Nanochain and vesicles formed by inclusion complexation of 4,4′-diaminobenzanilide with cyclodextrins

Figures & data

Figure 1. PM3-optimised structure of DABA.

Table 1. Absorption and fluorescence maxima of DABA with different solvents, α-CD and β-CD concentrations.

	Solvents and CD
Concentration of CD	λabs	log ϵ	λflu
Cyclohexane	298	4.00	331
			351
Dioxane	298	4.02	421s
			351
Acetonitrile	297	4.05	420
			342
Methanol	301	4.08	426
			351
Water	292	4.11	376
	232s	3.75	336
0.002 α-CD	292	4.13	376
	232s	3.81
0.01 α-CD	292	4.15	376
	232s	3.83
0.002 β-CD	293	4.20	376
	232s	3.81
0.01 β-CD	293	4.26	440
	232s	3.84	376
Binding constant 1:1
α-CD	352		463
β-CD	381		402
ΔG* for α-CD	−3.53		−3.69
ΔG* for β-CD	−3.57		−3.60

Note: s – shoulder, * – kcal mol⁻¹.

Figure 2. Fluorescence spectra of DABA in different α-CD (a) and β-CD (b) concentrations (M): (1) 0, (2) 0.001, (3) 0.002, (4) 0.004, (5) 0.006, (6) 0.008 and (7) 0.01 (λ_excitation − 300 nm). Inset figure: fluorescence intensity vs. α-CD and β-CD concentrations.

Table 2. Various prototropic maxima (absorption and fluorescence) of DABA in aqueous and β-CD medium.

	Aqueous medium		β-CD medium		α-CD medium
Species	λabs	λflu	λabs	λflu	λabs	λflu
Neutral	292	376	292	376	292	375
	232s		232s			336
Monocation	268	372	273	448	267	375
				374		325
Dication	260	367	268	367	–	–

Note: s – shoulder.

Table 3. Geometrical parameters of DABA before and after inclusion with α-CD and β-CD for the most stable inclusion complexes.

Parameters	DABA	DABA:α-CD	DABA:β-CD
Bond length (Å)
H4–H10	12.87	12.98	12.91
N1–N3	12.03	12.09	11.88
N1–N2	6.44	6.48	6.41
N3–N2	5.66	5.66	5.65
C4–C11	9.24	9.26	6.51
C1–C8	3.18	3.82	3.78
H-bond length (Å)
(–NH–)H4—O (1,4-linkage oxygen)	2.65
(–NH2)H3—O(1^0 OH)		2.59
(–NH2)H4—O(1^0 OH)		2.79
(–C═O)O—H(1^0 OH)		2.81
Bond angle (°)
C8–N2–C7	122.19	122.67	123.25
O–C7–N2	121.05	118.85	119.98
N2–C7–C1	115.26	116.72	115.72
C4–N1–H3	112.01	112.07	112.84
Dihedral angle (°)
C1–C7–N2–C8	163.80	163.99	−156.89
O–C7–N2–H6	−33.98	−163.86	171.39
N2–C7–C1–C6	−129.17	−137.30	120.79
O–C7–N2–C8	−18.79	−19.33	24.93

Figure 3. (Colour online) Side and upper views of optimised DABA:CD inclusion complex: (a, b) DABA:α-CD, and (c, d) DABA:β-CD inclusion complexes. Blue, white, ash and bright red colours indicate nitrogen, hydrogen, carbon and oxygen atoms, respectively.

Table 4. HOMO–LUMO energies and thermodynamic parameter values for the DABA:CD inclusion complexes (using the PM3 method).

Parameters	DABA	α-CD	β-CD	DABA:α-CD	DABA:β-CD
EHOMO (eV)	−8.31	−10.38	−10.35	−8.32	−8.28
ELUMO (eV)	−0.19	1.26	1.23	0.08	−0.08
ELUMO – EHOMO (eV)	8.12	11.64	11.58	8.40	8.20
μ	−4.25	−4.56	−4.56	−4.12	−4.18
η	4.06	5.81	5.79	4.20	4.10
ω	2.22	1.78	1.79	2.02	2.13
S	0.25	0.17	0.17	0.24	0.24
Dipole moment (D)	2.34	11.34	12.29	6.39	8.37
E*	8.93	−1247.52	−1457.63	−1248.37	−1461.80
ΔE*				−9.68	−13.10
G*	131.78	−676.16	−789.52	−546.96	−663.19
ΔG*				−2.38	−5.45
H*	170.04	−570.84	−667.55	−508.64	−509.95
ΔH*				−107.84	−12.44
S**	0.128	0.353	0.409	0.424	0.480
ΔS **				−0.057	−0.057
ZPVE*	150.95	634.47	740.56	787.45	892.55

Note: * – kcal mol⁻¹, ** – kcal mol⁻¹ K⁻¹, ZPVE – zero point vibrational energy.

Figure 4. (Colour online) LUMO and HOMO pictures of isolated DABA and its inclusion complexes. Blue, white, ash and bright red colours indicate nitrogen, hydrogen, carbon and oxygen atoms, respectively. The green and dark red colours indicate negative and positive parts of the molecules, respectively.

Figure 5. SEM images of (a) DABA, (b) α-CD, (c) β-CD, (d) DABA:α-CD and (e) DABA:β-CD inclusion complexes.

Figure 6. TEM images of the nanostructure formed by (a, b) α-CD/DABA and (c, d) β-CD/DABA.

Figure 7. (Colour online) Graphical representation for a chain-like agglomerates formed by α-CD:DABA inclusion complex.

Figure 8. Proposed mechanisms of nanovesicle formation between DABA and β-CD.