Geometry of chemically modified silica

Rustamov, I. R.; Farcas, T.; Ahmed, F.; Chan, F.; LoBrutto, Rosario; McNair, Harold M.; Kazakevich, Yuri

doi:10.1016/s0021-9673(00)01076-1

Cited by 155 publications

(120 citation statements)

References 20 publications

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“…They are collapsed on the silica surface. This model is consistent with the observations of Pages et al 13 on the freedom of movement of the chains and those of Rustamov et al 14 on the internal porosity of RPLC packing materials. It is hard even for solvent molecules to penetrate into the bonded layer.…”

Section: Peak Parking-moment Analysis Methodssupporting

confidence: 92%

“…It is hard even for solvent molecules to penetrate into the bonded layer. 14 They constitute a solvent layer, which contacts with the bonded ligand layer. 15,16 Gritti and Guiochon reported the thickness of the adsorbed monolayer of methanol and multilayer of acetonitrile as 0.25 and 1.36 nm, respectively, on C18-silica gels.…”

Section: Peak Parking-moment Analysis Methodsmentioning

confidence: 99%

“…13 It is highly improbable that surface diffusion can take place between the bonded ligands because of the collapse situation of the alkyl chains. 13,14 It is considered as the mechanism of surface diffusion that the adsorbate molecules migrate in the solvent layer under adsorbed state.…”

Section: Peak Parking-moment Analysis Methodsmentioning

confidence: 99%

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Peak Parking-Moment Analysis Method for the Measurement of Surface Diffusion Coefficients

2009

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The peak parking (PP)-moment analysis (MA) method was applied to the measurement of surface diffusion coefficients (Ds) in reversed-phase liquid chromatography using a C18-silica gel and an aqueous solution of methanol (70 vol%). The values of Ds measured by the PP-MA method were in agreement with those obtained by the pulse response (PR)-MA method, which is one of powerful strategies for the quantitative study on the mass transfer kinetics in columns and stationary phases. It was demonstrated that the PP-MA method is an alternative for the experimental measurement of Ds. The mechanism of surface diffusion was considered on the basis of molecular diffusion by introducing a restriction energy (Er) for surface diffusion. Physical meanings of Er were discussed by analyzing the correlation between the enthalpy change due to sample retention (Qst) and Ds. It seems that surface diffusion of a sample molecule is restricted by its retention strength and by the solvent structure formation due to the hydrophobic solvation of the stationary phase surface.

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Section: Peak Parking-moment Analysis Methodssupporting

confidence: 92%

Section: Peak Parking-moment Analysis Methodsmentioning

confidence: 99%

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Peak Parking-Moment Analysis Method for the Measurement of Surface Diffusion Coefficients

2009

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“…Notably, hold-up volumes of the columns investigated were obtained by static pycnometry (Table 3), which consists of filling the columns successively with two distinct solvents of different densities and weighing the filled columns accurately. [27] Similar values of permeability [28] (K F = 2.09-2.20 10 À14 m 2 ) were finally obtained for the three sugar-silica columns, which is slightly lower than achieved with the Hypersil APS2 and diol-modified columns (Table 3).…”

supporting

confidence: 60%

Synthesis of Sugar‐Based Silica Gels by Copper‐Catalysed Azide–Alkyne Cycloaddition via a Single‐Step Azido‐Activated Silica Intermediate and the Use of the Gels in Hydrophilic Interaction Chromatography

Moni

Ciogli

D’Acquarica

et al. 2010

Chemistry A European J

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Novel sugar-based silica gels were prepared by exploiting the copper-catalysed azide-alkyne cycloaddition (CuAAC) of two different sugar alkynes, namely, ethynyl C-galactoside 1 and propargyl O-lactoside 2, with new single-step azido-activated silica gels. The fully characterised stationary phases were generally used for hydrophilic interaction chromatography (HILIC), with particular application in the stereoselective separation of monosaccharides. Dynamic HILIC (DHILIC) experiments were performed to evaluate the influence of mutarotation on the chromatographic peak shapes of two interconverting sugar anomers. The potential of such materials was shown in the separation of other highly polar compounds, including amino acids and flavonoids.

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“…Many models are proposed to express the analyte distribution between the eluent and the stationary phase. [30][31][32][33] Recent investigations have shown that alkyl chains bonded to the silica surface are densely packed or liquid-like 32) and that methanol forms a monomolecular adsorbed layer on a silica surface on the top of collapsed bonded layer.…”

Section: Resultsmentioning

confidence: 99%

Hydrophobicity Parameters Determined by Reversed-Phase Liquid Chromatography. XV: Optimal Conditions for Prediction of log Poct by Using RP-HPLC Procedures.

Yamagami

Kawase

Iwaki

2002

CHEMICAL & PHARMACEUTICAL BULLETIN

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Recently, in connection with the remarkable development of computational technologies for rational drug designs, the necessity has become apparent of rapid measurement or estimation of molecular properties of chemicals having a potential for medical use. In particular, hydrophobicity (as expressed by the logarithm of 1-octanol/water partition coefficient, log P oct ) is identified as one of the most important properties that govern potencies; its prediction has attracted much attention from medicinal chemists, agrochemists and many investigators in various fields such as pharmacology, toxicology, environmental chemistry and food chemistry. 1,2)Instead of measuring log P oct by the standard but time-consuming shake-flask method, reversed-phase chromatography (RP-HPLC) has increasingly been used as a powerful tool to predict log P oct from the readily accessible retention factor, log k, (given by kϭ(t R Ϫt 0 )/t 0 where t 0 and t R express elution times of the non-retained substance and sample, respectively).Extensive studies have been made to establish an optimal RP-HPLC system providing a good linearity between log P oct and log k.3-10) Many workers have used an ODS-type column with methanol-water mobile phases to obtain a normalized parameter, log k W (k W : the retention factor extrapolated to 0% organic modifier), as an alternative to log P oct . 3,5,8) In our experience, this log k W approach works well for non-polar solutes but tends to provide overestimated log P oct values for strong H-acceptors. [10][11][12][13][14][15] From systematic studies of log k obtained under various HPLC conditions for typical heteroaromatic compounds such as (di)azines, furans and thiophenes, we were led to the conclusion that the use of an eluent containing around 50% methanol, which usually provides a more direct correlation with log P oct , is the most convenient and practical procedure for rapid estimation of log P oct provided H-donors (amphiprotic compounds) are treated separately.11-15) Our results so far obtained are illustrated graphically in Fig. 1. This conclusion has been derived from the following results.First, we have shown that, for each series of monosubstituted (di)azines, log P oct can be excellently correlated with log k in different compositions of methanol-water eluents by a general formula Eq. 1 containing two terms correcting for H-bonding effects: 16) log kϭalog P oct ϩrs I ϩsS HA ϩconst.( 1) where the s I parameter represents the Charton's inductive electronic substituent constant, 17) and S HA designates the substituent H-acceptor scale that we have recently defined where the value of S HA is set at unity for H (the unsubstituted * To whom correspondence should be addressed. The use of log k derived from reversed phase (RP)-HPLC retention times provides a convenient method for estimating log P oct values (P oct : 1-octanol/water partition coefficient). In order to establish optimal HPLC conditions, the difference between chromatographic (C18 modified column and aqueous methanol eluents) and bulk solve...

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Geometry of chemically modified silica

Cited by 155 publications

References 20 publications

Peak Parking-Moment Analysis Method for the Measurement of Surface Diffusion Coefficients

Peak Parking-Moment Analysis Method for the Measurement of Surface Diffusion Coefficients

Synthesis of Sugar‐Based Silica Gels by Copper‐Catalysed Azide–Alkyne Cycloaddition via a Single‐Step Azido‐Activated Silica Intermediate and the Use of the Gels in Hydrophilic Interaction Chromatography

Hydrophobicity Parameters Determined by Reversed-Phase Liquid Chromatography. XV: Optimal Conditions for Prediction of log Poct by Using RP-HPLC Procedures.

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