scholarly journals Stability Study of Four Layer Aurivillius Oxide of AxBi4-xTi4O15 (A = Ca, Sr, Ba): Atomistic Simulation

2020 ◽  
Vol 3 (2) ◽  
pp. 157
Author(s):  
Akram La Kilo ◽  
La Alio ◽  
La Ode Aman ◽  
Jafar La Kilo
Keyword(s):  
Atomistic Simulation ◽  
Research Method ◽  
Constant Pressure ◽  
Geometry Optimization ◽  
Lattice Energy ◽  
Stability Study ◽  
Perovskite Layer ◽  
Buckingham Potential ◽  
Lattice Energies ◽  
The Stability

Aurivillius is bismuth layered structure ferroelectrics that can be applied as memory, sensor, and catalyst. This research aimed to study the stability of AxBi4-xTi4O15 Aurivillius (A = Ca, Sr, and Ba). Dopants (A) partially substitute Bi at the sites of Bi(1) and Bi(2) of the perovskite layer. This research method is an atomistic simulation using by the GULP code. Simulations were carried out by means of AxBi4-xTi4O15 geometry optimization at constant pressure, using the Buckingham potential. The results showed that the increase in the concentration of dopants substituting Bi accompanied by an increase in lattice energies. The most stable Aurivillius was CaxBi4-xTi4O15 (x = 16.3%) carried out by Bi substitution at Bi(2) site, with lattice energy, -1668.227 eV. Aurivillius stability decreases by increasing the size of the dopant. The maximum concentration number of A dopant substituting Bi was discussed.

Calculation of the CONH dipole contribution to lattice energies of amides, polyamides, and polypeptides

1964 ◽  
Vol 278 (1372) ◽  
pp. 91-109 ◽  
Keyword(s):  
Hydrogen Bonding ◽  
Total Energy ◽  
Lattice Energy ◽  
Nylon 6 ◽  
Kcal Mole ◽  
Protein Molecules ◽  
Lattice Energies ◽  
The Stability ◽  
Α Helix ◽  
Dipole Energy

The dipole energy of a lattice of point dipoles in the configurations of the polyamides 6.6 and 6, of tetradecanamide, and of α and β forms of poly-L-alanine are calculated. The dipole forces contribute 4·8 kcal/mole to the lattice energy of nylon 6.6 of which 93 % arises from the collinear arrays of CONH dipoles along the ‘ a ’ axis. For nylon 6 the total energy is 4·6 kcal/ mole. In tetradecanamide the total energy is 3·9 kcal/mole of which only 0·7 kcal/mole arise from the dimer pairs of CONH 2 groups. The calculated energy for β poly-L-alanine is 5·7 kcal/ mole but only 1·8 kcal/mole for the α helix. The dipole forces only stablize the α helix for molecules containing more than 14 CONH groups. Below this length the dipole energy is repulsive. CO...HN hydrogen bonding contributes to the stability of the helix. Changes in configuration of protein molecules from α to β forms are probably facilitated by a balance between dipole forces and hydrogen bonding which vary reciprocally with changing configurations of the CONH group contacts.

scholarly journals Study on the Stability of Trivalent Cations Doped Zirconia through Atomistic Modeling

2019 ◽  
Vol 22 (4) ◽  
pp. 129-135
Author(s):  
Akram La Kilo ◽  
Triwahyuni S. Umamah ◽  
Lukman A. R. Laliyo
Keyword(s):  
Geometry Optimization ◽  
Lattice Energy ◽  
Atomistic Modeling ◽  
Cell Parameters ◽  
Short Range Potential ◽  
Atomistic Modelling ◽  
Trivalent Cations ◽  
The Difference ◽  
The Stability ◽  
Good Agreement

The aim of this research was to study the stability of the structure of the ZrO2 doped with trivalent oxide Zr1-xMxO2-δ (M = La3+, Nd3+, Sm3+, Eu3+, Gd3+, Y3+, Er3+, Yb3+ and Lu3+ through atomistic modelling and bond valence sum method. Short range potential used in this study was Buckinghams’ potential. Result of geometry optimization at constant pressure shown both cell parameters of ZrO2 was in good agreement with experimental results because of the difference was only 0.11%. Increasing the concentration and the size of substituting dopant of ZrO2 makes the lattice energy of the doped structure was more positive so that the stability of the doped ZrO2 structure decreases. The decrease in the stability of ZrO2 doped with Y3+, Er3+, Yb3+ and Lu3+was smaller than ZrO2 doped with La3+, Nd3+, Sm3+, Eu3+ and Gd3+. BVS results shown that the structure of ZrO2 doped with La3+was not appropriate because it has different value of BVS was more than 0.1

scholarly journals Theoretical investigation of the lattice energy of urea: Insight from DFT using systematic cluster method

2017 ◽  
Vol 13 (4) ◽  
pp. 632-636
Author(s):  
Nur Najwa Alyani Mohd Nabil ◽  
Lee Sin Ang
Keyword(s):  
Solid State ◽  
Theoretical Investigation ◽  
Lattice Energy ◽  
Cluster Method ◽  
Lattice Energies ◽  
The Stability ◽  
The One ◽  
The Individual ◽  
Small Clusters ◽  
Systematic Cluster

Lattice energy is the energy needed to form crystals of a compound from the individual molecules. It is related to the stability of a compound in the solid state. In this study, systematic cluster method has been applied to obtain the lattice energy of urea. Using this method, the effect of solid state environment is included in a systematic way. Starting from the small clusters containing a few molecules, the largest cluster we studied contains 84 molecules. In order to improve the results from the cluster method using Gaussian 09 program, correction using the D3BJ program was included. The results show that, when compared to the experimental value, the lattice energies obtained were under-estimated for all the theoretical levels considered. Generally, application of the systematic cluster method shows decrease in calculated lattice energy as more molecules were included in the clusters and becomes closer to the experimental value of urea. Of all the levels considered, B3LYP/DEF2-TZVP with correctional terms provides the closest value to the one from the experiment.

On the reliability of volume-based thermodynamics for inorganic-organic salts and coordination compounds with uncharged ligands

2017 ◽  
Author(s):  
Robson de Farias
Keyword(s):  
Coordination Compound ◽  
Coordination Compounds ◽  
Formation Enthalpy ◽  
Lattice Energy ◽  
Chemical Hardness ◽  
Acid Anion ◽  
Organic Salts ◽  
Density Values ◽  
Lattice Energies

In the present work, the reliability of the volume-based thermodynamics (VBT) methods in the calculation of lattice energies is investigated by applying the “traditional” Kapustinskii equation [8], as well as Glasser-Jenkins [3] and Kaya [5] equations to calculate the lattice energies for Na, K and Rb pyruvates [9-11] as well as for the coordination compound [Bi(C<sub>7</sub>H<sub>5</sub>O<sub>3</sub>)<sub>3</sub>C<sub>12</sub>H<sub>8</sub>N<sub>2</sub>] [17] (in which C<sub>12</sub>H<sub>8</sub>N<sub>2</sub> = 1,10 phenathroline and C<sub>7</sub>H<sub>5</sub>O<sub>3</sub><sup>-</sup>= <i>o</i>-hyddroxybenzoic acid anion). As comparison, the lattice energies are also calculated using formation enthalpy values for sodium pyrivate and [Bi(C<sub>7</sub>H<sub>5</sub>O<sub>3</sub>)<sub>3</sub>C<sub>12</sub>H<sub>8</sub>N<sub>2</sub>]. For the pyruvates, is verified that none of the considered approach, Kapustinskii, Glasser, Kaya or density, provides values that agrees in an acceptable % difference, with the lattice energy values calculated from the formation enthalpy values. However, it must be pointed out that Kaya approach, with deals with a chemical hardness approach is the better one for such kind of inorganic-organic salts. Based on data obtained for [Bi(C<sub>7</sub>H<sub>5</sub>O<sub>3</sub>)<sub>3</sub>C<sub>12</sub>H<sub>8</sub>N<sub>2</sub>] is concluded that the only one VBT method that provides reliable lattice energies for compounds with bulky uncharged ligands is that one based on density values (derived by Glasser-Jenkins).

First Principles Investigation of the Stability and the Chemical Behavior of Hydrogen in ThCoH4

2011 ◽  
Vol 66 (3) ◽  
pp. 269-274
Author(s):  
Samir F. Matar
Keyword(s):  
Negative Charge ◽  
Geometry Optimization ◽  
Full Geometry Optimization ◽  
Intermetallic Matrix ◽  
Charge Analysis ◽  
The Stability ◽  
The One ◽  
Site Selective ◽  
Bader Charge Analysis ◽  
Positively Charged

We address the changes in the electronic structure brought by the insertion of hydrogen into ThCo leading to the experimentally observed ThCoH4. Full geometry optimization positions the hydrogen in three sites stabilized in the expanded intermetallic matrix. From a Bader charge analysis, hydrogen is found to be in a narrow iono-covalent (~−0.6) to covalent (~−0.3) bonding which should enable site-selective desorption. The overall chemical picture shows a positively charged Thδ+ with the negative charge redistributed over a complex anion {CoH4}δ− with δ~1.8. Nevertheless this charge transfer remains far from the one in the more ionic hydridocobaltate anion CoH54− in Mg2CoH5, due to the largely electropositive character of Mg.

scholarly journals Limitations and Challenges in the Stability of Cysteamine Eye Drop Compounded Formulations

2021 ◽  
Vol 15 (1) ◽  
pp. 2
Author(s):  
Cristina Martín-Sabroso ◽  
Mario Alonso-González ◽  
Ana Fernández-Carballido ◽  
Juan Aparicio-Blanco ◽  
Damián Córdoba-Díaz ◽  
...  
Keyword(s):  
Shelf Life ◽  
Stability Study ◽  
Eye Drops ◽  
Microbiological Analysis ◽  
Nitrogen Gas ◽  
Long Term Stability ◽  
Main Degradation Product ◽  
The Stability ◽  
Unstable Molecule

Accumulation of cystine crystals in the cornea of patients suffering from cystinosis is considered pathognomonic and can lead to severe ocular complications. Cysteamine eye drop compounded formulations, commonly prepared by hospital pharmacy services, are meant to diminish the build-up of corneal cystine crystals. The objective of this work was to analyze whether the shelf life proposed for six formulations prepared following different protocols used in hospital pharmacies is adequate to guarantee the quality and efficacy of cysteamine eye drops. The long-term and in-use stabilities of these preparations were studied using different parameters: content of cysteamine and its main degradation product cystamine; appearance, color and odor; pH and viscosity; and microbiological analysis. The results obtained show that degradation of cysteamine was between 20% and 50% after one month of storage in the long-term stability study and between 35% and 60% in the in-use study. These data confirm that cysteamine is a very unstable molecule in aqueous solution, the presence of oxygen being the main degradation factor. Saturation with nitrogen gas of the solutions offers a means of reducing cysteamine degradation. Overall, all the formulae studied presented high instability at the end of their shelf life, suggesting that their clinical efficacy might be dramatically compromised.

scholarly journals FORMULATION, CHARACTERIZATION AND STABILITY STUDY OF FAST DISSOLVING THIN FILM CONTAINING ASTAXANTHIN NANOEMULSION USING HYDROXYPROPYLMETHYL CELLULOSE POLYMER

2021 ◽  
pp. 17-22
Author(s):  
LUSI NURDIANTI ◽  
IYAN SOPYAN ◽  
TAOFIK RUSDIANA
Keyword(s):  
Thin Film ◽  
Mechanical Characteristics ◽  
Storage Conditions ◽  
Stability Study ◽  
Matrix System ◽  
Stability Studies ◽  
Casting Method ◽  
Hydroxypropylmethyl Cellulose ◽  
The Stability ◽  
Physical And Mechanical Characteristics

Objective: The present study was conducted to formulate and characterize the thin film containing astaxanthin nanoemulsion (TF-ASN) using Hydroxypropylmethyl Cellulose (HPMC) polymer as a film matrix system. The stability studies in different storage conditions were also performed. Methods: Astaxanthin nanoemulsion (As-NE) was prepared by using self-nanoemulsifying method, followed by incorporation into the HPMC matrix system by solvent casting method to forming TF-ASN. Evaluation of TF-ASN was performed by physical and mechanical characterizations. Stability study was carried out in both of accelerated (temperature of 40±2 °C/75±5% RH) and non-accelerated (at ambient temperature) conditions. Assay of astaxanthin in individual TF-ASN was determined compared to pure astaxanthin. Results: TF-ASN had good physical and mechanical characteristics that suitable for intraoral administration. Conclusion: For the study of stability under different storage conditions, it was proven that nanoemulsion form was packed in a HPMC matrix could enhance the stability of the astaxanthin.

scholarly journals The stability study of a plane engine

2000 ◽  
Vol 27 (1) ◽  
pp. 35-44
Author(s):  
Rafał Kołodziej ◽  
Tomasz Nowicki
Keyword(s):  
Stability Study ◽  
The Stability

scholarly journals Physicochemical Properties and Stability of Microencapsulated Betacyanin Pigments from Red Dragon Fruit Peels and Flesh

2020 ◽  
pp. 141-148
Author(s):  
Rosalinda C Torres ◽  
Rowelain Mae G Yumang ◽  
Chelsea Kate F Jose ◽  
Danielle Camille P Canillo
Keyword(s):  
Moisture Content ◽  
Physicochemical Properties ◽  
Morphological Characterization ◽  
Stability Study ◽  
Natural Colorant ◽  
Hygroscopic Moisture ◽  
Dragon Fruit ◽  
The Stability ◽  
Spray Dried ◽  
Hylocereus Polyrhizus

Dragon fruit (Hylocereus polyrhizus) is known for its purple-coloured peels and pulp, which can be attributed to the presence of betalains. In this study, the potential of red dragon fruit as a source of natural colorant was investigated. Betacyanins were extracted from red dragon fruit peels and flesh in 1:3 ratio with water. Microencapsulation by spray-drying was done by adding 5% and 10% (w/v) maltodextrin (DE 11.8) to peels and flesh extracts, respectively. The spray-dried colorant powders all obtained <10% moisture content, 5.261-6.409 g/100g hygroscopic moisture content, and 5.317-7.349(mg/100L) betacyanin content. Morphological characterization revealed spherical, agglomerated particles with visible cracks on the surface. The stability study conducted showed that pigment retention was lowest at 70°C and highest at 4°C. Keywords: Hylocereus polyrhizus; Red dragon fruit; Betacyanin; Microencapsulation; Physicochemical properties

scholarly journals A Fast and Validated HPLC Method for Simultaneous Determination of Dopamine, Dobutamine, Phentolamine, Furosemide, and Aminophylline in Infusion Samples and Injection Formulations

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Fuchao Chen ◽  
Baoxia Fang ◽  
Sicen Wang
Keyword(s):  
Mobile Phase ◽  
Dosage Form ◽  
Limit Of Detection ◽  
Hplc Method ◽  
Stability Study ◽  
Precision Data ◽  
Column Temperature ◽  
Ich Guidelines ◽  
Limit Of Quantitation ◽  
The Stability

A simple, fast, and validated HPLC method was developed for the simultaneous quantization of five cardiovascular agents: dopamine (DPM), dobutamine (DBM), phentolamine (PTM), furosemide (FSM), and aminophylline (APL) either in infusion samples or in an injection dosage form. The proposed method was achieved with a 150 mm × 4.6 mm, 5.0 μm C18 column, by using a simple linear gradient. Mobile phase A was buffer (50 mM KH2PO4) and mobile Phase B was acetonitrile at a flow rate of 1.0 mL/min. The column temperature was kept at 30°C, and the injection volume was 20 μL. All analytes were separated simultaneously at a retention time (tr) of 3.93, 5.84, 7.06, 8.76, and 9.67 min for DPM, DBM, PTM, FSM, and APL, respectively, with a total run time of less than 15.0 min. The proposed method was validated according to ICH guidelines with respect to accuracy, precision, linearity, limit of detection, limit of quantitation, and robustness. Linearity was obtained over a concentration range of 12.0–240.0, 12.0–240.0, 20.0–200.0, 6.0–240.0, and 10.0–200.0 μg/mL DPM, DBM, PTM, FSM, and APL, respectively. Interday and intraday accuracy and precision data were recorded in the acceptable limits. The new method has successfully been applied for quantification of all five drugs in their injection dosage form, infusion samples, and for evaluation of the stability of investigated drugs in mixtures for endovenous use. The results of the stability study showed that mixtures of DPM, DBM, PTM, FSM, and APL in 5% glucose or 0.9% sodium chloride injection were stable for 48 hours when stored in polypropylene syringes at 25°C.

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