Randomization tests to identify significant effects in experimental designs for robustness testing

The screening designs applied in robustness tests are usually fractional factorial or Plackett-Burman designs. Different methods to identify significant factor effects estimated from experimental designs for robustness testing are described. In this paper, the use of randomization tests as a statistical interpretation method is examined and compared with both graphical (half-normal probability plot) and statistical methods, such as the estimation of error based on a priori considered negligible effects and the algorithm of Dong. It was found that all statistical methods usually gave similar results, i.e. the same effects are found to be significant. However, sometimes randomization tests indicate either less or more significant factor effects compared to the other methods, regardless the design size. Both randomization tests and the algorithm of Dong become unreliable when about 50% of the examined factors are significant. In such situation, it is advisable to perform an experimental design from which enough negligible effects can be estimated. The graphical interpretation method did not always succeed in indicating the correct number of significant effects.     

The photo-stabilising action of metal chelates in polypropylene: Part IX—Practical synergism with other commercial systems and the importance of calcium stearate

The photo-stabilising action of three metal chelates (Cyasorb UV 1084, Irganox 1425 and Irgastab 2002) in a number of synergistic formulations with three commercial stabilising systems (Weston 618, Cyasorb UV 531 and Tinuvin 770), in polypropylene films has been examined. The results show that, although antagonistic effects are observed at some mass ratios, synergistic effects prevail at others. The effects are a function of the particular formulation.The addition of calcium stearate to the stabilising mixture can have marked effects on the observed behaviour. Thus, an antagonistic effect can become synergistic if calcium stearate is used in the formulation. The results have scientific and technological implications as calcium stearate is often used as a processing aid in the stabilisation of polypropylene.     

Comparison of matrix effects in HPLC-MS/MS and UPLC-MS/MS analysis of nine basic pharmaceuticals in surface waters

When developing an LC-MS/MS-method matrix effects are a major issue. The effect of co-eluting compounds arising from the matrix can result in signal enhancement or suppression. During method development much attention should be paid to diminishing matrix effects as much as possible. The present work evaluates matrix effects from aqueous environmental samples in the simultaneous analysis of a group of 9 specific pharmaceuticals with HPLC-ESI/MS/MS and UPLC-ESI/MS/MS: flubendazole, propiconazole, pipamperone, cinnarizine, ketoconazole, miconazole, rabeprazole, itraconazole and domperidone. When HPLC-MS/MS is used, matrix effects are substantial and can not be compensated for with analogue internal standards. For different surface water samples different matrix effects are found. For accurate quantification the standard addition approach is necessary. Due to the better resolution and more narrow peaks in UPLC, analytes will co-elute less with interferences during ionisation, so matrix effects could be lower, or even eliminated. If matrix effects are eliminated with this technique, the standard addition method for quantification can be omitted and the overall method will be simplified. Results show that matrix effects are almost eliminated if internal standards (structural analogues) are used. Instead of the time-consuming and labour-intensive standard addition method, with UPLC the internal standardization can be used for quantification and the overall method is substantially simplified.     

Linear and two-photon absorption properties of interacting polar chromophores: standard and unconventional effects.

Investigations into the effects of electrostatic interactions on linear and two-photon absorption (TPA) properties are probed using a reference polar chromophore and different related compounds. Compounds in which a passive charge is present near the active chromophore, as well as dimers of the reference molecule, were studied. The combined experimental and theoretical investigation demonstrates that strong modulation of the properties can be attained. In particular, the TPA response of dimers is heavily affected by unconventional excitonic effects, that is, beyond the standard Heitler-London approximation. These effects, which stem from purely electrostatic interactions, lower the nonlinear optical response in the investigated case by an additional amount (up to 20%), and are expected to enhance the TPA cross section in other supramolecular alignments. Electrostatic interactions cannot be overlooked when modelling or investigating highly concentrated and/or confined samples, as are usually needed in many applications. The correct knowledge of their effects can be exploited to guide engineering at the molecular and supramolecular level.     

Hofmeister effects in enzymatic activity: weak and strong electrolyte influences on the activity of Candida rugosa lipase

The effects of weak and strong electrolytes on the enzymatic activity of Candida rugosa lipase are explored. Weak electrolytes, used as buffers, set the pH, while strong electrolytes regulate the ionic strength. The interplay between pH and ionic strength has been assumed to be the determinant of enzymatic activity. In experiments that probe activities by varying these parameters, there has been little attention focused on the role of specific electrolyte effects. Here we show that both buffers and the choice of background electrolyte ion strongly affect the enzymatic activity of Candida rugosa lipase. The effects here shown are dramatic at high salt concentration; indeed, a 2 M concentration of NaSCN is able to fully inactivate the lipase. By contrast, Na2SO4 acts generally as an activator, whereas NaCl shows a quasi-neutral behavior. Such specific ion effects are well-known and are classified among the "Hofmeister effects". However, there has been little awareness of them, or of their potential for optimization of activities in the enzyme community. Rather than the effects per se, the focus here is on their origin. New insights into mechanism are proposed.     

Studies of a radio frequency inductively coupled argon plasma for optical emission spectrometry—III. Interference effects under compromise conditions for simultaneous multi-element analysis

This work concerns interference effects in a 0.7-kW, 50-MHz inductively coupled plasma (ICP) provided with an ultrasonic nebulizer (USN) and desolvation apparatus (DA). The observations were made under (ICP) conditions adopted previously as “compromise conditions for simultaneous multi-element analysis.” Various matrices and analytes were considered.An arrangement of two identical USN's with separate DA's was used to distinguish between interferences due to processes in the plasma (“plasma effects”) and the nebulizer—desolvation apparatus (“nebulizer—desolvation effects”). The latter were identified as “desolvation effects” and attributed to a variation in the loss of analyte in the DA. This desolvation effect, whose magnitude varies between ±10%, is related to the difference in volatility between matrix and analyte. The experiments revealed plasma effects that cannot be reconciled with the common pictures of ionization interference and are not due to incomplete volatilization or dissociation either. Possible explanations are considered. The overall interference level in the ICP studied is discussed and practical conclusions regarding the use of desolvation, “pure” aqueous solutions as standards, and spectroscopic buffers are drawn.     

Toward calculations of the 129Xe chemical shift in Xe@C60 at experimental conditions: relativity, correlation, and dynamics

We calculate the 129Xe chemical shift in endohedral Xe@C60 with systematic inclusion of the contributing physical effects to model the real experimental conditions. These are relativistic effects, electron correlation, the temperature-dependent dynamics, and solvent effects. The ultimate task is to obtain the right result for the right reason and to develop a physically justified methodological model for calculations and simulations of endohedral Xe fullerenes and other confined Xe systems. We use the smaller Xe...C6H6 model to calibrate density functional theory approaches against accurate correlated wave function methods. Relativistic effects as well as the coupling of relativity and electron correlation are evaluated using the leading-order Breit-Pauli perturbation theory. The dynamic effects are treated in two ways. In the first approximation, quantum dynamics of the Xe atom in a rigid cage takes advantage of the centrosymmetric potential for Xe within the thermally accessible distance range from the center of the cage. This reduces the problem of obtaining the solution of a diatomic rovibrational problem. In the second approach, first-principles classical molecular dynamics on the density functional potential energy hypersurface is used to produce the dynamical trajectory for the whole system, including the dynamic cage. Snapshots from the trajectory are used for calculations of the dynamic contribution to the absorption 129Xe chemical shift. The calculated nonrelativistic Xe shift is found to be highly sensitive to the optimized molecular structure and to the choice of the exchange-correlation functional. Relativistic and dynamic effects are significant and represent each about 10% of the nonrelativistic static shift at the minimum structure. While the role of the Xe dynamics inside of the rigid cage is negligible, the cage dynamics turns out to be responsible for most of the dynamical correction to the 129Xe shift. Solvent effects evaluated with a polarized continuum model are found to be very small.     

二氧化碳电催化还原中的电解质效应（英文）

二氧化碳(CO₂)电催化还原反应利用可再生能源将CO₂转化为高值燃料和化学品,是一种新型的碳中和技术。CO₂电催化还原反应在电极/电解质界面上进行,因此除催化剂以外,电解质对提高CO₂电催化还原反应性能同样至关重要。本文深度剖析了CO₂电催化还原反应中的电解质效应,结合近几年的最新研究进展,详细讨论了局部p H、阳离子、阴离子和离子交换膜等电解质组成和性质对电催化活性和产物选择性的影响,阐述了电解质效应的催化作用机制。本文特别强调了电化学原位红外/拉曼等振动光谱在电解质效应机理研究方面的优势以及面向实际应用的膜电极CO₂电解器中阴离子、阳离子、水、液体产物等物质传输对活性、选择性、能量效率及CO₂利用效率等关键催化性能指标的影响。本文最后提出了当前电解质效应研究中存在的挑战,并展望了未来的研究机遇和发展趋势。     

Chemical accuracy in ab initio thermochemistry and spectroscopy: current strategies and future challenges

The current state of the art in wavefunction-based electronic structure methods is illustrated via discussions of the most important effects incorporated into a selection of high-accuracy methods chosen from the chemical literature. If one starts with a high-quality correlation treatment, such as provided by the CCSD(T) coupled cluster method, the leading effects include convergence of the results with respect to the 1-particle basis set, (outer)core/valence correlation, scalar relativistic effects and a number of smaller effects. For thermochemical properties such as the heat of formation, the zero-point vibrational energy also becomes important, introducing its own set of difficulties to the computational approach. Changes in the various components as the chemical systems incorporate heavier elements and as the size of the systems grows are also considered. Finally, challenges arising from the desire to extend existing methods to transition metal and heavier elements are considered.     

Investigation of substituent effects on the 1H and 13C NMR spectra of ferrocene analogues of chalcones

The transmission of electronic effects across the ferrocene analogues of chalcones [3-aryl-1-ferrocenyl-2-propene-1-ones (series 1) and 1-aryl-3-ferrocenyl-2-propene-1-ones (series 2)], as well as the conformations of both types of ferrocene analogues have been studied. The ferrocene analogues of chalcones of series 1 were found to be in a non-planar conformation. Their H-α and C-α chemical shifts are more sensitive to the resonance than to the inductive effects of substituents. The C-α chemical shifts of the ferrocene analogues of chalcones of series 2 are more sensitive to the inductive than to the resonance effects of substituents. The transmission of the substituent effects to the ferrocene moiety is also briefly discussed.     

Chemistry and biology of terpene trilactones from Ginkgo biloba

Ginkgo biloba, the ginkgo tree, is the oldest living tree, with a long history of use in traditional Chinese medicine. In recent years, the leaf extracts have been widely sold as phytomedicine in Europe and as a dietary supplement worldwide. Effects of Ginkgo biloba extracts have been postulated to include improvement of memory, increased blood circulation, as well as beneficial effects to sufferers of Alzheimer's disease. The most unique components of the extracts are the terpene trilactones, that is, ginkgolides and bilobalide. These structurally complex molecules have been attractive targets for total synthesis. Terpene trilactones are believed to be partly responsible for the neuromodulatory properties of Ginkgo biloba extracts, and several biological effects of the terpene trilactones have been discovered in recent years, making them attractive pharmacological tools that could provide insight into the effects of Ginkgo biloba extracts.     

The incorporation of hydration forces determined by continuum electrostatics into molecular mechanics simulations

A new technique is presented for incorporating hydration forces into molecular mechanics simulations. The method assumes the classical continuum approximation, where a solvated molecule is represented as a low-dielectric cavity of arbitrary shape embedded in a continuous region of high dielectric constant. Electrostatic effects are computed by first calculating the distribution of polarization charge (induced by the configuration of solute fixed charges) at the molecular surface. The hydration force at a particular atom is then found as the sum of the coulombic interaction with the induced surface charge, plus a purely mechanical contribution that arises from the pressure of the polarized solvent as it is pulled toward the solute. A procedure is developed to use the computed hydration forces in conjunction with the CHARMM molecular mechanics package to carry out energy minimizations in which the effects of solvation are explicitly included. This new technique also allows a detailed analysis of the relative balance of coulombic, hydration, and steric energies as a function of molecular conformation. The method is applied to the test case of a zwitterionic tripeptide (LYS-GLY-GLU), and the computational results suggest that hydration effects can play a significant role in determining a stable conformation for a solvated polar molecule. The future application to larger molecules is discussed.     

Heat Effects in ZLC Experiments

The problem of nonisothermal desorption in a zero length column (ZLC) experiment is considered theoretically. Simple analytical expressions for the ZLC desorption curve are derived for certain limiting situations in which the governing equations reduce to a linear form. More general numerical solutions are calculated for a wide range of experimental conditions assuming both negligible mass transfer resistance and finite mass transfer resistance controlled by intraparticle diffusion. A simple criterion for negligible thermal effects is developed. It is shown that when the ZLC technique is applied to the measurement of diffusion in unaggregated zeolite crystals, as originally intended, heat effects are generally insignificant. However, when applied to the measurement of macropore diffusion in relatively large adsorbent particles heat effects can become important and may cause major modification of both the desorption rate and the shape of the desorption curve. A recent experimental ZLC study carried out with commercial adsorbent particles, under conditions of macropore diffusion control, showed an anomalous dependence of the desorption rate on both temperature and particle size. These effects can be qualitatively explained by the nonisothermal model. A more precise quantitative representation of these experiments will require a more refined model incorporating a nonlinear equilibrium isotherm as well as intraparticle diffusional resistance.     

A local approach to delocalized electronic systems: semilocal evaluation of the cohesive energies of tight-binding Hamiltonians

Starting from strongly localized N-electron functions built from either pure atomic orbitals or fully localized bond molecular orbitals, it is possible to evaluate the ground state energy of a periodic lattice ruled by a tight-binding Hamiltonian without explicitly introducing the monoelectronic crystal orbitals. The method consists of a self-consistent perturbation of the zeroth-order wave function which incorporates high order effects and offers reasonable convergence properties. Along this framework, a single variable per bond type is introduced, namely the amplitude of the charge transfer. The method leads to a set of coupled equations which can be numerically solved, if not analytically. Short-range delocalization effects under periodic conditions are explicitly taken into account and relatively accurate cohesive energies are estimated for regular homoatomic and heteroatomic one-dimensional chains as well as for honeycomb lattices. In addition, good agreement with experiment for the distortion amplitude in polyacetylene is obtained. This exploratory tool may be easily extended to more sophisticated Hamiltonians, for which the solutions are not accessible. Since our approach only introduces short-range delocalization effects, its performance questions the importance of the specifically collective delocalization effects.     

Spin-orbit effects in electron transfer in neptunyl(VI)-neptunyl(V) complexes in solution

The spin-orbit effects were investigated on the complexes involved in the electron self-exchange between Np(V) and Np(VI) in both the outer-sphere and inner-sphere mechanisms, the latter for binuclear complexes containing hydroxide, fluoride, and carbonate as bridging ligands. Results obtained with the variation-perturbation and the multireference single excitation spin-orbit CI calculations are compared. Both effects due to different relaxations of spinors within a multiplet (spin-orbit relaxation) and scalar (electrostatic) relaxation effects in the excited states are accounted for in the latter scheme. The results show that the scalar (electrostatic) relaxation is well described by the single-excitation spin-orbit CI, and that spin-orbit relaxation effects are small in the Np complexes, as in the lighter d-transition elements but in contrast to the main group elements.     

Nondigestible oligosaccharides as dietary fiber

An overview is presented of the most important oligosaccharides that are classified as dietary fiber. Their occurrence and structures as well as their various physiological effects are described. The scientific evidence for health effects, associated with these physiological effects, along with the applications in the food industry, are also discussed.     

Reaction field effects on the electronic structure of carbon radical and ionic centers

We examine solvent effects on carbon radical and ionic centers of HCXY by including a self-consistent reaction-field into the AM 1 and MNDO electronic structure models to mimic dielectric effects. We find that such concepts as merostability are principally solvent effects, and that, as expected, molecules with large dipoles or with charge assymmetry are stabilized more by solvent than those with atoms that are more electrically neutral. Of some importance in this study is the finding that conformation is also dependent on solvation and that change in geometry must be considered if an accurate estimate is to be made of energy differences such as those examined in the calculations of merostabilization.     

Photochemistry of N-acylimino-isoquinolinium and -quinolinium betaines

The photochemical behavior of N-acyliminoisoquinolinium and -quinolinium betaines has been investigated. In contrast to pyridinium betaines, the principal course of reaction is the 1,2-migration of N-acylamino groups. Substituent effects as well as solvent effects are observed. The results are rationalized in terms of diaziridine intermediates.