Present and future of expert systems in food analysis

This paper presents an overview of the most relevant contributions in the field of expert system (ES) applications in chemical analysis of foods, along with a critical discussion of future, would-be developments. It illustrates the possibilities offered as well as the fact that quality control laboratories should be aware of the power of artificial intelligence that modern computer technology affords. It is worth noting that the applications described are straightforward with a certain versatility and can, therefore, be implemented for other analytes and/or food samples. Special attention is devoted to the promising distributed knowledge-based systems due to their potential advantages over the existing centralized approaches, as inferred from a recent example of application to the on-line monitoring of some key chemical parameters in the course of a food production process. Short and middle term predictions concerning the potential of ES in food analysis are also made.     

含茂金属的双组分或多组分催化体系的研究与应用

评述了含茂金属的双组分或多组分催化体系的基础研究与应用。大多数含茂金属的双组分或多组分催化体系用于制备宽分子量分布聚烯烃,尤其是宽分布聚乙烯,少数用于制备支化或嵌段聚合物。双组分或多组分催化体系已经成为分子剪裁与材料设计的重要手段之一。     

Hartree Fock instabilities in the S4N 4 2+ dication

The HF singlet stability of the S₄N ₄ ²⁺ dication is investigated. At the experimental bond length, R _SN=1.545 Å, the D _4h solution is stable but at 2.00 Å a C _2v broken symmetry solution is of lower energy. Population analysis shows that C _2v solution has a nitrogen -hole on one of the unique nitrogens. The sulphur -hole (found for the anion S₃N ₃ ^– at this distance) is not a local minimum.     

The Shannon entropy of high-dimensional hydrogenic and harmonic systems

There exists an increasing interest on the dimensionality dependence of the entropic properties for the stationary states of the multidimensional quantum systems in order to contribute to its emergent informational representation, which extends and complements the standard energetic representation. Nowadays, this is specially so for high-dimensional systems as they have been recently shown to be very useful in both scientific and technological fields. In this work, the Shannon entropy of the discrete stationary states of the high-dimensional harmonic (ie, oscillator-like) and hydrogenic systems is analytically determined in terms of the dimensionality, the potential strength, and the state's hyperquantum numbers. We have used an information-theoretic methodology based on the asymptotics of some entropy-like integral functionals of the orthogonal polynomials and hyperspherical harmonics which control the wave functions of the quantum states, when the polynomial parameter is very large; this is basically because such a parameter is a linear function of the system's dimensionality. Finally, it is shown that the Shannon entropy of the D-dimensional harmonic and hydrogenic systems has a logarithmic growth rate of the type D log D when D → ∞.     

Utilization of Donor–Acceptor Interactions for the Catalytic Acceleration of Nucleophilic Additions to Aromatic Carbonyl Compounds

A conceptually new method for the catalytic electrophilic activation of aromatic carbonyl substrates, by utilizing donor–acceptor interactions between an electron‐deficient macrocyclic boronic ester host ( [2+2] _BTH‐F ) and an aromatic carbonyl guest substrate, was realized. In the presence of a catalytic amount of [2+2] _BTH‐F , dramatic acceleration of the nucleophilic addition of a ketene silyl acetal towards either electron‐rich aromatic aldehydes or ketones was achieved. Several control experiments confirmed that inclusion of the aromatic substrates within [2+2] _BTH‐F , through efficient donor–acceptor interactions, is essential for the acceleration of the reaction.     

Interaction of a finite quantum system with an infinite quantum system that contains a single one-parameter eigenvalue band

Interaction of a finite quantum system that contains ρ eigenvalues and eigenstates with an infinite quantum system that contains a single one-parameter eigenvalue band is considered. A new approach for the treatment of the combined system is developed. This system contains embedded eigenstates with continuous eigenvalues , and, in addition, it may contain isolated eigenstates with discrete eigenvalues . Two ρ × ρ eigenvalue equations, a generic eigenvalue equation and a fractional shift eigenvalue equation are derived. It is shown that all properties of the system that interacts with the system can be expressed in terms of the solutions to those two equations. The suggested method produces correct results, however strong the interaction between quantum systems and . In the case of the weak interaction this method reproduces results that are usually obtained within the formalism of the perturbation expansion approach. However, if the interaction is strong one may encounter new phenomena with much more complex behavior. This is also the region where standard perturbation expansion fails. The method is illustrated with an example of a two-dimensional system that interacts with the infinite system that contains a single one-parameter eigenvalue band. It is shown that all relevant completeness relations are satisfied, however strong the interaction between those two systems. This provides a strong verification of the suggested method.     

Free energy of an inhomogeneous polymer–polymer–solvent system. II

A complete expression for the enthalpy of mixing of inhomogeneous polymer–polymer–solvent systems applicable for small as well as large concentration fluctuations has been developed. This is used to express the free energy of inhomogeneous polymer–polymer–solvent systems in an extended form of the Landau-Ginzburg functional. The gradient energy parameters obtained here are consistent with the published results. The free energy functional has been applied to develop a generalized continuity equation for spinodal decomposition in polymer–polymer systems. A linearized version of this continuity equation has been used to study the effect of the gradient terms on the dominant wavelength during spinodal decomposition.     

The multi-step phosphorelay mechanism of unorthodox two-component systems in E. coli realizes ultrasensitivity to stimuli while maintaining robustness to noises

E. coli has two-component systems composed of histidine kinase proteins and response regulator proteins. For a given extracellular stimulus, a histidine kinase senses the stimulus, autophosphorylates and then passes the phosphates to the cognate response regulators. The histidine kinase in an orthodox two-component system has only one histidine domain where the autophosphorylation occurs, but a histidine kinase in some unusual two-component systems (unorthodox two-component systems) has two histidine domains and one aspartate domain. So, the unorthodox two-component systems have more complex phosphorelay mechanisms than orthodox two-component systems. In general, the two-component systems are required to promptly respond to external stimuli for survival of E. coli. In this respect, the complex multi-step phosphorelay mechanism seems to be disadvantageous, but there are several unorthodox two-component systems in E. coli. In this paper, we investigate the reason why such unorthodox two-component systems are present in E. coli. For this purpose, we have developed simplified mathematical models of both orthodox and unorthodox two-component systems and analyzed their dynamical characteristics through extensive computer simulations. We have finally revealed that the unorthodox two-component systems realize ultrasensitive responses to external stimuli and also more robust responses to noises than the orthodox two-component systems.     

Supersaturation-Based Drug Delivery Systems: Strategy for Bioavailability Enhancement of Poorly Water-Soluble Drugs

At present, the majority of APIs synthesized today remain challenging tasks for formulation development. Many technologies are being utilized or explored for enhancing solubility, such as chemical modification, novel drug delivery systems (microemulsions, nanoparticles, liposomes, etc.), salt formation, and many more. One promising avenue attaining attention presently is supersaturated drug delivery systems. When exposed to gastrointestinal fluids, drug concentration exceeds equilibrium solubility and a supersaturation state is maintained long enough to be absorbed, enhancing bioavailability. In this review, the latest developments in supersaturated drug delivery systems are addressed in depth.     

APPLICATIONS OF ISOCYANATION FOR POLYMER SYSTEMS

Isocyanate is a highly unsaturated compound. It reacts readily with compounds containing active proton such as alcohol, phenol, acid, and amine through isocyanation. In this article, this very useful synthesis route is reviewed with regard to applications of isocyanation for the synthesis of polyurethanes, polyurethane ionomers, polyamides, polyimides, polyamide-imides, interpenetrating network polymers, polymers for membrane separation, comb- and star-polymers, functional monomers, and new stabilizers.

     

Foods As Dispersed Systems. Thermodynamic aspects of composition-property relationships in formulated food

Although most components contribute to structural and physical properties of food, the two main construction materials are proteins and polysaccharides in their molecular and colloidal dispersions. Native biopolymers in biological system interact specifically, whereas they are mainly denatured and interact non-specifically in formulated food. Most food components have limited miscibility on a molecular level and form multicomponent, heterophase and non-equilibrium dispersed systems. A thermodynamic approach is applicable for studying structure-property relationships in formulated foods since their structures are based on non-specific interactions between components. Thermodynamically-based operations, such as mixing of components, changing temperature and/or pH, underlie processing conditions. To simplify considerations, attention will focus only on the effects of thermodynamic incompatibility of biopolymers on food dispersion functionality. The excluded volume effect of the macromolecules is the main reason for their immiscibility. Molecular mimicry of globular proteins causes their more-than-ten-fold-higher miscibility compared to classical polymers. Biopolymer incompatibility results in phase-separated liquid and gel-like aqueous systems. In highly volume-occupied systems aggregation, crystallisation and gelation of biopolymers and their adsorption at oil/water interfaces favour an increase in the free volume, accessible for macromolecules. This revised version was published online in July 2006 with corrections to the Cover Date.     

Photometric probe for studying substrate-tether systems

An aromatic diazonium ion is considered as a reactive probe for determining the ability of a substrate-tether system to isolate adjacent, immobilized species. The immobilized probe molecule can either hydrolyze to the colorless phenol or couple to give a highly colored azo compound. The product distribution depends on whether the substrate-tether system permits interaction of adjacent species. The geometric form (cis vs. trans) of the azo compound which may form is affected by the nature of the substrate and the tether. The cis form is favored over the normally stable trans form when the substrate-tether system holds opposite ends of the doubly immobilized azo molecules together instead of stretching them apart.     

Calorimetric Analysis of Vesicular Systems

A number of studies of micellar aggregation in aqueous solutions of ethylene oxide-propylene oxide block copolymers — using high sensitivity differential scanning calorimetry (HSDSC) — are reviewed. The review attempts to show how the calorimetric output can be analysed, using a model fitting procedure, to obtain estimates for various thermodynamic parameters, which characterise the micellization event, as observed by HSDSC. These important parameters include: T _1/2 the temperature at which half the surfactant has been incorporated into micelles; H _cal — the calorimetric enthalpy for the process which is measured by integration of the calorimetric output; H _vH — the van't Hoff enthalpy — which characterises the functional dependence of the equilibrium composition of the system upon temperature and which is derived from the application of the van't Hoff isochore to the data analysis procedure; C _p — the heat capacity change between the initial and final states;and n the aggregation number.Using this data it is possible to examine how extent of aggregation functionally varies with temperature. Subsequent interpolation of these thermal aggregation plots permits an examination of how the extent of aggregation is affected by changes in solution composition under isothermal conditions. A large body of data is presented which shows how co-solvents, co-solutes and pH affect the aggregation process in aqueous solution.This revised version was published online in November 2005 with corrections to the Cover Date.     

Multistage Organic Redox Systems—A General Structural Principle

A general structural principle for organic compounds that have the capacity for two-stage electron transfer is based on the following reaction sequence: In this scheme one or both of the entities X may be replaced by Y^?. The radical partners in these systems often have very high thermodynamic stability. The choice of the end groups X and Y, (partial) inclusion of n-systems in rings, alteration of the number of vinylene groups, and aza-substitution make many variations possible. By means of this general structural principle numerous known compounds are brought together and new redox systems are simultaneously set up. The aim of the present review is to demonstrate the broad applicability of this principle, to indicate its significance for science and industry, and to describe some reactions.     

Tuning Aqueous Supramolecular Polymerization by an Acid-Responsive Conformational Switch

Besides their widespread use in coordination chemistry, 2,2’-bipyridines are known for their ability to undergo cis–trans conformational changes in response to metal ions and acids, which has been primarily investigated at the molecular level. However, the exploitation of such conformational switching in self-assembly has remained unexplored. In this work, the use of 2,2’-bipyridines as acid-responsive conformational switches to tune supramolecular polymerization processes has been demonstrated. To achieve this goal, we have designed a bipyridine-based linear bolaamphiphile, 1 , that forms ordered supramolecular polymers in aqueous media through cooperative aromatic and hydrophobic interactions. Interestingly, addition of acid (TFA) induces the monoprotonation of the 2,2’-bipyridine moiety, leading to a switch in the molecular conformation from a linear (trans) to a V-shaped (cis) state. This increase in molecular distortion along with electrostatic repulsions of the positively charged bipyridine-H⁺ units attenuate the aggregation tendency and induce a transformation from long fibers to shorter thinner fibers. Our findings may contribute to opening up new directions in molecular switches and stimuli-responsive supramolecular materials.     

Excess molar properties of ternary system (ethanol + water + 1,3-dimethylimidazolium methylsulphate) and its binary mixtures at several temperatures

The density, dynamic viscosity, and refractive index of the ternary system (ethanol + water + 1,3-dimethylimidazolium methylsulphate) at T = 298.15 K and of its binary systems 1,3-dimethylimidazolium methylsulphate with ethanol and with water at several temperatures T = (298.15, 313.15, and 328.15) K and at 0.1 MPa have been measured over the whole composition range. From these physical properties, excess molar volumes, viscosity deviations, refractive index deviations, and excess free energy of activation for the binary systems at the above mentioned temperatures, were calculated and fitted to the Redlich–Kister equation to determine the fitting parameters and the root-mean-square deviations. For the ternary system, the excess properties were calculated and fitted to Cibulka, Singh et al., and Nagata and Sakura equations. The ternary excess properties were predicted from binary contributions using geometrical solution models.