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Biomedical subjects

B L Phillips

Publications and source records attributed to B L Phillips.

At least 19 recordsLinked to original sources
PubMed2004

Nearly uniform MgO-supported pentaosmium cluster catalysts.

[Os5C(CO)14]2- was synthesized on the surface of MgO by reductive carbonylation of adsorbed Os3(CO)12 at 548 K and 1 bar. The supported species were characterized by infrared (IR), 13C NMR, and extended X-ray absorption fine structure (EXAFS) spectroscopies. The IR and EXAFS data are consistent with the presence of [Os5C(CO)14]2-, formed in a yield of about 65%, along with smaller osmium carbonyl clusters. As the supported clusters were decarbonylated in flowing He or H2, they were characterized by IR and EXAFS spectroscopies, which indicate that the decarbonylation was complete after each treatment at 573 K. The EXAFS data characterizing the sample treated in He determine an Os-Os first-shell coordination number of 3.4, matching that of [Os5C(CO)14]2- and indicating that the Os5C frame was retained after decarbonylation in He. Treatment of MgO-supported [Os5C(CO)14]2- in H2 at 573 K resulted in the formation of aggregated osmium clusters larger than Os5C. The catalytic activity of Os5C for toluene hydrogenation was found to be an order of magnitude less than that of the aggregated osmium clusters, which are metallic in character.

Journal Article↗
PubMed2001

Water exchange in fluoroaluminate complexes in aqueous solution: a variable temperature multinuclear NMR study.

An 17O, 19F, and 27Al NMR study of fluoroaluminate complexes (AlFn(H2O)6-n((3-n)+), n = 0, 1, and 2) in aqueous solution supports the idea that for each substitution of a bound water molecule by a fluoride anion, the exchange rate of bound water with free water increases by about 2 orders of magnitude. New rate coefficients for exchange of inner-sphere water molecules in AlF(H2O)5(2+) are kex(298) = 230(+/-20) s(-1), DeltaH(dagger) = 65(+/-3) kJ mol(-1), and DeltaS(dagger) = 19(+/-10) J mol(-1) K(-1). The corresponding new values for the AlF2(H2O)4(+) complex are: kex(298) = 17 100(+/-500) s(-1), DeltaH(dagger) = 66(+/-2) kJ mol(-1), and DeltaS(dagger) = 57(+/-8) J mol(-1) K(-1). When these new results are combined with those of our previous study,(4) we find no dependence of the solvent exchange rate, in either AlF(H2O)5(2+) or AlF2(H2O)4(+), on the concentration of fluoride or protons over the range of SigmaF = 0.06-0.50 M and [H(+)] = 0.01-0.44 M. A paramagnetic shift of 27Al resonances results from addition of Mn(II) to the aqueous solution as a relaxation agent for bulk waters. This shift allows resolution of the AlFn(H2O)6-n((3-n)+) species in 27Al NMR spectra and comparison of the speciation determined via thermodynamic calculations with that determined by 27Al, 19F, and 17O NMR.

Algorithms↗
PubMed2001

Reactivity of site-isolated metal clusters: propylidyne on gamma-Al2O3-supported Ir4.

To contrast the reactivity of supported metal clusters with that of extended metal surfaces, we investigated the reactions of tetrairidium clusters supported on porous gamma-Al2O3 (Ir4/gamma-Al2O3) with propene and with H2. Infrared, 13C NMR, and extended X-ray absorption fine-structure spectroscopy were used to characterize the ligands formed on the clusters. Propene adsorption onto Ir4/gamma-Al2O3 at 298 K gave stable, cluster-bound mu3-propylidyne. Propene adsorbed onto Ir4/gamma-Al2O3 at 138 K reacted at approximately 219 K to form a stable, highly dehydrogenated, cluster-bound hydrocarbon species approximated as CxHy (such as, for example, C3H2 or C2H). H2 reacted with Ir4/gamma-Al2O3 at 298 K, forming ligands (likely hydrides), which prevented subsequent reaction of the clusters with propene to form propylidyne. Propylidyne on Ir4 was stable in helium or H2 as the sample was heated to 523 K, whereupon it reacted with oxygen of the support to give CO. Propylidyne on Ir4 did not undergo isotopic exchange in the presence of D2 at 298 K. In contrast, the literature shows that propylidyne chemisorbed on extended metal surfaces is hydrogenated in the presence of H2 (or D2) and exchanges hydrogen with gaseous D2 at room temperature; in the absence of H2, it decomposes thermally to give hydrocarbon fragments at temperatures much less than 523 K. The striking difference in reactivities of propylidyne on clusters and propylidyne on extended metal surfaces implies the requirement of ensembles of more than the three metal surface atoms bonded to propylidyne in the surface reactions. The results highlight the unique reactivity of small site-isolated metal clusters.

Journal Article↗
PubMed2000

Solid-state and high-resolution liquid 119Sn NMR spectroscopy of some monomeric, two-coordinate low-valent tin compounds: very large chemical shift anisotropies.

High-resolution liquid- and solid-state 119Sn NMR spectroscopy was used to study the bonding environment in the series of monomeric, two-coordinate Sn(II) compounds of formula Sn(X)C6H3-2,6-Trip2 (X = Cl, Cr(eta 5-C5H5)(CO)3, t-Bu, Sn(Me)2C6H3-2,6-Trip2; Trip = C6H2-2,4,6-i-Pr3). The trends in the principal components of the chemical shift tensor extracted from the solid-state NMR data were consistent with the structures determined by X-ray crystallography. Furthermore, the spectra for the first three compounds displayed the largest 119Sn NMR chemical shift anisotropies (up to 3798 ppm) of any tin compound for which data are currently available. Relaxation time based calculations for the dimetallic compound 2,6-Trip2H3C6Sn-Sn(Me)2C6H3-2,6-Trip2 suggests that the chemical shift anisotropy for the two-coordinate tin center may be as much as ca. 7098 ppm, which is as broad as the 1 MHz bandwidth of the NMR spectrometer.

Journal Article↗
PubMed1998

Effect of sugars on headgroup mobility in freeze-dried dipalmitoylphosphatidylcholine bilayers: solid-state 31P NMR and FTIR studies.

The effect of the carbohydrates trehalose, glucose, and hydroxyethyl starch (HES) on the motional properties of the phosphate headgroup of freeze-dried dipalmitoylphosphatidylcholine (DPPC) liposomes was studied by means of 31P NMR, Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The results show that trehalose, which is a strong glass former (Tg = 115 degreesC), elevates the onset of the lipid headgroup rotations and preserves some rotational mobility of the phosphate headgroups after cooling from the liquid-crystalline state. Glucose (Tg = 30 degreesC), a very effective depressant of the phase transition temperature of freeze-dried DPPC, markedly elevates the initiation of the temperature of headgroup rotations. On the other hand, the monosaccharide does not preserve the headgroup disordering when cooled from the liquid-crystalline state. These effects are consistent with formation of hydrogen bonds between the OH groups of the sugar and the polar headgroups of DPPC. They show, however, that hydrogen bonding is not sufficient for preservation of the dynamic properties of freeze-dried DPPC. HES, although a very good glass former (Tg > 110 degreesC), does not depress the phase transition temperature and affects only slightly the rotational properties of freeze-dried DPPC. This lack of effect of HES is associated with the absence of direct interactions with the lipid phosphates, as evidenced by the FTIR results. These data show that vitrification of the additive is not sufficient to affect the dynamic properties of dried DPPC.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1996

MRI confirmation of accuracy of freehand placement of mesial temporal lobe depth electrodes in the investigation of intractable epilepsy.

Stereotactic techniques are commonly used to place intracerebral depth electrodes. We placed 15 depth electrodes (9R, 6L) freehand, orthogonally into temporal lobes in 12 patients undergoing monitoring with subdural strip electrodes in the evaluation of their intractable epilepsy. Coronal MRI was performed with the electrodes in place. The mean distance from the closest depth electrode contact to the hippocampus was 0.8 mm (range 0-5 mm). In 11 instances the closest contact was either within or making contact with the hippocampus, and in another three it was within 3 mm. For 13 electrodes, the most distal contact was the closest to the hippocampus, for two the penultimate contact was closest. There were no complications from electrode placement. Ictal onset was mesial temporal in 11 patients and frontal in one. Temporal onset was detectable in the depth electrode in each case, usually simultaneously with the onset in the subdural electrode although often the discharge was better developed in the depth electrode. We conclude that freehand placement of depth electrodes orthogonally into the temporal lobe can achieve a degree of accuracy sufficient to localize seizure onset in the mesial temporal lobe.

Adolescent↗
PubMed1988

Magnetic resonance imaging and clinical correlations in multiple sclerosis.

We examined the relationship between magnetic resonance imaging (MRI) cerebral findings and clinical evaluations in 66 patients with clinically definite multiple sclerosis (MS). MRI observations included total number and location of lesions visualized, degree of periventricular involvement, degree of degeneration of the corpus callosum, and extent of generalized parenchymal atrophy. Overall physical disability was evaluated by the Kurtzke Expanded Disability Status Scale (EDSS) and individual symptoms were rated according to the Kurtzke Functional Systems (FS) scale. Our results suggest that MRI brain abnormalities are significantly related to the overall severity of disease, but MRI is not particularly useful to predict the presence or absence of individual symptoms. These findings do suggest that the MRI may provide useful information to monitor clinical progression of patients with MS, but the lesions visualized need not always be symptomatic nor are we sure that all symptomatic lesions, particularly in the spinal cord and optic nerves, will be visualized.

Adult↗
PubMed1987

Oral theophylline and diuretics improve pulmonary mechanics in infants with bronchopulmonary dysplasia.

We studied the effects of orally administered theophylline and diuretics (chlorothiazide and spironolactone) on pulmonary mechanics in 16 infants with bronchopulmonary dysplasia. Their gestational age (mean +/- SD) was 28.5 +/- 3.4 weeks, and postnatal age at the time of study 19.5 +/- 10.7 weeks. The infants were randomized to two groups. Group 1 received successively placebo, theophylline, and theophylline plus diuretics; Group 2 received theophylline, placebo, and placebo plus diuretics on successive 4-day periods. Pulmonary function was measured before beginning the study (baseline) and at the end of each 4-day period. No significant changes in pulmonary function were noted after treatment with placebo. After treatment with theophylline, dynamic compliance (Cdyn) increased from baseline (mean +/- SD) 0.075 +/- 0.017 to 0.091 +/- 0.028 mL/cm H2O/cm (P less than 0.01), airway resistance (Raw) decreased from 67.19 +/- 36.71 to 41.44 +/- 22.50 cm H2O/L/sec (P less than 0.001), maximal expiratory flow at functional residual capacity (VmaxFRC) increased from 0.261 +/- 0.240 to 0.357 +/- 0.299 thoracic gas volume (TGV)/sec (P less than 0.01), and time constant decreased from 0.312 +/- 0.224 to 0.275 +/- 0.247 sec (P less than 0.02). After treatment with combined placebo and diuretics, Cdyn increased to 0.103 +/- 0.023 mL/cm H2O/cm (P less than 0.05), Raw decreased to 31.76 +/- 24.90 cm H2O/L/sec (P less than 0.001), VmaxFRC increased to 0.638 +/- 0.595 TGV/sec (P less than 0.02), and time constant decreased to 0.180 +/- 0.141 sec (P less than 0.05). After treatment with combined theophylline and diuretics, Cdyn increased to 0.118 +/- 0.017 mL/cm H2O/cm (P less than 0.001), Raw decreased to 35.98 +/- 25.85 cm H2O/L/sec (P less than 0.02), VmaxFRC increased to 0.479 +/- 0.377 TGV/sec (P less than 0.02), and time constant decreased to 0.180 +/- 0.137 sec (P less than 0.01). We conclude that theophylline and diuretics have additive effects on the improvement of pulmonary function in infants with bronchopulmonary dysplasia.

Administration, Oral↗
PubMed1987

Persistently low blood retinol levels during and after parenteral feeding of very low birth weight infants: examination of losses into intravenous administration sets and a method of prevention by addition to a lipid emulsion.

Very low birth weight infants have little storage of hepatic retinol and are, therefore, highly dependent upon an exogenous supply. The recent association between low serum retinol level and bronchopulmonary dysplasia and the persistently low serum levels of retinol during total parenteral nutrition prompted a prospective study to evaluate serial changes in serum retinol levels during 1 month of total parenteral nutrition (retinol dose 455 micrograms/d) and again during 1 month of total enteral feeding (retinol dose 200 to 300 micrograms/d) in the same infants. Infants were divided into two groups. Group 1 consisted of infants weighing less than 1,000 g (n = 24) and group 2 consisted of infants weighing 1,000 to 1,500 g (n = 17). Although initial mean levels of retinol were similar in both groups (14.8 +/- 0.9 and 13.5 +/- 0.7 micrograms/dL), there was wide variation between infants. In group 1 infants, there was a significant (P less than .01) decline in retinol level by the second week of life (to 9.2 +/- 1 micrograms/dL), which persisted during total parenteral nutrition, but increased to 13.4 +/- 2 after 1 week of enteral feeding. This level was maintained throughout enteral feeding. In group 2 infants, there was no significant change in serum retinol level throughout the study. During total parenteral nutrition, several infants had retinol levels below 10 micrograms/dL, a level associated with signs of retinol deficiency in older children. Because losses of retinol are known to occur in smaller volume total parenteral nutrition solutions, it was speculated that losses of retinol in our patients were due to retinol losses in the total parenteral nutrition delivery system.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug Stability↗