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J. Phys. Chem. C 2009, 113, 15838–15844

Self-Assembly of Stereoisomers of p-tert-Butyl Thiacalix[4]arenes Tetrasubstituted at the Lower Rim by a Tertiary Amide Group with Cations of p- and d-Elements in the Organic Phase Ivan I. Stoikov,*,† Elena A. Yushkova,† Anastas A. Bukharaev,‡ Dmitry A. Biziaev,‡ Sufia A. Ziganshina,‡ and Ilya Zharov§ Department of Chemistry, Kazan State UniVersity, A.M. ButleroV Chemical Institute, 420008, Kazan, KremleVskaya, 18, Russian Federation, ZaVoisky Physical-Technical Institute, 420029, Kazan, Sibirsky tract, 10/7, Russian Federation, and UniVersity of Utah, Salt Lake City, Utah 84112 ReceiVed: March 31, 2009; ReVised Manuscript ReceiVed: July 31, 2009

The ability of p-tert-butyl thiacalix[4]arenes tetrasubstituted at the lower rim by morpholide and pyrrolidide groups in cone, partial cone, and 1,3-alternate conformations to recognize cations of p- (Al3+, Pb2+) and d(Fe3+, Co3+, Ni2+, Cu2+, Cd2+, Hg2+) elements has been studied by the picrate extraction method, dynamic light scattering (DLS), and atomic force microscopy (AFM). The hydrodynamic diameters of supramolecular associates, polydispersity index of host-guest systems, and molecular weight of nanoscale aggregates consisting of p-tert-butyl thiacalix[4]arenes and metal nitrates have been determined by the correlation spectroscopy method. It was shown that the investigated macrocycles are effective extractants for metal cations. All the investigated thiacalix[4]arenes are able to form dimers of about 1 nm with metal cations and nanoscale particles of 238 and 212 nm with Ni2+ and Pb2+ cations, respectively. Introduction Self-associating and self-organizing processes which provide spontaneous generation of the polymolecular associates from separate compounds in a narrow conditions interval are an interesting topic of supramolecular chemistry. Amino acids, proteins, nucleotides, nucleic acids, and phospholipids refer to the main building blocks of biological nanostructures in nature.1 However, supramolecular chemistry offers new opportunities for creating supramolecular associates varied on the structural level of organization2 which are based on synthetic receptor molecules and cationic, anionic, and neutral substrates. As a rule, the molecular design of the host molecules with the required spatial orientation of structural fragments, binding centers, and functional groups is necessary not only for creating target molecular structure with certain chemical and physical properties, but also for providing the possibility to change the structure of the above architectures under external forces. The creation of such model structures is necessary for understanding and studying the main principles and advantages of supramolecular self-assembling. One of the most productive approaches to the development of the receptor structures designed for selective interaction with certain substrates consists of the modification of the appropriate macrocyclic platform by suitable reagents.3 For this purpose, various platforms are currently being used, e.g., crown ethers, calix- and calixresorcinarenes, and cyclodextrins.3,4 The chemistry of thiacalix[4]arenes has recently received development. The modification of the p-tert-butyl thiacalix[4]arenes with various functional groups at the upper and lower rim, the variation of the receptor configuration that allowed one * To whom correspondence should be addressed. Phone: +7-8432315462. Fax: +7-843-2752253. E-mail: [email protected]. † Kazan State University. ‡ Zavoisky Physical-Technical Institute. § University of Utah.

ligand molecule to bind two and more cations, and also the macrocyclic size (for example, due to replacement of the original methylene bridges between the aromatic units in calixarenes by sulfur atoms) allow those macrocycles to selectively recognize cations and form supramolecular associates. As was found, calix[4]arenes containing donor binding centers such as the oxygen atom of amide5 and ether and ketone6 groups showed a very high ability to bind alkali metal ions. The high selectivity of these ligands depends on the size of the pseudocavity containing the large number of oxygen atoms and being well suitable for certain cations. The complexation ability of soft donor atoms such as nitrogen and sulfur of various functional groups to cations of p- and d-elements with various geometry coordinations has been much less investigated. Thus, the formation of the complexes host-guest and supramolecular aggregates depends on the coordination path of the substratum. In this work, the ability of p-tert-butyl thiacalix[4]arenes tetrasubstituted at the lower rim by morpholide and pyrrolidide groups in cone, partial cone, 1,3-alternate conformations to recognize cations of p- (Al3+, Pb2+) and d- (Fe3+, Co3+, Ni2+, Cu2+, Cd2+, Hg2+) elements has been studied by the picrate extraction method, dynamic light scattering (DLS), and atomic force microscopy (AFM). Experimental Methods The Degree of Extraction. The picrates were prepared by stepwise addition of 3.02 × 10-4 M Al(NO3)3, Pb(NO3)2, Fe(NO3)3, Co(NO3)3, Ni(NO3)2, Cu(NO3)2, Cd(NO3)2, and Hg(NO3)2 to 2.32 × 10-4 M aqueous picric acid solution; in this case, the solutions were weakly acidic (pH 4). Distilled water was used for the preparation of all aqueous solutions. Aqueous picrate solution (3 mL, 2.32 × 10-4 M) and 3 mL of a 2.32 × 10-4 M solution of thiacalix[4]arene derivatives in CH2Cl2 (chemical pure) were shaken for 30 min at room temperature (22 °C). The absorbance Ai of the aqueous phase

10.1021/jp902904n CCC: $40.75  2009 American Chemical Society Published on Web 08/17/2009

Tetrasubstituted p-tert-Butyl Thiacalix[4]arenes

after extraction and that of the aqueous phase before extraction, A0, were measured at the wavelength of the maximum absorption of the picrate ion, λmax ) 355 nm. The percentage of the extracted cation was calculated as the ratio 100 × (A0 - Ai)/ A0. Five independent experiments were carried out for each combination of a ligand and metal picrate. Extraction Constants Log Kex and Stoichiometry of the Complexes. Extraction experiments were performed at various ligand concentrations (1.00 × 10-4 to 2.50 × 10-4). Picrates were prepared by stepwise addition of a 3.02 × 10-4 M Al(NO3)3, Pb(NO3)2, Fe(NO3)3, Co(NO3)3, Ni(NO3)2, Cu(NO3)2, Cd(NO3)2, and Hg(NO3)2 to 2.32 × 10-4 M aqueous picric acid solution; in this case, the solutions were weakly acidic (pH 4). The log Kex and n values were determined from the plot of log (a/1 - a) vs. log [L]org. as described elsewhere.7 Three independent experiments were carried out for each system. Dynamic Light Scattering (DLS). The particle sizes were determined by Zetasizer Nano ZS instrument at 20 °C. The instrument contains a 4 mW He-Ne laser operating at a wavelength of 633 nm and incorporates noninvasive backscatter optics (NIBS). The measurements were performed at a detection angle of 173° and the measurement position within the quartz cuvette was automatically determined by the software. The solutions of the investigated systems were prepared by addition of metal nitrate to 10 mL of 10-4 M solution of thiacalixarene derivatives in CH2Cl2 (HPLC). The mixture was mechanically shaked for 2 h and then magnetically stirred in a thermostated water bath at 20 °C for 1 h. The final concentration of metal nitrates in 10 mL of CH2Cl2 (HPLC) was 2.32 × 10-4 M. Three independent experiments were carried out for each combination of a ligand and metal nitrate. Static Light Scattering (SLS). For the definition of molecular weight of supramolecular associates a series of solutions in CH2Cl2 (HPLC) with various concentration of p-tert-butyl thiacalix[4]arene derivatives and metal cations were prepared at 20 °C. The solvent scattering was measured followed by the various concentrations of sample. From these measurements a Debye plot was generated. This is a plot of the variation in average intensity versus the concentration. The intercept of the extrapolation to zero concentration is calculated. Three independent experiments were carried out for each system. Atomic Force Microscopy (AFM). Imaging was carried out with a Solver P47 AFM (NT-MDT, Russia) equipped with a tube scanner, in tapping mode, using NSG-11 cantilevers with silicon probes (force constant: 5-22 N/m) at a scan frequency of 0.7 Hz. Images are processed with the NT-MDT software package. The solutions of the investigated systems were prepared by addition of metal nitrate to 10 mL of a 10-4 M solution of thiacalixarene derivatives in CH2Cl2 (HPLC). The mixture was mechanically shaked for 2 h and then magnetically stirred in a

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TABLE 1: Percent of Extraction (% E) of Metal Ions by Conformational Isomers of the p-tert-Butyl Thiacalix[4]arene Derivatives 1-6a,b absorption with cations CH2Cl2 Al3+ Fe3+ Ni2+ Cu2+ Co3+ Pb2+ Hg2+ Cd2+

6(1 28 ( 3 5(1 3(1 5(2 6(2 10 ( 2 5(1

cone

partial cone

1,3-alternate

4

1

5

2

6

3

55 ( 2 60 ( 2 65 ( 2 63 ( 1 55 ( 3 98 ( 1 79 ( 2 55 ( 1

12 ( 3 32 ( 2 8(2 9(2 8(1 52 ( 2 45 ( 1 10 ( 3

32 ( 2 55 ( 3 31 ( 2 30 ( 1 32 ( 2 92 ( 2 79 ( 1 34 ( 1

8(1 31 ( 2 9(1 9(2 17 ( 1 24 ( 3 46 ( 2 11 ( 1

81 ( 1 94 ( 1 71 ( 3 79 ( 1 78 ( 3 82 ( 1 92 ( 1 81 ( 1

39 ( 1 60 ( 3 36 ( 3 37 ( 2 32 ( 2 35 ( 2 38 ( 3 39 ( 3

Extraction conditions: [L] ) 2.5 × 10-3 M, [MPicn] ) 2.32 × 10 M.10 b (: standard deviation. a

-4

thermostated water bath at 20 °C for 1 h. The final concentration of metal nitrates in 10 mL of CH2Cl2 (HPLC) was 2.32 × 10-4 M. Results and Discussion Picrate Extraction Method, the Percents of Extraction. The abilities of p-tert-butyl thiacalix[4]arene tetrasubstituted with the tertiary amide fragments in three conformations for molecular recognition of p- and d-element ions were estimated by using the picrate extraction method. This method is widely used for the investigation of complexion properties of the synthetic receptors toward metal cations8 and includes the determination of the degree of extraction by host molecules from the water into the organic phase. The metal cations of p- (Al3+, Pb2+) and d- (Fe3+, Co3+, Ni2+, Cu2+, Cd2+, Hg2+) elements were selected as guests because of their biochemical significance and toxicity properties.9 The degree of guest extraction by the p-tert-butyl thiacalix[4]arenes 1-6 functionalized with tertiary amide substituents as well as the extraction constants and the stoichiometry of the metal cation-p-tert-butyl thiacalixarene complexes in organic phase were determined as described below. The influence of the nature of the substitutes on the binding efficiency toward metal cation was also investigated. One can see (Table 1) that p-tert-butyl thiacalixarenes 4-6 tetrasubstituted by a pyrrolidide group are effective extractants in comparison with p-tert-butyl thiacalixarenes 1-3. Two factors can influence changes of extraction properties of p-tert-butyl thiacalix[4]arene derivatives from morpholide 1-3 to pyrrolidide 4-6, i.e., the decrease in the volume and increase in the electron donation ability of the substitutes. The correlation of extraction properties of 1,3-alternate (3 and 6) was found. It was shown that the size of the substitutes is the major factor affecting the binding efficiency of p-tert-

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butyl thiacalix[4]arene tetrasubstituted by tertiary amide groups toward p- and d-metal cations. The ion radius of the cations of investigated p- and d-elements varies from 0.067 nm for Al3+ to 0.133 nm for Pb2+.11 Both cone 1, 4 and partial cone 2, 5 are selective extractants toward voluminous cations of Pb2+ and Cu2+ (0.116 and 0.133 nm, respectively).11 In the case of rather compact pyrrolidide substitutes, the receptors 4-6 do not provide steric congestion for coordination of p- and d-metal cations with small radius (0.067 nm for Al3+ and 0.109 nm for Cd2+).11 The influence of p-tert-butyl thiacalix[4]arene configuration on the extraction efficiency was found only for pyrrolidides 4-6. The extraction efficiency toward p- and d-metal cations by p-tert-butyl thiacalix[4]arene 4-6 decreased in the range 1,3alternate > cone > partial cone. The tendency was not proved for morpholides because cone 1 and partial cone 2 were found to be poor extractants for all the metal ions. 1,3-Alternate 3 was a more effective receptor for the cations of p- and d-elements investigated. Probably the interposition of the coordination centers of metal cations, i.e., amides fragments, oxygen atoms of the phenolic groups, π-electronic density of aromatic units in a macrocycle and the bridging sulfur atom in the structure of p-tert-butyl thiacalix[4]arene in 1,3-alternates 3, 6 configuration is well preorganized for the binding of the cations of p- and d-elements. Thus, the influence of spatial and electronic factors on the interaction of p-tert-butyl thiacalix[4]arene derivatives with cations of p- and d-elements was investigated on the example of p-tert-butyl thiacalix[4]arene tetrasubstituted at the lower rim by morpholide and pyrrolidide groups. It was established that the pyrrolidide fragment increases the extraction efficiency toward p- and d-metal cations by p-tert-butyl thiacalix[4]arene tetrasubstituted by tertiary amide groups in comparison with those containing morpholide groups. The influence of configuration of p-tert-butyl thiacalix[4]arene functionalized with pyrrolidide and morpholide groups at the lower rim on their receptor properties toward various metal cations was shown. Extraction Constants Log Kex and Complex Stoichiometry. To quantify the ability of the p-tert-butyl thiacalix[4]arene derivatives 1-6 in three conformations to recognize p- and d-metal ions, the extraction constants and the stoichiometry of the cation-p-tert-butyl thiacalixarene complexes formed in organic phase were determined by using the picrate extraction method (Table 2). It was shown that the complex stoichiometry depends on the receptor configuration that allows one ligand molecule to bind two and more cations. The complex stoichiometry of Al3+, Ni2+, Fe3+, and Hg2+ ions was found to be approximately 1:1 only for 4 (cone) functionalized with pyrrolidide groups. The appropriate values of extraction constants log Kex varied from 6.5 to 7.7 (Table 2). All four ligating groups located on one side of the macrocycle plane can participate in the binding of these cations. The stoichiometry of partial cone and 1,3-alternate complexes is either 2:1 or 1:1. Pb2+and Hg2+ ions form 1:1 complexes in the organic phase with 6 (1,3-alternate) with log Kex ) 6.9 and 8.0, respectively. However, only the small Fe3+ ion forms 3:1 complexes in the organic phase with 2 (partial cone). Ni2+, Co3+ cations react with 2 (partial cone), Al3+ with 5 (partial cone), and Ni2+, Fe3+, Cu2+, Cd2+, Pb2+, Al3+, and Hg2+ with 3 (1,3-alternate) and give 2:1 complexes in the organic phase. Their log Kex values do not exceed 4.7. This means that in this case both pairs of functional groups interact with a guest ion independently with each other and structural changes caused by ion complexation on one side of 1,3-alternate

Stoikov et al. TABLE 2: Percent of Extraction (% E), Extraction Constants (log Kex), and Stoichiometry (n) of the Complexes of 1-6 with Cations of p- and d-Elements in the Organic Phasea,b cations cone (1) partial cone (2)

1,3-alternate (3)

cone (4)

partial cone (5) 1,3-alternate (6)

3+

Fe Hg2+ Pb2+ Ni2+ Fe3+ Co3+ Cu2+ Hg2+ Hg2+ Co3+ Al3+ Fe3+ Pb2+ Cd2+ Cu2+ Ni2+ Pb2+ Hg2+ Co3+ Fe3+ Ni2+ Al3+ Cd2+ Al3+ Cd2+ Pb2+ Hg2+

n

log Kex

0.47 ( 0.12 0.59 ( 0.05 0.57 ( 0.05 0.48 ( 0.05 0.36 ( 0.03 0.49 ( 0.04 0.69 ( 0.05 0.72 ( 0.06 0.41 ( 0.01 0.66 ( 0.04 0.47 ( 0.04 0.45 ( 0.03 0.47 ( 0.03 0.42 ( 0.01 0.48 ( 0.01 0.54 ( 0.04 2.08 ( 0.12 0.97 ( 0.08 0.66 ( 0.06 0.99 ( 0.09 1.05 ( 0.03 1.05 ( 0.04 0.50 ( 0.05 0.47 ( 0.02 0.75 ( 0.02 0.92 ( 0.02 1.14 ( 0.02

4.07 ( 0.29 5.70 ( 0.17 5.17 ( 0.13 3.98 ( 0.14 3.93 ( 0.08 3.91 ( 0.09 4.42 ( 0.26 5.40 ( 0.16 4.43 ( 0.04 5.13 ( 0.11 4.35 ( 0.10 4.86 ( 0.10 4.43 ( 0.08 4.28 ( 0.04 4.75 ( 0.04 5.14 ( 0.14 12.70 ( 0.48 7.69 ( 0.31 5.36 ( 0.25 6.45 ( 0.24 6.68 ( 0.08 6.55 ( 0.13 4.68 ( 0.21 4.62 ( 0.05 6.26 ( 0.06 6.95 ( 0.06 8.03 ( 0.07

a [L]org.,init ) 10-4 to 2.5 × 10-3 M, [MPicn]aq,init. ) 2.32 × 10-4 M.10 b (: standard deviation.

and partial cone do not cause significant hindrance for binding on another side. However, the macrocycles 1, 4 and metal cations are able to form complexes consisting of two or more receptor molecules: cone 4 with Pb2+ and Cd2+, and cone 1 with Fe3+, Hg2+, and Pb2+. The complex stoichiometry was equal to about 1:2 and 2:1, respectively. The formation of 3:2 complexes is typical for all three stereoisomers reacted with Co3+ (cone 4, 1,3-alternate 3), Cu2+, Hg2+ (partial cone 2), and Cd2+ (1,3-alternate 6). Thus, two receptor molecules can participate in the binding of three cations. Such a 3:2 stoichiometry of the complexes may explain the ability of the systems to further associate with formation of both dimers and supramolecular aggregates. Self-Assembly of Aggregates Consisting of p-tert-Butyl Thiacalix[4]arenes Derivatives and Metal Cations in the Organic Phase. Dynamic light scattering (DLS) is one of the methods used for particle size determination. The ability of the systems consisting of p-tert-butyl thiacalix[4]arenes 1-6 and metal nitrates of p- (Al3+, Pb2+) and d- (Fe3+, Co3+, Ni2+, Cu2+, Cd2+, Hg2+) elements to self-assemble was investigated under the same conditions as picrate extraction (Table S1 and S2 in the Supporting Information). The systems consisting of the macrocycles and some cations not included in Tables S1 and S2 (see the Supporting Information) did not show selfassociation abilities. The measurements were carried out in 3 h after the solution preparation at 20 °C. The ability of the systems consisting of p-tert-butyl thiacalix[4]arenes 1-6 to undergo self-association was investigated earlier.12 As was shown, the pyrrolidide derivative in cone conformation is able to form self-associates - dimers with hydrodynamic diameters of about 1.4 nm (Figure 1, structures A and B).12 Similar feature of p-tert-butyl thiacalix[4]arene 4 can affect the aggregation abilities with some cations of p- and d-elements.

Tetrasubstituted p-tert-Butyl Thiacalix[4]arenes

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Figure 1. The possible structures of p-tert-butyl thiacalix[4]arene aggregates with metal cations.

It was shown that all the macrocycles are able to form dimers (Figure 1, structures C and D) with cations of p- and d-elements except for p-tert-butyl thiacalix[4]arene 4 with Pb2+ and Ni2+ (Table S2 in the Supporting Information). It was established that the systems consisting of macrocycles 1-6 and metal cations formed other kinds of associates with a size of more than 100 nm except that of dimers with a size of about 1 nm. Similar three-modal size distributions of intensities with the main peak of about 1.0 nm, the second peak of about 295.0 nm, and the third peak of about 3767.5 nm are shown in Figure 2A for the system consisting of the macrocycles 4 and Hg2+ cations. However, the transformations of the size distributions by intensity into the volume and number distributions by Mie theory13 were found to be monomodal with the main peak of 0.8 nm (Figure 2B,C). A similar tendency was observed for p-tert-butyl thiacalix[4]arene 4 with Pb2+ and Ni2+ cations. Thus, nanoscale aggregates with a hydrodynamic diameter of about 212 and 238 nm, respectively, were major particles in these systems. The ability of the systems to form nanoscale associates depends on three factors, i.e., the configuration of the macrocycle and the nature of the substrates and that of binding centers. One can see (Figure 3) that all the investigated compounds can form nanoscale particles with metal cations not only due to the coordination of the bridging sulfur atom but also due to the oxygen atoms of the phenyl and amide groups.14,15 The ability of the macrocycles containing pyrrolidide groups to form associates changes in the following range: cone > 1,3-alternate > partial cone. Another tendency was observed for p-tert-butyl thiacalix[4]arenes 1-3 functionalized with morpholide groups: partial cone, 1,3-alternate > cone. In the case of macrocycle 4 tetrasubstituted by the compact pyrrolidide group in the cone configuration, the formation of dimers (Figure 4) and aggregates was observed with both the voluminous cations of Cd2+, Pb2+, Hg2+ and cations of p- and d-elements (Ni2+, Fe3+, Co3+, Al3+) with small radius. However, the change of the special orientation of the binding site affects the ability of macrocycles 5 and 6 to associate with cations different in size. Partial cone 5 is able to form dimers only with small Al3+ cations and 1,3-alternate 6 with voluminous Cd2+, Pb2+, and Hg2+ cations. In the case of p-tert-butyl thiacalix[4]arene 2, the size of p- and d-metal cations does not influence the ability for aggregation, but, cone 1 only forms dimers with small Fe3+ cations and 1,3-alternate 3 with both small Al3+, Co3+, Fe3+ cations and big Hg2+, Pb2+ cations.

The decrease of the volume and increase of the electron donation ability of the pyrrolidide substitutes in comparison with morpholide groups of macrocycles 1 and 4 in the cone configuration influence the ability of the systems to form associates with various cations. p-tert-Butyl thiacalix[4]arenes 1 are able to form dimers only with “hard” Fe3+ cations; however, in the case of compact pyrrolidide substitutes of receptor 4, the aggregation is possible with the formation of supramolecular aggregates containing “soft” Ni2+ and Pb2+ cations. Also, molecular weights were determined to specify the quantity of structural fragments (N), i.e. the number of p-tertbutyl thiacalix[4]arene molecules and metal cations which form nanoscale associates.16 The stoichiometry ratio (n (G:H)) determined by the picrate extraction method and the molecular weights of nanoscale particles determined by DLS are necessary for an estimation of the quantity of receptor and substrate molecules forming supramolecular associates. As was shown, the molecular weights of nanoscale particles consisting of macrocycles 1-6 and metal cations were determined also by DLS and correspond to those of the dimers (Table 3). Pyrrolidide 4 in the cone configuration with Pb2+ and Ni2+ cations is able to form only one supramolecular aggregate with 23 and 19 p-tert-butyl thiacalix[4]arene molecules, respectively. As was shown, only these systems showed an abnormally high value of the extraction constant (Table 2). Also, for the determination of the aggregate stability of the systems by DLS, second virial coefficients (A2, mL · mol/g2) were quantified. The second virial coefficient (A2) describes the interaction strength between the particles and the solvent or appropriate dispersant medium.17 For the samples with A2 > 0, the particles “attract” the solvent more than themselves and tend to form a stable solution. When A2 < 0, the particles “attract” themselves more than the solvent, and therefore can aggregate. When A2 ) 0, the particle-solvent interaction strength is equal to the molecule-molecule interaction strength. This solvent can be ascribed as a θ solvent. The negative value of the second virial coefficient characterizes the ability of the systems containing macrocycles 4 and Pb2+, Co3+, and Al3+ cations only to form aggregates (Table 3). The surface morphology of the self-assembled aggregates with hydrodynamic diameter distributions by intensity of about 212 and 238 nm determined by DLS was investigated by atomic force microscopy (AFM). Figure 5 shows AFM images of the

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Figure 2. Size distributions by intensity (A), volume (B), and number (C) for the system consisting of molecules for p-tert-butyl thiacalix[4]arenes functionalized with pyrrolidide units in cone conformation and Hg2+ cation in CH2Cl2 (HPLC).

Figure 3. Possible coordination paths of a “hard” (A) and “soft” (B) acid by conformational isomers of thiacalix[4]arenes.

same region of the surface of the supramolecular associates consisting of p-tert-butyl thiacalix[4]arene 4 and Pb2+, Ni2+

cations. It was found that pyrrolidide 4 in the cone configuration with lead and nickel cations forms a supramolecular assembly, depending on the nature of the guest molecules, in a (Figure 5a,b) “stretched” or (Figure 5c,d) “helical” arrangement, respectively. According to the AFM images, the “helical” aggregates with Ni2+ cations exhibit a width, length of about 144 nm and a height of 3 nm, while the “stretched” associates with Pb2+ cations exhibit a width of about 117 nm, length of about 190 nm, and a height of 13 nm. Comparing the two images, it was found that the p-tert-butyl thiacalix[4]arenes 4 with lead cations are able to form more densely packed aggregates than those with nickel cations. This finding coincides well with estimates of molecular weight of those associates. Thus, the molecular weight of the nanoscale particles with Pb2+ cations, having more dense packing, is about 31.05 larger than the molecular weight of the aggregates with Ni2+ cations (25.35).

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Figure 4. Possible structure of dimers of cone 4 with metal ions corresponding to 1:1 (C), 2:1 (A), or 3:2 (B) stoichiometry.

TABLE 3: Extraction Constants (log Kex) and Stoichiometry (n (G:H)), Structural Fragments Quantity (N), Molecular Weight (MW), Second Virial Coefficient (A2, mL · mol/g2) of the Aggregates in the System Consisting of p-tert-Butyl Thiacalix[4]arene Derivatives 1-6 and Metal Cations in CH2Cl2 (HPLC)a

a

system

MW

A2, mL · mol/g2

N

n (G:H)

log Kex

cone (1) + Fe(NO3)3 partial cone (2) + Cu(NO3)2 partial cone (2) + Hg(NO3)2 partial cone (2) + Co(NO3)3 partial cone (2) + Fe(NO3)3 partial cone (2) + Ni(NO3)2 1,3-alternate (3) + Hg(NO3)2 1,3-alternate (3) + Co(NO3)3 1,3-alternate (3) + Pb(NO3)2 1,3-alternate (3) + Fe(NO3)3 1,3-alternate (3) + Al(NO3)3 cone (4) + Pb(NO3)2 cone (4) + Hg(NO3)2 cone (4) + Co(NO3)3 cone (4) + Cd(NO3)2 cone (4) + Ni(NO3)2 cone (4) + Fe(NO3)3 cone (4) + Al(NO3)3 partial cone (5) + Al(NO3)3 1,3-alternate (6) + Cd(NO3)2 1,3-alternate (6) + Pb(NO3)2 1,3-alternate (6) + Hg(NO3)2

3.06 ( 0.39 2.70 ( 1.33 3.68 ( 0.60 3.28 ( 0.62 2.39 ( 0.28 3.60 ( 0.68 3.62 ( 1.09 2.91 ( 1.52 3.95 ( 2.61 3.94 ( 0.84 3.84 ( 1.39 31.05 ( 1.62 3.02 ( 0.69 2.78 ( 0.51 3.35 ( 2.11 25.35 ( 4.55 3.10 ( 0.89 2.83 ( 0.84 2.83 ( 0.84 2.56 ( 0.49 3.82 ( 1.35 3.47 ( 1.37

6.28 ( 0.35 20.15 ( 3.80 4.36 ( 0.39 4.58 ( 0.52 7.05 ( 0.99 0.46 ( 0.59 8.51 ( 0.88 15.25 ( 1.09 18.60 ( 3.98 7.27 ( 0.70 8.27 ( 1.29 -0.13 ( 0.01 8.44 ( 0.70 -0.54 ( 0.90 26.05 ( 5.35 0.20 ( 0.10 2.11 ( 1.34 -0.46 ( 0.78 2.81 ( 1.71 2.23 ( 0.89 3.82 ( 1.33 8.75 ( 2.03

1.8 0.9 1.1 1.9 1.2 2.2 1.9 0.9 2.1 2.3 2.3 11.7 2.0 0.9 2.0 18.8 2.2 2.0 1.8 0.8 2.5 2.3

2:1 3:2 3:2 2:1 3:1 2:1 2:1 3:2 2:1 2:1 2:1 1:2 1:1 3:2 2:1 1:1 1:1 1:1 2:1 3:2 1:1 1:1

4.1 4.4 5.4 3.9 3.9 4.0 4.4 5.1 4.4 4.9 4.3 12.7 7.7 5.4 4.7 6.7 6.5 6.5 4.6 6.3 6.9 8.0

(: standard deviation of experiments.

Figure 5. AFM images, at 5 µm scan range (a, c), 1,3 µm scan range (b), and 1,2 µm scan range (d), of 4 with Ni2+ (a, b) and Pb2+ (c, d) nitrate.

Interestingly, the length of the nanoparticles, according to the AFM images, is smaller than the size distributions by intensity measured by DLS, but is comparable with the hydrodynamic diameter distribution by number.

Thus, it was established by DLS that the ability of p-tertbutyl thiacalix[4]arenes to form nanoscale aggregates with cations of p- and d-elements depends on the macrocycle configuration, possible paths of the coordination of the metal

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cations with the ligands, the size of cations, and also the stoichiometry and extraction constants of the systems determined by the picrate extraction.

material is available free of charge via the Internet at http:// pubs.acs.org.

Conclusions

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In this work, the ability of p-tert-butyl thiacalix[4]arenes tetrasubstituted at the lower rim by morpholide and pyrrolidide groups in the cone, partial cone, and 1,3-alternate conformations to recognize cations of p- (Al3+, Pb2+) and d- (Fe3+, Co3+, Ni2+, Cu2+, Cd2+, Hg2+) elements was studied by the picrate extraction method, DLS, and AFM. It was shown that p-tert-butyl thiacalixarenes tetrasubstituted by the pyrrolidide group were effective extractants in comparison with p-tert-butyl thiacalixarenes containing morpholide groups. All the investigated thiacalix[4]arenes are able to form dimers of about 1 nm with metal cations, and nanoscale particles of 238 and 212 nm with Ni2+ and Pb2+ cations, respectively. The size of the particles consisting of metal cations and p-tert-butyl thiacalix[4]arenes tetrasubstituted at the lower rim depends on the configuration of macrocycles and the nature of the substrate and that of binding centers. Acknowledgment. The financial support of RFBR (08-0391106-CRDF), CRDF (RUC1-2910-KA-07), the joint program of CRDF, and the Ministry of Science and Education of Russian Federation “Fundamental Researches and Higher Education” (REC-007) is gratefully acknowledged. Supporting Information Available: Tables giving the size of aggregates and area intensity, volume, and number for peaks 1-3 for tetrasubstituted p-tert-butyl thiacalix[4]arenes 1-6. This

References and Notes

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