Stephen D. Kinrade

Silicon-29 NMR evidence of a transient hexavalent silicon complex in the diatom Navicula pelliculosa

Cultures of the freshwater diatom Navicula pelliculosa were synchronized by silicon starvation, fed a 29Si-enriched silicate solution, and then studied by 29Si NMR spectroscopy. Two NMR resonances could be detected reproducibly, the ever-present orthosilicic acid peak at −71 ppm and a weak signal at −131.5 ppm that was only seen after the diatoms had been allowed six hours to accumulate the 29Si. When the initial culture medium was enriched in 15N, the −131.5 ppm resonance narrowed significantly which, taken with the peaks unique chemical shift, implies the existence of an organosilicon complex containing hexavalent silicon coordinated to at least one nitrogen. The signal is the first direct evidence of an organosilicon complex formed during the life cycle of an organism.

Aqueous hypervalent silicon complexes with aliphatic sugar acids

Silicon-29 and carbon-13 NMR spectroscopy is employed to determine the structures of stable five- and six-coordinated organosilicon complexes formed by the addition of certain aliphatic acid carbohydrates (such as gluconic acid, glucoheptonic acid and saccharic acid) to aqueous alkaline silicate solutions.

Effects of carbonation on the leachability and compressive strength of cement-solidified and geopolymer-solidified synthetic metal wastes.

The effects of accelerated carbonation on the compressive strength and leachability of fly ash-based geopolymer and ordinary portland cement (OPC) doped with Cd(II), Cr(III), Cr(VI), Cu(II), Pb(II) or Zn(II) salts were investigated. Cement was effective at immobilizing Cd, Cr(III), Cu, Pb and Zn under both the Synthetic Precipitation Leaching Procedure (SPLP) and the Toxicity Characteristic Leaching Procedure (TCLP), but ineffective for retaining Cr(VI). Carbonated cement maintained its ability to immobilize Cd, Cr(III), Pb and Zn, but, under acidic TCLP conditions, was much worse at retaining Cu. Geopolymer was effective at immobilizing Cr(III) and Cu, and, to a lesser degree, Cd, Pb and Zn in SPLP leaching tests. Only Cr(III) was immobilized under comparatively acidic TCLP testing conditions. Carbonation did not change the metal retention capacity of the geopolymer matrix. Metal doping caused compressive strengths of both geopolymer and cement to decrease. Carbonation increased the compressive strength of cement, but decreased that of the geopolymer. Geochemical equilibrium modeling provided insight on the mechanisms of metal immobilization.

Chapter 4 A primer on the aqueous chemistry of silicon

A fundamental understanding of aqueous silicate chemistry is a prerequisite to unraveling silicons (Si) role in living systems. Owing primarily to the advent of 29Si nuclear magnetic resonance (NMR) spectroscopy, the depth of that understanding has increased dramatically over the past two decades. By comparison, details of the biochemistry of Si are sparse. Although several proteins and amino acids believed to be associated with silicates have been isolated, no organosilicon compounds have so far been identified under physiological conditions. Nevertheless, hypervalent Si complexes have very recently been shown to form in the presence of aliphatic polyols and polyol acids, such as mannitol and saccharic acid, respectively. Such simple aliphatic hydrocarbons may play a crucial role in the uptake, transport, and deposition of Si in nature. The objective of this paper is to provide an overview of the speciation, equilibria, and chemical exchange kinetics of Si in aqueous environments, along with an examination of applicable methods of chemical analysis.

NMR evidence of pentaoxo organosilicon complexes in dilute neutral aqueous silicate solutions

Silicon-29 NMR spectra of a neutral, dilute aqueous silicic acid solution, with a pH and Si concentration typical of soil solutions, reveal that a significant fraction of the silicon is incorporated in two five-coordinated organosilicon complexes when sodium gluconate is present.

The silicon supplement ‘Monomethylsilanetriol’ is safe and increases the body pool of silicon in healthy Pre-menopausal women

BackgroundMonomethylsilanetriol (MMST) has been used for decades as an oral silicon supplement for bone and connective tissue health, although there are no formal data on its in vivo utilisation or safety following sustained dosing.MethodsTo investigate whether MMST contributes to the body pool of silicon and, secondly, to establish its safety following 4 weeks’ supplementation in humans, twenty-two healthy pre-menopausal women (22–38 years) were recruited and supplemented with MMST at the maximum daily recommended dose (10.5 mg Si/day) for 4 weeks in a double-blind, randomised, placebo-controlled, cross-over design (i.e. 8 weeks in total). Fasting serum and urine samples were collected at baseline and at the end of the 4-week supplementation/placebo periods for analysis of total silicon by inductively coupled plasma optical emission spectrometry, MMST by proton nuclear magnetic resonance spectroscopy and full serum biochemistry. Participants also reported on, by questionnaire, their health, well-being and quality of life at 0, 4 and 8 weeks.ResultsOverall, 4-weeks supplementation with MMST significantly increased total fasting Si concentrations in serum and urine (P ≤ 0.003; paired t-test). MMST was semi-quantifiable in serum and quantifiable in urine, but only accounted for ca. 50% and 10%, respectively, of the increased total-Si concentration. There were no reported adverse effects (i.e. changes to health and well-being) or serum biochemical changes with MMST versus placebo.ConclusionsOur data indicate that oral MMST is safe, is absorbed and undergoes sufficient metabolism in vivo to raise fasting serum silicon levels, consistent with other well absorbed forms of dietary silicon (e.g. orthosilicic acid). It thus appears to be a suitable silicon supplement.

Aqueous silicate chemistry in zeolite synthesis

Publisher Summary This chapter presents an overview of what nuclear magnetic resonance (NMR) can legitimately tell us about the mechanism of zeolite synthesis, while pointing out its limitations and the various pitfalls inherent in its application to the study of zeolites, and report experimental evidence in support of a clathration hypothesis of zeolite formation in media containing organic solutes. The chapter also considers the existence of double 5- and double 6-ring polyanions, and notes the novel chemistry of aqueous stannosilicates. Information provided by solution NMR experiments indicates that organic-mediated synthesis of zeolites proceeds via open cage intermediate structures at the crystal surface that are stabilized kinetically by hydrophobic clathration shells. Although, the initial results of 29Si NMR experiments on zeolite precursor solutions were originally misinterpreted, 29Si NMR continues to provide the clearest and most instructive picture of the chemistry of zeolite formation.

The Peroxysilicate Question. 29Si-NMR Evidence for the Role of Silicates in Alkaline Peroxide Brightening of Mechanical Pulp

Abstract The influence of hydrogen peroxide on the chemistry of aqueous silicates was investigated by high-resolution 29Si-NMR and electrochemical methods. The observations indicate that dissolved silicates form labile complexes with radical H2O2-decomposition products, possibly O2·−. An important role of soluble silicates in peroxide bleaching liquors thus might be to affect the activity of free radical species which mediate H2O2 bleaching and decomposition reactions. Attempts to prepare the widely reported peroxysilicates from silicate/H2O2/NaOH mixtures resulted in the isolation of Na2O2·8H2O.

Divergent effects of orthosilicic acid and dimethylsilanediol on cell survival and adhesion in human osteoblast-like cells.

Although dietary silicon (Si) is recognized to be an important factor for the growth and development of bone and connective tissue, its biochemical role has yet to be identified. The predominant Si-containing species in blood and other biofluids is orthosilicic acid, Si(OH)(4). Dimethylsilanediol, (CH(3))(2)Si(OH)(2), is an environmental contaminant that results from decomposition of silicone compounds used in personal hygiene, health care and industrial products. We examined the in vitro effects of both Si species on the survival (colony forming efficiency), proliferation (DNA content), differentiation (alkaline phosphatase activity) and adhesion (relative protein content) of the human osteoblast-like cell lines Saos-2 and hFOB 1.19. Orthosilicic acid yielded a small, dose-dependent decrease in Saos-2 cell survivability up to its 1,700 micromol/L solubility limit, by which point survival was 20% less than that of untreated cells. This negative association, although small, correlated with a reduction in the proliferation and adhesion of Saos-2 cells as well as of hFOB 1.19 and osteoclast-like GCT cells. By contrast, dimethylsilanediol treatment had no discernable influence on Saos-2 survivability at concentrations up to 50 micromol/L, and yet significantly enhanced cell survival at higher doses. Moreover, dimethylsilanediol did not affect proliferation or adhesion of any cell line. The findings show that orthosilicic acid and dimethylsilanediol affect osteoblast-like cells very differently, providing insight into the mechanism by which silicon influences bone health, although the specific site of Si activity remains unknown. There was no evidence to suggest that dimethylsilanediol is cytotoxic at environmental/physiological concentrations.

Two substituted cubic octameric silicate cages in aqueous solution

Two novel silicate anions, a singly-substituted cubic octamer (double four-ring cage with a pendant orthosilicate group) and its dimeric counterpart (two octameric cages linked by a single siloxane bridge), are detected by 29Si NMR spectroscopy in concentrated tetraalkylammonium silicate solutions at the low alkalinity and high SiO2 concentration typical of zeolite synthesis slurries.