Synthesis and Structural Characterization of Mono-and Di-nuclear Zinc(Ⅱ) Coordination Compounds of Triphenylphosphoniopropionate

Two novel coordination compounds of Zn(Ⅱ) with Ph_3P+(CH_2)_2CO-_2(L), namely, [ZnL_4(H_2O)_2]·(ClO_4)_2·2H_2O(compound 1) and [Zn_2Cl_4(μ-L-O,O′)_2](compound 2), have been prepared. The single crystal X-ray structure analysis of these compounds indicates that in compound 1 the Zn(Ⅱ) atom is coordinated by four monodentate carboxylato groups on the equatorial plane and two aqua ligands occupy the axial coordination positions. The pendant oxygen atoms form strong hydrogen bonds with the aqua molecules which results in the stability of this structure. In compound 2, two Zn(Ⅱ) atoms are bridged by a pair of carboxylato groups, showing a skew-bridge mode, and thus enabling a long Zn(Ⅱ)…Zn(Ⅱ) separation. As we know, it is a dinuclear coordination compound with the longest Zn…Zn separation.

Structures and Properties of Two Pb^Ⅱ Compounds and Theoretical Study of 2,4-Oxybis（benzoic acid）

Two Pb^Ⅱ coordination polymers [Pb（oba）（2,2′-bipy）]·1.5H2O（1） and [Pb（oba）（phen）]（2）（H2oba = 2,4-oxybis（benzoic acid）, 2,2′-bipy = 2,2′-bipyridine, phen = 1,10-phenanthroline） were synthesized by hydrothermal reactions and characterized by single-crystal X-ray diffraction, thermogravimetric analyses, IR spectroscopy and elemental analysis. Structures of compounds 1 and 2 are similar. Compounds 1 and 2 show 1D wavy chains, which are further connected through aromatic π-π stacking interactions to expand into 2D wavelike networks. The crystal structure of 2,4-oxybis（benzoic acid） ligand（3） was obtained, and its full geometry optimization was carried out by using DFT methods at the B3LYP/6-31G（d） level. The calculated data show that the bond distances and bond angles were very close to the experimental data. The values of the frontier orbital energies indicate that this configuration is stable. Moreover, the solid-state fluorescence properties of 1-3 have also been investigated.

Syntheses,Crystal Structures and Fluorescence Properties of Two Mononuclear Copper(Ⅱ) Compounds

Two new compounds,1（[Cu（IDB_）2]Cl_2·2CH_3CH_2OH·2H_2O（IDB = N,N-di（2-benzimidazolylmethyl）imine]） and 2（[Cu（EDTB）]·2[C_6H_4（OH）COO]·6H_2O（EDTB = N,N,N＇,N＇-tetrakis-[（2-benzimidazolyl）methyl]-1,2-ethanediamine]）,have been synthesized and their crystal structures were determined by single-crystal X-ray diffraction. Crystal 1 belongs to the triclinic system,space group P1 with a = 9.565（2）,b = 9.863（2）,c = 10.252（3） ？,α = 81.915,β = 88.330,γ = 87.347°,V = 956.28（40） ？3,Z = 1,F（000） = 427,D_c = 1.419 g/cm3,Mr = 817.27 and μ（MoKα） = 0.764 mm^（-1）. The final R indices（I 〉 2σ（I））： R = 0.0505,wR = 0.1417; R indices（all data）： R = 0.0591,wR = 0.1525. Crystal 2 is of triclinic system,space group P1 with a = 11.487（3）,b = 13.396（4）,c = 17.977（5） ？,α = 73.899（5）,β = 86.629（5）,γ = 65.018（4）°,V = 2403.8（12） ？3,Z = 2,F（000） = 1072,D3c = 1.417 g/cm,Mr = 1025.54,μ（MoKα） = 0.528 mm^（-1）. The final R indices（I 〉 2σ（I））： R = 0.0769,w R = 0.163 2; R indices（all data）： R = 0.0769,wR = 0.1632. The two compounds exhibit mononuclear structures. The copper（Ⅱ） atom of crystal 1 is six-coordinated by four nitrogen atoms of benzimidazole groups and two amine nitrogen atoms from the ligand IDB to adopt a distorted octahedral coordination geometry. The copper（Ⅱ） atom of crystal 2 is six-coordinated by four nitrogen atoms of benzimidazole groups and two amine nitrogen atoms from the ligand EDTB to show a distorted octahedral coordination geometry. Particularly,the two compounds exhibit fluorescent properties at room temperature in ethanol.

基于4-羟基间苯二甲酸和含氮杂环配体的Zn(Ⅱ)配合物的合成、晶体结构与荧光性质研究

在水热法条件下,4-羟基间苯二甲酸(H 2HPHA)和锌离子分别与1,2二(吡啶-4-基)乙烯(dpee)及4,4′-联吡啶(4,4′-bpy)反应得到了2个三维的配位聚合物[Zn(HPHA)(dpee)·(DMA)2]n(配合物1)和[Zn(HPHA)2(4,4′-bpy)2·DMA]n(配合物2)。用X射线单晶衍射测定了配合物的晶体结构,结果显示:配合物1属于单斜晶系,C2空间群,每个不对称单元由一个锌离子,一个4-羟基间苯二甲酸配体及一个1,2-二(吡啶-4-基)乙烯组成;配合物2属于单斜晶系,P12/c1空间群,每个不对称单元由两个锌离子,两个4-羟基间苯二甲酸配体及两个4,4′-联吡啶配体组成。荧光光谱分析结果表明:配合物1的最强激发峰和发射峰在分别在251和397 nm,配合物2的最强激发峰和发射峰分别在415和513 nm。热重分析表明两个配合物在室温下稳定。

Two Novel Zinc Compounds with in situ Formation of Dimethylamine Ligand

The investigation of the supramolecular interactions between the zinc chloride salts and the crown ether in tetrahydrofuran （THF） with the diffusion of in situ formed DMA （DMA = dimethylamine） ligand leads to two novel zinc-DMA compounds, [（H3O）·（18C-6）][ZnCl3（DMA）] 1 and [（HDMA）·（18C-6）][ZnCl3（DMA）] 2 （18C-6 = 18-crown-6）, whose emissions fall into the blue-emission field. Crystal data for compound 1： monoclinic, space group P21/c, a = 8.753（1）, b = 14.538（2）, c = 19.969（3）A, β = 110.121（7）°, V = 2386.2（5）A^3, T = 293（2） K, Z = 4, Mr = 500.14, Dc= 1.392 g/cm^3,μ = 1.395 mm^-1, F（000） = 1048, S = 1.006, R = 0.0611 and wR = 0.1755 for 3676 observed reflections with I 〉 2σ（I） and 235 parameters. For 2： triclinic, space group P1^-, a = 9.2672（4）, b = 11.8778（2）, c = 13.3846（1） A, a = 67.09（1）, β = 75.54（2）, ）,γ = 81.32（2）°, V = 1311.74（6） A^3, T = 293（2） K, Z = 2, Mr = 527.21, Dc = 1.335 g/cm^3,μ = 1.271 mm^-1, F（000） = 556, S = 1.006, R = 0.0393 and wR = 0.1034 for 3839 observed reflections with I〉 2σ（I）.

Literature Review of the Use of Zinc and Zinc Compounds in Paper-Based Microfluidic Devices

Zinc and its compounds, alloys and composites play an important role in the modern day world and find application in almost every aspect that can improve the quality of our lives. This ranges from supplements and pharmaceuticals that are meant to improve our health and wellbeing to additives meant to guard or reduce corrosion in metals. However, over the past several years, a new area of technology has been garnering a great deal of attention and has made use of zinc and its compounds. This is with reference to paper-based microfluidic technology that offers several advantages and that keeps expanding in the amount of applications it covers. In this paper, a review is offered for the applications that have used zinc or zinc compounds in paper-based microfluidic devices.

Crystal Structures,Luminescent Properties and Hirshfeld Surface Analyses of Zn(Ⅱ)and Cd(Ⅱ)Compounds Based on 1-(2-Carboxyl-phenyl)-3-(pyridin-2-yl)pyrazole

Two compounds,[Zn2（Hcppp）2（cppp）2（H2O）2]·2 NO3·6 H2O（1） and [Cd（Hcppp）2Cl2]· 3H2O（2）（Hcppp = 1-（2-carboxyl-phenyl）-3-（pyridin-2-yl）pyrazole）,are synthesized and characterized by IR,TGA and X-ray single-crystal/powder diffraction.Compound 1 crystallizes in monoclinic system,space group P21/c with a = 9.894（2）,b = 15.856（3）,c = 20.430（4） A,β = 101.70（3）°,V = 3138.5（11） A3,Z = 2,Mr = 1457.94,Dc = 1.543 g/cm^3,F（000） = 1504,R = 0.0278 and wR = 0.0749 for 6157 observed reflections（I 〉 2σ（I））.Compound 2 crystallizes in triclinic system,space group P1 with a = 9.1424（4）,b = 11.6427（5）,c = 16.1345（7） A,α = 102.6430（10）°,β = 95.4530（10）°,γ = 104.0060（10）°,V = 1605.94（12） A3,Z = 2,Mr = 767.88,Dc = 1.588 g/cm^3,F（000） = 776,R = 0.0307 and wR = 0.0764 for 6275 observed reflections（I 〉 2σ（I））.Compound 1 exhibits a binuclear structure while compound 2 shows a mononuclear structure.In compound 1,two cppp-ligands display the μ2-kN,N′：k O and two Hcppp ligands show the μ1-kN,N′ coordination modes.However,two Hcppp ligands connect one Cd（Ⅱ） cation and exhibit the μ1-kN,N′ binding mode in compound 2.The compounds are both studied using Hirshfeld surface analyses and 2D fingerprint plots.The luminescent properties are also discussed.

Synthesis,Spectra,X-ray Diffraction and Thermal Studies of New Zn(Ⅱ) Compounds Based on Dibenzoylmethane

Two new zinc（Ⅱ） compounds with dibenzoylmethane and N-donor ancillary ligands,[Zn（μ-pyz）（dbm）_2]_n（1） and [Zn（dbm）_2（μ-bpe）Zn（dbm）_2]（2）（Hdbm = dibenzoylmethane,pyz = pyrazine and bpe = 1,2-bis（4-pyridyl）ethane）,have been prepared and characterized using elemental analysis,IR,~1H NMR and 13 C NMR spectroscopy,and studied by thermal gravimetric analysis as well as single-crystal X-ray diffraction. The crystal and molecular structures of 1 and 2 have been solved by X-ray diffraction and they turned out to be a one-dimensional coordination polymer with linear dispositions of metal atoms and binuclear compound,respectively. These one-dimensional polymers are further connected to form a 3D supramolecular network by C–H···O（only in 2） and π-π interactions.

柱前衍生化法测定复方氨基酸注射液(18AA-Ⅱ)中氨基酸的含量

目的建立复方氨基酸注射液(18AA-Ⅱ)的柱前衍生化含量分析方法。方法以邻苯二甲醛联合9-芴甲基氯甲酸酯(OPA-FMOC)进行在线衍生,采用Zorbax Eclipse-AAA柱,以40 mmol/L NaH_(2)PO_(4)溶液(pH7.8)为流动相A,乙腈-甲醇-水(45:45:10)为流动相B,梯度洗脱,检测波长338、262 nm,柱温40℃。结果各氨基酸之间分离度良好,线性相关系数均不小于0.9994,平均回收率99%~103%,重复性RSD均小于2%。结论该法稳定、准确、高效,可为复方氨基酸注射液的含量测定和质量评估提供参考,并首次报道了OPA-FMOC衍生分析法中赖氨酸峰面积重复性不佳的优化方法。

A New 2D Zinc(Ⅱ) Coordination Polymer Constructed by Imidazole-4,5-dicarboxylic Acid(H_3IDC) and 1,4-Bis(imidazol-1-ylmethyl)-benzene(bix)

A new 2D Zn（Ⅱ） coordination polymer [Zn（HIDC）（bix）0.5]n（1） was obtained by the hydrothermal reaction of ZnCl2,imidazole-4,5-dicarboxylic acid（H3IDC） and 1,4-bis（imidazol-1-ylmethyl）-benzene（bix） with a 2：2：1 mole ratio.X-ray diffraction crystal structural analysis reveals it crystallizes in monoclinic,space group P21/n with a = 12.125（3）,b = 10.541（3）,c = 12.484（3） ,β = 115.834（4）°,V = 1436.0（6） 3,Mr = 338.60,Z = 4,Dc = 1.566 Mg·m-3,F（000） = 684,μ（MoKα） = 1.730 mm-1,the final R = 0.0439 and wR = 0.0888 for 2101 observed reflections with I ≥ 2σ（I）.In 1,each zinc（Ⅱ） ion is five-coordinated with a slightly distorted trigonal bipy-ramidal coordination geometry,and each μ2-HIDC2-acts as a bridge to bond two neighboring Zn（Ⅱ） ions,leading to a 1D zigzag chain architecture.The adjacent zigzag chains are further linked by μ2-bix to form an infinite 2D network structure.The fluorescence spectrum of 1 exhibits intense emission at 466 nm when excited at 397 nm in solid state at room temperature.

Absorbed Bioactive Compounds Replicate GuanxinⅡ-Induced Endothelium-Associated in/ex vivo Vasodilation

Objective:To develop an interference-free and rapid method to elucidate GuanxinⅡ(GXⅡ)'s representative vasodilator absorbed bioactive compounds(ABCs)among enormous phytochemicals.Methods:The contents of ferulic acid,tanshinol,and hydroxysafflor yellow A(FTA)in GXⅡ/rat serum after the oral administration of GXⅡ(30 g/kg)were detected using ultra-performance liquid chromatography-mass spectrometry.Totally 18 rats were randomly assigned to the control group(0.9%normal saline),GXⅡ(30 g/kg)and FTA(5,28 and 77 mg/kg)by random number table method.Diastolic coronary flow velocity-time integral(VTI),i.e.,coronary flow or coronary flow-mediated dilation(CFMD),and endothelium-intact vascular tension of isolated aortic rings were measured.After 12 h of exposure to blank medium or 0.5 mmol/L H_(2)O_(2),endothelial cells(ECs)were treated with post-dose GXⅡof supernatant from deproteinized serum(PGSDS,300μL PGSDS per 1 m L of culture medium)or FTA(237,1539,and 1510 mg/m L)for 10 min as control,H_(2)O_(2),PGSDS and FTA groups.Nitric oxide(NO),vascular endothelial growth factor(VEGF),endothelin-1(ET-1),superoxide dismutase(SOD),malondialdehyde(MDA)and phosphorylated phosphoinositide 3 kinase(p-PI3K),phosphorylated protein kinase B(p-AKT),phosphorylated endothelial nitric oxide synthase(p-e NOS)were analyzed.PGSDS was developed as a GXⅡproxy of ex vivo herbal crude extracts.Results:PGSDS effectively eliminates false responses caused by crude GXⅡpreparations.When doses equaled the contents in GXⅡ/its post-dose serum,FTA accounted for 98.17%of GXⅡ-added CFMD and 92.99%of PGSDS-reduced vascular tension.In ECs,FTA/PGSDS was found to have significant antioxidant(lower MDA and higher SOD,P<0.01)and endothelial function-protective(lower VEGF,ET-1,P<0.01)effects.The increases in aortic relaxation,endothelial NO levels and phosphorylated PI3K/Akt/e NOS protein induced by FTA/PGSDS were markedly abolished by NG-nitro-L-arginine methyl ester(L-NA,e NOS inhibitor)and wortmannin(PI3K/AKT inhibitor),respectively,indicating an endothelium-dependent vasodilation via the PI3K/AKT-e NOS pathway(P<0.01).Conclusion:This study provides a strategy for rapidly and precisely elucidating GXⅡ's representative in/ex vivo cardioprotective absorbed bioactive compounds(ABCs)-FTA,suggesting its potential in advancing precision ethnomedicine.

Extraction of manganese and zinc from their compound ore by reductive acid leaching

Comprehensive utilization of low grade manganese?zinc compound ore containing lead and silver with a method of reductive acid leaching was studied.According to theφ?pH diagram of Mn?Zn?H2O system,Mn and Zn can be leached simultaneously in the pH range of?2to5.61.The results showed that both hydrogen peroxide and sucrose were effective reductants which could intensify the simultaneous leaching of Mn and Zn into leachate as well as enrich Pb and Ag in the residue.95.88%of Mn and99.23%of Zn were extracted when the compound ore was leached with hydrogen peroxide in sulfuric acid media,meanwhile the contents of Pb and Ag in the residue were enriched to13.21%and489.36g/t,respectively.When sucrose was used as the reductant,the leaching efficiencies of Mn and Zn separately achieved98.26%and99.62%,and contents of Pb and Ag in the residue were as high as13.92%and517.87g/t,respectively.

A Novel Three-dimensional Triazole-based Zinc(Ⅱ) Coordination Polymer Controlled by the Spacers of Dicarboxylate Ligand with(4~2,6~2,8~2)(4,6~2,8~3) Topology

A novel mixed-ligand coordination polymer [Zn(BTA)(ip)0.5]n(1, HBTA = benzotriazole, H2 ip = isophthalic acid) has been synthesized under hydrothermal conditions, which was further characterized by X-ray diffraction, IR spectrum, elemental analysis and TG-DTA experiments. Complex 1 crystallizes in monoclinic system, space group Pnma with a = 8.9731(5), b = 22.0477(12), c = 10.0217(5) ?, V = 1982.66(18) ?3, Z = 8, C10 H6 ZnN3 O2, Mr = 265.55, Dc = 1.779 g/cm3, μ = 2.462 mm-1, F(000) = 1064, the final R = 0.0225 and wR = 0.0652 with I > 2σ(I). This complex is a 3 D framework with the(42,62,82)(4,62,83) topology. Furthermore, the thermal stability of complex 1 is observed to be dependent on the polymeric structure nature. Strong solid-state luminescence emissions suggest that complex 1 is a good candidate for light emission materials.

Synthesis,Crystal Structure and Fluorescent and Thermal Stability Properties of the Zinc(Ⅱ) Complex [Zn(C_(15)H_(11)O_3)_2(C_(12)H_8N_2)_2]·5H_2O

A new complex has been synthesized with o-methylbenzoyl-benzoic acid（HL） and 1,10-phenanthroline（phen） in the mixture of water and ethanol. It crystallizes in monoclinic, space group C2/c with a = 13.6328（18）, b = 17.7876（18）, c = 19.998（2）, β = 104.720（4）o, C54H48N4O11Zn, Mr = 994.33, V = 4690.2（9）3, Dc = 1.408 g/cm3, Z = 4, F（000） = 2072, μ（MoKα） = 0.59 mm-1, R = 0.0736 and wR = 0.2029. The crystal structure shows that the zinc ions are coordinated with two oxygen atoms from two HL molecules and four nitrogen atoms from two phen molecules, forming distorted octahedral coordination geometry. The fluorescent and thermal stability properties of the complex are studied. The result shows that it has one fluorescent emission band at around 412 nm. In addition, the complex is stable under 210 ℃.

Synthesis and Characterization of Two Binuclear Macrocyclic Zinc(Ⅱ) Complexes by Anion Exchange

Two macrocyclic zinc（Ⅱ） complexes {[ZnL（VO3）2]·0.33H2O}n（1） and [ZnL（H2O）2][Ni（CN）4]（2）（L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane） have been obtained from the reactions of [ZnL]（ClO4）2 with NH4VO3 and K2[Ni（CN）4], respectively, and structurally characterized by elemental analysis, IR, XRPD, TG and X-ray diffraction. Single-crystal X-ray diffraction analyses indicated that the Zn（Ⅱ） atom lies on an inversion center and is octahedrally coordinated by four nitrogen atoms of the tetradentate macrocyclic ligand in the equatorial plane and two oxygen atoms of [VO4] tetrahedra in the axial positions in 1, and two oxygen atoms of two water molecules in 2. Complex 1 shows a three-dimensional structure, which is constructed by the links of [VO3]nn- chains with [ZnL]2＋, forming one-dimensional channels occupied by guest water molecules. The monomers of [ZnL（H2O）2]2＋ and [Ni（CN）4]2- are connected through the intermolecular hydrogen bonds to form a two-dimensional sheet in complex 2.

Hydrothermal Synthesis, Crystal Structure and Fluorescence Properties of a Three-dimensional Triply-bridged Binuclear Zinc(Ⅱ) Complex [Zn_2(Mba)_3(Phen)_2EtOH)]·ClO_4

The novel complex [Zn2（Mba）3（Phen）2EtOH）]·ClO4 （Hrnba = methoxybenzoic acid, Phen = 1,10-phenanthroline, EtOH = ethanol） was synthesized by hydrothermal reactions, and its structure was determined by X-ray diffraction. The crystal belongs to the triclinic system, space group Pi with a = 1.15362（1）, b = 1.3655（3）, c = 1.61451（1） nm, α= 72.842（2）, β = 83.259（3）, y = 72.083（2）°, V = 2.3112（6） nm3, Z = 2,μ（MoKa） = 11.71 cm-1, F（000） = 1120, R = 0.0552 and wR = 0.1157 （I 〉 2σ（I））. The two centric zinc（H） ions in the complex locate in a distorted octahedral coordination geometry and a distorted trigonal bipyramid coordination geometry, respectively. Two bridging bidentate carboxyl groups and a μ2-O carboxyl group from three methoxybenzoic acids act as the bridge to link two Zn（Ⅱ） ions. The asymmetric units are connected by π-π packing interactions between aromatic rings to form a three-dimensional supramolecular network. The experimental results show a good fluorescence property for the complex.

Hydrothermal Syntheses,Crystal Structures,and Characterization of Two Zinc(Ⅱ)Complexes Containing Flexible Bis(benzimidazole)Ligands

Two zinc（II） complexes, namely, [Zn（L1）Cl2]2 （1） and {[Zn（L2）（tbta）]·3H2O}n （2） （L1 = 1,3-bis（2-methylbenzimidazol-1-ylmethyl）benzene, H2tbta = tetrabromoterephthalic acid, L2 = 1,3-bis（2-methylbenzimidazol-1-yl）-2-propanol） have been successfully obtained under hydrothermal conditions. Complex 1 displays binuclear structure which is further extended into a 1D supramolecular chain through π–π stacking. Complex 2 features 2D （4,4） network based on L2/tbta2– double linker. The thermal stability, fluorescence properties and catalytic activities of two complexes for degradation of Methyl orange in a Fenton-like process were discussed.

Synthesis, Crystal Structure and Biological Properties of One Zinc(Ⅱ) Complex Based on 4-Acyl Pyrazolone Derivative

[Zn（L）（CH3OH）3]（H2L = N-（1-phenyl-3-methyl-4-propenylidene-5-pyrazolone）-salicylidene hydrazide） has been synthesized by the reaction of zinc nitrate and ligand H2 L. The complex crystallizes in orthorhombic system, space group Pbca with a = 5.888（15）, b = 14.564（14）, c = 22.20（2） , V = 5137（8） 3, Z = 8 and F（000） = 2184. The ligand serves as a negative bivalent tridentate chelating agent to coordinate with the central zinc（II） atom. DNA-binding was studied by UV-Vis spectral analysis and ethidium bromide（EB） displacement experiments. The results showed that the DNA-binding constant of the complex is 5.1×104 M–1. Antitumor activity of [Zn（L）（CH3OH）3] and the ligand have been investigated by MTT assay, which indicated that the complex has better cytotoxicity to Eca-109 and He La than free ligand.

Crystal Structure and Luminescent Properties of a 3D Cd(Ⅱ) Compound Constructed from Succinate and 3,6-Di(4-pyridyl)pyridazine

A three-dimensional（3D） coordination polymer,[Cd（SC）（DPPD）]_n（1,H_2SC = succinic acid and DPPD = 3,6-di（4-pyridyl）pyridazine）,has been synthesized by the solvothermal reaction of Cd（NO_3）_2·4H_2O with H_2 SC and DPPD at 120 ℃ in DMF solvent. Compound 1 crystallizes in the monoclinic system,space group P2_1/c,with a = 10.7993（4）,b = 11.7705（3）,c = 13.5336（6） A,V = 1678.89（11） A^3,Z = 4,C18H14N4O_4 Cd,M_r = 462.73,D_c = 1.831 g/cm^3,μ = 1.335 mm^（-1）,F（000） = 920.0,the final R = 0.0500 and wR = 0.1567 for 3714 observed reflections with I 〉 2s（I）. In compound 1,the Cd（Ⅱ） ions are linked by the SC^2– ligands to give a two-dimensional（2D） undulating sheet based on the centrosymmetric dinuclear Cd_2（COO）_2 units. The 2D sheets are further connected by the DPPD ligands to produce a 3D structure,which is a 6-connected（4^4·6·^10·8） topological network based on the dinuclear Cd_2（COO）_2 node. Compound 1 exhibits a photoluminescent emission with a maximum at 540 nm upon excitation at 460 nm.