Hydroxyl Oxygen Research Articles

Active sites for the selective hydrodeoxygenation of m-cresol on WOx-modified Pt

Adsorption and reaction of m-cresol on Pt(111) and WOx-modified Pt(111) surfaces was characterized using temperature programmed desorption (TPD), high resolution electron energy loss spectroscopy (HREELS), and X-ray photoelectron spectroscopy (XPS). The results of this study show that on Pt(111) a strong interaction between the aromatic ring and the Pt surface facilitates CC bond cleavage resulting in decomposition at relatively low temperatures. In contrast, on WOx-modified Pt(111), m-cresol bonds to oxygen vacancy sites on the WOx deposits via the hydroxyl oxygen with the aromatic ring tilted away from the surface, resulting in a bonding configuration that promotes selective CO bond cleavage and limits ring hydrogenation. XPS results also show that interactions at the Pt-WOx interface help stabilize submonolayer WOx deposits in a partially reduced state, thereby maintaining a high concentration of the oxygen vacancy adsorption sites.

Electrochemical removal of amoxicillin using a Cu doped PbO2 electrode: Electrode characterization, operational parameters optimization and degradation mechanism

This work investigated the electrochemical degradation of amoxicillin (AMX) in aqueous solution with Cu-PbO2 electrode. The main influence factors on the degradation of AMX, such as Na2SO4 concentration, initial AMX concentration, current density and initial pH value, were analyzed in detail. Under the optimal conditions, the removal rates of AMX and chemical oxygen demand (COD) reached 99.4% and 46.3% after 150 min treatment. The results indicated that the electrochemical degradation of AMX fitted pseudo-first-order reaction kinetics. Compared with undoped PbO2 electrode, Cu-PbO2 electrode had a smaller crystal size, more proportion of hydroxyl oxygen species, greater AMX and chemical oxygen demand (COD) removal efficiency, higher average current efficiency (ACE) and lower electrical efficiency per log order (EE/O). Electrochemical oxidation using Cu-PbO2 electrodes was an effective way to eliminate amoxicillin in aqueous solution. Moreover, a possible degradation pathway including ring open and mineralization was proposed by intermediate products determined by GC-MS method. This paper could provide basic data and technique reference for the amoxicillin wastewater pollution control.

Na-promoted Pt/Al2O3 activity stability for the complete oxidation of HCHO at room temperature

A series of Na-doped Pt/Al2O3 catalysts with 0.2 wt% of Pt loading and 0–6 wt% Na loading was prepared to investigate the HCHO complete oxidation at room temperature. Powder XRD, BET and XPS were used to characterize the bulk structure and texture of catalysts, as well as the ratio of hydroxyl oxygen to lattice oxygen. A long-term catalyst stability test (50 h on reaction stream) was conducted under severe conditions of a large space velocity of 180,000 mL/h/g, a high HCHO concentration of 80 ppm and dry conditions (relative humidity of 0%). An appropriate amount of doped-Na (2 wt%) contributed to a remarkable improvement of activity and stability of the Na-doped 0.2 wt% Pt/Al2O3 catalyst.

A Bacteriochlorin-Based Metal-Organic Framework Nanosheet Superoxide Radical Generator for Photoacoustic Imaging-Guided Highly Efficient Photodynamic Therapy.

Hypoxic tumor microenvironment is the bottleneck of the conventional photodynamic therapy (PDT) and significantly weakens the overall therapeutic efficiency. Herein, versatile metal–organic framework (MOF) nanosheets (DBBC‐UiO) comprised of bacteriochlorin ligand and Hf6(µ3‐O)4(µ3‐OH)4 clusters to address this tricky issue are designed. The resulting DBBC‐UiO enables numerous superoxide anion radical (O2 −•) generation via a type I mechanism with a 750 nm NIR‐laser irradiation, part of which transforms to high toxic hydroxyl radical (OH•) and oxygen (O2) through superoxide dismutase (SOD)‐mediated catalytic reactions under severe hypoxic microenvironment (2% O2), and the partial recycled O2 enhances O2 −• generation. Owing to the synergistic radicals, it realizes advanced antitumor performance with 91% cell mortality against cancer cells in vitro, and highly efficient hypoxic solid tumor ablation in vivo. It also accomplishes photoacoustic imaging (PAI) for cancer diagnosis. This DBBC‐UiO, taking advantage of superb penetration depth of the 750 nm laser and distinct antihypoxia activities, offers new opportunities for PDT against clinically hypoxic cancer.

Synthesis, structural characterization and DNA binding affinity of new bioactive nano‐sized transition metal complexes with sulfathiazole azo dye for therapeutic applications

The azo dye ligand 4‐(5‐chloro‐2‐hydroxyphenylazo)‐N‐thiazol‐2‐ylbenzenesulfonamide (H2L) formed by the coupling reaction of sulfathiazole and p‐chlorophenol was synthesized and characterized using elemental analysis and Fourier transform infrared (FT‐IR) as well as UV–visible spectra. Nano‐sized divalent Cu, Co, Ni, Mn and Zn complexes of the synthesized azo dye ligand were prepared and investigated using various spectroscopic and analytical techniques. Elemental and thermal analyses indicated the formation of the Cu(II), Ni(II) and Mn(II) complexes in a molar ratio of 1:2 (L:M) while Co(II) and Zn(II) complexes exhibited a 1:1 (M:L) ratio. FT‐IR spectral studies confirmed the coordination of the ligand to the metal ions through the phenolic hydroxyl oxygen, azo nitrogen, sulfonamide oxygen and/or thiazole nitrogen. The geometric arrangements around the central metal ions were investigated applying UV–visible and electron spin resonance spectra, thermogravimetric analysis and molar conductance measurements. X‐ray diffraction patterns revealed crystalline nature of H2L and amorphous nature of all synthesized complexes. Transmission electron microscopy images confirmed nano‐sized particles and their homogeneous distribution over the complex surface. Antibacterial, antifungal and antitumour activities of the investigated complexes were screened compared with familiar standard drugs to confirm their potential therapeutic applications. The Cu(II) complex showed IC50 of 3.47 μg ml−1 (5.53 μM) against hepatocellular carcinoma cells, which means that it is a more potent anticancer drug compared with the standard cisplatin (IC50 = 3.67 μg ml−1 (12.23 μM)). Furthermore, the Co(II), Ni(II), Cu(II) and Zn(II) complexes displayed IC50 greater than that of an applied standard anticancer agent (5‐flurouracil) towards breast carcinoma cells. Hence, these complexes can be considered as promising anticancer drugs. The mode of binding of the complexes with salmon serum DNA was determined through electronic absorption titration and viscosity studies.

Purification of an iron-binding peptide from scad (Decapterus maruadsi) processing by-products and its effects on iron absorption by Caco-2 cells.

This work was aimed at producing peptides containing iron-binding capabilities from scad (Decapterus maruadsi) processing by-product with alcalase hydrolysis. The chelating peptides were purified by ultrafiltration, immobilized-metal affinity chromatography, gel filtration chromatography, and reversed-phase high-performance liquid chromatography. A novel iron-binding peptide was purified with 1,386.63Da molecular weight and amino acid sequence of QKGTYDDYVEGL. The peptide binds to iron mainly through carboxyl and hydroxyl oxygen bonds. The iron-binding peptide can significantly promote the absorption of inorganic iron in Caco-2 cells. These results have contributed to development of the peptide from scad processing by-products hydrolyzate in iron supplementations. PRACTICAL APPLICATIONS: Iron deficiency is one of the most common and widespread nutritional disorders in the world. Iron-peptide chelates may be suitable for iron-fortification. Our study shows that a peptide purified from scad processing by-product has iron-chelating activity, and significantly increases iron absorption by Caco-2 cells. Hence, this peptide has potential application as a novel carrier for enhancing iron absorption.

Oxychlorination Redispersion of Pt Catalysts: Surface Species and Pt-Support Interactions Characterized by X-ray Absorption and FT-IR Spectroscopy

To help elucidate the oxychlorination redispersion reaction mechanism, the surface species formed on the surface of γ-Al2O3 was characterized by X-ray absorption spectroscopy (XAS). The efficacy of redispersion was assessed by the Pt–Pt coordination number (CNPt–Pt) of redispersed, and then reduced samples. A nearly fully redispersed complex (Ptrd52) was prepared by treating a sintered model Pt/γ-Al2O3 catalyst at 520 °C, Air/EDC (ethylene dichloride) of 30, and WHSV (Weight Hourly Space Velocity) of 0.07 h−1 for 16 h. For investigating temperature effects, samples treated at 460 (Ptrd46) and 560 °C (Ptrd56) were also prepared for comparison. It was found that, while an octahedral resembling Pt(Os)3–4(O–Cl)2–3 (Os represents support oxygen or hydroxyl oxygen) complex was formed on γ-Al2O3 of Ptrd52, less O–Cl ligands were formed on the redispersed complexes, Ptrd46 and Ptrd56. A negative correlation of CNPt–Pt with CNPt–Cl* (Cl* represents the Cl atom in O–Cl ligand) for these three samples further suggested that the formation of Pt–O–Cl played a key role in the redispersion process. Pt–O–Cl could be formed in the reaction of reactive Cl⋅ and PtO2. At an operation temperature of lower-than-optimal temperatures of 520 °C, less Cl2 dissociation and less O–Cl ligands were formed. On the other hand, higher temperatures may facilitate Cl2 dissociation, but reduce the equilibrium conversion of HCl to Cl2, leading to increased HCl reaction with Pt (PtO2) clusters to form Pt–Cl (Cl is the atom bonded directly to Pt), and decreased formation of Pt–O–Cl.

Syntheses, crystal structures and insulin mimetic activity of maltolato- and ethylmaltolato-coordinated oxidovanadium(V) complexes with N′-(3-ethoxy-2-hydroxybenzylidene)-3-methylbenzohydrazide

Two new oxidovanadium(V) complexes, [VOLL1] and [VOLL2], where L is the dianionic form of N′-(3-ethoxy-2-hydroxybenzylidene)-3-methylbenzohydrazide (H2L), L1 is maltolatel, and L2 is ethylmaltolate, have been prepared. Both H2L and the complexes have been characterized by elemental analysis, IR, UV–Vis and NMR spectra. The structures of the compounds were further confirmed by single crystal X-ray diffraction. The aroylhydrazone ligand coordinates to the V atoms through the phenolate oxygen, imino nitrogen and enolate oxygen. The maltolate and ethylmaltolate ligands coordinated to the V atoms through the carbonyl oxygen and deprotonated hydroxyl oxygen. The V atom in each complex is in octahedral coordination. The complexes were administered intragastrically to both normal and alloxan-diabetic mice. The biological activity results show that the complexes at doses of 10.0 and 20.0 mg V·kg−1, can significantly decrease the blood glucose level in alloxan-diabetic mice, but the blood glucose level in the treated normal mice was not altered.

Water compatible imprinted polymer prepared in water for selective solid phase extraction and determination of ciprofloxacin in real samples

A novel water compatible ciprofloxacin imprinted polymer is synthesized in water via a green, non-toxic and environmentally friendly polymerization process. Hydrophilic groups, including anionic chlorine, hydroxyl, and carbonyl oxygen provided by a bifunctional monomer comprising 1-allyl-3-vinylimidazole chloride and 2-hydroxyethyl methacrylate, are introduced into the imprinted material, which allows the polymer to interact strongly with imprinting molecule via hydrogen bonds, electrostatic and π-π dipole interactions in aqueous solution. Rebinding experiments show that the obtained molecularly imprinted polymer (MIP) presents special molecular recognition towards quinolone antibiotics (ciprofloxacin, levofloxacin and pefloxacin mesylate) in aqueous matrices. The adsorption process of ciprofloxacin on MIP and non-imprinted polymer (NIP) substrates involves spontaneous exothermic reactions, and the maximum rebinding capacities of ciprofloxacin on MIP and NIP at 25 °C are 19.96 and 8.86 mg g−1, respectively. The excellent selectivity and hydrophilicity of this imprinted polymer makes it suitable for use as an adsorbent in solid phase extraction. Under the optimized conditions, the presented MIP-SPE protocol exhibits a wide linear range between 0.29 and 1.47 × 105 μg L−1 and has been successfully applied for the separation and enrichment of trace ciprofloxacin in real water, soil and pork samples with satisfactory recoveries of 87.33–102.50%. The proposed study implies the promising prospect of this green and water compatible MIP in highly effective recognition and separation of trace quinolones in complex matrics.

Morphology-controlled self-assembled nanostructures of octa(phenoxy)-substituted phthalocyaninato manganese(III) and their nonlinear optical properties: Solvent effect on tuning the intermolecular interaction

Two different morphological nanostructures of 2,3,9,10,16,17,23,24- octakis(phenoxy) phthalocyaninato manganese(III) complex (MnCl[Pc(OPh)8]), with good uniformity and monodispersity, are successfully fabricated through a simple solution self-assembly strategy. Depending mainly on the intermolecular π-π interaction between the phthalocyanine rings, phthalocyaninato manganese complex self-assemble into rod-like nanostructures with H-type aggregation in n-hexane. In contrast, the MnO coordination interactions between the hydroxyl oxygen in solvated methanol molecule and manganese center of neighboring MnCl[Pc(OPh)8] molecule, lead to the formation of spherical nanostructures with J-type aggregation in methanol. Comparative investigation results clearly reveal the solvent coordination effect on tuning the intermolecular interaction and the morphology of the self-assembled MnCl[Pc(OPh)8] nanostructures. In addition, further investigation about the nonlinear optical properties of self-assembled aggregates indicate that the nanostructures fabricated from MnCl[Pc(OPh)8] exhibited reverse saturation absorption in n-hexane and saturation absorption in methanol.

Hydrothermal Synthesis of Rare-Earth Modified Titania: Influence on Phase Composition, Optical Properties, and Photocatalytic Activity.

In order to expand the use of titania indoor as well as to increase its overall performance, narrowing the band gap is one of the possibilities to achieve this. Modifying with rare earths (REs) has been relatively unexplored, especially the modification of rutile with rare earth cations. The aim of this study was to find the influence of the modification of TiO2 with rare earths on its structural, optical, morphological, and photocatalytic properties. Titania was synthesized using TiOSO4 as the source of titanium via hydrothermal synthesis procedure at low temperature (200 °C) and modified with selected rare earth elements, namely, Ce, La, and Gd. Structural properties of samples were determined by X-ray powder diffraction (XRD), and the phase ratio was calculated using the Rietveld method. Optical properties were analyzed by ultraviolet and visible light (UV-Vis) spectroscopy. Field emission scanning electron microscope (FE-SEM) was used to determine the morphological properties of samples and to estimate the size of primary crystals. X-ray photoelectron spectroscopy (XPS) was used to determine the chemical bonding properties of samples. Photocatalytic activity of the prepared photocatalysts as well as the titania available on the market (P25) was measured in three different setups, assessing volatile organic compound (VOC) degradation, NOx abatement, and water purification. It was found out that modification with rare earth elements slows down the transformation of anatase and brookite to rutile. Whereas the unmodified sample was composed of only rutile, La- and Gd-modified samples contained anatase and rutile, and Ce-modified samples consisted of anatase, brookite, and rutile. Modification with rare earth metals has turned out to be detrimental to photocatalytic activity. In all cases, pure TiO2 outperformed the modified samples. Cerium-modified TiO2 was the least active sample, despite having a light absorption tail up to 585 nm wavelength. La- and Gd-modified samples did not show a significant shift in light absorption when compared to the pure TiO2 sample. The reason for the lower activity of modified samples was attributed to a greater Ti3+/Ti4+ ratio and a large amount of hydroxyl oxygen found in pure TiO2. All the modified samples had a smaller Ti3+/Ti4+ ratio and less hydroxyl oxygen.

Synthesis and Crystal Structure of a Polymeric Copper(II) Complex Derived from 2-Hydroxy-5-methylbenzaldehyde Oxime with Antibacterial Activities

A centrosymmetric O-bridged polynuclear copper(II) complex, [CuL2]n, where L is the deprotonated form of the Schiff base ligand 2-hydroxy-5-methylbenzaldehyde oxime, has been prepared and characterized by IR, UV and single-crystal X-ray determination. There is a crystallographic inversion center in the complex. The Cu atom in the complex is coordinated by the phenolate oxygen, imino nitrogen and hydroxyl oxygen atoms from two Schiff base ligands, forming octahedral geometry. The complex was tested in vitro for its antibacterial activity.

Formation of Metal Complexes with Malate Anions: Quantum-Chemical Modeling

Quantum-chemical modeling of anionic forms of malic acid H2mal and the model complex [VV(O)2(mal)]– in which the mal2– ligand is coordinated to the metal ion through its carboxyl and hydroxyl oxygen atoms has been performed by the DFT M06/631G(d,p) method. It has been demonstrated that the participation of the hydroxyl group, which loses its proton only in an alkaline medium, in the formation of malate complexes in an acidic medium is not due to its acid dissociation, but to the process of competitive replacement by a more electropositive metal ion. Calculations show that the simultaneous absence of the protons at the carboxyl and hydroxyl groups leads to electron excess in the region of the –CH2–CHO– bonding. The formation of bonds with electropositive metal ions decreases the electron density in this region, which results in the stabilization of the doubly charged anion.

A theoretical study on the effect of cyano group on the proton transfer process of 10-hydroxybenzo[h]quinoline

The proton transfer processes of 10-hydroxybenzo[h]quinoline (HBQ) and its cyano derivatives (4CN-HBQ, 7CN-HBQ and 7,9CN-HBQ) were studied by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) in ethyl acetate. The optimized geometric structures and infrared spectra show that the intramolecular hydrogen bond of enol form structure is weakened when the cyano group substitutes on the pyridine ring and that is strengthened when the cyano group substitutes on the phenol ring in the S0 state. Electron spectra show that the substitution of cyano group also has a significant effect on electron spectra. The reason for the change in the electron spectra can be obtained from the analysis of frontier molecular orbitals (MOs). The calculated potential barriers for proton transfer of these four molecules are 6.83, 7.83, 4.87 and 2.79 kcal/mol respectively in the S0 state, illustrating that the presence, position and number of cyano groups affect the proton transfer processes to some extent. After vertical excitation to the S1 state, the proton transfer processes of these four molecules become barrierless because of the promotion of charge transfer. Through the analysis of Mulliken charge, it can be found that the cyano group, an electron-withdrawing group, can change the strength of hydrogen bond by withdrawing the electronic charge from hydroxyl oxygen or neighboring nitrogen atom of its ring and thus affects the barrier in the S0 state.

Crystal structures and magnetic properties of nitroxide radical-coordinated copper(II) and cobalt(II) complexes

The crystal structures and magnetic properties of three coordination compounds constructed from various nitroxide radicals L and MII(hfac)2(H2O)2 building blocks (M = Cu or Co and hfac = hexafluoroacetylacetonato) are described. In [(1)Cu(hfac)2]n, 4, the radical ligand L is coordinated to the metal through the oxygen atom of the nitroxide group and oxygen atom of its hydroxyl group, leading to a one-dimensional chain system. In [(2)2Cu(hfac)2]n, 5, two hydroxyl oxygen atoms of the radical ligand are coordinated to the metal, and the CoII centers adopt distorted octahedral geometry to give a mononuclear compound. For [(L)Cu(hfac)2]n, 6, the oxygen atom of the nitroxide group and nitrogen atom of the amino group of L are coordinated to the metal, leading to a one-dimensional chain system. The magnetic susceptibility study of the copper coordination compound 4 revealed weak ferromagnetic interactions between the metal center and the organic radical. The cobalt coordination compounds 5 and 6 both show antiferromagnetic interactions.

A DFT study on the effect of oxygen vacancies and H2O in Mn-MOF-74 on SCR reactions.

As one of the main air pollutants, nitrogen oxides (NOx) have serious effects on human health and the environment. In our previous study, we found that Mn-MOF-74 shows excellent catalytic performance for the selective catalytic reduction (SCR) reaction with NH3 being the reductant (NH3-SCR) at low temperature. To obtain a further understanding of the NH3-SCR mechanism in Mn-MOF-74, in this paper, we investigated two important parts of the NH3-SCR process in Mn-MOF-74 using the density functional theory (DFT) method. On the one hand, the structural characteristics of two types of oxygen vacancies of Mn-MOF-74, namely carboxyl oxygen vacancies and hydroxyl oxygen vacancies, and their adsorption properties to reaction species were calculated. It was found that the oxygen vacancies not only activate the reaction species, but also promote the desorption of NO2 molecules from metal sites for the subsequent rapid SCR reactions. On the other hand, we studied the effect of H2O on the structural stability and catalytic performance of Mn-MOF-74. It was found that the interaction of Mn-O bonds was weakened by H2O. Therefore, the influence of H2O should be considered for the future design of MOF-based catalysts for the SCR process.

Eutectic System Based on Urea and Potassium Sodium Tartrate

Deep eutectic solvents (DESs) are considered as better alternative solvents in chemical and physical processes. The binary mixture of urea and potassium sodium tartrate is explored in this study. A eutectic system is determined at composition made up of 33% potassium sodium tartrate and 67% urea (1:2 molar ratio). This eutectic system has a freezing point of 19.83 ± 0.76 °C, density of 1.1971 ± 0.0003 g mL-1, and viscosity of 34.4226 ± 0.0665 cP. The most stable conformation for the adduct of urea and potassium sodium tartrate with water molecules was determined through density functional calculations. The gas phase total energy for the adduct was determined as -5576863 kJ mol-1. Electrostatic interactions between the cations and the carboxylate sites are present, H-bonding between protons of urea and the hydroxyl oxygen of the tartrate, and intramolecular H-bonding between the hydroxyl and carboxylate sites of tartrate are accounted in the structure. The total energy associated with nonbonding interactions is computed as -826 kJ mol-1, which suggests that these interactions stabilize the formation of the DES system of potassium sodium tartrate and urea.

Effects of drying methods on drying characteristics, physicochemical properties and antioxidant capacity of okra

Results of an experimental study were presented and discussed for hot air drying with horizontal cut (HC-HA) or vertical cut (VC-HA) at 55, 60, 65, 70, 75, and 80 °C, respectively, and heat pump drying with HC (HC-HP) or VC (VC-HP) at 40, 50, 60, and 70 °C, respectively, on drying characteristic, colour quality, chemical compositions (vitamin C, chlorophyll, total phenolic and polysaccharide) and antioxidant capacity (2,2-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl radical scavenging capacity and oxygen radical absorbance capacity (ORAC)) of okra samples. Results showed VC had shorter drying time than that of HC both during HA and HP. The effective moisture diffusivity determined by Weibull distribution function ranged from 0.992 × 10−9 m2/s to 4.409 × 10−9 m2/s for HA, and 1.915 × 10−9 m2/s to 5.291 × 10−9 m2/s for HP. The drying activation was 37.00, and 35.91 kJ/mol for the samples of HC-HA and VC-HA, 29.25, and 21.40 kJ/mol for HC-HP and VC-HP, respectively. A comprehensive evaluation of quality attributes indicated that HP was more suitable for okra drying as it improved drying rate and drying quality compared with HA. The optimal sample quality (higher contents of chemical compositions and better colour quality) was found in okra treated with VC-HP at 50 °C.

Tautomerism and conformational analysis in 3-fluoropiperidin-2-one inform on F···HO intramolecular hydrogen bond

Whether hydroxyl hydrogen is directed towards a Lewis base substituent in an alkyl chain due to intramolecular hydrogen bonds or to avoid repulsion between the hydroxyl oxygen and the substituent is a debatable topic and difficult to probe. This is still more challenging when fluorine is the Lewis base substituent. This work reports a theoretical approach capable of dissecting the contributions from hydrogen bond and repulsion, allowing to decide which interaction dominates the orientation of the hydroxyl group in a high-energy tautomer of 3-fluoropiperidin-2-one. A comparison between the potential energy curves for the hydroxyl rotation in the axial and equatorial conformers revealed that repulsion between fluorine and oxygen contributes by ca. 1.2 kcal mol−1 to destabilize the cis isomer, while intramolecular hydrogen bond between fluorine and the hydroxyl group amounts by ca. 0.9 kcal mol−1 favoring the trans isomer. These are not the major effects governing the conformational equilibrium of the studied compound, which is rather dictated by N⋯O steric repulsion, but the obtained outcomes can be valuable to understand the role of F⋯H(O) hydrogen bonds in conformational analysis and, ultimately, in the design of performance fluorinated aliphatic alcohols.

Chemically Accurate Relative Folding Stability of RNA Hairpins from Molecular Simulations.

To benchmark RNA force fields, we compared the folding stabilities of three 12-nucleotide hairpin stem loops estimated by simulation to stabilities determined by experiment. We used umbrella sampling and a reaction coordinate of end-to-end (5' to 3' hydroxyl oxygen) distance to estimate the free energy change of the transition from the native conformation to a fully extended conformation with no hydrogen bonds between non-neighboring bases. Each simulation was performed four times using the AMBER FF99+bsc0+χOL3 force field, and each window, spaced at 1 Å intervals, was sampled for 1 μs, for a total of 552 μs of simulation. We compared differences in the simulated free energy changes to analogous differences in free energies from optical melting experiments using thermodynamic cycles where the free energy change between stretched and random coil sequences is assumed to be sequence-independent. The differences between experimental and simulated ΔΔ G° are, on average, 0.98 ± 0.66 kcal/mol, which is chemically accurate and suggests that analogous simulations could be used predictively. We also report a novel method to identify where replica free energies diverge along a reaction coordinate, thus indicating where additional sampling would most improve convergence. We conclude by discussing methods to more economically perform these simulations.