The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

Interest in catalysis by metal nanoparticles (NPs) is increasing dramatically, as reflected by the large number of publications in the last five years. This field, "semi-heterogeneous catalysis", is at the frontier between homogeneous and heterogeneous catalysis, and progress has been made in the efficiency and selectivity of reactions and recovery and recyclability of the catalytic materials. Usually NP catalysts are prepared from a metal salt, a reducing agent, and a stabilizer and are supported on an oxide, charcoal, or a zeolite. Besides the polymers and oxides that used to be employed as standard, innovative stabilizers, media, and supports have appeared, such as dendrimers, specific ligands, ionic liquids, surfactants, membranes, carbon nanotubes, and a variety of oxides. Ligand-free procedures have provided remarkable results with extremely low metal loading. The Review presents the recent developments and the use of NP catalysis in organic synthesis, for example, in hydrogenation and C--C coupling reactions, and the heterogeneous oxidation of CO on gold NPs.

Nanoparticles as Recyclable Catalysts: The Frontier between Homogeneous and Heterogeneous Catalysis

While the nanocatalysis field has undergone an explosive growth during the past decade, there have been very few studies in the area of shape-dependent catalysis and the effect of the catalytic process on the shape and size of transition metal nanoparticles as well as their recycling potential. Metal nanoparticles of different shapes have different crystallographic facets and have different fraction of surface atoms on their corners and edges, which makes it interesting to study the effect of metal nanoparticle shape on the catalytic activity of various organic and inorganic reactions. Transition metal nanoparticles are attractive to use as catalysts due to their high surface-to-volume ratio compared to bulk catalytic materials, but their surface atoms could be so active that changes in the size and shape of the nanoparticles could occur during the course of their catalytic function, which could also affect their recycling potential. In this Feature Article, we review our work on the effect of the shape of the colloidal nanocatalyst on the catalytic activity as well as the effect of the catalytic process on the shape and size of the colloidal transition metal nanocatalysts and their recycling potential. These studies provide important clues on the mechanism of the reactions we studied and also can be very useful in the process of designing better catalysts in the future.

Catalysis with transition metal nanoparticles in colloidal solution: nanoparticle shape dependence and stability.

Pd catalysis of C-C bond formations is briefly reviewed from the angle of nanoparticles (NPs) whether they are homogeneous or heterogeneous precatalysts and whether they are intentionally preformed or generated from a Pd derivative such as Pd(OAc)2. The most studied reaction is the Heck coupling of halogenoarenes with olefins that usually proceeds at high temperature (120-160 degrees C). Under such conditions, the PdII precursor is reduced to Pd0, forming PdNPs from which Pd atom leaching, subsequent to oxidative addition of the aryl halide onto the PdNP surface, is the source of very active molecular catalysts. Other C-C coupling reactions (Suzuki, Sonogashira, Stille, Negishi, Hiyama, Corriu-Kumada, Ullmann, and Tsuji-Trost) can also be catalyzed by species produced from preformed PdNPs. For catalysis of these reactions, leaching of active Pd atoms from the PdNPs may also provide a viable molecular mechanistic scheme. Thus, the term "PdNP catalysis of C-C coupling" used in this review refers to this function of PdNPs as precursors of catalytically active Pd species (i.e., the PdNPs are precatalysts of C-C coupling reactions).

Palladium nanoparticles as efficient green homogeneous and heterogeneous carbon-carbon coupling precatalysts: a unifying view.

Heterogeneous catalysis on chitosan-based materials: a review

Chitosan-stabilized Pt (chi-Pt) or Pd (chi-Pd) colloidal nanoparticles catalyst prepared with various chitosan–metal molar ratios and reducing agents were characterized. Chitosan could stabilize Pt and Pd with minimum chitosan:M ratio of 5:1 and 2:1 respectively. The finest and well-dispersed particles of chi-Pt or chi-Pd were obtained when methanol or NaBH 4 were used as the reducing agents. Chi-Pt and chi-Pd reduced by hydrazine gave aggregated particles in all chitosan molar ratios. Chitosan could control particle size of Pt or Pd to within 1.9–2.2 nm when CH 3 OH or NaBH 4 was used as the reducing agents. Palladium or Platinum catalysis on cyclooctene hydrogenation gave cyclooctane. Hydrogenation of octene catalyzed by chi-Pd gave octane, 2-octene and 3-octene while chi-Pt prepared by methanol reduction showed 99.99% selectivity and conversion to octane. The catalytic activity of chi-Pt was higher than chi-Pd for both the hydrogenations.

Synthesis of chitosan-stabilized platinum and palladium nanoparticles and their hydrogenation activity

Metabolomic studies on obesity and type 2 diabetes mellitus have led to a number of mechanistic insights into biomarker discovery and comprehension of disease progression at metabolic levels. This article reviews a series of metabolomic studies carried out in previous and recent years on obesity and type 2 diabetes, which have shown potential metabolic biomarkers for further evaluation of the diseases. Literature including journals and books from Web of Science, Pubmed and related databases reporting on the metabolomics in these particular disorders are reviewed. We herein discuss the potential of reported metabolic biomarkers for a novel understanding of disease processes. These biomarkers include fatty acids, TCA cycle intermediates, carbohydrates, amino acids, choline and bile acids. The biological activities and aetiological pathways of metabolites of interest in driving these intricate processes are explained. The data from various publications supported metabolomics as an effective strategy in the identification of novel biomarkers for obesity and type 2 diabetes. Accelerating interest in the perspective of metabolomics to complement other fields in systems biology towards the in-depth understanding of the molecular mechanisms underlying the diseases is also well appreciated. In conclusion, metabolomics can be used as one of the alternative approaches in biomarker discovery and the novel understanding of pathophysiological mechanisms in obesity and type 2 diabetes. It can be foreseen that there will be an increasing research interest to combine metabolomics with other omics platforms towards the establishment of detailed mechanistic evidence associated with the disease processes.

Metabolomics – the complementary field in systems biology: a review on obesity and type 2 diabetes

Insulin resistance is characterized by hyperglycaemia, dyslipidaemia and oxidative stress prior to the development of type 2 diabetes mellitus. To date, a number of mechanisms have been proposed to link these syndromes together, but it remains unclear what the unifying condition that triggered these events in the progression of this metabolic disease. There have been a steady accumulation of data in numerous experimental studies showing the strong correlations between mitochondrial dysfunction, oxidative stress and insulin resistance. In addition, a growing number of studies suggest that the raised plasma free fatty acid level induced insulin resistance with the significant alteration of oxidative metabolism in various target tissues such as skeletal muscle, liver and adipose tissue. In this review, we herein propose the idea of long chain fatty acid-induced mitochondrial dysfunctions as one of the key events in the pathophysiological development of insulin resistance and type 2 diabetes. The accumulation of reactive oxygen species, lipotoxicity, inflammation-induced endoplasmic reticulum stress and alterations of mitochondrial gene subset expressions are the most detrimental that lead to the developments of aberrant intracellular insulin signalling activity in a number of peripheral tissues, thereby leading to insulin resistance and type 2 diabetes.

Mitochondrial dysfunction as a central event for mechanisms underlying insulin resistance: the roles of long chain fatty acids

A structural study of epoxidized natural rubber (ENR-50) and its cyclic dithiocarbonate derivative was carried out using NMR spectroscopy techniques. The overlapping (1)H-NMR signals of ENR-50 at δ 1.56, 1.68-1.70, 2.06, 2.15-2.17 ppm were successfully assigned. In this work, the C=S and quaternary carbon of cyclic dithiocarbonate. All other (1)H- and (13)C-NMR chemical shifts of the derivative remain unchanged with respect to the ENR-50.

https://www.mdpi.com/1420-3049/17/9/10974/pdf

A Structural Study of Epoxidized Natural Rubber (ENR-50) and Its Cyclic Dithiocarbonate Derivative Using NMR Spectroscopy Techniques

Hydroxyapatite (HA) is a desirable implant material due to its biocompatibility and osteoconductive properties. In this paper, we report a simple and economical approach to produce pure nanoporous HA using a hydroxyapatite-chitosan (HA-CS) template. The removal of chitosan through calcination leads to HA containing nanosize pores. Surface morphology analysis performed on both uncalcined and calcined HA-CS revealed disordered but interconnected pores. The removal of chitosan also resulted in a more even distribution of HA nanoparticles and a higher surface area. Both X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analyses confirmed that the obtained material consisted of primarily highly crystalline noncarbonated hydroxyapatite.

/pdf/synthesis-and-characterisation-of-pure-nanoporous-3sosd2hr2k.pdf

Mohamad Hafizi Abu Bakar

Papers

Synthesis of chitosan-stabilized platinum and palladium nanoparticles and their hydrogenation activity

Metabolomics – the complementary field in systems biology: a review on obesity and type 2 diabetes

Mitochondrial dysfunction as a central event for mechanisms underlying insulin resistance: the roles of long chain fatty acids

A Structural Study of Epoxidized Natural Rubber (ENR-50) and Its Cyclic Dithiocarbonate Derivative Using NMR Spectroscopy Techniques

Synthesis and Characterisation of Pure Nanoporous Hydroxyapatite