Anion Sensing with Luminescent Quantum Dots – A Modular Approach Based on the Photoinduced Electron Transfer (PET) Mechanism

A CdSe–ZnS quantum dot (QD) has been surface functionalised with 1-(2-mercapto-ethyl)-3-phenyl-thiourea in the fluorophore–spacer–receptor format typical of Photoinduced Electron Transfer (PET) based organic dye sensors. The resulting QD conjugate was tested for selectivity toward the tetrabutylammonium salts of fluoride, chloride, bromide, hydrogen sulfate and acetate. Addition of fluoride, chloride and acetate ions resulted in an approximate 90% quenching of the original fluorescence intensity, while bromide and hydrogen sulfate had almost no effect. The observed quench was attributed to an increase in the reduction potential of the receptor upon anion binding resulting in an increase in PET from the excited QD to the receptor and a concomitant reduction in fluorescence intensity. The selectivity and sensitivity were comparable to an analagous organic dye based sensor where a similar receptor was bound to an anthracene fluorophore. Thus a modular approach is evident where a receptor used in an organic dye based sensor can be adapted and successfully used with QD’s.     

Luminescent Detection of ATP in Aqueous Solution Using Positively Charged CdSe–ZnS Quantum Dots

Commercially available CdSe–ZnS Quantum Dots (QDs) have been modified by exchanging the hydrophobic surface ligands with (2-mercaptoethyl)-trimethylammonium chloride. The resulting water soluble conjugate was titrated with solutions of adenosine triphosphate (ATP), adenosine diphosphate, adenosine monophosphate, guanosine triphosphate (GTP), guanosine diphosphate and guanosine monophosphate in 0.01 M 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer (pH 7.4). A strong fluorescence quench of about 80% was observed for ATP, a quench of 25% was observed for GTP while the others had virtually no effect. The quenching effect of ATP and GTP was attributed to the high negative charge density associated with these substrate’s resulting in a strong attraction to the QD surface enabling them to engage in electron transfer with the excited QD. The lack of fluorescence quenching associated with the other nucleotides was most likely due to their reduced charge density resulting in a lower affinity for the QD surface.     

Antitumor Activity and Physicochemical Properties of New Thiosemicarbazide Derivative and Its Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) Complexes

A novel biologically active thiosemicarbazide derivative ligand L (N-[(phenylcarbamothioyl)amino]pyridine-3-carboxamide) and a series of its five metal(II) complexes, namely: [Co(L)Cl₂], [Ni(L)Cl₂(H₂O)], [Cu(L)Cl₂(H₂O)], [Zn(L)Cl₂] and [Cd(L)Cl₂(H₂O)] have been synthesized and thoroughly investigated. The physicochemical characterization of the newly obtained compounds has been performed using appropriate analytical techniques, such as ¹H and ^l3C nuclear magnetic resonance (NMR), inductively coupled plasma (ICP), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR) and magnetic measurements. In order to study the pharmacokinetic profile of the compounds, ADMET analysis was performed. The in vitro studies revealed that the synthesized compounds exhibit potent biological activity against A549 human cancer cell line.     

Degradation of biologically active substances by vapor-phase hydrogen peroxide

We have examined the potential of vapor-phase hydrogen peroxide (VPHP) for degradation of 21 structurally different pharmaceutical substances. Our results show that VPHP can be used to degrade pharmaceuticals, but it was not universally applicable to all the drugs tested. Structural analysis revealed a significant correlation of the molecular structure of a compound with its susceptibility to VPHP. Tertiary amino groups seem to be the initiation centers, although the overall susceptibility of a substance depends on other factors also. Several tested substances underwent significant structural changes, suggesting a possible decrease in their biological activity. As far as we are aware, this is one of the first reports of application of VPHP to the decontamination of hazardous chemicals.     

Needle-Trap Device (NTD) Packed with Reduced Graphene Oxide (rGO) for Sample Preparation Prior to the Determination of Polycyclic Aromatic Hydrocarbons (PAHs) from Aqueous Samples by Gas Chromatography–Mass spectrometry (GC-MS)

A needle trap device (NTD) was developed for the extraction of polycyclic aromatic hydrocarbons (PAHs) from liquid samples followed by determination by gas chromatography–mass spectrometry (GC-MS). The extraction was performed using the dynamic sampling approach, in which a liquid sample was pumped through the system. Due to the flexibility and softness of graphene, its application in NTD may be difficult. Herein, the effectiveness of reduced graphene oxide (rGO) packed in NTD in dynamic extraction of PAHs was evaluated. Several experimental parameters, such as the adsorbent mass, eluent type and its volume, as well as the sample volume were optimized to achieve satisfactory performance for dynamic extraction. Comparative studies showed that the extraction performance of rGO-NTD was better than using NTDs packed with other sorbents such as activated carbon. The recovery rate for reduced graphene oxide exceeded 92%. Comparison of dynamic and headspace sampling showed comparable results but the dynamic mode is more suitable for field measurements. The recovery rates of PAHs spiked in water samples were from 76.5 to 100.2% and the relative standard deviation values were from 2.7 to 7.5% under the optimal conditions. This work reveals the potential of NTD with a graphene-based material for sample preparation before chromatographic analysis of liquid samples.     

Studies on Acoustic Behavior, Viscosity, and Density of Some Commercial Extractants and Their Molecular Interaction with Diluent, Modifier, and Extractant

Acoustical and viscosity measurements have been made for binary liquid mixtures of commercially available solvent extractants, LIX reagents such as LIX 622 and LIX 860 in benzene, amyl alcohol, and tri-n-butyl phosphate (TBP) at 303.15 K. The measured values of ultrasonic velocity, density, and viscosity have been utilized to compute some acoustic as well as thermodynamic parameters such as intermolecular free length, L _f, isentropic compressibility, _s, molar volume, V, and Gibb's excess free energies of activation of viscous flow, G*^E. These parameters along with the derived values of isentropic compressibility, _s ^E, intermolecular free length, L _f ^E, and molar volume, V ^E, have been utilized for a comparative study of molecular interactions between the components present in different liquid systems. The experimental ultrasonic velocities for aforementioned mixtures have been compared with theoretically estimated velocities using different empirical relations, and the relative merits of these theories and relations have been discussed in terms of percentage variation.     

Synthesis of poly(disulfide)s with narrow molecular weight distributions via lactone ring-opening polymerization

We report the first example of controlled polymerization of poly(disulfide)s with narrow molecular weight distributions. 1,4,5-oxadithiepan-2-one (OTP), a disulfide-containing 7-membered ring lactone, was polymerized by using the diphenylphosphate (DPP) catalyzed lactone ring-opening polymerization method. The polymerization proceeded in a living manner, and the resulting polymers displayed very narrow polydispersity index (PDI) values below 1.1 and excellent backbone degradability responding to reducing conditions and UV irradiation.

We report the first example of controlled polymerization of poly(disulfide)s with narrow molecular weight distributions.     

Hyperreflexivity of bilattices

The notion of a bilattice was introduced by Shulman. A bilattice is a subspace analogue for a lattice. In this work the definition of hyperreflexivity for bilattices is given and studied. We give some general results concerning this notion. To a given lattice L we can construct the bilattice \(\sum {_L} \). Similarly, having a bilattice Σ we may consider the lattice \(\mathcal{L}_\Sigma \). In this paper we study the relationship between hyperreflexivity of subspace lattices and of their associated bilattices. Some examples of hyperreflexive or not hyperreflexive bilattices are given.