China
Africa
Explore chapters and articles related to this topic
Drug Substance and Excipient Characterization
Published in Dilip M. Parikh, Handbook of Pharmaceutical Granulation Technology, 2021
Parind M. Desai, Lai Wah Chan, Paul Wan Sia Heng
Raman spectroscopy and IR spectroscopy complement each other. The former measures a change in polarization, whereas the latter measures a change in dipole moment. IR-inactive vibrations can be strong in Raman spectra and vice versa. For example, vibrations in the wavenumber region of l0–400 cm‒1 are more easily studied by Raman than by IR spectroscopy. One advantage of the Raman spectroscopy method is that no sample preparation is required, thus the likelihood of inducing phase changes through sample preparation is avoided. However, representative sampling is critical for quantitative analysis. The results are affected by the particle size of the material. The use of Fourier transform Raman spectrometers with a longer wavelength laser of 1064 nm eliminates the problem of any fluorescent background. With the utilization of fiber optics, real-time crystallization can be monitored. Thus, this method is useful for in-line monitoring of pharmaceutical processes.
Particles and Radiation
Published in Rob Appleby, Graeme Burt, James Clarke, Hywel Owen, The Science and Technology of Particle Accelerators, 2020
Rob Appleby, Graeme Burt, James Clarke, Hywel Owen
In other words, , and the oscillating current is equivalent to an oscillating dipole moment. The dipole moment of a given charge separation is just , so we may write
Determining and Drawing Molecular Geometry and Polarity
Published in Patrick E. McMahon, Rosemary F. McMahon, Bohdan B. Khomtchouk, Survival Guide to General Chemistry, 2019
Patrick E. McMahon, Rosemary F. McMahon, Bohdan B. Khomtchouk
Molecular polarity measures the total vector sum of all bond polarities in a complete molecule; this is termed the molecular dipole moment. The dipole moment is proportional to the strength of each individual bond dipole and to the direction of each bond dipole distributed around a central atom. Bond dipoles pointing in the same direction add to produce a larger vector sum for the molecular dipole. Bond dipoles pointing in opposite directions partially or completely subtract (cancel out) to produce a smaller vector sum for the molecular dipole.
Modeling of the structure and forecasting properties of dihydroquercetin derivatives
Published in Drug Development and Industrial Pharmacy, 2022
A. K. Boshkayeva, R. A. Omarova, S. K. Ordabayeva, A. D. Serikbayeva, G. G. Umurzakhova, A. J. Massakbayev
Using the AM1, PM3, and RM1 methods, spatial characteristics were calculated in order to select the most optimal method for further calculations. The results of quantum-chemical studies of model derivatives of dihydroquercetin carried out by the RM1 method have been obtained. The most optimal calculation method was chosen on the data basis of calculating the bond lengths between atoms. Calculations of the enthalpies of formation of model molecules made it possible to evaluate their thermodynamic stability. An analysis of these charge characteristics on atoms in model molecules made it possible to determine the reaction center for each molecule. The reactivity of the studied models was evaluated by comparing the energies of the boundary Molecular Orbitals (HOMO and LUMO), as well as the difference in their values. An analysis of the electric dipole moments allowed us to determine the preferred (polar) nature of the solvents for the studied model molecular systems. Using benzoyl chloride acylation, new compounds are obtained - as derivatives of DHQ.
Formulation of amorphous ternary solid dispersions of dapagliflozin using PEG 6000 and Poloxamer 188: solid-state characterization, ex vivo study, and molecular simulation assessment
Published in Drug Development and Industrial Pharmacy, 2020
Nabil K. Alruwaili, Ameeduzzafar Zafar, Syed Sarim Imam, Khalid Saad Alharbi, Sultan Alshehri, Tilal Elsaman, Fadhel Ahmed Alomar, Sultan Akhtar, Usama A. Fahmy, Nabil A. Alhakamy, Mohammed Salem Alshammari
Polyethylene glycol 6000 (PEG 6000) and poloxamer 188 (PLX 188) have been widely used alone or in combination with other carriers in the preparation of SD [12,17,18]. PEG and PLX are a water-soluble carrier used for the improvement of solubility of the poorly soluble drugs. The use of PLX has been approved by FDA as a therapeutic agent to reduce viscosity [19], and it helps to improve the wettability and stability of SDs. The use of microwave (MW) irradiation method is commonly used to prepare SDs formulations for solubility and bioavailability enhancement [20]. In this technique, the sample kept in contact with the electromagnetic waves between the radio and infrared frequencies over the range of 0.3 ± 300 GHz. These waves penetrate into samples, causing oscillation and finally generate the heat [21]. The constant generated heat takes place inside the material and then passes to the entire volume with the constant heating rate. The dipole moment of the molecules absorbs the MW energy and converts them into the heat. It helps to convert the crystalline form of the drug to the amorphous forms and hence improves the drug solubility [22].
A model of lipid rearrangements during pore formation in the DPPC lipid bilayer
Published in Journal of Liposome Research, 2018
We have assumed that the modelled structure of a pore should be of geometry as often presented in the literature of lipid bilayers, e.g. (Neu and Krassowska 1999, Fuertes et al.2010, Smith and Weaver 2011), that is inverted, i.e. with the pore radius narrowing symmetrically towards the centre (Figures 1 and 2). We have also assumed that the pore wall is defined by the carbon atoms of the glycerol in the DPPC, and the phosphocholine part occupies the polar part of the considered pore. In the case of DPPC, the polar part is made up from the choline groups which form zwitterions (dipolar ions), with the negative charge close to the phosphate group and the positive charge close to the NH3 group. Further, under the healthy physiological pH condition the choline group possesses a stable dipole moment. The dipoles tend to align with the direction of the externally applied electrical field, but due to the thermal fluctuations of the dipoles, the pore wall is in fact a dynamically changing surface. Its permeability is hence dependent not only on the structure (geometry) but also on the electrical field within the pore. Assuming that the pore wall is formed by the glycerol part of the lipid molecule enables estimation of the size of the pore irrespective of the temporal configuration of the polar part of the lipid molecules.