RSC Advances

Ulloa, Carolina Olea; Ponce-Vargas, Miguel; de Mattos Piccoli, Rafael; Caramori, Giovanni F.; Frenking, Gernot; Muñoz-Castro, Alvaro

doi: 10.1039/c4ra12859apmid: N/A

[2.2.2]Paracyclophane is a versatile π-cryptating structure, which can exhibit η2:η2:η2 and η6:η6:η6 coordination with metal ions, involving two or six carbon atoms in each aromatic ring. According to the nature of the metallic cation, the interaction can occur at the centre of the cage or upper face of the structure, which is determined mainly by the ligand-to-metal charge transfer ruled by symmetry and energetic considerations, and thus by the nature of the cation–π interaction. For Ag(i), the 5s-Ag shell is close in energy to the frontier orbitals of paracyclophane, resulting in the formation of a bonding combination with the symmetric combination of the π2-type levels, which leads to a non-centered conformation. In contrast, the Sn(ii) case exhibits a largely favourable bonding interaction with the π2 and π3 type levels, which involve the 5p-Sn shell and result in a centered conformation. The interaction between the metal and paracyclophane was studied via molecular orbitals diagram, energy decomposition analyses (EDA) and non-covalent indexes (NCI).

Gurikov, P.; Raman, S. P.; Weinrich, D.; Fricke, M.; Smirnova, I.

doi: 10.1039/c4ra14653kpmid: N/A

A novel technique for the preparation of alginate aerogels, that utilizes high pressure CO2, is presented. In pressurized carbon dioxide at 5 MPa and 298 K, a suspension of calcium carbonate dispersed in a sodium alginate solution undergoes irreversible gelation without additional pH modifiers or crosslinkers. Solvent exchange to ethanol at ambient conditions followed by supercritical drying with carbon dioxide resulted in alginate aerogels with remarkable properties compared to the state of the art. They are very light with densities down to 0.06 ± 0.02 g cm−3, translucent and possess a fibrillar structure with both meso- and macroporosity. For selected samples, the surface area and mesopore volume are found to be 545 ± 77 m2 g−1 and 6.98 cm3 g−1, respectively. Thermal conductivity measurements using the hot-wire method revealed excellent thermal insulation properties: thermal conductivity was determined to be in the range of (18–22) ± 2 mW m−1 K−1. Although the initial aerogels are flexible to a certain extent, they can be classified as viscoplastic materials and their compression indicates improved flexibility and retained mesoporosity. A possible approach for the production of alginate aerogels in an integrated one-pot process – that combines gelation, solvent exchange and supercritical drying – is outlined.

Islam, Md. Tariqul; Ganesan, P.; Cheng, Ji

doi: 10.1039/c4ra15728apmid: N/A

The motion and interaction of a bubble pair in a non-Newtonian fluid (xanthan gum solution) were numerically simulated using a volume of fluid (VOF) method, in which the continuous surface tension model and the power-law model were adopted to represent the surface tension and rheological properties of non-Newtonian fluids, respectively. The effects of the initial horizontal bubble interval, oblique alignment and rheological properties of non-Newtonian fluids on a pair of bubbles rising side-by-side are evaluated in this study. The results indicate that for the case with a non-dimensional initial horizontal bubble interval h* = 4.0, the interaction between the bubbles shows a minimal repulsive effect. Moreover, for the oblique angle alignment a greater repulsive force between the bubbles was seen when the angle was reduced. However, oblique coalescence occurred due to the higher attraction between the bubbles at higher angles, which is independent of the flow index. It is also found that the repulsion effect as well as the variation of the bubble shape from spherical to irregular are more significant at a lower flow index (n < 0.5) due to the shear-thinning effect as well as the differences in their flow field structures.

Li, Xiao-Shui; Chen, Xi; Yuan, Bi-Feng; Feng, Yu-Qi

doi: 10.1039/c4ra13878cpmid: N/A

Metal oxide affinity chromatography has become one of the most widely used strategies for phosphopeptide enrichment prior to mass spectrometry analysis, but some defects still exist in this approach due to the complex physical and chemical properties of the metal oxide surface. Although the simultaneous phosphorylation of adjacent amino acids may greatly affect the bioactivity of the protein, there are few reports on the specific enrichment of multi-phosphopeptides. In this work, we report a highly selective enrichment method for capturing phosphopeptides or multi-phosphopeptides based on phosphonate-modified metal oxides. Compounds with different numbers of phosphate groups were adsorbed on the surface of ZrO2 and TiO2 to obtain phosphonate-modified metal oxides. Among them, phosphoric acid modified metal oxides (1P-ZrO2 and 1P-TiO2) could significantly enhance their selectivity towards phosphopeptides; and alendronate-modified metal oxides (2P-ZrO2 and 2P-TiO2) showed high selectivity for the enrichment of multi-phosphopeptides. In addition, the detection sensitivity was greatly improved by using these novel materials. The mechanism of the specific enrichment was considered to be ligand exchange and blocking of strong adsorption sites by the compounds containing the phosphate group. Finally, tryptic digests of proteins of human Jurkat-T cell lysate were further used to demonstrate the selectivity and specificity of ZrO2, 1P-ZrO2 and 2P-ZrO2.

Kumar, P. P. Praveen; Suresh, Cherumuttathu H.; Haridas, V.

doi: 10.1039/c4ra14389bpmid: N/A

We have synthesized two cystine containing molecules S1 (pyrene-labelled) and S2 (tryptophan-labelled) and demonstrated that the former can detect Cu2+, and the latter can detect Hg2+ in acetonitrile. The 1 : 1 mixture of S1 and S2 forms a heterodimeric system S1 : S2, which was confirmed by mass spectrometric, UV-Visible and fluorescence spectroscopic studies. Additional proof for the formation of S1 : S2 came from 1H NMR, CD, ITC, ultramicroscopic and computational studies. The supramolecularly assembled S1 : S2 detects Pb2+ in nanomolar levels. A control compound S3 containing tryptophan and pyrene units showed totally different binding properties compared to S1, S2 and S1 : S2. DFT studies on S1 : S2 establish that S1 in S1 : S2 adopts an extended conformation, thereby keeping the pyrene units proximal to the indole moiety of S2 for energy transfer. The binding of Pb2+ with S1 : S2 brings the two pyrene units into proximity resulting in a folded structure and the formation of the excimer. These results clearly demonstrate a hitherto unknown and unexpected organization of two fluorescent molecules leading to a new supramolecular system capable of Pb2+ detection.

Drori, Ran; Davies, Peter L.; Braslavsky, Ido

doi: 10.1039/c4ra12638fpmid: N/A

Antifreeze proteins (AFPs) aid the survival of cold-adapted organisms by inhibiting the growth of ice crystals in the organism. The binding of AFPs to ice separates the melting point from the freezing point of the ice crystal (thermal hysteresis, TH). Although AFPs were discovered more than 40 years ago, the mechanism by which they inhibit ice growth remains unclear. The distance between surface-bound AFPs is thought to correlate directly with the TH activity; however, this correlation has never been experimentally established. A novel microfluidics system was used here to obtain ice crystals covered with GFP-tagged AFPs in an AFP-free solution. This method permits calculation of the surface density of bound AFPs. Fluorescence intensity analysis revealed that the distance between ∼3 nm-long AFPs on the ice surface was 7–35 nm, depending on the AFP solution concentration and time of its exposure to ice. A direct correlation between these distances and the measured TH activity was found for a representative insect AFP, but not for a typical fish AFP. Insect AFPs accumulate over multiple ice crystal planes, especially the basal plane. Fish AFPs, which cannot bind to the basal plane, change the shape of the crystal to minimize the basal plane area. Thus, we postulate that the surface density of fish AFPs on the prism plane is not directly indicative of the TH activity, which ends when ice grows out of the basal plane and is a function of the basal plane area. These results significantly contribute to our understanding of the AFP mechanism and will be helpful in applying these proteins in different fields.

Peng, Yang; Yan, Ziren; Wu, Ying; Di, Junwei

doi: 10.1039/c4ra13653epmid: N/A

The electrocatalytic efficiency of metal nanoparticles depends on their structures as well as compositions. The analytical performance of four Ag-based metal (Ag, AgPt, AgAu, and AgAuPt) nanostructure modified electrodes for detection of hydrogen peroxide was investigated. Silver nanoparticles (Ag NPs) were deposited on an indium tin oxide (ITO) film coated glass surface. Then Ag NPs were used as sacrificed template to generate AgPt, AgAu, and AgAuPt hybrid hollow nanostructures using a galvanic replacement reaction. The AgAuPt nanocages (AgAuPt NCs) show the highest sensitivity for electrochemical detection of hydrogen peroxide in all the metal nanostructures. This modified electrode exhibits a linear current response to hydrogen peroxide concentration in the range of 4 μM to 4 mM with a detection limit of 2 μM at an applied potential of −0.35 V. These results indicate that AgAuPt NCs could be a promising electrochemical material for detection of hydrogen peroxide.

Wang, Yongjie; Liu, Xinquan; Zhang, Jiaozhen; Liu, Guangpu; Liu, Yan; Wang, Kaiming; Yang, Min; Cheng, Huiling; Zhao, Zhongxi

doi: 10.1039/c4ra13350apmid: N/A

Water-soluble polysaccharides were extracted from the Zizyphus jujuba cv. Muzao using an ultrasonically assisted extraction method and fractionated by DEAE-Sepharose Fast Flow ion-exchange chromatography. The relevant fractions (HJP1 and HJP3) were subjected to structural analysis by using characterization techniques such as acid hydrolysis, partial acid hydrolysis, periodate oxidation-Smith degradation, methylation, FT-IR spectral and NMR spectral analysis. Both HJP1 and HJP3 were determined to be acidic polysaccharides with a molecular weight of 6.762 × 104 Da and 2.936 × 104 Da, respectively, comprising of mannose, rhamnose, galactose, galacturonic acid, glucose and arabinose. The demonstrated data (monosaccharide composition, methylation analysis and 13C NMR spectrum) points to the presence of type I rhamnogalacturonan (containing arabinogalactan/arabinan side chains) domains and typical pectic polysaccharides, with homogalacturonan (methyl and acetyl esterified). The results from in vitro antitumor studies indicate that both HJP1 and HJP3 could inhibit the growth of human HepG2 cells and HJP3 had stronger cytotoxicity against HepG2 cells than HJP1, suggesting that these polysaccharides could potentially be used in liver cancer prevention and treatment.

Yoldas, Aykut; Algi, Fatih

doi: 10.1039/c4ra14182bpmid: N/A

A novel, simple and efficient dual channel probe built on an imidazo-phenanthroline scaffold with a boronic acid unit, viz. 3-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenylboronic acid, is disclosed. It is found that this novel probe induces chromogenic and fluorogenic responses to Fe(ii) and Zn(ii) ions, respectively. To our best knowledge, this is one of the rare examples of dual channel responsive probes that can be used for visual detection of Fe(ii) and turn-on fluorogenic detection of Zn(ii) ions, simultaneously.

Ganot, Nitzan; Redko, Boris; Gellerman, Gary; Tshuva, Edit Y.

doi: 10.1039/c4ra13484bpmid: N/A

Two diaminobis(phenolato) Ti(iv) complexes were separately combined with azatoxin, camptothecin or cisplatin and underwent in vitro cytotoxicity analysis toward HT-29 and NCI-H1229 cancer cell lines. The methylated salan derivative exhibited synergistic effects with cisplatin at varying ratios toward both lines, when the compounds were administered fresh and simultaneously, implying great medicinal potential.