Single-step, size-controlled synthesis of colloidal silver nanoparticles stabilized by octadecylamine

A single step process for the synthesis of size-controlled silver nanoparticles has been developed using a bifunctional molecule, octadecylamine (ODA). Octadecylamine complexes to Ag+ ions electrostatically, reduce them, and subsequently stabilizes the nanoparticles thus formed. Hence, octadecylamine simultaneously functions as both a reducing and a stabilizing agent. The amine-capped nanoparticles can be obtained in the form of dry powder, which is readily redispersible in aqueous and organic solvents. The particle size, and the nucleation and growth kinetics of silver nanoparticles could be tuned by varying the molar ratio of ODA to AgNO3. The UV-vis spectra of nanoparticles prepared with different concentrations of ODA displayed the well-defined plasmon band with maximum absorption around 425 nm. The formation of silver metallic nanoparticles was confirmed by their XRD pattern. The binding of ODA molecule on the surface of silver has been studied by FT-IR and NMR spectroscopy. The formation of well-dispersed spherical Ag nanoparticles has been confirmed by TEM analysis. The particle size and distribution are found to be dependent on the molar concentration of the amine molecule. Open aperture z-scans have been performed to measure the nonlinearity of Ag nanoparticles. (C) 2015 Published by Elsevier B.V.

Efficient and practical synthesis of modular chiral beta-organochalcogeno amines, ArYCH2CH(R)NH2, and single crystal structures of (S) - MsOCH2CH(Bz)NH3+ center dot Cl- and (R)-MsOCH2CH(Ph)NH3+ center dot Cl-

Modular chiral I3-organochalcogeno amines, ArYCH2CH(R)NH2 (4a-4g) where R = Me, Bz, Ph; and ArY = PhS, BzSe and 4-MeOC6H4Te respectively have been synthesized and characterized. Compounds 4a-4g were synthesized (Method II) from chiral aminoalkyl 13-methanesulfonate hydrochlorides, MsOCH2CH(R)NH3+ center dot Cl- (2a-2c) through nucleophilic displacement of MsO- with organochalcogenolate (ArY-). In another attempt (Method I) chiral beta-organotelluro amines (4a-4c) were prepared by deprotection of chiral N-boc I3-organotelluro amides, 4-MeOC6H4TeCH2CH(R)NH-Boc (3a-3c), which in turn, 13,-,1 were made from chiral N-boc 13-methanesulfonate amides (la-lc) and ArTeNa. 1H, and FTIR spectra of all the compounds (3a-3c and 4a-4g) were characteristic. The composition of 3a-3c was determined by elemental analysis. The a]TD values of 3b-3c and 4a-4g were determined. The single crystal structures of (S)-2b and (R)-2c were determined by X-Ray diffraction studies. Both (S)-2b and (R)2c were crystallized in orthorhombic system and the Flack parameter x was found 0.08(12) and 0.00(2) respectively. The crystal of (S)-2b contain two asymmetric units with gauche (A) and staggered (B) conformations. There are NH Cl-, NH-O and CH-O intra and intermolecular secondary interactions in (S)-2b and (R)-2c resulting in supramolecular structures. (C) 2015 Elsevier By. All rights reserved.

A new synthesis of Entacapone and report on related studies

A new synthesis of the catechol-O-methyltransferase (COMT) inhibitor, entacapone (E-isomer) has been achieved under mild conditions by amine-mediated demethylation of the precursor 2-Cyano-3-(3- hydroxy-4-methoxy-5-nitrophenyl) prop-2-eneamide, wherein the methoxyl group adjacent to a nitro group gets demethylated under nucleophilic attack. Similar demethylation was achieved on ethyl 2-cyano-3-(3, 4-dimethoxy-5-nitrophenyl) prop-2-enoate, 2-cyano-3-(3,4-dimethoxy-5-nitrophenyl)-N,N-diethylprop-2-enamide, ethyl 2-cyano-3-(3-hydroxy-4-methoxy-5-nitrophenyl) prop-2-enoate and ethyl 2-cyano-3-(4-methoxy-3-nitrophenyl) prop-2-enoate. The scope of demethylation has been studied. Analogues of ethyl 2-cyano-3-(3, 4-dimethoxy-5-nitrophenyl) prop-2-enoate wherein a methoxyl group is not adjacent to a NO (2) group are unaffected and phenolic derivatives yield the amine salts. Entacapone has been converted to salts with organic bases. The crystal structure of the isomer of entacapone (Z-isomer), a significant human metabolite of E-isomer has been established. NMR methods for deriving E and Z geometry and other similar molecules have been successfully established, mainly by studying the proton coupled C-13 spectra. Preliminary studies reveal in vitro activity for some compounds against tuberculosis (TB) and dengue.

Molecular Cage Impregnated Palladium Nanoparticles: Efficient, Additive-Free Heterogeneous Catalysts for Cyanation of Aryl Halides

Two shape-persistent covalent cages (CC1(r) and CC2(r)) have been devised from triphenyl amine-based trialdehydes and cyclohexane diamine building blocks utilizing the dynamic imine chemistry followed by imine bond reduction. The cage compounds have been characterized by several spectroscopic techniques which suggest that CC1(r) and CC2(r) are 2+3] and 8+12] self-assembled architectures, respectively. These state-of-the-art molecules have a porous interior and stable aromatic backbone with multiple palladium binding sites to engineer the controlled synthesis and stabilization of ultrafine palladium nanoparticles (PdNPs). As-synthesized cage-embedded PdNPs have been characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and powder X-ray diffraction (PXRD). Inductively coupled plasma optical emission spectrometry reveals that Pd@CC1(r) and Pd@CC2(r) have 40 and 25 wt% palladium loading, respectively. On the basis of TEM analysis, it has been estimated that as small as similar to 1.8 nm PdNPs could be stabilized inside the CC1(r), while larger CC2(r) could stabilize similar to 3.7 nm NPs. In contrast, reduction of palladium salts in the absence of the cages form structure less agglomerates. The well-dispersed cage-embedded NPs exhibit efficient catalytic performance in the cyanation of aryl halides under heterogeneous, additive-free condition. Moreover, these materials have excellent stability and recyclability without any agglomeration of PdNPs after several cycles.

Chitosan Immobilized Porous Polyolefin As Sustainable and Efficient Antibacterial Membranes

Polyolefinic membranes have attracted a great deal of interest owing to their ease of processing and chemical inertness. In this study, porous polyolefin membranes were derived by selectively etching PEO from PE/PEO (polyethylene/poly(ethylene oxide)) blends. The hydrophobic polyolefin (low density polyethylene) was treated with UV-ozone followed by dip coating in chitosan acetate solution to obtain a hydrophilic-antibacterial surface. The chitosan immobilized PE membranes were further characterized by Fourier transform infrared spectroscope (FTIR) and X-ray photoelectron spectroscope (XPS). It was found that surface grafting of chitosan onto PE membranes enhanced the surface roughness and the concentration of nitrogen (or amine) scaled with increasing concentration of chitosan (0.25 to 2% wt/vol), as inferred from Kjeldahl nitrogen analysis. The pure water flux was almost similar for chitosan immobilized PE membranes as compared to membranes without chitosan. The bacterial population, substantially reduced for membranes with higher concentration of chitosan. For instance, 90 and 94% reduction in Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) colony forming unit respectively was observed with 2% wt/vol of chitosan. This study opens new avenues in designing polyolefinic based antibacterial membranes for water purification.

Engineering a multi-biofunctional composite using poly(ethylenimine) decorated graphene oxide for bone tissue regeneration

Toward preparing strong multi-biofunctional materials, poly(ethylenimine) (PEI) conjugated graphene oxide (GO_PEI) was synthesized using poly(acrylic acid) (PAA) as a spacer and incorporated in poly( e-caprolactone) (PCL) at different fractions. GO_PEI significantly promoted the proliferation and formation of focal adhesions in human mesenchymal stem cells (hMSCs) on PCL. GO_PEI was highly potent in inducing stem cell osteogenesis leading to near doubling of alkaline phosphatase expression and mineralization over neat PCL with 5% filler content and was approximate to 50% better than GO. Remarkably, 5% GO_ PEI was as potent as soluble osteoinductive factors. Increased adsorption of osteogenic factors due to the amine and oxygen containing functional groups on GO_ PEI augment stem cell differentiation. GO_ PEI was also highly efficient in imparting bactericidal activity with 85% reduction in counts of E. coli colonies compared to neat PCL at 5% filler content and was more than twice as efficient as GO. This may be attributed to the synergistic effect of the sharp edges of the particles along with the presence of the different chemical moieties. Thus, GO_ PEI based polymer composites can be utilized to prepare bioactive resorbable biomaterials as an alternative to using labile biomolecules for fabricating orthopedic devices for fracture fixation and tissue engineering.

A Deep-Blue Electroluminescent Device Based on a Coumarin Derivative

The design and synthesis is reported of 7-(9H-carbazol-9-yl)-4-methylcoumarin (Cz-Cm), comprising a carbazole donor moiety and a 4-methylcoumarin acceptor unit, for use in a blue organic light-emitting diode. A detailed solid state, theoretical and spectroscopic study was performed to understand the structure-property relationships. The material exhibits deep-blue emission and high photoluminescence quantum yield both in solution and in a doped matrix. A deep-blue electroluminescence emission at 430nm, a maximum brightness of 292cdm(-2) and an external quantum efficiency of 0.4% was achieved with a device configured as follows: ITO/NPD (30nm)/TCTA (20nm)/CzSi(10nm)/10wt% Cz-Cm:DPEPO (10nm)/TPBI (30nm)/LiF (1nm)/Al ITO=indium tin oxide, NPD=N,N-di(1-naphthyl)-N,N-diphenyl-(1,1-biphenyl)-4,4-diamine, TCTA=tris(4-carbazoyl-9-ylphenyl)amine, CzSi=9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole, DPEPO=bis2-(diphenylphosphino)phenyl]ether oxide, TPBI=1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene].

七氟丁酸酐有序超薄膜的制备与结构

在涂敷有聚合物PEI涂层的单晶硅表面上制备了HFBA单层分子膜,接触角测量及XPS结果表明,HFBA在PEI表面产生了化学吸附发生了化学键合(酰胺键),形成了低表面能的HFBA单分子层膜.这一吸附反应的动力学行为可能表现为Langmuir单分子层化学吸附.

Fabrication and bio-functionalization of tetrahedral amorphous carbon thin films for bio sensor applications

Tetrahedral amorphous carbon (ta-C) thin films are a promising material for use as biocompatible interfaces in applications such as in-vivo biosensors. However, the functionalization of ta-C film surface, which is a pre-requisite for biosensors, remains a big challenge due to its chemical inertness. We have investigated the bio-functionalization of ta-C films fabricated under specific physical conditions through the covalent attachment of functional biomolecular probes of peptide nucleic acid (PNA) to ta-C films, and the effect of fabrication conditions on the bio-functionalization. The study showed that the functional bimolecular probes such as protected long-chain ω-unsaturated amine (TFAAD) can be covalently attached to the ta-C surface through a well-defined structure. With the given fabrication process, electrochemical methods can be applied to the detection of biomolecular interaction, which establishes the basis for the development of stable, label-free biosensors. © 2011 Elsevier B.V. All rights reserved.

Role of G protein coupled inwardly rectifier K+ channels (GIRK) on the neurobiology depression

353 págs.

Asymmetric organocatalytic cascade reactions

302 p. : gráf.

Structural requirements for catalysis: studies on RTEM-1 β-lactamase

β-lactamases are a group of enzymes that confer resistance to penam and cephem antibiotics by hydrolysis of the β-lactam ring, thereby inactivating the antibiotic. Crystallographic and computer modeling studies of RTEM-1 β-lactamase have indicated that Asp 132, a strictly conserved residue among the class A β-lactamases, appears to be involved in substrate binding, catalysis, or both. To study the contribution of residue 132 to β-lactamase function, site saturation mutagenesis was used to generate mutants coding for all 20 amino acids at position 132. Phenotypic screening of all mutants indicated that position 132 is very sensitive to amino acid changes, with only N132C, N132D, N132E, and N132Q showing any appreciable activity. Kinetic analysis of three of these mutants showed increases in K_M, along with substantial decreases in k_(cat). Efforts to trap a stable acyl-enzyme intermediate were unsuccessfuL These results indicate that residue 132 is involved in substrate binding, as well as catalysis, and supports the involvement of this residue in acylation as suggested by Strynadka et al.

Crystallographic and computer modeling studies of RTEM-1 β-lactamase have indicated that Lys 73 and Glu 166, two strictly conserved residues among the class A β-lactamases, appear to be involved in substrate binding, catalysis, or both. To study the contribution of these residues to β-lactamase function, site saturation mutagenesis was used to generate mutants coding for all 20 amino acids at positions 73 and 166. Then all 400 possible combinations of mutants were created by combinatorial mutagenesis. The colonies harboring the mutants were screened for growth in the presence of ampicillin. The competent colonys' DNA were sequenced, and kinetic parameters investigated. It was found that lysine is essential at position 73, and that position 166 only tolerated fairly conservative changes (Aspartic acid, Histidine, and Tyrosine). These functional mutants exhibited decreased kcat's, but K_M was close to wild-type levels. The results of the combinatorial mutagenesis experiments indicate that Lysis absolutely required for activity at position 73; no mutation at residue 166 can compensate for loss of the long side chain amine. The active mutants found--K73K/E166D, K73KIE166H, and K73KIE166Y were studied by kinetic analysis. These results reaffirmed the function of residue 166 as important in catalysis, specifically deacylation.

The identity of the residue responsible for enhancing the active site serine (Ser 70) in RTEM-1 β-lactamase has been disputed for some time. Recently, analysis of a crystal structure of RTEM-1 β-lactamase with covalently bound intermediate was published, and it was suggested that Lys 73, a strictly conserved residue among the class A β-lactamases, was acting as a general base, activating Ser 70. For this to be possible, the pK_a of Lys 73 would have to be depressed significantly. In an attempt to assay the pK_a of Lys 73, the mutation K73C was made. This mutant protein can be reacted with 2-bromoethylamine, and activity is restored to near wild type levels. ^(15)N-2-bromoethylamine hydrobromide and ^(13)C-2-bromoethylamine hydrobromide were synthesized. Reacting these compounds with the K73C mutant gives stable isotopic enrichment at residue 73 in the form of aminoethylcysteine, a lysine homologue. The pK_a of an amine can be determined by NMR titration, following the change in chemical shift of either the ^(15)N-amine nuclei or adjacent Be nuclei as pH is changed. Unfortunately, low protein solubility, along with probable label scrambling in the Be experiment, did not permit direct observation of either the ^(15)N or ^(13)C signals. Indirect detection experiments were used to observe the protons bonded directly to the ^(13)C atoms. Two NMR signals were seen, and their chemical shift change with pH variation was noted. The peak which was determined to correspond to the aminoethylcysteine residue shifted from 3.2 ppm down to 2.8 ppm over a pH range of 6.6 to 12.5. The pK_a of the amine at position 73 was determined to be ~10. This indicates that residue 73 does not function as a general base in the acylation step of the reaction. However the experimental measurement takes place in the absence of substrate. Since the enzyme undergoes conformational changes upon substrate binding, the measured pK_a of the free enzyme may not correspond to the pK_a of the enzyme substrate complex.

Progress towards the total synthesis of a spermine-conjugated dynemicin analog

Progress towards the synthesis of the spermine-conjugated Dynemicin analog 4 is described. The synthetic route starts with the Michael addition of menthyl acetoacetate to trans-ethyl crotonate followed by a Dieckman condensation to form the cyclohexanedione 14 which, through a series of chemical reactions, is transformed into the quinone imine 6. Key features in the route include the Suzuki coupling reaction of the aryl boronic acid 11 and the enol triflate 12, thermal deprotection/internal amidation of the biaryl 19, cis addition of the (Z)-enediyne 33 to the quinoline 25, intramolecular acetylide addition to a carbonyl within the ketone 29, and an addition/elimination of the cyanophthalide to the quinone imine 6 to form the anthraquinone 36 utilizing the Kraus and Sugimoto methodology.

Carbon-carbon bond forming reactions from bis(carbene)-platinum(II) complexes and olefin polymerization and oligomerization using group 4 post-metallocene complexes

A long-standing challenge in transition metal catalysis is selective C–C bond coupling of simple feedstocks, such as carbon monoxide, ethylene or propylene, to yield value-added products. This work describes efforts toward selective C–C bond formation using early- and late-transition metals, which may have important implications for the production of fuels and plastics, as well as many other commodity chemicals.

The industrial Fischer-Tropsch (F-T) process converts synthesis gas (syngas, a mixture of CO + H₂) into a complex mixture of hydrocarbons and oxygenates. Well-defined homogeneous catalysts for F-T may provide greater product selectivity for fuel-range liquid hydrocarbons compared to traditional heterogeneous catalysts. The first part of this work involved the preparation of late-transition metal complexes for use in syngas conversion. We investigated C–C bond forming reactions via carbene coupling using bis(carbene)platinum(II) compounds, which are models for putative metal–carbene intermediates in F-T chemistry. It was found that C–C bond formation could be induced by either (1) chemical reduction of or (2) exogenous phosphine coordination to the platinum(II) starting complexes. These two mild methods afforded different products, constitutional isomers, suggesting that at least two different mechanisms are possible for C–C bond formation from carbene intermediates. These results are encouraging for the development of a multicomponent homogeneous catalysis system for the generation of higher hydrocarbons.

A second avenue of research focused on the design and synthesis of post-metallocene catalysts for olefin polymerization. The polymerization chemistry of a new class of group 4 complexes supported by asymmetric anilide(pyridine)phenolate (NNO) pincer ligands was explored. Unlike typical early transition metal polymerization catalysts, NNO-ligated catalysts produce nearly regiorandom polypropylene, with as many as 30-40 mol % of insertions being 2,1-inserted (versus 1,2-inserted), compared to <1 mol % in most metallocene systems. A survey of model Ti polymerization catalysts suggests that catalyst modification pathways that could affect regioselectivity, such as C–H activation of the anilide ring, cleavage of the amine R-group, or monomer insertion into metal–ligand bonds are unlikely. A parallel investigation of a Ti–amido(pyridine)phenolate polymerization catalyst, which features a five- rather than a six-membered Ti–N chelate ring, but maintained a dianionic NNO motif, revealed that simply maintaining this motif was not enough to produce regioirregular polypropylene; in fact, these experiments seem to indicate that only an intact anilide(pyridine)phenolate ligated-complex will lead to regioirregular polypropylene. As yet, the underlying causes for the unique regioselectivity of anilide(pyridine)phenolate polymerization catalysts remains unknown. Further exploration of NNO-ligated polymerization catalysts could lead to the controlled synthesis of new types of polymer architectures.

Finally, we investigated the reactivity of a known Ti–phenoxy(imine) (Ti-FI) catalyst that has been shown to be very active for ethylene homotrimerization in an effort to upgrade simple feedstocks to liquid hydrocarbon fuels through co-oligomerization of heavy and light olefins. We demonstrated that the Ti-FI catalyst can homo-oligomerize 1-hexene to C₁₂ and C₁₈ alkenes through olefin dimerization and trimerization, respectively. Future work will include kinetic studies to determine monomer selectivity by investigating the relative rates of insertion of light olefins (e.g., ethylene) vs. higher α-olefins, as well as a more detailed mechanistic study of olefin trimerization. Our ultimate goal is to exploit this catalyst in a multi-catalyst system for conversion of simple alkenes into hydrocarbon fuels.

Bimetallic olefin polymerization catalysis : mechanisms and applications of proximal effects

This dissertation covers progress with bimetallic polymerization catalysts. The complexes we have designed were aimed at expanding the capabilities of homogeneous polymerization catalysts by taking advantage of multimetallic effects. Such effects were examined in group 4 and group 10 bimetallic complexes; proximity and steric repulsion were determined to be major factors in the effects observed.

Chapters 2 and 3 introduce the rigid p-terphenyl dinucleating framework utilized in most of this thesis. The permethylation of the central arene allows for the separation of syn and anti atropisomers of the terphenyl compounds. Kinetic studies were carried out to examine the isomerization of the dinucleating bis(salicylaldimine) ligand precursors. Metallation of the syn and anti bis(salicylaldimine)s using Ni(Me)2(tmeda) and excess pyridine afforded dinickel bisphenoxyiminato complexes with a methyl and a pyridyl ligand on each nickel. The syn and anti atropisomers of the dinickel complexes were structurally characterized and utilized in ethylene and ethylene/α-olefin polymerizations. Monometallic analogues were also synthesized and tested for polymerization activity. Ethylene polymerizations were performed in the presence of primary, secondary, and tertiary amines – additives that generally deactivate nickel polymerization catalysts. Inhibition of this deactivation was observed with the syn atropisomer of the bimetallic species, but not with the anti or monometallic analogues. A mechanism was proposed wherein steric repulsion of the substituents on proximal nickel centers disfavors simultaneous ligation of base to both of the metal centers. The bimetallic effect has been explored with respect to size and binding ability of the added base.

Chapter 4 presents the optimization of the bisphenoxyimine ligand synthesis and synthesis of syn and anti m-terphenyl analogues. Metallation with NiClMe(PMe₃)₂ yielded phosphine-ligated dinickel complexes, which have been structurally characterized. Ethylene/1-hexene copolymerizations in the presence of amines using Ni(COD)₂ as a phosphine scavenger showed significantly improved activity relative to the pyridine-ligated analogues. Incorporation of amino olefins in copolymerizations with ethylene was accomplished, and a mechanism was proposed based on proximal effects. Copolymerization trials with a variety of amino olefins and ethylene/1-hexene/amino olefin terpolymerizations were completed.

Early transition metal complexes based on the rigid p-terphenyl framework were designed with a variety of donor sets (Chapter 5 and Appendix B). Chapter 5 details the use of syn dizirconium di[amine bis(phenolate)] complexes for isoselective 1-hexene and propylene homopolymerizations. Ligand variation and monometallic complexes were studied to determine the origin of tacticity control. A mechanistic proposal was presented based on the symmetry at zirconium and the steric effects of the proximal metal center. Appendix B covers additional studies of bimetallic early transition metal complexes based on the p-terphenyl. Dititanium, dizirconium, and asymmetric complexes with bisphenoxyiminato ligands and derivatives thereof were targeted. Progress toward the synthesis of these complexes is described along with preliminary polymerization data. 1-hexene/diene copolymerizations and attempted polymerizations in the presence of ethers and esters with the syn dizirconium di[amine bis(phenolate)] complexes demonstrate the potential for further applications of this system in catalysis.

Appendix A includes work toward palladium catalysts for insertion polymerization of polar monomers. These complexes were based on dioxime and diimine frameworks with the intent of binding Lewis acidic metals at the oxime oxygens, at pendant phenolic donors, or at pendant aminediol moieties. The synthesis and structural characterization of a number of palladium and Lewis acid complexes is presented. Due to the instability of the desired species, efforts toward isolation of the desired complexes proved unsuccessful, though preliminary ethylene/methyl acrylate copolymerizations using in situ activation of the palladium species were attempted.