Hard link concept

The hard link concept is much easier conceptually than neighboring. Hard links are applied between entries in different databases and exist everywhere there is a logical connection between entries. For instance, if a PubMed entry talks about the sequencing of a cosmid, a hard link is established between the PubMed entry and the corresponding nucleotide entry. If an open reading frame in that cosmid codes for a known protein, a hard link is established between the nucleotide entry and the protein entry. If, by sheer luck, the protein entry has an experimentally deduced structure, a hard link would be placed between the protein entry and the structural entry. The hard link relationships between databases is illustrated in Figine 7.1. 

Although sophisticated electronic structure methods may be able to accurately predict a molecular structure or the outcome of a chemical reaction, the results are often hard to rationalize. It therefore becomes difficult to apply the findings to other similar systems. Qualitative theories, on the other hand, are unable to provide accurate results, but they may be useful for gaining insight, e.g. why a certain reaction is favoured over another. They also provide a link to many concepts used by experimentalists. 

Baekeland had to make important discoveries before he could bridge the gap between the initial concept and final products. In particular, he found that the base-catalysed condensation of phenol and formaldehyde can be carried out in two parts. If the process is carefully controlled, an intermediate product can be isolated, either as a liquid or a solid, depending on the extent of reaction. At this stage, the material consists of essentially linear molecules and is both fusible and soluble in appropriate solvents. When heated under pressure to 150 °C, this intermediate is converted to the hard, infusible solid known as bakelite . This second stage is the one at which the three-dimensional cross-linked network develops. 

The concept of linking PCR and ELISA for ultrasensitive protein analysis soon sparked the imagination of laboratory scientists, and they developed a method that separates the concept of antibody-DNA linkage from hard-to-obtain protein chimeras. An easy way to establish the desired coupling was accessible with the streptavidin/biotin binding system The tetravalent protein STV, from Streptomyces avidii [19], derived, for example, as a recombinant core protein with optimized properties [20], or as its egg-yolk... 

For the sake of correctness, it is necessary to note that we disregarded such theoretically important concepts as the linked cluster (linked connected graph) theorem and the exclusion principle violating (EPV) diagrams. This is in accordance with our aim to maintain the practical nature of this review. The linked cluster theorem and EPV diagrams are of importance in the fourth and higher orders of the perturbation theory which, in our opinion, shall hardly be accessible to routine calculations in the foreseeable future. For detailed information on the linked cluster theorem and EPV diagrams see Refs.9,33,34,4a ... 

Central to the stability and chemistry of complexes formed by mixed donor ligands are two key concepts of coordination chemistry. The first is the chelate effect, which applies to all polydentate ligands, and reflects the increase in stability of a type of complex as monodentate donor molecnles are replaced by polydentates with donors linked by chelate rings. The hard-soft acid-base theory is particnlarly relevant to mixed donor ligands where donors of distinctly different character may bind to a central metal ion. The like prefers like concept means hard nonpolarizable donor atoms (N and O, for example) bond preferentially to hard nonpolarizable metal... 

One remarkable consequence of the concept introduced is that in the case of strong vibronic interaction (Equation (2b)), the off-diagonal vibronic energy JSF1 is correlated with the chemical hardness r] of the distorted complex or molecule (Equation (4)). This is an observable quantity thus, the vibronic model is directly linked to the experiment.5... 

However, the concept and philosophy of clinical pharmacy is not yet implemented in all hospitals and is found even less among community pharmacists. Most community pharmacists saw clinical pharmacy linked to hospital practice and hardly adapted to the needs of the community practice setting. That is probably the reason why the pharmaceutical care concept was formulated by Hepler and Strand. But with the concept of pharmaceutical care, we carry the same risk as with clinical pharmacy. Many people are talking about the concept, but few are putting in the effort and means required to put it into practice. 

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