2,4,8,10-Tetraoxaspiro[5,5]undecanes tetrasubstituted at the 3 and 9 positions with groups incorporating diaminotriazines can be used for the construction of extensively hydrogen-bonded networks by the strategy of molecular tectonics. Four such compounds, tectons 1-4, were made by short and efficient syntheses involving bisketalization of pentaerythritol and subsequent reactions. Unlike tectons typically used in previous studies, compounds 1-4 are flexible and chiral, and they orient four sticky diaminotriazine groups in a distorted tetrahedral geometry. Tecton 1 crystallizes from DMF/toluene as an inclusion compound of approximate composition 1.8DMF.xH2O. In the resulting structure, each tecton participates in a total of 16 hydrogen bonds. Eight of these bonds involve four principal neighbors, and the tectons linked in this way define a distorted diamondoid network. Despite 8-fold interpenetration, 60% of the volume of the network is available for including guests. The guests are disordered and occupy parallel helical channels that have cross sections of approximately 11 x 12 A2 at the narrowest points. These channels provide access to the interior of the crystals and permit guests to be exchanged quantitatively without loss of crystallinity. It is noteworthy that tecton 1, despite its flexibility, small size, and structural simplicity, is apparently unable to find a periodic three-dimensional structure in which the dictates of hydrogen bonding and close packing are satisfied simultaneously.

PB1-F2 is a nonstructural accessory protein of Influenza A virus described to enhance the mortality and the morbidity of the virus in a host-dependent manner. In this work, an electrochemical biosensor based on an immunodetection system was developed to follow the oligomerization of PB1-F2 during the viral cycle. The immunosensor was based on conductive polypyrrole modified with ferrocenyl groups as a redox marker for enhancing signal detection. Antibodies specific for monomeric or oligomeric PB1-F2 forms were immobilized on polypyrrole matrix via biotin/streptavidin layer. We demonstrated that this electrochemical biosensor sensitively detects PB1-F2 in both conformational forms. The linear range extends from 5 nM to 1.5 μM and from 5 nM to 0.5 μM for monomeric and oligomeric PB1-F2, respectively. The calculated limit of detection was 0.42 nM for monomeric PB1-F2 and 16 nM for oligomers. The biosensor platform allows the detection and quantification of PB1-F2 in lysates of infected cells during viral cycle. We show that at early stages of viral cycle, PB1-F2 is mainly monomeric but switched to amyloid-like structures at a later stage of infection. The quantification of two protein structural forms points out that PB1-F2 expression profiles and kinetics of oligomerization are cell-type-dependent.

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