Stability under Physiological Conditions

4 Which Quadruplexes are the Most Stable Intra-, Bi- or Tetramolecular Parallel or Antiparallel  

This important question has been addressed by several teams. Lu et al concluded that the parallel strand structure is thermodynamically more stable than the antiparallel one. Petraccone et reached a similar conclusion the tetramolecular structure is thermodynamically more stable than the bimole-cular one, which, in turn, is more stable than the unimolecular one. 

Nevertheless, one should note that it is not straightforward to compare the stability of structures with different molecularities. For example, the comparison of equilibrium association constants for unimolecular, bi- or tetramolecular quadruplexes is meaningless, as these constants are not expressed in the same units (unit-less, M and respectively). Similarly, a comparison of the AG° might be deceptive. For example, if one compares an intramolecular structure with a bimolecular one (self-complementary) which have the same Tm = 60°C at 1 pM strand concentration, one will determine a hG°(Tm) of 0 and —9.2 kcal moN respectively. Does this mean that the intermolecular complex is more stable Clearly not One faces a similar problem when comparing association rate constants (kon), which are expressed in s  

If one is interested in the thermal stability of the preformed complexes, it is clear that tetramolecular complexes are the most heat stable. For example, a small oligonucleotide such as TG4T may form a parallel quadruplex with four quartets its thermal stability in is so high that it can resist boiling at least for a few minutes whereas one may observe the thermal denaturation of G4T4G4 and (G4T4)4 under identical conditions. 

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The most important application recently developed for synthetic liposomes is as potential drug carriers for controlled release, especially for cancer chemotherapy (7). In general, the success of liposomes as vehicles for the transport of specific drugs will largely depend on their stability under physiological conditions. Unlike the naturally occurring membranes, the synthetic vesicles have very limited stability, and this is a... 

It has been estimated that using available neutron intensities such as 102 neutrons / (cm2-s) concentrations of 10B from 10—30 Jg/g of tumor with a tumor cell to normal cell selectivity of at least five are necessary for BNCT to be practical. Hence the challenge of BNCT lies in the development of practical means for the selective delivery of approximately 109 10B atoms to each tumor cell for effective therapy using short neutron irradiation times. Derivatives of 10B-enriched Ww-borane anions and carboranes appear to be especially suitable for BNCT because of their high concentration of 10B and favorable hydrolytic stabilities under physiological conditions. 

Within the medicinal field, bacterial cellulose alone was shown to be a versatile material for the construction of artificial blood vessels, an application which clearly benefits from the structural features of cellulose in combination with its chemical stability under physiological conditions [52], Other applications use cellulose for the production of implantable capsules [53], and even sensors [54], Another interesting biomedical application is the use of cellulose in films supporting wound healing, due to the hydrating characteristics of these cellulose-containing films [55], Besides, cellulose and cellulose derivatives are used as haemostatic agents [56], The latter two fields of application for cellulose have just recently been reviewed in the cited literatiu-e, and are thus not discussed in detail here. 

For many of the Au(III) compounds investigated, a problem is their stability under physiological conditions. 

Gd + center contains seven unpaired electrons, binds a considerable number of water molecules, and rapidly exchanges them with bulk water molecules. Practical MRI contrast agents should have (1) high solubility in neutral aqueous media, (2) high thermodynamic and kinetic stability under physiological conditions, (3) non-toxicity, (4) fast excretion, and (5) tissue selectivity. 

Bis-phosphonates may act as bridging ligands giving dinuclear platinum(II) complexes with high stability under physiological conditions. The dinuclear complexes were found to overcome multidrug resistance on several cancer cell lines [24]. 

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