Explore chapters and articles related to this topic
Structure of Matter
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
In crystals, the situation is different, as the number of electrons shared is usually large, depending on the crystal structure and the atom. Consequently, electrons can be found at many different energy levels, in an energy range comparable to an energy band, called the valence band.
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
X-ray diffractometry may be carried out using a powder x-ray or a single crystal diffractometer. The latter is used to elucidate the crystal structure while the powder x-ray diffractometer is for general purpose. The polymorphs of material have different crystal packing arrangements and thus produce different x-ray diffractograms with characteristic peaks that are related to lattice distances (Figure 3.8a). The extent of conversion of a crystalline drug to the amorphous form during processing can be determined by comparing the magnitude of their characteristic peaks [47]. The sharp peaks (Figure 3.8a) indicate a crystalline component, whereas broad diffraction peak or features (also referred to as “halo”) indicate an amorphous component (Figure 3.8b). The powder x-ray diffractometry method is non-destructive and requires a very small sample of the material, which can be examined without further processing. For structural determination, good single crystals are used in a single crystal diffractometer. Synchrotron sources have been employed to obtain high-resolution electron diffraction patterns for very small crystals or crystals of complex compounds. Very sensitive charge-coupled detectors have enabled electron diffraction patterns to be recorded in a few seconds using very low electron currents. In addition, microdiffractometers with 2D area detectors have been developed for quick data acquisition [48].
Organotin Chemistry
Published in Nate F. Cardarelli, Tin as a Vital Nutrient:, 2019
The higher molecular weights resulting from associaton can be detected in the gas phase by finding fragments higher than the parent molecular ion or polytin-bearing fragments in the mass spectrum, by a higher-than-parent molecular weight from colligative properties in solution, from larger nmr |1J(119Sn-13C)| or |2J(119Sn-C-1H)| spin-spin couplings in solution,10 from reduced energy ν(OC=O) modes in either the solution or solid states or from lowered tin-119m Mössbauer isomer shifts (IS) and enhanced quadrupole splittings (QS), the resolution of spectra at ambient temperatures, or from the small slope of the temperature dependence of the area under the Moss-bauer resonances in the solid state.11–14 The assumption must be made that the associated species survive transfer from the solid state to dilute solution to the gas phase. From the X-ray diffraction results come the detailed molecular and crystal structure parameters for the solid.7–9 Close intermolecular Sn···O contact distances, wider carbon-tin-carbon angles, and the suggestive juxtaposition of potentially bonded groups can help decide the coordination number at the tin-metal center and the molecularity of the solid. The X-ray data will also tell whether the original stereochemistry of the steroid has been preserved on organotin esterification.
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.
Interdependency of influential parameters in therapeutic nanomedicine
Published in Expert Opinion on Drug Delivery, 2021
Seyed Mehdi Kamali Shahri, Shahriar Sharifi, Morteza Mahmoudi
Different types of crystal lattice of ultrafine titanium dioxide NPs have various effects on human bronchial epithelial cells through induction of oxidative damage. More specifically, a rutile-like crystal/prism-shaped structure seemed to promote cell toxicity via oxidative damage to lipid peroxidation and DNA, resulting in micronuclei formation, in contrast to sized NPs with anatase-like/octahedral crystal structures, which were nontoxic [26]. In some cases, the crystal structure of NPs is altered by contact with environments including water, biological fluids, and other dispersion media or condition (e.g. temperature). The extent or type of change in crystal structure depends on the specific condition. For example, rearrangement of zinc sulfide (ZnS) NPs into a well-ordered structure happens upon contact with water [27]. Additionally, ZnS NPs 3 nm in size (unlike bulk ZnS) undergo reversible structural changes; slow drying and ultrasonic agitation switched between distorted and crystalline structures (respectively). Molecular modeling confirmed those experimental results and indicated low activation energy for the transformation of ZnS NPs [28].
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).