Chemical Factors
Michael J. Kennish in Ecology of Estuaries Physical and Chemical Aspects, 2019
Estuaries receive silicon from riverine systems in dissolved form, via the weathering of silicate minerals in rocks and the leaching of soils, and in particulate form as detrital quartz and clays (alumino silicates). In waters having a pH <9, dissolved silicon is present as silicic acid (H4SiO4).1 Early workers253 proposed that dissolved silicon is removed in estuaries by the formation and flocculation of polymeric silicon during mixing with electrolytes in seawater, because the mean concentration of dissolved silicon in river water (13.1 mg/ℓ)18 exceeds that in seawater (0 to 10 mg/ℓ)21 and because much of the silicon in river water presumably occurs in colloidal form. Some early investigators ascribed nearly 100% removal of dissolved silicon to nonbiological processes during the early stages of estuarine mixing. Liss,17 in a literature review of silicon studies, doubts the occurrence of a colloidal fraction of silicon in river water, which would make direct coagulation of silicon unlikely during estuarine mixing. Additionally, field studies by Burton et al.254 and Burton and Liss255 connote that only about 10 to 20% of dissolved silicon is removed during estuarine mixing. Liss17 places the level of removal of dissolved silicon in the range of 0 to 30% of the riverine flux, with most probably being removed during the early stages of mixing. A recent detailed treatment of silicon behavior in marine systems can be found in Aston.256
Catalog of Herbs
James A. Duke in Handbook of Medicinal Herbs, 2018
Decoctions, poultices, and teas are used for various forms of cancer including polyps, abdominal, and oral cancers.4 In Guatemala, used for bone cancer. Also, used for cancer of breast, intestines, kidney, lip, liver, stomach, and tongue.4 Decoction of plant is astringent and is used as a styptic and to reduce the swelling of eyelids; is diuretic and is used in bladder and kidney affections, and is also used for cystic ulceration, cystitis, dropsy, dysuria, fever, gonorrhea, gout, hematopoietic ailments, hemoptysis, gravel, rheumatism, and tuberculosis. Ashes of plant used for acidity of stomach and dyspepsia. Cooling and astringent, it is used for cystic ulceration, hemorrhages, and ulcers in urinary passages. Externally, the decoction will stop bleeding and heal wounds, and reduce the swelling of eyelids.2 Fractured bones are said to heal faster when horsetail is taken.28 The high silica content is said to render it especially effective in pulmonary consumption,27 but Tyler concludes no evidence supports the hypothesis that the silica and silicic acid derivatives in the drug promote the healing of bleeding tubercular lesions in the lung.37
Biomedical Accelerator Mass Spectrometry
Graham Lappin, Simon Temple in Radiotracers in Drug Development, 2006
Isotopes of biological interest that have been studied by AMS include 3H, 26Al, 36Cl, 41Ca, 32Si, and 129I. Tritium (3H), with a half-life of 12.3 years, is a useful tracer in the study of xenobiotic metabolism (Section 3.2.1) and has been analyzed by AMS. 26Al is the only long-lived radioisotope of aluminum (with a half-life of 740,000 years). It has been suggested that aluminum could be involved in the development of anemia, Alzheimer’s disease, and renal failures.7-41Ca has a half-life of 103,000 years and can be used to investigate osteoporosis and other bone diseases.8 36Cl and 129I (with half-lives of 301,000 and 15.7 million years, respectively) are of interest in biomedicine, as they have importance in general metabolism. These isotopes can be measured down to a sensitivity of >10-14 using AMS.9,10 Elements such as Fe, Ni, and Se can be present in proteins and have vital metabolic functions in living organisms. The absorption and renal elimination of silicic acid in humans have been studied using 32Si and AMS.1132S is a strongly interfering isobar of 32Si, and a gas-filled magnet technique is required to separate them.
Intravitreal safety profiles of sol-gel mesoporous silica microparticles and the degradation product (Si(OH)4)
Published in Drug Delivery, 2020
Yaoyao Sun, Kristyn Huffman, William R. Freeman, Michael J. Sailor, Lingyun Cheng
The pore size of an intravitreal particulate drug delivery system is an important parameter in terms of release rate of the payload and the elimination rate of the vehicle material. Characterizing the dissolution rate and vitreous elimination profile of silicic acid is an important part of optimizing the intravitreal delivery system using mesoporous silica particles. In order to investigate the rate at which sol-gel silica degrades into silicic acid, an in vitro release experiment was carried out. We tested 3 different sized particles for in vitro silicic acid release, 15 µm/10 nm, 25–45 µm/50 nm and 15 µm/100 nm (particle diameter/pore diameter). Briefly, 2 mg of sol-gel silica particles was weighed into a 1.5 mL microcentrifuge tube with 1200 µL of PBS. The vials were incubated at 37 °C. The vials were centrifuged at 5,000 rpm for 5 minutes, and 1000 uL of the supernatant was collected and stored at –80 °C. Then, 1000 uL of PBS was added back to each of the tubes to restore the volume of the dissolution medium. The experiment was carried out daily and all samples were analyzed by the end of week 3. The concentration of silicic acid was determined by ICP-OES.
Current status and prospect for future advancements of long-acting antibody formulations
Published in Expert Opinion on Drug Delivery, 2023
Puneet Tyagi, Garrett Harper, Patrick McGeehan, Shawn P Davis
Silica has attracted considerable interest in drug delivery in the recent past due to its advantageous properties, including biodegradability and biocompatibility [27,28]. Silica degrades in the body to silicic acid and is subsequently eliminated from the body via renal excretion [29]. Having been approved by the FDA as GRAS (generally regarded as safe), silica is a common ingredient in oral and topical formulations. In comparison to PLGA polymers, silica degradation does not create an acidic environment as silicic acid has the first pKa at 9.84 [30]. In one of our earlier studies, we reported a sustained release of an active mAb from a silica matrix formed by the polymerization of alkoxysilanes, Si(OR)4, using a technique known as the sol-gel process [31]. By changing the manufacturing process parameters, it is possible to vary the number of the OH groups and specific surface area (from a dense gel to highly porous), both influencing the biodegradation rate of silica. The matrix is slowly dissolved when in contact with body fluids. However, use for silica for injectable long-term therapy needs to be thoroughly investigated for potential side effects.
Related Knowledge Centers
- Biomineralization
- Chemical Compound
- Chemistry
- Monomer
- Oligomer
- Oxide
- Polymer
- Silicon
- Hydroxy Group
- Conjugate