Thiol Linker Research Articles

Development and characterization of functionalized glyco thiolate capped gold nanoparticles for biological applications.

Glyco-gold nanoparticles (AuNPs) in aqueous dispersions were prepared by two approaches, namely direct reduction and ligand substitution methods. In the direct method, potassium salts of glyco thiols, with the general formula (C6H11O6)NH(CH2) n CH2SK (where L1, n = 1; L2, n = 2; L3, n = 3, L4, n = 4; L5, n = 5), were used as reducing and capping agents to give the glyco thiolate capped gold nanoparticles (AuNPs G1-G5); meanwhile in the ligand exchange experiments, L1-L5 and their acetylated forms (L6-L8) replaced citrate ions in citrate-capped gold nanoparticles to give additional AuNPs G6-G11. UV-visible spectroscopy, surface charge (ζ-potential,) measurements and transmission electron microscopy (TEM) were used for physical and chemical characterization of all the resultant AuNPs. The ζ-potential studies of AuNPs prepared through the direct method revealed that the surface charge is dependent on the length of the alkyl unit of (C6H11O6)NH(CH2) n CH2S- ligands. TEM images of the acetylated and non-acetylated glyco thiolate capped gold nanoparticles (AuNPs G6-G11) prepared via the ligand exchange method indicate that the size and shape of the gold nanoparticles remained the same as those of the citrate-capped gold nanoparticles used to prepare them. Selected AuNPs were tested on peripheral blood mononuclear cells (PBMCs) and the A549 cancer cell line to investigate their respective toxicity and cytotoxicity profiles. All AuNPs showed indiscriminate activity against both PBMCs and A4549 cells, although the gold nanoparticles having an acetylated glyco moiety with an amino propyl thiol linker as the ligand (G10) prepared via the citrate exchange method had better selectivity (PBMCs >59 mg mL-1 and for A549 ∼7 μg mL-1).

Synthetic Lipomannan Glycan Microarray Reveals the Importance of α(1,2) Mannose Branching in DC-SIGN Binding.

Lipomannan (LM), a glycophospholipid found on the cell surface of mycobacteria, involves the virulence and survival in host cells. However, there is little to no information on how exactly mannan alignment, including the number of mannose units and the branched motif of LM, affects protein engagement during host-pathogen interactions. In this study, we synthesized the exact substructures of the LM glycans that consist of an α(1,6) mannan core, with and without the complete α(1,2) mannose branching, and comparatively studied their protein-carbohydrate interactions. The synthetic LM glycans were equipped with a thiol linker for immobilizations on the surfaces of microarrays. As per our findings, the presence of the branching α(1,2) mannose on the LM glycans increases their binding toward the dendritic cell-specific intercellular adhesion molecule-3 grabbing non-integrin receptor. An increase in the number of mannose units on the glycans also increases the binding with the mannose receptor. Thus, the set of synthetic glycans can serve as a useful tool to study the biological activities of LM and can provide a better understanding of host-pathogen interactions.

Functionalizing gold with single strand DNA: novel insight into optical properties via combined spectroscopic ellipsometry and nanolithography measurements.

We have studied the self-assembly of 22-base oligonucleotides bound by a short alkyl thiol linker (C6-ssDNA) on flat Au films. The self-assembled monolayer (SAM) was modified by addition of a spacer (mercaptohexanol, MCH). Molecular depositions were monitored in situ by spectroscopic ellipsometry (SE). SAMs were characterized in a liquid environment by coupling SE (difference spectra method) with Atomic Force Microscope (AFM) measurements. We exploited the biofilm thickness obtained by AFM nanolithography and imaging to solve the refractive index/thickness correlation in optical measurements on ultrathin molecular layers. The combined SE/AFM analysis provided reliable estimates of the thickness and the refractive index of the biofilm in the NIR region (650-1300 nm) and revealed new aspects of DNA molecular organization: exposure to MCH leads to an increase of both film thickness and refractive index, which points to a reorganization of C6-ssDNA film. We show that the contribution of the thiol/Au interface has to be included in the optical model to obtain a more reliable determination of the refractive index of the biofilm in a liquid. The careful, correlative characterization of the mixed C6-ssDNA/MCH SAM represents a key step towards the optimization of a robust detection scheme based on helix-helix hybridization.

Colour and SERS patterning using core-satellite nanoassemblies.

We explore spatial control of the formation of core-satellite nanoassemblies on glass substrates. UV irradiation leads to the photooxidative desorption of thiol linkers from gold nanoparticles deposited on the substrates, thereby prohibiting further assembly in the irradiated region. The distribution of assemblies and monomers yields a pattern with stark contrasts in colour and Raman enhancement. Our findings can be utilised in the fabrication of microfluidic SERS sensors, colour displays, photonic devices, and metamaterials.

Silver nanoparticles supported onto a stainless steel wire for direct-immersion solid-phase microextraction of polycyclic aromatic hydrocarbons prior to their determination by GC-FID.

The authors describe a new coating for use in solid-phase microextraction (SPME). Silver nanoparticles (AgNPs) were prepared by using gallic acid or glucose as the reducing agents, and then supported onto a stainless steel wire that was previously coated with a silver mirror. Coating with AgNPs was performed by a layer-by-layer approach of up to eight cycles of consecutive deposition of AgNPs and the thiol linker 1,8-octanedithiol. This procedure allows proper control of the coating thickness. Thicknesses are 3.2μm and 3.5μm with AgNPs obtained with gallic acid and glucose, respectively. This is in agreement with theoretical estimations (3.8μm). The fibers were used in the direct-immersion SPME-GC-FID determination of 16 polycyclic aromatic hydrocarbons (PAHs) from different waters. The performance of the method was compared to the one using polydimethylsiloxane fibers (100μm), which is the most suitable commercial SPME fiber for PAHs. Despite the low thickness of the AgNP coatings (compared to PDMS), the analytical features of the method using the most adequate coating (AgNPs prepared with gallic acid) include: (a) limits of detection down to 0.6ng·mL-1; (b) intra-day, inter-day, and inter-fiber precisions (expressed as RSDs) lower than 22, 26 and 25%, respectively; and (c) an operational lifetime of ~150 extractions/desorption cycles. The analysis of various spiked environmental waters using these fibers resulted in adequate analytical performance. Graphical abstract Silver nanoparticle based coatings for solid-phase microextraction fibers were prepared by a layer-by-layer approach. They were used for determination of 16 PAHs in waters by gas chromatography. Limits of detection are < 14μg·L-1 and intra-day, inter-day, and inter-fiber precisions are <26%.

Influence of amine and thiol modifications at the 3′ ends of single stranded DNA molecules on their adsorption on gold surface and the efficiency of their hybridization

Adsorption of molecules of DNA (deoxyribonucleic acid) or modified DNA on gold surfaces is often the first step in construction of many various biosensors, including biosensors for detection of DNA with a particular sequence. In this work we study the influence of amine and thiol modifications at the 3′ ends of single stranded DNA (ssDNA) molecules on their adsorption on the surface of gold substrates and on the efficiency of hybridization of immobilized DNA with the complementary single stranded DNA. The characterization of formed layers has been carried out using infrared spectroscopy and atomic force microscopy. As model single stranded DNA we used DNA containing 20 adenine bases, whereas the complementary DNA contained 20 thymine bases. We found that the bands in polarization modulation-infrared reflection-adsorption spectroscopy (PM-IRRAS) spectra of layers formed from thiol-modified DNA are significantly narrower and sharper, indicating their higher regularity in the orientation of DNA on gold surface when using thiol linker. Also, hybridization of the layer of thiol-modified DNA containing 20 adenine bases with the respective DNA containing thymine bases leads to formation of much more organized structures than in the case of unmodified DNA or DNA with the amine linker. We conclude that the thiol-modified ssDNA is more promising for the preparation of biosensors, in comparison with the amine-modified or unmodified ssDNA. We have also found that the above-mentioned modifications at the 3′ end of ssDNA significantly influence the IR spectrum (and hence the structure) of polycrystalline films formed from such compounds, even though adsorbed fragments contain less than 5% of the DNA chain. This effect should be taken into account when comparing IR spectra of various polycrystalline films formed from modified and unmodified DNA.

Synthesis of a Thiol Building Block for the Crystallization of a Semiconducting Gyroidal Metal-sulfur Framework

We present a method for preparing thioester molecules as the masked form of the thiol linkers and their utilization for accessing a semiconducting and porous metal-dithiolene network in the highly ordered single crystalline state. Unlike the highly reactive free-standing thiols, which tend to decompose and complicate the crystallization of metal-thiolate open frameworks, the thioester reacts in situ to provide the thiol species, serving to mitigate the reaction between the mercaptan units and the metal centers, and to improve crystallization consequently. Specifically, the thioester was synthesized in a one-pot procedure: an aromatic bromide (hexabromotriphenylene) reacted with excess sodium thiomethoxide under vigorous conditions to first form the thioether intermediate product. The thioether was then demethylated by the excess thiomethoxide to provide the thiolate anion that was acylated to form the thioester product. The thioester was conveniently purified by standard column chromatography, and then used directly in the framework synthesis, wherein NaOH and ethylenediamine serve to revert in situ the thioester to the thiol linker for assembling the single-crystalline Pb(II)-dithiolene network. Compared with other methods for thiol synthesis (e.g., by cleaving alkyl thioether using sodium metal and liquid ammonia), the thioester synthesis here uses simple conditions and economical reagents. Moreover, the thioester product is stable and can be conveniently handled and stored. More importantly, in contrast to the generic difficulty in accessing crystalline metal-thiolate open frameworks, we demonstrate that using the thioester for in situ formation of the thiol linker greatly improves the crystallinity of the solid-state product. We intend to encourage broader research efforts on the technologically important metal-sulfur frameworks by disclosing the synthetic protocol for the thioester as well as the crystalline framework solid.

SYNTHESIS OF AN AZIDE–THIOL LINKER FOR HETEROGENEOUS POLYMER FUNCTIONALIZATION VIA THE “CLICK” REACTION

In this study, the synthesis of a telechelic linker bearing both azide and thiol functional groups was described. The reaction conditions were investigated to optimize the reaction yield. The product was analyzed using thin layer chromatography (TLC) and proton nuclear magnetic resonance (1H NMR). The employment of the obtained azide–thiol linker in heterogeneous polymer “click” functionalization was demonstrated for the first time, which was monitored by an online FT–IR method. The obtained telechelic azide–thiol linker is envisioned to be useful chemical tools to link macromolecular chains via orthogonal click reactions.

Exploratory Testing of Diatom Silica to Map the Role of Material Attributes on Cell Fate

Porous silica is an attractive biomaterial in many applications, including drug-delivery systems, bone-graft fillers and medical devices. The issue with porous silica biomaterials is the rate at which they resorb and the significant role played by interfacial chemistry on the host response in vivo. This paper explores the potential of diatom-biosilica as a model tool to assist in the task of mapping and quantifying the role of surface topography and chemical cues on cell fate. Diatoms are unicellular microalgae whose cell walls are composed of, amorphous nanopatterned biosilica that cannot be replicated synthetically. Their unique nanotopography has the potential to improve understanding of interface reactions between materials and cells. This study used Cyclotella meneghiniana as a test subject to assess cytotoxicity and pro-inflammatory reactions to diatom-biosilica. The results suggest that diatom-biosilica is non-cytotoxic to J774.2 macrophage cells, and supports cell proliferation and growth. The addition of amine and thiol linkers have shown a significant effect on cytotoxicity, growth and cytokine response, thus warranting further investigation into the interfacial effects of small chemical modifications to substrate surfaces. The overall findings suggest diatom-biosilica offers a unique platform for in-depth investigation of the role played by nanotopography and chemistry in biomedical applications.

Surface-enhanced Raman scattering investigation of targeted delivery and controlled release of gemcitabine.

Advanced and metastatic cancer forms are extremely difficult to treat and require high doses of chemotherapeutics, inadvertently affecting also healthy cells. As a result, the observed survival rates are very low. For instance, gemcitabine (GEM), one of the most effective chemotherapeutic drugs used for the treatment of breast and pancreatic cancers, sees only a 20% efficacy in penetrating cancer tissue, resulting in <5% survival rate in pancreatic cancer. Here, we present a method for delivering the drug that offers mitigation of side effects, as well as a targeted delivery and controlled release of the drug, improving its overall efficacy. By modifying the surface of gold nanoparticles (AuNPs) with covalently bonded thiol linkers, we have immobilized GEM on the nanoparticle (NP) through a pH-sensitive amide bond. This bond prevents the drug from being metabolized or acting on tissue at physiological pH 7.4, but breaks, releasing the drug at acidic pH, characteristic of cancer cells. Further functionalization of the NP with folic acid and/or transferrin (TF) offers a targeted delivery, as cancer cells overexpress folate and TF receptors, which can mediate the endocytosis of the NP carrying the drug. Thus, through the modification of AuNPs, we have been able to produce a nanocarrier containing GEM and folate/TF ligands, which is capable of targeted controlled-release delivery of the drug, reducing the side effects of the drug and increasing its efficacy. Here, we demonstrate the pH-dependent GEM release, using an ultrasensitive surface-enhanced Raman scattering spectroscopy to monitor the GEM loading onto the nanocarrier and follow its stimulated release. Further in vitro studies with model triple-negative breast cancer cell line MDA-MB-231 have corroborated the utility of the proposed nanocarrier method allowing the administration of high drug doses to targeted cancer cells.

Tip-Specific Functionalization of Gold Nanorods for Plasmonic Biosensing: Effect of Linker Chain Length.

Gold nanorods are promising platforms for label-free biosensing. We have functionalized gold nanorods with biotin thiol linkers of increasing chain length and evaluated their ability in the molecular detection of streptavidin. We have found an unexpected effect of the increase in linker length, which resulted in a substantial improvement of the plasmon response at surface saturation. The plasmon peak shift increased from 5 to 14 nm, i.e., more than twice the response, between the short and long biotin linkers. This effect is observed only for site-selective tip functionalization, whereas for a full biotin coating there is no improvement observed with the linker length. The improved plasmon response for tip functionalization is attributed to low biotin coverage but is directed to the most sensitive regions, which, combined with a longer chain linker, reduces the steric hindrance for streptavidin binding on the rod's surface. The model sensors were further characterized by measuring their dose-response curves and binding kinetic assays. Simulations of the discrete dipole approximation give theoretical plasmon shifts that compare well with the experimental ones for the long linker but not with those of the short linker, thus suggesting that steric hindrance affects the latter. Our results highlight the importance of specifically functionalizing the plasmonic hot spots in nanoparticle sensors with the adequate density of receptors in order to maximize their response.

Lignin-Based Materials Through Thiol-Maleimide "Click" Polymerization.

In the present report an environmentally friendly approach to transforming renewable feedstocks into value-added materials is proposed. This transformation pathway was conducted under green conditions, without the use of solvents or catalyst. First, controlled modification of lignin, a major biopolymer present in wood and plants, was achieved by esterification with 11-maleimidoundecylenic acid (11-MUA), a derivative from castor oil that contains maleimide groups, following its transformation into 11-maleimidoundecanoyl chloride (11-MUC). Different degrees of substitution were achieved by using various amounts of the 11-MUC, leading to an efficient conversion of lignin hydroxy groups, as demonstrated by 1 H and 31 P NMR analyses. These fully biobased maleimide-lignin derivatives were subjected to an extremely fast (ca. 1 min) thiol-ene "click" polymerization with thiol-containing linkers. Aliphatic and aromatic thiol linkers bearing two to four thiol groups were used to tune the reactivity and crosslink density. The properties of the resulting materials were evaluated by swelling tests and thermal and mechanical analyses, which showed that varying the degree of functionality of the linker and the linker structure allowed accurate tailoring of the thermal and mechanical properties of the final materials, thus providing interesting perspectives for lignin in functional aromatic polymers.

Diamondoid-based molecular junctions: a computational study

In this work, we deal with the computational investigation of diamondoid-based molecular conductance junctions and their electronic transport properties. A small diamondoid is placed between the two gold electrodes of the nanogap and is covalently bonded to the gold electrodes through two different molecules, a thiol group and a N-heterocyclic carbene molecule. We have shown that the thiol linker is more efficient as it introduces additional electron paths for transport at lower energies. The influence of doping the diamondoid on the properties of the molecular junctions has been investigated. We find that using a nitrogen atom to dope the diamondoids leads to a considerable increase of the zero bias conductance. For the N-doped system we show an asymmetric feature of the I–V curve of the junctions resulting in rectification within a very small range of bias voltages. The rectifying nature is the result of the characteristic shift in the bias-dependent highest occupied molecular orbital state. In all cases, the efficiency of the device is manifested and is discussed in view of novel nanotechnological applications.

Highly Sensitive and Selective Surface-Enhanced Raman Spectroscopy Label-free Detection of 3,3',4,4'-Tetrachlorobiphenyl Using DNA Aptamer-Modified Ag-Nanorod Arrays.

An improved label-free approach for highly sensitive and selective detection of 3,3',4,4'-tetrachlorobiphenyl (PCB-77), a type of polychlorinated biphenyl, via surface-enhanced Raman spectroscopy (SERS) using DNA aptamer-modified Ag-nanorod arrays as the effective substrate is reported. The devised system consists of Ag-nanorod (Ag-NR) arrays with the PCB-77 binding aptamers anchored covalently to the Ag surfaces through a thiol linker. The aptamers are made of single-stranded DNA (ssDNA) oligomers, with one end standing on the Ag surface, and upon conjugation with PCB-77, the ssDNA molecules can change their conformation to hairpin loops, so that the Raman intensity of guanines at the other end of the DNA strand increases accordingly. As such, the intensity ratio I(656 cm(-1))/I(733 cm(-1)) increases concomitantly with the increase of the concentration of PCB-77, making the quantitative evaluation of trace amounts of PCB-77 attainable. Moreover, it is found that the DNA aptamer-based Ag-NR arrays can be more responsive with a lower and optimal density of the DNA molecules modified on the substrate surface, and the best sensitivity for detection of PCB-77 can be achieved with the lower detection limit approaching 3.3 × 10(-8) M. This work therefore demonstrates that the design of aptamer-modified Ag-NRs can be used as a practically promising SERS substrate for label-free trace detection of persistent organic pollutants (POPs) in the environment.

Fabrication of an electrochemical DNA-based biosensor for Bacillus cereus detection in milk and infant formula

This paper describes fabrication of a DNA-based Au-nanoparticle modified pencil graphite electrode (PGE) biosensor for detection of Bacillus cereus, causative agent of two types of food-borne disease, i.e., emetic and diarrheal syndrome. The sensing element of the biosensor was comprised of gold nanoparticles (GNPs) self-assembled with single-stranded DNA (ssDNA) of nheA gene immobilized with thiol linker on the GNPs modified PGE. The size, shape and dispersion of the GNPs were characterized by field emission scanning electron microscope (FESEM). Detection of B. cereus was carried out based on an increase in the charge transfer resistance (Rct) of the biosensor due to hybridization of the ss-DNA with target DNA. An Atomic force microscope (AFM) was used to confirm the hybridization. The biosensor sensitivity in pure cultures of B. cereus was found to be 100 colony forming units per milliliter (CFU/mL) with a detection limit of 9.4×10−12molL−1. The biosensor could distinguish complementary from mismatch DNA sequence. The proposed biosensor exhibited a rapid detection, low cost, high sensitivity to bacterial contamination and could exclusively and specifically detect the target DNA sequence of B. cereus from other bacteria that can be found in dairy products. Moreover, the DNA biosensor exhibited high reproducibility and stability, thus it may be used as a suitable biosensor to detect B. cereus and to become a portable system for food quality control.

Demonstration of Improved Charge Transfer in Graphene/Au Nanorods Plasmonic Hybrids Stabilized by Benzyl Thiol Linkers

Hybrids based on graphene decorated with plasmonic gold (Au) nanostructures are being investigated as possible materials combination to add to graphene functionalities of tunable plasmon resonance and enhanced absorption at selected wavelength in the visible-near-infrared region of the spectrum. Here, we report a solution drop-casting approach for fabricating stable hybrids based on chemical vapor deposition (CVD) graphene and Au nanorods, which are able to activate effective charge transfer from graphene. We demonstrate that CVD graphene functionalization by benzyl thiol (BZT) provides the linker to strong anchoring, via S-Au bonds, Au nanorods to graphene. Optical measurements by spectroscopic ellipsometry give evidence of the introduction of plasmon resonances at 1.85 and 2.25 eV in the Au nanorods/BZT/graphene hybrids, which enable surface enhanced Raman scattering (SERS) detection. Furthermore, an effective electron transfer from graphene to Au nanorods, resulting in an enhancement of p-type doping of graphene with a consequent decrease of its sheet resistance, is probed by Raman spectroscopy and corroborated by electrical measurements.

Drug-DNA Conjugated Gold Nanoparticles for the Treatment of Acute Myeloid Leukemia

INTRODUCTIONNovel therapies are needed for acute myeloid leukemia as only ~60% of children are cured despite maximally intensive cytotoxic chemotherapy. Functionalized gold nanoparticles (AuNP) are utilized for many biomedical applications and represent a potentially novel therapeutic approach in leukemia. We enhanced this technology by developing an AuNP system that selectively releases molecularly targeted drugs in leukemia cells. METHODSAuNPs were functionalized with short, double-stranded oligonucleotides with sequence complementarity to genes overexpressed in or unique to a leukemia cell (e.g. survivin or AML/ETO). Only the anti-sense oligonucleotide is covalently bound to the nanoparticle via a thiol linker. Thus, after entering leukemia cells, the endogenous targeted oncogene mRNA can bind to its complementary sequence on the AuNP and displace the non-covalently bound oligonucleotide which, in our system, is conjugated to the multi-tyrosine kinase inhibitor dasatinib. As a binary reaction, the amount of dasatinib-conjugated oligonucleotide released from the nanoparticle is directly proportional to both the presence and abundance of the complementary mRNA present in a cell. We evaluated AuNP uptake into multiple AML cell lines, as well as normal hematopoietic cells. The effect of dasatinib-AuNPs on dasatinib-sensitive leukemia cell lines was evaluated using proliferation assays, annexin V staining, and cell colony assays. Toxicity in T-cells and CD34+ cells was assessed with T-cell activation and p-SRC assays, respectively. RESULTSConjugation of dasatinib to an oligonucleotide complementary to a region of the survivin gene did not perturb its ability to inhibit SRC and c-KIT kinases in vitro. Leukemia cells demonstrate highly efficient AuNP uptake when cultured alone or with up to a 100-1000 fold excess of normal bone marrow cells. Treatment of K562 leukemia cells, containing a BCR/ABL translocation and high levels of survivin mRNA, with dasatinib-AuNPs resulted in dose-dependent p-SRC and p-CRKL inhibition. Furthermore, K562 cells also showed significantly impaired proliferation, increased apoptosis, and formed fewer colonies in methylcellulose. Conversely, normal T-cells and CD34+ cells, which express less survivin than leukemia cells, were significantly less affected by dasatinib-AuNPs than dasatinib alone as measured by T-cell activation assays and p-SRC levels, respectively. CONCLUSIONSThis method of using functionalized AuNPs to deliver and activate dasatinib in leukemia cells augments drug efficacy while minimizing toxicity and thus represents a novel therapeutic strategy for AML. Ongoing work is underway to characterize the mechanism of preferential AuNP uptake in leukemia cells and assessing in vivo activity using a murine xenotransplantation model of leukemia. DisclosuresNo relevant conflicts of interest to declare.

Probing the Dependence of Electron Transfer on Size and Coverage in Carbon Nanotube–Quantum Dot Heterostructures

As a model system for understanding charge transfer in novel architectural designs for solar cells, double-walled carbon nanotube (DWNT)–CdSe quantum dot (QD) (QDs with average diameters of 2.3, 3.0, and 4.1 nm) heterostructures have been fabricated. The individual nanoscale building blocks were successfully attached and combined using a hole-trapping thiol linker molecule, i.e., 4-mercaptophenol (MTH), through a facile, noncovalent π–π stacking attachment strategy. Transmission electron microscopy confirmed the attachment of QDs onto the external surfaces of the DWNTs. We herein demonstrate a meaningful and unique combination of near-edge X-ray absorption fine structure (NEXAFS) and Raman spectroscopies bolstered by complementary electrical transport measurements in order to elucidate the synergistic interactions between CdSe QDs and DWNTs, which are facilitated by the bridging MTH molecules that can scavenge photoinduced holes and potentially mediate electron redistribution between the conduction bands ...

Thioether-Mediated Degenerative Chain-Transfer Cationic Polymerization: A Simple Metal-Free System for Living Cationic Polymerization

Cationic degenerative chain-transfer polymerization of vinyl ethers and p-alkoxystyrenes was investigated using a series of thioethers as a reversible chain-transfer agent via the equilibrium between a growing carbocationic species and the resulting sulfonium intermediate in the presence of a small amount of triflic acid (TfOH) as a cationogen. The stable thioether, which was easily prepared from isobutyl vinyl ether (IBVE) and n-butanethiol, efficiently controls the molecular weight of the resulting poly(IBVE) up to Mn ∼ 1 × 105 with narrow molecular weight distributions (MWDs) (Mw/Mn ∼ 1.2). Upon increasing the bulkiness of the alkyl substituents in the thiols (R–SH; R: n-Bu < s-Bu < t-Bu) or those in the monomers (CH2═CHOR′, R′: ethyl < isobutyl < cyclohexyl), the MWDs became broader due to the slower formation of the sulfonium intermediate for the degenerative chain-transfer reaction. For p-methoxystyrene, thioethers derived from bulkier alkylthiols or more electron-rich thiophenols are more effective. A silyl-protected difunctional dithioether produced telechelic polymers possessing hydroxyl groups at both chain ends and stable thiol linkers in the middle of the polymer chains. These polymers were subsequently used in chain-extension reactions in conjunction with diisocyanates and diols as chain extenders to be converted into high molecular weight polymers linked via urethane linkages.

A comparative study of electron transport in benzene molecule covalently bonded to gold and silicon electrodes for pioneering the electron transport properties of silicon quantum dot-molecule hybrid polymers

In order to pioneer the electron transport properties of silicon (Si) quantum dot-molecule hybrid polymers, we investigate the electron transport properties of the benzene molecule in silicon (Si) semiconductor electrodes, based on nonequilibrium Green's function (NEGF) method coupled with density functional theory (DFT), in comparison with conventional gold (Au) metal electrodes, with three different anchoring linker groups: thiol for dithiol-benzene (DTB), methylene for dimethyl-benzene (DMB), and direct bonding for benzene (Ph). It is interestingly found that, due to band gap nature of the Si semiconductor electrodes, the molecular junctions with the Si electrodes show no current up to the bias voltage of around 0.8 V. In addition, the DTB molecular junctions in the Si semiconductor electrodes connected with Si–S bond show higher conducting properties than other DMB and Ph molecular junctions directly coupled to the electrodes with the Si–C bonds (DMB < Ph < DTB). The electron transport properties of the molecules in the two different electrodes are analyzed on the basis of the understanding transmission spectra, projected density of states (PDOS), and molecular orbitals. We believe that the use of thiol linker may open new possibility in the molecular electronics with the Si semiconductor electrodes and the Si QD-molecule hybrid polymers concept.