Spectroscopic study of complex formation between aliphatic amines and chromogenic calix[4]arene derivatives

Journal of Molecular Structure 480–481 (1999) 289–292

Spectroscopic study of complex formation between aliphatic amines and chromogenic calix[4]arene derivatives I. Mohammed-Ziegler a,*, M. Kubinyi a, A. Grofcsik a, A. Gru¨n b, I. Bitter b a Department of Physical Chemistry, Technical University of Budapest, 1521 Budapest, Hungary Department of Organic Chemical Technology, Technical University of Budapest, 1521 Budapest, Hungary

b

Received 24 August 1998

Abstract The complexation properties of two new calix[4]arene derivatives were studied by UV/Vis spectroscopy. They have been found to bind aliphatic amines, lithium and calcium ions in equilibrium reactions, particularly in polar solvents. The reaction is indicated through the emergence of a new band. The equilibrium constants of complex formation in the case of some ligand– substrate compositions have been determined. 䉷 1999 Elsevier Science B.V. All rights reserved. Keywords: Calix[4]arene; Optical recognition; Aliphatic amine; Ion-selectivity

1. Introduction The application of calix[4]arene derivatives as ligands for electrochemical and/or optical sensors (optrodes) is promising in chemical analysis, since they are capable of binding metal ions selectively [1–3]. The complexation of neutral molecules, preferably amines by calixarenes has also aroused the interest of the researchers in the past years [4]. In the near future these ligands may play an important role in the selective determination of chiral biogene amines in physiological fluids [5]. In our systematic work various sets of chromogenic calixarene molecules have been synthesized and their complex formation with metal ions have been studied with spectroscopic methods [6,7]. In the present work the complex forming properties of two new calix[4]arene derivatives were investigated by measuring their UV/Vis spectra in different solvents in the

presence of alkali/alkaline earth metal ions and aliphatic amines. The compounds are represented by formulae 1a and 1b.

* Corresponding author. 0022-2860/99/$ - see front matter 䉷 1999 Elsevier Science B.V. All rights reserved. PII: S0022-286 0(98)00701-7

412, 268*

407, 271*

405, 268*

437, 298*

3-aminopropanol 1,3-Di-aminopropane n-Butyl-amine

t-Butyl-amine

Diethylene triamine Triethyl-amine

278*

415, 275*

320, 258 407, 201*

— Propyl-amine

411, 315, 244* 412, 322, 244* 416, 314, 248* 424, 321, 256*

322, 245 412, 320, 244* 413, 311, 244* 415, 242*

Calixarene 1a Solvent CCl4 Dioxane

Amine

327, 246*

426, 313, 242* 429, 249*

419, 245*

424, 242*

425, 239*

330, 236 420, 239*

CH2Cl2

440, 336*

442, 340*

432, 337*

431, 340*

450

440

336 440

Acetone

443, 321

435, 313, 230* 443, 235*

439, 291, 227* 447, 302, 230* 435, 230*

327 442, 231*

CH3CN

437, 320, 232*

437, 240*

441, 232*

425, 241*

434, 232*

430, 228*

327 431, 232*

Ethanol

280*

441, 320, 269* 440, 275*

428, 273*

446, 275*

430, 269*

304 428, 270*

314, 254*

447, 312, 247* 429, 256*

427, 249*

430, 244*

314, 245 427, 312, 243* 426, 243*

Calixarene 1b Solvent CCl4 Dioxane

Table 1 Absorption maxima (nm) of 1a and 1b in the presence of amines (for explanation of the asterisks see text)

440, 318, 248*

446, 310, 241* 436, 254*

433, 244*

431, 243*

429, 239*

317, 236 433, 240*

CH2Cl2

434, 335*

436, 336*

436, 336*

434, 336*

432, 339*

433, 337*

436, 334 434, 336*

Acetone

437, 322, 235*

433, 237*

437, 237*

434, 240*

432, 231*

431, 232*

437, 318 429, 234*

CH3CN

441, 319, 231*

440, 318, 232* 417, 236*

415, 237*

414, 229*

414, 229*

315, 224 416, 228*

Ethanol

290 I. Mohammed-Ziegler et al. / Journal of Molecular Structure 480–481 (1999) 289–292

I. Mohammed-Ziegler et al. / Journal of Molecular Structure 480–481 (1999) 289–292

291

Table 2 Equilibrium constants (in dm 3/mol) of the 1 : 1 complex formation in acetone Calixarene

1a 1b

Substrate Propylamine

1,3-Diamino-propane

Diethylene triamine

Li ⫹

Ca 2⫹

19.7 277

137 787

447 711

81.0 263

1640 167

The four benzene rings are arranged conically, so that the two hydroxyl and two ester groups (in 1a) or two hydroxyl groups and one dicarboxamide (in 1b) form a co-ordination sphere where cations can be bound. Owing to the two –NO2 auxochromic groups connected to the phenolic hydroxyl groups through conjugated electron systems, the molecules are expected to change their UV/Vis spectra significantly upon complexation. The preparation of compound 1a has already been described [8], whereas 1b was synthesized analogously by the nitration of the appropriate bridged calixarene [9]. 2. Experimental In preliminary qualitative measurements 5 × 10 ⫺5 mol dm ⫺3 solutions of 1a and 1b were prepared in each solvent. When the complex formation with amines was studied, 100 ml of the respective amine (about 10 4-fold excess) was added into 3 ml solutions of the ligands. In the study of the ion-selectivity the samples were saturated with the bromide salts of alkali and alkaline earth metals. The stoichiometry of the complexes were determined by Job’s method [10], applying 5 × 10 ⫺4 mol dm ⫺3 acetonic solutions of the components. The equilibrium constants of the complex formations were determined by varying the concentrations of the reactants. 3. Results and discussion The UV/Vis spectra of 1a and 1b were recorded in ethanol, acetonitrile, acetone, dichlorometane, 1,4dioxane and carbon tetrachloride. Table 1 summarizes the absorption maxima of the ligands 1, in the absence and in the presence of aliphatic amines. The longest wavelength absorption maxima of the ligands fall around 330 nm, except that of 1b in acetone and

acetonitrile, in which a weak bound appears around 440 nm indicating a small scale complex formation with the solvent. After addition of the amines a new band arises with the absorption maximum between 407 and 447 nm, providing evidence for the complexation of the substrates. The absorption spectra of the amines in the various solvents were also recorded and the bands attributed to the uncomplexed amines have been marked with asterisks in the table. Many times they overlap with the lower energy p – p * excitation of the benzene rings of the calixarenes. As can be seen, the complex formation is strong not only in acetone and in acetonitrile (aprotic, polar solvents) but also in ethanol (protic solvent) as well. The effect is weaker in apolar solvents, particularly in carbon tetrachloride. The strength of the complex formation depends primarily on the order of the amine. Primary monoamines are complexed strongly, the reaction with diethylene triamine is partial (as confirmed by quantitative measurements), whereas only a small proportion of triethylamine is complexed. As to the complexation of alkali and alkaline earth metal ions, it was found that ligands 1a and 1b are capable of binding lithium and calcium ions selectively in contrast to sodium, potassium and magnesium ions. The absorption maxima of the new band in the spectra of the metal complexes fall between 405 and 441 nm, practically in the same range as in the case of amine complexes. The dependence on the solvent was also similar, in polar solvents the complex formation with lithium and calcium ions was effective while in apolar solvents it was poor. The lithium complexes in acetonitrile and the calcium complexes in ethanol have an extra absorption band with the following wavelengths (nm)/absorbances: Li ⫹ –1a 269/1.274, Li ⫹ –1b 269/2.274 (acetonitrile), Ca 2⫹ – 1a 265/3.049, Ca 2⫹ –1b 265/1.596 (ethanol). The origin of these bands needs further investigation, but

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their appearance means that even Li ⫹ and Ca 2⫹ can be detected selectively in these two solvents. The stoichiometric measurements show that both ligands form LS type complexes (L ˆ ligand, S ˆ substrate) with propylamine and Li ⫹, whereas in the case of amines with two terminal amino groups (1,3diamino-propane and diethylene triamine) and the doubly charged Ca 2⫹ ion L2S type complexes are detected when the reactants are present in comparable concentrations. On adding the amine or Ca 2⫹ ion in large excess LS complex is also formed. Table 2 shows the equilibrium constants of complex formation between some substrates and ligands 1. These data characterize quantitatively the selectivity of the complex formation. 4. Conclusion Selective optical recognition of aliphatic primary amines and Li ⫹/Ca 2⫹ ions was observed in various solvents with ligand 1a and 1b. A significant enhancement (Kc1b/Kc1a ⬃ 1.6–14) of the stability of complexes was achieved in case of the bridged ligand 1b of more rigid structure with each substrate (except Ca 2⫹). Probably, the amine binding process is the complexation of RNH3⫹ ion formed by the protonation of the NH2 group with one of the strongly acidic nitrophenol moieties. The complex is stabilized by electrostatic and hydrogen bonding interactions. Investigations of ligands of type 1b supplied with chromogenic functions to develop sensors for biomimetic application are underway.

Acknowledgements The authors are grateful to the Hungarian Ministry of Education (contract number 0340/1997) and to the Hungarian Research Foundation for financial support (contract numbers T 025561 and T017327) and to Varga Jo´zsef Foundation (I. Mohammed-Ziegler).

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