Functionalization of the methylene groups of p-tert-butylcalix[4]arene: S-C,N-C,and C-C bond formation

Reaction of the calixarene derivative 7 with two exocyclic double bonds with carbon-, nitrogen-, oxygen-, or sulfur-containing nucleophiles afforded bis(spirodienone) derivatives substituted at two opposite methylene groups in a trans fashion. LiAlH(4) reduction of the bis(spirodienone) derivatives with two methylenes functionalized by thiomethoxy, diethyl malonate, or anilino substituents yielded trans methylene-substituted calix[4]arenes. Upon standing in solution, the calixarene derivative incorporating SMe groups on the bridges underwent trans right harpoon over left harpoon cis isomerization. An equilibration study performed on this calixarene derivative (tetrachloroethane-d(2), 430 K) indicated that the cis isomer is the form of lower free energy.     

Q-switched ytterbium doped fiber laser using multi-walled carbon nanotubes saturable absorber

A Q-switched ytterbium-doped fiber laser(YDFL)is proposed and demonstrated using a newly developed multi-walled carbon nanotubes polyethylene oxide(MWCNTs-PEO)film as a passive saturable absorber(SA).The saturable absorber is prepared by mixing the MWCNTs homogeneous solution into a dilute PEO polymer solution before it is left to dry at room temperature to produce thin film.Then the film is sandwiched between two FC/PC fiber connectors and integrated into the laser cavity for Q-switching pulse generation.The laser generates a stable pulse operating at wavelength of 1060.2 nm with a threshold pump power of 53.43 mW.The YDFL generates a stable pulse train with repetition rates ranging from7.92 to 24.27 kHz by varying 980-nm pump power from 53.42 to 65.72 mW.At 59.55-mW pump power,the lowest pulse width and the highest pulse energy are obtained at 12.18μs and 143.5 nJ,respectively.     

Deuteron quadrupole coupling constants in crystals with symmetrical hydrogen bonds

Deuteron quadrupole coupling constants for the free formic and trifluoroacetic acid molecules, for their acid anions and for the maleate anion were calculated using the INDO method. The results are compared with experimental values for potassium deuterium maleate and bistrifluoroacetate.     

Mechanical and Morphological Properties of Bio-Phenolic/Epoxy Polymer Blends

Polymer blends is a well-established and suitable method to produced new polymeric materials as compared to synthesis of a new polymer. The combination of two different types of polymers will produce a new and unique material, which has the attribute of both polymers. The aim of this work is to analyze mechanical and morphological properties of bio-phenolic/epoxy polymer blends to find the best formulation for future study. Bio-phenolic/epoxy polymer blends were fabricated using the hand lay-up method at different loading of bio-phenolic (5 wt%, 10 wt%, 15 wt%, 20 wt%, and 25 wt%) in the epoxy matrix whereas neat bio-phenolic and epoxy samples were also fabricated for comparison. Results indicated that mechanical properties were improved for bio-phenolic/epoxy polymer blends compared to neat epoxy and phenolic. In addition, there is no sign of phase separation in polymer blends. The highest tensile, flexural, and impact strength was shown by P-20(biophenolic-20 wt% and Epoxy-80 wt%) whereas P-25 (biophenolic-25 wt% and Epoxy-75 wt%) has the highest tensile and flexural modulus. Based on the finding, it is concluded that P-20 shows better overall mechanical properties among the polymer blends. Based on this finding, the bio-phenolic/epoxy blend with 20 wt% will be used for further study on flax-reinforced bio-phenolic/epoxy polymer blends.     

One-Step Synthesis of Stable Colloidal Gold Nanoparticles Through Bioconjugation with Bovine Serum Albumin in Harsh Environments

In saline solutions with NaCl concentrations less than that typical of blood plasma and bodily fluids, gold nanoparticles (GNPs) aggregate and precipitate because of GNP cation complexation with the Cl^? anions in the solution. It is difficult to retain stable colloidal GNPs within any saline solution for a relatively long time without aggregation and precipitation. In this study, we developed a method to synthesize stable GNPs in harsh anion-containing environments. GNPs were formed by laser ablation in a saline solution, and their stabilization was achieved by adding bovine serum albumin (BSA) to the NaCl solution; this has been shown to be a quick, efficient approach to producing stable colloidal GNPs. GNP nanoclusters in saline solutions with and without BSA were observed via high-resolution transmission electron microscopy and selected area electron diffraction. The results reveal that our methodology yields colloidal GNPs with long-term stability in a BSA-containing saline solution.     

Synthetic Analogues of Naturally Occurring Spider Toxins: Synthesis of 2‐(Hydroxyphenyl)propanamides of Spermidine and Spermine

In a study on structure‐activity relationships of spider toxins, six model compounds, namely the spermidine derivatives 6 , 8 , and 16 as well as the spermine derivatives 24 , 27 , and 32 were synthesized. The synthesis proceeds through stepwise construction of the polyamine backbone, including protection and deprotection of the amino functions. The differentiation of the derivatives by analytical and spectroscopic methods is discussed.     

Syntheses of the Macrocyclic Spermine Alkaloids (±)‐Budmunchiamine A – C

The syntheses of four macrocyclic spermine alkaloids, (±)‐budmunchiamine A – C ( 1a – c ) and (±)‐budmunchiamine L4 ( 1 ), were accomplished by Michael addition of spermine to the α,β‐unsaturated esters 3a – d , followed by cyclization of the resulting α,ω‐tetraamino esters 4a – d with triethoxyantimony; N‐methylation of the amino lactams 6a – c yielded the budmunchiamines A – C ( 1a – c ).     

Synthetic Analogues to the Spermidine‐Spermine Alkaloid Tenuilobine

Naturally occurring spider and wasp toxins are potent inhibitors of glutamate receptors in the central nervous system. They consist of a polyamine backbone and carboxylic acids or amino acids linked by peptide bonds. In some respects, the plant alkaloid tenuilobine, a derivative of spermine and spermidine, shows structural similarities to these toxins. In the present paper, the synthesis of the five tenuilobine analogs 12 , 13 , 15 , 24 , and 25 is described. These derivatives differ in their aromatic carboxylic acid subunits and in the polyamine moiety.