[Re-evaluation of the x-ray examination of acoustic nerve tumors, particularly of the methods advanced by Stenvers and Towne].
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Humans↗
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Differing effects of T4 DNA ligase in the modulation of the damage induced in mammalian cells by either X-rays or restriction endonucleases.
BACKGROUND: Of the different lesions induced by X-rays, DNA double-strand breaks (DSBs) are considered the main cause of chromosomal aberrations and cell death. Restriction endonucleases (REs) induce only DNA DSBs and have frequently been used to mimic the effects of ionizing radiation in the study of DNA damage and repair. METHODS: The present work makes use of clonogenic and cytogenetic assays to study the effect of T4 DNA ligase on modulating the damage induced by either X-rays or an RE (MspI) that produces breaks with cohesive ends. A CHO cell line defective in ligase III activity (EM9) and its corresponding parental line (AA8) were used. RESULTS: Our results show that T4 DNA ligase increased cell survival and decreased chromosomal aberrations in cells treated with MspI, suggesting that most RE-induced DSBs can be repaired by a simple ligation. This enzyme was, however, unable to promote repair of the DNA damage induced by X-rays. Analysis of the ratios of exchange-type aberrations to chromatid break-type aberrations indicated that T4 ligase increased misrejoining of the DNA damage induced by X-rays. The results were similar in EM9 and AA8 cells, although the effect was greater in the cells deficient in DNA strand break rejoining. In addition, depending on whether the end strand break structure is 3'-hydroxyl and 5'-phosphoryl (REs) or more complex (X-rays), T4 DNA ligase could either promote the correct repair or, conversely, increase misrejoining. CONCLUSION: The present results confirm the idea that DNA DSBs induced by cohesive cutting RE are repaired by different mechanisms than those induced by X-rays causing cell lethality.
Animals↗
Thiol- and thioether-based bifunctional chelates for the {M(CO)3}+ core (M = Tc, Re).
By analogy to the recently described single amino acid chelate (SAAC) technology for complexation of the {M(CO)3}+ core (M = Tc, Re), a series of tridentate ligands containing thiolate and thioether groups, as well as amino and pyridyl nitrogen donors, have been prepared: (NC5H4CH2)2NCH2CH2SEt (L1); (NC5H4CH2)2NCH2CH2SH (L2); NC5H4CH2N(CH2CH2SH)2 (L3); (NC5H4CH2)N(CH2CH2SH)(CH2CO2R) [R = H (L4); R = -C2H5 (L5). The {Re(CO)3}+ core complexes of L1-L5 were prepared by the reaction of [Re(CO)3(H2O)3]Br or [NEt4]2[Re(CO)3Br3] with the appropriate ligand in methanol and characterized by infrared spectroscopy, 1H and 13C NMR spectroscopy, mass spectrometry, and in the case of [Re(CO)3(L2)] (Re-2) and [Re(CO)3(L1)Re(CO)3Br2] (Re-1a) by X-ray crystallography. The structure of Re-2 consists of discrete neutral monomers with a fac-Re(CO)3 coordination unit and the remaining coordination sites occupied by the amine, pyridyl, and thiolate donors of L2, leaving a pendant pyridyl arm. In contrast, the structure of Re-1a consists of discrete binuclear units, constructed from a {Re(CO)3(L1)}+ subunit linked to a {Re(CO)3Br2}- group through the sulfur donor of the pendant thioether arm. The series of complexes establishes that thiolate donors are effective ligands for the {M(CO)3}+ core and that a qualitative ordering of the coordination preferences of the core may be proposed: pyridyl nitrogen approximately thiolate > carboxylate > thioether sulfur > thiophene sulfur. The ligands L1 and L2 react cleanly with [99mTc(CO)3(H2O)3]+ in H2O/DMSO to give [99mTc(CO)3(L1)]+ (99m)Tc-1) and [99mTc(CO)3(L2)] (99mTc-2), respectively, in ca. 90% yield after HPLC purification. The Tc analogues 99mTc-1 and 99mTc-2 were subjected to ligand challenges by incubating each in the presence of 1000-fold excesses of both cysteine and histidine. The radiochromatograms showed greater than 95% recovery of the complexes.
Amino Acids↗
Catalytic asymmetric aldol reactions in aqueous media using chiral bis-pyridino-18-crown-6-rare earth metal triflate complexes.
Catalytic asymmetric aldol reactions in aqueous media have been developed using Pr(OTf)(3) and chiral bis-pyridino-18-crown-6 1. In the asymmetric aldol reaction using rare earth metal triflates (RE(OTf)(3)) and 1, slight changes in the ionic diameters of the metal cations greatly affected the diastereo- and enantioselectivities of the products. The substituents (MeO, Br) at the 4-position of the pyridine rings of the crown ether did not significantly affect the selectivities in the asymmetric aldol reaction, although they affected the binding ability of the crown ether with RE cations and the catalytic activity of Pr(OTf)(3)-crown ether complexes. From X-ray structures of RE(NO(3))(3)-crown ether complexes, it was found that they had similar structures regardless of the RE cations and the crown ethers used. Accordingly, the binding ability of the crown ether with the RE cation and the catalytic activity of the complex are important for attaining high selectivity in the asymmetric aldol reaction. Various aromatic and alpha,beta-unsaturated aldehydes and silyl enol ethers derived from ketones and a thioester can be employed in the catalytic asymmetric aldol reactions using Pr(OTf)(3) and 1, to provide the aldol adducts in good to high yields and stereoselectivities. In the case using the silyl enol ether derived from the thioester, 2,6-di-tert-butylpyridine significantly improved the yields of the aldol adducts.
Journal Article↗
Chest x-rays; analysis of data from reading and re-reading films.
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Humans↗
The measurement of corticosteroid induced dermal atrophy by a radiological method.
Dermal atrophy due to the application of Clobetasolpropionate has been detected and measured by an X-ray method after four weeks topical application to the forearm. This effect was found to have recovered when the subjects were re X-rayed eight weeks after they had stopped using the steroid preparation.
Administration, Topical↗
Fluoride ion donor properties of TcO2F3 and ReO2F3: X-ray crystal structures of MO2F3.SbF5 (M = Tc, Re) and TcO2F3.XeO2F2 and Raman and NMR spectroscopic characterization of MO2F3.PnF5 (Pn = As, Sb), [ReO2F2(CH3CN)2][SbF6], and [Re2O4F5][Sb2F11].
The fluoride ion donor properties of TcO2F3 and ReO2F3 toward AsF5, SbF5, and XeO2F2 have been investigated, leading to the formation of TcO2F3.PnF5 and ReO2F3.PnF5 (Pn = As, Sb) and TcO2F3.XeO2F2, which were characterized in the solid state by Raman spectroscopy and X-ray crystallography. TcO2F3.SbF5 crystallizes in the monoclinic system P2(1)/n, with a = 7.366(2) A, b = 10.441(2) A, c = 9.398(2) A, beta = 93.32(3) degrees, V = 721.6(3) A3, and Z = 4 at 24 degrees C, R1 = 0.0649, and wR2 = 0.1112. ReO2F3.SbF5 crystallizes in the monoclinic system P2(1)/c, with a = 5.479(1) A, b = 10.040(2) A, c = 12.426(2) A, beta = 99.01(3) degrees, V = 675.1(2) A3, and Z = 4 at -50 degrees C, R1 = 0.0533, and wR2 = 0.1158. TcO2F3.XeO2F2 crystallizes in the orthorhombic system Cmc2(1), with a = 7.895(2) A, b = 16.204(3) A, c = 5.198(1) A, beta = 90 degrees, V = 665.0(2) A3, and Z = 4 at 24 degrees C, R1 = 0.0402, and wR2 = 0.0822. The structures of TcO2F3.SbF5 and ReO2F3.SbF5 consist of infinite chains of alternating MO2F4 and SbF6 units in which the bridging fluorine atoms on the antimony are trans to each other. The structure of TcO2F3.XeO2F2 comprises two distinct fluorine-bridged chains, one of TcO2F3 and the other of XeO2F2 bridged by long Tc-F...Xe contacts. The oxygen atoms of the group 7 metals in the three structures are cis to each other and to two terminal fluorine atoms and trans to the bridging fluorine atoms. The 19F NMR and Raman spectra of TcO2F3.PnF5 and ReO2F3.PnF5 in SbF5 and PnF5-acidified HF solvents are consistent with dissociation of the adducts into cis-MO2F2(HF)2+ cations and PnF6- anions. The energy-minimized geometries of the free MO2F2+ cations and their HF adducts, cis-MO2F2(HF)2+, have been calculated by local density functional theory (LDFT), and the calculated vibrational frequencies have been used as an aid in the assignment of the Raman spectra of the solid MO2F3.PnF5 adducts and their PnF5-acidified HF solutions. In contrast, ReO2F3.SbF5 ionizes in SO2ClF solvent to give the novel Re2O4F5+ cation and Sb2F11- anion. The 19F NMR spectrum of the cation is consistent with two ReO2F2 units joined by a fluorine bridge in which the oxygen atoms are assumed to lie in the equatorial plane. The [ReO2F2(CH3CN)2][SbF6] salt was formed upon dissolution of ReO2F3.SbF5 in CH3CN and was characterized by 1H, 13C, and 19F NMR and Raman spectroscopies. The ReO2F2(CH3CN)2+ cation is a pseudooctahedral cis-dioxo arrangement in which the CH3CN ligands are trans to the oxygens and the fluorines are trans to each other.
Journal Article↗
Ulnar variance in Kienböck's disease.
Forty four patients with forty seven wrists suffering from Kienböck's disease were re-examined. The mean observation time was 20.5 years. In all forty seven wrists the treatment had been immobilization. Using a standard X-ray projection, and a reliable method of ulnar variance measuring, the ulnar variance was determined by three observers independently. Comparing the result with the ulnar variance in normal wrists we found the so-called "ulnar minus variant" overrepresented in patients with Kienböck's disease. However, comparing X-rays taken at the time of diagnosis with X-rays at re-examination, we found in eight out of forty seven wrists that a subchondral bone formation in the distal radium opposite the lunate bone had taken place. This bone formation will tend to enhance the negative value of ulnar variance measurements, and suggests an explanation of the overrepresentation of "ulnar minus variants" in Kienböck's disease. Excluding these eight wrists from the material and comparing the mean ulnar variance value in the remaining thirty nine wrists with the mean value in normal wrists no statistical difference was shown. Based on these observations it seems unlikely that the "ulnar minus variant" has any bearing on the cause of Kienböck's disease.
Adolescent↗
Diagnostic strategy for pulmonary tuberculosis in a low-incidence country: results of chest X-ray and sputum cultured for Mycobacterium tuberculosis.
The referral centre of tuberculosis in the municipality of Copenhagen, Denmark was the setting for this study, which aimed to assess the diagnostic strategy (chest X-ray and clinical mycobacteriology) in pulmonary tuberculosis. Patient records and chest X-rays were examined for all patients who had sputum or gastric lavage examined for Mycobacterium tuberculosis (Mtb) from 1 January 1992 to 30 April 1994. All chest X-rays were re-evaluated by a trained lung specialist, who did not know the results of sputum culture. Evaluation was referred to one of seven X-ray categories, and compared to the results of culture. Culture of sputum or gastric lavage were positive for Mtb in 54 (14%) of 392 patients; in 61% of 59 patients with X-ray changes thought to be due to tuberculosis (TB); in 20% of 51 patients with X-ray changes compatible with TB; in 14% of 35 patients with previous TB and radiographically active TB; in 2% of 103 patients with previous TB, but not radiographically active TB; in 1% of 112 patients with X-ray changes thought to be due to other disease; and none out of 32 patients with normal X-ray. Even in this highly selected material, it is relatively expensive to find the very few cases of active TB in patients with chest X-ray changes not suspected to be due to TB. It is recommended that: (1) examination of sputum for Mtb should always be preceded by X-ray of the chest in a low-prevalence country; (2) routine culture of sputum for Mtb is restricted to patients with X-ray changes typical or compatible with active TB; and (3) exceptions to this general rule should be made on the basis of the individual's clinical history.
Adolescent↗
Re-irradiation of rat tails to necrosis at six months after treatment with a "tolerance" dose of x rays or neutrons.
Rat tails were re-irradiated to necrosis levels at about six months after various fractionated treatments with 290 kV X rays or 14 MeV neutrons. The X ray dose required to produce necrosis in half of a group of tails (ND50), which had been heavily X-irradiated six months before, was 91+/-4% of the ND50 for aged controls. After prior neutron-irradiation, however, this value was 87+/-4% (neutrons in second treatment) or 75+/-5% (X rays in second course). The "effective" oxygenation of mouse tails at this time after X-irradiation was similar to that of controls; thus these percentage dose values indicate the remarkable tolerance of this organized tissue to a second course of X-irradiation, and the presence of more residual injury in neutron-irradiated tissues.
Animals↗
Methods of X-ray assessment in rheumatoid arthritis: a re-evaluation.
We have re-examined the value of hand radiographs in the assessment of joint damage in rheumatoid arthritis in a series of related studies. Our objectives were: to assess the reproducibility of scoring hand radiographs and the relationships between different types of changes; to analyse the correlations between radiographic changes and hand function; and to assess the inter-relation between hand changes and overall joint damage. We confirmed the reproducibility of radiological assessments and showed that two observers can reproducibly score hand radiographs separately for joint space loss and erosions; both of these correlated with the Larsen score derived from standard radiographs. However, hand radiographic changes were not closely related to hand function; nor did they predict damage to large joints. Finally, examination of changes in 13 joint groups showed that there is a weak relationship between damage and disease duration, and the rate of damage is greatest in the initial years. We conclude that the status of hand radiography as a measure of overall outcome in rheumatoid arthritis remains an open question.
Arthritis, Rheumatoid↗
Derivatives of 1,3,5-triamino-1,3,5-trideoxy-cis-inositol as versatile pentadentate ligands for protein labeling with Re-186/188. prelabeling, biodistribution, and X-ray structural studies.
The pentadentate H3bhci [1,3,5-trideoxy-1, 3-bis((2-hydroxybenzyl)amino)-cis-inositol] and its bifunctionalized analogue H3bhci-glu-H [1,3,5-trideoxy-1, 3-bis((2-hydroxybenzyl)amino)-5-glutaramido-cis-inositol] were synthesized, and their coordination chemistry was investigated with inactive rhenium, with no carrier added Re-188 and with carrier added Re-186. The neutral Re(V) complexes [ReO(bhci)] and [ReO(bhci-glu-H)] are formed in good yields starting from [ReOCl3(P(C6H5)3)2] or in quantitative yield directly from [186/188ReO4]- in aqueous solution by reduction with Sn(II) or Sn(0). The X-ray structures of [ReO(bhci)] and [ReO(bhci-glu-H)] were elucidated revealing pentadentate "side on" coordination of the ligands to the "Re=O" core. The basic cyclohexane frame adopts a chair form in the case of [ReO(bhci)] and a twisted boat form in the case of [ReO(bhci-glu-H)]. [ReO(bhci)] crystallizes in the monoclinic space group C2/c with a = 27.425(3), b = 14.185(1), c = 19.047(2) A, and beta = 103.64(2) degrees and [ReO(bhci-glu-H)] in the monoclinic space group P21/c with a = 13.056(3), b = 10.180(1), c = 22.378(5) A, and beta = 98.205(9) degrees. Both 188Re complexes are stable in human serum for at least 3 days without decomposition. After injection into mice, [ReO(bhci-glu)]- is readily excreted through the intestines, while [ReO(bhci)] is excreted by intestines, liver, and the kidneys. TLC investigations of the urine showed exclusively the complexes [ReO(bhci-glu-H)] and [ReO(bhci)], respectively, and no decomposition products. For derivatization of antibodies, the carboxylic group of [ReO(bhci-glu-H)] was activated with N-hydroxysuccinimide, which required unusually vigorous reaction conditions (heating). The anti colon cancer antibody mAb-35 [IgG and F(ab')2 fragment] was labeled with [186/188ReO(bhci-glu)] to a specific activity of up to 1.5 mCi/mg (55 MBq/mg) with full retention of immunoreactivity. Labeling yields followed pseudo-first-order kinetics in antibody concentration with the ratio of rates between aminolysis and hydrolysis being about 2. Biodistributions of 186Re-labeled intact mAb-35 as well as of its F(ab')2 fragment in tumor-bearing nude mice revealed good uptake by the tumor with only low accumulation of radioactivity in normal tissue.
Animals↗
The characterization of waste cathode-ray tube glass.
New re-use applications are needed to address the relatively large quantity of waste electronic products generated in the world. Cathode-ray tubes (CRTs) from computer monitors and TV sets are a large component of such waste. The three glass components of CRTs are the funnel, panel and neck, which are produced by various manufacturers and are now collected by asset-recovery centres. In this paper, we characterize waste funnel and panel glass from dismantled cathode-ray tubes with a view to assisting the development of new re-use applications. The heavy metal (lead, barium, and strontium) content of such glass represents an acute risk to the environment. Our results of the chemical composition for different kinds of waste CRT glass including black & white and color CRTs show that CRT glass from different producers have generally similar chemical compositions. In particular, the compositions of funnel and panel black & white CRT glass are similar, but are different to those of panel and funnel color CRT glass. We also measured the following specific properties of each type of CRT glass: density, glass transition temperature, and linear coefficient of thermal expansion. It was found that the coefficients of thermal expansion of CRT glass do not vary with their composition. In contrast, the measured densities and glass transition temperatures do vary with composition. On the basis of our experimental data and data found in the literature, we outline the main properties of several waste CRT glass currently in circulation. The aim of this study was to provide the data required to determine if this kind of waste could be entirely (or partially) re-used and to aid the search for promising methods of treatment.
Computer Terminals↗
New N(3)S donor ligand small peptide analogues of the N-mercaptoacetyl-glycylglycylglycine ligand in the clinically used Tc-99m renal imaging agent: evidence for unusual amide oxygen coordination by two new ligands.
Three new X-ray structurally characterized Re(V)O complexes, ReO(MEG(3)H(2)) (10), ReClO(MAEG(2)H(3)) (11), and [ReO(MECG(2)H(2))](2) (12), were prepared from protected forms of three new ligands, mercaptoethyl-glycylglycylglycine (MEG(3)H(5)), mercaptoacetamide-ethyl-glycylglycine (MAEG(2)H(5)), and mercaptoethyl-carbamoylmethyl-glycylglycine (MECG(2)H(5)). (Subscript on H indicates the number of dissociable protons.) Mercaptoacetyltriglycine (MAG(3)H(5)) is the ligand precursor for the clinically used Tc-99m renal imaging agent. The new potentially N(3)S donor ligands have a glycylglycine carboxyl end as in MAG(3)H(5), but a secondary amine (sp(3) N) replaces one amide (sp(2) N) of MAG(3)H(5). ReO(MEG(3)H(2)) (10) is a typical five-coordinate pseudo-square-pyramidal complex with the oxo ligand at the apex and the trianionic form of MEG(3)H(5) coordinated in the basal plane via N(3)S. In the other complexes, the quadridentate ligand has N(2)OS ligation, with the carbonyl oxygen of the glycyl amide group coordinated trans to the oxo ligand. This unusual ligation mode, which is facilitated by the preferred endo configuration of the ligated glycyl sp(3) N, leaves a vacant basal coordination site. In 11, the chloro ligand completes the equatorial plane, whereas, in 12, a glycine carboxylate oxygen of the ligand on the partner Re completes the equatorial plane. Both complexes thus possess an unexpected pseudo-octahedral geometry. For 10, 11, and 12, the (1)H NMR spectra, monitored from high to low pH, exhibited changes only when the pH was lowered below 6. This finding indicates that at physiological pH these complexes possess the desirable characteristic of existing as one monomeric species having only one ionization state, with the coordinated sp(3) N deprotonated. Below pH 6 and above pH approximately 4, changes in the (1)H NMR shifts indicate that this sp(3) N has become protonated. Thus, the N(3)S ligands in all three complexes exhibit normal coordination above pH approximately 4. However, X-ray data for 11 and 12 and some NMR evidence for 11 indicate that the ligands of the two complexes rearrange at low pH (<3). The striking differences between the solution- and solid-state structures reinforce the caveat that solution structural studies conducted at physiological pH are necessary in order to gain insight into the nature of radiopharmaceuticals.
Crystallography, X-Ray↗
Late effects of X-ray treatment of warts.
Five to 22 years after warts on hands and feet were treated by X ray, 1122 patients with a total of 3675 warts were re-examined. X-Ray therapy had been given as one dose of 3000 r using 29 kV with a 0.3-mm Al filter; 19% of the warts had been given two treatments. Sequelae were seen in 4.8% of the sites where warts had been given one X-ray treatment and in 12.2% of the sites after two treatments. These side effects include hyperkeratosis in the pressure areas of palms and soles and atrophy primarily in areas with a thin cutis. There was no evidence of malignant transformation in any treatment site, and there were no deep-seated side effects such as ostitis or tendinitis.
Adolescent↗
Developing the {M(CO)3}+ core for fluorescence applications: Rhenium tricarbonyl core complexes with benzimidazole, quinoline, and tryptophan derivatives.
Tridentate ligands derived from benzimidazole, quinoline, and tryptophan have been synthesized, and their reactions with [NEt4]2[Re(CO)3Br3] have been investigated. The complexes 1-4 and 6 and 7 exhibit fac-{Re(CO)3N3} coordination geometry in the cationic molecular units, while 5 exhibits fac-{Re(CO)3N2O} coordination for the neutral molecular unit, where N3 and N2O refer to the ligand donor groups. The ligands bis(1-methyl-1H-benzoimidazol-2-ylmethyl)amine (L1), [bis(1-methyl-1H-benzoimidazol-2-ylmethyl)amino]acetic acid ethyl ester (L2), [bis(1-methyl-1H-benzoimidazol-2-ylmethy)amino]acetic acid methyl ester (L3), [bis(quinolin-2-ylmethyl)amino]acetic acid methyl ester (L4), 3-(1-methyl-1H-indol-3-yl)-2-[(pyridin-2-ylmethyl)amino]propionic acid (L5), 2-[bis(pyridin-2-ylmethyl)amino]-3-(1-methyl-1H-indol-3-yl)propionic acid (L6), and 2-[bis(quinolin-2-ylmethyl)amino]-3-(1-methyl-1H-indol-3-yl)propionic acid (L7) were obtained in good yields and characterized by elemental analysis, 1D and 2D NMR, and high-resolution mass spectrometry (HRMS). The rhenium complexes were obtained in 70-85% yields and characterized by elemental analysis, 1D and 2D NMR, HRMS, IR, UV, and luminescence spectroscopy, as well as X-ray crystallography for [Re(CO)3(L1)]Br (1), {[Re(CO)3(L2)]Br}2.NEt4Br . 8.5H2O (3(2).NEt4Br . 8.5H2O), [Re(CO)3(L4)]Br (4), and [Re(CO)3(L6)]Br (6). Crystal data for C21H19BrN5O3Re (1): monoclinic, P2(1)/c, a = 13.1851(5) A, b = 16.1292(7) A, c = 10.2689(4) A, beta = 99.353(1) degrees , V = 2154.8(2) A3, Z = 4. Crystal data for C56H73Br3N11O18.50 Re2 (3(2).NEt4Br . 8.5H2O): monoclinic, C2/c, a = 34.7760(19) A, b = 21.1711(12) A, c = 20.3376(11) A, beta = 115.944(1) degrees , V = 13464.5(1) A3, Z = 8. Crystal data for C26H21BrN3O5Re (4): monoclinic, P2(1)/c, a = 16.6504(6) A, b = 10.1564(4) A, c = 14.6954(5) A, beta = 96.739(1) degrees , V = 2467.9(2) A3, Z = 4. Crystal data for C27H24BrN4O5Re (6): monoclinic, P2(1), a = 8.7791(9) A, b = 16.312(2) A, c = 8.9231(9) A, beta = 90.030(1) degrees , V = 1277.8(2) A3, Z = 2.
Benzimidazoles↗
Molecular Rhenium(V) Oxotransferases: Oxidation of Thiols to Disulfides with Sulfoxides. The Case of Substrate-Inhibited Catalysis.
Re(O)Cl(3)(PPh(3))(2), 1, and Re(O)Cl(3)(OPPh(3))(Me(2)S), 2, catalyze the oxidation of thiols to disulfides with sulfoxides under mild conditions. Catalyst 1 exhibits an induction period which features PPh(3) oxidation to OPPh(3) prior to disulfide formation. This lag is absent when 2 is the catalyst precursor. Otherwise, 1 and 2 display comparable kinetics and concentration dependencies. The catalytic reactions are first-order in catalyst, inhibited by thiol, and first-order in sulfoxide at low sulfoxide concentrations. Thiol inhibits the oxygen-transfer reaction because it competes with sulfoxide for coordination on rhenium. Sulfoxides must bind to rhenium in order to be activated for oxo transfer. Ligand substitution reactions of 1 and 2 display kinetics that are consistent with a dissociative (D) mechanism: the substitution rate is zero-order in entering ligand and inhibited by departing ligand. The first-order rate constant for the formation of a 5-coordinate intermediate is 0.06 s(-)(1). As the sulfoxide concentration is increased, the reaction rate increases to reach a maximum and then begins to decline. The catalytic turnover rate at optimal conditions (maximum k(cat) for PhS(O)Me is 180 h(-)(1)) approaches the rate of ligand substitution in these rhenium(V) complexes. Rate retardation at high sulfoxide concentrations is due to catalyst deactivation; sulfoxides oxidize the rhenium(V) catalyst to ReO(4)(-), which is inactive. Dimethyl sulfoxide (DMSO) is more efficient than aryl sulfoxides at oxidizing the catalyst, a fact that could be rationalized by the thermodynamics of S-O bond strength. Thus, aryl sulfoxides, such as PhS(O)Me, appear to be more reactive than alkyl ones. The oxygen-transfer reaction, therefore, is not involved in the rate-controlling step and the rate is limited by ligand substitution. The rhenium(V) catalyst in these reactions acts as a Lewis acid and activates the sulfoxide via coordination: the sulfoxide ligand and not the metal is the bearer of the transferred oxygen. A single-crystal X-ray structure of Re(O)Cl(3)(OPPh(3))(Me(2)S), 2, has been solved: space group Pcmn, a = 8.863(6) Å, b = 14.269(9) Å, c = 18.45(1) Å, Z = 4; the structure was refined to final residuals R = 0.028 and R(w) = 0.035.
Journal Article↗
Dynamics of Re(2,2'-bipyridine)(CO)3Cl MLCT formation and decay after picosecond pulsed X-ray excitation and femtosecond UV excitation.
The dynamics of Re(2,2'-bipyridine)(CO)3Cl MLCT state formation and decay were determined after femtosecond UV laser excitation and picosecond pulsed X-ray excitation, in an N,N-dimethylformamide (DMF) solution as well as in its solid form. At room temperature, after UV excitation, this MLCT excited state emits both in DMF solution and in the solid form. Transient absorption spectra were measured in solution at various delay times following excitation by a 160 fs, 390 nm laser pulse. There was a prompt absorption increase at around 460 nm occurring within the pump probe convolution (<1 ps), which was assigned to the formation of the 3MLCT state. This transient absorbance was constant over 100 ps. In contrast to the solution state, in the solid state, the emission maximum slightly red-shifts with increasing time after laser excitation. In both solid and solution the emission rises within the system response time. The solid sample exhibited a 1.4 ns emission decay that was not observed for the solution sample. The emission rise from a solid sample after 20 ps pulsed X-ray excitation was significantly slower than the system's time resolution. It is proposed that kinetically energetic electrons are ejected following X-ray induced ionisation, creating ionised tracks in which energetic cations and electrons take time to recombine yielding delayed 3MLCT states that emit.
Carbon Monoxide↗