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PubMed2003

Synthesis of beta-substituted alpha-amino acids with use of iridium-catalyzed asymmetric allylic substitution.

The asymmetric synthesis of beta-substituted alpha-amino acids with use of iridium-catalyzed allylic substitution was described. The Ir-catalyzed allylic substitution of diphenylimino glycinate with allylic phosphates proceeded smoothly even at 0 degrees C and gave branch products with high enantioselectivity (up to 97% ee), when chiral bidentate phosphite bearing the 2-ethylthioethyl group was employed. In addition, both diastereomers of the branch products were synthesized stereoselectively by simply switching the base employed. These methods were also applied to the asymmetric synthesis of quaternary alpha-amino acids.

Alkylation↗
PubMed2004

Application of P,N-sulfinyl imine ligands to iridium-catalyzed asymmetric hydrogenation of olefins.

The utility of a novel class of P,N-ligands incorporating a chiral sulfinyl imine moiety is demonstrated in the iridium-catalyzed hydrogenation of both functionalized and unfunctionalized olefins, in which enantioselectivities of up to 94% are achieved. The modularity of the P,N-sulfinyl ligand class is highlighted by the facile preparation of a variety of sterically and electronically different ligands. Interesting structure-activity data for both the phosphine and sulfinamide components is provided by this expanded ligand set.

Alkenes↗
PubMed2005

Iridium nanocrystal synthesis and surface coating-dependent catalytic activity.

Iridium (Ir) nanocrystals were synthesized by reducing (methylcyclopentadienyl)(1,5-cyclooctadiene)lr with hexadecanediol in the presence of four different capping ligand combinations: oleic acid and oleylamine, trioctylphosphine (TOP), tetraoctylammonium bromide (TOAB), and tetraoctylphosphonium bromide (TOPB). The oleic acid/oleylamine-capped nanocrystals were of the highest quality, with the narrowest size and shape distribution. The Ir nanocrystals were tested for their ability to catalyze the hydrogenation of 1-decene as a model reaction. The oleic acid/oleylamine and TOP-capped nanocrystals were both catalytically dead. TOAB and TOPB-coated nanocrystals both catalyzed 1-decene hydrogenation, with the TOPB-coated nanocrystals exhibiting the highest turnover frequencies. Recycling through several catalytic reactions increased the catalytic activity, presumably as a result of ligand desorption and increased exposure of the metal surface, with ligand desorption eventually leading to precipitation and significantly decreased activity.

Catalysis↗
PubMed2002

Stereoselective synthesis of trans beta-lactams through iridium-catalyzed reductive coupling of imines and acrylates.

[reaction: see text] Iridium-catalyzed reductive coupling of acrylates and imines provides trans beta-lactams with high diastereoselection. The optimal catalyst allows for the synthesis of trans beta-lactams bearing aromatic, alkenyl, and alkynyl side chains. This reaction appears to proceed through a reductive Mannich addition-cyclization mechanism. Examination of substituent effects reveals a linear Hammett correlation for both the N-aryl group on the imine and the aryloxy group on the acrylate, thereby pointing to rate-determining cyclization in the reaction mechanism.

Acrylates↗
PubMed2006

Subtle stereochemical and electronic effects in iridium-catalyzed isomerization of C-allyl glycosides.

[reaction: see text] Stereoselective isomerization of C-allyl glycosides into (E)-C-vinyl glycosides or (Z)-exo-glycals was carried out in the presence of the cationic iridium(I) catalyst [(Ph(2)MeP)(2)Ir(cod)PF(6)]. The products of the isomerization were affected by the relative 1,2-stereochemical relationships and by the nature of the protecting groups. These effects are discussed along with a plausible reaction mechanism.

Catalysis↗
PubMed2007

Iridium-catalyzed conversion of alcohols into amides via oximes.

[reaction: see text] The iridium catalyst [Ir(Cp*)Cl2]2 is effective for the rearrangement of oximes to furnish amides. The reaction has been combined with catalytic transfer hydrogenation between an alcohol and alkene to allow the conversion of alcohols into amides in a one-pot process.

Alcohols↗
PubMed2002

Diastereoselective formation of chiral iridium hydrides containing the chiral P,N-chelate ligand (4S)-2-(2-(diphenylphosphino)phenyl)-4-isopropyl-1,3-oxazoline.

The iridium complex [Ir(mu-Cl)(PN)(PPh3)]2 (1) reacts with H2 affording only the kinetic isomer OC-6-55-C of the dihydride [IrClH2(PN)(PPh3)] (2) and with methanol yielding, also exclusively, the thermodynamic isomer OC-6-53-C (2b) of the same dihydride; complex 2b has been characterised by X-ray diffractometric methods.

Chelating Agents↗
PubMed2003

An iridium oxide reference electrode for use in microfabricated biosensors and biochips.

In this paper we argue for the use of iridium oxide (IrO(x)) electrodes as quasi-reference electrodes in microfabricated biosensors and biochips that operate in buffered solutions. The simple microfabrication of these electrodes consists of a one-step electrodeposition of IrO(x) onto a microfabricated platinum (Pt) electrode. The IrO(x) electrode potential was found to vary less than 20 mV over 9 days after stabilization for 1 day in a phosphate-buffered saline (PBS) solution; this behavior of the electrode potential was found to be easily reproduced. Moreover, the electrode potential was found to vary by less than 15 mV in the initial hour of its use; this behavior of the electrode potential was also found to be reproducible. The performance of a microfabricated glucose sensor employing an IrO(x) reference electrode is characterized in this paper in order to evaluate the usefulness of this new IrO(x) electrode as a quasi-reference electrode. The glucose sensor consists of a recessed microfabricated Pt electrode array, an electrodeposited IrO(x) film, an inner layer composed of an electropolymerized poly(m-phenylenediamine)/glucose oxidase (PMPD/GOx) film, and an outer or protective layer composed of Teflon and polyurethane (PU) films. The response of this sensor was found to be equivalent to the response of the same sensor employing a commercial Ag/AgCl reference electrode. These results show that a microfabricated IrO(x) electrode can be used as a quasi-reference electrode in microfabricated biosensors and biochips operating in buffered solutions.

Biosensing Techniques↗
PubMed1999

Interstitial iridium-192 implantation for recurrent and/or locally advanced head and neck cancer.

We report our experience with the use of interstitial iridium-192 implantation in the management of patients with recurrent and locally advanced squamous cell carcinoma of the head and neck. Between June 1992 and July 1998 this technique was employed in the management of two groups of patients: (1) a primary group, comprising 42 patients who had presented for the first time with advanced head and neck disease, and had therefore not undergone any previous treatment; and (2) a salvage group of 16 patients with recurrent disease previously treated with external beam radiotherapy (four received therapy to the neck, one to the cheek, eight to the tongue and three to the floor of the mouth). The follow-up in each group was short, ranging from 3 to 56 months. The overall response in the primary group was 38/42 (90%). A complete response was achieved in 35/42 (83%). In the salvage group, the overall response was 13/16 (81%); 4/16 (25%) showed a complete response and 9/16 (56%) a partial response. The estimated percentage surviving at 1 year for patients with primary disease is 70% (95% confidence interval (CI) 54-86). For those receiving salvage therapy the estimated percentage surviving at 1 year is 45% (95% CI 19-71).

Adult↗
PubMed1990

[Value of irradiation alone of generally inoperable endometrial cancer with high dose rate iridium 192].

Surgery should be an integral part of the management of the patient suffering from endometrial cancer. Only patients with severe internal diseases should be treated with radiation therapy alone. Although radiation therapy alone can cure endometrial cancer, the survival figures are poorer than for the operation. At the University of Vienna (1st Department of Gynaecology), 267 patients with endometrial cancer were treated by radiation therapy alone (Afterloading iridium192 technique). 5-year survival (life table method) for all patients was 65.2%. In stage I, 5-year survival was 66.9%, and in stage II 46.7%, respectively. For up to 69 years of age the survival was 76.6%, for 70 years and more 61.8%, for grading I 78.8%, for grading II and III only 55.4%, respectively. With radium226 technique, the survival rate was only 56%, while 65.2% were reached with the Iridium technique. All differences are significant. External irradiation (cobalt60) was employed as combined treatment in only 9.4% of the cases. Intrauterine and intravaginal applications were performed without anaesthesia and the hospitalisation time was only one day per week. The relapse rate in stage I/b was 14.8% and in stage II 30%, respectively. Therefore, the dose of intracavitary treatment should be changed and external irradiation used more often.

Aged↗
PubMed2003

A case of subglottic carcinoma effectively treated with intraluminal irradiation using low dose rate iridium-192 thin wires combined with external beam irradiation.

Subglottic carcinoma is rare and has a poor prognosis. It is usually treated with surgical resection, external beam irradiation (EBR) and/or a combination of both. Intraluminal irradiation (IR) as a curative treatment for subglottic carcinoma has never been reported. We report a case of subglottic carcinoma in a 66-year-old man, who was effectively treated with IR combined with EBR. IR was conducted using low dose rate iridium-192 thin wires at a subglottic mucosal dose of 5.1-6.0 Gy per fraction, with a total dose of 43.8 Gy in eight fractions. EBR was administered, using cobalt-60 and 6 MV X-rays delivered at 2 Gy per fraction, with a total dose of 66 Gy in 33 fractions. Complete response was obtained without serious complications and no recurrence occurred in the 79-month follow-up period. IR combined with EBR is useful as a potential curative treatment. It should be considered as one of the treatment options for subglottic carcinoma.

Aged↗
PubMed1988

Bilateral pelvic lymphadenectomy, iridium 192 template, and external beam therapy for localized prostatic carcinoma: complications and results.

Thirty-five patients with prostatic adenocarcinoma were treated by bilateral pelvic lymphadenectomy and temporary implantation of iridium 192 strands with adjuvant external beam radiotherapy. With the implant the prostate received between 3,200 and 3,500 gray (Gy) followed in two weeks by small-field external beam irradiation for an additional dose of approximately 3,400 Gy. Morbidity included an ileofemoral thrombosis in one patient, and transient radiation proctitis in four patients; one patient required transurethral prostatic resection for obstruction at one year. Local response of the primary tumor was dramatic in every case at three-month follow-up. In 11 of 15 patients (73%), biopsy at one year showed no evidence of disease.

Adenocarcinoma↗
PubMed1989

Acute radiodermatitis from occupational exposure to iridium 192.

Industrial radiography using the man-made radioisotope iridium 129 is commonplace in the southern states. Despite established procedures and safeguards, accidental exposure may result in typical acute radiodermatitis. We have presented a clinical example of this phenomenon.

Acute Disease↗
PubMed2000

Chronic neural stimulation with thin-film, iridium oxide electrodes.

Experiments were conducted to assess the effect of chronic stimulation on the electrical properties of the electrode-tissue system, as measured using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Silicon, micromachined probes with multiple iridium oxide stimulating electrodes (400-1600 micron 2) were implanted in guinea pig cortex. A 10-17 day post-operative recovery period was followed by five days of monopolar stimulation, two hours/electrode each day using biphasic, constant current stimulation (5-100 microA, 100 microseconds/phase). EIS and CV data were taken before and after stimulation. The post-stimulation impedance [at mid-range frequencies (100 Hz-100 kHz)] consistently and significantly decreased relative to prestimulation levels. Impedance magnitude increased permanently at low frequencies (< 100 Hz), correlating to a change in the charge storage capacity (the area under a cyclic voltammagram). Impedance magnitude significantly increased during the recovery period, though this increase could be mostly reversed by applying small currents. A mathematical model of the electrode-tissue system impedance was used to analyze in vivo behavior. The data and modeling results shows that applying charge to the electrode can consistently reduce the impedance of the electrode-tissue system. Analysis of explanted probes suggests that the interaction between the tissue and electrode is dependent on whether chronic pulses were applied. It is hypothesized that the interface between the tissue and metal is altered by current pulsing, resulting in a temporary impedance shift.

Animals↗
PubMed2006

Potential-biased, asymmetric waveforms for charge-injection with activated iridium oxide (AIROF) neural stimulation electrodes.

The use of potential biasing and biphasic, asymmetric current pulse waveforms to maximize the charge-injection capacity of activated iridium oxide (AIROF) microelectrodes used for neural stimulation is described. The waveforms retain overall zero net charge for the biphasic pulse, but employ an asymmetry in the current and pulse widths of each phase, with the second phase delivered at a lower current density for a longer period of time than the leading phase. This strategy minimizes polarization of the AIROF by the charge-balancing second phase and permits the use of a more positive anodic bias for cathodal-first pulsing or a more negative cathodic bias for anodal-first pulsing to maximize charge injection. Using 0.4-ms cathodal-first pulses, a maximum charge-injection capacity of 3.3 mC/cm2 was obtained with an 0.6-V bias (versus Ag/AgCl) and a pulse asymmetry of 1:8 in the cathodal and anodal pulse widths. For anodal-first pulsing, a maximum charge capacity of 9.6 mC/cm2 was obtained with an asymmetry of 1:3 at an 0.1-V bias. These measurements were made in vitro in carbonate-buffered saline using microelectrodes with a 2000 microm2 surface area.

Animals↗