Guanosine gels

Guschlbauer W, Chantot JF, Thiele D (1990) Four-stranded nucleic acid structures 25 years later from guanosine gels to telomer DNA. J Biomol Struct Dyn 8 491-511... 

G-quadruplexes can also be stabilized by divalent cations, including Sr "", Ba "", and stmjjgg 8-bromo-guanosine gel melting transition... 

Selection-coupled analysis/phase segregation. One strategy for simplifying the analytical challenge is to use phase segregation. Three subclasses are possible. In the first of these, a phase transition is part of the selection process. This includes not only the familiar crystallization-induced enantiomeric enrichment discussed above but also the experiments (primarily employed in experiments directed toward the production of novel materials) such as those described by Lehn and coworkers in 2005. In this study, an acylhydrazone library was created from guanosine hydrazide and a mixture of aldehydes (Fig. 1.22) in the presence of metal ions, formation of G-quartet structures led to the production of a gel. 

Guanosine, adenine, HPLC-UV at 254 nm and Separation on dextran-based gels Sephadex... 

Guanosine (87 g, 0.31 mL, predried for two days under vacuum at 100°C over P205) was combined with acetic anhydride (180 mL, 1.9 mol), pyridine (90 mL, 1.11 mol) and DMF (245 mL) and heated in oil bath at 75°C. The reaction was monitored by TLC on silica gel plates eluted with mixture of ethyl acetate DMF l-butanol (6 3 1). After 2 hours, the guanosine was consumed and the 2,3, 5 -tri-0-acetylguanosine was observed to be the major product. The mixture was concentrated under vacuum. The residue was suspended in ethyl ether 2-propanol (1 1) and the solid collected by filtration was recrystallized from absolute ethanol. The product was dried at 80°C under vacuum to obtain 106.9 g (84%) of 2, 3, 5 -tri-0-acetylguanosine as a fluffy white solid M.P. 229-233°C. 

Quite a different form of exopolyphosphatase was purified from the vacuolar sap of S. cerevisie (Andreeva et al., 1998b). Its molecular mass determined by gel filtration was 245 kDa. This exopolyphosphatase hydrolysed PolyP3 only slightly, and its specific activity increased with the increase in PolyP chain length (Table 6.6). It was unable to hydrolyse adenosine- and guanosine-tetraphosphates and was insensitive to antibodies inhibiting the low-molecular-mass exopolyPase of the cytosol (Table 6.4). This enzyme was stimulated by divalent metal cations to a much lesser extent than 40 kDa exopolyphosphatase (Table 6.5) and was inhibited by EDTA (Table 6.4). The inhibitory effect of EDTA is explained by the binding of Co2+, which is the best activator of the vacuolar exopolyphosphatase at 0.1 mM. 

The adsorptive and voltammetric characteristics of Cu(II) complexes with guanine, guanosine and adenosine were exploited [120] in order to detect these bases after separation by capillary zone electrophoresis, and the enzyme-mimic catalytic activity of a DNA-Cu2+ complex [121] was used to develop an amperometric quinacrine sensor using an oxygen electrode covered by the complex entrapped in polyacrylamide gel. 

Thus guanosine and several of its derivatives, including the 3 - and 5 -phosphates, form gels in which tetrameric hydrogen-bonded arrangements are stacked in a form reminiscent of the quadruple helix [534, 698]. 

A related case is given by the component selection occurring in the generation of a hydrogel phase based on dynamically connected guanosine-quartet derivatives, driven by formation of the constituent that yields the most stable gel in a sort of phase selection process (see also Fig. 5 in [50]). 

Mihai S Le, Due Y, Cot D, Barboiu M (2010) Sol-gel selection of hybrid G-quadruplex architectures from dynamic supramolecular guanosine libraries. J Mater Chem 20 9443-9448... 

Modifications of the basic technique are required in some instances. Guanosine is not soluble until it is oxidized. To avoid formation of unmanageable clumps during oxidation, the 0.1 mmol of guanosine is first dispersed in 1 ml of distilled water. Periodate solution is then added, and the solution is stirred well during oxidation. Nearly all the oxidized guanosine dissolves, usually producing a viscous solution or gel. This state is maintained until the sodium borohydride addition step. 

Guanosine, guanylic acid, but not guanine alone form gels in aqueous media. No other nucleic acid or nucleoside shows this behavior. Addition of excess... 

M alkali salt is essential without it guanosine produces well-defined crystals, but no gel. X-ray fiber diffraction studies of the gel indicate the formation of quadruple helices. (Fig. 8.6.5) (Saenger, 1984). Similar quadruple helices are also formed by corresponding DNA (Wheelhouse et al, 1998)... 

A polyacrylamide-boronate affinity gel, Affi-gel 601 , has been used for the separation of cyclic adenosine monophosphate, cyclic guanosine monophosphate, and cyclic cytidine monophosphate from their corresponding 5-nucleotides and nucleosides. A simple direct assay of 3 5 -cyclic nucleotide phosphodiesterase activity has been developed, based on the use of the gel. 

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