Lactonic sophorolipids (LSL) are glycolipid biosurfactants produced in large quantity by yeast fermentation. Chemical or enzymatic modification of naturally produced sophorolipids is an effective route to improve their functional properties. For the first time, ring-opening cross metathesis (RO/CM) was used to convert natural LSL to a unique family of modified sophorolipids. Reaction conditions for RO/CM of LSL with n-alkyl acrylates, trans-3-hexene, 1-hexene and ethylene were investigated. For the RO/CM of n-alkyl acrylates with LSL, %-conversions greater than 95% within 1 h resulted from conducting reactions in THF at 60°C using 5 mol% of Grubbs second generation ruthenium based catalyst (M2). The RO/CM reaction of LSL with ethylene performed at 3 bar under an ethylene atmosphere using Grubbs first generation (G1) (10 mol%) as the catalyst in dichloromethane (room temperature, 5 h) gave complete conversion of LSL to the corresponding ring-opened product. Ethanolysis of LSL RO/CM products generated a series of medium chain (C10-C14) SL-surfactants and fatty acid co-products. Values of surface tension reduction at the air-water interface versus Log (C) for modified SLs were measured by the Wilhelmy plate method. Minimum surface tension values varied as a function of the hydrophobic character of modified SLs. The modified SL from RO/CM with 1-hexene (SL-14) gave the largest surface tension reduction and lowest CMC (to 34 mN/m and 0.15 mM, respectively) and showed a similar surface tension reduction behavior as n-dodecyl-b-D-maltoside (Mal-C12). Increasing the number of carbons in the hydrophobic segment for the homologous series of n-alkyl sophorosides results in an almost linear decrease in log(CMC), with B ¼ 0.18 AE 0.03. This number is smaller than that of other related surfactants such as alkyl-b-D-glycosides and alkyl-b-D-maltosides.Practical applications: Modified sophorolipids can be used in a wide variety of applications such as stabilization of oil-in-water dispersions, antimicrobials and various cleaning operations.
Oligomers of PNA:PNA duplexes with different amino acids appended to one strand of each duplex have been synthesized and studied for their chiral optical properties. The terminal amino acid is known to affect both the handedness and amplitude of the CD signal from a given duplex. Here we have investigated an extended set of duplexes with several different amino acids appended, determining the CD, absorbance, and denaturation behavior of these chains in water and glycerol. Thermal unfolding profiles of the duplexes together with NMR data point to conformational heterogeneity as a function of amino acid, oligomer length, and solvent. The results suggest that the PNA:PNA double helix has access in solution to a dynamic ensemble of conformational states rather than a single dominant state. The conformational ensemble varies as a function of oligomer length according to the cooperative properties of the competing conformations of the double helix. A simplified statistical theoretical model allowing only two conformational states with distinct cooperative properties consistent with the denaturation results can account for much of the experimental data. This conformational heterogeneity in PNA duplexes is reflected in significantly greater flexibility of PNA:DNA duplexes relative to either DNA or RNA double helices. The results demonstrate that the principles of chiral cooperativity such as seen in the sergeants and soldiers and majority rule experiments must be altered when the structure of the system becomes a variable depending on the chiral information input.
Antimicrobial dendrimeric peptides (AMDP) are a relatively new class of agents displaying repetitive functional groups on a branched core. Previously, we have investigated the length requirement for antimicrobial activity of peptides consisting of repeated arginine (R) and tryptophan (W) side chains and found that even short linear RW repeats are active, providing a starting point for a de novo design of multivalent structures. In this study, we synthesized and tested a new synthetic dendrimer, 2D-24, for its antimicrobial activity against Pseudomonas aeruginosa, including the wild-type PAO1 and its mucoid mutant PDO300. This synthetic AMDP was found to kill planktonic cells of both PAO1 and PDO300 in a dose-dependent manner, with nearly complete killing of both strains observed when treated with 50 μM of this agent. In addition to planktonic cells, 2D-24 was also found to kill biofilm cells of both strains in a dose-dependent manner. For example, treatment with 30 μM 2D-24 led to 94.4 ± 1.4 and 93.9 ± 4.2 % killing of PAO1 and PDO300 biofilm cells, respectively. Furthermore, 2D-24 was effective in killing multidrug-tolerant persister cells of PAO1 and PDO300. While higher concentrations of 2D-24 were required to kill persister cells, combinations of 2D-24 with ciprofloxacin, tobramycin, or carbenicillin showed synergistic effects on killing persister cells of both strains. Based on hemolysis assays using sheep erythrocytes and a coculture model of PAO1 and human epithelial cells, 2D-24 was found to kill P. aeruginosa cells at concentrations that are not toxic to mammalian cells.
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