Solvent-Free Reaction for Unsymmetrical Organodisulfides with High Purity and Application as Cathode-Active Materials.

Unsymmetrical disulfides, in which different organic groups are bonded to disulfide bonds, have been synthesized by cross-coupling reactions using thiols as substrates. However, due to the low-binding energy of unsymmetrical disulfides, its disproportionation occurs based on the side reactions with nucleophilic thiols, resulting in the impurity of symmetric disulfides. In this study, we developed a solvent-free synthesis method for unsymmetrical disulfides using thiosulfonates, thiols, and a base. This synthetic method enabled us to obtain highly pure diaryl-substituted unsymmetrical disulfides with particularly low-binding energy without control over the nucleophilicity and elimination properties of the substrate. Furthermore, it was observed that the disproportionation of unsymmetrical disulfides occurred in the solvent. This means that solvent-free condition is one of the factors to obtain unsymmetrical disulfides. As a new application of unsymmetrical disulfides, we applied unsymmetrical disulfides to cathode active materials of lithium batteries based on the reversible multi-electron redox activity of S-S bonds. The batteries using unsymmetrical disulfide cathode-active materials with a carbon nanotube exhibited initial capacities of 127 and 158 Ah/kg, equal to 42 and 53% of their theoretical ones. We demonstrated that unsymmetrical disulfides could be used as cathode-active materials for rechargeable batteries.

Formation of octacalcium phosphate with incorporated dicarboxylate ions containing disulfide bonds.

Octacalcium phosphate (OCP) is a layered compound capable of incorporating carboxylate ions within its interlayer structure. In this study, we successfully synthesised OCP with incorporated 3,3'-dithiodipropionate ions. Our finding is beneficial for the development of novel OCP-based materials with dynamic properties derived from disulfide bonds.

Development of bioinspired damage-tolerant calcium phosphate bulk materials.

Improving the damage tolerance and reliability of ceramic artificial bone materials, such as sintered bodies of hydroxyapatite (HAp), that remain in vivo for long periods of time is of utmost importance. However, the intrinsic brittleness and low damage tolerance of ceramics make this challenging. This paper reports the synthesis of highly damage tolerant calcium phosphate-based materials with a bioinspired design for novel artificial bones. The heat treatment of isophthalate ion-containing octacalcium phosphate compacts in a nitrogen atmosphere at 1000°C for 24 h produced an HAp/ß-tricalcium phosphate/pyrolytic carbon composite with a brick-and-mortar structure (similar to that of the nacreous layer). This composite exhibited excellent damage tolerance, with no brittle fracture upon nailing, likely attributable to the specific mechanical properties derived from its unique microstructure. Its maximum bending stress, maximum bending strain, Young's modulus, and Vickers hardness were 11.7 MPa, 2.8 × 10‒2, 5.3 GPa, and 11.7 kgf/mm2, respectively. The material exhibited a lower Young's modulus and higher fracture strain than that of HAp-sintered bodies and sintered-body samples prepared from pure octacalcium phosphate compacts. Additionally, the apatite-forming ability of the obtained material was confirmed in vitro, using a simulated body fluid. The proposed bioinspired material design could enable the fabrication of highly damage tolerant artificial bones that remain in vivo for long durations of time.

Ultra-High-Capacity Lithium Metal Batteries Based on Multi-Electron Redox Reaction of Organopolysulfides including Conductive Organic Moieties.

Recently, organic polysulfides have been synthesized as cathode active materials exceeding the battery performance of sulfur. However, the conventional organic polysulfides have exhibited capacities lower than the theoretical capacity of sulfur because the π-organic moieties do not conjugate with the sulfur chains. In this work, the organopolysulfides, synthesized via inverse vulcanization using disulfide compounds, exhibited higher capacities equal to the theoretical capacity of sulfur because of enhanced electronic conductivity based on the conjugation between organic moieties and sulfur chains. Furthermore, the organopolysulfide including 1,3-dhitiol-2-thione moiety exhibited the highest capacity because of the enhanced electronic conductivity. This finding will pave the way to develop next-generation rechargeable batteries.

Effects of risedronate, alendronate, and minodronate alone or in combination with eldecalcitol on bone mineral density, quality, and strength in ovariectomized rats.

Combination therapy of active vitamin D3 with some bisphosphonates (BPs) has been reported to be clinically beneficial. However, combination therapy of eldecalcitol (ELD) with BP has to date not been validated as to whether it is beneficial in the clinical setting. Preclinical studies suggested that simultaneous treatment with ELD and some BPs is more effective than monotherapy. However, the relative potency of various BPs, when used in combination with ELD, is completely unknown. In this study, we examined and compared the effects of risedronate (RIS), alendronate (ALN), and minodronate (MIN) alone or in combination with ELD on bone mass, microarchitecture, strength, and material properties in ovariectomized Sprague-Dawley rats aged 13 weeks. RIS, ALN, MIN, and ELD were administered five times weekly for 16 weeks. Micro-computed tomography analysis, compression test, and Fourier transform infrared (FTIR) imaging analysis were performed 16 weeks after treatment initiation. Trabecular and cortical bone mineral density (BMD) in the fourth lumbar vertebra (L4) significantly increased in the RIS + ELD, ALN + ELD, and MIN + ELD groups compared with the vehicle group. Moreover, the bone microarchitecture of L4 in all the BP + ELD groups also significantly improved. On mechanical testing of L4, the maximum load was significantly increased in the RIS + ELD and ALN + ELD groups. FTIR analysis revealed that the mineral-to-collagen ratio of trabecular bone in L3 of all the BP + ELD groups was significantly increased compared with the vehicle group. By contrast, the carbonate-to-phosphate ratio, a parameter of mineral immaturity, was significantly decreased in the RIS + ELD and ALN + ELD groups. BP + ELD improved the BMD and structural properties of the bone to a similar extent. RIS + ELD and ALN + ELD also improved bone strength. Furthermore, treatment with BP + ELD improved the bone material. These results suggest that the combination therapy of BP and ELD is beneficial and warrants further clinical trials.

Comparison of the Efficacy and Renal Safety of Bisphosphonate Between Low-Dose/High-Frequency and High-Dose/Low-Frequency Regimens in a Late-Stage Chronic Kidney Disease Rat Model.

The efficacy and renal safety of low-dose/high-frequency (LDHF) dosing and high-dose/low-frequency (HDLF) dosing of bisphosphonates (BPs) are comparable in patients with normal kidney function but might be different in patients with late-stage chronic kidney disease (CKD). This study aimed to compare the efficacy and renal safety of two different dosage regimens of a BP, alendronate (ALN), in stage 4 CKD using a rat model. Male, 10-week-old Sprague-Dawley rats were subjected to either 5/6 nephrectomy or sham surgery. The animals received subcutaneous administration of vehicle (daily) or ALN in LDHF dosage regimen (LDHF-ALN: 0.05 mg/kg/day) or HDLF dosage regimen (HDLF-ALN: 0.70 mg/kg/2 weeks). Medications commenced at 20 weeks of age and continued for 10 weeks. Micro-computed tomography, histological analysis, infrared spectroscopic imaging, and serum and urine assays were performed to examine the efficacy and renal safety of the ALN regimens. Both LDHF-ALN and HDLF-ALN increased bone mass, improved micro-structure, and enhanced mechanical properties, without causing further renal impairment in CKD rats. Histologically, however, HDLF-ALN more efficiently suppressed bone turnover, leading to more mineralized trabecular bone, than LDHF-ALN in CKD rats, whereas such differences between LDHF-ALN and HDLF-ALN were not observed in sham rats. Both LDHF-ALN and HDLF-ALN showed therapeutic effects on high bone turnover osteoporosis in CKD stage 4 rats without causing further renal impairment. However, as HDLF-ALN more efficiently suppressed bone turnover than LDHF-ALN in late-stage CKD, HDLF-ALN might be more appropriate than LDHF-ALN for fracture prevention in high bone turnover osteoporosis patients with late-stage CKD.

Degree of orientations of collagen fibers and bone apatite crystals in rat femora by infrared dichroism imaging.

OBJECTIVES: The degree of orientations of collagen fibers and bone apatite crystals affects bone strength. We demonstrated that collagen fibers were aligned along the long axis of bone and that the degree of collagen fiber orientation changed with aging using infrared (IR) dichroism imaging. In this study, we developed a technique for evaluating bone apatite crystal orientation using IR dichroism imaging to investigate the relationships between collagen fiber and bone apatite crystal orientations. METHODS: Femora were harvested from male Sprague Dawley rats of different ages (6, 12, and 33 weeks); they were then embedded in poly (methyl methacrylate) and sectioned with a microtome into 3-µm longitudinal sections. The angle-dependent Fourier transform infrared (FTIR) spectra for sections were collected using FTIR imaging, and collagen fiber and bone apatite crystal orientations in the sections were assessed using IR dichroism imaging. RESULTS: Collagen fibers and poorly crystalline apatite in the femoral cortical bone were longitudinally aligned; however, the stoichiometric hydroxyapatite crystal and all of the bone apatite were not aligned. The degree of poorly crystalline apatite orientation was higher in 33-week-old rats than in 6-week-old rats. CONCLUSIONS: Poorly crystalline apatite in the rat femoral cortical bone was aligned along the collagen fibers. The degree of poorly crystalline apatite orientation and collagen fiber orientation in the femoral cortical bone increased until at least 33 weeks; meanwhile, on aging, the stoichiometric hydroxyapatite crystal was not longitudinally aligned.

Quick and easy sample preparation without resin embedding for the bone quality assessment of fresh calcified bone using fourier transform infrared imaging.

Fourier transform infrared (FTIR) imaging is a powerful tool for the assessment of bone quality; however, it requires the preparation of thin bone sections. Conventional poly(methyl methacrylate) (PMMA) embedding for the preparation of sections takes more than two weeks and causes denaturation of the bone. Development of a quick and easy sample preparation technique without denaturation is needed for accurate clinical evaluation of fresh calcified bone using FTIR imaging. Frozen sectioning allows the quick and easy preparation of thin sections without denaturation, but it requires a substrate with good chemical resistance and improved heat shock resistance. Polypropylene (PP) film afforded both good chemical resistance and greater heat shock resistance, and the 4-µm-thick PP film coated with glue was thin enough for the IR beam to pass through it, while the optical anisotropy of infrared bands overlapping with PO43- band was negligible. The bone quality of femoral thin sections prepared by the conventional PMMA embedding and sectioning procedure (RESIN-S) or the newly developed frozen sectioning procedure (FROZEN-S) was evaluated by FTIR imaging. The mineral-to-matrix ratio and crystallinity in the RESIN-S sections were higher than those in the FROZEN-S sections, whereas the carbonate-to-phosphate ratio in the RESIN-S sections was lower than that in the FROZEN-S sections. In RESIN-S, the increased mineral-to-matrix ratio could be caused by dehydration, and the increased crystallinity and decreased carbonate-to-phosphate ratio might be consequence of dissolution of bone mineral during PMMA embedding. Therefore, the combined use of PP film coated with glue and the frozen sectioning procedure without denaturation appears well suited to the assessment of the bone quality of fresh calcified bone using FTIR imaging.

Magnesium prevents phosphate-induced vascular calcification via TRPM7 and Pit-1 in an aortic tissue culture model.

Previous clinical and experimental studies have indicated that magnesium may prevent vascular calcification (VC), but mechanistic characterization has not been reported. This study investigated the influence of increasing magnesium concentrations on VC in a rat aortic tissue culture model. Aortic segments from male Sprague-Dawley rats were incubated in serum-supplemented high-phosphate medium for 10 days. The magnesium concentration in this medium was increased to demonstrate its role in preventing VC, which was assessed by imaging and spectroscopy. The mineral composition of the calcification was analyzed using Fourier transform infrared (FTIR) spectroscopic imaging, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) mapping. Magnesium supplementation of high-phosphate medium dose-dependently suppressed VC (quantified as aortic calcium content), and almost ablated it at 2.4 mm magnesium. The FTIR images and SEM-EDX maps indicated that the distribution of phosphate (as hydroxyapatite), phosphorus and Mg corresponded with calcium content in the aortic ring and VC. The inhibitory effect of magnesium supplementation on VC was partially reduced by 2-aminoethoxy-diphenylborate, an inhibitor of TRPM7. Furthermore, phosphate transporter-1 (Pit-1) protein expression was increased in tissues cultured in HP medium and was gradually-and dose dependently-decreased by magnesium. We conclude that a mechanism involving TRPM7 and Pit-1 underpins the magnesium-mediated reversal of high-phosphate-associated VC.

Mineral Composition of Phosphate-Induced Calcification in a Rat Aortic Tissue Culture Model.

AIM: High phosphorus conditions promote vascular calcification (VC) in both chronic kidney disease (CKD) patients and experimental models. However, the composition of medial calcification has not been accurately determined, so the objective of this study was to evaluate the mineral composition of calcification in a tissue culture model, not a cell culture system. METHODS: Aortic rings obtained from male Sprague-Dawley rats were incubated in serum-supplemented medium for 10 days. The inorganic phosphate (Pi) concentration of the medium was increased to induce VC, which was assessed by histology, imaging, and spectroscopy. The mineral composition of the calcification was analyzed using Fourier transform infrared (FTIR) spectroscopic imaging, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) mapping. RESULTS: The calcium content significantly increased only in aortic rings cultured for 10 days in the high-Pi medium (HiP: 3.8 mmol/L). The concentration of the phosphate transporter Pit-1 in the aortic tissue exposed to HiP was higher than that in the control incubated sections. The FTIR images and spectra indicated that PO4(3-) was mostly distributed as hydroxyapatite in the medial calcification of aortic rings cultured in HiP. A small quantity of carbonate was identified. The SEM-EDX overlay map demonstrated that phosphorus and calcium simultaneously accumulated and localized in the area of medial calcification induced by exposure to HiP. CONCLUSION: This is the first report of accurate determination of the chemical composition of aortic medial calcification. Exposure to high Pi concentration augments aortic calcification via an increase in Pit-1, which mainly contains calcium phosphate.

Vitamin K-dependent carboxylation of osteocalcin affects the efficacy of teriparatide (PTH(1-34)) for skeletal repair.

Teriparatide (PTH1-34) promotes skeletal repair and increases bone mass. Vitamin K is involved in bone mineralization as a coenzyme of γ-carboxylase for Gla proteins, and therefore vitamin K insufficiency caused by malnutrition or therapeutic intake of the vitamin K antagonist warfarin could affect the efficacy of PTH1-34 therapy for bone repair. In the present study, we investigated whether vitamin K influences the efficacy of PTH1-34 therapy for bone repair in a rat osteotomy model. Female 12-week-old Sprague-Dawley rats were subjected to a closed midshaft osteotomy of the femur and randomized into four groups (n=10 per group): vehicle, PTH1-34 (daily 30 µg/kg/day subcutaneous injection)+solvent (orally, three times a week), PTH1-34+warfarin (0.4 mg/kg/day orally, three times a week), and PTH1-34+vitamin K2 (menatetrenone, 30 mg/kg/day orally, three times a week). Serum γ-carboxylated and uncarboxylated osteocalcin (Gla-OC and Glu-OC) levels and radiographic healing were monitored every 2 weeks. Skeletal repair was assessed by micro-computed tomography, mechanical testing, and histology at 8weeks after surgery. PTH1-34 amplified the osteotomy-induced increase in Gla-OC and improved the mechanical properties as well as the volumetric bone mineral tissue density of the fracture callus. Concurrent use of warfarin decreased the response to PTH1-34 therapy in terms of mechanical recovery, probably by impairing mineralization due to the lack of Gla-OC. Although the effects of combination therapy with PTH1-34 and vitamin K2 on bone repair did not significantly exceed those of PTH1-34 monotherapy in rats fed sufficient dietary vitamin K, postoperative Gla-OC levels were correlated with the mechanical properties of the osteotomized femur in PTH1-34-treated rats regardless of the use of warfarin or vitamin K2. These findings suggest the importance of vitamin K dependent γ-carboxylation of OC for realizing the full effects of PTH1-34 on skeletal repair.

Retention of fetuin-A in renal tubular lumen protects the kidney from nephrocalcinosis in rats.

The serum glycoprotein fetuin-A is an important inhibitor of extraosseous calcification. The importance of fetuin-A has been confirmed in fetuin-A null mice, which develop widespread extraosseous calcification including the kidney. However, the mechanism how fetuin-A protects kidneys from nephrocalcinosis remains uncertain. Here, we demonstrate that intratubular fetuin-A plays a role in the prevention of nephrocalcinosis in the proximal tubules. Although normal rat kidney did not express mRNA for fetuin-A, we found punctate immunohistochemical staining of fetuin-A mainly in the S1 segment of the proximal tubules. The staining pattern suggested that fetuin-A passed through the slit diaphragm, traveled in the proximal tubular lumen, and was introduced into proximal tubular cells by megalin-mediated endocytosis. To test this hypothesis, we inhibited the function of megalin by intravenous injection of histidine-tagged soluble receptor-associated protein (His-sRAP), a megalin inhibitor. His-sRAP injection diminished fetuin-A staining in the proximal tubules and led to urinary excretion of fetuin-A. We further analyzed the role of fetuin-A in nephrocalcinosis. Continuous injection of parathyroid hormone (PTH) 1-34 induced nephrocalcinosis mainly in the proximal tubules in rats. His-sRAP retained fetuin-A in renal tubular lumen and thereby protected the kidneys of PTH-treated rats from calcification. Our findings suggest that tubular luminal fetuin-A works as a natural inhibitor against calcification in the proximal tubules under PTH-loaded condition.

Independent control of grafting density and conformation of single-stranded DNA brushes.

We describe self-assembly of ssDNA brushes that exploits the intrinsic affinity of adenine nucleotides (dA) for gold surfaces. The grafting density and conformation of these brushes is deterministically controlled by the length of the anchoring dA sequences, even in the presence of thymine nucleotides (dT). We produce and characterize brushes of model block-oligonucleotides, d(T(m)-A(n)), with systematically varied lengths m and n of the thymine and adenine blocks [denoted d(T(m)) and d(A(n)), respectively]. The hairpin conformation, dominant for self-complementary d(T(m)-A(n)) oligos in solution, is disrupted by the high preferential affinity of dA for gold surfaces. As a result, the d(T(m)-A(n)) oligos adsorb as a brush of d(T) strands immobilized via the d(A) blocks. Quantitative analysis by FTIR spectroscopy and x-ray photoelectron spectroscopy (XPS) reveals a unique feature of DNA immobilization via d(A) blocks: The surface density of dA nucleotides is close to saturation and is nearly independent of d(A) block length. Accordingly, the lateral spacing (grafting density) of the d(T) blocks is determined by the length of the d(A) blocks. The d(T) blocks extend away from the surface in a brush-like conformation at a lateral spacing 2-3 times larger (a grafting density 5-10 times lower) than in analogous films immobilized via standard thiol linkers. This combination of brush-like conformation and low saturation grafting density is expected to increase the efficiency of DNA hybridization at surfaces. Therefore, immobilization via d(A) blocks offers a method of producing DNA brushes with controlled properties for applications in biotechnology and nanotechnology.

Alkanethiols on platinum: multicomponent self-assembled monolayers.

We have studied the formation of self-assembled monolayers (SAMs) of n-alkanethiols on platinum thin films using X-ray photoelectron spectroscopy (XPS), reflection-absorption infrared spectroscopy (RAIRS), spectroscopic ellipsometry (SE), and contact angle (CA) measurements. Specifically, SAMs of 1-hexanethiol, 1-dodecanethiol, and 1-octadecanethiol were grown on polycrystalline Pt films, and the effects of Pt surface preparation, deposition conditions, and solvent treatments on the initial quality and stability of the monolayer in air were investigated. The SAMs prepared under ambient conditions on piranha-cleaned and UV/ozone-cleaned substrates were compared to monolayers formed on template-stripped Pt in an inert atmosphere. We found that alkanethiols deposited from 1 mM ethanolic solutions on piranha-cleaned Pt formed densely packed monolayers in which alkyl chains were oriented close to the surface normal. Stored in the laboratory ambient, these monolayers were unchanged over about 1 week but were largely oxidized in about 1 month. No evidence was found of molecules being weakly bound within the monolayer or having undergone C-S bond scission; however, three distinct sulfur states were observed for all samples in the XPS of the S 2p region. The lowest- and highest-binding-energy components are assigned to alkylthiolate and partially oxidized alkylthiolate species, respectively. The remaining S 2p component (approximately one-third of the sulfur layer), intermediate in binding energy between the other two components, is attributed to a chemisorbed species with a S binding configuration distinct from the majority alkylthiolate: for example, S bound to Pt bound to O, S with a different Pt coordination number, or S in an adsorbed disulfide.

Nucleobase orientation and ordering in films of single-stranded DNA on gold.

We demonstrate how the orientation and ordering of DNA bases in ultrahigh vacuum (UHV) and ambient environments can be determined using complementary spectroscopic methods. Near-edge X-ray absorption fine structure (NEXAFS) with fluorescence detection, X-ray photoelectron (XPS), and Fourier transform infrared (FTIR) spectroscopies are used to quantify the coverage, chemical composition, orientation, and ordering of thymine bases in model self-assembled monolayers of thymine homo-oligonucleotides [oligo(dT)] on gold. We find that, in monolayers of thiol-modified oligo(dT), thymine bases tend to orient parallel to the Au substrate, and this preferential orientation is significantly more pronounced in monolayers of thiolated 5-mers compared to 25-mers. We interpret this preferential orientation as a signature of significant correlations (local ordering) between individual nuleobases, which offers a way to quantify and compare nucleobase interactions in films under both ambient and UHV conditions.

Quantitative characterization of DNA films by X-ray photoelectron spectroscopy.

We describe the use of self-assembled films of thiolated (dT)25 single-stranded DNA (ssDNA) on gold as a model system for quantitative characterization of DNA films by X-ray photoelectron spectroscopy (XPS). We evaluate the applicability of a uniform and homogeneous overlayer-substrate model for data analysis, examine model parameters used to describe DNA films (e.g., density and electron attenuation length), and validate the results. The model is used to obtain quantitative composition and coverage information as a function of immobilization time. We find that when the electron attenuation effects are properly included in the XPS data analysis, excellent agreement is obtained with Fourier transform infrared (FTIR) measurements for relative values of the DNA coverage, and the calculated absolute coverage is consistent with a previous radiolabeling study. Based on the effectiveness of the analysis procedure for model (dT)25 ssDNA films, it should be generally valid for direct quantitative comparison of DNA films prepared under widely varying conditions.

Oligomerization and pore formation of a sphingomyelin-specific toxin, lysenin.

Lysenin is a novel protein derived from coelomic fluid of the earthworm Eisenia foetida, which specifically recognizes sphingomyelin and induces cytolysis. The mechanism underlying lysenin-induced cell lysis has not been clarified. In this report we studied the interaction of lysenin with red blood cells as well as artificial liposomes. Our results showed that lysenin bound membranes and assembled to SDS-resistant oligomers in a sphingomyelin-dependent manner, leading to the formation of pores with a hydrodynamic diameter of approximately 3 nm. Antibody scanning analysis suggested that the C-terminal region of lysenin was exposed, whereas the N-terminal was hidden in the isolated oligomer complex. Differential scanning calorimetry revealed that lysenin interacted with both hydrophilic head group and hydrophobic hydrocarbon tails of sphingomyelin. Oligomerization but not binding was affected by the amide-linked fatty acid composition of sphingomyelin, suggesting the role of membrane fluidity in the oligomerization step.

Quantitative analysis and characterization of DNA immobilized on gold.

We describe the complementary use of X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy to quantitatively characterize the immobilization of thiolated (dT)(25) single-stranded DNA (ssDNA) on gold. When electron attenuation effects are accurately accounted for in the XPS analysis, the relative coverage values obtained by the two methods are in excellent agreement, and the absolute coverage can be calculated on the basis of the XPS data. The evolution of chemically specific spectral signatures during immobilization indicates that at lower coverages much of the DNA lies flat on the surface, with a substantial fraction of the thymine bases chemisorbed. At higher immobilization densities, the (dT)(25) film consists of randomly coiled ssDNA molecules each anchored via the thiol group and at possibly one or two other bases. We use two examples to demonstrate how the quantitative analysis can be applied to practical problems: the effects of different buffer salts on the immobilization efficiency; the immobilization kinetics. Buffers with divalent salts dramatically increase the efficiency of immobilization and result in very high surface densities (>5 x 10(13)/ cm(2)), densities that may only be possible if the divalent counterions induce strong attractive intermolecular interactions. In contrast with previous reports of alkanethiol adsorption kinetics on gold, ssDNA immobilization in 1 M phosphate buffer does not occur with Langmuir kinetics, a result attributable to rearrangement within the film that follows the initial adsorption.

Base-dependent competitive adsorption of single-stranded DNA on gold.

We characterize the room-temperature adsorption of single-stranded DNA homo-oligonucleotides from solution onto polycrystalline Au films, including competitive adsorption between all possible pairs of unmodified oligomers. Fourier transform infrared (FTIR) and X-ray photoelectron (XPS) spectroscopy analysis of the resulting films shows that oligonucleotides adsorb with a strongly base-dependent affinity, adenine (A) > cytosine (C) >/= guanine (G) > thymine (T). In competitive adsorption experiments on Au, oligo(dA) strongly dominates over the other oligonucleotides. The relative adsorption affinity of oligo(dA) is so great that it competes effectively against adsorption of thiolated oligomers and even causes hybridized oligo(dA).oligo(dT) duplexes to denature in the presence of Au.