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At least 19 recordsLinked to original sources
PubMed2005

Effects of steric constraint on chromium(III) complexes of tetraazamacrocycles, 2. Comparison of the chemistry and photobehavior of the trans-dichloro- and trans-dicyano- complexes of cyclam, 1,4-C2-cyclam, and 1,11-C3-cyclam.

The synthesis and characterization of several Cr(III) complexes of the constrained macrocyclic ligand 1,11-C3-cyclam (1,4,8,11-tetraazabicyclo[9.3.3]heptadecane) is reported. Only trans complexes are formed, and the structure of trans-[Cr(1,11-C3-cyclam)Cl2]PF6 is presented. The chemical and photophysical behavior of the 1,11-C3-cyclam complexes are compared with those of the corresponding cyclam (1,4,8,11 tetraazacyclotetradecane) and 1,4-C2-cyclam (1,4,8,11-tetraazabicyclo[10.2.2]hexadecane) complexes. The aquation rate of trans-[Cr(1,11-C3-cyclam)Cl2]+ is similar to that of the corresponding 1,4-C2-cyclam complex and is more than 5 orders of magnitude faster than the cyclam counterpart. A monotonic increase in the extinction coefficient is observed on going from the cyclam complexes to the 1,11-C3-cyclam complexes to the 1,4-C2-cyclam complexes, and this is related to the degree of centrosymmetry in each complex. The trans-[Cr(1,11-C3-cyclam)(CN)2]+ complex is a weak emitter in aqueous solution with a room-temperature emission maximum at 724 nm (tau=23 micros). Like the corresponding 1,4-C2-cyclam complex (tau=0.24 micros), the 1,11-C3-cyclam complex shows no deuterium-isotope effect in room-temperature solution. This is in marked contrast to the corresponding cyclam complex which has an emission lifetime of 335 micros and a significant deuterium isotope effect in room-temperature solution. Low temperature (77K) data are also presented in an attempt to understand the differences in photophysical behavior.

Aza Compounds↗
PubMed2000

Mononuclear (nitrido)iron(V) and (oxo)iron(IV) complexes via photolysis of [(cyclam-acetato)FeIII(N3)]+ and ozonolysis of [(cyclam-acetato)FeIII(O3SCF3)]+ in water/acetone mixtures.

Reaction of the monoanionic, pentacoordinate ligand lithium 1,4,8,11-tetraazacyclotetradecane-1-acetate, Li(cyclam-acetate), with FeCl3 yields, upon addition of KPF6, [(cyclam-acetato)FeCl]PF6 (1) as a red microcrystalline solid. Addition of excess NaN3 prior to addition of KPF6 yields the azide derivative [(cyclam-acetato)FeN3]PF6 (2a) as orange microcrystals. The X-ray crystal structure of the azide derivative has been determined as the tetraphenylborate salt (2b). Reaction of 1 with silver triflate yields [(cyclam-acetato)Fe(O3SCF3)]PF6 (3), which partially dissociates triflate in nondried solvents to yield a mixture of triflate and aqua bound species. Each of the iron(III) derivatives is low-spin (d5, S = 1/2) as determined by variable-temperature magnetic susceptibility measurements, Mössbauer and EPR spectroscopy. The low-spin iron(II) (d6, S = 0) complexes 1red and 2ared have been prepared by electrochemical and chemical methods and have been characterized by Mössbauer spectroscopy. Photolysis of 2a at 419 nm in frozen acetonitrile yields a nearly colorless species in approximately 80% conversion with an isomer shift delta = -0.04 mm/s and a quadrupole splitting delta EQ = -1.67 mm/s. A spin-Hamiltonian analysis of the magnetic Mössbauer spectra is consistent with an FeV ion (d3, S = 3/2). The proposed [(cyclam-acetato)FeV=N]+ results from the photooxidation of 2a via heterolytic N-N cleavage of coordinated azide. Photolysis of 2a in acetonitrile solution at -35 degrees C (300 nm) or 20 degrees C (Hg immersion lamp) results primarily in photoreduction via homolytic Fe-Nazide cleavage yielding FeII (d,6 S = 0) with an isomer shift delta = 0.56 mm/s and quadrupole splitting delta EQ = 0.54 mm/s. A minor product containing high-valent iron is suggested by Mössbauer spectroscopy and is proposed to originate from [((cyclam-acetato)Fe)2(mu-N)]2+ with a mixed-valent (FeIV(mu-N)FeIII))4+S = 1/2 core. Exposure of 3 to a stream of oxygen/ozone at low temperatures (-80 degrees C) in acetone/water results in a single oxidized product with an isomer shift delta = 0.01 mm/s and quadrupole splitting delta EQ = 1.37 mm/s. A spin-Hamiltonian analysis of the magnetic Mössbauer yields parameters similar to those of compound II of horseradish peroxidase which are consistent with an FeIV=O monomeric complex (S = 1).

Journal Article↗
PubMed2006

Design of an NO photoinduced releaser xerogel based on the controlled nitric oxide donor trans-[Ru(NO)Cl(cyclam)](PF6)2 (cyclam=1,4,8,11-tetraazacyclotetradecane).

The immobilization and properties of the nitric oxide donor trans-[Ru(NO)Cl(cyclam)](PF(6))(2), RuNO, entrapped in a silica matrix by the sol-gel process is reported herein. The entrapped nitrosyl complex was characterized by spectroscopic (UV-vis, infrared (IR), X-ray photoelectron, and (13)C and (29)Si MAS NMR) and electrochemical techniques. The entrapped species exhibit one characteristic absorption band in the UV-vis region of the electronic spectrum at 354 nm and one IR nu(NO) stretching band at 1865 cm(-1), as does the RuNO species in aqueous solution. Our results show that trans-[Ru(NO)Cl(cyclam)](PF(6))(2) can be entrapped in a SiO(2) matrix with preservation of the molecular structure. However, in a SiO(2)/SiNH(2) matrix, the complex undergoes a nucleophilic attack by the amine group at the nitrosonium. Irradiation of the complex, entrapped in the SiO(2) matrix, with light of 334 nm, resulted in NO release. The material was regenerated to its initial nitrosyl form by reaction with nitric oxide.

Amines↗
PubMed1999

Stepwise Complexation of Ni(II) and Cu(II) Ions by 6,6'-C-spirobi(cyclam) (cyclam = 1,4,8,11-Tetraazacyclotetradecane), L(1). Syntheses and Redox Chemistry of [M(H(2)L(1))]X(4) (M = Cu(2+), Ni(2+)), [Cu(2)(L(1))]X(4), and [CuNi(L(1))]X(4) (X = ClO(4)(-)) and the X-ray Crystal Structure of [Cu(2)(L(1))](ClO(4))(4).

In aqueous HClO(4), the cation [H(4)(L(1))](4+) where L(1) is 6,6'-C-spirobi(cyclam) (cyclam = 1,4,8,11-tetraazacyclotetradecane), complexes Cu(2+) and Ni(2+) ions in a stepwise fashion to form [M(H(2)L(1))](ClO(4))(4) (M = Cu(2+) and Ni(2+)) from which [CuNi(L(1))](ClO(4))(4) has been prepared selectively. The preparation and the structure of [Cu(2)(L(1))](ClO(4))(4) (empirical formula, C(19)H(44)N(8)Cu(2)Cl(4)O(16); space group, triclinic; P&onemacr;; a = 8.1815(6) Å, b = 12.6098(9) Å, c = 16.6565(12) Å, alpha = 80.3890(10) degrees, beta = 76.5840(10) degrees, gamma = 87.1750(10) degrees, V = 1647.9(2) Å(3), and Z = 2; of the 9531 total reflections collected, 6779 reflections with I > 2sigma(I) on least-squares refinement provided final R(1) = 0.0657 and wR(2) = 0.1424) are also reported. The cyclic voltammograms (1.0 M NaCl, 0.1 M H(+); Pt electrodes; all E(1/2) vs NHE) of [M(H(2)L(1))](4+) (M = Cu(2+) and Ni(2+)) ions show single waves for the Cu(II)/Cu(III) couple (E(1/2) = 0.79 V, irreversible) and the Ni(II)/Ni(III) couple (E(1/2) = 0.56 V, reversible), respectively. In CH(3)CN (0.1 M Et(4)NClO(4)), the [Cu(2)(L(1))](4+) ion shows a reversible wave for the Cu(II)-Cu(II)/Cu(II)-Cu(III) couple ((1)E(1/2) = 1.120 V) and an irreversible wave for the Cu(II)-Cu(III)/Cu(III)-Cu(III) couple ((2)E(1/2) = 1.430 V). Similarly, a reversible wave for the Cu(II)-Ni(II)/Cu(II) -Ni(III) couple ((1)E(1/2) = 0.750 V) and an irreversible wave for the Ni(III)-Cu(II)/Ni(III)-Cu(III) couple ((2)E(1/2) = 1.20 V) are observed in the case of the [Cu(II)Ni(II)(L(1))](4+) ion. The [Cu(2)(L(1))](4+) ion (g( perpendicular) = 2.120, g( parallel) = 2.256 and 2.196, A( parallel) = 150 G, and D( parallel) = 75 G) and the mixed valent species [Cu(II)Ni(III)(L(1))](5+) (for Cu(2+), g( perpendicular) = 2.060, g( parallel) = 2.219, and A( parallel) = 100 G; for Ni(3+) in sulfate media, g( perpendicular) = 2.204 and g( parallel) = 1.967) and [Cu(II)Cu(III)(L(1))](5+) (g(xx)() = 1.982, g(yy)() = 2.155, g(zz)() = 2.386, A(yy)() = 80 G, and A(zz)() = 120 G) show dipolar-dipolar interaction. In the mixed-valent ions, due to strong electrostatic repulsion from either the Ni(III) or Cu(III) ions, significantly smaller A( parallel) (or A(zz)()) values are observed for the Cu(2+) ion compared to 200 G in the mononuclear ions. Also, the [Cu(II)Ni(II)(L(1))](4+) in aqueous HClO(4) and the [Ni(2)(L(1))](4+) ion in CH(3)NO(2) show a tendency to reduce perchlorate very slowly.

Journal Article↗
PubMed2000

Disposition in rats of N-pyridinium-propyl-cyclam, N-triethylammonium-propyl-cyclam, and N-[Triethylammonium]-3-propyl-[15]ane-N5, potential cartilage imaging agents.

Quaternary ammonium compounds are known to highly concentrate in articular cartilages after i.v. administration. This property was used to synthesize new potential radiodiagnostic agents for joint imaging. Pharmacokinetic study was performed in rats for three new compounds: N-pyridinium-propyl-cyclam (NPPC), N-triethylammonium-propyl-cyclam (NTPC), and N-[triethylammonium]-3-propyl-[15]ane-N5 (NTP 15-5). After i.v. administration, [(3)H]NPPC and [(3)H]NTPC highly and rapidly concentrated in articular cartilage, this uptake being followed by a single exponential decrease with half-lives of, respectively, 75 and 82 min. Except cartilage, only the kidney was highly labeled. After complexation of (99m)Tc by NPPC, NTPC, and NTP 15-5, only (99m)Tc-NTP 15-5 exhibited a high affinity for cartilage. On the other hand, the pharmacokinetic behavior of (99m)Tc-NTPC and (99m)Tc-NPPC was very different from those of their (3)H-labeled analogs. Concentration in cartilaginous tissues was strongly diminished, and liver and bone were highly labeled. For all labeled species, the major route of excretion was urine, and HPLC analysis showed that [(3)H]NTPC and [(3)H]NPPC were excreted under their unchanged form. On the other hand, no (99m)Tc-NTPC and (99m)Tc-NPPC were found in the urine, the radioactivity being mainly due to free technetium, contrary to (99m)Tc-NTP 15-5, which was excreted in the urine under the complexed form. These data can explain the striking differences observed between the three (99m)Tc-labeled molecules, the lack of concentration of (99m)Tc-NTPC, and (99m)Tc-NPPC in cartilages in comparison with their (3)H-labeled analogs due to an instability in vivo of these technetiated complexes.

Animals↗
PubMed1972

The role of the gut flora in the metabolism of cyclamate.

1. [(14)C]Cyclamate was not metabolized when incubated with the liver, spleen, kidney or blood of rats of rabbits kept on a cyclamate-containing diet, and that had become converters of cyclamate into cyclohexylamine. 2. [(14)C]Cyclamate was converted into cyclohexylamine when incubated under anaerobic conditions with the contents of the caecum, colon or rectum or with the faeces of cyclamate-pretreated rats. Similar results were obtained with cyclamate-pretreated rabbits. With cyclamate-pretreated guinea pigs, which did not readily convert cyclamate into cyclohexylamine, the colon contents showed only low activity in this respect. 3. The faeces of a human converter of [(14)C]cyclamate into cyclohexylamine were also very active, but became less active when cyclamate was removed from his diet. 4. On subculturing the organisms from the contents of the colon and rectum of rats, the ability to convert cyclamate into cyclohexylamine was lost during three subcultures, but the loss of the activity was considerably decreased by subculturing in the presence of cyclamate. 5. Incubation of rat faeces in broths containing cyclamate increased their ability to metabolize cyclamate, but similar treatment of rabbit and human faeces suppressed this activity. 6. When rats are kept on a cyclamate diet the number of clostridia in the faeces increased considerably. In human dietary cyclamate did not appear to alter the counts of various faecal micro-organisms. 7. The gut organisms that appear to develop the ability to convert cyclamate into cyclohexylamine are clostridia in rats, enterobacteria in rabbits and enterococci in man. 8. [(14)C]Cyclohexylamine injected into the caecum or colon of rats is readily absorbed and excreted in the urine. 9. It appears that on continued intake of cyclamate the gut flora develop the ability to convert cyclamate into cyclohexylamine, which is then absorbed and excreted mainly in the urine, although a small proportion is metabolized to other compounds.

Animals↗
PubMed2002

In vivo effects of the controlled NO donor/scavenger ruthenium cyclam complexes on blood pressure.

Ruthenium(II/III) complexes able to bind and release NO* were tested in vivo, in conscious Wistar rats instrumented for continuous blood pressure (BP) measurement and administration of in bolus injections (5 to 100 nmol/Kg i.v.) of trans-[Ru(II)Cl(NO+)(cyclam)](PF6)2 (cyclam-NO) or sodium nitroprusside (SNP). For normotensive rats, cyclam-NO produced a sustained 10% BP reduction of basal MAP during 7 +/- 0.4 to 11 +/- 0.3 min. In acute hypertensive rats, cyclam-NO produced BP reduction 3-fold larger than in normotensive rats and similar to that of SNP (maximal effect: 41 +/- 1.3 vs. 45 +/- 2.2 mmHg, respectively). However, the duration of the effect of cyclam-NO was 13 to 21-fold longer than that of SNP. The hypotensive effect of cyclam-NO was fully blocked in presence of continuous infusion of a NO* scavenger, carboxy-PTIO (6 mmol/Kg/min), or of the inhibitor of cGMP activation, methylene blue (83 nmol/Kg/min), or of the cyclam-NO precursor, trans-[RuCl(tfins)(cyclam)](tfms) (cyclam-tfms) (500 mmol/Kg/min). The long lasting BP reduction of cyclam-NO can be interpreted in terms of a slower rate of NO* release (k-NO = 2.2 x 10(-3) S(-1) at 35 degrees C) following chemical reduction (E(0') = 0.10 V vs NHE). In summary, cyclam-NO showed an hypotensive effect around 20 times longer than SNP in either normotensive or hypertensive rats, which was completely inhibited by methylene blue or carboxy-PTIO. Continuous infusion of cyclam-tfms completely blocked the hypotensive effect of cyclam-NO by scavenging the NO* released by the reduced cyclam-NO.

Animals↗
PubMed1972

The fate of cyclamate in man and other species.

1. (14)C-labelled cyclamate has been administered to guinea pigs, rabbits, rats and humans. When given orally to these species on a cyclamate-free diet, cyclamate is excreted unchanged. In guinea pigs some 65% of a single dose is excreted in the urine and 30% in the faeces, the corresponding values for rats being 40 and 50%, for man, 30-50% and 40-60%, and for rabbits, 90 and 5%, the excretion being over a period of 2-3 days. 2. Cyclamate appears to be readily absorbed by rabbits but less readily by guinea pigs, rats and humans. 3. If these animals, including man, are placed on a diet containing cyclamate they develop the ability to convert orally administered cyclamate into cyclohexylamine and consequently into the metabolites of the latter. The extent to which this ability develops is variable, the development occurring more readily in rats than in rabbits or guinea pigs. In three human subjects, one developed the ability quite markedly in 10 days whereas two others did not in 30 days. Removal of the cyclamate from the diet caused a diminution in the ability to convert cyclamate into the amine. 4. In rats that had developed the ability to metabolize orally administered cyclamate, intraperitoneally injected cyclamate was not metabolized and was excreted unchanged in the urine. The biliary excretion of injected cyclamate in rats was very small, i.e. about 0.3% of the dose. 5. The ability of animals to convert cyclamate into cyclohexylamine appears to depend upon a continuous intake of cyclamate and on some factor in the gastrointestinal tract, probably the gut flora.

Animals↗
PubMed2003

Effects of steric constraint on chromium(III) complexes of tetraazamacrocycles. Chemistry and excited-state behavior of 1,4-C2-cyclam complexes.

The synthesis and characterization of several Cr(III) complexes of the constrained macrocyclic ligand 1,4-C(2)-cyclam = 1,4,8,11-tetraazabicyclo[10.2.2]hexadecane is reported. The ligand appears to form only trans complexes, and the structure of trans-[Cr(1,4-C(2)-cyclam)Cl(2)]PF(6) is presented. The constraint imposed by the additional C(2) linkage distorts the bond angles significantly away from the ideal values of 90 and 180 degrees. The effect of the distortion is to enhance the aquation rate of trans-[Cr(1,4-C(2)-cyclam)Cl(2)](+) (k(obs) for trans-[Cr(1,4-C(2)-cyclam)(H(2)O)(2)](3+) formation = 6.5 x 10(-)(2) s(-)(1), 0.01M HNO(3), 25 degrees C) by over 5 orders of magnitude relative to trans-[Cr(cyclam)Cl(2)](+). The complexes trans-[Cr(1,4-C(2)-cyclam)Cl(2)](+) and trans-[Cr(1,4-C(2)-cyclam)(CN)(2)](+) are found to have extinction coefficients four to five times higher than their cyclam analogues, owed to the lack of centrosymmetry caused by the steric constraint. The trans-[Cr(1,4-C(2)-cyclam)(CN)(2)](+) complex is a very weak emitter in aqueous solution with a broad room-temperature emission centered at 735 nm (tau = 0.24 micros). Extended photolysis (350 nm, 15 h) of trans-[Cr(1,4-C(2)-cyclam)(CN)(2)](+) in aqueous solution results in CN(-) ligand loss. This is in stark contrast to its unconstrained cyclam analogue, which is photoinert and has a room-temperature emission lifetime of 335 micros.

Bridged Bicyclo Compounds, Heterocyclic↗