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At least 127 records · Page 7Linked to original sources
PubMed2002

N-(2-Mercaptoethyl)picolylamine as a diaminomonothiolate ligand for the "fac-[Re(CO)3]+" core.

N-(2-Mercaptoethyl)picolylamine (MEPAH) was studied as a potentially biologically relevant ligand for the "fac-[M(CO)(3)](+)" core (M = Re, (99)Tc, (99m)Tc). To this end, the complex Re(CO)(3)(MEPA) was synthesized. The reaction of MEPAH with fac-[Re(CO)(3)(MeCN)(3)](+) took place over the course of seconds, showing the high affinity possessed by this ligand for the "fac-[Re(CO)(3)](+)" core. A single-crystal X-ray diffraction study was performed confirming the nature of Re(CO)(3)(MEPA), a rare mononuclear rhenium(I) thiolate complex. Additional exploration into derivatization of the ligand backbone has afforded the analogous N-ethyl complex, Re(CO)(3)(MEPA-NEt). The high affinity of the ligand for the metal coupled with the ease of its derivatization implies that utilization of this ligand system for the purposes of (99m)Tc-radiopharmaceutical development is promising.

Binding Sites↗
PubMed2003

Quantum chemistry can locally improve protein crystal structures.

We have re-refined the X-ray structure of the heme site in cytochrome c553, supplementing the crystallographic data with quantum chemical geometry optimizations, instead of the molecular mechanics force field used in standard crystallographic refinement. By comparing the resulting structure, obtained using medium-resolution data (170 pm), with an atomic-resolution structure (95 pm) of the same protein, we show that the inclusion of quantum chemical information into the refinement procedure improves the structure significantly. Thus, errors in the Fe-ligand distances are reduced from 3 to 32 pm in the low-resolution structure to 0-5 pm in the re-refined structure, one side-chain atom changes its conformation (a movement by 214 pm toward its position in the high-resolution structure), and the R factors are improved by up to 0.018. Thus, quantum refinement may be a powerful method to obtain an accurate structure for interesting parts of a protein.

Crystallography, X-Ray↗
PubMedDate not supplied

Radiology in family practice: experience in community practice.

This study examined the utilization and interpretation of office x-rays in community practice. Analysis of physician and practice descriptive data obtained by survey from the Minnesota Academy of Family Physicians Research Network, a representative sample of family physicians in Minnesota, leads to these conclusions: (1) Most (87.3%) of the study physicians have on-site x-ray facilities. (2) An extensive variety of x-rays is obtained in the office. (3) Most (54.2%) family physicians interpret their own x-rays and self-select those they want re-read by a radiologist; 43.8% referred all x-rays to a radiologist. (4) Of those who self-select x-rays for referral, 68.9% refer 10% or fewer films. (5) Reasons for referral are: (a) to follow an "a priori" decision, (b) to make a diagnosis when clinical findings are inconclusive, (c) to confirm the physician's own clinical diagnosis, (d) to protect from medical-legal problems, and (e) to consult because of the seriousness of the problem. The study physicians also believe that the interpretation of office x-rays is a basic skill of the family physician, that residents should be trained to interpret 90% or more of their office x-rays, and that radiologists should be used as consultants on the basis of identified need similar to the way other consultants are used. The study also showed that decision criteria for referral are based on sound clinical and quality of care issues, that liability concerns have a definite influence on referral rates for x-ray interpretation, and that a contractual reading arrangement with a radiologist and close proximity to a radiologist both tend to increase his or her use.

Adult↗
PubMed2005

Design and synthesis of site directed maleimide bifunctional chelators for technetium and rhenium.

A new family of heterobifunctional linkers (L1-L9) containing a terminus consisting of a tridentate donor set for coordination of the {M(CO)(3)}(+) core (M = Tc, Re), and a thiol reactive maleimide group has been prepared conveniently and in high yield under Mitsunobu reaction conditions by the coupling of an appropriate alcohol derivative with maleimide. The rhenium complexes [Re(CO)(3)(Lx)]Br (x= 1-9) were prepared in good yields from the reactions of the ligands and (NEt(4))(2)[Re(CO)(3)Br(3)] in refluxing methanol. The ligands and their Re complexes were characterized by (1)H and (13)C NMR, IR, and ESI-MS. Ligand L4 and [Re(CO)(3)(L5)]Br have been structurally characterized by X-ray crystallography. Photoexcitation of solutions of the complexes [Re(CO)(3)(Lx)]Br (x= 4-6) gives rise to intense and prolonged luminescence at room temperature (fluorescence lifetimes of ca. 16 micros). The ligands and their Re complexes react smoothly at the maleimide linker with sulfhydryl groups of peptides and proteins at room temperature in phosphate-buffered saline (PBS, pH 7.4) to form stable thioether bioconjugates. The photoluminescence properties of the labeled conjugates are similar to those of the parent complexes, but with even longer lifetimes. The ligands can also be labeled at room temperature with (99m)Tc to give chemically robust complexes. The corresponding hydrazinonicotinamide derivative N-[5-(6'-hydrazinopyridine-3'-carbonyl)aminopentyl]maleimide (L10) was also prepared. While coupling of L10 to cysteine ethylester and synthesis of the rhenium derivative [ReCl(3)(HYNIC-maleimide)(2)] were successfully accomplished, attempts to couple [ReCl(3)(HYNIC-maleimide)(2)] to glutathione or BSA yielded intractable mixtures.

Chelating Agents↗
PubMed2000

Stereostructure and anti-inflammatory activity of three diastereomers of ocobullenone from Ocotea bullata.

A novel diastereomer of ocobullenone. designated as sibyllenone, was isolated from the stem bark of mature Ocotea bullata in the course of a search for anti-inflammatory compounds from this plant. The stereostructure was established by X-ray crystallography and corroborated by NOESY analysis. Ocobullenone, obtained previously, was re-isolated and crystallised successfully for X-ray analysis, thus making possible an accurate spatial comparison of ocobullenone, iso-ocobullenone and the new stereoisomer. Tested pharmacologically for cyclooxygenase-1 and 2, and 5-lipoxygenase inhibition, sibyllenone was the only compound from O. bullata which showed good inhibitory activity towards 5-lipoxygenase.

Anti-Inflammatory Agents↗
PubMed2002

Mutagenicity of low-filtered 30 kVp X-rays, mammography X-rays and conventional X-rays in cultured mammalian cells.

PURPOSE: To measure the mutagenic effectiveness of low-filtered 30 kVp X-rays, mammography X-rays and conventional (200 kVp) X-rays in mammalian cells. MATERIALS AND METHODS: Two different cell lines and mutation assays were used. Exponentially growing SV40-transformed human fibroblasts were exposed to graded doses of mammography (29 kVp, tungsten anode, 50 microm Rh filter) or conventional X-rays and the frequency of 6-thioguanine-resistent HPRT-deficient mutants was determined. Exponentially growing hamster A(L) cells, which contain a single human chromosome 11 conferring the expression of the human surface protein CD59, were subjected to magnetic cell separation (MACS) in order to remove spontaneous mutants before irradiation with low-filtered 30 kVp (tungsten anode, 0.5 mm Al filter) or conventional X-rays. Fractions of radiation-induced CD59- mutants were quantified by flow-cytometry after immunofluorescence labelling of CD59 proteins. RESULTS: Mammography X-rays were more effective than conventional X-rays at inducing killing of human fibroblasts, whereas 30 kVp X-rays and conventional X-rays were about equally effective at killing Al. cells. Mutant frequencies were linearly related to dose in both mutation assays. An RBE = 2.7 was calculated for the yield of HPRT mutants in human fibroblasts exposed to mammography relative to conventional X-rays and an RBE = 2.4 was obtained for the CD59 mutant frequency in A(L) cells irradiated with low-filtered 30 kVp relative to conventional X-rays. CONCLUSIONS: Both low-filtered 30 kVp and mammography X-rays are mutagenic in mammalian cells in vitro. It is unknown if and how the enhanced mutagenicity of mammography X-rays measured in human cells in vitro translates into breast cancer risk for predisposed women with an enhanced inherited risk for breast cancer. Although the ICRP guidelines attribute the same relative biological effectiveness to all radiations of low LET, including X- and gamma-radiations of all energies for radiobiological protection purposes including the assessment of risks in general terms, they also state that 'for the estimation of the likely consequences of an exposure of a known population, it will sometimes be better to use absorbed dose and specific data relating to the relative biological effectiveness of the radiations concerned and the probability coefficients relating to the exposed population' (ICRP 1991: 32). This latter statement may apply for the population of familial predisposed women. We hope that the presented data on the enhanced mutagenicity of mammography X-rays may stimulate a re-evaluation of the risk assessment of mammography for familial predisposed women. In the meantime, one should be cautious and avoid early and frequent mammography exposure of predisposed women. Alternative examination methods should be applied for these women with an inherited increased risk for breast cancer.

Animals↗
PubMed2001

Isotachophoretic separation behavior of rare-earth EDTA chelates and analysis of minor rare-earth elements in an iron ore by bidirectional isotachophoresis-particle-induced X-ray emission.

Mobilities of 16 anions of rare-earth-EDTA 1:1 chelate (RE-EDTAs) were isotachophoretically measured by using two leading electrolytes (pH 3.6 and 6.0) in order to assess their separation behavior. The leading electrolyte was 20 mM hydrochloric acid. The pH of the solution was adjusted to 3.6 by adding beta-alanine and to 6.0 by adding histidine. The obtained mobilities were very close to each other in the range 20.1x10(-5)-21.9x10(-5) cm2 V(-1) s(-1) with the minimum mobilities for Pr-EDTA and Nd-EDTA for pH 3.6 and 6.0, respectively, and pH dependence was hardly observed. On the basis of the above knowledge. minor rare-earth elements in a standard iron ore sample were determined as RE-EDTAs by bidirectional isotachophoresis-particle-induced X-ray emission (PIXE), where the Fe(II) matrix digested by alkali fusion was separated as Fe(II)Phen3(2+) (phen = 1,10-phenanthroline). Since 5% of the total iron was still detected as Fe(III)EDTA- and might disturb PIXE analysis of RE-EDTA-, itaconic acid was used as the spacer for Fe(III)EDTA- and RE-EDTA-. The fractions of RE-EDTA- were successfully analyzed off-line by a multielemental analytical method, PIXE [analytical result (3.62% (w/w) as RE2O3]; the nominal value was 3.37% (w/w) as RExOy.

Chelating Agents↗
PubMed2003

Molecular and electronic structures of bis-(o-diiminobenzosemiquinonato)metal(II) complexes (Ni, Pd, Pt), their monocations and -anions, and of dimeric dications containing weak metal-metal bonds.

Two series of square planar, diamagnetic, neutral complexes of nickel(II), palladium(II), and platinum(II) containing two N,N-coordinated o-diiminobenzosemiquinonate(1-) pi radical ligands have been synthesized and characterized by UV-vis and (1)H NMR spectroscopy: [M(II)((2)L(ISQ))(2)], M = Ni (1), Pd (2), Pt (3), and [M(II)((3)L(ISQ))(2)] M = Ni (4), Pd (5), Pt (6). H(2)[(2)L(PDI)] represents 3,5-di-tert-butyl-o-phenylenediamine and H(2)[(3)L(PDI)] is N-phenyl-o-phenylenediamine; (L(ISQ))(1-) is the o-diiminobenzosemiquinonate pi radical anion, and (L(IBQ))(0) is the o-diiminobenzoquinone form of these ligands. The structures of complexes 1, 4, 5, and 6 have been (re)determined by X-ray crystallography at 100 K. Cyclic voltammetry established that the complete electron-transfer series consisting of a dianion, monoanion, neutral complex, a mono- and a dication exists: [M(L)(2)](z)z = -2, -1, 0, 1+, 2+. Each species has been electrochemically generated in solution and their X-band EPR and UV-vis spectra have been recorded. The oxidations and reductions are invariably ligand centered. Two o-diiminobenzoquinones(0) and two fully reduced o-diiminocatecholate(2-) ligands are present in the dication and dianion, respectively, whereas the monocations and monoanions are delocalized mixed valent class III species [M(II)(L(ISQ))(L(IBQ))](+) and [M(II)(L(ISQ))(L(PDI))](-), respectively. One-electron oxidations of 1 and trans-6 yield the diamagnetic dications [cis-[Ni(II)((2)L(ISQ))((2)L(IBQ))](2)]Cl(2) (7) and [trans-[Pt(II)((3)L(ISQ))((3)L(IBQ))](2)](CF(3)SO(3))(2) (8), respectively, which have been characterized by X-ray crystallography; both complexes possess a weak M.M bond and the ligands adopt an eclipsed configuration due to weak bonding interactions via pi stacking.

Journal Article↗
PubMed2005

In situ XANES study of Mn in promoted sulfated zirconia catalysts.

Mn-promoted sulfated zirconia catalysts (2 wt% Mn) were investigated in situ, during the catalyst activation, isomerization of n-butane, and subsequent re-activation, using X-ray absorption spectroscopy of the Mn K-edge. The average valence of Mn in the catalysts, as determined from the edge position, was found to change from either 2.65 or 2.77 in the calcined samples to about 2.5 during activation in He (703 K for 30 min). During the isomerization of n-butane (1% in He, 80 ml min-1, 0.5 g catalyst at 333 K), the average Mn valence did not change further. When the catalyst was activated in 50% O2 the average valence only decreased from about 2.78 to 2.72. In this case, the average valence during the isomerization reaction decreased at a nearly constant rate both during the induction of activity and deactivation of the catalyst. The data do not support a stoichiometric redox reaction involving the promoter as initiator of the isomerization. However, a higher Mn valence after activation was indicative of a higher maximum conversion. It is concluded that the promoter cations function through modification of the structure of the zirconia.

Butanes↗
PubMed1988

Inter-chain proline:proline contacts contribute to the stability of the triple helical conformation.

The triple helical conformation observed in the collagen group of proteins is related to the presence of large numbers of imino residues and is derived from the stereochemical properties of these residues. The triple helix is stabilized by increasing numbers of these residues. Hydrogen bonds are usually considered to be a major factor in the formation and stability of protein conformation, however, imino residues are not hydrogen bond donors. We have evaluated the role of these residues in stabilizing the triple helix by re-examining two X-ray based structures of the triple helical polypeptide (Pro-Pro-Gly)10 using molecular mechanics calculations. The two minimized structures are comparable in energy and have helical parameters close to the starting values for each starting structure. Our studies suggest that clusters of close van der Waals contacts between proline residues in adjacent chains contribute significantly to the stability of the triple helix. Preliminary NMR studies support this concept. We propose that non-bonded interactions between proline residues may be a significant stabilizing force in the triple helix generated by (Pro-Pro-Gly)10.

Chemical Phenomena↗
PubMed1992

Cancer incidence among Danish Thorotrast-exposed patients.

BACKGROUND: Studies of groups of patients given injections of the alpha-emitting x-ray contrast medium Thorotrast may provide information on human alpha-ray carcinogenesis. PURPOSE: We re-established a formerly identified cohort of neurological patients receiving injections of Thorotrast for cerebral arteriography and assessed their incidence of cancer. METHODS: Using the national population register, the Danish Cancer Registry, and other registers, we determined the incidence of cancer among Thorotrast-injected patients. Incidence ratios were standardized to the general population and computed for different cancer sites. RESULTS: The cumulative risk for cancer at all sites (excluding brain tumors where the standardized incidence ratio [SIR] was 28) reached 86% 50 years after Thorotrast injection. SIR was greatly elevated at all sites except the brain and CNS (3.3, 95% confidence interval = 3.0-3.7), mainly because of liver cancers (SIR = 126) as well as leukemia (SIR = 10) for which a relationship was found between the time since injection and the estimated dose (but not the age at injection). Other sites with significantly increased risks of cancer included the gallbladder and extrahepatic bile ducts (SIR = 14), peritoneum (SIR = 8.6), sites of multiple myeloma (SIR = 4.6), metastatic sites (SIR = 12), and unspecified sites (SIR = 11). Cancers of the lung and breast also occurred in significant excess, but no relationship between SIR and volume of injected Thorotrast or time since injection was observed. Cancer risk was increased at most other sites, although this increase was not statistically significant. CONCLUSION: Alpha radiation may account for the increased risk of tumors of the liver, gallbladder, and peritoneum as well as leukemia and multiple myeloma, whereas confounding factors most probably contribute to the increased risks at other sites.

Adult↗
PubMed2003

Relationship between endogenous indole-3-acetic acid and abscisic acid changes and bark recovery in Eucommia ulmoides Oliv. after girdling.

Eucommia ulmoides (Eucommiaceae), a traditional Chinese medicinal plant, is often subjected to severe manual peeling of its bark. If the girdled trunk is well protected from desiccation, new bark forms within 1 month. It has been proposed that phytohormones play a key role in this process. Research has been conducted to determine the distribution of endogenous indole-3-acetic acid (IAA) and abscisic acid (ABA) during the bark recovery, using high-performance liquid-chromatography (HPLC) and fluoro-immuno-localization techniques. Results showed that, from 2 d after girdling, the IAA content in the recovering bark (RB) increased markedly while that of ABA decreased. The opposite pattern was observed during progressive re-establishment of the tissues. Immuno-localization showed that most of the IAA was located in the RB tissue layers undergoing cell division, dedifferentiation and (re)differentiation, such as xylary rays, immature xylem, phellogen and cambial regions. This study also provides evidence that IAA and ABA are involved in the bark reconstitution.

Abscisic Acid↗
PubMedDate not supplied

Combined use of gemcitabine and radiation in mice.

The aim of this study was to explore, in a murine tumor, if the effectiveness of radiation, in doses and schedules commonly used in clinical practice is potentiated by the combined use of the recently developed drug gemcitabine. Gemcitabine (30-360 mg/kg b.w.) was administered i.p. in female C3D2F1 mice bearing a mammary adenocarcinoma alone or combined with X-rays. Firstly, gemcitabine (single administration) was administered alone or at 20 min, 4 h, and 24 h before X-ray treatments. The significant effect observed only at 24 h time interval, depended on the X-ray dose and not on the gemcitabine dose. Secondly, 4 gemcitabine administrations every 3 days were used in fractionated combined schedules (overall treatment time of 10 days). We studied the relationship among different doses of gemcitabine, alone or combined with 10 daily X-ray treatments (2 Gy/fraction). We observed an interactive effect of gemcitabine up to its threshold dose of 60 mg/kg/fraction. Furthermore, 10 X-ray daily treatments and 4 X-ray treatments every 3 days (total doses 20-40 Gy) were performed with gemcitabine 60 mg/kg/fraction to study the effect of different doses and schedules of X-rays. Tumor growth delays increase with higher X-ray doses, and this occurs more with 4 X-ray treatments than with 10 X-ray treatments. Our results re-affirm the uselessness of high gemcitabine doses, and indicate the effectiveness of combined gemcitabine-radiation fractionated protocols.

Animals↗
PubMedDate not supplied

[Treatment of diaphyseal pseudoarthrosis with transosseous osteosynthesis by the Ilizarov method. Radiographic signs of reparative osteogenesis].

The main phases of ossification are shown-based on the results achieved by re-examining the X-ray pictures of 14 patients affected by tubular bones pseudoarthrosis treated with Ilizarov's closed compression-distraction osteosynthesis. The roentgen signs in particular are examined which are considered as expressive of positive evolution of the pseudoarthrosis. An outline of X-ray evolution of nonunions is also proposed, referring to the peculiar biological characters of ossification under compression-distraction stimulation.

Adult↗
PubMed2006

Induction of G2 arrest and apoptosis of raji cells by continuous low-dose beta irradiation with 188Re-perrhenate.

Continuous irradiation with exponentially reducing beta-rays induces cell death, known as apoptosis. The aim of this study was to investigate the G2 arrest and apoptosis caused by the beta-ray emitted by the radioisotope (188)Re. Doses of 0.4 Gy (3.7 MBq), 4 Gy (37 MBq), and 40 Gy (370 MBq), were added to Blymphoma Raji cells, and cell viability, apoptosis, and DNA cell-cycle changes were assayed. (188)Re showed time- and dose-dependent effects on cell viability and on cell apoptosis and necrosis. At a (188)Re dose of 0.4 Gy, G(2) cell-cycle arrest was observed after 16 hours, and 4,6-diamidino-2-phenylindole (DAPI) staining indicated a slow, time-dependent increase in apoptotic bodies. At a (188)Re dose of 40 Gy, DNA fragmentation was observed at 2 hours, indicative of early damage in the nucleus. In summary, our results showed that continuous irradiation with low-dose beta-rays induced G(2) arrest and progressive apoptosis, which may be characteristic mechanisms of radionuclide therapy.

Apoptosis↗
PubMed2003

Synthesis and luminescence behaviour of novel heterodecanuclear silver(I)-rhenium(I) alkynyl complexes. X-ray crystal structures of [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(Me2bpy)(CO)3]4](PF6)2 and [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(Br2phen)(CO)3]4](PF6)2.

A novel series of luminescent heterodecanuclear mixed-metal alkynyl complexes, [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(N--N)(CO)3]4](PF6)2, (N--N = tBu2bpy, Me2bpy, phen, Br2phen), have been successfully synthesized; the X-ray crystal structures of [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(Me2bpy)(CO)3]4](PF6)2 and [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(Br2phen)(CO)3]4](PF6)2 have also been determined.

Journal Article↗