Sequences in dendrons and dendrimers

Sequential incorporation of a variety of functional groups forms the basis for specificity in biomacromolecules. Introduction of such diversity and sequencing ability in artificial macromolecules is fundamentally interesting. In this paper, three different synthetic approaches have been used to build dendrons and dendrimers in which all the monomer units are different from each other. The synthetic strategies described in this paper involve the use of (i) an ABB(p) monomer, (ii) an ABB' monomer, and (iii) an ABB(m) monomer. The complementarity and the versatility of these synthetic approaches should render them useful for a variety of applications.     

Lanthanum ion–impregnated granular activated carbon for the removal of phenol from aqueous solution: Equilibrium and kinetic study

The current study discusses application of the lanthanum ions (La³⁺) as an activating agent incorporated /immobilized into coconut shell–based granular activated carbon (GAC) for porosity development; subsequently, the carbon material is used for the adsorption of phenol from aqueous solutions. The new carbons were characterized using FTIR, XRD, CHNO, burn off, and carbon yield. The surface functional groups were determined by Boehm titration. The Brunauer–Emmett–Teller (BET) surface area of the carbons is 953 m² g⁻¹ (GACLa1073), 997 m² g⁻¹ (GAC383), and 973 m² g⁻¹ (GACO383). Langmuir, Freundlich, Dubinin–Radushkevich, and John–Sivanandan Achari (J-SA) isotherm models on the equilibrium isotherm data were examined for the new carbon-phenol system. It is found that the Langmuir isotherm fits better with a monolayer adsorption capacity, highest for GACLa1073 (387.59 mg g⁻¹) followed by GAC383 (303.03 mg g⁻¹) and GACO383 (197.62 mg g⁻¹). Kinetic studies reveal that the adsorption system follows the pseudo–second-order kinetic model. Isotherm analysis by the phase change method of John-Sivanandan Achari (J-SA) isotherm gives a better insight into adsorption phenomena, which is accompanied by regeneration studies of carbon with >75% for GACLa1073 after three cycles.     

Functional group diversity in dendrimers

[structure: see text] A methodology for synthesizing dendrons with different peripheral functionalities is described. The benzyl ether-based dendrons reported here were synthesized using allyl and methoxymethyl ether-based protection-deprotection strategies.     

Synthesis and characterization of soluble low‐bandgap oligothiophene‐[all]‐S,S‐dioxides‐based conjugated oligomers and polymers

The synthesis and characterization of a new family of soluble oligothiophene‐S,S‐dioxides and their use as building blocks to form polythiophene‐S,S‐dioxides via microwave‐assisted Stille coupling polymerization are described. Incorporation of the sulfone group into the polythiophene backbone leads to narrowing of the polymer bandgap, and while the energies of both Frontier orbitals in polythiophene‐S,S‐dioxide are lower with respect to polythiophenes, this tendency is considerably stronger for the lowest unoccupied molecular orbital than for the highest occupied molecular orbital, resulting in greater electron‐accepting ability. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis,solid‐state,and charge‐transport properties of conjugated polythiophene‐S,S‐dioxides

An alkylated semiconducting polymer comprising alternating bithiophene‐[all]‐S,S‐dioxide and aromatic monothiophene units in the polymer backbone was synthesized with the intent of modifying the energy gap and lowest unoccupied molecular orbital for use as a stable n‐type semiconductor. Films spun from this semiconducting polymer were characterized utilizing X‐ray scattering, near edge X‐ray absorption fine structure spectroscopy, ultraviolet photoelectron spectroscopy, and thin‐film field effect transistors to determine how oxidation of the thiophene ring systems impacts the structural and electronic properties of the polymer. The thiophene‐S,S‐dioxide polymers have lower optical and electrical band gaps than corresponding thiophene polymers. X‐ray scattering results indicate that the polymers are well ordered with the π–π stacking distances increased by 0.4 Å relative to analogous thiophene polymers. The electrical stability of these polymers is poor in transistors with a drop in the field effect mobility by approximately one order of magnitude upon addition of just 5% of the thiophene‐S,S‐dioxide unit in a copolymer with thiophene. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

PdNi-decorated manganite nanocatalyst for electrooxidation of ethylene glycol in alkaline media

PdNi bimetallic nanoparticles coated onto manganite (MN) nanocatalyst was used for ethylene glycol (EG) and glycerol (Gly) electrooxidation in alkaline media. The MN nanorods were prepared by hydrothermal method, and the PdNi was coated on the rods by an in situ reduction method. The prepared nanocomposite was characterized by scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM), Energy dispersive X-ray spectroscopy (EDS), and electrochemical methods. The SEM and TEM images exhibit the formation of nanorods of 10?nm and also show the formation of nanocrystalline PdNi on the walls of the MN nanorods. This study shows that the MN nanorods can be excellent support material and they supply oxygen to the catalyst, by which the catalytic activity is enhanced. The electrooxidation reactions in strong alkaline condition containing various concentrations of EG have been studied. Among the different concentrations, 9?M KOH/6?M EG exhibits the highest activity. PdNi/MN nanocatalyst exhibits better activity even in higher electrolytic concentrations of EG and alkali.     

Coulometric estimation of ferrocyanides

Summary The utility of controlled potential coulometry for the accurate estimation of ferrocyanides has been established. The method is accurate and rapid and in both these aspects it compares favourably with other methods of estimation. The details for coulometric method have been worked out and the extent of interference of other radicals like chloride has been investigated.     

Synthesis of dendrimers with multifunctional periphery using an ABB' monomer

A new methodology using an ABB' monomer for synthesizing dendrons with multiple functionalities in the periphery is described.     

Probing every layer in dendrons

Dendrons with a fluorescent probe in a specific location have been synthesized and characterized. Accessibility of guest molecules to each of these layers was then analyzed using an intermolecular photoinduced electron-transfer process. Comparisons of the accessibility among each layer of the dendron and among the generations are provided.     

Multi-element substituted hydroxyapatites: synthesis,structural characteristics and evaluation of their bioactivity,cell viability,and antibacterial activity

Synthesis of unsubstituted and multi-element (magnesium, zinc and cobalt) substituted hydroxyapatites (HAP) with varying stoichiometric compositions and evaluation of their morphological and structural characteristics, degree of crystallinity, bioactivity, cytotoxicity and antibacterial activity are addressed. The morphological features are not altered much following the substitution of Mg²⁺, Zn²⁺, and Co²⁺ in the HAP lattice. Nevertheless, their substitution exerts a strong influence on the structural characteristics HAP. Rietveld refinement analysis of the X-ray diffraction patterns indicates a decrease in crystallinity and mineralogical composition of HAP phase, which is accompanied with an increase of β-tricalcium phosphate (β-TCP) phase along with Co₃O₄ phase. Broadening of the PO₄^3? peaks and a decrease in intensity of the OH^? peak are observed by Fourier-transform infrared spectra. A decrease in intensity, broadening and a slight shift in Raman band (at 961?cm^?1 for HAP) towards the lower side suggest the incorporation of Mg, Zn, and Co, disordering of the crystal structure of HAP and formation of β-TCP as additional phase besides HAP. The MgZnCo-HAP’s exhibits a better bioactivity, cell viability and anti-bacterial activity than the unsubstituted HAP. However, a decrease in cell viability and anti-bacterial activity are observed when the stoichiometric ratio of the substituent elements is relatively higher.

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