Deposition of DNA-functionalized gold nanospheres into nanoporous surfaces

We report the deposition of DNA-conjugated gold nanospheres into arrays of surface nanopores obtained from hexagonally ordered thin polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer films on silicon. The deposition occurs spontaneously from aqueous solution and is driven by either electrostatic interactions or specific DNA hybridization events between the DNA nanospheres and the surface nanopores. To mitigate this spontaneous deposition, we have chemically modified the nanopores with either positively charged aminosilanes or oligonucleotide probe sequences. The deposition of DNA nanospheres into the surface nanopores was characterized by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). We have observed preferential immobilization of individual DNA nanospheres within the nanopores, based on the size matching between the two entities. The inclusion density and selectivity of DNA nanosphere deposition into the surface nanopores was found to depend predominantly on the methods through which the nanoporous surfaces were prepared and chemically functionalized.     

Ultrafast intermolecular electron transfer dynamics: Perylene in electron-accepting micellar medium

The dynamics of ultrafast photoinduced intermolecular electron transfer (ET) from the excited singlet (S1) state of perylene (Pe) to an electron-accepting cationic surfactant molecule, N-cetylpyridinium chloride (CPC), in aqueous micellar solutions has been investigated using the femtosecond transient absorption spectroscopic technique with temporal resolution of 120 fs. The Pe molecule is localized at or near the micellar surface, where it coexists with the pyridinium moieties (headgroups of the micelle) of the surfactant molecule. Following photoexcitation of Pe, an electron is transferred to the neat and geometrically restricted headgroup of the micelle. Dynamics of the forward ET process as well as the geminate recombination or back ET (BET) process have been followed by monitoring the temporal evolution of the S1 state of Pe and the cation radical of Pe (Pe*+), respectively. The multiexponential forward ET process indicates that the ET dynamics is highly correlated with the spatial distributions of the micellar headgroups around a donor Pe molecule and thus dependent on the donor-acceptor distance. The distance-dependent ET and BET rates have been calculated following the method of Weidemaier and Fayer (J. Chem. Phys. 1995, 102, 3820) to get the best fit parameters for the multiexponetial temporal profiles for the S1 state of Pe as well as Pe*+. Because the acceptor is a constituent of the neat micellar medium, their confinement on the surface of the microheterogeneous medium provides a very large concentration such that, even though the forward transfer rate is 0.06 ps(-1) at the distance of closest approach, the ET process is complete within a 200-ps time domain. If the concepts of distribution of ET distances are utilized, the possible role of material diffusion on the kinetics of forward ET is ruled out. This is an experimental study to show, for the first time, the ultrafast distance-dependent light-induced ET dynamics following both the excited state of the donor and the cation radical formed in an ET process using the transient absorption spectroscopic technique in a self-reactive restrictive environment.     

Can functionalized cucurbituril bind actinyl cations efficiently? A density functional theory based investigation

The feasibility of using cucurbituril host molecule as a probable actinyl cation binders candidate is investigated through density functional theory based calculations. Various possible binding sites of the cucurbit[5]uril host molecule to uranyl are analyzed and based on the binding energy evaluations, μ(5)-binding is predicted to be favored. For this coordination, the structure, vibrational spectra, and binding energies are evaluated for the binding of three actinyls in hexa-valent and penta-valent oxidation states with functionalized cucurbiturils. Functionalizing cucurbituril with methyl and cyclohexyl groups increases the binding affinities of actinyls, whereas fluorination decreases the binding affinities as compared to the native host molecule. Surprisingly hydroxylation of the host molecule does not distinguish the oxidation state of the three actinyls.     

Emulsion of aqueous-based nonspherical droplets in aqueous solutions by single-chain surfactants: templated assembly by nonamphiphilic lyotropic liquid crystals in water

Single-chain surfactants usually emulsify and stabilize oily substances into droplets in an aqueous solution. Here, we report a coassembly system, in which single types of anionic or non-ionic surfactants emulsify a class of water-soluble nonamphiphilic organic salts with fused aromatic rings in aqueous solutions. The nonamphiphilic organic salts are in turn promoted to form droplets of water-based liquid crystals (chromonic liquid crystals) encapsulated by single-chain surfactants. The droplets, stabilized against coalescence by encapsulated in a layer (or layers) of single chain surfactants, are of both nonspherical tactoid (elongated ellipsoid with pointy ends) and spherical shapes. The tactoids have an average long axis of ～9 μm and a short axis of ～3.5 μm with the liquid crystal aligning parallel to the droplet surface. The spherical droplets are 5-10 μm in diameter and have the liquid crystal aligning perpendicular to the droplet surface and a point defect in the center. Cationic and zwitterionic surfactants studied in this work did not promote the organic salt to form droplets. These results illustrate the complex interplay of self-association and thermodynamic incompatibility of molecules in water, which can cause new assembly behavior, including potential formation of vesicles or other assemblies, from surfactants that usually form only micelles. These unprecedented tactoidal shaped droplets also provide potential for the fabrication of new soft organic microcapsules.     

Dynamic properties of water around a protein-DNA complex from molecular dynamics simulations

Formation of protein-DNA complex is an important step in regulation of genes in living organisms. One important issue in this problem is the role played by water in mediating the protein-DNA interactions. In this work, we have carried out atomistic molecular dynamics simulations to explore the heterogeneous dynamics of water molecules present in different regions around a complex formed between the DNA binding domain of human TRF1 protein and a telomeric DNA. It is demonstrated that such heterogeneous water motions around the complex are correlated with the relaxation time scales of hydrogen bonds formed by those water molecules with the protein and DNA. The calculations reveal the existence of a fraction of extraordinarily restricted water molecules forming a highly rigid thin layer in between the binding motifs of the protein and DNA. It is further proved that higher rigidity of water layers around the complex originates from more frequent reformations of broken water-water hydrogen bonds. Importantly, it is found that the formation of the complex affects the transverse and longitudinal degrees of freedom of surrounding water molecules in a nonuniform manner.     

Sensitivity of polar solvation dynamics to the secondary structures of aqueous proteins and the role of surface exposure of the probe

The structure and dynamics of water around a protein is expected to be sensitive to the details of the adjacent secondary structure of the protein. In this article, we explore this sensitivity by calculating both the orientational dynamics of the surface water molecules and the equilibrium solvation time correlation function of the polar amino acid residues in each of the three helical segments of the protein HP-36, using atomistic molecular dynamics simulations. The solvation dynamics of polar amino acid residues in helix-2 is found to be faster than that of the other two helices (the average time constant is smaller by a factor of 2), although the interfacial water molecules around helix-2 exhibit much slower orientational dynamics than that around the other two helices. A careful analysis shows that the origin of such a counterintuitive behavior lies in the dependence of the solvation time correlation function on the surface exposure of the probe-the more exposed is the probe, the faster the solvation dynamics. We discuss that these results are useful in explaining recent solvation dynamics experiments.     

Magnetostatic modulation of nonlinear refractive index and absorption in quantum wires

The magnetic-field dependence of the nonlinear differential refractive index Δnand absorption Δα in quantum wires—measured by non-degenerate pump and probe spectroscopy—is investigated theoretically. The nonlinearities arise from population saturation of the excitonic state under optical pumping and the formation of biexcitons (excitonic molecules). Both Δnand Δ α exhibit positive and negative peaks at certain pump and probe detuning frequencies associated with the formation of biexcitons and bleaching of excitons, respectively. The amplitude, lineshape and the frequency at which these peaks occur can be modulated by a magnetic field which opens up the possibility of realizing novel magneto-optical devices. Additionally, the magnetic field may allow us to realize a relatively large variation in the differential refractive index over a range of frequencies without significant accompanying absorption, thereby allowing the observation of optical bistability.     

Some remarks on the dynamical origin of charge and space-time quantisation

It is argued here that the concept of dynamical origin of charge as formulated in a previous paper requires the quantisation of space-time. Indeed, in this scheme, it is pointed out that the quantisation of electric charge in unit ofe is a direct consequence of this space-time quantisation.     

Study of gain flatness for multi-channel amplification in single stage EDFA for WDM applications

In this paper, gain flatness is studied for simultaneous 16-ITU-T channel amplifications at C-band (1,532–1,558 nm) in a single stage EDFA for WDM application at different average inversion levels. The inversion levels are varied due to the change of the input signal levels from the targeted operating point and also for dropping few numbers of channels. Specially designed gain flattening filter (GFF) is used in order to get the flat gain with gain variation ±0.5 dB for −20 dBm/ch input signal power (total input signal power is −8.0 dBm) at a fixed average inversion level which is maintained by proper selection of optimum fibre length and pump power. A specific loss spectrum of GFF is obtained by writing a chirped fibre Bragg grating of length 20 mm. Gain variations are studied by changing the total input signal levels from −8.0 dBm to −20.0 dBm and maintained within 20.0 ± 0.5 dB by using automatic gain control (AGC) circuit. About 15 out of 16 channels are dropped and observed ± 0.5 dB gain-variation which is an important parameter in optical network system.