Studies on optical absorption and structural properties of Fe doped CdS quantum dots

Fe doped CdS quantum dots have been prepared using simple precursors by chemical precipitation technique. Fe doped CdS quantum dots have been synthesized by mixing cadmium nitrate, sodium sulfide and adding Fe under suitable conditions. X-ray diffraction analysis reveals that undoped and Fe doped CdS crystallizes in hexagonal structure. The lattice constants of Fe doped CdS nanoparticles decreased slightly with incorporation of Fe and no secondary phase was observed. The average grain size of the nanoparticles is found to lie in the range of 2.8–4.2 nm. HRTEM results show that undoped and 3.75% Fe doped CdS nanoparticles exhibit a uniform size distribution and average size of the nanoparticles is about 2–3 nm. Raman spectra show that 1LO and 2LO peaks of the Fe doped CdS samples are slightly red shifted compared with those of undoped CdS. Optical absorption spectra of Fe doped CdS nanoparticles exhibited red shift.     

Synthesis,characterization, and heterogeneous catalysis of polymer‐supported poly(propyleneimine) dendrimer stabilized gold nanoparticle catalyst

We report here, the synthesis of two types of heterogeneous nanoparticle catalysts viz., polymer‐supported poly(propyleneimine)‐G2 dendrimer stabilized gold nanoparticle catalysts using crosslinked poly(4‐vinylpyridine) matrix (PSP4VP) as support material. The grafting of dendrimer on the surface of P4VP beads was characterized by FTIR spectrophotometer and CHN analyses. The immobilization of AuNPs was characterized by UV‐Vis spectrum, SEM, and HRTEM studies. The resultant polymer‐supported dendrimer stabilized AuNPs were used as a heterogeneous catalyst for the reduction of 4‐nitrophenol. The catalytic activity is found to be excellent and it can also be reused many times by simple filtration and activity remains maintained. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2525–2532, 2010     

What does pressure decide to cook with orientationally disordered plastic phase of cubane: an orientational glass or crystal?

The effect of pressure on the structure and reorientational motion of molecules in orientationally disordered (OD) crystalline phase of cubane has been investigated in detail using variable shape molecular simulations in constant-pressure constant-temperature ensemble. Complete orientational ordering occurs at a pressure of 1.0 GPa and the OD phase transforms to an orientationally ordered phase at this pressure. The transition is associated with a kink in the variation of structural parameters such as cell parameters, unit-cell volume, and interaction energy. This transition is also associated with an anomaly in specific heat. Above this transition pressure, the structural quantities display only smaller changes with further increase in pressure. The structure of high-pressure orientationally ordered (HPOO) phase has been characterized using radial distribution functions and orientational distribution function. From detailed analysis of the structure of HPOO phase we conclude that it is isostructural with low-temperature orientationally ordered phase. The OD phase has four times larger compressibility than the HPOO phase.     

Pressure induced orientational ordering in p-terphenyl

Three different interaction potentials existing in the literature along with a model proposed here have been used to model p-terphenyl under standard conditions. Of these, the model that predicts the room-temperature crystal structure well has been used to understand the behavior of p-terphenyl under pressure. Lattice parameters show good agreement with the X-ray diffraction values reported by Puschnig et al. (Puschnig, P.; Heimel, G.; Weinmeier, K.; Resel, R.; Ambrosch-Draxl, C. High Pressure Res. 2002, 22, 105). The nonplanar structure of p-terphenyl transforms to a planar structure with gradual disappearance of disorder associated with ring flipping. We show that the transformation is accompanied by a change in the potential energy profile from W-shaped to a U-shaped form, which is associated with complete planarization between 1.0 and 1.5 GPa. Our results reported here are in excellent agreement with X-ray diffraction results which also suggest the existence of a similar transition as a function of pressure in polyphenyls such as biphenyl and p-hexaphenyl. Interestingly, the amplitude of the torsional motion is largest at an intermediate pressure of 1.0 GPa. This is attributed to the rather flat potential energy landscape which occurs during the transition from W- to U-shaped potential.     

Preparation of nitropyridines by nitration of pyridines with nitric acid

Nitration of pyridines 1a-o with nitric acid in trifluoroacetic anhydride, gave the corresponding 3-nitropyridines 6a-n in yields of 10-83%.     

Raman and infrared spectra and normal vibrations of N-methylpropionamide and N-deuterated N-methyl propionamide

Raman and infrared spectra of N-methyl-propionamide and N-deuterated N-methyl-propionamide were recorded in various states of aggregation—pure amide, in solution and vapour state—and the frequency changes of the functional groups were studied. The implane skeletal vibrations of N-methyl-propionamide and its deuterated compound were calculated treating these molecules as six-body problems. The distribution of potential energy of each normal mode among various symmetry co-ordinates was calculated and the nature of the amide I, II and III bands and the mixing up of the inplane vibrational frequencies of N-methyl-propionamide and the deuterated amide are discussed on a quantitative basis.     

Associative Pattern Recognition Through Macro-molecular Self-Assembly

Journal of Statistical Physics - We show that macro-molecular self-assembly can recognize and classify high-dimensional patterns in the concentrations of N distinct molecular species. Similar to...