Interactions of water with trisiloxane rings. I. Experimental analysis

Wallace, Stephen C.; West, Jon K.; Hench, Larry L.

doi:10.1016/0022-3093(93)90238-s

Cited by 52 publications

(26 citation statements)

References 16 publications

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“…With Raman spectroscopy hydrolysis by a nucleophilic water molecule has been observed to be responsible for the structural changes observed in porous type VI silica. 8,13 MO calculations show a very low-energy pathway for the hydrolysis reaction due to formation of a pentacoordinate silicon transition state, similar to the results of the present calculation.…”

Section: Discussionsupporting

confidence: 91%

“…drolysis pathways. Hydrolysis of siloxane (Si−O−Si) bonds has been modeled using AM1 7 semi-empirical quantum mechanical molecular orbital theory 8,9 and, using Raman Spectroscopy, 12,13 observed in porous type VI gel silica. 10,11 In this study the same AM1 method was used to calculate the reaction pathways for the hydrolysis of 1,1,3,3-tetramethyldisiloxane-1,3-diol.…”

Section: Introductionmentioning

confidence: 99%

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Theoretical analysis of hydrolysis of polydimethylsiloxane (PDMS)

West

1997

J. Biomed. Mater. Res.

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Silicones (polydimethylsiloxane, PDMS) are the materials currently used in most breast implants. ICP and FTIR analysis of the tissue capsule around aged breast implants and in vitro models show that Si-containing material is leaking from the PDMS implants. In this study, the hydrolysis of PDMS has been theoretically modeled using a semiempirical quantum mechanical method called AM1. The activation barrier for removing a methanol monomer was found to be +82 Kcal/mol while the removal of a methane monomer was +41 Kcal/mol. Using the same AM1 method, hydrolysis of the identical to Si-O-Si identical to bond also has been modeled for pentasilicic acid and, in this study, for 1,1,3,3,-fetramethyldisiloxane-1,3-diol. The barrier to the removal of a silicon-containing tetrahedron for both studies was found to be +27 Kcal/mol. This is approximately one and a half times smaller than the energy of that needed to remove a methyl group. The pentacoordinated silicon-activated transition state for hydrolysis of PDMS may provide an energetically favorable pathway for development of a surface that will enhance chemisorption of charged protein molecules, and such a pathway may show up in NMR studies of the hydrolysis of PDMS.

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Section: Discussionsupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Theoretical analysis of hydrolysis of polydimethylsiloxane (PDMS)

West

1997

J. Biomed. Mater. Res.

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“…The large rings, four-, five-, and six-membered, were modeled by Bell and Dean 17 and the concentration of threemembered rings is estimated from Raman data. 18 If the adsorption energy, ⌬H f , is weighted for bulk silica using these concentration fractions, then the average adsorption for one lysine molecule per silica ring is −3.6 kcal/mol, as shown in Table III. This great a value is technically not realistic, because only those rings exposed to the active site on the lysine chain will be affected.…”

Section: Discussionmentioning

confidence: 99%

Molecular modeling study of adsorption of poly-L-lysine onto silica glass

West

Latour

Hench

1997

J. Biomed. Mater. Res.

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A research program was initiated with both experimental and computational chemistry based molecular modeling components to investigate specific amino acid-surface interactions. The experimental portion of this study, with details reported elsewhere, investigated the adsorption of selected molecular weights of poly(L-lysine) onto silica glass microspheres with the adsorption enthalpy per adsorbed mer determined to be -0.23 +/- 0.13 kcal/mol (mean +/- 95% confidence interval). Molecular modeling of this system was then conducted using two approaches: an AM1 semiempirical molecular orbital method to predict L-lysine/glass interaction energy and an MM2 molecular mechanics method to investigate the structural configuration for poly(L-lysine). The modeling predicted a minimum energy configuration of a rotational backbone structure for poly(L-lysine) with approximately one full rotation occurring about every 8 mers, and that the amine side chains of the L-lysine will hydrogen bond with the silica surface with an average adsorption energy of approximately -0.34 kcal/mol/mer. The molecular modeling results are in good agreement with the experimentally measured value and provide insights into possible molecular-level behavior which would be very difficult to determine by experimental analyses alone. This work demonstrates the use of molecular modeling in conjunction with experimental studies to investigate complex molecular interactions.

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“…This powerful (and computationally demanding) approach revealed a number of interesting features: undercoordinated Si centers, formed on the as-created surface, spontaneously dissociate water at room temperature and will be presumably hydroxylated in a fully hydrated sample; water is also attracted to Lewis acids such as Na + and Ca 2+ cations, which populate the as-created BG surface in significant amounts. Perhaps the most surprising finding of these simulations was the low affinity of water for small rings, comprising two or three silicate units, which also represent common structural features of BG and silica surfaces (35)(36)(37)(38). The CPMD-DFT calculations clearly highlighted that, despite their internal strain, opening of these rings through water adsorption and dissociation is hindered by a significant energy barrier (0.62 eV), possibly in connection with the presence of alternative, more favorable water adsorption sites such as the Lewis acids mentioned before (34).…”

Section: Introductionmentioning

confidence: 97%

Modeling the Water−Bioglass Interface by Ab Initio Molecular Dynamics Simulations

Tilocca

Cormack

2009

ACS Appl. Mater. Interfaces

107

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The hydration of the surface of a highly bioactive silicate glass was modeled using ab initio (Car-Parrinello) molecular dynamics (CPMD) simulations, focusing on the structural and chemical modifications taking place at the glass-water interface immediately after contact and on the way in which they can affect the bioactivity of these materials. The adsorption of a water dimer and trimer on the dry surface was studied first, followed by the extended interface between the glass and liquid water. The CPMD trajectories provide atomistic insight into the initial stages relevant to the biological activity of these materials: following contact of the glass with an aqueous (physiological) medium, the initial enrichment of the surface region in Na+ cations establishes dominant Na+-water interactions at the surface, which allow water molecules to penetrate into the open glass network and start its partial dissolution. The model of a Na/H-exchanged interface shows that Ca2+-water interactions are mainly established after the dominant fraction of Na is leached into the solution. Another critical role of modifier cations was highlighted: they provide the Lewis acidity necessary to neutralize OH(-) produced by water dissociation and protonation of nonbridging oxygen (NBO) surface sites. The CPMD simulations also highlighted an alternative, proton-hopping mechanism by which the same process can take place in the liquid water film. The main features of the bioactive glass surface immediately after contact with an aqueous medium, as emerged from the simulations, are (a) silanol groups formed by either water dissociation at undercoordinated Si sites or direct protonation of NBOs, (b) OH(-) groups generally stabilized by modifier cations and coupled with the protonated NBOs, and (c) small rings, relatively stable and unopened even after exposure to liquid water. The possible role and effect of these sites in the bioactive process are discussed.

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Interactions of water with trisiloxane rings. I. Experimental analysis

Cited by 52 publications

References 16 publications

Theoretical analysis of hydrolysis of polydimethylsiloxane (PDMS)

Theoretical analysis of hydrolysis of polydimethylsiloxane (PDMS)

Molecular modeling study of adsorption of poly-L-lysine onto silica glass

Modeling the Water−Bioglass Interface by Ab Initio Molecular Dynamics Simulations

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