Bioinspired Diiron Complex with Proton Shuttling and Redox-Active Ligand for Electrocatalytic Hydrogen Evolution.

A µ-oxo diiron complex, featuring the pyridine-2,6-dicarboxamide-based thiazoline-derived redox-active ligand, H2L (H2L = N2,N6-bis(4,5-dihydrothiazol-2-yl)pyridine-2,6-dicarboxamide), was synthesized and thoroughly characterized. [FeIII-(µ-O)-FeIII] showed electrocatalytic hydrogen evolution reaction activity in the presence of different organic acids of varying pKa values in dimethylformamide. Through electrochemical analysis, we found that [FeIII-(µ-O)-FeIII] is a precatalyst that undergoes concerted two-electron reduction to generate an active catalyst. Fourier transform infrared spectrum of reduced species and density functional theory (DFT) investigation indicate that the active catalyst contains a bridged hydroxo unit which serves as a local proton source for the Fe(III) hydride intermediate to release H2. We propose that in this active catalyst, the thiazolinium moiety acts as a proton-transferring group. Additionally, under sufficiently strong acidic conditions, bridged oxygen gets protonated before two-electron reduction. In the presence of exogenous acids of varying strengths, it displays electro-assisted catalytic response at a distinct applied potential. Stepwise electron-transfer and protonation reactions on the metal center and the ligand were studied through DFT to understand the thermodynamically favorable pathways. An ECEC or EECC mechanism is proposed depending on the acid strength and applied potential.

Implications of the Pore Size of Graphitic Carbon Nitride Monolayers on the Selectivity of Dual-Boron Atom Catalysts for the Reduction of N2 to Urea and Ammonia: A Computational Investigation.

The formation of urea by electrocatalytic means remains a great challenge due to the lack of a suitable catalyst that is capable of not only activating inert N2 and CO2 molecules but also circumventing the complexity associated with subsequent reaction steps leading to urea formation. Herein, by means of comprehensive density functional theory simulations, we investigate the catalytic activity of highly stable transition-metal-free dual-boron atom-doped graphitic carbon-nitride monolayers with different pore sizes toward urea production under ambient conditions. As per the results, dual boron atoms impregnated in g-C2N and g-C6N6 monolayers with large pore diameters can successfully activate the N2 molecule and lead to the spontaneous formation of the *NCO*N intermediate, which is the most crucial step for urea formation via direct coupling of N2 and CO2. Interestingly, the B2@g-C2N and B2@g-C6N6 favor urea production with low limiting potentials of -1.11 and -1.18 V compared to very high limiting potentials of -1.71 and -1.88 V, respectively, for ammonia synthesis, leading to an almost 100% Faradaic efficiency for urea formation over ammonia. The dual-boron doping in g-C3N4 with a smaller pore size depicts comparatively weaker N2 adsorption than g-C2N and g-C6N6 counterparts. Further, B2@g-C3N4 prefers ammonia formation at a very low limiting potential of -0.40 V compared to a very high limiting potential of -2.11 V for urea formation. Thus, our findings clearly highlight the critical role played by the pore size of carbon-nitride monolayers in tuning the reactivity and catalytic activity of dual-boron atom catalysts toward urea formation in a selective manner, thereby providing valuable guidance in exploring other highly efficient urea catalysts.

Optimizing the NRR activity of single and double boron atom catalysts using a suitable support: a first principles investigation.

Designing cost effective transition-metal free electrocatalysts for nitrogen fixation under ambient conditions is highly appealing from an industrial point of view. Using density functional theory calculations in combination with the computational hydrogen electrode model, we investigate the N2 activation and reduction activity of ten different model catalysts obtained by supporting single and double boron atoms on five different substrates (viz. GaN, graphene, graphyne, MoS2 and g-C3N4). Our results demonstrate that the single/double boron atom catalysts bind favourably on these substrates, leading to a considerable change in the electronic structure of these materials. The N2 binding and activation results reveal that the substrate plays an important role by promoting the charge transfer from the single/double boron atom catalysts to the antibonding orbitals of *N2 to form strong B-N bonds and subsequently activate the inert NN bond. Double boron atom catalysts supported on graphene, MoS2 and g-C3N4 reveal very high binding energies of -2.38, -2.11 and -1.71 eV respectively, whereas single boron atom catalysts supported on graphene and g-C3N4 monolayers bind N2 with very high binding energies of -1.45 and -2.38 eV, respectively. The N2 binding on these catalysts is further explained by means of orbital projected density of states plots which reflect greater overlap between the N2 and B states for the catalysts, which bind N2 strongly. The simulated reaction pathways reveal that the single and double boron atom catalysts supported on g-C3N4 exhibit excellent catalytic activity with very low limiting potentials of -0.67 and -0.36 V, respectively, while simultaneously suppressing the HER. Thus, the current work provides important insights to advance the design of transition-metal free catalysts for electrochemical nitrogen fixation from an electronic structure point of view.

Probing the Site-Specific Reactivity and Catalytic Activity of Ag n (n = 15-20) Silver Clusters.

Density functional theory calculations within the framework of generalized gradient approximation (GGA), meta-GGA, and local functionals were carried out to investigate the reactivity and catalytic activity of Ag n (n = 15-20) clusters. Our results reveal that all the Ag n clusters in this size range, except Ag20, adsorb O2 preferably in the bridged mode with enhanced binding energy as compared to the atop mode. The O2 binding energies range from 0.77 to 0.29 in the bridged mode and from 0.36 to 0.15 eV in the atop mode of O2 adsorption. The strong binding in the case of the bridged mode of O2 adsorption is also reflected in the increase in O-O bond distance. Natural bond orbital charge analysis and vibrational frequency calculations reveal that enhanced charge transfer occurs to the O2 molecule and there is significant red shift in the stretching frequency of O-O bond in the case of the bridged mode of O2 adsorption on the clusters, thereby confirming the above results. Moreover, the simulated CO oxidation reaction pathways show that the oxidation of the CO molecule is highly facile on Ag16 and Ag18 clusters involving small kinetic barriers and higher heats toward CO2 formation.

Role of magnetization on catalytic pathways of non-oxidative methane activation on neutral iron carbide clusters.

Methane has emerged as a promising fuel due to its abundance and clean combustion properties. It is also a raw material for various value-added chemicals. However, the conversion of methane to other chemicals such as olefins, aromatics, and hydrocarbons is a difficult task. In recent years, ionic iron carbide clusters have been explored as potential catalysts for efficient direct methane conversion. Herein, we have investigated the gas-phase methane conversion process on various neutral iron carbide clusters with different Fe:C ratios using density functional theory. Reaction pathways were studied on mononuclear and trinuclear iron carbide clusters in the three lowest energy spin multiplicity channels. Three descriptors - methane binding energy, the effective energy barrier for C-H bond activation, and the effective energy required for methyl radical evolution - were chosen to identify the best catalyst among the clusters considered. Isomers of Fe3C6 (Fe3C6-iso) and Fe3C9 (Fe3C9-iso) are recognized as being the most promising catalysts among all the clusters considered here because they require the least methyl radical evolution energy, a step that is crucial in methane conversion to higher hydrocarbon but also requires the most energy.

Comparison of percutaneous nephrolithotomy under epidural anesthesia versus general anesthesia: A randomized prospective study.

INTRODUCTION: PCNL has revolutionized the treatment of renal calculi putting almost an end to the era of open stone surgery. The procedure can safely be carried out under general anesthesia (GA) or regional anesthesia viz. spinal anesthesia (SA), epidural anesthesia (EA) or combined spinal and epidural anesthesia (CSE). AIMS AND OBJECTIVES: We evaluated the surgical outcome after PCNL in two groups of patients randomly divided to undergo procedure under GA or EA. PATIENTS AND METHODS: Two hundred and thirty patients with American Society of Anesthesiologists (ASA) score <3 were randomly divided into two groups according to the type of anesthesia: i.e. GA (n=110) or EA (n=120). All patients underwent PCNL in prone position. Puncture was done using Bulls eye technique under fluoroscopic guidance and tract dilated using serial dilators up to 24Fr-28 Fr. Demographics, perioperative and postoperative parameters were noted and data analysed. RESULTS: The two groups were comparable in terms of mean age, distribution of stone location, and stone burden. The stone free rate was 90.9% in GA group and 89.2% in EA group and the difference was statistically insignificant (P= 0.659). The requirement for auxiliary procedures was similar between the two groups. A significant difference in pain score was seen in favor of EA group during early post-operative period (P< 0.05). CONCLUSION: It seems that PCNL can be performed safely and effectively under regional epidural anesthesia with results comparable to general anesthesia with the added advantage of less immediate postoperative pain and analgesic requirement.

Surface functionalization: an efficient alternative for promoting the catalytic activity of closed shell gold clusters.

Surface functionalization through adsorption of ligands or non-metal atoms is considered to be an interesting and viable approach for tuning the physicochemical properties of gold clusters. Highly stable and magic numbered electronic configurations of thiolate protected gold clusters such as Au25(SR)18, Au38(SR)24etc. with intriguing properties are the direct manifestation of the rich chemistry of the Au-S interface. The present investigation discerns the CO oxidation activity of structurally well characterized sulphur functionalized gold cluster anions AumS4-, m = 6-10. To establish an in-depth understanding, their activities are analyzed and compared with the corresponding pristine gold clusters. It is seen that sulphur functionalization irrespective of a closed or open shell nature leads to a significant decrease in the O2 adsorption energies on the anionic gold clusters. However, in sharp contrast to O2 adsorption, surface functionalization gives rise to multifarious catalytic behavior in AumS4- clusters with catalytic activity ranging from low (for Au6S4-, Au8S4-) to moderate (for Au9S4-, Au10S4-) to very high (for Au7S4-) for CO oxidation. It is interesting to note that the closed shell Au7S4- and Au9S4- clusters with poor O2 adsorption show remarkably low activation barriers and enhanced catalytic activity as compared to the open shell AumS4- clusters with an odd number of electrons. In particular, in the case of Au7S4- the lowest activation energy barriers of 0.01 and 0.21 eV are obtained, making the CO oxidation reaction facile. Moreover, ab initio molecular dynamics are performed to confirm the enhanced catalytic behaviour of Au7S4- and its dynamical stability during the desorption of CO2 molecule from its surface.

Molecular and Dissociative Adsorption of Oxygen on Au-Pd Bimetallic Clusters: Role of Composition and Spin State of the Cluster.

Utilization of molecular oxygen as an oxidizing agent in industrially important reactions is the ultimate goal to design environmentally benign processes under ambient conditions. However, the high thermal stability and a large O-O dissociation barrier in O2 molecule pose a great challenge toward its successful application in the oxidative chemistry. To achieve this goal, different catalysts based on monometallic and bimetallic clusters have been developed over the years to promote binding and dissociation of molecular oxygen. The successful design of efficient metal cluster catalysis needs an in-depth knowledge of synergistic effects between different metal atoms and intrinsic catalytic mechanisms for O2 adsorption and dissociation. Here, we present a systematic theoretical investigation of reaction pathways for O2 adsorption and dissociation on Au8, Pd8, and Au8-n Pd n (n = 1-7) nanoclusters in different spin states. The density functional calculations point out that the O2 dissociation barriers can be significantly reduced with the help of certain bimetallic clusters along specific spin channels. Our results particularly indicate that Au5Pd3 and Au1Pd7 show very large O2 binding energies of 1.76 and 1.69 eV, respectively. The enhanced O2 binding subsequently leads to low activation barriers of 0.98 and 1.19 eV along the doublet and quartet spin channels, respectively, without the involvement of any spin flip-over for O2 dissociation. Furthermore, the computed O2 dissociation barriers are significantly low as compared to the already reported barriers (1.95-3.65 eV) on monometallic and bimetallic Au-Ag clusters. The results provide key mechanistic insights into the interaction and dissociation of molecular oxygen with Au-Pd clusters, which can prove informative for the design of efficient catalysts for oxidative chemistry involving molecular oxygen as a reactant.

Coloplasty Neorectum versus Straight Anastomosis in Low Rectal Cancers.

Introduction. Patients with the diagnosis of carcinoma rectum after random allocation were assigned to 2 groups. One group was subjected to total mesorectal excision with coloplasty neorectum reconstruction and another group to total mesorectal excision with straight anastomosis. This randomization was done by odds and even method by the sister in charge of the ward to avoid bias in randomization. The study included 42 patients with diagnosis of carcinoma rectum from 4 to 12 centimeters from anal verge. Composite incontinence score, bladder function, and sexual function were considered as the main outcome measures. Results. All patients of transverse coloplasty group had mild or moderate composite incontinence score while 7 (36.8%) patients of straight anastomosis group had a severe score at 7th POD (P < 0.05). At 6 months, 100% patients in transverse coloplasty group had a nil score which was not achieved by any of the patients in the other group. An intragroup comparison showed an improvement in score with time in both groups more marked in transverse coloplasty group. Conclusion. Transverse coloplasty group showed a better QOL so far as anal incontinence is considered. However, no statistically significant difference was achieved when comparing bladder and sexual dysfunction between the two groups.

Cyclin D1 G870A polymorphism and risk of colorectal cancer: a case control study.

The present study aimed to analyse the role of cyclin D1 A870G polymorphism in modulating the susceptibility to colorectal cancer (CRC) in the Kashmiri population. The genotype distribution of the cyclin D1 gene in 130 CRC cases in comparison with 160 healthy controls was investigated. No direct significant association between cyclin D1 genotypes and CRC was observed; however, the AG and AA genotypes were found to be associated with an increased risk of CRC compared to the GG genotype, with an almost 2-fold increase in OR. This study suggests that the cyclin D1 polymorphism is associated with an increased risk of CRC in the Kashmiri population.

Biliary ascariasis as a cause of post-cholecystectomy syndrome in an endemic area.

BACKGROUND: Post-cholecystectomy syndrome encompasses numerous biliary, pancreatic and other entities. Biliary ascariasis is a common cause of adult biliary disease in an endemic area. Post-cholecystectomy biliary ascariasis, a cause of post- cholecystectomy syndrome although not yet defined is frequently seen in this part of the world. METHOD: Between Jan. 1990 and Jan. 2001, 104 cases of post-cholecystectomy biliary ascariasis were seen. Ultrasonography was found to be an excellent tool for diagnosing and monitoring of the worms inside the biliary tract. Endoscopic retrograde cholangiopancreatography had both diagnostic and therapeutic value. RESULTS: The majority (68.2%) of patients responded to conservative treatment. Surgical treatment was advocated in 18.2%, which included 2 patients with liver abscesses. Endoscopic extraction of worms was successful in 48.2%. CONCLUSION: Post-cholecystectomy biliary ascariasis as a cause of post-cholecystectomy syndrome needs to be included in the list of causes for post-cholecystectomy syndrome. Although the majority of patients respond to conservative treatment but endoscopic extraction or surgical intervention may be needed. Routine deworming of patients undergoing cholecystectomy both preoperatively and postoperatively should be done in all patients in endemic areas of ascariasis. Although this entity is rare in Europe and United States, due to population migration and increased travel, it is necessary for surgeons in these countries to be aware of this condition.

Surgical management of splenic hydatidosis.

PURPOSE: This study was conducted to evaluate the surgical management of splenic hydatidosis in an area where the disease is endemic. METHOD: Over a period of 16 years, 26 patients with splenic hydatidosis underwent surgery in our department. Preoperative investigations included plain abdominal X-ray, serology, ultrasonography, and computed tomography. RESULTS: In our series, splenic hydatidosis represented 3.5% of total abdominal hydatidosis. The majority of patients presented with abdominal discomfort and palpable swelling in the left hypochondrium. Twenty-two patients were operated on electively and 4 as emergency cases, including 2 with ruptured hydatids and 2 with infected hydatids of the spleen. Isolated splenic hydatid cysts were present in 21 patients, associated liver hydatid cysts in 4, and diffuse abdominal hydatidosis in 1 patient. All patients underwent splenectomy except for one patient who initially had partial splenectomy for a lower polar cyst. This patient also ended up undergoing a splenectomy for postoperative hemorrhage. One patient died on the sixth postoperative day (mortality rate 3.8%) as a result of multiorgan failure, and 4 developed minor complications (morbidity 15.4%). CONCLUSION: Splenic hydatidosis, although rare, is the third most common type of hydatidosis after liver and lung hydatidosis. This entity should thus be kept in mind when encountering a splenic cyst especially in areas where the disease is endemic. A splenectomy remains the treatment of choice because it demonstrates low morbidity and mortality rates.

Ascariasis-induced empyema of gallbladder: report of a case.

A rare case of a 52-year-old woman with empyema of the gallbladder due to ascariasis causing an obstruction in the cystic duct is presented. She was admitted on September 20, 2000, and on September 23 an emergency cholecystectomy was performed. Ultrasonography is a highly sensitive and specific method for diagnosing gallbladder ascariasis, and a cholecystectomy is considered mandatory for the treatment of empyema of the gallbladder.