The source of chemical bonding

Developments in the application of quantum mechanics to the understanding of the chemical bond are traced with a view to examining the evolving conception of the covalent bond. Beginning with the first quantum mechanical resolution of the apparent paradox in Lewis’s conception of a shared electron pair bond by Heitler and London, the ensuing account takes up the challenge molecular orbital theory seemed to pose to the classical conception of the bond. We will see that the threat of delocalisation can be overstated, although it is questionable whether this should be seen as reinstating the issue of the existence of the chemical bond. More salient are some recent developments in a longstanding discussion of how to understand the causal aspects of the bonding interaction—the nature of the force involved in the covalent link—which are taken up in the latter part of the paper.     

Influences of the chemical structure on the activity of new inhibitory compounds of the angiotensin-converting enzyme

The ACE inhibitory activity of some perimidines, chinazolinones and amidinohydrazones is described. Relations were found between the chemical structure and the inhibitory activity on the ACE.     

Mechanism of induction of tyrosine in rat liver by phenothiazine derivatives and related chemical compounds]

Increase of hepatic tyrosine-alpha-ketoglutarate transaminase is observed in Rats (Wistar strain) after intraperitoneal administration of tricyclic compounds (phenothiazin and related structure derivatives). This is an induction process: actinomycine D inhibits this effect. This action is not mediated by glucocorticoids: induction persists in adrenalectomized Rats. The mechanism of action is different too: additive effects are found after simultaneous injection of glucocorticoid and tricyclic drug.     

Influences of the chemical structure on the activity of new inhibitory compounds of the angiotensin-converting enzyme

Summary The ACE inhibitory activity of some perimidines, chinazolinones and amidinohydrazones is described. Relations were found between the chemical structure and the inhibitory activity on the ACE.     

Hydrogen bonding by the sulphydryl group of glutathione

Summary The occurrence of hydrogen bond in the sulphydryl group of glutathione was investigated by means of Raman Spectroscopy. Evidence is obtained that SH group is free and H-bonding does not occur.     

Hydrogen bonding by the sulphydryl group of glutathione.

The occurrence of hydrogen bond in the sulphydryl group of glutathione was investigated by means of Raman Spectroscopy. Evidence is obtained that SH group is free and H-bonding does not occur.     

Photobiochemistry without light

Summary Efficient excited state formation — much higher than that hitherto expected — may occur in organelles and in intact cells. Excited triplet states can be enzymatically generated in high yields by different routes. An example is the oxidation of isobutanal to acetone and formic acid, catalyzed by horseradish peroxidase. Other enzymatic systems that generate triplet carbonyls are linear aliphatic aldehydes when oxidized by peroxidase/O₂, or the indole-3-acetic acid/peroxidase/O₂-reaction. The latter is widespread in plants.This new field — photobiochemistry without light — has led to a growing awareness of the idea that cells may utilize excited states to trigger photochemical processes even in the dark. Such phenomena are of considerable importance, also for the understanding of weak photon emission from biological systems.     

Photobiochemistry without light

Efficient excited state formation - much higher than that hitherto expected - may occur in organelles and in intact cells. Excited triplet states can be enzymatically generated in high yields by different routes. An example is the oxidation of isobutanal to acetone and formic acid, catalyzed by horseradish peroxidase. Other enzymatic systems that generate triplet carbonyls are linear aliphatic aldehydes when oxidized by peroxidase/O2, or the indole-3-acetic acid/peroxidase/O2-reaction. The latter is widespread in plants. This new field - photobiochemistry without light - has led to a growing awareness of the idea that cells may utilize excited states to trigger photochemical processes even in the dark. Such phenomena are of considerable importance, also for the understanding of weak photon emission from biological systems.     

Life without myoglobin

Hemoproteins are widely distributed among prokaryotes, unicellular eukaryotes, plants and animals [1]. Myoglobin, a cytoplasmic hemoprotein that is restricted to cardiomyocytes and oxidative skeletal myofibers in vertebrates, has been proposed to facilitate oxygen transport to the mitochondria [1-3]. This cytoplasmic hemoprotein was the first protein to be subjected to definitive structural analysis and has been a subject of long-standing and ongoing interest to biologists [1-3]. Recently, we utilized gene disruption technology to generate mice that are viable and fertile despite a complete absence of myoglobin [4]. This unexpected result led us to reexamine existing paradigms regarding the function of myoglobin in striated muscle.     

Mechanics without mechanisms

At the time of Heinrich Hertz's premature death in 1894, he was regarded as one of the leading scientists of his generation. However, the posthumous publication of his treatise in the foundations of physics, Principles of Mechanics, presents a curious historical situation. Although Hertz's book was widely praised and admired, it was also met with a general sense of dissatisfaction. Almost all of Hertz's contemporaries criticized Principles for the lack of any plausible way to construct a mechanism from the “hidden masses” that are particularly characteristic of Hertz's framework. This issue seemed especially glaring given the expectation that Hertz's work might lead to a model of the underlying workings of the ether.In this paper I seek an explanation for why Hertz seemed so unperturbed by the difficulties of constructing such a mechanism. In arriving at this explanation, I explore how the development of Hertz's image-theory of representation framed the project of Principles. The image-theory brings with it an austere view of the “essential content” of mechanics, only requiring a kind of structural isomorphism between symbolic representations and target phenomena. I argue that bringing this into view makes clear why Hertz felt no need to work out the kinds of mechanisms that many of his readers looked for. Furthermore, I argue that a crucial role of Hertz's hypothesis of hidden masses has been widely overlooked. Far from acting as a proposal for the underlying structure of the ether, I show that Hertz's hypothesis ruled out knowledge of such underlying structure.     

Non-synaptic chemical neurotransmission

Summary Images with apparently gemmulofugal polarity in the EPL of the olfactory bulb are the result of sectioning, along misleading planes, gemmulopetal synapses containing postsynaptic vesicles. Unless one accepts a bidirectional conduction for chemical synapses, the internal granule cells lack actual gemmulofugal synapses and the neurotransmitter contained in their vesicles must act at non-synaptic membranes.Supported by grant MA4183 of the Medical Research Council of Canada.     

Molecular paleontology

Molecular paleontology, i.e., the recovery of DNA from ancient human, animal, and plant remains is an innovative research field that has received progressively more attention from the scientific community since the 1980s. In the last decade, the field was punctuated by claims which aroused great interest but eventually turned out to be fakes - the most famous being the sequence of dinosaur DNA later shown to be of human origin. At present, the discipline is characterized by some certainties and many doubts. We know, for example, that we have reasonable chances to recover authentic DNA from a mammoth carcass, while our chances are negligible (or nonexistent) in the case of a dynastic mummy from Egypt. On the other hand, though we are developing convincing models of DNA decay in bone, we are not yet able to predict whether a certain paleontological or archeological site will yield material amenable to DNA analysis. This article reviews some of the most important and promising investigations using molecular paleontology approaches, such as studies on the conservation of DNA in human bone, the quest for ancient DNA in permafrost-frozen fauna, the Tyrolean iceman, and the Neandertals. Received 5 April 2001; received after revision 5 July 2001; accepted 5 July 2001     

分子电子学

作为纳米电子学的一个重要分支,分子电子学在近年来得到了巨大的发展,并成为国际上研究的热点。本文介绍了各种分子器件的制作技术及基本工作原理,回顾了近年来分子电子学的最新进展,展望了分子电子学的未来发展。     

No understanding without explanation

Scientific understanding, this paper argues, can be analyzed entirely in terms of a mental act of “grasping” and a notion of explanation. To understand why a phenomenon occurs is to grasp a correct explanation of the phenomenon. To understand a scientific theory is to be able to construct, or at least to grasp, a range of potential explanations in which that theory accounts for other phenomena. There is no route to scientific understanding, then, that does not go by way of scientific explanation.