Thioacylation reactions for the surface functionalization of phosphorus-containing dendrimers

The functionalization of phosphorus-containing dendrimers was easily achieved through thioacylation reactions involving new dendrimers capped with dithioester end groups and various functionalized amines. These reactions were successfully applied to the first generation (12 end groups) and the third generation of the dendrimer (48 end groups) and allowed their functionalization by various primary or secondary amines, alcohols, glycols, and azides. [reaction: see text]     

Assessing internal structure of polymer assemblies from 2D to 3D CryoTEM: Bicontinuous micelles

The self-assembly behaviour of block copolymers in solution has been of significant interest over the past two decades for a number of applications — for example, as delivery vectors and micro-reactors. More recently, attention has turned to the formation of aggregates with complex internal structure, such as multi-compartment micelles and the so-called “Janus” particles (biphasic aggregates) for their promising application as vectors for the simultaneous inclusion of chemically-different encapsulates and their possible catalytic and templating properties. The challenge has been to observe these complex aggregates in such a way as to be able to characterise their internal morphology whilst preserving their intricate structure. To this end, cryogenic transmission electron microscopy (cryoTEM) has become a powerful and indeed a necessary tool for the elucidation and observation of self-assembled polymer systems. Through its use, a new class of complex micelles has been discovered: amphiphilic block copolymer nanospheres with internal bicontinuous structure. These structures have been observed from a variety of block copolymer amphiphiles, although rarely. Intriguingly, there is no seemingly obvious unifying blueprint for their formation. This review will present the importance of cryoTEM in the elucidation and characterisation of internally-structured polymeric aggregates in recent years and highlight its significance in the definition of bicontinuous dispersions.     

Theoretical study of the CO catalytic oxidation on Au/SAPO‐11 zeolite

Quantum chemistry calculations were carried out, using ONIOM2 methodology, to investigate the CO adsorption and oxidation on gold supported on Silicoaluminophospates (SAPO) molecular sieves Au/SAPO‐11 catalysts. Two models were studied, one containing one Au atom per site (Au? SAPO‐11), and the other with two Au atoms per site (Au₂? SAPO‐11). The results reveal that the CO adsorption and oxidation are exothermic on Au/SAPO11 with an ΔE of ?41.0 kcal/mol and ΔE = ?52.0 kcal/mol, for the adsorption and oxidation, respectively. On the Au₂? SAPO‐11 model, the CO adsorption and oxidation reaction occur, with a ΔE of ?29.7 kcal/mol and ?52 kcal/mol, respectively. According to our results, the oxidation reaction exhibits an Eley‐Rideal type mechanism with adsorbed CO. The theoretical calculations reveal that this type of material could be interesting to disperse Au and consequently to strengthen its catalytic use for different reactions. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2573–2582, 2010     

Spectral Investigations of Solvatochromism and Preferential Solvation on 1,4-Dihydroxy-2,3-Dimethyl-9,10-Anthraquinone

Solvatochromic and preferential solvation of 1,4-dihydroxy-2,3-dimethyl-9,10-anthraquinone (DHDMAQ) have been investigated using optical absorption and fluorescence emission techniques. Optical absorption spectra of DHDMAQ in different solvents show the intra molecular charge transfer band in the region 400–550nm. The observed blue shift with solvent polarity indicates the delocalisation of the excited state, owing to reduction in quasiaromaticity of the chelate rings formed by intra molecular hydrogen bonds, due to electrostatic or hydrogen bonding interaction. This is also confirmed by the observed low oscillator strength and the transition dipole moment. The observed quantum yield of DHDMAQ in different solvents is due to the inter molecular hydrogen bond in the excited state in addition to the intra molecular hydrogen bond. It also reveals from the low oscillator strength, which indicates that the radiative decay is low. Excited state dipole moment of DHDMAQ is calculated by solvatochromic data and it shows a lower value than ground state dipole moment. The preferential solvation parameter shows that in dimethyl formamide (DMF) + ethanol mixture, the DHDMAQ is preferentially solvated by ethanol in DMF rich region and by DMF in ethanol rich region. In the case of DMF + dichloromethane mixture DHDMAQ is preferentially solvated by DMF.     

Theoretical study of Au/SAPO-11 catalyst and its potential use in thiophene HDS

Quantum chemistry calculations were carried out, using ONIOM2 methodology, in order to investigate the thiophene interaction with gold supported on silicoaluminophospates molecular sieves (Au/SAPO-11) catalysts. Two models were studied, one containing one Au atom per site, and the other with two Au atoms per site. Thiophene adsorption was found to be η¹ type. This adsorption presents a ΔH of ?13.2 and ?9.7 kcal/mol, for the models with one Au atom (Au/SAPO-11), and two Au atoms (Au₂/SAPO-11), respectively. The partial hydrogenation of the thiophene–Au/SAPO-11 and thiophene–Au₂/SAPO-11 complexes gives 2,5-dihydrothiophene (DHT), with a ΔH of ?23.0 and ?36.8 kcal/mol, respectively. 2-Butene production was found in both models with further hydrogenation. Likewise the direct butadiene elimination is achieved, but only with the separated Au dimer (ΔH = ?17.5 kcal/mol).     

Controlling Internal Pore Sizes in Bicontinuous Polymeric Nanospheres

Complex polymeric nanospheres were formed in water from comb‐like amphiphilic block copolymers. Their internal morphology was determined by three‐dimensional cryo‐electron tomographic analysis. Varying the polymer molecular weight (MW) and the hydrophilic block weight content allowed for fine control over the internal structure. Construction of a partial phase diagram allowed us to determine the criteria for the formation of bicontinuous polymer nanosphere (BPN), namely for copolymers with MW of up to 17 kDa and hydrophilic weight fractions of ≤0.25; and varying the organic solvent to water ratio used in their preparation allowed for control over nanosphere diameters from 70 to 460 nm. Significantly, altering the block copolymer hydrophilic–hydrophobic balance enabled control of the internal pore diameter of the BPNs from 10 to 19 nm.     

Fluorescence Quenching of 1,4-Dihydroxy-2,3-Dimethyl-9,10-Anthraquinone by Silver Nanoparticles: Size Effect

Size effect of silver nano particles on the photophysical properties of 1,4-dihydroxy-2,3-dimethyl-9,10-anthraquinone (DHDMAQ) have been investigated using optical absorption and fluorescence emission techniques. Silver nanoparticles of different sizes have been prepared by Creighton method using magnetic stirrer and ultrasonic field. Quenching of fluorescence of DHDMAQ has been found to increase with decrease in the size of the silver nanoparticles. Stern–Volmer quenching constants have also been calculated.