Nuclear Magnetic Resonance Chemical Shift as a Probe for Single-Molecule Charge Transport

Existing modelling tools, developed to aid the design of efficient molecular wires and to better understand their charge-transport behaviour and mechanism, have limitations in accuracy and computational cost. Further research is required to develop faster and more precise methods that can yield information on how charge transport properties are impacted by changes in the chemical structure of a molecular wire. In this study, we report a clear semilogarithmic correlation between charge transport efficiency and nuclear magnetic resonance chemical shifts in multiple series of molecular wires, also accounting for the presence of chemical substituents. The NMR data was used to inform a simple tight-binding model that accurately captures the experimental single-molecule conductance values, especially useful in this case as more sophisticated density functional theory calculations fail due to inherent limitations. Our study demonstrates the potential of NMR spectroscopy as a valuable tool for characterising, rationalising, and gaining additional insights on the charge transport properties of single-molecule junctions.

Enhanced charge transport across molecule-nanoparticle-molecule sandwiches

The electrical properties of large area molecular devices consisting of gold nanoparticles (GNPs) sandwiched between a double layer of alkanedithiol linkers have been examined. These devices have been fabricated by a facile bottom-up assembly in which an alkanedithiol monolayer is first self-assembled on an underlying gold substrate followed by nanoparticle adsorption and then finally assembly of the top alkanedithiol layer. These devices are then sandwiched between the bottom gold substrates and a top eGaIn probe contact and current-voltage (I-V) curves recorded. Devices have been fabricated with 1,5-pentanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol and 1,10-decanedithiol linkers. In all cases the electrical conductance of the double SAM junctions with GNPs is higher than the corresponding and much thinner single alkanedithiol SAM. Competing models for this enhanced conductance are discussed and it is suggested to have a topological origin arising from how the devices assemble or structure during the fabrication, which gives more efficient cross device electron transport pathways without the GNPs producing short circuits.

Single molecule vs. large area design of molecular electronic devices incorporating an efficient 2-aminepyridine double anchoring group

When a molecule is bound to external electrodes by terminal anchor groups, the latter are of paramount importance in determining the electrical conductance of the resulting molecular junction. Here we explore the electrical properties of a molecule with bidentate anchor groups, namely 4,4'-(1,4-phenylenebis(ethyne-2,1-diyl))bis(pyridin-2-amine), in both large area devices and at the single molecule level. We find an electrical conductance of 0.6 × 10-4G0 and 1.2 × 10-4G0 for the monolayer and for the single molecule, respectively. These values are approximately one order of magnitude higher than those reported for monodentate materials having the same molecular skeleton. A combination of theory and experiments is employed to understand the conductance of monolayer and single molecule electrical junctions featuring this new multidentate anchor group. Our results demonstrate that the molecule has a tilt angle of 30° with respect to the normal to the surface in the monolayer, while the break-off length in the single molecule junction occurs for molecules having a tilt angle estimated as 40°, which would account for the difference in their conductance values per molecule. The bidentate 2-aminepyridine anchor is of general interest as a contact group, since this terminal functionalized aromatic ring favours binding of the adsorbate to the metal contact resulting in enhanced conductance values.

Hemlock Woolly Adelgid (Hemiptera: Adelgidae) Abundance and Hemlock Canopy Health Numerous Years After Imidacloprid Basal Drench Treatments: Implications for Management Programs

Hemlock woolly adelgid (Adelges tsugae [Annand]), an invasive insect in the eastern United States, has caused widespread decline of eastern hemlock, Tsuga canadensis (L.) Carriére. Imidacloprid basal drench treatments were assessed 4-7 yr after a single treatment to determine hemlock woolly adelgid population suppression and effects on hemlock canopy health. The effects of sampling site, years post-treatment, and hemlock diameter at breast height (DBH) size classes were evaluated relative to imidacloprid treatment on hemlock woolly adelgid populations and hemlock canopy health characteristics. The influence of hemlock woolly adelgid populations on canopy health characteristics was also assessed. Imidacloprid treatments resulted in low-level hemlock woolly adelgid populations 7 yr post-treatment. Hemlock woolly adelgid was present on more hemlocks 7 yr compared with 4-6 yr post-treatment. Smaller hemlocks, dosed with 0.7 g active ingredient (AI)/2.5 cm DBH, had higher populations of hemlock woolly adelgid than the largest size class, which were treated at twice that dosage. Concentrations of imidacloprid and its olefin metabolite below the LC₅₀ were sufficient for suppression of hemlock woolly adelgid populations, which suggests an additive effect of imidacloprid and olefin that compounds hemlock woolly adelgid mortality over many generations. Hemlock woolly adelgid populations observed in this study were too low to have an observable effect on hemlock canopy health, indicating that application intervals of up to 7 yr may be adequate to protect hemlocks.

Assessment of Imidacloprid and Its Metabolites in Foliage of Eastern Hemlock Multiple Years Following Treatment for Hemlock Woolly Adelgid, Adelges tsugae (Hemiptera: Adelgidae), in Forested Conditions

Widespread decline and mortality of eastern hemlock, Tsuga canadensis (L.) Carrière, have been caused by hemlock woolly adelgid, Adelges tsugae (Annand) (HWA) (Hemiptera: Adelgidae). The current study is a retrospective analysis conducted in collaboration with Great Smoky Mountains National Park (GRSM) to determine longevity of imidacloprid and its insecticidal metabolites (imidacloprid olefin, 5-hydroxy, and dihydroxy) in GRSM's HWA integrated pest management (IPM) program. Foliage samples were collected from three canopy strata of hemlocks that were given imidacloprid basal drench treatments 4-7 yr prior to sampling. Foliage was analyzed to assess concentrations in parts per billion (ppb) of imidacloprid and its metabolites. Imidacloprid and its olefin metabolite were present in most, 95 and 65%, respectively, branchlets 4-7 yr post-treatment, but the 5-hydroxy and dihydroxy metabolites were present in only 1.3 and 11.7%, respectively, of the branchlets. Imidacloprid and olefin concentrations significantly decreased between 4 and 7 yr post-treatment. Concentrations of both imidacloprid and olefin were below the LC50 for HWA 5-7 yr post-treatment. Knowledge of the longevity of imidacloprid treatments and its metabolite olefin can help maximize the use of imidacloprid in HWA IPM programs.

Single-molecule solvation-shell sensing

We present a new route to single-molecule sensing via solvation shells surrounding a current-carrying backbone molecule. As an example, we show that the presence of a water solvation shell "gates" the conductance of a family of oligothiophene-containing molecular wires, and that the longer the oligothiophene, the larger is the effect. For the longest example studied, the molecular conductance is over 2 orders of magnitude larger in the presence of a shell comprising just 10 water molecules. A first principles theoretical investigation of electron transport through the molecules, using the nonequilibrium Green's function method, shows that water molecules interact directly with the thiophene rings, significantly shifting transport resonances and greatly increasing the conductance. This reversible effect is confirmed experimentally through conductance measurements performed in the presence of moist air and dry argon.

Bifunctional electrocatalysis in pt-ru nanoparticle systems

Pt-Ru alloys are prominent electrocatalysts in fuel cell anodes as they feature a very high activity for the oxidation of reformate and methanol. The improved CO tolerance of these alloys has been discussed in relation to the so-called ligand and bifunctional mechanisms. Although these effects have been known for many years, they are still not completely understood. A new approach that bridges the gap between single crystals and practical catalysts is presented in this paper. Nanoparticulate model systems attached to an oxidized glassy carbon electrode were prepared by combining both ligand-stabilized and spontaneously deposited Pt and Ru nanoparticles. These electrodes showed very different voltammetric responses for CO and methanol oxidation. The cyclic voltammograms were deconvoluted into contributions attributed to Pt, Ru, and Pt-Ru contact regions to quantify the contribution of the latter to the bifunctional mechanism. Scanning transmission electron microscopy confirmed the proximity of Pt and Ru nanoparticles in the different samples.

Site-specific interactions of copper(II) ions with heparin revealed with complementary (SRCD, NMR, FTIR and EPR) spectroscopic techniques

The interactions between Cu(II) ions and heparin were investigated using several complementary spectroscopic techniques. NMR indicated an initial binding phase involving specific coordination to four points in the structure that recur in slightly different environments throughout the heparin chain; the carboxylic acid group and the ring oxygen of iduronate-2-O-sulfate, the glycosidic oxygen between this residue and the adjacent (towards the reducing end) glucosamine and the 6-O-sulfate group. In contrast, the later binding phase showed little structural specificity. One- and two-dimensional correlated FTIR revealed that complex out of phase (asynchronous) conformational changes also occurred during the titration of Cu(II) ions into heparin, involving the CO and N-H stretches. EPR demonstrated that the environments of the Cu(II) ions in the initial binding phase were tetragonal (with slightly varied geometry), while the later non-specific phases exhibited conventional coordination. Visible spectroscopy confirmed a shift of the absorbance maximum. Titration of Cu(II) ions into a solution of heparin indicated (both by analysis of FTIR and EPR spectra) that the initial binding phase was complete by 15-20 Cu(II) ions per chain; thereafter the ions bound in the non-specific mode. Hetero-correlation spectroscopy (FTIR-CD) improved resolution and assisted assignment of the broad CD features from the FTIR spectra and indicated both in-phase and more complex out of phase (synchronous and asynchronous, respectively) changes in interactions within the heparin molecule during the titration of Cu(II) ions.

Single-Molecule Conductance of Redox Molecules in Electrochemical Scanning Tunneling Microscopy

Experimental data and theoretical notions are presented for 6-[1'-(6-mercapto-hexyl)-[4,4']bipyridinium]-hexane-1-thiol iodide (6V6) "wired" between a gold electrode surface and tip in an in situ scanning tunneling microscopy configuration. The viologen group can be used to "gate" charge transport across the molecular bridge through control of the electrochemical potential and consequently the redox state of the viologen moiety. This gating is theoretically considered within the framework of superexchange and coherent two-step notions for charge transport. It is shown here that the absence of a maximum in the Itunneling versus electrode potential relationship can be fitted by a "soft" gating concept. This arises from large configurational fluctuations of the molecular bridge linked to the gold contacts by flexible chains. This view is incorporated in a formalism that is well-suited for data analysis and reproduces in all important respects the 6V6 data for physically sound values of the appropriate parameters. This study demonstrates that fluctuations of isolated configurationally "soft" molecules can dominate charge transport patterns and that theoretical frameworks for compact monolayers may not be directly applied under such circumstances.

Protein–GAG interactions: new surface-based techniques, spectroscopies and nanotechnology probes

New approaches, rooted in the physical sciences, have been developed to gain a more fundamental understanding of protein–GAG (glycosaminoglycan) interactions. DPI (dual polarization interferometry) is an optical technique, which measures real-time changes in the mass of molecules bound at a surface and the geometry of the bound molecules. QCM-D (quartz crystal microbalance-dissipation), an acoustic technique, measures the mass and the viscoelastic properties of adsorbates. The FTIR (Fourier-transform IR) amide bands I, II and III, resulting from the peptide bond, provide insight into protein secondary structure. Synchrotron radiation CD goes to much shorter wavelengths than laboratory CD, allowing access to chromophores that provide insights into the conformation of the GAG chain and of β-strand structures of proteins. To tackle the diversity of GAG structure, we are developing noble metal nanoparticle probes, which can be detected at the level of single particles and so enable single molecule biochemistry and analytical chemistry. These new approaches are enabling new insights into structure–function relationships in GAGs and together they will resolve many of the outstanding problems in this field.

Fullerene-linked Pt nanoparticle assemblies

Fullerene-Pt nanoparticle assemblies were prepared by attachment and immobilisation of different Pt nanoparticles on a gold electrode using molecular layers of C60 as a linker system. These assemblies were active for the methanol oxidation following treatment with CO.

A gravimetric analysis of protein-oligosaccharide interactions

Interactions between an immobilized, heparin-derived octasaccharide and growth factors have been observed using a quartz crystal microbalance-dissipation (QCM-D). This device can measure the amount of growth factors binding to the octasaccharide surface and also the change of dissipation of the surface. Dissipation is a measure of how the adhered material 'damps' the surface vibrations. The octasaccharides were anchored through their reducing ends by the intermediary of the alkanethiol molecule, which covalently binds to the crystal surface through the thiol group. As expected, heparin sulphate binding growth factors bound to the octasaccharide, but the change in mass of growth factor bound per unit change in dissipation is different for the different growth factors. Suggesting that the structures of the various growth factor-octasaccharide complexes are different, therefore, indicates that the change in dissipation can give insights into the structure, orientation and packing of the oligosaccharide-growth factor complexes.

Reflection anisotropy spectroscopy: A new probe for the solid-liquid interface

Introducing reflection anisotropy spectroscopy (RAS) as a new probe for solid-liquid interfaces, we present results for the Au(110)/electrolyte interface which serves as a model system. We demonstrate that RAS is sensitive to surface phase transitions, step morphology, and electronic surface states. Using an empirical approach, the RA spectra are reproduced and features are identified which reflect the known character of the bias voltage driven (2x1) to (1x1) phase transition. RAS is established as an experimental technique to probe the electronic structure of solid-liquid interfaces in real time to study a wide range of interface properties.

A nanometre-scale electronic switch consisting of a metal cluster and redox-addressable groups

So-called bottom-up fabrication methods aim to assemble and integrate molecular components exhibiting specific functions into electronic devices that are orders of magnitude smaller than can be fabricated by lithographic techniques. Fundamental to the success of the bottom-up approach is the ability to control electron transport across molecular components. Organic molecules containing redox centres-chemical species whose oxidation number, and hence electronic structure, can be changed reversibly-support resonant tunnelling and display promising functional behaviour when sandwiched as molecular layers between electrical contacts, but their integration into more complex assemblies remains challenging. For this reason, functionalized metal nanoparticles have attracted much interest: they exhibit single-electron characteristics (such as quantized capacitance charging) and can be organized through simple self-assembly methods into well ordered structures, with the nanoparticles at controlled locations. Here we report scanning tunnelling microscopy measurements showing that organic molecules containing redox centres can be used to attach metal nanoparticles to electrode surfaces and so control the electron transport between them. Our system consists of gold nanoclusters a few nanometres across and functionalized with polymethylene chains that carry a central, reversibly reducible bipyridinium moiety. We expect that the ability to electronically contact metal nanoparticles via redox-active molecules, and to alter profoundly their tunnelling properties by charge injection into these molecules, can form the basis for a range of nanoscale electronic switches.

Effect of topical and subcutaneous epinephrine in combination with topical thrombin in blood loss during immediate near-total burn wound excision in pediatric burned patients

Bleeding is a major concern during burn wound excision. To evaluate the efficacy of epinephrine to control blood loss, a prospective cohort of 42 pediatric patients were examined. Half of the patients received topical epinephrine to excised wounds and donor sites and subcutaneous epinephrine to scalp donor sites during total burn excision, while the other half did not. Both groups of patients received bovine topical thrombin sprayed at a concentration of 1000 U/ml. Mean blood loss in the epinephrine group was 1090 ml (range 20-4000), with a blood loss of 0.48+/-0.12 ml/cm2 excised, while the control group was 1271 ml (range 40-3750) and 0.51+/-0.15 ml/cm2. Differences in preoperative and postoperative hematocrits were respectively -3.4+/-7.8 and -4.6+/-7.5. The groups were not statistically different in this analysis. Subgroup analysis by age, burn size and time of burn to excision showed no differences. No complications or side effects of the use of the vasopressor solution occurred. In conclusion, no differences in blood loss were found between the groups. The routine use of local epinephrine during total wound excision in combination with topical thrombin in pediatric patients operated within 24 h after the admission may not be necessary. The effect of topical thrombin on blood loss should be analyzed separately.

An approach to long-range electron transfer mechanisms in metalloproteins: in situ scanning tunneling microscopy with submolecular resolution

In situ scanning tunneling microscopy (STM) of redox molecules, in aqueous solution, shows interesting analogies and differences compared with interfacial electrochemical electron transfer (ET) and ET in homogeneous solution. This is because the redox level represents a deep indentation in the tunnel barrier, with possible temporary electronic population. Particular perspectives are that both the bias voltage and the overvoltage relative to a reference electrode can be controlled, reflected in spectroscopic features when the potential variation brings the redox level to cross the Fermi levels of the substrate and tip. The blue copper protein azurin adsorbs on gold(111) via a surface disulfide group. Well resolved in situ STM images show arrays of molecules on the triangular gold(111) terraces. This points to the feasibility of in situ STM of redox metalloproteins directly in their natural aqueous medium. Each structure also shows a central brighter contrast in the constant current mode, indicative of 2- to 4-fold current enhancement compared with the peripheral parts. This supports the notion of tunneling via the redox level of the copper atom and of in situ STM as a new approach to long-range electron tunneling in metalloproteins.

Acetaminophen in the management of background pain in children post-burn

This retrospective review evaluated the pain management of 395 acutely burned pediatric patients who were treated by a pain management protocol emphasizing acetaminophen as the initial medication to control background pain. Pain was assessed by using standardized instruments based on observations by patients, nurses, and parents. Morphine was added when scheduled acetaminophen (10-15 mg/kg/4 hr) did not control background pain. Fifty percent of the children received only acetaminophen to control background pain. Younger children and children with the smallest burns, regardless of age, were likely to be managed with acetaminophen alone. Most peak serum concentrations of acetaminophen were less than 10 micrograms/mL. When needed, children also received medication for painful procedures, anxiety, and posttraumatic stress symptoms. These additional medications were not more frequently given to children receiving only acetaminophen for background pain. These data suggest that acetaminophen is a safe, useful medication for the control of post-burn background pain in some children.

The effect of erythropoietin in normal healthy volunteers and pediatric patients with burn injuries

BACKGROUND

Surgical procedures result in blood loss that can require replacement transfusions. Such therapy may result in multiple adverse sequelae, including transmission of infectious diseases and immune impairment. Alternative therapies are therefore desirable.

METHODS

We evaluated the ability of recombinant human erythropoietin (rEPO) to increase red blood cell production in both normal healthy volunteers and patients with burn injuries. The effect of rEPO on immune function in the volunteers was also evaluated. The volunteers received 150 units/kg rEPO daily for 7 days, with immune function and hematopoiesis assayed on days 0, 7, and 14. The patients with burn injuries received either 500 units/kg/day rEPO with iron supplementation or merely the iron.

RESULTS

rEPO increased erythropoiesis in both the volunteers and the patients with burn injuries. Failure to provide iron supplementation to the volunteers resulted in significant depletion of iron stores with a concomitant impairment in immune function that paralleled the iron depletion.

CONCLUSIONS

rEPO therapy offers the potential to increase red blood cell production in surgical patients. Failure to provide iron supplementation in patients receiving rEPO can lead to a rapid depletion of iron stores and may contribute to an immune dysfunction.

Inhibition of thromboxane synthesis reduces endotoxin-induced right ventricular failure in sheep

BACKGROUND AND METHODS

There is a marked decrease of the right ventricular ejection fraction after the administration of a bolus of endotoxin to sheep. This hemodynamic response may be the result of thromboxane-mediated pulmonary hypertension. Right ventricular function was studied in an ovine model after the administration of endotoxin (1 microgram/kg Escherichia coli) with and without pretreatment with OKY-046, a selective thromboxane synthetase inhibitor.

RESULTS

OKY-046 attenuated the endotoxin-induced increase in pulmonary arterial pressure and prevented the early decreases in right ventricular ejection fraction and cardiac output. However, thromboxane synthetase inhibition failed to prevent endotoxin-induced hypoxemia. The marked increase in plasma thromboxane concentrations, which is usually seen after the administration of endotoxin, was prevented by pretreating the animals with OKY-046. On the other hand, increased plasma prostacyclin concentrations were observed in sheep treated with the thromboxane synthetase inhibitor.

CONCLUSION

This series of experiments shows that the early endotoxin-induced decrease in right ventricular ejection fraction can be alleviated by the application of OKY-046.

Halothane markedly reduces mesenteric blood flow but does not impair gut mucosal oxygenation in pigs

We investigated the effect of halothane on in mesenteric blood flow and gut mucosal oxygenation. Pittman-Moore mini-pigs (n = 6) were chronically instrumented with aortic, pulmonary arterial (Swan-Ganz), and mesenteric venous catheters and an intestinal tonometer. Blood flow in the superior mesenteric artery was measured with an ultrasonic flow probe. On the day of the experiment, data were obtained before and during halothane administration (1.5% end-tidal). Halothane caused a marked decrease in mesenteric blood flow, associated with an increase in mesenteric vascular resistance. Likewise mesenteric oxygen delivery and consumption were significantly decreased under halothane, while the oxygen extraction rate of the intestine was not significantly changed. There was no significant change in intramucosal gut pH after halothane administration, which indicates that an adequate mucosal tissue oxygenation was maintained. We conclude that the marked halothane-induced reduction in mesenteric blood flow did not seem to impair the oxygenation of the gut mucosa in our experimental model.

Fuel Ethanol from Cellulosic Biomass

Ethanol produced from cellulosic biomass is examined as a large-scale transportation fuel. Desirable features include ethanol's fuel properties as well as benefits with respect to urban air quality, global climate change, balance of trade, and energy security. Energy balance, feedstock supply, and environmental impact considerations are not seen as significant barriers to the widespread use of fuel ethanol derived from cellulosic biomass. Conversion economics is the key obstacle to be overcome. In light of past progress and future prospects for research-driven improvements, a cost-competitive process appears possible in a decade.

Early burn wound excision significantly reduces blood loss

The hypothesis that near-total early excision of large burns in children can be performed safely with a reduction in blood loss was tested. Of 1662 acutely burned patients admitted to this institution between 1982 and 1989, 594 underwent near-total excision of cutaneous flame or scald burn injuries in a single procedure. Operations took less than 3 hours and there were no operative deaths. Blood losses in burns of more than 30% total body surface area (TBSA) were significantly less at 0.40 +/- 0.06 mL/cm2 and 0.49 +/- 0.49 mL/cm2 excised when surgery was performed within the first 24 hours or after the 16th day after burn, respectively, when compared to 0.75 +/- 0.02 mL/cm2 for those excised between 2 and 16 days after burn (p less than 0.05). Blood loss for burns of less than 30% TBSA was of 1.19 +/- 0.13 mL/cm2. Early excision did not increase mortality rate when compared to later excision times. We suggest that near-total excision of large burns within the first 24 hours reduces blood requirements and morbidity without adversely altering hemodynamic stability or increasing mortality risks.

Monitoring patients during helicopter flight

In 11 patients being transported via helicopter we monitored heart rate, arterial oxygen saturation, and systolic blood pressure with a pulse oximeter. We were able to obtain vital signs in 10 of 11 patients. The pulse oximeter was a useful tool in monitoring vital signs intraflight.

Does measurement of systolic blood pressure with a pulse oximeter correlate with conventional methods?

The pulse oximeter is commonly used in the operating room. We evaluated the use of a pulse oximeter to monitor systolic blood pressure in 20 healthy volunteers and 42 anesthetized patients. We compared the pulse oximeter method of measuring systolic blood pressure with the cuff methods using Korotkoff sounds and Doppler ultrasound as well as with direct pressure measurement through an intraarterial cannula. Systolic blood pressure values obtained by pulse oximeter correlated well with values obtained by other conventional methods. The best correlation was found with Doppler ultrasound (r = 0.996) and the worst with arterial cannulation (r = 0.880). We conclude that this method can be used intraoperatively to measure systolic blood pressure.

Long-term airway sequelae in a pediatric burn population

All admissions to the Shriner's Burn Institute in Galveston over a 5-year period were reviewed. One hundred of 1,092 patients admitted (9.2%) required airway support (endotracheal intubation or tracheostomy) for more than 24 hours. All clinical variables relating to general presentation and airway care were tabulated. Children who required open airway operations for resolution of acquired airway defects were analyzed separately. No predictive factors could be identified. Guidelines for optimal airway management in the burned child are reviewed.

The effect of solubilization on the properties of the insulin receptor of human placental membranes

The insulin receptor for human placental membranes has been solubilized in Triton X-100 and its properties have been examined in detail. Binding of [125 I]iodoinsulin to the soluble receptor is markedly inhibited by increas-ng concentrations of Triton X-100, due to a fall in receptor affinity. In 0.02--0.10% Triton X-100, the soluble receptor exhibits all the essential characteristics of the intact or particulate receptor. These include strict specificity for insulin and its analogues, increase in steady state binding with decrease in temperature, a pH optimum at 7.8--8.0, and negatively cooperative site-site interactions. The initial association rate of [125 I]iodoinsulin and the soluble receptor is a direct function of temperature, but the level of steady-state binding is lower at higher temperatures due to a marked increase in dissociation rate. Scatchard binding plots are curvilinear and show a large increase in affinity at 4 C with no change in total binding capacity (R0); increased binding to the particulate placental membrane at 4 C is due chiefly to an increase in R3. Negative cooperatively in the soluble receptor has been confirmed by kinetic experiments; thus, the dissociation of [125I]iodoinsulin from the receptor in the presence of "infinite" dilution is accelerated in the presence of 10(-8) M unlabeled insulin. The apparent molecular weight of the placental receptor, determined by gel filtration on 6% agarose, is approximately 300,000. These studies show that the basic properties of the insulin receptor do not depend on it being an integral conponent of the cell membrane.

The total synthesis of (±)-laurinterol and related compounds

(�)-Debromolaurinterol acetate (21c) has been synthesized from 2,4- dibromo-5-methoxytoluene by an eight-step sequence which constitutes a formal total synthesis of each of the racemates of laurinterol (1), debromolaurinterol(2), aplysin (3), and debromo-aplysin (4), because of previous interconversions of these sesquiterpenes.