What’s CUR≟

The chapter of the student affiliates of the American Chemical Society at the University of Tennessee at Martin has won three commendable and eighteen consecutive outstanding ratings, the most consecutive ratings of any student affiliate chapter, from the Society Committee on Education of the American Chemical Society. The activities of the chapter involve a great deal of pedagogic or literal chemistry, that is the members learn and communicate several aspects of chemistry from the chapter programs. In addition, a special chemistry or camaraderie results when members prepare for and participate in the various club projects and activities. This article briefly describes specific activities of UTM student affiliates that help to develop both the literal and the special chemistry among members. Finally, The High School Science Bowl, which is a most electrifying and rejuvenating activity, is described in greater detail for the information of other chemistry clubs.     

What is dietary fiber?

Dietary fiber consists of the remnants of the edible plant cell, polysaccharides, lignin, and associated substances resistant to digestion (hydrolysis) by human alimentary enzymes. This physiological definition has been translated into a chemical method (AOAC Method 985.29), which has recently been shown to miss substances of 10, 11, and 12 degrees of polymerization. It also fails to precipitate some hydrolysis-resistant oligosaccharides which contain many physiological properties expected in dietary fiber, such as inulin and oligofructose, indigestible dextrin (Fibersol-2), galactooligosaccharides and the synthetic polymer polydextrose. The Executive Board of the American Association of Cereal Chemists has appointed a committee to explore the possibility of expanding the definition or chemical methodology for dietary fiber to accommodate components that are not hydrolyzed by human alimentary enzymes, yet have the physiological attributes normally associated with dietary fiber. However, the present review suggests that the current definition is sufficient, along with new methodology, to detect recently discovered components of the dietary fiber complex.     

What is Conservation Science?

‘Conservation science’ or ‘cultural heritage research’ is defined through a discussion of research needs, training and employment patterns world-wide, and trends in published work. Parallels with mainstream polymer science are drawn throughout. Some aspects are discussed in more detail: traditional paint composites; studies in modern, synthetic, paint composites; the relevance of accelerated ageing to a range of polymer types.     

What does polycondensation mean?

This contribution has the function of an introduction to the entire volume. It deals with several fundamental definitions and classifications related to the chemistry of polycondensation processes, and it includes modifications of the classical theory of step-growth polymerizations.     

What makes epothilones stick?

The potent epothilone tubulin polymerization promoters have been studied extensively by synthetic and SAR approaches. The paper by Buey et al. (, this issue of Chemistry & Biology) adds a new depth of mechanistic understanding by a careful analysis of the tubulin polymerization mechanism of the epothilones.     

What exactly is uncertainty?

Uncertainty is defined in VIM3 as a ‘parameter’ but that, in my view, is a mistake that detracts from the clarity of the concept. Trying to overcome the resulting difficulties while retaining ‘parameter’ has brought about progressive amendments to the definition, and an increasing list of footnotes that have failed to resolve the issue. Surely the uncertainty of a result is the density function (or mass function) that best describes the probability of possible values of the measurand.     

Halogenation in Fungi: What Do We Know and What Remains to Be Discovered?

In nature, living organisms produce a wide variety of specialized metabolites to perform many biological functions. Among these specialized metabolites, some carry halogen atoms on their structure, which can modify their chemical characteristics. Research into this type of molecule has focused on how organisms incorporate these atoms into specialized metabolites. Several families of enzymes have been described gathering metalloenzymes, flavoproteins, or S-adenosyl-L-methionine (SAM) enzymes that can incorporate these atoms into different types of chemical structures. However, even though the first halogenation enzyme was discovered in a fungus, this clade is still lagging behind other clades such as bacteria, where many enzymes have been discovered. This review will therefore focus on all halogenation enzymes that have been described in fungi and their associated metabolites by searching for proteins available in databases, but also by using all the available fungal genomes. In the second part of the review, the chemical diversity of halogenated molecules found in fungi will be discussed. This will allow the highlighting of halogenation mechanisms that are still unknown today, therefore, highlighting potentially new unknown halogenation enzymes.     

What does shape a topological atom?

In this pedagogical communication after demonstrating the legitimacy for using the quantum theory of atoms in molecules (QTAIM) to non-Coulombic systems, Hookean H₂ ⁺/H₃ ²⁺ species are used for AIM analysis. In these systems, in contrast to their Coulombic counterparts, electron density is atom-like and instead of expected two/three topological atoms, just a single topological atom emerges. This observation is used to demonstrate that what is really “seen” by the topological analysis of electron densities is the clustering of electrons. The very trait of monotonic decay of electron density around the “centers” of clustering guarantees the appearance of topological atoms as basin of attraction of the gradient vector field of the electron density. Although observations with Hookean molecules may seem disappointing at first glance, a careful reasoning points to the fact that the QTAIM methodology is extendable to novel domains, by a knowledge of the morphology of underlying densities, beyond the typical Coulombic systems.     

The Physics and Radiochemistry of Solar Neutrino Detectors: What Have We Learned and What Can We Expect?

The situation in solar neutrino science has changed drastically in the past decade, with results now available from five neutrino experiments that use different methods to look at different regions of the solar-neutrino energy-spectrum. While the goal of all of these experiments is physics, they all rely heavily on chemistry and radiochemistry. Three of these experiments are radiochemical, the ³⁷Cl detector and the two different forms of ⁷¹Ga detectors used in GALLEX and SAGE are based on the chemical isolation and counting of the radioactive products of neutrino interactions. The other two, Kamiokande and its improved successor, Super- Kamiokande, detect neutrinos in real time; however, they also depend sensitively on radiochemistry in that (as in all the solar neutrino detectors) radioactive contaminants must be controlled at very low levels. It is noteworthy that all of these experiments (a) have detected solar neutrinos, but (b) all report deficits of the observed neutrinos relative to the predictions of standard solar models — the so-called "solar neutrino problem". In this paper, I review the basic principles of operation of these neutrino detectors, report their recent results, and discuss some of the interpretations that are now in vogue. I then describe some of the new neutrino detectors that are under construction or being developed, and discuss the kinds of new results we might expect to see in the early years of the new millennium.     

What is an atom in a molecule?

The derivation of the Hirshfeld atoms in molecules from information theory is clarified. The importance for chemistry of the concept of atoms in molecules (AIM) is stressed, and it is argued that this concept, while highly useful, constitutes a noumenon in the sense of Kant.     

What I like about Hückel theory

We start with some biographical notes on Erich Hückel, in the context of which we also mention the merits of Otto Schmidt, the inventor of the free-electron model. The basic assumptions behind the HMO (Hückel Molecular Orbital) model are discussed, and those aspects of this model are reviewed that make it still a powerful tool in Theoretical Chemistry. We ask whether HMO should be regarded as semiempirical or parameter-free. We present closed solutions for special classes of molecules, review the important concept of alternant hydrocarbons and point out how useful perturbation theory within the HMO model is. We then come to bond alternation and the question whether the pi or the sigma bonds are responsible for bond delocalization in benzene and related molecules. M?bius hydrocarbons and diamagnetic ring currents are other topics. We come to optimistic conclusions as to the further role of the HMO model, not as an approximation for the solution of the Schr?dinger equation, but as a way towards the understanding of some aspects of the Chemical Bond.     

What Is the Structure of Pterodonoic Acid?

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What ion is generated when ionizing acetonitrile?

It has long been assumed that ionizing neutral acetonitrile produces ions with the same atomic connectivity, CH(3)CN(+*). Recent calculations on the C(2)H(3)N(+*) potential energy surface have suggested that it may be difficult to generate pure CH(3)CN(+*) when ionizing acetonitrile. We have probed the interconversion of CH(3)CN(+*) and its lower energy isomer CH(2)CNH(+*) by calculation, collision-induced dissociation mass spectrometry and ion-molecule reaction. The latter ion, ionized ketenimine, is co-generated upon electron or chemical ionization of neutral acetonitrile in the ion source of a mass spectrometer. An estimate of the ratio of the two isomers can be obtained from their respective ion-molecule reactions with CO(2) or COS. CH(3)CN(+*) reacts by proton-transfer with CO(2) and charge transfer with COS, whereas CH(2)CNH(+*) is unreactive.     

What can positronium tell us about adsorption?

The condensation and evaporation of n-heptane at 298 K in mesopores of silica material obtained by the polymer templating method have been studied by PALS measurements. It is demonstrated that the ortho-positronium lifetimes and intensities provide valuable information on pore filling and emptying which are not accessible from a conventional adsorption experiment. The results confirm the specific adsorption mechanism of n-heptane in pores with narrow openings (ink-bottle shape) which is different from that known for other pore geometries. The results from PALS experiment are compared to those derived from the conventional n-heptane and nitrogen adsorption data.