Polyglycerol-derived amphiphiles for the solubilization of single-walled carbon nanotubes in water: a structure-property study

A series of nonionic amphiphiles derived from polyglycerol dendrons were studied for their ability to solubilize and isolate single-walled carbon nanotubes. The amphiphiles possessed differently sized polar head groups, hydrophobic tail units, and various aromatic and non-aromatic groups between the head and tail groups. Absorbance analysis revealed that amphiphiles with anchor groups derived from pyrene were far inferior to those that possessed simple linear aliphatic tail groups. Absorbance and near-infrared fluorescence analyses revealed a weak dependence on the dendron size of the head group, but a strong positive trend in suspended nanotube density and fluorescence intensity for amphiphiles with longer tail units. Variations in the moieties linking the head and tail groups led to a range of effects on the suspensions, with linkers imparting flexibility and a bent shape that gave improved performance overall. This was illustrated most dramatically by a pair of benzamide-containing amphiphiles, the para isomer of which showed evidence in the fluorescence data of increased nanotube aggregate formation when compared with the meta isomer. In addition, statistical AFM was used to illustrate more directly the microscopic differences between amphiphiles that were effective at nanotube bundle disruption and those that were not.     

Modified method for filling micro-HPLC-columns

Summary A new method is introduced for packing micro-columns with an ID (inner diameter) of 320 m. The advantage of this method is the extraordinary economy of the packing material employed and the high reliability in production. The theoretical plate height ranges from 7 to 8 m for 3 m particles.     

Vibrational spectra of chloroform, freon-11 and selected isotopomers in the terahertz region

The fundamental bands of the CCl₃ asymmetric deformation modes of selected isotopomers of chloroform (CHCl₃) and freon-11 (CFCl₃) have been measured in a static cell at ambient temperature using a laser-based source of tunable radiation in the terahertz region of the electromagnetic spectrum. The analysis of the rotational contours of the bands enabled the derivation of the fundamental frequencies with an accuracy of better than 3 GHz.     

Positively Charged Nanoaggregates Based on Zwitterionic Pillar[5]arene that Combat Planktonic Bacteria and Disrupt Biofilms

Bacterial biofilms are difficult to eradicate because they are less susceptible to antibiotics and more easily develop resistance. Therefore, there is an urgent need for new materials that can combat planktonic bacteria and disrupt established biofilms. To tackle this challenge, we design a multifunctional zwitterionic pillar[5]arene, which can self‐assemble into weakly positively charged nanoaggregates that exhibit antibacterial activity against Gram‐negative Escherichia coli (DH5α) and Gram‐positive Staphylococcus aureus (SH1000) bacterial strains in solution. In addition, the zwitterionic pillar[5]arene can efficiently disrupt pre‐existing Escherichia coli (DH5α) biofilms and kill the biofilm‐enclosed bacteria without rapid generation of resistance.     

Determination of the chromophore structures in the photoinduced reaction cycle of phytochrome

The chromophore structures in the parent states Pr and Pfr as well as in the photocycle intermediate Lumi-R of oat phytochrome phyA are determined by comparison of the experimental resonance Raman spectra with calculated Raman spectra that have been obtained by density functional theory calculations (B3LYP) using scaled force fields. The spectra were calculated for various tetrapyrrole geometries including more than twenty different methine bridge isomers. For the parent states Pr and Pfr the best agreement in terms of vibrational frequencies, isotopic shifts, and Raman intensities was achieved with the ZZZasa and ZZEssa geometry, respectively. For the first intermediate Lumi-R, the chromophore geometry is concluded to be the ZZEasa configuration. These finding imply that the primary step of the photoactivation of phytochrome is the Z/E isomerization of the C-D methine bridge double bond, whereas the single bond remains in the anti conformation. The subsequent transition to the physiologically active state Pfr includes a (partial) single bond rotation of the A-B methine bridge.     

Excess partial molar enthalpies,entropies, Gibbs energies,and volumes in aqueous dimethylsulfoxide

The excess partial molar enthalpies, the vapor pressures, and the densities of dimethylsulfoxide (DMSO)–H₂O mixtures were measured and the excess partial molar Gibbs energies and the partial molar volumes were calculated for DMSO and for H₂O. The values of the excess partial molar Gibbs energies for both DMSO and H₂O are negative over the entire composition range. The results for the water-rich region indicated that the presence of DMSO enhances the hydrogen bond network of H₂O. Unlike monohydric alcohols, however, the solute-solute interaction is repulsive in terms of the Gibbs energy. This was a result of the fact that the repulsion among solutes in terms of enthalpy surpassed the attraction in terms of entropy. The data in the DMSO-rich region suggest that DMSO molecules form clusters which protect H₂O molecules from exposure to the nonpolar alkyl groups of DMSO.     

In situ hydrolysis of imine derivatives on Au(111) for the formation of aromatic mixed self-assembled monolayers: multitechnique analysis of this tunable surface modification

This paper presents a novel method for preparing aromatic, mixed self-assembled monolayers (SAMs) with a dilute surface fraction coverage of protonated amine via in situ hydrolysis of C═N double bond on gold surface. Two imine compounds, (4'-(4-(trifluoromethyl)benzylideneamino)biphenyl-4-yl)methanethiol (CF(3)-C(6)H(4)-CH═N-C(6)H(4)-C(6)H(4)-CH(2)-SH, TFBABPMT) and (4'-(4-cyanobenzylideneamino)biphenyl-4-yl)methanethiol (CN-C(6)H(4)-CH═N-C(6)H(4)-C(6)H(4)-CH(2)-SH, CBABPMT), self-assembled on Au(111) to form highly ordered monolayers, which was demonstrated by infrared reflection absorption spectroscopy (IRRAS) and X-ray photoelectron spectroscopy (XPS). A nearly upright molecular orientation for CF(3)- and CN-terminated SAM was detected by near edge X-ray absorption fine structure (NEXAFS) measurements. Afterward, the acidic catalyzed hydrolysis was carried out in chloroform or an aqueous solution of acetic acid (pH = 3). Systematic studies of this hydrolysis process for CN-terminated SAM in acetic acid at 25 °C were performed by NEXAFS measurements. It was found that about 30% of the imine double bonds gradually cleaved in the first 40 min. Subsequently, a larger hydrolysis rate was observed due to the freer penetration of acetic acid in the SAM and resultant more open molecular packing. Furthermore, the molecular orientation in mixed SAMs did not change during the whole hydrolysis process. This partially hydrolyzed surface contains a controlled amount of free amines/ammonium ions which can be used for further chemical modifications.