Manganese (II) selective PVC based membrane sensor using a Schiff base

N,N′,N″,N′′′-1,5,8,12-tetraazadodecane-bis(salicylaldiminato)(H₂L) has been used as ionophore for preparing Mn²⁺ selective sensor. Membranes of different composition with regard to ratio of H₂L:PVC:NPOE:NaTPB have been prepared and investigated. The best performance was obtained with the membrane of composition 10:150:150:10 (H₂L:PVC:NPOE:NaTPB) (w/w; mg). This membrane generated linear potential response in the concentration range of 5.0 × 10⁻⁶ to 1.0 × 10⁻¹ M with a Nernstian slope of 30.0 mV/decade of activity and fast response time (10 s). Hydrogen ion does not effect to the performance of sensor in the pH range 3.0-6.5. The sensor was found to be sufficient selective for Mn²⁺ over a number of alkali, alkaline and heavy metal ions and could therefore be used for the determination of manganese in various samples by direct potentiometry.     

Development of electrochemical sensors for nano scale Tb(III) ion determination based on pendant macrocyclic ligands

The two macrocyclic pendant ligands 3,4,5:12,13,14-dipyridine-2,6,11,15-tetramethyl-1,7,10,16-tetramethylacrylate-1,4,7,10,13,16-hexaazacyclooctadeca-3,13-di ene (L₁) and 3,4,5:12,13,14-dipyridine-2,6,11,15-tetramethyl-1,7,10,16-tetra(2-cyano ethane)-1,4,7,10,13,16-hexaazacyclooctadeca-3,13-diene (L₂) have been synthesized and explored as neutral ionophores for preparing poly(vinylchloride) (PVC) based membrane sensors selective to Tb(III) ions. Effects of various plasticizers and anion excluders were studied in detail and improved performance was observed. The best performance was obtained for the membrane sensor having a composition of L₁: PVC:1-CN:NaTPB in the ratio of 6: 32: 58: 4 (w/w; mg). The performance of the membrane based on L₁ was compared with polymeric membrane electrode (PME) as well as with coated graphite electrode (CGE). The electrodes exhibit Nernstian slope for Tb³⁺ ions with limits of detection of 3.4 × 10⁻⁸ mol L⁻¹ for PME and 5.7 × 10⁻⁹ mol L⁻¹ for CGE. The response time for PME and CGE was found to be 10 s and 8 s, respectively. The potentiometric responses are independent of the pH of the test solution in the pH range 3.0-7.5 for PME and 2.0-8.5 for CGE. The CGE has found to work satisfactorily in partially non-aqueous media upto 30% (v/v) content of methanol, ethanol and 20% (v/v) content of acetonitrile and could be used for a period of 5 months. The CGE was used as indicator electrode in the potentiometric titration of Tb³⁺ ions with EDTA and in determination of fluoride ions in various samples. It can also be used in direct determination of Tb³⁺ ions in tap water and various binary mixtures with quantitative results.     

Metallo-tetraazaporphyrin based anion sensors: regulation of sensor characteristics through central metal ion coordination

The iron(III) and cobalt(III) complexes of 2,3,7,8,12,13,17,18-octakis(benzylthio)-5,10,15,20-tetraazaporphyrin, (OBTAP) were synthesized and incorporated into PVC matrix as ionophores to fabricate anion selective membrane electrodes that exhibit selective potentiometric response to azide and nitrite ions, respectively. The membrane of [Fe(OBTAP)]⁺ (III) with a composition of 6:190:200 (III:DBP:PVC) (w/w), and of [Co(OBTAP)]⁺ (IV) with a composition of 10:148:200 (IV:DOP:PVC) (w/w), i.e. 1a and 2b, respectively (where DBP:dibutylphthalate and DOP=dioctylphthalate) gave the best performance. The membrane 1a showed a slope of 29.2±0.2 mV per decade of activity for N₃⁻ in the working concentration range of 8.9×10⁻⁶ to 1.0×10⁻¹ M. The membrane 2b showed a slope of 30.0±0.2 mV per decade of activity for NO₂⁻ in the working concentration range of 1.1×10⁻⁵ to 1.0×10⁻¹ M. The membranes worked satisfactorily in the pH range of 4.3-10.5 (1a) and 2.8-6.4 (2b) and had fast response time of 12±2 and 13±2 s, respectively. Electrodes exhibited a high degree of selectivity for N₃⁻ and NO₂⁻, respectively, over several other monovalent and bivalent anions. Only SCN⁻ and S²⁻ (at >1.0×10⁻⁴ M) cause moderate interference for electrode 1a and Cl⁻ and S²⁻ (at >1.0×10⁻⁵ M) for electrode 2b. They gave reproducible results with the relative standard deviation in the observed values of potentials (σ) of 1.96 and 1.80 mV for electrodes 1a and 2b, respectively, from the least-squares fit line. The 90% confidence limit lies within ±0.2 mV per decade of activity. Reproducible results were obtained over a period of 5 months. Their performance in non-aqueous solvent mixtures having up to 50% (v/v) methanol, ethanol and acetone were evaluated and were found satisfactory. The proposed sensors are superior in terms of detection limit and response time in comparison to the reported ones.     

Comparative studies of neodymium (III)-selective PVC membrane sensors

Sensors based on two neutral ionophores, N,N′-bis((1H-pyrrol-2-yl)methylene)cyclohexane-1,2-diamine (L₁) and 3,3′-(cyclohexane-1,2-diylbis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)bis(5-hydroxymethyl)pyridine-2-ol) (L₂) are described for quantification of neodymium (III). Effect of various plasticizers; 2-nitrophenyloctylether (o-NPOE), dibutyl butylphosphonate (DBBP), tri-n-butyl phosphates (TBP), dioctylpthalate (DOP) and chloronapthalen (CN) and anion excluder, sodiumtetraphenylborate (NaTPB) has been studied. The membrane composition of PVC:o-NPOE:ionophore (L₁):NaTPB (w/w; mg) of 150:300:5:5 exhibited best performance. The sensor with ionophore (L₁) exhibits significantly enhanced selectivity towards neodymium (III) in the concentration range 5.0 × 10⁻⁷ to 1.0 × 10⁻² M with a detection limit of 1.0 × 10⁻⁷ M and a Nernstian compliance (19.8 ± 0.3 mV decade⁻¹ of activity) within pH range 4.0-8.0. The response time of sensor was found as 10 s. The influence of the membrane composition and possible interfering ions has also been investigated on the response properties of the electrode. The fast and stable response, good reproducibility and long-term stability of the sensor are observed. The sensor has been found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol or acetonitrile and could be used for a period of 3 months. The selectivity coefficients determined by using fixed interference method (FIM) indicate high selectivity for neodymium. The proposed electrode shows fairly good discrimination of neodymium (III) from other cations. The application of prepared sensor has been demonstrated in the determination of neodymium (III) in spiked water samples.     

Comparative studies of ONNO-based ligands as ionophores for palladium ion-selective membrane sensors

Palladium sensors based on two neutral ionophores, N,N′-bis(acetylacetone) cyclohexanediamine (L₁) and N,N′-bis(o-hydroxyacetophenone)-1,2-cyclohexanediamine (L₂) for quantification of palladium ions are described. Effect of various plasticizers (o-NPOE, DBP, DEP, DOP, TBP, and CN) and anion excluder, sodium tetra phenyl borate (NaTPB) has been studied. The best performance is obtained with a membrane composition of PVC:o-NPOE:ionophore (L₁):NaTPB of 150:300:5:5 (%, w/w). The sensor exhibits significantly enhanced selectivity towards palladium ion over the concentration range 1.0 × 10⁻⁸ to 1.0 × 10⁻¹ M with a lower detection limit of 4.0 × 10⁻⁹ M and a Nernstian compliance (29.1 ± 0.3 mV decade⁻¹ of activity) within pH range 2.0-6.0 and fast response time of 10 s. Influence of the membrane composition and possible interfering ions has also been investigated on the response properties of the electrode. Fast and stable response, good reproducibility and long-term stability of the sensor are demonstrated. The sensor has been found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol and acetonitrile and could be used for a period of 4 months. Selectivity coefficients determined with fixed interference method (FIM) indicate high selectivity for palladium. The proposed electrode shows fairly good discrimination of palladium from other cations. The application of prepared sensor has been demonstrated in determination of palladium ions in spiked water sample.     

Nickel pyrazolyl borate complexes: Synthesis, structure and analytical application in biological and environmental samples as anion selective sensors

A [{hydrotris(3-phenyl-5-methyl-1-pyrazolyl)borate}(3-phenyl-5-methyl-pyrazole) nickel chloride] [Tp^Ph,MeNi(Cl)Pz^Ph,MeH] (I) has been synthesized and explored as ionophores for the preparation of a poly (vinyl chloride) (PVC) membrane sensor for azide and thiocyanate anions. The compounds [Tp^Ph,MeNi(N₃)Pz^Ph,MeH] (II) and [Tp^Ph,MeNi(SCN)Pz^Ph,MeH] (III) were characterized by their crystal structures and proved to be bonded as monodentate through nitrogen atom of azide and thiocyanate anion. Potentiometric investigations also indicate high affinity of this receptor for thiocyanate and azide ions. PVC based membranes of I using as hexadecyltrimethylammonium bromide (HTAB) cation discriminator and o-nitrophenyloctyl ether (o-NPOE), dibutylphthalate (DBP), acetophenone (AP) and tributylphosphate (TBP) as plasticizing solvent mediators were prepared and investigated as SCN⁻ and N₃⁻ selective sensors. The best performance was shown by the membrane of thiocyanate with composition (w/w) of (I) (7%):PVC (31%):DBP (60%):HTAB (2%). This sensor works well over a wide concentration range 5.3 × 10⁻⁷ to 1.0 × 10⁻² M with Nernstian compliance (59.2 mV decade⁻¹ of activity) within pH range 2.5-9.0 with a response time of 11 s and showed good selectivity for thiocyanate ion over a number of anions. The sensor exhibits adequate life (3 months) and could be used successfully for the determination of thiocyanate content in human urine, saliva and river water samples. While the membrane of [Tp^Ph,MeNi(Cl)Pz^Ph,MeH] ionophore with composition (I) (6%):HTAB (4%):PVC (31%):TBP (59%) showed highest sensitivity and widest linear range for azide ion. These sensors exhibit the maximum working concentration range of 8.1 × 10⁻⁶ to 1.0 × 10⁻² M with Nernstian slope of 59.3 mV decade⁻¹ of activity. It can be applied for the monitoring of the azide ions concentration in aqueous black tea and orange juice samples.     

Comparative studies on Tb (III)-selective PVC membrane sensors

A new terbium selective sensor based on N-(2-hydroxyphenyl)-3-(2-hydroxyphenylhydroxyphenylimino)-N-phenylbutanamidine (L₁) and N,N′-bis((1H-indole-3-yl)methylene)butane-1,4 diamine (L₂) as a ionophore is reported. Effect of various plasticizers; 2-nitrophenyloctylether (o-NPOE), dibutyl butylphosphonate (DBBP), chloronaphthelene (CN), dioctylphthalate (DOP) and tri-(2-ethylhexyl)phosphate (TEHP) with anion excluder, potassium tetrakis (p-chloropheny1)borate (KTpClPB) have been studied. The membrane with a composition of ionophore (L₁):KTpClPB:PVC:o-NPOE (w/w, %) in ratio of 3.0:5.0:30.0:62.0 exhibited enhanced selectivity towards terbium ions (III) in the concentration range of 3.5 × 10⁻⁷ to 1.0 × 10⁻² M with a detection limit of 1.2 × 10⁻⁷ M and a Nernstian slope (20.0 ± 0.5 mV dec⁻¹ activity). The sensors showed the working pH range to be 3.5-7.5 with response time of 11 s. The sensor has been found to work satisfactorily in partially non-aqueous media up to 15% (v/v) content of methanol, ethanol or acetonitrile and could be used for a period of 3 months. The selectivity coefficients indicated high selectivity for terbium (III). The fast and stable response, good reproducibility and long-term stability of the sensors were observed. The application of the sensor has been demonstrated in determination of terbium (III) ions in spiked water samples.     

Oxidative and hydrolytic DNA cleavage by Cu(II) complexes of salicylidene tyrosine schiff base and 1,10 phenanthroline/bipyridine

Ternary Cu(II) complexes [Cu(II)(saltyr)(B)] (1,2), (saltyr = salicylidene tyrosine, B = 1,10 phenanthroline (1) or 2,2′ bipyridine (2)) were synthesized and characterized by various techniques. The complexes exhibit square pyramidal (CuN₃O₂) geometry. CT-DNA binding studies revealed that the complexes show good binding propensity (K_b = 3.47 × 10⁴ M⁻¹ and 3.01 × 10⁴ M⁻¹ for 1 and 2, respectively). The role of these complexes in the oxidative and hydrolytic DNA cleavage was studied. The catalytic ability of 1 and 2 follows the order: 1 > 2. The rate constants for the hydrolysis of phosphodiester bond were determined as 2.80 h⁻¹ and 2.11 h⁻¹ for 1 and 2, respectively. It amounts to (0.58-0.77) × 10⁸ fold rate enhancement compared to non-catalyzed DNA cleavage, which is significant.     

Macrocycles with two exclusive hydrogen-bonding modes

A series of large, 44-membered macrocycles 7a-e were synthesized and characterized, which display two different diagonal binding modes. The unsubstituted macrocycle 7a strongly binds naphthalene-2,6-dicarboxylate through hydrogen bonds with the association constant (K_a ± 15%) of 4500 M⁻¹ in 40% (v/v) CD₃CN/CDCl₃ at 23 ± 1 °C. Introduction of an electron-withdrawing substituent (Cl) at all four corners increases the binding affinity (22,000 M⁻¹ for 7b), while that of an electron-donating substituent (pyrrolidinyl) greatly decreases it (150 M⁻¹ for 7c). The same propensity has been observed with macrocycles 7d and 7e bearing different substituents at two diagonal corners, suggesting that the relative population of the binding modes would be modulated by controlling the electron density of the aromatic ring.     

A novel strapped porphyrin receptor for molecular recognition

A novel strapped porphyrin receptor Zn1, in which two electron-rich bis(p-phenylene)-34-crown ether-10 units are incorporated, has been designed and synthesized from the newly developed intermediate 7 for investigating new chemistry of molecular recognition. ¹H NMR and UV-Vis studies revealed that Zn1 displays relatively weak binding abilities to neutral electron deficient naphthalene-1,8,4,5-tetracarboxydiimide (NDI) derivatives 13 (no simple complexing stoichiometry was observed), 19 (K_a=48(±5) M⁻¹) and 30 (K_a=46(±5) M⁻¹) in chloroform-d, strong binding ability to pyridine derivative 25, (K_a=1.5(±0.12)×10³ M⁻¹) in chloroform, moderately strong binding ability to tetracationic compound 35·4PF₆ (K_a=475(±50) M⁻¹) in acetone-d₆, and very strong binding affinity to compound 22 (K_a=6.5(±0.7)×10⁵ M⁻¹), which consists of one pyridine and two NDI units, in chloroform. Remarkable cooperative effect of the intermolecular metal-ligand coordination and donor-acceptor interactions in complex Zn1·22 was observed by comparing the complexing behaviors between Zn1 and the appropriately designed guests. Complex Zn1·22 possesses an unique three-dimensional tri-site binding feature. For comparison, the complexing affinity of 1 toward compounds 13, 19, and 30 in chloroform-d and 35·4PF₆ in acetone-d₆ has also been investigated and the binding patterns in different complexes were explored. The results demonstrate that strapped porphyrin derivatives are ideal precursors for constructing new generation of three-dimensional multi-site artificial receptors for molecular recognition and host-guest chemistry.     

Control of molecular weight distribution in polycondensation polymers 2. Poly(ether ketone) synthesis

Synthesis of aromatic poly(ether ketone) (3) with a narrow molecular weight distribution (M_w/M_n) was investigated via polycondensation. M_ns of 3 could be controlled varying the feed ratio of monomer (1) and initiator (2) maintaining relatively narrow M_w/M_ns (<1.3). The kinetics of polycondensation obeyed a first-order relationship between polycondensation time and -(1/[2]₀) ln([1]/[1]₀), and the rate of polycondensation was estimated as 2.57 mol⁻¹ L h⁻¹. MALDI-TOF mass analysis of 3 indicated that polycondensation should proceed via chain growth manner to give 3 having an initiator unit in each chain end.     

Neutral carriers based polymeric membrane electrodes for selective determination of mercury (II)

The potentiometric response characteristics of mercury ion-selective membrane electrodes based on 2-amino-6-purinethiol (I₁) and 5-amino-1, 3, 4-thiadiazole-2-thiol (I₂) were described. Ion selectivities were tested for various plasticizers, which were used as solvent mediators to incorporate the ionophores into the membrane. Effects of experimental parameters such as membrane composition, nature and amount of plasticizers and additives, pH and concentration of internal solution on the potential response of Hg²⁺ electrodes were investigated. The best performance was obtained with the electrode having a membrane composition (w/w) of (I₁) (3.17%): PVC (31.7%): DOP (dioctylpthalate) (63.4%): NaTPB (sodium tetraphenylborate) (1.58%). The proposed electrode reveals a Nernstian response over Hg²⁺ ion in the concentration range of 7.0 × 10⁻⁸-1.0 × 10⁻¹ M with limit of detection 4.4 × 10⁻⁸ M. The electrode shows good discrimination toward Hg²⁺ ion with respect to most common cations. It shows a short response time (10 s) for whole concentration range and can be used for 2 months without any considerable divergence in potentials. For evaluation of the analytical applicability, the electrode was used in the determination of Hg²⁺ ion in different environmental and biological samples. The practical utility of the membrane electrode has also been observed in the presence of surfactants.     

Novel fluorimetric bulk optode membrane based on 5,8-bis((5′-chloro-8′-hydroxy-7′-quinolinyl)methyl)-2,11-dithia-5,8-diaza-2,6-pyridinophane for selective detection of lead(II) ions

A novel fluorescence chemical sensor for the highly sensitive and selective determination of Pb²⁺ ions in aqueous solutions is described. The preliminary potentiometric and spectrofluorimetric complexation studies in solution revealed that the lipophilic ligand 5,8-bis((5′-chloro-8′-hydroxy-7′-quinolinyl)methyl)-2,11-dithia-5,8-diaza-2,6-pyridinophane (L2) forms a highly stable and selective [PbL2]²⁺ and [Pb(L2)₂]²⁺ complexes which results in a strong fluorescence quenching of the ligand. Thus, a novel fluorescence Pb²⁺ sensing system was prepared by incorporating L2 as a neutral lead-selective fluoroionophore in the plasticized PVC membrane containing tetrakis(p-chlorophenyl) borate as a liphophilic anionic additive. The response of the sensor is based on the strong selective fluorescence quenching of L2 by Pb²⁺ ions. At pH 5.5, the proposed sensor displays a calibration curve over a wide concentration range of 3.0 × 10⁻⁷ to 2.5 × 10⁻² M with a relatively fast response time of less than 5 min. In addition to high stability, reversibility and reproducibility, the sensor shows a unique selectivity towards Pb²⁺ ion with respect to common coexisting cations. The proposed fluorescence optode was successfully applied to the determination of lead in plastic toys and tap water samples.     

Substituent effect on anthracene-based bisboronic acid glucose sensors

Earlier we communicated an anthracene-based bisboronic acid sensor for glucose. Aimed at understanding the substituent effect, we have introduced various functional groups, such as the cyano, nitro, and fluoro group on the boronic acid moiety of this glucose sensor. Fluorescent binding studies indicated that the cyano-substituted sensor (4a) has the highest affinity (K 2540 M⁻¹) for glucose, but the lowest selectivity (three-fold over fructose); the fluoro-substituted compound (4c) shows the lowest affinity (630 M⁻¹) and a modest selectivity (15-fold over fructose); and the unsubstituted one (1a) shows the highest selectivity over fructose (43-fold) and a modest affinity (1472 M⁻¹).     

Multiple hydrogen-bond-induced supramolecular nanostructure from a pincer-like molecule and a [60]fullerene derivative

A new supramolecular self-assembled system between a perylene bisimide bearing diaminopyridine-substituted isophthalamide groups (PP) and a [60]fullerene containing barbituric acid moiety (C₆₀bar) through a complementary six-point hydrogen-bonding interaction was constructed. The formation of hydrogen bonding was confirmed by ¹H NMR spectra studies in CDCl₃. Fluorescence quenching experiments indicated that the fluorescence of PP was greatly quenched by the hydrogen-bonded C₆₀bar (K_sv=2.71×10⁴ M⁻¹). A steady and rapid cathodic 0.15 μA cm⁻² photocurrent response of the PP/C₆₀bar film deposited onto an ITO electrode was produced under the irradiation of 20 mW cm⁻² white light, indicating the presence of photo-induced electron transfer between PP and C₆₀bar. TEM images showed that spherical particles were fabricated by the self-assembly of PP and C₆₀bar through hydrogen-bonding interaction.     

PVC based 5,10,15,20-tetrakis (4-methoxyphenyl) porphyrinatocobalt(II) membrane potentiometric sensor for arsenite

PVC based membranes of 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrinatocobalt(II) (TMOPP-Co) (I) as electroactive material with dibutyl butyl phosphonate (DBBP), dioctyl phthalate (DOP), 1-chloronaphthalene (CN), tri-n-butyl phosphate (TBP) and tris(2-ethylhexyl) phosphate (TEP) as plasticising solvent mediators have been prepared and tried for arsenite determination. The membrane having a composition 150:5:150 (PVC:I:DBBP) exhibited the best results with linear potential response in the concentration range of 7.9 × 10⁻⁵ to 1.0 × 10⁻¹ M of AsO₂⁻ with a slope of 28.8 mV/decade. The useful pH range of the sensor is 6.0-10.5. The membrane worked satisfactorily in non-aqueous medium up to 5% (v/v) non-aqueous content. The selectivity coefficient values for mono- and divalent anions indicate good selectivity for arsenite over a large number of anions.     

Heavy analogues of the 6π-electron anionic ring systems: Cyclopentadienide ion and cyclobutadiene dianion

The heavy analogues of the anionic 6π-electron systems, lithium 1,2-disila-3-germacyclopentadienide 2⁻ · [Li⁺(thf)], 1,2-disila-3,4-digerma- and 1,2,3,4-tetrasilacyclobutadiene dianions 7²⁻ · 2[K⁺(thf)₂] and 8²⁻ · 2[K⁺(thf)₂], were synthesized by the reduction of the neutral precursors 1, 3 and 4, respectively. 2⁻ · [Li⁺(thf)], the heavy analogue of the cyclopentadienide ion, is an aromatic compound, whereas 7²⁻ · 2[K⁺(thf)₂] and 8²⁻ · 2[K⁺(thf)₂], the heavy analogues of the cyclobutadiene dianion, are both non-aromatic.     

Synthesis and characterization of phosphorous-bridged bisphenoxy titanium complexes and their application to ethylene polymerization

Phosphorous-bridged bisphenoxy titanium complexes were synthesized and their ethylene polymerization behavior was investigated. Bis[3-tert-butyl-5-methyl-2-phenoxy](phenyl)phosphine tetrahydrofuran titanium dichloride (4a) was obtained by treatment of 3 equiv of n-BuLi with bis[3-tert-butyl-2-hydroxy-5-methylphenyl](phenyl)phosphine hydrochloride salt (3a) followed by TiCl₄(THF)₂ in THF. THF-free complexes 5a-5d were synthesized more conveniently by the direct reaction of MOM-protected ligands (2a-2d) with TiCl₄ in toluene. X-ray analysis of 4a revealed that the ligand is bonded to the octahedral titanium (IV) center in a facial fashion and two chlorine atoms possess cis-geometry. Complexes 4a and 5a-5d were utilized as catalyst precursors for ethylene polymerization. Complex 5c gave high molecular weight polyethylene (M_w = 1,170,000, M_w/M_n = 2.0) upon activation with Al(ⁱBu)₃/[Ph₃C][B(C₆F₅)₄] (TB). Ethylene polymerization activity of 5d activated with Al(ⁱBu)₃/TB reached 49.0 × 10⁶ g mol (cat) ⁻¹ h⁻¹.     

Copper(II) complexes of N4 tetradentate ligands with flexible alkyl spacers: Crystal structure,DNA binding and cleavage studies

Mononuclear copper(II) complexes, [Cu L1] (ClO₄)₂ (1), [Cu L2] (ClO₄)₂ (2) and [Cu L3] (ClO₄)₂ (3) with quadridentate Schiff base ligands L1 (N,N′-bis-pyridin-2-ylmethyl-butane-1,4-diimine), L2 (N,N′-bis-pyridin-2-ylmethyl-pentane-1,5-diimine) and L3 (N,N′-bis-pyridin-2-ylmethyl-hexane-1,6-diimine) have been synthesized and characterized. The crystal structure data of 1 reveals the existence of the complex in two different geometries, namely a square pyramid and a distorted octahedron, which eventually leads to the packing of the molecule into helical and anti-parallel structures respectively. Absorption titration studies with calf thymus DNA for all three complexes are suggestive of groove binding with binding constant values for 1, 2 and 3 being 2.6 ± 0.2 × 10⁴ M⁻¹, 11.5 ± 0.2 × 10⁴ M⁻¹ and 1.83 ± 0.2 × 10⁴ M⁻¹ respectively. Control cleavage experiments using pBR 322 plasmid DNA and distamycin suggest minor groove binding for these complexes. In the presence of ascorbic acid, the complexes show efficient DNA cleavage, the order of efficiency being 1 > 2 ≅ 3.     

Synthesis and electrochemical properties of new cobalt and manganese phthalocyanine complexes tetra-substituted with 3,4-(methylendioxy)-phenoxy

The synthesis and electrochemical properties of new cobalt and manganese phthalocyanine complexes, tetra-substituted with 3,4-(methylendioxy)-phenoxy at the peripheral (complexes 3 and 5) and non-peripheral (complexes 4 and 6) positions, are reported. Complexes 3 and 4 showed Q-band absorption, in DMF, at 668 and 686 nm, respectively while Q-band due to complexes 5 and 6 appeared at 732 and 760 nm, respectively in CHCl₃. All the complexes showed well resolved redox processes attributed to both metal and ring based processes. Complexes 3 and 4 showed four redox processes, labeled I, II, III and IV. For complex 3, process I (Co^IPc⁻²/Co^IPc⁻³) was observed at −1.45 V, II (Co^IIPc⁻²/Co^IPc⁻²) at −0.38 V, III (Co^IIIPc⁻²/Co^IIPc⁻²) at +0.49 V and IV (Co^IIIPc⁻¹/Co^IIIPc⁻²) at +0.97 V versus Ag|AgCl. Similar processes were observed for complex 4 at −1.36 V, −0.27 V, +0.56 V, +1.03 V versus Ag|AgCl, respectively. Complexes 5 and 6 showed two redox processes (I and II). For complex 5, these processes appeared at −0.79 V (Mn^IIPc⁻²/Mn^IIPc⁻³, I) and −0.07 V versus Ag|AgCl (Mn^IIIPc⁻²/Mn^IIPc⁻², II), while for complex 6, they were observed at −0.86 V and −0.04 V versus Ag|AgCl. Spectroelectrochemistry was used to probe and confirm the origin of these processes.