Thermodynamic Stability,Spectroscopic Identification,and Gas Storage Capacity of CO₂–CH₄–N₂ Mixture Gas Hydrates: Implications for Landfill Gas Hydrates

Lee, Hyeong-Hoon,Ahn, Sook-Hyun,Nam, Byong-Uk,Kim, Byeong-Soo,Lee, Gang-Woo,Moon, Donghyun,Shin, HyungJoon,Han, Kyu Won,Yoon, Ji-Ho AmericanChemical Society 2012 Environmental science & technology Vol.46 No.7

<P>Landfill gas (LFG), which is primarily composed of CH<SUB>4</SUB>, CO<SUB>2</SUB>, and N<SUB>2</SUB>, is produced from theanaerobicdigestion of organic materials. To investigate the feasibility ofthe storage and transportation of LFG via the formation of hydrate,we observed the phase equilibrium behavior of CO<SUB>2</SUB>–CH<SUB>4</SUB>–N<SUB>2</SUB> mixture hydrates. When the specificmolar ratio of CO<SUB>2</SUB>/CH<SUB>4</SUB> was 40/55, the equilibriumdissociation pressures were gradually shifted to higher pressuresand lower temperatures as the mole fraction of N<SUB>2</SUB> increased.X-ray diffraction revealed that the CO<SUB>2</SUB>–CH<SUB>4</SUB>–N<SUB>2</SUB> mixture hydrate prepared from the CO<SUB>2</SUB>/CH<SUB>4</SUB>/N<SUB>2</SUB> (40/55/5) gas mixture formed a structureI clathrate hydrate. A combination of Raman and solid-state <SUP>13</SUP>C NMR measurements provided detailed information regarding the cageoccupancy of gas molecules trapped in the hydrate frameworks. Thegas storage capacity of LFG hydrates was estimated from the experimentalresults for the hydrate formations under two-phase equilibrium conditions.We also confirmed that trace amounts of nonmethane organic compoundsdo not affect the cage occupancy of gas molecules or the thermodynamicstability of LFG hydrates.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/esthag/2012/esthag.2012.46.issue-7/es203389k/production/images/medium/es-2011-03389k_0005.gif'></P>

Electric Field Effectson the Adsorption of CO ona Graphene Nanodot and the Healing Mechanism of a Vacancy in a GrapheneNanodot

Liu, Hongguang,Lee, Jin Yong AmericanChemical Society 2012 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.116 No.4

<P>It is well known that the external electric field caneffectivelymodify the electronic structures and transport properties of low-dimensionalsystems. However, to our knowledge, the corresponding atomic structureand adsorption property changes of a graphene carbon network underdifferent applied electric fields have not been investigated. Herein,using first-principles DFT calculations, we have systematically exploredthe CO adsorption on the pristine graphene nanodot and the defectiveone by taking the external electric field into account. It is foundthat the electric field can increase the CO adsorption energy andthere is a barrier for CO–vacancy recombination that is mostlybelieved to remerge instantaneously when they come close to each other.Also, we proposed a mechanism for the subsequent healing of a monovacancyon a graphene nanodot by interaction with CO molecules, leading tothe restoration of a pristine hexagonal carbon network.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2012/jpccck.2012.116.issue-4/jp210719r/production/images/medium/jp-2011-10719r_0008.gif'></P>

Size-Dependent Interactionsbetween Au Nanoparticlesand DNA in Electrochemical Oxidation by Metal Complexes

Wu, Qiong,Kang, Hee Kyung,Oh, Byul Nim,Kim, Jinheung AmericanChemical Society 2012 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.116 No.14

<P>Single-stranded oligonucleotides (ssDNA) containing guaninebasesin their sequences were adsorbed onto gold nanoparticles (AuNPs) byelectrostatic interaction. Cyclic voltammetry of Ru(bpy)<SUB>3</SUB><SUP>2+</SUP> in the presence of the ssDNA-AuNP complex resultedin an enhanced anodic current due to the oxidation of the guaninebases of DNA. The current obtained with ssDNA-AuNP appeared much smallerthan the corresponding ssDNA alone. This current reduction was dueto the decrease in solvent accessibility of the guanines in ssDNAimmobilized to AuNPs. A progressive decrease in the current was observedin the titration of AuNPs to ssDNA, and a minimum current was eventuallyobtained, indicating complete binding of ssDNA. The size dependencesof AuNPs on the interaction between ssDNA and AuNP were also studied,and the ssDNA adsorbed to 5 nm AuNPs was more solvent-accessible forthe Ru mediator than 13 and 30 nm AuNPs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2012/jpccck.2012.116.issue-14/jp209470g/production/images/medium/jp-2011-09470g_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp209470g'>ACS Electronic Supporting Info</A></P>

Highly Selective CysteineDetection and Bioimagingin Zebrafish through Emission Color Change of Water-Soluble ConjugatedPolymer-Based Assay Complex

Kwon, Na Young,Kim, Daigeun,Jang, Geunseok,Lee, Jung Hyo,So, Ju-Hoon,Kim, Cheol-Hee,Kim, Tae Hyeon,Lee, Taek Seung AmericanChemical Society 2012 ACS APPLIED MATERIALS & INTERFACES Vol.4 No.3

<P>A new concept for rapid, label-free cysteine sensing method is proposed via possible naked eye-detection of red-to-blue emission color change. Intermolecular exciton migration in conjugated polyelectrolyte-based assay complex is adopted to enhance selectivity and sensitivity for cysteine sensing by formation and dissociation of polymer Hg2+-thymine assay complex in the absence and presence of cysteine, respectively. The assay complex shows red emission due to cooperative aggregation of conjugated polyelectrolyte, thymine, and Hg2+. Upon exposure to cysteine, the assay complex dissociates into individual molecules showing transparent, blue-emitting solution, because cysteine extracts Hg2+ from the assay complex via more favorable binding between cysteine and Hg2+.</P>

Synthesis and Photodynamicsof Fluorescent Blue BODIPY-PorphyrinTweezers Linked by Triazole Rings

Eggenspiller, Antoine,Takai, Atsuro,El-Khouly, Mohamed E.,Ohkubo, Kei,Gros, ClaudeP.,Bernhard, Claire,Goze, Christine,Denat, Franck,Barbe, Jean-Michel,Fukuzumi, Shunichi AmericanChemical Society 2012 The Journal of physical chemistry A Vol.116 No.15

<P>Novel zinc porphyrin tweezers in which two zinc porphyrins were connected with pi-conjugated boron dipyrromethenes (BDP meso-Por(2) and BDP beta-Por(2)) through triazole rings were synthesized to investigate the photoinduced energy transfer and electron transfer. The UV-vis spectrum of BDP beta-Por(2) which has less bulky substituents than BDP meso-Por(2) exhibits splitting of the Soret band as a result of the interaction between porphyrins of BDP beta-Por(2) in the excited state. Such interaction between porphyrins of both BDP beta-Por(2) and BDP meso-Por(2) is dominant at room temperature, while the coordination of the nitrogen atoms of the triazole rings to the zinc ions of the porphyrins occurs at low temperature. The conformational change of the BDP-porphyrin composites was confirmed by the changes in UV-vis and fluorescence spectra depending on temperature. Photodynamics of BDP meso-Por2 and BDP beta-Por(2) has also been investigated by laser flash photolysis. Efficient singlet-singlet energy transfer from the ZnP to the pi-conjugated BDP moiety of both BDP meso-Por2 and BDP beta-Por(2) occurred in opposite direction as compared to energy transfer from conventional BDP to ZnP due to the pi-conjugation in nonpolar toluene. In polar benzonitrile, however, additional electron transfer occurred along with energy transfer.</P>

Fine-Tuning of MolecularEnergy Level of AlternatingCopolymers On the basis of [1,2,5]Thiadiazolo[3,4-<i>g</i>]quinoxaline Derivatives for Polymer Photovoltaics

Lee, Yoonkyoo,Jo, Won Ho AmericanChemical Society 2012 The Journal of Physical Chemistry Part C Vol.116 No.15

<P>A series of low-bandgap alternating copolymers consistingof electron-accepting[1,2,5]thiadiazolo[3,4-<I>g</I>]quinoxaline (TQ) derivativesand electron-donating fluorene or carbazole were synthesized via theSuzuki coupling reaction. For the purpose to fine-tune the molecularenergy level of alternating copolymers and thus to improve chargetransfer between polymers and PCBM, two different TQ derivatives substitutedwith strongly electron-donating butoxy group or weakly electron-donatingthienyl group were synthesized and used as a building block of alternatingcopolymers. Copolymers with butoxy-substituted TQ have proper lowestunoccupied molecular orbital (LUMO) energy levels for effective chargedissociation between polymer and PCBM, whereas the LUMO levels ofcopolymers with thienyl-substituted TQ are too close to that of PCBMto be effective for charge dissociation. The power conversion efficiencywas achieved up to 2.17%, which is the highest value among the TQ-basedpolymer solar cells, when the blend of copolymer with butoxy-substitutedTQ and [6,6]-phenyl-C<SUB>71</SUB>-butyric acid methyl ester was usedas an active layer material in bulk heterojunction solar cells.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2012/jpccck.2012.116.issue-15/jp2124247/production/images/medium/jp-2011-124247_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp2124247'>ACS Electronic Supporting Info</A></P>

Synergistic Interactionbetween Substrate and SeedParticles in Ultrathin Ultrananocrystalline Diamond Film Nucleationon SiO₂ with Controlled Surface Termination

Lee, Hak-Joo,Jeon, Hyeongtag,Lee, Wook-Seong AmericanChemical Society 2012 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.116 No.16

<P>We have investigated the effect of surface modification on the dispersion of nanodiamond seeds on the SiO2-coated Si substrate, to enable the ultrathin ultrananocrystalline diamond (UNCD) coating on the substrate, by direct current plasma-assisted chemical vapor deposition (DC-PACVD) using hydrogen-rich chemistry. The ultrasonically dispersed seed density on the SiO2-coated Si wafer was so much lower than that on the pristine Si wafer that the void-free ultrathin UNCD coating was impossible. For surface modification, we have exposed the substrate to (1) the hydrogen/hydrocarbon plasma in the DC-PACVD chamber or (2) the hydrocarbon atmosphere in the hot filament chemical vapor deposition (HF-CVD) chamber, prior to the ultrasonic seeding. The exposure to hydrocarbon or to its plasma greatly reduced the seed density, while exposure to hydrogen plasma drastically enhanced it by a factor of 6, which enabled a void-free ultrathin UNCD coating as thin as 30 nm. The UNCD film and the substrate surface before and after the surface treatment were characterized by XPS, NEXAFS, FTIR, Raman spectroscopy, HR-SEM, HR-TEM, EDX, and the zeta potential analyzer. The effects of the pretreatments on the seed density were explained by Si-OH or Si-CH3 termination and by the consequent change on (1) the zeta potentials of the substrate and (2) that of the nanodiamond particles in the seeding suspension.</P>

Development of Dye-SensitizedSolar Cells Composed of Liquid Crystal Embedded, Electrospun Poly(vinylidenefluoride-<i>co</i>-hexafluoropropylene) Nanofibers as PolymerGel Electrolytes

Ahn, Sung Kwang,Ban, Taewon,Sakthivel, P.,Lee, Jae Wook,Gal, Yeong-Soon,Lee, Jin-Kook,Kim, Mi-Ra,Jin, Sung-Ho AmericanChemical Society 2012 ACS APPLIED MATERIALS & INTERFACES Vol.4 No.4

<P>In order to overcome the problems associated with the use of liquid electrolytes in dye-sensitized solar cells (DSSCs), a new system composed of liquid crystal embedded, polymer electrolytes has been developed. For this purpose, three types of DSSCs have been fabricated. The cells contain electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (e-PVdF-co-HFP) polymer gel electrolyte, with and without doping with the liquid crystal E7 and with a liquid electrolyte. The morphologies of the newly prepared DSSCs were explored using field emission scanning electron microscopy (FE-SEM). Analysis of the FE-SEM images indicate that the DSSC composed of E7 embedded on e-PVdF-co-HFP polymer gel electrolyte has a greatly regular morphology with an average diameter. The ionic conductivity of E7 embedded on e-PVdF-co-HFP polymer gel electrolyte was found to be 2.9 X 10(-3) S/cm at room temperature, a value that is 37% higher than that of e-PVdF-co-HFP polymer gel electrolyte. The DCCS containing the E7 embedded, e-PVdF-co-HFP polymer gel electrolyte was observed to possess a much higher power conversion efficiency (PCE = 6.82%) than that of an e-PVdF-co-HFP nanofiber (6.35%). In addition, DSSCs parameters of the E7 embedded, e-PVdF-co-HFP polymer gel electrolyte (V-oc = 0.72 V, J(sc) = 14.62 mA/cm(2), FF = 64.8%, and PCE = 6.82% at 1 sun intensity) are comparable to those of a liquid electrolyte (V-oc = 0.75 V, J(sc) = 14.71 mA/cm(2), FF = 64.9%, and PCE = 7.17%, both at a 1 sun intensity).</P>

Surface-Enhanced RamanScattering of 4-Aminobenzenethiolon Ag and Au: pH Dependence of <i>b</i>₂-TypeBands

Kim, Kwan,Kim, Kyung Lock,Shin, Dongha,Choi, Jeong-Yong,Shin, Kuan Soo AmericanChemical Society 2012 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.116 No.7

<P>The surface-enhanced Raman scattering (SERS) of 4-aminobenzenehtiol (4-ABT) has seen a surge of interest recently, since its SERS spectral features are dependent not only on the kinds of SERS substrates but also on the measurement conditions. The most unusual SERS feature is the appearance of b(2)-type bands in the region 1100-1500 cm(-1), in contrast to their absence in the normal Raman spectrum, but their origin is not yet clarified. However, propositions have been made suggesting that their appearance is associated with either a charge transfer phenomenon or a surface-induced photoreaction product such as 4,4'-dimercaptoazobenzene (4,4'-DMAB). In this work, we found that the b(2)-type bands of 4-ABT are strongly affected also by the solution pH. Regardless of the excitation wavelength and kind of SERS substrates, the b(2)-type bands appeared very weakly or negligibly at acidic pHs, while they were observed very distinctly at basic pHs. For the case of 4,4'-DMAB, any such pH dependence was not observed at all in its SERS spectra. Since the pH dependence in the SERS of 4-ABT was observed reversibly, the appearance and disappearance of the b(2)-type bands must have nothing to do with formation of any surface-induced photoreaction product like 4,4'-DMAB. Consulting the pH-dependent UV-vis absorption spectra and ab initio quantum mechanical calculation, the disappearance of the b(2)-type bands at acidic pHs is presumed to be associated with the upshift of the lowest unoccupied molecular orbital level of 4-ABT caused by protonation of the amine group: the charge transfer resonance chemical enhancement will then be less likely to occur.</P>

Effect of Single-BaseMutation on Activity and Foldingof 10-23 Deoxyribozyme Studied by Three-Color Single-Molecule ALEXFRET

Jung, Jiwon,Han, Kyu Young,Koh, Hye Ran,Lee, Jihyun,Choi, Yoon Mi,Kim, Christine,Kim, Seong Keun AmericanChemical Society 2012 The journal of physical chemistry. B, Condensed ma Vol.116 No.9

<P>We investigated the effect of single-base mutation onthe RNA-cleavingactivity and ion-induced folding of 10-23 deoxyribozyme at the single-moleculelevel by 3-color ALEX FRET (alternating laser excitation fluorescenceresonance energy transfer). We found that substitution or deletionof a single base in the active region of the enzyme leads to a differentfolding pathway and enzymatic activity for all three mutants studied,but the severity of the effect was dependent on the type of mutationand the mutation site. We suggest that mutation of even a single basemay result in a considerably different ionic and hydrogen-bondinginteractions. Structural changes of 10-23 deoxyribozyme as it successivelybinds with Mg<SUP>2+</SUP> and the substrate were also unambiguouslyidentified by the current single-molecule-detection method.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpcbfk/2012/jpcbfk.2012.116.issue-9/jp2117196/production/images/medium/jp-2011-117196_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp2117196'>ACS Electronic Supporting Info</A></P>