A general method to determine ionization constants of responsive polymer thin films

A general method has been developed to determine the ionization constants of polymer thin films based on the stimuli-responsiveness of the polymer. Robust polymer films were fabricated on silicon wafers and gold slides using perfluorophenyl azide (PFPA) as the coupling agent. The ionization constants were measured by a number of techniques including ellipsometry, dynamic contact angle goniometry, and surface plasmon resonance imaging (SPRi). Using poly(4-vinylpyridine) (P4VP) as the model system, P4VP thin films were fabricated and the ionization constants of the films were measured taking advantage of the pH responsive property of the polymer. The pK(a) determined by ellipsometry, ~4.0, reflects the swelling of the polymer film in response to pH. The pK(a) value calculated from the dynamic contact angle measurements, ~5.0, relies on the change in hydrophilicity/hydrophobicity of the films as the polymer undergoes protonation/deprotonation. The pK(a) value measured by SPRi, ~4.9, monitors in situ the change of refractive index of the polymer thin film as it swells upon protonation. This was the first example where SPRi was used to measure the ionization constants of polymers.     

Carboxyalkyl peptoid PNAs: synthesis and hybridization properties

N^γ-Carboxyalkyl modified peptide nucleic acids (PNAs), containing the four canonical nucleobases, were prepared via solid-phase oligomerization. The inserted peptoid monomers 1 and 2 were constructed through simple synthetic procedures, utilizing appropriate glycidol and iodoalkyl electrophiles. Thermal denaturation studies, performed with complementary antiparallel DNA strands, demonstrated that the length of the N^γ-side chain strongly influences the modified PNAs hybridization properties. Moreover, multiple negative charges on the oligoamide backbone, when present on γ-nitrogen C₆ side chains proved to be beneficial for the oligomers’ water solubility and DNA hybridization specificity.     

Two-photon excitation with pico-second fluorescence lifetime imaging to detect nuclear association of flavanols

Two-photon excitation enabled for the first time the observation and measurement of excited state fluorescence lifetimes from three flavanols in solution, which were ∼1.0 ns for catechin and epicatechin, but <45 ps for epigallocatechin gallate (EGCG). The shorter lifetime for EGCG is in line with a lower fluorescence quantum yield of 0.003 compared to catechin (0.015) and epicatechin (0.018).     

Inclusion controlled lanthanide-imidazolium functionalised carboxylate complexation

Imidazolium functionalized carboxylic acid forms a multi-component material with p-sulfonatocalix[4]arene and aquated lanthanide ions, stabilising dinuclear metal complexes for Y(3+) and Gd(3+). These have the simplest binding of two bridging carboxylates between the two metal centres (Y(3+)), or the same arrangement along with the simplest binding of one carboxylate bridging two metal ions for the larger metal ion (Gd(3+)).     

Solid-phase-assisted synthesis of targeting peptide-PEG-oligo(ethane amino)amides for receptor-mediated gene delivery

In the forthcoming era of cancer gene therapy, efforts will be devoted to the development of new efficient and non-toxic gene delivery vectors. In this regard, the use of Fmoc/Boc-protected oligo(ethane amino)acids as building blocks for solid-phase-supported assembly represents a novel promising approach towards fully controlled syntheses of effective gene vectors. Here we report on the synthesis of defined polymers containing the following: (i) a plasmid DNA (pDNA) binding domain of eight succinoyl-tetraethylenpentamine (Stp) units and two terminal cysteine residues; (ii) a central polyethylene glycol (PEG) chain (with twenty-four oxyethylene units) for shielding; and (iii) specific peptides for targeting towards cancer cells. Peptides B6 and c(RGDfK), which bind transferrin receptor and α(v)β(3) integrin, respectively, were chosen because of the high expression of these receptors in many tumoral cells. This study shows the feasibility of designing these kinds of fully controlled vectors and their success for targeted pDNA-based gene transfer.     

Apolar carbohydrates as DNA capping agents

Mono- and disaccharides have been shown to stack on top of DNA duplexes stabilizing sequences with terminal C-G base pairs. Here we present an apolar version of glucose and cellobiose as new capping agents that stack on DNA increasing considerably its stability with respect to their natural polyhydroxylated mono- and disaccharide DNA conjugates.     

Surface Defects Activating New Reaction Paths: Formation of Formate during Methanol Oxidation on Ru(0001)

Methanol was co‐adsorbed with oxygen on Ru(0001) under conditions approaching those of real catalysts: at room temperature and at relatively high pressures and exposures, together with a comparative analysis of flat and defective surfaces. To clarify reaction routes, parallel exposures to formaldehyde and oxygen have also been analyzed. It is found that for both mixtures of gases, a new reaction path is activated on defective surfaces, in which methanol is oxidized to formate. Furthermore, at variance with pure methanol adsorption, apart from CO, various intermediates are observed in both flat and defective surfaces. On flat surfaces, formaldehyde and formyl are recognized whereas on defective ones methoxy and formate are detected. A model involving steering effects is presented, which accounts for the activity of surface defects towards the synthesis of formate.     

State Independence for Tunnelling Processes Through Black Hole Horizons and Hawking Radiation

Tunnelling processes through black hole horizons have recently been investigated in the framework of WKB theory, discovering an interesting interplay with Hawking radiation. In this paper, we instead adopt the point of view proper of QFT in curved spacetime, namely, we use a suitable scaling limit towards a Killing horizon to obtain the leading order of the correlation function relevant for the tunnelling. The computation is done for a certain large class of reference quantum states for scalar fields, including Hadamard states. In the limit of sharp localization either on the external side or on opposite sides of the horizon, the quantum correlation functions appear to have thermal nature. In both cases the characteristic temperature is referred to the surface gravity associated with the Killing field and thus connected with the Hawking one. Our approach is valid for every stationary charged rotating non-extremal black hole. However, since the computation is completely local, it covers the case of a Killing horizon which just temporarily exists in some finite region, too. These results provide strong support to the idea that the Hawking radiation, which is detected at future null infinity and needs some global structures to be defined, is actually related to a local phenomenon taking place even for local geometric structures (local Killing horizons), existing just for a while.     

Role of hydrogen in dimerizaton of aluminum clusters: a theoretical study

We have used density functional theory to investigate how Al(13) cluster dimers can be formed with or without a bridging hydrogen. We have identified several stable dimers in which 0, 1, or 2 hydrogen atoms link two bare clusters together. Each of these structures can adsorb further H atoms in atop sites on the surface of the dimer. Additional dimers were identified with 3 and 4 H atoms linking the clusters but these are only stable in the multihydrogenated form. Reaction profiles for the formation of these dimers from a range of cluster and H atom combinations indicate that the dimer structures are energetically favored over the isolated clusters. This observation may have significant implications for the design of cluster-assembled materials.