Bulusu Jagannadh

A Glycerol‐based Carbon Catalyst for the Preparation of Biodiesel

Biodiesels are alternative fuels that comprise methyl esters of long-chain fatty acids derived from vegetable oils and animal fats. The preparation of biodiesels from high-quality oils, such as sunflower, soybean, and rape seed oil, is technologically uncomplicated, as the process only involves transesterification. The main challenge for biodiesel technology is the handling of oils that contain high levels of free fatty acids (FFAs), such as jatropha oil, karanja oil, and animal fats, which involves both esterification and transesterification. The economic feasibility of biodiesels mainly concerns the development of green solid catalysts for high-FFA oils, in order to avoid mineralacid catalysts such as sulfuric acid for the esterification of FFA, and the efficient utilization of the major byproducts, such as oilseed cakes and glycerol. The rapid growth of the biodiesel industry has resulted in an oversupply of glycerol, which has become a burden until new markets are created for glycerol by the development of new products. 11] Here, we disclose the synthesis and performance of a glycerol-based heterogeneous “green” catalyst for the preparation of biodiesel from fatty acids. Huge amounts of sulfuric acid are consumed world-wide because of its use as homogeneous catalyst for the production of industrially important chemicals. Sulphuric-acid-based processes involve high energy consumption, a difficult separation of the catalyst from the homogenous reaction mixtures, and are expensive as well as chemically wasteful. Recyclable heterogeneous solid-acid catalysts have gained attention as replacement for liquid-acid catalysts such as sulfuric acid. The use of heterogeneous catalysts offers several intrinsic advantages over their homogeneous counterparts, such as ease of product separation and reusability. However, to maintain economic viability heterogeneous catalysts should exhibit activities and selectivities comparable to, or superior to, existing homogeneous catalysts. A catalyst for the esterification reaction is termed effective if it can provide a higher number of strong acid sites that can withstand deactivation by water produced during the reaction. Although a considerable volume of literature exists on the esterification of simple aliphatic and aromatic acids using various solid-acid catalysts, such as resins, zeolites, heteropoly acids, super acids, and niobium acid, only a few reports have described the esterification of fatty acids. These catalysts have low densities of effective acid sites and, thus, cannot achieve adequate performances in acid-catalyzed reactions in the presence of water. Hence, there is a need to synthesize reusable, inexpensive, and water-tolerant solid-acid catalysts with strong active sites by employing simple preparation protocols; without showing leaching into the reaction medium; and without any change in their structure after reaction. To overcome some of the above problems, typical carbonbased solid-acid catalysts have been prepared from aromatic hydrocarbons such as benzene, naphthalene, anthracene, perylene, and coronene by heating the substrate in concentrated sulfuric acid for 15 h at 523 K; the resultant catalyst being used for ethyl acetate formation. The catalysts, however, had several drawbacks such as softness, leaching of aromatic molecules during liquid-phase reactions above 100 8C, and rapid loss of catalytic activity. Another class of carbon catalysts, resulting from the incomplete carbonization of natural products such as sugar, starch, or cellulose, followed by sulfonation, has also been reported. Even though these catalysts were employed for the esterification of fatty acids, their preparation was very tedious, involving heating of the substrate to 400 8C for 15 h followed by sulfonation with large volumes of concentrated sulfuric acid (1:20 wt/vol) at 150 8C for 15 h. In the present Communication we report the synthesis of a carbon catalyst with a high density of sulfonic acid groups ACHTUNGTRENNUNG( SO3H) that is based on the relatively cheap raw material glycerol, which is obtained as a byproduct in biodiesel processing (Figure 1), and project its utility as an efficient solid-acid catalyst from its esterification activity and reusability. The glycerolbased carbon catalyst was obtained by in situ partial carbonization and sulfonation of glycerol with sulfuric acid, in a ratio of 1:4 (wt/wt) in a single-pot reaction within 40 min. The yield

LiBF4-catalyzed formation of fused pyrano- and furanobenzopyrans

Lithium tetrafluoroborate efficiently catalyzes an unusual cyclization of o-hydroxybenzaldimines with 2,3-dihydrofuran and 3,4-dihydro-2H-pyran at ambient temperature to afford a class of new pyrano- and furanobenzopyran derivatives in excellent yields with high diastereoselectivity.

Self-assembly of cyclic homo- and hetero-β-peptides with cis- furanoid sugar amino acid and β-hGly as building blocks

The design, synthesis and characterization of a new class of peptide nanotubes, self-assembled from cyclic homo- and hetero-β-peptides based on cis-furanoid sugar amino acid and β-hGly residues are described; these results represent the expansion of the conformational pool of cis β-sugar amino acids in the design of peptide nanotubes.

Formation of left-handed helices in hybrid peptide oligomers with cis β-sugar amino acid and L-Ala as building blocks

Residue based control of specific helical folding is explored in hybrid peptide oligomers consisting of alternating L-Ala and cis-beta-furanoid sugar amino acid (FSAA) residues as building blocks; two series of these hybrid oligomers are designed, synthesized and extensively characterized by using NMR, CD, FT-IR and MD simulation studies; results show the co-existence of left-handed 11- and 14/15-helical conformations in these short oligomers of Boc-(alpha/beta) and Boc-(beta/alpha) series.

Sc(OTf)3-catalyzed synthesis of pyrano[3,2-b]-1-benzopyrans from D-glycals

Glycals react smoothly with o-hydroxybenzaldehydes and trimethyl orthoformate in the presence of a catalytic amount of scandium triflate under mild reaction conditions to afford the corresponding cis-annelated pyranobenzopyrans in good yields with high diastereoselectivity.

4-N-pyridin-2-yl-benzamide nanotubes compatible with mouse stem cell and oral delivery in Drosophila

p-aminobenzoic acid (PABA), a structural moiety of many commercial drugs, is self-assembled with linker alkyl side chains to form tubular nanostructures. The tubes exhibited fluorescence either intrinsic or from fluorescent molecules embedded in the wall during self-assembly. Uptake and inter-cellular delivery of the conjugated nanotubes in human cancer cells and in mouse embryonic stem cells were demonstrated by fluorescence imaging and flow cytometry. Biocompatibility, cytotoxicity and clearance were monitored both ex vivo in mouse multipotent embryonic stem cells and in vivo in adult Drosophila. Accumulation of nanotubes had no adverse effects and abnormalities on stem cell morphology and proliferation rate. A distinct distribution of two separate nanotubes in various internal organs of Drosophila interprets that accumulation of nanomaterials might be interdependent on the side chain modifications and physiological settings of cell or tissue types. Unlike carbon nanomaterials, exposure of PABA nanotubes does not produce any hazards including locomotion defects and mortality of adult flies. Despite differential uptake and clearance from multiple live tissues, the use of self-assembled nanotubes can add new dimensions and scope to the development of dual-purpose oral carriers for the fulfilment of many biological promises.

Highly efficient synthesis of 3-alkyl/aryl-4-aryl-1,2,3,4-tetrahydroisoquinolines from N,N-dibenzylaminols

Abstract Substituted tetrahydroisoquinolines are synthesized in optically pure form using a Grignard reaction of N , N -dibenzyl aminol and Friedel–Crafts cyclization as the key steps.

Sub-cellular internalization and organ specific oral delivery of PABA nanoparticles by side chain variation

BackgroundOrganic nanomaterials having specific biological properties play important roles in in vivo delivery and clearance from the live cells. To develop orally deliverable nanomaterials for different biological applications, we have synthesized several fluorescently labelled, self-assembled PABA nanoparticles using possible acid side chain combinations and tested against insect and human cell lines and in vivo animal model. Flurophores attached to nanostructures help in rapid in vivo screening and tracking through complex tissues. The sub-cellular internalization mechanism of the conjugates was determined. A set of physio-chemical parameters of engineered nanoskeletons were also defined that is critical for preferred uptake in multiple organs of live Drosophila.ResultsThe variability of side chains alter size, shape and surface texture of each nanomaterial that lead to differential uptake in human and insect cells and to different internal organs in live Drosophila via energy dependent endocytosis. Our results showed that physical and chemical properties of C-11 and C-16 acid chain are best fitted for delivery to complex organs in Drosophila. However a distinct difference in uptake of same nanoparticle in human and insect cells postulated that different host cell physiology plays a critical role in the uptake mechanism.ConclusionsThe physical and chemical properties of the nanoparticle produced by variation in the acid side chains that modify size and shape of engineered nanostructure and their interplay with host cell physiology might be the major criteria for their differential uptake to different internal organs.

Efficient conformational sampling of multiconformational cyclic molecules: application to 1,4,7,10,13-Pentaoxacyclopentadecane

The result of an exhaustive search of low-energy conformers of 1,4,7,10,13-Pentaoxacyclopentadecane is presented. The search method combines the generation of large number of trial conformers using local nonstochastic deformations known as the Conflex method, which is coupled to AMBER force field as the minimizer. The extent of the conformational space sampled was evaluated from the view point of the number of duplicates of each conformer, generation of inclusion type structures without considering the substrate and the spread of the allowed torsion angles visited during the search. It is shown that the conformational search is exhaustive and efficient as conformers, which the metal coordinated crown ether complexes adopt, were generated. Free energies using the AMBER structures were calculated using the model of Cramer and Truhlar. The study suggests that 1,4,7,10,13-Pentaoxacyclopentadecane exists as a mixture of conformers in solution. The results show the efficiency of the method and could be the method of choice in the design of synthetic macrocyclic receptors.

Synthesis and cellular uptake of cell delivering 2,6-pyridinediylbisalkanamide submicron-sized sheets in HeLa cells

2,6-Pyridinediylbisalkanamides were synthesized, using diaminopyridine (DAP) as a linker and alkyl chains of varying lengths, that upon self-assembly form submicron-sized sheets and their uptake into the cytoplasm of HeLa cells was studied by confocal microscopy.