Dithiolene Moiety Research Articles

Log P Estimation of 1,2-Dithiole-3-thiones and 1,2-Dithiole-3-ones: A Comparison of Experimental and Calculative Approaches

To estimate experimental log P values of formerly described 5-formyl- and 5-acyl-dithiole-3-thiones (DTT) and -dithiole-3-ones (DTO) and to check the validity of five log P calculation programs via experimental log P for a database of 68 DTT and DTO. Experimental log P values were measured by means of octanol/water partitioning; for determining solute concentrations in water, RP-HPLC with spectrophotometric detection was used. For calculating log P, the fragmental methods ACD/log P, CLOGP, and KOWWIN, the atom-based approach XLOGP, and the whole-molecule approach QLOGP were applied. Quality of calculations significantly differs depending on the subset under consideration. For database compounds 01-48, comprising alkyl and aryl substitution in 4- and 5-position, the fragmental methods ACD/log P, CLOGP, and KOWWIN perform significantly better than the atom-based approach XLOGP and the whole-molecule method QLOGP. For database compounds 49-68, comprising formyl and acyl substitution in 4- and 5-position, superiority of the whole-molecule method QLOGP over the substructure-based approaches is observed. The strong underestimation of log P for compounds 49-68 probably indicates hidden physicochemical phenomena resulting from the juxtaposition of the acyl and dithiole moieties. All calculation methods included in this study need a thorough refinement to adequately cope with particular solvation behavior suspected to prevail in formyl- or acyl-DTT and DTO, which represent a chemical class of high pharmacological interest.

A series of neutral radical CpNi(dithiolene)˙ complexes

The heteroleptic neutral radical dithiolene complexes CpNi(dmit)., CpNi(dsit). and CpNi(dmid).(dmit=1,3-dithiole-2-thione-4,5-dithiolate; dsit=1,3-dithiole-2-thione-4,5-diselenolate; dmid=1,3-dithiole-2-one-4,5-dithiolate) are obtained from the reaction of (Cp2Ni)BF4 with either (n-Bu4N)[Ni(dmit)2] and (n-Bu4N)[Ni(dmid)2] or PhSb(dmit) and PhSb(dsit), respectively. The three complexes reduce reversibly to the corresponding Ni(II) anions and oxidize reversibly to the cationic state. As deduced from DFT calculations performed on CpNi(dmit)., the SOMO of these complexes is essentially localized on the dithiolene moiety with little metal contribution. CpNi(dsit). is isostructural with CpNi(dmit). and crystallizes in the monoclinic system, space group P2(1). In the solid-state structures of both CpNi(dmit). and CpNi(dsit)., molecules interact through a three-dimensional set of intermolecular interactions mediated by short SS, SeSe and SSe contacts, as confirmed from the temperature and field dependence of the magnetic susceptibility by the observation of an antiferromagnetic ground state below T(Neel)=27 K in CpNi(dmit)., 18 K in CpNi(dsit).. Finally, CpNi(dmid). crystallizes in the orthorhombic system, space group Pnma. Molecules organize into uniform chains through the stacking of the dmid moieties in a sigma-type face-to-face overlap.

Coordination of nickel and copper dithiolate to 2,2′‐bipyridine‐based π‐conjugated polymers

Abstractπ‐Conjugated polymers (Poly1–Poly3) containing a 2,2′‐bipyridine (bpy) unit were subjected to coordination to nickel and copper dithiolate for the purpose of manipulating the photophysical properties. The absorption maximum peak of Poly1 [maximum wavelength (λmax) = 446 nm] redshifted by 36 nm upon the coordination of bpy to NiCl2, which produced Poly1–NiCl2. A further bathochromic shift was observed in the spectrum of Poly1–mntNi [mntNi = (maleonitrile dithiolate)nickel; λmax = 499 nm] bearing the dithiolate ligand, which stemmed from the extension of the conjugated system over the nickel dithiolate moiety through the bpy unit. An increase in the [Ni]/[bpy] ratio in Poly1–mntNi rendered the original maximum peak at 446 nm smaller and the lower energy charge‐transfer peak at 499 nm larger; the isosbestic points remained at 380 and 475 nm. The green fluorescence (λmax = 504 nm) emitted from Poly1 markedly diminished upon the coordination of nickel dithiolate because of the effective energy transfer. The absorption maximum peak of Poly1–mntNi in chloroform at 499 nm blueshifted to 471 nm when the volume ratio of the chloroform/N,N‐dimethylformamide solvent reached 10:90. The coordination of nickel dithiolate to Poly2 and Poly3 also brought about redshifts of the absorption maximum peaks of as much as 55 and 61 nm, respectively. The absorption maximum peak of Poly1–(phenyldithiolate)nickel(pdtNi) (λmax = 474 nm) redshifted by 28 nm in comparison with that of Poly1, whereas the magnitude of the shift of Poly1–bis(thiophenoxide)nickel(btpNi) bearing two thiophenoxide ligands was 20 nm. Poly1–mntCu with a tetrahedral copper center was also investigated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2631–2639, 2004

Ground and excited state spectral comparisons of models for sulfite oxidase

Determining the contributions of thiolate and ene-1,2-dithiolate donors to the underlying electronic structure of the Mo site in sulfite oxidase (SO) has been a goal pursued by inorganic chemists for almost twenty years. The use of the hydrotris(3,5-dimethyl-1-pyrazolyl)borate ligand provided the framework for the first low-symmetry oxo-molybdenum(V) models in which the oxo donor was cis to the dithiolene moiety of benzene-1,2-dithiolate. Recent work from the Carrano and Kirk laboratories has produced a second-generation model of the SO active site based upon the (2-dimethylethanethiol)bis(3,5-dimethylpyrazolyl)methane heteroscorpionate ligand. Use of this heteroscorpionate framework provides for an oxo-molybdenum(V) complex with both a thiolate and an ene-1,2-dithiolate in the equatorial plane. In addition to providing a good structural model, the heteroscorpionate thiolate offers a constrained O–Mo–S thiolate–C torsion angle of ∼115°, closer to that of the ∼90° O–Mo–S Cys–C torsion angle observed in the chicken liver SO active site than can be obtained with thiophenolate ligands. This constrained torsion angle allows for the examination of how second-coordination sphere effects influence the electronic structure of the Mo site. Here we compare and contrast the molecular and electronic structures of these first- and second-generation models of the SO active site. Additionally, the electron paramagnetic resonance (EPR) parameters for both of these models are compared with those measured for the Mo(V) form of both low pH ( lpH) and high pH ( hpH) forms of SO in order to determine what insight these structural models can offer about the electronic structure of the active site of SO.

Mechanistic Studies of Human Molybdopterin Synthase Reaction and Characterization of Mutants Identified in Group B Patients of Molybdenum Cofactor Deficiency

Biosynthesis of the molybdenum cofactor involves the initial formation of precursor Z, its subsequent conversion to molybdopterin (MPT) by MPT synthase, and attachment of molybdenum to the dithiolene moiety of MPT. The sulfur used for the formation of the dithiolene group of MPT exists in the form of a thiocarboxylate group at the C terminus of the smaller subunit of MPT synthase. Human MPT synthase contains the MOCS2A and MOCS2B proteins that display homology to the Escherichia coli proteins MoaD and MoaE, respectively. MOCS2A and MOCS2B were purified after heterologous expression in E. coli, and the separately purified subunits readily assemble into a functional MPT synthase tetramer. The rate of conversion of precursor Z to MPT by the human enzyme is slower than that of the eubacterial homologue. To obtain insights into the molecular mechanism leading to human molybdenum cofactor deficiency, site-specific mutations identified in patients showing symptoms of molybdenum cofactor deficiency were generated. Characterization of a V7F substitution in MOCS2A, identified in a patient with an unusual mild form of the disease, showed that the mutation weakens the interaction between MOCS2A and MOCS2B, whereas a MOCS2B-E168K mutation identified in a severely affected patient attenuates binding of precursor Z.

Structural Basis for Potent Slow Binding Inhibition of Human Matrix Metalloproteinase-2 (MMP-2)

The zinc-dependent gelatinases belong to the family of matrix metalloproteinases (MMPs), enzymes that have been shown to play a key role in angiogenesis and tumor metastasis. These enzymes are capable of hydrolyzing extracellular matrix (ECM) components under physiological conditions. Specific and selective inhibitors aimed at blocking their activity are highly sought for use as potential therapeutic agents. We report herein on a novel mode of inhibition of gelatinase A (MMP-2) by the recently characterized inhibitors 4-(4-phenoxphenylsulfonyl)butane-1,2-dithiol (inhibitor 1) and 5-(4-phenoxphenylsulfonyl) pentane-1,2-dithiol (inhibitor 2). These synthetic inhibitors are selective for MMP-2 and MMP-9. We show that the dithiolate moiety of these inhibitors chelates the catalytic zinc ion of MMP-2 via two sulfur atoms. This mode of binding results in alternation of the coordination number of the metal ion and the induction of conformational changes at the microenvironment of the catalytic zinc ion; a set of events that is likely to be at the root of the potent slow binding inhibition behavior exhibited by these inhibitors. This study demonstrates a distinct approach for the understanding of the structural mechanism governing the molecular interactions between potent inhibitors and catalytic sites of MMPs, which may aid in the design of effective inhibitors.

The active site of arsenite oxidase from Alcaligenes faecalis.

Arsenite oxidase, a member of the DMSO reductase family of molybdenum enzymes, has two molecules of guanosine dinucleotide molybdenum cofactor coordinating the molybdenum at the active site. X-ray absorption spectroscopy indicates that the Mo-S bonds shorten from 2.47 to 2.37 A upon reduction with the physiological substrate. It also indicates the presence of an oxo ligand at 1.70 A in both oxidized and reduced forms of the enzyme, together with a short, 1.83 A, Mo-O bond in the oxidized form that is lost upon reduction. Resonance Raman spectroscopy indicates that the two pterin dithiolene moieties have different aromaticities, with one, the Q-pterin, having a more discrete dithiolate structure while the other, the P-pterin, has considerable pi-delocalization. Our results indicate that the structure of arsenite oxidase is intermediate between that seen in other molybdenum enzymes, in which one ligand to the metal is provided by the polypeptide (serine, cysteine, or selenocysteine), and tungsten enzymes that lack a peptide ligand.

Use of medium effects to tune the Delta E(1/2) values of bimetallic and oligometallic compounds.

The redox potentials of bis(fulvalene)dinickel, 1, and the tetrakis(ferrocenyl)nickel dithiolene complex 2 have been measured in a variety of nonaqueous electrolytes. The difference in E1/2 values of the two successive one-electron oxidations of 1 (i.e., DeltaE1/2 values) increased from a low of 212 mV in anisole/[NBu4]Cl to a high of 850 mV in CH2Cl2-Na[B(C6H3(CF3)2)4], reflecting an increase of over 1010 in the comproportionation constant (Kcomp = [1+]2/[1][12+]). Six reversible one-electron processes are possible for compound 2, the four oxidations arising from the ferrocenyl substituents, and the two reductions arising from the Ni dithiolene moiety. The E1/2 spreads of the four oxidation waves and the two reduction waves are both highly sensitive to medium effects. For both 1 and 2, the largest DeltaE1/2 values for cationic products are found in solvents of low polarity and donor strength containing electrolyte salts having large anions and small cations. Conversely, the smallest DeltaE1/2 values for anionic products are found under these conditions, culminating in the observation of a single two-electron reduction wave for 2/22- in CH2Cl2-Na[B(C6H3(CF3)2)4]. A combination of solvation and ion-pairing effects must be considered, and may be used to advantage, when using DeltaE1/2 values as a measure of electronic interactions between redox centers in compounds containing two or more electron-transfer sites.

α-Thioxothioamides: A Formal [4+1] Cycloaddition Reaction with Isocyanides and Diisocyanides and its Application to a New Straightforward Formation of Extended Tetrathiafulvalenes

A number of 2-(alkylimino) and 2-(arylimino)-1,3-dithioles (aza DTFs) bearing push-pull substituents have been prepared under mild conditions according to the title procedure. This novel strategy relies upon the fact that the use of conjugated diisocyanides allows an effective synthesis of new extended tetrathiafulvalenes (TTFs). The two dithiole moieties are linked by a conjugated framework that incorporates a phenyl, biphenyl or azobiphenyl group. High and low temperature measurements are required in order to understand the complex 1H and 13C NMR spectra of the prepared mono-, bis- and tris-(1,3-dithiole) derivatives. Their electrochemical oxidations are also described.

X-ray Crystal Structure of the Trimeric N-terminal Domain of Gephyrin

Gephyrin is a ubiquitously expressed protein that, in the central nervous system, forms a submembraneous scaffold for anchoring inhibitory neurotransmitter receptors in the postsynaptic membrane. The N- and C-terminal domains of gephyrin are homologous to the Escherichia coli enzymes MogA and MoeA, respectively, both of which are involved in molybdenum cofactor biosynthesis. This enzymatic pathway is highly conserved from bacteria to mammals, as underlined by the ability of gephyrin to rescue molybdenum cofactor deficiencies in different organisms. Here we report the x-ray crystal structure of the N-terminal domain (amino acids 2-188) of rat gephyrin at 1.9-A resolution. Gephyrin-(2-188) forms trimers in solution, and a sequence motif thought to be involved in molybdopterin binding is highly conserved between gephyrin and the E. coli protein. The atomic structure of gephyrin-(2-188) resembles MogA, albeit with two major differences. The path of the C-terminal ends of gephyrin-(2-188) indicates that the central and C-terminal domains, absent in this structure, should follow a similar 3-fold arrangement as the N-terminal region. In addition, a central beta-hairpin loop found in MogA is lacking in gephyrin-(2-188). Despite these differences, both structures show a high degree of surface charge conservation, which is consistent with their common catalytic function.

ChemInform Abstract: Synthesis and Reactivity Studies of Model Complexes for Molybdopterin-dependent Enzymes

The molybdenum cofactor (Moco)-containing enzymes are divided into three classes that are named after prototypical members of each family, viz. sulfite oxidase, DMSO reductase and xanthine oxidase. Functional or structural models have been prepared for these three prototypical enzymes: (i) The complex [MoO2(mnt)2]2− (mnt2−=1,2-dicyanoethylenedithiolate) has been found to be able to oxidize hydrogen sulfite to HSO4− and is thus a functional model of sulfite oxidase. Kinetic and computational studies indicate that the reaction proceeds via attack of the substrate at one of the oxo ligands of the complex, rather than at the metal. (ii) The coordination geometries of the mono-oxo [Mo(VI)(O-Ser)(S2)2] entity (S2=dithiolene moiety of molybdopterin) found in the crystal structure of R. sphaeroides DMSO reductase and the corresponding des-oxo Mo(IV) unit have been reproduced in the complexes [M(VI)O(OSiR3)(bdt)2] and [M(VI)O(OSiR3)(bdt)2] (M=Mo,W; bdt=benzene dithiolate). (iii) A facile route has been developed for the preparation of complexes containing a cis-Mo(VI)OS molybdenum oxo, sulfido moiety similar to that detected in the oxidized form of xanthine oxidase.

Synthesis and reactivity studies of model complexes for molybdopterin-dependent enzymes

The molybdenum cofactor (Moco)-containing enzymes are divided into three classes that are named after prototypical members of each family, viz . sulfite oxidase, DMSO reductase and xanthine oxidase. Functional or structural models have been prepared for these three prototypical enzymes: (i) The complex [MoO 2(mnt) 2] 2− (mnt 2−=1,2-dicyanoethylenedithiolate) has been found to be able to oxidize hydrogen sulfite to HSO 4 − and is thus a functional model of sulfite oxidase. Kinetic and computational studies indicate that the reaction proceeds via attack of the substrate at one of the oxo ligands of the complex, rather than at the metal. (ii) The coordination geometries of the mono-oxo [Mo(VI)(O-Ser)(S 2) 2] entity (S 2=dithiolene moiety of molybdopterin) found in the crystal structure of R. sphaeroides DMSO reductase and the corresponding des-oxo Mo(IV) unit have been reproduced in the complexes [M(VI)O(OSiR 3)(bdt) 2] and [M(VI)O(OSiR 3)(bdt) 2] (M=Mo,W; bdt=benzene dithiolate). (iii) A facile route has been developed for the preparation of complexes containing a cis-Mo(VI)OS molybdenum oxo, sulfido moiety similar to that detected in the oxidized form of xanthine oxidase.

Vicinal Dithiol-binding Agent, Phenylarsine Oxide, Inhibits Inducible Nitric-oxide Synthase Gene Expression at a Step of Nuclear Factor-κB DNA Binding in Hepatocytes

Inflammatory cytokine interleukin 1beta induces inducible nitric-oxide synthase (iNOS) mRNA and its protein, which are followed by increasing the production of nitric oxide, in primary cultures of rat hepatocytes. Nuclear factor-kappaB (NF-kappaB), an important transcription factor for iNOS gene expression, is also activated and translocated to the nucleus. In the present study, we found that vicinal dithiol-binding agent, phenylarsine oxide (PAO), inhibited the induction of iNOS protein and mRNA as well as the release of nitrite (nitric oxide metabolite) into the culture medium. Simultaneous addition of a vicinal dithiol compound, 2, 3-dimercaptopropanol, with PAO completely abolished these inhibitions. PAO could not prevent either degradation of an inhibitory protein, IkappaB, of NF-kappaB or translocation of NF-kappaB to the nucleus. However, electrophoretic mobility shift assay demonstrated that PAO decreased the interaction between NF-kappaB and its binding consensus oligonucleotide. Transfection experiments with iNOS promoter-luciferase construct revealed that PAO inhibited NF-kappaB binding to DNA. These results indicate that PAO inhibits iNOS gene expression at a step of NF-kappaB binding to DNA by modifying its vicinal dithiol moiety, which may play a crucial role for the iNOS regulation in hepatocytes.

A New Type of π-Electron Donors with One Dithiole Unit: Substituted 7-(1,3-Dithiol-2-ylidene)-7-hydrobenz[d,e]anthracenes

New electron donors 11a–c bearing only one 1,3-dithiole ring conjugated with an acene backbone have been synthesized by Wittig–Horner reactions from 7H-benz[d,e]anthracen-7-one (10) and differently substituted phosphonate esters 9a–c. The donor properties of 11 have been characterized by means of both experimental techniques and quantum chemical calculations. Cyclic voltammetry measurements on the novel compounds predict donor abilities comparable to those of TTF and BEDT-TTF. The voltammograms show a multi-stage redox behaviour with oxidation up to the trication, where the first two oxidation processes take place at very close potentials. These processes have been assigned to a simultaneous oxidation of the dithiole and acene moieties on the basis of DFT/B3-P86/6-31G* theoretical calculations. Whereas the neutral compound and the monocation exhibit butterfly-shaped non-planar structures, the dication is fully aromatic and consists of a closed-shell, singly charged, planar polyacenic unit and a singly charged dithiole ring. The third redox process can be assigned to a second oxidation of the acene unit. The high aromaticity of the dication, coupled with the particular donor ability of the acene unit are shown to be the key factors in accounting for the electrochemical behaviour and the enhanced donor properties of the novel compounds. Theoretical calculations also help to rationalize the UV/Vis data in that they predict the appearance of a low-energy, intramolecular charge-transfer absorption band for the neutral compounds. Stable charge-transfer complexes with a 2:3 (D/A) stoichiometry have been prepared by reaction with the strong acceptors TCNQF4 and DDQ.

The molybdenum cofactors – perspective from crystal structure

The field of molybdopterin-containing enzymes has experienced an infusion of excitement as a result of several reports of high-resolution X-ray crystallographic structures including the tungsten-containing aldehyde oxidoreductase from the hyperthermophile Pyrococcus furiosus and three different studies on a single enzyme, DMSO reductase. The tungstoprotein was the first of the reported structures and contained several crucial features [1]. The structure provided unequivocal proof for coordination of Mo to the dithiolene moiety of molybdopterin, a finding subsequently confirmed in all of the other structures. Thus the crystal structures have categorically ruled out alternative modes of binding of Mo to the pterin, as proposed by Fischer et al. [2]. Secondly, the structure of the W-containing aldehyde oxidoreductase revealed an unexpected feature of the W cofactor, i.e., chelation of W to the dithiolenes of two molybdopterin molecules. A third important finding of this study was the presence of a pyran ring resulting from the fusion of the 3b-hydroxyl of the side chain of the pterin to C-7 of the pterin ring, now known to be a universal property of the protein-bound cofactor. The 2 :1 ratio of pterin to metal is not unique to W-containing enzymes, since both Rhodobacter DMSO reductase and Escherichia coli formate dehydrogenase have been found to contain bis(MGD)-Mo [3]. So far, the 2 :1 pterin-to-Mo ratio has been found only in MGD-containing enzymes. The presence of the tricyclic pterin was unexpected, since three derivatives of molybdopterin, Form A, Form B, and dicarboxamidomethyl molybdopterin contain linear 6-alkyl side chains [4]. Two other derivatives, Form B and urothione, contain a thiophene ring rather than a pyran ring [4]. Since these derivatives are formed from molybdoenzvmes under mild conditions, the formation of the pyran ring must be a freely reversible process, with ring opening occurring as soon as the pterin is released from the protein. It is likely that the pyran adduct formation stabilizes the pterin ring against oxidative modifications that could disrupt the structure of the cofactor. The structures of Form B and urothione suggest that oxidation of the pterin ring could cause cis-trans isomerization of the dithiolene, leading to weakened binding of Mo and facilitating the formation of the thiophene ring. The crystal structures of aldehyde oxidoreductase from Desulfovibrio gigas [5], and DMSO reductase from Rhodobacter sphaeroides [6] as well as Rhodobacter capsulatus [7] have elicited considerable interest, the former because of its homology to the xanthine oxidase family of hydroxylases and the latter because of the considerable differences seen in Mo coordination in three different structural studies. The implications of these findings are discussed below.

Solitaire-Porphyrazines: Synthetic, Structural, and Spectroscopic Investigation of Complexes of the Novel Binucleating Norphthalocyanine-2,3-dithiolato Ligand

We have developed the synthesis of unsymmetrical metalloporphyrazines of the form M[pz(A:B3)], where A and B refer to two different types of peripheral functionality, and have used it to prepare new bi- and trimetallic solitaire-porphyrazines in which A represents a mono- or bimetallic moiety. The macrocyclic complexes described are based on the binucleating ligand, [M(norphthalocyanine-2,3-dithiolate)]2-, [M(norpc)]2-. This can be thought of as a metalloporphyrazine where B is a fused benzo ring; A represents two thiolates fused at the β-pyrrole positions to form a dithiolene moiety that can bind a transition-metal ion in addition to one within the macrocyclic cavity. solitaire-Porphyrazines have been synthesized by chelation of [(L-L)M‘]2+ to the [M(norpc)]2- ligand where M = “2H”, Ni, Cu, or Mn-Cl, L-L is a bis(diphosphino) or bis(diamino) group and M‘ = Ni, Pd, or Pt. Crystal structures have been obtained for 11b, where the [H2(norpc)]2- ligand coordinates the diphosphinopalladium moiety, [Pd(dppf)]2+...

The effect of the central linkage on the mass spectrometric behaviour of extended tetrathiafulvalenes

AbstractThe electron ionization‐induced fragmentation pattern of extended tetrathiafulvalenes has been studied by exact mass measurements, metastable ion analysis and collision‐induced dissociation mass spectrometry. The influence on the fragmentation of the central bridge linking the dithiole moieties is discussed.

Star-Porphyrazines: synthetic, structural, and spectral investigation of complexes of the polynucleating porphyrazineoctathiolato ligand

We have devised a new polynucleating porphyrinic ligand, porphyrazine-2,3,7,8,12,13,17,18-octathiolato, (pz) (S - ) 8 , the molecular structure of which may be thought of as a porphyrazine (tetraazaporphyrin) with four dithiolene moieties peripherally fused at the β-positions.

Derivatization of dithiols and certain monothiols with phenylarsine oxide for gas chromatography

Dithiols and certain monothiols reacted with phenylarsine oxide to give derivatives suitable for gas chromatography. Dihydrolipoic acid (6,8-dimercapto- n-octanoic acid) was thus determined after derivatization of the dithiol moiety to a dithiarsolane followed by extractive alkylation of the carboxyl group to the benzyl ester. 2,3-Dimercapto-1-propanol was converted into a dithiarsane, whereas bioxatriarsolane derivatives were obtained from dithiothreitol and dithioerythritol (the threo and erythro isomers of 1,4-dimercapto-2,3-butanediol) as each thiol group and its adjacent hydroxyl group in these compounds reacted with the arsenical. Mercaptoethanol and mercaptoacetic acid were also successfully derivatives for gas chromatography with phenylarsine oxide but α-toluenethiol and 1-dodecanethiol were not.

Free radical addition of hydrogen sulfide and thiols to linseed oil and methyl oleate

AbstractFree radical additions of hydrogen sulfide, ethanedithiol, and 1,6‐hexanedithiol have been made to methyl oleate and linseed oil with ultraviolet radiation. Reactions were carried out in dichloromethane at −70C and in benzene at 25C. With the dithiols, a new dibasic ester has been prepared from methyl oleate in which bridging is accomplished through a dithiol moiety. Hydrogen sulfide has been added to linseed oil in suitable solvents at both −70C and 25C. It appears that zero‐order kinetics control the additions at both temperatures. Infrared data show a linear relationship between mercapto absorption and the amount of sulfur incorporated. Nuclear magnetic resonance (NMR) spectra demonstrate a decrease in olefinic protons with an increase in sulfur content. Fair agreement on the extent of reaction exists between data from NMR, sulfur content, and infrared analyses. Hydrogen sulfide‐treated linseed oil films air‐dry slowly at room temperature; at 250C for 1 hr under a CO2 atmosphere these oils cure to brown films with Sward Rocker values of 24 to 32 and pencil hardness values of five to greater than six. Pencil hardness and alkali resistance increased with sulfur content. The film from the 4.2% sulfur sample resisted alkali at room temperature for 24 hr.