Ru-Fe异金属化合物及其在Au表面上SAM的电化学研究

为使不对称Ru-Fe化合物能在表面上自组装形成单分子膜,对trans-RuCl(dppm)₂(C≡CFc)[Fc=C₅H₄FeC₅H₅,dppm=(C₆H₅)₂PCH₂P(C₆H₅)₂](1)进行修饰,得到Ru(dppm)₂(C≡CFc)(C≡CPhOCH₃)(2),[Ru(dppm)₂(C≡CFc)(N≡CCH₂CH₂NH₂)][PF₆](3)和[Ru(dppm)₂(C≡CFc)(N≡CCH₂CH₂NHC(O)·(CH₂)₁₀SH)][PF₆](4),并详细研究了该系列化合物的电化学性质.循环伏安结果显示出Ru周围配体得失电子能力的差别,直接影响了Ru中心的氧化-还原性,但这种影响并没有通过共轭的炔键传递到二茂铁中的Fe中心.化合物4可以在Au表面上自组装形成稳定、有序的单分子膜.还利用循环伏安法研究了单分子膜的形成过程及其表面覆盖率.     

THE MEASUREMENT OF PLASTIC DEFORMATION AND CRACK GROWTH IN CRACKED SPECIMENS BY SAM

In this paper,scanning acoustic microscope(SAM) was used to obtainsome characteristic photographs which explain the mesoscopic information of severalcracked specimens.New results on subsurface information of steel,nickel andaluminium were presented.Plastic deformation and crack initiation were observed andanalysed.The length of crack propagation was measured.SAM is particularly suited tothe study of many mesoscopic phenomena in material science because it can imagemesoscopic subsurface feature without sectioning.It is revealed that SAM has a brightfuture in the field of mesomechanics.     

Reflection Absorption Infrared Spectroscopy Characterization of SAM Formation from 8-Mercapto-N-(phenethyl)octanamide Thiols with Phe Ring and Amide Groups

Multifunctional amide-containing self-assembled monolayers (SAMs) provide prospects for the construction of interfaces with required physicochemical properties and distinctive stability. In this study, we report the synthesis of amide-containing thiols with terminal phenylalanine (Phe) ring functionality (HS(CH₂)₇CONH(CH₂)₂C₆H₅) and the characterization of the formation of SAMs from these thiols on gold by reflection absorption infrared spectroscopy (RAIRS). For reliable assignments of vibrational bands, ring deuterated analogs were synthesized and studied as well. Adsorption time induced changes in Amide-II band frequency and relative intensity of Amide-II/Amide-I bands revealed two-state sigmoidal form dependence with a transition inflection points at 2.2 ± 0.5 and 4.7 ± 0.5 min, respectively. The transition from initial (disordered) to final (hydrogen-bonded, ordered) structure resulted in increased Amide-II frequency from 1548 to 1557 cm⁻¹, which is diagnostic for a strongly hydrogen-bonded amide network in trans conformation. However, the lateral interactions between the alkyl chains were found to be somewhat reduced when compared with well-ordered alkane thiol monolayers.     

Influence of primary ion species on the secondary cluster ion emission process from SAMs of hexadecanethiol on gold

In order to investigate the secondary cluster ion emission process of organo-metallic compounds under keV ion bombardment, self-assembled monolayers (SAMs) of alkanethiols on gold are ideal model systems. In this experimental study, we focussed on the influence of the primary ion species on the emission processes of gold-alkanethiolate cluster ions from a hexadecanethiol SAM on gold. For this purpose, we carried out time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements using the following primary ion species and acceleration voltages: Ar⁺, Xe⁺, SF₅⁺ (10 kV), Bi⁺, Bi₃⁺(25 kV), Bi₃²⁺, Bi₅²⁺, Bi₇²⁺ (25 kV).It is well known that molecular ions M⁻ and gold-alkanethiolate cluster ions Au_xM_y⁻ with M = S-(CH₂)₁₅-CH₃, x − 3 ≤ y ≤ x + 1, x, y > 0, show intense peaks in negative mass spectra. We derived yields Y_SI exemplarily for the molecular ions M⁻ and the gold-hexadecanethiolate cluster ions Au_y+1M_y⁻ up to y = 8 and found an exponentially decreasing behaviour for increasing y-values for the cluster ions.In contrast to the well-known increase in secondary ion yield for molecular secondary ions when moving from lighter to heavier (e.g. Ar⁺ to Xe⁺) or from monoatomic to polyatomic (e.g. Xe⁺ to SF₅⁺) primary ions, we find a distinctly different behaviour for the secondary cluster ions. For polyatomic primary ions, there is a decrease in secondary ion yield for the gold-hexadecanethiolate clusters whereas the relative decrease of the secondary ion yield ξ_Y with increasing y remains almost constant for all investigated primary ions.     

Engineered SAM Synthetases for Enzymatic Generation of AdoMet Analogs with Photocaging Groups and Reversible DNA Modification in Cascade Reactions

Methylation and demethylation of DNA, RNA and proteins has emerged as a major regulatory mechanism. Studying the function of these modifications would benefit from tools for their site‐specific inhibition and timed removal. S‐Adenosyl‐L‐methionine (AdoMet) analogs in combination with methyltransferases (MTases) have proven useful to map or block and release MTase target sites, however their enzymatic generation has been limited to aliphatic groups at the sulfur atom. We engineered a SAM synthetase from Cryptosporidium hominis (PC‐ChMAT) for efficient generation of AdoMet analogs with photocaging groups that are not accepted by any WT MAT reported to date. The crystal structure of PC‐ChMAT at 1.87 Å revealed how the photocaged AdoMet analog is accommodated and guided engineering of a thermostable MAT from Methanocaldococcus jannaschii. PC‐MATs were compatible with DNA‐ and RNA‐MTases, enabling sequence‐specific modification (“writing”) of plasmid DNA and light‐triggered removal (“erasing”).     

Effect of cavitation intensity control on self-assembling of alkanethiols on gold in room temperature ionic liquids

This study investigates the effect of cavitation intensity on self-assembling of alkanethiol molecules on gold in room temperature ionic liquids (RTILs) under low frequency ultrasound irradiation (20 kHz). The use of RTILs, with low vapor pressure, enabled cavitation activity to be controlled up to quenching through pressure decrease within an argon-saturated atmosphere. This control possibility was used to acquire deeper insights into the role of cavitation on self-assembling processes. It was shown by electrochemical, contact angles and Polarization Modulation - Infrared Reflection Absorption Spectroscopy (PM-IRRAS) measurements that cavitation activates orientation and organization of self-assembled monolayers (SAM). X-ray Photoelectron Spectroscopy (XPS) revealed that, even if chemical adsorption of molecules is highly activated under ultrasound irradiation, it is not dependent on acoustic cavitation intensity.     

Supramolecular nanostructures based on bacterial reaction center proteins and quantum dots

Design of the nanostructures based on membrane proteins (the key functional elements of biomembranes) and colloid nanoparticles is a fascinating field at the interface of biochemistry and colloids, nanotechnology and biomedicine. The review discusses the main achievements in the field of ultrathin films prepared from bacterial reaction center proteins and light-harvesting complexes, as well as these complexes tagged with quantum dots. The principles of preparation of these thin films and their structure and properties at different interfaces are described; as well as their characteristics estimated using a combination of the modern interfacial techniques (absorption and fluorescence spectroscopy, atomic force and Brewster angle microscopy, etc.) are discussed. Further approaches to develop the nanostructures based on the membrane proteins and quantum dots are suggested. These supramolecular nanostructures are promising prototypes of the materials for photovoltaic, optoelectronic and biosensing applications.     

Possible key intermediates in arsenic biochemistry: Synthesis and identification by liquid chromatography electrospray ionization mass spectrometry and high resolution mass spectrometry

Arsenic is a type 1 carcinogen and its toxicity is critically dependent on chemical speciation. However, after decades of research, the biogenesis of at least fifty naturally occurring arsenic species is still not well understood.Here, based on experimental work, it is proposed a set of pathways for the formation of multiple arsenic species that might help to clarify the present situation.These are focused on the thiol protein arsenic bond and on its interaction with reactive metabolites. In fact, arsenic bound to glutathione interacting with sulfur adenosyl methionine (SAM), MethylCB₁₂ and AdoCB₁₂, forms a number of complexes that might be key intermediates in arsenic biochemistry. These include dimethylarsino glutathione (DMAG) m/z 412 [M + H]⁺, synthesized non-enzymatically from glutathione and cacodylate. Trimethylarsonio glutathione (TMAG) m/z 426 [M]⁺ synthesized from DMA, GSH and SAM, apparently by a classical Challenger methylcarbonium attack. Tetramethyl arsonium ion m/z 135 [M]⁺ is formed in a third step, apparently by carbanion methylation. The presence of trimethylarsine oxide (TMAO) m/z 137 [M + H]⁺ is attributed to the hydrolysis of TMAG or TMA, or to carbanion methylation of dimethylarsinoyl glutathione (m/z 428 [M]⁺) formed from cacodylate and GSH. Cantoni type attacks of DMAG on SAM were unsuccessful, eventually due to competition of the trivalent S⁺ atom of SAM for the As^III atom attack. The presence of dimethylarsonio diglutathione (DMADG m/z 717 [M]⁺), is suggested to result from a GS^- attack on dimethylarsenoyl glutathione (m/z 428 [M + H]⁺). The presence of dimethylarsenoyladenosine (m/z 372 [M + H]⁺), trimethylarsenosugar adenine (m/z 370 [M]⁺), and dimethylthioarsenosugar adenine (m/z 388 [M + H]⁺), is explained by the synthesis of the pecursor dimethylarsonio-adenosine glutathione DMAAG (m/z 661 [M]⁺), a likely source of oxo-and trimethylated arsenosugars, as well as of thio-arsenosugars by the cleavage of its S-C bond. The results gathered suggest that cell vacuoles might play a major role in arsenic metabolism, and that the dominance of oxo-As sugars, in algae extracts, may be supported by a mechanism of synthesis independent of DMAAG (m/z 661).They also offer an explanation for the reason why arsenobetaine, and tetramethylarsonium are loosely bound to biotic tissues. Four arsenic species new to science, to the best of our knowledge, and a number of known arsenic compounds were synthesized in this work, identified by HPLC–ESI-MSⁿ and FTICR–ESI-MS, and suggestions regarding their mechanisms of synthesis were advanced. These results provide a framework for arsenic biochemistry which may explain the origin of a significant part of arsenic known metabolites.     

A Sensitive Nanoporous Gold-Based Electrochemical DNA Biosensor for Escherichia coli Detection

A sensitive electrochemical DNA biosensor based on a mixed monolayer structure self-assembled at nanoporous gold (NPG) electrode surface was prepared for Escherichia coli (E. coli) detection. The NPG was fabricated on gold electrode, onto which thiolated oligonucleotides (SH-DNA) and mercaptohexanol (MCH) were covalently linked forming a mixed self-assembled monolayer (SAM). The hybridization between the SH-DNA/MCH modified biosensor and E. coli DNA was monitored with differential pulse voltammetry measurement using methylene blue (MB) as the hybridization indicator. The biosensor can detect 1 × 10^?12 M DNA target and 50 cfu/μL E. coli without any nucleic acid amplification steps. The detection limit was lowered to 50 cfu/mL after 5.0 h of incubation.