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Selective unidirectional transport of barium ions between droplets in a water-in-chloroform emulsion is demonstrated. Gold nanoparticles (GNPs) modified with a thiolated crown ether act as barium ion complexing shuttles that carry the ions from one population of droplets (source) to another (target). This process is driven by a steep barium ion concentration gradient between source and target droplets. The concentration of barium ions in the target droplets is kept low at all times by the precipitation of insoluble barium sulfate. A potential role of electrostatically coupled secondary processes that maintain the electroneutrality of the emulsion droplets is discussed. Charging of the GNP metal cores by electron transfer in the presence of the Fe(ii)/Fe(iii) redox couple appears to affect the partitioning of the GNPs between the water droplets and the chloroform phase. Processes have been monitored and studied by optical microscopy, Raman spectroscopy, cryogenic scanning electron microscopy (cryo-SEM) and zeta potential. The shuttle action of the GNPs has further been demonstrated electrochemically in a model system., Crown-ether modified gold nanoparticles act as charge transporters between aqueous droplets. The thermodynamic driving force for this continuous non-equilibrium process is precipitation of BaSO4 in one population of droplets.

Wood is a natural composite material. However, its relatively low mechanical properties restrict the use in advanced structural applications but recent studies have shown that Compressed Wood (CW), with superior mechanical properties due to material densification, could be utilised in timber products and timber connections as an alternative to energy-intensive adhesives and metals. However, the limited literature available on the mechanical properties of CW makes it chanllenging to utilise them in the development of new products and structures. To address this issue, this paper presents a comprehensive test programme and an extensive database of CW materials. It includes experimental results of over 720 material tests that were conducted on CW materials. The fundamental tests under compression, tension, bending, embedment, yield moment, shear and impact tests were undertaken. The results obtained from this study will help engineers utilise more CW to develop new products and connections. The results are also compared with the characteristic values of solid wood from the literature. As the densification of wood significantly improves strength and stiffness, this work will contribute towards the substantial uptake of CW in the building and construction industry with great benefits to the environment. peer-reviewed 2023-08-03

Glued-laminated timber (glulam) beams and cross-laminated timber (CLT) panels are increasingly being used as structural members for buildings, because of their excellent mechanical properties, ability to be processed into larger structural sections and environmental benefits. Nevertheless, the inclusion of adhesives during their production raises environmental concerns due to the release of Volatile Organic Compounds (VOCs) and formaldehyde, which also causes difficulties in recycling. This environmental burden has led to the development of adhesive free laminated timber (AFLT) beams and cross-laminated (AFCLT) panels, which are intended to be used as alternatives to glulam beams and CLT panels in structural applications. In this paper, details of the materials and manufacturing processes for the AFLT beams and AFCLT panels are described, followed by the structural tests and the observed failure modes. Furthermore, parametric studies are carried out to investigate the effects of the following factors on the structural response, i.e. lamella species, dowel species, dowel insertion angles, dowel diameters and configurations, number of dowels (or dowel spacing), section sizes and number of interfaces. It is found that the flexural modulus and flexural strength of the 26 AFLT beams and 26 AFCLT panels are in the range of 1.1–5.3 GPa and 19.3–38.2 MPa, respectively. The experimental results are compared with commonly used glulam beams and CLT panels. The results are useful in understanding the mechanical properties of AFLT beams and AFCLT panels fastened with compressed wood dowels, and constitutes useful structural design information for future construction and structural applications, as well as providing data to validate the finite element modelling. In addition, the study has demonstrated a practical and sustainable approach in timber construction, which may lead to a substantial reduction in the use of structural adhesives and environmental benefits.

Engineered Wood Products (EWPs) are increasingly being used as construction and building materials. However, the predominant use of petroleum-based adhesives in EWPs contributes to the release of toxic gases (e.g. Volatile Organic Compounds (VOCs) and formaldehyde) which are harmful to the environment. Also, the use of adhesives in EWPs affects their end-of-life disposal, reusability and recyclability. This paper focusses on dowel laminated timber members and densified wood materials, which are adhesive free and sustainable alternatives to commonly used EWPs (e.g. glulam and CLT). The improved mechanical properties and tight fitting due to spring-back of densified wood support their use as sustainable alternatives to hardwood fasteners to overcome their disadvantages such as loss of stiffness over time and dimensional instability. This approach would also contribute to the uptake of dowel laminated timber members and densified wood materials for more diverse and advanced structural applications and subsequently yield both environmental and economic benefits. The authors wish to record their appreciation to Interreg North-West Europe (NWE) funded by the European Regional Development Fund (ERDF) for supporting the project (Towards Adhesive Free Timber Buildings (AFTB) - 348). peer-reviewed

In this study, we developed a constitutive law for wood useful as a user material subroutine (Umat) in Abaqus software. To calibrate the model, compression/tensile tests were carried out on simple geometry samples and to check the validity, we subsequently considered two simulation cases; namely the push out double shear and the four-point bending tests. Moreover, we developed a generic Python script for each test to be used repeatedly for parametric studies. All the numerical aspects are controlled by a user-friendly graphical interface that can display the relevant results and performs simultaneous comparisons with the experimental results. Firstly, the properties of the compressed and uncompressed wood were identified in the longitudinal, radial and tangential directions using a quasi-inverse problem. Then these properties are used in the simulation of the two numerical tests. Consequently, the obtained numerical joint-slip versus load curve from the push out double shear simulation agrees well with the experimental curve. Furthermore, dowel laminated timber tested in four-point bending were correctly simulated and provided numerical results very close to experimental results.

Gold nanoparticles with variable hydrophobicity have been prepared in three different size regimes following established methods. The control of hydrophobicity was achieved by complexation of the 18-crown-6-CH2-thiolate ligand shell with potassium ions. Potassium dependent phase transfer of these particles from dispersion in water to chloroform was demonstrated, and the equilibrium partitioning of the particles in water–chloroform liquid/liquid systems was quantified by optical spectroscopy. The gradual complexation of the ligand shell with potassium ions was further monitored by zeta potential measurements. Potassium dependent insertion of nanoparticles into the phospholipid bilayer membrane of vesicles in aqueous dispersion has been demonstrated by cryogenic transmission electron microscopy (cryo-TEM). Nanoparticle-dependent potassium ion transport across the vesicle membrane has been established by monitoring the membrane potential with fluorescence spectroscopy using a potential sensitive dye.

The most common differential pulse techniques are analyzed and their responses are compared. Depending on whether or not the initial conditions are re-established before the application of each double pulse we distinguish between double pulse and multipulse differential techniques. The nomenclature employed in the literature is clarified to avoid future confusion. The differences and similarities between the double pulse and multipulse responses are studied for electrode processes of any degree of reversibility, analysing the advantages and disadvantages of each method. The effect of the electrode size is also discussed, establishing the conditions under which the voltammograms obtained by different techniques are coincident or not. © 2011 Elsevier B.V. All rights reserved.

To investigate the permeation of two ionisable drug molecules, warfarin and verapamil, across artificial membranes. For the first time since the introduction of the parallel artificial membrane permeation assay (PAMPA) in 1998, in situ permeation-time profiles of drug molecules are studied.The method employs a rotating-diffusion cell where the donor and acceptor compartments are separated by a lipid-impregnated artificial membrane. The permeation of the solute is investigated under well-defined hydrodynamic conditions with control over the unstirred water layer. The flux of the permeating molecule is analysed in situ using UV spectrophotometry.In situ permeation-time profiles are obtained under hydrodynamic control and used to determine permeability coefficients. An advanced analytical transport model is derived to account for the membrane retention, two-way flux and pH gradient between the two compartments. Moreover, a numerical permeation model was developed to rationalise the time-dependent permeation profiles. The membrane permeability, intrinsic permeability and unstirred water permeability coefficients of two drug molecules are obtained from two independent methods, hydrodynamic extrapolation and pH profiling, and the results are compared.Both warfarin and verapamil exhibit high permeability values, which is consistent with the high fraction absorbed in human. Our results demonstrate that a considerable lag-time, varying with the solute lipophilicity and stirring rate, exists in membrane permeation and leads to incorrect compound ranking if it is not treated properly. Comparison of the permeability data as a function of pH and stirring rate suggests that some transport of the ionized molecules occurs, most likely via ion-pairing.

The changes in interparticle spacing upon hydration and dehydration of drop-cast films of hydrophilic gold nanoparticles (GNP) have been measured in situ with nanometer resolution using WetSTEM and ESEM. These subtle variations correlate well with the corresponding changes in the optical spectra and perceived color as well as changes in the electrical conductivity of the films. AC impedance analysis allows us to differentiate between resistive and capacitive components and to evaluate how these depend on average particle spacing and the water content of the matrix, respectively. Thin films of this type are well-known structures used for development of sensors and diagnostics.

A bifunctional molecular linker containing both aryl diazonium and trioxolane groups was synthesised and its ability to sequentially functionalise glassy carbon and covalently immobilise heme investigated. Functionalisation was demonstrated by electrochemical techniques.

Understanding of the electrochemical properties of graphene, especially the electron transfer kinetics of a redox reaction between the graphene surface and a molecule, in comparison to graphite or other carbon-based materials, is essential for its potential in energy conversion and storage to be realized. Here we use voltammetric determination of the electron transfer rate for three redox mediators, ferricyanide, hexaammineruthenium, and hexachloroiridate (Fe(CN)(6)(3-), Ru(NH3)(6)(3+), and IrCl(6)(2-), respectively), to measure the reactivity of graphene samples prepared by mechanical exfoliation of natural graphite. Electron transfer rates are measured for varied number of graphene layers (1 to ca. 1000 layers) using microscopic droplets. The basal planes of mono- and multilayer graphene, supported on an insulating Si/SiO(2) substrate, exhibit significant electron transfer activity and changes in kinetics are observed for all three mediators. No significant trend in kinetics with flake thickness is discernible for each mediator; however, a large variation in kinetics is observed across the basal plane of the same flakes, indicating that local surface conditions affect the electrochemical performance. This is confirmed by in situ graphite exfoliation, which reveals significant deterioration of initially, near-reversible kinetics for Ru(NH3)(6)(3+) when comparing the atmosphere-aged and freshly exfoliated graphite surfaces.

Devices that exploit electricity produced by electroactive bacteria such as Geobacter sulfurreducens have not yet been demonstrated beyond the laboratory scale. The current densities are far from the maximum that the bacteria can produce because fundamental properties such as the mechanism of extracellular electron transport and factors limiting cell respiration remain unclear. In this work, a strategy for the investigation of electroactive biofilms is presented. Numerical modeling of the response of G. sulfurreducens biofilms cultured on a rotating disk electrode has allowed for the discrimination of different limiting steps in the process of current production within a biofilm. The model outputs reveal that extracellular electron transport limits the respiration rate of the cells furthest from the electrode to the extent that cell division is not possible. The mathematical model also demonstrates that recent findings such as the existence of a redox gradient in actively respiring biofilms can be explained by an electron hopping mechanism but not when considering metallic-like conductivities.

Hexanethiolate gold monolayer-protected clusters (C6-MPCs) with an average core diameter of 1.8 nm and a capacitance of 0.6 aF are synthesised by a two-phase method. These clusters are functionalised with (6-ferrocenyl)-1-hexanethiol by a place exchange reaction at different molar ratios. The average number of ferrocene centres per cluster determined by (1)H NMR is ten, seven and four. Differential pulse voltammetry and cyclic voltammetry measurements for cluster solutions in 0.1 M TBAPF(6)/Tol:AN (2:1) clearly show the response of the Fc(+)/Fc redox couple and of quantized double layer (QDL) charging events of the gold core. A transition from single to multiple electron-transfer response for the redox couple is observed as the number of ferrocene units per cluster is increased. The distances between the redox moieties are estimated considering a homogeneous distribution of the redox sites on the nanoparticle ligand shell. In all the cases, the inter-ferrocene average separation is too large to observe self-exchange reactions and the most likely electron-transfer pathway is by fast rotational diffusion. The oxidation of the ferrocene groups results in an electrostatic switching-off of electron transfers between the electrode and the nanoparticle core.

The absorption of light and the rotation of polarized light near an absorption band is discussed for finite polymers. Only zero‐order wavefunctions and first‐order energies are considered for the polymer, which is treated as a rigid array of identical groups. The length dependence of the optical properties is calculated. The resulting equations are applied to the polypeptide α helix and 310 helix, polyadenylic acid, and dye complexes with these molecules.

We have examined the nature of the circular dichroism band at 330 mμ for a series of copolymers of β-p-nitrobenzyl L-aspartate with β-benzyl L-aspartate. The circular dichroism band arises from an electronic transition in the nitroaromatic group. In order to interpret the effect quantitatively, we employed a simplified statistical treatment and curve fitting for six copolymers. Both approaches gave consistent results, which indicates that the dichroism comes from pairwise interactions between two nitrobenzyl groups. We constructed a molecular model that meets the constraints and requirements of the analyses developed in this paper. In this model, it is proposed that the main chain forms a right-handed α-helix and that nitrobenzyl groups separated by four residues interact with each other.

The spectrophotometric titrations of various classes of acid polysaccharides (polycarboxylates, polysulfates, mucopolysaccharides and heparinoids) in dilute solution using four metachromatic dyes are described. Acridine orange was found to be applicable for quantitative analysis in all four groups of polymers. The equivalent weights obtained with this dye using about 25 μg of polymer were within 1–8% of the values obtained by other analytical methods. Methylene blue was found to be applicable for polymers where at least one negative site occurs regularly per sugar ring. Proflavine gave quantitative titrations with highly charged polymers and neutral red with polymers of relatively low charge density. Titration curves with methylene blue and proflavine also provide a spectrophometric means of distinguishing between acidic polymers with relatively homogeneous and non-homogeneous charge distributions.

One hundred hypothetical polynucleotides of varying chain length and composition and of random sequence were generated and their chemical degradation simulated by a computer. Included in the study were 20 hypothetical polymers with the composition and chain length of a transfer RNA. A second computer program attempted to reconstruct the sequences from the nucleotide composition and the simulated fragments produced. Approximately 700 reconstructions were attempted from various sets of fragments generated from the 100 polymers. The dependence of the probability of reconstructing the original sequences on the methods of producing and isolating the fragments was studied.

Optical properties of complexes of plant sulfated polysaccharides with basic dyes have been examined. Spectral shifts in the dye have been used as the basis for quantitative analysis of anionic sites in these compounds. The κ- and λ-carrageenans have been shown to give characteristically different titration curves. Other, similar, plant extractives have been shown to fall into one or the other of these two classes. Cotton effects in the region of the absorption spectrum of the dye have been discovered, indicating the presence of long range order and asymmetry in the λ-C2 carrageenan. The relation of the optical effects to each other and to the structure of the polymer is discussed briefly in terms of recent developments in the theory of metachromasy.

A strategy is developed for obtaining molecular interaction energy functions by shaping energy surfaces to fit equilibrium energy and geometry data for strongly coupled systems in the gas phase such as the carboxylic acid dimers. The surface is shaped such that its lowest point corresponds to the known energy and equilibrium geometry. The procedures and simulation techniques used to accomplish this are described. The formic acid dimer was successfully used as a model system to derive a set of 1 - 4 - 6 - 12 atom-atom interaction energy functions. The atom-atom terms were transferred to acetic acid and used to calculate the mechanically stable conformations of acetic acid dimers. The calculated acetic acid dimer conformation of lowest energy is in excellent agreement with that experimentally determined. The experimental energy of acetic acid dimerization was not available for comparison.

The coulombic interaction between pairs of trinucleotides has been computed from quantum theory. The results are discussed in terms of their relation to hydrogen bonds and stacking in such systems and to the mechanism by which messenger RNA codons recognize transfer RNA nodocs.

Explicit expressions for the DK and RK associated with the excitation of regular oligomers from their ground states to the Kth exciton state as functions of N, P, μ, μ∥, μt, and μr have been derived on the assumption that the only perturbation Vij to the N singly excited states results from exciton transfer between adjacent residues, V12. The DK relation predicts the occurrence of a perpendicularly polarized absorption band arising from μ⟂ and a parallel polarized band from μ∥ with maxima at K = [2(N + 1)/P] and 1, which are shifted from the monomer band by 2V12 cos(2π/P) and 2V12cos[π/(N + 1)], respectively. Overlapping of the bands, which may occur in oligomers, decreases rapidly with N, leaving two perfectly polarized bands in the polymer. Within each band which includes only a few levels near the maxima, the most probable transition may be associated with all of the intensity for very short chains but only 40.2–50% (⟂) and 80.9% (∥) as N ∞ (polymer case). A relation was derived by which V12 may be simply calculated from μ, μr, μt, μ∥, a, and z. The nearest neighbor theory was compared with experiment by calculating a reasonable set of the relevant parameters which exactly account for known spectral shifts.

Summary The kinetics of inhibition of histamine methyltransferase (S-adenosylmethio-nine:histamine N-methyltransferase, EC 2.1.1.8) by serotonin, chlorpromazine and a number of their derivatives has been investigated. Lineweaver-Burk plots showed that these compounds act as non-competitive inhibitors with Ki values ranging from 13 to 130 μM. Dialysis experiments showed the inhibition to be kinetically reversible. The electronic nature of the complex formed between enzyme and inhibitor has been investigated by molecular-orbital calculations of selected reactivity indices of these two groups of compounds. The principal characteristic of the electronic configuration of these compounds which appears to determine their relative Ki values is their ability to donate electrons, as measured by the energy of their highest filled molecular orbitals. It is suggested, on the basis of the data presented, that the formation of the enzyme-inhibitor complex involves partial or total transfer of one or more electrons from the inhibitor to the enzyme.

The problem of determining the sequence of a biopolymer from its fragments is stated in mathematical terms. Using concrete properties of a free monoid, certain general classes of biopolymers are shown to be insolvable from fragment data produced by complete digestion where enzymes specific for any possible combination of chemical bonds are employed.

Spectroscopic studies indicate that the anionic dye Biebrich scarlet binds and stacks to polycations in an analogous way to cationic dyes on polyanions. Both exciton and dispersion interactions are needed to account for the spectral shifts and intensity changes. The low stacking coefficients are suggestive but not strong evidence for helical structure in the polycations examined. Calculations based on exciton theory using the observed spectral shifts, show that the dyes lie on the outside of the polymers, probably in a radial orientation.

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Changes in taste acuity accompany various disease processes and are useful in diagnosis. Lingual lesions may decrease acuity for salt and sweet, maxillary dentures decrease acuity for sour...

Experimental conditions were determined under which spectral changes in proflavine due to binding to nucleic acids can be quantitatively analyzed by starting with the maximally-saturated complex (1 dye per phosphate group) and keeping the amount of bound dye constant (negligible free dye) as the number of sites is increased. Calculation of various optical parameters shows that both a blue shift in frequency and decrease in oscillator strength occur in the spectra of 1- to-1 complexes of proflavine with native and denatured DNA and RNA, and that the extent of hypochromism is greater for denatured DNA and RNA than for native DNA. At ratios of sites-to-dye (P/D) greater than one, the red-shifted spectrum of the “strong-binding” complexes appears. The redistribution of dyes on excess sites is similar for denatured and native DNA up to P/D= 5. However, quantitative and qualitative differences in the spectra of these complexes occur at higher P/D. The data emphasize the multiplicity in geometry of binding, discussed by others in regard to native DNA, and elucidate the origin of several features of the induced optical activity of proflavine in these complexes.