Synthesis Of Cp Research Articles

Preparation and properties of polyvinyl alcohol/chitosan-based hydrogel with dual pH/NH3 sensor for naked-eye monitoring of seafood freshness

To address the issue of food spoilage causing health and economic loss, we developed a pH/NH3 dual sensitive hydrogel based on polyvinyl alcohol/chitosan (PVA/CS) containing chitosan-phenol red (CP). The CP was synthesized via Mannich reaction and immobilized it in PVA/CS hydrogel through freezing/thawing method to prepare the final PVA/CS/CP hydrogel. The synthesis of CP was confirmed by 1H NMR, FT–IR, XRD, UV–vis, and XPS. The characteristics of hydrogel were evaluated by FT–IR, XRD, SEM, mechanical properties, thermal stability, leaching, and color stability tests. The PVA/CS/CP hydrogel showed distinctly different color at various pH and NH3 vapor levels (yellow to purple). The hydrogel exhibited obvious color changes (ΔE = 46.95) in response to shrimp spoilage, stored at 4 °C. It showed positive and strong correlation between the ΔE values of the indicator hydrogel and total volatile basic nitrogen (TVB-N) as (R2 = 0.9573) and with pH as (R2 = 0.8686), respectively. These results clearly show that the PVA/CS/CP hydrogel could be applied for naked-eye real-time monitoring of seafood freshness in intelligent packaging.

Synthetic investigations of the diisocyanide‐bridged Cp*‐cobalt rectangles

AbstractThis study explores the utilization of 1,4‐diisocyanobenzene as a linear bridging ligand for the assembly of organometallic CpCo or Cp*Co complexes. Overcoming solubility challenges, the synthesis of organometallic Cp* cobalt complexes incorporating bridging 1,4‐diisocyanobenzene ligands was successfully achieved, while similar CpCo complexes were not attainable. The presented approach encompasses investigations into both stepwise and self‐assembly synthetic pathways, leading to the construction of a rectangular tetranuclear complex [(Cp*CoI)4(μ‐1,4‐CNC6H4NC)4](OTf)4 (3). Through single‐crystal x‐ray diffraction and spectroscopic techniques such as infrared, nuclear magnetic resonance, and electrospray ionization‐mass spectrometry, the cobalt‐isocyanides complexes were characterized.

Reactions of (mesityl)n(methyl)2-nsilylene complexes with pyridine-N-oxide (n = 1 and 0): formation of silanone complexes and a disiloxanyloxy complex.

Silanones (OSiR2), a heavier congener of ketones (R2CO), are highly reactive species that are readily converted to oligomeric siloxane (O-SiR2)n. Coordination of silanones to the transition-metal fragments to afford silanone-coordinated complexes is a reliable silanone stabilization method. Recently, our group reported the synthesis, structures, and reactivity of dimesityl-substituted silanone complexes Cp*(OC)2M{OSiMes2(L)}(SiMe3) (M = W, Mo, L: Lewis base, Cp*: η5-C5Me5, Mes: 2,4,6-Me3C6H2). Herein, to investigate the effect of substituents on the silicon atom during the formation of a silanone complex, we demonstrated the use of Mes and smaller Me groups. As a result, the formation of Mes(Me)-substituted silanone molybdenum complex Cp*(OC)2Mo{OSiMes(Me)(py)}(SiMe3) (5b, py: pyridine) was suggested, the silanone tungsten complex Cp*(OC)2W{OSiMes(Me)(DMAP)}(SiMe3) (4a, DMAP: 4-(dimethylamino)pyridine) was obtained, and a dimethyl-substituted disiloxanyloxy(dioxo) complex Cp*(O)2W(OSiMe2OSiMe3) (9) was formed. The reaction of 4a with PMe3 proceeded via the elimination of DMAP and migration of the SiMe3 group to the oxygen atom of the silanone ligand to afford Cp*(OC)2W(SiMes(Me)OSiMe3)(PMe3) (11a). The Mo complex Cp*(OC)2Mo(SiMes(Me)OSiMe3)(PMe3) (11b) was produced by the reaction of Cp*(OC)2Mo{SiMes(Me)}(SiMe3) (7b) with pyridine-N-oxide in the presence of PMe3.

PKa of alcohols dictates their reactivity with reduced uranium-substituted thiomolybdate clusters.

The uranium-substituted thiomolybdate cluster, (Cp*3Mo3S4)UCp*, has been demonstrated as a model for water reduction by single uranium atoms supported on a molybdenum sulfide surface (U@MoS2). In this study, the scope of O-H bond activation is expanded through the investigation of the reactivity of various alcohols with differing pKa values for the -OH proton. The reaction of (Cp*3Mo3S4)UCp* with stoichiometric amounts of methanol, phenol, 2,6-dichlorophenol, and nonafluoro-tert-butyl alcohol affords the corresponding mono-alkoxide species, (Cp*3Mo3S4)Cp*U(OR), via a uranium-metalloligand cooperative activation of the O-H bond. This observed reactivity is analogous to the O-H bond activation reported by (Cp*3Mo3S4)UCp* in the presence of water. However, addition of tert-butanol induces protonolysis of the Cp* ligand on uranium, resulting in the formation of a uranium tris-tert-butoxide cluster, (Cp*3Mo3S4)U(OtBu)3. Independent synthesis of (Cp*3Mo3S4)Cp*U(OtBu) was possible via an alternative pathway, eliminating sterics as a justification for the observed discrepancy in reactivity. These results offer insight into the role the -OH proton pKa plays in dictating the mechanism of O-H bond activation of alcohols by the uranium-substituted thiomolybdate cluster.

Synthesis and near-infrared photothermal conversion of Cp*Rh-based [2]-catenanes in trapezoidal metallacycles

Minor differences among pyridine ligands led to [2]-catenanes with dramatically different stacking modes of the building blocks, which facilitated the production of assemblies with different photothermal conversion abilities.

Size-controlled synthesis and near-infrared photothermal response of Cp* Rh-based metalla[2]catenanes and rectangular metallamacrocycles

A variety of research reports on novel supramolecular topologies have been published over the last years. However, it is still a great challenge to tap into the inner functional properties of these complexes. Herein, two tetranuclear metallamacrocycles 1 and 2 and four octonuclear [2]catenanes 3–6 were constructed successfully via a coordination-driven self-assembly strategy, by conscious design and use of the tetramethyl bidentate pyridine ligand L1, and the appropriate selection of six binuclear half-sandwich rhodium building units with different longitudinal dimensions. The complexes have been fully characterized by single crystal X-ray diffraction analysis and NMR spectroscopy. Furthermore, near-infrared photothermal studies of the obtained [2]catenanes reveal different photothermal response in solid and solution states, which may be attributed to a strong fluorescence quenching effect of the half-sandwich organometallic fragment and different conjugated effect of Cp*Rh based building blocks in the interlocking structures. The photothermal conversion efficiencies of [2]catenanes 4–6 fall in the range 30.5%–16.5% respectively. This contribution aims to play a key role in the experimental development of Cp*-based photothermal materials.

On the Reactivity of Mes*P(PMe3 ) towards Aluminum(I) Compounds - Evidence for the Intermediate Formation of Phosphaalumenes.

Phosphaalumenes are the heavier isoelectronic analogs of alkynes and have eluded facile synthesis until recently. We have reported that the combination of a phosphinidene transfer agent, Ar TerP(PMe3 ) (Ar Ter=2,6-Ar2 -C6 H3 ), with (Cp*Al)4 (Cp*=C5 (CH3 )5 ) afforded the phosphaalumenes Ar TerPAlCp* as isolable, violet, thermally stable compounds. In here we describe attempts to utilize Mes*P(PMe3 ) (Mes*=2,4,6-tBu3 -C6 H2 ) as a phosphinidene source in combination with different Al(I) precursors, namely Dip NacnacAl (Dip Nacnac=HC[C(Me)NDip]2 , Dip=2,6-iPr2 -C6 H3 ), (Cp*Al)4 and Cp3t Al (Cp3t =1,2,4-tBu3 -C5 H2 ). In all cases the formation of phosphaalumenes was not observed, however, their intermediate formation is indicated by formation of the dimer [Cp*Al(μ-PMes*)]2 (2) and C-H-bond activation products along the putative P=Al bond, giving unusual 1,2-P,Al-tetrahydronaphtalene derivatives 1 and 4, clearly underlining the role the sterically demanding group on phosphorus plays in these transformations. The reactivity studies are supported by theoretical studies, demonstrating a thermodynamic preference for the C-H activation products. Additionally, we show that there are potential pitfalls in the synthesis of Cp*2 AlH, the precursor to make (Cp*Al)4 and give recommendations how to circumvent these.

Synthesis, characterization, and structure determination of Cp*Ir(dpms)Cl

Bipyridyl ligands are commonplace in catalysis. Structurally similar to this ligand class with unique properties is the novel di-(2-pyridyl)methanesulfonate (dpms) ligand, which is prepared and reacted with [Cp*IrCl2]2 to afford Cp*Ir(dpms)Cl (1) in high yield. Its single-crystal X-ray structure indicates an exo–(κ2) conformation of the ligand, with the sulfonate group directed away from the iridium center. Halogen exchange by treatment of 1 with NaI gives the iodide derivative, Cp*Ir(dpms)I (2). Abstraction of the halogen from 1 using AgPF6 generates [Cp*Ir(dpms)]PF6 (3), which was not found to activate the CH bonds of benzene.

A preliminary study on the synthesis of biogenic derived hydroxyapatite /medicinal plant extracts composite for potential bone tissue engineering applications

The bone minerals of Hydroxyapatite (Ca10(PO4)6OH2, HAP) are widely utilized in bone repair because of its close similarity to human hard tissues like bone and teeth. HAP has good biocompatible and osteoconductive properties. Naturally derived HAP materials have been widely used in various fields of biomedical applications like filling bones and coating in orthopedics and dental implantation. Hydroxyapatite has considerable mechanical properties, bioactivity, nontoxicity and does not cause any allergic reaction when placed inside the body. To develop an antimicrobial composite for the enhancement of the properties in the tissue engineering applications, HAP powders were prepared by refluxing the cuttlebone (Cb) with diammonium hydrogen phosphate. To the obtained Cb-HAP powders, Carica papaya (Cp) leaf extract was mixed under ultrasonic irradiation techniques to form the Cp induced Cb-HAP composite. Thus, the present work is a preliminary study on the synthesis of Cb-HAP powders and Cp induced Cb-HAP composite for tissue engineering applications. Furthermore, the phase structure and functional group analysis of the prepared composites were investigated through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR). The morphology of the prepared composite was evaluated by using the Scanning electron microscope (SEM). In addition, the antibacterial activities of the composites were investigated against gram positive and gram-negative pathogens such as E. coli and S. aureus through disc diffusion method. From the obtained results, it can be clear that the Cp induced Cb-HAP exhibited enhanced bacterial inhibition. The observed physicochemical and antibacterial activity suggest that the Cp induced Cb-HAP composite can serve as potential biocomposite for bone tissue engineering applications.

Inhibition of Sphingosine Kinase Activity Enhances Immunogenic Cell Surface Exposure of Calreticulin Induced by the Synthetic Cannabinoid 5-epi-CP-55,940.

Background: Endogenous and synthetic cannabinoids have been shown to induce cancer cell death through the accumulation of the sphingolipid, ceramide (Cer). Recently, we have demonstrated that Cer accumulation enhances the induction of immunogenic cell death (ICD). Objectives: The primary objective of this study was to demonstrate that (±) 5-epi CP 55,940 (5-epi), a by-product of the chemical synthesis of the synthetic cannabinoid CP 55,940, induces ICD in colorectal cancer (CRC) cells, and that modulation of the sphingolipid metabolic pathway through inhibition of the sphingosine kinases (SphKs) enhances these effects. Methods: A cell culture model system of human CRC cell lines was employed to measure the cell surface and intracellular production of markers of ICD. The effects of 5-epi, alone and in combination with SphK inhibitors, on production of Cer through the de novo sphingolipid synthesis pathway were measured by Liquid Chromatography - Tandem Mass Spectrometry (LC/MS/MS)-based sphingolipidomic analysis. Cell surface exposure of calreticulin (ectoCRT), a hallmark of ICD, was measured by flow cytometry. Examination of the effects of 5-epi, alone and in combination with SphK inhibitors, on the intracellular signaling pathway associated with ICD was conducted by immunoblot analysis of human CRC cell lines. Results: Sphingolipidomic analysis indicated that 5-epi induces the de novo sphingolipid synthetic pathway. 5-epi dose dependently induces cell surface exposure of ectoCRT, and inhibition of Cer metabolism through inhibition of the SphKs significantly enhances 5-epi-induced ectoCRT exposure in multiple CRC cell lines. 5-epi induces and SphK inhibition enhances activation of the cell death signaling pathway associated with ICD. Conclusions: This study is the first demonstration that cannabinoids can induce the cell surface expression of ectoCRT, and potentially induce ICD. Moreover, this study reinforces our previous observation of a role for Cer accumulation in the induction of ICD and extends this observation to the cannabinoids, agents not typically associated with ICD. Inhibition of SphKs enhanced the 5-epi-induced signaling pathways leading to ICD and production of ectoCRT. Overexpression of SphK1 has previously been associated with chemotherapy resistance. Thus, targeting the SphKs has the potential to reverse chemotherapy resistance and simultaneously enhance the antitumor immune response through enhancement of ICD induction.

OmpF porin from Yersinia ruckeri as pathogenic factor: Surface antigenic sites and biological properties

Bacterium Yersinia ruckeri as a pathogen induces causative agent of intestinal fish disease called enteric redmouth disease (ERM) is known. In this study, outer membrane OmpF porin from the Y. ruckeri (YrOmpF) has been identified as a pathogenic factor which affects host macrophage activation and life cycle of eukaryotic cells. Using synthetic peptides corresponding to the sequences of the outer loops of YrOmpF L1 loop of the porin is most involved in the structure of B epitopes on the surface of the microbial cell it was found. T epitopes of the isolated YrOmpF trimer not only by linear, but also by discontinuous determinants, which is due to the secondary structure of the protein are represented. It was shown that YrOmpF was twice more cytotoxic to THP-1 cells (human monocytes, cancer cells) in comparison with CHH-1 cells (Oncorhynchus keta cardiac muscle cell, non-cancer cells). It was found YrOmpF induce cell cycle S-phase arrest in both normal CHH-1 and cancer THP-1 cells. In the cancer cells observed effect was most pronounce. In addition, we have observed an induction of apoptosis in THP-1 cell line treated with YrOmpF for 48 h at IC50 (48.6 μg/ml). Significant cytotoxic effect of YrOmpF on primary mouse peritoneal macrophages been detected as well. Of note, co-incubation of macrophages with anti-YrOmpF antibodies could decrease the amount of lactate dehydrogenase, while the number of living cells significantly increased. YrOmpF stimulates the activity of the phagocytic bactericidal systems especially of the oxygen-independent subsystem it was found. Antibodies against YrOmpF decreased MPO release and CP synthesis by peritoneal macrophages and increased their viability.

The [3+2] Annulation of CF3-Ketimines by Re Catalysis: Access to CF3-Containing Amino Heterocycles and Polyamides.

SummaryTransition metal catalyzed [3 + 2] annulation of imines with double bonds via directed C-H activation offers a direct access to amino cyclic motifs. However, owing to weak coordination and steric hindrance, trifluoromethylated ketimines have been an unaddressed challenge for TM-catalyzed annulations. Here, a rhenium-catalyzed [3 + 2] annulation of trifluoromethylated ketimines with isocyanates via C(sp2)-H activation has been disclosed. This approach provides an efficient platform for rapid access to a privileged library of CF3-containing iminoisoindolinones and polyamides by utilizing challenging CF3-ketimines as the annulation component. The capability of gram scale synthesis, the post-functionalization of the cyclization adduct, the derivation of complex natural molecules and the facile synthesis of polyamides highlight a diversity of synthetic potential of the current methodology.

Weakly Coordinated Cobaltacycles: Trapping Catalytically Competent Intermediates in Cp*CoIII Catalysis.

Herein, we disclose the synthesis of metallacyclic Cp*CoIII complexes containing weakly chelating functional groups. We have employed these compounds not only as an exceptional platform for accessing some of the most widely invoked transient intermediates in C-H functionalization processes but also as competent catalysts in different Cp*Co-catalyzed transformations, including a benchmark coupling reaction.

Weakly Coordinated Cobaltacycles: Trapping Catalytically Competent Intermediates in Cp*CoIIICatalysis

AbstractHerein, we disclose the synthesis of metallacyclic Cp*CoIIIcomplexes containing weakly chelating functional groups. We have employed these compounds not only as an exceptional platform for accessing some of the most widely invoked transient intermediates in C−H functionalization processes but also as competent catalysts in different Cp*Co‐catalyzed transformations, including a benchmark coupling reaction.

The effects of leguminous supplementation on ammoniated rice straw based completed feed on nutrient digestibility on in vitro microbial protein synthesis

Legume is the best source of protein to ruminant. Tannin content in legumes can provide protein by pass for ruminant. This study was conducted to determine the effect supplementation of legumes (Leucaena leucocephala) as substitute of concentrate on nutrient digestibility and microbial protein synthesis of the completed feed based on ammoniated rice straw. The study was conducted in an in vitro used a randomized block design where there were 3 treatments dan 5 replications. The treatments were A. 40% ammoniated rice straw + 60% concentrate, B. 40% ammoniated rice straw + 50% concentrate + 10% Leucaena leucocephala, C. 40% ammoniated rice straw + 40% concentrate +10, + 20% Leucaena leucocephala. The results showed that the addition of of Leucaena leucocephala had increased the digestibility of DM, OM, CP and microbial protein synthesis (p< 0.05). Increased doses of Leucaena leucocephala until 20% decreased digestion of nutrition compared with dose 10% but was still higher than control. In conclusion, the supplementation of Leucaena leucocephala on completed feed based on ammoniated rice straw in vitro can increase nutrient degradability. Supplementation of 10% and 20% Leucaena leucochepala were suitable to be used for further studies, therefore in vivo experiment is required to study the effects on animal production.

Synthesis and characterization of Cp*Ir-dithiolene-o-carborane phosphine complexes: A continuous investigation of B−H⋯π interaction

ABSTRACTB−H⋯π interaction has attracted increasing attention after its experimental and theoretical verifications in [Ir(PR3)(S2C2B10H10)] (R = C6H4X, X = H, F, OMe) complexes. In such a template, the entropic factors are excluded by using triphenylphosphines as sterically crowding ligands, which leads to the direct observation of B−H⋯π hydrogen bonds at room temperature in both solution and solid state. In this work, new Ir − dithiolene-o-carborane templates with sterically less crowding mono/diphenylphosphine ligands were designed and experimentally synthesised. As a result, non-covalent B−H⋯π hydrogen bonds were detected at low temperatures (down to −80°C) in C1 by using low temperature NMR techniques. Furthermore, variable temperature NMR measurement of C0 with triphenylphosphine ligation was also performed which indicates the slow rotation of Ir−P bond and the reinforced B−H⋯π interaction at low temperature. These experimental results are consistent with the previous theoretical prediction of the B−H⋯π interaction at low temperature in the B2H6⋯benzene model. Additionally, if monophosphine ligand is replaced by diphosphine, a new type of intermolecular B−H⋯π interaction has been crystallographically observed in solid state.

Synthesis and Reactivity of Cp*IrIII Complexes with a C–S Chelate Displaying Metal/Sulfur Bifunctionality

A half-sandwich thiolatoiridium complex bearing a five-membered C–S chelating ligand has been synthesized via cyclometalation of triphenylmethyl mercaptan. The thiametallacycle crystallizes as a coordinatively saturated dimer, bridged with the thiolato ligand. Two-electron donors, such as phosphines and CO, readily coordinate to the thiametallacycle having a bimetallic core to afford the corresponding mononuclear C–S chelating thiolato complexes. The thiolato moiety is alkylated with electrophilic organic halides, including methyl iodide, benzyl bromide, and allyl halides, to yield the corresponding mononuclear thioether complexes in a stereoselective manner that validates the nucleophilic character of the coordinating sulfur atom on the thiairidacycle. By treatment of the dinuclear complex with alkynes, the carbon–carbon triple bonds insert into the thiolato–metal bond selectively to give the corresponding tridentate thioether complexes having a metal–sulfur bond. The insertion of unsymmetrical acetylene...

Effects of maturity at harvest on the nutritive value and ruminal digestion of Eragrostis tef (cv. Moxie) when fed to beef cattle.

Teff (Eragrostis tef cv. Moxie), a warm-season annual grass, could be an excellent forage for beef cattle. However, there is limited information on its nutritive value to cattle when harvested at different stages of maturity. Thus, the objective of this research was to determine the effect of feeding teff hay harvested at the boot (BT), early-heading (EH), or late-heading (LH) stages of maturity on nutrient intake, ruminal fermentation characteristics, omasal nutrient flow, and N utilization in beef cattle. Six ruminally cannulated beef heifers (mean initial BW ± SD, 476 ± 32.6) were used in a replicated 3 × 3 Latin square design with 28-d periods (18 d for adaptation and 10 d for measurements). Dry matter intake was measured daily. Indwelling pH loggers were used to measure ruminal pH from days 21 to 28. Ruminal fluid and omasal digesta were collected from days 26 to 28 to determine fermentation characteristics and omasal nutrient flow. Fecal and urine samples to quantify N excretion were also collected (days 26 to 28). Blood samples for plasma urea-N (PUN) determination were collected 3 h post-feeding on day 28. There were no changes (P > 0.28) in the ADF or NDF content of teff with advancing maturity, but indigestible NDF increased (P < 0.01) with increasing maturity. Maturity had no effect (P ≥ 0.14) on DMI, and ruminal total short-chain fatty acid (SCFA) concentration, pH, digestibility, and outflow of DM, OM, NDF, ADF, and CP. However, the CP content of BT hay was greater (P < 0.01) than for EH and LH hay (18.1, 14.1, and 11.5%, respectively, DM basis), and this resulted in the higher CP intake (P < 0.01) for heifers fed the BT than the EH and LH hay. Consequently, ruminal ammonia-N (NH3-N) concentration was greater (P < 0.01) for heifers fed BT than EH and LH hay, thereby possibly explaining the tendency for a decrease (P = 0.08) in PUN concentration, and a decrease (P < 0.01) in the excretion of total N, urine N, and urea-N (UUN) with advancing maturity. However, fecal N excretion (g/d) did not differ (P = 0.76). In conclusion, despite a decrease in CP intake and ruminal NH3-N concentration, feeding beef heifers EH and LH compared to BT teff hay did not compromise ruminal digestion and outflow of DM, OM, NDF, ADF, and CP, and microbial protein synthesis. Advancing maturity in teff hay also resulted in a decrease in the excretion of total N and urine N and UUN when fed to cattle.

Copper(II) Triflate As a Reusable Catalyst for the Synthesis of trans-4,5-Diamino-cyclopent-2-enones in Water.

trans-4,5-Diamino-cyclopent-2-enones (CP) are usually prepared by Lewis acid-catalyzed condensation of furfural and a secondary amine in an organic solvent. The reaction proceeds through the formation of a Stenhouse salt (SS) intermediate followed by an electrocyclization reaction to afford the desired CP. Herein, we described the use of Cu(OTf)2 as a very efficient catalyst for the synthesis of CP in water at room temperature. Furthermore, the mild reaction conditions, catalyst reusability, and outstanding functional group tolerance suggest that this CP platform can be further used in chemical biology.

A Kinetic Model of Nonenzymatic RNA Polymerization by Cytidine-5′-phosphoro-2-aminoimidazolide

The nonenzymatic polymerization of RNA may have enabled copying of functional sequences during the origin of life. Recent progress utilizing 5′-phosphoro-2-aminoimidazole activation has reinvigorated the possibility of using nonenzymatic RNA polymerization for copying arbitrary sequences. However, the reasons why 2-aminoimidazole (AI) is a superior activation group remain unclear. Here we report that the predominant mechanism of polymerization using cytidine-5′-phosphoro-2-aminoimidazolide (Cp*) involves a 2-aminoimidazolium-bridged dinucleotide (Cp*pC) intermediate. To explore the role of this intermediate, we first identify and quantify four reactions involving the synthesis and breakdown of Cp*pC that occur in the absence of the primer–template duplex. We then analyze the dependence of the rate of polymerization on the concentration of the Cp*pC intermediate in the presence and absence of the competitive inhibitor Cp. We also show that the contribution of the monomer Cp* to the polymerization rate is negligible under our primer extension conditions. Finally, we use the experimentally determined rate constants of these reactions to develop a kinetic model that helps explain the changing rate of nonenzymatic RNA polymerization over time. Our model accounts for the concentration of Cp*pC formed by Cp* under primer extension conditions. The model does not completely account for the decline in polymerization rate observed over long times, which indicates that additional important inhibitory processes have not yet been identified. Our results suggest that the superiority of 2-aminoimidazole over the traditional 2-methylimidazole activation is mostly due to the higher level of accumulation of the imidazolium-bridged intermediate under primer extension conditions.