Real-time probing of the growth dynamics of nanoparticles using potentiometric ion-selective electrodes

This Communication demonstrates the ability of potentiometric ion-selective electrodes (ISE) to probe the growth dynamics of metal nanoparticles in real-time. The new monitoring capability is illustrated using a solid-contact silver ISE for monitoring the hydroquinone-induced precipitation of silver on gold nanoparticle seeds. Potential-time recordings obtained under different conditions are used to monitor the depletion of the silver ion during the nanoparticle formation and shed useful insights into the growth dynamics of the nanoparticles. Such potentiometric profiles correlate well with the analogous optical measurements. The new real-time electrochemical probing of the particle growth process reflects the direct, rapid and sensitive response of modern ISE to changes in the level of the precipitated metal ion from the bulk solution and holds considerable promise for probing the preparation of different nanoscale materials.     

Fluorescence probing of albumin-surfactant interaction

Protein-surfactant interactions were studied using bovine serum albumin (BSA) and the three surfactants sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and poly(oxyethylene)isooctyl phenyl ether (TX-100). The surfactants used belong to three broad classes, i.e., anionic, cationic, and nonionic. These categories of surfactants were used to elucidate the mechanism of surfactant binding to BSA, at pH 7. The interactions were followed fluorimetrically using both intrinsic tryptophan (Trp) fluorescence and the fluorescence of an external label. The aggregation behavior of the surfactants were studied in the presence of BSA. Steady-state fluorescence studies indicate that all three surfactants bind to BSA in a cooperative manner. This cooperative binding affects the binding of the external label to BSA. All these effects are also manifested in time-resolved fluorescence studies. The effects of surfactants on acrylamide quenching and energy transfer from Trp in BSA to bound dye provided valuable insights into the structural modification of BSA in presence of surfactants. The surfactant-induced conformational change of BSA was also confirmed by circular dichroism studies. However, among the three categories of surfactants, the nonionic surfactant shows the least interaction with BSA.     

Spectroscopic probing of bile salt-albumin interaction

Interaction of the bile salts, sodium cholate and sodium deoxy cholate with albumin has been probed by fluorescence and circular dichroism studies. Both covalently and non-covalently labeled protein have been used to follow the aggregation of bile salts in presence of protein and to study bile salt-protein interactions in general. Time resolved studies, in agreement with steady-state fluorescence and circular dichroism studies, indicate alteration of protein secondary structure due to positive co-operative effects in bile salt binding to protein. These studies also indicate that covalent labeling may not always be good for studying proteins as it causes alteration of protein secondary structure.     

Molecular dynamics simulations of polycarbonate doped with Lemke chromophores

In the search for optimal electro-optical modulating materials we report in this work molecular dynamics simulations of polycarbonate doped with Lemke chromophores which is a promising candidate system for materials with such functionality. The simulations cover the electric field poling effects on the chromophore order at a temperature above the glass transition temperature (Tg) of the material, the cooling procedure from liquid state to the glass state in the presence of the poling field, and the back relaxation of the system after removal of the field. Our study shows that electric field poling results in a higher chromophore order and that the order is also maintained during the cooling procedure with the poling field applied. In the liquid state, the applied poling field has little effect on the structure of the material. However, after the cooling procedure, the structure changes significantly because the polymer matrix tends to become closely packed. Our study thus indicates that for the bulk material, the structure of the host matrix is very important in determining the performance of the material.     

Probing the sub-microsecond photodissociation dynamics in gas-phase retinal chromophores

The photoinduced fragmentation of a retinal model chromophore (all-trans-n-butyl protonated Schiff-base retinal) was studied in vacuo using a new experimental technique. The apparatus is able to record the photodissociation yield of gas-phase biomolecular ions in the first microseconds after absorption. Together with the existing ion storage ring ELISA, which operates on the millisecond to second time scale, the complete decay dynamics of such molecules can now be followed. In the case of retinal, the time-dependent fragmentation yield observed after irradiation with a 410 nm laser pulse exhibits contributions from one- and two-photon absorption, which decay non-exponentially with lifetimes on the order of 1 ms and 1 micros, respectively. The decay can be simulated using a statistical model, yielding good agreement with the experimental findings on both the millisecond and the microsecond time scales. No indication for nonstatistical processes is found for this molecule, the upper limit for a possible direct rate being a factor of 10(4) below the observed statistical dissociation rate.     

Single molecule probing of dynamics in supercooled polymers

Fluorescence experiments with single BODIPY molecules embedded in a poly(methyl acrylate) matrix have been performed at various temperatures in the supercooled regime. By using pulsed excitation, fluorescence lifetime and linear dichroism time trajectories were accessible at the same time. Both observables have been analyzed without data binning. While the linear dichroism solely reflects single particle dynamics, the fluorescence lifetime observable depends on the molecular environment, so that the dynamics from the polymer host surrounding a chromophore contributes to this quantity. We observe that the lifetime correlation decays slightly faster than polarization correlation, indicating the occurrence of large angular reorientations. Additionally, dichroism time trajectories have been adducted to reveal directly the geometry of rotational dynamics. We identify small but also significantly larger rotational jumps being responsible for the overall molecular reorientation.     

Real-time detection of the interaction between anticancer drug daunorubicin and cancer cells by Au-MCNT nanocomposites modified electrodes

In this study,we have prepared the blending of gold nanoparticles-multiwalled nanotubes (Au-MCNTs) and then applied the new nanocomposites to modify the glassy carbon electrode (GCE) for highly sensitive detection of the interaction between anticancer drug daunorubicin (DNR) and cancer cells. Electrochemical analysis indicates that the Au-MCNT modified GCE shows high sensitivity and could track the real time response of cancer cells under DNR treatments. Therefore,this new nano-interface and Au-MCNT modifie...     

纳米金-多壁碳纳米管复合物修饰电极对柔红霉素作用癌细胞的实时检测

本文通过制备纳米金-多壁碳纳米管复合物(Au-MCNT)修饰玻碳电极,建立了抗癌药物柔红霉素(DNR)作用癌细胞的高灵敏检测方法,研究并追踪了DNR与癌细胞相互作用过程中细胞对DNR的电化学实时响应.结果表明,Au-MCNT修饰电极能实现抗癌药物DNR作用癌细胞的高灵敏实时检测.基于该纳米复合材料的电化学药物传感分析方法可作为抗癌研究中一种方便、快捷、灵敏的实时检测手段,在生物医学等领域具有良好的应用前景.     

Iron-sulfur proteins: structural chemistry of their chromophores and related systems

Intensive studies of iron-sulfur proteins were begun only a decade or so ago but many biological and physicochemical data have since been accumulated and summarized^[1–5]. As a result of the very recent X-ray analyses of the structures of rubredoxin^[6], ferredoxin (Peptococcus aerogenes)^[7] and the Chromatium vinosum high potential iron protein (Hipip)^[8], it has become possible to review our understanding of the nature and function of the inorganic chromophores in these proteins; to relate these findings to ‘model’ systems of varying relevance; but of more general interest, to comment on redox processes in biological systems particularly with respect to what might be termed electron transfer—allosteric effects in metalloenzymes.     

X-ray photoemission for probing charging/discharging dynamics

A novel technique is introduced for probing charging/discharging dynamics of dielectric materials in which X-ray photoemission data is recorded while the sample rod is subjected to +/-10.0 V square-wave pulses with varying frequencies in the range of 10(-3) to 10(3) Hz. For a clean silicon sample, the Si2p(Si(0)) peak appears at correspondingly -10.0 eV and +10.0 eV binding energy positions (20.0 eV difference) with no frequency dependence. However, the corresponding peak of the oxide (Si(4+)) appears with less than 20.0 eV difference and exhibits a strong frequency dependence due to charging of the oxide layer, which is faithfully reproduced by a theoretical model. In the simplest application of this technique, we show that the two O1s components can be assigned to SiO(x) and TiO(y) moeties by correlating their dynamical shifts to those of the Si2p and Ti2p peaks in a composite sample. Our pulsing technique turns the powerful X-ray photoemission into an even more powerful impedance spectrometer with an added advantage of chemical resolution and specificity.     

Autonomous DNA walker: probing cell membrane dynamics

正We are all familiar with DNA as the substance that encodes the genomes of all living things.In addition to genetic function,DNA is one of the smartest building blocks for innovative nanostructures.DNA walker is a kind of self-assembled molecular machine that mimics the movement of protein motors in living systems.Usually,DNA walker consists of three parts:a single stranded DNA track,several anchorage sites and a walker strand.The walker strand can move from one     

Study of the interaction between progesterone and beta-cyclodextrin by electrochemical techniques and steered molecular dynamics

The interaction of progesterone with beta-cyclodextrin (beta-CD) was studied by differential pulse polarography. The aim of the present work was to study the effect of beta-CD on the electrochemical behavior of progesterone in aqueous solution and also to analyze the molecular interactions involved in formation of the inclusion complex. The complex with stoichiometry of 1:1 was thermodynamically characterized. In addition, steered molecular dynamics (SMD) was used to investigate the energetic properties of formation of the inclusion complex along four different pathways (reaction coordinates), considering two possible orientations. From multiple trajectories along these pathways, the potentials of mean force for formation of the beta-CD progesterone inclusion complex were calculated. The energy analysis was in good agreement with the experimental results. In the beta-CD progesterone inclusion complex, a large portion of the steroid skeleton is included in the beta-CD cavity. The lowest energy was found when the D-ring of the guest molecule is located near the secondary hydroxyls of the beta-CD cavity. In the most probable orientation, one intermolecular hydrogen bond is formed between the O of the C-20 keto group of the progesterone and a secondary hydroxyl of the beta-CD.     

碳链相连双酞菁钴发色团之间的相对取向及距离

用分子激子理论分析了分子间及分子内酞菁二聚体中发色团的距离和相对取向, 说明了乙烷的1, 2位被酞菁取代后, 在溶液中的构象接近顺式。表明非链相互作用可克服空间阻碍导致有序结构形成。     

Excitation energies of retinal chromophores: critical role of the structural model

We employ a variety of highly-correlated approaches including quantum Monte Carlo (QMC) and the n-electron valence state perturbation theory (NEVPT2) to compute the vertical excitation energies of retinal protonated Schiff base (RPSB) models in the gas phase. We find that the NEVPT2 excitation energies are in good agreement with the QMC values and confirm our previous findings that the complete-active-space perturbation (CASPT2) approach yields accurate excitations for RPSB models only when the more recent zero-order IPEA Hamiltonian is employed. The excitations computed with the original zero-order formulation of CASPT2 are instead systematically red-shifted by more than 0.3 eV. We then focus on the full 11-cis retinal chromophore and show that the M06-2X and MP2 approaches provide reliable ground-state equilibrium structures for this system while the complete-active-space self-consistent field (CASSCF) geometry is characterized by significantly higher ground-state energies at the NEVPT2 and CASPT2 level. Our calibration of the structural model together with the general agreement of all highly-correlated excited-state methods allows us to reliably assign a value of about 2.3 eV to the vertical excitation of 11-cis RPSB in the gas-phase.     

碳链相连双酞菁钴发色团之间的相对取向及距离

用分子激子理论分析了分子间及分子内酞菁二聚体中发色团的距离和相对取向, 说明了乙烷的1, 2位被酞菁取代后, 在溶液中的构象接近顺式。表明非链相互作用可克服空间阻碍导致有序结构形成。     

Molecular dynamics simulation study of interaction between model rough hydrophobic surfaces

We study some aspects of hydrophobic interaction between molecular rough and flexible model surfaces. The model we use in this work is based on a model we used previously (Eun, C.; Berkowitz, M. L. J. Phys. Chem. B 2009, 113, 13222-13228), when we studied the interaction between model patches of lipid membranes. Our original model consisted of two graphene plates with attached polar headgroups; the plates were immersed in a water bath. The interaction between such plates can be considered as an example of a hydrophilic interaction. In the present work, we modify our previous model by removing the charge from the zwitterionic headgroups. As a result of this procedure, the plate character changes: it becomes hydrophobic. By separating the total interaction (or potential of mean force, PMF) between plates into the direct and the water-mediated interactions, we observe that the latter changes from repulsive to attractive, clearly emphasizing the important role of water as a medium. We also investigate the effect of roughness and flexibility of the headgroups on the interaction between plates and observe that roughness enhances the character of the hydrophobic interaction. The presence of a dewetting transition in a confined space between charge-removed plates confirms that the interaction between plates is strongly hydrophobic. In addition, we notice that there is a shallow local minimum in the PMF in the case of the charge-removed plates. We find that this minimum is associated with the configurational changes that flexible headgroups undergo as the two plates are brought together.     

Intramolecular interaction of chromophores in diprotonated dichalcones containing a biphenylene bridge structure

The relationships governing the change in the energy of intramolecular interaction of the chromophores in their diprotonated forms, i.e., the corresponding dihydroxydicarbonium ions, were analyzed on the basis of data on the electronic absorption spectra for sulfuric acid solutions of 23 unsaturated diketones containing a heterocyclic biphenylene bridge structure (the dibenzofuran, dibenzothiophene, carbazole, and 9-methylcarbazole rings). It was shown that the energy of intramolecular interaction of the chromophores increases with substitution of the heteroatom X of the bridge structure in the order O, S, NH, and NCH₃ and decreases with increase in the chain length of the conjugated chromophores and with the introduction of electron-donating substituents. The contributions from the resonance (E_res) and coulombic (E_cou) components to the total energy of intramolecular interaction of the chromophores were determined. The relationship between the factors giving rise to the energy characteristics of the intramolecular interaction between the chromophores in dichromophoric systems containing a bridge structure and the factors determining the transmission of the electronic effects in the ground state is discussed in terms of orbital analysis.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 1, pp. 22–28, January–February, 1987.