Effective surface motion on a reactive cylinder of particles that perform intermittent bulk diffusion

In many biological and small scale technological applications particles may transiently bind to a cylindrical surface. In between two binding events the particles diffuse in the bulk, thus producing an effective translation on the cylindrical surface. We here derive the effective motion on the surface allowing for additional diffusion on the cylindrical surface itself. We find explicit solutions for the number of adsorbed particles at one given instant, the effective surface displacement, as well as the surface propagator. In particular sub- and superdiffusive regimes are found, as well as an effective stalling of diffusion visible as a plateau in the mean squared displacement. We also investigate the corresponding first passage problem.     

Long-jump probabilities in a BGK model for surface diffusion

The jump-length probability distribution (JLPD) in a periodic system is studied using the solution of the linearized Boltzmann equation with BGK collision kernel. The equation is solved both by the matrix-continued-fraction method and by direct numerical simulations. The JLPDs obtained by the BGK equation are compared to those derived from other kinetic models, such as the Langevin (Fokker–Planck) model.     

Spatial scale-dependent tracer diffusion in bulk polycarbonate studied by holographic relaxation

The diffusion of a photochromic dye tracer in polycarbonate was studied by a holographic relaxation technique (forced Rayleigh scattering) at temperatures close to the glass transition temperature. By varying the holographic grating period the results could be interpreted via the spatial scale dependence of apparent diffusion coefficients within a two-state diffusion model. This indicates inhomogeneities on the scale of a few micrometers in the polymer glass.     

Determination of radioactive bulk and surface concentration by beta-detection

Electrolytes of alkaline zincate, acidified zinc sulphate, zinc-ammonia, zinc-ammonia-EDTA, zinc-EDTA/NaOH have been examined in order to verify their applicability for electrodeposition (ED) of zinc on stainless steel (SS) disc at ppm level. Operating parameters suitable for ED of zinc at 90% deposition (amount of zinc removed from plating solution) on SS disc using a total 1 ppm zinc in a 5 cm³ bath volume were determined. It helped to prepare radioactive source (⁶⁵Zn) using inactive Zn as carrier. Speciation of zinc in a Zn-oxalate-EDTA-ammonia bath has been computed.     

Importance of bulk and surface excess concentration in fast atom bombardment mass spectrometry of small peptides

The surface tension of hydrophilic and hydrophobic peptides in glycerol solution at various concentrations is measured by the du Nouy ring method. From these values the surface excess concentration is calculated by means of the Gibbs adsorption equation. The behaviour of the surface excess peptide concentration on the fast atom bombardment mass spectrometric response (protonated molecular ion) as a function of the bulk peptide concentration in glycerol is discussed in terms of parameters commonly used in surface chemistry. The experimental results showed a straightforward correlation between the sputtering of protonated molecular ions of peptides and surface excess peptide concentration. Further, there is good agreement with a model involving desorption/ionization in the first layers of the liquid matrix surface. It is additionally demonstrated that the surface excess concentration of each peptide will be different in glycerol solutions of identical bulk concentration and, as a consequence, any differences in protonated molecular ion yield will reflect differences in the surface activity of the peptides, which explains suppression phenomena in peptide mixtures such as tryptic peptide digest. Based on this finding, it can be assumed that a difference observed in the mass spectrometric response does not represent a substantial difference in ionization efficiency.     

Combined investigation of bulk diffusion and surface exchange parameters of silver catalyst coated yttrium-doped BSCF membranes

The combined effect of minor yttrium doping and silver catalyst deposition on the surface kinetics (k(chem)) and bulk diffusion (D(chem)) of BSCF (Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ)) perovskite membranes was explored using electrical conductivity relaxation (ECR) and validated using oxygen permeation measurements. Yttrium doping of BSCF to form Ba(0.5)Sr(0.5)Co(0.8)Fe(0.175)Y(0.025)O(3-δ) (BSCFY) improved both the surface exchange kinetics and the bulk diffusion by an average of 44% and 177% respectively, supporting improved oxygen permeation measurements. The deposition of a silver catalyst on BSCFY further improved the surface kinetics by 63-450% at intermediate operating temperatures (600-750 °C), and reduced the activation energy from 163 to 90 kJ mol(-1). Interestingly, these improvements did not translate into enhanced oxygen fluxes for the silver coated thicker 0.5 and 1 mm membranes, indicating that the oxygen ion transport was limited by bulk diffusion. However, oxygen permeation measurements on catalyst-coated 0.3 mm-thick membranes yielded improvements of 20-35% in the range 600-900 °C. The silver catalyst was beneficial in overcoming surface kinetic limitations for the thinner 0.3 mm BSCFY membranes, thus suggesting that the critical thickness of BSCFY membranes lies around ～0.4 mm and validating the ECR measurements.     

Dye diffusion in water-swollen cellulose membranes and in bulk water

Summary The generally accepted pore model for diffusion is modified by taking account the steric hindrance of diffusing molecules. The validity of the modified model is examined for the steady state diffusion measurement of eight dyes through four kinds of regenelated cellulose membranes, at 50 °C. Both the earlier and modified true diffusion coefficients, meaning the diffusivities of diffusing molecules within the water-filled cellulose pores, are obtained. The most reasonable explanation of these data is done under the assumption that the diffusion probability does not depend on the elongated diagonal of the diffusing molecule, but on the slightly larger radius than that of minimum cross-section of it. The diffusivities of diffusing molecules in the pores are little affected by the pore diameter of membranes, but they are in general 30 40% smaller than the free diffusion coefficients, obtained by capillary method.

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Zusammenfassung Das allgemein akzeptierte Porenmodell für Diffusion durch Membranen wurde abgewandelt and die sterische Hinderung der diffundierenden Moleküle berücksichtigt. Die Gültigkeit dieses veränderten Porenmodells wurde durch Messung der Diffusion von acht Farbstoffen durch vier Sorten von regenerierten Cellulosemembranen unter stationären Bedingungen bei 50 °C geprüft. Es wurden die bisherigen und die nach der vorliegenden Arbeit modifizierten realen Diffusionskoeffizienten erhalten; sie geben die Diffusivitäten der diffundierenden Moleküle in den mit Wasser gefüllten Celluloseporen an. Die Meßwerte können am einfachsten unter der Annahme erklärt werden, daß die Diffusionswahrscheinlichkeit nicht von der Längserstreckung der diffundierenden Moleküle, sondern von einem Radius abhängt, der etwas größer ist als der aus dem kleinsten Querschnitt berechnete. Die Diffusivitäten der Moleküle im Porenwasser sind wenig von der Porengröße der Membranen beeinflußt; sie sind im allgemeinen um 30–40% kleiner als die mit Hilfe der Kapillarmethode erhaltenen freien Diffusionskoeffizienten.

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With 3 figures and 4 tables     

Simulating surface diffusion and surface growth in ceramics

We examine the movement of ion pairs on the surfaces of simple oxides. Using temperature-accelerated dynamics the elementary processes involved are identified and the activation energies of these used as input to kinetic Monte Carlo simulations. Results are presented for the motion of BaO and SrO ion pairs on the (100) surfaces of BaO and SrO, respectively, and the formation of island pairs on these surfaces is studied. The simulations reveal the importance of exchange mechanisms in surface diffusion and growth of oxides. The importance of such reactions has been recognised previously for metallic surfaces but not for ionic systems, where it has been assumed that ionic surface diffusion is surface diffusion via the hopping motion of ion pairs from one surface site to another. Exchange mechanisms can dominate transport processes both on terraces and steps for both homoepitaxial and heteroepitaxial growth. We suggest the unavoidable mixing when an exchange mechanism operates must be considered when attempting to grow sharp interfaces in oxide nanostructures.     

Oxygen thermodesorption and role of oxygen diffusion in bulk silver

The activity of V-W-Ti-O catalysts for selective NO reduction by ammonia has been studied as a function of the physicochemical and catalytic properties of the support (TiO₂) produced in a number of ways and of the chemical nature of initial V and W compounds. We have formulated principal requrements for the chemical composition of a raw material for the development of a technology for producing honeycomb monolith catalysts with the necessary properties.     

EDOT‐diketopyrrolopyrrole copolymers for high bulk hole mobility and near infrared absorption

To obtain novel low‐bandgap materials with tailored hole‐transport properties and extended absorption, electron rich 3,4‐ethylenedioxythiophene is introduced as a comonomer in diketopyrrolo[3,4‐c]pyrrole copolymers with different aryl flanking units. The polymers are characterized by absorption and photoluminescence spectroscopy, dynamic scanning calorimetry, cyclic voltammetry, and X‐ray diffraction. The charge transport properties of these new materials are studied carefully using an organic field effect transistor geometry where the charge carriers are transported over a narrow channel at the semiconductor/dielectric interface. These results are compared to bulk charge carrier mobilities using space‐charge limited current (SCLC) measurements, in which the charge carrier is transported through the complete film thickness of several hundred nanometers. Finally, charge carrier mobilities are correlated with the electronic structure of the compounds. We find that in particular the thiophene‐flanked copolymer PDPP[T]₂‐EDOT is a very promising candidate for organic photovoltaics, showing an absorption response in the near infrared region with an optical bandgap of 1.15 eV and a very high bulk hole mobility of 2.9 × 10^?4 cm² V^?1 s^?1 as measured by SCLC. This value is two orders of magnitudes higher than SCLC mobilities reported for other polydiketopyrrolopyrroles and is in the range of the well‐known hole transporting polymer poly(3‐hexylthiophene). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 639–648     

Search for a small chromophore with efficient singlet fission: biradicaloid heterocycles

Of the five small biradicaloid heterocycles whose S(1), S(2), T(1), and T(2) adiabatic excitation energies were examined by the CASPT2/ANO-L-VTZP method, two have been found to meet the state energy criterion for efficient singlet fission and are recommended to the attention of synthetic chemists and photophysicists.     

Properties of small molecular drug loading and diffusion in a fluorinated PEG hydrogel studied by 1H molecular diffusion NMR and 19F spin diffusion NMR

R(f)-PEG (fluoroalkyl double-ended poly(ethylene glycol)) hydrogel is potentially useful as a drug delivery depot due to its advanced properties of sol-gel two-phase coexistence and low surface erosion. In this study, (1)H molecular diffusion nuclear magnetic resonance (NMR) and (19)F spin diffusion NMR were used to probe the drug loading and diffusion properties of the R(f)-PEG hydrogel for small anticancer drugs, 5-fluorouracil (FU) and its hydrophobic analog, 1,3-dimethyl-5-fluorouracil (DMFU). It was found that FU has a larger apparent diffusion coefficient than that of DMFU, and the diffusion of the latter was more hindered. The result of (19)F spin diffusion NMR for the corresponding freeze-dried samples indicates that a larger portion of DMFU resided in the R(f) core/IPDU intermediate-layer region (where IPDU refers to isophorone diurethane, as a linker to interconnect the R(f) group and the PEG chain) than that of FU while the opposite is true in the PEG-water phase. To understand the experimental data, a diffusion model was proposed to include: (1) hindered diffusion of the drug molecules in the R(f) core/IPDU-intermediate-layer region; (2) relatively free diffusion of the drug molecules in the PEG-water phase (or region); and (3) diffusive exchange of the probe molecules between the above two regions. This study also shows that molecular diffusion NMR combined with spin diffusion NMR is useful in studying the drug loading and diffusion properties in hydrogels for the purpose of drug delivery applications.     

Unique control of bulk reactivity by surface phenomena in a positive electrode of lithium battery

Layered LiNi_1/2Mn_1/2O₂ compound prepared by the classical coprecipitation method delivers a capacity loss upon cycling in a lithium battery, which increases upon the 5 first cycles, and then becomes less visible over the next 40 cycles. The charge–discharge polarization follows the same trend. The formation and the evolution of lithium-containing species on the grain surface of layered LiNi_1/2Mn_1/2O₂ and the interfacial charge transfer resistance have been carefully investigated upon cycling, by coupling ex situ ⁷Li MAS NMR and in situ electrochemical impedance spectroscopy. An important increase in the amount of lithiated surface species is observed during the first electrochemical cycles along with an increase of the charge transfer resistance. After reaching a maximum, both integrated intensity of the NMR signal and charge transfer resistance decrease, indicating a strong correlation between these two different surface characteristics, obtained from ex situ and in situ experiments, respectively. The evolution of surface species, probed by NMR and impedance spectroscopy, follow the same kind of variation as electrochemical parameters, demonstrating a unique control by surface phenomena of the overall electrochemical behavior of an electrode material of lithium battery.     

Phospholipid solubility determined by equilibrium distribution between surface and bulk phases

A general strategy is proposed for determining the very low aqueous solubility limits of bilayer-forming phospholipids. The strategy exploits the inherent surface activity of phospholipids and has been termed EDSB, which stands for Equilibrium Distribution between Surface and Bulk phases. In this report, EDSB has been used to determine the critical bilayer concentration of dilauroylphosphatidylycholine (DLPC), a short-chain bilayer-forming phospholipid. At room temperature in neutral pH buffer, CBC(DLPC) = 2.5 x 10(-)(8) M. Using a mole fraction concentration scale, this corresponds to a standard-state free energy change of -12.8 kcal/mol for DLPC bilayer membrane formation.     

Binding site optimisation for artificial enzymes by diffusion NMR of small molecules

A binding site optimisation protocol for the design of artificial enzymes based on "small molecule-small molecule" binding studies by diffusion NMR is presented. Since the reaction chosen was the hydrolysis of ester 1 ([4-(4-carboxy-1-oxobutyl)-aminobenzyl]-phenethyl ester), an analogous phosphonate ester 2 ([4-(4-carboxy-1-oxobutyl)-aminobenzyl]-phosphonic phenethyl ester) was selected as a suitable transition state analogue (TSA). The key objective of the NMR studies was to find a unit with functional groups capable of binding to the acidic sites of the TSA. Nine dipeptides, mainly with basic and hydroxyl groups, were used and their affinity to the TSA was studied by measuring the change in the diffusion coefficient, D(pep), upon binding by pulse field gradient NMR. The value of D(pep) at 298 K in D(2)O at pD 5, 7 and 10 was measured both in free solution, and mixtures containing one dipeptide and the TSA. As both components are low molecular weight species with M < 500, a TSA-to-dipeptide ratio of 10:1 was used to detect significant changes in D(pep). The results revealed that dipeptides with basic residues show higher affinity to the TSA than those with hydroxyl or aliphatic side chains in aqueous solutions. The dipeptide showing the most significant relative change in D(pep) was H-Arg-Arg-OH, and the binding constant was estimated to be 86 L M(-1) by measuring D(pep) at varying concentrations of the TSA. In addition, binding of the TSA to a new water-soluble polymer with a polyallylamine backbone and randomly distributed Arg-Arg binding sites was examined, and the binding constant was estimated to be > or =1500 L M(-1). As confirmed by further catalytic activity tests, polymers containing Arg-Arg as a binding site are capable of significant rate accelerations in the hydrolysis of ester 1.     

Detection of DNA hybridisation in a diluted serum matrix by surface plasmon resonance and film bulk acoustic resonators

Nanomolar quantities of single-stranded DNA products ~100 nucleotides long can be detected in diluted 1% serum by surface plasmon resonance (SPR) and film bulk acoustic resonators (FBARs). We have used a novel FBAR sensor in parallel with SPR and obtained promising results with both the acoustic and the optical device. Oligonucleotides and a repellent lipoamide, Lipa-DEA, were allowed to assemble on the sensor chip surfaces for only 15 min by dispensing. Lipa-DEA surrounds the analyte-binding probes on the surface and effectively reduces the non-specific binding of bovine serum albumin and non-complementary strands. In a highly diluted serum matrix, the non-specific binding is, however, a hindrance, and the background response must be reduced. Nanomolar concentrations of short complementary oligos could be detected in buffer, whereas the response was too low to be measured in serum. DNA strands that are approximately 100 base pairs long at concentrations as low as 1-nM could be detected both in buffer and in 1% serum by both SPR and the FBAR resonator.