Photochemistry of Potassium Ferrocyanide and its Reaction with Uridine 5′-monophosphate in Aqueous Solution under Ultraviolet Irradiation

The photochemical reaction of potassium ferrocyanide (K\begin{document}$ _4 $\end{document}Fe(CN)\begin{document}$ _6 $\end{document}) exhibits excitation wavelength dependence and non-Kasha rule behavior. In this study, the excited-state dynamics of K\begin{document}$ _4 $\end{document}Fe(CN)\begin{document}$ _6 $\end{document} were studied by transient absorption spectroscopy. Excited state electron detachment (ESED) and photoaquation reactions were clarified by comparing the results of 260, 320, 340, and 350 nm excitations. ESED is the path to generate a hydrated electron (e\begin{document}$ _{\rm{aq}}^{-} $\end{document}). ESED energy barrier varies with the excited state, and it occurs even at the first singlet excited state (\begin{document}$ ^{1} $\end{document}T\begin{document}$ _{\rm{1g}} $\end{document}). The \begin{document}$ ^{1} $\end{document}T\begin{document}$ _{\rm{1g}} $\end{document} state shows \begin{document}$ {\sim} $\end{document}0.2 ps lifetime and converts into triplet [Fe(CN)\begin{document}$ _{6} $\end{document}]\begin{document}$ ^{4-} $\end{document} by intersystem crossing. Subsequently, \begin{document}$ ^{3} $\end{document}[Fe(CN)\begin{document}$ _{5} $\end{document}]\begin{document}$ ^{3-} $\end{document} appears after one CN\begin{document}$ ^{-} $\end{document} ligand is ejected. In sequence, H\begin{document}$ _{2} $\end{document}O attacks [Fe(CN)\begin{document}$ _{5} $\end{document}]\begin{document}$ ^{3-} $\end{document} to generate [Fe(CN)\begin{document}$ _{5} $\end{document}H\begin{document}$ _{2} $\end{document}O]\begin{document}$ ^{3-} $\end{document} with a time constant of approximately 20 ps. The \begin{document}$ ^{1} $\end{document}T\begin{document}$ _{\rm{1g}} $\end{document} state and e\begin{document}$ _{\rm{aq}}^{-} $\end{document} exhibit strong reducing power. The addition of uridine 5\begin{document}$ ' $\end{document}-monophosphate (UMP) to the K\begin{document}$ _{4} $\end{document}Fe(CN)\begin{document}$ _{6} $\end{document} solution decrease the yield of e\begin{document}$ _{\rm{aq}}^{-} $\end{document} and reduce the lifetimes of the e\begin{document}$ _{\rm{aq}}^{-} $\end{document} and \begin{document}$ ^{1} $\end{document}T\begin{document}$ _{\rm{1g}} $\end{document} state. The obtained reaction rate constant of \begin{document}$ ^{1} $\end{document}T\begin{document}$ _{\rm{1g}} $\end{document} state and UMP is 1.7\begin{document}$ {\times} $\end{document}10\begin{document}$ ^{14} $\end{document} (mol/L)\begin{document}$ ^{-1}\cdot $\end{document}s\begin{document}$ ^{-1} $\end{document}, and the e\begin{document}$ _{\rm{aq}}^{-} $\end{document} attachment to UMP is \begin{document}$ {\sim} $\end{document}8\begin{document}$ {\times} $\end{document}10\begin{document}$ ^{9} $\end{document} (mol/L)\begin{document}$ ^{-1}\cdot $\end{document}s\begin{document}$ ^{-1} $\end{document}. Our results indicate that the reductive damage of K\begin{document}$ _{4} $\end{document}Fe(CN)\begin{document}$ _{6} $\end{document} solution to nucleic acids under ultraviolet irradiation cannot be neglected.     

Conformations and Structures of Ethoxycarbonyl Isothiocyanate Revealed by Rotational Spectroscopy

The ethoxycarbonyl isothiocyanate has been investigated by using supersonic jet Fourier transform microwave spectroscopy. Two sets of rotational spectra belonging to conformers TCC (with the backbone of C\begin{document}$ - $\end{document}C\begin{document}$ - $\end{document}O\begin{document}$ - $\end{document}C, C\begin{document}$ - $\end{document}O\begin{document}$ - $\end{document}C=O, and O\begin{document}$ - $\end{document}C(=O)\begin{document}$ - $\end{document}NCS being trans, cis, and cis arranged, respectively) and GCC (\begin{document}$ gauche $\end{document}, cis, and cis arrangement of the C\begin{document}$ - $\end{document}C\begin{document}$ - $\end{document}O\begin{document}$ - $\end{document}C, C\begin{document}$ - $\end{document}O\begin{document}$ - $\end{document}C=O, and O\begin{document}$ - $\end{document}C(=O)\begin{document}$ - $\end{document}NCS) have been measured and assigned. The measurements of \begin{document}$ ^{13} $\end{document}C, \begin{document}$ ^{15} $\end{document}N and \begin{document}$ ^{34} $\end{document}S mono-substituted species of the two conformers have also been performed. The comprehensive rotational spectroscopic investigations provide accurate values of rotational constants and \begin{document}$ ^{14} $\end{document}N quadrupole coupling constants, which lead to structural determinations of the two conformers of ethoxycarbonyl isothiocyanate. For conformer TCC, the values of \begin{document}$ P_{ \rm{cc}} $\end{document} keep constant upon isotopic substitution, indicating that the heavy atoms of TCC are effectively located in the \begin{document}$ ab $\end{document} plane.     

Effects of Peptide Backbone Amide-to-Ester Bond Substitution on the Cleavage Frequency in Electron Capture Dissociation and Collision-Activated Dissociation

Probing the mechanism of electron capture dissociation on variously modified model peptide polycations has resulted in discovering many ways to prevent or reduce $ {\text{N}} - {{\text{C}}_α } $ {\text{N}} - {{\text{C}}_α } bond fragmentation. Here we report on a rare finding of how to increase the backbone bond dissociation rate. In a number of model peptides, amide-to-ester backbone bond substitution increased the frequency of $ {\text{O}} - {{\text{C}}_α } $ {\text{O}} - {{\text{C}}_α } bond cleavage (an analogue of $ {\text{N}} - {{\text{C}}_α } $ {\text{N}} - {{\text{C}}_α } bonds in normal peptides) by several times, at the expense of reduced frequency of cleavages of the neighboring $ {\text{N}} - {{\text{C}}_α } $ {\text{N}} - {{\text{C}}_α } bonds. In contrast, the ester linkage was only marginally broken in collisional dissociation. These results further highlight the complementarity of the reaction mechanisms in electron capture dissociation (ECD) and collision-activated dissociation (CAD). It is proposed that the effects of amide-to-ester bond substitution on fragmentation are mainly due to the differences in product ion stability (ECD, CAD) as well as proton affinity (CAD). This proposal is substantiated by calculations using density functional theory. The implications of these results in relation to the current understanding of the mechanisms of electron capture dissociation and electron transfer dissociation are discussed.     

The Radical Anions and Trianions of 1,8-Diphenylnaphthalene and of Some of its Derivatives Containing a Cyclophane Substructure

The radical anions of 1,8-diphenylnaphthalene ( 1 ) and its decadeuterio-(D₁₀- 1 ) and dimethyl-( 2 ) derivatives, as well as those of [2.0.0] (1,4)benzeno(1,8)naphthaleno(1,4)benzenophane ( 3 ) and its olefinic analogue ( 4 ) have been studied by ESR and ENDOR spectroscopy, At a variance with a previous report, the spin population in \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{-\kern-4pt {.}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {2}^{-\kern-4pt {.}} $\end{document} is to a great extent localized in the naphthalene moiety. A similar spin distribution is found for \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {3}^{-\kern-4pt {.}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {4}^{-\kern-4pt {.}} $\end{document}. The ground conformations of \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{-\kern-4pt {.}} $\end{document}-\documentclass{article}\pagestyle{empty}\begin{document}$ \rm {4}^{-\kern-4pt {.}} $\end{document} are chiral of C₂ symmetry. For \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{-\kern-4pt {.}} $\end{document}, an energy barrier between these conformations and the angle of twist about the bonds linking the naphthalene moiety with the phenyl substituents were estimated as ca. 50 kJ/mol and ca. 45°, respectively. The radical trianions of 1 , D₁₀- 1 , and 2 , have also been characterized by their hyperfine data. In \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{3-\kern-4pt {.}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {2}^{3-\kern-4pt {.}} $\end{document}, the bulk of the spin population resides in the two benzene rings so that these radical trianions can be regarded as the radical anions of ‘open-chain cyclophanes’ with a fused naphthalene π-system bearing almost two negative charges. The main features of the spin distribution in both \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{-\kern-4pt {.}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{3-\kern-4pt {.}} $\end{document} are correctly predicted by an HMO model of 1 .     

Unravelling Hydrogen Adsorption Kinetics on Ir(111) Electrode in Acid Solutions by Impedance Spectroscopy

The kinetics for hydrogen (H) adsorption on Ir(111) electrode has been studied in both HClO\begin{document}$ _4 $\end{document} and H\begin{document}$ _2 $\end{document}SO\begin{document}$ _4 $\end{document} solutions by impedance spectroscopy. In HClO\begin{document}$ _4 $\end{document}, the adsorption rate for H adsorption on Ir(111) increases from 1.74\begin{document}$ \times $\end{document}10\begin{document}$ ^{-8} $\end{document} mol\begin{document}$ \cdot $\end{document}cm\begin{document}$ ^{-2} $\end{document}\begin{document}$ \cdot $\end{document}s\begin{document}$ ^{-1} $\end{document} to 3.47\begin{document}$ \times $\end{document}10\begin{document}$ ^{-7} $\end{document} mol\begin{document}$ \cdot $\end{document}cm\begin{document}$ ^{-2} $\end{document}\begin{document}$ \cdot $\end{document}s\begin{document}$ ^{-1} $\end{document} with the decrease of the applied potential from 0.2 V to 0.1 V (vs. RHE), which is ca. one to two orders of magnitude slower than that on Pt(111) under otherwise identical condition. This is explained by the stronger binding of water to Ir(111), which needs a higher barrier to reorient during the under potential deposition of H from hydronium within the hydrogen bonded water network. In H\begin{document}$ _2 $\end{document}SO\begin{document}$ _4 $\end{document}, the adsorption potential is ca. 200 mV negatively shifted, accompanied by a decrease of adsorption rate by up to one order of magnitude, which is explained by the hindrance of the strongly adsorbed sulfate/bisulfate on Ir(111). Our results demonstrate that under electrochemical environment, H adsorption is strongly affected by the accompanying displacement and reorientation of water molecules that initially stay close to the electrode surface.     

The Radical Anions of 1,2-diphenylcyclohexene and Structurally Related Compounds. Conformational ESR and ENDOR studies

ESR, ENDOR, and TRIPLE resonance studies have been performed on the radical anions of 1,2-diphenylcyclohex-1-ene ( 4 ), 1,2-di(perdeuteriophenyl)cyclohex-1-ene ((D₁₀) 4 ) the trans-configurated 3,4-diphenyl-8-oxabicyclo[4.3.0]non-3-ene ( 5 ) and its 2,2,5,5-tetradeuterio derivative (D₄) 5 , and 2,3-diphenyl-8,9,10-trinorborn-2-ene ( 6 ). The spectra of \documentclass{article}\pagestyle{empty}\begin{document}$ 4^{- \atop \dot{}} $\end{document} exhibit strong temperature dependence along with a specific broadening of ESR hyperfine lines and proton ENDOR signals. The coupling constant, which bears the main responsibility for these features, is that of the β-protons in the quasi-equatorial positions of the cyclohexene ring, and the experimental findings are readily rationlized in terms of relatively modest conformational changes without invoking the inversion of the half-chair form. The hyperfine data for the β-protons in \documentclass{article}\pagestyle{empty}\begin{document}$ 5^{- \atop \dot{}} $\end{document} closely resemble the corresponding low-temperature values for \documentclass{article}\pagestyle{empty}\begin{document}$ 4^{- \atop \dot{}} $\end{document}, However, the ‘unusual’ features observed for \documentclass{article}\pagestyle{empty}\begin{document}$ 4^{- \atop \dot{}} $\end{document} are absent in the ESR and ENDOR spectra of \documentclass{article}\pagestyle{empty}\begin{document}$ 5^{- \atop \dot{}} $\end{document}, because the half-chair conformation of the cyclohexene ring in \documentclass{article}\pagestyle{empty}\begin{document}$ 5^{- \atop \dot{}} $\end{document} is deprived of its flexibility. Although the boat form of this ring in \documentclass{article}\pagestyle{empty}\begin{document}$ 6^{- \atop \dot{}} $\end{document} is also rigid, the spectra of \documentclass{article}\pagestyle{empty}\begin{document}$ 6^{- \atop \dot{}} $\end{document} are temperature-dependent, due to an interconversion between two propeller-like conformations of the phenyl groups. The pertinent barrier is 30 ± 5 kJ ·mol^?1. An analogous interconversion presumably takes place in \documentclass{article}\pagestyle{empty}\begin{document}$ 4^{- \atop \dot{}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ 5^{- \atop \dot{}} $\end{document} as well, but, unlike \documentclass{article}\pagestyle{empty}\begin{document}$ 6^{- \atop \dot{}} $\end{document}, it is not amenable to experimental study.     

Kinetic studies of Cl-atom reactions with selected aromatic compounds using the photochemical reactor-FTIR spectroscopy technique

Relative rate constant measurements have been carried out on the Cl-atom reactions with benzene, chlorobenzene, toluene, xylene, and styrene in 740 torr of air at room temperature (295 K), using the photochemical reactor-FTIR spectroscopy technique. The Cl atoms were generated by the UV photolysis of Cl₂, and the reference compounds were CHF, Cl for benzene and chlorobenzene and isobutane for toluene xylene and styrene. Using the absolute rate constant for these two reference compounds reported in the literature, the following kinetic data were obtained for the study compounds (in units of cm³s⁻¹). \settabs 2 \columns \+Benzene & $(1.3\pm 0.3)\times 10 ^ {-15}$\cr \+Chlorobenzen & $(9.8\pm 2.4)\times 10 ^ {-16}$\cr \+Toluene & $(5.9\pm 0.5)\times 10 ^ {-11}$\cr \+o-Xylene & $(1.5\pm 0.1)\times 10 ^ {-10}$\cr \+m-Xylene & $(1.4\pm 0.1)\times 10 ^ {-10}$\cr \+p-Xylene & $(1.5\pm 0.1)\times 10 ^ {-10}$\cr \+Styrene & $(3.6\pm 0.3)\times 10 ^ {-10}$\cr The quoted error bars are for ± 2σ. The present kinetic results are compared with available literature data to update and expand the kinetics database for Cl-atom reactions of organic compounds. The results are also analyzed to provide insights into the reaction mechanism for the Cl-atom initiated oxidation of benzene under atmospheric conditions. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 349–358, 1997     

Rovibronic Spectrum of PbS in 19520-22900 cm-1

The rovibronic spectrum of PbS in the range of 19520 -22900 cm\begin{document}$ ^{\bf{-1}} $\end{document} are investigated using the laser ablation-laser induced fluorescence method. The spectra in this range are assigned as the transitions of \begin{document}$ A-X$\end{document} and \begin{document}$ B-X$\end{document} according to the spectral analyzation. The upper electronic state of the transition in the range of 19520-22900 cm\begin{document}$ ^{\bf{-1}} $\end{document} is analyzed and discussed, and it is concluded that the upper state, \begin{document}$A $\end{document}, is a mixture of \begin{document}${ }^3 \Pi_{0^{+}} $\end{document} and \begin{document}$ { }^3 \Sigma_{0^{+}}^{-}$\end{document}states, the \begin{document}${ }^3 \Pi_{0^{+}} $\end{document} state is in domination. The spectrum in the range of 22025 -22900 cm\begin{document}$ ^{\bf{-1}} $\end{document} is assigned as the \begin{document}$ B^3 \Pi_1-X^1 \Sigma^{+}$\end{document} transition. The molecular constants of these two transitions are derived from the observed spectra. The Frank-Condon factors (FCFs) of these two transitions are also calculated using the RKR/LEVEL method. All the results are compared with the reported theoretical and experimental results, showing that the \begin{document}$A $\end{document} state is a mixing state which is in consistent with Balasubramanian's relativistic configuration interaction calculation result. And our calculated FCFs are in agreement with our recorded spectra.     

Structure of Protonated Heterodimer of Proline and Phenylalanine: Revealed by Infrared Multiphoton Dissociation Spectroscopy and Theoretical Calculations

The infrared multiphoton dissociation (IRMPD) spectrum of the protonated heterodimer of ProPheH\begin{document}$ ^+ $\end{document}, in the range of 2700-3700 cm\begin{document}$ ^{-1} $\end{document}, has been obtained with a Fourier-transform ion cyclotron mass spectrometer combined with an IR OPO laser. The experimental spectrum shows one peak at 3565 cm\begin{document}$ ^{-1} $\end{document} corresponding to the free carboxyl O-H stretching vibration, and two broad peaks centered at 2935 and 3195 cm\begin{document}$ ^{-1} $\end{document}. Theoretical calculations were performed on the level of M062X/6-311++G(d, p). Results show that the most stable isomer is characterized by a charge-solvated structure in which the proton is bound to the unit of proline. Its predicted spectrum is in good agreement with the experimental one, although the coexistence of salt-bridged structures cannot be entirely excluded.     

GW/BSE Nonadiabatic Dynamics Simulations on Excited-State Relaxation Processes of Zinc Phthalocyanine-Fullerene Dyads: Roles of Bridging Chemical Bonds

In this work, we employ electronic structure calculations and nonadiabatic dynamics simulations based on many-body Green function and Bethe-Salpeter equation (GW/BSE) methods to study excited-state properties of a zinc phthalocyanine-fullerene (ZnPc-C\begin{document}$ _{60} $\end{document}) dyad with 6-6 and 5-6 configurations. In the former, the initially populated locally excited (LE) state of ZnPc is the lowest S\begin{document}$ _1 $\end{document} state and thus, its subsequent charge separation is relatively slow. In contrast, in the latter, the S\begin{document}$ _1 $\end{document} state is the LE state of C\begin{document}$ _{60} $\end{document} while the LE state of ZnPc is much higher in energy. There also exist several charge-transfer (CT) states between the LE states of ZnPc and C\begin{document}$ _{60} $\end{document}. Thus, one can see apparent charge separation dynamics during excited-state relaxation dynamics from the LE state of ZnPc to that of C\begin{document}$ _{60} $\end{document}. These points are verified in dynamics simulations. In the first 200 fs, there is a rapid excitation energy transfer from ZnPc to C\begin{document}$ _{60} $\end{document}, followed by an ultrafast charge separation to form a CT intermediate state. This process is mainly driven by hole transfer from C\begin{document}$ _{60} $\end{document} to ZnPc. The present work demonstrates that different bonding patterns (i.e. 5-6 and 6-6) of the C\begin{document}$ - $\end{document}N linker can be used to tune excited-state properties and thereto optoelectronic properties of covalently bonded ZnPc-C\begin{document}$ _{60} $\end{document} dyads. Methodologically, it is proven that combined GW/BSE nonadiabatic dynamics method is a practical and reliable tool for exploring photoinduced dynamics of nonperiodic dyads, organometallic molecules, quantum dots, nanoclusters, etc.     

Rearrangement of the Radical Anions of 1,6-Bridged[10]Annulenes to Derivatives of 5H-Benzocycloheptene and Benzotropylium

The rearrangement products obtained upon reduction of 1,6-methano[10]-annulene ( 1 ) and its 11-halogen derivatives have been studied by ESR. and, in part, by ENDOR. spectroscopy. These derivatives comprise 11,11-difluoro- ( 2 ), 11-fluoro- ( 3 ), 11,11-dichloro- ( 4 ) and 11-bromo-1,6-methano[10]annulene ( 5 ), as well as the 2,5,7,10-tetradeuteriated compounds 2 -D₄ and 3 -D₄. The studies of the secondary products in question have been initiated by the finding that the radical anion of 11,11-dimethyltricyclo[4.4.1.0^1,6]undeca-2,4,7,9-tetraene ( 12 ), i.e., the prevailing valence isomer of 11,11-dimethyl-1,6-methano[10]annulene, undergoes above 163 K a rearrangement to the radical anion of 5,5-dimethylbenzocycloheptene ( 14 ). A rearrangement of this kind also occurs for the radical anion of the parent compound 1 , albeit only above 323 K. The lower reactivity of 1 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} relative to 12 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} is rationalized by the assumption that the first and rate determining step in the case of 1 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} is the valence isomerization to the radical anion of tricyclo[4.4.1.0^1,6]undeca-2,4,7,9-tetraene ( 1a ). In the reducing medium used in such reactions (potassium in 1,2-dimethoxyethane), the final paramagnetic product of 1 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} is not 5H-benzocycloheptene ( 15 ), but the benzotropylium radical dianion ( ). This product ( ) is also obtained from the radical anions of the halogen-substituted 1,6-methano[10]annulenes, 2 to 5 , in the same medium. The temperatures required for the conversion of 2 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 3 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} into lie above 293 and 243 K, respectively, whereas the short-lived species 4 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 5 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} undergo such a rearrangement already at 163 K. The stability of the four halogen-substituted radical anions thus decreases in the sequence 2 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} > 3 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} > 4 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} ≈ 5 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}. Replacement of 2 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 3 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} by 2 -D₄\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 3 -D₄\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}, respectively, leads to 1,4,5,8-tetradeuteriobenzotropylium radical dianion ( ). Experimental evidence and theoretical arguments indicate that the rearrangements in question are initiated by a loss of one ( 3 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 5 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}) or two ( 2 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 4 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}) halogen atoms. Such a reaction step must involve the intermediacy of the radical 19 · (see below) which rapidly isomerizes to the benzotropylium radical 16 :. Support for the transient existence of 19 . is provided by the thermolysis of 1,6-methano [10]annulene-11-t-butylperoxyester (6) which yields 16 . in a temperature dependent equilibrium with a mixture of its dimers ( 16 ₂). In the hitherto unreported ESR. spectra of 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}. and 3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}, the coupling constants of the ring protons differ considerably from the analogous values for the radical anions of other 1,6-bridged [10]annulenes. These differences strongly suggest that the fluoro-substitution substantially affects the character of the singly occupied orbital.     

The Radical Ions of Naphtho [1,8-cd]-[1,2,6]thiadiazine and Some of Its Derivatives

The radical cations and anions of naphtho [1,8-cd]-[1,2,6]thiadiazine (1) and 6,7-dihydroacenaphtho [5, 6-cd]-[1,2,6]thiadiazine (2) , as well as the radical anion of acenaphtho [5, 6-cd]-[1,2,6]thiadiazine (3) have been characterized by ESR. spectroscopy. The π-spin distributions in the radical cations \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\oplus \atop \dot{}}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ 2^{\oplus \atop \dot{}}$\end{document} strongly resemble those in the iso-π-electronic phenalenyl radical. A prominent feature of the radical anions \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}}$\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$ 2^{\ominus \atop \dot{}}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{\ominus \atop \dot{}}$\end{document} is the substantial localization of the π-spin population on the thiadiazine fragment. These findings are satisfactorily accounted for by HMO models using conventional heteroatom parameters.     

Effect of Optical Depth on Study of Chemical Properties of Massive Star Forming Clumps

Here we present the study on chemical properties of massive star forming clumps using N\begin{document}$ _2 $\end{document}H\begin{document}$ ^+ $\end{document}(1-0), H\begin{document}$ ^{13} $\end{document}CO\begin{document}$ ^+ $\end{document}(1-0), HCN(1-0) and HN\begin{document}$ ^{13} $\end{document}C(1-0) data from the literature [Astron. Astrophys. 563 , A97 (2014)]. We found that abundances of H\begin{document}$ ^{13} $\end{document}CO\begin{document}$ ^+ $\end{document} and HN\begin{document}$ ^{13} $\end{document}C are affected by H\begin{document}$ _2 $\end{document} column densities. As the median values of these two abundances increase by nearly 10 times from stages A to B, H\begin{document}$ ^{13} $\end{document}CO\begin{document}$ ^+ $\end{document} and HN\begin{document}$ ^{13} $\end{document}C are suitable for tracing the evolution of massive star forming clumps. The order of rapidity in growth of abundances of all the four studied molecules from stages A to B, is H\begin{document}$ ^{13} $\end{document}CO\begin{document}$ ^+ $\end{document}, HCN, HN\begin{document}$ ^{13} $\end{document}C, and N\begin{document}$ _2 $\end{document}H\begin{document}$ ^+ $\end{document}, from the highest to the lowest. Our results suggest that the observing optically thin molecular lines with high angular resolution are necessary to study the chemical evolution of massive star forming clumps.     

Rate constants for the reactions of molecular iodine with Cl,SiCl3, and SiH3 at 298 K

Rate constants k₁, k₂, and k₃ have been measured at 298 K by means of a laser photolysis-laser magnetic resonance technique and (or) by a laser photolysis-infrared chemiluminescence detection technique (LMR and IRCL, respectively). \hfill\hbox to 12em{$\rm Cl+I_2\longrightarrow ICl+I;$}\hbox to 8em{$\rm {\it k}_1=(2.5\pm 0.7)\times 10^{-10}(IRCL)$}\hfill(1)\\\hfill\hbox to 12em{}\hbox to 8em{$\rm {\it k}_1=(2.8\pm 0.8)\times 10^{-10}(LMR)$}\hfill \\\hfill\hbox to 12em{$\rm SiCl_3+I_2\longrightarrow SiCl_3I+I;$}\hbox to 8em{$\rm {\it k}_2=(5.8\pm 1.8)\times 10^{-10}(IRCL)$}\hfill (2)\\\hfill\hbox to 12em{$\rm SiH_3+I_2\longrightarrow SiIH_3+I;$}\hbox to 8em{$\rm {\it k}_3=(1.8\pm 0.46)\times 10^{-10}(LMR)$}\hfill (3)\\ As an average of the LMR and IRCL results we offer the value k₁ = (2.7 ± 0.6) × 10⁻¹⁰. Units are cm³ molecule⁻¹ s⁻¹; uncertainties are 2σ including precision and estimated systematic errors. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 25–33, 1997.     

Structural Dynamics of Amyloid β Peptide Binding to Acetylcholine Receptor and Virtual Screening for Effective Inhibitors

The interaction between Amyloid β (Aβ) peptide and acetylcholine receptor is the key for our understanding of how Aβ fragments block the ion channels within the synapses and thus induce Alzheimer's disease. Here, molecular docking and molecular dynamics (MD) simulations were performed for the structural dynamics of the docking complex consisting of Aβ and α7-nAChR (α7 nicotinic acetylcholine receptor), and the inter-molecular interactions between ligand and receptor were revealed. The results show that A\begin{document}$ \beta_{25-35} $\end{document} is bound to α7-nAChR through hydrogen bonds and complementary shape, and the A\begin{document}$ \beta_{25-35} $\end{document} fragments would easily assemble in the ion channel of \begin{document}$ \alpha $\end{document}7-nAChR, then block the ion transfer process and induce neuronal apoptosis. The simulated amide-I band of A\begin{document}$ \beta_{25-35} $\end{document} in the complex is located at 1650.5 cm\begin{document}$ ^{-1} $\end{document}, indicating the backbone of A\begin{document}$ \beta_{25-35} $\end{document} tends to present random coil conformation, which is consistent with the result obtained from cluster analysis. Currently existing drugs were used as templates for virtual screening, eight new drugs were designed and semi-flexible docking was performed for their performance. The results show that, the interactions between new drugs and \begin{document}$ \alpha $\end{document}7-nAChR are strong enough to inhibit the aggregation of A\begin{document}$ \beta_{25-35} $\end{document} fragments in the ion channel, and also be of great potential in the treatment of Alzheimer's disease.     

The Radical Anion of 1,2-Diphenylcyclopentene

ESR. and ENDOR. studies are reported for the radical anions of 1,2-diphenylcyclopentene ( 3 ) and its di(pe+deuteriophenyl)-derivative (3-D₁₀). Comparison of the coupling constants of the phenyl protons in 3 \documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document}. with the analogous values for the radical anions of 1,2-diphenyl substituted cyclopropene ( 1 ) and cyclobutene ( 2 ) reveals regular changes in the sequence 1 \documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document}, 2 \documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document}, 3 \documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document}, which are caused by an increasing twist of the phenyl groups about the C(1), C(1′)- and C(2), C(1″)-bonds linking them to the ethylene fragment. Such a twist is shown to be also responsible for the large difference in the coupling constants of the methylene β-protons in 3 \documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document}. (0.659 and 0.293 mT). It is suggested that - in order to minimize the losses caused by this twist in the π-delocalization energy - the 2 p_z-axes at the centres 1 and 2 deviate from a perpendicular orientation to the mean plane of the cyclopentene ring. A deviation by 19° from such an orientation is required to account for the observed β-proton coupling constants in terms of their conventional cos²-dependence on the dihedral angles θ.     

Designer Mg-Mg and Zn-Zn Single Bonds Facilitated by Double Aromaticity in the M2B7-(M=Mg,Zn) Clusters

The simple homodinuclear M

\begin{document}$ - $\end{document}

M single bonds for group II and XII elements are difficult to obtain as a result of the fulfilled s

\begin{document}$ ^2 $\end{document}

electronic configurations, consequently, a dicationic prototype is often utilized to design the M

\begin{document}$ ^+ $\end{document}\begin{document}$ - $\end{document}

M

\begin{document}$ ^+ $\end{document}

single bond. Existing studies generally use sterically bulky organic ligands L

\begin{document}$ ^- $\end{document}

to synthesize the compounds in the L

\begin{document}$ ^- $\end{document}\begin{document}$ - $\end{document}

M

\begin{document}$ ^+ $\end{document}\begin{document}$ - $\end{document}

M

\begin{document}$ ^+ $\end{document}\begin{document}$ - $\end{document}

L

\begin{document}$ ^- $\end{document}

manner. However, here we report the design of Mg

\begin{document}$ - $\end{document}

Mg and Zn

\begin{document}$ - $\end{document}

Zn single bonds in two ligandless clusters, Mg

\begin{document}$ _2 $\end{document}

B

\begin{document}$ _7 $\end{document}\begin{document}$ ^- $\end{document}

and Zn

\begin{document}$ _2 $\end{document}

B

\begin{document}$ _7 $\end{document}\begin{document}$ ^- $\end{document}

, using density functional theory methods. The global minima of both of the clusters are in the form of M

\begin{document}$ _2 $\end{document}\begin{document}$ ^{2+} $\end{document}

(B

\begin{document}$ _7 $\end{document}\begin{document}$ ^{3-} $\end{document}

), where the M

\begin{document}$ - $\end{document}

M single bonds are positioned above a quasi-planar hexagonal B

\begin{document}$ _7 $\end{document}

moiety. Chemical bonding analyses further confirm the existence of Mg

\begin{document}$ - $\end{document}

Mg and Zn

\begin{document}$ - $\end{document}

Zn single bonds in these clusters, which are driven by the unusually stable B

\begin{document}$ _7 $\end{document}\begin{document}$ ^{3-} $\end{document}

moiety that is both

\begin{document}$ \sigma $\end{document}

and

\begin{document}$ \pi $\end{document}

aromatic. Vertical detachment energies of Mg

\begin{document}$ _2 $\end{document}

B

\begin{document}$ _7 $\end{document}\begin{document}$ ^- $\end{document}

and Zn

\begin{document}$ _2 $\end{document}

B

\begin{document}$ _7 $\end{document}\begin{document}$ ^- $\end{document}

are calculated to be 2.79 eV and 2.94 eV, respectively, for the future comparisons with experimental data.

     

Dynamics of ternary complex formation in the reaction of diaquoanthranilato-N,N-diacetatonickelate(II) with 2,2′-bipyridine and 1,10-phenanthroline

Dynamics of ternary complex formation in the reaction of diaquoanthranilato-N, N-diacetatonickelate(II) with 2,2′-bipyridine and 1,10-phenanthroline. $\rm Ni(ada)(H_2O)_2^{-}$ $+$ $L\rightleftharpoons Ni(ada)(L)^{-}$ $+$ $2 H_20;$ $- {{d[Ni(ada)^{-}]}\over{dt}}$ $=$ $k_f[Ni(ada)^{-}][L]+k_d\ [Ni(ada)(L)];$ $\ ada^{3-}=$anthranilate-N, N-diacetate; and L=bipy or phen. The kinetics of formation of ternary complexes by diaquoanthranilato-N, N-diacetatonickelate(II). [Ni(ada)(H₂O)]⁻ with 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen) have been studied under pseudo-first-order conditions containing excess bipy or phen by stopped-flow spectrophotometry in the pH range 7.1–7.8 at 25°C and λ = 0.1 mol dm⁻³. In each case, the reaction is first-order with respect to both Ni(ada)⁻ and the entering ligand (ie., bipy, phen). The reactions are reversible. The forward rate constants are: $k^{\rm Ni(ada)}_{\rm Ni(ada)(bipy)}=0.87\times10^3{\rm dm}^3 {\rm mol}^{-1}{\rm s}^{-1}$, . $k^{\rm Ni(ada)}_{\rm Ni(ada)(phen)}=1.87\times10^3{\rm dm}^3 {\rm mol}^{-1}{\rm s}^{-1}$; and the reverse rate constants are: $k^{\rm Ni(ada)(bipy)}_{\rm Ni(ada)}=1.0{\rm s}^{-1}$ and $k^{\rm Ni(ada)(phen)}_{\rm Ni(ada)}=2.0{\rm s}^{-1}$. The corresponding stability constants of ternary complex formation are: and , . The observed rate constants and huge drops in stability constants in ternary complex formation agree well with the mechanism in which dissociation of an acetate arm of the coordinated ada³⁻ prior to chelation by the aromatic ligand occurs. The observations have been compared with the kinetics of ternary complex formation in the reaction Ni(ada)⁻ - glycine in which the kinetics involves a singly bonded intermediate, N(ada)((SINGLE BOND)O(SINGLE BOND)N)²⁻ in rapid equilibrium with the reactants followed by a sluggish ring closure step. The reaction with the aromatic ligands conforms to a steady-state mechanism, while for glycine it gets shifted to an equilibrium mechanism. The cause of this difference in mechanistic pathways has been explained. © 1996 John Wiley & Sons, Inc.