Biomimetic Approach toward Visible Light-Driven Hydrogen Generation Based on a Porphyrin-Based Coordination Polymer Gel.

There has been a widespread interest in developing self-assembled porphyrin nanostructures to mimic nature's light-harvesting processes. Herein, porphyrin-based coordination polymer gel (CPG) has been developed as a "soft" photocatalyst material for hydrogen (H2) production from water under visible light. The CPG offers a hierarchical nanofibrous network structure obtained through self-assembly of a terpyridine alkyl-amide appended porphyrin (TPY-POR)-based low molecular weight gelator with ruthenium ions (RuII) and produces H2 with a rate of 5.7 mmol g-1 h-1 in the presence of triethylamine (TEA) as a sacrificial electron donor. Further, the [Fe2(bdt)(CO)6] (dbt = 1,2-benzenedithiol) cocatalyst, which can mimic the activity of iron hydrogenase, is coassembled in the CPG and shows remarkable improvement in H2 evolution (catalytic activity; rate ∼10.6 mmol g-1 h-1 and turnover number ∼1287). The significant enhancement in catalytic activity was supported by several controlled experiments, including femtosecond transient absorption (TA) spectroscopy and also DFT calculation. The TA study supported the cascade electron transfer process from porphyrin core to [Ru(TPY)2]2+ center, and subsequently, the electron transfers to the cocatalyst [Fe2(bdt)(CO)6] for H2 production.

A highly contorted push-pull naphthalenediimide dimer and evidence of intramolecular singlet exciton fission.

Singlet fission is a process by which two molecular triplet excitons are generated subsequent to the absorption of one photon. Molecules that enable singlet fission have triplet state energy at least half of the bright singlet state energy. This stringent energy criteria have challenged chemists to device new molecular and supramolecular design principles to modulate the singlet-triplet energy gap and build singlet fission systems from a wide range of organic chromophores. Herein, we report for the first time intramolecular singlet fission in the seminal naphthalenediimide (NDI) scaffold constrained in a push-pull cyclophane architecture, while individually the NDI chromophore does not satisfy the energy criterion. The challenging synthesis of this highly contorted push-pull cyclophane is possible from the preorganized pincer-like precursor. The special architecture establishes the shortest co-facial NDI⋯NDI contacts (3.084 Å) realized to date. Using broadband femtosecond transient absorption, we find that the correlated T-T pair forms rapidly within 380 fs of photoexcitation. Electronic structure calculations at the level of state-averaged CASSCF (ne,mo)/XMCQDPT2 support the existence of the multi-excitonic T-T pair state, thereby confirming the first example of singlet exciton fission in a NDI scaffold.

Parallel triplet formation pathways in a singlet fission material.

Harvesting long-lived free triplets in high yields by utilizing organic singlet fission materials can be the cornerstone for increasing photovoltaic efficiencies potentially. However, except for polyacenes, which are the most studied systems in the singlet fission field, spin-entangled correlated triplet pairs and free triplets born through singlet fission are relatively poorly characterized. By utilizing transient absorption and photoluminescence spectroscopy in supramolecular aggregate thin films consisting of Hamilton-receptor-substituted diketopyrrolopyrrole derivatives, we show that photoexcitation gives rise to the formation of spin-0 correlated triplet pair 1(TT) from the lower Frenkel exciton state. The existence of 1(TT) is proved through faint Herzberg-Teller emission that is enabled by vibronic coupling and correlated with an artifact-free triplet-state photoinduced absorption in the near-infrared. Surprisingly, transient electron paramagnetic resonance reveals that long-lived triplets are produced through classical intersystem crossing instead of 1(TT) dissociation, with the two pathways in competition. Moreover, comparison of the triplet-formation dynamics in J-like and H-like thin films with the same energetics reveals that spin-orbit coupling mediated intersystem crossing persists in both. However, 1(TT) only forms in the J-like film, pinpointing the huge impact of intermolecular coupling geometry on singlet fission dynamics.

Visible-Light-Driven Photocatalytic CO2 Reduction to CO/CH4 Using a Metal-Organic "Soft" Coordination Polymer Gel.

The self-assembly of a well-defined and astutely designed, low-molecular weight gelator (LMWG) based linker with a suitable metal ion is a promising method for preparing photocatalytically active coordination polymer gels. Here, we report the design, synthesis, and gelation behaviour of a tetrapodal LMWG based on a porphyrin core connected to four terpyridine units (TPY-POR) through amide linkages. The self-assembly of TPY-POR LMWG with RuII ions results in a Ru-TPY-POR coordination polymer gel (CPG), with a nanoscroll morphology. Ru-TPY-POR CPG exhibits efficient CO2 photoreduction to CO (3.5 mmol g-1 h-1 ) with >99 % selectivity in the presence of triethylamine (TEA) as a sacrificial electron donor. Interestingly, in the presence of 1-benzyl-1,4-dihydronicotinamide (BNAH) with TEA as the sacrificial electron donor, the 8e- /8H+ photoreduction of CO2 to CH4 is realized with >95 % selectivity (6.7 mmol g-1 h-1 ). In CPG, porphyrin acts as a photosensitizer and covalently attached [Ru(TPY)2 ]2+ acts as a catalytic center as demonstrated by femtosecond transient absorption (TA) spectroscopy. Further, combining information from the in situ DRIFT spectroscopy and DFT calculation, a possible reaction mechanism for CO2 reduction to CO and CH4 was outlined.

Photogeneration of Long-Lived Triplet States through Singlet Fission in Lycopene H-Aggregates.

Molecular triplet excitons produced through singlet fission (SF) usually have shorter triplet lifetimes due to exciton-exciton recombination and relaxation pathways, thereby resulting in complex device architectures for SF-boosted solar cells. Using broadband transient absorption spectroscopy, we here show that the photoexcitation of nanostructured lycopene H-aggregates at room temperature produces free triplets with an unprecedented 35-fold enhancement in the lifetime compared to those localized on the monomer backbone. The observed rise of a spectrally blue-shifted correlated T-T pair state in ∼19 ps with distinct vibronic features provides the basis for SF-induced triplet generation.

Reactional state in lepromatous leprosy simulating Sweet's syndrome.

Erythema nodosum leprosum (ENL) or Type-2 lepra reaction is a manifestation of type-III hypersensitivity response, and usually occurs in certain cases of lepromatous and borderline lepromatous leprosy. ENL may present as widespread crops of erythematous, inflamed nodules and papules. Rare variants of ENL mimicking pemphigus or Sweet's syndrome (SS) have been documented. Here, we report an unusual case of persistent ENL in a 52-year-old lady, which we could diagnose with the help of skin biopsy and histopathological examination.

Acute acalculus cholecystitis in dengue fever.

Atypical manifestations of dengue fever (DF) and dengue haemorrhagic fever (DHF) involving different organs are being increasingly recognised, especially in the dengue endemic areas. We report an atypical presentation of DF in a 22 year old lady presenting with fever and acute pain in the right hypochondrium, diagnosed to be acute acalculus cholecystitis (AAC).

Atypical central nervous system involvement in acute organophosphorous poisoning.

Extrapyramidal syndrome is an uncommon sequelae of acute organophosphorous (OP) poisoning. It is a manifestation of the intermediate syndrome described in OP poisoning. It may or may not be associated with neuroimaging changes in the striatum. We present a case of acute OP poisoning with interesting positive CT scan findings.

Blue rubber bleb nevus syndrome causing refractory anaemia.

Blue Rubber Bleb Nevus Syndrome (BRBNS) is a rare angiomatosis characterized by distinctive cutaneous and gastrointestinal venous malformations that result in gastrointestinal haemorrhage and iron-deficiency anaemia secondary to the bleeding episodes. We hope to emphasize the possibility of recurrent melaena in BRBNS and heighten physicians' awareness about the disease to contribute to its early detection.

Dyslipidaemia in rheumatoid arthritis in a tertiary care centre in Eastern India--a non-randomised trial.

Dyslipidaemia in rheumatoid arthritis, is associated with accelerated atherosclerosis. A nonrandomised trial was conducted to find out the proportion of rheumatoid arthritis patients suffering from dyslipidaemia and change in lipid levels after an intervention with antirheumatic drugs in a tertiary care centre in Eastern India from April 2006 to July 2008. The trial was done on 161 diagnosed patients of rheumatoid arthritis (fulfilling the American College of Rheumatology criteria) on lipid levels. Lipids estimations were done enzymatically by semi-autoanalyser and dyslipidaemia was defined by taking the cut-off value of National Cholesterol Education Programme-Adult Treatment Panel III (NCEP-ATP III) guidelines. Patients with other comorbid illness and on statins were excluded. Disease activity score 28 (DAS-28) was also employed for evaluating disease activity. Patients were followed up to 10 -12 weeks for repeat lipid level estimation. Using the high cut-off values of NCEP-ATP III, 39.1% of the patients showed dyslipidaemia in initial visit. Low high density lipoprotein cholesterol (HDL-C) was the commonest abnormality seen in 37.2%. In the follow-up study after getting disease modifying antirheumatic drugs (methotrexate, sulfasalazine, hydroxychloroquine) therapy, 19.9% patients had dyslipidaemia again and there were increase in total cholesterol, low density lipoprotein cholesterol, HDL-C but triglyceride was reduced. Low HDL-C again became the commonest (17.9%) and rise in HDL-C level was statistically significant. DAS-28 showed a good reduction and significant negative correlation with HDL-C. Lipid abnormalities, common in Indian patients with rheumatoid arthritis, are also observed in Eastern India. Low HDL-C being the commonest abnormality. Disease activity in rheumatoid arthritis is inversely related to the lipid levels.

Drug-resistant salmonellosis.

After the development of plasmid-mediated resistance against first-line drugs, the emergence of chromosomally-mediated quinolone resistance in typhoid fever has become a major concern. Quinolone insensitivity and treatment failures with ciprofloxacin are being increasingly reported. However, third generation cephalosporins have come as a saviour. To overcome fluoroquinolone insensitivity, higher doses with longer duration of treatment is recommended. Moreover, return of chloramphenicol and furazolidone sensitivity shown by different studies is a welcome observation.