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At least 19 recordsLinked to original sources
PubMed1989

Aspects of dental plaque formation with special reference to colloid-chemical phenomena.

In order to investigate factors of importance for plaque formation and the rate of plaque formation 133 randomly selected individuals went through a 3-day period of plaque accumulation. From these individuals one group of "heavy" and one group of "light" plaque formers were selected for further studies. These subjects were investigated with reference to clinical, biochemical, biophysical and microbiological variables, that in the literature have been suggested to influence plaque formation. The collected data were analysed statistically both by comparisons between the two groups and by multiple regression. In the comparative analyses there were only minor differences between the groups, and no single studied variable was considered as the only explanation to the great difference in the amount of plaque formed after 3 days between "heavy" and "light" plaque formers. The multiple regression showed that the initial bacterial colonization of tooth surfaces was dependent on the clinical wettability of tooth surfaces, the saliva-induced aggregation of oral bacteria and finally the relative salivary flow conditions around the tooth surfaces where the bacterial samples were collected. On basis of these results, it was suggested that saliva and oral bacteria could at least partly be looked upon as being a biological colloid system system. Further studies were designed to investigate whether oral bacteria could be regarded as colloid particles or not, and to study the properties of saliva as a colloid suspending medium. These studies showed that bacteria suspended in different salt solutions were dependent on pH, ionic concentration and the valency of the cations in the solutions to be able to aggregate. The aggregating capacity further seemed to be specific for different bacterial species and strains. Addition of saliva from "heavy" and "light" plaque formers influenced the colloid stability of bacteria suspended in water in different ways. Saliva from "light" plaque formers gave a lower colloid stability in suspensions of a plaque-forming bacterium (Streptococcus sanguis) as compared to the addition of saliva from "heavy" plaque formers. No such differences were observed in suspensions of S. salivarius, which is normally not a plaque-forming bacterium. The results indicate that colloid-chemical processes might be involved in bacterial attachment to tooth surfaces, and that initial bacterial colonization of tooth surfaces at least partly follow general biophysical laws.

Adhesiveness↗
PubMed2003

An organic framework for a philosophical appreciation of chemical phenomena.

The aim of this paper is to show how chemistry gives rise to philosophical reflection. Initially, some general remarks on philosophy and science are offered in the light of recent reductive controversy surrounding them both. An appeal is made for a broader and deeper outlook. The philosophical outlook favored is one of openness towards the phenomena: rather than confine them to some "-ism" or other. The phenomena are seen as at least potentially "bathed" in more encompassing levels of being. The term "ontological suppleness" is later introduced in this spirit, to express how something at a given level, say electronegativity in chemistry, has significance at far higher levels of being-in this case, the emergence of life, and our planet's ecology as a whole. Similar consideration is given to the conversion of a carcinogen (benzene) into a "miracle drug" (aspirin). These illustrations are intended to highlight how science in general, including chemistry in particular, offers seamless transitions to what lies beyond the scope of science. What remains for us is to find a language adequate to deal with such transitions.

Journal Article↗
PubMed1990

Some marine ecological phenomena: chemical basis and biomedical potential.

Analysis of secondary metabolites derived from marine organisms has revealed a broad spectrum of novel molecular architecture. The function of these compounds in their natural habitat is linked to various aspects of species survival, and the compounds have also served as characteristic chemical markers through successive trophic levels. Fundamental questions concerning the locus of synthesis in complex and intricate assemblies of plants and animals and the pathways of biosynthesis are beginning to be answered. It is now apparent that the marine environment gives rise to some distinctive chemistry, which is generated along characteristic pathways. Some of the newly described compounds have already become valuable tools in biomedicine.

Animals↗
PubMed2004

Slow dynamics in gelation phenomena: from chemical gels to colloidal glasses.

We here discuss the results of three-dimensional Monte Carlo simulations of a minimal lattice model for gelling systems. We focus on the dynamics investigated by means of the time autocorrelation function of the density fluctuations and the particle mean-square displacement. We start from the case of chemical gelation, i.e., with permanent bonds, and characterize the critical dynamics as determined by the formation of the percolating cluster, as actually observed in polymer gels. By opportunely introducing a finite bond lifetime tau(b), the dynamics displays relevant changes and eventually the onset of a glassy regime. This has been interpreted in terms of a crossover to dynamics more typical of colloidal systems and a connection between classical gelation and recent results on colloidal systems is suggested. By systematically comparing the results in the case of permanent bonds to finite bond lifetime, the crossover and the glassy regime can be understood in terms of effective clusters.

Journal Article↗
PubMed1991

Solute-polymer-water interactions and their manifestations.

This paper reviews recent work on the interactions among solutes, polymers, and water in model food systems. Four possible combinations of ionic or non-ionic solutes and polymers are discussed in terms of their water sorption behavior. Comparisons between experimental values and values calculated by a mass balance equation are made. The salt-protein, sucrose-starch, and salt-starch combinations sorbed less water than that predicted by calculated sorption values. This was attributed to the inability of the interacted solutes to sorb their full complement of water. On the other hand, the sucrose-protein combination exhibited an increase in the amount of water sorbed over that calculated by the mass balance equation. This was attributed to the increased hydration of the protein component, due to an effect of the sucrose. One of the major factors involved in these solute-polymer interactions is the competition for water among the solutes and polymers. This competition, in turn, is greatly influenced by the "state" of the water associated with these components. Lastly, examples of how biological, chemical, and physico-chemical phenomena in foods are affected by these factors are also given. The phenomena discussed include mold germination, the Maillard reaction, ascorbic acid oxidation, protein functionality, starch gelatinization and retrogradation, and the complication of the order of mixing.

Carbohydrates↗
PubMed2000

Fluctuations and fractal noise in biological membranes.

Our understanding of cell structure and function derives from applications of a variety of physical and life science disciplines, methods and models to an important physiological process, namely, the exchange and transport of ions and molecules across biological membranes. We know that ion transport through membranes arises from a diversity of interrelated and interactive physical and chemical phenomena over a wide range of spatial and temporal scales. Among these phenomena common to all cellular structure and function include metabolism, kinetics of molecules, chemically mediated alteration of cell membrane electrical potential, membrane ion conductance, electrical signal propagation, and modulation by chemo- and mechanoreceptive mechanisms. This review focuses on the unique information contained in fluctuations in electrical properties associated with cell membrane ion transport.

Animals↗
PubMed1999

Femtochemistry.

The topic of femtochemistry is surveyed from both theoretical and experimental points of view. A time-dependent wave packet description of the photodissociation of the O---C---S molecule reveals vibrational motion in the transition-state region and suggests targets for direct experimental observation. Theoretical approaches for treating femtosecond chemical phenomena in condensed phases are featured along with prospects for laser-controlled chemical reactions by using tailored ultrashort chirped pulses. An experimental study of the photoisomerization of retinal in the protein bacteriorhodopsin is discussed with an aim to gain insight into the potential energy surfaces on which this remarkably efficient and selective reactions proceeds. Finally, a prospective view of new frontiers in femtochemistry is given.

Bacteriorhodopsins↗
PubMed1980

Prostaglandin I2 (prostacyclin).

Prostaglandin I2 (PGI2), or prostacyclin, is a recently discovered prostaglandin that affects many organ systems. It is both a potent inhibitor of platelet aggregation and a powerful vasodilator. The recent demonstration that it is the main prostaglandin synthesized by the blood vessel wall suggests that it may play an important role in limiting platelet-mediated thrombosis. However, despite considerable investigation, the exact physiological role of PGI2 has yet to be elucidated.

Animals↗
PubMed2006

Application of rigid body mechanics to theoretical description of rotation within F0F1-ATP synthase.

ATP synthase catalyses the formation of ATP from ADP and P(i) and is powered by the diffusion of protons throughout membranes down the proton electrochemical gradient. The protein consists of a water-soluble F(1) and a transmembrane F(0) proton transporter part. It was previously shown that the ring of membrane subunits rotates past a fixed subunit during catalytic cycle of the enzyme. However, many parameters of this movement are still unknown. In the present study the mutual protein movement in the membrane part of F(0)F(1)-ATP syntase has been analysed within the framework of rigid body mechanics. On the base of available experimental data it was shown that electrostatic interaction of two charged amino acids residues is able to supply quite enough energy for the rotation. The initial torque, which caused the rotation, was estimated as 3.7 pN nm and for this pattern the angular movement of c subunits complex could not physically have a period less than 10(-9)s. If membrane viscosity and elastic resistance were taken into account then the time of a whole turnover could rise up to 6.3 x 10(-3)s. It is remarkable that rotation will take place only under condition when the elasticity (Young's) module of the central stalk (gamma subunit and other minor subunits) is less than 5.0 x 10(7)N/m(2). Thus, for generally accepted structural parameters of ATP synthase, two-charge electrostatic interaction model does not permit rotation of the rotor if elastic properties of the central stalk are tougher than mentioned above. In order to explain the rotation under that condition one should either suppose a shorter distance between subunit a and c subunits complex or assume interaction of more than two charged amino acids residues.

Adenosine Triphosphate↗