Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Intact”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,603 records · Page 89
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Space shuttle flight (STS-45) of L8 myoblast cells results in the isolation of a nonfusing cell line variant

Myoblast cell cultures have been widely employed in conventional (1g) studies of biological processes because characteristics of intact muscle can be readily observed in these cultured cells. We decided to investigate the effects of spaceflight on muscle by utilizing a well characterized myoblast cell line (L8 rat myoblasts) as cultured in the recently designed Space Tissue Loss Flight Module "A" (STL-A). The STL-A is a "state of the art," compact, fully contained, automated cell culture apparatus which replaces a single mid-deck locker on the Space Shuttle. The L8 cells were successfully flown in the STL-A on the Space Shuttle STS-45 mission. Upon return to earth, reculturing of these spaceflown L8 cells (L8SF) resulted in their unexpected failure to fuse and differentiate into myotubes. This inability of the L8SF cells to fuse was found to be a permanent phenotypic alteration. Scanning electron microscopic examination of L8SF cells growing at 1g on fibronectin-coated polypropylene fibers exhibited a strikingly different morphology as compared to control cells. In addition to their failure to fuse into myotubes, L8SF cells also piled up on top of each other. When assayed in fusion-promoting soft agar, L8SF cells gave rise to substantially more and larger colonies than did either preflight (L8AT) or ground control (L8GC) cells. All data to this point indicate that flying L8 rat myoblasts on the Space Shuttle for a duration of 7-10 d at subconfluent densities results in several permanent phenotypic alterations in these cells.

STS-45 Shuttle Project↗
NASA NTRS1994

Cerebral versus systemic hemodynamics during graded orthostatic stress in humans

BACKGROUND: Orthostatic syncope is usually attributed to cerebral hypoperfusion secondary to systemic hemodynamic collapse. Recent research in patients with neurocardiogenic syncope has suggested that cerebral vasoconstriction may occur during orthostatic hypotension, compromising cerebral autoregulation and possibly contributing to the loss of consciousness. However, the regulation of cerebral blood flow (CBF) in such patients may be quite different from that of healthy individuals, particularly when assessed during the rapidly changing hemodynamic conditions associated with neurocardiogenic syncope. To be able to interpret the pathophysiological significance of these observations, a clear understanding of the normal responses of the cerebral circulation to orthostatic stress must be obtained, particularly in the context of the known changes in systemic and regional distributions of blood flow and vascular resistance during orthostasis. Therefore, the specific aim of this study was to examine the changes that occur in the cerebral circulation during graded reductions in central blood volume in the absence of systemic hypotension in healthy humans. We hypothesized that cerebral vasoconstriction would occur and CBF would decrease due to activation of the sympathetic nervous system. We further hypothesized, however, that the magnitude of this change would be small compared with changes in systemic or skeletal muscle vascular resistance in healthy subjects with intact autoregulation and would be unlikely to cause syncope without concomitant hypotension. METHODS AND RESULTS: To test this hypothesis, we studied 13 healthy men (age, 27 +/- 7 years) during progressive lower body negative pressure (LBNP). We measured systemic flow (Qc is cardiac output; C2H2 rebreathing), regional forearm flow (FBF; venous occlusion plethysmography), and blood pressure (BP; Finapres) and calculated systemic (SVR) and forearm (FVR) vascular resistances. Changes in brain blood flow were estimated from changes in the blood flow velocity in the middle cerebral artery (VMCA) using transcranial Doppler. Pulsatility (systolic minus diastolic/mean velocity) normalized for systemic arterial pressure pulsatility was used as an index of distal cerebral vascular resistance. End-tidal PACO2 was closely monitored during LBNP. From rest to maximal LBNP before the onset of symptoms or systemic hypotension, Qc and FBF decreased by 29.9% and 34.4%, respectively. VMCA decreased less, by 15.5% consistent with a smaller decrease in CBF. Similarly, SVR and FVR increased by 62.8% and 69.8%, respectively, whereas pulsatility increased by 17.2%, suggestive of a mild degree of small-vessel cerebral vasoconstriction. Seven of 13 subjects had presyncope during LBNP, all associated with a sudden drop in BP (29 +/- 9%). By comparison, hyperventilation alone caused greater changes in VMCA (42 +/- 2%) and pulsatility but never caused presyncope. In a separate group of 3 subjects, superimposition of hyperventilation during highlevel LBNP caused a further decrease in VMCA (31 +/- 7%) but no change in BP or level of consciousness. CONCLUSIONS: We conclude that cerebral vasoconstriction occurs in healthy humans during graded reductions in central blood volume caused by LBNP. However, the magnitude of this response is small compared with changes in SVR or FVR during LBNP or other stimuli known to induce cerebral vasoconstriction (hypocapnia). We speculate that this degree of cerebral vasoconstriction is not by itself sufficient to cause syncope during orthostatic stress. However, it may exacerbate the decrease in CBF associated with hypotension if hemodynamic instability develops.

NASA Discipline Cardiopulmonary↗
NASA NTRS1994

Negative regulators of cell proliferation

Cell proliferation is governed by the influence of both mitogens and inhibitors. Although cell contact has long been thought to play a fundamental role in cell cycling regulation, and negative regulators have long been suspected to exist, their isolation and purification has been complicated by a variety of technical difficulties. Nevertheless, over recent years an ever-expanding list of putative negative regulators have emerged. In many cases, their biological inhibitory activities are consistent with density-dependent growth inhibition. Most likely their interactions with mitogenic agents, at an intracellular level, are responsible for either mitotic arrest or continued cell cycling. A review of naturally occurring cell growth inhibitors is presented with an emphasis on those factors shown to be residents of the cell surface membrane. Particular attention is focused on a cell surface sialoglycopeptide, isolated from intact bovine cerebral cortex cells, which has been shown to inhibit the proliferation of an unusually wide range of target cells. The glycopeptide arrest cells obtained from diverse species, both fibroblasts and epithelial cells, and a broad variety of transformed cells. Signal transduction events and a limited spectrum of cells that are refractory to the sialoglycopeptide have provided insight into the molecular events mediated by this cell surface inhibitor.

Review↗
NASA NTRS1994

Characterization of the alpha-gamma and alpha-beta complex: evidence for an in vivo functional role of alpha-crystallin as a molecular chaperone

Previous studies have demonstrated that in vitro, alpha-crystallin can protect other lens proteins against extensive denaturation and aggregation. The mechanism of this protection involves preferential binding of the partially denatured protein to a central region of the native alpha-crystallin complex. To test whether a similar phenomenon might occur in vivo, a high molecular weight aggregate (HMWA) fraction was isolated from the aged bovine lens. Negative staining of this preparation revealed the presence of particles of 13-14 nm diameter, characteristic of alpha-crystallin. Immunolocalization of the same particles using antiserum specific for gamma- and beta-crystallins demonstrated preferential binding of these crystallins to the central region of the alpha-crystallin complex. Together, these results provide evidence that in the intact lens, the alpha-crystallins are functionally important molecular chaperones.

NASA Discipline Developmental Biology↗
NASA NTRS1993

Synthesis and characterization of N-parinaroyl analogs of ganglioside GM3 and de-N-acetyl GM3. Interactions with the EGF receptor kinase

A specific plasma membrane glycosphingolipid, known as ganglioside GM3, can regulate the intrinsic tyrosyl kinase activity of the epidermal growth factor (EGF) receptor; this modulation is not associated with alterations in hormone binding to the receptor. GM3 inhibits EGF receptor tyrosyl kinase activity in detergent micelles, in plasma membrane vesicles, and in whole cells. In addition, immunoaffinity-purified EGF receptor preparations contain ganglioside GM3 (Hanai et al. (1988) J. Biol. Chem. 263, 10915-10921), implying that the glycosphingolipid is intimately associated with the receptor kinase in cell membranes. Both the nature of this association and the molecular mechanism of kinase inhibition remain to be elucidated. In this report, we describe the synthesis of a fluorescent analog of ganglioside GM3, in which the native fatty acid was replaced with trans-parinaric acid. This glycosphingolipid inhibited the receptor kinase activity in a manner similar to that of the native ganglioside. A modified fluorescent glycosphingolipid, N-trans-parinaroyl de-N-acetyl ganglioside GM3, was also prepared. This analog, like the nonfluorescent de-N-acetyl ganglioside GM3, had no effect on receptor kinase activity. Results from tryptophan fluorescence quenching and steady-state anisotropy measurements in membranes containing these fluorescent probes and the human EGF receptor were consistent with the notion that GM3, but not de-N-acetyl GM3, interacts specifically with the receptor in intact membranes.

NASA Discipline Cell Biology↗
NASA NTRS1993

Mechanotransduction across the cell surface and through the cytoskeleton

Mechanical stresses were applied directly to cell surface receptors with a magnetic twisting device. The extracellular matrix receptor, integrin beta 1, induced focal adhesion formation and supported a force-dependent stiffening response, whereas nonadhesion receptors did not. The cytoskeletal stiffness (ratio of stress to strain) increased in direct proportion to the applied stress and required intact microtubules and intermediate filaments as well as microfilaments. Tensegrity models that incorporate mechanically interdependent struts and strings that reorient globally in response to a localized stress mimicked this response. These results suggest that integrins act as mechanoreceptors and transmit mechanical signals to the cytoskeleton. Mechanotransduction, in turn, may be mediated simultaneously at multiple locations inside the cell through force-induced rearrangements within a tensionally integrated cytoskeleton.

Non-NASA Center↗
NASA NTRS1993

The identification of a naturally occurring cell surface growth inhibitor related to a previously described bovine sialoglycopeptide

A 66-kDa sialoglycoprotein has been identified as the parental membrane molecule of an earlier described sialoglycopeptide (SGP), an 18-kDa molecule released by protease treatment of intact bovine cerebral cortex cells that was shown to be a potent inhibitor of cellular proliferation. The 66-kDa parental sialoglycoprotein (p-SGP) was purified approximately 2,400-fold, to apparent homogeneity, from bovine cerebral cortex cell membranes by its release during incubation with 3 M NaCl, preparative isoelectric focusing and lectin affinity chromatography. Although a membrane-associated molecule, the p-SGP appeared to be tightly bound to the cell membrane, since it was not released during incubations in the absence of 3 M NaCl. Incubation of the membrane preparations with 3 M urea proved to be too harsh, and the antigenicity required to follow the purification of the p-SGP was abolished. Analyses by SDS-PAGE, under reducing and nonreducing conditions, suggested that the p-SGP membrane component was a single polypeptide without subunit structure. The p-SGP was shown to be structurally related to the SGP fragment by immunoblots with IgG raised to the SGP inhibitor, and functionally related to the SGP by its ability to inhibit Swiss 3T3 proliferation at concentrations strikingly similar to that previous measured with the SGP fragment.

Non-NASA Center↗
NASA NTRS1993

The reducing agent dithiothreitol (DTT) does not abolish the inhibitory nicotinic response recorded from rat dorsolateral septal neurons

Previous intracellular recordings have demonstrated that dorsolateral septal nucleus (DLSN) neurons express a novel nicotinic receptor which produces a direct membrane hyperpolarization when activated by nicotinic agonists. Activation of the classical excitatory nicotinic receptors has been shown to require a disulfide bond involving the cysteines at positions 192 and 193 of the alpha subunits of the receptor. Reduction of this cystine bond with dithiothreitol (DTT) abolishes agonist activation of excitatory nicotinic receptors. We have now examined whether DTT treatment of the inhibitory nicotinic receptor on DLSN neurons also abolishes the inhibitory nicotinic response. We find that the inhibitory response persists after treatment of the neurons with 1 mM DTT, even if the reduction is followed by alkylation of the receptor with bromoacetylcholine to prevent possible reformation of disulfide bonds. This result suggests that the agonist binding site on the inhibitory nicotinic receptor does not require an intact disulfide bond, similar to the bond on the alpha subunit of the excitatory nicotinic receptor, for agonist activation of the receptor. Some of these results have been previously reported in abstract form.

NASA Discipline Number 16-10↗
NASA NTRS1993

Phenotypic characterization of xpr, a global regulator of extracellular virulence factors in Staphylococcus aureus

We recently described a Tn551 insertion in the chromosome of Staphylococcus aureus S6C that resulted in drastically reduced expression of extracellular lipase (M. S. Smeltzer, S. R. Gill, and J. J. Iandolo, J. Bacteriol. 174:4000-4006, 1992). The insertion was localized to a chromosomal site (designated omega 1058) distinct from the lipase structural gene (geh) and the accessory gene regulator (agr), both of which were structurally intact in the lipase-negative (Lip-) mutants. In this report, we describe a phenotypic comparison between strains S6C, a hyperproducer of enterotoxin B; KSI9051, a derivative of S6C carrying the Tn551 insertion at omega 1058; ISP546, an 8325-4 strain that carries a Tn551 insertion in the agr locus; and ISP479C, the parent strain of ISP546 cured of the Tn551 delivery plasmid pI258repA36. Compared with their respective parent strains, ISP546 and KSI9051 produced greatly reduced amounts of lipase, alpha-toxin, delta-toxin, protease, and nuclease. KSI9051 also produced reduced amounts of staphylococcal enterotoxin B. Coagulase production was increased in ISP546 but not in KSI9051. Using a mouse model, we also demonstrated that ISP546 and KSI9051 were far less virulent than ISP479C and S6C. We have designated the genetic element defined by the Tn551 insertion at omega 1058 xpr to denote its role as a regulator of extracellular protein synthesis. We conclude that xpr and agr are similar and possibly interactive regulatory genes that play an important role in pathogenesis of staphylococcal disease.

NASA Discipline Cell Biology↗
NASA NTRS1992

Altering the cellular mechanical force balance results in integrated changes in cell, cytoskeletal and nuclear shape

Studies were carried out with capillary endothelial cells cultured on fibronectin (FN)-coated dishes in order to analyze the mechanism of cell and nuclear shape control by extracellular matrix (ECM). To examine the role of the cytoskeleton in shape determination independent of changes in transmembrane osmotic pressure, membranes of adherent cells were permeabilized with saponin (25 micrograms/ml) using a buffer that maintains the functional integrity of contractile microfilaments. Real-time videomicroscopic studies revealed that addition of 250 microM ATP resulted in time-dependent retraction and rounding of permeabilized cells and nuclei in a manner similar to that observed in intact living cells following detachment using trypsin-EDTA. Computerized image analysis confirmed that permeabilized cells remained essentially rigid in the absence of ATP and that retraction was stimulated in a dose-dependent manner as the concentration of ATP was raised from 10 to 250 microM. Maximal rounding occurred by 30 min with projected cell and nuclear areas being reduced by 69 and 41%, respectively. ATP-induced rounding was also accompanied by a redistribution of microfilaments resulting in formation of a dense net of F-actin surrounding retracted nuclei. Importantly, ATP-stimulated changes in cell, cytoskeletal, and nuclear form were prevented in permeabilized cells using a synthetic myosin peptide (IRICRKG) that has been previously shown to inhibit actomyosin filament sliding in muscle. In contrast, both the rate and extent of cell and nuclear rounding were increased in permeabilized cells exposed to ATP when the soluble FN peptide, GRGDSP, was used to dislodge immobilized FN from cell surface integrin receptors.(ABSTRACT TRUNCATED AT 250 WORDS).

Non-NASA Center↗
NASA NTRS1992

Role of irregular otolith afferents in the steady-state nystagmus during off-vertical axis rotation

1. During constant velocity off-vertical axis rotations (OVAR) in the dark a compensatory ocular nystagmus is present throughout rotation despite the lack of a maintained signal from the semicircular canals. Lesion experiments and canal plugging have attributed the steady-state ocular nystagmus during OVAR to inputs from the otolith organs and have demonstrated that it depends on an intact velocity storage mechanism. 2. To test whether irregularly discharging otolith afferents play a crucial role in the generation of the steady-state eye nystagmus during OVAR, we have used anodal (inhibitory) currents bilaterally to selectively and reversibly block irregular vestibular afferent discharge. During delivery of DC anodal currents (100 microA) bilaterally to both ears, the slow phase eye velocity of the steady-state nystagmus during OVAR was reduced or completely abolished. The disruption of the steady-state nystagmus was transient and lasted only during the period of galvanic stimulation. 3. To distinguish a possible effect of ablation of the background discharge rates of irregular vestibular afferents on the velocity storage mechanism from specific contributions of the dynamic responses from irregular otolith afferents to the circuit responsible for the generation of the steady-state nystagmus, bilateral DC anodal galvanic stimulation was applied during optokinetic nystagmus (OKN) and optokinetic afternystagmus (OKAN). No change in OKN and OKAN was observed.(ABSTRACT TRUNCATED AT 250 WORDS).

NASA Discipline Neuroscience↗
NASA NTRS1992

Age-dependent loss of the C-terminal amino acid from alpha crystallin

Antiserum made against the C-terminal region of alpha-A crystallin was used to monitor the purification of a tryptic peptide containing the C-terminus of the molecule from fetal versus adult bovine lenses. Mass spectral analysis of the peptide preparations obtained from these lenses demonstrated the presence of a peptide (T20) containing an intact C-terminus from fetal lenses and the presence of an additional peptide (T20') from older lenses that contained a cleaved C-terminal serine. These results demonstrate an age-dependent processing of alpha-A crystallin in the bovine lens, resulting in removal of the C-terminal amino acid residue.

NASA Discipline Cell Biology↗
NASA NTRS1992

Short-term reversibility of ultrastructural changes in pulmonary capillaries caused by stress failure

We previously showed that when the pulmonary capillaries in anesthetized rabbits are exposed to a transmural pressure (Ptm) of approximately 40 mmHg, stress failure of the walls occurs with disruption of the capillary endothelium, alveolar epithelium, or sometimes all layers. The present study was designed to determine whether some of the ultrastructural changes are rapidly reversible when the capillary pressure is reduced. To test this, the Ptm was raised to 52.5 cmH2O for 1 min of blood perfusion and then reduced to 12.5 cmH2O for 3 min of saline-dextran perfusion, followed by intravascular fixation at the same pressure. In another group of animals, the pressure was elevated for 1 min of blood and 3 min of saline-dextran before being reduced. The results were compared with previous studies in which the capillary pressures were maintained elevated at 52.5 cmH2O during the entire procedure. Control studies were also done at sustained low pressures. The results showed that the number of endothelial and epithelial breaks per millimeter and the total fraction area of the breaks were reduced when the pressure was lowered. For example, the number of endothelial breaks per millimeter decreased from 7.1 +/- 2.1 to 2.4 +/- 0.7, and the number of epithelial breaks per millimeter fell from 11.4 +/- 3.7 to 3.4 +/- 0.7. There was evidence that the breaks that closed were those that were initially small and were associated with an intact basement membrane. The results suggest that cells can move along their underlying matrix by rapid disengagement and reattachment of cell adhesion molecules, causing breaks to open or close within minutes.(ABSTRACT TRUNCATED AT 250 WORDS).

Non-NASA Center↗
NASA NTRS1992

The ability of lens alpha crystallin to protect against heat-induced aggregation is age-dependent

Alpha crystallin was prepared from newborn and aged bovine lenses. SDS-PAGE and tryptic peptide mapping demonstrated that both preparations contained only the alpha-A and alpha-B chains, with no significant contamination of other crystallins. Compared with alpha crystallin from the aged lens, alpha crystallin from the newborn lens was much more effective in the inhibition of beta L crystallin denaturation and precipitation induced in vitro by heat. Together, these results demonstrate that during the aging process, the alpha crystallins lose their ability to protect against protein denaturation, consistent with the hypothesis that the alpha crystallins play an important role in the maintenance of protein native structure in the intact lens.

NASA Discipline Cell Biology↗
NASA NTRS1991

Characterization of the major cyanogen bromide fragment of alpha-A crystallin

Alpha crystallin from the bovine lens has been digested with cyanogen bromide, and the major fragment (CB-1) has been purified using reverse phase HPLC. Characterization of this fragment by Edman degradation and antisera to synthetic peptides indicates that it originates from alpha-A crystallin, but lacks the N-terminal methionine and the last 35 amino acids from the C-terminus of the molecule. The purified CB-1 fragment binds as well as native alpha crystallin to lens membrane, but is unable to self-assemble into the correct size of high molecular weight oligomeric complexes characteristic of the intact alpha-A chain. Together, these results demonstrate that the alpha-A chain is comprised of at least two functional domains, one of which is involved in binding of alpha-A crystallin to lens membrane, and another which is necessary for correct self-assembly of the molecule into high molecular weight oligomers.

Non-NASA Center↗
NASA NTRS1986

Augmented catecholamine uptake by the heart during hemorrhage in the conscious dog

Changes in arterial and coronary sinus concentrations of norepinephrine (NE) and epinephrine (E) in response to hemorrhage were examined in conscious dogs. Hemorrhage (45 +/- 3.2 ml/kg) decreased mean arterial pressure by 47 +/- 6%, left ventricular (LV) dP/dt by 38 +/- 6%, and mean left circumflex coronary blood flow by 47 +/- 6%, while heart rate increased by 44 +/- 13%. Increases in concentrations of arterial NE (5,050 +/- 1,080 from 190 +/- 20 pg/ml) and E (12,700 +/- 3,280 from 110 +/- 20 pg/ml) were far greater than increases in coronary sinus NE (1,700 +/- 780 from 270 +/- 50 pg/ml) and E (4,300 +/- 2,590 from 90 +/- 10 pg/ml). Net release of NE from the heart at rest was converted to a fractional extraction of 66 +/- 9% after hemorrhage. Fractional extraction of E increased from 16 +/- 6% at rest to 73 +/- 8% after hemorrhage. In cardiac-denervated dogs, hemorrhage (46 +/- 2.8 ml/kg) decreased mean arterial pressure by 39 +/- 15%, LV dP/dt by 36 +/- 10%, and mean left circumflex coronary blood flow by 36 +/- 13%, while heart rate increased by 24 +/- 10%. Hemorrhage increased arterial NE (1,740 +/- 150 from 210 +/- 30 pg/ml) and E (3,050 +/- 880 from 140 +/- 20 pg/ml) more than it increased coronary sinus NE (460 +/- 50 from 150 +/- 30 pg/ml) and E (660 +/- 160 from 90 +/- 20 pg/ml) but significantly less (P less than 0.05) than observed in intact dogs. These experiments indicate that hemorrhage, unlike exercise and sympathetic nerve stimulation, does not induce net overflow of NE from the heart.(ABSTRACT TRUNCATED AT 250 WORDS).

Non-NASA Center↗
NASA NTRS2004

Modeling the interaction Between Ethylene Diamine and Water Films on the Surface of a Carbon Nanotube

It has been observed that a carbon nanotube (CNT) AFM tip coated with ethylene diamine (EDA) penetrates the liquid water-air interface more easily than an uncoated nanotube tip. The EDA coating remains intact through repeated cycles of dipping and removal. In order to understand the physical basis for this observation, we use ab initio quantum chemistry calculations to study the EDA-CNT-water interaction and to parameterize a force field describing this system. Molecular dynamics (MD) simulations are carried out for EDA-water mixtures and an EDA-coated carbon nanotube immmed in water. These simulations are similar to our earlier MD study that characterized the CNT-water interface. The attractive CNT-EDA and CNT-water interactions arise primarily from van der Waals forces, and the EDA-EDA, EDA-water and water-water interactions are mainly due to hydrogen bond formation. The binding energ of single EDA molecule to the nanotube is nearly three times larger than the corresponding value found for water (4.3 versus 1.5 kcal mol, respectively). The EDA molecules readily stick to and diffuse along the CNT surface. As a resulf mixing of the EDA and water films does not occur on the timescale of the MD simulations. The EDA film reduces the hydrophobicity of the nanotube surface and acts like a prototypical surfactant in stabilizing the suspension of carbon nanotubes in water. For this presentation, we use the MD simulations to determine how the presence of the carbon nanotube surface perturbs the properties of EDA-water mixtures.

Jaffe, Richard L.↗
NASA NTRS2004

Gas-phase production of single-walled carbon nanotubes from carbon monoxide: a review of the hipco process

The latest process for producing large quantities of single-walled carbon nanotubes (SWNTs) to emerge from the Rice University, dubbed HiPco, is living up to its promise. The current production rates approach 450 mg/h (or 10 g/day), and nanotubes typically have no more than 7 mol % of iron impurities. Second-generation HiPco apparatus can run continuously for 7-10 days at a time. In the HiPco process nanotubes grow in high-pressure, high-temperature flowing CO on catalytic clusters of iron. Catalyst is formed in situ by thermal decomposition of iron pentacarbonyl, which is delivered intact within a cold CO flow and then rapidly mixed with hot CO in the reaction zone. Upon heating, the Fe(CO)5 decomposes into atoms that condense into larger clusters. SWNTs nucleate and grow on these particles in the gas phase via CO disproportionation: CO + CO --> CO2 + C (SWNT), catalyzed by the Fe surface. The concentration of CO2 produced in this reaction is equal to that of carbon and can therefore serve as a useful real-time feedback parameter. It was used to study and optimize SWNT production as a function of temperature, pressure, and Fe(CO)5 concentration. The results of the parametric study are in agreement with current understanding of the nanotube formation mechanism.

Review↗