Electrochemical and spectroscopic effects of mixed substituents in bis(phenolate)-copper(II) galactose oxidase model complexes

Nonsymmetric substitution of salen (1(R(1),R(2))) and reduced salen (2(R(1),R(2))) Cu(II)-phenoxyl complexes with a combination of -(t)Bu, -S(i)Pr, and -OMe substituents leads to dramatic differences in their redox and spectroscopic properties, providing insight into the influence of the cysteine-modified tyrosine cofactor in the enzyme galactose oxidase (GO). Using a modified Marcus-Hush analysis, the oxidized copper complexes are characterized as Class II mixed-valent due to the electronic differentiation between the two substituted phenolates. Sulfur K-edge X-ray absorption spectroscopy (XAS) assesses the degree of radical delocalization onto the single sulfur atom of nonsymmetric [1((t)Bu,SMe)](+) at 7%, consistent with other spectroscopic and electrochemical results that suggest preferential oxidation of the -SMe bearing phenolate. Estimates of the thermodynamic free-energy difference between the two localized states (ΔG(o)) and reorganizational energies (λ(R(1)R(2))) of [1(R(1),R(2))](+) and [2(R(1),R(2))](+) lead to accurate predictions of the spectroscopically observed IVCT transition energies. Application of the modified Marcus-Hush analysis to GO using parameters determined for [2(R(1),R(2))](+) predicts a ν(max) of ∼13600 cm(-1), well within the energy range of the broad Vis-NIR band displayed by the enzyme.

Stolbur phytoplasma transmission to maize by Reptalus panzeri and the disease cycle of maize redness in Serbia

Maize redness (MR), induced by stolbur phytoplasma ('Candidatus Phytoplasma solani', subgroup 16SrXII-A), is characterized by midrib, leaf, and stalk reddening and abnormal ear development. MR has been reported from Serbia, Romania, and Bulgaria for 50 years, and recent epiphytotics reduced yields by 40 to 90% in South Banat District, Serbia. Potential vectors including leafhoppers and planthoppers in the order Hemiptera, suborder Auchenorrhyncha, were surveyed in MR-affected and low-MR-incidence fields, and 33 different species were identified. Only Reptalus panzeri populations displayed characteristics of a major MR vector. More R. panzeri individuals were present in MR-affected versus low-MR fields, higher populations were observed in maize plots than in field border areas, and peak population levels preceded the appearance of MR in late July. Stolbur phytoplasma was detected in 17% of R. panzeri adults using nested polymerase chain reaction but not in any other insects tested. Higher populations of R. panzeri nymphs were found on maize, Johnsongrass (Sorghum halepense), and wheat (Triticum aestivum) roots. Stolbur phytoplasma was detected in roots of these three plant species, as well as in R. panzeri L(3) and L(5) nymphs. When stolbur phytoplasma-infected R. panzeri L(3) nymphs were introduced into insect-free mesh cages containing healthy maize and wheat plants, 89 and 7%, respectively, became infected. These results suggest that the MR disease cycle in South Banat involves mid-July transmission of stolbur phytoplasma to maize by infected adult R. panzeri. The adult R. panzeri lay eggs on infected maize roots, and nymphs living on these roots acquire the phytoplasma from infected maize. The nymphs overwinter on the roots of wheat planted into maize fields in the autumn, allowing emergence of phytoplasma-infected vectors the following July.

Defining the electronic and geometric structure of one-electron oxidized copper-bis-phenoxide complexes

The geometric and electronic structure of an oxidized Cu complex ([CuSal](+); Sal = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-(1R,2R)-diamine) with a non-innocent salen ligand has been investigated both in the solid state and in solution. Integration of information from UV-vis-NIR spectroscopy, magnetic susceptibility, electrochemistry, resonance Raman spectroscopy, X-ray crystallography, X-ray absorption spectroscopy, and density functional theory calculations provides critical insights into the nature of the localization/delocalization of the oxidation locus. In contrast to the analogous Ni derivative [NiSal](+) (Storr, T.; et al. Angew. Chem., Int. Ed. 2007, 46, 5198), which exists solely in the Ni(II) ligand-radical form, the locus of oxidation is metal-based for [CuSal](+), affording exclusively a Cu(III) species in the solid state (4-300 K). Variable-temperature solution studies suggest that [CuSal](+) exists in a reversible spin-equilibrium between a ligand-radical species [Cu(II)Sal(*)](+) (S = 1) and the high-valent metal form [Cu(III)Sal](+) (S = 0), indicative of nearly isoenergetic species. It is surprising that a bis-imine-bis-phenolate ligation stabilizes the Cu(III) oxidation state, and even more surprising that in solution a spin equilibrium occurs without a change in coordination number. The oxidized tetrahydrosalen analogue [CuSal(red)](+) (Sal(red) = N,N'-bis(3,5-di- tert-butylhydroxybenzyl)-1,2-cyclohexane-(1R,2R)-diamine) exists as a temperature-invariant Cu(II)-ligand-radical complex in solution, demonstrating that ostensibly simple variations of the ligand structure affect the locus of oxidation in Cu-bis-phenoxide complexes.

Spectroscopic and density functional theory studies of the blue-copper site in M121SeM and C112SeC azurin: Cu-Se versus Cu-S bonding

S K-edge X-ray absorption, UV-vis absorption, magnetic circular dichroism (MCD), and resonance Raman spectroscopies are used to investigate the electronic structure differences among WT, M121SeM, and C112SeC Pseudomonas aeruginosa (P.a) azurin. A comparison of S K-edge XAS of WT and M121SeM azurin and a CuII-thioether model complex shows that the 38% S character in the ground state wave function of the blue-copper (BC) sites solely reflects the Cu-SCys bond. Resonance Raman (rR) data on WT and C112SeC azurin give direct evidence for the kinematic coupling between the Cu-SCys stretch and the cysteine deformation modes in WT azurin, which leads to multiple features in the rR spectrum of the BC site. The UV-vis absorption and MCD data on WT, M121SeM, and C112SeC give very similar C0/D0 ratios, indicating that the C-term MCD intensity mechanism involves Cu-centered spin-orbit coupling (SOC). The spectroscopic data combined with density functional theory (DFT) calculations indicate that SCys and SeCys have similar covalent interactions with Cu at their respective bond lengths of 2.1 and 2.3 A. This reflects the similar electronegativites of S and Se in the thiolate/selenolate ligand fragment and explains the strong spectroscopic similarities between WT and C112SeC azurin.

Triazabicyclodecene: a simple bifunctional organocatalyst for acyl transfer and ring-opening polymerization of cyclic esters

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) is an effective organocatalyst for acyl transfer as well as the ring-opening polymerization of cyclic esters. Its high activity is attributed to its ability to simultaneously activate both esters and alcohols, as demonstrated in a model reaction. This unique mechanism makes TBD a remarkably simple example of a bifunctional catalyst. The simplicity of the reaction conditions, the ready commercial availability of the catalyst, and its high activity provide an accessible methodology to allow future studies of tailor-made polyesters.

Organocatalytic living ring-opening polymerization of cyclic carbosiloxanes

[reaction: see text] An organocatalytic route to narrowly dispersed poly(carbosiloxanes) of predictable molecular weight and end group fidelity is described. N-Heterocyclic carbenes (NHC) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) catalyze the ring opening of cyclic carbosiloxanes. The pK(b) of the catalyst is important in preventing adverse transetherification reactions and obtaining well-defined polymers. Mechanistic studies indicate that hydrogen bonding to TBD or the NHC activates alcohols or silanols for ring-opening reactions.

Stereoselective polymerization of rac- and meso-lactide catalyzed by sterically encumbered N-heterocyclic carbenes

New sterically encumbered N-heterocyclic carbene catalysts were synthesized and used to polymerize rac-lactide to give highly isotactic polylactide or meso-lactide to give heterotactic polylactide.

Organocatalytic Ring Opening Polymerization of Trimethylene Carbonate

A variety of organocatalysts has been surveyed in the ring opening polymerization of trimethylene carbonate. Excellent control was found for several of these catalysts yielding well-defined polycarbonates with molecular weights up to 50,000 g mol(-1), polydispersities below 1.08, and high end-group fidelity. Melt or bulk polymerization was accomplished without loss of control of molecular weight or polydispersity, and random ester-carbonate bulk polymerizations were also demonstrated. Furthermore, by combining disparate polymerization techniques using bifunctional initiators, the mild polymerization conditions allow for the preparation of new block copolymers. Hydrogen-bond activation of monomer and initiator/propagating species is proposed as the underlying mechanism, which can be tuned to mitigate adverse side reactions.

Monolayered organosilicate toroids and related structures: A phase diagram for templating from block copolymers

Here we report the controlled generation of micelle-templated organosilicate nanostructures resulting from self-assembly of a block copolymer/organosilicate mixture followed by organosilicate vitrification and copolymer thermolysis. Variation of solution condition and the copolymer/organosilicate mixture composition generates widely different film morphologies ranging from toroids to linear features to contiguous nanoporous monolayers. The use of reactive organosilicates for block copolymer templation generates functional inorganic nanostructures with thermal and mechanical stability.

Triazabicyclodecene: a simple bifunctional organocatalyst for acyl transfer and ring-opening polymerization of cyclic esters

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) is an effective organocatalyst for acyl transfer as well as the ring-opening polymerization of cyclic esters. Its high activity is attributed to its ability to simultaneously activate both esters and alcohols, as demonstrated in a model reaction. This unique mechanism makes TBD a remarkably simple example of a bifunctional catalyst. The simplicity of the reaction conditions, the ready commercial availability of the catalyst, and its high activity provide an accessible methodology to allow future studies of tailor-made polyesters.

Thiourea-Based Bifunctional Organocatalysis: Supramolecular Recognition for Living Polymerization

A versatile, metal-free, organocatalytic approach to the living ring-opening polymerization of lactide using a bifunctional thiourea-tertiary amine catalyst is described. Mild and highly selective polymerization conditions produced poly(lactides) with predictable molecular weights and extremely narrow polydispersities ( approximately 1.05), characteristic of a living polymerization. The extraordinary selectivity of this catalyst system for polymerization relative to transesterification is remarkably unusual. The low polydispersities and exceptional control observed are a consequence of selective transesterification of lactide relative to the open chain esters. Presumably, the ring strain of lactide provides both a driving force for the polymerization and a kinetic preference for polymerization relative to transesterification with catalyst. We postulate that the initiating/propagating alcohol is activated by acid-base interaction with the tertiary amine moiety and the carbonyl of the lactide monomer is simultaneously activated by hydrogen bonding to the thiourea moiety of the catalyst.

Mechanistic Insights from Reactions between Copper(II)−Phenoxyl Complexes and Substrates with Activated C−H Bonds

The reactivities of two copper(II)-phenoxyl analogues of the oxidized, active form of the metalloenzyme galactose oxidase, [1tBu2]+ and [2tBu2]+, have been studied using the substrates benzyl alcohol and 9,10-dihydroanthracene, for a total of four reactions. The reaction stoichiometries in all cases show a 2:1 ratio of oxidant to benzaldehyde or anthracene product, indicating that [1tBu2]+ and [2tBu2]+ behave ultimately as only one-electron oxidants, but the reaction kinetics each indicate that only a single copper(II)-phenoxyl complex is involved in the rate-determining step. For each substrate, rate laws indicate that [1tBu2]+ and [2tBu2]+ react by different mechanisms: one proceeds by a simple bimolecular reaction, while the other first enters into a substrate-binding equilibrium before subsequently reacting by an intramolecular reaction. The reactions proceeding by the latter mechanism have faster overall rates, which correlates to a lower entropic barrier for the substrate-binding mechanism. Correlation of the reaction rates with the C-H bond dissociation energies of substrates as well as significant deuterium kinetic isotope effects indicates that the rate-determining steps involve hydrogen atom abstraction from the activated C-H bonds. A variable-temperature study (268-308 K) of the nonclassical KIE of the [1tBu2]+/benzyl alcohol reaction (kH/kD = 15 at 298 K) failed to show evidence for quantum tunneling. The rapid sequence by which a second 1 equiv of copper(II)-phenoxyl oxidant completes the reaction after the rate- and product-determining hydrogen atom abstraction step cannot be probed kinetically. Comparisons are made to the reactivities of other copper(II)-phenoxyl complexes reported in the literature and to galactose oxidase itself.

Snapshots of a metamorphosing Cu(II) ground state in a galactose oxidase-inspired complex

The novel ligand 2,6-bis[S-(3,5-di-tert-butyl-2-hydroxyphenyl)sulfanylmethyl]pyridine (H(2)L1) and its copper(II) complex Cu(L1), 1, were synthesized with the aim of constructing a model of the active site of the enzyme galactose oxidase (GOase). Cyclic voltammetry studies show that 1 undergoes ligand-based quasi-reversible oxidations (phenolate/phenoxyl) and reversible metal-based reduction [copper(II)/copper(I)] similar to those of GOase, but at potentials much higher and lower, respectively, than those found for the enzyme. At room temperature, spectrophotometric titrations show that 1 binds strongly to 1 equiv of pyridine. In frozen solutions (77 K), 1 quantitatively binds both pyridine and ethers (e.g., 1,4-dioxane) as assessed by X- and Q-band EPR spectroscopy. Profound shifts in the pattern of g values result, from rhombic (g(1) > g(2) > g(3)) in toluene to either inverted axial patterns (g(1) = g(2) >> g(3)) in the presence of ethers or a near-axial pattern (g(1) >> g(2) > g(3)) in the presence of pyridine. Crystallographic analyses of the parent complex 1.MeCN, the dioxane-bridged dimer [(Cu(L1))(2)((mu-1,4)-1,4-dioxane)].(Me(2)CO)(2) (2), and the pyridine complex [Cu(L1)(pyridine)] (3) show that the pyridine and ether ligands bond to copper at a sixth octahedral position left vacant by the pentadentate NO(2)S(2) coordination mode of L1(2-) and induce perturbations of its geometry. Hybrid DFT calculations based on the crystallographic coordinates combined with perturbation theory expressions for the g values of a d(9) system correlate the results from EPR spectroscopy to the proportions of d(x)(2)(-)(y)(2) and d(z)(2) character in the relevant copper-centered unoccupied molecular orbital. The combination of spectroscopic, structural, and computational results for this set of copper(II) complexes provides a demonstrative example of the physical phenomena underlying rhombic EPR spectra of d(9) systems.

Intramolecular charge transfer and biomimetic reaction kinetics in galactose oxidase model complexes

One-electron oxidation of two structurally similar CuII-diphenolate complexes, 1 and 2, creates EPR-silent CuII-phenoxyl complexes [1]+ and [2]+ that mimic the oxidized form of the enzyme galactose oxidase (GOase). Both model complexes display novel NIR absorptions assigned to phenolate-phenoxyl charge transfer that resemble a tyrosinate-tyrosyl charge-transfer band observed in the enzymatic system. [1]+ and [2]+ react with benzyl alcohol to form 0.5 equivs of benzaldehyde per complex; biomimetic reduction to CuI-phenol complexes is not observed, but such species may exist transiently. Initial kinetic studies show that [2]+ reacts faster with benzyl alcohol than does [1]+, despite being a significantly weaker oxidant (DeltaE degrees = 370 mV). This acceleration is ascribed to mechanistic differences: [2]+ appears to bind substrate prior to the rate-determining step. Large, nonclassical kinetic isotope effects confirm C-H bond cleavage as the rate-determining step in the reactions of both [1]+ and [2]+ with benzyl alcohol, as is the case for GOase.

Oxidatively robust monophenolate-copper(II) complexes as potential models of galactose oxidase

Cupric complexes of a novel phenanthroline-phenolate ligand have strongly distorted coordination geometries and electrochemical properties conducive to modeling the spectroscopy and reactivity of the enzyme galactose oxidase.

Porphyrins incorporating heterocyclic N-oxides: (oxidopyridyl)porphyrins, porphyrin-N-oxides, and a tirapazamine-porphyrin conjugate

Porphyrins containing one to four 4-pyridyl groups as meso-substituents were synthesized via a mixed aldehyde condensation, and then "N-oxidized" with m-chloroperbenzoic acid to produce five novel (oxidopyridyl) porphyrins and seven porphyrin-N-oxides, which were characterized by analysis and spectroscopic methods, especially NMR; an X-ray crystal structure of 5-(1-oxido-4-pyridyl)-10,15,20-triphenylporphyrin was also obtained. Crystals of (oxidopyridyl)triphenylporphyrin are tetragonal, a = b = 15.174(1), c = 13.709(1) Å, Z = 4, space group I2d. The structure was solved by direct methods and refined by full-matrix least-squares procedures to R = 0.031 (Rw = 0.026) for 685 reflections with I [Formula: see text] 3σ(I). Sulfonation of two of the (oxidopyridyl)porphyrins was achieved readily with no loss of oxygen from the oxidopyridyl groups. Tirapazamine (3-amino-1,2,4-benzotriazine-1,4-di-N-oxide) was treated with triphosgene to yield the previously reported 2H-[1,2,4]oxadiazolo[3,2-c][1,2,4]benzotriazin-2-one-5-oxide (1); this reacts like an isocyanate and with 5-(4-aminophenyl)-10,15,20-triphenylporphyrin yields a tirapazamine-porphyrin conjugate (2).Key words: porphyrin-N-oxides, (oxidopyridyl)porphyrins, tirapazamine.

Genetic analysis of tolerance to maize streak virus in maize

Maize streak, incited by maize streak geminivirus (MSV), is a major disease limiting maize (Zea mays L.) production over widespread areas of Africa. To understand the genetic basis of tolerance to MSV, recombinant inbred lines (RILs) derived from the cross of the MSV tolerant inbred Tzi4 with the MSV susceptible inbred Hi34, were evaluated for MSV tolerance. Experiments were conducted using controlled leafhopper (Cicadulina spp.) infestation in one glasshouse experiment at Namulonge, Uganda, and two field experiments at Centro Internacional de Mejoramiento de Maiz y Trigo, Harare, Zimbabwe. Eighty-seven RILs were genotyped at 82 loci by restriction fragment length polymorphism (RFLP) analysis. The association between genotype at RFLP marker loci and MSV tolerance was determined using single-factor analysis of variance (SFAOV), multiple regression, and interval mapping procedures. There was a significant association of MSV tolerance with RFLP markers on the short arm of chromosome 1. By SFAOV, the portion of the phenotypic variance explained by genotype class (R2) for the association between npi262 and the area under disease progress curve (AUDPC) measure of MSV tolerance was as high as 76% in field experiments. Interval mapping analyses (Knapp and Bridges 1990; Nelson 1997) identified the chromosome region bracketed by bnl12.06a and npi262 as explaining the largest proportion of the variation in MSV tolerance. After classification of symptom responses from the final field ratings into resistant and susceptible classes, qualitative analysis of data fit a chi-square test to a 1:1 Mendelian ratio, further indicating presence of a single major gene. Multipoint linkage analysis placed this gene, designated msv1, at a genetic distance of 3 cM distal to npi262. Identification of the tightly linked molecular marker locus npi262 should greatly aid ongoing conversion of susceptible African varieties to maize streak resistance.Key words: Zea mays L., Cicadulina spp., host resistance, gene mapping, molecular markers.

Interaction of Ht and Partial Resistance to Exserohilum turcicum in Maize

Components of northern leaf blight resistance in maize due to race-specific resistance controlled by the Ht gene, partial resistance derived from inbred H99, and a combination of the two kinds of resistance, were studied subsequent to inoculation with Exserohilum turcicum race O. Lesion types, number of lesions (lesion number), percent leaf area affected (severity), and area under the disease progress curve (AUDPC) based on lesion number and severity were assessed in field studies conducted at two locations in Uganda and one location in Ohio in 1993. Lesion types observed were consistent for genotypes across locations. In general, significant differences among genotypes for data based on lesion number and severity were consistent for AUDPC based on lesion number and severity, respectively, at all locations. In Ohio, both Ht and partial resistance were effective in limiting disease development. In Uganda, susceptible inbreds (A619, A635, and B73) generally had higher severity than genotypes with partial resistance (H99, Mo17, and Babungo 3). However, there was a difference in response among genotypes depending on disease intensity at each location. Ht resistance and moderate partial resistance did not greatly affect lesion number at the higher disease intensity location, compared with the susceptible inbreds, but at the lower disease intensity location genotypes with partial resistance had fewer lesions than susceptible inbreds or the Ht conversions of the susceptible inbreds. At both plot locations, genotypes with partial resistance had lower severity than the susceptible inbreds or Ht conversions of the susceptible inbreds. Hybrids derived from crossing H99 with genotypes with moderate levels of partial resistance (Mo17 and Babungo 3) did not have significantly lower lesion numbers than hybrids of susceptible inbreds crossed with H99, but severity was significantly lower on these hybrids at the high disease intensity location. Results indicate that the level of partial resistance in H99 would be as effective in controlling northern leaf blight as using Ht resistance, or a combination of Ht resistance and moderate levels of partial resistance as found in Mo17.

Intron-mediated enhancement of gene expression in maize (Zea mays L.) and bluegrass (Poa pratensis L.)

We report a strength comparison of a large variety of monocot and dicot intron-containing fragments inserted in the 5' untranslated leader, between the CaMV 35S promoter and the uidA gene (coding for the ß-glucuronidase: GUS). Relative strengths of the intron-containing fragments were evaluated by comparing transient GUS expression after particle bombardment in embryogenic maize and bluegrass suspension cultures. Our results confirm a dramatic dependence on the presence of an intron for chimeric gene expression in both species. On average, the maize first intron of ubi1 provided the highest enhancement of gene expression in maize and bluegrass (71- and 26-fold enhancement, respectively). Half of the introns tested affected gene expression differently in bluegrass and maize. This suggests that the intron-mediated enhancement of gene expression generally obtained with maize may not be fully applicable to all monocots. We also report enhancement of gene expression (92-fold) in a monocot species by a dicot intron (chsA intron).

Isolation and Partial Characterization of a Seed Lectin from Tepary Bean that Delays Bruchid Beetle Development

Four isolectin forms of a seed lectin from mature seed of tepary bean (Phaseolus acutifolius) were isolated using solubility fractionation, affinity chromatography, and high performance liquid chromatography. The subunits are polypeptides with an apparent molecular mass of 30,000 daltons. The 30 kilodalton subunits are produced starting approximately 13 days after flowering and subsequently comprise a major fraction of the proteins found in the mature seed. The amino terminus of each isolectin fraction was determined to be highly homologous with that of the subunits of common bean (Phaseolus vulgaris L.) phytohemagglutinin (PHA). The tepary isolectin cross-reacts with both erythroagglutinating and leucoagglutinating subunits of PHA antibodies, although differential cross-reactivity was noted. A seed protein fraction enriched in tepary bean lectin was found to be toxic to bean bruchid beetles (Acanthoscelides obtectus), when incorporated into their diets at incremental concentrations from (1-5% w/w) above that of PHA concentrations in mature seeds of the susceptible common bean variety "Red Kidney."

Evaluation of bond strength of six porcelain repair systems

The shear bond strength of six porcelain repair systems was evaluated in vitro at 48 hours and 3 months. Water storage and thermocycling significantly lowered the mean shear bond strength for all kits tested. However, at the end of 3 months Scotchprime resin had the highest mean bond strength. With current products, porcelain repair remains an interim clinical procedure.

Echocardiographic evaluation of the Valsalva Maneuver in healthy subjects and patients with and without heart failure

The Valsalva maneuver was evaluated by echocardiography in three groups: A) 10 normal volunteers, B) 10 patients with no history of heart failure and normal ejection fractions, and C) 10 patients with heart failure and depressed ejection fractions. Groups A and B had a significant fall in left ventricular internal dimensions and calculated stroke volume by end strain which returned rapidly to baseline in recovery without significant overshoot. Arterial pressure showed a signoidal strain pattern with a normal overshoot in early recovery in all group B patients. In group C ventricular dimensions did not diminish during strain; arterial pressures showed a "square wave" pressure elevation during strain without an overshoot in recovery. Echocardiography allows a new approach to evaluate further the left ventricular response to the Valsalva maneuver. Patients with severely depressed ejection fractions, unlike those with normal ventricular function, are unable to alter stroke output in response to acutely increased intrathoracic pressure. A square wave pressure response is a likely consequence of a fixed stroke output during the strain maneuver.

The influence of left ventricular stroke volume on aortic root motion: an echocardiographic study

Aortic root motion was studied in 24 normal volunteers at rest and during the Valsalva maneuver, isometric exercise, and amyl nitrite inhalation. In addition root motion was correlated with the stroke volumes determined at cardiac catheterization in 24 patients. The root has distinct systolic movement, the amplitude and duration of which were easily measured both at rest and during the interventions. At rest,the mean (+/-1 SE) systolic amplitude of the anterior aortic wall was 11.2 +/- 0.5 mm and that of the posterior wall 9.5 +/- 0.3 mm. During the strain phase of the Valsalva maneuver anterior wall amplitude fell to 8.2 +/- 0.4 mm and the posterior wall to 7.3 +/- 0.5 mm (P less than 0.001). With release, anterior wall amplitude rebounded to 12.5 +/- 0.8 mm and the posterior wall to 10.8 +/- o.5 mm, values greater than control (P less than 0.01). With isometric exercise there was no change in amplitude compared to rest; however, amyl nitrite caused an increase in the anterior wall to 13.5 +/-0.8 mm and posterior wall to 11.9 +/-0.6 mm (P less than 0.01). In the patient group the amplitude of posterior wall motion correlated weakly with cardiac index (r = 0.63) and stronger with stroke index (r = 0.78). This study quantifies the echocardiographic pattern of normal aortic root motion. The findings indicate that the aortic root motion is an index of stroke volume; they further suggest that root motion is acutely sensitive to variations in stroke volume since its amplitude changed in accord with the documented effects of the employed maneuvers on stroke volume.