No abstract

546.492+547.458.68The interaction of β-cyclodextrin with mercury(II) nitrate has been studied using UV, IR, and 1 H NMR spectroscopy, elemental analysis, and quantitative chemical analysis. The optimum conditions for complex formation were established. The stability constant of the 1:1 inclusion complex of β-cyclodextrin and nitrate was calculated. The formation of supermolecules of composition C 42 H 70 O 35 ⋅3Hg(NO 3 ) 2 in solution and on a silica surface chemically modified with β-cyclodextrin was shown.Introduction. Cyclodextrins are cyclic oligomers of α-D-glucose. They are widely used to increase the solubility and stability of medicinal and biologically active compounds and for chromatographic separation of mixtures of organic compounds because of their unique ability to form inclusion complexes with many organic molecules [1][2][3][4][5]. The application of cyclodextrins for the extraction, concentration, and analysis of toxic metals in environmental samples is promising. This may explain the vigorously developing research on the preparation of water-insoluble cyclodextrins [6] and their attachment to the surface of inorganic matrices [7-9]. β-Cyclodextrin was previously immobilized chemically on the surface of amorphous wide-pore silica [10][11][12]. The β-cyclodextrin-containing silica exhibited a high affinity for Hg(II) ions. Adsorption equilibrium is attained after only 15 min. The Hg(II) binding constant increases by two orders of magnitude compared with hydroxylated silica. Herein the interaction of β-cyclodextrin with mercury(II) nitrate in aqueous solution is studied in order to find the reasons for the high affinity of β-cyclodextrin-containing silica for Hg(II).Experimental. β-Cyclodextrin (Fluka, 99%) and Hg(NO 3 ) 2 (Khimlaborreaktiv, analytically pure) were used without further purification. UV absorption spectra of Hg(NO 3 ) 2 solutions were recorded on a Specord M-40 spectrophotometer in the wavelength range 260-400 nm in quartz cuvettes (l = 1 cm). The percent content of the various Hg(II) species in solution at pH 1-5 was calculated using the program Chemical Equilibria in AQuatic System. Elemental analyses were performed on an Elemental Analyzer EA 1110. IR spectra of powders were recorded on a Thermo Nicolet NEXUS single-beam Fourier IR spectrophotometer in the frequency range 4000-400 cm -1 . IR spectra were recorded using pressed disks of ~30 mg mass with pressing pressure 10 8 Pa. 1 H NMR spectra were measured at T = 25 o C in DMSO-d 6 on a Varian-VXR-300 (300 mHz) spectrometer with TMS internal standard. The Hg(II) content was determined using back titration with trilon [13].Results and Discussion. A symmetric absorption band with λ max = 302 nm and ε = 300 L/mol⋅cm ( Fig. 1) that belongs to the n → π * -transition of the N=O chromophore in the nitrate ion was recorded in the electronic spectrum of aqueous Hg(NO 3 ) 2 (0.001 M) [14]. Upon addition to the Hg(NO 3 ) 2 solution of given amounts of β-cyclodextrin, which has no characteristic absorption bands in the UV region, the abso...

The adsorption of Cd II cations on the surface of amorphous macroporous silicas chemically modified by β cyclodextrin and its functional derivatives was studied. The adsorption of Cd II cations was shown to follow the equation of the Freundlich isotherm for the heterogeneous surface. Analysis of the adsorption kinetic curves showed that two parallel processes occurred on the surface of β cyclodextrin containing silicas. A substantial increase in the adsorption of Cd(NO 3 ) 2 is a result of the formation of uncharged supramolecular structures on the surface of silica adsorbents. The composition of these structures depends on the polarizability of function al substituents of β cyclodextrins.Chemical immobilization of macrocyclic organic com pounds on the surface of oxide materials is accompanied by the formation of host-guest inclusion complexes with ions and molecules. As a result, active sites are formed, which are capable of sorbing and in this way extracting and concentrating trace amounts of toxic substances. 1-3 Among oxide materials, highly dispersed amorphous sili cas are undoubtedly advantageous. These adsorbents are characterized by high chemical, hydrolytic, thermal, and radiation stability, and the structure and reactivity of their active sites on the surface are well studied. 4-6The purpose of the present work is to study the effect of the surface structure of β cyclodextrin containing silicas on the adsorption of Сd II cations from weakly acidic dilute solutions. ExperimentalChemical immobilization of β cyclodextrin (β CD) was car ried out on the surface of highly dispersed amorphous macro porous silica (Silochrome C 120) by multistep chemical modifi cation. The interaction of hydroxylated silica (adsorbent 1) with γ aminopropyltriethoxysilane gave aminopropylsilochrome (adsorbent 2). Organosilicas chemically modified with β CD were synthesized by reacting aminopropylsilochrome with mono(toluenesulfonyl) β CD (adsorbent 3), the bromo substi tuted derivative of heptakis(toluenesulfonyl) β CD with amino propylsilochrome (adsorbent 4), and the bromoacetyl groups of adsorbent 4 with thiosemicarbazide (adsorbent 5).The structural adsorption parameters, chemical composi tion, and structure of the surface layer of the silica adsorbents (Table 1) were determined from the low temperature nitrogen adsorption isotherms, elemental and chemical analyses, poten tiometric titration, and data of thermogravimetry, IR spectros copy, and 1 Н NMR spectroscopy.The adsorption of cations Cd II was studied at 22 °C under static conditions by the method of separate weighed samples from 2.5•10 -4 -4.0•10 -3 М aqueous solutions of Cd(NO 3 ) 2 with pH ~1 at different contact times with silicas and at different concentrations of the equilibrium solution. Suspensions con taining 0.025 g of the silica adsorbent and 20 cm 3 of a Cd(NO 3 ) 2 solution were maintained at constant temperature for 4 h in a JULABO SW22 aqueous thermostat with continuous shaking. The content of Cd II in the starting and equilibrium solutions was determined...