319
equipped with a 4 mm HX MAS probe. Pack approximately
50 mg of the sample tightly into a zirconia rotor. Apply cross
polarization for
13
C excitation using an 80% linear ramp. During
13
C detection, 100 kHz Spinal-64 proton decoupling should be
applied [34–36]. The number of scans in the experiment should
be 1000.
3. Dissolve weighted amounts of dry lipid and IRB powder in
chloroform in order to prepare DPPC and IRB stock solutions.
The drug concentration should be 20 mol%. Prepare the mixtures by appropriate amounts of drug in a pure or complexed
form with 2-HP-β-CD. Evaporate the organic DPPC/IRB or
DPPC/complex IRB–2-HP-β-CD at room temperature under
a gentle stream of nitrogen and thereafter place them under
vacuum for 12 h and consequently a thin lipid film at the bottom of glass vials should be formed. The obtained mixtures
should be then fully hydrated (50% w/w deuterium-depleted
water) and this procedure will result in multilamellar vesicles
(MLVs). Alternatively, add complexed IRB–2-HP-β-CD compounds to the aqueous phase of readily formed DPPC MLV
dispersions.
4. Perform
13
C CP/MAS spectra at three temperatures (25, 35,
45 °C) to cover all mesomorphic states of DPPC bilayers.
4 Notes
1. Irbesartan’s alkyl chemical shifts are not modified significantly
when it is complexed in D 2 O while in micelles a clear and significant downfield chemical shift is observed. Interestingly, the
quintet at ca 1.43 ppm is better resolved when the complex is in
micelles than in D 2 O. The same trend is observed with cyclopentane ring. The differences in the aromatic region are very
interesting. Downfield, but also upfield, shifts are observed in
the micelle environment compared to that of D 2 O.
2. (a) The complexation of IRB with 2-HP-β-CD induces some
chemical shift changes to IRB. (b) The micelle environment
induces many chemical shift changes to IRB. (c) Protons 6a,
6b, 7a, 7b, 8a, 8b, 9a, 9b, 19, 20, 21, 22, and 28 are affected
most when IRB is complexed with 2-HP-β-CD and (d) when
the complex is transferred to SDS environment most of the
chemical shifts are affected significantly (Table 1, Figs. 2 and 3).
The
1
H NMR spectra of (a) irbesartan dissolved in D 2 O; (b)
2-HP-β-CD dissolved in D 2 O; (c) irbesartan dissolved in SDS
micelles; (d) IRB complexed with 2-HP-β-CD and dissolved in
D 2 O; and (e) IRB complexed with 2-HP-β-CD in SDS micelles
are presented in Figs. 2 and 3.
4.1 Notes Related
to Subheading 3.1
NMR Techniques Applied to Drug: Cyclodextrin Complexation
equipped with a 4 mm HX MAS probe. Pack approximately
50 mg of the sample tightly into a zirconia rotor. Apply cross
polarization for
13
C excitation using an 80% linear ramp. During
13
C detection, 100 kHz Spinal-64 proton decoupling should be
applied [34–36]. The number of scans in the experiment should
be 1000.
3. Dissolve weighted amounts of dry lipid and IRB powder in
chloroform in order to prepare DPPC and IRB stock solutions.
The drug concentration should be 20 mol%. Prepare the mixtures by appropriate amounts of drug in a pure or complexed
form with 2-HP-β-CD. Evaporate the organic DPPC/IRB or
DPPC/complex IRB–2-HP-β-CD at room temperature under
a gentle stream of nitrogen and thereafter place them under
vacuum for 12 h and consequently a thin lipid film at the bottom of glass vials should be formed. The obtained mixtures
should be then fully hydrated (50% w/w deuterium-depleted
water) and this procedure will result in multilamellar vesicles
(MLVs). Alternatively, add complexed IRB–2-HP-β-CD compounds to the aqueous phase of readily formed DPPC MLV
dispersions.
4. Perform
13
C CP/MAS spectra at three temperatures (25, 35,
45 °C) to cover all mesomorphic states of DPPC bilayers.
4 Notes
1. Irbesartan’s alkyl chemical shifts are not modified significantly
when it is complexed in D 2 O while in micelles a clear and significant downfield chemical shift is observed. Interestingly, the
quintet at ca 1.43 ppm is better resolved when the complex is in
micelles than in D 2 O. The same trend is observed with cyclopentane ring. The differences in the aromatic region are very
interesting. Downfield, but also upfield, shifts are observed in
the micelle environment compared to that of D 2 O.
2. (a) The complexation of IRB with 2-HP-β-CD induces some
chemical shift changes to IRB. (b) The micelle environment
induces many chemical shift changes to IRB. (c) Protons 6a,
6b, 7a, 7b, 8a, 8b, 9a, 9b, 19, 20, 21, 22, and 28 are affected
most when IRB is complexed with 2-HP-β-CD and (d) when
the complex is transferred to SDS environment most of the
chemical shifts are affected significantly (Table 1, Figs. 2 and 3).
The
1
H NMR spectra of (a) irbesartan dissolved in D 2 O; (b)
2-HP-β-CD dissolved in D 2 O; (c) irbesartan dissolved in SDS
micelles; (d) IRB complexed with 2-HP-β-CD and dissolved in
D 2 O; and (e) IRB complexed with 2-HP-β-CD in SDS micelles
are presented in Figs. 2 and 3.
4.1 Notes Related
to Subheading 3.1
NMR Techniques Applied to Drug: Cyclodextrin Complexation