Predicting the acidity constant of a goethite hydroxyl group from first principles

Accurate predictions of the acid-base behavior of hydroxyl groups at mineral surfaces are critical for understanding the trapping of toxic and radioactive ions in soil samples. In this work, we apply ab initio molecular dynamics (AIMD) simulations and potential-of-mean-force techniques to calculate the pK(a) of a doubly protonated oxygen atom bonded to a single Fe atom (Fe(I)OH(2)) on the goethite (101) surface. Using formic acid as a reference system, pK(a) = 7.0 is predicted, suggesting that isolated, positively charged groups of this type are marginally stable at neutral pH. Similarities and differences between AIMD and the more empirical multi-site complexation methodology are highlighted, particularly with respect to the treatment of hydrogen bonding with water and proton sharing among surface hydroxyl groups. We also highlight the importance of an electronic structure method that can accurately predict transition metal ion properties for goethite pK(a) calculations.     

Ultrafast α-like relaxation of a fragile glass-forming liquid measured using two-dimensional infrared spectroscopy

Ultrafast two-dimensional infrared (2D-IR) spectroscopy is used to study the picosecond dynamics of a vibrational probe molecule dissolved in a fragile glass former. The spectral dynamics are observed as the system is cooled to within a few degrees of the glass transition temperature (T(g)). We observe nonexponential relaxation of the frequency-frequency correlation function, similar to what has been reported for other dynamical correlation functions. In addition, we see evidence for α-like relaxation, typically associated with long-time, cooperative molecular motion, on the ultrafast time scale. The data suggests that the spectral dynamics are sensitive to cooperative motion occurring on time scales that are necessarily longer than the observation time.     

Transient excited-state absorption and gain spectroscopy of a two-photon absorbing probe with efficient superfluorescent properties

The synthesis, linear photophysical properties, two-photon absorption (2PA), excited-state transient absorption, and gain spectroscopy of a new fluorene derivative tert-butyl 4,4'-(4,4' (1E,1'E)-2,2'-(9,9-bis(2- (2-ethoxyethoxy)ethyl)-9H-fluorene-2,7-diyl)bis(ethene-2,1-diyl)bis(4,1 phenylene)]dipiperazine-1-carboxylate (1) are reported. The steady-state linear absorption and fluorescence spectra, along with excitation anisotropy, fluorescence lifetimes, and photochemical stability of 1 were investigated in a number of organic solvents at room temperature. The 2PA spectra of 1 with a maximum cross-section of ~ 300 GM were obtained with a 1 kHz femtosecond laser system using open-aperture Z-scan and two-photon-induced fluorescence methods. The transient excited-state absorption (ESA) and gain kinetics of 1 were investigated by a femtosecond pump-probe methodology. Fast relaxation processes (~1-2 ps) in the gain and ESA spectra of 1 were revealed in ACN solution, attributable to symmetry-breaking effects in the first excited state. Efficient superfluorescence properties of 1 were observed in a nonpolar solvent under femtosecond excitation. One- and two-photon fluorescence microscopy imaging of HCT 116 cells incubated with probe 1 was accomplished, suggesting the potential of this new probe in two-photon fluorescence microscopy bioimaging.     

Highly biocompatible, hollow coordination polymer nanoparticles as cisplatin carriers for efficient intracellular drug delivery

Highly biocompatible coordination polymer (Prussian Blue) nanoparticles (LC(50) > 1000 μg mL(-1)) with a hollow interior and a microporous framework (denoted as HPB) are utilized as an anticancer drug (i.e. cisplatin) capsule for chemotherapy of bladder cancer T24 cells.     

Continuous flow metal-free oxidation of picolines using air

The metal free, direct oxidation of 2-, 3-, and 4-picoline to the corresponding carboxylic acid using either oxygen or air has been developed under continuous flow conditions. Complete conversion for all three substrates was obtained at moderate temperatures and pressures within minutes.     

Block copolymer assisted synthesis of porous α-Ni(OH)(2) microflowers with high surface areas as electrochemical pseudocapacitor materials

Porous α-Ni(OH)(2) microflowers are successfully synthesized via a one-step aqueous-phase reaction assisted by block copolymers under mild conditions. The electrochemical measurement demonstrates that the α-Ni(OH)(2) microflowers calcined at 200 °C are capable to deliver a specific capacity of 1551 F g(-1) in 6 M KOH solution, suggesting their high potential as a novel electrochemical pseudocapacitor.     

Shape persistence delivers lock-and-key chloride binding in triazolophanes

Triazolophanes have recently surfaced as a new class of shape-persistent macrocycles that bind anions. Bearing only triazole- and phenyl-derived CH hydrogen bond donors, these receptors have shown extraordinary Cl(-) binding strengths (>10(6) M(-1), CH(2)Cl(2)). The attributes of the triazolophane that are responsible are presented herein alongside recent literature accounts that have utilized similar strategies in new and exciting supramolecular systems. This review describes how triazolophanes leverage the structural pre-organization characteristic of spherands to take advantage of non-traditional hydrogen bonds originating from extrinsic CH donors.     

Low rank Runge–Kutta methods,symplecticity and stochastic Hamiltonian problems with additive noise

In this paper we extend the ideas of Brugnano, Iavernaro and Trigiante in their development of HBVM (s,r$s,r$) methods to construct symplectic Runge–Kutta methods for all values of s$s$ and r$r$ with s≥r$s\ge r$. However, these methods do not see the dramatic performance improvement that HBVMs can attain. Nevertheless, in the case of additive stochastic Hamiltonian problems an extension of these ideas, which requires the simulation of an independent Wiener process at each stage of a Runge–Kutta method, leads to methods that have very favourable properties. These ideas are illustrated by some simple numerical tests for the modified midpoint rule.     

Formation of phosphino-substituted isocyanate by reaction of CO2 with group 2 complexes based on the (Me3Si)(i-Pr2P)NH ligand

The group 2 complexes [(Me(3)Si)(i-Pr(2)P)N](2)M(THF)(x) (M = Mg, x = 1; M = Ca/Sr, x = 2) as well as an unusual dimagnesium complex {[(Me(3)Si)(i-Pr(2)P)N](3)Mg}Mg(n-C(4)H(9)) have been prepared and characterized by multinuclear NMR spectroscopy and single crystal X-ray diffraction. Each complex was shown to react with CO(2) under extremely mild conditions (15 min, 1 atm, room temperature) to give the isocyanate (i-Pr)(2)P-N═C═O. The independent syntheses of (i-Pr)(2)P-N═C═O and the carbodiimide dimer [(i-Pr)(2)PNCNP(i-Pr)(2)](2) are also reported.     

Statistical properties of the electrophoretic collision of a long DNA molecule with a small obstacle

We present experimental results for the collision of a single λ-DNA molecule with isolated cylindrical nanoposts whose radii range from 350 nm to 1.37 μm. The experimental apparatus was fabricated in oxidized silicon using a plasma-thinning method. The probability density for the dimensionless holdup time is described by a gamma distribution, which accurately represents the behavior of the probability density for X collisions and U/J collisions for short-lived and long-lived collisions, respectively. The shape parameter of the gamma distribution reflects the nature of the short-lived collisions, whereas the scaling parameter captures the role of the finite size of the post on the U/J collisions. When rendered in an appropriate dimensionless form, the existing models for the role of electric field gradients extend to all post sizes, indicating that 350 nm is still well above the point-sized limit. Our experiments provide insights into a regime that is very challenging for numerical simulations but highly relevant for separation processes.