Diamine anchored molecular junctions of oligo(phenylene ethynylene) cruciform

Using diamine as anchoring group, the self-assembled monolayers (SAMs) based on oligo(phenylene ethynylene)s (OPEs) and cruciform OPEs with an extended tetrathiafulvalene (TTF) (OPE3 and OPE3-TTF) were successfully formed on the Au substrate and then utilized in molecular junctions by conductingprobe atomic force microscopy (CP-AFM).     

Improved and new syntheses of potential molecular electronics devices

New syntheses of ethyl and nitro substituted oligo(phenylene ethynylene)s (OPEs) have been developed. To further explore whether the presence of nitro functionality in OPEs leads to switching and memory capabilities, new nitro substituted OPEs have been designed and synthesized. An isatogen-based system, a structure that is isomeric to the nitro OPE, has been synthesized. Additionally, pyridine-based and chromium-based compounds have been synthesized. We surmise that redox reactions of these candidates may impart switching capabilities and electrochemical studies are shown. U-shaped OPEs were synthesized to inhibit leakage of metals deposited during formation of top contacts on self-assembled monolayers (SAMs). The OPEs contain either thiol-based moieties or isonitrile groups to enable formation of SAMs on metal substrates.     

Effect of polymer chain length on membrane perturbation activity of cationic phenylene ethynylene oligomers and polymers

The interactions of poly(phenylene ethynylene)- (PPE-) based cationic conjugated polyelectrolytes (CPEs) and oligo(phenylene ethynylene)s (OPEs) with different model lipid membrane systems were investigated to gain insight into the relationship between molecular structure and membrane perturbation ability. The CPE and OPE compounds exhibit broad-spectrum antimicrobial activity, and cell walls and membranes are believed to be their main targets. To better understand how the size, in terms of the number of repeat units, of the CPEs and OPEs affects their membrane disruption activities, a series of PPE-based CPEs and OPEs were synthesized and studied. A number of photophysical techniques were used to investigate the interactions of CPEs and OPEs with model membranes, including unilamellar vesicles and lipid monolayers at the air/water interface. CPE- or OPE-induced dye leakage from vesicles reveals that the CPEs and OPEs selectively perturb model bacterial membranes and that their membrane perturbation abilities are highly dependent on molecular size. Consistent with dye-leakage assay results, the CPEs and OPEs also exhibit chain-length-dependent ability to insert into 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG) monolayers. Our results suggest that, for PPE-based CPE and OPE antimicrobials, chain length can be tuned to optimize their membrane perturbation ability.     

Oligo(p‐phenylene‐ethynylene)‐Derived Super‐π‐Gelators with Tunable Emission and Self‐Assembled Polymorphic Structures

Linear π‐conjugated oligomers are known to form organogels through noncovalent interactions. Herein, we report the effect of π‐repeat units on the gelation and morphological properties of three different oligo(p‐phenylene‐ethynylene)s: OPE3 , OPE5 , and OPE7 . All of these molecules form fluorescent gels in nonpolar solvents at low critical gel concentrations, thereby resulting in a blue gel for OPE3 , a green gel for OPE5 , and a greenish yellow gel for OPE7 . The molecule–molecule and molecule–substrate interactions in these OPEs are strongly influenced by the conjugation length of the molecules. Silicon wafer suppresses substrate–molecule interactions whereas a mica surface facilitates such interactions. At lower concentrations, OPE3 formed vesicular assemblies and OPE5 gave entangled fibers, whereas OPE7 resulted in spiral assemblies on a mica surface. At higher concentrations, OPE3 and OPE5 resulted in super‐bundles of fibers and flowerlike short‐fiber agglomerates when different conditions were applied. The number of polymorphic structures increases on increasing the conjugation length, as seen in the case of OPE7 with n=5, which resulted in a variety of exotic structures, the formation of which could be controlled by varying the substrate, concentration, and humidity.     

液液提取-固相萃取-高效液相色谱-串联质谱测定人体血液中16种有机磷酸酯

人体体液中有机磷酸酯(OPEs)浓度的测定对于了解人体OPEs的暴露水平以及评估人体健康风险具有重要意义.然而,目前的研究大多数集中于尿液中OPEs代谢物含量的分析测定,将其作为人体OPEs暴露的生物标志物,而对人体血液中OPEs的分析研究较少,仅有的少量研究涉及的OPEs种类有限.该研究在优化前处理过程(固相萃取,S...     

Ru2(ap)4(sigma-oligo(phenyleneethynyl)) molecular wires: synthesis and electronic characterization

Reported in this contribution are the synthesis, characterization, and charge transport properties of wire-like Ru2(ap)4(OPEn), where ap is 2-anilinopyridinate and OPE is -(CCC6H4)nSCH2CH2SiMe3 with n = 1 (1) and 2 (2). Scanning tunneling microscopy (STM) measurements of compound 2 inserted into a SAM of C11 thiol reveal that molecule 2 exhibits (i) the stochastic switching characteristic of wire molecules embedded in insulating SAMs and (ii) higher conductivity than the C11 thiol SAM. More importantly, analysis of the molecular electronic decay constant (beta) exhibits a decrease of at least 15% as compared to purely organic molecular analogues. Hence, the transport characteristics of molecules can be significantly improved for nanoscale electronics through the incorporation of a Ru2 fragment into conjugated backbone.     

固相萃取-气相色谱/质谱联用法测定儿童手推车中3种有机磷酸酯阻燃剂

有机磷酸酯是一类重要的磷系阻燃剂,由于其具有类似持久性有机污染物(persistent organic pollutants, POPs)的性质,欧美等国家已纷纷设立相关法规限制其在儿童用品中的使用。目前国际和国内均未有儿童手推车中有机磷酸酯阻燃剂的检测标准。本文建立了儿童手推车中3种有机磷酸酯阻燃剂的超声萃取-弗罗里硅土固相萃取柱净化-气相色谱/质谱检测方法。该方法的加标回收率为89.5%~107.3%,检出限(3S/N)为0.01 mg/kg,定量限(10S/N)为0.1 mg/kg,能较好地排除基质干扰,适用于儿童手推车软垫材料中3种有机磷酸酯的定性和定量分析。37个样品的分析结果表明,磷酸三(2-氯丙基)酯(TCPP)的检出率为81.1%,含量范围为1.0~15312.8 mg/kg,依据欧盟玩具新指令2014/79/EU, TCPP超标(> 5 mg/kg)率为32.4%;其中2个样品中还检出了磷酸三(2-氯乙基)酯(TCEP)和磷酸三(1,3-二氯-2-丙基)酯(TDCP),含量范围为6.2~44.1 mg/kg,均已超标。可见,市场上的儿童手推车存在较高的有机磷酸酯阻燃剂暴露风险。     

Hydrogen bonding networks controllable by the substitution position of tetrathiafulvalene on the pyridine ring

Because of the effect of pyridine on the substituent position on the TTF group, TTF derivatives exhibit different assembly structures at the interface, which will be of great significance to the construction of functional nanostructures from the molecular design point of view.     

食品中有机磷酸酯阻燃剂检测技术的研究进展

有机磷酸酯(OPEs)是阻燃剂和塑化剂的主要原料,通常以添加形式存在于各种材料中,在生产和使用过程中伴随磨损和挥发易释放到环境中,现已成为新兴污染物。因为该类化合物的神经毒性、致癌性、破坏内分泌系统以及生殖系统等毒性,食品样品中OPEs的检测成为近年来关注的热点。该文重点围绕食品基质中OPEs检测存在的含量低、本底干扰严重、缺乏灵敏可靠分析方法等问题,对OPEs类化合物的性质、样品前处理、检测技术、质量控制等进行了全面评述。首先总结了30余种常见OPEs类化合物的类型、官能团、极性、沸点等理化性质,对可能的前处理和检测技术进行了理论分析;其次梳理了加速溶剂萃取(ASE)、基质固相分散萃取(MSPD)、微波辅助萃取(MAE)、超声辅助萃取(UAE)、QuEChERS、固相萃取(SPE)、凝胶渗透色谱(GPC)、分散固相萃取(d-SPE)等前处理方法在食品中OPEs化合物分析中的特点,其中UAE和QuEChERS结合多步净化能够有效降低高脂类食品的基质效应,具有良好应用前景;此外比较了气相色谱和液相色谱在分离和检测方面的优缺点,比较已有文献的检出限、回收率等数据;概括了标准品和内标物来源、过程污染与基质效应的产生原因和预防措施;最后对高分辨质谱筛查和鉴别OPEs未知代谢物,以及相关分析方法趋势进行了展望。     

A dinuclear Ni(II) complex with two types of intramolecular magnetic couplings: Ni(II)-Ni(II) and Ni(II)-TTF*+

A dinuclear Ni(II) complex involving tetrathiafulvalene (TTF) radicals as ligands has been prepared and characterized, [Ni2(mu-Cl)2(L*+)2(I3)4(I2)3.(H2O)2.(C4H8O)3 (1), L = 4,5-bis(2-pyridylmethylsulfanyl)-4',5'-ethylenedithiotetrathiafulvalene. There are two types of intramolecular magnetic exchange interactions, namely one ferromagnetic Ni(II)-Ni(II) and one antiferromagnetic Ni(II)-TTF*+. This study is new in the respect of revealing a magnetic exchange interaction between a TTF*+ radical and a paramagnetic transition metal ion. This is due to the fact of a direct binding of the transition metal ion to the skeleton of the TTF*+ radical.     

Tetrathiafulvalene–Oligo(para‐phenyleneethynylene) Conjugates: Formation of Multiple Mixed‐Valence Complexes upon Electrochemical Oxidation

Short monodisperse oligo‐ (para‐phenyleneethynylene) (pOPE) units bearing laterally attached tetrathio‐substituted tetrathiofulvalene (TTF) units have been synthesised from functionalised aromatic building blocks by using the Sonogashira cross‐coupling methodology. The unusual redox properties of these TTF–pOPE conjugates were observed by employing electrochemical methods, such as cyclic voltammetry and exhaustive electrolysis. We found that formally one half of the TTF units in the pOPE monomer 1 , dimer 2 , and trimer 3 (with 2, 4, and 6 TTF units, respectively) are electrochemically silent during the first‐step oxidation at 0.49 V. We propose the formation of persistent mixed‐valence complexes from the TTF and TTF^+. units present in an equal ratio. Such mixed‐valence dyads (single or multiple in the partially oxidised 1 – 3 ) exhibit an unusual stability towards oxidation until the potential of the second oxidation at 0.84 V is achieved. This finding suggests that below this potential the oxidation of the respective mix‐valence complexes is extremely slow.     

Formation of high-quality self-assembled monolayers of conjugated dithiols on gold: base matters

This Article reports a systematic study on the formation of self-assembled monolayers (SAMs) of conjugated molecules for molecular electronic (ME) devices. We monitored the deprotection reaction of acetyl protected dithiols of oligophenylene ethynylenes (OPEs) in solution using two different bases and studied the quality of the resulting SAMs on gold. We found that the optimal conditions to reproducibly form dense, high-quality monolayers are 9-15% triethylamine (Et(3)N) in THF. The deprotection base tetrabutylammonium hydroxide (Bu(4)NOH) leads to less dense SAMs and the incorporation of Bu(4)N into the monolayer. Furthermore, our results show the importance of the equilibrium concentrations of (di)thiolate in solution on the quality of the SAM. To demonstrate the relevance of these results for molecular electronics applications, large-area molecular junctions were fabricated using no base, Et(3)N, and Bu(4)NOH. The magnitude of the current-densities in these devices is highly dependent on the base. A value of β=0.15 ?(-1) for the exponential decay of the current-density of OPEs of varying length formed using Et(3)N was obtained.     

Determination of organophosphate flame retardants and plasticizers in lipid-rich matrices using dispersive solid-phase extraction as a sample cleanup step and ultra-high performance liquid chromatography with atmospheric pressure chemical ionization mass spectrometry

A fast, robust and highly sensitive analysis method for determination of trace levels of organophosphate ester (OPE) flame retardants and plasticizers in lipid-rich samples was presently developed, and based on ultra-high performance liquid chromatography-tandem mass spectrometry coupled to a positive atmospheric pressure chemical ionization source (UHPLC-MS/MS-APCI(+)). The target OPEs in the sample were extracted from the biota samples, such as egg and liver, by ultrasonic extraction, and cleaned up further by dispersive solid phase extraction (d-ESP). As a result, background contamination was largely reduced. Different dispersive ESP sorbents were tested and primary secondary amine (PSA) bonded silica sorbents showed the best recoveries for these target OPEs. The recoveries obtained were in the range 54–113% (RSD < 17%), with method limits of quantification (MLOQs) ranging between 0.06 and 0.29 ng/g in egg, and 0.05 and 0.50 ng/g w.w. in liver sample. The matrix effects (MEs) associated with using APCI(+) and ESI(+) sources were investigated. APCI(+) showed much less ion suppression than ESI(+) for the determination of these OPEs. For egg and liver samples, the APCI(+) ME values ranged from 40% to 94%, while ESI(+) ME values ranged from 0% to 36%. Although APCI(+) was used for the determination of OPEs, the ionization mechanism might mainly be a thermospray ionization process. This UHPLC-MS/MS-APCI(+) method showed good response linearity for calibration (R2 > 0.99). The proposed method was applied to real environmental bird egg and fish samples, where several OPE were quantifiable and different OPE patterns was observed between samples.     

New crown annelated tetrathiafulvalenes: synthesis, electrochemistry, self-assembly of thiol derivatives, and metal cation recognition

The synthesis of new S(2)O(4)-crown annelated tetrathiafulvalene (TTF) derivatives substituted with one terminal thiol group is described. Self-assembled monolayers (SAMs) of these compounds have been assembled on gold and platinum surfaces, the latter substrate giving improved quality films. SAMs of TTF derivative 16b are the most stable of those we have studied. Electrochemical data for SAMs of 5a, 5b, 8, 16a, and 16b in acetonitrile reveal two reversible one-electron waves, typical of the TTF system; the current increased linearly with scan rate, indicating a surface wave response. SAMs of 8, 16a, and 16b exhibited an electrochemical response in aqueous electrolytes, which was observed between 50 and 100 cycles. Moreover, if the potential scanned was limited to the first TTF oxidation, the cyclic voltammetry response was observed for at least 1000 cycles. Metal complexation by the crown ionophore of the SAMs in acetonitrile has been monitored by a positive shift in the first oxidation potential of the TTF unit (maximum DeltaE(1)(1/2) = 80 mV for Ag(+)). We also report the X-ray crystal structure of TTF-crown derivative 21 bearing two hydroxymethyl substituents, synthesized during the course of this work. The structure is characterized by infinite chains of molecules linked by strong intrachain hydrogen bonds between the terminal hydroxy groups.     

Isolation and characterization of four isomers of a C(60) bisadduct with a TTF derivative. Study of their radical ions.

A family of triads composed of C(60) attached by a rigid spacer to two identical TTF moieties has been synthesized, and some of the isomers have been isolated and characterized by UV-vis spectroscopy, LDI-TOF-MS, and HMBC NMR spectroscopy. AM1 semiempirical calculations of the dipolar moments and the heats of formation of the different isomers have been carried out in order to verify their assignments. Oxidation and reduction of the triads affords the derived radical ion systems, TTF(+*)-C(60)-TTF(+*) and TTF-C(60)(-*)-TTF, which were studied by EPR spectroscopy. Spin density distributions of these radical cations and radical anions show that the unpaired electron is located mainly on the TTF and fullerene moieties, respectively. However, while the EPR signals obtained from the radical cations are very similar for all the isomers, the structured signals observed for the radical anions arising from the coupling of the unpaired electron with the hydrogen atoms of the methylene bridges in the spacer show that there is a strong influence of the isomerism on the spin distribution. Importantly, the theoretical calculations of the spin density distributions of the radical anions fit well with the experimental EPR results.     

Dynamic and collective electrochemical responses of tetrathiafulvalene derivative self-assembled monolayers

Electroactive tetrathiafulvalene (TTF)-containing alkanethiol self-assembled monolayers (SAMs) were designed and synthesized to elucidate the relationship between electrochemical responses and film structures. Two TTF derivative molecules having one alkanethiol chain (1) and two alkanethiol chains (2) were utilized to modulate the molecular packing arrangements in the SAMs, and the formation and structure of the SAMs were characterized by surface plasmon resonance spectroscopy (SPR). SPR measurements in various contacting media demonstrated loose packing of SAM 1 and close packing of SAM 2 due to the different space fillings of the molecules. Two successive one-electron redox waves were observed for both SAMs by cyclic voltammetry. The peak widths of the redox waves were strongly dependent on the oxidation states of the TTF moieties, the packing arrangement of the SAMs, and the contacting medium. We found that TTF-based SAMs exhibited collective electrochemical responses induced by dynamic structural changes, depending on the degree of freedom for the component molecules in the SAMs. These results imply that the molecular design, taking into account the electrochemical responses, extends the available range of molecular-based functionalities in TTF-based SAMs.     

Synthesis of nitrile-terminated potential molecular electronic devices

Several potential molecular devices have been synthesized consisting of oligo(phenylene ethynylene) (OPE) backbones containing a terminal nitrile group alligator clip as a means of attachment to a metal surface. The synthesis of four new nitrile-containing OPEs is discussed, including an improved synthesis of an intermediate used in our prior production of OPEs containing acetate-protected thiol alligator clips.     

Effect of donor-acceptor substitution on the nonlinear optical properties of oligo(1,4-phenyleneethynylene)s studied by third harmonic generation spectroscopy

Third-harmonic generation (THG) spectroscopy was performed for oligo(1,4-phenyleneethynylene)s (OPEs) with terminal donor-acceptor (DA) substitution and compared to the results of merely donor substituted OPEs and regular OPE chains with 2,5-dipropoxy benzene rings. Both, extension of the conjugation and push-pull effect enhance the molecular hyperpolarizability gamma, even for the DAOPEs, which exhibit a hypsochromic shift of the long-wavelength absorption for increasing length L of the conjugated chain.     

Comparative study of electrochemically directed assembly versus conventional self-assembly of thioacetyl-terminated oligo(phenylene ethynylene)s on gold and platinum surfaces

The assembly of thioacetyl-terminated oligo(phenylene ethynylene)s (OPEs) on Au and Pt surfaces under an electric potential (electrochemical assembly, EA) was compared to assembly at an open circuit (conventional self-assembly, CSA). Cyclic voltammetry and ellipsometry were used to characterize the adsorption kinetics of self-assembled monolayers formed by these two techniques. The adsorption rate of the EA was remarkably faster at positive potentials but slower at negative potentials than that of the CSA, The EA at 400 mV proceeded about 800 times faster than the CSA when exposed to the same solution concentrations. The adsorption rates of both EA and CSA were found to be dependent on the molecular structures of OPEs. OPEs containing electron-donating groups assemble faster than those with electron-withdrawing groups. The amount of time that the thioacetyl-terminated OPE is in the presence of the base, for removal of the acetyl group to generate the thiolate, is called the deprotection time. Deprotection times play a critical role in achieving the maximum difference in adsorption rates between the EA and the CSA. The assembly must be initiated no later than 5 min after the basic deprotection is commenced so that the thiolate concentration remains low. The difference in the adsorption rates between EA and CSA might enable selective deposition of certain OPEs onto specific electrodes.     

两个四硫富瓦烯分子正离子自由基TTF·^＋之间的共价吸引作用

使用MP2／6-311G方法得到了四硫富瓦烯自由基正离子二聚体（TTF·^＋ -TTF·^＋）能量极小点的结构．这显示这种正离子间的吸引作用存在．这种新的吸引作用是望远镜形状的20中心2电子分子间共价π/π键．这种共价π/π键的键能约为-21kcal·mol^-1,它被正离子间的库伦排斥作用掩盖．有负离子围绕的四硫富瓦烯自由基正离子二聚体（TTF·^＋ -TTF·^＋）体系是稳定的．