Diazabicyclooctane Research Articles

Nacubactam Enhances Meropenem Activity against Carbapenem-Resistant Klebsiella pneumoniae Producing KPC.

Carbapenem-resistant Enterobacteriaceae (CRE) are resistant to most antibiotics, making CRE infections extremely difficult to treat with available agents. Klebsiella pneumoniae carbapenemases (KPC-2 and KPC-3) are predominant carbapenemases in CRE in the United States. Nacubactam is a bridged diazabicyclooctane (DBO) β-lactamase inhibitor that inactivates class A and C β-lactamases and exhibits intrinsic antibiotic and β-lactam "enhancer" activity against Enterobacteriaceae In this study, we examined a collection of meropenem-resistant K. pneumoniae isolates carrying blaKPC-2 or blaKPC-3; meropenem-nacubactam restored susceptibility. Upon testing isogenic Escherichia coli strains producing KPC-2 variants with single-residue substitutions at important Ambler class A positions (K73, S130, R164, E166, N170, D179, K234, E276, etc.), the K234R variant increased the meropenem-nacubactam MIC compared to that for the strain producing KPC-2, without increasing the meropenem MIC. Correspondingly, nacubactam inhibited KPC-2 (apparent Ki [Ki app] = 31 ± 3 μM) more efficiently than the K234R variant (Ki app = 270 ± 27 μM) and displayed a faster acylation rate (k2/K), which was 5,815 ± 582 M-1 s-1 for KPC-2 versus 247 ± 25 M-1 s-1 for the K234R variant. Unlike avibactam, timed mass spectrometry revealed an intact sulfate on nacubactam and a novel peak (+337 Da) with the K234R variant. Molecular modeling of the K234R variant showed significant catalytic residue (i.e., S70, K73, and S130) rearrangements that likely interfere with nacubactam binding and acylation. Nacubactam's aminoethoxy tail formed unproductive interactions with the K234R variant's active site. Molecular modeling and docking observations were consistent with the results of biochemical analyses. Overall, the meropenem-nacubactam combination is effective against carbapenem-resistant K. pneumoniae Moreover, our data suggest that β-lactamase inhibition by nacubactam proceeds through an alternative mechanism compared to that for avibactam.

Identification of Mutations in the mrdA Gene Encoding PBP2 That Reduce Carbapenem and Diazabicyclooctane Susceptibility of Escherichia coli Clinical Isolates with Mutations in ftsI (PBP3) and Which Carry blaNDM-1.

Penicillin-binding proteins (PBPs) are essential for bacterial cell wall biosynthesis, and several are clinically validated antibacterial targets of β-lactam antibiotics. We identified mutations in the mrdA gene encoding the PBP2 protein in two Escherichia coliblaNDM-1 clinical isolates that reduce susceptibility to carbapenems and to the intrinsic antibacterial activity of a diazabicyclooctane (DBO) PBP2 and β-lactamase inhibitor. These mutations coexisted with previously described mutations in ftsI (encoding PBP3) that reduce susceptibility to monobactams, penicillins, and cephalosporins. Clinical exposure to β-lactams is driving the emergence of multifactorial resistance that may impact the therapeutic usefulness of existing antibacterials and novel compounds that target PBPs.IMPORTANCE Emerging antibacterial resistance is a consequence of the continued use of our current antibacterial therapies, and it is limiting their utility, especially for infections caused by multidrug-resistant isolates. β-Lactams have enjoyed extensive clinical success, but their broad usage is linked to perhaps the most extensive and progressive example of resistance development for any antibacterial scaffold. In Gram-negative pathogens, this largely involves constant evolution of new β-lactamases able to degrade successive generations of this scaffold. In addition, more recently, alterations in the targets of these compounds, penicillin-binding proteins (PBPs), are being described in clinical isolates, which often also have multiple β-lactamases. This study underscores the multifactorial nature of β-lactam resistance by uncovering alterations of PBP2 that reduce susceptibility to carbapenems in E. coli clinical isolates that also have alterations of PBP3 and express the NDM-1 β-lactamase. The changes in PBP2 also reduced susceptibility to the intrinsic antibacterial activity of some diazabicyclooctane (DBO) compounds that can target PBP2. This may have implications for the development and use of the members of this relatively newer scaffold that are inhibitors of PBP2 in addition to their inhibition of serine-β-lactamases.

IID572: A New Potentially Best-In-Class β-Lactamase Inhibitor.

Resistance in Gram-negative bacteria to β-lactam drugs is mediated primarily by the expression of β-lactamases, and co-dosing of β-lactams with a β-lactamase inhibitor (BLI) is a clinically proven strategy to address resistance. New β-lactamases that are not impacted by existing BLIs are spreading and creating the need for development of novel broader spectrum BLIs. IID572 is a novel broad spectrum BLI of the diazabicyclooctane (DBO) class that is able to restore the antibacterial activity of piperacillin against piperacillin/tazobactam-resistant clinical isolates. IID572 is differentiated from other DBOs by its broad inhibition of β-lactamases and the lack of intrinsic antibacterial activity.

698. Nacubactam Inhibits Class A β-lactamases

BackgroundNacubactam, formerly RG6080 and OP0595 (Figure 1A), is a bridged diazabicyclooctane (DBO) that inactivates class A and class C β-lactamases. Unlike avibactam, the DBO that is approved for use in combination with ceftazidime, nacubactam also inhibits penicillin binding proteins (i.e., PBP2) in Enterobacteriaceae. We set out to determine the effectiveness of meropenem-nacubactam against Klebsiella pneumoniae clinical strains and to elucidate the structure–function relationships.MethodsMinimal inhibitory concentration (MIC) measurements using broth microdilution according to Clinical and Laboratory Standards Institute for meropenem (MERO) ± nacubactam (fixed concentration of 4 mg/L or fixed 1:1 ratio) was performed on 50 clinical K. pneumoniae strains (6 having OXA-48-like β-lactamases and 44 harboring KPC-2 or KPC-3) and 47 isogenic Escherichia coli strains harboring bla genes encoding K. pneumoniae carbapenemase (KPC) variants with single amino acid substitutions in residues that are involved in catalysis. IC50s for selected KPC-2 variants were determined on periplasmic extracts with varying concentrations of nacubactam using nitrocefin as a reporter substrate.ResultsThe MERO combinations with either 4 mg/L or a 1:1 ratio of nacubactam effectively lowered the MERO MICs of K. pneumoniae strains (Figure 1B). Similarly, all E. coli strains expressing blaKPC-2 variants were susceptible to the MERO-nacubactam combinations based on the breakpoint of MERO. The strains harboring K73R, S130G, and K234R had slightly elevated MERO-nacubactam MICs relative to wild type but did not have corresponding increases in MERO MICs. Strains with pBC SK-KPC2, K73R or S130G had 0.015 mg/L MERO MICs. The pBR322-K234R strain had a twofold lower MERO MIC than pBR322-KPC-2 (Figure 1C). The IC50 of cell extracts containing the K234R variant is 781 µM, which is 12-fold higher than that for KPC-2 (66 µM) (Figure 1C). Extracts containing the S130G variant were not inhibited by nacubactam (IC50 > 2.6 mM).ConclusionMeropenem-nacubactam is an effective β-lactam β-lactamase inhibitor combination for Enterobacteriaceae with KPC or OXA-48 β-lactamases. The single amino acid substitutions K73R, S130G, and K234R in KPC-2 affect the inactivation mechanism. Disclosures M. R. Jacobs, F. Hoffmann-La Roche Ltd.: Grant Investigator, Research grant. K. M. Papp-Wallace, F. Hoffmann-La Roche Ltd.: Grant Investigator, Research grant. R. A. Bonomo, F. Hoffmann-La Roche Ltd.: Grant Investigator, Research grant.

786. Ceftaroline and Avibactam? Is This a Potential Combination for Mycobacterium abscessus Infection?

Background Mycobacterium abscessus harbors a β-lactamase enzyme, BlaMab, able to hydrolyze penicillins, most cephalosporins and carbapenems. As of today, management of M. abscessus with β-lactams does not include combination of β-lactamase inhibitors. The potential benefit of combinations of several β-lactams with new diazabicyclooctane (DBO) inhibitors, such as relebactam and avibactam, has not been well studied. Based upon the ability to inhibit BlaMab by highly potent DBO inhibitors, our goal herein was to investigate the efficacy of a novel combination, ceftaroline (CEF) and avibactam (AVI), to restore susceptibility to β-lactam antibiotics and inhibit growth.MethodsMinimum inhibitory concentrations (MICs) of CEF with or without AVI were examined using the microdilution method.ResultsMIC50 and MIC90 of CEF is 8 mg/L; in the presence of 4 μg/mL of AVI, the MICs of CEF decreased to ≤4 mg/L in 31 of 35 cases (table).ConclusionOur results add to the growing evidence of using β-lactams as agents effective against Mycobacterial infections. Inhibition of the hydrolytic activity of (BlaMab) using DBOs such as AVI suggest that this combination should be evaluated in animal and clinical models.Table 1: MICs of M. abscessus Strains (mg/L).Avibactam (AV), Ceftaroline (CEF)CEFCEF+AVICEFCEF+AVI M. ab 15-10380.25 M. ab (ATCC)160.25 M. ab 15-44281 M. ab IDR1400012185320.25 M. ab 137-1056180.5 M. ab IDR14000111918<0.25 M. ab 15-305162 M. ab IDR130008519162 M. ab (bolletti) 15-148161 M. ab 138-479620.25 M. ab 16-492116-49161 M. ab (ATCC)32<215-228161 M. ab 16-2180.515-23580.5 M. ab 15-22880.5137-1061>1288 M. ab 15-2061281 M. ab 15-20632<0.25 M. ab 15-23580.5 M. ab 15-86640.5 M. ab 138-479632<215-305161 M. ab IDR1300085191616 M. ab 16-2120.5 M. ab IDR1400012185164 M. ab 15-10340.5 M. ab 15-86162 M. ab 15-14881 M. ab 132-105614115-442321 M. ab #341 M. ab 132-1056140.5 M. ab N140.5 M. ab #140.5 M. ab 60-20163232 M. ab #282 M. ab IDR14000111911616 M. ab #340.5 M. ab #14161 M. ab #4162 M. ab W281 M. ab #5>1284 M. ab #120.5<0.125 M. ab #6644 M. ab #13322 M. ab #740.5 M. ab #11160.5 M. ab #881 M. ab #10322 M. ab #9648 M. ab #741 M. ab #10648 M. ab #1160.5 M. ab #1140.5 M. ab #8180.25 M. ab #1240.5 M. ab #9324 M. ab #1340.5 M. ab #6321 M. ab #1481 M. ab #480.5 M. ab 60-20163232 M. ab #240.5 M. ab W280.5 M. ab #5>644 M. ab N140.5Disclosures All authors: No reported disclosures.

Synthesis of Avibactam Derivatives and Activity on β-Lactamases and Peptidoglycan Biosynthesis Enzymes of Mycobacteria.

There is a renewed interest for β-lactams for treating infections due to Mycobacterium tuberculosis and M. abscessus because their β-lactamases are inhibited by classical (clavulanate) or new generation (avibactam) inhibitors, respectively. Here, access to an azido derivative of the diazabicyclooctane (DBO) scaffold of avibactam for functionalization by the Huisgen-Sharpless cycloaddition reaction is reported. The amoxicillin-DBO combinations were active, indicating that the triazole ring is compatible with drug penetration (minimal inhibitory concentration of 16 μg mL-1 for both species). Mechanistically, β-lactamase inhibition was not sufficient to account for the potentiation of amoxicillin by DBOs. Thus, the latter compounds were investigated as inhibitors of l,d-transpeptidases (Ldts), which are the main peptidoglycan polymerases in mycobacteria. The DBOs acted as slow-binding inhibitors of Ldts by S-carbamoylation indicating that optimization of DBOs for Ldt inhibition is an attractive strategy to obtain drugs selectively active on mycobacteria.

Manufacturing of micro-scale polyurethane foams by reactive inkjet printing

Reactive inkjet printing (RIJ) was used as an additive manufacturing (AM) tool. Combined with polyurethane (PU) chemistry, it is shown that RIJ can be used to build micro-scale foams. Waterblown polyurethane foams (PUF) based on polyethylene glycol 200 (PEG200), glycerol ethoxylate (Star-PEG) and 1,6-hexamethylene diisocyanate (HDI) were used to prepare the foams. The system was catalyzed using iron(III) chloride, dibutyltin dilaurate (DBTL), diazabicyclo octane (DABCO) and bis(2-dimethylaminoethyl) ether. The influence of iron(III) chloride and DBTL were investigated by means of temperature profile measurements. The stability of the catalyst system was tested for 32 hours within the ink formulation. The ink formulations were then printed with a Dimatix DMP3000 (Fujifilm, USA) printer using a 16 nozzle printhead with a nominal 10 pL drop volume. The reaction of the inks and the building of PUF after printing were investigated by light microscopy and SEM. It seems favorable to use high amounts of catalyst in order to obtain a more porous structure.

WCK 5107 (Zidebactam) and WCK 5153 Are Novel Inhibitors of PBP2 Showing Potent "β-Lactam Enhancer" Activity against Pseudomonas aeruginosa, Including Multidrug-Resistant Metallo-β-Lactamase-Producing High-Risk Clones.

Zidebactam and WCK 5153 are novel β-lactam enhancers that are bicyclo-acyl hydrazides (BCH), derivatives of the diazabicyclooctane (DBO) scaffold, targeted for the treatment of serious infections caused by highly drug-resistant Gram-negative pathogens. In this study, we determined the penicillin-binding protein (PBP) inhibition profiles and the antimicrobial activities of zidebactam and WCK 5153 against Pseudomonas aeruginosa, including multidrug-resistant (MDR) metallo-β-lactamase (MBL)-producing high-risk clones. MIC determinations and time-kill assays were conducted for zidebactam, WCK 5153, and antipseudomonal β-lactams using wild-type PAO1, MexAB-OprM-hyperproducing (mexR), porin-deficient (oprD), and AmpC-hyperproducing (dacB) derivatives of PAO1, and MBL-expressing clinical strains ST175 (blaVIM-2) and ST111 (blaVIM-1). Furthermore, steady-state kinetics was used to assess the inhibitory potential of these compounds against the purified VIM-2 MBL. Zidebactam and WCK 5153 showed specific PBP2 inhibition and did not inhibit VIM-2 (apparent Ki [Kiapp] > 100 μM). MICs for zidebactam and WCK 5153 ranged from 2 to 32 μg/ml (amdinocillin MICs > 32 μg/ml). Time-kill assays revealed bactericidal activity of zidebactam and WCK 5153. LIVE-DEAD staining further supported the bactericidal activity of both compounds, showing spheroplast formation. Fixed concentrations (4 or 8 μg/ml) of zidebactam and WCK 5153 restored susceptibility to all of the tested β-lactams for each of the P. aeruginosa mutant strains. Likewise, antipseudomonal β-lactams (CLSI breakpoints), in combination with 4 or 8 μg/ml of zidebactam or WCK 5153, resulted in enhanced killing. Certain combinations determined full bacterial eradication, even with MDR MBL-producing high-risk clones. β-Lactam-WCK enhancer combinations represent a promising β-lactam "enhancer-based" approach to treat MDR P. aeruginosa infections, bypassing the need for MBL inhibition.

Variants of β-Lactamase KPC-2 That Are Resistant to Inhibition by Avibactam

KPC-2 is the most prevalent class A carbapenemase in the world. Previously, KPC-2 was shown to hydrolyze the β-lactamase inhibitors clavulanic acid, sulbactam, and tazobactam. In addition, substitutions at amino acid position R220 in the KPC-2 β-lactamase increased resistance to clavulanic acid. A novel bridged diazabicyclooctane (DBO) non-β-lactam β-lactamase inhibitor, avibactam, was shown to inactivate the KPC-2 β-lactamase. To better understand the mechanistic basis for inhibition of KPC-2 by avibactam, we tested the potency of ampicillin-avibactam and ceftazidime-avibactam against engineered variants of the KPC-2 β-lactamase that possessed single amino acid substitutions at important sites (i.e., Ambler positions 69, 130, 234, 220, and 276) that were previously shown to confer inhibitor resistance in TEM and SHV β-lactamases. To this end, we performed susceptibility testing, biochemical assays, and molecular modeling. Escherichia coli DH10B carrying KPC-2 β-lactamase variants with the substitutions S130G, K234R, and R220M demonstrated elevated MICs for only the ampicillin-avibactam combinations (e.g., 512, 64, and 32 mg/liter, respectively, versus the MICs for wild-type KPC-2 at 2 to 8 mg/liter). Steady-state kinetics revealed that the S130G variant of KPC-2 resisted inactivation by avibactam; the k2/K ratio was significantly lowered 4 logs for the S130G variant from the ratio for the wild-type enzyme (21,580 M(-1) s(-1) to 1.2 M(-1) s(-1)). Molecular modeling and molecular dynamics simulations suggested that the mobility of K73 and its ability to activate S70 (i.e., function as a general base) may be impaired in the S130G variant of KPC-2, thereby explaining the slowed acylation. Moreover, we also advance the idea that the protonation of the sulfate nitrogen of avibactam may be slowed in the S130G variant, as S130 is the likely proton donor and another residue, possibly K234, must compensate. Our findings show that residues S130 as well as K234 and R220 contribute significantly to the mechanism of avibactam inactivation of KPC-2. Fortunately, the emergence of S130G, K234R, and R220M variants of KPC in the clinic should not result in failure of ceftazidime-avibactam, as the ceftazidime partner is potent against E. coli DH10B strains possessing all of these variants.

Examination of Amine-Functionalised Anion-Exchange Membranes for Possible Use in the All-Vanadium Redox Flow Battery

The applicability of amine-functionalised anion-exchange membranes (AEMs) for use in the all-vanadium redox flow battery has been studied. A selection of radiation-grafted aminated membranes functionalised with dimethylamine, trimethylamine or diazabicyclo(2,2,2)octane were extensively tested. The success of each grafting process was confirmed by Raman and infrared spectroscopies, titrimetry and ionic conductivity measurements. The amine-functionalised membranes were found to have poor thermo-oxidative stability and high vanadium cation permeabilities. The results highlight the importance of balancing ionic conductivity with vanadium cation permeability and indicate that amine-based functional groups may not be suitably stable for the membranes to remain true AEMs when in use in the all-vanadium redox flow battery.

DABCO-promoted facile and convenient synthesis of novel isoxazolyl-1H-2,3-pyrrole dicarboxylates

Abstract Synthesis of isoxazolyl-1 H -2,3-pyrrole dicarboxylate ( 4 ) was simply achieved by one-pot three component reaction of isoxazole amine ( 1 ) with diethyl acetylenedicarboxylate (DEAD) ( 2 ), and glyoxal ( 3 ), in acetonitrile catalyzed by diazabicyclo octane (DABCO).

New β‐lactam–β‐lactamase inhibitor combinations in clinical development

Tazobactam was the most recent β-lactamase inhibitor to be approved in 1993. Since the approval of piperacillin-tazobactam, the complexity of β-lactamase-mediated resistance among Gram-negative bacilli has increased enormously. After more than 20 years since the first such combination, amoxicillin-clavulanic acid, was approved, several new β-lactam-β-lactamase inhibitor combinations have reached late-stage (phase II and beyond) clinical trials. These include ceftolozane-tazobactam (2:1, ratios of β-lactam to β-lactamase inhibitor in parentheses), ceftazidime-avibactam (4:1), ceftaroline-avibactam (1:1), and imipenem-cilastatin-MK-7655 (2:2:1 and 4:4:1). Avibactam and MK-7655 are diazabicyclooctane (DABCO) inhibitors and thus not β-lactams themselves; they include class A carbapenemases and class C enzymes within their spectra of activity. Ceftolozane is an antipseudomonal cephalosporin, and tazobactam is used to protect it against extended spectrum β-lactamases to which it is labile. Additional novel combinations are in preclinical development. This review will focus on the biochemistry, antimicrobial activity, pharmacodynamics, and clinical development of these novel combinations.

Effects of solubility characteristics of sensitiser and pH on the photooxidation of oil in tuna oil-added acidic O/W emulsions

The effects of sensitisers and pH on the oil oxidation of acidic O/W emulsions were studied under light by measuring hydroperoxide content and headspace oxygen consumption in the emulsions. The emulsions consisted of canola and tuna oil (2:1w/w, 32%), diluted acetic acid (64%), egg yolk powder (4%), chlorophyll b or erythrosine (5μM), and/or diazabicyclooctane (DABCO) or sodium azide (0.5M). The emulsion pH values were 2.67, 3.68, and 6.27. Chlorophyll increased oil oxidation in the emulsion under light via singlet oxygen production while erythrosine did not. DABCO significantly decreased photooxidation of the oil containing chlorophyll, suggesting singlet oxygen involvement. However, sodium azide increased photooxidation of the oil containing chlorophyll possibly via azide radical production under acidic conditions. The oil photooxidation was higher in the emulsion containing chlorophyll at pH 6.27 than at pH 2.67 or 3.68, primarily by singlet oxygen and secondarily by free radicals produced from hydroperoxide decomposition.

ChemInform Abstract: Photoreduction of 4,4′-Bipyridine by Triethylamine and by 1,4- Diazabicyclo(2.2.2)octane in Acetonitrile as Studied by Nanosecond Absorption and Raman Spectroscopies

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Insight into the Mechanism of Antimicrobial Poly(phenylene ethynylene) Polyelectrolytes: Interactions with Phosphatidylglycerol Lipid Membranes†Langmuir 25th Year: Molecular and macromolecular self-assemblies

The interactions of antimicrobial poly(phenylene ethynylene) (PPE)-based cationic conjugated polyelectrolytes (CPEs) with lipid membranes were investigated to gain insight into the mechanism of their biocidal activity. Three model membrane systems comprising negatively charged phosphatidylglycerol (PG) lipids were used to mimic the bacterial cell membrane, including unilamellar lipid vesicles in aqueous solution, lipid bilayer coated silica microspheres, and lipid monolayers at the air-water interface. Two PPE CPEs, one containing a thiophene moiety on the PPE repeat unit and the second containing a diazabicyclooctane (DABCO) moiety on the pendant side chain, were chosen, since the former exhibits distinct dark biocidal activity and the latter shows strong light-activated antimicrobial activity but little dark biocidal activity. The interactions of these two PPE polymers with lipid membranes were characterized in detail by CPE fluorescence spectral changes, fluorescence resonance energy transfer (FRET), fluorescence quenching, monolayer insertion, and dynamic light scattering assays. Both PPE polymers exhibit affinity for the anionic lipid membrane systems. Their concomitant association and insertion into the membrane leads to conformational changes of the PPE polymer from an aggregated state to a more extended state, as evidenced by the polymer's enhanced fluorescence and FRET between the polymer and rhodamine incorporated in the lipid membrane. In comparison, the thiophene polymer exhibits stronger interactions with PG lipid membranes than the DABCO-containing polymer. The former induces a larger fluorescence enhancement, shows faster transfer across the lipid membrane, and inserts more readily and to a higher extent into lipid monolayers. The observed differences between the two PPE polymers in their interactions with the lipid membrane may stem from their structural differences, as the DABCO-containing polymer has a much bulkier and larger pendant group on its side chain. The higher degree of membrane interaction and insertion, and subsequent membrane disorganization, of the thiophene polymer may account for its dark biocidal activity.

A heterocyclic organogallium peroxide with two dialkylgallium groups bridged by a peroxide dianion

Treatment of Li[H2GaR2] [R=CH(SiMe3)2] with the hydrogen peroxide adduct (H2O2)2.DABCO (DABCO=diazabicyclooctane) afforded a heterocyclic digallium peroxide, [R2Ga(micro,eta1,eta1-O2)(micro-OH)GaR2]Li(DABCO) (2), in which two dialkylgallium groups are bridged by an oxidizing peroxo and a hydroxo ligand.

Competition between coordination network and halogen bond network formation: towards halogen-bond functionalised network materials using copper-iodobenzoate units

The Cu2(3-iodobenzoate)4 paddlewheel has been investigated as a secondary building unit (SBU I) in the design and synthesis of a linear coordination network. The SBU was found to form halogen-bonded networks rather than coordination networks with simple short linkers such as 1,4-dioxane and diazabicyclo(2.2.2)octane (dabco). Increasing the linker size to 4,4′-bipyridine (bipy) resulted in a linear network containing both the paddlewheel SBU I and a new mononuclear SBU II. Further increase of linker size to 4,4′-bipyridylethane (bpe) results in two crystalline phases. The first consists of linear chains of SBU II and the second contains two types of network chain in one single crystal, single chains of SBU II along with double chains of a new dinuclear SBU III.

Unusually High Performance Photovoltaic Cell Based on a [60]Fullerene Metal Cluster−Porphyrin Dyad SAM on an ITO Electrode

A self-assembled monolayer (SAM) of a C60-triosmium cluster complex Os3(CO)7(CNR)(CNR')(mu3-eta2:eta2:eta2-C60) (ZnP-C60; R = (CH2)3Si(OEt)3, R' = ZnP) on an ITO surface exhibits ideal electrochemical responses as well as remarkable enhancement of the photocurrent generation. The diazabicyclooctane (DABCO) binding (ZnP)-C60/ITO/AsA/Pt cell shows the highest photocurrent generation quantum yield (19.5%) ever reported for the molecular photovoltaic cells based on the covalently linked donor-acceptor dyad structures. The high efficiency in photocurrent generation is ascribed to an efficient electron transfer from photoexcited porphyrin to fullerene, revealed by fluorescence lifetime measurements and transient absorption decay profiles. These results provide valuable information on the new strategy for the construction of molecular photonic devices and artificial photosynthetic systems on ITO electrodes.

Photoinduced electron- and energy-transfer processes of [60]fullerene covalently bonded with one and two zinc porphyrin(s): effects of coordination of pyridine and diazabicyclooctane to Zn atom

C60–zinc porphyrin (ZnP) dyad (ZnP–C60) and triad (ZnP–C60–ZnP) were synthesized to probe energy-transfer and electron-transfer processes in the absence and presence of pyridine and diazabicyclooctane (DABCO). The syntheses of C60–ZnP and ZnP–C60–ZnP were carried out by Diels–Alder cycloaddition between sulfolene moiety-containing porphyrin and C60. The photoinduced electron-transfer processes between the spatially positioned C60 and ZnP in the dyad and triad systems were investigated by time-resolved transient absorption and fluorescence measurements with changing solvent polarity. Upon excitation of the ZnP moiety, charge separation via an excited singlet state of ZnP takes place competitively with energy transfer to C60 generating the excited singlet state of C60, from which charge-separated states (ZnP˙+–C60˙− and ZnP˙+–C60˙−–ZnP) are also generated in polar solvents. Rates and efficiencies of energy transfer and charge separation for the triad are higher than those of the dyad. The generated charge-separated species recombine with lifetimes in the rage of 240–330 ns in polar solvents such as DMF, PhCN, and THF for both dyad and triad. In o-dichlorobenzene, although the lifetimes of charge-separated states are very short (<20 ns), coordination of DABCO and pyridine to ZnP in the dyad and triad producing relatively stable coordinated complexes gives rise to prolongation of the charge-separated states up to 460 ns.

Self-organisation in photoactive fullerene porphyrin based donor–acceptor ensembles

Complexation of ZnP-C60-ZnP triads with diazabicyclooctane (DABCO) leads to rigid assemblies that display considerably prolonged charge-separated states.