Search

A series of novel chalcone and thiol-Michael addition analogues was synthesized and tested against Mycobacterium tuberculosis and other clinically significant bacterial pathogens. Previously reported chalcone-like antibacterials (1a–c and 2) were used as a training set to generate a pharmacophore model. The chalcone derivative hit compound 3 was subsequently identified through a pharmacophore-based virtual screen of the Specs library of >200 000 compounds. Among the newly synthesized chalcones and thiol-Michael addition analogues, chalcones 6r and 6s were active (minimum inhibitory concentrations (MICs) = 1.56–6.25 μg/mL) against Gram-positive pathogens Bacillus anthracis and Staphylococcus aureus [methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA)]. The chalcone thiol-Michael addition derivatives 7j–m showed good to excellent antibacterial activities (MICs = 0.78–6.25 μg/mL) against Enterococcus faecalis, B. anthracis, and S. aureus. Interestingly, the amine-Michael addition analogue 12a showed promising anti-MRSA activity (MIC = 1.56 μg/mL) with a selectivity index of 14 toward mammalian Vero cells. In addition, evaluation of selected compounds against biofilm and planktonic S. aureus (MSSA and MRSA) revealed that 12a exhibited bactericidal activities in these assays, which was overall superior to vancomycin. These properties may result from the compounds dissipating the proton motive force of bacterial membranes.

Background Endophytic fungi are being recognized as vital and untapped sources of a variety of structurally novel and unique bioactive secondary metabolites in the field of natural products drug discovery. Herein, this study reports the isolation and characterization of secondary metabolites from an endophytic fungus Penicillium polonicum (NFW9) associated with Taxus fuana. Method The extracts of the endophytic fungus cultured on potato dextrose agar were purified using several chromatographic techniques. Biological evaluation was performed based on their abilities to inhibit tumor necrosis factor-alpha (TNF-α)-induced nuclear factor-kappa B (NF-κB) and cytotoxicity assays. Results Bioactivity-directed fractionation of the ethyl acetate extract of a fermentation culture of an endophytic fungus, Penicillium polonicum led to the isolation of a dimeric anthraquinone, (R)- 1,1',3,3',5,5'-hexahydroxy-7,7'-dimethyl[2,2'-bianthracene]-9,9',10,10'-tetraone (1), a steroidal furanoid (-)-wortmannolone (2), along with three other compounds (3-4). Moreover, this is the first report on the isolation of compound 1 from an endophytic fungus. All purified metabolites were characterized by NMR and MS data analyses. The stereo structure of compound 1 was determined by the measurement of specific optical rotation and CD spectrum. The relative stereochemistry of 2 was confirmed by single-crystal X-ray diffraction. Compounds 2-3 showed inhibitory activities in the TNF-α-induced NF-κB assay with IC50 values in the range of 0.47-2.11 µM. Compounds 1, 4 and 5 showed moderate inhibition against NF-κB and cancer cell lines. Conclusion The endophytic fungus Penicillium polonicum of Taxus fuana is capable of producing biologically active natural compounds. Our results provide a scientific rationale for further chemical investigations into endophyte-producing natural products, drug discovery and development.

On the basis of recently reported abyssinone II and olympicin A, a series of chemically modified flavonoid phytochemicals were synthesized and evaluated against Mycobacterium tuberculosis and a panel of Gram-positive and -negative bacterial pathogens. Some of the synthesized compounds exhibited good antibacterial activities against Gram-positive pathogens including methicillin resistant Staphylococcus aureus with minimum inhibitory concentration as low as 0.39 μg/mL. SAR analysis revealed that the 2-hydrophobic substituent and the 4-hydrogen bond donor/acceptor of the 4-chromanone scaffold together with the hydroxy groups at 5- and 7-positions enhanced antibacterial activities; the 2',4'-dihydroxylated A ring and the lipophilic substituted B ring of chalcone derivatives were pharmacophoric elements for antibacterial activities. Mode of action studies performed on selected compounds revealed that they dissipated the bacterial membrane potential, resulting in the inhibition of macromolecular biosynthesis; further studies showed that selected compounds inhibited DNA topoisomerase IV, suggesting complex mechanisms of actions for compounds in this series.

The temperature dependence of the structures of a wide range of mixed-cation Tutton’s salts of general formula K2xRb2–2x[Cu(H2O)6](SeO4)2 has been determined over the temperature range 90 to 320 K. Crystals with a high proportion of potassium adopt a different structure (form B) from those with a low ratio (form A). In both forms, the [Cu(H2O)6]2+ ion has an orthorhombically distorted tetragonally elongated coordination geometry, but the long and intermediate bonds occur with a different pair of water molecules in form A compared with form B. The alkali metal is surrounded by seven close oxygen atoms in form B but eight oxygen atoms in form A, and this difference in coordination number is associated with the change in the Cu–O bond distances via the hydrogen-bonding network. For crystals with between 32 and ∼41% potassium, a relatively sharp change from form B to A occurs on cooling, and the temperature at which this occurs increases approximately linearly as the proportion of potassium falls. For the who...

Three new withanolides, physaperuvin G (1), with physaperuvins I (2), and J (3), along with seven known derivatives (4-10), were isolated from the aerial parts of Physalis peruviana. The structures of 1-3 were determined by NMR, X-ray diffraction, and mass spectrometry. Compounds 1-10 were evaluated in lipopolysaccharide (LPS)-activated murine macrophage RAW 264.7 cells. Compounds 4, 5, and 10 with potent nitric oxide inhibitory activity in LPS-activated RAW 264.7 cells, with IC50 values in the range of 0.32-7.8μM. In addition, all compounds were evaluated for potential to inhibit tumor necrosis factor-alpha (TNF-α)-activated nuclear factor-kappa B (NF-κB) activity with transfected human embryonic kidney cells 293. Compounds 4-7 inhibited TNF-α-induced NF-κB activity with IC50 values in the range of 0.04-5.6μM.

New trinuclear iron(III) furoates with the general formula [Fe3O(α-fur)6(R–OH)3]X, where α-fur C4H3OCOO, R = CH3 (1), C2H5 (2), n-C3H7 (3), n-C4H9 (4), X = NO3− (1–4); [Fe3O(α-Fur)6(DMF)(CH3OH)2]NO3 (5); [Fe3O(α-Fur)6(H2O)(CH3OH)2]Cl (6); [Fe2MO(α-Fur)6(L)(H2O)2], where L = THF (7–9), DMF (10–12), M = Mn2+ (7, 10), Co2+ (8, 11), Ni2+ (9, 12) and [Fe2MO(α-Fur)6(3Cl-Py)3], where M = Mn2+ (13), Co2+ (14), Ni2+ (15); have been prepared and investigated by Mossbauer and IR spectroscopy. The X-ray crystal structure for the 1·2CH3OH complex indicates that it crystallizes in the monoclinic crystal system (P21/n) and has a structure typical of μ3-O-bridged trinuclear iron(III) compounds. Coordination compounds 1, 4, 7, 8 can be used as regulators of the biochemical composition of cyanobacterium Spirulina platensis biomass. The supplementation of these compounds, in concentrations exceeding 5–10 mg/l, increases the content of iron, amino acids, peptides and carbohydrates in Spirulina.

Low temperature photoisomerization of stilbene and 1,4-diphenyl-1,3-butadiene derivatives was found to vary depending on the organic glass employed in such studies. Examination of the combined results showed that the variation was more likely to arise from the rigidity of the organic glass at the temperature of irradiation rather than the composition of the organic glass; that is, the observed results are consistent with the possible softening of the glass that surrounds the excited substrate in the same manner as detected in the photolysis of ethyl iodide reported by Porter and co-workers. These observations successfully account for the apparent "disagreement" of reports from the Hawaii and the Florida State groups on the mechanism of photoisomerization in low temperature glasses.

Reaction of manganese acetate and lanthanide nitrates in the presence of excess of PhCOOH affords highly asymmetric dodecanuclear mixed-metal [Mn10Ln2(OH)(O)8(PhCOOH)(PhCOO)19] (Ln = PrIII (1), NdIII (2)) clusters. The similar reaction, but with only 2 equiv. of PhCOOH resulted in the compounds with higher nuclearity [Mn11Eu4(O)8(OH)8(PhCOO)18(NO3)2(H2O)6]NO3 · 4CH3CN (3). Variable-temperature solid-state magnetic susceptibility of 1 and 2 in the temperature range 1.8–300 K were carried out, and for both complexes antiferromagnetic exchange interactions between the metal centers were observed, giving an estimated S = 17/2 ground state. AC magnetic susceptibility data have revealed out-of-phase signals, which suggest that these complexes exhibit a slow relaxation of magnetization as observed in single-molecule magnets.

Chemical investigation of an endophytic fungus Chaetomium globosum isolated from leaves of Wikstroemia uva-ursi led to the isolation of two new azaphilones, chaetoviridins J and K (1 and 3), along with five known derivatives (2 and 4-7). The structures of azaphilones were determined by NMR, X-ray diffraction, Mosher's method, and CD analysis. The isolated compounds were evaluated for their cancer chemopreventive-potential based on their abilities to inhibit tumor necrosis factor alpha (TNF-α)-induced nuclear factor-kappa B (NF-κB). Compounds 4, 5, 7, and synthetic 8 and 9 inhibit nitric oxide (NO) production with IC50 values in the range of 0.3-5.8 μM. Compounds 4, 5, and 9 also displayed (TNF-α)-induced NF-κB activity with IC50 values in the range of 0.9-5.1 μM.

The temperature dependence of the structure of the mixed-anion Tutton salt K2[Cu(H2O)6](SO4)(2x)(SeO4)(2-2x) has been determined for crystals with 0, 17, 25, 68, 78, and 100% sulfate over the temperature range of 85-320 K. In every case, the [Cu(H2O)6]2+ ion adopts a tetragonally elongated coordination geometry with an orthorhombic distortion. However, for the compounds with 0, 17, and 25% sulfate, the long and intermediate bonds occur on a different pair of water molecules from those with 68, 78, and 100% sulfate. A thermal equilibrium between the two forms is observed for each crystal, with this developing more readily as the proportions of the two counterions become more similar. Attempts to prepare a crystal with approximately equal amounts of sulfate and selenate were unsuccessful. The temperature dependence of the bond lengths has been analyzed using a model in which the Jahn-Teller potential surface of the [Cu(H2O)6]2+ ion is perturbed by a lattice-strain interaction. The magnitude and sign of the orthorhombic component of this strain interaction depends on the proportion of sulfate to selenate. Significant deviations from Boltzmann statistics are observed for those crystals exhibiting a large temperature dependence of the average bond lengths, and this may be explained by cooperative interactions between neighboring complexes.

The temperature dependence of the bond lengths in the high temperature phase of [Cu(L)2][BF4]2 (L = 2,6-dipyrazol-1-ylpyridine) may be interpreted satisfactorily using a model of dynamic, Jahn–Teller (JT) vibronic coupling. The geometries of the three complexes in the asymmetric unit of the low temperature phase may be reproduced using parameters similar to those of the high temperature phase, but with significantly larger orthorhombic components of the strain interactions. The axial components of the strain for all the complexes in both phases are negative in sign and large in magnitude, and this is thought to reflect both the stronger σ-bonding power of pyridine compared with pyrazole and physical constraints of the amine ligand. A previous interpretation of the thermal behaviour of the high temperature phase in terms of a conformational equilibrium is re-evaluated.

Two species of red algae belonging to the genus Plocamium, P. hamatum from Moreton Bay, Queensland, and P. costatum, from Pandalowie Bay, South Australia, were investigated to assess their chemical variation and as potential sources of new halogenated monoterpenes. The hyphenated technique HPLC-UV-MS-SPE-NMR was used to assess the algal extracts and to determine its potential for accelerated identification of halogenated monoterpenes generally. A combination of the hyphenated and traditional chromatographic techniques resulted in the isolation and characterization of a total of 10 halogenated monoterpene metabolites, eight of which are reported for the first time. Their structures, including configurations, were determined through interpretation of their 1D and 2D NMR, mass spectrometric, infrared, and X-ray data. The two species of Plocamium produced different secondary metabolites and contained a significant number of new polyhalogenated monoterpenes. The investigation also showed the hyphenated technique HPLC-UV-MS-SPE-NMR to be useful for preliminary investigation of the chemical content of algal extracts.

The crystal structures of the Tutton salts (NH4)2-[Cu(H2O)6](SO4)2, diammonium hexaaquacopper disulfate, formed with normal water and isotopically substituted H2 18O, have been determined by X-ray diffraction at 9.5 K and are very similar, with Cu—O(7) the longest of the Cu—O bonds of the Jahn–Teller distorted octahedral [Cu(H2O)6]2+ complex. It is known that structural differences accompany deuteration of (NH4)2[Cu(H2O)6](SO4)2, the most dramatic of which is a switch to Cu—O(8) as the longest such bond. The present result suggests that the structural differences are associated with hydrogen-bonding effects rather than with increased mass of the water ligands affecting the Jahn–Teller coupling. The Jahn–Teller distortions and hydrogen-bonding contacts in the compounds are compared with those reported for other Tutton salts at ambient and high pressure.

The powder electron paramagnetic resonance spectra of ∼1% Cu doped into [Zn(bipy)2(NO2)]NO3 and [Zn(bipyam)2(NO2)]NO3, bipy = 2,2′-bipyridyl, bipyam = 2,2′-bipyridylamine, over the temperature range 4.2–300 K are reported. For [Zn/Cu(bipy)2(NO2)]NO3 a spectrum characteristic of a tetragonally elongated octahedral complex with a slight orthorhombic distortion is observed below ∼50 K, but above this temperature the signals associated with the two higherg-values gradually converge. At low temperature a spectrum similar to that of the bipy complex is observed for [Zn/Cu(bipyam)2(NO2)]NO3, but between 40 and 60 K the spectrum gradually changes to one characteristic of a tetragonalg-tensor with g∥ < g⊥. The spectra may be interpreted satisfactorily with a model in which the temperature dependence of theg-vainlues is estimated from the vibronic wavefunctions of a copper(II) complex under the influence of second-order Jahn-Teller coupling and a ligand field of tetragonal symmetry perturbed by crystal lattice forces. The results are consistent with the crystal structures reported for the compounds at various temperatures.

Four analogs of the carotenoprotein α-crustacyanin have been prepared by reconstitution with the all-transisomer of four new carotenoids (10-F, 10,10′-F2and 14-F-astaxanthins, and 10′-F-adonirubin). All four blue carotenoproteins exhibit absorption spectra similar to that of the natural α-crustacyanin with λmaxin the range of 613–625 nm. Different rates of pigment formation and yields were noted. F NMR spectra of pigments derived from the three 10F carotenoids have been recorded. Fourcisisomers of 14-F-astaxanthin and one of 10′-F-adonirubin were also isolated.

A synthetic route to the hindered Z,Z isomer of a cisoid 1,4-diphenyl-1,3-butadiene is described. Its crystal structure and properties are reported.

The temperature dependence of the structures of a wide range of mixed-cation Tutton's salts of general formula K2(x)Rb(2-2x)[Cu(H2O)6](SeO4)2 has been determined over the temperature range 90 to 320 K. Crystals with a high proportion of potassium adopt a different structure (form B) from those with a low ratio (form A). In both forms, the [Cu(H2O)6](2+) ion has an orthorhombically distorted tetragonally elongated coordination geometry, but the long and intermediate bonds occur with a different pair of water molecules in form A compared with form B. The alkali metal is surrounded by seven close oxygen atoms in form B but eight oxygen atoms in form A, and this difference in coordination number is associated with the change in the Cu-O bond distances via the hydrogen-bonding network. For crystals with between 32 and ∼41% potassium, a relatively sharp change from form B to A occurs on cooling, and the temperature at which this occurs increases approximately linearly as the proportion of potassium falls. For the whole range of mixed crystals, the bond lengths have been determined as a function of temperature. The data have been interpreted as a thermal equilibrium of the two structural forms of the [Cu(H2O)6](2+) ion that develops gradually as the temperature increases, with this becoming more pronounced as the proportions of the two cations become more similar. The temperature dependence of the bond lengths in this thermal equilibrium has been analyzed using a model in which the Jahn-Teller potential surface of the [Cu(H2O)6](2+) ion is perturbed by lattice strain interactions. The magnitude and sign of the orthorhombic component of this strain interaction depends upon the proportion of potassium to rubidium ions in the structure.

Bioassay-directed isolation and purification of the crude extract of Withania coagulans, using two assays for cancer chemopreventive mechanisms, led to the isolation of three new steroidal lactones, withacoagulin G (1), withacoagulin H (2), and withacoagulin I (3), along with six known derivatives (4-9). The structures and absolute stereochemistry of these compounds were determined on the basis of spectroscopic analyses, including 1D and 2D NMR, mass spectrometry, and CD analyses. The structure of 1 was confirmed using X-ray diffraction methods. Compounds 1-9 inhibited nitric oxide production in lipopolysaccharide-activated murine macrophage RAW 264.7 cells with IC(50) values in the range of 1.9-38.2 μM. Compounds 1 and 2 were the most active (IC(50) 3.1 and 1.9 μM, respectively). Withanolides 1-9 exhibited inhibition of tumor necrosis factor-α (TNF-α)-induced nuclear factor-kappa B (NF-κB) activation with IC(50) values in the range of 1.60-12.4 μM.

The crystal structures of (ND4)2[Cu(D2O)6](SO4)2 at 295 K, determined by X-ray diffraction at pressures of 1 bar, ∼1.5 kbar and ∼3.0 kbar, are reported. Between 1 bar and 1.5 kbar, the crystal structure changes to one almost identical to that of the corresponding hydrogenous compound at 1 bar. The structural change involves a 90° switch in the direction of the long bonds of the Cu(D2O)62+ ion, accompanied by a change in the hydrogen-bonding interactions of the ammonium cations. Comparison of these two structures with those at ∼15 K shows that at room temperature, for both the high (H) and low (L) pressure phases, the Cu complexes are in thermal equilibrium with the other structural isomer. Though one of these is energetically preferred in the H and the other in the L phase, the variation of the powder EPR spectrum with pressure indicates a continuous transition between both within ∼1 kbar and suggests that at ∼0.5 kbar the two orientations of the copper complex are similar in energy. However, the underlyi...

Various macrocyclic diaryl ethers are prepared via microwave assisted intramolecular or intermolecular Ullmann coupling.

Bioassay-guided fractionation of the hexane extract from the flowers of Vernonia cinerea (Asteraceae) led to the isolation of a new sesquiterpene lactone, 8α-hydroxyhirsutinolide (2), and a new naturally occurring derivative, 8α-hydroxyl-1-O-methylhirsutinolide (3), along with seven known compounds (1 and 4–9). The structures of the new compounds were determined by 1D and 2D NMR experiments and by comparison with the structure of compound 1, whose relative stereochemistry was determined by X-ray analysis. The isolated compounds were evaluated for their cancer chemopreventive potential based on their ability to inhibit nitric oxide (NO) production and tumor necrosis factor alpha (TNF-α)-induced NF-κB activity. Compounds 1, 2, 4, 5, and 9 inhibited TNF-α-induced NF-κB activity with IC50 values of 3.1, 1.9, 0.6, 5.2, and 1.6 μM, respectively; compounds 4 and 6–9 exhibited significant NO inhibitory activity with IC50 values of 2.0, 1.5, 1.2, 2.7, and 2.4 μM, respectively.

Microwave-assisted synthesis of macrocyclic diaryl ethers via intramolecular and/or bimolecular Ullmann coupling is described. Using the optimized conditions, a panel of macrocycles, with different substitution patterns, ring sizes, and linkers, has been successfully synthesized using microwave irradiation. To the best of our knowledge, this work represents the first examples of the microwave-assisted synthesis of macrocyclic diaryl ethers via intramolecular and/or bimolecular Ullmann coupling.

The crystal structures of trans-diaquabis(methoxyacetato)copper(II) and the isostructural nickel(II) complex have been determined over a wide temperature range. In conjunction with the reported behavior of the g-values, the structural data suggest that the copper(II) compound exhibits a thermal equilibrium between three structural forms, two having orthorhombically distorted, tetragonally elongated geometries but with the long and intermediate bonds to different atoms, and the third with a tetragonally compressed geometry. This is apparently the first reported example of a copper(II) complex undergoing an equilibrium between tetragonally elongated and compressed forms. The optical spectrum of single crystals of the copper(II) compound is used to obtain metal-ligand bonding parameters which yield the g-values of the compressed form of the complex and hence the proportions of the complex in each structural form at every temperature. When combined with estimates of the Jahn-Teller distortions of the different forms, the latter produce excellent agreement with the observed temperature dependence of the bond lengths. The behavior of an infrared combination band is consistent with such a thermal equilibrium, as is the temperature dependence of the thermal ellipsoid parameters and the XAFS. The potential surfaces of the different forms of the copper(II) complex have been calculated by a model based upon Jahn-Teller coupling. It is suggested that cooperative effects may cause the development of the population of tetragonally compressed complexes, and the crystal packing is consistent with this hypothesis, though the present model may oversimplify the diversity of structural forms present at high temperature.

The first example of a pressure-induced Jahn-Teller distortion switch has been observed in a single-crystal time-of-flight neutron diffraction study of the Tutton salt (ND[sub 4])[sub 2][Cu(D[sub 2]O)[sub 6]](SO[sub 4])[sub 2] at T = 15 K, P = 1 bar (D[sub L]) and T = 15 K, P = 1.5 kbar (D[sub H]). Also studied was the hydrogenous salt (NH[sub 4])[sub 2][Cu(H[sub 2]O)[sub 6]](SO[sub 4])[sub 2] at T = 14 K, P = 1.4 kbar (H[sub H]). The unit cell parameters are as follows: D[sub L], a = 9.451(2) [angstrom], b = 12.736(3) [angstrom], c = 6.096(1) [angstrom], [beta] = 107.13(2)[degrees], Z = 2, V = 701.2(3) [angstrom][sup 3], space group = P2[sub 1]/a; D[sub H], a = 9.136(1) [angstrom], b = 12.285(2) [angstrom], c = 6.371(1) [angstrom], [beta] = 106.28(2)[degrees], Z = 2, V = 686.4(2) [angstrom][sup 3], space group = P2[sub 1]/a; H[sub H], a = 9.068(2) [angstrom], b = 12.232(2) [angstrom], c = 6.340(1) [angstrom], [beta] = 106.44(2), Z = 2, V = 674.5(2) [angstrom][sup 3], space group = P2[sub 1]/a. Application of 1.5 kbar of pressure to the deuterated crystal produces a decrease in the lengths of the a and b axes by 0.315(2) and 0.451(4) [angstrom],more » respectively, whereas the c axis increases by 0.275(1) [angstrom]. Comparison of the D[sub L] and D[sub H] structures shows that the long axis of the Jahn-Teller distortion has switched by 90[degrees], i.e., Cu(1)-O(7) = 2.022(2) and Cu(1)-O(8) = 2.310(2) [angstrom] for D[sub L] vs Cu(1)-O(7) = 2.290(2) and Cu(1)-O(8) = 2.014(2) [angstrom] for D[sub H], so that the D[sub H] and H[sub H] structures are similar. 38 refs., 6 figs., 3 tabs.« less

The first example of a pressure-induced Jahn-Teller distortion switch has been observed in a single-crystal time-of-flight neutron diffraction study of the Tutton salt (ND[sub 4])[sub 2][Cu(D[sub 2]O)[sub 6]](SO[sub 4])[sub 2] at T = 15 K, P = 1 bar (D[sub L]) and T = 15 K, P = 1.5 kbar (D[sub H]). Also studied was the hydrogenous salt (NH[sub 4])[sub 2][Cu(H[sub 2]O)[sub 6]](SO[sub 4])[sub 2] at T = 14 K, P = 1.4 kbar (H[sub H]). The unit cell parameters are as follows: D[sub L], a = 9.451(2) [angstrom], b = 12.736(3) [angstrom], c = 6.096(1) [angstrom], [beta] = 107.13(2)[degrees], Z = 2, V = 701.2(3) [angstrom][sup 3], space group = P2[sub 1]/a; D[sub H], a = 9.136(1) [angstrom], b = 12.285(2) [angstrom], c = 6.371(1) [angstrom], [beta] = 106.28(2)[degrees], Z = 2, V = 686.4(2) [angstrom][sup 3], space group = P2[sub 1]/a; H[sub H], a = 9.068(2) [angstrom], b = 12.232(2) [angstrom], c = 6.340(1) [angstrom], [beta] = 106.44(2), Z = 2, V = 674.5(2) [angstrom][sup 3], space group = P2[sub 1]/a. Application of 1.5 kbar of pressure to the deuterated crystal produces a decrease in the lengths of the a and b axes by 0.315(2) and 0.451(4) [angstrom],more » respectively, whereas the c axis increases by 0.275(1) [angstrom]. Comparison of the D[sub L] and D[sub H] structures shows that the long axis of the Jahn-Teller distortion has switched by 90[degrees], i.e., Cu(1)-O(7) = 2.022(2) and Cu(1)-O(8) = 2.310(2) [angstrom] for D[sub L] vs Cu(1)-O(7) = 2.290(2) and Cu(1)-O(8) = 2.014(2) [angstrom] for D[sub H], so that the D[sub H] and H[sub H] structures are similar. 38 refs., 6 figs., 3 tabs.« less

The crystal structures of (ND4)2[Cu(D2O)6](SO4)2 at 295 K, determined by X-ray diffraction at pressures of 1 bar, ∼1.5 kbar and ∼3.0 kbar, are reported. Between 1 bar and 1.5 kbar, the crystal structure changes to one almost identical to that of the corresponding hydrogenous compound at 1 bar. The structural change involves a 90° switch in the direction of the long bonds of the Cu(D2O)62+ ion, accompanied by a change in the hydrogen-bonding interactions of the ammonium cations. Comparison of these two structures with those at ∼15 K shows that at room temperature, for both the high (H) and low (L) pressure phases, the Cu complexes are in thermal equilibrium with the other structural isomer. Though one of these is energetically preferred in the H and the other in the L phase, the variation of the powder EPR spectrum with pressure indicates a continuous transition between both within ∼1 kbar and suggests that at ∼0.5 kbar the two orientations of the copper complex are similar in energy. However, the underlyi...

X-ray diffraction combined with theoretical results obtained for isolated molecules can reveal many topologic features of the adiabatic potential energy surface (APS) of pseudo-Jahn-Teller Cu(II) complexes. Single-crystal x-ray results of acetatobis (1,10-phenanthroline)copper(II) perchlorate from 10 to 351 K are presented. The observed Cu-O bond length changes of 0.26 and 0.38 A are rationalized in terms of a one-dimensional APS with two nonequivalent minima. The Silver and Getz model of vibronic coupling applied to the temperature variation of the Cu-O bond lengths is not obeyed. The actual structures of the conformers associated with the energy minima were determined from the x-ray data. A means of estimating the pseudo-Jahn-Teller radius using mean-square vibrational amplitudes along the Cu-O bonds is also discussed.

The crystal structures of ammoniumzinc(II) sulfate hexahydrate and its deuterated analogue have been determined at 298 and 110 K. In marked contrast to the corresponding copper(II) compound, deuter...

The crystal structures of samples of deuterated ammonium copper(II) sulfate hexahydrate, in which a small fraction of the Cu2+ ions were replaced by Zn2+, have been determined. While the samples with lower Zn2+ concentrations have structures similar to that of the pure Cu2+ compound, the sample with 3.4% Zn2+ substitution has a structure similar to that observed for the unsubstituted compound at 1.5 kbar pressure, in which the long axis of the distorted Cu(D2O)6 2+ ion has switched from one pair of oxygen atoms to another pair.

The temperature-dependent electron paramagnetic resonance (EPR) spectrum of similar to 1% Cu(II) ions doped into Ba2Zn(HCO2)(6)center dot 4H(2)O was analyzed at the Q-band frequencies over the temperature range 100-350 K to obtain structural information about the local environment. It can be concluded that the host crystal imparts a large orthorhombic strain which mainly corresponds to a tetragonal compression imposed onto the (CuO6)-O-II species. This results in a copper center which adopts an orthorhombically distorted elongated geometry with the elongated axis perpendicular to the direction of the tetragonal compression due to the host crystal. There are two possible axes of elongation, and these represent two conformers separated by similar to 320 cm(-1). The thermal population of the higher energy level averages the g values, giving the observed temperature-dependent EPR spectra. The averaging process is between vibronic levels that are localized at two different minima of a single ground-state potential energy surface. These vibronic levels correspond to vibrational levels having different electronic properties. The determination of the host lattice strain parameters from the Cu(II) EPR spectra means that the guest ion is used as a probe of the environment of the Zn(II) site. The structural data derived from the lattice strain parameters are correlated with those from the Ba2Zn(HCO2)(6)center dot 4H(2)O crystal structure.

The crystal structures of [Cu3(bipyam–H)4Cl2]·H2O (1) and [Cu3(bipyam–H)4Br2]·H2O (2) where bipyam–H = bis(2-pyridyl)amide, have been determined by X-ray analysis, in the orthorhrombic space group Pnn2: (1), a= 14.092(3), b= 12.895(3), (c)= 11.190(2)A, Z= 2, and R= 0.032 for 2 453 observed and 2 029 unique reflections; (2), a= 14.186(3), b= 13.040(3), c= 11.313(2)A, Z= 2, and R= 0.043 for 1 574 observed and 1 465 unique reflections. The two structures are isomorphous with near isostructural [Cu3(bipyam–H)4X2] units in special positions of two-fold symmetry and a non-co-ordinated water molecule. The Cu3N12X2 chromophores involve nearly linear Cu3 units, Cu–Cu–Cu 178.4°(mean), terminated by the two halide anions. The four separate bipyam–H ligands act as tridentate ligands, involving co-ordination to the three separate copper(II) ions, with Cu–Cu distances of 2.471(1) and 2.468(1)A, for (1) and (2), respectively. If the Cu–Cu separations are ignored, the central Cu atom in both structures involves a four-co-ordinate rhombic coplanar CuN4 chromophore generated by the central amido nitrogens of the four bipyam–H ligands. The two terminal Cu atoms involve a square-based pyramidal CuN4X chromophore, generated by the terminal pyridine nitrogens of the four bipyam–H ligands and an axial halide anion. An average dihedral angle of 48° is involved between the planes of the pyridine rings of the individual bipyam–H ligands, which results in a spiral configuration of the [Cu3(bipyam–H)4X2] units. The spin-only magnetic moment of complex (1) is ca. 1.40 B.M. per Cu atom, consistent with antiferromagnetic coupling between the copper(II) atoms of the trimer. Both complexes are e.s.r. silent, again consistent with strong antiferromagnetic coupling. The electronic spectra of (1) and (2) have a band maximum at 15 500 cm–1, with a high-energy shoulder at 19 230 cm–1, consistent with the two different stereochemistries present.

The temperature dependence of the structure of the mixed-anion Tutton salt K2[Cu(H2O)6](SO4)(2x)(SeO4)(2-2x) has been determined for crystals with 0, 17, 25, 68, 78, and 100% sulfate over the temperature range of 85-320 K. In every case, the [Cu(H2O)6]2+ ion adopts a tetragonally elongated coordination geometry with an orthorhombic distortion. However, for the compounds with 0, 17, and 25% sulfate, the long and intermediate bonds occur on a different pair of water molecules from those with 68, 78, and 100% sulfate. A thermal equilibrium between the two forms is observed for each crystal, with this developing more readily as the proportions of the two counterions become more similar. Attempts to prepare a crystal with approximately equal amounts of sulfate and selenate were unsuccessful. The temperature dependence of the bond lengths has been analyzed using a model in which the Jahn-Teller potential surface of the [Cu(H2O)6]2+ ion is perturbed by a lattice-strain interaction. The magnitude and sign of the orthorhombic component of this strain interaction depends on the proportion of sulfate to selenate. Significant deviations from Boltzmann statistics are observed for those crystals exhibiting a large temperature dependence of the average bond lengths, and this may be explained by cooperative interactions between neighboring complexes.

The temperature dependence of the X-ray crystal structure and powder EPR spectrum of [(HC(Ph2PO)(3))(2)CU]-(ClO4)(2)center dot 2H(2)O is reported, and the structure at room temperature confirms that reported previously. Below similar to 100 K, the data imply a geometry with near elongated tetragonal symmetry for the [(HC(Ph2PO)(3))(2)Cu](2+) complex, but on warming the two higher Cu-O bond lengths and g-values progressively converge, and by 340 K the bond lengths correspond to a compressed tetragonal geometry. The data may be interpreted satisfactorily assuming an equilibrium among the energy levels of a Cu-O-6 polyhedron subjected to Jahn-Teller vibronic coupling and a lattice strain. However, agreement with the experiment is obtained only if the orthorhombic component of the lattice strain decreases to a negligible value as the temperature approaches 340 K.

The X-ray crystal structure of the highly crowded cis isomer of the lowest member of the homologs of β-carotene has been determined at 120K. The triene chromophore exists in the postulated bis-S-cis conformation, assuming the novel spiral shape suitable for secondary 1,6-orbital interaction.

Presentation des resultats cristallographiques aux deux temperatures, du comportement de distorsion en termes d'effet Jahn-Teller et d'une derivation simple reliant la difference d'energie entre conformeres aux distorsions observees a partir de la symetrie C 2

The crystal structure of pukeleimide C, a novel pyrrolic compound from a shallow-water variety of the marine blue-green alga Lyngbya majuscula , is reported.

Les complexes de Cu et de Zn cristallisent dans le systeme monoclinique, groupe d'espace P2 1/n

In its complex with CuI, dipyrimidin-2-yl disulphide is centrosymmetric and planar with a C–S–S–C torsion angle of 180° and a long S–S bond, 2·113(1)A.