical ◽  
Degenerative Disorders ◽  
Selection Of ◽  
Better Than

Alginate-based microencapsulation of live cells may offer the opportunity to treat chronic and degenerative disorders. So far, a thorough assessment of physical-chemical behavior of alginate-based microbeads remains cloudy. A disputed issue is which divalent cation to choose for a high performing alginate gelling process. Having selected, in our system, high mannuronic (M) enriched alginates, we studied different gelling cations and their combinations to determine their eventual influence on physical-chemical properties of the final microcapsules preparation,in vitroandin vivo. We have shown that used of ultrapure alginate allows for high biocompatibility of the formed microcapsules, regardless of gelation agents, while use of different gelling cations is associated with corresponding variable effects on the capsules’ basic architecture, as originally reported in this work. However, only the final application which the capsules are destined to will ultimately guide the selection of the ideal, specific gelling divalent cations, since in principle there are no capsules that are better than others.

Broadband EM radiation amplification by means of a monochromatically driven two-level system

2017 ◽  
Vol 31 (04) ◽  
pp. 1750027 ◽  
Author(s):  
Andrey V. Soldatov
Keyword(s):  
Dipole Moment ◽  
Quantum System ◽  
High Frequency ◽  
Laser Field ◽  
Diagonal Matrix ◽  
Matrix Elements ◽  
Level System ◽  
Dipole Moment Operator ◽  
Moment Operator ◽  
Radiation Amplification

It is shown that a two-level quantum system possessing dipole moment operator with permanent non-equal diagonal matrix elements and driven by external semiclassical monochromatic high-frequency electromagnetic (EM) (laser) field can amplify EM radiation waves of much lower frequency.

A COMPARISON OF VARIOUS MEANS OF MEASURING THE DEGREE OF DECOMPOSITION OF VIRGIN PEAT MATERIALS IN THE CONTEXT OF THEIR RELATIVE BIODEGRADABILITY

1979 ◽  
Vol 59 (4) ◽  
pp. 397-400 ◽  
Author(s):  
M. P. LÉVESQUE ◽  
S. P. MATHUR
Keyword(s):  
Chemical Properties ◽  
Fiber Content ◽  
Physical And Chemical Properties ◽  
Physical And Chemical ◽  
Better Than ◽  
And Chemical Properties

Eleven physical and chemical properties of 26 peat materials from a total of five virgin profiles were determined and statistically analyzed for correlations among attributes that relate to the degree of decomposition, and with the rates at which the materials biodegraded. Estimation of fiber content made routinely by pedologists in the field correlated with relative, biodegradability better than any other criterion of decomposition and humification.

Notizen: The Dipole Moment Function of HF Molecule Using Morse Potential

1977 ◽  
Vol 32 (8) ◽  
pp. 897-898 ◽  
Author(s):  
Y. K. Chan ◽  
B. S. Rao
Keyword(s):  
Wave Equation ◽  
Dipole Moment ◽  
Potential Function ◽  
Electric Dipole ◽  
Morse Potential ◽  
Moment Function ◽  
Matrix Elements ◽  
The Matrix ◽  
Vibration Rotation ◽  
Experimental Values

Abstract The radial Schrödinger wave equation with Morse potential function is solved for HF molecule. The resulting vibration-rotation eigenfunctions are then used to compute the matrix elements of (r - re)n. These are combined with the experimental values of the electric dipole matrix elements to calculate the dipole moment coefficients, M 1 and M 2.

scholarly journals NANOCOMPLEJO DE FOSFOPÉPTIDO DE CASEÍNA-FOSFATO DE CALCIO AMORFO (CPP-ACP) EN ODONTOLOGÍA: ESTADO DEL ARTE

2019 ◽  
Vol 30 (2) ◽  
Author(s):  
Cristhian Camilo Madrid Troconis ◽  
Sthefanie Del Carmen Perez Puello
Keyword(s):  
Dental Caries ◽  
Chemical Properties ◽  
Potassium Nitrate ◽  
Surface Pretreatment ◽  
Physico Chemical ◽  
External Agents ◽  
Risk Patients ◽  
Casein Phosphopeptide ◽  
Dental Surface ◽  
Better Than

Saliva and external agents containing different concentrations of sodium fluoride (NaF) promote the dental remineralization process. However, these resources may not be sufficient to counteract the multiple factors involved in the process of dental caries, especially in high-risk patients. There are alternatives that have been extensively researched, such as casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) which provides essential ions, like phosphate and calcium, acting as an adjuvant in the remineralization process. Manufacturers of CPP-ACP-based products also suggest that it can produce desensitizing effects. This nanocomplex has been used experimentally with some dental cements and adhesive systems, but it is important to clarify the effects of this procedure, and the remineralizing/desensitizing advantages it offers. The objective of this topic review was to present the state of the art on CPP-ACP nanocomplex. In terms of dental caries prevention, this remineralizing option is not better than NaF. CPP-ACP provides a dental desensitizing action, but it is temporary and less effective than other alternatives such as potassium nitrate or NaF. The experimental incorporation of CPP-ACP into dental cements should be controlled for not to compromise the physico-chemical properties of the material. The use of dental products based on this nanocomplex as dental surface pretreatment may decrease the bond strength of adhesive materials, but this effect is material dependent.

scholarly journals Determining Partial Atomic Charges for Liquid Water: Assessing Electronic Structure and Charge Models

2020 ◽  
Author(s):  
Bowen Han ◽  
Christine Isborn ◽  
Liang Shi
Keyword(s):  
Electronic Structure ◽  
Dipole Moment ◽  
Charge Transfer ◽  
Liquid Water ◽  
Quantum Chemical ◽  
Water Dimer ◽  
Atomic Charges ◽  
Molecular Dipole ◽  
Molecular Dipole Moment ◽  
Partial Atomic Charges

Partial atomic charges provide an intuitive and efficient way to describe the charge distribution and the resulting intermolecular electrostatic interactions in liquid water. Many charge models exist and it is unclear which model provides the best assignment of partial atomic charges in response to the local molecular environment. In this work, we systematically scrutinize various electronic structure methods and charge models (Mulliken, Natural Population Analysis, CHelpG, RESP, Hirshfeld, Iterative Hirshfeld, and Bader) by evaluating their performance in predicting the dipole moments of isolated water, water clusters, and liquid water as well as charge transfer in the water dimer and liquid water. Although none of the seven charge models is capable of fully capturing the dipole moment increase from isolated water (1.85 D) to liquid water (about 2.9 D), the Iterative Hirshfeld method performs best for liquid water, reproducing its experimental average molecular dipole moment, yielding a reasonable amount of intermolecular charge transfer, and showing modest sensitivity to the local water environment. The performance of the charge model is dependent on the choice of the density functional and the quantum treatment of the environment. The computed molecular dipole moment of water generally increases with the percentage of the exact Hartree-Fock exchange in the functional, whereas the amount of charge transfer between molecules decreases. For liquid water, including two full solvation shells of surrounding water molecules (within about 5.5 A of the central water) in the quantum-chemical calculation converges the charges of the central water molecule. Our final pragmatic quantum-chemical charge assigning protocol for liquid water is the Iterative Hirshfeld method with M06-HF/aug-cc-pVDZ and a quantum region cutoff radius of 5.5 A.<br>

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