Powders in Cosmetic Formulations
Heather A.E. Benson, Michael S. Roberts, Vânia Rodrigues Leite-Silva, Kenneth A. Walters in Cosmetic Formulation, 2019
The internal packing of the atoms, molecules or ions is known as the crystal structure. This internal arrangement will influence the way in which the crystal grows, and can determine the external shape of particles formed by precipitation or solidification. The overall shape of the crystal is termed the crystal habit, for example acicular (needle), prismatic, pyramidal, tabular, equant, columnar and lamellar types (Figure 13.3 ). Whilst these crystal habits have different external shapes, they might have the same internal structure as can be seen from their XRD patterns. The crystal habit acquired depends on the conditions of crystallisation such as solvent used, temperature, concentration and presence of impurities. Thus, it is very important to control these conditions during the preparation of crystalline raw materials to ensure batch-to-batch consistency in crystal habit. The crystal habit can influence the flow properties and compressibility of a powder material thereby affecting many aspects of the powder performance in both the manufacturing processes and final product.
Receptors and Signal Transduction Pathways Involved in Autonomic Responses
Kenneth J. Broadley in Autonomic Pharmacology, 2017
The amino acid sequences of the G protein-linked receptors have been determined and shown to consist of single polypeptide chains. None of the receptors have been crystallized, so that the three-dimensional geometry of the receptors is not yet known. Bacteriorhodopsin is the purple-membrane protein of Halobacterium halobium, a halophilic (salt-loving) bacterium, which contains a retinal chromophore similar to rhodopsin, the visual pigment of mammalian eyes. This 25 kDa protein has a photosynthetic function in the absence of oxygen, to pump protons (H+) from inside the bacterial cell to the outside, when it is exposed to light. As a result, ADP is converted to ATP. Bacteriorhodopsin is a membrane-spanning protein not coupled to a G protein, but probably making up the ion channel of the proton pump. It has been crystallized, making X-ray crystallography possible for elucidating the three-dimensional structure. High-resolution electron microscopy has shown this protein to consist of seven closely packed hydrophobic membrane-spanning α-helices extending nearly perpendicular to the plane of the membrane, some of the α-helices probably being tilted. Subsequently, the sequence of the visual pigment, bovine rhodopsin, was determined and its predicted structure was similar to that identified for bacteriorhodopsin. This model has served as the basis for the structural arrangement of all G protein-coupled receptors.
Physicochemical properties of respiratory particles and formulations
Anthony J. Hickey, Heidi M. Mansour in Inhalation Aerosols, 2019
Figure 1.1 illustrates the present model for quantifying the aggregate structure and strength. The primary particles compose a pseudo-lattice with vacancies which mainly define the aggregate density and strength. Such pseudo-lattice does not imply a long-range space ordering, like in crystal structure, but is an indication of the most probable packing with the maximum coordination number, K, whereas major defects affecting this number are attributed to vacancies. The structure without vacancies corresponds to the highest coordinated packing with powder density, ρmax, achievable for particles of a given shape but, in practice, can only be observed locally. Both parameters, K and ρmax, can be calculated for simple packing geometries, such as spheres within cubic or hexagonal structures; however, no general relationship between the packing fraction and coordination number is assumed here, unlike that in the semi-empirical relationships developed by Kendell or Rumpf (25,29). In the present model, the probability of finding a particle in its lattice position is ρ/ρmax where ρ is the aggregate density. Assuming the isotropic structure (no preferred orientation) for primary particles and considering the hypothetical fracture cross-sections (Figure 1.1), it can be written for the tensile strength, σT:
Deciphering deamidation and isomerization in therapeutic proteins: Effect of neighboring residue
Published in mAbs, 2022
Flaviyan Jerome Irudayanathan, Jonathan Zarzar, Jasper Lin, Saeed Izadi
Crystal structure analysis. It must be noted that a large fraction of combinations of ϕ & ψ dihedral angles explored in the dipeptide models are energetically inaccessible in folded proteins. To identify the relevant secondary structures for the NX and DX motifs in proteins, we collected ϕ & ψ angle distribution from all the antibody crystal structures available in the PDB. These distributions were analyzed using kernel density estimation (KDE) to arrive at the probability density function (PDF) of conformational preference for [N/D]X residues in ϕ & ψ space (Figure 3a and Figures S2-S16). Comparing the proton affinity calculations with the conformational PDF reveals that [N/D]G sites mainly populate the acidic left-handed α-helical conformations, whereas [N/D]A sites largely favor the basic right-handed helix (ϕ < 0 region) or the beta sheet. The latter agrees with a previous work showing that a steric interaction between the methyl group and the terminal carbonyl oxygen destabilizes all structures with ϕ ~ 120°, relative to glycine dipeptides.43 These results clearly explain why [N/D]A sites are often orders of magnitude less prone to degradation than [N/D]G sites.
Application of scCO2 technology for preparing CoQ10 solid dispersion and SFC-MS/MS for analyzing in vivo bioavailability
Published in Drug Development and Industrial Pharmacy, 2018
Rujie Yang, Yingchao Li, Jing Li, Cuiru Liu, Ping Du, Tianhong Zhang
The SEM micrographs of the pure CoQ10 (a), physical mixture (b), and CoQ10-SD (c) are shown in Figure 5. The pure CoQ10 (a) presented discrete, block-shaped crystal structure with different sizes and the similar crystal structure can be seen in the physical mixture (b). As expected, no crystal structure was observed in the CoQ10-SD, demonstrating that crystal CoQ10 was transformed into amorphous state when forming SD. Moreover, the particle size of CoQ10-SD was smaller than the others. As is well-known, CAB-O-SIL M-5 of fumed silica, as a hydrophilic colloidal silicon dioxide that consists of primary particles with small particle size (about 200 nm) and high specific surface area (200 ± 25 m2/g), favors the formation of CoQ10 with smaller particle size in CoQ10-SD. In short, the SEM study further confirmed the amorphous state of CoQ10 during the formation of SD, which was in agreement with the DSC and PXRD results.
Cell and molecular toxicity of lanthanum nanoparticles: are there possible risks to humans?
Published in Nanotoxicology, 2021
Amir Mohammad Malvandi, Sara Shahba, Abbas Mohammadipour, Seyed Hamidreza Rastegar-Moghaddam, Mahmoud Abudayyak
La NPs are found, naturally or chemically synthesized, in various compositions with other elements, including La(OH)3, LaF3, La2(CO3)3, LaPO4, LaBO3, LaOF, La2Sn2O7, and La2O3 NPs. La2O3 NPs are widespread nanomaterials used in various routes, released into the environment and food chains along which they can transmit and accumulate from lower to higher organisms (Balusamy et al. 2015; Ma et al. 2015). The La2O3 NP contains La and oxygen elements with the electronic configuration, [Xe] 5d1 6s2 and [He] 2s2 2p4, respectively. They are synthesized by calcinating the product resulting from the reaction between La acetate and NaOH at about 600°C. They are irregular sheet structures with spherical morphology and hexagonal crystal structure with less than 100nm size (Sisler et al. 2015,;Salavati-Niasari, Hosseinzadeh, and Davar 2011; Balusamy et al. 2015). Analysis of the chemical composition of La2O3 NP reveals the presence of La and oxygen, allowing the attachment with biomolecules since many biomolecules have a negative surface charge (Balusamy et al. 2012).
Related Knowledge Centers
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