Consecutive Hydrogenation Research Articles

Hydrogen bonding network in the electrical double layer mediates fast proton skipping to Get Rid of Fenton reaction pH dependence enables highly efficient alkaline water purification

A fundamental scientific quandary in environmental has always been the pH dependence in Fenton reaction, that is, the reaction kinetics decreases by approximately 1–3 orders of magnitude upon transitioning from an acidic to an alkaline state. Here, we discovered that protons significantly contribute to the Fenton reaction through an examination of the reaction's interfacial behavior characteristics. Proton transfer mediated by hydrogen bond network connectivity in the electric double layer is responsible for the pH dependence of Fenton reaction kinetics. On this basis, the surface potential of Fenton reaction catalyst was modified to optimize the distribution of H2O in the electrical double layer, enhancing the connectivity of the interfacial hydrogen bond network and providing a fast channel for rapid proton transfer. The consecutive hydrogen bond network mediates rapid proton hopping, increasing the proton concentration in the Helmholtz layer, and consequently promoting the proton conductivity from 5.38×10−7 S·cm−2 to 4.35×10−6 S·cm−2 in alkaline conditions for Fenton reaction. Meanwhile, the kinetics reaction rate was improved 20 times, and the pH dependence was reduced from 70.9 % to 12.6 %. This discovery clarifies the key role of the interfacial hydrogen bond network and proton transfer in Fenton reaction kinetics pH dependence. It provides new theories and methods for achieving alkaline high Fenton reaction kinetics.

Synthesis of Low-Symmetric α-Cobalt(II) Hydroxide-Incorporated Cyanuric Acid Layers with High Néel Temperature and Large Coercivity: Structure and Magnetism.

α-Cobalt(II) (CoII) hydroxide (compound 1) incorporating cyanuric acid layers was synthesized via the solvothermal method. 1 exhibited two distinct characteristics, which were different from reported α-CoII hydroxides. (i) The presence of abundant consecutive hydrogen bonds between the adjacent hydroxide layers enhanced the driving force of crystallization along the direction of the c axis. Thus, 1 revealed high crystallinity without the disorder phenomenon. (ii) 1 showed low symmetry. The configuration of CoTd sites did not follow the regular triangular net. The low symmetry favored the magnetic anisotropy. Thus, 1 revealed ferrimagnetic behavior with a high Néel temperature (TN = 56.8 K) and coercivity (Hc = 36 kOe at 2 K). The ferrimagnetic behavior of 1 was validated via the Hubbard U correction density functional theory.

Photocatalyzed Cascade Hydrogen Atom Transfers for Assembly of Multi-Substituted α-SCF3 and α-SCF2H Cyclopentanones.

A photocatalyzed formal (3+2) cycloaddition has been developed to construct original polysubstituted α-SCF3 cyclopentanones in a regio- and diastereoselective manner. This building block approach leverages trifluoromethylthio alkynes and branched/linear aldehydes, as readily available reaction partners, in consecutive hydrogen atom transfers and C-C bond formations. Difluoromethylthio alkynes are also compatible substrates. Furthermore, the potential for telescoped reaction starting from alcohols instead of aldehydes was demonstrated, as well as process automatization and scale-up under continuous microflow conditions. This prompted density functional theory (DFT) calculations to support a radical-mediated cascade process.

Photocatalyzed Cascade Hydrogen Atom Transfers for Assembly of Multi‐Substituted α‐SCF3 and α‐SCF2H Cyclopentanones

AbstractA photocatalyzed formal (3+2) cycloaddition has been developed to construct original polysubstituted α‐SCF3 cyclopentanones in a regio‐ and diastereoselective manner. This building block approach leverages trifluoromethylthio alkynes and branched/linear aldehydes, as readily available reaction partners, in consecutive hydrogen atom transfers and C−C bond formations. Difluoromethylthio alkynes are also compatible substrates. Furthermore, the potential for telescoped reaction starting from alcohols instead of aldehydes was demonstrated, as well as process automatization and scale‐up under continuous microflow conditions. This prompted density functional theory (DFT) calculations to support a radical‐mediated cascade process.

Hydroconversion of lignin-derived platform compound guaiacol to fuel additives and value-added chemicals over alumina-supported Ni catalysts

Hydroconversion of guaiacol (GUA) over γ-Al2O3 and phosphatized-γ-Al2O3 (γ-Al2O3(P)) supported Ni catalysts was initiated by Lewis-sites and active Ni sites. Conversion proceeded via transmethylation and hydrodemethylation/hydrodemethoxylation as major and minor pathways, respectively, resulting in mainly catechol and methylcatechols, and via series of consecutive hydrodehydroxylation (HDHY) and ring hydrogenation (HYD) reactions leading to partially and fully deoxygenated, saturated, and unsaturated products. High Ni-loading and high H2 pressure promoted the formation of cyclohexane and methyl-substituted cyclohexanes; however, above 300 °C the hydrogenation–dehydrogenation equilibrium favored the formation of benzene and methyl-substituted benzenes. Ni/γ-Al2O3(P) showed suppressed HYD/HDHY activity resulting in pronounced formation of catechol and/or phenol and their methyl-substituted derivatives. Surface phenolate species were substantiated as surface intermediates of hydrodeoxygenation. Phosphatizing reduced the concentration of both basic OH and Lewis acid (Al+) – Lewis base (O–) pair surface sites of the γ-Al2O3 support and, thereby, suppressed phenolate formation and hydrodeoxgenation.

Three-dimensional flower-like N-doped tungsten carbide for enhanced hydrogen evolution reaction

It has been critical and challenging to develop non-precious transition-metal-based eletrocatalysts with low-cost and long-term durability for efficient water splitting. Herein, self-supported nitrogen-doped tungsten carbide on iron-nickel foam (N-WC@INF) with three-dimensional flower-like structure was prepared by a simple hydrothermal reaction followed by simultaneous nitridation and carbonization. The resulting N-WC@INF exhibits an overpotential of 103 mV at a current density of 10 mA cm−2 in alkaline media and a low Tafel slope of 47 mV dec−1, accompanied by a negligible loss of overpotential after 30 h consecutive hydrogen evolution reaction (HER). Additionally, N-WC@INF shows promising activity for oxygen evolution reaction (OER) with an overpotential of 224 mV at 10 mA cm−2 and a low Tafel slope of 22 mV dec−1.

Replacing syngas by formic acid and acetic anhydride with advantages: tandem carbonylation of renewable terpenes and propenylbenzenes

The introduction of aldehyde and acetate functionalities in renewable terpenes and propenylbezenes provides useful feedstocks for fine chemicals, especially in the flavor and fragrance segment. Herein we report the rhodium catalyzed hydroformylation and the tandem hydroformylation/hydrogenation/O-acylation of biomass based propenylbenzenes and terpenes with a mixture of formic acid (FA) and acetic anhydride (Ac2O) as a cheaper and less dangerous alternative for flammable and toxic syngas (carbon monoxide and hydrogen mixture) used in the conventional hydroformylation. In addition, we were able to perform the consecutive aldehyde hydrogenation, followed by O-acetylation, formally adding a methyl acetate molecule in a C-C double bond in a tandem process, which was not feasible with the conventional hydroformylation. For propenylbenzenes containing a phenol moiety, the parallel acetoxylation of this group also took place. The protocol allowed to obtain aldehydes and mono- or diacetate esters, which are potentially valuable as fragrance components.

Driving tetracycline hydrochloride degradation and concomitant hydrogen peroxide photosynthesis in a neutral environment over sulphur and oxygen codoped carbon nitride

The investigation of an artificial photosynthesis system for contaminant treatment and consecutive hydrogen peroxide formation is imperative but challenging, whereas the conversion efficiency is relatively low and far away from the demand for social development. Herein, oxygen and sulphur were collectively introduced into carbon nitride nanosheets (OSCN), together with sufficient edge and basal plane active sites. The as-synthesized sample could achieve a degradation efficiency of 84% for 100 mg/L tetracycline hydrochloride, together with simultaneous hydrogen peroxide production of 366 μmol g−1 h−1 under environmentally friendly neutral conditions. Intriguingly, the addition of tetracycline hydrochloride can accelerate hydrogen peroxide generation, which thus in turn speed up tetracycline hydrochloride degradation. It was revealed that the optimized electronic structure, promoted light-harvesting, and enhanced charge carriers separation capacity are conducive for the synchronous oxygen reduction and contaminant oxidation procedure in large measure. Furthermore, the degradation and hydrogen peroxide generation can be maintained even after 15 cycles, demonstrating the stability of OSCN and its possibility for practical applications. The degradation pathway and in-deep reaction mechanism are carried out accordingly. Additionally, such a synchronously promoted reaction can be extended to some other pollutants, like phenol and 2,4-dichlorophenol. This interesting work provides a novel strategy for pollutants removal and concurrent hydrogen peroxide generation.

Air stable plasma passivation of GaAs at room temperature

GaAs surfaces require electrical and chemical passivation for semiconductor devices, but in order to have air stable passivation, high temperatures have been previously required in the passivation step. Here, we demonstrate air-stable, ex situ plasma passivation of GaAs using consecutive hydrogen and nitrogen plasmas at room temperature. No pre-clean using deoxidizing wet chemistry or other means is required. The hydrogen plasma step removes surface oxides and As, which leaves a Ga-rich layer that the nitrogen plasma then turns to GaN. The formed GaN layer efficiently passivates the surface. The plasma-passivated GaAs shows upto 5× room-temperature photoluminescence after 1 year, and room-temperature time-resolved photoluminescence demonstrates robust passivation even after 3 years, both comparisons to similarly aged unpassivated GaAs. Atomic force microscopy was used to confirm that the passivated surfaces can be made smooth enough for microelectronic applications. Grazing incidence x-ray diffraction indicated that the nitride films are amorphous, and energy-dispersive x-ray spectroscopy was used to estimate the nitrogen content. We used a common inductively coupled plasma reactive ion etching system for plasma passivation, thus enabling the rapid adoption of this technique.

Resistant effects determination of Lactobacillus supplementation on broilers to consecutive hydrogen sulfide exposure

Hydrogen sulfide (H2S) is one of the most irritant gases present in rearing stalls that suppress broilers' healthy growth, which is seriously required an effective alleviation method. In this study, Lactobacillus was supplemented to investigate the alleviative effects on broilers reared under consecutive H2S exposure. A total of 180 healthy 1-day-old male AA broilers with similar body weight (40.8 ± 1.0 g) were randomly allotted into the control treatment (CON), the hydrogen sulfide treatment (H2S), and the Lactobacillus supplement under H2S exposure treatment (LAC) for a 42-d-long feeding process. Growth and carcass performances, immunity-related parameters, intestinal development and cecal microbial communities, and blood metabolites were measured. Results showed that Lactobacillus supplement significantly increased the body weight gain (BWG) while reduced the mortality rate, abdominal fat and bursa of fabricius weight during the whole rearing time compared with H2S treatment (P < 0.05). Serum LPS, IL-1β, IL-2, and IL-6 contents were observed significantly increased after H2S treatment while remarkably decreased after Lactobacillus supplementation(P < 0.05). Intestinal morphology results showed a significant higher in the development of ileum villus height (P < 0.05). Cecal microbiota results showed the bacterial composition was significantly altered after Lactobacillus supplement (P < 0.05). Specifically, Lactobacillus supplement significantly decreased the relative abundance of Faecalibacterium, while significantly proliferated the relative abundance of Lactobacillus, Bifidobacterium, Clostridium, and Campylobacter (P<0.05). Metabolic results indicated that Lactobacillus supplement may alleviate the harmful effects caused by H2S through regulating the pyrimidine metabolism, starch and sucrose metabolism, fructose and mannose degradation, and beta-alanine metabolism. In summary, Lactobacillus supplement effectively increased BWG and decreased mortality rate of broilers under H2S exposure by enhancing the body's immune capacity, proliferating beneficial microbes (e.g., Lactobacillus and Bifidobacterium), and regulating the physiological pyrimidine metabolism, starch and sucrose metabolism, and beta-alanine metabolism.

Nanomicellar Electrolyte To Control Release Ions and Reconstruct Hydrogen Bonding Network for Ultrastable High-Energy-Density Zn-Mn Battery.

Zn-Mn batteries with two-electron conversion reactions simultaneously on the cathode and anode harvest a high voltage plateau and high energy density. However, the zinc anode faces dendrite growth and parasitic side reactions while the Mn2+/MnO2 reaction on the cathode involves oxygen evolution and possesses poor reversibility. Herein, a novel nanomicellar electrolyte using methylurea (Mu) has been developed that can encapsulate ions in the nanodomain structure to guide the homogeneous deposition of Zn2+/Mn2+ in the form of controlled release under an external electric field. Consecutive hydrogen bonding network is broken and a favorable local hydrogen bonding system is established, thus inhibiting the water-splitting-derived side reactions. Concomitantly, the solid-electrolyte interface protective layer is in situ generated on the Zn anode, further circumventing the corrosion issue resulting from the penetration of water molecules. The reversibility of the Mn2+/MnO2 conversion reaction is also significantly enhanced by regulating interfacial wettability and improving nucleation kinetics. Accordingly, the modified electrolyte endows the symmetric Zn∥Zn cell with extended cyclic stability of 800 h with suppressed dendrites growth at an areal capacity of 1 mAh cm-2. The assembled Zn-Mn electrolytic battery also demonstrates an exceptional capacity retention of nearly 100% after 800 cycles and a superior energy density of 800 Wh kg-1 at an areal capacity of 0.5 mAh cm-2.

HYDROGENATION TECHNOLOGY AND CHEMISTRY OF COTTONSEED OIL AND FATS

The presented research describes the hydrogenation technology and the chemistry of vegetable oils and fats using powder and stationary catalysts. The hydrogenation technology process includes various equipment and materials, i.e., equipment for hydrogenation, laboratory flow reactor, autoclave for hydrogenation on powder nickel-copper catalyst, hydrogenation catalysts, and selection of alloy stationary catalysts and their structure. The hydrogenation process includes selecting alloy nickelaluminum catalyst promoters, measuring the viscosity of hydrogenated fat, using static catalysts as forcontacts, kinetic regularities of cotton oil hydrogenation with new modifications of nickel-copperaluminum alloy promoted catalysts, and reception of food hydrogenated fat by consecutive hydrogenation of cotton oil on powder and stationary catalysts. Modifying immobile nickel-copperaluminum alloy catalysts also evolved with the addition of vanadium, rhodium, and palladium in the hydrogenation process. The cotton oil pre-contact hydrogenation on stationary and powder nickelcopper catalysts is a novel development. It ensures an increase in the physiological and nutritional value of margarine products based on hydrogenated food fat. Studying the influence of technological regimes of cotton oil hydrogenation on new modifications of stationary nickel-copper-aluminum promoted catalysts commenced. The obtained results established the technological parameters for acquiring food and confectionery salons by combining stationary and suspended catalysts. Likewise, a combination of stationary and suspended catalysts has instituted the industrial parameters for the production of food and confectionery salons based on the effects of technological regimes (temperature, pressure, oil, and hydrogen supply rates) of cottonseed oil hydrogenation on new modifications of stationary nickel-copper-aluminum promoted catalysts.

Understanding the Oxidative Properties of Nickel Oxyhydroxide in Alcohol Oxidation Reactions.

The NiOOH electrode is commonly used in electrochemical alcohol oxidations. Yet understanding the reaction mechanism is far from trivial. In many cases, the difficulty lies in the decoupling of the overlapping influence of chemical and electrochemical factors that not only govern the reaction pathway but also the crystal structure of the in situ formed oxyhydroxide. Here, we use a different approach to understand this system: we start with synthesizing pure forms of the two oxyhydroxides, β-NiOOH and γ-NiOOH. Then, using the oxidative dehydrogenation of three typical alcohols as the model reactions, we examine the reactivity and selectivity of each oxyhydroxide. While solvent has a clear effect on the reaction rate of β-NiOOH, the observed selectivity was found to be unaffected and remained over 95% for the dehydrogenation of both primary and secondary alcohols to aldehydes and ketones, respectively. Yet, high concentration of OH- in aqueous solvent promoted the preferential conversion of benzyl alcohol to benzoic acid. Thus, the formation of carboxylic compounds in the electrochemical oxidation without alkaline electrolyte is more likely to follow the direct electrochemical oxidation pathway. Overoxidation of NiOOH from the β- to γ-phase will affect the selectivity but not the reactivity with a sustained >95% conversion. The mechanistic examinations comprising kinetic isotope effects, Hammett analysis, and spin trapping studies reveal that benzyl alcohol is oxidatively dehydrogenated to benzaldehyde via two consecutive hydrogen atom transfer steps. This work offers the unique oxidative and catalytic properties of NiOOH in alcohol oxidation reactions, shedding light on the mechanistic understanding of the electrochemical alcohol conversion using NiOOH-based electrodes.

Mechanism determination on the interactive effects between host immunity and gut microbiome to resist consecutive hydrogen sulfide inhalation of laying hens

The study aims to investigate the underlying mechanism of the interactions between intestinal microbiota and host immunity-related parameters in response to H2S inhalation of layer hens. A total of 180 healthy 300-day-old Lohmann pink hens with similar body weight were randomly allotted into the control (CON) and the hydrogen sulfide (H2S) treatments for an 8-wk-long feeding procedure. Productive performances, antioxidant capacities, immunity-related parameters, blood metabolites, and cecal microbiota were measured to determine the physiological and gastrointestinal responses to H2S treatment. Results showed that feed intake, egg production, eggshell strength, Haugh unit, and relative yolk weight significantly declined under H2S treatment compared with CON (P < 0.05). Antioxidant and immunity-related parameters showed that glutathione peroxidase, IL-4, and TNF-α contents significantly decreased, whereas contents of IL-1β, IL-2, and IL-6 significantly increased after H2S treatment (P < 0.05). Further metabolic results showed H2S treatment upregulated 2-mercaptobenzothiazole, D-glucopyranuronic acid, deoxyuridine, cholic acid, and mimosine, etc., which mainly enriched into the pyrimidine metabolism, beta-alanine metabolism, valine, leucine, and isoleucine biosynthesis, and pantothenate and CoA biosynthesis pathways. Meanwhile, aceturic acid, 9-oxodecenoic acid, palmitoleic acid, lauric acid, linoleic acid, oleic acid, and valeric acid mainly contributed to the downregulated metabolites, and enriched into the biosynthesis of unsaturated fatty acids, amino sugar and nucleotide sugar metabolism, tryptophan metabolism and linoleic metabolism. Moreover, H2S treatment significantly proliferated the relative abundances of Faecalibacterium, Ruminococcaceae, and Streptococcus, while decreased Prevotella, Lactobacillus, Bifidobacterium, Clostridium, and Campylobacter (P < 0.05). The altered bacteria were functionally enriched in the carbohydrate metabolism, amino acid metabolism, and metabolism of cofactors and vitamins pathways. H2S treatment also significantly downregulated the expression of ZO-1, Claudin 4, and Claudin 7 (P < 0.05). In summary, intestinal microbial communities altered significantly to make proper adaptations in interacting with the host immune systems through the immunity-related metabolites secretion, and epithelial tight-junction-related genes expressions, purposely to regulate the productive performance under hydrogen sulfide inhalation.

Evaluating hydrogen risk management policy PR: Lessons learned from three hydrogen accidents in South Korea

Hydrogen energy has become a pivotal actor in achieving carbon neutrality by 2050 in the era of the climate crisis. Regardless of its importance, three consecutive hydrogen safety accidents and their aftermath in South Korea have aggravated the public's acceptance of hydrogen. Hydrogen-induced risks have always existed in our society regardless of technical improvement. Here, the task of the government is to manage the hydrogen risk to prevent hydrogen disasters. This study included three steps in its research design; 1) selecting experts through snowball sampling, 2) conducting a qualitative email survey, and 3) analyzing the qualitative answer sheet by applying semantic network analysis. We found that experts' evaluations of the Korean hydrogen PR policy were positive regarding responsiveness but negative regarding openness, guidelines, and control tower. Therefore, we suggest practical policy recommendations; the central government should play an important role in cultivating professional crisis management PR personnel and others.

Creating and Stabilizing an Oxidized Pd Surface under Reductive Conditions for Photocatalytic Hydrogenation of Aromatic Carbonyls.

Photocatalysis provides an eco-friendly route for the hydrogenation of aromatic carbonyls to O-free aromatics, which is an important refining process in the chemical industry that is generally carried out under high pressure of hydrogen at elevated temperatures. However, aromatic carbonyls are often only partially hydrogenated to alcohols, which readily desorbs and are hardly further deoxygenated under ambient conditions. Here, we show that by constructing an oxide surface over the Pd cocatalyst supported on graphitic carbon nitride, an alternative hydrogenation path of aromatic carbonyls becomes available via a step-wise acetalization and hydrogenation, thus allowing efficient and selective production of O-free aromatics. The PdO surface allows for optimum adsorption of reactants and intermediates and rapid abstraction of hydrogen from the alcohol donor, favoring fast acetalization of the carbonyls and their consecutive hydrogenation to O-free hydrocarbons. The photocatalytic hydrogenation of benzaldehyde into toluene shows a high selectivity of >90% and a quantum efficiency of ∼10.2% under 410 nm irradiation. By adding trace amounts of HCl to the reaction solution, the PdO surface remains stable and active for long-term operation at high concentrations, offering perspective for practical applications.

Scalable synthesis of Cu clusters for remarkable selectivity control of intermediates in consecutive hydrogenation

Subnanometric Cu clusters that contain only a small number of atoms exhibit unique and, often, unexpected catalytic behaviors compared with Cu nanoparticles and single atoms. However, due to the high mobility of Cu species, scalable synthesis of stable Cu clusters is still a major challenge. Herein, we report a facile and practical approach for scalable synthesis of stable supported Cu cluster catalysts. This method involves the atomic diffusion of Cu from the supported Cu nanoparticles to CeO2 at a low temperature of 200 °C to form stable Cu clusters with tailored sizes. Strikingly, these Cu clusters exhibit high yield of intermediate product (95%) in consecutive hydrogenation reactions due to their balanced adsorption of the intermediate product and dissociation of H2. The scalable synthesis strategy reported here makes the stable Cu cluster catalysts one step closer to practical semi-hydrogenation applications.

Facilitating the proton conductivity of polyvinyl alcohol based proton exchange membrane by phytic acid encapsulated Zn-azolate MOF

It is important but still challenging to develop high-performance proton exchange membranes (PEMs) which should meet the following requirements: consecutive proton-conducting channels, efficient proton transfer, and excellent stability. In this study, polyvinyl alcohol (PVA) composite membranes were constructed by loading post synthetically phytic acid (PA) encapsulated Zn-MOF, denoted as PVA@PA@Zn-MOF-X (X = 0, 2, 4, 6. wt%). The novel Zn-MOF with high thermal and pH stability has been synthesized from the zinc salt and dual ligands (H2NDI: 2,7-bis(3,5-dimethyl) dipyrazol-1,4,5,8-naphthalene-tetracarboxydiimide; HBTA: 1 H-benzotriazole) which can be employed to host PA as proton carriers. Composite membranes were evaluated by microstructure, thermal stability, mechanical property, dimensional stability, proton conductivity, and so forth. It is found that the codoping of PA encapsulated Zn-MOF with suitable content is more stability of the composite membranes. Furthermore, PVA@PA@Zn-MOF-4 shows the highest proton conductivity of 1.85 × 10-2 S cm-1 at 80 oC and 90% RH with relatively lower value for ion exchange capacity (0.58 mmol g-1) among the composite membranes. This phenomenon is attributed to the consecutive hydrogen bonding networks which are composed of the carbonyl oxygen sites within Zn-MOF, phosphate groups of PA, and hydroxyl groups of PVA, enhancing the efficiency of proton transport. This is a referable strategy for designing and constructing the high-performance PEMs for fuel cells.

Functional confinement of a zinc-oxide-supported gold catalyst enhances the direct synthesis of hydrogen peroxide

Due to the intensive energy consumption and environmental unfriendliness of the current industrial anthraquinone process for producing hydrogen peroxide, it is of interest to develop a clean and efficient alternative. Herein, we report that a zinc-oxide-supported gold catalyst encapsulated by a silica overlayer efficiently catalyzes the direct synthesis of hydrogen peroxide from carbon monoxide, oxygen, and water. Detailed characterizations demonstrate that the confinement effect of the silica overlayer may enhance hydrogen peroxide productivity by limiting the agglomeration of gold nanoparticles, inhibiting the hydrogen peroxide degradation activity, and improving the hydrophilicity of the catalyst surface. Isotope-labeling experiments and theoretical calculations reveal that both oxygen atoms in hydrogen peroxide come from molecular oxygen, and that a consecutive hydrogenation process is followed. This work poses a facile strategy to construct highly active catalysts for the direct synthesis of hydrogen peroxide, employing the confinement effects of an overlayer.

GB1 hairpin kinetics: capturing the folding pathway with molecular dynamics, replica exchange and optimal dimensionality reduction

We have performed molecular dynamics (MD) and replica-exchange (REMD) simulations of folding of the GB1 hairpin peptide in aqueous solution. REMD results were consistent with a cooperative zipper folding model. 120 MD trajectories at 320 K yielded relaxation times of 1.8 and 100 ns, with the slower assigned to global folding. The MD folding/unfolding transitions also followed the cooperative zipper model, specifying nucleation at the central turn followed by consecutive hydrogen bond formation. Formation of hydrogen bonds and hydrophobic contacts were highly correlated. Coarse-grained kinetic models constructed with the Optimal Dimensionality Reduction (ODR) approach found a folding time of 3.3 and unfolding time of 4.0 Additionally, relaxation times in the 130–170 ns range could be assigned to formation of the transition state and off-path intermediates. The unfolded state was the most highly populated and, significantly, most heterogenous, assembling the largest number of microstates, primarily composed of extended and turn structures. The folded state was also heterogenous, but a to a lesser degree, involving the fully folded and partially folded in-register hairpins at early stages of the zipper pathway. The transition state corresponded to the nucleated hairpin, with central turn and first beta-sheet hydrogen bond, while the off-path intermediates were off-register partial hairpins. Our simulation results were in excellent agreement with experimental data on folded fraction, relaxation time and folding mechanism. The new findings from this work suggest a highly cooperative zipper folding mechanism, nascent hairpin transition state and ∼100 ns relaxation related to intermediate formation. Communicated by Ramaswamy H. Sarma