Surface Modified Persistent Luminescence Probes for Biosensing and Bioimaging:A Review

Persistent luminescence materials (PLMs) are a class of unique lumi-nescent materials that can remain luminescent for a few milliseconds to days without constan...     

SERS- and Electrochemically Active 3D Plasmonic Liquid Marbles for Molecular-Level Spectroelectrochemical Investigation of Microliter Reactions

Liquid marbles are emergent microreactors owing to their isolated environment and the flexibility of materials used. Plasmonic liquid marbles (PLMs) are demonstrated as the smallest spectroelectrochemical microliter-scale reactor for concurrent spectro- and electrochemical analyses. The three-dimensional Ag shell of PLMs are exploited as a bifunctional surface-enhanced Raman scattering (SERS) platform and working electrode for redox process modulation. The combination of SERS and electrochemistry (EC) capabilities enables in situ molecular read-out of transient electrochemical species, and elucidate the potential-dependent and multi-step reaction dynamics. The 3D configuration of our PLM-based EC-SERS system exhibits 2-fold and 10-fold superior electrochemical and SERS performance than conventional 2D platforms. The rich molecular-level electrochemical insights and excellent EC-SERS capabilities offered by our 3D spectroelectrochemical system are pertinent in charge transfer processes.     

SERS‐ and Electrochemically Active 3D Plasmonic Liquid Marbles for Molecular‐Level Spectroelectrochemical Investigation of Microliter Reactions

Liquid marbles are emergent microreactors owing to their isolated environment and the flexibility of materials used. Plasmonic liquid marbles (PLMs) are demonstrated as the smallest spectroelectrochemical microliter‐scale reactor for concurrent spectro‐ and electrochemical analyses. The three‐dimensional Ag shell of PLMs are exploited as a bifunctional surface‐enhanced Raman scattering (SERS) platform and working electrode for redox process modulation. The combination of SERS and electrochemistry (EC) capabilities enables in situ molecular read‐out of transient electrochemical species, and elucidate the potential‐dependent and multi‐step reaction dynamics. The 3D configuration of our PLM‐based EC‐SERS system exhibits 2‐fold and 10‐fold superior electrochemical and SERS performance than conventional 2D platforms. The rich molecular‐level electrochemical insights and excellent EC‐SERS capabilities offered by our 3D spectroelectrochemical system are pertinent in charge transfer processes.     

Colloidal interactions mediated by end-adsorbing polymer-like micelles

We derive a statistical mechanical model for colloidal interactions mediated by polymer-like micelles (PLMs) that adsorb at the colloid surface. The model considers the end-adsorption and reversible scission of ideal chains, and is based on experimentally measurable parameters relevant to PLMs. The model predicts interparticle attractions due to micellar bridging that are stronger and longer-range than those encountered in ordinary telechelic polymers. Mapping the analytical potential onto the more familiar Double Yukawa potential allows, for the first time, accurate, a priori prediction of suspension microstructure and phase behavior when compared to experimental data for model nanoparticles dispersed in wormlike micelles over a range of solution conditions.     

Permeation liquid membrane for trace metal speciation in natural waters. Transport of liposoluble Cu(II) complexes

In this paper, the transport of Cu(II) in the presence of lipophilic Cu(II) organic complexes through permeation liquid membranes (PLMs) have been investigated. In natural waters, small organic compounds, which form liposoluble neutral complexes with Cu(II), are potentially toxic and bioavailable. Hence, to understand the role of liposoluble Cu(II) complexes in natural waters, four organic ligands: phthalic acid, bipyridyl, pyrocatechol and hydroxyquinoline, which form uncharged or lipophilic Cu(II) complexes, were tested. The results showed that the transport of lipophilic Cu(II) complexes through PLM depends on the lipophilicity of the complex. Applications of PLMs in natural waters are presented.     

Biosynthesis of phoslactomycins: cyclohexanecarboxylic acid as the starter unit

Phoslactomycins (PLMs) A-F, produced by actinomycetes are polyketide-type antibiotics derived from a hydroxycyclohexanecarboxylic acid or a cyclohexanecarboxylic acid starter unit. Feeding experiments with [2-¹³C]shikimic acid indicated that the C-18 carbon of PLMs comes from C-5 of shikimate. Further feeding studies of cis and trans-3-hydroxy[7-¹³C]cyclohexanecarboxylic acid, [7-¹³C]- and [²H₁₁]cyclohexanecarboxylic acid have suggested that the starter unit in the PLM biosynthesis is not cis-3-hydroxycyclohexanecarboxylate but cyclohexanecarboxylate and that PLM-B is produced initially, and subsequently converted to other analogs by hydroxylation and acylation.     

Stability of model membranes in the presence of organotin compounds

The influence of tri‐ and di‐alkyltins (TATs and DATs) as well as di‐ and triphenyltin compounds (DPhTs and TPhTs) on haemolysis of red blood cells (RBCs) and stability of planar lipid membranes (PLMs) has been studied. The results obtained show that the efficiency of TATs (trimethyl‐, triethyl‐, tri‐n‐propyl‐ and tributyl‐tin chlorides) in destroying PLMs did not differ greatly when the compounds were studied in solutions of physiological pH (phosphate buffer, pH 7.4). A decrease in pH to 5.0 caused small changes in the efficiency of the three largest TAT molecules and a significant decrease in the efficiency of trimethyltin chloride. Both haemolytic and PLM experiments showed that the most active TAT was tri‐n‐propyltin chloride. The destructive action of DAT (dimethyl‐ and dibutyltin) and DPhT dichlorides was somewhat more differentiated. Dimethyltin dichloride (DMT) interaction with model membranes was a little weaker than that of DPhT and dibutyltin dichlorides and all these compounds influenced the model membranes to a lesser extent than TATs or TPhT. To bring about comparable haemolysis effects the dichlorides had to be used at much greater concentrations than the chlorides. The haemolytic properties of the dichlorides, especially of that of DMT, significantly increased in solution at pH 5.0. TPhT chloride interacted with model membranes similarly to TAT chlorides. Also, no great difference in efficiency of this compound was found for the two buffer solutions used. Copyright © 2000 John Wiley & Sons, Ltd.     

Stabilization of alkylated azacrown ether by fatty acid at the air-water interface

The adsorbed amount of partially deuterated dihexadecyl-diaza-18-crown-6 ether (d-ACE16) in the presence of different chain length fatty acids as a function of surface pressure was determined by neutron reflectometry technique. The highest adsorbed amount of the azacrown ether was observed for the mixture of ACE16 with hexadecanoic (palmitic) acid, pointing to the importance of chain length matching between the two species for optimum stabilization of the mixed monolayer. The contrast variation technique was used to estimate the contribution to the total adsorbed amount from stearic acid and ACE16. It was found that the mixed Langmuir monolayer is stable against dissolution up to a surface pressure of 20 mN m(-1). Above this pressure, however, the spread and adsorbed amounts start to deviate, indicative of partial dissolution into the aqueous subphase. The consequences of this behavior for the transport of metal ions through the interfaces of permeation liquid membranes (PLMs) are discussed.     

cis-Delta(2,3)-double bond of phoslactomycins is generated by a post-PKS tailoring enzyme

The antifungal phoslactomycins (PLM A-F), produced by Streptomyces sp. HK803, are structurally unusual in that three of their four double bonds are in the cis form (Delta12,13, Delta14,15, Delta2,3). The PLM polyketide synthase (PKS) has the predicted dehydratase catalytic domain in modules 1, 2, and 5 required for establishing two of these cis double bonds (Delta12,13, Delta14,15), as well as the only trans Delta6,7 double bond. By contrast, the formation of the cis Delta2,3 in the unsaturated lactone moiety of PLMs has presented an enigma because the predicted dehydratase domain in module 7 is absent. Herein, we have demonstrated that the plmT2 gene product, with no homology to PKS dehydratase domains, is required for efficient formation of the cis Delta2,3 alkene. A series of new PLM products in which the C3 hydroxyl group is retained are made in plmT2 deletion mutants. In all of these cases, however, the hydroxyl group is esterified with malonic acid. These malonylated PLM products are converted to the corresponding cis Delta2,3 PLM products and acetic acid by a facile base-catalyzed decarboxylative elimination reaction. Complete or partial restoration of natural PLM production in a plmT2 deletion mutant can be accomplished by plasmid based expression of plmT2 or fos ORF4 (a homologous gene from the fostriecin biosynthetic gene cluster), respectively. The data indicate that dehydratase-independent pathways also function in establishment of unsaturated 6-membered lactone moieties in other PKS pathways and provide the first biosynthetic insights into the possible routes by which unusual malonylated polyketide products are generated.     

Roles of dynamic metal speciation and membrane permeability in metal flux through lipophilic membranes: general theory and experimental validation with nonlabile complexes

The study of the role of dynamic metal speciation in lipophilic membrane permeability in aqueous solution requires accurate interpretation of experimental data. To meet this goal, a general theory is derived for describing 1:1 metal complex flux, under steady-state and ligand excess conditions, through a permeation liquid membrane (PLM). The theory is applicable to fluxes through any lipophilic membrane. From this theory, fluxes in the three rate-limiting conditions for metal transport are readily derived, corresponding, namely, to (i) diffusion in the source solution, (ii) diffusion in the membrane, and (iii) the chemical kinetics of formation/dissociation of the metal complex in the interfacial reaction layer. The theory enables discussion of the reaction layer concept in a more general frame and also provides unambiguous criteria for the definition of an inert metal complex. The theoretical flux equations for fully labile complexes were validated in a previous paper. The general theory for semi- or nonlabile complexes is validated here by studying the flux of Pb(II) through PLMs in contact with solutions of Pb(II)-NTA and Pb(II)-TMDTA at different pHs and flow rates.     

Toxicity and model membrane modifying properties of organolead compounds

The influence of trialkylleads on haemolysis of red blood cells (RBCs), growth of Spirodela oligorrhiza and stability of planar lipid membranes (PLMs) at different pH of solution has been studied. The results obtained show that the efficiency of trialkylleads (methyl‐, ethyl‐, propyl‐ and butyl‐lead chlorides) in modifying the physiological and mechanical properties of the objects studied depended both on pH of solution and hydrophobicity of the compounds. Namely, it was found that this efficiency increased with pH of solution. The most significant increase was observed in PLM experiments. Also, the hydrophobicity of trialkylleads influenced the properties mentioned. The more hydrophobic a compound the greater was its haemolytic toxicity. The same applies to the physiological toxicity ­of the compounds, whose measure was 50% inhibition of plant growth. Generally, the sequence of modifying possibilities of the compounds studied at any pH of the solution was the following:

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