Selective fluorometric detection of polyamines using micellar electrokinetic chromatography with laser-induced fluorescence detection

The polyamines putrescine, cadaverine, spermine and spermidine were separated and quantified by micellar electrokinetic chromatography (MEKC) with laser-induced fluorescence detection. The derivatization reagent, 1-pyrenebutanoic acid succinimidyl ester (PSE), allowed for the selective detection of the polyamines at 490 nm. Multiple labeling of the polyamines with PSE allows the formation of intramolecular excimers that emit at longer wavelengths (450-520 nm) than mono-labeled analytes (360-420 nm). Optimal separation of the labeled polyamines was achieved using a separation buffer consisting of 10 mM phosphate pH 7.2, 30 mM cholate, and 30% acetonitrile. Using these conditions, the four polyamines were separated in under 10 min. Limits of detection for putrescine, cadaverine, spermine and spermidine were 6, 5, 15 and 13 nM, respectively. These are superior or comparable to those previously reported in the literature using fluorescence detection.     

Polyol-modified layered double hydroxides with attenuated basicity for a truly reversible capture of CO2

Dendrimers bearing hydroxyl groups supported by layered double hydroxides (CO₃–LDH) with Mg/Al ratio ranging from 1:1 to 5:1 showed improved properties for the reversible capture of carbon dioxide (CO₂). The adsorption capacity of the starting LDH was due to the intrinsic base-like behavior, and was found to depend on the Mg/Al ratio. When contacted with polyol dendrimers in aqueous media, no intercalation took place. This was explained in terms of low exfoliation grade of LDH and hydrophobic character of the dendrimer molecules. The latter rather adsorb on the external surface of the LDH stacks for low dendrimer loadings, or aggregate into organic clusters for higher contents. Analyses through thermal programmed desorption of CO₂ revealed that dendrimer incorporation advantageously attenuates the basicity strength of the starting LDH support, by lowering the desorption temperature. The OH groups of the organic moiety were found to display an amphoteric character, and act as the main adsorption sites. The weak interactions with CO₂ facilitate easier release of the major part of adsorbed CO₂ at temperature not exceeding 80–100 °C. On polyol organo-LDHs, the reversible CO₂ retention was discussed herein in terms of acid–base interactions. This concept allows envisaging the capture of diverse pollutants and other greenhouse gases by modifying the chemical groups on the dendritic moiety.     

An Amino‐Acid‐Based Self‐Healing Hydrogel: Modulation of the Self‐Healing Properties by Incorporating Carbon‐Based Nanomaterials

An amino‐acid‐based (11‐(4‐(pyrene‐1‐yl)butanamido)undecanoic acid) self‐repairing hydrogel is reported. The native hydrogel, as well as hybrid hydrogels, have been thoroughly characterized by using various microscopic techniques, including transmission electron microscopy (TEM), atomic force microscopy (AFM), Raman spectroscopy, fluorescence spectroscopy, FTIR spectroscopy, X‐ray diffraction, and by using rheological experiments. The native hydrogel exhibited interesting fluorescence properties, as well as a self‐healing property. Interestingly, the self‐healing, thixotropy, and stiffness of the native hydrogel can be successfully modulated by incorporating carbon‐based nanomaterials, including graphene, pristine single‐walled carbon nanotubes (Pr‐SWCNTs), and both graphene and Pr‐SWCNTs, within the native gel system. The self‐recovery time of the gel was shortened by the inclusion of reduced graphene oxide (RGO), Pr‐SWCNTs, or both RGO and Pr‐SWCNTs. Moreover, hybrid gels that contained RGO and/or Pr‐SWCNTs exhibited interesting semiconducting behavior.     

Molecularly imprinted polyaniline-polyvinyl sulphonic acid composite based sensor for para-nitrophenol detection

We report results of the studies relating to the fabrication and characterization of a conducting polymer based molecularly imprinted para-nitrophenol (PNP) sensor. A water pollutant, para-nitrophenol is electrochemically imprinted with polyvinyl sulphonic acid (PVSA) doped polyaniline onto indium tin oxide (ITO) glass substrate. This PNP imprinted electrode (PNPI-PANI-PVSA/ITO) prepared via chronopotentiometric polymerization and over-oxidation is characterized by Fourier transform infra-red spectroscopy (FT-IR), UV–visible (UV–vis) spectroscopy, contact angle (CA), scanning electron microscopy (SEM), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) studies. The response studies of PNPI-PANI-PVSA/ITO electrode carried out using DPV reveal a lower detection limit of 1 × 10⁻³ mM, improved sensitivity as 1.5 × 10⁻³ A mM⁻¹ and stability of 45 days. The PNPI-PANI-PVSA/ITO electrode shows good precision with relative standard deviation of 2.1% and good reproducibility with standard deviation of 3.78%.     

Synthesis, characterization and reactivity of some novel dinuclear mixed-ligand peroxouranium(VI) complexes

Novel anionic dinuclear mixed-ligand peroxo complexes of the type [(UO₂)₂(O₂)₃L(H₂O)₂]³⁻ (L = Histidinate, aspartate, salicylate, Imidazolate and glutamate) have been synthesized from the interaction of uranyl ion (UO₂²⁺) with peroxide (O₂²⁻) in the presence of the respective coligand (L) at pH 9–10. The sparingly soluble complexes were characterized by elemental analyses, FT-IR, laser Raman (LR) and UV-vis spectroscopy and solution electrical conductance measurements. Based on these studies, a double bridged dinuclear structure involving one peroxo and the mixed ligand L (via-COO⁻) has been tentatively proposed. Infra-red coupled with LR spectra evidenced structurally different metal bound peroxides (ν² and σ:σ). An aqueous solution of the salicylate and aspartate complexes have been shown to convert triphenylphosphine (PPh₃), cyclohexene, styrene and SO₂ to the corresponding OPPh₃, 1,2 cyclohexanediol, phenylethyleneglycol and SO₄²⁻, respectively.     

Branched and dendritic metallo-carbosiloxanes with OCH2PPh2MLn end-grafted units

A straightforward method for the preparation of metallo carbosiloxanes of type Si(OCH₂CH₂CH₂SiMe₂[OCH₂PPh₂M(CO)_n])₄ (n = 3, M = Ni, 7a; n = 4, M = Fe, 7b; n = 5: M = Mo, 7c; M = W, 7d), Si(OCH₂CH₂CH₂SiMe[OCH₂PPh₂Ni(CO)₃]₂)₄ (8) and Me₂Si(OCH₂CH₂CH₂SiMe[OCH₂PPh₂Ni(CO)₃]₂)₂ (11) is described. The reaction of Si(OCH₂CH₂CH₂SiMeXCl)₄ (1: X = Me, 2: X = Cl) or Me₂Si(OCH₂CH₂CH₂SiMeCl₂)₂ (9) with HOCH₂PPh₂ (3) produces Si(OCH₂CH₂CH₂SiMe₂(OCH₂PPh₂))₄ (4), Si(OCH₂CH₂CH₂SiMe(OCH₂PPh₂)₂)₄ (5) or Me₂Si(OCH₂CH₂CH₂SiMe(OCH₂PPh₂)₂)₂ (10) in presence of DABCO. Treatment of the latter molecules with Ni(CO)₄ (6a), Fe₂(CO)₉ (6b), M(CO)₅(Thf) (6c: M = Mo; 6d: M = W), respectively, gives the title compounds 7a-7d, 8 and 11 in which the PPh₂ groups are datively bound to a 16-valence-electron metal carbonyl fragment.The formation of analytical pure and uniform branched and dendritic metallo carbosiloxanes is based on elemental analysis, and IR, ¹H, ¹³C{¹H}, ²⁹Si{¹H} and ³¹P{¹H} NMR spectroscopic studies. In addition, ESI-TOF mass spectrometric studies were carried out.     

Relaxation of the rigid backbone of an oligoamide-foldamer-based α-helix mimetic: identification of potent Bcl-xL inhibitors

By conducting a structure-activity relationship study of the backbone of a series of oligoamide-foldamer-based α-helix mimetics of the Bak BH3 helix, we have identified especially potent inhibitors of Bcl-x(L). The most potent compound has a K(i) value of 94 nM in vitro, and single-digit micromolar IC(50) values against the proliferation of several Bcl-x(L)-overexpressing cancer cell lines.     

Induced detachment of coalescing droplets on superhydrophobic surfaces

Coalescence of a falling droplet with a stationary sessile droplet on a superhydrophobic surface is investigated by a combined experimental and numerical study. In the experiments, the droplet diameter, the impact velocity, and the distance between the impacting droplets were controlled. The evolution of surface shape during the coalescence of two droplets on the superhydrophobic surface is captured using high speed imaging and compared with numerical results. A two-phase volume of fluid (VOF) method is used to determine the dynamics of droplet coalescence, shape evaluation, and contact line movement. The spread length of two coalesced droplets along their original center is also predicted by the model and compared well with the experimental results. The effect of different parameters such as impact velocity, center to center distance, and droplet size on contact time and restitution coefficient are studied and compared to the experimental results. Finally, the wetting and the self-cleaning properties of superhydrophobic surfaces have been investigated. It has been found that impinging water drops with very small amount of kinetic impact energy were able to thoroughly clean these surfaces.     

A switchable palladium-complexed molecular shuttle and its metastable positional isomers

We report the design, synthesis, characterization, and operation of a [2]rotaxane in which a palladium-complexed macrocycle can be translocated between 4-dimethylaminopyridine and pyridine monodentate ligand sites via reversible protonation, the metal remaining coordinated to the macrocycle throughout. The substitution pattern of the ligands and the kinetic stability of the Pd-N bond means that changing the chemical state of the thread does not automatically cause a change in the macrocycle's position in the absence of an additional input (heat and/or coordinating solvent/anion). Accordingly, under ambient conditions any of the four sets of protonated and neutral, stable, and metastable co-conformers of the [2]rotaxane can be selected, manipulated, isolated, and characterized.     

A short and efficient synthesis of 5-hydroxymethylcyclopent-2-enol from d-glucose and its elaboration to the carbanucleoside (−)-carbovir

Introduction of an allyl functionality at C-3 of 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose followed by olefination at C-5 and C-6 provided 1,6-diene 5 which, upon ring closing metathesis and subsequent functional group manipulation, furnished the key cyclopentene diacetate 7, which was elaborated to carbanucleoside (−)-carbovir 1.