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Elements of Polymer Science
Published in E. Desmond Goddard, James V. Gruber, Principles of Polymer Science and Technology in Cosmetics and Personal Care, 1999
E. Desmond Goddard, James V. Gruber
The simplest average is the number-average molecular weight, , where is the number of species with molecular weight (Eq. 16) Physically, the number-average molecular weight can be determined by any technique that “counts” molecules based on the colligative properties of solutions , such as freezing point depression, boiling point elevation, and osmometry.
Detergent Phenomena in Membrane Protein Crystallization
Published in Hartmut Michel, Crystallization of Membrane Proteins, 1991
Most workers in the field know that micellar systems are “quite monodisperse”, but exhibit some polydispersity. The quantitative analysis is difficult. It consists of measuring the weight average and number average molecular weight of the micelles. The latter has eluded direct measurement, as vapor pressure osmometry is not sensitive enough. Polydispersity analysis of quasielastic light scattering data is particularly difficult for unimodal distributions, and observations of the asymptotic scattering in small angle techniques requires substantial surfactant concentrations, posing additioinal problems.
Production, Extraction and Characterization of Alginates from Seaweeds
Published in Gokare A. Ravishankar, Ranga Rao Ambati, Handbook of Algal Technologies and Phytochemicals, 2019
Faiez Hentati, Alina V. Ursu, Guillaume Pierre, Cedric Delattre, Bogdan Trica, Slim Abdelkafi, Gholamreza Djelveh, Tanase Dobre, Philippe Michaud
Size exclusion chromatography, coupled with: refractometer and/or Multi-Angle Light Scattering analysis (SEC-MALLS) and/or osmometer and/or viscometer are used to estimate the weight-average molecular weight (Mw), the number-average molecular weight (Mn), the radius of gyration (Rg), the hydrodynamic radius (Rh) and the polydispersity index (Ð = Mw/Mn) of alginates (Draget et al. 2006). Mw of sodium alginates were evaluated between 100 and 553 kg/mol depending on brown seaweeds species and extraction processes (Belalia and Djelali 2014; Khajouei et al. 2018; Hentati et al. 2018). As related by Draget et al. (2006) and confirmed by Belalia and Djelali (2014), alginates possessed a Ð ranging from 1.5 to 3. Ð values represent the size distribution of a particle population in polysaccharide solution. Recently, Morris et al. (2014) presented some hydrodynamic methodologies used to investigate the main shapes of polysaccharides in a dilute regime. As mentioned by authors, from some specific coefficients (power law) and parameters (Wales and Van Holde 1954) obtained by using SEC-MALLS in combination with viscometer, it is possible to give a well-established idea of the conformation, shape and flexibility of polysaccharides in solution. Low molecular weight alginates (Mw around 100 kg/mol) had Rh and Rg of 17.3–17.7 and 26.2 nm respectively (Khajouei et al. 2018; Hentati et al. 2018). As related by Morris et al. (2014), diverse sodium alginates with Mw ranging from 15–2700 kg/mol had Rg and Rh ranging from 40–190 nm and 25–55 nm respectively. Nevertheless, the structure factor (or shape factor) ρ = Rg/Rh provides better information regarding the polysaccharides shapes according to the specific conformation in dilute regime with: ρ = 2 (rigids rods), ρ = 1.7 (random coils) and ρ = 0.78 (hard spheres) (Burchard 1988).
Current trends in PLGA based long-acting injectable products: The industry perspective
Published in Expert Opinion on Drug Delivery, 2022
Omkara Swami Muddineti, Abdelwahab Omri
Usually, PLGA with higher molecular weight takes a long time to degrade and generate oligomers that are water-soluble in drug release. PLGA is available in various weight distributions and molecular weights in the market. Characterization of molecular weight of PLGA polymer is measured using the weighted average molecular weight (Mw), number average molecular weight (Mn), and polydispersity index [30]. During the synthesis of PLGA polymer, Mw, Mn, and PDI are greatly influenced by catalyst concentration, degree of vacuum, monomer purity, polymerization time, temperature, and quantity of molecular weight controller. The acceptance range of molecular weight is specific to each product and significantly affects inter batch variability, consequently on Q1 sameness. For instance, microspheres prepared with risperidone API as model drug showed minimal impact on API release even with a molecular weight difference of 10 kD [31].
Prolonged inhibitory effects against planktonic growth, adherence, and biofilm formation of pathogens causing ventilator-associated pneumonia using a novel polyamide/silver nanoparticle composite-coated endotracheal tube
Published in Biofouling, 2020
Sakkarin Lethongkam, Chalongrat Daengngam, Chittreeya Tansakul, Ratchaneewan Siri, Apisit Chumpraman, Manthana Phengmak, Supayang P. Voravuthikunchai
The structure of the polyamide resin was characterized based on one- and two- dimensional nuclear magnetic resonance (NMR) techniques including 1H, 13C, and DEPT 135 (Distortionless Enhancement by Polarization Transfer 135°) NMR as well as HMQC (Heteronuclear Multiple Quantum Correlation), HMBC (Heteronuclear Multiple Bond Correlation) and 1H-1H COSY (COrrelated SpectroscopY). The weight average molecular weight (Mw), the number average molecular weight (Mn), and the polydispersity index (PDI) were determined by Gel Permeation Chromatography (GPC). The wetting properties of the pristine and AgNPs-incorporated polyamide films were examined through contact angle (CA) measurement, using an optical contact angle measurement system with a test droplet volume of 10 µl. The surface energies of the coating, including the dispersive and polar components, were determined according to the Owens–Wendt–Rabel-and-Kaelble (OWRK) method (Owens and Wendt 1969; Kaelble 1970; Law and Zhao 2016). The test liquids used here were DI water, ethylene glycol, formamide, and ethanol. The surface morphology and topography of the coated ETT samples were evaluated by scanning electron microscopy (SEM) and atomic force microscoye (AFM).
Reduced administration frequency for the treatment of fungal keratitis: a sustained natamycin release from a micellar solution
Published in Expert Opinion on Drug Delivery, 2020
Yiyuan Guo, Fatemeh Karimi, Qiang Fu, Greg. G. Qiao, Hong Zhang
A general strategy for the synthesize of PEG-b-PGMA is illustrated in Figure 1. The macro-TTC was first synthesized via the EDC/DMAP coupling reaction. The preparation of PEG-based chain transfer agent (macro-TTC) was verified by analyzing the corresponding peaks in the 1H NMR spectra (Figure S1). A new proton resonance e’ (in Figure S1B) at 2 ppm assigned to the proton of amide group (-NHCO-) was observed, suggesting the successful preparation of macro-TTC. The number-average molecular weight (MnGPC) of 6.9 kDa with a dispersity (Ð) of 1.07 was determined for macro-TTC by GPC (Figure S2). Then, the block copolymer PEG-b-PGMA was synthesized via the RAFT polymerization of glycidyl methacrylate (GMA) using the prepared macro-TTC. After 19 h of polymerization, near quantitative conversion of GMA (ca. 99%, 30 GMA units) was achieved through 1H NMR analysis (Figure S1). Characteristic peaks m” and i” derived from methacrylate were observed after the RAFT polymerization (Figure S1C), which confirms the preparation of block copolymer PEG-b-PGMA. In addition, the GPC curve revealed a monomodal peak (MnGPC of 11.9 kDa) and a narrow dispersity (Ð = 1.23), suggesting a controlled polymerization (Figure S2).