Unspecific interactions

Among broadly active alkaloids, a distinction can be made between those that are able to form covalent bonds with proteins and nucleic acids, and those that modulate the conformation of proteins and nucleic acids by noncovalent bonding. 

Covalent modifications are the result when the following functional groups interact with proteins [18,25]  

Molecules of nitrogen-containing compounds, such as alkaloids, amines, and peptides, usually contain (under physiological conditions) positively charged N-atoms that can form ionic bonds with negatively charged amino acid residues of glutamic and aspartic acid in proteins. Both the covalent and the noncovalent interactions will modulate the three-dimensional protein structure, that is, the conformation that is so important for the bioactivities of proteins (enzymes. 

Lipophilic compounds, such as the various terpenoids, tend to associate with other hydrophobic molecules in a cell these can be biomembranes or the hydrophobic core of many proteins and of the DNA double helix [10,18,24,25]. In proteins, such hydrophobic and van der Waals interactions can also lead to conformational changes, and thus protein inactivation. A major target for terpenoids, especially saponins, is the biomembrane. Saponins (and, among them, the steroid alkaloids) can change the fluidity of biomembranes, thus reducing their function as a permeation barrier. Saponins can even make cells leaky, and this immediately leads to cell death. This can easily be seen in erythrocytes when they are attacked by saponins these cells burst and release hemoglobin (hemolysis) [1,6,17]. Among alkaloids, steroidal alkaloids (from Solanaceae) and other terpenoids have these properties. 

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The label-free detection of biomolecules is another promising field of application for SERS spectroscopy. Tiniest amounts of these molecules can be adsorbed by specific interactions with receptors immobilized on SERS-active surfaces. They can then be identified by their spectra, or specific interactions can be distinguished from unspecific interactions by monitoring characteristic changes in the conformation sensitive SERS spectra of the receptors. 

Interact with the lipoplex amines still available for protein unspecific interactions, reducing the holes left by the PEG moiety (Scheme 1). 

In drug studies, of main interest is the application of colloidal systems, which show specific and unspecific interaction with mainly lipophilic substances. An obvious application is the study of highly lipophilic and poorly absorbable drugs that are administered orally or transdermally (2). Such interactions with surface-active agents may either cause a diminution of the... 

The main difficulty with this technology is the possible interaction of target and/or ap tamer with the chip surface. The nature of this difficulty may be high unspecific interaction or high repulsion. For this reason, the most suitable sensor chip surface and optimal binding conditions must be determined for every target/aptamer combination. 

Besides, the review could conditionally be divided in accord with another criterion, (a) In Sections III-V and VII we discuss so-called unspecific interactions, which take place in a local-order structure of various polar liquids, (b) In Sections VI-IX we also consider specific interactions [16]. These are directly determined by the hydrogen bonds in water, are reflected in the band centered at 200 cm-1, which is termed here the R-band, and is characterized by some spectral features in the submillimeter wavelength range (from 10 to 100 cm-1). Note that sometimes in the literature the R-band is termed the translational band, since the peak frequency of this band does not depend on the moment of inertia I of a water molecule. 

The problem considered now is connected with unspecific interactions, which in some measure are similar in water and nonassociated liquids. We shall present... 

Spectral properties of water in the R-band range (near 200 cm-1), which are directly determined by H-bonding of water molecules, were termed [16] as stipulated by specific interactions. All other ones we shall term unspecific interactions. The latter were considered in Section V devoted to a pure hat-curved model capable of description of the Debye, librational, and partly R-bands (the ongoing background was considered in items 1-6 in Section V.A.1). 

Thus, specific interactions directly determine the spectroscopic features due to hydrogen bonding of the water molecules, while unspecific interactions arise in all or many polar liquids and are not directly related to the H-bonds. Now it became clear that the basis of four different processes (terms) used in Ref. [17] and mentioned above could rationally be explained on a molecular basis. One may say that specific interactions are more or less cooperative in their nature. They reveal some features of a solid state, while unspecific interactions could be understood in terms of a liquid state of matter, if we consider chaotic gas-like motions of a single polar molecule, namely, rotational motions of a dipole in a dense surroundings of other molecules. The modem aspect of the spectroscopic studies leads us to a conclusion that both gas-like and solid-state-like effects are the characteristic features of water. In this section we will first distinguish between the following two mechanisms of dielectric relaxation ... 

Because the labeled tetrapeptide does not bind to the unmodified solid support Amino-TentaGel, the observed fluorescence activity is not because of unspecific interaction with the solid support itself. 

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