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PubMed1981

Inferences on the nature of the apical sodium entry site in frog skin epithelium.

The inhibition and stimulation of short-circuit current in in vitro frog skin by a series of structural analogs of the diuretic drug amiloride were studied. Also, the inhibitory profile of a new experimental diuretic, 3-(3-amino-1,2,4-oxadiazol-5-yl)-5-chloro-2,6-pyrazinediamine, or CGS 4270, was determined. The major conclusions of our studies are: 1) amiloride remains the most effective inhibitor of Na+ entry, with both the pyrazine ring and the acylguanidine moiety being required for maximum activity; 2) CGS 4270 also inhibits Na+ transport in frog skin; it acts only from the external solution, is uncharged, is noncompetitive with Na+ and interacts noncompetitively with amiloride; the inhibition is independent of external calcium; and 3) benzimidazole increases amiloride-sensitive short-circuit current and this compound is competitive with amiloride. These results indicate that the putative Na+ entry protein contains multiple inhibitory sites and that compounds which stimulate Na+ entry may also bind at the same molecular locus as an inhibitor.

Amiloride↗

PubMed1980

[Synthesis of p-aminobenzenesulfonyldiazine].

New sulfones were synthesized; these are analogues of bis-(4-aminophenyl)sulfone (DDS) but contain, instead of one benzene nucleus, a heterocycle that is a pyrimidine, pyrazine or pyridazine nucleus. This was substituted with amine, methoxy, methyl groups or halogens in order to obtain long-acting drugs, similarly to those obtained in the field of sulfonamides. The synthesis was accomplished by reaction of sodium p-amino- or p-acetamidobenzensulfinate with the corresponding halodiazine; only the p-aminophenyl 3-aminopyridazin-6-yl sulfone was obtained by acid hydrolysis. The compounds showed good antitubercular activity in vitro.

Antitubercular Agents↗

PubMedDate not supplied

ICI 206,970: a novel eukalemic diuretic with calcium channel blocking activity.

ICI 206,970, an aminomethylphenol pyrazine derivative, produced diuretic and saluretic effects, but caused only minimal alterations in kaliuresis in dogs and rats after oral and parenteral administration. ICI 206,970, unlike HCTZ, increased diuretic activity in a more clearly defined dose-related manner, and did not reach the plateau level even up to a dose of 100 mg/kg p.o. The diuretic and natriuretic response is believed to be a combination of a direct effect on tubule function and changes in GFR, particularly at higher doses. Based upon studies in in vitro amphibian models for mimicking mammalian nephron, ICI 206,970 appeared to possess a furosemide-like activity in toad cornea and amiloride-like activity in toad bladder. It is concluded that ICI 206,970 is a potent eukalemic diuretic with the potential of multiple sites of renal action.

Animals↗

PubMed1994

Inhibition of microtubules and cell cycle arrest by a new 1-deaza-7,8-dihydropteridine antitumor drug, CI 980, and by its chiral isomer, NSC 613863.

CI 980 (NSC 613862; [S-(-)]) and NSC 613863 [R-(+)] are the two chiral isomers of ethyl 5-amino 1,2-dihydro-2-methyl-3-phenylpyrido[3,4-b]pyrazin-7-ylcar bamate (NSC 370147), which is a mitotic inhibitor with in vivo and in vitro activity against murine multidrug-resistant sublines. We have characterized the inhibition of in vitro microtubule assembly by the S (CI 980) and R (NSC 613863) enantiomers, their actions on the cytoplasmic microtubule network of epithelial-like PtK2 cells, and on the cell cycle of different human and murine leukemias and PtK2 cells. Assembly of purified tubulin, or tubulin plus microtubule-associated proteins, into microtubules was substoichiometrically inhibited by both compounds, which also induced a slow depolymerization of preassembled microtubules. Half inhibitory concentrations were 0.4-0.7 microM and 1.6-2.1 microM for the S and R isomers, respectively. Excess of both drugs induced polymerization of liganded tubulin into abnormal polymers similar to colchicine. The cytoplasmic microtubules of PtK2 cells were disrupted by both compounds in a concentration- and time-dependent manner, which was observed by indirect immunofluorescence microscopy and quantified by an enzyme-linked immunoassay of cytoskeletal tubulin. Half inhibitory concentrations were 6 nM S isomer, 100 nM R isomer, and 1 microM colchicine. Twenty nM S isomer or 500-700 nM R isomer gave nearly maximal effect. At these concentrations, half maximal microtubule depolymerization took place after 2 h of treatment. After drug removal, slow microtubule assembly and nearly complete reorganization of the cytoplasmic microtubules of PtK2 cells were observed (24 h). One nM S enantiomer or 25 nM R enantiomer induced mitotic arrest in 8 h in U937, HL60, and EL4 leukemias. PtK2 cells also stopped in mitosis after a 24-h incubation with 50 nM R isomer or 5 nM S isomer. The inhibition of cell division was irreversible in the leukemic cells, while PtK2 cells partially resumed growth. Although the interactions of CI 980 with microtubules in vitro are not very different from other drugs, it is a most potent cellular microtubule and mitotic inhibitor.

Animals↗

PubMed1993

Heterocyclic mono-N-oxides with potential applications as bioreductive anti-tumour drugs: Part 1. 8-Alkylamino-substituted phenylimidazo [1,2-a] quinoxalines.

A series of imidazo [1,2-a] quinoxaline mono-N-oxides and their 6- and 9-aza analogues have been substituted in the 8-position with a variety of secondary and tertiary amines, and the compounds evaluated as bioreductively activated cytotoxins. Cytotoxic action against hypoxic cells in vitro was critically dependent upon the structural nature of the 8-substituent and its basicity, with little dependence upon reduction potential. 1,2-Dihydro-8-(4-methylpiperazin-1-yl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (11) had differential hypoxic:oxic toxicity of 15.3 and some novel analogues had differential hypoxic:oxic toxicities of 7.5-17. Other related compounds with either substituted or unsubstituted 8-piperazinyl substituents, or certain straight-chain aminoalkyl substituents, show comparable activity in vitro. Less basic 8-substituents abolished activity, although the 8-morpholinyl derivatives (7 and 8) had differential hypoxic:oxic toxicities of 3-4. Substitution of the 4-phenyl ring with an electron-withdrawing group (F) improved hypoxic potency, but only with a small effect on hypoxic:oxic toxicity, whereas an electron-donating substituent (MeO) reduced hypoxic potency. Perhaps significantly, the 8-unsubstituted analogue 3 was 6-fold less potent, but had comparable differential cytotoxicity in vitro. The most effective novel hypoxia-selective cytotoxins synthesized were the bifunctional 2-nitro-imidazole derivative 1,2-dihydro-8-((4-(3-(2-nitro-1-imidazoyl)-1-hydroxypropyl)- piperazin-1-yl))-4-phenylimidazo [1,2-a] quinoxaline 5-oxide bishydrochloride (37) and its 9-aza analogue 38. These compounds also exhibited the lowest aerobic toxicities in vitro of the new compounds.

Antineoplastic Agents↗

PubMed1993

A micropuncture study on the renal site of action of ICI 206,970, a unique eukalemic diuretic.

The site of action of ICI 206,970, an aminomethylphenol pyrazine derivative, with effects on Na+ and water excretion similar to hydrochlorothazide, was determined using free-flow micropuncture and in vivo microperfusion techniques. Furosemide and ICI 206,970 were perfused into the loop of Henle, at a concentration of 10(-4) M. Furosemide reduced water, Na+ and K+ reabsorption by the loop, but ICI 206,970 had little effect. Amiloride and ICI 206,970 were perfused into the distal nephron at a concentration of 10(-4) M. Both compounds reduced the reabsorption of Na+ and secretion of K+, ICI 206,970 having a somewhat greater effect than amiloride at this dose. ICI 206,970 also reduced water reabsorption by the distal tubule. ICI 206,970 was infused i.v. at a dose of 10 mg/kg/hr into anesthetized rats, and its effect on reabsorption by various nephron segments was determined. This compound tended to reduce proximal reabsorption of Na+, K+ and water, but had little effect on reabsorption of electrolytes and water by the loop of Henle, or distal tubule reabsorption of Na+ and water. Distal K+ secretion decreased after administration of ICI 206,970. Reabsorption of electrolytes and water beyond the late distal nephron was not affected by the drug. Urinary excretion of Na+ and water was elevated, but K+ excretion remained unchanged after treatment with ICI 206,970. The sites of action of ICI 206,970 appear to be the proximal and distal nephron. Urinary excretion of Na+ and water was largely dependent on the effect of ICI 206,970 on proximal reabsorption, as this compound had little effect on loop of Henle or distal tubule reabsorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1996

Oncogenic potential of bifunctional bioreductive drugs.

Potential oncogenicity must be a factor of concern in the design and development of novel bioreductive drugs. In the present studies, the cytotoxicity and oncogenic transforming potential of a series of heterocyclic mono-N-oxides, designed to be used as bioreductive drugs, were examined using the mouse C3H 10T1/2 cell system. Exponential phase cultures of 10T1/2 cells were treated with graded doses of the bioreductive drugs for a 4 h period, either in air or hypoxia, at 37 degrees C. After treatment, cultures were replated for both survival and transformation assays. The fused pyrazine mono-N-oxide RB 90740 and its N-deoxy analogue, RB 92816, demonstrated a dose-dependent cytotoxicity and oncogenic transforming potency under aerobic conditions. Similarly, the indoloquinone E09 and the structurally related mitomycin C demonstrated dose dependence in both toxicity and oncogenic transforming potential. The most cytotoxic aromatic-N-oxides tested, RB 92816, also demonstrated the highest oncogenic transformation incidence. In hypoxia, the bioreductive metabolites of RB 90740 were substantially more cytotoxic and induced a higher oncogenic transformation yield than the drug in air. These data are consistent with the structure-activity relationship for bioreductive drugs in that heterocyclic-N-oxides with reactive side chains such as RB 92816 are cytotoxic and potentially carcinogenic.

Animals↗

PubMed1997

Metabolism and excretion of a novel antianxiety drug candidate, CP-93,393, in Long Evans rats. Differentiation of regioisomeric glucuronides by LC/MS/MS.

The absorption and metabolism of a novel antianxiety drug candidate, CP-93,393, ((7S, 9aS)-2-(pyrimidin-2-yl)-7-(succinimidomethyl)-octahydro-1H-p yrido[1, 2-a]pyrazine) were investigated in bile-cannulated Long Evans rats after oral administration of a single 30 mg/kg base equivalent dose of 14C-CP-93,393 (HCl salt). Urine, bile, plasma, and feces were collected and assayed for total radioactivity. Plasma samples were also analyzed for unchanged drug using an LC/MS/MS assay. Metabolic profiles of 14C-CP-93,393 were obtained in urine, bile, and plasma. Structural characterization of metabolites was carried out by LC/MS using a combination of full scan, product ion, constant neutral loss, and multiple reaction ion monitoring techniques. CP-93,393 was completely absorbed, as less than 1% of the administered radioactivity was recovered in the feces. The major portion of the radioactivity was recovered in bile, suggesting that the biliary route was the primary route of excretion. Total recovery of administered dose was 97.4 +/- 3.3% from male rats and 85.3 +/- 9.6% from female rats. Approximately 32% of the administered radioactive dose was recovered in urine of female rats, while only 20% was recovered in urine of male rats. In contrast, biliary recoveries of the radioactivity were higher for male rats (approximately 77% for males and 53% for females). Mean Cmax values for the unchanged CP-93, 393 and total radioactivity were significantly higher in the female rats than in the male rats. Similarly, mean AUC(0-t) values for the unchanged drug and radioactivity were also higher in female rats. These findings suggested that CP-93,393 was eliminated more rapidly in the male rats than in the female rats. CP-93,393 and a total of 16 metabolites were identified in urine, bile, and plasma. Based on the structures of oxidative metabolites, four metabolic pathways of CP-93,393 were identified: hydroxylation at the pyrimidine ring, hydroxylation at the succinimide ring, hydroxylation alpha to the nitrogen of the piperazine ring, and hydrolysis of amide bond of the succinimide ring. The major oxidative metabolites were excreted as sulfate and/or glucuronide conjugates. The structures of regioisomeric glucuronides were established by a novel tandem mass spectrometric technique. The glucuronides were dissociated at the orifice, and the resulting aglycones were then analyzed by MS/MS studies. The identified metabolites accounted for >90% of the total radioactivity present in urine, bile, and plasma.

Animals↗

PubMed1997

Metabolism and excretion of a new antianxiety drug candidate, CP-93,393, in cynomolgus monkeys: identification of the novel pyrimidine ring cleaved metabolites.

The metabolism and excretion of a new anxiolytic/antidepressant drug candidate, CP-93,393, ((7S, 9aS)-1-(2-pyrimidin-2-yl-octahydro-pyrido[1, 2-a]-pyrazin-7-yl-methyl)-pyrrolidine-2,5-dione) were investigated in cynomolgus monkeys after oral administration of a single 5 mg/kg dose of 14C-CP-93,393. Urine, bile, feces, and blood samples were collected and assayed for total radioactivity, parent drug, and metabolites. Total recovery of the administered dose after 6 days was 80% with the majority recovered during the first 48 hr. An average of 69% of the total radioactivity was recovered in urine, 4% in bile, and 7% in feces. Mean Cmax and AUC(0-infinity) values for the unchanged CP-93,393 were 143.2 ng/ml and 497.7 ng.hr/ml, respectively, in the male monkeys and 17.2 ng/ml and 13.7 ng.hr/ml, respectively, in the female monkeys. HPLC analysis of urine, bile, feces, and plasma from both male and female monkeys indicated extensive metabolism of CP-93,393 to several metabolites. The identification of metabolites was achieved by chemical derivatization, beta-glucuronidase/sulfatase treatment, and by LC/MS/MS, and the quantity of each metabolite was determined by radioactivity detector. CP-93,393 undergoes metabolism by three primary pathways, aromatic hydroxylation, oxidative degradation of the pyrimidine ring, and hydrolysis of the succinimide ring followed by a variety of secondary pathways, such as oxidation, methylation, and conjugation with glucuronic acid and sulfuric acid. The major metabolites, oxidation on the pyrimidine ring to form 5-OH-CP-93,393 (M15) followed by glucuronide and sulfate conjugation (M7 and M13), accounted for 35-45% of the dose in excreta. Two metabolites (M25 and M26) were formed by further oxidation of M15 followed by methylation of the resulting catechol intermediate presumably by catechol-O-methyl transferase. A novel metabolic pathway, resulting in the cleavage of the pyrimidine ring, was also identified. The metabolites (M18, M20, and M21) observed from this pathway accounted for 8-15% of the dose. Aliphatic hydroxylation of the succinimide ring was a very minor pathway in monkey. 5-Hydroxy-CP-93,393 (M15, 37-49%), its sulfate and glucuronide conjugates (M7 and M13, approximately 34%), and the pyrimidine ring cleaved product (M18, approximately 8%) were the major metabolites in monkey plasma. The identified metabolites accounted for approximately 90, 93, 97, and 92% of the total radioactivity present in urine, bile, plasma, and feces, respectively. The major in vivo oxidative metabolites were also observed after in vitro incubations with monkey liver microsomes.

Adrenergic alpha-2 Receptor Antagonists↗

PubMed1997

Treatment possibility of hypercholesterolaemia associated with hypertriglyceridaemia.

Thirty patients were investigated with hyperlipoproteinaemia, 15 patients with non-insulin dependent diabetes mellitus (NIDDM) and 15 with primary hyperlipoproteinaemia. The patients took 250 mg acipimox (5-metyl-pyrazine-carboxylic acid 4-oxide) 3 times per day for 2 months. Serum examinations were performed before and after 1 and 2 months of acipimox administration. After treatment the cholesterol and triglyceride levels decreased in both groups. Patients with NIDDM had 11% increase of high density lipoprotein-cholesterol (HDL-C) level at the end of the first, and 18% increase at the end of the second month, while patients with primary hyperlipoproteinaemia did not change significantly. The low density lipoprotein (LDL) level did not change significantly in either groups of patients. The apolipoprotein A 1 (apo A 1) levels increased significantly during the second month of acipimox administration. Uric acid levels decreased in both groups, but significant change could be detected mainly in the NIDDM group. Serum glucose level did not change in the non-diabetic patients, while it decreased significantly in the NIDDM group.

Apolipoprotein A-I↗

PubMed1998

Metabolism and excretion of a new anxiolytic drug candidate, CP-93, 393, in healthy male volunteers.

CP-93,393 [(7S,9aS)-1-(2-pyrimidin-2-yloctahydropyrido[1,2-a] pyrazin-7-ylmethyl)pyrrolidine-2,5-dione] is a new anxiolytic drug with highly selective serotonin 5-hydroxytryptamine 1A autoreceptor agonist, alpha2-adrenergic antagonist, and dopamine D2 agonist properties. The excretion, biotransformation, and pharmacokinetics of CP-93,393 were investigated in six healthy male volunteers after oral administration of a 5-mg dose of [14C]CP-93,393. The administered radioactivity was excreted predominantly in the urine. One week after administration of the dose, cumulative excretion amounted to 67.8 +/- 2.5% in the urine and 22.0 +/- 5.6% in the feces. In total, 89.8 +/- 5.7% of the radioactive dose was recovered in urine and feces. Mean maximum plasma concentration values for unchanged CP-93,393 were 10.92 and 1.02 ng/ml for poor metabolizers (PMs) and extensive metabolizers (EMs) of dextromethorphan, respectively. AUC0-infinity values for unchanged CP-93,393 were also greater for PMs than for EMs, whereas the mean maximum plasma concentration and AUC0-infinity values for total radioactivity were similar for the two phenotypes. Less than 0.5% of the dose was excreted in urine as unchanged drug for both EMs and PMs, suggesting extensive metabolism of CP-93,393 in both phenotypes. Hydroxylation at the 5-position of the pyrimidine ring was identified as the main metabolic pathway. 5-Hydroxy-CP-93,393 (M-15) and its glucuronide and sulfate conjugates (M-7 and M-13, respectively) accounted for approximately 51% of the administered dose in excreta of both PMs and EMs. Hydrolysis of the succinimide ring, in combination with 5-hydroxylation and/or conjugation or not, accounted for approximately 9% of the dose. A novel metabolite, apparently resulting from oxidative degradation of the pyrimidine ring, was characterized as the amidine analog M-18. M-15 (47-62%), its sulfate conjugate (M-13, approximately 9%), and the pyrimidine ring-cleaved product (M-18, 7-13%) were identified as the major circulating metabolites for both EMs and PMs. Therefore, CP-93,393 undergoes metabolism by three primary pathways, i.e. 1) aromatic hydroxylation followed by conjugation with glucuronic acid and sulfuric acid, 2) oxidative degradation of the pyrimidine ring, and 3) hydrolysis of the succinimide ring. The identified metabolites accounted for approximately 90, 91, and 92% of the total radioactivity present in urine, plasma, and feces, respectively. The major in vivo oxidative metabolites were also observed after in vitro incubations with human liver microsomes.

Administration, Oral↗

PubMed1997

Phase I and pharmacological study of CI-980, a novel synthetic antimicrotubule agent.

CI-980 (NSC 613862) is one of a novel class of 1,2-dihydropyrido[3, 4-b]pyrazines that inhibits tubulin polymerization, presumably by binding to the colchicine binding site of tubulin. In a Phase I and pharmacological study, 16 patients with advanced solid neoplasms were treated with CI-980 on a continuous 72-h infusion schedule at doses ranging from 3.0-5.4 mg/m2/day every 3 weeks. High rates of central nervous system (CNS) toxicity and neutropenia occurred in both minimally and heavily pretreated patients who were treated with CI-980 doses above 3.75 mg/m2/day, which is the maximum tolerated dose and the recommended dose for additional evaluations. CNS effects, characterized by neurocortical, mood, and cerebellar manifestations, were generally observed toward the end of the infusion and immediately posttreatment and usually resolved within 48 h after the completion of treatment. Toxicity was mild to modest at the 3.75 mg/m2/day dose level. Neither clinical nor pharmacological risk factors that may predispose patients to the development of CNS effects were evident. Although no objective antineoplastic activity was observed in this Phase I study, CI-980 steady-state plasma concentrations achieved at the recommended dose of 3.75 mg/m2/day (mean +/- SE, 5.74 +/- 0.54 nM) approached and exceeded concentrations that have been associated with significant activity in preclinical studies, indicating that additional disease-directed evaluations of CI-980 may be warranted.

Adult↗

PubMed1998

Measurement of interactions between polysaccharides and flavour compounds by exclusion size chromatography: advantages and limits.

Interactions between flavour compounds and polysaccharides have been studied by exclusion size chromatography, the Hummel and Dreyer method. Hydrogen bonding was found between 2-acetyl thiazole and dextrines of different degrees of polymerisation. The number of binding sites and the affinity constant increase by increasing the degree of polymerisation. Hydrogen bonding was also responsible for the interactions between xanthane and 1-octen-3-ol or 2-acetyl pyrazine, with 1 mole of 1-octen-3-ol bound per pentasaccharide repeating unit. Unfortunately, the number of flavour compounds, which can be studied with this method, is limited due to their low water solubility and their low UV absorption.

Chromatography, Gel↗

PubMed1998

Heat and storage effects on the flavour of peanuts.

Two peanut varieties, Giza 4 and Giza 5 were subjected to different heat treatments such as drying in solar drier at air speed 0.5 and 2 m/sec with average temperature 45 and 60 degrees C and heating in oven at 120 and 150 degrees C. The sensory evaluation of the two varieties showed insignificant differences among varieties and heating processes. A correlation between the sensory and instrumental data was found. The high sensory scores of samples heated at 150 degrees C were attributed to the presence of high concentration of pyrazines which were thought to contribute to flavour and aroma of fresh roasted peanut. A comparative study between the main chemical classes retained in peanut samples after storage for 3 months at room temperature showed that the aldehydes derived lipids increased significantly in the solar dried samples. The antioxidative components produced via Maillard reaction resulted in oxidative stability of the samples heated in oven.

Aldehydes↗

PubMed2000

Recognition-directed supramolecular assemblies of metal complexes of terpyridine derived ligands with self-complementary hydrogen bonding sites.

The synthesis and X-ray structures of three metal complexes with terpyridine-derived ligands that contain amino-pyrimidine and amino-pyrazine moieties are presented. They have been designed in view of directing their self-assembly into specific supramolecular arrays through molecular recognition interactions. The solid-state structures indeed reveal extensive hydrogen-bonded networks. The Co complex 4a with PF6- counterions builds a two-dimensional infinite interwoven grid through strong double hydrogen bonds (d(N-H-N) =2.918-3.018 A) between the amino groups and the N atoms of the rings, with all H-bonding sites saturated. Changing the anions to BF4- in 4b leads to a similar infinite but partially broken grid with a quarter of the H-bonding sites unsaturated (d(N-H-N)=2.984-3.206 A). In the case of the Zn complex 12 with triflate anions, half of the hydrogen bonds are formed. Only one of the two orthogonal ligands has hydrogen bonds (d(N-H-N) = 3.082, 3.096 A) to the neighbouring complexes and thus builds linear, supramolecular, polymeric chains. These structural differences are mainly attributed to crystal-packing effects caused by the different anions. The data presented here may also be regarded as a prototype for the generation of organised arrays through sequential self-assembly processes.

Journal Article↗

PubMed2000

Ladderlike oligomers; intramolecular hydrogen bonding, push-pull character, and electron affinity.

Symmetrical 2,5-bis(2-aminophenyl)pyrazines have been synthesized by application of the Stille coupling strategy. These cotrimers feature three important properties, namely strong intramolecular hydrogen bonding, push-pull character, and high electron affinity. The presence of intramolecular hydrogen bonds has been confirmed by 1H NMR, IR spectroscopy, and single-crystal X-ray diffraction. The hydrogen bond strength can be increased by substituting the amino groups with stronger electron-withdrawing functionalities. Despite the anticipated enhanced pi-conjugation through planarization, a hypsochromic shift was observed in the UV/Vis spectra, explained by a decrease in push-pull character. The electron affinity of the cotrimers was deduced from the first reduction potentials measured by cyclic voltammetry and is related to the electron-withdrawing character of the amino substituents. The results obtained have been compared with those of the corresponding 4-aminophenyl analogues and show that intramolecular hydrogen bonds can be used to design polymers with enhanced pi conjugation as well as a high electron affinity.

Journal Article↗

PubMed2002

Thermal-, pressure-, and light-induced spin transition in novel cyanide-bridged FeII-AgI bimetallic compounds with three-dimensional interpenetrating double structures (FeIILx[Ag(CN)2]2).G.

Low-spin, high-spin and spin-transition behaviours have been observed for the doubly interpenetrating three-dimensional bimetallic compounds (FeII(pz)[Ag(CN)2]2).pz (pz = pyrazine), (FeII(4,4'-bipy)2[Ag(CN)2]2) (4,4'-bipy = 4,4'-bipyridine), and (FeII(bpe)2[Ag(CN)2]2) (bpe = bispyridylethylene), respectively. The single crystals of the bpe derivative undergo a spin transition with a large hysteresis loop at about 95 K. After several warming and cooling cycles, the single crystals become a microcrystalline powder with 50% spin transition. Influence of pressure--as well as light-induced excited spin-state trapping (LIESST) on the thermal 50% spin transition of the microcrystalline sample has also been investigated. Thermal spin-transition behaviour has also been induced at pressures higher than 1 bar for the 4,4'-bipy derivative. Both the 4,4'-bipy and bpe derivatives show strong pressure dependence of the spin state at 300 K.

Journal Article↗

PubMed2002

Coupling of metal-based light-harvesting antennas and electron-donor subunits: trinuclear ruthenium(II) complexes containing tetrathiafulvalene-substituted polypyridine ligands.

Three new tetrathiafulvalene-substituted 2,2'-bipyridine ligands, cis-bpy-TTF(1), trans-bpy-TTF(1), and cis-bpy-TTF(2) have been prepared and characterized. X-ray analysis of trans-bpy-TTF(1) is also reported. Such ligands have been used to prepare two new trinuclear Ru(II) complexes, namely, [[(bpy)(2)Ru(micro-2,3-dpp)](2)Ru(bpy-TTF(1))](PF(6))(6) (9; bpy=2,2'-bipyridine; 2,3-dpp=2,3-bis(2'-pyridyl)pyrazine) and [[(bpy)(2)Ru(micro-2,3-dpp)](2)Ru(bpy-TTF(2))](PF(6))(6) (10). These compounds can be viewed as coupled antennas and charge-separation systems, in which the multichromophoric trinuclear metal subunits act as light-harvesting antennas and the tetrathiafulvalene electron donors can induce charge separation. The absorption spectra, redox behavior, and luminescence properties (both at room temperature in acetonitrile and at 77 K in a rigid matrix of butyronitrile) of the trinuclear metal complexes have been studied. For the sake of completeness, the mononuclear compounds [(bpy)(2)Ru(bpy-TTF(1))](PF(6))(2) (7) and [(bpy)(2)Ru(bpy-TTF(2))](PF(6))(2) (8) were also synthesized and studied. The properties of the tetrathiafulvalene-containing species were compared to those of the model compounds [Ru(bpy)(2)(4,4'-Mebpy)](2+) (4,4'-Mebpy=4,4'-dimethyl-2,2'-bipyridine) and [[(bpy)(2)Ru(micro-2,3-dpp)](2)Ru(bpy)](6+). The absorption spectra and redox behavior of all the new metal compounds can be interpreted by a multicomponent approach, in which specific absorption features and redox processes can be assigned to specific subunits of the structures. The luminescence properties of the complexes in rigid matrices at 77 K are very similar to those of the corresponding model compounds without TTF moieties, whereas the new species are nonluminescent, or exhibit very weak emissions relative to those of the model compounds in fluid solution at room temperature. Time-resolved transient absorption spectroscopy confirmed that the potentially luminescent MLCT states of 7-10 are significantly shorter lived than the corresponding states of the model species. Photoinduced electron-transfer processes from the TTF moieties to the (excited) MLCT chromophore(s) are held responsible for the quenching processes.

Journal Article↗