Supramolecular Recognition And Signaling Based On Argentophilic Metal Coordination Polymers And Ⅱ-Ⅵ Group Semiconductor Photoluminescent Nanocrystals

Cysteine (Cys) is vital naturally occurringα-amino acid in human body and its twoenantiomers actually play different roles. For example, the deficiency of L-Cys wouldlead to a series of serious diseases including AIDS, liver damage, and skin lesions.However, D-Cys is considered to interfere with many targets inside cells and furtherimpair cell growth. Although numerous recognition methods for L-Cys have beenreported, few involved Cys enantiomeric signaling. In order to understand the linksbetween enantiomeric Cys and related diseases, developing feasible while highlyselective and sensitive enantiomeric discrimination strategies for D- and L-Cys istherefore undoubtedly crucial. Traditional spectrophotometric methods employed assignaling means in molecular recognition and sensing fields often suffer from seriousspectral interferences in colored and/or fluorescent background. Therefore, it alsoremains a challenge to overcome this drawback. Development in supramolecularchemistry and metal nanostructure materials based on metal-metal interactions offer achance to manipulate metallophilicity via a specific interaction event, which wouldnot only allow a smart control of these supramolecular and metal nanostructurematerials, but also open a new field of research in molecular recognition and sensing.Based on these understandings, we intended to manipulate metal-metal interaction toconstruct novel molecular recognition and sensing platforms.The dissertation consists of five chapters.Chapter 1 introduces in general the coinage metal-metal interaction, reviews anddiscusses the development and applications of the metal-metal interaction insupramolecular chemistry and metal nanostructure materials. Fundamentalphotophysical properties and synthesis ofâ…¡-â…¥group semiconductorphotoluminescent nanocrystals are also described.Chapter 2 reports an enantiomeric discriminating strategy for Cys based on thein-situ formed Ag(I)-Cys coordination polymers facilitated by argentophilicity. Detailed investigations were conducted to clarify the origin of characteristicabsorption and CD signals. It was shown that these characteristic spectral signalsoriginate from ligand-to-metal charge transfer transition accompanied by metal-metalinteraction (LMMCT). Solution pH was found to be able to modulate themetallophilicity in the polymeric backbone composed of Ag(I)-Cys repeating unit.Such pH switching character not only allows to improve the selectivity of thissignaling strategy, but also offers a strong support of metallophilicity in Ag(I)-Cyspolymers. Limit of detection of this signaling platform for D- or L-Cys was calculatedto be down to 1μM level. On the basis of the molar extinction coefficient, a signalamplification was indicated in this strategy. It is expected that the present system canin principle serve as a signaling platform following the concept of manipulatingmetallophilicity for extended applications.Chapter 3 describes a highly selective anion-responsive reversible gel-sol statetransition in a supramolecular hydrogel of Ag(I)-glutathione (GSH) coordinationpolymers. To the best of our knowledge, this is the first example for highly selectiveanion-responsive reversible gel-sol state transition in supramolecular hydrogels. Largedifference of the stability constant of AgI from those of the other AgXs (X= F^-, Cl^-,Br^-, H₂PO₄^- and -SR) is considered responsible for the high selectivity towards I- thatresults in the depolymerization of Ag(I)-GSH supramolecular hydrogels. This allowsfor a visual semiquantitative assay for I^- by naked eyes. The released water moleculesin the gel-sol state transition process actually acted as the signal reporter whichoffered a signal amplification, since the weight of released water is ca. 660 times thatof the introduced I^- in case of 0.5% Ag(I)-GSH hydrogel. This strategy is expected inprinciple to be applicable to other species by following the smart gel-sol statetransition in designed supramolecular hydrogels.â…¡-â…¥group semiconductor photoluminescent nanocrystals following theunderstanding of Ag(I)-Cys(GSH) systems were then carried out that will bedescribed later.Chapter 4 presents a signaling system that operates under the photo-induced electron transfer (PET) mechanism usingâ…¡-â…¥group semiconductorphotoluminescent nanocrystals. Steady-state and time-resolved photoluminescent (PL)spectroscopy, thermodynamic energetic analysis, and electron paramagnetic resonance(EPR) experiments support for the PET quenching mechanism that the electrontransfers from conduction band (CB) of excited NCs to the ground state of MB. PL ofNCs could be restored by double stranded DNA (ds-DNA) by inhibiting this electrontransfer process via taking MB away through intercalation into and electrostaticinteractions with the DNA strands. Single stranded DNA (ss-DNA) could also restorethe PL of this nanohybrid but to a lower extent since only electrostatic interactionexists between MB and ss-DNA. This distinct difference therefore allows for aselective sensing of ds-DNA and ss-DNA and for probing DNA hybridization. Thenanohybrid strategy is expected to be of general applicability subject to a suitablechoice of an electron acceptor for theâ…¡-â…¥group semiconductor photoluminescentNCs and for interaction with a target species.Chapter 5 reports an aqueous phase synthetic route to D- and L-Cys-CdS NCsenantiomers using chiral Cys as a surface ligand based on the investigation ofAg(I)-Cys(GSH). It offers a new entry to understand the origin of optical activity ofâ…¡-â…¥group semiconductor chiral NCs.