Date of Award

6-2003

Document Type

Open Access

Degree Name

Bachelor of Science

Department

Chemistry

Language

English

Abstract

Fraiji et al. determined a binding constant (K) of 581 = 6 M-1 for the 1:1 complex between 2-acetylnaphthalene (2-AN) and β-cyclodextrin (β-CD) in H20 using fluorescence quenching experiments (Appl. Spectrosc. 1994, 48, 79). Molecular modeling experiments indicate the possibility of complex stabilization resulting from hydrogen bonds between the C=O group of 2-AN and the -OH groups on the rim of β-CD. To check this possibility, we measured the K of the 2-AN:trimethyl-β-CD (TM-β- CD) complex, where all rim -OH groups are converted to –OCH3. In this case, K decreases to 134 M-1. To show that this is due to reduced hydrogen bonding capability rather than steric influence, the K of 2-AN: β-CD was measured at high pH. K decreases to 276 M-1 at pH 13.5, and an inflection point is observed at pH 12.2 (which is the pKa of rim -OH groups). Therefore, our experiments confirm the significance of 2-AN carbonyl hydrogen bonding to β-CD -OH groups. Fluorescence studies were also performed with 1,5-DNSA, 2,6-MANS, and 2,6- TNS. K was 151M-1 for 1,5-DNSA: β-CD and 105M-1 for 1,5-DNSA:TM-β-CD. The smaller K for the TM-β-CD complex is probably due to steric effects associated with the rim -OCH, groups. Thermodynamic properties of the 2,6-MANS:TM-β-CD complex were investigated. ΔH and ΔS were calculated as -35 kJ/mol and -47 J/mol K, respectively. Catena and Bright calculated ΔH as -6.7 kJ/mol and AS as 50 J/mol K for the 2,6-MANS: β-CD complex (Anal. Chem. 1989, 61, 915). The methyl groups of the TM-β-CD make the cavity environment more hydrophobic than the natural β -CD, creating much stronger guest:host interations. The methyl groups also restrict the motion of 2,6-MANS, which overcomes the favored entropic effects of solvent replacement and solvent shell disturbance. The 2,6-TNS:TM-β-CD, K was calculated as 2358 M-1, compared to Catena and Bright's 1980 M-1 for the β-CD complex. The more hydrophobic cavity of TM-β-CD compensates for the loss of hydrogen bonding between the guest SO3- group and CD rim -OH groups. CE was employed for the separation of LSD (d-lysergic acid diethylamide), LAMPA (D-lysergic acid methylpropylamide) and iso-LSD using several types of cyclodextrins as buffer additives. A sample consisting of LSD, LAMPA, and iso-LSD was partially resolved (R>1) with 60 mM α-CD in a 50 mM acetate buffer, pH 4.03, at 15°C. Migration times were under 9 min. Another solution consisting of both 60 mM α-CD and 0.2 mM sulfated-β-CD in 50 mM acetate buffer, pH 4.03, at 25°C provided baseline separation (R> 1.5) of the sample mixture in a similar 9 min. time window. The reproducibility of migration times for both methods was 4-5% between days and 1% on the same day. Partial separation of LSD and LAMPA (R~1) was (observed in a 9 min. time window using 15 mM sulfated-α-CO in a 50 mM borate buffer, pH 8.51 at 25°C. Between day and same day reproducibilities were 2-3% and 1%, respectively.

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