Influences of Dilute Organic Adsorbates on the Hydration of Low-Surface-Area Silicates.

Competitive adsorption of dilute quantities of certain organic molecules and water at silicate surfaces strongly influence the rates of silicate dissolution, hydration, and crystallization. Here, we determine the molecular-level structures, compositions, and site-specific interactions of adsorbed organic molecules at low absolute bulk concentrations on heterogeneous silicate particle surfaces at early stages of hydration. Specifically, dilute quantities (∼0.1% by weight of solids) of the disaccharide sucrose or industrially important phosphonic acid species slow dramatically the hydration of low-surface-area (∼1 m(2)/g) silicate particles. Here, the physicochemically distinct adsorption interactions of these organic species are established by using dynamic nuclear polarization (DNP) surface-enhanced solid-state NMR techniques. These measurements provide significantly improved signal sensitivity for near-surface species that is crucial for the detection and analysis of dilute adsorbed organic molecules and silicate species on low-surface-area particles, which until now have been infeasible to characterize. DNP-enhanced 2D (29)Si{(1)H}, (13)C{(1)H}, and (31)P{(1)H} heteronuclear correlation and 1D (29)Si{(13)C} rotational-echo double-resonance NMR measurements establish hydrogen-bond-mediated adsorption of sucrose at distinct nonhydrated and hydrated silicate surface sites and electrostatic interactions with surface Ca(2+) cations. By comparison, phosphonic acid molecules are found to adsorb electrostatically at or near cationic calcium surface sites to form Ca(2+)-phosphonate complexes. Although dilute quantities of both types of organic molecules effectively inhibit hydration, they do so by adsorbing in distinct ways that depend on their specific architectures and physicochemical interactions. The results demonstrate the feasibility of using DNP-enhanced NMR techniques to measure and assess dilute adsorbed molecules and their molecular interactions on low-surface-area materials, notably for compositions that are industrially relevant.

Reactions and surface interactions of saccharides in cement slurries.

Glucose, maltodextrin, and sucrose exhibit significant differences in their alkaline reaction properties and interactions in aluminate/silicate cement slurries that result in diverse hydration behaviors of cements. Using 1D solution- and solid-state (13)C nuclear magnetic resonance (NMR), the structures of these closely related saccharides are identified in aqueous cement slurry solutions and as adsorbed on inorganic oxide cement surfaces during the early stages of hydration. Solid-state 1D (29)Si and 2D (27)Al{(1)H} and (13)C{(1)H} NMR techniques, including the use of very high magnetic fields (18.8 T), allow the characterization of the hydrating silicate and aluminate surfaces, where interactions with adsorbed organic species influence hydration. These measurements establish the molecular features of the different saccharides that account for their different adsorption behaviors in hydrating cements. Specifically, sucrose is stable in alkaline cement slurries and exhibits selective adsorption at hydrating silicate surfaces but not at aluminate surfaces in cements. In contrast, glucose degrades into linear saccharinic or other carboxylic acids that adsorb relatively weakly and nonselectively on nonhydrated and hydrated cement particle surfaces. Maltodextrin exhibits intermediate reaction and sorption properties because of its oligomeric glucosidic structure that yields linear carboxylic acids and stable ring-containing degradation products that are similar to those of the glucose degradation products and sucrose, respectively. Such different reaction and adsorption behaviors provide insight into the factors responsible for the large differences in the rates at which aluminate and silicate cement species hydrate in the presence of otherwise closely related saccharides.

Stereotactic body radiation therapy for nonresectable tumors of the pancreas.

BACKGROUND: Stereotactic body radiation therapy (SBRT) has emerged as a potential treatment option for local tumor control of primary malignancies of the pancreas. We report on our experience with SBRT in patients with pancreatic adenocarcinoma who were found not to be candidates for surgical resection. METHODS: The prospective database of the first 20 consecutive patients receiving SBRT for unresectable pancreatic adenocarcinomas and a neuroendocrine tumor under an IRB approved protocol was reviewed. Prior to SBRT, cylindrical solid gold fiducial markers were placed within or around the tumor endoscopically (n = 13), surgically (n = 4), or percutaneously under computerized tomography (CT)-guidance (n = 3) to allow for tracking of tumor during therapy. Mean radiation dose was 25 Gray (Gy) (range 22-30 Gy) delivered over 1-3 fractions. Chemotherapy was given to 68% of patients in various schedules/timing. RESULTS: Patients had a mean gross tumor volume of 57.2 cm(3) (range 10.1-118 cm(3)) before SBRT. The mean total gross tumor volume reduction at 3 and 6 mo after SBRT were 21% and 38%, respectively (P < 0.05). Median follow-up was 14.57 mo (range 5-23 mo). The overall rate of freedom from local progression at 6 and 12 mo were 88% and 65%. The probability of overall survival at 6 and 12 mo were 89% and 56%. No patient had a complication related to fiducial markers placement regardless of modality. The rate of radiation-induced adverse events was: grade 1-2 (11%) and grade 3 (16%). There were no grade 4/5 adverse events seen. CONCLUSION: Our preliminary results showed SBRT as a safe and likely effective local treatment modality for pancreatic primary malignancy with acceptable rate of adverse events.

Origins of saccharide-dependent hydration at aluminate, silicate, and aluminosilicate surfaces.

Sugar molecules adsorbed at hydrated inorganic oxide surfaces occur ubiquitously in nature and in technologically important materials and processes, including marine biomineralization, cement hydration, corrosion inhibition, bioadhesion, and bone resorption. Among these examples, surprisingly diverse hydration behaviors are observed for oxides in the presence of saccharides with closely related compositions and structures. Glucose, sucrose, and maltodextrin, for example, exhibit significant differences in their adsorption selectivities and alkaline reaction properties on hydrating aluminate, silicate, and aluminosilicate surfaces that are shown to be due to the molecular architectures of the saccharides. Solid-state (1)H, (13)C, (29)Si, and (27)Al nuclear magnetic resonance (NMR) spectroscopy measurements, including at very high magnetic fields (19 T), distinguish and quantify the different molecular species, their chemical transformations, and their site-specific adsorption on different aluminate and silicate moieties. Two-dimensional NMR results establish nonselective adsorption of glucose degradation products containing carboxylic acids on both hydrated silicates and aluminates. In contrast, sucrose adsorbs intact at hydrated silicate sites and selectively at anhydrous, but not hydrated, aluminate moieties. Quantitative surface force measurements establish that sucrose adsorbs strongly as multilayers on hydrated aluminosilicate surfaces. The molecular structures and physicochemical properties of the saccharides and their degradation species correlate well with their adsorption behaviors. The results explain the dramatically different effects that small amounts of different types of sugars have on the rates at which aluminate, silicate, and aluminosilicate species hydrate, with important implications for diverse materials and applications.

Strength improvement via coating of a cylindrical hole by layer-by-layer assembled polymer particles.

Negatively charged colloidal poly(methyl methacrylate-co-butyl acrylate) (P(MMA-BA)) particles and positively charged dissolved poly(ethyleneimine) (PEI) were adsorbed onto a cement block using a layer-by-layer (LBL) assembly technique. The block was fashioned so as to have a cylindrical hole running from one face to another along the long axis of the rectangular block, and a fluid containing either of the two charged materials was pumped through the block. The result was a film tens of micrometers thick, and the pressure required to crack the cement block was measured after one end of the hole was sealed. Latex particles with a T(g) near the use temperature showed the maximum improvement in the cracking stress of the blocks. In a multilayer coating with identically sized particles, the cracking stress of the blocks increased to an improvement of 25% and then dropped off with increasing number of layers, even though the relationship between film thickness and the number of layers was linear. An improvement of about 30% in the cracking stress of the coated blocks was obtained when using multiple layers with different particle sizes. The effects of the number of layers and particle size on the cracking stress suggest that both the morphology and the thickness of the film play a role in performance. Tests done under confinement, e.g., with an external stress applied to the outside of the blocks, suggest that not only does a film-forming mechanism contribute to performance but that filling of microcracks in the rock may also play a role.

Rheological comparison of organogelators based on iron and aluminum complexes of dodecylmethylphosphinic acid and methyl dodecanephosphonic acid.

Organogels were prepared from a 1:3 molar ratio of metal/ligand complexes of iron(III) or aluminum(III) with methyl dodecanephosphonic acid or dodecylmethylphosphinic acid at a concentration of 10 mM in dodecane. Gelation occurs spontaneously upon dissolution of the solid complex. Dynamic oscillatory measurements over the temperature range of 100-150 degrees C indicate that these materials behave as living polymers. Both reptation and reversible chain scission contribute to stress relaxation. The phosphonate ester complex gels are stronger than the corresponding dialkylphosphinate complex gels. Even at 150 degrees C, the phosphonate ester complexes maintained significant structure. Zero-shear viscosity activation energies are in the range of 26.5-61.2 kJ/mol, comparable to that for typical polymer melts.

Cyberknife radiosurgery for squamous cell carcinoma of vulva after prior pelvic radiation therapy.

Limited options exist for patients experiencing a local recurrence of vulvar malignancies after surgery and pelvic radiation. These recurrences often are associated with cancer-related skin desquamation and poor clinical outcomes. A new radiotherapeutic treatment modality for the previously irradiated patient is cyberknife radiosurgery, which uses a linear accelerator mounted on an industrial robotic arm to allow non-coplanar radiation therapy delivery with sub-millimeter precision. This study describes the first reported use of cyberknife radiosurgery for the treatment of recurrent vulvar cancer in three women.

Organogels with complexes of ions and phosphorus-containing amphiphiles as gelators. Spontaneous gelation by in situ complexation.

The properties of thermally reversible organogels that are formed spontaneously upon mixing a phosphonic acid monoester, monophosphonic acid, or bisphosphonate ester, each containing a long alkyl chain substituent, with one of several compounds of aluminum(III) and boron(III) in an organic liquid were studied by IR, NMR, optical microscopy, X-ray diffraction, and rheological techniques. Attempts to form gels with zirconium(IV) were unsuccessful. Gelation occurred at room temperature upon complexation, leading to the formation of entangled networks of elongated objects similar to giant, worm-like micelles. On the basis of the diversity of the liquids gelated, the minimum concentration of gelator required to make a gel at room temperature (typically <5 wt %), and the temporal and thermal stabilities of the gels, Al complexes of phosphonic acid monoesters were found to be better gelators than bisphosphonate complexes. Several of the gels formed from the monophosphonate-Al complexes were stable for very long periods when they were kept in sealed tubes at room temperature. When heated, they reverted to sols over wide temperature ranges. The nature of the gels and the complexes from which they were formed were correlated, especially for those with the phosphonic acid monoester. The results describe an interesting class of two-component gelators that can be made from freely flowing solutions by mixing the components at room temperature, without the need for a catalyst, radiation, or sonication. The properties of the gels can be modulated by careful choice of the structural variables in the phosphorus-containing latent gelators.

Organogels with Fe(III) complexes of phosphorus-containing amphiphiles as two-component isothermal gelators.

The properties of thermally reversible organogels in which the gelators consist of a phosphonic acid monoester, phosphonic acid, or phosphoric acid monoester and a ferric salt are probed by IR and NMR spectroscopies, optical microscopy, X-ray diffraction, rheology, and light and small-angle neutron scattering (SANS) techniques. This is one of a small number of two-component molecular gelator systems in which gelation can be induced isothermally. The data indicate that complexation between the phosphonate moieties and Fe(III) is accompanied by their in situ polymerization to form self-assembled fibrillar networks that encapsulate and immobilize macroscopically the organic liquid component. From SANS measurements, the cross-sectional radii of the cyclindrical fibers are ca. 15 A. The efficiencies of the gelators (based on the diversity of the liquids gelated, the minimum concentration of gelator required to make a gel at room temperature, and the temporal and thermal stabilities of the gels) have been determined. With a common ferric salt and liquid component, phosphonic acid monoesters are generally more efficient than phosphinic acids or phosphoric acid esters. Of the phosphonic acid monoesters, monophosphonates are better gelator components than bisphosphonates, and introduction of an omega-hydroxy group on the alkyl chain directly attached to phosphorus reduces significantly gelation ability. Several of the gels are stable for very long periods at room temperature. When heated, they revert to sols over wide temperature ranges. The structures of the gelator complexes and the mechanism of their formation and transformation to gels in selected liquids are examined as well.