Real and complex intersections between potential energy surfaces of the same symmetry in polyatomic systems

Two different viewpoints of possible intersections between potential energy surfaces of the same symmetry for polyatomic systems are considered and extended to the general framework of complex nuclear coordinates. The results of ab initio calculations for complex nuclear coordinates yield a surface of n-1 complex dimensions, where n is the number of nuclear degrees of freedom. This supports the traditional viewpoint that intersections (real or complex) can exist between potential energy surfaces of the same symmetry.     

Examination of intramolecular potential surfaces of flexible conjugated molecules by calculation of crystal structures. equilibrium geometries of chalc

A method for refinement of intramolecular potential surfaces of flexible molecules is proposed based on the knowledge of the equilibrium molecular geometry in the crystal and on a good first approximation to the intra- and intermolecular surfaces. The equilibrium conformation in the crystal is calculated by minimization of the total potential with respect to all Cartesian coordinates of the asymmetric unit as well as the components of the unit cell parameters. The initial approximations to the potential function are further refined with the purpose of obtaining better agreement between the calculated crystal equilibrium geometry and the corresponding X-ray results. The previously proposed QCFF/PI potential surfaces for conjugated hydrocarbons are re-examined by calculation of the crystal structures of chalcone, p-methylchalcone, p,p'-dimethylchalcone and α,ω-diphenyloctatetraene. The resulting potentials of the present refinement are somewhat shallower than the previous QCFF/PI surfaces. It is suggested that the application of the method as a model calculation may be considered a reliable “quasi-experimental” technique for the determination of gas phase equilibrium conformations.     

Polyethylene compounds with antimicrobial surface properties

The present study aims at antimicrobial polyethylene surfaces. To achieve this, LLDPE was compounded with the polymeric biocide poly(2-tert-butylaminoethyl) methacrylate TBAM (bulk modification with 1.5-5.0 wt.% of TBAM). Surfaces of these polymer compounds were then subjected to microbial assays. Using standard methods the colony forming units (CFU) for Escherichia coli and Staphylococcus aureus were determined on these surfaces. In all cases, polyethylene surfaces with highly antimicrobial properties were achieved. An average reduction of 10⁴ CFU ml⁻¹ compared to neat LLDPE was achieved. The surfaces of these LLDPE/TBAM compounds were assessed by electrokinetic (zeta potential) measurements. The results indicate a relation between the antimicrobial activity and the zeta-potential of the polymer compounds. Moreover, the antimicrobial compounds were investigated towards biofilm formation. Compared to pristine LLDPE, the surfaces of the polymer compounds showed less adhering biofilm after a testing period of 16 weeks.     

Electrochemical attachment of motile bacterial cells to gold

Selective attachment of Escherichia coli K-12 bacterial cells to charged gold surfaces was demonstrated. Electrostatic binding of E. coli K-12 bacterial cells to positively charged surfaces was observed starting at +750 mV. The binding of E. coli K-12 cells to positively charged gold surfaces is proposed to occur due to long-range electrostatic interactions between the negatively charged O-chain of lipopolysaccharide (LPS) molecules protruding the bacterial cell body and the electrode surface. Removing LPS alters the cellular surface charge and results in cellular attachment to negatively charged surfaces. Thus, applying an electrical potential allows for the direct, real time detection of live, dead or damaged bacterial cells. The attachment of E. coli K-12 bacterial cells to surfaces with an applied potential substantiates the hypothesis that an electrostatic interaction is responsible for the binding of bacterial cells to positively charged molecular assemblies on surfaces used for building bacterial microarrays.     

The lack of leaving-atom isotope effects on rotational state distributions in M* + H2 (HD) → MH(ν, N)+H (D) reactions: “Half-collision” classical trajectories on model H-M-H anisotropic potential surfaces

Simple “half-collision” classical trajectories on model potential surfaces show that the lack of leaving-atom isotope effects on initial rotational state distributions P(N) in reactions of the type M + H₂ (HD) → MH (ν, N)+H (D) would result from decomposition of H-M-H (D) intermediates on anisotropic potential surfaces.     

A useful mapping of triatomic potential energy surfaces

We present in this paper a mapping of triatomic three-dimensional Born-Oppenheimer potential energy surfaces V for which all arrangement channels are represented evenhandedly. This representation is very useful for visualizing the geometrical and dynamical properties of such surfaces.     

Effect of surface charge of polymeric micelles on in vitro cellular uptake

This work focuses on the interaction between polymeric micelles with different charged surfaces and cancer cells in order to study the influence of surface charge on the in vitro cellular uptake efficiency. The amphiphilic diblock copolymers poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) with different functional groups at the end of hydrophilic block were synthesized. The functional groups endue the micelles with different charges on the surfaces. The cellular uptake of micelles to T-24 cells (human bladder tumor cells), HepG2 cells (human liver hepatocellular carcinoma cell line) and Hela cells (human epithelial cervical cancer cells) was studied by means of flow cytometer and confocal laser scanning microscopy. The results indicate that the surface charges showed great influence on zeta potential of micelles at different pH values. The in vitro cellular uptake efficiency of micelles with different charged surfaces demonstrated different cellular uptake patterns to three kinds of cancer cells.     

Ab initio study of the conformations of chloromethyl formate and fluoromethyl formate

Ab initio calculations are reported for the conformational potential energy surfaces of chloromethyl formate and fluoromethyl formate at minimal basis set level. The halomethyl group is shown to lie Z to the carbonyl group. A plateau on the potential energy surface demonstrates that the halomethyl group can rotate freely. The halogen atom therefore moves from an antiperiplanar (ap) to a synclinal (sp) position with respect to the carbonyl group. The effects on IR spectra and dipole moments are discussed.     

Poly(N-isopropylacrylamide)-based thermo-responsive surfaces with controllable cell adhesion

Poly(N-isopropylacrylamide) (PNIPAAm)-based thermo-responsive surfaces can switch their wettability (from wettable to non-wettable) and adhesion (from sticky to non-sticky) according to external temperature changes. These smart surfaces with switchable interfacial properties are playing increasingly important roles in a diverse range of biomedical applications; these controlling cell-adhesion behavior has shown great potential for tissue engineering and disease diagnostics. Herein we reviewed the recent progress of research on PNIPAAm-based thermo-responsive surfaces that can dynamically control cell adhesion behavior. The underlying response mechanisms and influencing factors for PNIPAAm-based surfaces to control cell adhesion are described first. Then, PNIPAAm-modified two-dimensional flat surfaces for cell-sheet engineering and PNIPAAm-modified three-dimensional nanostructured surfaces for diagnostics are summarized. We also provide a future perspective for the development of stimuli-responsive surfaces.     

Theoretical study on the insertion reactions of the germylenoid H2GeClMgCl with RH (R = F, OH, NH2)

The insertion reactions of the germylenoid H₂GeClMgCl with RH (R = F, OH, NH₂) have been studied by using the DFT B3LYP and QCISD methods. The geometries of the stationary points on the potential energy surfaces of the reactions were optimized at the B3LYP/6-311+G(d, p) level of theory. The calculated results indicate that all the mechanisms of the three insertion reactions are identical to each other. The QCISD/6-311++G(d, p)//B3LYP/6-311+G(d, p) calculated potential energy barriers for the three insertion reactions of R = F, OH, and NH₂ are 164.62, 193.30, and 200.73 kJ mol^?1, and the reaction energies for the three reactions are ?57.46, ?35.65, and ?22.22 kJ mol^?1, respectively. Under the same situation, the insertion reactions should occur easily in the following order H-F > H-OH > H-NH₂. In THF solvent the insertion reactions get more difficult than in gas phase.     

Raman spectra of carbon monoxide adsorbed on silver electrodes

Weak Raman spectra of carbon monoxide on silver electrode surfaces exhibit frequency and intensity variations with changing potential. The frequency-potential dependence is rationalized in terms of electron-transfer to the antibonding π^* state of electrosorbed CO.     

Molecular interpretation of electrokinetic potentials

A discussion is given of the electrokinetic, or ζ-potential in terms of the slip process and the composition of the electric double layer. Electrokinetically, only the outer parts of double layers are active. The existence of a stagnant part is generally observed for aqueous solutions adjacent to solid surfaces. It is claimed that this stagnancy is caused by the spontaneous structuring of fluids near solid surfaces. Hence, it is a ubiquitous phenomenon and the thickness of the stagnant layer does not significantly depend on the wettability and the surface charge of the surfaces.     

Potential-dependant SERS interaction of ortho-substituted N-benzylamino(boronphenyl)methylphosphonic acid with Ag,Au, and Cu electrode surfaces

In this study we present surface-enhanced Raman spectroscopy (SERS) investigations of ortho-substituted N-benzylamino(boronphenyl)methylphosphonic acid (N-benzylamino-(2-boronphenyl)-R-methylphosphonic acid; o-PhR) adsorbed onto a roughened in oxidation–reduction cycles (ORC) Ag, Au, and Cu electrode surfaces at different applied electrode potentials. Based on the spectral changes in bandwidth and wavenumber of selected bands upon the alternation of the applied electrodes potential the manner and differences in the interaction of o-PhR with the Ag, Au, and Cu electrode surfaces were determined. Briefly, the spectral patterns on Ag and Au suggest that, generally, the both aromatic rings are involved in the o-PhR/electrode interaction, whereas the boronophenyl ring only interacts with Cu. Also, the boronic acid and phosphonic acid groups participate in the o-PhR interaction with all the types of electrodes. However, the type of the used electrode material and the applied electrode potential have influence onto the mode of adsorption.     

A SERS spectroelectrochemical investigation of the interaction of O-isopropyl-N-ethylthionocarbamate with copper surfaces

The interaction of the sulfide mineral flotation collector, O-isopropyl-N-ethylthionocarbamate (IPETC), with copper surfaces has been investigated by surface enhanced Raman scattering (SERS) spectroscopy. Adsorption of IPETC has been shown to involve a charge transfer process in which the sulfur atom in the organic species becomes bonded to a copper atom in the metal surface and the hydrogen is displaced from the nitrogen atom to form a hydrogen ion in solution. IPETC and copper IPETC compounds were characterised by ¹³C NMR and Raman spectroscopy to provide a basis for identifying surface species. The formal potential for the Cu ∣ IPETC system in acid and neutral solutions was found to be 0.131 V and the dependence of the reversible potential on IPETC concentration and on pH to be in agreement with the proposed mechanism. The SERS investigations showed that adsorption of IPETC commenced at a potential more than 0.31 V below the reversible value for the formation of the bulk copper compound; this behaviour is analogous to that previously found for the adsorption of other thiol collectors on metal and sulfide mineral surfaces. An estimate is made of the potential dependence of the interaction of IPETC with chalcocite.     

Novel aspects of ultrafast non-radiative processes

We outline a new approach to determine theoretically the time-dependent intensity of fluorescence I(t) in systems with intersecting potential energy surfaces and strong non-adiabatic effects. To a good approximation, I(t) is found to be proportional to the probability of occupying the upper electronic state times a suitable combination of potential energy pre-factors. In the limit of weak non-adiabatic effects, and when the initial state is a single zero-order state, this quantity reduces to the usual squared modulus of the autocorrelation function. For systems with strong non-adiabatic effects, the present theory predicts drastic deviations from the autocorrelation-function approximation.     

Maleimide functionalized silicon surfaces for biosensing investigated by in-situ IRSE and EQCM

A quantitative study of the electrodeposition of nominal 3–5 monolayers of p-maleimidophenyl (p-MP) with current transients, electrochemical quartz crystal microbalance (EQCM) and in-situ infrared spectroscopic ellipsometry (IRSE) is presented. In particular maleimide functionalized interfaces are of high interest for specific biosensing. Such surfaces are prepared electrochemically on Au-QCM, micro-crystalline silicon (μc-Si)-coated Au-QCM (μc-Si-Au-QCM) and crystalline silicon (c-Si(111)) surfaces. The electrodeposition of p-MP on μc-Si-Au-QCM is developed and is shown to be similar to that of Au-QCM sensors with a grafting efficiency of 0.5 after the first potential cycle. For subsequent deposition on silicon, the oligomer formation and thickness is limited due to a steric hindrance effect and the molecules size. The combination of used methods enabled the verification of grafted p-MP, evaluation of optical constants and thicknesses, and grafting efficiencies. The presented cooperative multi-method characterization gives a new analytical possibility for in-situ studies of electrochemically functionalized surfaces towards biosensing.     

Aggregation behavior of imidazolium-based chiral surfactant in aqueous solution

A novel imidazolium-based chiral surfactant with a Y-type hydrophobic chain, (S)-(+)-1-(2,3-bis(octanoyloxy)propyl)-3-methylimidazolium chloride ([Bopmim]Cl), was synthesized. The aggregation behavior of [Bopmim]Cl in aqueous solution was then investigated by surface tension, electrical conductivity, ¹H NMR, and fluorescence measurements. Compared with [C₁₂mim]Cl, the critical micelle concentration for [Bopmim]Cl is lower, indicating that the novel chiral surfactant has superior capacity to form micelles. A larger value of pC ₂₀, a greater minimum area per surfactant molecule (A _min), a smaller degree of counterion binding (β), and a looser aggregate are caused by the relatively larger Y-type hydrophobic chain of [Bopmim]Cl. Furthermore, analysis of the ¹H NMR spectra revealed that the introduced Y-type hydrophobic chain may prevent the hydrophobic group from forming an extended chain configuration and cause a changeover from trans to gauche conformations upon micellization. The micelles of the novel chiral surfactant may provide some potential applications in the stereochemical recognition of surfaces or of biological structures.     

CO organization at ambient pressure on stepped Pt surfaces: first principles modeling accelerated by neural networks

Step and kink sites at Pt surfaces have crucial importance in catalysis. We employ a high dimensional neural network potential (HDNNP) trained using first-principles calculations to determine the adsorption structure of CO under ambient conditions (T = 300 K and P = 1 atm) on these surfaces. To thoroughly explore the potential energy surface (PES), we use a modified basin hopping method. We utilize the explored PES to identify the adsorbate structures and show that under the considered conditions several low free energy structures exist. Under the considered temperature and pressure conditions, the step edge (or kink) is totally occupied by on-top CO molecules. We show that the step structure and the structure of CO molecules on the step dictate the arrangement of CO molecules on the lower terrace. On surfaces with (111) steps, like Pt(553), CO forms quasi-hexagonal structures on the terrace with the top site preferred, with on average two top site CO for one multiply bonded CO, while in contrast surfaces with (100) steps, like Pt(557), present a majority of multiply bonded CO on their terrace. Short terraced surfaces, like Pt(643), with square (100) steps that are broken by kink sites constrain the CO arrangement parallel to the step edge. Overall, this effort provides detailed analysis on the influence of the step edge structure, kink sites, and terrace width on the organization of CO molecules on non-reconstructed stepped surfaces, yielding initial structures for understanding restructuring events driven by CO at high coverages and ambient pressure.

A neural network potential trained using first-principles calculations enables to understand the adsorption configurations of carbon monoxide on stepped Pt surfaces at ambient pressure.     

Ab initio model potential and molecular dynamics simulation of Ag6 clusters

We present an approach to generate a model potential with parameters fitted to ab initio energetic surfaces. The potential includes two-, three- and four-body terms. Each of them consists of an exponential exchange and dispersion terms. The analytical form of the latter was taken from perturbation theory up to fourth order. We illustrate the present approach by constructing an ab initio model potential for the Ag₆ cluster. A molecular dynamics simulation using this potential reveals interesting features in the isomerization of the C _2v structure. A two step isomerization transition is observed: First, at temperatures around 350 K, the cluster structures fluctuate between two-dimensional isomers. At higher temperatures (450 K), fast transitions occur between two- and three-dimensional cluster configurations.     

In situ simultaneous determination the photolysis of multi-component PAHs adsorbed on the leaf surfaces of living Kandelia candel seedlings

A fiber-optic fluorimetry for in situ simultaneous determination of fluorine (Flu), phenanthrene (Phe) and fluoranthene (Fla) adsorbed on the leaf surfaces of Kandelia candel (Kc) seedlings was developed. Experimental results showed that the linear ranges for determination of Flu, Phe and Fla adsorbed on Kc leaves were 35-700, 5-900 and 2-450 ng/spot, respectively. The detection limits for Flu, Phe and Fla were 9.11, 1.65 and 0.90 ng/spot and with the relative standard deviations less than 10.32%, 7.56% and 4.29% (n = 9), respectively. The recovery results for Flu, Phe and Fla adsorbed on Kc leaves were 83.0-91.2, 78.5-88.5 and 91.5-107.3%, respectively. Under the laboratory experimental conditions, the photolysis processes of Flu, Phe and Fla individual and in mixtures adsorbed on the leaf surfaces of living Kc seedlings were studied. Results showed that the photolysis of Flu, Phe and Fla individual and in mixtures adsorbed on the leaf surfaces of Kc seedlings followed first-order kinetics with photolysis rates in the order of Flu > Fla > Phe on the Kc leaves. An antagonistic effect was found when the three polycyclic aromatic hydrocarbons (PAHs) were co-adsorbed on living Kc seedlings. The experimental results also indicated that photolysis was the main transformation pathway for Flu, Phe and Fla both individual and in mixtures adsorbed on Kc leaves, whereas disappearance of the adsorbed Flu, Phe and Fla as a result of volatilization and leaf absorption could be negligible during the experimental period.