TY - JOUR
T1 - Electron paramagnetic resonance study of the concentration of spin-label molecules in hydrated glass pores
AU - Cevc, P.
AU - Choi, C.
AU - Holly, R.
AU - Pintar, M. M.
PY - 1997/12/15
Y1 - 1997/12/15
N2 - Dehydration of porous glass hydrated with a 5 mM solution of the spin-label molecules 2,2,6,6-tetramethyl-4-acetamido-piperidine-1-oxyl (TMAPO) was studied with electron paramagnetic resonance at 9 GHz. The spin-label molecules' concentration remains constant, i.e., it follows the Langmuir isotherm when glass pores of 292±20 nm diameter are dehydrated. When the pore diameter is only 127±11 nm, or less, the Langmuir isotherm appears not to apply despite the fact that in smaller pores the surface-to-volume ratio is larger. The reason for this apparent failure could be the establishment of a water cluster phase which does not dissolve TMAPO, and/or it could be a kinetic effect of the spin-label molecules. In this report the possibility that the failure of the Langmuir isotherm is the consequence of ordered water clusters is examined. To account for the lower concentration of TMAPO in smallest pores, as much as 70% of total water volume has to consist of such water clusters, in agreement with an earlier proposal.
AB - Dehydration of porous glass hydrated with a 5 mM solution of the spin-label molecules 2,2,6,6-tetramethyl-4-acetamido-piperidine-1-oxyl (TMAPO) was studied with electron paramagnetic resonance at 9 GHz. The spin-label molecules' concentration remains constant, i.e., it follows the Langmuir isotherm when glass pores of 292±20 nm diameter are dehydrated. When the pore diameter is only 127±11 nm, or less, the Langmuir isotherm appears not to apply despite the fact that in smaller pores the surface-to-volume ratio is larger. The reason for this apparent failure could be the establishment of a water cluster phase which does not dissolve TMAPO, and/or it could be a kinetic effect of the spin-label molecules. In this report the possibility that the failure of the Langmuir isotherm is the consequence of ordered water clusters is examined. To account for the lower concentration of TMAPO in smallest pores, as much as 70% of total water volume has to consist of such water clusters, in agreement with an earlier proposal.
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U2 - 10.1063/1.474163
DO - 10.1063/1.474163
M3 - Article
AN - SCOPUS:5544301690
SN - 0021-9606
VL - 107
SP - 10225
EP - 10228
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
IS - 23
ER -