Molecular Dynamics Simulation of the Binding Interaction between Hormone Glucagon Protein and Self-Assembled Monolayer Molecules

Restrained molecular dynamics simulations were performed to study the binding affinity of the peptide with alkanethiols of different tail-groups, S（CH2）7CH3, S（CH2）7OH and S（CH2）7COOH, which self-assembled on Au（111） surface in the presence of water molecules. The curves of binding affinity were calculated by fixing the center of mass of the peptide at various distances from the assembling surface. Simulation results show that the binding affin- ity is in the order as COOH-SAMs〉OH-SAMs〉CH3-SAMs, while 100% COOH-SAMs〉5% COOH-SAMS in concentration. The effects on binding affinity by different tail-groups were also studied. Results show that the binding affinity between COOH-SAMs and the peptide is bigger than those of the others and increasing the acidity of COOH-SAMs will result in stronger attractive power.     

Polyisobutylene‐based polyurethanes. VIII. Polyurethanes with ‐O‐S‐PIB‐S‐O‐ soft segments

We describe the synthesis, characterization, and select properties of a novel polyurethane (PU) prepared using a new polyisobutylene diol, HO‐CH₂CH₂‐S‐PIB‐S‐CH₂CH₂‐OH, soft segment and conventional hard segments. The diol is synthesized by terminal functionalization of ally‐telechelic PIB followed by low‐cost thiol‐ene click chemistry. Properties of ‐S‐ containing PU (PIB_S‐PU) containing 72.5% PIB were investigated and compared to similar PUs made with HO‐PIB‐OH (PIB_O‐PU). Hydrolytic resistance was studied by contact with phosphate‐buffered saline, oxidative resistance by immersing in concentrated HNO₃, and metal ion oxidation resistance by exposure to CoCl₂/H₂O₂. Hydrolytic and oxidative resistances of PIB_S‐PU and PIB_O‐PU are similar and superior to a commercial PDMS‐based PU, Elast‐Eon? E2A. According to ¹H NMR spectroscopy the ‐S‐ in PIB_S‐PUs remained unchanged upon treatment with HNO₃, however, oxidized mainly to ‐SO₂‐ by CoCl₂/H₂O_2. Static mechanical properties of PIB_S‐PU and PIB_O‐PU are similar, except creep resistance of PIB_S‐PU is surprisingly superior. The thermal stability of PIB_S‐PUs is ～15 °C higher than that of PIB_O‐PU. FTIR spectroscopy indicates H bonded S atoms (N‐H…S) between soft and hard segments, which noticeably affect properties. DSC and XRD studies suggest random low‐periodicity crystals dispersed within a soft matrix. Energy dispersive X‐ray spectroscopy–scanning electron microscopy indicates homogeneous distribution of S atoms on PIB_S‐PU surfaces. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1119–1131     

Adsorption of 1,3‐Benzenedithiol and 1,3‐Benzenedimethanethiol on Gold Surfaces

The adsorption characteristics of 1,3‐benzenedithiol (1,3‐BDT) and 1,3‐benzenedimethanethiol (1,3‐BDMT) on Au surfaces are investigated by means of surface‐enhanced Raman scattering, UV/Vis absorption spectroscopy, and cyclic voltammetry (CV). 1,3‐BDMT is found to adsorb via two S–Au linkages at concentrations below monolayer coverage, but to have an upright geometry as the concentration increases on Au nanoparticles. On the other hand, 1,3‐BDT is found to adsorb by forming two S–Au linkages, regardless of concentration, based on the disappearance of the ν(SH)_free stretching band. Because of the absence of the methylene unit, 1,3‐BDT appeares not to self‐assemble efficiently on Au surfaces. The UV/Vis absorption spectroscopy and CV techniques are also applied to check the formation of self‐assembled monolayers of 1,3‐BDT and 1,3‐BDMT on Au. Density functional theory calculations based on a simple adsorption model using an Au₈ cluster are performed to better understand the nature of the adsorption characteristics of 1,3‐BDT and 1,3‐BDMT on Au surfaces.     

Anchoring of sulfur‐containing alkylphosphonic and semifluorinated alkylphosphonic molecules on a polycrystalline aluminum substrate

Self‐assembly on a polycrystalline aluminum substrate of two sulfur‐containing alkylphosphonic acids, CH₃? (CH₂)₁₁? S? (CH₂)₂? PO(OH)₂, and CF₃? (CF₂)₇? (CH₂)₂? S? (CH₂)₂? PO(OH)₂, has been compared with CH₃? (CH₂)₁₅? PO(OH)₂. The reaction of the phosphonic head groups with the hydroxyls at the alumina surface to form phosphonates was studied with X‐ray photoelectron spectroscopy (XPS) and polarization modulation infrared reflection‐absorption spectroscopy (PM‐IRRAS). Barrier effects of the resulting layers was assessed by electrochemical polarization curves. With the conditions used in the present work for the self‐assembly reaction, it appears that the sulfur‐containing molecules do not perform as well as CH₃? (CH₂)₁₅? PO(OH)₂ in terms of film quality. Questions are raised about the possibility that the sulfur‐containing molecules could undergo cleavage during surface modification. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of 3‐(ω‐Hydroxyalkoxy)isobenzofuran‐1(3H)‐ones by Trifluoroacetic Acid‐Mediated Lactonization of tert‐Butyl 2‐(1,3‐Dioxol‐2‐yl)‐ or 2‐(1,3‐Dioxan‐2‐yl)benzoates

An efficient two‐step method for the preparation of 3‐(2‐hydroxyethoxy)‐ or 3‐(3‐hydroxypropoxy)isobenzofuran‐1(3H)‐ones 3 has been developed. Thus, the reaction of 1‐(1,3‐dioxol‐2‐yl)‐ or 1‐(1,3‐dioxan‐2‐yl)‐2‐lithiobenzenes, generated in situ by the treatment of 1‐bromo‐2‐(1,3‐dioxol‐2‐yl)‐ or 1‐bromo‐2‐(1,3‐dioxan‐2‐yl)benzenes 1 with BuLi in THF at ?78°, with (Boc)₂O afforded tert‐butyl 2‐(1,3‐dioxol‐2‐yl)‐ or 2‐(1,3‐dioxan‐2‐yl)benzoates 2 , which can subsequently undergo facile lactonization on treatment with CF₃COOH (TFA) in CH₂Cl₂ at 0° to give the desired products in reasonable yields.     

Adsorption Sequence of Multifunctional Groups: A Study on the Reaction Pathway and the Adsorption Structure of Homocysteine on the Ge(100) Surface

We investigated the adsorption mechanism of homocysteine (HS? CH₂? CH₂? CH(NH₂)? COOH) on the Ge(100) surface along with its electronic structures and adsorption geometries to determine the sequence of adsorption of this amino acid′s functional groups using core‐level photoemission spectroscopy (CLPES) in conjunction with density functional theory (DFT) calculations. We found that the “SH‐dissociated OH‐dissociated N‐dative‐bonded structure” and the “SH‐dissociated OH‐dissociation‐bonded structure” were preferred at a monolayer (ML) coverage of 0.30 (lower coverage) and 0.60 (higher coverage), respectively. The “SH‐dissociated OH‐dissociated N‐dative‐bonded structure” was the most stable structure. Moreover, we systematically confirmed the sequence of adsorption of the functional groups of the homocysteine molecule on the Ge(100) surface, which is thiol group (? SH), carboxyl group (? COOH), and amine group (? NH₂).     

Pathways for the Non‐CO‐Involved Oxidation of Methanol on Pt(111)

The non‐CO‐involved oxidation of methanol (NCOIOM) on a Pt(111) surface is investigated by using density functional theory. Relative energy diagrams for the NCOIOM are established in which the reaction mechanisms for a catalytic cycle—including the associated barriers, the reactive energies, the intermediates, and the transient states—are shown. The results indicate that the reaction proceeds via the kinetically favored pathways: A) HCOH→HC(OH)₂→HCOOH→HCOO‐ [‐COOH]→CO₂ and B) CHO→HCOOH→HCOO‐ [‐COOH]→CO₂, with OH playing a key role in the entire process. The vibrational frequencies of the intermediate states derived from the calculations are in agreement with the experimental measurements.     

Stimuli‐responsive antifouling polyisobutylene‐based biomaterials via modular surface functionalization

This article demonstrates a new, modular approach to surface functionalization that harnesses chain entanglement. A layer of functionalized polyisobutylene, (PIB)‐ω, where ω = ‐OH, ‐thymine (T), ‐hexaethylene glycol (HEG), poly(ethylene glycol) (‐PEG‐OH), methoxy‐functionalized poly(ethylene glycol) (‐PEG‐OCH₃), and ‐tetraethylene glycol‐α‐lipoate (TEG‐αL) was adhered to PIB‐based thermoplastic elastomer (TPE) surfaces. X‐ray photoelectron spectroscopy (XPS) at angles ranging from 20° to 75° showed decreasing polar group concentration with increasing penetration depth, confirming segregation of polar groups toward the surface. Water contact angle (WCA) of the PIB‐based TPE dropped from 95° to 79°?83° upon coating, and soaking in water for 24 h further decreased the WCA. Dynamic WCA measurements showed 40–30° receding angles, showing that stimulus from an aqueous environment elicits enrichment of polar groups on the surface. Fibrinogen (Fg) adsorption on the various surfaces was quantified using surface plasmon resonance (SPR). Static and dynamic WCA did not vary significantly among TPE + PIB‐ω surfaces, but there were dramatic differences in Fg adsorption: 256 ng/cm² was measured on the native TPE, which dropped to 40 and 22 ng/cm² on PIB‐PEG‐OCH₃ and PIB‐PEG‐OH‐coated surfaces. PIB‐TEG‐αL‐coated surfaces presented the lowest Fg adsorption with 14 ng/cm². © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1742–1749     

First‐principles calculation of OH−/OH adsorption on gold nanoparticles

The OH^? and OH adsorption structures on Au₅₅ and Au₁₃ nanoparticles surfaces are analyzed using density functional theory. The most stable OH^? adsorption site of Au₅₅ and Au₁₃ nanoparticles is found to be the vertex top site followed by the (111)‐(100) edge bridge site. On the contrary, the stability order of OH adsorption is opposite to that of OH^?. The adsorption of OH^? is calculated to be weaker than that of OH, which shows different charge transfer and interactions with gold surface. Coadsorption on nanoparticles is studied to find that multiple OH^? species prefer the most stable sites of single OH^? adsorption. The hydrogen bonding between adsorbed OH^? on gold surface is a key factor in stabilizing the adsorbates on the Au surface. © 2015 Wiley Periodicals, Inc.     

Synthesis and degradation of end‐group‐functionalized polylactide

Three kinds of OH‐terminated polylactides were synthesized by the ring‐opening polymerization of lactide, with an alcohol such as dodecanol, glycerol, or pentaerythritol, in the presence of stannous octoate. Moreover, Cl‐, NH₂‐, and COOH‐terminated polylactides were synthesized from OH‐terminated polylactides. The end groups of the polylactides were identified by ¹H NMR and ¹³C NMR. According to thermal analysis, the cold crystallization temperatures of Cl‐, NH₂‐, and COOH‐terminated polylactides were higher than those of OH‐terminated polylactides. The thermal stability of OH‐terminated polylactides was poor, whereas NH₂‐ and Cl‐terminated polylactides were more resistant to thermal degradation. In a hydrolysis degradation test, the mass and molecular weight loss of COOH‐terminated polylactides were high, whereas those of Cl‐ and NH₂‐terminated polylactides were much lower. These end‐group effects were increased with an increasing number of chain arms. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 973–985, 2001     

Methanol oxidation on the PtPd(111) alloy surface: A density functional theory study

The mechanisms of methanol (CH₃OH) oxidation on the PtPd(111) alloy surface were systematically investigated by using density functional theory calculations. The energies of all the involved species were analyzed. The results indicated that with the removal of H atoms from adsorbates on PtPd(111) surface, the adsorption energies of (i) CH₃OH, CH₂OH, CHOH, and COH increased linearly, while those of (ii) CH₃OH, CH₃O, CH₂O, CHO, and CO exhibited odd‐even oscillation. On PtPd(111) surface, CH₃OH underwent the preferred initial C H bond scission followed by successive dehydrogenation and then CHO oxidation, that is, CH₃OH → CH₂OH → CHOH → CHO → CHOOH → COOH → CO₂. Importantly, the rate‐determining step of CH₃OH oxidation was found to switch from CO → CO₂ on Pt(111) to COOH → CO₂ + H on PtPd(111) with a lower energy barrier of 0.96 eV. Moreover, water also decomposed into OH more easily on PtPd(111) than on Pt(111). The calculated results indicate that alloying Pt with Pd could efficiently improve its catalytic performance for CH₃OH oxidation through altering the primary pathways from the CO path on pure Pt to the non‐CO path on PtPd(111).     

Water Soluble Gold(I)‐diacetyl‐1,3,5‐triaza‐7‐phosphaadamantane‐arylazoimidazole Complexes: Synthesis and Spectroscopic Study

Reaction of [Au(DAPTA)(Cl)] with RaaiR’ in CH2Cl2 medium following ligand addition leads to [Au(DAPTA)(RaaiR’)](Cl) [DAPTA＝diacetyl-1,3,5-triaza-7-phosphaadamantane, RaaiR’＝p-R-C6H4-N＝N- C3H2-NN-1-R’, (1—3), abbreviated as N,N’-chelator, where N(imidazole) and N(azo) represent N and N’, respectively; R＝H (a), Me (b), Cl (c) and R’＝Me (1), CH2CH3 (2), CH2Ph (3)]. The 1H NMR spectral measurements in D2O suggest methylene, CH2, in RaaiEt gives a complex AB type multiplet while in RaaiCH2Ph it shows AB type quartets. 13C NMR spectrum in D2O suggest the molecular skeleton. The 1H-1H COSY spectrum in D2O as well as contour peaks in the 1H-13C HMQC spectrum in D2O assign the solution structure.     

Selective Electrochemical Reduction of Carbon Dioxide to Ethanol on a Boron‐ and Nitrogen‐Co‐doped Nanodiamond

Electrochemical reduction of CO₂ to ethanol, a clean and renewable liquid fuel with high heating value, is an attractive strategy for global warming mitigation and resource utilization. However, converting CO₂ to ethanol remains great challenge due to the low activity, poor product selectivity and stability of electrocatalysts. Here, the B‐ and N‐co‐doped nanodiamond (BND) was reported as an efficient and stable electrode for selective reduction of CO₂ to ethanol. Good ethanol selectivity was achieved on the BND with high Faradaic efficiency of 93.2 % (−1.0 V vs. RHE), which overcame the limitation of low selectivity for multicarbon or high heating value fuels. Its superior performance was mainly originated from the synergistic effect of B and N co‐doping, high N content and overpotential for hydrogen evolution. The possible pathway for CO₂ reduction revealed by DFT computation was CO₂→*COOH→*CO→*COCO→*COCH₂OH→*CH₂OCH₂OH→CH₃CH₂OH.     

Manipulation of Structure on Silicon Surfaces via Chemical Adsorption

Via chemical adsorption, various films were assembled onto silicon surfaces. The structures and properties of the monolayer‐ or bilayer‐modified silicon surfaces, such as Si‐C₁₀H₂₀ CH₂OC(O)CF₃, Si‐C₁₀H₂₀CH₂OH, and Si‐C₁₀H₂₀‐CH₂‐NH‐C₁₈H₃₇, were investigated by various techniques. x‐ray photoelectron spectroscopy (XPS) gave clear proofs of the formation of octadecylamine layer and other kinds of layers on silicon surfaces. The contact angle measurements showed that the wettability of silicon surfaces was dominated by the terminal functional groups of the attached layers. Atomic force microscopy (AFM) observations showed that interesting patterns have formed on the monolayer‐ or bilayer‐modified silicon surfaces. Electrochemical impedance spectra (EIS) measurements showed that the Si‐C₁₀H₂₀CH₂‐NH‐C₁₈H₃₇ has a better ability to prevent charge transfer as compared with that of Si‐C₁₀H₂₀CH₂OH, which may find applications in the area of surface passivations.     

Asymmetrically Functionalized,Four‐Armed,Poly(ethylene glycol) Compounds for Construction of Chemically Functionalizable Non‐Biofouling Surfaces

Asymmetrically functionalized, four‐armed, Tween 20 derivatives that formed stable monomolecular films on solid substrates were designed and synthesized. Thiol‐modified Tween 20 was used for forming self‐assembled monolayers (SAMs) on gold, and maleimide‐modified Tween 20 was introduced onto SiO₂ surfaces with SAMs of (3‐mercaptopropyl)trimethoxysilane through Michael addition. These structurally modified Tween 20 compounds gave the original characteristics of Tween 20, non‐biofouling (from ethylene glycol groups) and functionalizable (from OH groups) properties, to each substrate. The non‐biofouling properties of the Tween 20‐coated gold and SiO₂ surfaces were investigated by surface plasmon resonance spectroscopy and ellipsometry, and these surfaces showed strong resistance against nonspecific adsorption of proteins. In addition, the biospecific binding of streptavidin was achieved after coupling of (+)‐biotinyl‐3,6,9‐trioxaundecanediamine onto the non‐biofouling surfaces through amide‐bond formation.     

Bi‐channel Surface Acoustic Wave Gas Sensor for Carbon Disulfide and Methanol Vapors in Polymer Plants

A C₆₀‐polyphenylacetylene (C₆₀‐PPA) and polyvinylpyrrolidone (PVP) coated two‐channel surface acoustic wave (SAW) crystal gas sensor with a homemade computer interface for data acquisition and data processing was developed and employed to detect carbon disulfide (CS₂) and methanol (CH₃OH) vapors in polymer plants. The frequency of surface acoustic wave oscillator decreases due to the adsorption of gas molecules on the coated materials of the SAW sensor. Six coating materials (C₆₀‐PPA, nafion, PPA, crytand [2,2], polyethene glycol and PVP) were used to adsorb and detect carbon disulfide and methanol gases. Adsorption of all the six coating materials to CS₂ and CH₃OH was found to be physical adsorption. The C₆₀‐PPA coated SAW detector exhibited more sensitive to CS₂ than the other coating materials. In contrast, the PVP coated SAW detector was more sensitive to CH₃OH than the other coating materials. With the two‐channel SAW sensor, the C₆₀‐PPA coated SAW showed a good detection limit of 0.4 ppm and good reproducibility with RSD of 3.37 % (n=10) for CS₂. Similarly, the PVP coated SAW also showed a good detection limit of 0.05 ppm and good reproducibility, with RSD of 0.86 % (n=10) for CH₃OH. The interference effect of other organic molecules on the SAW detection system was negligible, except for the irreversible adsorption of C₆₀‐PPA to propylamine. The frequency signals from the two‐channel SAW sensor array C₆₀‐PPA and PVP coatings were processed by a back‐propagation artificial neural network (BPN) and multiple regression analysis (MRA). Thus a two‐channel SAW sensor array with BPN and MRA has been successfully applied for the qualitative and quantitative analyses of CS₂ and CH₃OH in mixtures.     

Formation pathways of DMSO2 in the addition channel of the OH‐initiated DMS oxidation: A theoretical study

The production of dimethyl sulfoxide (DMSO) and dimethyl sulfone (DMSO₂) in the dimethyl sulfide (DMS) degradation scheme initiated by the hydroxyl (OH) radical has been shown to be very sensitive to nitrogen oxides (NO_x) levels. In the present work we have explored the potential energy surfaces corresponding to several reaction pathways which yield DMSO₂ from the CH₃S(O)(OH)CH₃ adduct [including the formation of CH₃S(O)(OH)CH₃ from the reaction of DMSO with OH] and the reaction channels that yield DMSO or/and DMSO₂ from the CH₃S(O₂)(OH)CH₃ adduct are also studied. The formation of the CH₃S(O₂)(OH)CH₃ adduct from CH₃S(OH)CH₃ (DMS‐OH) and O₂ was analyzed in our previous work. All these pathways due to the presence of NO_x (NO and NO₂) and also due to the reactions with O₂, OH and HO₂ are compared with the objective of inferring their kinetic relevance in the laboratory experiments that measure DMSO₂ (and DMSO) formation yields. In particular, our theoretical results clearly show the existence of NO_x‐dependent pathways leading to the formation of DMSO₂, which could explain some of these experimental results in comparison with experimental measurements carried out in NO_x‐free conditions. Our results indicate that the relative importance of the addition channel in the DMS oxidation process can be dependent on the NO_x content of chamber experiments and of atmospheric conditions. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009     

硫的取代对基态硫代乙酸单分子解离反应影响的理论研究

应用B3LYP方法,结合6-31G**、cc-pVDZ、aug-cc-pVDZ和cc-pVTZ基组对硫代乙酸的两种异构体CH3C(O)SH和CH3C(S)OH在基态势能面上的9个单分子反应进行了研究。本文计算预测硫代乙酸主要以CH3C(O)SH的形式存在,两种异构体均以顺式构象为优势构象。通过对比CH3C(O)SH、CH3C(S)OH和 CH3C(O)OH的反应性差异,我们可以得出结论：CH3C(O)OH中-OH基团的O被S取代后,只有当-SH作为一个整体参加反应时才对分子解离过程有较大影响;而C=O或C=S对反应性影响较小。     

Characterization of ultra‐thin polymer films by polarization modulation FTIR spectroscopy

Self assembly monolayers of octadecyltrichlorosilane Cl₃‐Si‐(CH₂)₁₇‐CH₃ and 17‐cyanopentadecyltrichlorosilane Cl₃‐Si‐(CH₂)₁₇‐CN on silicon wafers have been prepared by adsorption from solution. The molecular orientation within the monolayers was investigated by using Polarisation Modulation FTIR spectroscopy. Quantitative analysis reveals that both types of silanes – monofunctionalised and bifunctionalised – form highly ordered monolayers. A high degree of ordering as well as a small tilt angel of the molecular backbones with respect to the surface normal are indicated by the strength of the Si‐O‐Si stretching modes and the weakness of the CH₂ stretching modes. The decomposition of the terminal nitrile group of the substituted silane into a carboxyl group could be identified. The decomposition is caused by a high local HCl concentration, which develops upon binding of 17‐cyanopentadecyltrichlorosilane to the OH groups of the silicon surface.     

Syntheses and properties of ethoxylated double‐tail trisiloxane surfactants containing a propanetrioxy spacer

A new type of ethoxylated double‐tail trisiloxane surfactants containing a propanetrioxy spacer of the general formula ROCH₂CH(OR)CH₂O(CH₂CH₂O)_xCH₃ [R = Me₃SiOSiMe(CH₂)₃OSiMe₃, x = 8.4, 12.9, 22] has been synthesized. Their structures were characterized by ¹H‐NMR, ¹³C‐NMR and ²⁹Si‐NMR spectroscopy. The critical micelle concentration (CMC) values of these double‐tail trisiloxane surfactants were at the level of 10⁻⁵ mol l⁻¹, and the surface tension values of their aqueous solutions at CMC were in the range of 21‐24.9 mN m⁻¹. Only the double‐tail trisiloxane surfactant with average ethoxy units of 8.4 ( 1P ) possesseda good spreading ability (SA) value. Its SA values of aqueous solutions (5.0 × 10⁻³ mol l⁻¹) on parafilm and Ficus microcarpa leaf surfaces were more than 15 (within 10 min) and 13 (within 3 min), respectively. The trisiloxane surfactant 1P was also found to have the strongest hydrolysis resistant ability among all of the double‐tail trisiloxane surfactants prepared. Its aqueous solutions were stable for 130 days in an acidic environment (pH 4.0) and 59 days in an alkaline environment (pH 10.0) with surface tension values less than 23 mN m⁻¹. It is suggested that this surfactant can be used as a wetting agent or spreading agent in certain extreme pH environments. Copyright © 2011 John Wiley & Sons, Ltd.