Sandwich Complexes Research Articles

Simultaneous detection method for two cardiac disease protein biomarkers on a single chip modified with mixed aptamers using surface plasmon resonance

A simultaneous detection method for two cardiac disease protein biomarkers present in serum samples on a single planar gold chip using surface plasmon resonance (SPR) is described. The detection of N-terminal pro-brain natriuretic peptide (NT-proBNP) and tumor necrosis factor α (TNF-α), which are known as acute myocardial infarction (AMI) biomarkers, with predetermined clinically relevant concentrations was performed using mixed aptamers specific to each protein tethered on a single gold surface. After the binding of NT-proBNP and/or TNF-α to the mixed aptamers, an antibody specific to each target protein was injected to form a surface sandwich complex to improve selectivity. In order to adjust the dynamic ranges in the known clinically relevant concentration significantly different for NT-proBNP (0.13–0.24 nM) and TNF-α (0.5–3 pM), the surface density ratios of the corresponding pair of aptamer and antibody were first systematically determined, which were the 1:1 mixed aptamer chip with 40 nM anti-NT-proBNP and 100 nM anti-TNF-α. This allowed to establish the distinct dynamic ranges of 0.05–0.5 nM for NT-proBNP and 0.1–5 pM for TNF-α in a buffer, along with detection and quantification limits of 0.03 and 0.19 nM for NT-proBNP and 0.06 and 0.21 pM for TNF-α, respectively. The changes in refractive unit (RU) values observed when exposing both proteins at different concentrations alongside the corresponding fixed concentration of antibodies onto the 1:1 mixed aptamer chip were then correlated to the sum of RU values measured when using the injection of individual protein for evaluating each protein concentration. With a complete characterization of the simultaneous quantification of two protein concentrations in the buffer, the mixed aptamer chip was finally employed for direct measurements of NT-proBNP and TNF-α concentrations in undiluted serum samples from healthy controls and AMI patients. The results of simultaneous SPR measurements for the two proteins in the serum samples were further compared to the individual protein concentration results using an enzyme-linked immunosorbent assay.

Homoleptic Transition Metal Carbonyl Cations: Synthetic Approaches, Characterization and Follow-Up Chemistry.

ConspectusCarbon monoxide, CO, is one of the most important ligands in organometallic chemistry. It is an excellent π-acceptor and a moderate σ-donor. Therefore, most of the known transition metal carbonyls (TMCs) exhibit a zerovalent or even negative metal oxidation state (OS) of up to -4. However, given the right conditions, the carbonyl ligand also forms homoleptic cationic complexes with one or more transition metal atoms, the transition metal carbonyl cations (TMCCs), known with an OS of up to +3. Despite their long-standing history upon discovery of the first [M(CO)6]+ examples (M = Mn, Tc, Re) by E. O. Fischer in 1962 as well as their very fundamental nature, it took until the 1990s for the scope to be widened by Aubke, Strauss and Willner. Yet, many potential TMCC entries known from gas-phase mass spectrometry work remained unknown on preparative grounds. This is due to their high reactivity, which puts scientists to new challenges and encourages the development of suitable solvents, anions and oxidants, to cope with the demands of these fundamental salts─later referred to as pseudo-gas-phase conditions and innocent deelectronators and solvents.Hence, the utilization of extremely weakly coordinating perfluorinated alkoxyaluminates [Al(ORF)4]- and [F{Al(ORF)3}2]- (ORF = -OC(CF3)3) in combination with the polar but non- or weakly coordinating innocent solvents 1,2-difluorobenzene (oDFB) and 1,2,3,4-tetrafluorobenzene (TFB) yielded the first TMCC salts containing heptacoordinate [M(CO)7]+ (M = Nb, Ta) as well as paramagnetic [M(CO)6]+· (M = Cr, Mo, W) or [Ni(CO)4]+·. However, the use of typical inorganic oxidants Ag+, [NO]+ and Ag+/0.5 I2 regularly led to unwanted side reactions. For example, the Lewis acidic silver(I) cations form Lewis pairs with various Lewis basic TMCs yielding partly clustered [Agx{TMC}y]x+ complex salts, while nitrosonium cations may substitute for carbonyl ligands, forming [M(CO)x-1(NO)]+ complexes. The synergistic oxidizing reagent Ag+/0.5 X2 can add halonium ions X+ to the TMCs (X = Cl, Br, I). This prevented the synthesis of univalent group 8 TMCC salts. Yet, the application of radical cation salts of perfluorinated arenes as innocent deelectronators finally yielded salts of [Fe(CO)5]+· and [M3(CO)14]2+ (M = Ru, Os).TMCC salts are excellent starting materials, and the reaction of [Co(CO)5]+ and [Ni(CO)4]+· with benzene led to the previously unknown bis(benzene) sandwich complexes [Co(benzene)2]+ and [Ni(benzene)2]+·. Under the right conditions, even the very weakly bound oDFB-complex salts with [M(oDFB)2]+ (M = Co, Ni) cations form, useful as naked metal(I) synthons and for small-molecule activation.

Three Oxidative Addition Routes of Alkali Metal Aluminyls to Dihydridoaluminates and Reactivity with CO2.

Three distinct routes are reported to the soluble, dihydridoaluminate compounds, AM[Al(NONDipp )(H)2 ] (AM=Li, Na, K, Rb, Cs; [NONDipp ]2- =[O(SiMe2 NDipp)2 ]2- ; Dipp=2,6-iPr2 C6 H3 ) starting from the alkali metal aluminyls, AM[Al(NONDipp )]. Direct H2 hydrogenation of the heavier analogues (AM=Rb, Cs) produced the first examples of structurally characterized rubidium and caesium dihydridoaluminates, although harsh conditions were required for complete conversion. Using 1,4-cyclohexadiene (1,4-CHD) as an alternative hydrogen source in transfer hydrogenation reactions provided a lower energy pathway to the full series of products for AM=Li-Cs. A further moderation in conditions was noted for the thermal decomposition of the (silyl)(hydrido)aluminates, AM[Al(NONDipp )(H)(SiH2 Ph)]. Probing the reaction of Cs[Al(NONDipp )] with 1,4-CHD provided access to a novel inverse sandwich complex, [{Cs(Et2 O)}2 {Al(NONDipp )(H)}2 (C6 H6 )], containing the 1,4-dialuminated [C6 H6 ]2- dianion and representing the first time that an intermediate in the commonly utilized oxidation process of 1,4-CHD to benzene has been trapped. The synthetic utility of the newly installed Al-H bonds has been demonstrated by their ability to reduce CO2 under mild conditions to form the bis-formate AM[Al(NONDipp )(O2 CH)2 ] compounds, which exhibit a diverse series of eyecatching bimetallacyclic structures.

Recent advancement in surface modification of aramid fiber assisted by supercritical carbon dioxide

AbstractThe exceptional mechanical properties of aramid fibers make them a popular choice for high‐performance materials; despite that, their potential is limited due to their surface properties bonding energy and interfacial bonding strength with matrix materials. The enhanced resistance of poly‐aramid fibers (AFs) to severe surroundings and improved interlaminar adhesion in sandwich compounds with admirable mechanical characteristics are becoming a great challenge for various chemical and physical surface treatment techniques. Supercritical carbon dioxide (scCO2) is a popular and sustainable approach that can effectively bond and homogeneously deposit functional groups or nanoparticles and exhibit the excellent performance of fibber modification. This article examines aramid fibers' surface modification advancements using scCO2‐assisted techniques, including monomer grafting, impregnation, and functionalization with various functional groups and nanoparticles. Additionally, the article discusses the challenges faced in scCO2‐assisted aramid fiber modification and what the future holds for this technology.

Catalytic Undirected Meta-Selective C-H Borylation of Metallocenes.

Metallocenes are privileged backbones in the fields of synthetic chemistry, catalysis, polymer science, etc. Direct C-H functionalization is undoubtedly the simplest approach for tuning the properties of metallocenes. However, owing to the presence of multiple identical C(sp2 )-H sites, this protocol often suffers from low reactivity and selectivity issues, especially for the regioselective synthesis of 1,3-difunctionalized metallocenes. Herein, an efficient iridium-catalyzed meta-selective C-H borylation of metallocenes is reported. With no need of preinstalled directing groups, this approach enables a rapid synthesis of various boronic esters based on benzoferrocenes, ferrocenes, ruthenocene, and related half sandwich complex. A broad range of electron-deficient and -rich functional groups are all compatible with the process. Notably, C-H borylation of benzoferrocenes takes place exclusively at the benzene ring, which is likely ascribed to the shielding effect of pentamethylcyclopentadiene. The synthetic utility is further demonstrated by easy scalability to gram quantities, the conversion of boron to heteroatoms including N3 , SePh, and OAc, as well as diverse cross-coupling reactions.

Chemists roll out rings made from stacked sandwich complexes

Chemists roll out rings made from stacked sandwich complexes

Engineering Entropy-Driven Nanomachine-Mediated Morphological Evolution of Anisotropic Silver Triangular Nanoplates for Colorimetric and Photothermal Biosensing.

A DNA/RNA biosensor capable of single nucleotide variation (SNV) resolution is highly desirable for drug design and disease diagnosis. To meet the point-of-care demand, rapid, cost-effective, and accurate SNV detection is of great significance but still suffers from a challenge. In this work, a unique nonenzymatic dual-modal (multicolorimetric and photothermal) visualization DNA biosensor is first proposed for SNV identification on the basis of an entropy-driven nanomachine with double output DNAs and coordination etching of anisotropic silver triangular nanoplates (Ag TNPs). When the target initiates the DNA nanomachine, the liberated multiple output DNAs can be utilized as a bridge to produce a superparamagnetic sandwich complex. The incoming poly-C DNA can coordinate and etch highly active Ag+ ions at the tips of Ag TNPs, causing a shift in the plasmon peak of Ag TNPs from 808 to 613 nm. The more target DNAs are introduced, the more output DNAs are released and thus the more Ag+ ions are etched. The noticeable color changes of anisotropic Ag TNPs can be differentiated by "naked eye" and accurate temperature reading. The programmable DNA nanotechnology and magnetic extraction grant the high specificity. Also, the SNV detection results can be self-verified by the two-signal readouts. Moreover, the dual-modal biosensor has the advantages of portability, cost-effectiveness, and simplicity. Particularly, the exclusive entropy-driven amplifier liberates double output DNAs to bridge more poly-C DNAs, enabling the dual-modal visualization DNA biosensor with improved sensitivity.

Synthesis and properties of cyclic sandwich compounds.

Cyclic nanometre-scale sandwich complexes assembled from individual building blocks were synthesized. Sandwich complexes, in which a metal ion is π-coordinated by two planar aromatic organic rings belong to the foundations of organometallic chemistry. They have been successfully used in a wide variety of applications ranging from catalysis, synthesis and electrochemistry to nanotechnology, materials science and medicine1,2. Extending the sandwich structural motif leads to linear multidecker compounds, in which aromatic organic rings and metal atoms are arranged in an alternating fashion. However, the extension to a cyclic multidecker scaffold is unprecedented. Here we show the design, synthesis and characterization of an isomorphous series of circular sandwich compounds, for which the term 'cyclocenes' is suggested. These cyclocenes consist of 18 repeating units, forming almost ideally circular, closed rings in the solid state, that can be described by the general formula [cyclo-MII(μ-η8:η8-CotTIPS)]18 (M = Sr, Sm, Eu; CotTIPS = 1,4-(iPr3Si)2C8H62-). Quantum chemical calculations lead to the conclusion that a unique interplay between the ionic metal-to-ligand bonds, the bulkiness of the ligand system and the energy gain on ring closure, which is crucially influenced by dispersion interactions, facilitate the formation of these cyclic systems. Up to now, only linear one-dimensional multidecker sandwich compounds have been investigated for possible applications such as nanowires3-10. This textbook example of cyclic sandwich compounds is expected to open the door for further innovations towards new functional organometallic materials.

Dual Signal Amplification by Urease Catalysis and Silver Nanoparticles for Ultrasensitive Colorimetric Detection of Nucleic Acids.

Signal amplification techniques are highly desirable for the analysis of low-level targets that are closely related with diseases and the monitoring of important biological processes. However, it is still challenging to achieve this goal in a facile and economical way. Herein, we developed a novel dual signal amplification strategy by combining urease catalysis with the release of Ag+ from silver nanoparticles (AgNPs). This strategy was used for quantifying a DNA sequence (HIV-1) related with human immunodeficiency virus (HIV). DNA target HIV-1 hybridizes with the capture DNA probe on magnetic beads and the reporter DNA probe on AgNPs, forming a sandwich complex. The captured AgNPs are then transformed into numerous Ag+ ions that inactivate numerous ureases. Without catalytic production of ammonia from urea, the substrate solution shows a low pH 5.8 that will increase otherwise. The pH change is monitored by a pH indicator (phenol red), which allows for colorimetric detection. The proposed approach is sensitive, easy to use, economic, and universal, exhibiting a low detection limit of 9.7 fM (i.e., 1.94 attomoles) and a dynamic linear range of 4 orders for HIV-1 sequence detection.

B7 Be6 B7 : A Boron-Beryllium Sandwich Complex.

Planar boron clusters have often been regarded as "π-analogous" to aromatic arenes because of their similar delocalized π-bonding. However, unlike arenes such as C5 H5 - and C6 H6 , boron clusters have not previously shown the ability to form sandwich complexes. In this study, we present the first sandwich complex involving beryllium and boron, B7 Be6 B7 . The global minimum of this combination adopts a unique architecture having a D6h geometry, featuring an unprecedented monocyclic Be6 ring sandwiched between two quasi-planar B7 motifs. The thermochemical and kinetic stability of B7 Be6 B7 can be attributed to strong electrostatic and covalent interactions between the fragments. Chemical bonding analysis shows that B7 Be6 B7 can be considered as a [B7 ]3- [Be6 ]6+ [B7 ]3- complex. Moreover, there is a significant electron delocalization within this cluster, supported by the local diatropic contributions of the B7 and Be6 fragments.

B7Be6B7: A Boron‐Beryllium Sandwich Complex

AbstractPlanar boron clusters have often been regarded as “π‐analogous” to aromatic arenes because of their similar delocalized π‐bonding. However, unlike arenes such as C5H5− and C6H6, boron clusters have not previously shown the ability to form sandwich complexes. In this study, we present the first sandwich complex involving beryllium and boron, B7Be6B7. The global minimum of this combination adopts a unique architecture having a D6h geometry, featuring an unprecedented monocyclic Be6 ring sandwiched between two quasi‐planar B7 motifs. The thermochemical and kinetic stability of B7Be6B7 can be attributed to strong electrostatic and covalent interactions between the fragments. Chemical bonding analysis shows that B7Be6B7 can be considered as a [B7]3−[Be6]6+[B7]3− complex. Moreover, there is a significant electron delocalization within this cluster, supported by the local diatropic contributions of the B7 and Be6 fragments.

Orientational Isomerism and Its Reactivity of a Main Group Sandwich Anion [Ge9‐In‐Ge9]5–

Comprehensive SummaryTwo isomers of a sandwich‐type anion [Ge9‐In‐Ge9]5– were synthesized by controlling the chelating agents (2,2,2‐crypt/18‐C‐6). Further reactions with early/late transition metal complexes, Mo(CO)6 and Ni(COD)2, respectively, yielded two new types of inorganic sandwich derivatives: a half‐sandwich cluster [Ge9‐In‐Mo(CO)5]3– with a low‐valence In(I) center and an unsymmetrical sandwich‐type cluster {[(Ni@Ge9)In(Ni0.648@Ge9)]}5– due to the insertion of Ni atoms, respectively. The isolation of these new derivatives demonstrates the reactivity of sandwich‐type [Ge9‐In‐Ge9]5– acting as the precursor, which provides some enlightenment for constructing new inorganic sandwich compounds.

Schiff base functionalized 1,2,3-triazole derivative for Fe(III) ion recognition, as N,O,O-Fe-O,O,N sandwich complex: DFT analysis

The present research aims to synthesize Schiff base tethered 1,2,3-triazole derivative using Cu(I) catalyzed click reaction as a highly sensitive and selective optical chemosensor for the recognition of ferric ions. The synthesized probe was characterized using Fourier transform infrared spectroscopy (FTIR), NMR (1H and 13C), mass spectrometry, CHN analysis, and Thermal gravimetric analysis (TGA). The UV–vis spectroscopy was employed in eco-friendly EtOH:H2O (9:1 v/v) solvent media to investigate the optical properties of the developed chemosensor SBT, the association constant and limit of detection of Fe3+ was determined to be 2.6 × 104 M- 1 and 1.3 × 10-7 M establishing the designed SBT as a potent probe for analytical and practical applications. Additionally, the time-dependent study and pH sensitivity of the developed probe SBT and metal–ligand complex were also studied via UV–visible spectroscopy. Besides, FTIR spectra and TGA curve of the synthesized (SBT-metal complex) confirmed the binding of the metal–ligand complex. Furthermore, the real sample application for detection of Fe3+ in spinach (food rich in Iron) was analysed, and the SBT-based sensing system yielded a recovery rate of greater than 99.07%. The synthesized probe was also explored for its computational-based DFT studies via Gaussian 09 programs using the DFT method with (B3LYP)/-311G (d,p) basis set of hybrid density functional theory.

How Do Face-to-Face Stacked Aromatic Rings Activate Each Other to Electrophilic Aromatic Substitution?

We have found that face-to-face π-stacked aromatic rings show the propensity to activate one another toward electrophilic aromatic substitution through direct influence of the probe aromatic ring by the adjacent stacked ring, rather than through the formation of relay or "sandwich complexes." This activation remains in force even when one of the rings is deactivated through nitration. The resulting dinitrated products are shown to crystallize in an extended parallel offset stacked form, in stark contrast to the substrate.

Thienyl-Substituted Diboranes(4): Electronic Stabilization of Radicals Versus Increased Reactivity towards Bond Activation.

Low-valent main group chemistry involves a balancing act between steric and electronic stabilization of the electron-rich low oxidation state main group centers and their desired reactivity. Herein we show that the combination of sterically shielding mesityl and rotationally flexible 2-thienyl groups, the latter having the potential to be either electronically stabilizing or activating, at a diborane(4) provides a platform for both radical anion stabilization and unusual bond activation and rearrangement reactions. The addition of a Lewis base to a 1,2-dimesityl-1,2-dithienyldiborane(4) (1) results in direct and unprecedented C-H borylation of one thienyl substituent with cleavage of the B-B bond. The facile one-electron reduction of 1 yields a stable diboron radical anion through delocalization of its unpaired electron over the entire planar 1,2-dithienyldiboron framework, as evidenced by EPR spectroscopy and DFT calculations. The two-electron reduction of 1 with magnesium anthracene under more forcing conditions results in B-B bond cleavage and replacement of one thienyl sulfur atom by a mesitylboron moiety, leading to the formation of a magnesium complex of an η5 -diborafulvene dianion. Salt metathesis of the latter with [(η6 -p-cymene)RuCl2 ] affords a mixed ruthenium sandwich complex of an η5 -borylborole dianion. Calculations highlight both the structural and electronic changes in the boron-substituted heterocyclic C4 B dianion upon switching coordination from magnesium (diborafulvene dianion) to ruthenium (borylborole dianion).

Rhenium Biscorrole Sandwich Compounds: XAS Evidence for a New Coordination Motif.

The interaction of three free-base meso-tris(p-X-phenyl)corroles H3[TpXPC] (X = H, CH3, OCH3) with Re2(CO)10 at 235 °C in the presence of K2CO3 in o-dichlorobenzene has led to putative rhenium biscorrole sandwich compounds with the formula ReH[TpXPC]2. Density functional theory calculations and Re L3-edge extended X-ray absorption fine structure measurements suggest a seven-coordinate metal center, with the "extra" hydrogen located on one of the corrole nitrogens. The complexes can be deprotonated by a base such as 1,8-diazabicyclo[5.4.0]undec-7-ene, resulting in a substantial sharpening of the UV-vis spectra and split Soret bands, consistent with the generation of C2-symmetric anions. Both the seven-coordinate neutral and eight-coordinate anionic forms of the complexes represent a new coordination motif in the field of rhenium-porphyrinoid interactions.

Dynamic Magnetic Properties of Germole-ligated Lanthanide Sandwich Complexes.

The first germole-ligated single-molecule magnets are reported, with contrasting properties found for the near-linear sandwich complexes [(η8 -COT)Ln(η5 -CpGe ]- , where Ln=Dy (1Dy ) or Er (1Er ), COT is cyclo-octatetraenyl and CpGe is [GeC4 -2,5-(SiMe3 )2 -3,4-Me2 ]2- . Whereas 1Er has an energy barrier of 120(1) cm-1 in zero applied field and open hysteresis loops up to 10 K, the relaxation in 1Dy is characterized by quantum tunneling within the ground state.

Polynuclear sandwich derivatives of [10]annulene: A quantum chemical study

Density-functional theory (DFT) calculations at B3LYP/6-311+G(df,p) and M06/6-311+G(df,p) levels of theory predict the stability of new polynuclear sandwich complexes [Cu5(C10H10)2]+ and Ni5(C10H10)2 based on flat [10]annulene cycles.

Ferrocenoyl-substituted quinolinone and coumarin as organometallic inhibitors of SARS-CoV-2 3CLpro main protease.

The 3-chymotrypsin-like protease 3CLpro from severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is a potential target for antiviral drug development. In this work, three organometallic ferrocene-modified quinolinones and coumarins were compared to their benzoic acid ester analogues with regard to inhibition of 3CLpro using an HPLC-based assay with a 15mer model peptide as the substrate. In contrast to FRET-based assays, this allows direct identification of interference of buffer constituents with the inhibitors, as demonstrated by the complete abolishment of ebselen inhibitory activity in the presence of dithiothreitol as a redox protectant. The presence of the organometallic ferrocene moiety significantly increased the stability of the title compounds towards hydrolysis. Among the studied compounds, 4-ferrocenyloxy-1-methyl-quinol-2-one was identified as the most stable and potent inhibitor candidate. IC50 values determined for ebselen and this sandwich complex compound are (0.40±0.07) and (2.32±0.21) μM, respectively.

Frontispiece: Molecular Lanthanide Switches for Magnetism and Photoluminescence

Sandwich Compounds. Molecular lanthanide switches for magnetism and photoluminescence based on the distortion of the ligand sphere upon solvation are reported by Eufemio Moreno-Pineda, Mario Ruben, Peter W. Roesky in their Research Article (e202218107).