STUDIES OF SYSTEM II PHOTOCENTERS BY COMPARATIVE MEASUREMENTS OF LUMINESCENCE,FLUORESCENCE, AND OXYGEN EMISSION*

Abstract— New results are presented on the emission of oxygen by algae and chloroplasts illuminated by a sequence of short saturating flashes. These results favor the four-state hypothesis of Kok and co-workers, in which formation of oxygen requires the accumulation of four oxidants produced by four successive photoreactions. Deactivation of the more oxidized precursor states in the dark is studied under different conditions of preillumination. Our results suggest that both a one step and a two step mechanism of deactivation exist. In order to understand the biological significance of Kok's parameter α—the fraction of photochemical centers unable to react on each flash (“misses”)-we study reoxidation of acceptor Q after one flash by fluorescence techniques. It appears that a fraction of Q^- is reoxidized by a back reaction which cancels the effect of the preilluminating flash and is probably responsible for the misses. The results of some luminescence experiments are also reported. These experiments demonstrate that delayed emission of light is associated with the deactivation of states S₂ and S₃. It is possible that excitons produced by deactivation can be reabsorbed by active photochemical centers, which can modify considerably the deactivation process.     

COOPERATION OF CHARGES IN PHOTOSYNTHETIC O2 EVOLUTION-II. DAMPING OF FLASH YIELD OSCILLATION,DEACTIVATION*

Abstract— A quantitative analysis is made of a linear 4-step model for photosynthetic O₂ evolution in which each photochemical trapping center or an associated enzyme cycles through 5 oxidation states (S₀, S₁, S₂, S₃, S₄). The overall reaction is: S₀→ S₄, S₄→ S₀+ O₂, where k_d= rate of dark reaction. Based on data obtained with isolated chloroplasts, four aspects were considered: (1) The two perturbations which damp the oscillation of the O₂ flash yield in a flash sequence given after a dark period-(a) a failure rate (α) of the trapping centers in the photochemical conversion (‘misses’) and (b) double effective excitations in a fraction (8) of the centers which are in the S₀ and S₁ states (‘double hits’). Best fit with the experimental data is obtained for α= 0.1, β=0.05. (2) The kinetics and the mechanism of deactivation—the loss of + charges (O₂ precursors) in the dark. The momentary distribution of the four oxidation states (S₀-_-S₃) in a sample can be computed from the O₂ yields of four consecutive flashes with corrections for a and β. The time course of the various states in the dark following specific preilluminations reveals that deactivation proceeds in single equivalent steps: S₃→S₂, S₂,→S₁. S₁, itself stable in the dark, is the end product of deactivation. The ground state S₀ cannot be formed by deactivation in the dark but is only formed during illumination. (3) The various ratios [S₀]/[S₁] which can be observed in a sample after deactivation following different preilluminations with flashes or continuous light. (4) The transients of the O₂ evolution rate in weak continuous light as observed after deactivation with or without flash preillumination. In all instances satisfactory agreement is found between the observations and the predictions of the model.     

Cars study of vibrationally excited H2 produced in formaldehyde dissociation

Coherent anti-Stokes Raman scattering (CARS) has been used to observe H₂ from H₂CO + hv H₂ + CO. Photolysis of K = 1 (ortho) lines of the 2¹4¹ S₁ ← S₀ transition produced no para-H₂ (<4% statistical); and demonstrated nuclear spin conservation. H₂ states v = 1, 2 and 3 were comparably populated.     

ASYMMETRIC SYNTHESIS OF PROLINE USING COBALT(III)-TETRAAMINE COMPLEXES

Abstract

The decarboxylation reaction of δ -cis-β-[Co(L₁)(pdH)]²⁺ complex yielded δ -cis-β-[Co(L₁) (R-pro)]²⁺, while the δ -cis-β-[Co(L₂) (S-pro)]²⁺ was obtained from the reaction of δ -cis-β-[Co(L₂) (pdH)]²⁺, where L₁ is (3R)3-methyl-1, 6-bis[(2S)-pyrrolidin-2-yl]-2, 5-diazahexane, L₂ is (3S) 3-methyl-1, 6-bis-[(2S)-pyrrolidin-2-yl]-2, 5-diazahexane, and pdH is the pyrrolidine-2, 2-dicarboxylate ion. The asymmetrically synthesized prolines were isolated via the decomposition of the decarboxylated complexes. The proline isolated from δ -cis-β-[Co(L₁) (R-pro)]²⁺ showed a specific rotation of +12.0, representing a 24% excess of R-proline over S-proline, while the proline isolated from δ -cis-β-[Co(L₂) (S-pro)]²⁺ showed a specific rotation of -10.0, indicating a 20% excess of S-proline over R-proline.     

HETEROGENEITY OF THE QUINONE ELECTRON ACCEPTOR SYSTEM IN BACTERIAL REACTION CENTERS

Abstract— In reaction centers from Rhodopseudomonas viridis, biphasicity of the charge recombination kinetics between P⁺, the primary electron donor, and Q_A and Q_B^-, the primary and secondary quinone electron acceptors, respectively, have been analyzed by the flash-induced absorption change technique. We have studied the effect of quinone environment modifications on the ratio of the two phases for the P⁺Q_A- ([A_fast/A_slow]^a) and P⁺Q_B^- ([A_fast/A_slow]^b) charge recombination processes. In reaction centers from Rps. viridis reconstituted in phosphatidylcholine liposomes a notable influence of the nature of the Q_B pocket occupancy was observed on (A_fast/A_slow)^a. This ratio is much affected by the presence of o-phenanthroline compared to reaction centers with an empty Q_B pocket or with terbutryn present. Because o-phenanthroline was proposed to hydrogen bind His^L190, whereas terbutryn does not, we suggest that a His^LI90-Fe-His^M217 (the equivalent to His^LI90 in the Q_A pocket) “wire” may be involved in the existence of the two conformational states associated with the two phases of charge recombination. In chromat-ophores from the T₁ (Ser^L223→ Ala; Arg^L217→ His) and T₄ (Tyr^L222→ Phe) mutants no modification of the (A_fast/A_slow)^a ratio is detected, whereas the (A_fast/A_slow)^b ratios are substantially modified compared to the wild type (WT). In the T₃ mutant (Phe^L216→ Ser; Val^M263→ Phe [4.1 Å apart from Q_A]), (A_fast/A_slow)^a is notably changed compared to the WT. Our data show that any modification in the close protein environment of the quinones and/or of the His^L190 and His^M217 affects the equilibrium between the two reaction center states. This is consistent with the existence of two reaction center states from Rps. viridis, associated with two different conformations of the quinones-histidines-iron system. This “wire” allows both quinone protein pockets to interact over quite long distances.     

LOCATION OF THE CAROTENOID 2Ag-STATE AND ITS ROLE IN PHOTOSYNTHESIS

The location of the carotenoid 2A_g-state (S₁) was studied by fluorescence spectroscopy in two series of carotenoids. One consisted of natural polyenes like phytoene, phytofluene, β-carotene, and neurosporene, and the other of minicarotenes, i.e., compounds similar to β-carotene, but with a smaller number of double bonds (n=3–9). A decrease of the S₁-S₀ energy gap with n was observed in both series, and extrapolation to n= 11 gave the energies 14 500 and 13 200 cm^?1 for β-carotene and lycopene, respectively. The neurosporene S₁ state was located at ca 16 000 cm^?1. A good relationship between the nonradiative relaxation rate and the number of conjugation was observed. The rate increased by a factor of 2.5 per double bond. The possible role of the S₁ state in reversible carotenoid ← chlorophyll electron-exchange energy transfer is discussed.     

KINETICS OF THE REACTION OF SULFIMIDES WITH POTASSIUM HYDROXIDE IN METHANOL

Abstract

The reaction of sulfimides with hydroxide ion in methanol gave the corresponding sulfoxide (the solvolysis product) and/or the corresponding α-methoxysulfide (the Pummerer type product). The pseudo first order rates for the solvolysis reaction and the Pummerer type reaction were determined using a large excess of potassium hydroxide. The rates of the solvolyses are correlated with [sgrave] values and the values of ρ _X = +1.2 and ρ _Y = +0.8 were obtained for aryl methyl N-aryl-sulfonylsulfimides (p-XC₆H₄S(NSO₂C₆H₄Y-p)CH₃), and both the activation enthalpy and entropy calculated are δH≠ = 18.8 kcal mol^?1 and δS≠ = –23.9 e.u. (PhS(NSO₂C₆H₄CH₃-p)CH₃), respectively. Hammett correlation with [sgrave] values for the Pummerer type reaction gave ρz = +2.0 for N-aryl-sulfonyltetramethylenesulfimides ((CH₂)₄SNSO₂C₆H₄Z-p), and the activation enthalpy and entropy are δH≠ = 27.9 kcal mol^?1 and δS≠ = +13.3 eu ((CH₂)₄SNSO₂C₆H₄CH₃-p), respectively. All these observations suggest that the solvolysis reaction proceeds via the initial nucleophilic attack of hydroxide ion on the sulfur atom of the sulfimide namely via an S _N 2 process at the sulfur atom whereas the Pummerer type reaction proceeds by way of the E 1cb mechanism.     

Nonadiabatic photodissociation dynamics

The photodissociation dynamics of the triatomic (or pseudo‐triatomic) system in the nonadiabatic multiple electronic states is investigated by employing a time‐dependent quantum wave packet method, while the time propagation of the wave packet is carried out using the split‐operator scheme. As a numerical example, the photodissociation dynamics of CH₃I in three electronic states ¹Q₁(A′), ¹Q₁(A″), and ³Q₀₊ is studied and CH₃I is treated as a pseudotriatomic model. The absorption spectra and product vibrational state distributions are calculated and compared with previous theoretical work. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

CORRELATION BETWEEN THE BINDING OF FORMATE AND DECREASED RATES OF CHARGE TRANSFER THROUGH THE PHOTOSYSTEM II QUINONES

Abstract— The binding parameters of bicarbonate to the thylakoid membrane at different formate concentrations have been established [Stemler and Murphy (1983) Photochem. Phorobiol. 38, 701–707]. Based on these parameters, predictions could be made concerning the effects of bicarbonate and formate on photosynthetic electron flow. In this work these effects of various concentrations of bicarbonate and formate are measured and compared to predictions from the binding study. Electron flow is measured between Q_A and Q_B (the primary and secondary quinone acceptors) and Q_B and the plastoquinone pool. Also, these same concentration effects are determined for silicomolybdate supported oxygen evolution. It is found that the results of the bicarbonate binding study are in good agreement with the concentration dependence determined for the quinone reactions, as well as the silicomolybdate reaction. The bicarbonate concentrations required for half-maximal effects are approximately 100 μM, 300 μM and 1.3 mM in the presence of 0, 20 mM and 100 mM formate, respectively. It is concluded that a hierarchy of possible electron flow rates exist. The slowest rates occur when formate is bound. A substantially higher rate occurs when neither formate nor bicarbonate (< 2 μM) are present, but only chloride is present. The highest rates of electron flow occur when bicarbonate is bound. The Q_A- Q_B→ Qa Qb^? Qa^? Qb^2– PQ → Q_a Q_b- PQ^2–, and the silicomolybdate reactions all have the same concentration dependence on formate and bicarbonate. From this it is concluded that a single binding site for formate and bicarbonate affect all of these reactions. The possibility that multiple sites exist with approximately equal affinities for bicarbonate cannot be excluded.     

PRIMARY PRODUCTS IN THE FLASH PHOTOLYSIS OF TRYPTOPHAN*

There has been considerable interest in the photochemistry of tryptophan in connection with ultraviolet inactivation of enzymes. Earlier flash photolysis work has demonstrated that the hydrated electron (e^-_aq) is an initial product in the irradiation of indole derivatives, accompanied by a longer-lived transient absorption near 500 nm attributed to an aromatic radical species[1–5]. Similar transients were observed in a recent flash photolysis study of lysozyme[6] in which it was proposed that inactivation is a consequence of electron ejection from 1 to 2 essential tryptophan residues in the active center. However, there has been uncertainty concerning the tryptophan radical structure and its relationship to the triplet state and radical spectra reported for tryptophan photolysis in low-temperature rigid media. This note reports a flash photolysis investigation of L-tryptophan (Trp) and 1-Methyl-L-tryptophan (1-MeTrp) undertaken to clarify these points. The flash photolysis apparatus and methods employed are described in Ref. [6].     

Delayed fluorescence from the lowest 1B+3u state of anthracene,due to hetero-triplet—triplet annihilation of 3anthracene* and 3xanthone*

The P-type delayed fluorescence (DF) S_i→S_o of aromatic compounds results from the population of excited singlet states S_i by triplet—triplet annihillation (TTA) of molecules in their lowest and metastable triplet state T₁ : T₁ + T₁

S_i + S_o; S_i may be any excited singlet state whose excitation energy E(S_i ? 2 E(T₁). TTA of unlike molecules A and B (hetero-TTA) may lead to excited singlet states either of A or of B. In particular, if E(T_A¹) < E(T₁^B), hetero-TTA may lead to excited singlet states S_k^A which are not accessible by TTA of 2 T₁^A. In the present paper we report the first example of the detection of the DF from a very short-lived upper excited singlet state S_k^A which has been populated by hetero-TTA. The systems investigated are liquid solutions of A = anthracene-h₁₀ or anthracene-d₁₀ or 9,10-dimethylanthracene and B = xanthone in 1,1,2-trichlorotrifluoroethane at 243 K. S_k^A is the lowest ¹B_3U⁺ state (B_b state) of anthracene.     

STEREOELECTRONIC PROPERTIES OF PHOTOSYNTHETIC AND RELATED SYSTEMS — V. AB INITIO CONFIGURATION INTERACTION CALCULATIONS ON THE GROUND AND LOWER EXCITED SINGLET AND TRIPLET STATES OF ETHYL CHLOROPHYLLIDE a AND ETHYL PHEOPHORBIDE a

Abstract— Ab initio configuration interaction wavefunctions and energies are reported for the ground state and many low-lying excited singlet and triplet states of ethyl pheophorbide a (Et-Pheo a) and ethyl chlorophyllide a (Et-Chl a), and are employed in an analysis of the electronic absorption spectra of these systems. In both molecules the visible spectrum is found to consist of transitions to the two lowest-lying ¹(π, π*) states, S₁ and S₂. The configurational compositions of S₁ and S₂ in both molecules are similar, and are described qualitatively in terms of a four-orbital model. The S₁← S₀ transition in each case is predicted to be intense, and is largely in-plane y-polarized, while the S₂← S₀ transition is predicted to be extremely weak and in-plane polarized. The orientation of the S₂← S₀ transition dipole is not conclusively established in the present calculations. The Soret band in both molecules is composed of transitions to no less than ten states (S_3-S₁₂ in Et-Chl a and S₃-S₇S₉-S₁₂. and S₁₄ in Et-Pheo a), which exhibit primarily (π, π*) character. The configurational compositions of these states are generally a complex mixture of excitations from both occupied macrocyclic π molecular orbitals and occupied orbitals with electron density in the cyclopen-tanone ring and the carbomethoxy chain. No clear correspondences are evident between respective Soret states of the two systems. Transitions to these states are generally intense and display a variety of in-plane polarizations. Two additional Soret states of Et-Pheo a, S₈ and S₁₃, exhibit primarily (n. π*) character. S₈ is characterized by excitations from u and non-bonding regions of the carbomethoxy chain, while S₁₃ is described by n →π* excitations involving the nitrogen atom of ring II. No corresponding (n, π*) states were found for Et-Chl a. In both molecules the lowest two triplet states, T₁ and T₂, are found to lie lower in energy than S₁. while T, and S₁ are approximately degenerate. The configurational compositions of T₁-T₄ of both molecules are nearly identical, and may be described by a four-orbital model. However, the compositions of T₁-T₄ differ sharply from those of S₁ and S₂. A number of higher-lying ³(π, π*) states of both molecules (T₅-T₁₃ in Et-Chi a and T₈-T₉, T₁₁-T₁₃ in Et-Pheo a) are found to have energies similar to the singlet Soret states, relative to S₀. They are characterized by a complex mixture of configurations which do not include significant contributions involving the four-orbital model. In addition, two ³(n, π*) states of Et-Pheo a, T₁₀ and T₁₄, are found, which are somewhat analogous to S₈ and S₁₃. Additional data presented include the charge distributions and molecular dipole moments of the S₀. S₁, and T₁ states of both molecules, as well as energies and oscillator strengths of computed S_n←S₁ and T_n←₁ transitions.     

Energies and Spin States of FeS0/−, FeS20/−, Fe2S20/−, Fe3S40/−, and Fe4S40/− Clusters

The structures and energies of the electronic ground states of the FeS^0/?, FeS₂^0/?, Fe₂S₂^0/?, Fe₃S₄^0/?, and Fe₄S₄^0/? neutral and anionic clusters have been computed systematically with nine computational methods in combination with seven basis sets. The computed adiabatic electronic affinities (AEA) have been compared with available experimental data. Most reasonable agreements between theory and experiment have been found for both hybrid B3LYP and B3PW91 functionals in conjugation with 6‐311+G* and QZVP basis sets. Detailed comparisons between the available experimental and computed AEA data at the B3LYP/6‐311+G* level identified the electronic ground state of ⁵Δ for FeS, ⁴Δ for FeS^?, ⁵B₂ for FeS₂, ⁶A₁ for FeS₂^?, ¹A₁ for Fe₂S₂, ⁸A′ for Fe₂S₂^?, ⁵A′′ for Fe₃S₄, ⁶A′′ for Fe₃S₄^?, ¹A₁ for Fe₄S₄, and ¹A₂ for Fe₄S₄^?. In addition, Fe₂S₂, Fe₃S₄, Fe₃S₄^?, Fe₄S₄, and Fe₄S₄^? are antiferromagnetic at the B3LYP/6‐311+G* level. The magnetic properties are discussed on the basis of natural bond orbital analysis.     

INTERACTION OF HYDROXYLAMINE WITH THE WATER-OXIDIZING ENZYME INVESTIGATED VIA PROTON RELEASE*

Abstract— Photosynthetic water oxidation is a four-step redox process which is driven by a one-quantum-one-electron reaction center. Stepwise electron Abstract—ion from the water-oxidizing enzyme is accompanied by stepwise proton release with the following stoichiometric pattern at given half-rise times: 1 H⁺ (250 μs, S₀→ S₁):0 H⁺(S₁→ S₂): 1 H⁺ (200 μs, S₂→ S₃): 2 H⁺ (1.2 ms, S₃→ S₄→ S₀). (Förster and Junge, 1985, preceding article in this issue). Hydroxylamine at low concentrations (?100 μ M) appears to compete with water at the active site of the water- oxidizing enzyme. Its interference shifts the dark state of the water-oxidizing enzyme by two steps backwards (Bouges, 1971). We found that the hydroxylamine-induced shift was also reflected in the stoichiometric pattern and in the kinetics of proton-release. In the presence of hydroxylamine, two protons per reaction center were released with a half-rise time of ? 2 ms upon the first exciting flash given to dark adapted thylakoids. This was slower than observed for each of the protons released during unperturbed water oxidation. One proton was released upon the second flash. The half-rise time of the main component observed upon the second flash in hydroxylamine-treated samples agreed with the one observed upon the fourth flash in the absence of hydroxylamine, which had been attributed to the S₀→ S₁ transition. The two protons which were observed upon the first flash in hydroxylamine-treated thylakoids may be due to hydroxylamine oxidation or to the association of water to the catalytic manganese center after detachment of oxidized hydroxylamine from its binding site.     

5T2-1A1 Spin transition and residual paramagnetism in bis(2,4-bis(2-pyridyl)thiazole)iron(II) complexes: mössbauer effect and magnetism

The ⁵⁷Fe Mössbauer effect in [Fe(pythiaz)₂] (BF₄)₂ (I) and [Fe(pythiaz)₂] (C&O₄)₂ (II) has been studied between 298 and 4.2°K (pythiaz = 2,4-bis(2-pyridyl)thiazole). At 298°K compound I shows a doublet with ΔE_Q(⁵T₂) = 1.29 mm sec^?1 and δ^1S(⁵T₂) = +0.93 mm sec^?1 characteristic of a ⁵T₂ ground state. At 236°K, a second doublet, typical for a ¹A₁ ground state appears. The transition ⁵T₂ å ¹A₁ progresses as the temperature is lowered but levels off below ≈ 120°K. At 4.2°K, 59% of the intensity is due to the ¹A₁ state, and ΔE_Q(¹A₁) = 1.59 mm sec^?1 and δ^1S(¹A₁) = +0.26 mm sec^?1. In an applied magnetic field, V_zz(¹A₁) < 0 has been determined Similar results have been obtained with compound II.Debye-Waller factors f5_T2 and f1_A1. were determined from the Mössbauer spectra under the assumption of Curie-Weiss dependence of the magnetism for the ⁵T₂ and constant μ_eff for the ¹A₁ ground state. The resulting temperature dependence of f1_A1 is highly unusual thus suggesting complicated magnetic behaviour of both ground states in the transition region. Two mechanisms for the nature of the transition are discussed, a “spin-flip” mechanism being the physically more reasonable one. The assumption of a simple Boltzmann distribution (“spin equilibrium”) may be ruled out for the solid but could be encountered in solutions.     

MECHANISM OF THE PHOTOSENSITIZED REDOX REACTIONS OF ACRIDINE ORANGE IN AQUEOUS SOLUTIONS-A SYSTEM OF INTEREST IN THE PHOTOCHEMICAL STORAGE OF SOLAR ENERGY†

-We have carried out a very detailed study, using fluorescence and optical flash photolysis techniques, of the photoreduction of methyl viologen (MV²⁺) by the electron donor ethylene diamine tetraacetic acid (EDTA) in aqueous solution sensitized by the dye acridine orange (AOH⁺). A complete mechanism has been proposed which accounts for virtually all of the known observations on this reaction. This reaction is novel in that both the triplet and the singlet state of AOH⁺ appear to be active photochemically. We have shown that mechanisms previously proposed for this reaction are probably incorrect due to an artifact. At pH 7 the fluorescence quantum yield φ_s of AOH⁺ is 0.26 ± 0.02 and the fluorescence lifetime is 1.8 ± 0.2 ns. φ_s is pH dependent and reaches a maximum of 0.56 at pH 4. The fluorescence of AOH⁺ is quenched by MV²⁺ at concentrations above 1 mM and the quenching obeys Stern-Volmer kinetics with a quenching rate constant of (1.0 ± 0.1) × 10¹⁰M^?1 s^?1. The quenching of the AOH⁺ excited singlet state by MV²⁺ almost certainly returns the AOH⁺ to its ground state with no photochemistry occurring. EDTA also quenches the fluorescence of AOH· with Stern-Volmer kinetics but with a smaller rate constant (6.4 ± 0.5) × 10⁸M^?1s^?1 at pH 7. In this case the quenching is reactive resulting in the formation of semireduced AOH. In the presence of MV²⁺, flash irradiation of AOH⁺ does result in the reversible formation of the semireduced MV? which absorbs at 603 nm. We attribute this to a photochemical reaction of the triplet state of AOH⁺ with MV²⁺. The initial quantum yield for formation of MV? (φ_MV:)₀ was found to be constant at 0.10 ± 0.05 for [MV²⁺] from 5 × 10^?5 to 1.0 × 10^?3 with [AOH⁺] = 8 × 10^?6M. Previous workers had found that (φ_MV:)₀ appears to decrease with decreasing [AOH⁺]; however, on careful investigation, we found this was most probably due to quenching of the triplet state of AOH⁺ by trace amounts of oxygen. When EDTA is added to a mixture of AOH ⁺ and MV²⁺ at pH 7, the photochemical formation of MV? becomes irreversible as the [EDTA] is increased. The quantum yield for the irreversible formation of MV? exceeds 0.10 becoming as large as 0.16 for [EDTA] = 0.014M. This fact requires that an alternative photochemical process must be operative and we present evidence that this is a reaction of EDTA with the excited singlet state of AOH⁺ to produce the semi-reduced AOH- which then reacts with MV²⁺ to produce MV?. The full kinetic scheme was tested by computer simulation and found to be totally consistent. This also enabled the processing of a full set of rate constants. When colloidal PtO₂ was added to the optimal mixture [EDTA] = 3.4 × 10^?2M; [MV²⁺] = 5 × 10^?4M; [AOH⁺] = 4 × 10^?5M; pH6 H₂ gas was produced at a rate of 0.2μmol H₂h^?1. Thus, acridine orange should serve as an effective sensitizer in reactions designed to use solar energy to photolyze water.     

An Estimate of the Interatomic Distances in Monohaloacetylene Radical Cations from Photoelectron-spectroscopic Data

A convenient method is given for the semiquantitative determination of those changes ΔS_i in internal coordinates, which describe the structure of the radical cation M⁺(Ψ) relative to the neutral molecule M in its electronic ground state. The changes ΔS_i correspond to those associated with the relaxation process which follows the ionisation M + hv → M⁺(Ψ) + e, M⁺ being in the electronic state Ψ. The method, based on the procedure originally developped by Smith & Warsop [3], uses the spacing and relative intensity of the vibrational fine-structure components of the bands in the photoelectron spectrum of M. From these data are calculated the changes ΔQ_k in normal coordinates, which are then transformed into the ΔS_i by applying the L -matrix. The changes ΔR_CX, ΔR_CC and ΔR_CH which describe the structure of the radical cations of the four monohaloacetylenes I(X) (X = F, Cl, Br, I) in their ² II _Ω(1) and ² II _Ω(2) states have been determined. It is shown that the results are in agreement with theoretical expectation and that they confirm the band assignement proposed in a previous communication [2].     

乳酸类合成子构建的四连接螺旋手性配位聚合物的合成、结构和光催化性质

通过乳酸衍生物和3-溴-4-羟基苯甲酸的组合得到对映体3-溴-4-(((1R)-1-羧基乙基)氧基)苯甲酸(R-H₂bba)和3-溴-4-(((1S)-1-羧基乙基)氧基)苯甲酸(S-H₂bba)。以其为手性合成子在水热条件下分别与1,3-二(吡啶-4-基)丙烷(1,3-dpp)和Ni²⁺反应,构建了对映手性配位聚合物{[Ni(R-bba)(1,3-dpp)(H₂O)_0.5]·1.5H₂O}_n (HU12-R)和{[Ni(S-bba)(1,3-dpp)(H₂O)_0.5]·1.5H₂O}_n (HU12-S)。结构分析揭示HU12-R和HU12-S是具有dia网络特征的三维螺旋骨架。在骨架中,阴离子配体R-bba^2-和S-bba^2-分别与Ni²⁺中心连接在一起围绕2₁螺旋轴得到一对小的对映螺旋链,而1,3-dpp与Ni²⁺中心则围绕4₁螺旋轴构建出另外一对大的对映螺旋链。电化学测试显示HU12-R属n型半导体,具有低阻抗性质,对紫外可见光有很强的吸收能力。进一步光催化实验证实在紫外光照射下所得配合物对染料降解有明显催化效果。     

裸露金属簇状化合物K4PbxSn9-x的119Sn、207Pb多核核磁共振研究

本文对乙二胺溶液中裸露金属原子簇用¹¹⁹Sn及²⁰⁷Pb核磁共振作了研究。对每个峰做了标识。根据谱线强度进行分析,得知溶液中锡与铅的比例大于固体中的比例。从自由能的角度看,Pb₂Sn₇^4-是最不稳定的一种原子簇,本文还对谱线中各条线都进行了理论拟合,结果与实验相吻合。