Novel antimony-based antimicrobial drug targets membranes of Gram-positive and Gram-negative bacterial pathogens

Antimicrobial resistance (AMR) poses a significant worldwide public health crisis that continues to threaten our ability to successfully treat bacterial infections. With the decline in effectiveness of conventional antimicrobial therapies and the lack of new antibiotic pipelines, there is a renewed interest in exploring the potential of metal-based antimicrobial compounds. Antimony-based compounds with a long history of use in medicine have re-emerged as potential antimicrobial agents. We previously synthesized a series of novel organoantimony(V) compounds complexed with cyanoximates with a strong potential of antimicrobial activity against several AMR bacterial and fungal pathogens. Here, five selected compounds were studied for their antibacterial efficacy against three important bacterial pathogens: Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus. Among five tested compounds, SbPh4ACO showed antimicrobial activity against all three bacterial strains with the MIC of 50-100 µg/mL. The minimum bactericidal concentration/MIC values were less than or equal to 4 indicating that the effects of SbPh4ACO are bactericidal. Moreover, ultra-thin electron microscopy revealed that SbPh4ACO treatment caused membrane disruption in all three strains, which was further validated by increased membrane permeability. We also showed that SbPh4ACO acted synergistically with the antibiotics, polymyxin B and cefoxitin used to treat AMR strains of P. aeruginosa and S. aureus, respectively, and that at synergistic MIC concentration 12.5 µg/mL, its cytotoxicity against the cell lines, Hela, McCoy, and A549 dropped below the threshold. Overall, the results highlight the antimicrobial potential of novel antimony-based compound, SbPh4ACO, and its use as a potentiator of other antibiotics against both Gram-positive and Gram-negative bacterial pathogens.

IMPORTANCE

Antibiotic resistance presents a critical global public health crisis that threatens our ability to combat bacterial infections. In light of the declining efficacy of traditional antibiotics, the use of alternative solutions, such as metal-based antimicrobial compounds, has gained renewed interest. Based on the previously synthesized innovative organoantimony(V) compounds, we selected and further characterized the antibacterial efficacy of five of them against three important Gram-positive and Gram-negative bacterial pathogens. Among these compounds, SbPh4ACO showed broad-spectrum bactericidal activity, with membrane-disrupting effects against all three pathogens. Furthermore, we revealed the synergistic potential of SbPh4ACO when combined with antibiotics, such as cefoxitin, at concentrations that exert no cytotoxic effects tested on three mammalian cell lines. This study offers the first report on the mechanisms of action of novel antimony-based antimicrobial and presents the therapeutic potential of SbPh4ACO in combating both Gram-positive and Gram-negative bacterial pathogens while enhancing the efficacy of existing antibiotics.

NaGaSe2: A Water-Loving Multifunctional Non-van der Waals Layered Selenogallate

A missing member of well-known ternary chalcometallates, a sodium selenogallate, NaGaSe₂, has been synthesized by employing a polyselenide flux and stoichiometric reaction. Crystal structure analysis using X-ray diffraction techniques reveals that it contains supertetrahedral adamantane-type Ga₄Se₁₀ secondary building units. These Ga₄Se₁₀ secondary building units are further connected via corners to form two-dimensional (2D) [GaSe₂]_∞^- layers stacked along the c-axis of the unit cell, and the Na ions reside in the interlayer space. The compound has an unusual ability to absorb water molecules from the atmosphere or a nonanhydrous solvent to form distinct hydrated phases, NaGaSe₂·xH₂O (where x can be 1 and 2), with an expanded interlayer space, as verified by X-ray diffraction (XRD), thermogravimetric-differential scanning calorimetry (TG-DSC), desorption, and Fourier transform infrared spectroscopy (FT-IR) studies. The in situ thermodiffractogram indicates the emergence of an anhydrous phase before 300 °C with the decrease of interlayer spacings and reverting to the hydrated phase within a minute of re-exposure to the environment, supporting the reversibility of such a process. Structural transformation induced through water absorption results in an increase of Na ionic conductivity by 2 orders of magnitude compared to that of the pristine anhydrous phase, as verified by impedance spectroscopy. Na ions from NaGaSe₂ can be exchanged in the solid-state route with other alkali and alkaline earth metals in a topotactic or nontopotactic way, leading to 2D isostructural and three-dimensional networks, respectively. Optical band gap measurements show a band gap of ∼3 eV for the hydrated phase, NaGaSe₂·xH₂O, which is in good agreement with the calculated band gap using a density functional theory (DFT)-based method. Sorption studies further confirm the selective absorption of water over MeOH, EtOH, and CH₃CN with a maximum water uptake of 6 molecules/formula unit at a relative pressure, P/P₀, of 0.9.

Non-Antibiotic Antimony-Based Antimicrobials

A series of the eight novel organoantimony(V) cyanoximates of Sb(C₆H₅)₄L composition was synthesized using the high-yield heterogeneous metathesis reaction between solid AgL (or TlL) and Sb(C₆H₅)₄Br in CH₃CN at room temperature. Cyanoximes L were specially selected from a large group of 48 known compounds of this subclass of oximes on the basis of their water solubility and history of prior biological activity. The synthesized compounds are well soluble in organic solvents and were studied using a variety of conventional spectroscopic and physical methods. The crystal structures of all reported organometallic compounds were determined and revealed the formation of the distorted trigonal bipyramidal environment of the Sb atom and monodentate axial binding of acido-ligands via the O atom of the oxime group. The compounds are thermally stable in the solid state and in solution molecular compounds. For the first time, this specially designed series of organoantimony(V) compounds is investigated as potential non-antibiotic antimicrobial agents against three bacterial and two fungal human pathogens known for their increasing antimicrobial resistance. Bacterial pathogens included Gram-negative Escherichia coli and Pseudomonas aeruginosa, and Gram-positive Staphylococcus aureus. Fungal pathogens included Cryptococcus neoformans and Candida albicans. The cyanoximates alone showed no antimicrobial impact, and the incorporation of the SbPh₄ group enabled the antimicrobial effect. Overall, the new antimony compounds showed a strong potential as both broad- and narrow-spectrum antimicrobials against selected bacterial and fundal pathogens and provide insights for further synthetic modifications of the compounds to increase their activities.

Lithium selenometallates of triel elements, Li5MSe4 (M = Al and Ga), aliovalent doping and their ionic conductivity

Lithium selenometallates of Al and Ga have been synthesized. The Li-ion conductivity increases by almost five times upon Sn doping.

New in vitro highly cytotoxic platinum and palladium cyanoximates with minimal side effects in vivo

Several biologically active bivalent Pd and Pt complexes with two structurally similar cyanoxime ligands abbreviated as H(DECO): 2-oximino-2-cyano-N,N'-diethylacetamide, and H(PyrCO): 2-oximino-2-cyan-N-pyrrolidine acetamide were synthesized and characterized using spectroscopic methods, thermal analysis and X-ray crystallography. Structures revealed planar cis-geometry of studied complexes. Freshly obtained Pt(DECO)₂, Pd(DECO)₂, Pt(PyrCO)₂ and Pd(PyrCO)₂ complexes were used in for in vitro cytotoxicity assays using two different etiology human cancer cell lines HeLa and WiDr cells. Investigated compounds showed cytotoxicity levels at or above cisplatin. Pt(DECO)₂ was also tested in vivo in healthy C57BL/6 mice. The complex was administered at three different dosage (0, 7.5, 15 mg/kg, i.p. once/week), over a total period of 8 weeks. No changes were observed in the animal weight in the treated mice compared to the control dextrose-treated group. The levels of erythrocytes, leukocytes, and hemoglobin were within the normal level suggesting low myelotoxicity. Negligible cardiotoxicity was observed from the histological evaluation of the hearts from the treated animals. Results from the tail nerve conduction velocity (NCV) and nerve histomorphometry suggested no impact of Pt(DECO)₂ on peripheral nerves. The complex, however, induced certain hepatotoxicity and lead to the elevation of IL-6, a pro-inflammatory cytokine. Overall, Pt(DECO)2 showed minimal in vivo toxicity, thus presenting a promising candidate for future testing in animal models of cancer.

Synthesis and Characterization of Anionic Lanthanide(III) Complexes with a Bidentate Sulfonylamidophosphate (SAPh) Ligand

A series of new anionic lanthanide(III) complexes with the general formula NEt₄[LnL₄] (1-Ln; HL = dimethyl[(4-methylphenyl)sulfonyl]amidophosphate; Ln = La, Nd, Eu), were synthesized and characterized by IR, UV-vis, and NMR spectroscopies, the differential scanning calorimetry method, thermogravimetric and X-ray analysis, and photoluminescence measurements. Single-crystal structures of NEt₄[EuL₄] (1-Eu) were determined at 293 and 100 K and evidenced the single-crystal-to-single-crystal phase transition. Both phases are in the monoclinic crystal system in centrosymmetric groups of the same Laue class. The room temperature structure is in C2/c (No. 15), while low-temperature structure is in the P2₁/c (No. 14) space groups. The coordination environment geometry around the central europium(III) ion is a distorted square antiprism in both polymorphs, while the peripheral methoxy and tolyl groups show different orientations. This phenomenon indicates the occurrence of a thermally driven second-order phase transition during the cooling-heating process. The europium(III) complex exhibits an unusual emission spectrum, clearly dominated by the ⁵D₀-⁷F₄ bands, and an emission decay time equaling 3.5 ms, being among the highest values known for europium coordination compounds.

Chemistry and applications of cyanoximes and their metal complexes

During the past three decades, considerable research effort has been dedicated to a new class of organic ligands - cyanoximes - which have the general formula NC-C([double bond, length as m-dash]NOH)-R, where R is an electron-withdrawing group. The presence of the CN group makes cyanoximes ∼10 000 times more acidic and better ligands than other known conventional monoximes and dioximes. Also, in numerous cases, this group provides extra nitrogen donor atoms to support the formation of bridges between metal centres in the obtained coordination polymers. With 36 different R groups, the most abundant is the family of mono-cyanoximes, followed by 7 bis-cyanoximes which include aromatic and aliphatic spacers and, lately, tris-cyanoxime representing a 'tripod'. The total number of obtained and characterized compounds is 44. These simple, low molecular weight molecules represent a series of new excellent ampolydentate ligands - 'molecular Lego', or building blocks - for coordination and organometallic chemistry. Uncomplexed ligands, their alkali metal salts, and metal complexes show a large spectrum of biological activity, ranging from growth regulation in plants and antimicrobial activity, to significant in vitro and in vivo cytotoxicity against human cancers. Currently, there are more than three hundred cyanoxime-based complexes, synthesized and studied using a variety of different spectroscopic methods and X-ray analysis. In this review, the preparation and stereochemistry of cyanoxime ligands, their structures and properties, and the most interesting coordination compounds with a broad spectrum of practical applications are summarized.

Crystal and electronic structure of a hexacarbonyldiiron cluster tethered to naphthalene-2-thiolate ligands

The structure of the previously reported complex bis(μ-naphthalene-2-thiolato-κ²S:S)bis(tricarbonyliron)(Fe-Fe), [Fe₂(C₁₀H₇S)₂(CO)₆], has been characterized by X-ray diffraction. In the solid state, the dinuclear complex adopts a butterfly-like shape, with an equatorial-axial spatial orientation of the naphthalene groups covalently coupled to the [S₂Fe₂(CO)₆] unit. The asymmetric unit contains three independent [(μ-naphthalene-2-thiolato)₂Fe₂(CO)₆] molecules. These molecules show intermolecular π-π stacking interactions between the naphthalene rings, which was confirmed by Hirshfield surface analysis. The electronic spectrum of the complex recorded in acetonitrile shows a band centered at 350 nm (ℇ = 4.6 × 10³ M^-1 cm^-1) and tailing into the visible region. This absorption can be attributed to a π→π* electronic transition within the naphthalene moiety and a metal-based d→d transition.

PATHOGENETIC ADVANCES OF FOSINOPRIL SODIUM WITH HYDROCHLOROTHIAZIDE IN OBESE HYPERTENSIVE PATIENTS

Purpose - to improve antihypertensive therapy on the basis of studying the antioxidant properties of an angiotensin-converting enzyme (ACE) inhibitor (fosinopril sodium) and a diuretic (hydrochlorothiazide), their impact on endothelial dysfunction and pro-inflammatory cytokines activity in hypertensive patients with overweight and obesity. A combination of fosinopril sodium 20 mg/day and hydrochlorothiazid 12.5 mg/day was prescribed to 54 patients with essential hypertension of 1-3 grades, 30 to 65 years old . The control group included 10 healthy subjects matched for age and sex. During the course of combined antihypertensive therapy we observed a significant decrease of i-NOS activity, reduce of TNF-α type I of its soluble receptor (sTNF-αRI), and 8-iso-PgF2α in the patients. Activity of e-NOS, superoxide dismutase and catalase, in contrast, were increased in patients with hypertension and concomitant obesity. Thus, the improvement of endothelial function, a significant decrease autoimmune activation due to lower tension of oxidative stress in the examined patients optimizes use of a combination of fosinopril sodium and hydrochlorothiazid for differentiated therapy in hypertensive patients with obesity.

Temperature-dependent shape-responsive fluorescent nanospheres for image-guided drug delivery

Temperature-responsive nanoparticles used in conjunction with hyperthermia promise to provide synergistic effects for increasing drug efficacy. We propose a near-infared (NIR) fluorescent system based on a upper critical solution temperature (UCST) polymer, ISP2, integrated with a NIR fluorescent dye HITC for in vivo tracking. The system forms a nanoparticle that increases its volume as temperature increases, similar to the expansion of a Hoberman sphere. The nanospheres nearly doubled in size, from 80 nm to 140 nm, during a temperature increase from 40°C to 60°C.

A 1-D coordination polymer route to catalytically active Co@C nanoparticles

Pyrolysis of a 1-D polymeric cobalt(ii) coordination complex ([Co(BDC)(Mim)₂]_n, H₂BDC = benzenedicarboxylic acid; Mim = N-methylimidazole) results in the formation of carbon embedded fcc cobalt nanoparticle composites, Co@C.

Conjugated foldamers with unusually high space-charge-limited current hole mobilities

Charge carrier mobility and its optimization play a critical role in the development of cutting-edge organic electronic and optoelectronic devices. Even though space-charge-limited current (SCLC) hole mobilities as high as 1.4 cm(2) V(-1) s(-1) have been reported for microscopically sized highly ordered liquid-crystalline conjugated small molecules, the SCLC hole mobility of device-sized thin films of conjugated polymers is still much lower, ranging from 10(-6) to 10(-3) cm(2) V(-1) s(-1). Herein, we report the synthesis, characterizations, and thin-film SCLC mobility of three discotic conjugated polymers, INDT-TT, INDT-BT, and INDT-NDT. Optical studies indicate that polymer INDT-NDT adopts a folded conformation in solutions of good or poor solvents, whereas polymer INDT-TT stays as random monomeric chains in good solvents and interchain aggregates in poor solvents. INDT-BT polymer chains, however, stay as foldamers in dilute solutions of good solvents but interchain aggregates in concentrated solutions or poor solvents. Circular dichroism spectroscopy provides clear evidence for the helical folding of INDT-NDT in solutions. Thin films spin-coated from 1,2-dichlorobenzene solutions of the polymers show SCLC hole mobility of 2.20 × 10(-6), 8.79 × 10(-5), and 2.77 × 10(-2) cm(2) V(-1) s(-1) for INDT-TT, INDT-BT, and INDT-NDT, respectively. HRTEM and powder XRD measurements show that INDT-NDT pristine thin films contain nanocrystalline domains, whereas the INDT-TT and INDT-BT films are amorphous. Thin films of INDT-NDT:PC71BM blends show increased crystallinity and further improved SCLC hole mobility up to 1.29 × 10(-1) cm(2) V(-1) s(-1), one of the highest SCLC mobility values ever recorded on solution-processed organic semiconducting thin films. The persistent folding conformation of INDT-NDT is believed to be responsible for the high crystallinity of its thin films and its high SCLC mobilities.

1D polymeric platinum cyanoximate: a strategy toward luminescence in the near-infrared region beyond 1000 nm

We report the synthesis and properties of the first representative of a new class of PtL2 complexes with ambidentate mixed-donor cyanoxime ligands [L = 2-cyano-2-oximino-N,N'-diethylaminoacetamide, DECO (1)]. Three differently colored polymorphs of "Pt(DECO)2" (3-5) were isolated, with the first two being crystallographically characterized. The dark-green complex [Pt(DECO)2]n (5) spontaneously forms in aqueous solution via aggregation of yellow monomeric complex 3 into the red dimer [Pt(DECO)2]2 (4), followed by further oligomerization into coordination polymer 5. A spectroscopic and light-scattering study revealed a "poker-chips"-type 1D polymeric structure of 5 in which units are held by noncovalent metallophilic interactions, forming a Pt---Pt wire. The polymer 5 shows a broad absorption at 400-900 nm and emission at unusually long wavelengths in the range of 1000-1100 nm in the solid state. The near-infrared (NIR) emission of polymer 5 is due to the formation of a small amount of nonstoichiometric mixed-valence Pt(II)/Pt(IV) species during synthesis. A featureless electron paramagnetic resonance spectrum of solid sample 5 recorded at +23 and -193 °C evidences the absence of Pt(III) states, and the compound represents a "solid solution" containing mixed-valence Pt(II)/Pt(IV) centers. Exposure of KBr pellets with 5% 5 to Br2 vapors leads to an immediate ∼30% increase in the intensity of photoluminescence at 1024 nm, which confirms the role and importance of mixed-valence species for the NIR emission. Thus, the emission is further enhanced upon additional oxidation of Pt(II) centers, which improves delocalization of electrons along the Pt---Pt vector. Other polymorph of the "Pt(DECO)2" complex--monomer--did not demonstrate luminescent properties in solutions and the solid state. An excitation scan of 5 embedded in KBr tablets revealed an emission only weakly dependent on the wavelength of excitation. The NIR emission of quasi-1D complex 5 was studied in the range of -193 to +67 °C. Data showed a blue shift of λmax and a simultaneous increase in the emission line intensity with a temperature rise, which is explained by analogy with similar behavior of known quasi-1D K2[Pt(CN)4]-based solids, quantum dots, and quantum wells with delocalized carriers. The presented finding opens a route to a new class of platinum cyanoxime based NIR emissive complexes that could be used in the design of novel NIR emitters and imaging agents.

Synthesis and Characterization of Two Cyanoxime Ligands, Their Precursors, and Light Insensitive Antimicrobial Silver(I) Cyanoximates

High-yield syntheses of N-piperidine-cyanacetamide (1), N-morpholyl-cyanacetamide (4) and their oxime derivatives N-piperidine-2-cyano-2-oximino-acetamide (HPiPCO, 2) and N-morpholyc-2-cyano-2-oximino-acetamide (HMCO, 5) were developed using two-step preparations. At first, the reactions of neat cyanoacetic acid esters and the respective cyclic secondary amines such as piperideine and morpholine afforded pure cyanacetamides, which were converted into cyanoximes at room temperature using the nitrosation reaction with gaseous CH3ONO. The synthesized compounds were investigated by means of IR, 1H, 13C and UV-visible spectroscopy. Crystal structures of two starting substituted cyan-acetamides and two target cyanoximes were determined. Silver(I) complexes of AgL composition (L = PipCO, 3; MCO, 6) were prepared in high yield. Both metal complexes are thermally stable above 100oC, and remarkably stable to high intensity visible light. The stability of dried AgL compounds towards short wavelength UV-radiation (a frequently used germicidal light) was examined using diffusion reflectance spectroscopy. Both complexes demonstrate slow photoreduction within ~3 hrs, observable as a gradual color change and darkening due to the formation of fine (nano-scale) particles of metallic silver. The complex Ag(MCO), 6, is about 2.6 times less stable towards UV-radiation than its more lypophyllic analog Ag(PipCO), 3. Antimicrobial and biofilm growth inhibition properties of the prepared solid acrylate-based polymeric composites containing embedded silver(I) cyanoximates were investigated using three human pathogens: P. aeruginosa PAO1 (wound isolate), S. aureus NRS70 (methicillin resistant respiratory isolate), and S. mutans UA159 (cariogenic dental isolate). Studies showed that both 3 and 6 compounds completely abolished the growth of PAO1 at 0.5 weight % concentration, and the growth of UA159 and NRS70 at 1% concentration. Moreover, data demonstrates that complexes 3 and 6 also inhibit both planktonic and biofilm growth of Gram-positive and Gram-negative bacterial pathogens. The demonstrated thermal stability and pronounced antimicrobial activity of both silver(I) cyanoximates indicates the strong potential for the studied complexes to be used as light insensitive antimicrobial additives to light-curable adhesives that set indwelling devices in place.

The first bis-cyanoxime: synthesis and properties of a new versatile and accessible polydentate bifunctional building block for coordination and supramolecular chemistry

A new multidentate bifunctional organic ligand – di-N,N′-(2-cyano-2-oximinoacetyl)piperazine – was synthesized in high yield using a two-step procedure carried out under ambient conditions. At first, the reaction of piperazine and neat methylcyanoacetate led to the di-N,N′-(cyanoacetyl)piperazine (1), which then was converted into bis-cyanoxime, di-N,N′-(2-cyano-2-oximinoacetyl)piperazine (HL, 2) using a room temperature nitrosation reaction with gaseous methylnitrite. Synthesized bis-cyanoxime was characterized by 1H, 13C NMR, UV-visible, IR spectroscopy and the X-ray analysis. The ligand 2 exists as a mixture of three diastereomers arising from the syn- and anti-geometry of the cyanoxime group. The prolonged crystallization of 2 from an ethanol–water mixture leads to the formation of: (a) colorless crystals that according to the X-ray analysis contain a 51.2:48.8% co-crystallized mixture of both isomers that have the same H-bonding motif (minority), and (b) a white amorphous material that represents an almost pure anti-isomer (majority). The deprotonation of 2 leads to the formation of a yellow dianion that demonstrated pronounced solvatochromism of its n → π* transition in the nitroso-chromophore. The disodium salt Na2L·4H2O (3) was obtained from 2 using NaOC2H5 in ethanol. The new bis-cyanoxime 2 reacts with Tl2CO3 and AgNO3 in aqueous solutions with the formation of light-stable, sparingly soluble yellow precipitates of M′2L·xH2O composition (M′ = Tl, Ag; Tl = 4, x = 0; Ag = 5, x = 2). The reaction of 3 with Ni2+ or K2M′′Cl4 (M′′ = Pd, Pt) in aqueous solutions leads to NiL·4H2O (6), PdL·4H2O (7) and PtL·5H2O (8). The crystal structure of 4 was determined and revealed the formation of a 3D-coordination polymeric complex in which the bis-cyanoxime acts as a dianionic, bridging, formally decadentate ligand. Each Tl(I) center has two bonds (2.655, 2.769 Å), shorter than the sum of ionic radii Tl–O (oxime group), and three longer, >2.89 Å, mostly electrostatic Tl···O contacts, involving oxygen atoms of the amide-group and the oxime-group of neighboring units. Among several possible binding modes, the coordination of the bis-cyanoxime dianion of 2 adopted in complex 4 is unusual, and evidenced its great potential as a versatile building block for coordination and supramolecular chemistry.

Sodium-centered dodecanuclear Co(II) and Ni(II) complexes with 2-(phosphonomethylamino)succinic acid: studies of spectroscopic, structural, and magnetic properties

Two new isostructural cobalt(II) and nickel(II) polynuclear complexes with 2-(phosphonomethyl)aminosuccinic acid, H4PMAS, namely, Na[Co12(PMAS)6(H2O)17(OH)]·x2H2O, 1·x2H2O, and Na[Ni12(PMAS)6(H2O)17(OH)]·xH2O, 2·xH2O, have been synthesized for the first time from aqueous solutions and studied by single crystal X-ray diffraction, infrared, and UV-visible diffuse reflectance spectroscopy; TG/DTA analysis; and magnetochemistry. Both 1 and 2 crystallize in the rhombohedral crystal system with the R3[overline] space group with 1/6 of the Co12(PMAS)6 or Ni12(PMAS)6 moieties in the asymmetric unit. The X-ray refinements reveal the presence of 18 water sites, but unit cell charge balance requires that one water molecule must be an OH(-) anion, an anion which is disordered over the 18 sites. The PMAS(4-) ligand forms two five-membered and one six-membered chelation ring. Both 1 and 2 contain 24-membered metallacycles as a result of the bridging nature of the PMAS(4-) ligands. The resulting three-dimensional structures have one-dimensional channels with a sodium cation at the center of symmetry. The temperature dependence of the magnetic susceptibility reveals the presence of weak antiferromagnetic exchange coupling interactions in both 1 and 2. Two exchange coupling constants, J1 = -15.3(7) cm(-1) and J2 = -1.06(2) cm(-1) with S1 = S2 = 3/2 for the Co(1)···Co(1) and Co(1)···Co(2) exchange pathways, respectively, are required for 1, and J1 = -1.17(6) cm(-1) and J2 = -4.00(8) cm(-1) with S1 = S2 = 1 for the Ni(1)···Ni(1) and Ni(1)···Ni(2) exchange pathways, respectively, are required for 2, in order to fit the temperature dependence of the observed magnetic susceptibilities.

Half-sandwich ruthenium–arene complexes with thiosemicarbazones: synthesis and biological evaluation of [(η⁶-p-cymene)Ru(piperonal thiosemicarbazones)Cl]Cl complexes

The synthesis and characterization of a number of organometallic ruthenium(II) complexes containing a series of bidentate thiosemicarbazone ligands derived from piperonal is reported. The structure of compounds have been confirmed by spectroscopic analysis (IR and NMR) as well as X-ray crystallographic analysis of [(η⁶-p-cymene)Ru(pPhTSC)Cl]Cl (4) (pPhTSC is piperonal-N(4)-phenylthiosemicarbazone). The interaction of the complexes ([(η⁶-p-cymene)Ru(pEtTSC)Cl]Cl) (3) (pEtTSC is piperonal-N(4)-ethylthiosemicarbazone) and 4 with calf thymus DNA, human serum albumin (HSA) and pBR322 plasmid DNA were studied by spectroscopic, gel electrophoresis and hydrodynamic methods. The apparent binding constant for the interaction with DNA was determined to be 3.97×10³ M⁻¹ and 4.07×10³ M⁻¹ at 293 K for 3 and 4 respectively. The complexes bind strongly to HSA with binding constants of 2.94×10⁴ M⁻¹ and 12.2×10⁴ M⁻¹ at 296 K for 3 and 4 respectively. The in vitro anticancer activity of 3 and 4 has been evaluated against two human colon cancer cell line (HCT-116 and Caco-2) with IC50 values in the range of 26–150 μM. Both 3 and 4 show good activity as a catalytic inhibitor of human topoisomerase II at concentrations as low as 20 μM. The proficiency of 3 and 4 to act as antibacterial agents was also evaluated against six pathogenic bacterial strains with the best activity seen against Gram-positive strains.

Synthesis and structure of [(η(6)-p-cymene)Ru(2-anthracen-9-ylmethylene-N-ethylhydrazinecarbothioamide)Cl]Cl; biological evaluation, topoisomerase II inhibition and reaction with DNA and human serum albumin

We have synthesized and evaluated the biological properties of a compound of the type [η(6)-p-cymene)Ru(EtATSC)Cl]Cl (1) where EtATSC = 2-anthracen-9-ylmethylene-N-ethylhydrazinecarbothioamide, a thiosemicarbazone. The complex has been characterized by elemental analysis, spectroscopically (NMR, UV-Vis, and IR) and structurally by XRD. The in vitro anticancer activity of 1 has been evaluated against two human colon cancer cell lines. The IC(50) value for activity against HCT-116 was 224 ± 7 μM and 205 ± 5 μM against the Caco-2 cell line. The proficiency of 1 as an antibacterial agent was also evaluated against six bacterial strains. The minimum inhibitory concentration for Bacillus cereus was determined to be 5 μM and for Enterococcus faecalis it was 20 μM. At the maximum concentration tested the complex showed no activity against the Gram-negative strains. The complex binds strongly to human serum albumin with a binding constant of 1.37 ± 0.02 M(-1) at 308 K on a single binding site. It is also a strong binder to DNA with an apparent binding constant of 2.82 × 10(5) M(-1) at 308 K. 1 shows very good activity as a catalytic inhibitor of human topoisomerase II at concentrations as low as 20 μM.

Tin(IV) cyanoximates: synthesis, characterization, and cytotoxicity

In recent years, numerous organotin(IV) derivatives have exhibited remarkable cytotoxicity against several types of cancer. However, the properties of the cyanoxime-containing organotin(IV) complexes are unknown. Previously, it has been shown that cyanoximes displayed an interesting spectrum of biological activity ranging from growth-regulation to antimicrobial and pesticide detoxification actions. The work presented here attempts to combine the useful properties of both groups of compounds and investigate the likely antiproliferating activity of the new substances. A series of 19 organotin(IV) complexes, with nine different cyanoxime ligands, were anaerobically prepared by means of the heterogeneous metathesis reaction between the respective organotin(IV) halides (Cl, Br) and ML (M=Ag, Tl; L=cyanoximate anion), using an ultrasound in the CH3CN at room temperature. The compounds were characterized using spectroscopic methods (UV-visible, IR, 1H,13C NMR, 119Sn Mössbauer) and X-ray analysis. The crystal structures of the complexes revealed the formation of two types of tin(IV) cyanoximates: mononuclear five-coordinated compounds of R4-xSnLx composition (R=Me, Et, n-Bu, Ph; x=1, 2; L=cyanoximate anion), and the tetranuclear R8Sn4(OH)2O2L2 species (R=n-Bu, Ph). The latter complex contains a planar [Sn4(OH)2O2]2- core, consisting of three adjacent rhombs with bridging oxo and hydroxo groups. The tin(IV) atoms are five-coordinated and have distorted trigonal-pyramidal surrounding. This is the first instance when the organic anions were found to act as monodentate O-bound planar oxime ligands. All of the compounds were studied in vitro for antiproliferating activity, using human cervical cancer HeLa and WiDR colon cancer cell lines; cisplatin was used as a positive control substance. The two dibutyltin(IV) cyanoximates showed cytotoxicity similar and greater to that of cisplatin.

Double-Stranded Metal−Organic Networks for One-Dimensional Mixed Valence Coordination Polymers

The design of new types of metal-organic networks and the search for unusual crystal architecture represents an important task for modern inorganic and materials chemistry research. A group of new monosubstituted phenylcyanoximes, containing F, Cl, and Br atoms at the 2, 3, or 4 positions, were synthesized using the high yield nitrosation reaction with CH3-ONO and were spectroscopically (1H NMR, 13C NMR, UV-visible, IR, mass spectrometry) and structurally characterized. Results of X-ray analysis revealed nonplanar trans-anti geometry for 2-chlorophenyl(oximino)acetonitrile, H(2Cl-PhCO); a nonplanar anti configuration for 4-chlorophenyl(oximino)acetonitrile, H(4Cl-PhCO); and planar cis-syn geometry for 3-fluorophenyl(oximino)acetonitrile, H(3F-PhCO). All arylcyanoximes undergo deprotonation in solutions with the formation of colored anions exhibiting pronounced negative solvatochromism in a series of polar protic and aprotic solvents. Nine thallium(I) cyanoximates were obtained using the reaction between hot (approximately 95 degrees C) aqueous solutions of Tl2CO3 and solid powdery monohalogenated arylcyanoximes HL. Crystal structures of two Tl(I) cyanoximates [Tl(2Cl-PhCO) and Tl(4Br-PhCO)] contained centrosymmetric dimeric units (TlL)2 that are connected to a coordination polymer by means of an oxygen atom of the oxime group of the neighboring molecule. Cyanoxime anions act as bridging ligands in both structures where the polymeric motif consists of double-stranded Tl-O chains interconnected with the formation of zigzagging Tl2O2 planar rhombes. Thallium atoms form infinite linear arrays with close intermetallic separations. The nearest Tl(I)...Tl(I) distances are 3.838 and 4.058 angstroms in the Tl(2Cl-PhCO) and Tl(4Br-PhCO) structures, respectively, close to that in metallic thallium (3.456 angstroms). Monosubstituted phenyl groups are well aligned in pi-stacking columns that are perpendicular to the array of Tl(I) atoms and stabilize formed structures. Coordination polyhedrons of thallium(I) in these complexes represent distorted trigonal pyramids with stereoactive lone pair.

First bivalent palladium and platinum cyanoximates: synthesis, characterization, and biological activity

A series of five cyanoximes (compounds having the general formula NC-C(=NOH)-R, where R is an amide or carboxylic ester group) have been synthesized and spectroscopically and structurally characterized. These are 2-cyano-2-isonitrosoacetamide (later HACO), 2-cyano-2-isonitrosothioacetamide (HTCO), 2-cyano-2-isonitrosoethylacetate (HECO), 2-cyano-2-isonitroso-N-piperidinylacetamide (HPiPCO), and 2-cyano-2-isonitroso-N-morpholinylacetamide (HMCO). A high yield method of synthesis was developed for the last two previously unknown amidocyanoximes. Variable temperature (13)C NMR studies in DMSO-d(6) solutions allowed the determination of rotational energy barriers for these two new cyanoximes. The HPiPCO and HMCO oxime molecules adopt a trans-anti configuration in the solid state according to X-ray analysis. Reactions between aqueous solutions of K(+)L(-) (L = cyanoximate anions: TCO(-), PiPCO(-), and MCO(-)) and K(2)[MCl(4)] (M = Pd, Pt) resulted in the formation of ML(2) complexes. The crystal structure of Pd(MCO)(2).DMSO was determined and showed the formation of coplanar dimeric [Pd(MCO)](2) units with 3.13 A Pd...Pd separation. The complex adopts cis geometry with anions being in the nitroso form. In the presence of bivalent Pd and Pt, ACO(-) and ECO(-) anions completely or partially hydrolyze in aqueous solutions to the dianion of 2-cyano-2-isonitrosoacetic acid (AACO(2-)). The crystal structure of the product of the hydrolysis reaction, K(2)[Pd(AACO)(2)].4H(2)O, was determined. Data revealed planar and cis geometry of the [Pd(AACO)(2)](2)(-) anion where cyanoximes are in the nitroso form and adopt a cis-anti configuration. All synthesized cyanoxime ligands and nine of their Pd(II) and Pt(II) complexes were tested in vitro on antiproliferating activity using human cervical cancer HeLa cell lines, and cisplatin as a positive control substance. Two out of the nine studied complexes, Pd(MCO)(2) and Pt(MCO), were found to be active compounds inflicting death on 28% and 16% of the cells, respectively, with 55% value for the cisplatin under the same conditions.

Motexafin gadolinium reacts with ascorbate to produce reactive oxygen species

Motexafin gadolinium (MGd) oxidizes ascorbate, in neutral buffer and in cell culture, forming reactive oxygen species and a coordination polymer with oxalate.

Late first-row transition-metal complexes of texaphyrin

The preparation of first-row transition-metal complexes of texaphyrin, a porphyrin-like, monoanionic penta-aza macrocyclic ligand, is reported. Specifically, the synthesis of organic-soluble Mn(II) (1), Co(II) (2), Ni(II) (3), Zn(II) (4), and Fe(III) (5) texaphyrin derivatives and their water-soluble counterparts (6-10) from appropriate metal-free, nonaromatic macrocyclic precursors is described. It was found that metal cations of sufficient reduction potential could act to oxidize the nonaromatic macrocyclic precursor in the course of metal insertion. Complexes were characterized by X-ray diffraction analysis, electrochemistry, flash photolysis, and EPR spectroscopy. The structural and electronic properties of these "expanded porphyrin" complexes are compared with those of analogous porphyrins. Notably, the texaphyrin ligand is found to support the complexation of cations in a lower valence and a higher spin state than do porphyrins. Interactions between the coordinated cation and the ligand pi system appear to contribute to the overall bonding. Texaphyrin complexes of Mn(II), Co(II), and Fe(III) in particular may possess sufficient aqueous stability to permit their use in pharmaceutical applications.

Synthesis of a metal-free texaphyrin

The synthesis of a metal-free form of texaphyrin, an aromatic porphyrin-like macrocycle, is described. Previously, texaphyrins could only be obtained reproducibly in the form of metal complexes. Using ferrocenium cation as the oxidizing agent and starting with a reduced porphyrinogen-like nonaromatic form of texaphyrin, we isolated, in good yield, the metal-free oxidized texaphyrin as its HPF(6) salt. This product was characterized by X-ray diffraction analysis, UV-vis spectroscopy, and cyclic voltammetry. [structure: see text]

Redox cycling by motexafin gadolinium enhances cellular response to ionizing radiation by forming reactive oxygen species

PURPOSE

To examine the mechanism of radiation enhancement by motexafin gadolinium (Gd-Tex) in vitro.

METHODS AND MATERIALS

Oxidation of ascorbate and NADPH by Gd-Tex was evaluated in a neutral buffer. Growth inhibition of human uterine cancer cell line MES-SA was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) dye. Clonogenic assays were used to measure radiation response in MES-SA, A549 human lung carcinoma, E89, a CHO cell line variant deficient in glucose-6-phosphate dehydrogenase activity, and murine lymphoma cell lines LYAR and LYAS.

RESULTS

Gd-Tex catalyzed the oxidation of NADPH and ascorbate under aerobic conditions, forming hydrogen peroxide. Decreased viability was observed in MES-SA cells incubated with Gd-Tex in media containing NADPH or ascorbate. Gd-Tex and ascorbate increased fluorescence in dichlorofluorescin acetate-treated cultures. Synergistic effects on the aerobic radiation response in MES-SA and A549 were seen using Gd-Tex in combination with L-buthionine-(S,R)-sulfoximine (BSO). Incubation with Gd-Tex in the presence of ascorbate increased the aerobic radiation response of E89 and the apoptosis-sensitive B-cell line (LYAS).

CONCLUSIONS

Gd-Tex sensitizes cells to ionizing radiation by increasing oxidative stress as a consequence of futile redox cycling. Optimization of the concentration of ascorbate (or other reducing species) may be required when evaluating Gd-Tex activity in vitro.