Antifungicidal,antibacterial and antifertility activities of biologically active heterocyclic thiosemicarbazones and their coordination complexes with the dimethylsilicon moiety

Synthetic, structural and biological aspects of trigonal-bipyramidal, Me₂Si(NS)Cl and octahedral, Me₂Si(NS)₂ types of organosilicon (IV) complexes of heterocyclic thiosemicarbazones (N? SH) have been described. The complexes were characterized by elemental analysis, molecular weight determination, conductance measurements and electronic, infrared, ¹H and ¹³C NMR spectral studies. Some ligands and their corresponding dimethylsilicon (IV) complexes have been tested for their effects on several pathogenic fungi and bacteria. Two representative complexes have also been found to act as sterilizing agents by reducing the production of sperm in male mice.     

Preparation and 1H NMR study of complexes of trimethylplatinum(IV) with some tridentate schiff base ligands containing,N, O,and S donor atoms

The Schiff base ligands I–V, made by condensing either 2-acetylpyridine (I), 8-quinolinecarboxaldehyde (II and III), or o-methylthiobenzaldehyde (IV and V) with either N,N′-dimethyl-1,3-diaminopropane (I, II, and IV), 2-aminomethylpyridine (III), or 2-(2-aminoethyl)-pyridine (V), give ionic Pt^IVMe₃ complexes containing tridentate NNN- or SNN-bonded ligands. With PtMe₃Br ligand V gives a neutral complex XI in which it is coordinated only via the two N atoms. A monomeric Pt^IVMe₃ salicyladiminate complex results on treating the dimeric trimethylplatinum(IV) salicylaldehyde complex with the bidentate amine H₂N (CH₂)₃NMe₂. The complexes have been fully characterised by ¹H NMR spectroscopy.     

Synthesis, 119Sn Mössbauer spectroscopic studies and X-ray crystal structure determination of new seven-coordinate diorganotin(IV) complexes with S,N,N,N,S-pentadentate Schiff bases derived from 2,6-diacetylpyridine of S-methyl- and S-benzyldithiocarbazates

The reactions of the ligands 2,6-diacetylpyridine bis(S-methyldithiocarbazate)] (H₂dapmdtc) and 2,6-diacetylpyridine bis(S-benzyldithiocarbazate)] (H₂dapbdtc) with R_4-m SnCl _m (R = Me, ⁿ Bu, Ph; and m = 2) led to the formation of six seven-coordinate diorganotin(IV) complexes, which were studied by microanalysis, i.r., n.m.r (¹H, ¹¹⁹Sn) and Mössbauer spectroscopies. The X-ray structures determination of complexes [Me₂Sn(dapmdtc)], [Me₂Sn(dapbdtc)] and [Ph₂Sn(dapbdtc)] revealed the presence of neutral seven-coordinated complexes. The structures consist of monomeric units in which the Sn(IV) atom exhibits distorted pentagonal bipyramidal (PBP) geometry, with the S,N,N,N,S-donor systems of the ligands lying in the equatorial plane and organic groups in the apical positions. A correlation between Mössbauer and X-ray data based on the point-charge model is discussed.     

Synthese und Kristallstrukturen von heteronuklearen AgI/FeII‐Koordinationspolymeren: (Me3PhN)2[Ag2Fe(SCN)6], (Me3PhN)6[Ag6Fe3(ECN)18] (E = S,Se) und (Me3PhN)4[Ag2Fe(SCN)8]

The reaction of AgSCN with (Me₃PhN)₃[Fe(NCS)₆] in DMF yields two‐dimensional polymeric, heteronuclear complexes (Me₃PhN)₂[Ag₂Fe(SCN)₆] ( 1 ) and (Me₃PhN)₆[Ag₆Fe₃(SCN)₁₈] · CH₂Cl₂·DMF ( 2a ) with bridging SCN^? ligands, whereas additional (Me₃PhN)(SCN) leads to (Me₃PhN)₄[Ag₂Fe(SCN)₈] ( 3 ) with a one‐dimensional structure. The selenocyanato complex 2b , homologous to 2a , could also be prepared. Single crystal X‐ray structure determinations show, that the Ag⁺ ions in 1 and 2a are coordinated tetrahedrally by four S atoms, in 3 by one N and three S atoms of the bridging SCN^? ligands; six N atoms of the SCN^? or SeCN^? ligands bind to Fe²⁺ in an octahedral arrangement.     

Binary and Ternary Complexes of Copper(II) Involving N,N,N′,N′-Tetramethylethylenediamine (Me4en) and Various Biologically Relevant Ligands

Binary and ternary complexes of copper(II) involving N,N,N′,N′-tetramethylethylene-diamine (Me₄en) and various biologically relevant ligands containing different functional groups are investigated. The ligands (L) used are dicarboxylic acids, amino acids, peptides and DNA unit constituents. The ternary complexes of amino acids, dicarboxylic acids or peptides are formed by simultaneous reactions. The results showed the formation of Cu(Me₄en)(L) complexes with amino acids and dicarboxylic acids. The effect of chelate ring size of the dicarboxylic acid complexes on their stability constants was examined. Peptides form both Cu(Me₄en)(L) complexes and the corresponding deprotonated amide species Cu(Me₄en)(LH₋₁). The ternary complexes of copper(II) with (Me₄en) and DNA are formed in a stepwise process, whereby binding of copper(II) to (Me₄en) is followed by ligation of the DNA components. DNA constituents form both 1:1 and 1:2 complexes with Cu(Me₄en)²⁺. The concentration distribution of the complexes in solution was evaluated. [Cu(Me₄en)(CBDCA)] and [Cu(Me₄en)(malonate)] are isolated and characterized by elemental analysis and infrared measurements.     

Synthesis,Spectroscopic Characterization,Antimicrobial, Pesticidal and Nematicidal Activity of Some Nitrogen‐Oxygen and Nitrogen‐Sulfur donor Coumarins based Ligands and their Organotin(IV) Complexes

Series of new tin complexes are synthesized by classical thermal and microwave‐irradiated techniques. The biologically potent ligands 3‐formyl‐4‐chlorocoumarin semicarbazone (L¹H) and 3‐formyl‐4‐chlorocoumarin thiosemicarbazone (L²H), were prepared by the condensation of semicarbazide hydrochloride and thiosemicarbazide in ethanol with the particular ketone by using microwave as well as conventional methods. The tin(IV) complexes have been prepared by mixing Ph₃SnCl/Me₃SnCl/Me₂SnCl₂ in 1:1 and 1:2 molar ratios with monofunctional bidentate ligands. The structures of the ligands and their tin complexes were confirmed by the elemental analysis, melting point determinations, molecular weight determinations, IR, ¹H NMR, ¹³C NMR, ¹¹⁹Sn NMR, UV, mass spectral and X‐ray powder diffraction studies. On the basis of these studies it is clear that the ligands coordinated to the metal atom in a monobasic bidentate mode, by X$^{\cap}$ N donor system. Thus, suitable trigonal bipyramidal geometry for penta‐coordinated state and octahedral geometry for hexa‐coordinated state have been suggested for the 1:1 and 1:2 metal compounds. Both the ligands and their complexes have been screened for their antimicrobial, pesticidal and nematicidal activities. Copyright © 2011 John Wiley & Sons, Ltd.     

Diphosphine derivatives: Part 5. Ligand behaviour and vibrational spectra of coordinated tetraalkyl-1,2-dithioxodi-λ5-phosphanes (tetraalkyldiphosphine disulphides)

Vibrational data are reported for complexes of tetraethyl-,tetrapropyl-and tetrabutyl-1,2-dithioxodi-λ⁵-phosphanes (tetraalkyldiphosphine disulphides) P₂R₄S₂ with zinc, cadmium, mercury and cobalt halides. The P—P stretching frequencies in the coordinated ligands occur near 500 cm^?1, substantially higher than in the corresponding P₂Me₄S₂ complexes, most probably because of interactions with P—C—C deformation modes. In the F—C stretching region the spectra of the P₂Et₄S₂ complexes are consistent with (but do not necessarily prove) cis-chelate ligand geometry with Zn, Cd and Co halides, and gauche-chelate geometry with Hg halides. No M—S stretching vibrations can be identified above 250cm^?1.     

Copper(II) Complexes with Chiral Diaminodiamido Ligands: Solution and Structural Studies

Abstract

Three diaminodiamido ligands (S,S)-N,N′-bis(prolyl)ethanediamine (ProNN-2), (S,S)-N,N′-bis(N-methylvalyl)ethanediamine (Me₂ValNN-2), and (S,S)-N,N′-bis(N-methylphenylalanyl)-ethanediamine (Me₂PheNN-2) were synthesised and their complex formation equilibria with copper(II) investigated in aqueous solution by potentiometry and, for ProNN-2, by electronic spectrophotometry. ProNN-2 forms the species [CuLH]³⁺, [Cu₂L₂]⁴⁺, [Cu₂L₂H_?2]²⁺ and [CuLH_?2], Me₂PheNN-2 forms the complexes [CuLH]³⁺, [Cu₂L₂H_?2]²⁺ and [CuLH_?2], whereas Me₂ValNN-2 forms the monomer [CuLH_?1]⁺ but not the dimer. The dimeric cation [Cu₂L₂H_?2]²⁺, of Me₂PheNN-2 has severe steric requirements, as demonstrated by the X-ray crystal structure of the complex [Cu₂L₂H_?2]Cl₂· 12H₂O, of the corresponding non-methylated ligand. Since copper(II) complexes of the ligands examined are used as additives to the mobile phase to perform chiral resolution of D,L-amino acids in RP-HPLC, the present results provide valuable clues to an understanding of the mechanism of the enantiomeric separation.     

Infrared and mössbauer investigations on dimethyltin(IV) complexes with potentially tridentate dianionic ligands

Dimethyltin(IV) complexes with formulae Me₂Sn(IMDA)·H₂O, Me₂Sn(ODA)· H₂O and [Me₂Sn(OH)]₂(TDA) [IMDA²⁻ = iminodiacetate²⁻ (NOO); ODA²⁻ = oxydiacetate²⁻ (OOO); and TDA²⁻ = thiodiacetate²⁻ (SOO donor atoms)] have been obtained and their solid state coordination investigated. Infrared and Mössbauer spectroscopic evidence would suggest tridentate behaviour of the ligands in polymeric trans-dimethyl structures for Me₂Sn(IMDA)·H₂O and Me₂Sn(ODA)·H₂O with bridging carboxylate groups; polymeric tetrahedral environments around the two tin(IV) atoms could be inferred with TDA acting as bidentate dianionic ligand through ester type carboxylate groups in [Me₂Sn(OH)]₂(TDA), without involvement of the sulfur atom in coordination.     

Dilithium Hexaorganostannate(IV) Compounds

Hypercoordination of main‐group elements such as the heavier Group 14 elements (silicon, germanium, tin, and lead) usually requires strong electron‐withdrawing ligands and/or donating groups. Herein, we present the synthesis and characterization of two hexaaryltin(IV) dianions in form of their dilithium salts [Li₂(thf)₂{Sn(2‐py^Me)₆}] (py^Me=C₅H₃N‐5‐Me) ( 2 ) and [Li₂{Sn(2‐py^OtBu)₆}] (py^OtBu=C₅H₃N‐6‐OtBu) ( 3 ). Both complexes are stable in the solid state and solution under inert conditions. Theoretical investigations of compound 2 reveal a significant valence 5s‐orbital contribution of the tin atom forming six strongly polarized tin–carbon bonds.     

Neue nitridoverbrückte Dreikernkomplexe des Rheniums

New Trinuclear Rhenium Complexes with Bridging Nitrido Ligands Trinuclear complexes with bridging nitrido ligands between the rhenium atoms are formed when [ReN(Et₂dtc)₂ · (Me₂PhP)] (Et₂dtc^– = N,N‐diethyldithiocarbamate) reacts with TlCl or Pr(O₃SCF₃)₃. [Cl(Me₂PhP)₂(Et₂dtc)Re≡N–Re(N) · Cl₂(Me₂PhP)–N≡Re(Et₂dtc)(Me₂PhP)₂Cl] and [(Et₂dtc)₂ · (Me₂PhP)Re≡N–Re(N)(Et₂dtc)(Me₂PhP)–N≡Re(Me₂PhP) · (Et₂dtc)₂]⁺ contain two almost linear, asymmetric nitrido bridges. Additional, terminal nitrido ligands are located at the middle rhenium atoms.     

Halbsandwich‐Komplexe von Ruthenium(II), Rhodium(III) und Iridium(III) mit Tripeptidestern aus α‐, β‐ und γ‐Aminosäuren als Liganden. — Peptidsynthese und Cyclisierung zu Cyclotripeptiden am Metallzentrum

Metal Complexes with Biological Important Ligands. CXLII. Half Sandwich Complexes of Ruthenium(II), Rhodium(III), and Iridium(III) with Tripeptide Esters from α‐, β‐, and γ‐Amino Acids as Ligands. — Peptide Synthesis and Cyclization to Cyclotripeptides at Metal Centers Halfsandwich complexes of ruthenium, rhodium and iridium with deprotonated N, N', N"‐tripeptide ester ligands were obtained from chloro bridged compounds and tripeptide methyl esters ( 1—6 ) or by peptide synthesis at a metal centre ( 9—15 ). For the peptide synthesis at the complex (C₆Me₆)Ru coordinated dipeptide methyl esters from glycine and β‐alanine or γ‐amino butyric acid were elongated by an a‐amino acid methylester. The tripeptide ester Ru(η⁶‐C₆Me₆) complexes with chiral amino acid components and an “asymmetric” metal atom are formed with high diastereoselectivity. The tripeptide esters Gly‐Gly‐β‐AlaOMe, Val‐Gly‐β‐AlaOMe and Phe‐Gly‐β‐AlaOMe can be condensated at the (C₆Me₆)Ru complex with sodium methanolate to give triple deprotonated cyclic tripeptides.     

Coordination behavior of the carboxylate group in organotin(IV) derivatives of 2-[(2′,4′,6′-tribromophenylamido)]benzoic acid and 3-[(2′,4′,6′-tribromophenylamido)]propenoic acid: Spectroscopic studies

The complexes of two organic carboxylates (containing {O,O}-donor atoms) with Me₂Sn^(IV)Cl₂, n-Bu₂Sn^(IV)Cl₂, Bz₂Sn^(IV)Cl₂, Oct₂Sn^(IV)O, Me₃Sn^(IV)Cl, n-Bu₃Sn^(IV)Cl, Ph₃Sn^(IV)Cl, Ph₃Sn^(IV)Cl, and Bz₃Sn^(IV)Cl having ligand-to-metal ratios of 1: 2 and 1: 1 were prepared by two different methods. The FT-IR spectra clearly demonstrated that organotin(IV) moieties react with {O,O}-atoms of the ligands. It was found that in all cases the COO⁻ group was acting as bidentate in the solid state. The ¹¹⁹Sn NMR data revealed that the organotin(IV) moiety has a tetrahedral geometry in non-coordinating solvents. The biological activity of these compounds was compared with that of their precursors, and all the synthesized compounds show significant antibacterial activity. The antifungal activity of the complexes against six plant pathogens has been estimated. The complexes display marked toxicity against these fungi and are more fungitoxic than free acids. The compounds have also shown significant cytotoxicity against Brine Shrimp (Artemia salina). The article was submitted by the authors in English.     

Synthesis,characterization and antimicrobial activity of triorganotin(IV) derivatives of some bioactive Schiff base ligands

Triorganotin(IV) complexes of the type Me₃Sn[OC(R¹):CH(CH₃)C:NR²OH] and Ph₃Sn[OC(R′):CH(CH₃)C:NR″OH] (R′ = ─CH₃, ─C₆H₅; R″ = ─(CH₂)₂─, ─(CH₂)₃─) have been synthesized by the reactions of trimethyl/phenyltin(IV) chloride with the sodium salt of corresponding Schiff base ligands in unimolar ratio in refluxing tetrahydrofuran. All these compounds have been characterized using elemental analyses and their probable structures have been proposed on the basis of infrared, ¹H NMR, ¹³C NMR, ¹¹⁹Sn NMR and mass spectroscopic studies. In the trimethyltin(IV) derivatives the central tin atom is tetracoordinated, whereas in the analogous triphenyltin(IV)derivatives the central tin atom is pentacoordinated. All these ligands, metal precursors and corresponding triorganotin(IV) complexes have been screened for antimicrobial activities. A comparison of activities of the ligands and their corresponding triorganotin(IV) derivatives has been made. Attempts have also been made to relate the activity to the structure of these compounds.     

Antioxidative vs cytotoxic activities of organotin complexes bearing 2,6‐di‐tert‐butylphenol moieties

Two series of organotin(IV) complexes with Sn–S bonds on the base of 2,6‐di‐tert‐butyl‐4‐mercaptophenol ( L ¹ SH ) of formulae Me₂Sn(L¹S)₂ ( 1 ); Et₂Sn(L¹S)₂ ( 2 ); Bu₂Sn(L¹S)₂ ( 3 ); Ph ₂ Sn(L¹S)₂ ( 4 ); (L¹)₂Sn(L¹S)₂ ( 5 ); Me₃Sn(L¹S) ( 6 ); Ph₃Sn(L¹S) ( 7 ) (L¹ = 3,5‐di‐tert‐butyl‐4‐hydroxyphenyl), together with the new ones [Me₃SnCl(L²)] ( 8 ), [Me₂SnCl₂(L²)₂] ( 9 ) ( L ²  = 2‐(N‐3′,5′‐di‐tert‐butyl‐4′‐hydroxyphenyl)‐iminomethylphenol) were used to study their antioxidant and cytotoxic activity. Novel complexes 8 , 9 of Me_nSnCl_4 ? n (n = 3, 2) with Schiff base were synthesized and characterized by ¹H, ¹³C NMR, IR and elemental analysis. The crystal structures of compounds 8 and 9 were determined by X‐ray diffraction analysis. The distorted tetrahedral geometry around the Sn center in the monocrystals of 8 was revealed, the Schiff base is coordinated to the tin(IV) atom by electrostatic interaction and formation of short contact Sn–O 2.805 Å. In the case of complex 9 the distorted octahedron coordination of Sn atom is formed. The antioxidant activity of compounds as radical scavengers and reducing agents was proved spectrophotometrically in tests with stable radical DPPH, reduction of Cu²⁺ (CUPRAC method) and interaction with superoxide radical‐anion. Moreover, compounds have been screened for in vitro cytotoxicity on eight human cancer cell lines. A high activity against all cell lines with IC₅₀ values 60–160 nM was determined for the triphenyltin complex 7 , while the introduction of Schiff base decreased the cytotoxicity of the complexes. The influence on mitochondrial potential and mitochondrial permeability for the compounds 8 and 9 has been studied. It is shown that studied complexes depolarize the mitochondria but don't influence the calcium‐induced mitochondrial permeability transition.     

(2-Chlorobenzyl)tris(2-pyridinethiolato)tin(IV)

In the title compound, (2-chloro­benzyl)­tris­(pyridine-2-thiol­ato)-κ²N,S;κ²N,S;κS-tin(IV), [Sn(C₇H₆Cl)(C₅H₄NS)₃], two of the three pyridine-2-thiol­ato ligands (SPy) are bidentate and one is monodentate. The bonding C atom of the 2-chloro­benzyl group, the S atom of the monodentate SPy and the S and N atoms of the two bidentate SPy ligands form a distorted octahedron around the Sn atom. The three S atoms and the N atom of one of the bidentate SPy ligands occupy the equatorial positions, while the N atom of the second bidentate SPy ligand and the C(CH₂) atom are axial. The axial N—Sn—C angle of 157.9 (1)° demonstrates the heavy distortion of the octahedron.     

Spectroscopic and structural characterization of O,O′-(diphenylphosphineoxide)amidate and acetylacetonate complexes of pentacoordinate nickel(II)

Heteroleptic nickel pentacoordinate complexes with the macrocyclic ligands 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene (Me₃-mcN₃) or its 9-methyl derivative (Me₄-mcN₃), as ancillary ligands, and O,O′-(diphenylphosphineoxide)amidate ligands, [RC(O)NP(O)Ph₂]^¯ (R = C₆H₆ (1), C₅H₄N (2), C₄H₃S (3)), have been prepared as well as related acetylacetonate derivatives. The complexes have been studied by spectroscopic methods (IR, UV-Vis and ¹H NMR). In acetone solution, the complexes exhibit isotropically shifted ¹H NMR resonances. The full assignment of these resonances has been achieved using one- and two-dimensional ¹H NMR techniques. The single-crystal structures of {(Me₄-mcN₃)Ni[OP(Ph₂)NC(Tf)O]}[PF₆] (9) and {(Me₃-mcN₃)Ni(acac)}[PF₆] (10) have been established by X-ray diffraction.     

Neue Koordinationsverbindungen aus Triorganylzinn(IV)-dimesylamiden und Neutralliganden: Einkern- und Mehrkernkomplexe mit molekularer oder ionischer Kristallstruktur

Polysulfonylamines. CII. New Coordination Compounds Derived from Triorganyltin(IV) Dimesylamides and Uncharged Ligands: Mononuclear and Polynuclear Complexes with Molecular or Ionic Crystal Structures The purpose of this report is to draw attention to the remarkable versatility of the dimesylamides R₃SnA [A^– = (MeSO₂)₂N^–; R = Me ( 1 a ) or Ph ( 1 b )] as precursors for pentacoordinate triorganyltin(IV) complexes belonging to four distinct structural types. Representative complexes were prepared by treating 1 a or 1 b in the appropriate molar ratios with unidentate thiourea or urea-type ligands or with the bidentate ligand [Ph₂P(O)CH₂]₂ (DPPOE). The following compounds were characterized by X-ray analysis: [Me₃Sn(A)(thiourea)] ( 2 a ; monoclinic, space group P2₁/n), [Ph₃Sn(A)(tetramethylthiourea)] ( 2 b ; monoclinic, P2₁, two independent formula units), [Me₃Sn(1-methylurea)₂]⁺ · A^– ( 3 a ; monoclinic, P2₁/c), [Ph₃Sn(1,1-dimethylurea)₂]⁺ · A^– ( 3 c ; triclinic, P1), [{Ph₃Sn(A)}₂(μ-dppoe)] ( 4 ; triclinic, P1), [Ph₃Sn(μ-dppoe)]_nⁿ⁺ · n A^– · n MeCN ( 5 ; monoclinic, P2₁/c). The lattices of 2 a , 2 b and 4 contain discrete uncharged formula units which are mononuclear for 2 a and 2 b or dinuclear for 4 , whereas 3 a , 3 c and 5 have ionic structures featuring mononuclear cations for 3 a and 3 c or an infinite linear-polymeric cation for 5 . In all the structures, the tin atoms adopt trigonal-bipyramidal geometries, the apical positions being occupied in 2 a and 2 b by the S atom of the thiourea and one O atom of A^–, in 3 a and 3 c by the O atoms of two urea-type ligands, in 4 by an O atom of the bridging DPPOE molecule and one O atom of A^–, and in 5 by two phosphoryl O atoms from different bridging DPPOE ligands. In the structures of 2 a , 3 a and 3 c , the (thio)urea NH functions are connected to A^– via intermolecular or interionic N–H … O and N–H … N hydrogen bonds. Crystals of [{Me₃Sn(bipyH⁺ … A^–)}₂(μ-bipy)]²⁺ · 2 A^– ( 6 ; monoclinic, C2/c) formed adventitiously in a reaction mixture containing 1 a and 4,4′-bipyridine. The rod-like supramolecular cation of 6 (length ca. 4 nm) is built up from two Me₃Sn⁺ units bridged through bipy and unidentally coordinated by a monoprotonated bipy (= bipyH⁺), resulting in a trigonal-bipyramidal geometry around tin (N atoms apical); each of the terminal bipyH⁺ ligands forms an ⁺N–H … N^– hydrogen bond with one A^–.     

Coordination and Redox Isomerization in the Reduction of a Uranium(III) Monoarene Complex

Synthetic studies on the redox chemistry of trivalent uranium monoarene complexes were undertaken with a complex derived from the chelating tris(aryloxide)arene ligand (^Ad,MeArO)₃mes^3?. Cyclic voltammetry of [{(^Ad,MeArO)₃mes}U^III] ( 1 ) revealed a nearly reversible and chemically accessible reduction at ?2.495 V vs. Fc/Fc⁺—the first electrochemical evidence for a formally divalent uranium complex. Chemical reduction of 1 indicates that reduction induces coordination and redox isomerization to form a uranium(IV) hydride, and addition of a crown ether results in hydride insertion into the coordinated arene to afford uranium(IV) complexes. This stoichiometric reaction sequence provides structural insight into the mechanism of arene functionalization at diuranium inverted sandwich complexes.     

Kinetics of Gallium Removal from Transferrin and Thermodynamics of Gallium-Binding by Sulfonated Tricatechol Ligands

Abstract

The thermodynamics of complexation of gallium by tricatechol ligand analogues of enterobactin and the kinetics of gallium removal from human serum transferrin (Tf) by one of those ligands have been studied by UV spectrophotometry. The ligands are a sulfonated monomeric catechoylamide, DMBS (N,N-dimethyl-2,3-dihydroxy-5-sulfonatobenzamide), and four sulfonated triscatechoylamides, MECAMS (1,3,5-N,N',N”-tris(5-sulfonato-2,3-dihydroxybenzoyl)-triaminomethylbenzene), Me₃MECAMS (N, N', N-trimethyl-MECAMS), 3,4-LICAMS (N, N', N”-tris(5-sulfonato-2,3-dihydroxybenzoyl)-1,5,10-triazadecane), and (DiP)LICAMS (N, N”-diisopropyl-LICAMS). The individual orthohydroxyl protonation constants are 7.15 (DMBS), and (average values for the three protons of the tricatechols) 7.09 (MECAMS), 7.01 (LICAMS), 7.62 (Me₃MECAMS), and 7.75 ((DiP(LICAMS), in good agreement with average values obtained potentiometrically. The overall formation constants for binding of Ga³⁺ by these ligands are β₁₁₃ = 41.9 for DMBS, β₁₁₀ = 41.1 for LICAMS, 36.6 for (DiP)-LICAMS, and 39.1 for Me₃MECAMS. Gallium is removed from the two metal binding sites of Ga₂Tf in a process by 3,4-LICAMS that is first order in both Tf and ligand at different rates (277M^?1 min^?1 and 17M^?1 min^?1). These are 12 and 3.4 times the corresponding rates of iron removal from Fe₂Tf. The dissociation pathways of the gallium-ligand complexes upon protonation of the ligands were probed by whole spectrum analysis with the non-linear least-squares program REFSPEC. For all three triscatechoylamide complexes, protonation occurs in sequential one-proton reactions wth logK MLH_n (n = 1, 2, 3) equal to 5.93, 5.00, 2.4 for MECAMS: 5.8, 5.7, 3.0 for 3,4-LICAMS; 6.81,6.34, 3.0 for Me₃MECAMS; 6.34, 6.33, 4.3 for (DiP)LICAMS. First- and second-derivative spectra show that for complexes of trimeric ligands the last two protonations result in a complex with a completely dissociated catecholate arm, Ga(cat)₂-catH₂, similar to the Ga(DMBS)₂ complex observed with the monomer. In the linear complexes, the middle ligand arm is detached from the metal first. Addition of a fourth proton resulted in decomposition of the gallium-trimeric ligand complex.