Probing the energetics of organic–nanoparticle interactions of ethanol on calcite

Knowing the nature of interactions between small organic molecules and surfaces of nanoparticles (NP) is crucial for fundamental understanding of natural phenomena and engineering processes. Herein, we report direct adsorption enthalpy measurement of ethanol on a series of calcite nanocrystals, with the aim of mimicking organic–NP interactions in various environments. The energetics suggests a spectrum of adsorption events as a function of coverage: strongest initial chemisorption on active sites on fresh calcite surfaces, followed by major chemical binding to form an ethanol monolayer and, subsequently, very weak, near-zero energy, physisorption. These thermochemical observations directly support a structure where the ethanol monolayer is bonded to the calcite surface through its polar hydroxyl group, leaving the hydrophobic ends of the ethanol molecules to interact only weakly with the next layer of adsorbing ethanol and resulting in a spatial gap with low ethanol density between the monolayer and subsequent added ethanol molecules, as predicted by molecular dynamics and density functional calculations. Such an ordered assembly of ethanol on calcite NP is analogous to, although less strongly bonded than, a capping layer of organics intentionally introduced during NP synthesis, and suggests a continuous variation of surface structure depending on molecular chemistry, ranging from largely disordered surface layers to ordered layers that nevertheless are mobile and can rearrange or be displaced by other molecules to strongly bonded immobile organic capping layers. These differences in surface structure will affect chemical reactions, including the further nucleation and growth of nanocrystals on organic ligand-capped surfaces.The interactions between simple organic molecules and inorganic surfaces, nanoparticles (NP), and clusters with controlled properties provide fundamental insights to understand much more complicated natural phenomena, including biomineralization (1), contaminant and nutrient transport in soils and aquifers (2), and CO₂ transport and carbonate formation (3–5). Such organic–inorganic systems are also encountered in technological environments, particularly selective catalysis (6–8), enhanced oil recovery (9), self-assembly of colloidal NPs (10–13), and CO₂ capture and sequestration (14). Despite being well-documented qualitatively, the magnitudes of such interactions and their impact on the interface molecular configurations have barely been directly identified. In this context, NP plays a very active and crucial role linking the organic and inorganic worlds. Their high surface energies enable ready assembly with organic molecules (15). Such organic termination or capping may mask the original NP surface identity (4) (hydrophobicity, charge, and/or chemical group), resulting in a modified outer shell, which may feature unique configuration and functionality (electronic, optical, steric, and/or chemical) (1, 5, 16). However, a clear understanding of the organic ligand–NP interactions and surface chemistry–structure relations is still far from complete.Thorough thermodynamic study of the energetics of organic ligand capping of NPs is essential to understanding reactivity. Herein, we use calcite NPs with ethanol, as simple chain-like polar molecule, as representative of hydroxyl containing organic ligands. Calcite is the most stable calcium carbonate polymorph (17), well known for its ability to form numerous multifunctional nanoscale architectures with proteins made by organisms (18, 19). Previous studies by molecular dynamics (MD), density functional theory (DFT), and atomic force microscopy (AFM) suggest that, once adsorbed, ethanol molecules self-assemble to a highly ordered monolayer on the calcite surface (20, 21). A low ethanol density, spatially thin gap between the first and second layer of adsorbed ethanol is also predicted to exist (22). However, so far, no direct experimental evidence describes the energetics of such a unique surface configuration.Direct gas adsorption calorimetry was initially developed in our laboratory to measure the hydration enthalpy of NPs (23, 24). The experimental system includes a commercial gas adsorption analyzer coupled with a microcalorimeter (25). Recently, we have expanded its application to multiple gases, including CO₂, Kr, and Xe (26–28), on metal–organic frameworks. In this work, to explore the nature of organic ligand–NP interactions, ethanol vapor was used as the adsorbate, whereas a series of nanophase calcite particles was selected to represent a nanoscale inorganic material. The results show a complex pattern of adsorption energetics which lends support to the structural model proposed by computational and microscopic methods (20–22).Four high-quality commercial nanocalcite samples, characterized and used previously in a study of calcite surface energy (29), were used as adsorbents (Table S1). The details of direct gas adsorption calorimetry experiments are described in Materials and Methods.     

Propofol is not so safe for ERCP To the Editor

The Editor welcomes submissions for possible publication in the Letters to the Editor section that consist of commentary on an article published in the Journal or other relevant issues. Letters commenting on an article published in the Journal will be considered if they are received within 6 weeks of the time the article was published. Authors of the article being commented on will be given an opportunity to offer a timely response to the letter. Authors of letters will be notified that the letter has been received. Unpublished letters cannot be returned.     

Effect of ethanol on esophageal cell proliferation and the development ofN-methyl-N′-nitro-N-nitrosoguanidine induced-esophageal carcinoma in shrews

The effect of ethanol (EtOH) on esophageal cell proliferation and the development of esophageal cancers induced byN-methyl-N-nitro-N-nitrosoguanidine (MNNG) in shrews were investigated. Sequential histological examination was done, and cell proliferation was assessed by BrdU labeling. At 5 weeks of age, animals were given tap water, 2% EtOH, 50 ppm MNNG, or 50 ppm MNNG plus 2%, 5% or 10% EtOH in the drinking water. Administration of 10% and 5% EtOH simultaneously with MNNG caused death in 40% (10/25) within 4 days and in 20% (6/30) within 7 days respectively, whereas other treatments were well tolerated with no sudden deaths. Administration of 2% EtOH for 30 weeks caused a 2-fold increase, and that of MNNG caused a 4.5-fold increase in the proliferation index of the basal cells of the esophagus compared with control shrews, and MNNG plus 2% EtOH caused a 5.5-fold increase. In MNNG-treated shrews, with or without 2% EtOH administration, sequential histological examination of esophageal tissue revealed a similar change; dysplasia appeared at 30 weeks of age, squamous cell carcinoma occurred at 35 weeks of age, and the depth of invasion extended to adventitia at 45 weeks of age. These finding indicate that treatment with 2% EtOH promoted the proliferation of esophageal basal cells but did not alter the tumor induction period and did not have tumor-promoting activity. EtOHper se was not carcinogenic; no tumors were seen in shrews not administered MNNG.Abbreviations MNNG N-methyl-N-nitro-N-nitrosoguanidine - BrdU 5-bromo-2-deoxyuridine - PI pro liferating index This work was supported in part by the Science Research Promotion Fund of the Japanese Private School Promotion Foundation (1994, 1995)     

Comparative effect of intraduodenal and intrajejunal glucose infusion on the gut–incretin axis response in healthy males

The region of enteral nutrient exposure may be an important determinant of postprandial incretin hormone secretion and blood glucose homoeostasis. We compared responses of plasma glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), insulin and glucagon, and blood glucose to a standardised glucose infusion into the proximal jejunum and duodenum in healthy humans. Ten healthy males were evaluated during a standardised glucose infusion (2 kcal min⁻¹ over 120 min) into the proximal jejunum (50 cm post pylorus) and were compared with another 10 healthy males matched for ethnicity, age and body mass index who received an identical glucose infusion into the duodenum (12 cm post pylorus). Blood was sampled frequently for measurements of blood glucose and plasma hormones. Plasma GLP-1, GIP and insulin responses, as well as the insulin:glucose ratio and the insulinogenic index 1 (IGI₁) were greater (P<0.05 for each) after intrajejunal (i.j.) than intraduodenal glucose infusion, without a significant difference in blood glucose or plasma glucagon. Pooled analyses revealed direct relationships between IGI₁ and the responses of GLP-1 and GIP (r=0.48 and 0.56, respectively, P<0.05 each), and between glucagon and GLP-1 (r=0.70, P<0.001). In conclusion, i.j. glucose elicits greater incretin hormone and insulin secretion than intraduodenal glucose in healthy humans, suggesting regional specificity of the gut–incretin axis.