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      Volume 129, Issue 8

      August 2017,   pages  1092a-1325

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    • Cationic and neutral copper(I) iodide cluster MOFs derived from tridentate N-donor functionalized P(V) ligands: synthesis, structure and photophysical properties

      ASHOK YADAV MAHESH S DESHMUKH RAMAMOORTHY BOOMISHANKAR

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      Formation of cationic and neutral CuI cluster MOFs have been reported starting from tridentate phosphoramide ligands, [(NHR) ₃P = E] (L¹: R = 3-aminoquinolinyl (AQ), E = S; L²: R = 3-pyridyl (PY), E = S; L³: R = 3-aminoquinolinyl (AQ), E = O). By utilizing L¹, a cationic 2D-MOF {[(L¹) ₂ (Cu₆I₅)](OH) · 3DMF·4MeOH}n, 1 containing a rugby ball shaped discrete Cu₆I₅ cluster has been reported earlier. Formation of a new 3D-MOF {[(L²) ₂ (Cu₆I₄)](OH) ₂· 2DMF}n containing a Zintl type [(Cu₆I₄4) ² ⁺]n cluster chains is reported in this paper. A neutral cluster MOFs 3 with formula unit of {[Cu₄I₄L³ (CH₃CN)] · 2DMF · 3H₂O}n has been prepared from the ligand L³. Formation of the smaller Cu₄I₄ clusters in the MOF 3 is due to the presence of a MeCN ligation at one of the Cu(I) atoms which not only precludes the extension of the assembly in three dimension but also reduces the size of the obtained cluster. Unlike 1 which showed a ligand-assisted thermochromism, photophysical studies on the 3D-MOF 2 exhibited green phosphorescence at both 298 K and 77 K. The occurrence of the phosphorescence at 77 K in 2 is due to triplet cluster centered (³CC) excited state of the cluster as there is no ligand-centered transition observed at 298 K. The 2D-MOF 3 does not show any characteristic luminescence behavior as the presence of the acetonitrile coordination at one of the Cu(I) ion is believed to quench the emission by non-radiative pathways. Further, luminescence quenching experiments on 1 and 2 with aromatic nitro-analytes showed a very high sensing selectivity for picric acid (TNP) over other aromatic nitro-analytes.

    • N-(acyl)-N'-(ferrocenylidene)hydrazines and their nickel(II) complexes: Syntheses, structures and physical properties

      G NARENDRA BABU SAMUDRANIL PAL

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      The Schiff bases N-(acyl)-N’-(ferrocenylidene)hydrazines (HFcah (1) and HFcbh (2), where acyl = acetyl in 1 and benzoyl in 2 and H represents the dissociable amide proton) were synthesized in high yields (74 and 81%) by condensation reactions of equimolar amounts of ferrocene-carboxaldehyde and the corresponding acylhydrazines in presence of acetic acid in refluxing methanol.Reactions of Ni(OAc) ₂·4H ₂O, the Schiff bases (1 and 2) and NaOAc ·3H ₂O in 1:2:4 mole ratio in refluxing methanol afforded the diamagnetic iron(II)-nickel(II)- iron(II) species [Ni(Fcah) ₂] (3) and [Ni(Fcbh) ₂] (4) in 60 and 68% yields, respectively. Both Schiff bases and the two trinuclear complexes were characterized by elemental (CHN) analysis, mass spectrometric, various spectroscopic (IR, UV-Vis and 1H NMR) and cyclic voltammetric measurements. Molecular structures of 2, 3and 4 were determined by single crystal X-ray diffraction studies. The cyclopentadienide rings in the ferrocene moieties are essentially in eclipsed conformation in all three structures. Deprotonated Schiff base ligands in each complex (Fcah in 3 and Fcbh in 4) act as five-membered chelate ring forming azomethine-N and amidate-O donors and assemble a square-planar trans-N ₂O ₂ coordination environment around the nickel centre. The redox active 1–4 exhibit an iron centred redox couple in the potential range 0.23–0.50 V (vs. Ag/AgCl).

    • Palladium(II) and copper(I) complexes of wide angle bisphosphine, 1,4-bis((diphenylphosphino)methyl)benzene

      SAURABH KUMAR MARAVANJI S BALAKRISHNA

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      Oxidation reactions and synthesis of copper(I) and palladium(II) complexes of 1,4-bis ((diphenylphosphino) methyl)benzene (1) have been described. Due to the larger separation of phosphorus atoms, bisphosphine exhibits only bridging mode of coordination. The ligand is also ideally suited to form binuclear complexes and 1-D coordination polymers. Reaction of 1 with [Pd(η³−allyl)Cl] ₂ results in dipalladium(II) complex [{Pd(η³−allyl)Cl}₂{μ−Ph₂PCH₂C₆H₄CH₂PPh₂}] (4), whereas with copper halides, dimeric complexes of the type [{CuX}{μ−Ph₂PCH₂C₆H₄CH₂PPh₂}] ₂ (5 X = Cl, 6 X = Br and 7 X = I) were isolated. All the compounds have been fully characterized by spectroscopic and analytical methods. The molecular structures of bisulfide (3), Pd(II) and Cu(I) complexes were confirmed by single crystal X-ray analyses.

    • ‘Ionic crystals’ consisting of trinuclear macrocations and polyoxometalate anions exhibiting single crystal to single crystal transformation: breathing of crystals

      T ARUMUGANATHAN ASHA SIDDIKHA SAMAR K DAS

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      Ion pairing of trinuclear macrocation cluster (known as basic carboxylate), [M ₃ (μ ₃-O) (ClCH ₂COO) ₆ (H ₂O) ₃] ¹⁺ and a Keggin type polyoxometalate cluster anion [SiW ₁₂O₄₀] ⁴⁻ is stabilized with a number of crystal water molecules in composite type compounds [M ₃ (μ ₃-O)(ClCH ₂COO) ₆ (H ₂O) ₃] ₄[SiW ₁₂O₄₀] ·xH ₂O · 2ClCH ₂COOH [M = Fe ³⁺, x = 18(1); M = Cr ³⁺x = 14(2)]. When the crystals of 1 are heated at 85◦C and 135◦C for 3.5 hours in an open atmospheric condition, it goes to [Fe ₃ (μ ₃-O)(ClCH ₂COO) ₆ (H ₂O) ₃] ₄ [SiW ₁₂O₄₀] ·10H ₂O ·2ClCH ₂COOH (dehydrated 1-85o ≡ 1'), and [Fe ₃ (μ ₃-O) (ClCH ₂COO) ₆ (H ₂O) ₃] ₄ [SiW ₁₂O₄₀] · 8H ₂O · 2ClCH ₂COOH (dehydrated 1-135o ≡ 1'') respectively with the loss of considerable amount of lattice water molecules retaining their single crystallinity. On the other hand, the single crystals of compound 2, upon heating at 85◦C or 135◦C for 3.5 hours, undergo ‘crystal-to-crystal transformation’ to the single crystals of [Cr ₃ (μ ₃-O)(ClCH ₂COO) ₆ (H ₂O) ₃] ₄ [SiW₁₂O₄₀]·8H₂O·2ClCH ₂COOH (dehydrated 2 ≡ 2'). Crystal structure analyses show that the parent compounds 1 and 2 undergo molecular rearrangement (molecular motion in the solid state) in respective dehydrated compounds. Remarkably, these dehydrated crystals (1', 1'' and 2'), upon exposure to water vapor at an ambient condition, regenerate the crystals of parent compounds 1 and 2, respectively

    • Synthesis of meta-substituted monodentate phosphinite ligands and implication in hydroformylation

      SATEJ S DESHMUKH SHAHAJI R GAIKWAD SWECHCHHA PANDEY PRAMOD S MALI SAMIR H CHIKKALI

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      Synthesis of meta-substituted phosphinite ligands 3,3' (methoxyphosphanediyl) bis (N,Ndiethylaniline) (4a) and methoxybis(3-methoxyphenyl)phosphane (4b), in high yields, has been demonstrated. Typical phosphorus chemical shift between 110–120 ppm, appearance of methoxy protons and corresponding carbon, as well as ESI-MS spectra unambiguously confirmed the existence of phosphinite ligands 4a and 4b. To demonstrate the synthetic usefulness of 4a and 4b, these ligands were tested in the rhodium catalyzed hydroformylation of 1-octene. The diethylamine substituted ligand 4a was found to be highly active, whereas4bwas less reactive but revealed slightly better regioselectivity of 62% under optimized conditions.Additionally, 4a and 4b were found to catalyze the hydroformylation of styrene, 1-undecenol and 1,1-disubstituted functionalolefin, methyl methacrylate. Both the ligands displayed excellent conversion of styrene, and 4b revealed an excellent branch selectivity of 75%. Although 1-undecenol proved to be amenable to hydroformylation (85–90% conversion to aldehyde), both the ligands failed to discriminate between the linear and branched products. Substrate methyl methacrylate proved to be highly challenging and reduced conversion (between 33–42%) was observed under optimized conditions. Ligand 4a was found to be highly selective towards linear aldehyde (81% linear selectivity).

    • Nickel-catalyzed direct synthesis of dialkoxymethane ethers

      MURUGAN SUBARAMANIAN ABHIJIT BERA BHAGAVATULA L V PRASAD EKAMBARAM BALARAMAN

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      A simple and efficient method for the preparation of dialkoxymethane ethers (oxymethylene ethers) from alcohols and paraformaldehyde in the presence of commercially available nickel(II) salt is described. The reaction proceeds readily under neutral, solvent-free conditions using paraformaldehyde as a C1 source. The present strategy has a broad substrate scope including aliphatic (both primary and secondary) and aromatic alcohols and provides a benign method for the preparation of symmetrical dialkoxymethanes in good yields (up to 89%).

    • Synthesis and characterization of six-membered pincer nickelacycles and application in alkylation of benzothiazole

      HANUMANPRASAD PANDIRI DIPESH M SHARMA RAJESH G GONNADE BENUDHAR PUNJI

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      Six-membered pincer nickelacycle complexes have been synthesized and employed for the catalytic C–H bond alkylation of benzothiazole. The pincer nickelacycle, {κP, κC, κP-(2-i Pr₂ POCH₂ C₆H₃-6-CH₂OPi Pr₂)}NiBr, [(i Pr₄-POCCCOP)NiBr (2)] was synthesized by the reaction of 1,3-i Pr₂POCH₂-C₆H₄-CH₂OPi Pr₂ [(i Pr₄-POCCCOP)−H (1)] with (CH₃CN) ₂NiBr₂ in the presence of Et₃N via the C(2)–H activation on ligand 1. Treatment of [(i Pr₄-POCCCOP)NiBr] (2) with AgOAc afforded the complex [(i Pr₄-POCCCOP)Ni(OAc)] (3) in good yield. Both the complexes 2 and 3 were characterized by ¹H,¹³C and ³¹P-NMR spectral analysis. Further, the molecular structures of complexes 2 and 3 were established by X-ray crystallography. The complex 2 was found to be an active catalyst for the C–H bond alkylation of benzothiazole with alkyl halides containing β–hydrogen atoms.

    • Carboxylate-bridged Cu(II) coordination polymeric complex: synthesis, crystal structure, magnetic properties, DNA binding and electrochemical studies

      SABITHAKALA THATITURI BHARGAVI GOVINDUGARI VENKATA RAMANA REDDY CHITTIREDDY

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      A novel water-soluble carboxylate-bridged copper(II) coordination polymer,Cu-BIG was formed by the reaction of Cu(ClO₄)₂ ·6H₂O and tridentate benzimidazole-glycine conjugate ligand, 2-((1H-benzimidazol- 2-yl)methylamino) acetic acid, BIGH and its structure has been determined by IR, UV, powder XRD, VSM, CV, TGA, DTA, EPR and single crystal X-ray diffraction. Crystallographic studies indicate it to be a coordination polymer with P¯ı Space group. The asymmetric unit of complex contains two Cu(II) ions with elongated square pyramid geometry.The axial positions of theCu(II) atoms are occupied by the carbonyl oxygen of the carboxylate group with the bond distances Cu(1)–O(5)axial , 2.28Å, and Cu(2)–O(2)axial , 2.26Å. The two Cu(II) are connected through the carboxylic group present in BIGH, which provides electron mobilisation in the molecule and hence results in the soft ferromagnetic polymer. An in vitro antibacterial activity study of BIGH and Cu-BIG showed moderate activity against Bacillus subtilis. The DNA binding studies showed the interaction of Cu-BIG with CT-DNA.

    • Three coordination compounds based on benzene tetracarboxylate ligand: syntheses, structures, thermal behaviors and luminescence properties

      YUNLONG WU CHANGKUN XIA JUN QIAN JIMIN XIE

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      Using 1,2,3,5-benzenetetracarboxylic acid and different pyridyl ligands, three metalorganic coordination compounds, [Co(H ₃btec)(1,10-phen)(H ₂O) ₃][OH]·2H ₂O (1), [Co ₂ (btec)(2,2’-bipy) ₂-(H ₂O)]·H ₂O (2), {[Co ₁.₅ (H ₂btec)(4,4’-bipy)(H ₂O) ₂][Co ₀.₅ (4,4’-bipy)- (H ₂O) ₄][OH] ₂} · 2H ₂O (3), (H ₄btec = 1, 2, 3, 5-benzenetetracarboxylic acid, 1,10-phen = 1,10-phenanthroline, 2,2’-bipy = 2,2_-bipyridine, 4,4’-bipy= 4,4_ -bipyridine) were synthesized by hydrothermal method and characterized by elemental analysis, infrared spectroscopy, and single-crystal X-ray diffraction analysis. X-ray crystallographic studies reveal that 1 is a discrete 0D coordination compound, while 2 and 3 possess similar 2D network structures, which show a sql network with the point symbol of (4,4). Thermal analysis indicates that compounds 1 and 2 begin to collapse after 350◦C. Further, the UV-Vis DRS spectra and solid-state luminescent properties of 1–3 have also been studied.

    • Low temperature synthesis of fluorite-type Ce-based oxides of composition Ln₂Ce₂O₇ (Ln = Pr, Nd and Eu): photodegradation and Luminescence studies

      M MALATHI K SREENU GUNDEBOINA RAVI P VIJAYA KUMAR CH SUDHAKAR REDDY RAVINDER GUJE RADHA VELCHURI M VITHAL

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      In this work, we have studied the structural behavior of Fluortie-type (F-type) Ce-based oxides of compositions Ln₂Ce₂O₇ (Ln = Pr, Nd and Eu). F-type oxides can be considered as multi-functional materials due to the deficiency of anions. Pr₂Ce₂O₇ (PCO), Nd₂Ce₂O₇ (NCO) and Eu₂Ce₂O₇ (ECO) were prepared by ethylene glycol-assisted sol–gel method. The structural investigation of these oxides was carried out by Powder XRD and Rietveld refinement. All the materials were found to crystallize in the cubic lattice with space group $Fm\bar{3}m$. Raman spectra of these materials are reliable with their XRD data. The morphology and bandgap energy of all the samples were obtained from SEM and KM plot, respectively. The visible light photocatalytic performance of these oxides was examined against the degradation of methylene blue under ambient conditions. The photoluminescence property of the rare earth ionswas also studied, and the color coordinates were calculated using CIE 1931 chromaticity.

    • An efficient and rapid synthesis of 3-hydroxy-3-alkyl-2-oxindoles via Zn-mediated barbier-type reaction under aqueous conditions

      L RAJU CHOWHAN MARRI SAMEER REDDY NANDIGAMA SATISH KUMAR

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      A robust and rapid synthesis of 3-hydroxy-3-alkyl-2-oxindoles from isatins is described. This method introduces an ecofriendly, un-activated Zn dust, solid NH₄Cl and substrates under aqueous conditions, which has produced the product in moderate to good yields. Without using column chromatography, majority of the compounds were isolated in analytically pure form. The progress of the reaction could be visualized by naked eye.

    • Facile route for the regioselective synthesis of 1,4-disubstituted 1,2,3-triazole using copper nanoparticles supported on nanocellulose as recyclable heterogeneous catalyst

      MITALI CHETIA ABDUL A ALI ANKUR BORDOLOI DIGANTA SARMA

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      In this work, a green and efficient methodology has been developed for the synthesis of 1,2,3-triazoles by ‘copper nanoparticles supported on nanocellulose (CuNPs/NC)-catalyzed azide-alkyne cycloaddition reaction in glycerol, an environmentally benign solvent, with excellent yields. The present catalyst wascharacterized by TEM, XRD, SEM-EDX and FT-IR spectroscopy. The reusability of the prepared nanocatalyst was examined up to five times without significant loss of catalytic activity.

    • A simple and sensitive fluorescent probe for specific detection of cysteine

      YAN-FEI KANG HAI-XIA QIAO YA-LI MENG ZHEN-HUI XIN LI-PING GE JIN-NAN ZHENG YI-NA WANG

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      Afluorescent probe, with simplicity of structure and convenience of synthesis, is capable of detecting cysteine over other biothiols, such as homocysteine and glutathione. The detection limit of 60nM and 190-fold increase in fluorescence intensity offer advantage for detection of Cys in biological systems. Furthermore, the probe 1 could be applied in bioimaging.

    • An efficient catalyst-free synthesis of novel chromeno[4,3-b]quinolones through Michael initiated ring closure (MIRC) reaction with in situ generated 3-(arylmethylene)chroman-2,4-diones

      SUDESH KUMARI JITENDER M KHURANA

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      A catalyst-free multicomponent reaction capable of affording a wide range of eighteen novel chromeno[4,3-b]quinolone derivatives (6a–6r) via one-pot two-step domino protocol, in ethylene glycol is reported. Catalyst-free conditions along with green solvent system make the process eco-friendly as well aseconomical. High yields of the products were obtained in short reaction times by forming three new bonds and one stereocenter in a single operation. The salient features of the present protocol are short reaction times, eco-friendly solvents, high yields and easy work-up procedure.

    • A novel synthesis of chromone based unnatural α-amino acid derivatives

      VENU KANDULA RAMAKRISHNA GUDIPATI ANINDITA CHATTERJEE MURALIDARAN KALIYAPERUMALA SATYANARAYANA YENNAM MANORANJAN BEHERA

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      An efficient method for the preparation of chromone based α-amino acid derivatives by alkylation of glycinate schiff base with 3-bromomethyl chromone as well as 2-bromomethyl chromone has been described. Using this method, 2-amino-3-(4-oxo-2-chromenyl)propanoic acid and 2-amino-3-(4-oxo-3- chromenyl)propanoic acid, two novel chromone-amino acid conjugates have been prepared. Furthermore, the separation of chromone amino acid enantiomers by chiral column chromatography was accomplished.

    • Phthalocyanine and azaphthalocyanines containing eugenol: synthesis, DNA interaction and comparison of lipase inhibition properties

      GÜNAY KAYA KANTAR ÖZLEM FAİZ ONUR ŞAHİN SELAMİ ŞAŞMAZ

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      Novel eugenol-substituted zinc(II) azaphthalocyanines (ZnAzaPcs)were synthesised and their lipase inhibition and DNA binding properties compared with phthalocyanines (Pcs) containing eugenol. This is the first study on lipase inhibition and DNA binding of Pcs and AzaPcs containing a pharmacophore group, such as eugenol. The novel ZnAzaPcs were characterised using a combination of FT-IR, ¹HNMR, ¹³CNMR, UV–Vis, MS and elemental analysis. The crystal structures of two pyrazine compounds were also determined by the single crystal diffraction technique. This study showed that two phthalocyanines compounds (3a and 4a) could be potential lipase inhibitor agents due to greater hydrophobicity than other azaphtalocyanines. Compound 4a displayed lowest IC₅₀ value. Non-intercalative binding to DNA was identified only for compound 2a.

    • Synthesis, characterization and in vitro antibacterial activity of novel phthalazine sulfonamide derivatives

      MARZIEH ABBASI SEYED MOHAMAD REZA NAZIFI ZAHRA SADAT NAZIFI AHMAD REZA MASSAH

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      Several phthalazine derivatives were synthesized by the one-pot three-component condensation in good to high yields in the presence of diatomite-SO3H as a solid acid catalyst. Then, a series (n=14) of phthalazine sulfonamides were synthesized by the reaction phthalazine sulfonyl chloride and various amines under solvent-free conditions. The prepared compounds were screened for antibacterial activity against Escherichia coli (E. coli ATCC 25922) and Staphylococcus aureus (S. aureus ATCC 5213) as gram negative and positive respectively. Also, in silico physicochemical parameters of synthesized compounds were studied to predict absorption and permeability using Molinspiration online property calculation server.

    • Chaotropes trigger conformational rearrangements differently in Concanavalin A

      SHREYASI ASTHANA SUJIT KUMAR BHUTIA HAREKRUSHNA SAHOO SUMAN JHA

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      Concanavalin A (ConA) is a plant lectin having industrial and biological applications. Concanavalin A changes conformation upon exposure to different stress conditions, like exposure to sodium dodecyl sulphate, guanidine hydrochloride, varying hydronium ion potential, etc. The conformational changes were studied using circular dichroism spectroscopy and the structural rigidity of ConA was explored using fluorescence spectroscopy, taking tryptophan as an intrinsic and 8-anilino-1-naphthalenesulfonic acid as an extrinsic fluorescence probes, in different stress conditions. ConA loses the quaternary structure in all the studied stress conditions, which further leads to denaturation of the protein. However, the mechanism of denaturation varied with the studied conditions, like different SDS concentrations and hydronium ion potentials, wherein the proteinundergoes a conformational rearrangement from β-sheet to α-helix. Moreover, GdnHCl triggered complete denaturation of ConA into a predominantly random coil conformation. The results suggested that denaturation of ConA follows different pathways depending on the chemical properties and concentrations of the denaturants used.

    • Theory for electrochemical impedance spectroscopy of heterogeneous electrode with distributed capacitance and charge transfer resistance

      SHWETA DHILLON RAMA KANT

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      Randles-Ershler admittance model is extensively used in the modeling of batteries, fuel cells, sensors etc. It is also used in understanding response of the fundamental systems with coupled processes like charge transfer, diffusion, electric double layer charging and uncompensated solution resistance. Wegeneralize phenomenological theory for the Randles-Ershler admittance at the electrode with double layer capacitance and charge transfer heterogeneity, viz., non-uniform double layer capacitance and charge transfer resistance (c d and R CT). Electrode heterogeneity is modeled through distribution functions of R CT and c d, viz., log-normal distribution function. High frequency region captures influence of electric double layer while intermediate frequency region captures influence from the charge transfer resistance of heterogeneous electrode. A heterogeneous electrode with mean charge transfer resistance $\bar{R CT}$ shows faster charge transfer kinetics over a electrode with uniform charge transfer resistance ($\bar{R CT}$). It is also observed that a heterogeneous electrode having high mean with large variance in the R CT and c d can behave same as an electrode having low mean with small variance in the R CT and c d. The origin of coupling of uncompensated solution resistance (between working and reference electrode) with the charge transfer kinetics is explained. Finally, our model provides a simple route to understand the effect of spatial heterogeneity.

    • Effect of force and location of bottleneck for particle moving through window under encapsulation

      ANIRBAN SHARMA PRADIP KR GHORAI

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      One of the central assumptions to explain appearance of an anomalous diffusion regime in microporous materials is the cancellation of forces experienced by a moving particle at the bottleneck. In this work, we examine this issue of force cancellation inside a microporous material exploring the diffusion path and cross-checking bottleneck associated with diffusion. Conventional wisdom is that window of a microporous material is the bottleneck for diffusion. Our study reveals that bottleneck for diffusion is not at the window, it is always 2.6 Å to 3.0 Å away from the window plane and depending on guest size, it lies in different partsof the inner surface of α-cage. Window has significant effect in diffusion process only when diffusing particle size is comparable or larger than the window free diameter. Window does not play any role if particle size is smaller than window free diameter. We show that in the anomalous diffusion regime there is no signature of force cancellation at the window. Activation energy and total force along the diffusion path are responsible for the existence of anomalous diffusion regime in microporous materials.

    • Solvolysis of organophosphorus pesticide parathion with simple and α nucleophiles: a theoretical study

      CHANDAN SAHU ABHIJIT K DAS

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      Density functional theory (DFT) has been used to study the solvolysis process of the organophosphorus compound, O,O-diethyl p-nitrophenyl thiophosphate (Parathion, PTH) with α-nucleophiles [hydroxylamine anion (NH2O), hydroperoxide (HOO) and simple nucleophile methylthiolate (CH3S) in both gas and aqueous phases. Formation of a trigonal bipyramidal intermediate at the phosphorus center followed by elimination of leaving group is considered to be the major solvolyzed pathway through addition-elimination scheme. In this study, although there are two possible orientations for incoming nucleophiles with respect to the substrate, the present reaction mechanism is found to be independent of this relative orientation. The proposed addition-elimination mechanism has been first explored here. The results indicate that the α-effect is observed in presence of solvent. Free energy barriers for NH2O and HOO are comparable and lower than that for the simple nulcleophile, CH3S. An important physical insight of this study is that there is a significant influence of the reaction medium on the nucleophilic reaction for solvolysis of PTH irrespective of the relative orientation of incoming nucleophile group.

    • Regioselectivity in the hetero-Diels–Alder reactions of styrenes with 2-aza-1,3-butadiene: a DFT study

      SAFA ALI-ASGARI JAFAR IZADI NIA SAMIRA ZALI

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      In this work, regioselectivity was investigated in the hetero-Diels–Alder reactions of styrenes (without substituent and with para-substituted groups)with 2-aza-1,3-butadiene from thermodynamic (Hammett study), electronic (HSAB criterion) and kinetic viewpoints. Furthermore, the effect of the presence of catalyst was inspected by the NBO analysis in addition to kinetic studies. The calculations were performed by the Gaussian 09 program at the B3LYP/6-311++G** level of theory in the gas phase. Thermodynamically, the stability difference between the two regioisomeric products is not significant, especially, in the reactions of styrenes with electron-releasing substituents. Kinetically, the obtained regioselectivity is in favor of formation of 4-regioisomers, especially, in the presence of BF3 catalyst (in agreement with the NBO results). On thebasis of the HSAB criterion, 5-regioisomers have preference, only in the reactions of styrenes with the strong electron-withdrawing substituents.

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