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PubMed2003

High thermodynamic stability and extraordinary kinetic inertness of copper(II) complexes with 1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid): example of a rare isomerism between kinetically inert penta- and hexacoordinated copper(II) complexes.

In an aqueous solution at room temperature, 1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid) (H(4)L(1)) and Cu(I) (I) form a pentacoordinated (pc) complex, pc-[Cu(L(1))](2-), exhibiting conformation I of the cyclam ring. At high temperature, the complex isomerises to a hexacoordinated isomer, trans-O,O-[Cu(L(1))](2-), with a trans-III conformation of the cyclam ring. In pc-[Cu(L(1))](2-), four ring nitrogen atoms and one phosphonate oxygen atom are arranged around Cu(I) (I) in a structure that is half-way between a trigonal bipyramid and a tetragonal pyramid, with one phosphonic acid group uncoordinated. In the trans-O,O-[Cu(L(1))](2-) isomer, the nitrogen atoms form a plane and the phosphonic acid groups are in a mutually trans configuration. A structurally very similar ligand, 4-methyl-1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid) (H(4)L(2)), forms an analogous pentacoordinated complex, pc-[Cu(L(2))](2-), at room temperature. However, the complex does not isomerise to the octahedral complex analogous to trans-O,O-[Cu(L(1))](2-). Because of the high thermodynamic stability of pc-[Cu(L(1))](2-), (logbeta=25.40(4), 25 degrees C, I=0.1 mol dm(-3) KNO(3)) and the formation of protonated species, Cu(I) (I) is fully complexed in acidic solution (-log [H(+)] approximately 3). Acid-assisted decomplexation of both of the isomers of [Cu(H(2)L(1))] takes place only after protonation of both uncoordinated oxygen atoms of each phosphonate moiety and at least one nitrogen atom of the cycle. The exceptional kinetic inertness of both isomers is illustrated by their half-lives tau(1/2)=19.7 min for pc-[Cu(H(2)L(1))] and tau(1/2) about seven months for trans-O,O-[Cu(H(2)L(1))] for decomplexation in 5 M HClO(4) at 25 degrees C. The mechanism of formation of pc-[Cu(L(1))](2-) is similar to those observed for other macrocyclic complexes.

Journal Article↗
PubMed2007

Exceptional affinity of nanostructured organic-inorganic hybrid materials towards dioxygen: confinement effect of copper complexes.

We report the exceptional reactivity towards dioxygen of a nanostructured organic-inorganic hybrid material due to the confinement of copper cyclam within a silica matrix. The key step is the metalation reaction of the ligand, which can occur before or after xerogel formation through the sol-gel process. The incorporation of a Cu(II) center into the material after xerogel formation leads to a bridged Cu(I)/Cu(II) mixed-valence dinuclear species. This complex exhibits a very high affinity towards dioxygen, attributable to auto-organization of the active species in the solid. The remarkable properties of these copper complexes in the silica matrix demonstrate a high cooperative effect for O(2) adsorption; this is induced by close confinement of the two copper ions leading to end-on mu-eta(1):eta(1)-peroxodicopper(II) complexes. The anisotropic packing of the tetraazamacrocycle in a lamellar structure induces an exceptional reactivity of these copper complexes. We show for the first time that the organic-inorganic environment of copper complexes in a silica matrix fully model the protecting role of protein in metalloenzymes. For the first time an oxygenated dicopper(II) complex can be isolated in a stable form at room temperature, and the reduced Cu(2) (I,I) species can be regenerated after several adsorption-desorption cycles. These data also demonstrate that the coordination scheme and reactivity of the copper cyclams within the solid are quite different from that observed in solution.

Adsorption↗
PubMed1994

Tumor incidence in a chemical carcinogenesis study of nonhuman primates.

This report covers a 32-year period of an ongoing chemical carcinogenesis study in nonhuman primates, which was initiated by the National Cancer Institute in 1961. Autopsy records of 373 breeders and normal controls showed very low incidence of spontaneous malignant tumors in cynomolgus (1.5%) and rhesus (2.8%) monkeys, but considerably higher incidence in African green monkeys (8%). A large number of substances including a variety of food additives, food components, environmental contaminants, N-nitroso compounds, "classical" rodent carcinogens, antineoplastic agents, and immunosuppressive agents have been evaluated for long-term carcinogenic activity. Food components tested which are probably most relevant to human exposure are the artificial sweeteners, cyclamate and saccharin. After 22 years of continuous dosing, neither cyclamate nor saccharin have shown any evidence of carcinogenic effects. Similarly, the tumorigenic potential of arsenic and DDT was negligible after dosing for 15-22 years. In contrast, the fungal food contaminants, aflatoxin B1 (AFB1) and sterigmatocystin (SMT), were found to be potent hepatocarcinogens. AFB1 also induced adenocarcinomas of the pancreas, osteosarcomas, and other tumors. Also, the aglycone of cycasin, MAM acetate, induced a variety of tumors, but primarily hepatocellular and renal cell carcinomas. The compounds most recently introduced into the colony include three heterocyclic amines present in cooked meat. One of these compounds, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) has proven to be one of the most potent hepatocarcinogens in the history of the monkey project, inducing malignant liver tumors in 65% of animals over a 7-year period of exposure. Of the classical rodent carcinogens studied, urethane was the only one which produced malignant tumors in the monkeys. Conversely, all except two of the N-nitroso compounds were carcinogenic. Diethylnitrosamine (DENA) was the most potent and predictable hepatocarcinogen in cynomolgus, rhesus, and African green monkeys. However, when administered intraperitoneally to galagos (a prosimian), DENA induced primarily mucoepidermoid carcinoma of the nasal cavity. N-Methyl-N-nitrosourea (MNU) was the only carcinogen persistently producing tumors in the digestive tract, mostly squamous cell carcinomas of the esophagus. Among the antineoplastic and immunosuppressive agents, procarbazine (MIH) was the only unequivocal carcinogen, with a 33% tumor incidence, causing acute nonlymphocytic leukemia in most of the cases.

Animals↗
PubMed1984

Effects of solute concentration on vasopressin stimulated cyclic AMP generation in the rat medullary thick ascending limbs of Henle's loop.

We examined effects of osmolality or sodium concentration on vasopressin induced cyclic AMP generation in the medullary thick ascending limbs isolated from collagenase treated rat kidneys. Vasopressin-stimulated cyclic AMP generation was increased as a function of NaCl concentration of the incubation medium. Addition of sucrose was also effective in enhancing the vasopressin-stimulated cyclic AMP, whereas addition of urea was without effect. When incubation medium was made hypertonic with sodium cyclamate, vasopressin-stimulated cyclic AMP generation was also enhanced. When choline chloride was used instead of sodium cyclamate, only an insignificant increase in the hormone-stimulated cyclic AMP generation was observed. These results suggest that the responsiveness of the rat medullary thick ascending limbs to vasopressin is regulated, at least in part, by transmembrane osmotic gradient.

Animals↗
PubMed1985

Electrogenic calcium transport in plasma membrane of rat pancreatic acinar cells.

ATP-dependent 45Ca2+ uptake was investigated in purified plasma membranes from rat pancreatic acinar cells. Plasma membranes were purified by four subsequent precipitations with MgCl2 and characterized by marker enzyme distribution. When compared to the total homogenate, typical marker enzymes for the plasma membrane, (Na+,K+)-ATPase, basal adenylate cyclase and CCK-OP-stimulated adenylate cyclase were enriched by 43-fold, 44-fold, and 45-fold, respectively. The marker for the rough endoplasmic reticulum was decreased by fourfold compared to the total homogenate. Comparing plasma membranes with rough endoplasmic reticulum, Ca2+ uptake was maximal with 10 and 2 mumol/liter free Ca2+, and half-maximal with 0.9 and 0.5 mumol/liter free Ca2+. It was maximal at 3 and 0.2 mmol/liter free Mg2+ concentration, at an ATP concentration of 5 and 1 mmol/liter, respectively, and at pH 7 for both preparations. When Mg2+ was replaced by Mn2+ or Zn2+ ATP-dependent Ca2+ uptake was 63 and 11%, respectively, in plasma membranes; in rough endoplasmic reticulum only Mn2+ could replace Mg2+ for Ca2+ uptake by 20%. Other divalent cations such as Ba2+ and Sr2+ could not replace Mg2+ in Ca2+ uptake. Ca2+ uptake into plasma membranes was not enhanced by oxalate in contrast to Ca2+ uptake in rough endoplasmic reticulum which was stimulated by 7.3-fold. Both plasma membranes and rough endoplasmic reticulum showed cation and anion dependencies of Ca2+ uptake. The sequence was K+ greater than Rb+ greater than Na+ greater than Li+ greater than choline+ in plasma membranes and Rb+ greater than or equal to K+ greater than or equal to Na+ greater than Li+ greater than choline+ for rough endoplasmic reticulum. The anion sequence was Cl greater than or equal to Br greater than or equal to 1 greater than SCN greater than NO3 greater than isethionate greater than cyclamate greater than gluconate greater than SO2(4) greater than or equal to glutarate and Cl- greater than Br greater than gluconate greater than SO2(4) greater than NO3 greater than 1 greater than cyclamate greater than or equal to SCN, respectively. Ca2+ uptake into plasma membranes appeared to be electrogenic since it was stimulated by an inside-negative K+ and SCN diffusion potential and inhibited by an inside-positive diffusion potential. Ca2+ uptake into rough endoplasmic reticulum was not affected by diffusion potentials. We assume that the Ca2+ transport mechanism in plasma membranes as characterized in this study represents the extrusion system for Ca2+ from the cell that might be involved in the regulation of the cytosolic Ca2+ level.

Adenosine Triphosphate↗
PubMed1990

The role of sucrose-sensitive neurons in ingestion of sweet stimuli by hamsters.

The relationship between sweet preference and activity in sucrose-sensitive chorda tympani nerve fibers was investigated in hamsters (Mesocricetus auratus). Without exception, hamsters increased consumption of aqueous solutions of nonsweet 0.1 M NaCl, 0.001 M quinine-HCl, 0.01 M citric acid, 0.001 M dithiothreitol, 0.01 M pyridine, 0.01 M 2-phenylethanol, 0.005 M i-amyl acetate, 0.01 M vanillin, half-saturated 1-menthol and 0.033 mM capsaicin if they were made sweet by adding 0.5 M sucrose. Since sucrose activates chorda tympani S fibers, activity in these nerve fibers may be sufficient for increased preference. To determine if S-fiber activity is necessary for preference, equally preferred sweet stimuli were presented to the tongue while recording responses of single chorda tympani fibers. S fibers were clearly activated by 0.03 M sucrose, 0.001 M Na saccharin, 0.01 M D-phenylalanine, 0.1 M glycine, 0.005 M dulcin and 0.03 M Na 2-mercaptoethanesulfonate but not by 0.01 M Ca cyclamate and 0.003 M Na 3-nitrobenzenesulfonate. Ca cyclamate weakly activated H fibers and Na 3-nitrobenzenesulfonate weakly activated N fibers. Thus, S-fiber chorda tympani activity may be sufficient but not necessary for sweet preference, which may be influenced by activity in fibers of other taste nerves.

Animals↗
PubMed1994

Experimental study of the internal signal of alliesthesia induced by sweet molecules in rats.

To identify the preabsorptive signal that arouses alliesthesia, we compared the effects of five sweet molecules: glucose (3 g.5 ml-1), cyclamate (0.280 g.5 ml-1), saccharin (0.016 g.5 ml-1), aspartame (0.020 g.5 ml-1), and mannitol (3 g.5 ml-1) on the intestive aversive responses of rats. In Experiment 1, the sweet stimuli were adjusted to taste similarly sweet, and they were administered orally; they aroused similar ingestive responses. In Experiment 2, an isovolumetric load of each of the five molecules was administered in the stomach and its influence on ingestive/aversive response aroused by oral sucrose was recorded. Negative alliesthesia was obtained after gastric loads of glucose and mannitol, but not after gastric loads of cyclamate, saccharin, and aspartame.

Administration, Oral↗
PubMed1981

Studies to evaluate artificial sweeteners, especially Remsen--Fahlberg saccharin, and their possible impurities, for potential mutagenicity by the Salmonella/mammalian liver microsome test.

Cyclamate, cyclohexylamine, saccharin, boiled saccharin, 3 organic extracts of this sweetener and 9 possible impurities, including OTS and PTS, were evaluated for potential mutagenic activity by the Salmonella/mammalian liver microsome test on Salmonella typhimurium TA1535, TA100, TA1537 and TA98 (extracts only on TA98) with doses up to at least 2500 micrograms per plate with and without metabolic activation. No mutagenic activity was established either for cyclamate, cyclohexylamine or saccharin, or for some of the possible impurities of saccharin synthesized by the Remsen--Fahlberg or Maumee process. Only 1 organic extract gave inconclusive results in 3 consecutive experiments. No mutagenic activity was noted for saccharin refluxed for 2 h in solution.

Animals↗
PubMed1976

Long-term and multigeneration toxicity studies with cyclohexylamine hydrochloride.

Cyclohexylamine (CHA), the metabolite of cyclamate produced in varying degree by gastrointestinal microorganisms, was subjected to a 2-year multi-generation feeding study in rats, at dosages of 15, 50, 100, and 150 mg/kg/d. Observations included growth, feed efficiency, clinical and hematological tests, reproduction, teratology, mortality and gross and microscopic pathology. Rats from the first litters of each generation from F0 through F4 were mated to produce the next succeeding generation. Those from the second litters of F1 through F4 were also mated, half the dams being delivered by hysterotomy for teratological examination, while litters from the other half were raised to maturity. Except for some non-progressive growth retardation in the higher dosage groups, due to lower food consumption, the physical and clinical observations in the test groups fell substantially within normal limits and were not significantly different from the untreated controls. Reproduction rates were normal in all groups but at the higher dosages the size of the litters and their weaning weights were slightly reduced. At the 150 mg/kg level, histopathological examination revealed mucosal thickening of the bladder walls and evidence of renal calcification; however, no bladder tumors were seen, such as occurred in the chronic feeding study in which rats received 2500 mg/kg of a cyclamate: saccharin (10 : 1) mixture. A significantly higher incidence of testicular atrophy, characteristic of aged rats, was observed in the F0 group at the highest dosage level; however, these males continued to be fertile, in two cases up to 6 consecutive matings.

Animals↗
PubMed1976

Sugar binding to purified fractions from bovine taste buds and epithelial tissue. Relationships to bioactivity.

Binding of various sugars was compared in purified subfractions of taste buds isolated from bovine circumvallate papillae and of non-taste bud-bearing epithelium isolated from tissue surrounding these papillae. Binding of 14C-labeled sugars was greater in purified subfractions obtained from taste bud than from non-taste bud-bearing tissue and was, in general, greater in those taste bud subfractions in which a greater membrane purification was achieved. Binding specificity of the 14C-labeled sugars sucrose, fructose, glucose and of 14C-labeled cyclamate and saccharine was measured by competition of each 14C-labeled sugar or synthetic sweetener with its unlabeled homologous sugar in P4(B) taste bud subfractions; this binding, as shown for sucrose, was reversible and temperature dependent. Essentially no competition of the 14C-lageled sugars sucrose, fructose, glucose or 14C-labeled cyclamate and saccharine by their respective unlabeled homologues occurred in epithelial tissue P4(B) subfractions; this binding was not reversible. Binding specificity was further observed by the competition of 14C-labeled sucrose, fructose and glucose with each unlabeled sugar for binding sites on P4(B) taste bud subfractions; unlabeled sucrose was more effective in competing with each 14C-labeled surgar than was unlabeled fructose or glucose. The relatively non-sweet sugar lactose did not compete with 14C-labeled lactose in P4(B) subfractions from either taste bud or non-taste bud-bearing epithelial tissue. Binding of 14C-labeled sucrose in purified P4(B) bud subfractions was inhibited by increased concentrations of unlabeled sucrose, phospholipase C, neuraminidase, EDTA, NaCl and urea. Dissociation constants for sugar or synthetic sweetener binding were low (approx. 10(-3) M) but in a rank order (sucrose greater than fructose greater than glucose greater than saccharine) consistent with preference and electrophysiological responses in cow. The cow is behaviorally indifferent to saccharine and lactose consistent with the data obtained in the present study.

Animals↗
PubMed1987

Labeling of antibodies with 64Cu using a conjugate containing a macrocyclic amine chelating agent.

The conjugation of a model antibody (rabbit-anti-HSA-IgG) with a functionalized derivative of cyclam (1-(3-aminopropyl)-4-methyl-1,4,8,11-tetraazacyclotetradecane) is reported. Coupling of this derivative to the antibodies was accomplished using commercially available heterobifunctional coupling agents. The conjugation technique produced minimal effects on the antibody binding activity. 64Cu complexes with this cyclam derivative have excellent stability in human serum and aqueous solutions containing 1 mM EDTA. The high stability of these Cu-complexes suggests that this system, or other analogous systems, may be useful for production of stable 67Cu-immunotherapeutic agents.

Copper Radioisotopes↗
PubMed2005

The 188Re(III)-EDTA complex--a multipurpose starting material for the preparation of relevant 188Re complexes under mild conditions.

An easy and gentle method for the preparation of 188Re(V) complexes with bidentate and tetradentate ligands is described starting from the precursor complex 188Re(III)-EDTA. That complex is prepared at room temperature in acidic solution and reacts by a combined re-oxidation/ligand exchange reaction with appropriate ligands like DMSA or ECD (DMSA = dimercapto succinic acid, ECD = L,L-ethylene dicysteine diethyl ester) or en, tau, and cyclam (en = ethylene diamine, tau = 1,4,8,11-tetraazaundecane, cyclam = 1,4,8,11-tetraazacyclo-tetradecane) to the 188Re(V)-oxo- and dioxocomplexes, respectively. The chelates were unambiguously identified by chromatographic comparison with spectroscopically characterised samples or known 99mTc-kit reconstitutions. The reaction succeeds under mild conditions (room temperature, short time, neutral or weak basic solutions) with high yields and has potential for labelling of sensitive biomolecules with 188Re.

Journal Article↗
PubMed2006

Development of a new oat-based probiotic drink.

In the present work, a whole-grain oat substrate was fermented with lactic acid bacteria to obtain a drink, combining the health benefits of a probiotic culture with the oat prebiotic beta-glucan. The levels of several factors, such as starter culture concentration, oat flour and sucrose content, affecting the fermentation process, were established for completing a controlled fermentation for 8 h. The viable cell counts reached at the end of the process were about 7.5 x 10(10) cfu ml(-1). It was found that the addition of sweeteners aspartame, sodium cyclamate, saccharine and Huxol (12% cyclamate and 1.2% saccharine) had no effect on the dynamics of the fermentation process and on the viability of the starter culture during product storage. Beta-glucan content in the drink (0.31-0.36%) remained unchanged both throughout fermentation and storage of the drink. The shelf life of the oat drink was estimated to 21 days under refrigerated storage.

Avena↗
PubMed1998

The in vivo behavior of copper-64-labeled azamacrocyclic complexes.

The use of copper radioisotopes in imaging and therapy applications has created a greater need for bifunctional chelates (BFCs) for complexing copper radioisotopes to biomolecules. It has been demonstrated that the charge and lipophilicity of the Cu-BFC complex has a significant effect on the in vivo behavior of the radiolabeled Cu-BFC-biomolecule conjugate. To evaluate the effects of charge, stability, and macrocyclic backbone size on the biological behavior of 64Cu complexes, a series of macrocyclic 64Cu complexes have been prepared, and the biodistributions of these agents were evaluated in normal Sprague-Dawley rats. Two macrocyclic backbones, dodecane and tetradecane, were evaluated; cyclen, DOTA, and DO2A were dodecane backbone derivatives, and cyclam, TETA, and et-cyclam were tetradecane backbone derivatives. The biodistributions of the 64Cu-labeled complexes correlated with differences in the size of the macrocycle backbone and the formal charge of the complex. All compounds showed uptake and clearance through the liver and kidneys; however, the positively charged 64Cu complexes showed significantly higher uptake in both of these organs than did the negatively charged or neutral complexes. 64Cu-TETA, a negatively charged complex with the tetradecane backbone, had the most efficient clearance by 24 hours' postinjection. These data suggest that negatively charged complexes may have more favorable clearance properties when used as BFCs.

Animals↗
PubMed2000

Spectroscopic properties and ligand field analysis of cis-diazido(1,4,8,11-tetraazacyclotetradecane)chromium(III) azide.

The emission and excitation spectra of cis-[Cr(cyclam)(N3)2](N3) (cyclam = 1,4,8,11-tetraazacyclotetradecane) taken at 77 K are reported. The infrared and visible spectra at room temperature are also measured. The vibrational intervals due to the electronic ground state are extracted from the far-infrared and emission spectra. The ten electronic bands due to spin-allowed and spin-forbidden transitions are assigned. Using the observed transitions, a ligand field analysis has been performed to determine the bonding property of azido group in the chromium(III) complex. It is found that azide ligand has weak sigma- and pi-donor properties toward chromium(III) ion. The zero-phonon line in the excitation spectrum splits into two components by 249 cm(-1), and the large 2Eg splitting can be reproduced by the ligand field theory.

Absorption↗
PubMed2001

Synthesis of 14-oxa-1,4,8,11-tetraazabicyclo[9.5.3]nonadecane(L1) and a spectroscopic and structural study of [Ni(L1)(ClO4)](ClO4) and of the macrobicyclic precursor diamide complex, [Ni(HL2)](ClO4); chloride substitution kinetics of the corresponding [Ni(III)(L1)]3+ species.

The pentadentate ligand 14-oxa-1,4,8,11-tetraazabicyclo[9.5.3]nonadecane (L1) has been synthesized by the high dilution cyclization of 1-oxa-4,8-diazacyclododecane ([10]aneN(2)O) (1) with 1,3-bis(alpha-chloroacetamido)propane (2) and subsequent reduction of the diamide intermediate. The structure [Ni(L1)(ClO(4))](ClO(4)) (P2(1)/c (no. 14), a = 8.608(3), b = 16.618(3), c = 14.924(4) A, beta = 91.53(3) degrees converged at R = 0.050 (R(w) = 0.046) for 307 parameters using 2702 reflections with I > 2sigma(I). For the nickel(II) complex of the (monodeprotonated) precursor diamide ligand 14-oxa-1,4,8,11-tetraazabicyclo[9.5.3]nonadecane-3,9-dione (H(2)L2), [Ni(HL2)](ClO(4)) (Pbca (no. 61), a = 15.1590(3), b = 13.235(2), c = 18.0195(6) A), the structure converged at R = 0.045 (R(w) = 0.038) for 265 parameters using 1703 reflections with I > 3sigma(I). In the reduced system, the cyclam-based ligand adopts a trans-III configuration. The [Ni(L1)(ClO(4))](2+) ion is pseudooctahedral with the Ni-O(ether) 2.094(3) A distance shorter than the Ni-O(perchlorate) 2.252(4) A. The nickel(II) and nickel(III) complexes are six-coordinate in solution. Oxidation of [Ni(L1)(OH(2))](2+) with K(2)S(2)O(8) in aqueous media yielded an axial d(7) Ni(III) species (g( perpendicular) = 2.159 and g( perpendicular) = 2.024 at 77 K). The [Ni(L1)(solv)](2+) ion in CH(3)CN showed two redox waves, Ni(II/I) (an irreversible cathodic peak, E(p,c) = -1.53 V) and Ni(III/II) (E(1/2) = 0.85 V (reversible)) vs Ag/Ag(+). The complex [Ni(HL2)](ClO(4)) displays square-planar geometry with monodeprotonation of the ligand. The ether oxygen is not coordinated. Ni-O(3) = 2.651(6) A and Ni-O(3a) = 2.451(12) A, respectively. The Ni(III/II) oxidation at E(1/2) = 0.24 V (quasi-reversible) vs Ag/Ag(+) is considerably lower than the saturated system. The kinetics of Cl(-) substitution at [Ni(L1)(solv)](3+) are pH dependent. Detachment of the ether oxygen atom is proposed, with insertion of a protonated water molecule which deprotonates at a pK(a) more acidic than in the corresponding cyclam complex. Mechanistic implications are discussed.

Journal Article↗
PubMed2002

Electronic energy self-exchange with macrocyclic chromium(III) complexes.

The luminescence lifetimes of N-deuterated Cr(III) complexes of macrocyclic tetraamine ligands, trans-CrN(4)X(2)(n)()(+), are substantially longer than those of their undeuterated counterparts in room temperature solution. Thus, excited-state emission quenching of the longer lived species by the shorter lived species may be studied by analyzing the decay profile following pulsed excitation. Flash photolysis experiments were carried out for three deuterated/undeuterated pairs of trans-CrN(4)X(2)(n)()(+) complexes (where X = CN-, NH(3), and F-). For the trans-Cr(cyclam)(CN)(2)(+) system in H(2)O, it was determined that energy transfer was occurring between the deuterated and undeuterated species. Although the rate constant of energy transfer was too fast to measure explicitly, it could be bracketed as k(et) >>7 x 10(6) M(-1) s(-1). For this reaction it was possible to measure an equilibrium constant which was very near 1.0. For trans-Cr(cyclam)(NH(3))(2)(3+) in DMSO, it was also established that energy transfer was occurring and rate constants of 2.4 x 10(6) M(-1) s(-1) (mu = 0.1) and 9.7 x 10(6) M(-1) s(-1) (mu = 1.0) were determined by a Stern-Volmer analysis. For trans-Cr(tet a)F(2+) in H(2)O, no energy transfer was observed, which implies that the rate constant is <<3 x 10(5) M(-1) s(-1). Because these energy-transfer reactions represent self-exchange energy transfer and are thus thermoneutral, we are able to analyze the results using Marcus theory and draw some conclusions about the relative importance of nuclear reorganization and electronic factors in the overall rate.

Algorithms↗
PubMed2002

Variation in the coordination mode of arenedisulfonates: syntheses and structural characterization of mononuclear and dinuclear cadmium(II) arenedisulfonate complexes with two- to zero-dimensional architectures.

Seven cadmium(II) arenedisulfonate compounds, namely [Cd(2,2'-bpy)(2)(H(2)O)(peds)].4H(2)O (1), [Cd(2)(2,2'-bpy)(4)(H(2)O)(2)(1,5nds)](1,5nds).4H(2)O (2), [Cd(cyclam)(1,5nds)](2) (3), ([Cd(inia)(2)(H(2)O)(2)(2,6nds)].4H(2)O)(n)(4), ([Cd(inia)(2)(H(2)O)(2)(bpds)].4H(2)O)(n)(5), ([Cd(2)(inia)(4)(H(2)O)(3)(peds)(2)].2H(2)O)(n)(6), and [Cd(1,5nds)(H(2)O)(2)](n) (7), where 2,2'-bpy = 2,2'-bipyridyl, cyclam = 1,4,8,11-tetraazacyclotetradecane, inia = isonicotinamide, nds = naphthalenedisulfonate, bpds = 4,4'-biphenyldisulfonate, and peds = 4,4'-phenyletherdisulfonate, have been obtained from aqueous solution by using similar procedures and structurally characterized by X-ray single-crystal diffraction, IR spectroscopy, and thermal gravimetric analysis. In 1, the peds anion coordinates as a monodentate ligand, leading to a mononuclear unit. In 2 and 3, the 1,5nds anions coordinate as mu(2)-bridging ligands in different modes, producing charged or neutral dinuclear clusters. In 4 and 5, 2,6nds and bpds behave as mu(2)-spacers, resulting in 1-dimensional polymers. While in 6, the peds acts both as terminal and bridging ligands with the SO(3)(-) groups being either monodentate or mu(2)-bridging, creating a knotted 1-dimensional polymer with dinuclear clusters as the repeating units. In 7, 1,5nds acts as a bridging ligand with each SO(3)(-) coordinated as a mu(2)-bridging group to adjacent Cd(II) centers, leading to a 2-dimensional polymer. Together with the reported ([Cu(en)(2)(1,5nds)].2H(2)O)(n) (8), all of the six possible coordination modes adopted by organodisulfonate anions, on the assumption that each SO(3)(-) group could be monodentate or mu(2)-bridging, are realized by introducing nitrogen-containing organic ligands as auxiliaries.

Journal Article↗