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The chemical basis of the blue-black to pink-orange color change on cooking of lobster, due to thermal denaturation of an astaxanthin-protein complex, alpha-crustacyanin, in the lobster carapace, has so far been elusive. Here, we investigate the relaxation of the astaxanthin pigment from its bound enolate form to its neutral hydroxyketone form, as origin of the spectral shift, by analyzing the response of UV-vis spectra of a water-soluble 3-hydroxy-4-oxo-beta-ionone model of astaxanthin to increases in pH, and by performing extensive quantum chemical calculations over a wide range of chemical conditions. The enolization of astaxanthin is consistent with the X-ray diffraction data of beta-crustacyanin (PDB code: 1GKA) whose crystals possess the distinct blue color. We find that enolate formation is possible within the protein environment and associated with a large bathochromic shift, thus offering a cogent explanation for the blue-black color and the response to thermal denaturation and revealing the chemistry of astaxanthin upon complex formation., Funding Agencies|Bildungs- und Kultur-departement des Kantons Luzern, Switzerland; Swedish Research Council; Olle Engkvist Foundation; Nuffield Foundation; School of Chemistry, University of Manchester; European Molecular Biology Laboratory

The chemical basis of the blue-black to pink-orange color change on cooking of lobster, due to thermal denaturation of an astaxanthin-protein complex, alpha-crustacyanin, in the lobster carapace, has so far been elusive. Here, we investigate the relaxation of the astaxanthin pigment from its bound enolate form to its neutral hydroxyketone form, as origin of the spectral shift, by analyzing the response of UV-vis spectra of a water-soluble 3-hydroxy-4-oxo-beta-ionone model of astaxanthin to increases in pH, and by performing extensive quantum chemical calculations over a wide range of chemical conditions. The enolization of astaxanthin is consistent with the X-ray diffraction data of beta-crustacyanin (PDB code: 1GKA) whose crystals possess the distinct blue color. We find that enolate formation is possible within the protein environment and associated with a large bathochromic shift, thus offering a cogent explanation for the blue-black color and the response to thermal denaturation and revealing the chemistry of astaxanthin upon complex formation., Funding Agencies|Bildungs- und Kultur-departement des Kantons Luzern, Switzerland; Swedish Research Council; Olle Engkvist Foundation; Nuffield Foundation; School of Chemistry, University of Manchester; European Molecular Biology Laboratory

The chemical basis of the blue-black to pink-orange color change on cooking of lobster, due to thermal denaturation of an astaxanthin-protein complex, alpha-crustacyanin, in the lobster carapace, has so far been elusive. Here, we investigate the relaxation of the astaxanthin pigment from its bound enolate form to its neutral hydroxyketone form, as origin of the spectral shift, by analyzing the response of UV-vis spectra of a water-soluble 3-hydroxy-4-oxo-beta-ionone model of astaxanthin to increases in pH, and by performing extensive quantum chemical calculations over a wide range of chemical conditions. The enolization of astaxanthin is consistent with the X-ray diffraction data of beta-crustacyanin (PDB code: 1GKA) whose crystals possess the distinct blue color. We find that enolate formation is possible within the protein environment and associated with a large bathochromic shift, thus offering a cogent explanation for the blue-black color and the response to thermal denaturation and revealing the chemistry of astaxanthin upon complex formation., Funding Agencies|Bildungs- und Kultur-departement des Kantons Luzern, Switzerland; Swedish Research Council; Olle Engkvist Foundation; Nuffield Foundation; School of Chemistry, University of Manchester; European Molecular Biology Laboratory

The chemical basis of the blue-black to pink-orange color change on cooking of lobster, due to thermal denaturation of an astaxanthin-protein complex, alpha-crustacyanin, in the lobster carapace, has so far been elusive. Here, we investigate the relaxation of the astaxanthin pigment from its bound enolate form to its neutral hydroxyketone form, as origin of the spectral shift, by analyzing the response of UV-vis spectra of a water-soluble 3-hydroxy-4-oxo-beta-ionone model of astaxanthin to increases in pH, and by performing extensive quantum chemical calculations over a wide range of chemical conditions. The enolization of astaxanthin is consistent with the X-ray diffraction data of beta-crustacyanin (PDB code: 1GKA) whose crystals possess the distinct blue color. We find that enolate formation is possible within the protein environment and associated with a large bathochromic shift, thus offering a cogent explanation for the blue-black color and the response to thermal denaturation and revealing the chemistry of astaxanthin upon complex formation., Funding Agencies|Bildungs- und Kultur-departement des Kantons Luzern, Switzerland; Swedish Research Council; Olle Engkvist Foundation; Nuffield Foundation; School of Chemistry, University of Manchester; European Molecular Biology Laboratory

The chemical basis of the blue-black to pink-orange color change on cooking of lobster, due to thermal denaturation of an astaxanthin-protein complex, alpha-crustacyanin, in the lobster carapace, has so far been elusive. Here, we investigate the relaxation of the astaxanthin pigment from its bound enolate form to its neutral hydroxyketone form, as origin of the spectral shift, by analyzing the response of UV-vis spectra of a water-soluble 3-hydroxy-4-oxo-beta-ionone model of astaxanthin to increases in pH, and by performing extensive quantum chemical calculations over a wide range of chemical conditions. The enolization of astaxanthin is consistent with the X-ray diffraction data of beta-crustacyanin (PDB code: 1GKA) whose crystals possess the distinct blue color. We find that enolate formation is possible within the protein environment and associated with a large bathochromic shift, thus offering a cogent explanation for the blue-black color and the response to thermal denaturation and revealing the chemistry of astaxanthin upon complex formation., Funding Agencies|Bildungs- und Kultur-departement des Kantons Luzern, Switzerland; Swedish Research Council; Olle Engkvist Foundation; Nuffield Foundation; School of Chemistry, University of Manchester; European Molecular Biology Laboratory

Non-fused 3,6-dihydro-2H-1,3-thiazine-2-thiones constitute a so far rather unexplored class of compounds, with the latest report dating back more than two decades. Thiazine-2-thiones contain an endocyclic dithiocarbamate group, which is often found in pesticides, in substrates for radical chemistry and in synthetic intermediates towards thioureas and amidines. We now report the multicomponent reaction (MCR) of in situ-generated 1-azadienes with carbon disulfide. With this reaction, a one-step protocol towards the potentially interesting 3,6-dihydro-2H-1,3-thiazine-2-thiones was established and a small library was synthesized.

info:eu-repo/semantics/published

info:eu-repo/semantics/published

Non-fused 3,6-dihydro-2H-1,3-thiazine-2-thiones constitute a so far rather unexplored class of compounds, with the latest report dating back more than two decades. Thiazine-2-thiones contain an endocyclic dithiocarbamate group, which is often found in pesticides, in substrates for radical chemistry and in synthetic intermediates towards thioureas and amidines. We now report the multicomponent reaction (MCR) of in situ-generated 1-azadienes with carbon disulfide. With this reaction, a one-step protocol towards the potentially interesting 3,6-dihydro-2H-1,3-thiazine-2-thiones was established and a small library was synthesized.

The first examples of vinylidene complexes of the cycloheptatrienyl tungsten system [W(C=CHR)(dppe)(η-C7H7)]+ (dppe = Ph2PCH2CH2PPh2; R = H, 3; Ph, 4; C6H4-4-Me, 5) have been synthesised by reaction of [WBr(dppe)(η-C7H7)], 1, with terminal alkynes HC[triple bond, length as m-dash]CR; a one-pot synthesis of 1 from [WBr(CO)2(η-C7H7)] facilitates its use as a precursor. The X-ray structure of 4[PF6] reveals that the vinylidene ligand substituents lie in the pseudo mirror plane of the W(dppe)(η-C7H7) auxiliary (vertical orientation) with the phenyl group located syn to the cycloheptatrienyl ring. Variable temperature 1H NMR investigations on [W(C[double bond, length as m-dash]CH2)(dppe)(η-C7H7)][PF6], 3, estimate the energy barrier to rotation about the W[double bond, length as m-dash]Cα bond as 62.5 ± 2 kJ mol−1; approximately 10 kJ mol−1 greater than for the molybdenum analogue. Deprotonation of 4 and 5 with KOBut yields the alkynyls [W(C≡CR)(dppe)(η-C7H7)] (R = Ph, 6; C6H4-4-Me, 7) which undergo a reversible one-electron oxidation at a glassy carbon electrode in CH2Cl2 with E½ values approximately 0.12 V negative of Mo analogues. The 17-electron radicals [6]+ and [7]+ have been investigated by spectroelectrochemical IR, UV-visible and EPR methods. The electronic structures of representative vinylidene (3) and alkynyl (6) complexes have been investigated at the B3LYP/Def2-SVP level. In both cases, electronic structure is characterised by a frontier orbital with significant metal dz2character and this dominates the structural and spectroscopic properties of the system.

The first examples of vinylidene complexes of the cycloheptatrienyl tungsten system [W(C=CHR)(dppe)(η-C7H7)]+ (dppe = Ph2PCH2CH2PPh2; R = H, 3; Ph, 4; C6H4-4-Me, 5) have been synthesised by reaction of [WBr(dppe)(η-C7H7)], 1, with terminal alkynes HC[triple bond, length as m-dash]CR; a one-pot synthesis of 1 from [WBr(CO)2(η-C7H7)] facilitates its use as a precursor. The X-ray structure of 4[PF6] reveals that the vinylidene ligand substituents lie in the pseudo mirror plane of the W(dppe)(η-C7H7) auxiliary (vertical orientation) with the phenyl group located syn to the cycloheptatrienyl ring. Variable temperature 1H NMR investigations on [W(C[double bond, length as m-dash]CH2)(dppe)(η-C7H7)][PF6], 3, estimate the energy barrier to rotation about the W[double bond, length as m-dash]Cα bond as 62.5 ± 2 kJ mol−1; approximately 10 kJ mol−1 greater than for the molybdenum analogue. Deprotonation of 4 and 5 with KOBut yields the alkynyls [W(C≡CR)(dppe)(η-C7H7)] (R = Ph, 6; C6H4-4-Me, 7) which undergo a reversible one-electron oxidation at a glassy carbon electrode in CH2Cl2 with E½ values approximately 0.12 V negative of Mo analogues. The 17-electron radicals [6]+ and [7]+ have been investigated by spectroelectrochemical IR, UV-visible and EPR methods. The electronic structures of representative vinylidene (3) and alkynyl (6) complexes have been investigated at the B3LYP/Def2-SVP level. In both cases, electronic structure is characterised by a frontier orbital with significant metal dz2character and this dominates the structural and spectroscopic properties of the system.

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The reaction of uranyl nitrate hexahydrate with the maleonitrile containing Schiff base 2,3-bis[(4-diethylamino-2-hydroxybenzylidene)amino]but-2-enedinitrile (salmnt((Et2N)2)H(2)) in methanol produces [UO2(salmnt((Et2N)2))(H2O)] (1) where the uranyl equatorial coordination plane is completed by the N2O2 tetradentate cavity of the (salmnt((Et2N)2))(2-) ligand and a water molecule. The coordinated water molecule readily undergoes exchange with pyridine (py), dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF) and triphenylphosphine oxide (TPPO) to give a series of [UO2(salmnt((Et2N)2))(L)] complexes (L = py, DMSO, DMF, TPPO; 2-5, respectively). X-Ray crystallography of 1-5 show that the (salmnt((Et2N)2))(2-) ligand is distorted when coordinated to the uranyl moiety, in contrast to the planar structure observed for the free protonated ligand (salmnt((Et2N)2)H(2)). The Raman spectra of 1-5 only display extremely weak bands (819-828 cm(-1)) that can be assigned to the typically symmetric O=U=O stretch. This stretching mode is also observed in the infrared spectra for all complexes 1-5 (818-826 cm(-1)) predominantly caused by the distortion of the tetradentate (salmnt((Et2N)2))(2-) ligand about the uranyl equatorial plane resulting in a change in dipole for this bond stretch. The solution behaviour of 2-5 was studied using NMR, electronic absorption and emission spectroscopy, and cyclic voltammetry. Complexes 2-5 exhibit intense absorptions in the visible region of the spectrum due to intramolecular charge transfer (ICT) transitions and the luminescence lifetimes (<5 ns) indicate the emission arises from ligand-centred excited states. Reversible redox processes assigned to the {UO2}(2+)/{UO2}(+) couple are observed for complexes 2-5 (2: E-1/2 = -1.80 V; 3,5: E-1/2 = -1.78 V; 4: E-1/2 = -1.81 V : vs. ferrocenium/ferrocene {Fc(+)/Fc}, 0.1 M Bu4NPF6) in dichloromethane (DCM). These are some of the most negative half potentials for the {UO2}(2+)/{UO2}(+) couple observed to

The reaction of uranyl nitrate hexahydrate with the maleonitrile containing Schiff base 2,3-bis[(4-diethylamino-2-hydroxybenzylidene)amino]but-2-enedinitrile (salmnt((Et2N)2)H(2)) in methanol produces [UO2(salmnt((Et2N)2))(H2O)] (1) where the uranyl equatorial coordination plane is completed by the N2O2 tetradentate cavity of the (salmnt((Et2N)2))(2-) ligand and a water molecule. The coordinated water molecule readily undergoes exchange with pyridine (py), dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF) and triphenylphosphine oxide (TPPO) to give a series of [UO2(salmnt((Et2N)2))(L)] complexes (L = py, DMSO, DMF, TPPO; 2-5, respectively). X-Ray crystallography of 1-5 show that the (salmnt((Et2N)2))(2-) ligand is distorted when coordinated to the uranyl moiety, in contrast to the planar structure observed for the free protonated ligand (salmnt((Et2N)2)H(2)). The Raman spectra of 1-5 only display extremely weak bands (819-828 cm(-1)) that can be assigned to the typically symmetric O=U=O stretch. This stretching mode is also observed in the infrared spectra for all complexes 1-5 (818-826 cm(-1)) predominantly caused by the distortion of the tetradentate (salmnt((Et2N)2))(2-) ligand about the uranyl equatorial plane resulting in a change in dipole for this bond stretch. The solution behaviour of 2-5 was studied using NMR, electronic absorption and emission spectroscopy, and cyclic voltammetry. Complexes 2-5 exhibit intense absorptions in the visible region of the spectrum due to intramolecular charge transfer (ICT) transitions and the luminescence lifetimes (<5 ns) indicate the emission arises from ligand-centred excited states. Reversible redox processes assigned to the {UO2}(2+)/{UO2}(+) couple are observed for complexes 2-5 (2: E-1/2 = -1.80 V; 3,5: E-1/2 = -1.78 V; 4: E-1/2 = -1.81 V : vs. ferrocenium/ferrocene {Fc(+)/Fc}, 0.1 M Bu4NPF6) in dichloromethane (DCM). These are some of the most negative half potentials for the {UO2}(2+)/{UO2}(+) couple observed to

info:eu-repo/semantics/published

We report the synthesis, structures and magnetic properties of a series of chromium(iii) metal-centered triangle (or "star") clusters, [Cr 4RC(CH2O)32(4,4′- R′2-bipy)3Cl6] [R = Et, R′ = H (2); R = HOCH2, R′ = H (3); R = Et, R′ = tBu (4)], prepared by two-step solvothermal reactions starting from [CrCl 3(thf)3]. The product of the first stage of this reaction is the salt [Cr(bipy)2Cl2]2[Cr 2Cl8(MeCN)2] (1). In the absence of the diimine, a different family of tetrametallics is isolated: the butterfly complexes [Cr4EtC(CH2O)32NH(C(R) NH)22Cl6] (R = Me (5), Et (6), Ph (7)] where the chelating N-acetimidoylacetamidine NH(C(R)NH)2 ligands are formed in situ via condensation of the nitrile solvents (RCN) under solvothermal conditions. Magnetic measurements show the chromium stars to have an isolated S = 3 ground state, arising from antiferromagnetic coupling between the central and peripheral metal ions, analogous to the well-known Fe(iii) stars. Bulk antiferromagnetic ordering is observed at 0.6 K. The butterfly complexes have a singlet ground state, with a low-lying S = 1 first excited state, due to dominant wing-body antiferromagnetic coupling. © 2011 The Royal Society of Chemistry

We report the synthesis, structures and magnetic properties of a series of chromium(III) metal-centered triangle (or >star>) clusters, [Cr 4{RC(CH2O)3}2(4,4′- R′2-bipy)3Cl6] [R = Et, R′ = H (2); R = HOCH2, R′ = H (3); R = Et, R′ = tBu (4)], prepared by two-step solvothermal reactions starting from [CrCl 3(thf)3]. The product of the first stage of this reaction is the salt [Cr(bipy)2Cl2]2[Cr 2Cl8(MeCN)2] (1). In the absence of the diimine, a different family of tetrametallics is isolated: the butterfly complexes [Cr4{EtC(CH2O)3}2{NH(C(R) NH)2}2Cl6] (R = Me (5), Et (6), Ph (7)] where the chelating N-acetimidoylacetamidine NH(C(R)NH)2 ligands are formed in situ via condensation of the nitrile solvents (RCN) under solvothermal conditions. Magnetic measurements show the chromium stars to have an isolated S = 3 ground state, arising from antiferromagnetic coupling between the central and peripheral metal ions, analogous to the well-known Fe(III) stars. Bulk antiferromagnetic ordering is observed at 0.6 K. The butterfly complexes have a singlet ground state, with a low-lying S = 1 first excited state, due to dominant wing-body antiferromagnetic coupling. © 2011 The Royal Society of Chemistry.

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A series of chromophoric salts has been prepared in which 4-(diphenylamino)phenyl (Dpap) electron donor groups are connected to electron-accepting diquaternized 2,2′-bipyridyl (diquat) units. The main aim is to combine large quadratic and cubic nonlinea

The research towards more efficient organic molecules for second-order nonlinear optical (NLO) applications has resulted in substantial improvements of the molecular nonlinear polarizabilities. Different strategies for increasing NLO responses at the molecular level in ionic chromophores are reviewed. However, only a small subset of the highly efficient non-centrosymmetric molecules also forms non-centrosymmetric crystals at the bulk level. Examples of success in achieving polar crystals of molecular salts are presented. Such crystals with a high number density of aligned dipolar chromophores are promising materials for efficient second-order NLO applications, such as terahertz generation via difference frequency mixing.

info:eu-repo/semantics/published

info:eu-repo/semantics/published

info:eu-repo/semantics/published