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Published in Paul Pumpens, Single-Stranded RNA Phages, 2020
Witherell and Uhlenbeck (1989) characterized by the nitrocellulose filter binding assay the interaction between the Qβ coat and its operator hairpin of 29 nucleotides in length covering the −9 to +20 region according to the replicase start. The association constant Ka of 400 μM−1 was determined at 4°C, 0.2 M ionic strength, pH 6.0. The salt dependence of Ka revealed that four to five ion pairs might be formed in the complex, although approximately 80% of the free energy of complex formation was contributed by nonelectrostatic interactions. The truncation experiments revealed that the Qβ coat binding required only the presence of a hairpin with an eight-base-pair stem and a three-base loop, while the sequence of the stem was not important for the Qβ coat recognition and only one of the three loop residues was essential. Remarkably, a bulged adenosine was not required for the Qβ coat binding. It was concluded that the Qβ coat binding was achieved primarily by the secondary structure and not by the sequence of the operator.
Immunoglobulins
Published in Constantin A. Bona, Francisco A. Bonilla, Textbook of Immunology, 2019
Constantin A. Bona, Francisco A. Bonilla
The association constant is often called the affinity constant, or simply the affinity of antibody for antigen. Antibody affinities are most often in the range 105–1011 L/mole. Antibody affinity is biologically significant since it determines the minimum concentrations of reactants at which effective interactions occur. High-affinity antibodies react with their complementary antigens when the concentration of either is low.
Antigen-antibody reactions
Published in Gabriel Virella, Medical Immunology, 2019
Antibody affinity can be defined as the attractive force between the complementary configurations of the antigenic determinant and the antibody-combining site. Experimentally, the reaction is best studied with antibodies directed against monovalent haptens. The reaction, as previously mentioned, is reversible and can be defined by the following equation: where k1 is the association constant and k2 the dissociation constant.
Nanoparticle carrier co-delivery of complementary antibiofilm drugs abrogates dual species cariogenic biofilm formation in vitro
Published in Journal of Oral Microbiology, 2022
Guilherme Roncari Rocha, Kenneth R. Sims, Baixue Xiao, Marlise I. Klein, Danielle S.W. Benoit
Absorbance spectroscopy was performed to analyze drug loading within NPC. Previous work showed tt-farnesol and myricetin loading within NPC cores and coronas, respectively [30,48]. Therefore, only compound 1771 was reported here. Data revealed that electrostatic interactions occurred between compound 1771 and the NPC corona. In particular, changes in the absorbance curve were observed using multiple concentrations of compound 1771 spanning 195–1,560 µM at a constant NPC concentration of 0.10 mM or 2.7 mg/mL. Generally, absorbances were lower for free drug in solution compared to drug-loaded NPCs (Figure 3B) with a peak shift from 285 to 290 nm for free drug versus drug-loaded NPC (Figure 3A). A shoulder also occurred between 240 and 250 nm with drug-loaded NPC that was absent in drug-only controls. Increases in intensities, shifts in maximum absorbance wavelengths, and appearance of shoulders indicated strong electrostatic interactions between drug and NPC. Subsequently, absorbance data were used for a double-reciprocal plot to extract an association constant (Ka) of 4.6 × 103 M−1. The linear correlation of Ka (R2 = 0.92) highlighted the electrostatic interaction based on a host-guest binding model between the NPC and 1771, which was concentration-dependent (Figure 3C) [47,53].
A mechanistic review on the dissolution phase behavior and supersaturation stabilization of amorphous solid dispersions
Published in Drug Development and Industrial Pharmacy, 2021
P. Ashwathy, Akshaya T. Anto, M. S. Sudheesh
Nuclear overhauser effect spectroscopy (NOESY) and Diffusion-ordered NMR spectroscopy (DOSY) has been used to study drug–polymer interactions and supersaturation stabilization in polymeric micelles formed during the dissolution of ASDs prepared from amphipathic polymers [24,25]. The cross-peaks between phenyl group of a drug phenytoin and isopropyl group of the polymer (C12)-tailed poly (N-isopropylacrylamide) (PNIPAm) by NOESY confirms the presence of interaction. This observation was also substantiated by the measurement of drug and polymer association constant by DOSY. The association constant between drug and polymer increases with increasing micellar corona polymer chain density showing drug–polymer interaction in the dissolution media and an enhanced propensity toward supersaturation stabilization. The main advantage of these techniques is to understand the drug–polymer interaction which forms the basis of aggregate formation and sustained supersaturation during dissolution.
Development and characterization of orodispersible film containing cefixime trihydrate
Published in Drug Development and Industrial Pharmacy, 2020
Qurrat-ul-ain Khan, Muhammad Irfan Siddique, Fatima Rasool, Muhammad Naeem, Muhammad Usman, Muhammad Zaman
The phase solubility study is an essential and generally accepted tool to assess the impact of CD on the solubility of drug and the apparent stability of complexation [25]. Phase solubility studies showed a curve of an AL type and there was a formation of 1:1 inclusion complex according to Higuchi and Connors diagram. Linearity was found in the solubility trends (Figure 1). The range of association constant was 200–5000 M−1, and calculated constant was within the range. Stable inclusion complexes were assured by the value of Ks. Usually, it is seen that in phase solubility diagram, non-linear trend showed by poorly soluble drugs. Additionally, a slope less than 1 can be demonstrative of a 1:1 stoichiometry concerning concentration of β-CD. For processing, the optimum ratio of 1:1 was prudent to be taken. As the higher ratio, increases the solubility of CFX but these ratio cannot take in this present investigation because these will increase the final weight of the film, film with heavy texture can`t be peeled out from the petri dish and lead to increase in disintegration time as well. So, it is reasonable to take 1:1 w/w as an optimum ratio for further study.