01939nas a2200181 4500008004100000022001400041245010000055210006900155260007100224300001600295490000800311520123300319100001901552700001601571700001701587700002401604856012901628 2015 eng d a1520-610600aHydrogen bond and ligand dissociation dynamics in fluoride sensing of Re(I)-polypyridyl complex0 aHydrogen bond and ligand dissociation dynamics in fluoride sensi a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcNOV a14952-149580 v1193 a

Hydrogen bonding interaction plays an essential role in the early phases of molecular recognition and colorimetric sensing of various anions in aprotic media. In this work, the host-guest interaction between fac-[Re(CO)(3)Cl(L)] with L = 4-([2,2'-bipyridin]-4-yl)phenol and fluoride ions is investigated for the hydrogen bond dynamics and the changing local coordination environment. The stoichiometric studies using H-1 NMR and ESI-MS spectroscopies have shown that proton transfer in the H-bonded phenol-fluoride complex activates the dissociation of the CO ligand in the Re(I) center. The phenol-to-phenolate conversion during formation of HF2- ion induces nucleophilic lability of the CO ligand which is probed by intraligand charge transfer (ILCT) and ligand-to-metal charge transfer (LMCT) transitions in transient absorption spectroscopy. After photoexcitation, phenol-phenoxide conversion rapidly equilibrates in 280 fs time scale and the ensuing excited state [ReII(bpy(center dot-)-phenolate(-))(CO)(3)Cl]* undergoes CO dissociation in the ultrafast time scale of similar to 3 ps. A concerted mechanism of hydrogen cleavage and coordination change is established in anion sensing studies of the rhenium complex.

1 aVerma, Sandeep1 aAute, Sunil1 aDas, Amitava1 aGhosh, Hirendra, N. uhttps://library.ncl.res.in/content/hydrogen-bond-and-ligand-dissociation-dynamics-fluoride-sensing-rei-polypyridyl-complex-101787nas a2200205 4500008004100000022001400041245012000055210006900175260000900244300001600253490000800269520105100277100001901328700002701347700001701374700001601391700003001407700001701437856012701454 2016 eng d a0002-786300aCounteranion driven homochiral assembly of a cationic C-3-symmetric gelator through ion-pair assisted hydrogen bond0 aCounteranion driven homochiral assembly of a cationic C3symmetri cSEP  a11113-111160 v1383 a

The helical handedness in achiral self-assemblies is mostly complex due to spontaneous symmetry breaking or kinetically controlled random assembly formation. Here an attempt has been made to address this issue through chiral anion exchange. A new class of cationic achiral C-3-symmetric gelator devoid of any conventional gelation assisting functional units is found to form both right-and left-handed helical structures. A chiral counteranion exchange-assisted approach is successfully introduced to control the chirality sign and thereby to obtain preferred homochiral assemblies. Formation of anion-assisted chiral assembly was confirmed by circular dichroism (CD) spectroscopy, microscopic images, and crystal structure. The X-ray crystal structure reveals the construction of helical assemblies with opposite handedness for (+)- and (-)-chiral anion reformed gelators. The appropriate counteranion driven ion-pair-assisted hydrogen-bonding interactions are found responsible for the helical bias control in this C-3-symmetric gelator.

1 aMaity, Arunava1 aGangopadhyay, Monalisa1 aBasu, Arghya1 aAute, Sunil1 aBabu, Sukumaran, Santhosh1 aDas, Amitava uhttps://library.ncl.res.in/content/counteranion-driven-homochiral-assembly-cationic-c-3-symmetric-gelator-through-ion-pair01603nas a2200169 4500008004100000245008200041210006900123260000800192300001600200490000800216520102100224100001901245700001601264700001701280700002401297856011201321 2016 eng d00aProton-coupled electron transfer in a hydrogen-bonded charge transfer complex0 aProtoncoupled electron transfer in a hydrogenbonded charge trans cOCT a10780-107850 v1203 aA proton-coupled electron transfer (PCET) reaction in a hydrogen bonded charge-transfer (CT) complex of 4-([2,2'-bipyridin]-4-yl)phenol (bpy-phenol) with a F- ion has been investigated by ultrafast time-resolved transient absorption spectroscopy. The phenolic receptor molecule, bpy-phenol, binds to the F- ion through a hydrogen bond and senses the F- ion-via the Stokes-shifted CT band. Upon photoexcitation, CT from the phenol residue to the bpy residue promotes proton transfer from the phenol radical cation (ArOH center dot+) to the fluoride ion at ultrafast time scales of <150 fs (instrument response function limited) and 3 ps, separately. The fast and slow proton-transfer times are linked to two different types of hydrogen-bonding networks between the phenol residue and fluoride ion. Crystalline water in the fluoride salt hydrates mediates the proton-transfer reaction. This work demonstrates the participation of a hydrogen-bonded water bridge within a PCET reaction in a water restricted environment.1 aVerma, Sandeep1 aAute, Sunil1 aDas, Amitava1 aGhosh, Hirendra, N. uhttps://library.ncl.res.in/content/proton-coupled-electron-transfer-hydrogen-bonded-charge-transfer-complex01821nas a2200157 4500008004100000245015300041210006900194260000800263490000700271520118300278100002401461700001701485700001601502700001801518856012701536 2017 eng d00aDemonstrating the role of anchoring functionality in interfacial electron transfer dynamics in newly synthesized BODIPY-TiO2 nanostructure composite0 aDemonstrating the role of anchoring functionality in interfacial cMAY0 v413 aNew Bodipy derivatives (Dye 1 and 2) having catechol or resorcinol functionality for anchoring to the nanostructured (NS) TiO2 surfaces have been synthesized. Extended conjugation at one of the two pyrrole rings at the C3 position has helped us in achieving the desired control in tuning the optical and redox properties of the BODIPY based dye molecules. Relative emission quantum yields (em1 = ~52 ± 2% and em2 = 54 ± 2%) are found to be much higher in polar aprotic solvent (acetonitrile), while this are found to be substantially lower for dye 1 in polar protic solvent. Steady state optical absorption studies reveal the formation of a strong charge transfer complex between dye 1 and NS-TiO2, while this interaction is much weaker for dye 2. Transient absorption studies have been carried out for 1/NS-TiO2 and 2/NS-TiO2 systems following excitation with a laser source of 400 nm for understanding the charge transfer dynamics. Results of the transient absorption spectral studies helped in elucidating role of anchoring functionality in influencing the dynamics of the interfacial electron transfer and the charge recombination process in ultrafast time scale.1 aGhosh, Hirendra, N.1 aDas, Amitava1 aAute, Sunil1 aMaity, Partha uhttps://library.ncl.res.in/content/demonstrating-role-anchoring-functionality-interfacial-electron-transfer-dynamics-newly02261nas a2200241 4500008004100000245014200041210006900183260000800252300001400260490000700274520140700281100001601688700001601704700001901720700002201739700002401761700002001785700002301805700002001828700002501848700001701873856012901890 2017 eng d00aPhoto-induced cytotoxicity and anti-metastatic activity of ruthenium(II)-polypyridyl complexes functionalized with tyrosine or tryptophan0 aPhotoinduced cytotoxicity and antimetastatic activity of rutheni cMAY a6634-66440 v463 aThe synergistic effect of oxygen, light, and photosensitizer (PS) has found applications in medicine for the treatment of cancer through photodynamic therapy (PDT). Induction of apoptosis to cancerous cells will prevent tumor metastasis that spreads cancer cells to the neighboring organs/tissues. Herein, we report the two apoptotic Ru(II)-polypyridyl complexes that are functionalized with pendant amino acid moieties tyrosine (1) and tryptophan (2), respectively. These two water soluble complexes were found to interact strongly (K-a(1) = (1.18 +/- 0.28) x 10(5) M-1 and K-a(2) = (1.57 +/- 0.77) x 10(5) M-1) with CT-DNA. Isothermal titration calorimetry (ITC) studies revealed that these complexes bind to CT-DNA through an entropically driven process. Both the complexes showed photo-induced cytotoxicity and exhibit apoptotic activity under photo-irradiation conditions. The comet assay indicated that these complexes can damage cellular DNA, which is attributed to the significant build-up of O-1(2) level even on irradiation with low intensity light (10 J cm(-2), lambda(Range) 450-480 nm). This photoinduced DNA damage and apoptosis in A549 cells was induced by reactive oxygen species (ROS) and occurred through up-regulation of apoptotic marker caspase-3. Control experiments under dark conditions revealed an insignificant cytotoxicity towards these cells for two photosensitive molecules.1 aRamu, Vadde1 aAute, Sunil1 aTaye, Nandaraj1 aGuha, Rweetuparna1 aWalker, Michael, G.1 aMogare, Devaraj1 aParulekar, Apoorva1 aThomas, Jim, A.1 aChattopadhyay, Samit1 aDas, Amitava uhttps://library.ncl.res.in/content/photo-induced-cytotoxicity-and-anti-metastatic-activity-rutheniumii-polypyridyl-complexes02146nas a2200193 4500008004100000245015900041210006900200260000800269300001400277490000700291520141500298100001601713700001801729700001601747700001801763700001701781700002401798856013001822 2017 eng d00aProton-coupled electron-transfer processes in ultrafast time domain: evidence for effects of hydrogen-bond stabilization on photoinduced electron transfer0 aProtoncoupled electrontransfer processes in ultrafast time domai cMAR a3455-34650 v233 aThe proton-coupled electron-transfer (PCET) reaction is investigated for a newly synthesized imidazoleanthraquinone biomimetic model with a photoactive RuIIpolypyridyl moiety that is covalently coupled to the imidazole fragment. Intramolecular H-bonding interactions between imidazole and anthraquinone moieties favor the PCET process; this can be correlated to an appreciable positive shift in the one-electron reduction potential of the coordinated anthraquinone moiety functionalized with the imidazole fragment. This can also be attributed to the low luminescence quantum yield of the RuII-polypyridyl complex used. The dynamics of the intramolecular electron-transfer (ET) and PCET processes are studied by using femtosecond transient absorption spectroscopy. The steady- state spectroscopic studies and the results of the time- resolved absorption studies confirm that H- bonded water molecules play a major role in both ET and PCET dynamics as a proton relay in the excited state. The electron- transfer process is followed by a change in the H- bonding equilibrium between AQ and imidazole in acetonitrile solvent, and protonation of AQ(-) water leads to PCET in the presence of water. A slower forward and backward electron- transfer rate is observed in the presence of D2O compared with that in H2O. These results provide further experimental support for a detailed understanding of the PCET process.1 aDey, Ananta1 aDana, Jayanta1 aAute, Sunil1 aMaity, Partha1 aDas, Amitava1 aGhosh, Hirendra, N. uhttps://library.ncl.res.in/content/proton-coupled-electron-transfer-processes-ultrafast-time-domain-evidence-effects-hydrogen01189nas a2200229 4500008004100000022001400041245011500055210006900170260000800239300001400247490000700261520041100268100001500679700001600694700002500710700001800735700002000753700002100773700002000794700001700814856012800831 2018 eng d a1359-734500aTracking HOCl concentrations across cellular organelles in real time using a super resolution microscopy probe0 aTracking HOCl concentrations across cellular organelles in real  cFEB a1849-18520 v543 a

BODIPY derivative, SF-1, exclusively shows a fluorescence ON response to HOCl and images endogenously generated HOCl in RAW 264.7 macrophages. Widefield and super resolution structured illumination microscopy images confirm localization in the Golgi complex and lysosomes, and hence specifically detects HOCl generated in these organelles. SF-1 is compatible with 3D-SIM imaging of individual cells.

1 aAli, Firoj1 aAute, Sunil1 aSreedharan, Sreejesh1 aAnila, H., A.1 aSaeed, Hiwa, K.1 aSmythe, Carl, G.1 aThomas, Jim, A.1 aDas, Amitava uhttps://library.ncl.res.in/content/tracking-hocl-concentrations-across-cellular-organelles-real-time-using-super-resolution03024nas a2200193 4500008004100000022001400041245017500055210006900230260000900299300001400308490000700322520228300329100001602612700001802628700001602646700001702662700002402679856012702703 2019 eng d a1474-905X00aHydrogen bond assisted photoinduced intramolecular electron transfer and proton coupled electron transfer in an ultrafast time domain using a ruthenium-anthraquinone dyad0 aHydrogen bond assisted photoinduced intramolecular electron tran cOCT  a2430-24410 v183 a

Quinones play a significant role as primary electron acceptors in the natural photosynthetic system of photosystem II, and their reduction is known to be facilitated by hydrogen-bond donors or protonation. In this study, a ruthenium(ii) polypyridyl complex 1 coupled to an anthraquinone (AQ) functionality through a rigid imidazole (Im) spacer has been synthesized to examine the effect of H-bonding on both the thermal and photoinduced electron transfer reactions. The anthraquinone moiety of complex 1 is fused to a benzi-imidazole system bearing C & xe001;(OMIDLINE)-M-AQ HORIZONTAL ELLIPSISHNIm based H-bonding at one side of the anthraquinone moiety so that intramolecular hydrogen bonding from the imidazole group to the nearby quinone carbonyl can occur. The hydrogen bond formation involving the semiquinone radical anion produced through the photoinduced reduction process in Ru-im-AQ and the imidazole proton in complex 1 resulted in a significant positive shift of one electron reduction potential of complex 1. The kinetics for the formation of the charge-separated states was explored by using femtosecond transient absorption spectroscopy. Hydrogen bonding between water and the reduced anthraquinone accounted for thermodynamic and kinetic stabilization of these charge-separated states. An attempt has been made to assess the relative importance of the driving force and solvent polarity, in the rates of photoinduced electron transfer in complex 1. The 490 nm transient absorption band of anthraquinone radical anions (AQ(-)) and a broad absorption in the 580-750 nm region having maxima at similar to 690 nm have been observed and this is attributed to the generation of a transient Ru3+-species of the corresponding complex 1. Addition of water entails an acceleration of electron transfer rates by a factor of 3.33. The system investigated may serve as a model for the mechanistic diversity of PCET reactions in general with water as a primary proton donor. Furthermore, our studies are relevant for understanding proton-coupled electron transfer (PCET) reactivity of electronically excited states at a fundamental level because changes in hydrogen-bonding strength accompanying changes in redox states may be regarded as a variant form of PCET.

1 aDey, Ananta1 aDana, Jayanta1 aAute, Sunil1 aDas, Amitava1 aGhosh, Hirendra, N. uhttps://library.ncl.res.in/content/hydrogen-bond-assisted-photoinduced-intramolecular-electron-transfer-and-proton-coupled