Hydrogen-bond Connectivity Research Articles

Insight into the phase equilibrium of mycophenolic acid cocrystals

In this study, mycophenolic acid-nicotinamide (MPA-NAM) and mycophenolic acid-acetoguanamine (MPA-AGA) cocrystals were synthesized and characterized using single-crystal X-ray diffraction, Fourier transform spectroscopy and thermal analysis. Intrinsic intermolecular interactions were investigated through Hirshfeld surface and electrostatic potential surface analysis. The results indicated that MPA-NAM and MPA-AGA cocrystals possessed the same types of hydrogen bonds but different hydrogen bond connectivity. Thermodynamic studies revealed that MPA-NAM and MPA-AGA cocrystals exhibited incongruent dissolution behaviors in the chosen solvent. Model regression results indicate that the 1:1 complex formation existed during the dissolution of the MPA-NAM cocrystal, whereas 1:1 and 1:2 solution complexes presented in the MPA-AGA cocrystal. The complicated complexation in the MPA-AGA cocrystal induced all fragments of MPA-AGA to possess higher energies, facilitating MPA-AGA cocrystal precipitation from the solution, which was testified by Energy calculations.

The Loss of Interfacial Water-Adsorbate Hydrogen Bond Connectivity Position Surface-Active Hydrogen as a Crucial Intermediate to Enhance Nitrate Reduction Reaction.

The electrochemical nitrate reduction reaction (NO3RR) offers a promising solution for remediating nitrate-polluted wastewater while enabling the sustainable production of ammonia. The control strategy of surface-active hydrogen (*H) is extensively employed to enhance the kinetics of the NO3RR, but atomic understanding lags far behind the experimental observations. Here, we decipher the cation-water-adsorbate interactions in regulating the NO3RR kinetics at the Cu (111) electrode/electrolyte interface using AIMD simulations with a slow-growth approach. We demonstrate that the key oxygen-containing intermediates of the NO3RR (e.g., *NO, *NO2, and *NO3) will stably coordinate with the cations, impeding their integration with the hydrogen bond network and further their hydrogenation by interfacial water molecules due to steric hindrance. The *H can migrate across the interface with a low energy barrier, and its hydrogenation barrier with oxygen-containing species remains unaffected by cations, offering a potent supplement to the hydrogenation process, playing the predominant factor by which the *H facilitates NO3RR reaction kinetic. This study provides valuable insights for understanding the reaction mechanism of NO3RR by fully considering the cation-water-adsorbate interactions, which can aid in the further development of the electrolyte and electrocatalysts for efficient NO3RR.

Building ultra-stable and low-temperature aqueous zinc–organic batteries via noncovalent supramolecular self-assembly strategy

Zinc-organic batteries (ZOB) have garnered significant attention owing to their design flexibility and abundant raw materials. However, a notable drawback arises from the tendency of organic electrodes to dissolve in the electrolyte during cycling, resulting in diminished cycle stability and a shortened lifespan. Herein, we propose a noncovalent supramolecular self-assembly approach to address the challenge of organic electrode dissolution, namely the hydrogen-bonded organic polymer (HOP) is introduced as the cathode ensuring the electrolyte/electrode stability in ZOB. The HOP comprises perylene anhydride units characterized by robust strong π-π stacking and hydrogen bond connections. This configuration enables the reversible storage of Zn2+/H3O+ through CO/CO bond conversion, as validated by in-situ ATR-FTIR and ex-situ XPS analyses. Employing a 1 m Zn(OTF)2 electrolyte, the Zn//HOP cell exhibited stable cycling at room temperature for 20,000 cycles with nearly 80 % capacity retention and operated at –5 °C for 300 cycles with 100 % capacity retention. Our findings explore the noncovalent supramolecular self-assembly strategy in producing organic electrodes resistant to dissolution.

Research on the hot densification mechanism of biomass wastes based on molecular dynamics simulation and components adjustment method

The hot densification process can be used to prepare the biofuel pellets and diversified densification materials with suitable mechanical strength to overcome the natural defects of low energy density and loose structure of biomass wastes and achieve the high value utilization of the renewable resources. In this study, the two typical biomass wastes, cotton stalk (CS) and Chinese fir wood sawdust (WS) are used for the hot densification investigation (85 °C), and the microscopic evolution behavior of the biomass components during the hot densification process is explored through the combination of the component adjustment method and molecular dynamics simulation. The results show that cellulose is the key component to the mechanical strength of biomass pellet, which plays the crucial role of skeleton support in the densification process, and the strength of pellet is positively correlated with the increasing addition ratio of cellulose. Furthermore, crystalline cellulose exhibits the strongest bonding properties in the hot densification process due to the formation of rich hydrogen bonds and the increasing intermolecular attraction force. Lignin has the poorest capability for hydrogen bond formation, and its addition increases the van der Waals repulsive forces, resulting in the poorest densification performance. Hemicellulose shows the better adhesion capability than lignin due to its glassy transition (83.34 °C) and the suitable addition can greatly improve the mechanical property of the pellet, up to 14.26 MPa. There exists the strongest synergistic effect between cellulose and hemicellulose, which is beneficial to the bonding performance between particles to different extent. Hot densification process can promote the formation of hydrogen bond connections between molecules/atoms and the increase of the van der Waals repulsive force in the further compression. The densification performance of biomass is the combined effect of the physical forces, including electrostatic force and van der Waals force.

Weakened Interfacial Hydrogen Bond Connectivity Drives Selective Photocatalytic Water Oxidation toward H2O2 at Water/Brookite-TiO2 Interface.

The formation of H2O2 through the two-electron photocatalytic water oxidation reaction (WOR) is significant but encounters the competition with the four-electron O2 evolution reaction. Recent studies showed a crystal-phase dependence in H2O2 selectivity, where high purity brookite TiO2 (b-TiO2) exhibits remarkable H2O2 selectivity in contrast to the common rutile phase TiO2 (r-TiO2). However, the origin of such a structure-induced selectivity preference remains elusive, primarily due to the complexities associated with the solid-liquid interface system and excited-state chemistry. Herein, we conducted a comprehensive investigation into the selectivity mechanism of WOR at the water/b-TiO2(210) and water/r-TiO2(110) interfaces, employing first-principles molecular dynamics simulations and microkinetic analyses. Intriguingly, our results reveal that the intrinsic catalytic ability of the b-TiO2(210) itself does not enhance H2O2 selectivity compared to r-TiO2(110). Instead, it is the weakened interfacial hydrogen bond connectivity, modulated by the herringbone-like local atomic structure of the b-TiO2(210) surface, that determines the selectivity. Specifically, this weakened H-bond connectivity (i.e., local low water density) at the interface, owing to the strong water adsorption and distinct adsorption orientation, can stabilize the OH• radical and inhibit its deprotonation, leading to an improved H2O2 selectivity. By contrast, the relatively strong interface H-bond connectivity established over r-TiO2(110) accelerates the deprotonation of OH•, with the OH• coverage being 3 orders of magnitude lower than at the water/b-TiO2(210) interface. This study quantitatively demonstrates that the local H-bond structure (water density) at the liquid/solid interface significantly influences photocatalytic selectivity, and this insight may offer a rational approach to enhance the H2O2 selectivity.

Weakened Hydrogen Bond Connectivity Promotes Interfacial Mass Transfer for Industrial Level Scalable Biomass Electrooxidation

5-Hydroxymethylfurfural electrooxidation reaction (HMFOR) has recently garnered significant attention in the field of biomass conversion. However, the sluggish kinetics of HMFOR cause gridlock in energy conversion efficiency. Herein, we pinpoint...

A new nanohybrid particle reinforced multifunctional active packaging film for efficiently preserving postharvest fruit

This study aimed to develop a multifunctional active packaging film for fruit preservation. In detail, a series of gelatin (Gel) composite films were prepared by employing chitosan-ferulic acid-titanium dioxide nanohybrid particles (CFT NPs) as filler into Gel film and then their structural, physical, and functional properties were characterized to determine a nanocomposite film with the optimal performances. The results showed that synthesized CFT NPs posed exceptional performances (UV absorption, antioxidant activity, antibacterial ability, etc). After incorporating into Gel film, CFT-Gel films possessed denser network structure owing to the hydrogen bond connection between Gel and CFT NPs. The addition of CFT NPs significantly (P < 0.05) enhanced mechanical and barrier properties for water vapor, oxygen, and carbon dioxide of nanocomposite films, especially for CFT-Gel film with 0.40 mg/mL of CFT NPs (CFT0.40-Gel). CFT0.40-Gel film also showed enhanced UV shielding (∼100% at 200–400 nm), antioxidant ability (2-fold∼3-fold enhancement), and high relative bacteriostatic rate (>95% against Escherichia coli and Staphylococcus aureus under ultraviolet catalysis due to the generation of reactive oxygen species). Moreover, hemolysis assay proved the good bio-safety of CFT-Gel films. Further, CFT0.40-Gel film was successfully applied in the preservation of non-climacteric fruit (strawberries) and climacteric fruit (bananas), as the evidence of its good preservation ability. Therefore, the multifunctional CFT0.40-Gel film possessed great application prospect in fruit preservation. Meanwhile, this work provided a feasible strategy for designing a multifunctional active food packaging.

Protonation-State Dependence of Hydration and Interactions in the Two Proton-Conducting Channels of Cytochrome c Oxidase.

Cytochrome c Oxidase (CcO), a membrane protein of the respiratory chain, pumps protons against an electrochemical gradient by using the energy of oxygen reduction to water. The ("chemical") protons required for this reaction and those pumped are taken up via two distinct channels, named D-channel and K-channel, in a step-wise and highly regulated fashion. In the reductive phase of the catalytic cycle, both channels transport protons so that the pumped proton passes the D-channel before the "chemical" proton has crossed the K-channel. By performing molecular dynamics simulations of CcO in the O→E redox state (after the arrival of the first reducing electron) with various combinations of protonation states of the D- and K-channels, we analysed the effect of protonation on the two channels. In agreement with previous work, the amount of water observed in the D-channel was significantly higher when the terminal residue E286 was not (yet) protonated than when the proton arrived at this end of the D-channel and E286 was neutral. Since a sufficient number of water molecules in the channel is necessary for proton transport, this can be understood as E286 facilitating its own protonation. K-channel hydration shows an even higher dependence on the location of the excess proton in the K-channel. Also in agreement with previous work, the K-channel exhibits a very low hydration level that likely hinders proton transfer when the excess proton is located in the lower part of the K-channel, that is, on the N-side of S365. Once the proton has passed S365 (towards the reaction site, the bi-nuclear centre (BNC)), the amount of water in the K-channel provides hydrogen-bond connectivity that renders proton transfer up to Y288 at the BNC feasible. No significant direct effect of the protonation state of one channel on the hydration level, hydrogen-bond connectivity, or interactions between protein residues in the other channel could be observed, rendering proton conductivity in the two channels independent of each other. Regulation of the order of proton uptake and proton passage in the two channels such that the "chemical" proton leaves its channel last must, therefore, be achieved by other means of communication, such as the location of the reducing electron.

In vitro and in silico inhibitory validation of Tapinanthus cordifolius leaf extract on alpha-glucosidase in the management of type 2 diabetes

The anti-diabetic properties of medicinal plants are becoming more widely recognized. To identify potential anti-diabetic agents for diabetes drug discovery, the current study used in vitro and in silico approaches to assess the alpha glucosidase inhibitory activities of Tapinanthus cordifolius (TC) leaf extracts and its bioactive components respectively. In vitro alpha glucosidase inhibitory assay was carried out on TC extract and fractions at various concentrations (50–1600 µg/mL), and the compounds with alpha glucosidase inhibitory potentials were identified using molecular docking, pharmacophore modelling, and molecular dynamics simulation. The crude extract exhibited the highest activity with an IC50 value of 248 μg/mL. Out of the 42 phytocompounds of the extract, α-Tocopherol-β-d-mannoside gave the lowest binding energy of −6.20 Kcal/mol followed by, 5-Ergosterol (−5.46 kcal/mol), Acetosyringone (−4.76 kcal/mol), and Benzaldehyde, 4-(Ethylthio)-2,5-Dimethoxy-(−4.67 kcal/mol). The selected compounds interacted with critical active site amino acid residues of alpha-glucosidase, just like the reference ligand. Molecular dynamics simulation revealed the formation of a stable complex between α-glucosidase and α-Tocopherol-β-d-mannoside, with ASP 564 sustaining two hydrogen bond connections for 99.9 and 75.0% of the simulation duration, respectively. Therefore, the selected TC compounds, especially α-Tocopherol-β-d-mannoside might be explored for future research and development as diabetic medicines. Communicated by Ramaswamy H. Sarma

Ni/TiO2 heterostructures derived from phase separation for enhanced electrocatalysis of hydrogen evolution and biomass oxidative upgrading in anion exchange membrane electrolyzers.

The construction of heterostructures is an effective strategy to enhance electrocatalysis for hydrogen evolution reactions (HERs) and biomass oxidative upgrading. In this work, a Ni/TiO2 heterostructure prepared by a phase-separation strategy was adopted as a bifunctional electrocatalyst for HERs and biomass oxidation in alkaline media. Due to the optimized hydrogen adsorption energetics as well as the interfacial water structure and hydrogen bond connectivity in the electrical double layer, Ni/TiO2 exhibited high activity for HERs with an overpotential of 28 mV at 10 mA cm-2 and good durability at 1000 mA cm-2 for over 100 h in an anion exchange membrane (AEM) electrolyzer. In addition, Ni/TiO2 showed high catalytic performance for the oxidation of biomass-based platform compound 5-hydroxymethylfurfural (HMF) to high-value added compound 2,5-furandicarboxylic acid (FDCA). Continuous production of FDCA with a yield >95% was achieved in the AEM electrolyzer for over 50 h. The superior HMF oxidation performance on the Ni/TiO2 heterostructure compared to Ni resulted from stronger HMF adsorption, lower Ni3+-O formation potential, longer Ni3+-O bond and smaller Ni crystal size.

Hydrogen-Bonded Framework of a Polyanionic Cluster and Its Growth from 2D to 3D for Dual-Selective Adsorption and pH-Controlled Oxidation.

For fabricating a hydrogen-bonded framework with a stabilized hybrid structure for versatile functional properties, an inorganic polyanionic cluster that bears covalently grafted organic groups for hydrogen bond connection is synthesized. By modifying two guanine groups into a disklike polyoxometalate [Mn(OH)6Mo6O18]3- on both sides symmetrically, a polyanionic hybrid building block is obtained. With the cluster serving as a bridge and the grafted guanine unit serving as the binding sites, a polyoxometalate built-in hydrogen-bonded framework in the form of a square lattice shape within a two-dimensional plane has been fabricated as a single-layer assembly. In a further step, the counterion connection and hydrophilic/hydrophobic effect are used to drive the growth of layered framework assembly along the perpendicular direction. The resulting cluster-embedded framework possesses permanent porosity and inner-layer ionic characteristics after activation, which allows the framework to exhibit both high charge-/size-selective adsorption of organic cations and pH-controlled catalytic oxidation of methionine via the charged property.

Artificial Water Channels—Progress Innovations and Prospects

Artificial Water Channels—Progress Innovations and Prospects

Enhancement of Vitamin K2 Efflux in Bacillus subtilis Natto via a Potential Protein Receptor for Increased Yield

Bacillus subtilis is one of the few strains that can secrete synthetic menaquinone-7 (MK-7) to the outside of the cell, and its purpose and mechanism have not been clearly studied. As an amphiphilic protein naturally synthesized by Bacillus subtilis, the BslA protein may be involved in the inversion of extracellular vitamin K2 solubility. The protein structure in UniProt was used to search for the possible binding sites of MK-7, and the analysis of the higher ranking results of the genetic algorithm showed that the ASP166 residue was likely to be the binding site. They could form a stable hydrogen bond connection through ASP166, and approximately 7 proteins formed the conformation of a fixed naphthoquinone ring. We isolated and obtained the BslA protein by Ni-NTA affinity chromatography. Then, MK-7 was modified by BslA in vitro. A series of experiments, such as SEM, XPS, and WCA, showed that MK-7 and BslA proteins can realize self-assembly and transform from fat-soluble to water-soluble complexes. When the bslA protein in Bacillus subtilis natto was overexpressed, its MK-7 synthesis ability was further improved, especially the extracellular MK-7 content, which increased by 16%. This finding suggests that the BslA protein in Bacillus subtilis is likely to be involved in the extracellular secretion of MK-7 as a receptor.

Blackening and blackening control of litopenaeus vannamei during storage at low temperature

ABSTRACT Litopenaeus vannamei easily blackens during cold storage. To inhibit blackening and improve thestorage quality of prawns, in this study, konjac glucomman (KGM)-epigallocatechin gallate (EGCG) topological microgel was formed and used for storage and preservation of prawns to improve their antioxidant properties. The effect of KGM-EGCG topological microgel on inhibiting shrimp blackening was studied by measuring the sensory evaluation score, pH value, TVB-N value, K value, PPO activity, and the effect of changes in the total number of bacteria of KGM-EGCG-treated prawnsduring storage. SEM and FTIR results showed that during the KGM-EGCG binding process, thenumber of hydrogen bond connections and the intermolecular force increased. Results also showed that the KGM microgel can effectively embed EGCG and enhance its stability to achieve a better controlled release effect. Compared with the EGCG group and untreated group, KGM-EGCG microgel has better anti-PPO activity and can better maintain the organoleptic quality and inhibitbacterial growth of Litopenaeus vannamei. Therefore, the KGM-EGCG microgel could slow down the increase in pH value, the production of volatile base nitrogen, and the increase in K value, and effectively extend the shelf life of Litopenaeus vannamei from 3 d to 6 d, providing a theoreticalbasis for the research of KGM functional gel and a reference for the deep processing and valueenhancement of green tea and shrimp.

Improving hygroscopic stability of palmatine chloride by forming a pharmaceutical salt cocrystal of palmatine chloride-gallic acid with neutral molecule

In order to ameliorate the hygroscopicity of palmatine chloride (PMTCl), an unreported salt cocrystal (2(C21H22O4NCl)·C7H6O5·2CH3OH, PMTCl-GA) of palmatine chloride with gallic acid (GA) has been designed and synthesized by a solvent evaporation method. Structure analysis shows that the asymmetric unit of PMTCl-GA includes two PMT cations, two chloride anions, a GA neutral molecule and two methanol molecules. Simultaneously, two PMT cations, two chloride anions, two GA neutral molecule are alternately linked by O–H⋯Cl, C–H⋯Cl and C–H⋯O hydrogen bonds to form synthon R46 (30). On this basis, the 2D layered structure is formed by C–H⋯O hydrogen bond connection, and then adjacent 2D layered structures are connected by C–H⋯O hydrogen bond to form a 3D supramolecular structure. The hygroscopic stability of PMTCl-GA is significantly higher than that of PMTCl, thus it is conjectured that in PMTCl-GA, GA neutral molecule and methanol participate in the self-assembly process of a salt cocrystal, occupying the binding sites between chloride anions with strong hydration ability and external water molecules, which reduces the binding ability of PMTCl-GA with external water molecules. This work has suggested that the physicochemical properties of ionic active pharmaceutical ingredients can be improved by introducing neutral components to form a salt cocrystal. Although the hygroscopic stability of PMTCl-GA was markedly improved compared to that of PMTCl, unfortunately, the solubility of PMTCl-GA was reduced compared to PMTCl, which still needs to be discussed in the subsequent research. In addition, the antibacterial activity of PMTCl-GA against S. aureus, S. albus and E. coli compared with the PMTCl was improved in vitro at different concentrations.

Identification of medicinal compounds as potential inhibitors for mutated isocitrate dehydrogenases against chondrosarcoma.

Chondrosarcoma is the third most common cartilaginous bone tumour that is insusceptible to radio- and chemotherapy and it is inclined to metastasis. These resistant qualities are facilitated by mutant variants of isocitrate dehydrogenases (IDH) 1-2 enzyme. These mutant enzymes promote oncogenesis of chondrocytes by changing their epigenetic wardrobe leading to tumour formation. Presently, there are lack of drugs available to be exploited as a remedy for this disease. On the other hand, majority of chemotherapeutic drugs induce cytotoxicity in the cancer cells at the cost of harming surrounding healthy cells, jeopardizing human life. The current study is focused on screening various medicinal compounds against IDH1 and IDH2 combined with insilico gene expression, cancer cells cytotoxicity and ADMET (absorption, distribution, metabolism, excretion and toxicity) studies to elucidate the molecular mechanism against chondrosarcoma and also to uncover pharmacokinetic profile of these compounds. Screening of 5000+compounds filtered two efficacious compounds (Artocarpetin and 5-Galloylquinic acid) capable of establishing hydrogen bond connections with both IDH variants. Other studies showed that these compounds downregulate ITGAV, CARPIN1, CCL5 and COG5 and TNFRSF10B gene that reduces chondrogenesis and inflammation, Artocarpetin and 5-galloylquinic acid are TP53 expression enhancer and inhibit MM9 expression that promote immunomodulation and apoptosis in these cancers. These compounds are both active against CHSA8926 and CHSA011 cell line of chondrosarcoma. However, the ADME profile of 5-galloylquinic acid is slightly unsatisfactory based on druglikness and bioavailability score criteria as compared to artocarpetin. Both of these compounds are class-5 chemicals and require high doses to elicit adverse response. Our results suggest that artocarpetin and 5-galloylquinic acid are efficacious drug candidates and could be further exploited to validate these findings in vitro.

Deep eutectic solvent-assisted synthesis of porous Ni2CO3(OH)2/SiO2 nanosheets for ultra-efficient removal of anionic dyes from water

Wastewater treatment is a severe environment issue, especially the discharge of excessive synthetic dyestuffs in the aquatic environment. In this study, a facile binary deep eutectic solvothermal process plus silica surface modification was successfully applied for preparation of porous nanosheet Ni2CO3(OH)2/SiO2 composites. The composites show powerful anionic dyes removal ability due to the high specific surface areas, hydrogen bond connection, coordination effect and strong electrostatic interactions with anionic dyes. A maximum adsorption capacity of 2637 mg g−1 at neutral pH (ca.7) and 303 K was achieved for Ni2CO3(OH)2/SiO2 composite to adsorb Congo red, a representative anionic dye. Moreover, the composite has an excellent specificity for anionic dyes and could maintain above 95% removal efficiency after 5 cycles. Therefore, the as-prepared nanocomposites could be qualified as candidates for industrial environmental remedy. Furthermore, the proposed material preparation strategy could be extended to fabricate various advanced energy and environmental materials.

A study on KIF1A gene missense variant analysis and its protein expression and structure profiles of an autism spectrum disorder family trio

To analyze the pathogenic variants of the KIF1A gene and its corresponding protein structure in an autism spectrum disorder (ASD) family trio carrying harmful missense variants in the KIF1A gene. The peripheral blood DNA of the patient and his parents was extracted and sequenced using whole exome sequencing (WES) technology and verified by Sanger sequencing. Bioinformatics software SIFT, PolyPhen-2, Mutation Taster, and CADD software were used to analyze the harmfulness and conservation of variants. The Human Brain Transcriptome (HBT) database was used to analyze the expression of the KIF1A gene in the brain. PredictProtein and SWISS-MODEL were further used to predict the secondary structure and tertiary structure of KIF1A wild-type protein and variant protein. PyMOL V2.4 was utilized to investigate the change of hydrogen bond connection after protein variant. The WES sequencing revealed a missense variant c.664A>C (p.Asn222His) in the child's KIF1A gene, and this variant was a de novo variant. The harmfulness prediction results suggest that this variant is harmful. By analyzing expression level of KIF1A gene in the brain. It is found that KIF1A gene widely expressed in various brain regions during embryonic development. By analyzing the variant protein structure, the missense variant of KIF1A will cause many changes in the secondary structure of protein, such as alpha-helix, beta-strand, and protein binding domain. The connection of hydrogen bond and spatial structure will also change, thereby changing the original biological function. The KIF1A gene may be a risk gene for ASD.

Molecular dynamics simulations reveal statistics and microscopic mechanisms of water permeation in membrane-embedded artificial water channel nanoconstructs.

Understanding water transport mechanisms at the nanoscale level remains a challenge for theoretical chemical physics. Major advances in chemical synthesis have allowed us to discover new artificial water channels, rivaling with or even surpassing water conductance and selectivity of natural protein channels. In order to interpret experimental features and understand microscopic determinants for performance improvements, numerical approaches based on all-atom molecular dynamics simulations and enhanced sampling methods have been proposed. In this study, we quantify the influence of microscopic observables, such as channel radius and hydrogen bond connectivity, and of meso-scale features, such as the size of self-assembly blocks, on the permeation rate of a self-assembled nanocrystal-like artificial water channel. Although the absolute permeation rate extrapolated from these simulations is overestimated by one order of magnitude compared to the experimental measurement, the detailed analysis of several observed conductive patterns in large assemblies opens new pathways to scalable membranes with enhanced water conductance for the future design.

Threefold helical assembly via hy-droxy hydrogen bonds: the 2:1 co-crystal of bi-cyclo-[3.3.0]octane-endo-3,endo-7-diol and bi-cyclo-[3.3.0]octane-endo-3,exo-7-diol.

Reduction of bi-cyclo-[3.3.0]octane-3,7-dione yields a mixture of the endo-3,endo-7-diol and endo-3, exo-7-diol (C8H14O2) isomers (5 and 6). These form (5)2·(6) co-crystals in the monoclinic P21/n space group (with Z = 6, Z' = 1.5) rather than undergoing separation by means of fractional recrystallization or column chromatography. The mol-ecule of 5 occupies a general position, whereas the mol-ecule of 6 is disordered over two orientations across a centre of symmetry with occupancies of 0.463 (2) and 0.037 (2). Individual diol hy-droxy groups associate around a pseudo-threefold screw axis by means of hydrogen bonding. The second hy-droxy group of each diol behaves in a similar manner, generating a three-dimensional hydrogen-bonded network structure. This hydrogen-bond connectivity is identical to that present in three known helical tubuland diol-hydro-quinone co-crystals, and the new crystal structure is even more similar to two homologous aliphatic diol co-crystals.