Desorption of nitric acid from boehmite and gibbsite

Solid-state Fourier transform infrared spectroscopy (FTIR), evolved gas analysis-FTIR (EGA-FTIR), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC) have been used to investigate the desorption of nitric acid from boehmite and from gibbsite. Samples containing between 3 and 36% of adsorbed nitric acid by mass were prepared by placing the mineral in a 70% nitric acid solution or by the adsorption of nitric acid vapors in humid air. FTIR established that water-solvated nitrate was the main species adsorbed on the surface of either mineral under these conditions. The water-solvated nitrate vaporized as nitric acid at approximately 400 K with an enthalpy of desorption of approximately 50 kJ/mol for both surfaces. A second nitric acid desorption occurred at approximately 450 K and had an enthalpy of desorption of 85 kJ/mol (95 kJ/mol) for boehmite (gibbsite). This was assigned as desorption of partially solvated aluminum hydroxylated nitrate. Monodentate and bridging nitrate were also observed on the boehmite. These species desorbed at approximately 725 K as NO2 and O2 with an enthalpy of reaction of approximately 55 kJ/mol of NO2 desorbed.     

Validation of a one-step extraction/methylation method for determination of fatty acids and cholesterol in marine tissues

A simple and fast direct extraction/methylation with methanolic hydrogen chloride was validated for determination of fatty acids (FA) in marine tissues. Three parameters: reaction time, temperature and presence of non-polar solvent, were studied by an experimental 2(3) full factorial design. The method was validated for five different types of samples; cod liver (high lipid content >60%, mainly triacylglycerol), cod muscle (low lipid content, approximately 1%, mainly phospholipids), cod plasma (lipid content, approximately 2%, mainly lipoprotein complex, high water amount), cod testis (lipid content approximately 3%, high levels of cholesterol), and herring muscle (lipid content approximately 7%). The one-step procedure for extraction/methylation of wet tissues was compared with the traditional procedure of extraction of the lipids by the Folch method (chloroform/methanol, 2:1, v/v), followed by methylation. The two methods gave similar FA profiles. The one-step extraction/methylation procedure gave a higher recovery of the total FA than the traditional procedure. Problems with carry-over peaks of cholesterol from previous samples were avoided by application of extra long GC temperature programs. The cholesterol decomposed to some degree under the preceding methanolysis step, giving several peaks in the chromatograms. The decomposition peaks were identified by mass spectrometry as cholestdienes originating from dehydration of cholesterol, a metylether of cholesterol and a cholesteryl chloride. These cholesterol artefacts can be used for quantitative determination of cholesterol in the samples. Standard samples of cholesterol were determined with high accuracy, (R(2)>0.99), and cholesterol in cod plasma was compared with good agreement (R(2)=0.97) to an enzymatic method.     

13C-labeled N-acetyl-neuraminic acid in aqueous solution: detection and quantification of acyclic keto, keto hydrate, and enol forms by 13C NMR spectroscopy

Aqueous solutions of N-acetyl-neuraminic acid (Neu5Ac, 1) labeled with (13)C at C1, C2, and/or C3 were analyzed by (13)C NMR spectroscopy to detect and quantify the acyclic forms (keto, keto hydrate, enol) present at varying pHs. In addition to pyranoses, solutions contained the keto form, based on the detection of C2 signals at approximately 198 ppm (approximately 0.7% at pH 2). Spectra of [2-(13)C] and [3-(13)C] isotopomers contained signals arising from labeled carbons at approximately 143 and approximately 120 ppm, respectively, which were attributed to enol forms. Solution studies of [1,2,3-(13)C3] 1 substantiated the presence of enol (approximately 0.5% at pH 2). Enol was not detected at pH > 6.0. A C2 signal observed at approximately 94 ppm was identified as C2 of the keto hydrate (approximately 1.9% at pH 2), based partly on its abundance as a function of solution pH. Density functional theory (DFT) calculations were used to study the effect of enol and hydrate structure on J(CH) and J(CC) values involving C2 and C3 of these forms. Solvated DFT calculations showed that (2)J(C2,H3) in cis and trans enols have similar magnitudes but opposite signs, making this J-coupling potentially useful to distinguish enol configurations. Solvent deuterium exchange studies of 1 showed rapid incorporation of (2)H from (2)H2O at H3 axial in the pyranoses at p(2)H 8.0, followed by slower exchange at H3 equatorial. The acyclic keto form, which presumably participates in this reaction, must assume a pseudo-cyclic conformation in solution in order to account for the exchange selectivity. Weak (13)C signals arising from labeled species were also observed consistently and reproducibly in aqueous solutions of (13)C-labeled 1, possibly arising from products of lactonization or intermolecular esterification.     

Characterization and mechanism of formation of tandem lesions in DNA by a nucleobase peroxyl radical

5,6-Dihydro-2'-deoxyuridin-6-yl (1) was independently generated via photolysis of 3. The radical is an analogue of the major reactive species produced from thymidine upon reaction with hydroxyl radical, which is the dominant DNA-damaging agent produced by the indirect effect of gamma-radiolysis. Under aerobic conditions, the peroxyl radical (2) derived from 1 reacts approximately 82% of the time with either the 5'- or 3'-adjacent nucleotide to produce two contiguously damaged nucleotides, known as tandem lesions. The structures and distribution of tandem lesions were investigated using probes that selectively detect abasic sites, ESI-MS/MS, and competition kinetics. In addition to 2-deoxyribonolactone, nonoxidized abasic sites were detected. 18O-Labeling verified that H2O was the source of oxygen in the abasic sites, but that O2 was the source of the oxygen in the 5,6-dihydro-6-hydroxy-2'-deoxyuridine derived from 2. ESI-MS/MS experiments, in conjunction with isotopic labeling, identified several products and provided direct evidence for peroxyl radical addition to the adjacent thymine bases. Kinetic studies revealed that peroxyl radical addition to the 5'-thymine was favored by approximately 4-5-fold over C1'-hydrogen atom abstraction from the respective deoxyribose ring, and that 2-deoxyribonolactone formation accounts for approximately 11% of the total amount of tandem lesions produced. These results suggest that tandem lesions, whose biochemical effects are largely unknown, constitute a major family of DNA damage products produced by the indirect effect of gamma-radiolysis.     

The 2-norbornyl cation via the fragmentations of exo- and endo-2-norbornyloxychlorocarbenes: distinction without much difference

exo- and endo-2-norbornyloxychlorocarbenes (7) were generated photochemically from the corresponding diazirines (6). Both carbenes fragmented to [2-norbornyl cation (carbon monoxide) chloride] ion pairs in MeCN or 1,2-dichloroethane solutions. Products included exo-norbornyl chloride (8), endo-norbornyl chloride (9), norbornene (10), and nortricyclene (11). Fragmentation activation energies were very low (< approximately 4 kcal/mol) and, as a result, the (laser flash photolytic) rate constants for fragmentation were essentially identical for exo-7 and endo-7 ( approximately 5 x 10(5) s(-1) in MeCN). Due to chloride return within the ion pairs, product distributions from exo- and endo-7 differed, with more endo-chloride formed from the endo-carbene: the 8/9 product ratio in MeCN was approximately 41 from exo-7, but only 4.6 from endo-7. Norbornene, formed by proton transfer to Cl(-) within the ion pairs, was a major product in both cases (44% from exo-7 and 62% from endo-7). In MeOH/MeCN, up to 28% of exo-2-norbornyl methyl ether formed at the expense of some of the norbornene, but even in 100% MeOH, the norbornyl chloride products of ion pair return still accounted for 46% and 31% of the exo-7 and endo-7 product mixtures (accompanied by 26-32% of norbornene). Electronic structure calculations on the ground states and fragmentation transition states of exo-7 and endo-7 are presented.     

Determination of vitamin D2 in emulsified nutritional supplements by solid-phase extraction and column-switching high-performance liquid chromatography with UV detection

This paper deals with a method for solid-phase extraction of trace amounts of vitamin D2 (VD2, 19 ng/g) from emulsified nutritional supplements, which contain 50 kinds of compounds, followed by column-switching high-performance liquid chromatography (HPLC) with UV detection at 265 nm. VD2 is present at 1000-20,000,000 times lower concentration than other components. Bond Elut C18 cartridge was chosen as for the emulsified nutritional supplements after comparison with eight other types. A sample solution was applied to the solid-phase extraction cartridge and VD2 was eluted by methanol followed by HPLC. The effects of sample pH, eluent composition and eluate volume on the retention and elution of VD2 on Bond Elut C18 cartridge were examined. The resulting method was simple, rapid (analysis time: approximately 20 min), sensitive (detection limit: approximately 0.1 ng per injection (200 microl) at a signal-to-noise ratio 3:1), and reproducible (relative standard deviation: approximately 6.2%, n=5). The calibration graph for VD2 was linear in the range of 0.1-3 ng per injection (200 microl). Recovery of VD2 was approximately 80% by the standard addition method.     

Extraction of antimony and arsenic from fresh and freeze-dried plant samples as determined by HG-AAS

Six extraction media (acetic acid, EDTA, tetrabutylammonium hydroxide, NaOH, MeOH/H2O, acetonitrile/H2O) were tested for their ability to extract antimony (Sb) and arsenic (As) from freeze-dried poplar leaves, pine shoots and spruce shoots, as well as from a peat matrix. Additionally, the extraction efficiency of Sb and As in fresh and freeze-dried elder leaves and poplar leaves was compared. Total concentrations of Sb and As of aliquots (approximately 220 mg) of the freeze-dried samples were analysed by flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS) after open vessel digestion with adequate mixtures of nitric, sulfuric, hydrochloric, and perchloric acid. Three reference materials GBW 07602 Bush Branches and Leaves, GBW 07604 Poplar Leaves, and SRM 1575 Pine Needles were analysed with every batch of samples to ensure the accuracy and precision of the applied analytical procedures. The use of hydrofluoric acid in the digestion mixture leads to distinctly lower As values (down to 40%) than actual concentrations in the investigated plant materials. Extraction efficiencies were generally low and lower for Sb than for As. Solutions of 0.66 mol L(-1) NaOH liberated highest amounts of Sb with approximately 10% for poplar leaves, and approximately 19% each for pine shoots and spruce shoots. Distinctly higher concentrations of As in NaOH extracts of poplar leaves (22%), pine shoots (32%), and spruce shoots (36%) were quantified. Extraction experiments resulted in yields of 7-9% from fresh elder and poplar leaves, respectively, and 8-13% for freeze-dried samples for Sb. The corresponding values for As were 10-35% for the fresh material and 7-37% for the freeze-dried samples.     

Structural characteristics of silica sonogels prepared with additions of isopropyl alcohol

Wet silica gels with approximately 1.4 x 10(-3) mol SiO2/cm3 and approximately 92 vol % liquid phase were obtained from sonohydrolysis of tetraethoxysilane (TEOS) with different additions of isopropyl alcohol (IPA). The IPA/TEOS molar ratio R was changed from 0 to 4. Aerogels were obtained by supercritical CO2 extraction. The samples were analyzed by small-angle X-ray scattering (SAXS) and nitrogen adsorption. The wet gels exhibit mass fractal structure with fractal dimension increasing from D approximately 2.10 to D approximately 2.22, characteristic length xi decreasing from approximately 9.5 to approximately 6.9 nm, as R increases from 0 to 4, and an estimated characteristic length for the primary silica particles lower than approximately 0.3 nm. The supercritical process apparently eliminates a fraction of the porosity, increasing the mass fractal dimension and shortening the fractality domain in the mesopore region. The fundamental role of isopropyl alcohol on the structure of the resulting aerogels is to decrease the porosity and the pore mean size as R changes from pure TEOS to R = 4. A secondary structure appearing in the micropore region of the aerogels can be described as a mass/surface fractal structure, with correlated mass fractal dimension Dm approximately 2.7 and surface fractal dimension Ds approximately 2.3, as inferred from SAXS and nitrogen adsorption data.     

Determination of flavanol and procyanidin (by degree of polymerization 1-10) content of chocolate, cocoa liquors, powder(s), and cocoa flavanol extracts by normal phase high-performance liquid chromatography: collaborative study

An international collaborative study was conducted on an HPLC method with fluorescent detection (FLD) for the determination of flavanols and procyanidins in materials containing chocolate and cocoa. The sum of the oligomeric fractions with degree of polymerization 1-10 was the determined content value. Sample materials included dark and milk chocolates, cocoa powder, cocoa liquors, and cocoa extracts. The content ranged from approximately 2 to 500 mg/g (defatted basis). Thirteen laboratories representing commercial, industrial, and academic institutions in six countries participated in the study. Fourteen samples were sent as blind duplicates to the collaborators. Results from 12 laboratories yielded repeatability relative standard deviation (RSDr) values that were below 10% for all materials analyzed, ranging from 4.17 to 9.61%. The reproducibility relative standard deviation (RSD(R)) values ranged from 5.03 to 12.9% for samples containing 8.07 to 484.7 mg/g. In one sample containing a low content of flavanols and procyanidins (approximately 2 mg/g), the RSD(R) was 17.68%. Based on these results, the method is recommended for Official First Action for the determination of flavanols and procyanidins in chocolate, cocoa liquors, powder(s), and cocoa extracts.     

Reversible modulation of quantum dot photoluminescence using a protein- bound photochromic fluorescence resonance energy transfer acceptor

Multiple copies ( approximately 20) of Escherichia coli maltose binding protein (MBP) were coordinated to luminescent semiconductor quantum dots (QDs) via a C-terminal oligohistidine segment. The MBP was labeled with a sulfo-N-hydroxysuccinimide-activated photochromic BIPS molecule (1',3-dihydro-1'-(2-carboxyethyl)-3,3-dimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-(2H)-indoline]) at two different dye-to-MBP ratios; D/P = 1 and 5. The ability of MBP-BIPS to modulate QD photoluminescence was tested by switching BIPS from the colorless spiropyran (SP) to the colored merocyanine (MC) using white light (>500 nm) or UV light ( approximately 365 nm), respectively. QDs surrounded by MBP-BIPS with D/P = 1 were quenched on average approximately 25% with consecutive repeated switches, while QDs surrounded by MBP-BIPS with D/P = 5 were quenched approximately 60%. This result suggests a possible use of BIPS-labeled proteins in QD-based nanostructures as part of a threshold switch or other biosensing device.     

Universal growth of microdomains and gelation transition in agar hydrogels

Investigations were carried out on aqueous sols and gels of agar (extracted from red seaweed Gelidiella acerosa) to explore the growth of microdomains en route to gelation. Isothermal frequency sweep studies on gel samples revealed master plots showing power-law dependence of gel elastic modulus, |G*|, on oscillation frequency, omega as |G*| approximately omegan, independent of temperature, with 0.5Tg). The S(q,t) behavior close to the gel transition point (Tg approximately (38+/-3 degrees C determined from rheology) followed a stretched exponential function: S(t)=A exp(-t/ts)beta. The beta factor increased from 0.25 to 1 as the gel temperature approached 25 degrees C from Tg, and relaxation time, ts, showed a peak at T approximately 30 degrees C. The SLS data (in the sol state) suggested the scaling of scattered intensity, Is(q) approximately epsilon(-gamma) (epsilon=(T/Tg-1), T>Tg) with gamma=0.13+/-0.03, and the presence of two distinct domains characterized by a Guinier regime (low q) and a power-law regime (high q). Close to and above Tg (+2 degrees C), IS(q) scaled with q as Is(q) approximately q(-alpha) with alpha=2.2+/-0.2, which decreased to 1.4+/-1 just below Tg (-2 degrees C), implying a coil-helix transition for 0.2% (w/v) and 0.3% (w/v) samples. For a 0.01% sample, alpha=3.5+/-0.5 which indicated the presence of spherical microgels.     

A systematic resolution of sulfur in reticulated vitreous carbon using X-ray absorption spectroscopy

Sulfur K-edge X-ray absorption spectroscopy (XAS) was used to characterize the approximately 0.1% sulfur found both in native reticulated vitreous carbon (RVC) foam and in RVC oxidatively modified using 0.2 M KMnO4 in 2 M H2SO4. Sulfur valences and functional groups were assessed using K-edge XAS spectral curve-fitting and employing explicit sulfur compounds as models. For native RVC, these were episulfide (approximately 3%), thianthrene (approximately 9%), disulfide (approximately 10%), sulfenate ester (approximately 12%), benzothiophene (approximately 24%), N,N'-thiobisphthalimide (approximately 30%), alkyl sulfonate (approximately 1.2%), alkyl sulfate monoester (approximately 6%), and sulfate dianion (approximately 6%). Permanganate oxidation of RVC diminished sulfenic sulfur to approximately 9%, thianthrenic sulfur to approximately 7%, and sulfate dianion to approximately 1% but increased sulfate monoester to approximately 12%, and newly produced sulfone (approximately 2%) and sulfate diester (approximately 5%). A simple thermodynamic model was derived that allows proportionate functional group comparisons despite differing (approximately +/-15%) total sulfur contents between RVC batches. The limits of accuracy in the XAS curve-fitting analysis are discussed in terms of microenvironments and extended structures in RVC carbon that cannot be exactly modeled by small molecules. Sulfate esters cover approximately 0.15% of the RVC surface, increasing to approximately 0.51% following permanganate/sulfuric acid treatment. The detection of episulfide directly corroborates a proposed mechanism for the migration of elemental sulfur through carbon.     

Nanoporous TiO2 and WO3 films by anodization of titanium and tungsten substrates: influence of process variables on morphology and photoelectrochemical response

The photoelectrochemical response of nanoporous films, obtained by anodization of Ti and W substrates in a variety of corrosive media and at preselected voltages in the range from 10 to 60 V, was studied. The as-deposited films were subjected to thermal anneal and characterized by scanning electron microscopy and X-ray diffraction. Along with the anodization media developed by previous authors, the effect of poly(ethylene glycol) (PEG 400) or D-mannitol as a modifier to the NH4F electrolyte and glycerol addition to the oxalic acid electrolyte was studied for TiO2 and WO3, respectively. In general, intermediate anodization voltages and film growth times yielded excellent-quality photoelectrochemical response for both TiO2 and WO3 as assessed by linear-sweep photovoltammetry and photoaction spectra. The photooxidation of water and formate species was used as reaction probes to assess the photoresponse quality of the nanoporous oxide semiconductor films. In the presence of formate as an electron donor, the incident photon to electron conversion efficiency (IPCE) ranged from approximately 130% to approximately 200% for both TiO2 and WO3 depending on the film preparation protocol. The best photoactive films were obtained from poly(ethylene glycol) (PEG 400) containing NH4F for TiO2 and from aqueous NaF for WO3.     

Determination of hexabromocyclododecane diastereoisomers and tetrabromobisphenol A in water and sediment by liquid chromatography/mass spectrometry.

A method to determine alpha-, beta- and gamma-hexabromocyclododecane (HBCD) and tetrabromobisphenol A (TBBPA) in water and sediments was presented using solid phase extraction (SPE) and/or solvent extraction. Recoveries from sediments were approximately 100% for all the chemicals, while recoveries of alpha-, beta- and gamma-HBCDs from water were dependent on the extraction method. In the case of dichloromethane (CH2Cl2) extraction, recoveries of alpha-, beta- and gamma-HBCD from landfill leachates were 77%, 88% and 92%, respectively. Technical difficulties in HBCD measurement are discussed in terms of the physico-chemical properties of HBCD isomers. The method was applied to landfill samples and marine sediment.     

Characteristics of fatty acids and essential oil from sweet fennel (Foeniculum vulgare Mill. var. dulce) and bitter fennel fruits (F. vulgare Mill. var. vulgare) growing in Turkey

Oil content in sweet and bitter fennels was obtained 12.22% and 14.41%, respectively. The C(18:1 c6), C(18:2), C(18:1 c9) and C(16:0) acids corresponding to approximately 97% of total oil was recorded as principal fatty acids. The ratios of essential oil from sweet and bitter fennels were found similar (average 3.00%). trans-Anethole, estragole and fenchone were found to be the main constituents in both fennels. The compound with the highest value in the two oil samples was trans-anethole as 95.25% (sweet) and 75.13% (bitter). While estragole was found in bitter fennel oil in a remarkable amount (15.51%), sweet fennel oil contained small amounts of estragole (2.87%). Fenchone was found <1% in sweet and approximately 5% in bitter fennel. p-Anisaldehyde in bitter fennel essential oil, and alpha-pinene and gamma-terpinene in sweet fennel essential oil were not recorded, and these compounds were found very low or <1%.     

Development of a rapid and sensitive high-performance liquid chromatographic method to determine CYP2D6 phenotype in human liver microsomes

Dextromethorphan is a probe substrate to determine CYP2D6 phenotype. The conversion of dextromethorphan to dextrorphan by CYP2D6 accounts for approximately 60% of total metabolism. Most analytical methods utilize complicated labor- and time-intensive sample processing methods with several liquid-liquid extraction (LLE) steps. Our goal was to develop a non-LLE based rapid and sensitive HPLC method, to measure dextromethorphan metabolism in human liver microsomes. A solid-phase filtration based reverse-phase HPLC method with fluorescence detection was developed and validated. Human liver (n = 6) microsomal incubations were carried out with dextromethorphan, under optimum conditions. The analytes were separated by one-step centrifugal filtration with Nanosep separation units. The filtrate was injected ( 50 microL) into a Waters Alliance 2690 HPLC system. Metabolic incubations were also conducted to determine levels using LLE for comparisons. The Nanosep separation step reduced the extraction time from 3h to 40 min. The limit of quantitation was 23.8 nM (9.7 ng/mL), recovery was approximately 98%, the mean precision values were <10% RSD for the controls (80, 320 and 640 nM) and mean percentage error was <5%. Michaelis-Menten parameters were determined to distinguish CYP2D6 phenotypes. A rapid and sensitive HPLC method is reported, which may be suitable for automation and allows phenotyping of human liver microsomes.     

Development and validation of reversed phase liquid chromatographic method utilizing ultraviolet detection for quantification of irinotecan (CPT-11) and its active metabolite, SN-38, in rat plasma and bile samples: application to pharmacokinetic studies

A new, simple, sensitive and specific reversed-phase high performance liquid chromatographic (HPLC) method using ultraviolet detection was developed and validated for the analysis of CPT-11 (lambda(max)=254 nm, 365 nm) and its major active metabolite, SN-38 (lambda(max)=380 nm) in rat plasma and bile. The sample pre-treatment from plasma involved a single protein precipitation step with cold acetonitrile. In case of bile, liquid-liquid extraction with dichloromethane: tert-butyl methyl ether (3:7) was carried out. Topotecan, a structurally related camptothecin, was used as an internal standard. An aliquot of 50 microL was injected onto a C-18 column. The chromatographic separation was achieved by gradient elution consisting of acetonitrile and water (pH 3.0 adjusted with 20% o-phosphoric acid) at a flow rate of 1.0 ml/min. Total run time for each sample was 30 min. All the analytes viz. topotecan, CPT-11, SN-38 were well separated with retention times of 11.4, 13.4 and 15.5 min, respectively. Method was found to be selective, linear (R(2) approximately 0.999), accurate (recovery+/-15%) and precise (<5% C.V.) in the selected concentration ranges for both the analytes. The quantification limit for CPT-11 was 40 ngml(-1) and for SN-38 was 25 ngml(-1). The percent extraction efficiency was approximately 97% for CPT-11 and SN-38 from plasma while extraction recovery of CPT-11 and SN-38 from bile was approximately 70% and approximately 60%, respectively. The method was successfully used to determine plasma and biliary excretion time profiles of CPT-11 and SN-38, following oral and intravenous CPT-11 administration in rats. In the present study, irinotecan showed an absolute bioavailability of 30% as calculated from the pharmacokinetic data.     

Determination of residual oil in diesel oil by spectrofluorimetric and chemometric analysis

Multivariate calibration (PLS), principal components analysis (PCA) and linear discriminant analysis (LDA), associated to synchronous spectrofluorimetry, were used to identify and quantify non-transesterified residual vegetable oil in diesel oil with the addition of 2% of biodiesel (B2). The addition of residual oil, one of the easiest ways of adultering fuel, damages engines and leads to tax evasion. Using this method, the samples of diesel oil, B2, and B2 contaminated with residual oil were classified correctly and separated into three well-defined groups. The quantification of residual oil in B2 was carried out in the 0-25% (w/w) band, RMSEC and RMSEP values ranging from 0.26 to 0.48% (w/w) and 1.6-2.6% (w/w), respectively. The method is highly sensitive and efficient to identify and quantify this type of adulterant in which 100% of the samples were correctly classified and the average relative error was approximately 4% in the range 0.5-25% (w/w).     

Control of protein adsorption: molecular level structural and spatial variables

The adsorption of fibrinogen (Fb) and bovine serum albumin onto polycrystalline Au coated with HS(CH2)3O(CH2CH2O)5CH3 was determined by surface plasmon resonance from bare Au (0% coverage) to the complete ( approximately 100% coverage) self-assembled monolayer (SAM). Both proteins exhibit similar adsorption curves with common onset ( approximately 60% coverage) and range ( approximately 60% to 80% coverage) of minimal protein adsorption. Reflection-absorption infrared spectroscopic data show that widespread order is not present in the films over this range of coverage, indicating loosely packed, bound oligomers that are uniformly distributed and fully screen the underlying substrate. On the basis of our data, we propose a mechanism of protein rejection by oligo(ethylene oxide) (OEO)-modified surfaces in terms of changes in free energy (DeltaGsystem; system = protein + surface) due to oligomer conformational constriction over an area greater than the contact area. Minimal protein adsorption corresponds to the maximum DeltaGsystem for a given compression. This controlled study of protein adsorption provides insights into the molecular level understanding of protein adsorption unavailable from previous polymer and comparative SAM studies.     

A new route to self-assembled tin dioxide nanospheres: fabrication and characterization

Nearly monodispersed self-assembled tin dioxide (SnO2) nanospheres with intense photoluminescence (PL) were synthesized using a new wet chemistry technique. Instead of coprecipitating stannous salts, bulk tin (Sn) metal was oxidized at room temperature in a solution of hydrogen peroxide and deionized water containing polyvinylpyrrolidone (PVP) and ethylenediamine (EDA). SnO2 nanocrystals were produced with diameters of approximately 3.8 nm that spontaneously self-assembled into uniform SnO2 nanospheres with diameters of approximately 30 nm. Analysis was performed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV-vis absorption spectroscopy, PL spectroscopy, and fluorescence lifetime measurements. The SnO2 nanospheres displayed room-temperature purple luminescence with an intense band at 394 nm (approximately 3.15 eV) and a high quantum yield of approximately 15%, likely as a result of emission from the surface states of SnO2/PVP complexes. The present study could open a new avenue to large-scale synthesis of self-assembled functional oxide nanostructures with technological applications as purple emitters, biological labels, gas sensors, lithium batteries, and dye-sensitized solar cells.