柔性双咪唑配体环状金（Ⅰ）配合物的合成、表征及荧光性质

采用扩散法制备了2个基于柔性双咪唑配体的Au(Ⅰ)配合物,[Au_2(m-bitmb)_2][AuCl_2]Cl·2CH_3OH (1)和[Au_2(m-bitmb)_2][AuCl_2]_2·2CH_3CN (2)(m-bitmb=1,3-bis(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene),并使用X射线单晶衍射、元素分析、XRD等测试手段进行了表征,研究了配合物的荧光性质。结构分析结果表明配合物1和2均具有M_2L_2的环状结构单元,其结构中双齿配体mbitmb均采用顺式构型参与配位,M_2L_2结构单元通过π-π堆积相互作用排列而形成一维链状结构。配合物1和2具有更强的π-π堆积作用,但亲金性稍弱。通过对比2种配合物和配体的荧光发射,发现配合物中存在的亲金相互作用对其荧光性质具有很重要的影响和作用。     

3-(2-吡啶基)-1,2,4-三唑配体Co(Ⅱ)Cu(Ⅱ)和Cd(Ⅱ)配合物的合成、结构及荧光性质（英文）

利用3-(2-吡啶基)-1,2,4-三唑配体(HL)和不同的金属盐设计合成了5个配合物[Co(HL)_2(H_2O)_2](NO_3)_2(1)、[Cu_2(L)_2(NO_3)_2(H_2O)_4](2)、 [Cu_2(L)_2(AcO)_2(H_2O)_2]·6H_2O(3)、[Cu_2(L)_2(HL)_2(ClO_4)_2]·2CH_3CN(4)和[Cd_2(L)_2(HL)_2(NO_3)_2]·2H_2O(5),并通过X射线单晶衍射、红外、元素分析、X射线粉末衍射和热重对配合物结构进行了表征。测试结果表明配合物1具有单核结构,并且可以通过氢键的相互作用形成二维超分子结构。配合物2~5为双核结构。配合物2和5可以通过氢键的相互作用形成二维超分子结构。配合物3通过氢键的相互作用形成三维超分子结构。研究了配合物中HL配体的配位模式。此外,研究了配体HL和配合物1和5的固态荧光性质及荧光寿命。     

稀土2-[2-(4-苯甲酸甲酯)乙烯基]-8-羟基喹啉配合物的合成、表征及荧光性质

在甲醇体系中,用常规溶液法由自行设计合成的配体2-[2-(4-苯甲酸甲酯)乙烯基]-8-羟基喹啉(C_(19)H_(15)NO_3, HL)和稀土硝酸盐(Ln(NO_3)_3·nH_2O)反应合成了6个相应的配合物[Ln(NO_3)(L)_2](Ln=Nd,1; Sm,2; Eu,3; Gd,4; Tb,5; Dy,6);配体用红外光谱、核磁共振、单晶X射线衍射进行表征和结构测定;配合物用元素分析、红外光谱、摩尔电导、热重分析进行表征。室温下,测定了配体和配合物的荧光光谱及配合物的荧光寿命,结果表明:配体本身在575 nm处有较强的荧光发射,当形成配合物后,仍然表现为配体的发光而没有出现稀土中心离子的特征发光;与此同时,依中心离子的不同出现了不同程度的荧光增强或减弱现象,并伴随一定程度的红移或蓝移现象。     

基于D(-)/L(+)-对羟基苯甘氨酸配体的两个铜配合物的合成、结构和电化学性质

利用手性配体D(-)/L(+)-对羟基苯甘氨酸(D/L-Hhpg)与铜盐在溶液法条件下合成2个手性配合物{[Cu(D-hpg)(phen)(NO_3)]·1.5H_2O}_n(1)和{[Cu(L-hpg)(phen)(NO_3)]·2H_2O}_n(2),(phen=1,10-菲咯啉)。对2个配合物进行了元素分析、红外光谱、粉末X射线衍射、单晶X射线衍射、固态圆二色谱表征及热重-差热分析。配合物1和2是正交晶系,P2_12_12_1手性空间群,二者均为1D链状结构并通过氢键作用形成3D超分子结构。有趣的是,配合物1和2中的配位硝酸根与晶格水分子之间的氢键作用使它们分别生成了沿b轴方向的左手和右手超分子螺旋链。此外,基于配合物1和2的中心金属离子为Cu(Ⅱ),进一步探究了电化学性能。循环伏安结果表明生成的配合物具有电化学活性,在扫描速率为0.025～1.0 V·s~(-1)范围内,配合物制备的碳糊电极上的电化学过程是由表面控制的。     

萘咪唑类稀土配合物的晶体结构和荧光性质（英文）

通过2-(2′-羟基-3′-甲氧基)萘咪唑(HL)和Ln(NO)_3·6H_2O反应,合成了4种单核稀土配合物[Ln(HL)_2(NO_3)_3]·CH_2Cl_2(Ln=Sm(1),Eu(2),Tb(3))和[Ln(HL)_2(NO_3)_2(CH_3OH)]NO_3·CH_3OH(Ln=Yb(4))。X射线单晶衍射分析表明配合物1~4均通过配体萘环间的π-π作用呈现蝴蝶状结构。荧光性质表明仅有配合物4显示Yb3+稀土离子的特征发光,固态和在乙腈溶液中的荧光寿命分别为8.27μs和4.40μs。     

基于2-氨基-3-羟基-吡啶Schiff碱的双核Ni(Ⅱ)和Zn(Ⅱ)配合物:合成、超分子结构和光谱性质（英文）

合成了2个2-氨基-3-羟基-吡啶Schiff碱双核Ni(Ⅱ)和Zn(Ⅱ)配合物,[Ni(L~1)(DMF)]_2(1)(H_2L~1=4-羟基-3-((3-羟基-吡啶-2-亚氨基))-苯并吡喃-2-酮)和[Zn(L~2)(H_2O)]_2·2DMF(2)(H_2L~2=2-((3,5-二溴-2-羟基)-氨基)-吡啶-3-醇),并通过元素分析、红外光谱、紫外-可见吸收光谱、荧光光谱及X射线单晶衍射分析等手段进行了表征。X射线单晶衍射分析结果表明:配合物1和2均具有双核结构,均由2个金属离子和2个配体单元以及2个配位的溶剂分子组成,不同的是配合物2含有2个溶剂分子。配合物1和2都是单斜晶系、P2_1/c空间群,且中心金属Ni(Ⅱ)和Zn(Ⅱ)离子的空间构型均为五配位的扭曲的四方锥。此外,配合物1和2通过分子间氢键、C-H…π及π…π作用形成3D超分子结构。此外,讨论了H_2L~1,H_2L~2及其相应的Ni(Ⅱ)和Zn(Ⅱ)配合物的荧光性质。配体H_2L~1和H_2L~2呈现蓝色发射,最大发射波长λ_(em)分别为457和473 nm,而配合物1和2显示绿色发射,λ_(em)分别为543和538 nm。     

喹啉和吡啶取代三芳基三唑的两个铜配合物的合成与晶体结构（英文）

分别以3-(2-吡啶基)-4-(4-甲基苯基)-5-(2-喹啉基)-1,2,4-三氮唑(L~1)和3-(2-吡啶基)-4-(4-氟苯基)-5-(2-喹啉基)-1,2,4-三氮唑(L~2)作为配体,合成了2个新的单核铜配合物:trans-[Cu(L~1)_2(NO_3)(H_2O)]NO_3·H_2O(1)和trans-[Cu(L~2)_2(NO_3)(H_2O)]NO_3·H_2O(2),对其进行了红外、元素分析和单晶结构表征。2个配合物都属于三斜晶系,P1空间群。单晶结构表明,配合物1和2中的铜离子均处于一个扭曲的八面体配位环境[Cu N_4O_2],轴向上各有一个水分子和一个硝酸根配位。配体的吡啶氮原子和三氮唑的一个氮原子参与配位,而喹啉的氮原子不配位。配合物晶体中存在O-H…O、C-H…O、C-H…N氢键和C-H…π相互作用,从而连接单核配合物形成三维网络。     

一种三核铜(Ⅱ)配合物{[Cu(HL)(EtOH)]2Cu}的合成及结构研究

通过双肟配体H₄L(H₄L=6,6′-二羟基-2,2′-[1,2-亚乙基二氧双(氮次甲基)]二酚)与水合乙酸铜反应,合成了一个新的铜配合物{[Cu(HL)(EtOH)]₂Cu},并进行了元素分析、红外光谱和X-射线单晶衍射测定。结果表明,该配合物为三核结构,由3个Cu^Ⅱ离子、2个配位的(HL)^3-单元、2个配位的乙醇分子组成。且配合物通过分子间C-H…O氢键形成了一个二维超分子结构。     

3-乙基-2-乙酰吡嗪缩N(4)-(对甲苯)氨基硫脲Ga(Ⅲ)、In(Ⅲ)配合物的合成、晶体结构和DNA结合性质（英文）

以3-乙基-2-乙酰吡嗪N(4)-(对甲苯)氨基硫脲(HL)为原料,合成了[Ga(L)_2]NO_3·4CH_3OH (1)和[In(L)_2]NO_3·1.75CH_3OH (2)两种新型配合物,并进行了X射线衍射分析表征。结果表明,配合物1和配合物2同构但具有不同数目的结晶甲醇分子。每个配合物的金属中心被2个拥有[N_2S]供体的配体阴离子包围,采取扭曲的八面体配位几何。此外,荧光光谱表明配合物与DNA的相互作用强于配体。     

一种2-甲基-3-羟基喹啉-4-甲酸单核铜(Ⅱ)配合物的合成、晶体结构、理论计算与性质

以2-甲基-3-羟基喹啉-4-甲酸和1,10-菲咯啉为原料,经溶剂热法合成了一种新颖的Cu(Ⅱ)配合物,[Cu(L)(Phen)(H_2O)]·CH_3OH(1,HL=2-甲基-3-羟基喹啉-4-甲酸,Phen=1,10-菲咯啉),并通过红外光谱、元素分析、单晶衍射、固态漫反射、光致发光及理论计算对其结构和性质进行了研究。单晶结构分析表明配合物1的晶体属于单斜晶系,P2_1/c空间群,是一种零维(0D)结构的单核体。固态光致发光表明其为蓝紫色光发射体。时间密度泛函理论(TDDFT)计算表明其发射归属于配体-配体电荷转移(LLCT)。固态漫反射测量显示该化合物存在1.91 eV的窄带能隙。     

Synthesis and spectral studies of some new dimeric [(μ-Cl)2M2(L)2 · xTHF] [M = Zn(II) and Hg(II)] complexes containing Schiff-base ligands

A series of binuclear Schiff-base complexes of zinc(II) and mercury(II) containing bidentate ligands (HL) [HL?=?salicylidene-2-methyl-1-aminobenzene (HL¹), salicylidene-2-aminopyridine (HL²), and salicylidene-3-nitro-1-aminobenzene (HL³)] with “N” and “O” donors have been synthesized by simple metathetic reactions of anhydrous metal chlorides with sodium salts of Schiff bases (in tetrahydrofuran (THF)/MeOH) in equimolar ratio to produce [(µ-Cl)₂M₂(L)₂?·?xTHF] [where M?=?Zn(II) and Hg(II); L?=?HL¹, HL², and HL³; x?=?0 for (1), (4), (6) and x?=?2 for (2), (3), (5)]. The main emphasis on the complexes [(µ-Cl)₂M₂(L)₂?·?2THF] (2), (3), and (5) is given due to their five-coordinate environment around metal ions. The complexes have been characterized by elemental analyses (M, Cl, C, H, N), melting point, and spectral (FT-IR, ¹H-NMR, and ¹³C-NMR) studies. The structural composition of the complexes has been determined by FAB-MS spectral studies. FAB-MS showed the isotopic molecular ion peak [M⁺] and fragments supporting the formulation. Powder X-ray diffraction study of 6 is also reported showing the crystallite size (404.5?Å) of the complex.     

The d metal-sulfosalicylate complexes: Herring-bone, ladder and double-stranded chain frameworks with green luminescences

Assembly of 5-sulfosalicylic acid (H₃L) and d¹⁰ transition metal ions (Cd^II, Ag^I) with the neutral N-donor ligands produces five new complexes: [Cd₂(HL)₂(4,4′-bipy)₃]_n·2nH₂O (1), {[Cd₂(μ₂-HCO₂)₂(4,4′-bipy)₂(H₂O)₄][Cd(HL)₂(4,4′-bipy)(H₂O)₂]}_n (2), {[Cd(4,4′-bipy)(H₂O)₄][HL]·H₂O}_n (3), [Cd(HL)(dpp)₂(H₂O)]_n·4nH₂O (4), {[Ag(4,4′-bipy)][Hhbs]}_n (5) (4,4′-bipy=4,4′-bipyridine, dpp=1,3-di(pyridin-4-yl)propane, H₂hbs=4-hydroxybenzenesulfonic acid, the decarboxylation product of H₃L). Complex 1 adopts a 5-connected 3D bilayer topology. Complex 2 has the herring-bone and ladder chain, which are extended to a 3D network via hydrogen bonding. In 3–4 complexes, 3 is a 3D supermolecular structure formed by polymeric chains and 2D network of HL²⁻, while 4 gives the double-stranded chains. In 5, ladder arrays are stacked with the 2D networks of Hhbs⁻ anions in an –ABAB– sequence. Complexes 1–4 display green luminescences in solid state at room temperature, while emission spectra of 3 and 4 show obvious blue-shifts at low temperature.     

Syntheses,spectroscopy, and X-ray structures of 3-{(R)-(Ar)-ethylimino}-1,3-dihydro-indol-2-one (Ar = Ph,MeOC6H4, BrC6H4, 1-naphthyl) and [Rh(η4-cod){3-((R)-(Ar)-ethylimino)-3H-indol-2-olato}]

Condensation of 1H-indole-2,3-dione (isatin) with (R)-(Ar)-ethylamines gives enantiopure Schiff bases, 3-{(R)-(Ar)-ethylimino}-1,3-dihydro-indol-2-one (HL) {Ar?=?Ph (HL1), 2-MeOC₆H₄ (HL2), 4-MeOC₆H₄ (HL3), 4-BrC₆H₄ (HL4), and 1-naphthyl (HL5)}. The Schiff bases readily coordinate to [Rh(μ-O₂CMe)(η⁴-cod)]₂ (cod?=?1,5-cyclooctadiene) to give mononuclear [Rh(η⁴-cod){3-((R)-(Ar)-ethylimino)-3H-indol-2-olato}] {Ar?=?Ph (1), 4-MeOC₆H₄ (2), and 4-BrC₆H₄ (3)}, respectively. The Schiff bases and complexes have been fully characterized by IR, UV-Vis, ¹H-NMR, mass, and circular dichroism (CD) spectrometry. Polarimetry and CD measurements show the enantiopurity of the Schiff bases as well as the complexes. ¹H NMR measurements reveal slow conversion of the lactam to the enol form of the Schiff bases in solution. In the solid state the lactam form dominates as shown by crystal structures of HL1 and HL4. While gross structural features of both are similar, the molecules differ significantly in the relative orientations of the aryl and lactam rings. The difference is mostly rotation about the N2–C9 bond with different C8–N2–C9–C11 torsion angle of +89.77(12)° for HL1 and C2–N2–C9–C11 of +106.8(3)° for HL4.     

Synthesis and physiochemical studies on binuclear Cu(II) complexes derived from 2,6-[(N-phenylpiperazin-1-yl)methyl]-4-substituted phenols

Preparation of the ligands HL¹ = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-ethylphenol; HL² = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-methoxyphenol and HL³ = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-nitrophenol are described together with their Cu(II) complexes with different bridging units. The exogenous bridges incorporated into the complexes are: hydroxo [Cu₂L(OH)(H₂O)₂](ClO₄)₂.H₂O (L¹=1a, L² =1b, L³ =1c), acetato [Cu₂L(OAc)₂]ClO₄.H₂O (L¹ =2a, L² =2b, L³ =2c) and nitrito [Cu₂L¹(NO₂)₂(H₂O)₂]ClO₄.H₂O (L¹=3a, L² =3b, L³ =3c). Complexes1a,1b,1c and2a,2b,2c contain bridging exogenous groups, while3a,3b,3c possess only open μ-phenolate structures. Both the ligands and complexes were characterized by spectral studies. Cyclic voltammetric investigation of these complexes revealed that the reaction process involves two successive quasireversible one-electron steps at different potentials. The first reduction potential is sensitive to electronic effects of the substituents at the aromatic ring of the ligand system, shifting to positive potentials when the substituents are replaced by more electrophilic groups. EPR studies indicate very weak interaction between the two copper atoms. Various covalency parameters have been calculated.     

[Boranato-bis(dimethylphosphonium-methylid)]-Komplexe der do- und d10-Metalle: Li,Be, Mg,Zn, Cd,Hg, Al und Ga

Dehydrohalogenation and metallation of boranato-bis-trimethylphosphonium salts (1), using two equivalents of a lithiumalkyl in tetrahydrofuran, leads to a solvated organolithium reagent H₂B[(CH₃)₂PCH₂]₂Li (3) which can be converted into a 1:1n1-complex with tetramethylethylenediamin (4).3 reacts with anhydrous metal(II) halides to form spirocyclic coordination compounds of the type H₂B[(CH₃)₂PCH₂]₂ M[CH₂P(CH₃)₂]₂BH₂ (5–9,M=Be, Mg, Zn, Cd, Hg). The reaction of [(CH₃)₃PBH₂P(CH₃)₃]Br (1) with lithium tetramethylmetalates Li[M(CH₃)₄],M=Al, Ga, on heating in the absence of a solvent affords the metallocycles H₂B[(CH₃)₂PCH₂]₂ M(CH₃)₂ (10, 11) with evolution of methane. The products can be sublimed from the reaction mixture. The proposed structures of the new compounds, with tetrahedrally coordinated central atoms and strong covalent metal-carbon interactions, are supported by mass, IR and¹H,⁷Li,¹¹B,¹³C, and³¹P NMR spectra. Compound9 represents a rare case of a tetracoordinate organomercurial, compound5 is the first nonionic tetraalkylberyllate.

     

Synthesis,Structure, and Properties of Nickel(II) and Cobalt(II) Coordination Compounds with Optically Active Diaminodioxime (H2L) Derived from 3-Carene. Molecular and Crystal Structures of the [Ni(H2L)(NO3)]NO3 and [Ni(HL)]ClO4 · H2O Complexes

Nickel(II) and cobalt(II) complexes with optically active diaminodioxime (H₂L, the derivative of 3-carene) of the compositions [Ni(H₂L)NO₃]NO₃ (I), Ni(H₂L)Cl₂ (II), [Ni(HL)]ClO₄ · H₂O (III), and Co(H₂L)Cl₂ (IV), were synthesized. According to X-ray diffraction data, the structures of the paramagnetic compound I and diamagnetic complex III are ionic. In the cation of I, the distorted NiN₄O₂ octahedron is formed by the N atoms of the tetradentate cyclic ligand (H₂L molecule) and by the O atoms of NO₃ ^–; anion functioning as bidentate cyclic ligands. In the cation of III, the NiN₄ coordination unit is a distorted square formed upon coordination of the tetradentate cyclic ligand, HL^–; anion. The data of magnetochemistry and UV-Vis, IR, and Raman spectroscopy suggest that paramagnetic complexes II and IV contain a distorted octahedral polyhedron MCl₂N₄ (M = Ni, Co).     

N-(1-亚氨基乙基)乙脒铂配合物合成、结构和性质

四氯合铂酸钾分别与邻、间、对磺基苯甲酸在乙腈和水中利用水热合成获得了3个铂的N-(1-亚氨基乙基)乙脒配合物:[Pt(NIA)₂]·(2-sb)·2H₂O(1),[Pt(NIA)₂]·(3-sb)·3H₂O(2)和[Pt(NIA)₂]·(1,4-dsb)·2H₂O(3)(NIA=N-(1-亚氨基乙基)乙脒,2-sb^2-=2-磺基苯甲酸二价阴离子、3-sb^2-=3-磺基苯甲酸二价阴离子、1,4-dsb^2-=1,4-二磺基苯二价阴离子)。合成过程中发生了乙氰三聚以及4-sb^2-转变为1,4-dsb^2-的反应。对配合物进行了元素分析、红外、紫外、荧光、热重和粉末X射线衍射表征,并利用单晶X射线衍射测定了配合物的晶体结构。3个配合物为阳离子-阴离子物种,阳离子为[Pt(NIA)₂]²⁺,中心金属离子四配位平面构型;阴离子与阳离子、水形成氢键,组成一个三维网络结构,但3个配合物的氢键模式不同。配合物在热稳定性、荧光性质上有一定差异。     

Synthesis and structure of copper(II) coordination compounds with 8-quinolinecarboxaldehyde thio- and 4-phenylthiosemicarbazones

8-Quinolinecarboxaldehyde thiosemicarbazone (HL) and copper form compounds with a metal: ligand ratio of 1: 1 in which the ligand is either the neutral molecule or the monohydric acid anion. Its acidic properties are enhanced not only as a result of coordination but also due to the electronic effect of substituents in the thiosemicarbazide moiety. 8-Quinolinecarboxaldehyde 4-phenylthiosemicarbazone (HL¹) is coordinated only as the anion. The structures of [Cu(HL)SO₄]₂, [Cu(L)NO₃]₂, and [Cu(L¹)NO₃]₂ · 0.25H₂O, and free HL¹ were studied. The tendency of the complexes to dimerization and association with acid anions or sulfur atoms of the organic ligands as bridges was established. In binuclear compounds with closely spaced magnetic centers, no exchange interaction between them was found. The copper coordination compounds with HL are able to suppress the growth of cancer cells 41M and SK-BR-3 and are promising objects for investigation as anticancer drugs.     

Synthesis,characterization, DNA-binding,and antioxidant activities of four copper(II) complexes containing N-(3-hydroxybenzyl)-amino amide ligands

Four new substituted amino acid ligands, N-(3-hydroxybenzyl)-glycine acid (HL₁), N-(3-hydroxybenzyl)-alanine acid (HL₂), N-(3-hydroxybenzyl)-phenylalanine acid (HL₃), and N-(3-hydroxybenzyl)-leucine acid (HL₄), were synthesized and characterized on the basis of ¹H NMR, IR, ESI-MS, and elemental analyses. The crystal structures of their copper(II) complexes [Cu(L₁)₂]·2H₂O (1), [Cu(L₂)₂(H₂O)] (2), [Cu(L₃)₂(CH₃OH)] (3), and [Cu(L₄)₂(H₂O)]·H₂O (4) were determined by X-ray diffraction analysis. The ligands coordinate with copper(II) through secondary amine and carboxylate in all complexes. In 2, 3, and 4, additional water or methanol coordinates, completing a distorted tetragonal pyramidal coordination geometry around copper. Fluorescence titration spectra, electronic absorption titration spectra, and EB displacement indicate that all the complexes bind to CT-DNA. Intrinsic binding constants of the copper(II) complexes with CT-DNA are 1.32?×?10^6?M^?1, 4.32?×?10^5?M^?1, 5.00?×?10^5?M^?1, and 5.70?×?10^4?M^?1 for 1, 2, 3, and 4, respectively. Antioxidant activities of the compounds have been investigated by spectrophotometric measurements. The results show that the Cu(II) complexes have similar superoxide dismutase activity to that of native Cu, Zn-SOD.     

Spectral and electrochemical studies of ruthenium(II) complexes with N-methyl-4-nitrobenzaldehyde and N-methyl-4-nitrobenzophenone thiosemicarbazone: Potential anti-trypanosomal agents

N⁴-Methyl-4-nitrobenzaldehyde thiosemicarbazone (H4NO₂Fo4M), N⁴-methyl-4-nitrobenzophenone thiosemicarbazone (H4NO₂Bz4M) and their ruthenium(II) complexes [Ru(4NO₂Fo4M)₂(PPh₃)₂] (1), [Ru(4NO₂Bz4M)₂(PPh₃)₂] (2), [Ru(4NO₂Fo4M)₂(dppb)] (3) and [Ru(4NO₂Bz4M)₂(dppb)] (4) (dppb = 1,4-bis(diphenylphospine)butane) were obtained and characterized. The crystal structure of H4NO₂Fo4M has been determined. Electrochemical studies have shown that the nitro anion radical, one of the proposed intermediates in the mechanism of action of nitro-containing anti-trypanosomal drugs, is formed at approximately −1.00 V in the free thiosemicarbazones as well as in their corresponding ruthenium(II) complexes, suggesting their potential to act as antitrypanosomal drugs. The natural fluorescence of H4NO₂Fo4M, H4NO₂Bz4M and complexes (1)–(4) provides a way to identify and to monitor their concentration in biological systems.