UV-Vis, fluorescence and NMR spectroscopic investigations on inclusion properties of a designed tetrahomocalix[8]arene with fullerenes C60 and C70 in solution

The present article reports the spectroscopic investigations on non-covalent interaction of fullerenes C(60) and C(70) with a macrocyclic receptor molecule, namely, 1,3,5,7-tetrahomo-p-tert-butylcalix[8]arene (1) in toluene. Jobs method of continuous variation reveals 1:1 stoichiometry for the fullerene complexes of 1. The most fascinating feature of the present study is that 1 binds selectively C(60) compared to C(70) as obtained from binding constant (K) data of C(60)-1 (K(C60-1)) and C(70)-1 (K(C70-1)) complexes which are enumerated to be 265,000 dm(3) mol(-1) and 63,43 dm(3) mol(-1), respectively, and selectivity in binding (K(C60-1)/K(C70-1)) is estimated to be 4.18 as obtained from UV-Vis study. Steady state fluorescence studies reveal quenching of fluorescence of 1 in presence of fullerenes and the K value of the C(60)-1 and C(70)-1 complexes are estimated to be 80,760 and 68,780 dm(3) mol(-1), respectively, with selectivity in binding (K(C60-1)/K(C70-1)) ~1.18. (1)H NMR analysis provides very good support in favor of strong binding between C(60) and 1. The high value of K value for C(60)-1 complex indicates that 1 forms an inclusion complex with C(60).     

Retention of enzymatic activity of alpha-amylase in the reductive synthesis of gold nanoparticles

In this paper, we report the generation of Au nanoparticles (NPs), using a pure enzyme for the reduction of AuCl4(-), with the retention of enzymatic activity in the complex. As a model system, alpha-amylase was used to readily synthesize and stabilize Au NPs in aqueous solution. Although several other enzymes were also pursued for the synthesis, it was interesting to observe that only alpha-amylase and EcoRI could produce Au NPs. Following NP synthesis, the activity of the enzyme was retained in the Au NP-alpha-amylase complex. The presence of Au NPs and alpha-amylase in the complex was established by UV-visible and FT-IR spectroscopy, X-ray diffraction (XRD) and transmission electron microscopic (TEM) measurements. Our observations suggest that the presence of free and exposed S-H groups is essential in the reduction of AuCl4(-) to Au NPs. Structural analysis of the enzymes showed that both alpha-amylase and EcoRI enzymes have free and exposed S-H groups in their native form and thus are suitable for the generation of NPs, whereas the other ones used here do not have such groups. Fortuitously, the enzymatic functional group of alpha-amylase is positioned opposite to that of the free and exposed S-H group, which makes it ideal for the production of Au NPs; binding of the enzyme to Au NPs via Au-S bond and also retention of the biological activity of the enzyme.     

Inclusion properties of 3-fluoromesotetraphenylporphyrin with C60 and C70

To improve the selectivity ratio of C70 over C60, a new designer molecule, viz., 3-fluoromesotetraphenylporphyrin (1) has been reported in the present investigations. Fluorescence studies reveal that the Q-absorption band of 1 gets sufficient quenching effect upon addition of both C60 and C70. Binding constants (K) of the C60/1 and C70/1 complexes are estimated to be 580 and 10,800 dm3 mol(-1), respectively. Thus, K(C70)/K(C60) is approximately 19 which is very large and even comparable with other macrocyclic host molecules like calix[5]arene, azacalix[m]arene[n]pyridine, cyclotriveratrylenophane and calixarene bisporphyrin. 1H NMR chemical shift measurements show that the -NH- proton of 1 suffers more shifts in presence of C70 compared to C60. This finding also offers a good support in favor of high K value for C70/1 complex as well as large selectivity ratio of C70 over C60.     

Total Synthesis of Isodaphlongamine H: A Possible Biogenetic Conundrum

Herein we describe the first synthetic efforts toward the total synthesis of isodaphlongamine H, a calyciphylline B‐type alkaloid. The strategy employs a chemoenzymatic process for the preparation of a functionalized cyclopentanol with a quaternary center. This molecule is elaborated to form an enantiopure 1‐aza‐perhydrocyclopentalene core, representing rings A and E of all calyciphylline B‐type alkaloids. Further transformations involve the formation of a cyclic enaminone, 1,4‐conjugate addition with a cyclopentenyl subunit, and intramolecular aldol cyclization to achieve a pentacyclic intermediate, ultimately forming isodaphlongamine H in a total of 24 steps from the commercially available compound 2‐carbethoxycyclopentanone. Isodaphlongamine H exhibits promising inhibitory activity against a panel of human cancer cell lines.     

Simple Chemical Route Synthesis of Fe2O3 Nanoparticles and its Application for Adsorptive Removal of Congo Red from Aqueous Media: Artificial Neural Network Modeling

Nanocrystalline Fe₂O₃ powder was synthesized by a simple chemical route involving FeCl₃ and NaOH. The Fe₂O₃ powder thus prepared was characterized using x-ray diffraction study, scanning electron microscopy, and Fourier transform infrared spectroscopy. The adsorption properties of crystalline Fe₂O₃ powder have been investigated with an aim to explore a possible low cost and efficient way to remove Congo red (CR) from waste water. Fe₂O₃ powder was found as an excellent adsorbent for CR from aqueous medium. Adsorption capacity as much as 203.66 mg g^?1 is reported at room temperature. Effect of different experimental parameters such as reaction pH, initial CR dye concentration, adsorbent dose, and reaction temperature were studied on adsorption capacity of Fe₂O₃ powder and modeled by artificial neural network (ANN). Optimal ANN structure (4–5–1) shows minimum mean squared error (MSE) of 0.00235 and determination coefficient (R²) of 0.991 with Levenberg–Marquardt algorithm. Isotherm analysis of experimental data exhibited better fit to the Langmuir isotherm. The adsorption process was found to follow second-order kinetics as depicted by the analysis of experimental results. Thermodynamic study shows that the adsorption process is endothermic, spontaneous, and thermodynamically favorable in the temperature range of 27°C to 60°C.     

Differential-pulse anodic-stripping voltammetric determination of traces of lead in high-purity copper after its separation by ion exchange

Trace amounts of lead in copper can be determined by differential-pulse anodic-stripping voltammetry after separating it from the matrix. Lead was quantitatively retained on a small Dowex 1-X4 ion-exchange column, without retaining copper when present as a copper-amine complex in solutions containing 0.2 M sodium hydroxide. Subsequent desorption was done with 2 M nitric acid. After deposition for 1 min on a hanging mercury drop electrode and subsequent stripping, the limit of detection was 2 ng ml^?1 and the limit of quantification was 6.6 ng ml^?1. Recoveries of lead were checked by standard addition to copper solution.     

Synthesis, structure and properties of delocalized transition metal chelates: Diazoketiminato chelates of Co(III) and Pt(II)

The reactions of HL 1 [where HL is 1N-(2-pyridyl-2-methyl)-2-arylazoaniline and is formulated as ArN = NC₆H₄N(H)(CH₂C₅H₄N); Ar = C₆H₅ (for HL¹) or p-MeC₆H₄ (for HL²) or p-ClC₆H₄ (for HL³)] with K₂PtCl₄ and Co(ClO₄)₃ · 6H₂O afforded the (L)PtCl and [(L)₂Co]ClO₄ complexes, respectively. The HL ligands bind the platinum(II) and cobalt(III) centres in a tridentate (N,N,N) fashion, forming new diazoketiminato chelates upon dissociating the amino proton. The X-ray structures of (L³)PtCl and [(L³)₂Co]ClO₄ were determined. Redox properties of the new complexes have been examined.     

A new chelating resin containing 2-aminothiophenol: Synthesis characterization and determination of mercury in waste water using <Superscript>203</Superscript>Hg radiotracer

A new stable chelating resin was synthesized by incorporating 2-aminothiophenol into Merrifield polymer through C-N covalent bond and characterized by elemental analysis, IR and thermal study. The sorption capacity of the newly formed resin for Hg²⁺ as a function of pH has been studied using ²⁰³Hg radioisotope. The resin exhibits no affinity to alkali or alkaline earth metal ions and common anions. The separation of mercury(II) in presence of different alkali and alkaline earth metal ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺), common anions (ClO₄ ⁻, SO₄ ²⁻) and other diverse ions (Ag⁺, Cu²⁺, Pb²⁺, Fe³⁺, Ni²⁺ and Zn²⁺) has been checked. In column operation it has been observed that Hg²⁺ content of the waste water can be removed at usual pH of natural water. Mercury was determined by isotope dilution method and the concentration of Hg²⁺ in the waste water spiked with ²⁰³Hg was found to be 0.05 to 0.09 μg/ml.     

Digestion of titanium bearing geologic materials involving microwaves

An environmentally friendly and rapid digestion procedure involving 10 mL of acid mixture (HNO3 : HCl : HF = 2:2:1) for 0.1 g of sample in closed vessel microwave digester following heating program : 250W for 10 min., hold time 2 min., 600 W for 17 min, and Ventilation time 10 min was developed. The operating parameters were varied and optimized by factorial design approach using "Steepest Ascent" method. The validity of the recommended digestion procedure were examined by analyzing several well characterized standard reference materials such as diabase (W2), basalt (BIR-1, JB-3, BHVO-1), granite (G2), gabbro (JGb-1), Mn-nodule (Nod-A-1, Nod-P-1), sediment (STSD-4, LKSD-2), limestone (KH-2), soil (SAu-1), ilmenite (IGS-31), rutile (IGS-32), Zircon (IGS-35) and titanium dioxide (SRM-154b) employing both inductively coupled plasma-atomic emission spectrometry (ICP-AES) and well known spectrophotometric method. An excellent agreement between the methods and the certified values of standard reference materials suggest that the digestion procedure can be used for quality control and allied purposes.