The Quenching and Sonication Effect on the Mechanical Strength of Silver Nanowires Synthesized Using the Polyol Method

This study aims to determine the effect of fast cooling (quenching) on thermal properties, mechanical strength, morphology and size of the AgNWs. The synthesis of AgNWs was carried out at three different quenching-medium temperatures as follows: at 27 °C (ambient temperature), 0 °C (on ice), and −80 °C (in dry ice) using the polyol method at 130 °C. Furthermore, the AgNWs were sonified for 45 min to determine their mechanical strength. Scanning electron microscopy analysis showed that the quenched AgNWs had decreased significantly; at 27 °C, the AgNWs experienced a change in length from (40 ± 10) to (21 ± 6) µm, at 0 °C from (37 ± 8) to (24 ± 8) µm, and at −80 °C from (34 ± 9) to (29 ± 1) µm. The opposite occurred for their diameter with an increased quenching temperature: at 27 °C from (200 ± 10) to (210 ± 10) nm, at 0 °C from (224 ± 4) to (239 ± 8) nm, and at −80 °C from (253 ± 6) to (270 ± 10) nm. The lower the temperature of the quenching medium, the shorter the length and the higher the mechanical strength of AgNWs. The UV-Vis spectra of the AgNWs showed peak absorbances at 350 and 411 to 425 nm. Thermogravimetric analysis showed that AgNWs quenched at −80 °C have better thermal stability as their mass loss was only 2.88%, while at the quenching temperatures of 27 °C and 0 °C the mass loss was of 8.73% and 4.17%, respectively. The resulting AgNWs will then be applied to manufacture transparent conductive electrodes (TCEs) for optoelectronic applications.     

Reinventing Hsp90 Inhibitors: Blocking C‐Terminal Binding Events to Hsp90 by Using Dimerized Inhibitors

Heat shock protein 90 (Hsp90) is a molecular chaperone (90 kDa) that functions as a dimer. This protein facilitates the folding, assembly, and stabilization of more than 400 proteins that are responsible for cancer development and progression. Inhibiting Hsp90’s function will shut down multiple cancer‐driven pathways simultaneously because oncogenic clients rely heavily on Hsp90, which makes this chaperone a promising anticancer target. Classical inhibitors that block the binding of adenine triphosphate (ATP) to the N‐terminus of Hsp90 are highly toxic to cells and trigger a resistance mechanism within cells. This resistance mechanism comprises a large increase in prosurvival proteins, namely, heat shock protein 70 (Hsp70), heat shock protein 27 (Hsp27), and heat shock factor 1 (HSF‐1). Molecules that modulate the C‐terminus of Hsp90 are effective at inducing cancer‐cell death without activating the resistance mechanism. Herein, we describe the design, synthesis, and biological binding affinity for a series of dimerized C‐terminal Hsp90 modulators. We show that dimers of these C‐terminal modulators synergistically inhibit Hsp90 relative to monomers.     

Synthesis of sansalvamide A peptidomimetics: triazole, oxazole, thiazole, and pseudoproline containing compounds

Peptidomimetic-based macrocycles typically have improved pharmacokinetic properties over those observed with peptide analogs. Described are the syntheses of 13 peptidomimetic derivatives that are based on active Sansalvamide A structures, where these analogs incorporate heterocycles (triazoles, oxazoles, thiazoles, or pseudoprolines) along the macrocyclic backbone. The syntheses of these derivatives employ several approaches that can be applied to convert a macrocyclic peptide into its peptidomimetic counterpart. These approaches include peptide modifications to generate the alkyne and azide for click chemistry, a serine conversion into an oxazole, a Hantzsch reaction to generate the thiazole, and protected threonine to generate the pseudoproline derivatives. Furthermore, we show that two different peptidomimetic moieties, triazoles and thiazoles, can be incorporated into the macrocyclic backbone without reducing cytotoxicity: triazole and thiazole.     

Isolation of Magnetospirillum magneticum AMB-1 mutants defective in bacterial magnetic particle synthesis by transposon mutagenesis

Nonmagnetic mutants of Magnetospirillum magneticum AMB-1 were recovered following mini-Tn5 transposon mutagenesis. Transconjugants with kanamycin resistance were obtained at a frequency of 2.7 × 10⁻⁷ per recipient. Of 3327 transconjugants, 62 were defective for bacterial magnetic particle (BMP) synthesis. The frequency of independent transposition events for nonmagnetic mutants was about 1.4% in transconju gants. Further analysis of DNA sequences flanking transposon by inverted polymerase chain reaction allowed isolation of at least 10 genes or DNA sequences involved in BMP synthesis in M. magneticum AMB-1.     

Sanguinamide B analogs: identification of active macrocyclic structures

We report the synthesis of three new sanguinamide B (San B) analogs. We substituted in amino acids along the San B backbone with an N-Me, glycine, or an aromatic moiety (Phe or d-Phe) generating twelve derivatives in total. Testing in HCT-116 colon cancer cell lines resulted in establishing a structure–activity relationship. Our data show that the substitution of l- or d-Phe adjacent to the thiazole in the San B backbone locks the macrocycle into a single conformer, but only d-Phe analogs are cytotoxic. We demonstrate that the conformation of the macrocycle is extremely sensitive to stereochemistry and amino acid placement.     

Synthetic anthracyclinones-XXVII anthracyclinones by intramolecular marschalk reaction : Synthesis of the feudomycinones and rhodomycinones

1,4,5-Trihydroxy-9,10-anthraquinone is transformed regioselectively to the α-hydroxy dichlorides 18-21, which are cyclized to yield predominantely the naturally configurated 9,10-trans-diols 1,3,26, and 27 (80 to 96% d.e.). The monotrifluoroacetates 38-40 derived from the trans-diols are hydroxylated via bromination at C-7 to yield almost exclusively the 7,9-cis-9,10-trans-triols α₁-rhodomycinone (4), feudomycinone D (7), and 4-0-methyl-β-rhodomycinone (42). The feudomycinones A (5) and C (6) are obtained with less chemo- and stereoselectivity by hydroxylation of the l0 Deoxycompounds 33 and 34.     

Solubilities of families of heterocyclic polynuclear aromatics in organic solvents and their mixtures

The solubilities of anthracene, acridine, xanthene, thioxanthene, carbazole, dibenzofuran, and dibenzothiophene have been experimentally determined in benzene, cyclohexane, thiophene, and pyridine from ambient temperature to approximately 440 K. The results have been correlated using the classical equation for solid-liquid solubility to obtain the experimental activity coefficient of the solute in the solvent. These experimental activity coefficients have been regressed, using three common solution models, to find the binary interaction parameters needed in those models. The solubilities of biphenyl, dibenzofuran, and dibenzothiophene have been experimentally determined in five binary mixtures of the solvents. The experimental activity coefficients have been found and compared to the values predicted by the four solution models, using the binary interaction parameters obtained from the solubilities in the pure solvents and solventsolvent binary interaction parameters obtained from literature vaporliquid equilibria data. The effect of substituting various heteroatoms into the ring structure has been discussed.