Modelling Photosynthesis with ZnII-Protoporphyrin All-DNA G-Quadruplex/Aptamer Scaffolds

All-DNA scaffolds act as templates for the organization of photosystem I model systems. A series of DNA templates composed of Zn^II-protoporphyrin IX (Zn^IIPPIX)-functionalized G-quadruplex conjugated to the 3′- or 5′-end of the tyrosinamide (TA) aptamer and Zn^IIPPIX/G-quadruplex linked to the 3′- and 5′-ends of the TA aptamer through a four-thymidine bridge. Effective photoinduced electron transfer (ET) from Zn^IIPPIX/G-quadruplex to bipyridinium-functionalized tyrosinamide, TA-MV²⁺, bound to the TA aptamer units is demonstrated. The effectiveness of the primary ET quenching of Zn^IIPPIX/G-quadruplex by TA-MV²⁺ controls the efficiency of the generation of TA-MV^+.. The photosystem-controlled formation of TA-MV^+. by the different photosystems dictates the secondary activation of the ET cascade corresponding to the ferredoxin-NADP⁺ reductase (FNR)-catalysed reduction of NADP⁺ to NADPH by TA-MV^+., and the sequestered alcohol dehydrogenase catalysed reduction of acetophenone to 1-phenylethanol by NADPH.     

Interaction of Metal Complexes with G‐Quadruplex DNA

Guanine‐rich sequences of DNA can assemble into tetrastranded structures known as G‐quadruplexes. It has been suggested that these secondary DNA structures could be involved in the regulation of several key biological processes. In the human genome, guanine‐rich sequences with the potential to form G‐quadruplexes exist in the telomere as well as in promoter regions of certain oncogenes. The identification of these sequences as novel targets for the development of anticancer drugs has sparked great interest in the design of molecules that can interact with quadruplex DNA. While most reported quadruplex DNA binders are based on purely organic templates, numerous metal complexes have more recently been shown to interact effectively with this DNA secondary structure. This Review provides an overview of the important roles that metal complexes can play as quadruplex DNA binding molecules, highlighting the unique properties metals can confer to these molecules.     

Light‐Harvesting Phthalocyanine–Diketopyrrolopyrrole Derivatives: Synthesis,Spectroscopic, Electrochemical,and Photochemical Studies

A new family of light‐harvesting zinc phthalocyanine (ZnPc)–diketopyrrolopyrrole (DPP) hybrids have been synthesized and characterized. The absorption spectral measurements showed that the major absorptions of DPP (450–600 nm) are complementary to those of zinc phthalocyanine (300–400 and 600–700 nm). Therefore, the designed hybrids absorb over a broad range in the visible region. The geometric and electronic structures of the dyads were probed by initio B3LYP/6‐311G methods. The majority of the HOMOs were found to be located on the ZnPc, while the majority of the LUMOs were on the DPP units. The DPP units serve as the antenna, which upon excitation undergo efficient singlet–singlet energy transfer to the attached ZnPc units. The formed singlet ZnPc, in turn, donates its electron to the electron‐deficient DPP forming the low‐lying radical ion pairs ZnPc^.+–DPP^.? (energy=1.44–1.56 eV as calculated from the electrochemical measurements). The excited‐state events were confirmed by using a transient absorption technique in the picosecond–microsecond time range, as well as a time‐resolved emission technique. The rates of energy transfer from the singlet DPP to ZnPc were found to be extremely fast >10¹⁰ s^?1, while the rates of electron transfer from the singlet excited state of ZnPc to DPP were found to be 3.7–6.6×10⁹ s^?1.     

Specific Binding of a d‐RNA G‐Quadruplex Structure with an l‐RNA Aptamer

G‐quadruplex (G4) structures are of general importance in chemistry and biology, such as in biosensing, gene regulation, and cancers. Although a large repertoire of G4‐binding tools has been developed, no aptamer has been developed to interact with G4. Moreover, the G4 selectivity of current toolkits is very limited. Herein, we report the first l ‐RNA aptamer that targets a d ‐RNA G‐quadruplex (rG4). Using TERRA rG4 as an example, our results reveal that this l ‐RNA aptamer, Ap3‐7, folds into a unique secondary structure, exhibits high G4 selectivity and effectively interferes with TERRA‐rG4–RHAU53 binding. Our approach and findings open a new door in further developing G4‐specific tools for diverse applications.     

Excitation‐Wavelength‐Dependent,Ultrafast Photoinduced Electron Transfer in Bisferrocene/BF2‐Chelated‐Azadipyrromethene/Fullerene Tetrads

Donor–acceptor distance, orientation, and photoexcitation wavelength are key factors in governing the efficiency and mechanism of electron‐transfer reactions both in natural and synthetic systems. Although distance and orientation effects have been successfully demonstrated in simple donor–acceptor dyads, revealing excitation‐wavelength‐dependent photochemical properties demands multimodular, photosynthetic‐reaction‐center model compounds. Here, we successfully demonstrate donor– acceptor excitation‐wavelength‐dependent, ultrafast charge separation and charge recombination in newly synthesized, novel tetrads featuring bisferrocene, BF₂‐chelated azadipyrromethene, and fullerene entities. The tetrads synthesized using multistep synthetic procedure revealed characteristic optical, redox, and photo reactivities of the individual components and featured “closely” and “distantly” positioned donor–acceptor systems. The near‐IR‐emitting BF₂‐chelated azadipyrromethene acted as a photosensitizing electron acceptor along with fullerene, while the ferrocene entities acted as electron donors. Both tetrads revealed excitation‐wavelength‐dependent, photoinduced, electron‐transfer events as probed by femtosecond transient absorption spectroscopy. That is, formation of the Fc⁺–ADP–C₆₀^.? charge‐separated state upon C₆₀ excitation, and Fc⁺–ADP^.?–C₆₀ formation upon ADP excitation is demonstrated.     

A G‐Quadruplex/Hemin Complex with Switchable Peroxidase Activity by DNA Hybridization

A hemin‐binding DNA G‐quadruplex (also known as a hemin aptamer or DNAzyme) has been previously reported to be able to enhance the peroxidase activity of hemin. In this work, we described a DNAzyme structure that had an effector‐recognizing part appearing as a single stranded DNA linkage flanked by two split G‐quadruplex halves. Hybridization of the single stranded part in the enzyme with a perfectly matched DNA strand (effector) formed a rigid DNA duplex between the two G‐quadruplex halves and thus efficiently suppressed the enzymatic activity of the G‐quadruplex/hemin complex, while the mismatched effector strand was not able to regulate the peroxidase activity effectively. With 2,2′‐azinobis(3‐ethylbenzthiazoline)‐6‐sulfonic acid (ABTS) as an oxidizable substrate, we were able to characterize the formation of the re‐engineered G‐quadruplex/hemin complex and verify its switchable peroxidase activity. Our results show that the split G‐quadruplex is an especially useful module to design low‐cost and label‐free sensors toward various biologically or environmentally interesting targets.     

Large Porphyrin Squares from the Self‐Assembly of meso‐Triazole‐Appended L‐Shaped meso–meso‐Linked ZnII–Triporphyrins: Synthesis and Efficient Energy Transfer

meso‐Triazolyl‐appended Zn^II–porphyrins were readily prepared by Cu^I‐catalyzed 1,3‐dipolar cycloaddition of benzyl azide to meso‐ethynylated Zn^II–porphyrin (click chemistry). In noncoordinating CHCl₃ solvent, spontaneous assembly occurred to form tetrameric array ( 3 )₂ from meso–meso‐linked diporphyrins 3 , and dodecameric porphyrin squares ( 4 )₄ and ( 5 )₄ from the L ‐shaped meso–meso‐linked triporphyrins 4 and 5 . The structures of these assemblies were examined by ¹H NMR spectra, absorption spectra, and their gel permeation chromatography (GPC) retention time. Furthermore, the structures of the dodecameric porphyrin squares ( 4 )₄ and ( 5 )₄ were probed by small‐ and wide‐angle X‐ray scattering (SAXS/WAXS) measurements in solution using a synchrotron source. Excitation‐energy migration processes in these assemblies were also investigated in detail by using both steady‐state and time‐resolved spectroscopic methods, which revealed efficient excited‐energy transfer (EET) between the meso–meso‐linked Zn^II–porphyrin units that occurred with time constants of 1.5 ps^?1 for ( 3 )₂ and 8.8 ps^?1 for ( 5 )₄.     

Engineering Bisquinolinium/Thiazole Orange Conjugates for Fluorescent Sensing of G‐Quadruplex DNA

Lighting up : A G‐quadruplex‐specific fluorescent probe was designed combining the specificity of the pyridodicarboxamide motif for guanine quadruplexes and the fluorescence properties of thiazole orange. While the assembly of the two partners through a flexible linker leads to a nonselective probe, merging them in a single, rigid scaffold leads to a dye that elicits the properties required for G‐quadruplex sensing.

     

Water Molecules Gating a Photoinduced One‐Electron Two‐Protons Transfer in a Tyrosine/Histidine (Tyr/His) Model of Photosystem II

We investigate a biomimetic model of a Tyr_Z/His₁₉₀ pair, a hydrogen‐bonded phenol/imidazole covalently attached to a porphyrin sensitizer. Laser flash photolysis in the presence of an external electron acceptor reveals the need for water molecules to unlock the light‐induced oxidation of the phenol through an intramolecular pathway. Kinetics monitoring encompasses two fast phases with distinct spectral properties. The first phase is related to a one‐electron transfer from the phenol to the porphyrin radical cation coupled with a domino two‐proton transfer leading to the ejection of a proton from the imidazole–phenol pair. The second phase concerns conveying the released proton to the porphyrin N₄ coordinating cavity. Our study provides an unprecedented example of a light‐induced electron‐transfer process in a Tyr_Z/His₁₉₀ model of photosystem II, evidencing the movement of both the phenol and imidazole protons along an isoenergetic pathway.     

Ultrafast Photoinduced Energy and Electron Transfer in Multi‐Modular Donor–Acceptor Conjugates

New multi‐modular donor–acceptor conjugates featuring zinc porphyrin (ZnP), catechol‐chelated boron dipyrrin (BDP), triphenylamine (TPA) and fullerene (C₆₀), or naphthalenediimide (NDI) have been newly designed and synthesized as photosynthetic antenna and reaction‐center mimics. The X‐ray structure of triphenylamine‐BDP is also reported. The wide‐band capturing polyad revealed ultrafast energy‐transfer (k_ENT=1.0×10¹² s^?1) from the singlet excited BDP to the covalently linked ZnP owing to close proximity and favorable orientation of the entities. Introducing either fullerene or naphthalenediimide electron acceptors to the TPA‐BDP‐ZnP triad through metal–ligand axial coordination resulted in electron donor–acceptor polyads whose structures were revealed by spectroscopic, electrochemical and computational studies. Excitation of the electron donor, zinc porphyrin resulted in rapid electron‐transfer to coordinated fullerene or naphthalenediimide yielding charge separated ion‐pair species. The measured electron transfer rate constants from femtosecond transient spectral technique in non‐polar toluene were in the range of 5.0×10⁹–3.5×10¹⁰ s^?1. Stabilization of the charge‐separated state in these multi‐modular donor–acceptor polyads is also observed to certain level.     

Semiconductor/Covalent‐Organic‐Framework Z‐Scheme Heterojunctions for Artificial Photosynthesis

A strategy to covalently connect crystalline covalent organic frameworks (COFs) with semiconductors to create stable organic–inorganic Z‐scheme heterojunctions for artificial photosynthesis is presented. A series of COF–semiconductor Z‐scheme photocatalysts combining water‐oxidation semiconductors (TiO₂, Bi₂WO₆, and α‐Fe₂O₃) with CO₂ reduction COFs (COF‐316/318) was synthesized and exhibited high photocatalytic CO₂‐to‐CO conversion efficiencies (up to 69.67 μmol g^?1 h^?1), with H₂O as the electron donor in the gas–solid CO₂ reduction, without additional photosensitizers and sacrificial agents. This is the first report of covalently bonded COF/inorganic‐semiconductor systems utilizing the Z‐scheme applied for artificial photosynthesis. Experiments and calculations confirmed efficient semiconductor‐to‐COF electron transfer by covalent coupling, resulting in electron accumulation in the cyano/pyridine moieties of the COF for CO₂ reduction and holes in the semiconductor for H₂O oxidation, thus mimicking natural photosynthesis.     

A Charge‐Stabilizing,Multimodular, Ferrocene–Bis(triphenylamine)–Zinc‐porphyrin–Fullerene Polyad

A novel multimodular donor–acceptor polyad featuring zinc porphyrin, fullerene, ferrocene, and triphenylamine entities was designed, synthesized, and studied as a charge‐stabilizing, photosynthetic‐antenna/reaction‐center mimic. The ferrocene and fullerene entities, covalently linked to the porphyrin ring, were distantly separated to accomplish the charge‐separation/hole‐migration events leading to the creation of a long‐lived charge‐separated state. The geometry and electronic structures of the newly synthesized compound was deduced by B3LYP/3‐21G(*) optimization, while the energy levels for different photochemical events was established using data from the optical absorption and emission, and electrochemical studies. Excitation of the triphenylamine entities revealed singlet‐singlet energy transfer to the appended zinc porphyrin. As predicted from the energy levels, photoinduced electron transfer from both the singlet and triplet excited states of the zinc porphyrin to fullerene followed by subsequent hole migration involving ferrocene was witnessed from the transient absorption studies. The charge‐separated state persisted for about 8.5 μs and was governed by the distance between the final charge‐transfer product, that is, a species involving a ferrocenium cation and a fullerene radical anion, with additional influence from the charge‐stabilizing triphenylamine entities located on the zinc‐porphyrin macrocycle.     

A New Approach for the Photosynthetic Antenna–Reaction Center Complex with a Model Organized Around an s‐Triazine Linker

Two new artificial mimics of the photosynthetic antenna‐reaction center complex have been designed and synthesized (BDP‐H₂P‐C₆₀ and BDP‐ZnP‐C₆₀). The resulting electron‐donor/acceptor conjugates contain a porphyrin (either in its free‐base form (H₂P) or as Zn‐metalated complex (ZnP)), a boron dipyrrin (BDP), and a fulleropyrrolidine possessing, as substituent of the pyrrolidine nitrogen, an ethylene glycol chain terminating in an amino group C₆₀‐X‐NH₂ (X=spacer). In both cases, the three different components were connected by s‐triazine through stepwise substitution reactions of cyanuric chloride. In addition to the facile synthesis, the star‐type arrangement of the three photo‐ and redox‐active components around the central s‐triazine unit permits direct interaction between one another, in contrast to reported examples in which the three components are arranged in a linear fashion. The energy‐ and electron‐transfer properties of the resulting electron‐donor/acceptor conjugates were investigated by using UV/Vis absorption and emission spectroscopy, cyclic voltammetry, and femtosecond transient absorption spectroscopy. Comparison of the absorption spectra and cyclic voltammograms of BDP‐H₂P‐C₆₀ and BDP‐ZnP‐C₆₀ with those of BDP‐H₂P, BDP‐ZnP and BDP‐C₆₀, which were used as references, showed that the spectroscopic and electrochemical properties of the individual constituents are basically retained, although some appreciable shifts in terms of absorption indicate some interactions in the ground state. Fluorescence lifetime measurements and transient absorption experiments helped to elucidate the antenna function of BDP, which upon selective excitation undergoes a rapid and efficient energy transfer from BDP to H₂P or ZnP. This is then followed by an electron transfer to C₆₀, yielding the formation of the singlet charge‐separated states, namely BDP‐H₂P ^.+‐ C₆₀ ^.? and BDP‐ZnP ^.+‐ C₆₀ ^{. ?}. As such, the sequence of energy transfer and electron transfer in the present models mimics the events of natural photosynthesis.     

Synthesis of New DNA G‐Quadruplex Constructs with Anthraquinone Insertions and Their Anticoagulant Activity

1,4‐Dihydroxyanthraquinone and 1,8‐dihydroxyanthraquinone were alkylated with 3‐bromopropan‐1‐ol and subsequently transformed into the corresponding DMT protected phosphoramidite building blocks for insertion into loops of the G‐quadruplex of the thrombin binding aptamer (TBA). The 1,4‐disubstituted anthraquinone linker led to a significant stabilization of the G‐quadruplex structure upon replacing a T in each of two neighboring lateral TT loops and a 26.2° increase in thermal melting temperature was found. CD Spectra of the modified quadruplexes confirmed anti‐parallel conformations in all cases under potassium buffer conditions as previously observed for TBA. Although the majority of the anthraquinone modified TBA analogues showed a decrease in clotting times in a fibrinogen clotting assay when compared to TBA, modified aptamers containing a 1,8‐disubstituted anthraquinone linker replacing G₈ or T₉ in the TGT loop showed improved anticoagulant activities. Molecular modeling studies explained the increased thermal melting temperatures of anthraquinone‐modified G‐quadruplexes.     

Hetero Face‐to‐Face Porphyrin Array with Cooperative Effects of Coordination and Host–Guest Complexation

We successfully synthesized a hetero face‐to‐face porphyrin array composed of ZnTPP and RuTPP(DABCO)₂ (TPP: 5, 10, 15, 20‐tetraphenylporphyrin, DABCO: 1,4‐diazabi‐cyclo[2.2.2]octane) in 2:1 molar ratio. A cyclic Zn porphyrin dimer (ZnCP) was also used as the host molecule for the Ru porphyrin. In the latter, the Ru‐DABCO bonding in RuTPP(DABCO)₂ was stabilized by the host‐guest complexation. Reaction progress kinetic analysis of the ligand substitution reaction of RuTPP(DABCO)₂ and that in ZnCP revealed the stabilization mechanism of the Ru‐DABCO bonding. Photoinduced electron transfer (PET) from the Zn porphyrin to the Ru porphyrin was observed in the porphyrin array. The host‐guest stabilization of unstable complex for construction of a donor—acceptor–donor structure is expected to be a new method for an artificial photosynthesis.     

Platinum Alloy Tailored All‐Weather Solar Cells for Energy Harvesting from Sun and Rain

Solar cells that can harvest energy in all weathers are promising in solving the energy crisis and environmental problems. The power outputs are nearly zero under dark conditions for state‐of‐the‐art solar cells. To address this issue, we present herein a class of platinum alloy (PtM_x, M=Ni, Fe, Co, Cu, Mo) tailored all‐weather solar cells that can harvest energy from rain and realize photoelectric conversion under sun illumination. By tuning the stoichiometric Pt/M ratio and M species, the optimized solar cell yields a photoelectric conversion efficiency of 10.38 % under simulated sunlight irradiation (AM 1.5, 100 mW cm^?2) as well as current of 3.90 μA and voltage of 115.52 μV under simulated raindrops. Moreover, the electric signals are highly dependent on the dripping velocity and the concentration of simulated raindrops along with concentrations of cation and anion.     

Prolonged Hot Electron Dynamics in Plasmonic‐Metal/Semiconductor Heterostructures with Implications for Solar Photocatalysis

Ideal solar‐to‐fuel photocatalysts must effectively harvest sunlight to generate significant quantities of long‐lived charge carriers necessary for chemical reactions. Here we demonstrate the merits of augmenting traditional photoelectrochemical cells with plasmonic nanoparticles to satisfy these daunting photocatalytic requirements. Electrochemical techniques were employed to elucidate the mechanics of plasmon‐mediated electron transfer within Au/TiO₂ heterostructures under visible‐light (λ>515 nm) irradiation in solution. Significantly, we discovered that these transferred electrons displayed excited‐state lifetimes two orders of magnitude longer than those of electrons photogenerated directly within TiO₂ via UV excitation. These long‐lived electrons further enable visible‐light‐driven H₂ evolution from water, heralding a new photocatalytic paradigm for solar energy conversion.