Three-way Principal Components Analysis for fluorescence spectroscopic classification of algae species

Excitation-emission matrices (EEM) from fluorescence spectroscopy may contain characteristic information about different algae species. As a result of measurements, one gets a whole stack of EEMs each of them corresponding to one species. Such a stack of matrices has to be understood as a cubic data array spanned by the dimensions ‘excitation’, ‘emission’ and ‘species’. The interpretation of higher dimensional data arrays requires efficient tools from multivariate data analysis. In this paper, it is illustrated how Three-way Principal Components Analysis as the appropriate generalization of conventional Principal Components Analysis may serve as a powerful method for classification of algae species. Received: 31 May 1996 / Revised: 1 July 1996 / Accepted: 4 Juli 1996     

Doctoral Study Programmes in Europe

For a long time, obtaining a PhD in Belgium and in a number of other European countries was based on the philosophy of ‘learning-by-doing’ under the exclusive supervision of a promoter. The completion of the PhD dissertation usually led to a research or staff position. Now, many of today’s young scientists need to build their career outside the university where employers are as interested in the applicant’s skills as in their knowledge. Highly-qualified research scientists are needed in many sectors of society but require a background in its political, economical and cultural dimensions, and additional management, social and communication skills, including the ability to speak other European languages. However, although the purpose of the doctorate is the creation of a multidisciplinary scientist with broad academic qualifications, many research projects at present are restricted to subjects within a particular discipline. The acquirement of the ‘social’ skills through the ‘learning-by-doing’ concept proves to be very difficult, especially if one considers the increase of graduate students at present times. Therefore, additional study programmes for doctoral students are required. In this paper the doctoral study programme of the University of Antwerpen is described, as well as a short survey of comparable initiatives in Western Europe. Received: 25 January 1996 / Accepted: 7 June 1996     

Doctoral Study Programmes in Europe

For a long time, obtaining a PhD in Belgium and in a number of other European countries was based on the philosophy of ‘learning-by-doing’ under the exclusive supervision of a promoter. The completion of the PhD dissertation usually led to a research or staff position. Now, many of today’s young scientists need to build their career outside the university where employers are as interested in the applicant’s skills as in their knowledge. Highly-qualified research scientists are needed in many sectors of society but require a background in its political, economical and cultural dimensions, and additional management, social and communication skills, including the ability to speak other European languages. However, although the purpose of the doctorate is the creation of a multidisciplinary scientist with broad academic qualifications, many research projects at present are restricted to subjects within a particular discipline. The acquirement of the ‘social’ skills through the ‘learning-by-doing’ concept proves to be very difficult, especially if one considers the increase of graduate students at present times. Therefore, additional study programmes for doctoral students are required. In this paper the doctoral study programme of the University of Antwerpen is described, as well as a short survey of comparable initiatives in Western Europe. Received: 25 January 1996 / Accepted: 7 June 1996     

The chemical ‘Knight’s Move’ relationship: what is its significance?

Similarities in properties among pairs of metallic elements and their compounds in the lower-right quadrant of the Periodic Table have been named the ‘Knight’s Move’ relationship. Here, we have undertaken a systematic study of the only two ‘double-pairs’ of ‘Knight’s Move’ elements within this region: copper-indium/indium-bismuth and zinc-tin/tin-polonium, focussing on: metal melting points; formulas and properties of compounds; and melting points of halides and chalcogenides. On the basis of these comparisons, we conclude that the systematic evidence for ‘Knight’s Move’ relationships derives from similarities in formulas and properties of matching pairs of compounds in the same oxidation state. Physical properties, such as melting points, do not provide consistent patterns and trends and hence should not be considered as a common characteristic of this relationship.     

New Routes for Thermal Analysis and Calorimetry As Applied to Polymeric Systems

Over the last few decades there has been a strong decrease in the number of Thermal Analysis and Calorimetry (TA and C) ‘practitioners’ - scientists who know the in sand outs of TA and C and its (im)possibilities and are capable of initiating new developments. By contrast, an increasing number of TA and C ‘users’ are scarcely able to acquire in-depth knowledge of TA and C. It is therefore of great importance that national TA and C societies create the infrastructure for dedicated education. In addition, the feasibility of setting up one or more expertise centers per country, where ‘practitioners’ can do research,carry out contract research and give advice to users, needs to be investigated. Equally important, the TA and C community needs to address a number of challenges in the coming decade with the aim of controlling the ‘knowledge cycle’ in the field of polymers: to translate non-optimal properties into improved processing conditions or even a more suitable macromolecular architecture, in order to reduce the lead times for the development and optimization of materials. Although Thermal Analysis and Calorimetry can generally be considered to be ‘mature’, in specific subareas a large number of new developments take place. A few examples of these developments and of state-of-the-art TA and C are given:quantitative heat capacity measurements by means of DSC; (very) high pressure DSC;real-time morphological analysis and temperature-modulated X-ray analysis. In addition, anew form of TA and C is discussed: High Performance DSC (HPer DSC), which is also a high rate DSC and a high throughput DSC. This revised version was published online in July 2006 with corrections to the Cover Date.     

Modulated-Temperature Thermomechanical Analysis of Fibres

The application of modulated temperature programming to thermomechanical analysis affords a method for measuring the ‘true’ thermal expansion coefficients of materials that deform irreversibly during normal TMA. This may arise from creep under the applied load or changes in dimensions due to relaxation of orientation. Acrylic fibres made with various degrees of orientation shrink to different extents on heating but all show the same ‘true’ thermal expansion coefficients using this approach. The application of modulated temperature programming to Dynamic Mechanical Analysis is also discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Controversy and complementarity in mechanistic organic chemistry. The transition state and structural theories reexamined

It is proposed that molecular phenomena may only be described within the framework of the Complementarity Principle (‘CP’), and that scientific controversy may originate in the essential incompatibility of complementary representations. Complementarity based on the temporal Uncertainty Principle leads to new insights into transition state theory, microscopic reversibility and the Curtin-Hammett Principle. An empirical application of the ‘CP’ to the structural theory leads to a revision of present concepts of ‘reaction dynamics’, with the Principle of Least Nuclear Motion (‘PLNM’) emerging as a general alternative to electronic theories of reactivity. In fact, it is argued that the ‘PLNM’ is a better basis for the Woodward-Hoffmann rules than is orbital symmetry. A more flexible approach to organic reaction mechanisms is thus indicated. Also, as the basis of the structural theory is fundamentally uncertain, and the present theory of X-ray diffraction apparently incompatible with the ‘UP’, a reinterpretation of the Bragg equation has been attempted.     

Chemical morphology: The chemistry of our shape, <Emphasis Type="Italic">in vivo</Emphasis> and <Emphasis Type="Italic">in vitro</Emphasis>

Our shape is defined and maintained by the connective tissues (skin, tendons, cartilages, blood vessels, etc.) or more precisely by their extracellular matrices. These highly ordered supramolecular organisations are modules of protein fibrils held together by elastic carbohydrate strings. I called these the ‘shape modules.’ The ‘laws.’ which underpin this tissue jigsaw, the changes which come with age and the insight that the concepts give in economically important disorders such as osteoarthrosis begin to provide a new and coherent picture stretching across the animal world and its evolution. This structure/function picture is built on biochemical analyses, which developed into histochemical microscopy and thence into electron histochemistry, and from nuclear magnetic resonance (NMR), molecular modelling and computer simulations on the physicochemical and biomechanical side. As usual, originality bred dissent.     

The mole: definition versus practical use

Most base units in the SI relate to specific sensoric qualities our body is able to observe: space, heat, brightness, etc. The base unit ‘mole’ incorporates intellectual insight: the atomistic perception of the world. This perception is a quintessence of over 300 years of scientific research. The quintessence, from Dalton’s ‘The sceptical chymist’ to Perrin’s Nobel Prize in 1926 and Pauling’s ‘Nature of the Chemical Bond’ in 1939, results in the conclusion that the base unit of the SI quantity ‘amount of substance’ is not the mole but the dimensionless entity.     

Identification of an enantiotropic system with hindered multiphase transitions

Some preliminary considerations suggest that the so-called ‘compensation law’ is a result of the misinterpretation of evaluation procedure. The both parameters: pre-exponential factor and activation energy are calculated from the same set of experimental data. A confidence ellipse could describe the precision of these parameters. In the case of using the least square method for straight-line parameters evaluation, we could calculate a axes of the ellipse, using experimental data. If the observed relationship between pre-exponential factor and activation energy agree with the ‘pre-calculated’ direction of main axis of confidence ellipse, we have a strong support to believe that the observed ‘compensation’ effect is only an artificial effect of misinterpretation. Some calculations performed for a published experimental data have confirmed these suspicions. This also, indirectly indicates that precision of such experiments is probably lower than expected.     

‘Lab-in-reaction-cell’ cyclic injection analysis as an opportunity for the miniaturization of flow analysis

The method of cyclic injection analysis in the ‘lab-in reaction-cell’ mode has been proposed for the miniaturization of flow analysis; the hydraulic scheme of this mode assumes the formation of the analytical forms of the analytes and their detection directly in the reaction cell of the cyclic injection analyzer through the combination of the latter with the measurement cuvette of a fiber optic spectrophotometer. The possibilities of the proposed solution are illustrated by the example of the determination of ‘active chlorine’ in aqueous media. A procedure has been developed for the automated photometric determination of ‘active chlorine’ in the range from 0.2 to 1.3 mg/L in aqueous media in a 125 μL sample, the duration of one analysis being 2.5 min.     

Thermogravimetric Study of Carbonization Processes for Industrial Porous Co-polymers of Spherical Granules

The industrial porous co-polymers and resins in the form of spherical granules include three main matrices which serve as the basis of the large-scale production of ion-exchange materials: styrene/divinylbenzene, vinylpyridine/divinylbenzene and acrylonitrile/divinylbenzene. Complex thermal methods (TG, DTG and DTA) were used to study the carbonization processes of various industrial products utilized as starting materials for the preparation of synthetic active carbons. The DTG results, the thermal effects observed during the programmed heating of samples, and the mass-spectrometric and IR-spectroscopic data up to 800°C provided a picture of a multi-stage carbonization process. This includes the removal of moisture from the polymer matrices, the primary cross-linking of the chains, their aromatization and condensation due to the cross-linking of polynuclear structures, and the removal of ‘excess carbon’ as simple molecules and free radicals of hydrocarbon type. The results promoted the choice of the optimal regimes in which to carryout the isothermal pyrolysis of various polymer matrices and preliminary chemical modifications to increase the yields on carbon and to prepare synthetic active carbons such as those of SCN, SCAN and SCS types. General schemes were proposed for the chemical reactions accompanying the carbonization process for these polymer matrices. This revised version was published online in August 2006 with corrections to the Cover Date.     

TG of a cotton fabric impregnated by sodium borate decahydrate (Na2B4O7·10H2O) as a flame-retardant

The effect of sodium borate decahydrate as a nondurable treatment on the flammability of 100% cotton fabric (woven plain 150 g m⁻²) has been investigated in this paper. The laundered bone-dried massed samples were impregnated with suitable concentrations of sodium borate decahydrate. Each bunches of fabrics were dipped into individual aqueous solutions of the salt, followed by means of squeeze rolls and drying at 110°C. By using a ‘vertical flame spread test’ the optimum add-on values to impart flame-retardancy onto cotton fabric was determined to be as 4.24 g salt per 100 g fabric. The objective of this study is thermogravimetry (TG) investigation of pure cotton, treated one with the salt at its optimum efficiency. So that outcomes could be compared and commented, finally the results obtained are in favor of ‘Chemical action theory’, ‘Condensed phase retardation’, ‘Dust or wall effect theory’ and also ‘Gas dilution theory’.     

Extraction of humic acids from a natural matrix by alkaline pyrophosphate. Evaluation of the molecular weight of fractions obtained by ultrafiltration

 Fractions of humic acids, resolved by ultrafiltration of extracts from a sample of peat treated with alkaline pyrophosphate solution, have been submitted to high-performance size-exclusion chromatography, with the aim of determining the molecular weight distributions. Anomalous peaks, located at retention volumes higher than those corresponding to the main signal, are present in the elution profiles relative to the lightest fractions. These peaks are more intense when using a refractive index detector rather than a UV detector. Elemental analysis data for the lightest fractions suggested that the spurious peaks are due to the presence of inorganic material. The hypothesis that pyrophosphate interacts with humic acids in the course of the extraction has been confirmed by colorimetric determination of the phosphorus content in the different fractions. As a consequence, the extraction procedure has been modified by using 0.1 mol/L NaOH as extractant. The average molecular weights of the various fractions, following NaOH extraction, result in substantial agreement with those obtained following pyrophosphate solution extraction (if the ‘pyrophosphate peaks’ present in the chromatographic profile are discarded in the calculations). Received: 18 November 1996 / Revised: 18 February 1997 / Accepted: 23 February 1997     

Plasters and mortars in the central building of the university of Pavia

Plasters and mortars taken from the walls of the ancient hospital ‘San Matteo’ of Pavia (Italy), were investigated with thermal and other techniques. From the data collected, two groups of materials were brought out: the first one, containing the plasters, is remarkably richer in calcite than the second group, formed by the mortars. These findings allow one to relate these groups to two historical periods: the middle of the XV century, and the end of the XVIII century. Some hypotheses may also be made on the compositions of the binding/inert fractions adopted in preparing these materials in the building yards of the two periods.     

Hydroxyl orientations in cellobiose and other polyhydroxyl compounds: modeling versus experiment

Theoretical and experimental gas-phase studies of carbohydrates show that their hydroxyl groups are located in homodromic partial rings that resemble cooperative hydrogen bonds, albeit with long H…O distances and small O–H…O angles. On the other hand, anecdotal experience with disaccharide crystal structures suggested that these clockwise ‘c’ or counter-clockwise (reverse ‘r’) sequences are not prevalent in the crystalline state. The situation was clarified with quantum mechanics calculations in vacuum and in continuum solvation, as well as Atoms-In-Molecules analyses. From the experimental side, the Cambridge Structural Database was searched. Geometric criteria for these sequences were developed. A criterion based on 120° ranges of hydroxyl orientations accepted 4% of sequences as having ‘c,c’ or ‘r,r’ orientations instead of the 7% expected based on chance. Criteria based on an O–H…O angle > 90° and a 90° lower limit of the absolute value of the H–O–C…H improper torsion accepted 7.0% of the 358 sequences as ‘c,c’ or ‘r,r’. Highly variable orientation of the hydroxyl groups in crystals was seen to depend mostly on strong inter-residue or intermolecular hydrogen bonds. That lack of specific orientation in general for the crystal structures was supported by the solvated calculations that showed very little variation in the energy when one of the hydroxyl groups in 1,2-dihydroxycyclohexane was rotated. The vacuum calculations found the energy to vary with rotation by more than 4 kcal/mol, confirming the gas-phase experiments and calculations on more complicated molecules. Molecules examined in some detail include scyllo inositol and native and methylated cellobiose.     

The pyrolytic graphite surface as an enzyme substrate: microscopic and spectroscopic studies

We have conducted a series of experiments to explore the surface of the polished pyrolytic graphite ‘edge’ electrode as routinely prepared for use in protein film voltammetry. Our investigations have included nitrogen porosimetry and scanning electron microscopy. The nitrogen adsorption revealed a Brunauer–Emmett–Teller surface area ∼10⁴ times greater than the geometric surface area of the electrode. The pore-size distribution calculated by the Horváth–Kawazoe method showed that 10–18% of the pore volume arises from pores having widths >10 nm and, thus, should be accessible to enzymes, although much of the exposed ‘wall’ surface may be inactive for enzyme binding or electron transfer: for example, it may be mainly basal plane. Scanning electron micrographs of the abraded pyrolytic graphite edge showed differing scales of surface damage caused by the abrasion and the presence of many cracks in the surface where thin platelets had been removed.This work is dedicated to Prof. Alan Bond on the occasion of his 60th birthday. Alan’s enthusiasm for the complexities of diffusion control persuaded one of us (F.A. Armstrong) to try and avoid it altogether in protein electrochemical studies.     

Depth Profiling (ICP-MS) Study of Trace Metal ‘Grains’ in Solid Asphaltenes

Knowledge of trace metal ‘grains’ in asphaltenes could play a significant role in enhancing refining and processing of crudes and also in providing useful information on mechanistic and migratory features linked to asphaltenes. These metals originate directly from interaction of oils with source-rock, mineral matter, and formation water and their accumulation in asphaltene matrices could vary from oil well to oil well. Suitable asphaltene samples were subjected to high-performance ICP-MS laser depth profiling (213 nm) to depths of 50 μm at 5 μm intervals. The study was conducted in the absence of standardization and characteristic intensities originating from the metals of interest were measured. Ten metal profiles were investigated (Na, Mg, Al, Mn, Fe, Zn, Sr, Pb, V, and Ni). The experimental results showed non-uniform distribution of trace metals and identified areas where such metals agglomerate. The data suggested that certain chemical and physical conditions within the structure of asphaltenes are favorable for metal ‘grain’ formation at specific points. The exact mechanism for this behavior is not clear at this stage, and has considerable scope for future studies, including mathematical modeling simulations of asphaltenes. We also found that solid asphaltenes could be a useful forerunner of scale formation.     

Use of the ‘characteristic function’ for modelling repeatability precision

The ‘characteristic function’ is a two-parameter function relating precision or uncertainty in analytical results to the concentration of the analyte. In previous papers, in this series, it has been shown to provide a good model of precision measured: (a) under reproducibility conditions and (b) under ‘instrumental’ conditions. The present study shows that it is also a valuable model for precision estimated under repeatability conditions. The study data were large sets of duplicated results obtained for the purposes of quality control on typical test materials in routine analysis. As the analytes exhibited concentration ranges encompassing between one and three orders of magnitude, there was ample scope to demonstrate goodness of fit to the function under different circumstances.