Simultaneous binding of a cyclophane and classical intercalators to DNA: observation of FRET-mediated white light emission

Abstract

DNA-assisted Förster resonance energy transfer (FRET) between an anthracene-based cyclophane (CP) and mono- and bis-intercalators such as propidium iodide (PI) and ethidium homodimer-1 (EHD), respectively, has been studied using various photophysical and biophysical techniques. The cyclophane and PI exhibited simultaneous binding to DNA at all concentrations studied and showed DNA-assisted FRET from the excimer of cyclophane with a FRET efficiency of ca. 71%. On the other hand, the bis-intercalator EHD, only at lower concentrations (<3 μM), can act as an acceptor for the energy transfer process with a lower efficiency of ca. 44%. At higher concentrations (>15 μM), EHD, on account of its higher binding affinity, displaces cyclophane from the DNA scaffold. Employing the ternary system comprising of the cyclophane, DNA and PI and fine-tuning the concentrations of the components in a molar ratio of 1 : 0.75 : 0.05 (CP : DNA : PI) we have demonstrated white light emission with CIE coordinates (0.35, 0.37).

Influence of a Polyneurotransmitter on DNA-Mediated Förster-Based Resonance Energy Transfer: A Path Leading to White Light Generation

“…The fluorescence quantum yield for the donor (ϕ D ) in the absence of the acceptor (DAPI-ct-DNA in PBS 7.4) has been measured employing quinine sulfate in 0.5 M H 2 SO 4 as the standard and obtained as around 0.34, which again matches excellently with the reported quantum yield of the donor, i.e., DAPI-ct-DNA . Again, another important parameter for the determination of R 0 is the molecular orientation factor (κ 2 ), and considering the restricted rotation of the probe molecules in the DNA structure, the value is estimated to be 1.25. , Therefore, putting the inputs of J (λ), ϕ D , and κ 2 and also the refractive index of the PBS medium ( n ) as 1.335, we have calculated the Förster distance, R 0 , as 3.58 nm. The distance between the donor and the acceptor molecules ( r ) has been calculated using eq , and it is obtained as 2.78 nm.…”

“…Therefore, from this discussion, it can be easily concluded that the WL-emitting system of our present study shows the capability to retain corresponding optical properties of the solution phase in the gel matrix, and thus in the near future, the system can definitely be upgraded to a respective solid-state-based WL-emitting device. Therefore, the specific differences and distinct advantages of the present WL emissive system (i.e., DAPI-ct-DNA-EtBr/F-PDA) discussed in this particular study over other DNA-based WL systems − can be understood from the (a) use of a fluorescent nanoparticle system (F-PDA) derived from an extremely important and biologically relevant neurotransmitter molecule, DA, (b) better optical and emissive property (i.e., better correlation with the pure WL emissive system), and (c) excellent retainment of the WL emissive properties in the agarose gel matrix along with the solution phase in the case of our discussed WL system (DAPI-ct-DNA-EtBr/F-PDA).…”

“…DAPI acts as a minor groove binder, , whereas EtBr serves as an intercalator , to DNA. Now, the simultaneous binding of the suitable DNA binding probes has been observed as a consequence of Förster-based energy transfer (FRET) from one probe molecule to another. − This FRET is a distance-dependent energy transfer approach, and its rate is observed to obey an inverse sixth power dependence of the distance (1/ r 6 ) between the donor and the acceptor molecules . Although FRET is commonly used as a guiding tool for determining the distance of separation between the donor and acceptor molecules, and as a consequence the structural and conformational parameters for different complex biomolecules, very recently FRET has been utilized as an efficient route for white light (WL) generation, ultimately resulting in WL-based optoelectronic systems. − …”

Preferential Binding of Thioflavin T to AT-Rich DNA: White Light Emission through Intramolecular Förster Resonance Energy Transfer

“…This unique AT-selective intercalation mode of cationic ThT molecules could be ascribed to the more electrostatic negative potential of AT pairs compared to the GC pairs and positive potential of cytosine region. 30 It must be mentioned here that for both ThT and EtBr, the apparent binding constant values 31 are in the same order (10 5 M −1 ), and hence, the change in fluorescence intensity is not that significant when ThT is added to the EtBr-AT DNA complex as seen from Figure S8. Our molecular docking results (for all three DNA) also support the same magnitude of binding for both ThT and EtBr bound DNA, discussed next.…”

“…The Forster distance for this process was estimated by using eq 6. 24 R Q J 0.211 ( ) 6) In this case, we have taken the orientation factor (κ 2 ) as 1.25; 31,35 η is the refractive index, and Q D is the relative quantum yield of donor (ThT). The Forster distance (R 0 ) values in the presence of AT-rich DNA and GC-rich DNA were calculated to be ∼3.36 and ∼2.77 nm, respectively.…”