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Nasal and Pulmonary Drug Delivery Systems
Published in Ambikanandan Misra, Aliasgar Shahiwala, In-Vitro and In-Vivo Tools in Drug Delivery Research for Optimum Clinical Outcomes, 2018
Pranav Ponkshe, Ruchi Amit Thakkar, Tarul Mulay, Rohit Joshi, Ankit Javia, Jitendra Amrutiya, Mahavir Chougule
Generally, the prodrug approach is intended to modify the drug molecules for the favorable physicochemical and biological characteristics for better absorption. Various linkages on the drug moiety or modulation in the lipophilicity or hydrophilicity of the drug moiety can be utilized to target certain receptors or transporters. The altered chemistry and affinity of the prodrugs may lead to improved absorption. Limited solubility of the drug molecule can be challenging for nasal delivery; therefore, to improve the aqueous solubility, forming an aqueous soluble derivative may be the one of the approaches for enhancing drug diffusion via nasal mucosa delivery, utilizing the concentration gradient of the diffusion process. Several papers have been published involving such water-soluble prodrug approaches which include. Phosphocholine-linked prodrugs, succinate, and polyethylene glycol polymer conjugate, phosphate alkali metal salt of the drug moiety (Pezron, Mitra et al. 2002). Furthermore, transporter-specific and tissue-specific targeting prodrug approaches are the recent trend in the nasal drug delivery. Nasal absorption of relatively small, impermeable drug molecules can be enhanced by amino acid prodrug techniques. Different acyclovir prodrugs using L-aspartate beta-ester, L-lysyl, and L-phenylalanyl esters and in situ perfusion studies showed that L-aspartate beta-ester of acyclovir significantly enhanced the nasal absorption compared to other ester prodrugs, and suggested that this nasal uptake route involve an active transport (Yang, Gao et al. 2001). The derivatization of prodrugs has the great potential to enhance drug stability and target the transporters and membrane enzymes. Future strategies of prodrugs in nasal delivery may be targeted to achieve improved nasal-to-brain delivery exploring the transporter and enzyme-specific prodrug approaches (Pezron, Mitra et al. 2002).
Investigations on dielectric relaxations, memory and thermistor applications in a liquid crystal nematogen
Published in Liquid Crystals, 2023
The observed loss peaks are identified to follow Debye’s type of relaxation. The observed dielectric relaxation (collective excitations) in a thermally stabilised nematic phase involves contributions from the azimuthal angle ϕ (tuned by the coupling of the transverse dipole moment µt along the direction of director). This is found to respond at higher frequencies of MHz to few KHz regions, in nematic phase. The benzene ring on either side of the mesogen is referred as rigid core while the alkyloxy chain along with hydrogen bond moiety is referred as flexible moiety. Furthermore, this molecular model comprises of alternate rigid and flexible moieties. Usually high frequencies are associated with rigid core and low-frequency relaxations are associated with flexible moiety. The rigid core instantly get aligned quickly and hence need more magnitude of relaxation frequencies while flexible moieties takes more time for alignment and hence needs less relaxation frequencies.
Liquid crystal and photophysical properties of laterally fluorinated azo-ester materials
Published in Liquid Crystals, 2022
Salwa J. Kamal, Noordini M. Salleh, H.N.M. Ekramul Mahmud, N. Idayu Zahid
DSC thermogram of laterally monofluorinated compound F1 (without terminal group) exhibited only one transition peak upon heating and cooling, implying no phase transition into mesophase at all (Figure 2). A similar observation was also reported [32] for the laterally neat and laterally methyl-substituted analogues of F1 (see C1 and M1, respectively, in Table 2). These results suggest that the length of 2-methylbutoxy terminal chain is too short to induce a mesophase in the hydrogen-terminated derivatives. Upon introduction of polar substituent at the opposite terminal, those terminally substituted derivatives are transformed into mesomorphic compounds as shown by the experimental results (Table 2). The replacement of terminal hydrogen by the polar substituent at the p-position of the ester phenyl moiety affects the polarisation of mesogenic group, facilitating the formation of mesophase [40,41]. This mesomorphic behaviour reveals that polar substituent, regardless electron-donating or electron-withdrawing is essential for mesophase formation.
Theoretical investigation on the structure and antioxidant activity of (+) catechin and (−) epicatechin – a comparative study
Published in Molecular Physics, 2020
S. Anitha, S. Krishnan, K. Senthilkumar, V. Sasirekha
Many studies reported that antioxidant activity of CT and ECT is mainly due to their high redox properties that are responsible for the inhibition of various oxidative free radicals [36–40]. The antioxidant behaviour of CT and ECT present in various plant extract was evaluated by various experimental antioxidant assays, such as 1,1-diphenyl-1-picrylhydrazyl , 2, 2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (), nitric oxide ,ferric reducing antioxidant power (FRAP) and experimental results show that CT and ECT are powerful antioxidants [41–43]. Mendoza-Wilson et al. [44] reported that CT and ECT are similar in molecular structure, but their chemical reactivity properties are different. Leopoldini et al. [45] stated that the antioxidant ability of CT is depending on its planar geometry. Hydrogen bond interaction at catechol moiety is also the main feature responsible for the antioxidant activity of ECT [46]. Vagánek et al. [47] reported that the absence of C2=C3 double bond at C ring has a large impact on the antioxidant ability of ECT. Besides, it has been shown that the reactivity of flavan-3-ols is further altered thermodynamically in accordance with the effect of solvents [48,49].