Synthesis of d1-4,5,6-trinor-3,7-inter-m-phenylene-3-oxaprostaglandins including one which inhibits platelet aggregation

The synthesis of $\text{d1}$-4,5,6-trinor-3,7-inter-$\text{m}$-phenylene-3-oxaprostaglandins oxaprostaglandins of the E₁ and F₁α series⁷ from 6-endo-(1-heptenyl)-bicyclo[3:1:0]hexan-3-one (III), is described. Preliminary biological screening data for gerbil colon smooth muscle stimulation, rat blood pressure and substrate specificity toward 15-hydroxyprostaglandin dehydrogenase is presented. Platelet function studies, both $\text{in vitro}$ and $\text{in vivo}$ of $\text{d1}$-4,5,6-trinor-3,7-inter-$\text{m}$-phenylene-3-oxa-PGE₁, methyl ester (VIII) are presented.     

Synthesis of dl-4,5,6-trinor-3,7-inter-m-phenylene-3oxaprostaglandins including one which inhibits platelet aggregation.

The synthesis of dl-4,5,6-trinor-3,7-inter-m-phenylene-3-oxaprostaglandins of the E1 and F1alpha series from 6-endo-(1-heptenyl)-bicyclo[3:1:0]hexan-3-one (III), is described. Preliminary biological screening data for gerbil colon smooth muscle stimulation, rat blood pressure and substrate specificity toward 15-hydroxyprostaglandin dehydrogenase is presented. Platelet function studies, both in vitro and in vivo of dl-4,5,6-trinor-3,7-inter-m-phenylene-3-oxa-PGE1, methyl ester (VIII) are presented.     

Interactions of prostaglandin E1 (PGE1) and LRH on anterior pituitary function

Numerous biochemical pathways influence the synthesis and release of anterior pituitary hormones. Releasing factors extracted from the hypothalamus and prostaglandins (PGs) appear to alter a common biochemical activity, adenyl cyclase, in pituitary cells. Luteinizing hormone releasing hormone (LRH), prostaglandin (PGE₁), 7 oxa-13-prostynoic acid and cycloheximide were tested for individual and interacting effects on the in vitro release of FSH, LH and prolactin from hemipituitaries of 15 day old female rats. LRH (10 ng/ml) consistently released both LH and FSH in all in vitro experiments and inhibited prolactin release in 1 of 2 experiments. Lower concentrations (5 and 1 ng/ml) also stimulated LH and FSH release but did not influence prolactin release. Concurrent depletion of stored LH and FSH in the gland was observed. PGE₁ in a 6.5 hour incubation increased the storage of LH within the gland in the absence of LRH. In a 1.5 hour incubation in the presence of LRH, storage of LH was also increased. PGE₁ had no effect on LH and FSH release; however, in 1 of 2 experiments it stimulated prolactin release in the absence of LRH. Prostynoic acid stimulated LH and FSH release but did not synergize with LRH action in the same tissue. Cycloheximide did not affect LH release during the first 30 minutes of incubation; however, the release during the subsequent 1 hour was significantly inhibited. Similar tissue also exposed to cycloheximide was still responsive to LRH during the latter 1 hour incubation period. Cycloheximide had no effect on prolactin storage and release from the same tissue.     

Influence of dietary vitamin E on prostaglandin biosynthesis in rat blood

A vitamin E (-tocopherol) deficient diet stimulated prostaglandin biosynthesis in coagulating rat blood. Prostaglandins were extracted from serum, purified and bioassayed. The identity of prostaglandin E₂ was confirmed by gas chromatography-mass spectrometry. Withholding vitamin E from the diet caused a marked increase in PGE₂ and a lesser increase in PGF₂ production in serum. In rats maintained on diets containing different concentrations of vitamin E, serum concentrations of PGE₂ and PGF₂ were inversely related to serum concentrations of -tocopherol. These data suggest that in vivo -tocopherol inhibits the endogenous conversion of arachidonic acid into PGE₂ and PGF₂. The possibility that -tocopherol may inhibit the formation of endoperoxide intermediates of PGE₂ and PGF₂ biosynthesis and subsequent induction of platelet aggregation is discussed.     

Cooperative erythropoietic assay of several steroid metabolites in polycythemic mice

A blinded cooperative assay of several androstane and pregnane steroid metabolites has been carried out in order to determine whether 5β-H derivatives are as active as testosterone in stimulating in vivo erythropoiesis. The steroids tested were: testosterone, 5-dihvdrotestosterone, 5β-dihydrotestosterone, 5β-pregnane-3,20-dione, 3-dihydroxy-5β-pregnàne-11,20-dione and 3β-hydroxy-5β-pregnan-20-one. The incorporation of radioactive iron into newly formed red cells in exhypoxic polycythemic mice was used to compare the effects of the steroids. Testosterone and 5-dihydrotestosterone both produced significant increases in ⁵⁹Fe incorporation. 5β-dihydrotestosterone, 5β-pregnane-3,20-dione, 3-hydroxy-5β-pregnane-11,20-dione and 3β-hydroxy-5β-pregnan-20-one were all devoid of significant erythropoietic activity in polycythemic mice in almost all instances. Thus, under the conditions chosen, this study failed to demonstrate that 5β-steroids increase radioactive iron incorporation in red cells of exhypoxic polycythemic mice.     

Chemomodulatory effects of Terminalia chebula against nickel chloride induced oxidative stress and tumor promotion response in male Wistar rats

Nickel, a major environmental pollutant is a known potent nephrotoxic agent. In this communication we report the chemopreventive effect of Terminalia chebula on nickel chloride (NiCl₂) induced renal oxidative stress, toxicity and cell proliferation response in male Wistar rats. Administration of NiCl₂ (250 μmoL Ni/kg body weight) to male Wistar rats resulted in an increase in the reduced renal glutathione content (GSH), glutathione-S-transferase (GST), glutathione reductase (GR), lipid peroxidation (LPO), H₂O₂ generation, blood urea nitrogen (BUN) and serum creatinine with a concomitant decrease in the activity of glutathione peroxidase (p<0.001). Nickel chloride (NiCl₂) treatment also induced tumor promotion markers, viz., ornithine decarboxylase (ODC) activity and thymidine [³H] incorporation into renal DNA (p<0.001). Prophylactic treatment of rats with T. chebula (25 mg/kg body weight and 50 mg/kg body weight) daily for one week resulted in the diminution of NiCl₂ mediated damage as evident from the down regulation of glutathione content, GST, GR, LPO, H₂O₂ generation, BUN, serum creatinine, DNA synthesis (p<0.001) and ODC activity (p<0.01) with concomitant restoration of GPx activity. Thus, the present investigation suggests that T. chebula extract could be used as therapeutic agent for cancer prevention as evident from this study where it blocks or suppresses the events associated with chemical carcinogenesis.     

Effects of CO2-bath immersion (100 ppm) on thermoregulatory responses in humans

The effects of CO₂ (100 ppm) bathing were investigated. It was found that the chest blood flow, chest sweat rate and tympanic temperature were significantly greater during the immersion in CO₂ bathing than in freshwater bathing (P<0.05). Thus, CO₂ bathing at 100 ppm could produce cutaneous vasodilatation in the immersed skin, affecting thermoregulation.     

The rhodium(III) trisacetonitrile complexes: a re-investigation of the synthesis of fac- and mer- [RhCl3(CH3CN)3], their characterization by 2D NMR spectroscopy and the X-ray crystal structure of mer-[RhCl3(CH3CN)3] · CH3CN

It is shown that the reaction of RhCl₃·3H₂O with acetonitrile normally produces mixtures of mer- and fac-[RhCl₃(CH₃CN)₃] (1a and 1b, respectively). The IR and ¹H NMR spectra of these isomers were re-investigated. Their two-dimensional (¹⁰³Rh,¹H) NMR spectra were also recorded. Equilibrium and exchange studies of 1a and 1b in CD₃C were performed. It was found that in 1a the exchange rate of the nitrile molecule trans to Cl is much faster than those of mutually trans nitriles. Also the nitrile molecules in 1b underwent fast exchange in CD₃CN; however, their rate was slightly faster than that of the more labile CH₃CN in 1a. The X-ray crystal structure of mer-[RhCl₃(CH₃CN)₃]·CH₃CN (1c) was determined. Crystal data: triclinic space group

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Kinetics of nucleophilic attack on coordinated organic moieties Part 29. Mechanism of addition of tertiary phosphines and phosphites to the tropylium ring of [M(CO)3(η-C7H7] (M = Cr, Mo, W) cations

Kinetic studies of the addition of a wide range of tertiary phosphines and phosphites to the tropylium ring of the cation [Cr(CO)₃(η⁷-C₇H₇]⁺ (1) reveal the two-term raw, k_obs = k₁[PR₃] + k₋₁. This is consistent with the reversible equilibrium process (i) which is also confirmed from IR and ¹H NMR studies. In the case of the highly basic nucleophiles PBu₃ⁿ and PEt₂Ph, the rate is dominated by the k₁ term and the equilibrium lies far to the right.

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The first-order rate constants k₁, for addition to the tropylium ring decrease markedly down the series PBu₃ⁿ>PEt₂Ph>P(4-MeOC₆H₄)₃>P(4-MeC₆H₄)₃>P(C₆H_{11 3}>PPh₂(4-MeC₆H₄)>PPh₃>P(2-CNC₂H₄)₃>P(OBuⁿ)₃ (overall variation 10⁴). This reactivity order parallels the decreasing electron availability at the phosphorus centres, as confirmed by the linear correlation between log k₁ and the Tolman Σ_χ values for the nucleophiles. Excellent Hammett and Brønsted correlations are also observed for ring addition by a range of P(4-XC₆H₄)₃ nucleophiles. The Brønsted slope, , of 0.7 conirms the major importance of basicity in determining nucleophilicity towards cation 1. Kinetic studies of the related additions of PBu₃ⁿ to the cations [M(CO)₃(η⁷-C₇H₇]⁺ (M = Mo, W) reveal the rate law, Rate = k₁[M][PBu₃ⁿ, and show only a small dependence of k₁ on the nature of metal (Cr>WMo; 2:1.1:1). These data, together with the associated activation parameters, support a mechanism involving direct addition (k₁) of the phosphorus nucleophiles to the tropylium ring, and are inconsistent with initial rate-determining attack at the metal centre.     

Preparation of trimethylsilyl alkyne complexes of bis(pentamethylcyclopentadienyl)zirconium, (η-C5Me5)2Zr(RC≡CSiMe3), and their regioselective reactions with nitrous oxide

Benzene solutions of Cp^*₂ZrCl₂ (1) (Cp^* = η⁵-C₅Me₅) react with the alkynes Me₃SiC≡CPh, Me₃SiC≡C(c-C₅H₉) and Me₃SiC≡CCMe₃ in the presence of Na/Hg amalgam to afford high yields of the respective alkyne complexes Cp^*₂Zr(Me₃SiC≡CPh) (2), Cp^*₂Zr{Me₃SiC≡C(c-C₅H₉)} (3) and Cp^*₂Zr(Me₃SiC≡CCMe₃) (4) as crystalline compounds. Complex 2 crystallizes in the triclinic space group with a = 9.791(6), b = 10.466(6), c = 15.756(12) Å, = 86.09 (5), β = 72.09(5), γ = 72.06(4)° and Z = 2. The least-squares refinement converged to R(F) = 0.0604 and R(wF) = 0.0628 for the 3655 unique data with F_o > 4σ (F_o). Salient metrical parameters of the bound alkyne include the following: C(30)-C(31) = 1.340(9) Å; Zr-C(30) = 2.178(6) Å; Zr-C(31) = 2.219(5) Å; C(30)-C(31)-Si = 141.0(5)°; C(31)-C(30)-C(26) = 135.5(5)°. Nitrous oxide reacts with 2 or 3 to afford ((5) R = Ph; (6) R = c-C₅H₉) and 1 equiv. of N₂ via an intermediate, , which is unstable with respect to loss of dinitrogen to give the oxametallacyclobutene derivatives 5 and 6. The oxygen-atom insertion is regiospecific for the Zr-C bond that is attached to the carbyl (Ph or c-C₅H₉) substituent. Under similar conditions, complex 4, in which the alkyne is particularly labile, gives a myriad of products in its reaction with N₂O.     

Correlation of structure and emission in solid state copper(I) complexes; [Cu4I4(CH3CN)2(L)2], L = aniline derivative

Four complexes of the type [Cu₄I₄(CH₃CN)₂(L)₂], L = aniline derivative: Cu₄I₄(CH₃CN)₂(2,6-dimethylaniline)₂ (I), triclinic, , a = 12.449(3), B = 14.108(6), C = 10.606(4) Å, = 73.46(3), β = 95.00(2), γ = 73.42(3)°, V = 1682.3(10) ų; Cu₄I₄(CH₃CN)₂(o-ethylaniline)₂ (II), triclinic,

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, V = 1734.0(8) ų; Cu₄I₄(CH₃CN)₂(6-ethyl-o-toluidine)₂ (III), orthorhombic, Pnam, a = 14.976(6), b = 21.187(6), C = 12.545(2) Å, V = 3980.7(2) ų; Cu₄I₄(CH₃CN)₂(p-anisidine)₂ (IV), monoclinic, A2/a, A = 20.032(10), B = 7.863(1), C = 18.715(9) Å, β = 101.56(4)°, V = 2888.0(2) ų; were examined by single crystal X-ray diffraction. Complexes I and II have no internal symmetry elements, III has an internal mirror and IV has a two-fold axis. Ab initio calculations based on the atomic positional parameters of complexes containing the three types of symmetry elements reveal HOMO orbitals to be dominated by the p orbitals of the iodine atoms whereas the LUMO orbitals contain major contributions from copper based p orbitals.     

Olefin versus sulfur coordination of benzo[b]thiophene (BT) in Cp(CO)2Re(η:η-μ2-BT)Cr(CO)3

Reactions of Cr(CO)₃(η⁶-BT), in which the Cr is π-coordinated to the benzene ring of benzo[b]thiophene (BT), with Cp′(CO)₂Re(THF), where Cp′ = η⁵-C₅H₅ or η⁵-C₅Me₅, give the products Cp′(CO)₂Re(η²:η⁶-μ₂-BT)Cr(CO)₃ in which the Cr remains coordinated to the benzene ring and Re is bound to the C(2)=C(3) double bond. An X-ray diffraction study of Cp(CO)₂Re(η²:η⁶-μ₂-BT)Cr(CO)₃ (3) provides details of the geometry. This structure contrasts with that of the Cp′(CO)₂Re(BT) complexes that exist as mixtures of isomers in which the BT is coordinated to the Re through either the double bond (2,3-η²) or the sulfur (η¹(S)). Thus, the electron-withdrawing Cr(CO)₃ group in 3 stabilizes the 2,3-η² mode of BT coordination to the Cp′(CO)₂Re fragment. Implications of these results for catalytic hydrodesulfurization of BT are discussed. Crystal data for 3: triclinic, space group

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Structural studies on [Mo3S4] and [Mo3S4Cu] complexes with tripodal ligands providing various NxOy (x + Y = 3) donor sets

The interaction of 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (taci) and its N-methylated derivative 1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol (tdci) with the incomplete [Mo₃S₄]⁴⁺ cube and the heterometallic [Mo₃S₄Cu]⁴⁺ cube have been investigated by X-ray analysis. The crystal structures of [Mo₃S₄(taci+ rmC₃H₆O-H₂O)₃-4H]·2OH₂O (1a, rhombohedral, space group R32, A = 15.964(3), C = 40.59(1) Å, Z = 6), [Mo₃S₄(tdci)₃]Br₄·9.5EtOH·5H₂O (2a, triclinic, space group

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and [CuBrMo₃S₄(tdci)₃]Br₃·11 H₂O·EtOH (3a, monoclinic, space group P2,/n, A = 14.887(3), B = 22.570(4), C = 21.974(5) Å, β = 98.54(2)°, Z = 4) revealed andN-N-O and an N-O-O coordination mode for taci and tdci, respectively. In 1a, taci is coordinated as an anion with deprotonated oxygen and nitrogen donors. In addition, the non-coordinating amino group reacted with one equivalent; of acetone, forming a Schiff base condensation product. For 2a, short Mo---O bonds and high pK_a values (compared to the aqua ion [Mo₃S₄(H₂O)₉]⁴⁺) indicate the formation of a zwitterionic form of the tdci ligand with coordinated alkoxo groups and peripheral dimethylammonium groups. No significant differences were found for the structural properties of the Mo-tdci fragment in 2a and 3a. The coordination modes of taci and tdci, as observed in the solid state, are in agreement with the previously reported solution structures, established by NMR spectroscopy. They are attributed to the specific steric requirements of the two ligands and to a pronounced preference of the [Mo₃(μS)₃(μ₃S)]⁴⁺ core to coordinate a nitrogen donor trans to μ₃S.     

Borrelia Burgdorferi Upregulates the Adhesion Molecules E-selectin, P-selectin, ICAM-1 and VCAM-1 on Mouse Endothelioma Cells in vitro

In order to obtain more information on processes leading to Borrelia burgdorferi-induced inflammation in the host, we have developed an in vitro model to study the upregulation of cell surface expression of adhesion molecules on endothelial cells by spirochetes. A mouse endothelioma cell line, derived from brain capillaries, bEnd3, was used as indicator population. bEnd3 cells were incubated with preparations of viable, inactivated or sonicated spirochetes and the expression of E-selectin, P-selectin, ICAM-1 and VCAM-1 was monitored by immunocytochemistry and quantified by cell surface ELISA. We show that all three spirochetal preparations are able to upregulate cell surface expression of E-selectin, P-selectin, ICAM-1 and VCAM-1 on bEnd3 cells in a dose-dependent manner. The kinetics of cell surface expression of the individual adhesion molecules in the presence of Borrelia burgdorferi showed maxima at about 50 h of incubation or later; this was distinct from results obtained with sonicated-preparations of Escherichia coli bacteria or with enterobacterial LPS where peak expression was observed between 4 h and 16 h. The fact that Borrelia burgdorferi does not contain conventional LPS suggests that the mode of induction of adhesion molecules on endothelial cells is influenced by the phenotype of bacteria. At the peak of spirochete-induced cell surface expression of adhesion molecules (≈50 h), bEnd3 cells were found to bind cells of a VLA-4⁺ B lymphoma line (L1-2) much more efficiently than untreated control cells. The binding of L1-2 cells to presensitized bEnd3 cells was significantly inhibited (more than 75%) in the presence of monoclonal antibodies to both VLA-4 and its endothelial counterreceptor VCAM-1. These findings demonstrate that Borrelia burgdorferi organisms are able to induce functionally active adhesion molecules on endothelial cells in vitro and suggest that E-selectin, P-selectin, ICAM-1 and VCAM-1 play an important role in the pathogenesis of spirochetal infection.     

The synthesis and characterization of a cationic technetium(V) phenylimido complex. The X-ray crystal structure of [TcCl2(NPh)(PMe2Ph)3](BPh4)

The reaction of the neutral Tc(V) phenylimido complex [TcCl₃(NPh)(PPh₃)₂] with excess PMe₂Ph in refluxing MeOH gives the cationic, tris-dimethylphenylphosphine complex [TcCl₂(NPh)(PMe₂Ph)₃]⁺, which is isolated as the tetraphenylborate salt. The IR spectrum of the crystalline product shows a medium intensity band at 1102 cm⁻¹ which is assigned to ν(TcN) from the phenylimido core. The ¹H NMR spectrum of the diamagnetic complex shows a series of multiplets in the aryl region and three distinct signals near 2 ppm from the phosphine methyl groups. The X-ray crystal structure, which is the first for a cationic technetium organoimido complex, shows a meridional arrangement of phosphine ligands with a chloride ligand coordinated trans to the phenylimido unit. The TcN bond length of 1.711(2) Å is consistent with the dianionic nature of the organonitrogen core. The Tc---N---C bond angle of 178.8(2)° reflects the sp hybridization of the phenylimido nitrogen atom. The coordination geometry is best described as a distorted octahedron. Crystal data for C₅₄H₅₈BCl₂NP₃Tc: triclinic space group

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. Structure solution based on 9986 observed reflections converged at R = 3.65%, R_w = 5.43%, GOF = 1.82.     

Complement is required for the induction of endotoxic fever in guinea pigs and mice

(1) Cobra venom factor (CVF)-induced hypocomplementemia dose-dependently attenuates the febrile responses of guinea pigs and mice to intraperitoneally (ip) but not to intravenously (iv) injected endotoxic bacterial lipopolysaccharide (LPS). (2) Iv but not ip LPS causes fever in complement component 3 (C3) gene-ablated mice, but neither iv nor ip LPS evokes a body core temperature (T_c) rise when WT and these mice's C5a receptors type 1 are blocked. C5 knockout mice also do not develop fever following either iv or ip LPS. C5a thus appears to be a critical mediator of LPS fever. (3) C5 knockouts develop fever in response to intracerebroventricularly (icv) injected LPS or prostaglandin (PG)E₂; the site of action of C5a is therefore peripheral rather than central. (4) The initiation of the febrile responses to both iv and ip LPS is temporally correlated with the appearance of LPS in the liver's Kupffer cells (Kc). (5) PGE₂ is released by liver in immediate response to the injection of CVF into the portal vein of anesthetized guinea pigs; its level rises quickly to its maximum. LPS injected similarly also evokes a quick release of PGE₂ from the liver; it, however, is prevented by prior hypocomplementation. (6) Neither LPS nor IL-1β induces PGE₂ release from Kc in vitro within the first hour after treatment, but serum C and C plus LPS or IL-1β very quickly trigger PGE₂ increases of similar magnitudes, catalyzed non-differentially by cyclooxygenase (COX)-1 and COX-2. Kc would thus appear to be the principal site of action of C5a, inducing the release of PGE₂. (7) PGE₂ is detectable in the plasma of conscious guinea pigs in temporal correlation with the onset of the T_c rise following ip LPS; cytokines appear significantly later. (8) Taken together, these results indicate that LPS-activated C, rather than LPS or IL-1β by itself, triggers PGE₂ release by Kc. This PGE₂ could be the factor that stimulates vagal afferents, thereby providing the signal to the brain that mediates the febrile response.     

The effect of temperature changes on the spontaneous activity in the neural ganglia of the cockroach, Periplaneta americana

1. 1.|The effect of localized heating or protocerebrum (bp), the prothoracic (t₁), metathoracic (t₃) and the sixth abdominal (a₆) ganglion on the spontaneous neuronal firing rate in these ganglia was investigated in Periplaneta americana.

2. 2.|In almost every case heating the ganglion increased the firing rate. The most heat sensitive were bp, t₃ and t₁, a₆ was much less so.

3. 3.|In bp and t₁ the firing rate stayed on an increased level even 90 s after the thermal stimulus was over.

4. 4.|The differentiated thermosensitivity of the tested ganglia is discussed in terms of thermoregulatory behaviour of the cockroach.

Effects of indomethacin on intestinal secretion, prostaglandin E and cyclic AMP: Evidence against a role for prostaglandins in cholera toxin-induced secretion

The effects of indomethacin on intestine mucosal cAMP, intestinal fluid secretion, and mucosal and fluid PGE were studied in rabbits in vivo following challenge with cholera toxin. Indomethacin had no effect on cholera toxin-induced fluid secretion or cAMP accumulation. Inhibition of PGE synthesis was achieved by the administration of two but not one injection of indomethacin. These studies provide evidence against a role for PGE in mediating cholera toxin-induced secretion and point out the need to measure prostaglandin levels when using prostaglandin synthetase inhibitors in vivo.     

The effects of carbon dioxide concentration on oxygen evolution and fluorescence transients in synchronous cultures of Chlorella pyrenoidosa

1. 1. The steady-state fluorescence yield of Chlorella pyrenoidosa is strongly affected by CO₂ concentration: the yield is approximately 2-fold higher in the presence than in the absence of CO₂. During induction, in the presence of saturating CO₂, accelerating oxygen evolution is paralleled by rising fluorescence (M₂-P₃ transient); in the absence of CO₂, fluorescence yield remains at the low M₂ level.

2. 2. Both illumination and CO₂ content are important in determining the steady-state fluorescence yield: at lower illuminations, lower concentrations of CO₂ are required to obtain a maximum fluorescence yield.

3. 3. The slow fluorescence transients are not affected directly by pH but only indirectly through the CO₂ concentration.

4. 4. The CO₂-dependent fluorescence rise (M₂-P₃ transient) is most readily observed in cells harvested early in the light period of a synchronous culture, but it can also be elicited in cells harvested during the dark period.

5. 5. Addition of 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU) to CO₂-deprived cells raises the fluorescence yield approximately 4-fold, that is to the same high level as cells supplied with CO₂ and DCMU.

6. 6. The effects of CO₂ provide a new example of a marked parallelism between photosynthetic electron transport and fluorescence. To explain such parallelism, it seems necessary to postulate large changes in the de-excitation processes within Photosystem II units or in the distribution of excitation between Photosystems I and II.

From the {Cu(μ2-S)N}4 butterfly architecture to the {Cu(μ3-S)N}12 double wheel

Copper(I) complexes with {Cu(μ₂-S)N}₄ and {Cu(μ₃-S)N}₁₂ core portions of butterfly-shaped or double wheel architectures have been isolated in the reaction of Cu(I) with the Schiff base ligand C₆H₄(CHNC₆H₄S)₂, “iso-abt”, under different conditions. containing the tetranuclear electroneutral complex is formed by the reaction of CuI in acetonitrilic solution and recrystallization from DMF, whereas containing dodecanuclear wheels is accessible starting from CuBF₄. Complexes 2 and 4 represent the first examples of cyclic complexes with the same overall stoichiometry but different ring sizes. The ligand induces two different coordination environments around copper(I) by switching between μ₂- and μ₃-sulfur bridging modes.